Patent Publication Number: US-9408732-B2

Title: Reduced-profile slide and lock stent

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application claims from the benefit of U.S. Provisional Application No. 61/785,914, filed Mar. 14, 2013, titled “REDUCED-PROFILE SLIDE AND LOCK STENT,” the entirety of which is incorporated herein by reference. 
     RELATED APPLICATIONS 
     In certain respects, this U.S. patent application is related in subject matter to U.S. patent application Ser. No. 13/083,508 filed Apr. 8, 2011, which claims priority to U.S. Patent Application No. 61/322,843, filed Apr. 10, 2010. In some respects, this application is also related in subject matter to U.S. Pat. No. 7,947,071. Each of the aforementioned patents and applications is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosures relate generally to expandable medical implants for maintaining support of a body lumen, and more specifically, to a uniform stent having improved mechanical and post-deployment dynamic capabilities. 
     2. Description of the Related Art 
     Various embodiments of vascular implants; such as stents, thrombus filters, and heart valves, are used in their various embodiments for medical applications. Of these vascular devices, one of the leading candidates as a stent device and structural component is the radially expandable and slidably engaged stent as disclosed in commonly owned U.S. Pat. No. 6,033,436; U.S. Pat. No. 6,224,626; and U.S. Pat. No. 6,623,521; the disclosures of which are hereby incorporated by reference in their entirety. These radially expandable and slidably engaged stents offer the strength of prior expandable stents with the added improvements of low cross-section deliverability, less bulk material thickness, high resolution fitting, and shape customization such as hourglass-shape configurations. 
     Other radially expandable and slidably engaged stents; such as those disclosed in U.S. Pat. No. 5,797,951; U.S. Pat. No. 5,549,662; and U.S. Pat. No. 5,733,328; further describe the state of the art and their disclosures are hereby incorporated by reference. 
     Although promising candidates for use as implantable devices and device components, these known radially expandable and slidably engaged stents have mechanical and vasodynamic limitations of which the inventors of the present application set out to address. These limitations can be characterized as deployment related limitations, and limitations related to vasodynamic capabilities. 
     Deployment related limitations of prior art stents are herein described. Intravascular space; especially that of a patient in need of a vascular implant, is generally inconsistent and varies upon the individual with respect to curvature, plaque buildup and other luminary obstructions. Furthermore, the shape and structure of the stent may impact the rate and order that discrete areas of the stent deploy, e.g., expand. For instance, one portion of the stent may expand prior to a second portion of the stent. Such inconsistent and/or non-uniform deployment may render deployment and placement of prior art stents more difficult and less predictable. 
     Procedures are available to physicians such as balloon angioplasty, which aid in the reduction of plaque prior to stenting. However, even after such procedures, vascular characteristics remain patient delineated and largely inconsistent. Inconsistencies in vascular characteristics; such as the interference due to a luminary occlusion, require flexibility, distribution of material strength, and vascular adaptability of devices to be implanted. 
     SUMMARY 
     In accordance with at least one of the embodiments disclosed herein is a realization that the configuration of a vascular implant, such as a stent, affects the deployment characteristics of the implant. For example, the shape and structure of the stent may impact the rate and order that discrete areas of the stent deploy, e.g., expand. For instance, based at least in part on the characteristics of the stent, one portion of the stent may expand prior to a second portion of the stent. In some embodiments, the stent can be designed with characteristics such that the stent advantageously deploys substantially equally along a longitudinal length of the stent. Accordingly, various embodiments disclosed herein provide a stent that can be deployed or expanded in a generally uniform manner without binding. 
     Further, in accordance with at least some embodiments disclosed herein is the realization that a helical stent can often experience binding or deployment problems as the helical arrangement unwinds, which must occur from either or both ends of the helical stent. As a result, expansion in the center of the helical stent delayed until the helix is “unwound” from its ends. These expansion characteristics are unsatisfactory as they provide nonuniform deployment and structural properties. Accordingly, in order to address these deficiencies, the inventors of the present application have developed various embodiments of a reversing helical stent having a reversing helical backbone that advantageously provides vastly improved deployment and structural characteristics. Further details such embodiments are provided herein, and can incorporate various features, structures, material configurations, and other attributes such as those disclosed in the copending U.S. patent application Ser. No. 12/577,018, filed Oct. 9, 2009, titled “EXPANDABLE SLIDE AND LOCK STENT,” the entirety of which is incorporated herein by reference. 
     Further, in accordance with some embodiments is the realization that the shape and structure of a stent can impact whether the stent undergoes a twisting or rotation about a longitudinal axis of the stent during deployment. In certain instances, it can be advantageous to reduce or minimize the twisting of a stent during expansion, e.g., to facilitate expansion of the stent by reducing friction between components of the stent and/or between the stent and the vasculature. For example, the stent can include a longitudinally-extending structure (e.g., a backbone or backbone member) that can extend at least partially (e.g. helically) around a circumference of the stent. In some cases, such a configuration can promote deployment, provide torsional flexibility, and reduce twisting of the stent. As disclosed herein, embodiments are disclosed herein that enable such a configuration to not only provide portable flexibility, but to also provide reduced binding of the stent during deployment. 
     In accordance with some embodiments, the stent can comprise at least one backbone coupled with at least one rail member. The backbone can generally extend along a longitudinal axis of the stent. The rail member can generally extend in a circumferential direction of the stent. Thus, the rail member can define a portion of a circumference of the tubular member. Generally, the rail member can be configured to permit one-way sliding movement of the backbone relative to the rail member so as to permit expansion of the tubular member from the collapsed state to the expanded state. 
     The backbone can extend helically about the tubular member. In some embodiments, the backbone can comprise a reversing helical shape or configuration. A “reversing helical” shape can be defined as one that changes its circumferential direction as it extends in an axial direction. In some embodiments, a path of a reversing helical backbone can extend helically about the tubular member in a first axial direction and a first circumferential direction and change its path to a second circumferential direction. For example, changing course from the first to the second circumferential direction can include changing from a clockwise circumstantial direction to a counterclockwise circumferential direction. However, these are compression direction can also be varied in only the counterclockwise or clockwise circumferential directions. 
     In some embodiments, the reversing helical backbone can define one or more elbows or points where the direction or path of the backbone changes. Further, the shape of the backbone can also define at least one peak or high point and at least one trough or low point. For example, when seen from a side view, the backbone can extend in a generally upward direction having an overall positive slope until reaching a peak or uppermost point. Likewise, the backbone can extend from the peak in a generally downward direction having an overall negative slope until reaching a trough or lowermost point. In some embodiments, the shape of the backbone can comprise a plurality of peaks and troughs. Thus, the reversing helical shape can be characterized as comprising an undulating shape, a zig-zag shape, a wave pattern, a sinusoidal shape, and/or the like. Surprisingly, such a configuration can promote deployment of the stent. Additionally, such a configuration can allow for stent characteristics to be modified and/or selected for the requirements of a particular application, e.g., rate of expansion of the stent, force to expand the stent, etc. 
     Additionally, in some embodiments, at least some of the peaks and/or valleys of the backbone of the stent can be pointed or sharply angled, e.g. a sawtooth, triangle, or the like. In some embodiments, at least some of the peaks and/or valleys of the backbone of the stent can be curved, smoothed, rounded, chamfered, filleted, or the like. Further, in some embodiments, some of the peaks and valleys of the backbone can be pointed while others are rounded. In some embodiments, a generally rounded or smooth curve at a peak or valley can promote an overall rounded shape of the stent. Further, a generally pointed peak or valley may promote a desired strength, flexibility or rigidity characteristic. Thus, some embodiments of the stent can be configured to create localized stiffness, strength, flexibility, patency, roundness, and/or other characteristics by manipulating the shape of peaks and valleys and the angular direction of the backbone, as discussed further herein. For example, a rounded peak may reduce the tendency for the peak to protrude into the lumen of the stent. Thus such a feature can assist in maintaining the patency of the lumen. 
     In accordance with some embodiments, the reversing helical backbone can be curvilinear. For example, the reversing helical backbone can comprise one or more continuous curves, one or more smooth curves, a continuously variable curvature, and/or the like. In some instances, the reversing helical backbone can be formed in an undulating reversing helical configuration. For example, the reversing helical configuration can extend generally in a wave pattern, a sawtooth pattern, a triangular pattern, a rectangular pattern, a zig-zag pattern, and/or the like. Further, the backbone can extend in a regular, repeating, and/or symmetrical pattern. However, in other embodiments of the stent, the backbone can extend in an irregular, non-repeating, and/or asymmetrical pattern. 
     Accordingly, the reversing helical configuration of the backbone can comprise nearly any wave form. For example, the reversing helical configuration can have a substantially constant amplitude. The amplitude is the distance between the adjacent peak and valley, as measured perpendicular to a longitudinal axis of the backbone. In other embodiments, the reversing helical configuration can have a substantially non-constant, varying, or changing amplitude. 
     Furthermore, in some embodiments, the reversing helical configuration can have a substantially constant period. The period is the distance or interval between adjacent peaks or adjacent valleys, as measured parallel to the longitudinal axis of the backbone. In other embodiments, the reversing helical configuration of the backbone can have a substantially non-constant, varying, or changing period. In some cases, the period can include one peak and one valley. In some embodiments, the period can include two peaks and one valley. In some embodiments, the period includes two valleys and one peak. In some cases, the period may span the entire length of the stent. 
     In accordance with at least some embodiments disclosed herein is the realization that the angular direction of the longitudinally-extending backbone structure can affect the characteristics of the stent. For example, a shallower angle (in relation to the longitudinal axis of the stent) can ease deployment of the stent. Conversely, a steeper angle (in relation to the longitudinal axis of the stent) can provide enhanced longitudinal flexibility of the stent and/or radial strength of the stent. As discussed further herein, surprising and advantageous results regarding the flexibility and deployment characteristics of a stent have been achieved by the inventors of the present application through implementing stent configurations disclosed herein. In particular, outstanding results have been obtained through implementing stent configurations having a reversing helical backbone with smooth or curvilinear peaks and valleys and a series of short-phase angle deviations along the length of the backbone between consecutive peaks and valleys. 
     Furthermore, in some embodiments, the reversing helical configuration can be defined as comprising a plurality of short-phase or leg elements. For example, in a backbone having a sinusoidal reversing helical configuration, each portion of the sinusoid from a valley toward a peak can be a short-phase or leg element, and each portion of the sinusoid from a peak toward a valley can be a short-phase or leg element. Generally, adjacent leg elements can have opposite slopes, e.g., a leg element with a positive slope will normally follow a leg element with a negative slope, and vice-versa. 
     In some embodiments, one or more of the short-phase or leg elements can be generally straight, generally curvilinear, or define a sub-pattern or variable shape configuration. For example, in some embodiments one or more of the leg elements can itself comprise a wave pattern, a sawtooth pattern, a triangular pattern, a rectangular pattern, a zig-zag pattern, and/or the like. Thus, in some cases, the backbone can have a reversing helical configuration and one or more of the leg elements can have a pattern that deviates from a generally straight length. In particular, some embodiments of the stent can provide a sinusoidal reversing helical backbone having a wave sub-pattern that extends between the peaks and troughs of the sinusoidal reversing helical backbone. 
     In some embodiments, the amplitude of the sub-pattern or variable shape of the leg elements is less than the amplitude of the reversing helical backbone. Surprisingly, the use of a sub-pattern on a reversing helical backbone has been found to advantageously promote uniform deployment of the stent. For example, it has been found that such a pattern-on-pattern configuration can reduce twisting and/or promote deployment of the stent. Furthermore, such a configuration can also exhibit the advantage of allowing stent characteristics to be modified and/or selected for the requirements of a particular application, e.g., rate of expansion of the stent, force to expand the stent, etc. For example, localized characteristics of the stent can be designed for given results, which provides substantial advantages and customization ability for the stents. 
     Furthermore, the inventors have also determined that embodiments of the reversing helical stents disclosed herein can also advantageously permit the implementation of longer stents that were not possible with certain prior art stents. Such prior art stents exhibited a “critical length” because their length was limited due to the expansion force requirements of the stent and the expansion force limitations of the catheter balloon. Above a certain size, some balloons were not strong enough to properly deploy such stents. In particular, a helical stent might create undue stress on the balloon toward the center of the stent due to the binding problems discussed above. However, embodiments of the reversing helical stent discussed herein can equalize the expansive force required to deploy the stent and avoid localized binding (and the additional force needed thereat) to expand the stent. Thus, embodiments of the reversing helical stent disclosed herein do not have the same critical length limitations as other helical stents. 
     Although many of the structural features discussed herein may be shown and described with reference to the circumferential orientation of the stent, some of the features and advantages provided by the reversing helical configuration can be implemented in the width dimension of the stent (e.g., along the radial direction of the stent). In some cases, the reversing helical configuration can be present in the thickness dimension of the backbone (e.g., in a radial dimension of the stent). Some embodiments can have a reversing helical configuration in the width and thickness dimensions of the backbone. 
     It is also contemplated that embodiments disclosed herein can reduce or minimize the twisting of a stent during expansion. Reducing or minimizing twisting can, for example, reduce friction between components of the stent and/or between the stent and the vasculature. In some instances, a reversing helical configuration can reduce binding of the stent during deployment by, for example, decreasing the relative motion of different components of the stent during expansion. For example, the reversing helical configuration can reduce the rotation of one end of the stent during expansion, from the vantage of a second end of the stent. 
     A further realization in accordance with at least one of the embodiments disclosed herein is that the configuration of the stent can impact the deployed shape of the stent. In some embodiments it may be desirable for the deployed stent to be substantially round, e.g., circular in cross-section. A substantially round stent can facilitate, for example, improvement of stent strength and placement of the stent in the vasculature. In at least one of the embodiments disclosed herein, a stent can include features to facilitate a substantially round shape in the deployed state. The stent can include one or more components, such as a longitudinally-extending structure (e.g., a backbone), that promotes the roundness of the stent. For example, the backbone can be shaped substantially as a sinusoid. In particular, at least one peak of the sinusoidal backbone is curved, e.g., not formed as a pointed peak or having a sharp angle. Such a rounded peak can promote an overall rounded shape or roundness of the stent. For example, the rounded peak can reduce the tendency for the peak to protrude into the lumen of the stent. 
     In some embodiments, surprising results have been found in further promoting roundness by implementing configurations in which the rail members are selectively oriented in opposing circumferential directions. For example, some embodiments, a first rail member can extend circumferentially in a first direction and a second rail member can extend circumferentially in a second direction. In some arrangements, the direction in which the first and second rail members extend can be related to or dependent upon the angle between the rail member and longitudinally-extending structure. For example, in some cases, the first and second rail members extend in a given circumferential direction such that the angle between the rail member and longitudinally-extending backbone or structure is an acute angle. Accordingly, it has been determined that, compared to stents with other features, e.g., non-reversing structures, a reversing helical backbone can promote roundness of the stent. 
     In some embodiments, the backbone can comprise one or more engagement elements. The engagement element can comprise a slot, indentation, passageway, aperture, protrusion, and/or other such structures. In many embodiments illustrated herein, the engagement element comprises a slot that can be configured to receive corresponding rail members, which extend along the circumferential axis of the stent. In some cases, the slots and/or rail members have a locking mechanism configured to permit only one-way sliding movement of the rail members with respect to the slots. In some cases, the locking mechanism can comprise one or more teeth, ridges, paddles, detents, ratchets, ramps, hooks, stops, and/or the like. 
     In some embodiments, the slots can be angled with respect to the longitudinal axis of the stent, which can advantageously effect the characteristics of the stent. For example, a shallower angle (in relation to the longitudinal axis of the stent) can decrease the force required to expand the stent, and thus can ease deployment of the stent. A steeper angle (in relation to the longitudinal axis of the stent) can increase the longitudinal flexibility of the stent and/or radial strength of the stent, and thus provide a stronger yet more flexible stent. 
     In some cases, the slot angle can be determined at least in part by the position of the slot along the aforementioned reversing helical configurations of the backbone and/or the leg element. For example, positioning the slot on a more steeply angled portion of reversing helical configurations can generally produce a steeper slot angle. Conversely, positioning the slot on a more shallowly angled portion of reversing helical configurations can generally produce a shallower slot angle. 
     The slot can be disposed at an angle that is different from the angle of the leg element overall (relative to the longitudinal axis of the stent). For example, in some cases a leg element is angled at about 10° to about 45° from the longitudinal axis of the stent, and the slot is angled at about 5° to about 60° from the longitudinal axis of the stent. In some embodiments, the absolute value of the slot angle can be between at least about 0 degrees and/or less than or equal to about 60 degrees. The absolute value of the slot angle can also be between at least about 10 degrees and/or less than or equal to about 50 degrees. Further, the absolute value of the slot angle can be between at least about 20 degrees and/or less than or equal to about 40 degrees. The slot angle can also vary between at least about 30 degrees and/or less than or equal to about 35 degrees. Finally, as illustrated, the absolute value of the slot angle can be approximately 10 degrees, 33 degrees, 40 degrees. Further, it is contemplated that the slot angle can be any variety or combination of desired angles that are configured to facilitate ease of expansion on the one hand and stent flexibility on the other hand. 
     In embodiments with multiple slots, each slot can be disposed at an angle that is different than the angle of adjacent slots. For example, in an embodiment with three slots, the first slot can be angled at a first angle, the second slot can be angled at a second angle, and the third slot can be angled at a third angle, wherein the first, second, and third angles are not equal. 
     Generally, each slot angle can be selected. Advantageously, in light of the above-discussed realization that different angles of the stent components can impact stent characteristics, employing slot angles that are selectable allows the stent to be customized for specific applications. For example, in applications in which radial strength and/or longitudinal flexibility are desired, the steeper slot angles can be employed; in applications in which ease of expansion is desired, shallower slot angles can be employed. Beneficially, it has been found that a stent having a combination of steep and shallow slot angles can provide a balance of radial strength, longitudinal flexibility, and ease of expansion. 
     As discussed above, the tubular member can include one or more rail members that are slidably coupled to a backbone and define a portion of the circumference of the tubular member. The term “rail member” can refer to on or more elongate, circumferentially extending rails that interconnect with at least one backbone the stent. The rail members in some embodiments can be coupled to or formed with an adjacent rail member to form a radial element. For example, the radial element can be generally U-shaped with a pair of rail members extending therefrom. Some embodiments can include a plurality of adjacent rail members or radial elements that interconnect with one or more respective backbones. Further, groups of rail members and/or radial elements can be circumferentially associated to form a circumferential band or radial module. In some arrangements, each radial element within a radial module can be coupled to a different backbone. For example, in an embodiment with a radial module having first and second radial elements, the first radial element can be coupled to a first backbone and the second radial element can be coupled to a second backbone. 
     In some arrangements, each radial element within a radial module can be slidingly engaged with an engagement element of a different backbone. In some embodiments, the engagement element can comprise a slot, a passage, a channel, and/or aperture extending through or along a backbone. For example, in an embodiment with a radial module having first and second radial elements, the first radial element can be slidingly received in an engagement element in a second backbone and a second radial element can be slidingly received in an engagement element in a first backbone. Of course, other numbers and combinations of radial elements and backbones are contemplated, e.g., one, three, four, etc. As previously discussed, the radial element and/or the slot can be configured to provide one-way sliding movement of the radial element with respect to the engagement element. 
     A further realization in accordance with at least one of the embodiments disclosed herein is that a modular stent can advantageously permit a given stent design provide multiple stent lengths. In such a design, the overall length of the stent can be increased or decreased by adding or subtracting modules. As similarly noted above, the modules can provide a circumferential and corresponding axial length to the stent. Further, the axial length of a module can correspond to the periodicity of the backbone, whether having a reversing helical or regular helical configuration. Thus, modular construction can refer to the use of one or more modules or sections that may be used to build the entire length of the stent. Modular construction generally also allows for addition and subtraction of the modules or sections in order to reach a desired size. Further, longitudinal modules or sections, including a backbone and corresponding rail members or radial elements, can also added or removed to a stent construction in order to modify the maximum and minimum diameters of the stent. Thus, a stent with a modular construction can advantageously be modified (by adding or subtracting longitudinal or circumferential sections or modules) to provide, for example, a desired expanded diameter or length. For example, additional backbones can be added to the stent to provide an increased expanded diameter. Further, additional radial modules or sections can be added to provide a longer stent (which would require increasing the length of the backbone and providing additional rail members or radial elements corresponding thereto). 
     In some embodiments, an expandable slide and lock stent is provided in which the stent comprises a tubular member having a circumference and a longitudinal axis. The stent can comprise a first backbone and a second backbone and at least one rail member. The first and the second backbones can each have a reversing helical shape. The first and second backbones can extend along at least a portion of the circumference and along the longitudinal axis. In some embodiments, the first and second backbones can be reversing helical backbones defining a generally curvilinear sub-form extending along the backbones between a peak and a valley of the reversing helical backbones. 
     In some embodiments, at least one of the first and second backbones can define one or more discrete segments. The discrete segments can comprise that portion of the backbone extending between engagement elements of the backbone. Further, the discrete segments can also comprise the portion of the backbone at which the engagement elements are positioned. Furthermore, a backbone can be divided into two or more, and in some embodiments, four or more discrete segments. The number of discrete segments can be even or odd, as long as the overall path of the backbone achieves a desired angular orientation, flexibility profile, and strength characteristics. 
     The discrete segments can define a discrete helix angle. The discrete helix angle can be a general measurement of the angular direction of the discrete segment relative to the longitudinal axis of the stent. In some embodiments, one or more of the discrete segments of the backbone can define a discrete helix angle that is the same as or different from the discrete helix angle of another discrete segment. Further, in some embodiments, the discrete helix angle can be referred to as a slot angle measured at an engagement element or slot of the backbone. 
     Furthermore, some embodiments can be configured such that one or more of the discrete segments are generally curvilinear. The curvilinear shape can have increasingly positive slope, a decreasingly positive slope, increasingly negative slope, or a decreasingly negative slope. Thus, in contrast to straight or pointed portions of a backbone, the curvilinear discrete segments can provide improved flexibility, bending strength, and roundness of the stent. 
     The rail member can define proximal and distal ends. The proximal end of the rail member can be coupled to the first backbone. The distal end of the rail member can extend from the first backbone in the circumferential direction. The rail member can be configured to engage with an engagement element in the second backbone. Further, the rail member can be configured to provide one-way movement of the second backbone away from the first backbone such that the tubular member can be expanded between a collapsed diameter and an expanded diameter. 
     The reversing helical shape of the backbones can comprise a reversing undulating shape. The reversing helical shape can comprise a portion having a positively trending slope and a portion having a negatively trending slope. At least one of the portions having a positively trending slope and the portion having a negatively trending slope can further comprise a plurality of wave forms. The plurality of wave forms can comprise a plurality of continuous curves. Further, the intersection of the rail member and the second backbone can be at an oblique angle. 
     The stent can further comprising a plurality of rail members defining proximal and distal ends. The proximal end of each of the rail members can be coupled to the first backbone. The distal end of each of the rail members can extend from the first backbone in the circumferential direction and can be configured to intersect and pass through one of a plurality of slots in the second backbone. 
     Further, one or more of the slots in the backbone can define a slot angle that extends skew relative to the longitudinal axis of the stent. For example, these slot angles of the slots in the backbone can be different from each other, as discussed further herein. For example, in some embodiments, each of the slot angles can be disposed at a different angle with respect to the longitudinal axis compared to adjacent slot angles. Further, the slot angles can also be generally equal to each other. 
     In some embodiments, the rail member can comprise one or more teeth for engaging the slot to provide one-way expansion of the stent. Accordingly, and some embodiments, the slot can comprise a central passage and at least one internal recess for engaging the teeth of the rail member. 
     In accordance with another embodiment, methods for forming the stands and stent components are provided. For example, any of the embodiments disclosed herein can be formed by initially forming the structures disclosed, such as the reversing helical backbone, the discrete segments (depending on their configuration), and the like. For example, a method for forming a stent can be provided which comprises: forming a central passage as a first through hole in the backbone in a circumferential direction of stent, and forming the at least one internal recess as a second through hole in the backbone in a direction transverse to a circumferential direction of the central passage such that the first and second through holes partially overlap. 
     Next, in accordance with some embodiments, an expandable stent is provided that can comprise a plurality of radial components interconnected to form a tubular member. The stent can comprise at least one reversing helical backbone having a plurality of slots and further comprising a plurality of rail members. The reversing helical backbone can define a generally curvilinear sub-form extending along the backbone between a peak and a valley of the reversing helical backbone. Further, the rail members can be received into the slots of the helical support member to facilitate one-way expansion of the stent. The expandable stent can be made from a bioresorbable polymer. Further, these stent can be configured to exhibit structural properties equivalent to a metal stent. 
     Furthermore, a radial structure, module or element for forming an expandable slide and lock polymer stent can be provided which comprises an undulating helical backbone and a plurality of the elongate ribbed elements. The undulating helical backbone can half a plurality of engagement slots and a plurality of connection slots. The at least one engagement slot can be spaced between consecutive connection slots along the backbone. The plurality of elongate rib elements can have proximal and distal portions. The proximal portion can be interconnectable with one or more connections slots of the continuously slotted backbone. Each rib element can be positionable generally circumferentially about the longitudinal axis and have a fixed engagement at a nonperpendicular angle with respect to the helical backbone. 
     The plurality of elongate rib elements can be arranged to interconnect with at least one other undulating helical backbone of another radial element so as to form an expandable tubular skeleton. The elongate rib elements can have a one-way slidable engagement with the engagement slots of the helical backbone of the other radial element. The tubular skeleton can be configured to expand radially between a collapsed diameter and an expanded diameter upon circumferential motion of the slidable engagement of the rib elements to the helical backbones. Further, the slidable engagement can include a mechanism restraining collapse of the tubular skeleton from the expanded diameter towards the collapsed diameter. 
     In some embodiments, the undulating helical backbone can comprise portions of reduced thickness for allowing at least partial nesting of an elongate rib element thereagainst. Further, a pair of elongate rib elements can be interconnected at their distal portions by a crossbar. The crossbar can comprise an offset portion configured to at least partially receive an elongate rib of an adjacent radial element for reducing a passing profile of a stent formed using a plurality of radial elements. Next, the undulating helical backbone can extend helically at a generally fixed radius and helix angle relative to the longitudinal axis. The engagement slot can comprise a through slot that defines a central axis extending in a generally circumferential direction and within a plane that is perpendicular to the longitudinal axis of the radial element, the central axis of the engagement slot can extend at a non-perpendicular angle relative to the helical backbone. 
     In accordance with at least one of the embodiments disclosed herein is an expandable slide and lock stent. The stent can comprise a tubular member with a circumference and longitudinal axis. The stent can further comprise at least a first backbone and a second backbone, the first and the second backbones each having a reversing helical shape, the first and second backbones extending along at least a portion of the circumference and along the longitudinal axis, and a rail member defining proximal and distal ends, the proximal end of the rail member being coupled to the first backbone, the distal end of the rail member extending from the first backbone in the circumferential direction, the rail member configured to engage with an engagement element in the second backbone. The rail member can be configured to provide one-way movement of the second backbone away from the first backbone such that the tubular member can be expanded between a collapsed diameter and an expanded diameter. The rail member can further extend circumferentially beyond the engagement element in the second backbone to engage at least one circumferentially adjacent backbone. The circumferentially adjacent backbone can have one or more portions having a recessed surface profile, the recessed-profile portion being aligned to engage the rail member extending circumferentially from second backbone, the engagement with the rail member with the recessed portion providing a reduced radial profile of the engaged rail member and backbone. 
     In some embodiments, the circumferentially adjacent backbone can be the first backbone. In some embodiments, the stent can further comprise a third backbone, wherein the circumferentially adjacent backbone can be the third backbone. In some embodiments, the reduced radial profile of the rail member engaged with the recessed portion can provide a smaller overall stent profile diameter. In some embodiments, the engagement of the recessed portion with the rail members can provide improved stent retention as mounted on a balloon catheter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The abovementioned and other features of the embodiments disclosed herein are described below with reference to the drawings of the embodiments. The illustrated embodiments are intended to illustrate, but not to limit the embodiments. The drawings contain the following figures: 
         FIGS. 1 and 2  show planar representations of two embodiments of a stent or stent assembly, illustrating different interconnecting arrangements of the backbones and radial elements. 
         FIG. 3  shows an assembly in which rail members of the radial elements are generally obliquely oriented with respect to the stent longitudinal axis, and perpendicular to the backbones, according to an embodiment. 
         FIGS. 4A and 4B  show a stent assembly with backbones arrayed generally in an slanted or helical orientation, having portion which is parallel to the stent axis, according to an embodiment. 
         FIG. 5  shows a stent assembly with multiple locally non-slanted backbone portions, according to an embodiment. 
         FIGS. 6, 7, and 8  each show embodiments of stent assemblies in which the backbones have bi-directional, multidirectional or continuously variable backbone orientation along the stent longitudinal axis, according to an embodiment. 
         FIGS. 9A-9D  illustrate an embodiment with multi-directional rail member arrays, in expanded and collapsed configurations. 
         FIGS. 10A-10F  illustrate alternative embodiments in which the teeth or locking members are provided with one or more relieving holes or indentions located within the rail member, according to an embodiment. 
         FIGS. 11A-11D  illustrate the engagement of teeth or locking members on the rail members of the radial element, according to an embodiment. 
         FIG. 12A  illustrates a stent embodiment having rail modules with rail members, in the compacted state, according to an embodiment. 
         FIG. 12B  illustrates the stent embodiment of  FIG. 12A  in the expanded state, according to an embodiment. 
         FIG. 13A  illustrates an end view of the stent embodiment of  FIG. 12A  in a tubular configuration, according to an embodiment. 
         FIG. 13B  illustrates an end view of the stent embodiment of  FIG. 12B  in the tubular configuration, according to an embodiment. 
         FIG. 14A  illustrates a perspective view of the stent embodiment of  FIG. 12A  in the tubular configuration, according to an embodiment. 
         FIG. 14B  illustrates a flexed or bent configuration of the stent embodiment of  FIG. 12A  in the tubular configuration, as potentially deployed in a curving vascular lumen, according to an embodiment. 
         FIGS. 15A and 15B  schematically illustrate the relation of backbones to rail members, according to an embodiment. 
         FIG. 16  illustrates a detail of a mid portion of the stent assembly of  FIG. 12A , according to an embodiment. 
         FIG. 17A  illustrates a plan view of an embodiment of a backbone of the stent embodiment of  FIG. 12A , according to an embodiment. 
         FIG. 17B  illustrates an elevation view of an embodiment of a backbone of the stent embodiment of  FIG. 12A , according to an embodiment. 
         FIG. 17C  illustrates a focused view of a portion of the stent embodiment of  FIG. 17A , according to an embodiment. 
         FIGS. 17D and 17E  illustrate focused views of a slot of the stent embodiment of  FIG. 17B , according to an embodiment. 
         FIG. 18  illustrates a radial element having a pre-formed shape, according to an embodiment. 
         FIGS. 19A-19B  illustrate embodiments of a backbone having a pre-formed shape, according to an embodiment. 
         FIGS. 20A-20D  illustrate an assembly process of mounting embodiments of rail members to an embodiments of backbone, according to an embodiment. 
         FIG. 21  illustrates a stent embodiment having a backbone profile which facilitates reduced profile in the compacted stent configuration, according to an embodiment. 
         FIGS. 22A, 22B and 22C  illustrate cross sections of example portions of the structural backbones of the stent assembly of  FIG. 21 , according to an embodiment. 
         FIG. 23  illustrates a cross-section perpendicular to those of  FIGS. 22A-C , cut along the circumferential extent of a rail member, according to an embodiment. 
         FIG. 24A  illustrates a top view of a backbone alignment of the stent assembly of  FIG. 21 , according to an embodiment. 
         FIG. 24B  illustrates a side elevation view of the stent assembly of  FIG. 24B , according to an embodiment. 
         FIG. 25  illustrates a side elevation view of a portion of a backbone of the stent assembly of  FIG. 12 , according to an embodiment. 
         FIG. 26  illustrates a side elevation view of a portion of a backbone of the stent assembly of  FIG. 21 , according to an embodiment. 
         FIGS. 27A-B  and  28 A-B shows comparative photographic representations of stent assemblies of  FIGS. 12 and 21 , shown compacted and mounted on a balloon delivery catheter, according to an embodiment. For each, subfigure A is an oblique perspective and subfigure B is an inset shown a side view. 
         FIG. 29  shows a high-resolution micro-X-ray-tomography scan of a cross-cross-section of a stent assembly of  FIG. 21  in compacted configuration, according to an embodiment. 
         FIG. 30  illustrates a three-view depiction of a detail portion of a backbone of a stent assembly of  FIG. 21 , according to an embodiment. 
         FIG. 31  illustrates a top and side section depiction of a detail portion of a rail member of a stent assembly of  FIG. 21 , according to an embodiment. 
         FIG. 32  illustrates a set of nine micro-CT scans, indicated as a-j, similar to the scan of  FIG. 29 , taken at longitudinally adjacent sections (labeled a though j) of a compacted stent assembly of  FIG. 21 , according to an embodiment. 
         FIG. 33  illustrates a photographic side view of stent such as scanned in the  FIG. 32 , showing section lines generally representative of the scans a though j of  FIG. 32 , according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As will be discussed herein, embodiments of the stent summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings. This detailed description of embodiments, set out below to enable one having skill in the art to build and use one particular implementation, is not intended to limit the enumerated claims, but to serve as a particular example thereof. While the description sets forth various embodiments in specific detail, it will be appreciated that the description is illustrative only and should not be construed in any way as limiting the same. Furthermore, various applications of the embodiments, and modifications thereto, which can occur to those who are skilled in the art, are also encompassed by the general concepts described herein. 
     Overview 
     As discussed herein, in accordance with at least one of the embodiments disclosed herein is the realization that a vascular implant may experience a number of mechanical limitations related to delivery. For example, some portions of the vasculature are curved or substantially non-cylindrical. These portions of the vasculature have proven difficult to deploy stent devices. Sometimes, the curvature of the vessel can cause a deployed stent to fold, especially in stents with insufficient flexibility in the design. Curved vessels further increase the potential for hinging and denting as described in further detail below. 
     A vascular implant may also experience a number of countering forces post-deployment. Some of these countering forces are a result of what is herein referred to as vasodynamics; the resulting movements, constrictions and contortions of the vasculature. Of these countering forces is crush force, caused by post-expansion elastic recoil of the vessel. 
     Additionally, some stents experience an occlusion-derived impaction force; a point force derived from the impact of a luminary occlusion directly onto the device; such a luminary occlusion can be plaque or a thrombus. Other countering forces such as dilation, and contortion, are to be discussed in further detail below. 
     In accordance with an aspect of at least some embodiments is the realization that known radially expandable and slidably engaged stents can experience what the inventors of this application refer to herein as “hinging.” Many slidably-engaged expandable stents possess a common limitation where the engagements are generally longitudinally aligned, thereby inherently creating an alignment of failure points. A failure point is a weakness in a stent design, usually a point where two parts are joined together in a less than permanent fashion such as an engagement between slidably-engaged rail members and/or radial modules. When an amount of radial pressure is exerted on the expanded stent, the stent tends to buckle or fold at the failure point. A series of failure points that are longitudinally aligned can act as a perforation in the material and cause a substantial weakness and propensity for hinging. 
     Another plaque-related problem is herein referred to as “denting.” Denting is caused by an inherent device pattern weakness where a vaso-occlusion can drive a portion of at least one stent module into the luminary space, thereby substantially enhancing the effect of the vaso-occlusion. Such an occlusion or dent can lead to collection of thrombus or flow distortions which are problematic and can increase stenosis. 
     Vascular plaque is typically non-uniform and often forms in a bulky occlusion, such an occlusion can place added stress on the stent via a point force, and increase the risk of hinging or denting. 
     The inventors of the present application have recognized that denting can significantly dampen or interfere with vasodynamics, and therefore may cause an increase in realized stenosis. Furthermore, denting may not be immediately apparent to the implanting physician where a polymer stent is adapted for increased ductility over time. 
     In accordance with at least one of the embodiments disclosed herein is a realization that the configuration of a vascular implant, such as a stent, may effect the deployment characteristics of the implant. For example, the shape and structure of the stent may impact the rate and order that discrete areas of the stent deploy, e.g., expand. For instance, based at least in part on the characteristics of the stent, one portion of the stent may expand prior to a second portion of the stent. In some embodiments, the stent can be designed with characteristics such that the stent advantageously deploys substantially equally along a longitudinal length of the stent. Accordingly, various embodiments disclosed herein provide a stent that can be deployed or expanded in a generally uniform manner without binding. 
     In accordance with some embodiments disclosed herein, the stent can be slidably expandable. The geometry of the stent may be generally described as a tubular member. The tubular member can have a collapsed state and an expanded state. 
     Many devices are fabricated from a biodegradable polymer which may become substantially more ductile and flexible with the progression of time up to a point of water absorption equilibrium. As water is absorbed, the polymer material becomes bendable or ductile. Differing polymer compositions will have a varied rate of moisture absorption. The inventors of the present application recognized the benefits of controlled water absorption into the polymer material such as a reduced propensity for microfissures. Furthermore, the inventors of the present application recognized detriments such as a propensity for denting where the design pattern provides unsupported adjacent components. The likelihood of denting occurrences is increased for stent patterns lacking the support of a structural backbone, especially when there are unsecured corners or other points having a propensity for weakness. Often, the extent to which denting occurs cannot be determined until several hours after the deployment procedure, hence the importance to minimize the potential for denting and improving the design pattern of the target device. 
     In accordance with at least one of the embodiments disclosed herein, the inventors of the present application have recognized that a mechanically-improved stent design will overcome one or more of the limitations set out above, and will further set out to increase adaptability to the dynamics of the vasculature. 
     Many prior art stent embodiments are designed around crush force and maintaining patency of a luminary space. Although patency of the lumen is of primary concern, there are other factors which must be addressed in an effort to go beyond functionality, but rather to move toward the successful treatment and healing of a vessel. 
     The vasculature is a dynamic system. Although it is difficult to quantify, the vasculature may experience a number of dynamic movements at any given moment in time. Of these is a wave-like dilation, which presents variability in the interior diameter of the vessel at a given location. Dilation can occur from a change in blood pressure or other change in the circulation. Additionally, portions of the vasculature can experience a contortion or twist like motion in addition to dilation. Where there is plaque or a luminary occlusion, the vasculature can experience a resistance to these natural movements. Such a resistance can cause the adjacent tissue to undergo a cytotic response, such as the division of cells, or intravascular cell growth known as neointimal growth. Neointimal growth is a new or thickened layer of arterial intima formed especially on a prosthesis or in atherosclerosis by migration and proliferation of cells. 
     Clinical data generally shows that stent implants stimulate neointimal growth in the vessel immediately subsequent to implantation. Neointimal growth is acceptable up to a point where blood pressure is substantially increased or where the lumen is obstructed and blood can no longer efficiently pass. 
     It is thought that resistance to vasodynamics, among other things, can dramatically increase stenosis surrounding an implanted vascular device. Therefore, it is critical to understand the dynamics of the vasculature and to design a stent capable of maintaining patency of the lumen while promoting the motions associated with vasodynamics such as periodic dilation and contortion. A stent designed to incorporate the dynamics of the vasculature can better serve to treat and ultimately heal the vessel. 
     Generally, neointimal growth surrounds and encompasses the implanted stent, leaving the stent to reside substantially within the new vessel wall. It is in this state that stent mechanics are critical in minimizing further stenosis. 
     Although stents can be made of generally any biocompatible material, there is a movement toward the use of stents fabricated from a biodegradable and bioresorbable polymer. Biodegradation is the structural decomposition of a polymer, often occurring as bulk erosion, surface erosion, or a combination thereof. Bioresorption includes the cellular metabolism of the degraded polymer. The inventors of the present application have set out to design a stent capable of utilizing the degradation and resorption properties of the polymer to enhance the healing and treatment of the vessel. 
     In some embodiments, there is provided a stent having a uniform distribution of failure points. This uniform distribution can minimize, if not eliminate the potential for hinging and denting. Further, in some embodiments, there is provided a stent having a rotationally flexible backbone capable of adaption to vasodynamic movements, thereby minimizing stenosis of the vasculature. 
     In some embodiments, there is provided a stent design capable of being efficiently encapsulated with neointimal growth, such that initial degradation of the stent material will transform the stent into a rotationally flexible and vaso-adaptive support within the new vessel wall. 
     In summary, there remains a need for an improved radially expandable and slidably engaged luminary support structure: one that uniformly distributes failure points about the device so as to prevent hinging, one that provides adequate support to components so as to prevent denting, one that embraces the effects of water absorption so as to prevent micro fissures while providing effective stenting to the vasculature, one that is capable of restoring vaso-motion to the treated vessel upon neo-intima containment, and one that embraces known properties of radially expandable and slidably engaged support structures such as low cross-section deliverability, less bulk material thickness, high resolution fitting, and shape customization such as hourglass-shape configurations. 
     An expandable stent is disclosed in accordance with an embodiment of the present inventions. The stent can provide radial support to maintain patency of a lumen, a flexible vaso-adaptive backbone structure, and a uniform circumferential distribution of slidable engagements. 
     Aside from radial expansion and an ability to maintain patency of the body lumen, the present disclosure provides solutions to the aforementioned problems of hinging, denting and restriction of vasodynamic movements. 
     In accordance with at least one of the embodiments disclosed herein is the realization that a propensity for hinging is increased in stent designs having an alignment of engagement means that are substantially parallel with respect to the longitudinal axis of the stent. Further, in accordance with at least one of the embodiments disclosed herein is the realization that a potential for denting can be minimized by incorporating a support backbone to secure the extremities and corners of those members or features associated with maintaining patency of the lumen, herein elongate members. 
     Additionally, in accordance with at least one of the embodiments disclosed herein is the realization of the importance of providing a stent having flexibility sufficient to promote and adapt to natural vasodynamic movements while maintaining patency of the lumen. Further, stenosis can be minimized by improving the flexibility of the stent so as to provide adaption to vasodynamic movements such as wave-like dilation and contortion movements. 
     The term “stent” is used herein to designate embodiments for placement in (1) vascular body lumens (i.e., arteries and/or veins) such as coronary vessels, neurovascular vessels and peripheral vessels for instance renal, iliac, femoral, popliteal, subclavian and carotid; and in (2) nonvascular body lumens such as those treated currently i.e., digestive lumens (e.g., gastrointestinal, duodenum and esophagus, biliary ducts), respiratory lumens (e.g., tracheal and bronchial), and urinary lumens (e.g., urethra); (3) additionally such embodiments can be useful in lumens of other body systems such as the reproductive, endocrine, hematopoietic and/or the integumentary, musculoskeletal/orthopedic and nervous systems (including auditory and ophthalmic applications); and, (4) finally, stent embodiments can be useful for expanding an obstructed lumen and for inducing an obstruction (e.g., as in the case of aneurysms). 
     The term “stent” is further used herein to designate embodiments such as; support structures for maintaining patency of a body lumen; support structures for anchoring thrombus filters and heart valves; as well as support structures for the distribution and delivery of therapeutic agents as well as other devices. 
     In the following description of embodiments, the term “stent” can be used interchangeably with the term “prosthesis” and should be interpreted broadly to include a wide variety of devices configured for supporting a segment of a body passageway. 
     Furthermore, it should be understood that the term “body passageway” encompasses any lumen or duct within a body, such as those described herein. 
     Still further, it should be understood that the term “shape-memory material” is a broad term that can include a variety of known shape memory alloys, such as nickel-titanium alloys, as well as any other materials that return to a previously defined shape after undergoing substantial plastic deformation. 
     The term “radial strength,” as used herein, describes the external pressure that a stent is able to withstand without incurring clinically significant damage. Due to their high radial strength, balloon expandable stents are commonly used in the coronary arteries to ensure patency of the vessel. During deployment in a body lumen, the inflation of the balloon can be regulated for expanding the stent to a particular desired diameter. Accordingly, balloon expandable stents can be used in applications wherein precise placement and sizing are important. Balloon expandable stents can be used for direct stenting applications, where there is no pre-dilation of the vessel before stent deployment, or in prosthetic applications, following a pre-dilation procedure (e.g., balloon angioplasty). During direct stenting, the expansion of the inflatable balloon dilates the vessel while also expanding the stent. 
     General Stent Geometry 
     In accordance with the principles disclosed herein, the geometry of the stent may be generally described as a tubular member. The tubular member can be expanded from a collapsed state to an expanded state. 
     In accordance with these various features, the slidably engaged expandable stent can include at least one backbone or backbone member coupled with at least one rail member, elongate member or radial element. As discussed herein, a plurality of rail members (also referred to as elongate members or rails), such as two or more, can be coupled together to form a radial element. The backbone and the rail member and/or radial element can define a circumference of the tubular member. Generally, the rail member is configured to permit one-way sliding movement of at least one of the backbones (in relation to the rail member), so as to permit expansion of the tubular member from the collapsed state to the expanded state. 
     In some embodiments, the stent can comprise one or more reversing helical backbones. Many of the reversing helical backbones of the embodiments described herein provides a high degree of longitudinal structural integrity combined with longitudinal flexibility and radial strength, both in the compacted and deployed configurations. One or more elongate members, elongate rails, or radial elements can extend from the backbone and can interlock with one or more other backbones to form an interwoven circumferential surface that provides crush strength and radial stiffness without unduly inhibiting longitudinal or rotational flexibility. In some embodiments, the generally circumferential alignment of the radial elements allows the elongate members to engage each other and the backbone in a configuration which provides “hoop-strength,” thus providing a substantial increase overall longitudinal “beam” stiffness. In some embodiments, the generally circumferential alignment of the radial elements allows the elongate members to engage each other and the backbone without direct coupling in a configuration to provide “hoop-strength” and a substantial increase overall longitudinal “beam” stiffness. In certain embodiments, the stent structure may be described as expandable tubular “skeleton” assembly defined by the systematic movable interconnection of a plurality reversing helical “backbones” via a plurality of circumferentially arranged rail or “rib” elements. 
     In some embodiments, the backbone comprises one or a plurality of engagement elements. The engagement element can comprise a slot, indentation, passageway, aperture, protrusion, and/or other such structures. In many embodiments illustrated herein, the engagement element comprises at least one slot. In other words, embodiments of the backbone can be configured to comprise one or a series of slots formed along the backbone for facilitating interconnection of the backbone assembly with one or more rail members or radial elements. This may be referred to as a continuously slotted backbone. The slots of the backbone can be advantageous by reducing the tendency for hinging, kinking, and buckling of the stent. Indeed, in some cases, the slots in the backbone can provide for local areas of reduced stiffness and/or enhances flexibility. Further, in conjunction with the unique reversing helical backbone structure and slide-and-lock expansion mechanism of embodiments disclosed herein, the slotted backbone can also contribute to superior flexion and crush strength of the stent. 
     Generally, the backbone comprises a reversing helical shape, such as a shape that has an alternating positive and negative slope. For example, the reversing helical shape can be a zig-zag, undulation, wave pattern, or the like. In some cases, the reversing helical shape is curvilinear or a series of continuous curves, smooth curves, continuous variable curvature, or the like. In some arrangements, the reversing helical shape is symmetrical along the longitudinal axis of the stent. For example, in some embodiments the backbone comprises a sinusoidal shape. 
     As discussed above, a “reversing helical” shape can be defined as one that changes its circumferential direction as it extends in an axial direction. In some embodiments, a path of a reversing helical backbone can extend helically about the tubular member in a first axial direction and a first circumferential direction and change its path to a second circumferential direction. For example, changing course from the first to the second circumferential direction can include changing from a clockwise circumstantial direction to a counterclockwise circumferential direction. However, these are compression direction can also be varied in only the counterclockwise or clockwise circumferential directions. 
     In some embodiments, the reversing helical backbone can define one or more elbows or points where the direction or path of the backbone changes. Further, the shape of the backbone can also define at least one peak or high point and at least one trough or low point. For example, when seen from a side view, the backbone can extend in a generally upward direction having an overall positive slope until reaching a peak or uppermost point. Likewise, the backbone can extend from the peak in a generally downward direction having an overall negative slope until reaching a trough or lowermost point. In some embodiments, the shape of the backbone can comprise a plurality of peaks and troughs. Thus, the reversing helical shape can be characterized as comprising an undulating shape, a zig-zag shape, a wave pattern, a sinusoidal shape, and/or the like. Surprisingly, such a configuration can promote deployment of the stent. Additionally, such a configuration can allow for stent characteristics to be modified and/or selected for the requirements of a particular application, e.g., rate of expansion of the stent, force to expand the stent, etc. 
     Additionally, in some embodiments, at least some of the peaks and/or valleys of the backbone of the stent can be pointed or sharply angled, e.g. a sawtooth, triangle, or the like. In some embodiments, at least some of the peaks and/or valleys of the backbone of the stent can be curved, smoothed, rounded, chamfered, filleted, or the like. Further, in some embodiments, some of the peaks and valleys of the backbone can be pointed while others are rounded. In some embodiments, a generally rounded or smooth curve at a peak or valley can promote an overall rounded shape of the stent. Further, a generally pointed peak or valley may promote a desired strength, flexibility or rigidity characteristic. Thus, some embodiments of the stent can be configured to create localized stiffness, strength, flexibility, patency, roundness, and/or other characteristics by manipulating the shape of peaks and valleys and the angular direction of the backbone, as discussed further herein. For example, a rounded peak may reduce the tendency for the peak to protrude into the lumen of the stent. Thus such a feature can assist in maintaining the patency of the lumen. 
     In accordance with some embodiments, the reversing helical backbone can be curvilinear. For example, the reversing helical backbone can comprise one or more continuous curves, one or more smooth curves, a continuously variable curvature, and/or the like. In some instances, the reversing helical backbone can be formed in an undulating reversing helical configuration. For example, the reversing helical configuration can extend generally in a wave pattern, a sawtooth pattern, a triangular pattern, a rectangular pattern, a zig-zag pattern, and/or the like. Further, the backbone can extend in a regular, repeating, and/or symmetrical pattern. However, in other embodiments of the stent, the backbone can extend in an irregular, non-repeating, and/or asymmetrical pattern. 
     Accordingly, the reversing helical configuration of the backbone can comprise nearly any wave form. For example, the reversing helical configuration can have a substantially constant amplitude. The amplitude is the distance between the adjacent peak and valley, as measured perpendicular to a longitudinal axis of the backbone. In other embodiments, the reversing helical configuration can have a substantially non-constant, varying, or changing amplitude. 
     Furthermore, in some embodiments, the reversing helical configuration can have a substantially constant period. The period is the distance or interval between adjacent peaks or adjacent valleys, as measured parallel to the longitudinal axis of the backbone. In other embodiments, the reversing helical configuration of the backbone can have a substantially non-constant, varying, or changing period. In some cases, the period can include one peak and one valley. In some embodiments, the period can include two peaks and one valley. In some embodiments, the period includes two valleys and one peak. In some cases, the period may span the entire length of the stent. 
     In accordance with at least some embodiments disclosed herein is the realization that the angular direction of the longitudinally-extending backbone structure can affect the characteristics of the stent. For example, a shallower angle (in relation to the longitudinal axis of the stent) can ease deployment of the stent. Conversely, a steeper angle (in relation to the longitudinal axis of the stent) can provide enhanced longitudinal flexibility of the stent and/or radial strength of the stent. As discussed further herein, surprising and advantageous results regarding the flexibility and deployment characteristics of a stent have been achieved by the inventors of the present application through implementing stent configurations disclosed herein. In particular, outstanding results have been obtained through implementing stent configurations having a reversing helical backbone with smooth or curvilinear peaks and valleys and a series of short-phase angle deviations along the length of the backbone between consecutive peaks and valleys. 
     Furthermore, in some embodiments, the reversing helical configuration can be defined as comprising a plurality of short-phase or leg elements. For example, in a backbone having a sinusoidal reversing helical configuration, each portion of the sinusoid from a valley toward a peak can be a short-phase or leg element, and each portion of the sinusoid from a peak toward a valley can be a short-phase or leg element. Generally, adjacent leg elements can have opposite slopes, e.g., a leg element with a positive slope will normally follow a leg element with a negative slope, and vice-versa. 
     In some embodiments, one or more of the short-phase or leg elements can be generally straight, generally curvilinear, or define a sub-pattern or variable shape configuration. For example, in some embodiments one or more of the leg elements can itself comprise a wave pattern, a sawtooth pattern, a triangular pattern, a rectangular pattern, a zig-zag pattern, and/or the like. Thus, in some cases, the backbone can have a reversing helical configuration and one or more of the leg elements can have a pattern that deviates from a generally straight length. In particular, some embodiments of the stent can provide a sinusoidal reversing helical backbone having a wave sub-pattern that extends between the peaks and troughs of the sinusoidal reversing helical backbone. 
     In some embodiments, the amplitude of the sub-pattern or variable shape of the leg elements is less than the amplitude of the reversing helical backbone. Surprisingly, the use of a sub-pattern on a reversing helical backbone has been found to advantageously promote uniform deployment of the stent. For example, it has been found that such a pattern-on-pattern configuration can reduce twisting and/or promote deployment of the stent. Furthermore, such a configuration can also exhibit the advantage of allowing stent characteristics to be modified and/or selected for the requirements of a particular application, e.g., rate of expansion of the stent, force to expand the stent, etc. For example, localized characteristics of the stent can be designed for given results, which provides substantial advantages and customization ability for the stents. 
     Various embodiments described herein can provide for a polymeric stent that exhibits advantageous structural properties that are comparable to those of a metal stent. For example, research has illustrated that the helical backbone construction, paired with the slide-and-lock interconnection of radial elements, can be used in a polymer stent such that the advantages of bioresorbability and superior structural stiffness and strength (similar to that of a metal stent) can be realized. This significant advance in stent technology allows other preferable materials—not just metals—to be used in a stent to achieve desirable material properties, while ensuring that the necessary structural properties of the stent are also achieved. 
     The slidably engaged radial elements can be configured for unidirectional slidable movement so as to permit the radial expansion of the tubular member. In an embodiment, the stent can define a first collapsed diameter, and a second expanded diameter. The slidably engaged expandable stent is adapted to be expandable between at least the first collapsed diameter and at least the second expanded diameter. 
     In some embodiments, the slidably engaged expandable stent is configured with two radial modules, each radial module being slidably engaged and configured for unidirectional expansive movement. Each radial module can include a backbone, a first elongate member and a second elongate member. In some embodiments, the elongate members are annular elongate members; in some embodiments, the elongate members are ring-like members elongated from the backbone. The elongate members can be slidably engaged with slots and can be configured for unidirectional slidable movement. 
     The slidably engaged expandable stent in some embodiments has a plurality of radial elements, including a first radial element and a second radial element. These radial elements can be substantially commonly oriented with respect to the backbone. The second radial element can be axially or circumferentially offset with respect to the first radial element. 
     The axially or circumferential offsetting of rail members and/or radial elements allows a distribution of slidable engagements. Such a distribution of slidable engagements is said to render the stent uniform with respect to mechanical failure points; as the slidable engagements are generally the weakest mechanical points in the design. Slidable engagements are herein defined as the engagement means between two slidably engaged radial modules. In some embodiments, the slidable engagements are defined by the interlocking of slots and contained rail members of the slidably engaged radial elements. 
     The slots can further comprise a locking member. A locking member can be, for example, a tooth, a deflectable tooth, stop, ridge, paddle, detent, ratchet, ramp, hook, or the like. In some embodiments, the slots comprise a number of stops inside the surface or cavity of the slot. In another embodiment, the slots comprise at least one tooth adjacent to the entry side of the slot. 
     The slots can be angled with respect to the longitudinal axis of the stent, which can to provide further advantages to the stent. For example, it has been determined that a shallower angle (in relation to the longitudinal axis of the stent) can decrease the force required to expand the stent, and thus can ease deployment of the stent. A steeper angle (in relation to the longitudinal axis of the stent) can increase the longitudinal flexibility of the stent and/or radial strength of the stent, and thus provide a stronger yet more flexible stent. Thus, appropriate slot angles may be selected to promote desired stent characteristics. 
     Additionally, the elongate members can be configured to comprise at least one conjugate locking member. A conjugate locking member is essentially a component designed to engage with the locking member. In some embodiments, a conjugate locking member is adapted to fit be engaged by the locking member. In one embodiment, the conjugate locking member is one of a tooth, a deflectable tooth, or a stop. A locking member and a conjugate locking member define an engagement means whereby the radial elements, rail members, and/or radial modules are slidably engaged. Exemplary conjugate locking members are described in co-pending U.S. patent application Ser. No. 12/577,018, filed Oct. 9, 2009, titled “EXPANDABLE SLIDE AND LOCK STENT,” the entirety of which is incorporated herein by reference. 
     The backbone can comprise a flexible link, such as a spring link. Alternatively, the flexible backbone can be made of an elastomeric polymer material sufficient to promote adaption to vasodynamic movements. Elastomeric polymers are defined in the art, however for illustrative purposes examples can include polycaprolactone, polydioxanone, and polyhexamethylcarbonate. 
     Various embodiments of the stents disclosed herein can incorporate various features, structures, material configurations, and other attributes of Applicant&#39;s patents and co-pending patent applications, such as U.S. patent application Ser. Nos. 11/016,269, 11/455,986, 11/196,800, 12/193,673, 11/399,136, 11/627,898, 11/897,235, 11/950,351, 11/580,645, 11/680,532, and U.S. Pat. No. 6,951,053, each of which are hereby incorporated by reference in their entireties. 
     EXAMPLES 
       FIGS. 1-20D  illustrate examples of stent embodiments having aspects of the embodiments disclosed herein. For clarity of the stent structure, certain of these figures illustrate various stent embodiments in a flat (e.g., unrolled) state. It should be understood, however, that such for delivery and/or implantation in a vascular structure, such embodiments can be rolled to form a tubular member. Although parts of the stent may have been illustrated as being on opposite sides of the stent (see, e.g.,  FIG. 9A , elements  732   a  and  735 ) for clarity, in the rolled state such elements can be slidingly engaged (see, e.g.,  FIG. 9C ). Various figures include a representation of a longitudinal axis  640  of a stent if formed into a tubular member. The longitudinal axis  640  can provide a frame of reference in measuring relative angles and orientations of components of the stents disclosed herein. However, the longitudinal axis  640  may not in all figures represent a center axis of the stent, but instead represent an axis extending parallel to a center axis of the stent. 
     Cross-Over Rail Pattern Versus Discrete Rail Modules 
       FIGS. 1 and 2  show planar representations of the circumferential surfaces (in the tubular state) of embodiments of a stent or stent assembly. The examples of  FIGS. 1 and 2  illustrate two different interconnecting arrangements of the elongate members or rail members of the stents, which extend generally circumferentially so as to integrate the stent assembly. The embodiments illustrated have generally U-shaped rail elements and three backbones. Other embodiments have more or fewer than three backbones. In other embodiments, the rail members need not be U-shaped, e.g., alternative shapes, such as “W-shaped” members and the like, may be advantageously employed). 
       FIG. 1  shows a stent assembly  650  with 3 backbones  652   a - c . The plurality of rail members or rail elements  654  are arranged in triplet patterns bonded to respective adjacent backbones. In this arrangement, cutting lines AA, BB and CC can be seen to cross all three backbones without intersecting any rail member. In this sense, the rail members may be described as being arranged in distinct radial modules. The radial modules may contain more or fewer than three rail members. 
     Further, in some embodiments, rail members or radial elements of a circumferentially extending radial module can be positioned adjacent to or at least partially overlap with rail members or radial elements of another circumferentially extending radial module. The spacing or overlap of adjacent radial modules can promote stiffness and flexibility of the stent. 
     For example, in the assembled tubular stent is illustrated in  FIG. 1 , a separation between distinct radial modules can promote a relative degree of flexibility at these junctions (the regions of cutting lines AA, BB and CC). 
     Further,  FIG. 2  shows an assembly  660  with a plurality of backbones  662   a - c . The plurality of rail members  664  are arranged in an overall cross-over pattern with respect to adjacent rail members. In this arrangements, cutting lines A′A′ and B′B′ can be seen to necessarily cross one or more rail members in traversing the array of backbones. In this sense, the rail members may be described as being integrated in a cross-over or partial overlap arrangement, without distinct or separated radial modules. As discussed above, in the assembled tubular stent, such a cross-over arrangement can promote radial strength and continuity along the axis of the stent. 
     As with other embodiments of this disclosure, the concepts illustrated in  FIGS. 1 and 2  may be used in combination. For example, one or more portions of the stent length may have a crossover pattern (e.g., a robust center section adjacent a lesion or plaque being supported radially), while other portions may be arranged as distinct modules (e.g., distal and proximal terminal modules suited to flexing to vessel contours). 
     Rail Pattern Perpendicular to Helical or Slanted Backbones 
     While many of the examples described herein have patterns of rail members oriented generally perpendicular relative to the stent longitudinal axis  640  (and generally obliquely oriented with respect to the helical or slanted portions of the backbones), alternative arrangements may be employed without departing from the unique and novel aspects disclosed herein. 
     For example,  FIG. 3  shows an assembly  670  with three backbones  672   a - c , arrayed generally parallel with one another, and set at an angle relative to the stent longitudinal axis  640 . The rail elements  674 , however, are generally aligned perpendicular to the backbones  672   a - c . As may be seen in Arrow  677 , the direction of sliding of the toothed portion of the rail member  674  with respect to the backbone pass-through slot is at an angle to the stent axis. 
     Note that in  FIG. 3 , as well as in several of the figures beginning with  FIG. 1 , the elements of the stent assembly may be shown in an untrimmed or unfinished configuration, with portions  676   a  of the rail members extending outward beyond the bonding slots of the backbone. These portions are provided for manufacturing convenience during assembly and the bonding and/or affixing of rail elongate portions to backbone structure. The extended portions may be trimmed to final shape  676   b  by known methods (blades, laser cutting, and the like) during the final assembly process. Similarly, in many of the figures, an extended proximal and distal portions of backbones is shown, which may be trimmed to a final desired length as a manufacturing procedure. 
     Non-Slanted Backbone Portions 
     It is often desirable to have the stent deploy or expand within a lumen in a uniform manner along its axis. In other cases, it may be desired to have portions of the stent deploy before or later than others. A balloon-based deployment system may tend to apply greater force or pressure at certain points along the stent axis, or inflate sooner at different longitudinal points. The stent structure may be tailored to achieve the desired deployment sequence. 
     In at least some deployment scenarios it may be advantageous, at certain longitudinal portions of the stent backbones, to have less mechanical resistance to expansion of the rail members through the pass-through engagement elements, than at other longitudinal portions. For example, where a balloon catheter deployment system tends to inflate more readily in the center than at the terminal ends, it may be advantageous to compensate for this by having less resistance to expansion of the terminal portions of the stent (or one end) than in a center portion. Thus, in some arrangements the stent can advantageously be configured to mitigate non-uniform expansion of the balloon catheter, e.g., the stent can be configured to expand substantially uniformly although the balloon catheter expands non-uniformly. 
       FIGS. 4A and 4B  show a stent assembly  680  with three backbones  682   a - c , arrayed generally parallel to one another in an locally slanted or helical orientation.  FIG. 4B  is a detail of the upper-left corner of  FIG. 4A . Rail members  684  are arranged bonded to the backbones and passing though slots in adjacent backbones. However, one or more of the backbones (e.g., all three in the example illustrated) may have a portion  685  which is less slanted or generally parallel to the stent axis. This less slanted or generally parallel portion  685  can facilitate motion of the rail elongate elements  684  through the pass through slots being generally parallel to the backbone at the un-slanted portion  686   a , and generally oblique to the backbone at slanted portion  686   b.    
     In certain cases, in an assembly of generally helically aligned or slanted backbones, a short section of backbone parallel to the axis of the stent at a terminal end of the stent cab enhance radial rigidity of the stent, particularly where the terminal end is supported by the last rail in sequence of the array, such as the left-hand portion of  682   a . Thus a non-slanted terminal backbone portion may be advantageously included one or more of the backbones of a stent assembly, e.g., stent assembly  680 . 
       FIG. 5  shows a stent assembly  690  with three backbones  692   a - c  arrayed generally parallel to one another in a generally slanted or helical orientation. Similar to the example shown in  FIGS. 4A and 4B , one or more of the backbones  692   a - c  can include multiple portions that are locally non-slanted or less-slanted (e.g., generally parallel to the stent longitudinal axis  640 ). In  FIG. 5 , several of these portions are marked with circles. For example, in some embodiments, one or more of the left end, right end, and/or a middle portion of at least one of the backbone  692   a - c  can contain such a non-slanted or less-slanted portion. In the particular example illustrated in  FIG. 5 , each backbone has three spaced-apart non-slanted portions. As shown, rail pass-through slot portions  696   a  can be provided with a perpendicular backbone-rail member alignment where the backbone portion is non-slanted. In this manner the deployment characteristics of the assembly may be tailored along the longitudinal axis of the stent, while maintaining an overall slanted or helical backbone pattern. 
     Bi-Directional, Multi-Directional or Variable-Directional Backbone Arrays 
     While many of the examples described have patterns of backbones oriented generally helical array, generally at a consistent angle to the stent longitudinal axis, alternative arrangements may be employed without departing from the unique and novel aspects disclosed herein. 
     In the example assembly  700  shown in  FIG. 6 , each backbone  702   a - c  has a slant angle that reverses at the mid-portion of the assembly. As shown, some embodiments can further include a medial non-slanted portion. As noted above, the inventors have noted that a “non-reversing” helical stent tends to unwind from either end toward the center, which creates binding and increased resistance to expansion in the center of the stent. Surprisingly, the inventors have determined that creating a stent with a reversing helical backbone and positioning the peak or apex of the reversing helical backbone at about the midpoint of the stent can reduce the tendency of the stent to bind during expansion. 
     However, by implementing the reversing helix illustrated in  FIG. 6 , the inventors have surprisingly determined that deployment of the stent can be more uniform and that binding is reduced in the center of the stent. In solving this problem, the inventors have also noted that a decreased amount of binding attributable to the helical arrangement takes place at approximately the one-quarter and three-quarter marks of the stent—the points between the ends and the center point where the helix reverses. Accordingly, as discussed further herein, the inventors have invented new and unique solutions for reducing and/or eliminating binding of the stent in these and other areas where localized binding may build. 
     In the example assembly  710  shown in  FIG. 7 , each backbone  712   a - c  includes a curvilinear portion and defines has a slant angle or slope (with respect to the stent axis) that is continuously variable from proximal end to distal end. This continuously variable curve extending between respective peaks and valleys of the backbones can provide superior flexibility and deployment characteristics, as discussed herein. In the illustrated embodiment of  FIG. 7 , the slope changes from negative to positive (as viewed from left to right in the figure) at the valleys of the backbones or midpoint of the assembly, giving the backbone an overall cosine wave appearance in this illustration. The rounded apex of the cosine wave can inhibit the apex from protruding into the lumen when the stent is in the rolled configuration. Avoiding such protrusions can be advantageous at least for the reason that such protrusions can block flow through a portion of the lumen. Additionally, inhibiting the apex from protruding into the lumen, can facilitate an overall round shape of the stent, as discussed above. Further, compared to a stent having a sharply angled peak (which could become entangled with or even puncture vasculature or the catheter balloon) the rounded apex of the cosine wave can generally slide against vasculature or the catheter balloon, thus facilitating delivery and deployment of the stent assembly. 
     Like the example of  FIG. 7 , in the example assembly  720  shown in  FIG. 8 , each backbone  722   a - c  includes a curvilinear portion and also has a slant angle or slope (with respect to the stent axis) that is continuously variable from proximal end to distal end. In the illustrated embodiment, the slope changes from positive to negative (as viewed from left to right in the figure) at the peaks of the backbones or midpoint of the assembly, giving the backbone an overall sine wave appearance in this illustration. As discussed above, the rounded apex of the wave can inhibit the apex from protruding into the lumen of the stent, can promote a more round overall stent shape, and can avoid entanglement during delivery and deployment. Further, as shown, in some cases a trident or W-shaped rail member  714   b  or  724   b  can be provided at the apex of the sine or cosine shape or enhancing flexibility and strength of stent at the peaks or valleys of the backbones. 
     In the examples of  FIGS. 7 and 8 , the backbone array provides a smooth transition between portions that are minimally sloped and portions that are markedly sloped. Many of the other embodiments illustrated in the appended figures provide similar advantages. 
     The absolute value of the overall helix angle (the angle at which a backbone extends relative to the longitudinal axis  640  of the stent) of the backbones of embodiments of the stent can be between at least about 15 degrees and/or less than or equal to about 60 degrees. The absolute value of the overall helix angle of the backbones can also be between at least about 20 degrees and/or less than or equal to about 50 degrees. Further, the absolute value of the overall helix angle of the backbones can be between at least about 22 degrees and/or less than or equal to about 30 degrees. In some embodiments, the absolute value of the overall helix angle of the backbones can be about 25 degrees. 
     Bi-Directional or Multi-Directional Rail Member Arrays 
     While many of the examples described have patterns of rail members or radial elements oriented in a consistent direction from proximal to distal end of the array, alternative arrangements may be employed without departing from the unique and novel aspects disclosed herein. 
       FIGS. 9A-9D  illustrate an embodiment that provides an improved deployed shape of the stent. In some embodiments it may be desirable for the deployed stent to be substantially round, e.g., circular in cross-section. The illustrated embodiment includes one or more components, such as a longitudinally-extending structure (e.g., a backbone) and a unique rail member arrangement that promotes the roundness of the stent. In some embodiments, excellent results for further promoting stent roundness have been found by implementing configurations in which rail members are selectively oriented in opposing circumferential directions. 
     For example, some embodiments, a first rail member can extend circumferentially in a first direction and a second rail member can extend circumferentially in a second direction. In the example assembly  730  shown in  FIGS. 9A-9D , the direction of orientation of arrays of the rail members or radial elements is reversed at the peaks of the backbones or at a midpoint of the stent assembly. In this particular example, the backbones  732   a - c  are arrayed similarly to the example of  FIGS. 7 and 8 , e.g., each backbone  732   a - c  is generally curvilinear and has a slant angle or slope with respect to the stent axis that changes direction of slope in the middle portion. Thus, the backbones can be described as reversing helical backbones having smooth or curved peaks and valleys. 
     With respect to the peaks or middle portion of the backbone array (shown in the expanded position in  FIG. 9A  and in the collapsed position in  FIG. 9B ), the rail members  734  are oriented with cross-members  735  of the U or W shaped rail members extending “upward” (in the drawing), and thus extending to the “outside” of the adjacent backbone curvature  732   a . With respect to the left and right end portions of the backbone array, the rail members are oriented with cross-members  735  of the rail members  734  extending “downward” (in the drawing), and thus also extending to the “outside” of the adjacent backbone curvature  732   c.    
     In the illustrated embodiment, as in the embodiment of  FIGS. 1 and 2 , the middle portion of the rail member array is a distinct radial module from the end portions. In other words, the embodiment illustrated in  FIG. 9A  illustrates three radial modules that are spaced apart from each other and provide, in a tubular member, independent circumferential modules. However, within the middle portion, the rail members form a crossover arrangement. Accordingly, as discussed above, in such an embodiment the middle portion can include enhanced radial strength and continuity along the axis of the stent, while the end portions can have enhanced flexibility to flex to vessel contours. 
     In some arrangements, the direction in which the first and second rail members extend can be related to or dependent upon the angle between the rail member and longitudinally-extending structure. For example, in some cases, the first and second rail members extend in a given circumferential direction such that the angle between the rail member and longitudinally-extending backbone or structure is an acute angle. Accordingly, it has been determined that, compared to stents with other features, e.g., non-reversing structures, a reversing helical backbone can promote roundness of the stent. 
     As shown, the backbone can be shaped substantially as a sinusoid. In particular, at least one peak of the sinusoidal backbone can be curved, e.g., not formed as a pointed peak or having a sharp angle. Such a rounded peak can further promote an overall rounded shape or roundness of the stent. For example, the rounded peak can reduce the tendency for the peak to protrude into the lumen of the stent. 
     Enhanced Tooth Deflection and Resiliency 
       FIGS. 10A-10F  illustrate alternative embodiments of the teeth or locking members provided on the elongate elements or rails of the various embodiments shown herein for engaging with the backbones in or adjacent the pass-through slots. Each of  FIGS. 10A-10F  shows a portion of rail  774  including a plurality of teeth  772 . In some embodiments, the teeth are positioned on multiple edges of each elongate element. In other embodiments, the teeth are on positioned a single edge, such as is shown in  FIGS. 10A-10F . 
     The embodiments shown the  FIGS. 10A-10F  each have one or more relieving openings  776  located within the rail member, which can reduce stress concentrations as the teeth  772  are deflected as they pass through the slot during stent expansion. In some cases, the relieving openings  776  may decrease force needed to deflect the teeth  772 . Advantageously, the relieving opening  776  can also promote stiffness of the tooth in the opposite direction, thus enhancing the one-way ratcheting configuration of the stent. Further, such relieving openings  776  can allow for a shallower configuration of the teeth to be employed, thus promoting manufacturability and reducing the amount of material than is removed to form the teeth  772 . 
     Such relieving openings  776  may extend through the material of the rail  744  (open holes) or may only extend partially through the material on one or both sides (indentations). The relieving openings  776  may, for example, prevent or reduce stresses in the teeth  772  during deployment so as to avoid or reduce plastic deformation, and to increase the effective rebound of the tooth as it passes beyond the pass-through slot of the backbone. 
     Note that the teeth  772  need not necessarily have a toothlike appearance, and alternative profiles may be employed, as shown in  FIGS. 10E and 10F . In these embodiments, the locking portion is rounded, and depresses inward under the forces of deployment. 
       FIGS. 11A-11D  show the action of engagement teeth or locking members provided on the elongate elements or rails of the rail members, configured for engagement with slots in the backbones of the stent embodiments described herein. In some respects, the example shown is particularly similar to the locking mechanism depicted in the embodiments of  FIGS. 12A-14B , discussed below. In the example of  FIGS. 11A-11D , the rail member  770  includes a pair of elongate rails  773   a  and  773   b  (note: there may be more than two, e.g., see member  724   b  in  FIG. 8 ). 
     A reference frame for the rail member  770  may be defined relative to the backbone to which it is to be fixedly mounted, joined or bonded in the assembled stent. In this reference frame, each of rails  773   a - b  of member  770  has a proximal end  772   a - b  configured to be fixedly mounted or bonded to a supporting backbone (e.g.,  782   a  in  FIG. 12A ). In this reference frame, the rail elements  773   a - b , as assembled, will extend distally to engage a sliding slot  787  of an adjacent backbone (e.g.,  782   b  in  FIG. 12A ). Each of rails  773   a - b  includes a medial portion  774   a - b  supporting a locking mechanism  776   a - b . In the illustrated embodiment, the locking mechanism  776  is disposed on only one side of rail  773 . Other embodiments have at least some of the locking mechanism  776  disposed on both sides of the rail  773   a  and/or  773   b . The rails  773   a  and  773   b  are joined at their distal ends by cross-member  775 . In alternative embodiments, where member  770  has more than two rails, cross-member  775  may join more than two rails. 
     In the detail drawing  FIG. 11B , it may be seen that the locking mechanism  776  comprises a sequential plurality of locking elements  777 , which are illustrated as being tooth-like in this example. The locking elements  777  can be separated by indented connecting regions  778 . In some cases, at least one stress management or relieving opening  779  is disposed adjacent connecting regions  778 . The relieving opening  779  can facilitate adjustment of the characteristics (e.g., flexibility, rebound, and the like) of the locking elements  777  by the selection of the shape, position, and/or size of the opening  779 . 
     The drawing of  FIG. 11C  and the photograph of  FIG. 11D  depict a stent locking assembly  771  composing the medial portion  774  disposed to pass through slot  787   b  of the backbone  782 . During radial expansion of the stent upon deployment, one or more of the locking elements or teeth  777   a  can enter the proximal opening of slot  787   b  and become deflected inward by engagement with the slot. This deflection is illustrated by deflected tooth  777   b , seen together with the superimposed undeflected shape as a dashed line. It may be seen that, as the adjacent tooth  777   b  is deflected, the relieving opening  779  may also deform under the deflection stress to a deformed shape  779 ′, shown as a dashed line. 
     As the tooth element  777   c  passes distally beyond slot  787   b , the tooth  777   b  rebounds to approximately the shape of the un-deflected tooth  777   a , so as to prevent radial contraction (proximal motion of rail portion  774 ). Relieving opening  779  may be configured to reduce or eliminate plastic deformation of locking mechanism  776  as the locking elements  777  are deflected during slot engagement, so as to improve the rebound of deflected tooth  777   b . The shape of tooth  777   a  upon rebound is configured to inhibit the tooth  777   a  from re-entering the distal opening of slot  787   b , so as to inhibit contraction of the stent. In this process, the tooth  777   c  may deflect outward to increase the positive nature of the locking assembly  771 . The relieving opening  779  may deform under the locking stress to form a different shape  779 ″. 
     Stent Assemblies with Extended Rail Arrays 
       FIGS. 12A and 12B  depict an alternative stent embodiment  780 , in which additional modules of rail members are included. Like the embodiment of  FIGS. 9A-9D , the embodiment  780  has at least a first module of rail members  784  directed in a generally perpendicular direction relative to the stent axis (e.g., downward in the illustrations of  FIGS. 12A and 12B ), and at least a second module of rail members  785  directed generally opposite the first module of rail members  784  and generally perpendicular relative to the stent axis (e.g., upward in the illustrations of  FIGS. 12A and 12B ). 
     In the example shown in  FIGS. 12A and 12B , each of the modules  784 ,  785  can comprise a group of three overlapping rail members  784   a - c ,  785   a - c . Each rail member can be joined or mounted to at least one backbone (three backbones  782   a - c  are illustrated) at attachment point  786 . Each rail member  784  can comprise a plurality of space-apart generally parallel rails  784 ′,  784 ″ that can be connected by a distal cross member  784 ″. Rail members  785  can be similarly structured. 
     In addition to being proximally mounted to at least one backbone, each of the individual rails or the rail members  784   a - c ,  785   a - c  can engage and pass slidably through a slot  787  in an adjacent backbone. As discussed above, although  FIGS. 12A and 12B  diagrammatically show assembly  780  as planar shape, these figures represent a generally tubular stent assembly  780 . As shown by arrow  788   a , the rail members  784   c  mounted to backbone  782   c  can be configured to pass slidably through slots of adjacent backbone  782   a , and similarly arrow  788   b  indicates that rails member  785   a  mounted to backbone  782   a  can be configured to pass slidably through slots in backbone  782   c.    
       FIG. 12A  illustrates a compacted form of stent assembly  780 , in which the toothed portion  789  of each rail of rail members  784   a - c ,  785   a - c  is positioned distal to the corresponding engagement slot  787  (indicated as  787   a ). In some embodiments, the backbones  782   a - c  are disposed closely adjacent one another and/or nested. In some embodiments, in the compacted configuration, the stent  780  is configured to mount on a collapsed balloon catheter. 
       FIG. 12B  illustrates a radially expanded form of the stent assembly  780 , in which the toothed portion  789  of each rail of the rail members  784   a - c ,  785   a - c  is positioned at least partially within the corresponding engagement slot  787  (indicated as  787   b ). In some embodiments, in the radially expanded state of the stent  780 , the backbones  782   a - c  are disposed at a substantial separation from one another, as would typically be configured for deployment at a larger tubular diameter supporting a treated vascular or other body lumen. In this configuration the toothed portion  789  can inhibit radial contraction of the stent  780 . 
     In the illustrated embodiment, each backbone  782   a - c  has an overall slant angle or slope θ (with respect to the stent axis) and can be disposed as a generally helical portion in the tubular stent body. In some embodiments, the overall slope angle θ reverses (shown as +0 and −θ in  FIG. 12A ) adjacent each rail module  784 ,  785 , so as to form an overall zig-zag shape. In the example shown, each backbone includes three distinct helical portions of substantial pitch, and the stent assembly  780  comprises four rail modules, each oppositely aligned relative its each adjacent rail modules. In the example shown in  FIGS. 12A and 12B , the slope angle θ of each portion is about 25 degrees, although it may be greater or less than this. 
       FIGS. 13A and 13B  illustrate end-on views (looking down the open lumen) of the stent  780  in the compacted and expanded stent configurations, respectively. In these figures, stent  780  is viewed as if viewing the perspective view of  FIG. 14A  looking at the axis of the drawing from the right hand side. The view is, in essence, a cross section of the stent through rail member  784   a . These views also correspond to viewing the assembly  780  in  FIGS. 12A and 12B  from the left hand side of the figure plane (when the stent is in the rolled configuration). 
     As may be seen in the compacted configuration of  FIG. 13A , the rail member  784   a  is mounted at its proximal end to backbone  782   a . Rail member  784   a  extends clockwise in the figure to pass through slot  787  in adjacent backbone  782   b . As shown, the locking mechanism  776   a  normally is positioned beyond the slot  787  when the stent  780  is in the compacted configuration. The other backbone and rail member assemblies  782   b - 784   b ,  782   c - 784   c  are disposed and configured similarly in clockwise fashion, each rail member  784   b ,  784   c  also passing through a slot  787  in an adjacent backbone. A deflated balloon catheter  800  is represented by phantom lines inside the perimeter defined by the compacted stent assembly  780 . In some embodiments, a retractable/removable sheath  802  surrounds the compacted stent assembly  780  until the stent is in position within a lumen at a treatment site. 
     As may be seen in the radially expanded configuration of  FIGS. 13B and 14A , the balloon  800  of the catheter assembly has been inflated to an extended diameter  800 ′, expanding the perimeter of stent assembly  780  radially outward. During such expansion, each backbone  782   a - c  generally moves circumferentially farther away from each adjacent backbone than it was in the compacted state. As a result, each rail member  784  moves with respect to its respective engagement slot  787  such that after the expansion the engagement slot  787  is positioned at a more distal portion of the rail member  784 . Such movement eventually results in the locking mechanism  776  being at least partially engaged within the slot with at least one of the locking elements  777  inhibiting radial contraction of the rail member  784 , e.g., in the manner shown in  FIGS. 11C and 11D . Note that cross member  775  of each rail member lies at the outside the perimeter defined by adjacent rail members, spanning across these adjacent rail members. Such an arrangement advantageously can maintain the distal end of the deployed rail member  784  securely outside of the vascular lumen following retraction and removal of the balloon catheter  800 . 
       FIG. 14B  illustrates a flexed or bent configuration of stent assembly  780  as deployed in a curving vascular lumen. In some embodiments, the spring-like configuration and longitudinal continuity of the plurality of backbones  782   a - c  can permit the tubular assembly to be smoothly flexed to follow a curved lumen. Additionally, in some embodiments, the regular rib-like structure comprising a plurality of circumferentially aligned rail members  784   a - c ,  785   a - c  can provide radial strength and support for the lumen wall. 
       FIGS. 15A and 15B  illustrate schematically the relation of the backbones (e.g.,  782   a  and  782   b ) to the rail members  784 .  FIG. 15A  is a cross-sectional side view of a portion of backbone  782   a , illustrating the proximal ends  772   a - b  of one rail member mounted in backbone recess  786  (e.g., by adhesive or solvent bond  786   b ), and showing the elongate rail elements  773   a - b  on and adjacent rail member passing through the slots  787   a  of the backbone.  FIG. 15B  illustrates a single rail member  784  in cross section, having a proximal portion  773  mounted to backbone  782   a  at recess  786 , and passing through slot  787   a  of adjacent backbone  782   b.    
     Overall and Localized Backbone Slope 
       FIG. 16  is a detail of a mid portion of the compacted stent assembly  780  shown in  FIG. 12A , and the elements are labeled as in  FIG. 12A . As shown, the backbone  782   b  can include an overall helix angle for the backbone portion shown (θoa). In general, a steeper overall helix angle contributes to a deployed stent that has greater longitudinal flexibility and radial strength. In contrast, a shallower overall helix angle normally contributes to an assembly that may be expanded during balloon deployment with a reduced tendency to twist as it expands, thereby promoting a smoother and more uniform deployment. The overall helix angle may be selected to provide desired stent characteristics. For example, in some cases the overall helix angle is selected to balance between the aforementioned general properties. 
     In some arrangements, although the overall helix angle θoa may be in one direction (e.g., positive) a portion of the stent assembly  780  may include one or more regions with an opposite slope (e.g., negative). For example, the overall helix angle θoa may be negative, but a portion of the stent assembly may be positive, before reversing and trending downward again. Further, as illustrated in  FIG. 17 , the backbone can comprise a plurality of discrete segments. The discrete segments can be that portion of the backbone extending between engagement elements of the backbone. Further, the discrete segments can comprise the portion(s) of the backbone corresponding to the engagement elements of the backbone. In some embodiments, each of these discrete segments can comprise a discrete helix angle or slot angle. In some embodiments, such as when the discrete segment is an engagement element (such as a slot), the discrete helix angle may be referred to as a slot angle. A discussion of the overall helix angle and the discrete helix angle or slot angle follows. 
     Normally, the reversing helical shape of the backbone can comprise at least one portion that trends positive and at least one portion that trends negative. A positive trend is a portion or the backbone that has a positive overall helix angle, regardless of the discrete helix angles of the individual or discrete segments. A negative trend is a portion or the backbone that has a negative overall helix angle, regardless of the discrete helix angles of the individual or discrete segments. In some cases, within one or both of the positive and negative trending portions there can be one or more sections that are sloped oppositely to the trend. For example, a negatively trending portion can include a positively sloped section. Likewise, positively trending portion can include a negatively sloped section. Generally, the oppositely sloped section is minor compared to the trending portion. For example, in some embodiments the oppositely sloped section is less than about 25% of the length of the trending portion. In some embodiments the oppositely sloped section has an amplitude that is less than about 30% of the amplitude of the trending portion. 
     Surprisingly, a backbone having a reversing (e.g., a zig-zag) helix angle, such as is shown in  FIGS. 12A and 12B , can promote an advantageous balance between these general properties so as to provide enhanced longitudinal flexibility and radial strength in combination with a reduced tendency to twist upon deployment. In contrast, a substantially continuous overall slope (such as in the backbones of the embodiment of  FIGS. 1-3 ) does not provide the same advantages. 
     In addition to the generally overall helical alignment of the backbone portions indicated by angle θoa, it may be seen that each helical portion (e.g., each leg of the zig-zag) has a local reversing helical shape, e.g., a small-pitch undulation or waviness. Contrast the small-pitch undulation or waviness of the backbones  782   a - c  of  FIGS. 12A-12D  with the backbone alignment shown in  FIG. 9A . This localized non-uniformity results all or some of the slot  787  having a characteristic centerline slope incrementally different than the overall slope, the difference denominated dθ1, dθ2, dθ3, dθ4, . . . dθn. 
     In the example shown in  FIG. 16 , each slot portion  787   a  has approximately the same value of dθ relative to the overall helical angle θoa, although this need not be so. The values of dθ may each be different from adjacent slots and may have a positive variation or negative variation. For example,  FIGS. 17A-C  illustrate plan, elevation, and partial focused views of an example backbone  792  that is generally similar to the backbone  782   a  (shown in  FIGS. 12A and 12B ) and has different dθ values. In this example, the overall helix angle of each of three slanted portions (the three legs of the zig-zag) is about 25 degrees or −25 degrees. As discussed further above, the absolute value of the overall helix angle of the backbone can be between at least about 15 degrees and/or less than or equal to about 60 degrees. The absolute value of the overall helix angle of the backbones can also be between at least about 20 degrees and/or less than or equal to about 50 degrees. Further, the absolute value of the overall helix angle of the backbones can be between at least about 22 degrees and/or less than or equal to about 30 degrees. In some embodiments, the absolute value of the overall helix angle of the backbones can be about 25 degrees. As shown, the plurality of slots  797  are normally distributed longitudinally along the backbone  792  to provide sliding engagement for an array of rail members, such as members  784 ,  785  in  FIGS. 12A and 12B . 
     The approximate angle of the mid-line of each slot  797  is indicated. As shown, this embodiment includes a relatively small slot angle of about 10 degrees, and medium slot angle of about 33 degrees and a steeper slot angle of about 40 degrees. Of course, this embodiment is only one example and various other slot angle values and arrangements are contemplated. In some embodiments, the absolute value of the slot angle can be between at least about 0 degrees and/or less than or equal to about 60 degrees. The absolute value of the slot angle can also be between at least about 10 degrees and/or less than or equal to about 50 degrees. Further, the absolute value of the slot angle can be between at least about 20 degrees and/or less than or equal to about 40 degrees. The slot angle can also vary between at least about 30 degrees and/or less than or equal to about 35 degrees. Finally, as illustrated, the absolute value of the slot angle can be approximately 10 degrees, 33 degrees, 40 degrees. Further, it is contemplated that the slot angle can be any variety or combination of desired angles that are configured to facilitate ease of expansion on the one hand and stent flexibility on the other hand. 
     For example, in some embodiments, two of the slot angles values are equal. In some embodiments, the middle slot has the greatest slot angle value. In some embodiments, at least one of the slot angles values is equal to the overall helical angle θoa. In some embodiments, the average or the median of the slot angles values is about equal to the overall helical angle θoa. 
     Generally, a steeper slot angle enhances longitudinal flexibility and radial strength of the stent, thereby promoting a stent that is both stronger and more elastic. In contrast, a shallower slot angle generally enhances expansion of the stent deployment and reduces the tendency of the stent twist as it expands, thereby promoting a stent with a smoother and more uniform deployment. 
     The individualized slot angles of the slots  797  as provided by the tailored undulations or waiviness of the backbone as shown in  FIG. 17B  allows further refinement of deployment characteristics. Surprisingly, it has been found that a slope angle in the region of slot  787   a  may be selected to promote more uniform and predictable stent deployment as the stent is radially expanded by a balloon catheter at a selected vascular treatment site. As discussed above, angles may be selected to promote strength and flexibility, or a highly uniform deployment behavior. In some embodiments, angles are selected to promote a sequential opening longitudinally, for example, configured to match balloon inflation characteristics. 
     As shown in  FIGS. 17D and 17E , the slot angle dθ for each slot may be measured in at least two locations. As shown in  FIG. 17D , in some embodiments, the slot angle dθ is the angle between a line connecting the midpoints of sidewalls  798   a ,  798   b  of the slot  797  and a line parallel with the longitudinal axis of the stent. In other embodiments, the slot angle dθ can be measured as the angle between a tangent to a midpoint of the lower edge 799 of the slot  797  and a line parallel with the longitudinal axis of the stent, as shown in  FIG. 17E . 
     Additionally, although the above discussion characterizes the backbone as being divided into discrete parts whose angular orientation is taken at the slots of the backbone, the angular orientation of discrete parts of the backbone can also be taken in similar fashion for those segments of the backbone extending between the slots of the backbone. As illustrated in  FIG. 17B , the discrete segments extending between the slots of the backbone can be generally curvilinear and define an increasingly or decreasingly positive slope (as shown on the immediate left side of a peak along a leg of the backbone) and/or define an increasingly or decreasingly positive slope (as shown on the immediate right side of a peak along a leg of the backbone). 
     In some embodiments, these discrete segments can be generally curvilinear and provide the “rise” or “fall” component of the helical extension of the backbone while the slot extends generally parallel relative to the longitudinal axis of the stent. In other words, in some embodiments, only the discrete segments extending between the slots would extend in a helical direction. However, as discussed extensively herein, the incorporation of curved or curvilinear segments in some embodiments can enhance the flexibility and strength of the stent. In other embodiments, the discrete segments and the slots of the backbone can all be curvilinear or generally straight and extend in a direction generally parallel to the relative to the longitudinal axis or helically about the axis. 
     Stent Device Manufacture, Processes and Assembly 
     The overall stent device manufacturing process may include any or all of the following sub-steps in any effective operational order: 
     Polymer synthesis, compounding and/or mixing. 
     Non-polymer materials, such as a biocompatible metal material, such as a bioerodable alloy or non-bioerodable alloy. All or some parts may be metallic, and metal sheet processing steps below may be functionally equivalent to polymer oriented steps below. 
     Optional composite materials, e.g., reinforcing materials, drug carrier particles, and the like. 
     Polymer film pressing, molding and/or thermal processing. 
     Multi-layer film. 
     Drug coating of polymer film. 
     Cutting of parts from polymer film, e.g., laser cutting. In some embodiments, different parts of the stent may have different film composition or structure. 
     Industrial precision part forming methods, injection molding, 3-D printing, UV stereo-forming, and the like. 
     Drug coating of formed parts, e.g., anti-restenosis compound applied in polymer/solvent carrier, such as by spraying, dipping, or the like. 
     Pre-forming and/or molding of parts, e.g., pre-shaped backbones and rail members (see, e.g.,  FIGS. 18, 19A, and 19B ). 
     Assembly of stent in semi-compacted configuration, e.g.: 
     tooling to hold and manipulate parts; 
     grooved mandrels to hold backbone assembly, 
     insertion of rail members though slide slots; 
     bonding of rail members in bond recesses or bond-slots (such as with adhesive bonding, solvent bonding, heat or energy bonding, or the like); 
     trimming of excess material and/or assembly tabs from parts; and/or 
     optional post-assembly treating, coating and/or polishing. 
     Inspection and quality control of assembled stent. 
     Final stent compaction and mounting on balloon catheter (e.g., iris-like uniform compaction devices, heat, pressure, fluids, vacuum and/or pressure applied to balloon, and the like). 
     Packaging and sterilization of stent/catheter product (e.g., E-beam Irradiation, chemical sterilization, or the like). 
     The stent can be made from many types of biocompatible materials. For example, polymer compositions suitable for making the stent embodiments described herein are described in published patent application US2010-0228,343, Brandom, et al.; “Phase-Separated Biocompatible Polymer Compositions For Medical Uses”. See, e.g., Tables 2 and 3 of that publication, and related description, which teach the preparation and testing of a copolymers of I2DTE (di-iodo-desaminotyrosyl tyrosine ethyl ester) and PCL (polycaprolactone) of different molecular weights, such as Poly(85% I2DTE-co-8% PCL10K-co-7% PCL1.25K carbonate). 
     Other biocompatible materials may be employed. Likewise, composite and/or layered materials may be employed. Different parts, such as rail members and backbones, may have differing polymer composition and/or different material properties (e.g., different layer structure, heat treatment or annealing history, composite content or the like). In alternative embodiments combination of polymer and metallic materials may be employed. Bioerodable metallic materials such as alloys and coated metals may be employed for the stent structure without departing from the unique and novel aspects disclosed herein. Bioerodable metallic materials may comprised magnesium, iron alloys, zinc, manganese and the like. 
       FIGS. 18, 19A, and 19B  illustrate pre-formed backbone and rail member parts having a pre-formed shape between the same parts as cut from flat sheet polymer (see, e.g.,  FIGS. 11, 17A, and 17B ) and the shape as finally assembled in a complete stent structure (such as  FIGS. 13A-14B ). For example, the parts may be shaped in molds or other tooling by application of pressure, heat, optionally moisture, and the like or combinations of those. Such pre-forming or pre-shaping of parts such as backbones  782  and rail members  784  may advantageously reduce or eliminate plastic deformation, residual stresses, or other changes to material properties during the process of assembling and mounting the stent. Pre-forming or pre-shaping of parts may also simplify and promote convenience in the assembly process, and promote precision in alignment of parts for bonding or the like. 
       FIG. 18  shows a typical rail member  784 , which has been pre-formed to have an overall curvature approximating the curved surface of the tubular stent assembly, and in which the proximal rail end portions  772   a  and  772   b  have been given a greater curvature (smaller radius) approximating the curvature of these portions in the compacted stent assembly (see, e.g.,  FIG. 13A ). 
       FIGS. 19A and 19B  show typical backbones  852  and  854  that have been given a pre-formed shape approximating the shape in the assembled stent. The backbone  852  in  FIG. 19A  has a reversing helical shape (see  FIGS. 14A and 14B ), such that only the inside surface  856  (facing toward center of assembled stent lumen) is apparent in the plane of the drawing. In contrast, backbone  854  in  FIG. 19B  has a continuous helical shape, in which both inside surface  856  and outside surface  857  (facing outward from assembled stent lumen) is apparent in the plane of the drawing. 
       FIGS. 20A-20D  show details of the assembly process of mounting rail members (e.g.,  784 - 785  of  FIGS. 12A and 12B ) during assembly, which is applicable to core bonded assemblies (e.g., embodiments in which the rail member is bonded to the backbone) of the various alternative embodiments described herein. In such assemblies, the typical sequence is to pass rail members through the sliding slots of the adjacent backbone prior to fixedly mounting the rail member to its supporting backbone. In some cases, grooved or conformably-shaped mandrels are used for securing the backbones during assembly of the stent structure. 
       FIGS. 20A and 20B  shows the preliminary step of inserting the proximal ends of the rail members  772  through the slots  787  in the adjacent backbone  782   b  in the direction shown by the arrow.  FIGS. 20C and 20D  show a subsequent step of fixedly mounting the proximal rail member ends  772  to supporting backbone  782   a . In this example, an adhesive bond is formed between the rail end  772  and the surface of recess  786  using a bonding agent  860 . An amount or portion of bonding agent  860  may be deposited in recess  786 , followed by pressing rail end  772  down into recess  786 . Specialized positioning or clamping tooling may be provided for convenience and consistency in this mounting process. In one example, a bonding agent  860  may comprise a solvent which allows the material of backbone  782  to adhere to the material of rail end  772 . For example, an agent comprising methylene chloride or a similar solvent may be applied to bond polymer parts comprising a copolymer of I2DTE and PCL. In other examples, agent  860  may comprise cross-linking or UV curable adhesive. In yet another example, energy such a locally applied heat or ultrasound may be used to bond rail  772  to backbone  782 . In yet other examples, a fitting or fastener may be employed. 
     Stent Embodiments with Recessed Portions 
       FIG. 21  illustrates an alternative embodiment generally similar to that of  FIGS. 12A-C , having a backbone profile which facilitates reduced profile in the compacted stent configuration. For example, some embodiments include recessed and/or nesting portions, as discussed in further detail below. 
       FIG. 21  depicts, in planar representation, an example of an alternative stent embodiment  900  in a compacted configuration having a structural assembly closely similar in its general arrangement to the stent assembly  780 , shown in  FIG. 12A . The stent can be structurally similar to stent assembly  780 , and can include the components discussed above. The stent assembly  900  can comprise backbones  901 A,  901 B and  901 C arranged with a plurality of modules, M1, M2, M3, and M4, which can have having generally “U” shaped rail members  902  (similar to members  770  of  FIGS. 11A-D ). Each rail member  902  can comprise a plurality of spaced-apart, generally parallel rails  908  that can be connected by a distal cross member  909 . Although four modules M1-M4 are illustrated, the stent could have fewer or more modules. 
     During expansion, the backbones  901  can be configured to generally move circumferentially farther away from an or each adjacent backbone compared to the compacted state of the stent, thus allowing for expansion of the stent assembly. As in stent  780 , in this example each module can be oriented circumferentially in the opposite sense to each adjacent module. In the particular example shown, various ones of the U members are substantially the same shape, or similarly structured as another member, and variations are indicated by numbers 1-6 at the tips, although such similarity need not be so. 
     The stent backbones  901 A, B, C can comprise at least three different sections. For example, as shown in  FIG. 21 , the backbones can comprise an open bond slot  903 , a closed pass-through slot  904 , and a recessed portion  905 . The positioning and order of these sections can vary throughout the backbones of the stents. For example, as shown in  FIG. 21 , the sections can proceed in the order of open bond slot  903 , recessed portion  905 , pass-through slot  904 . This order can be repeated along the stent backbones, allowing for the attachment of the U rail modules, or can be reversed, thereby allowing for the vertical flip of the rail modules. However, the order of the sections is not limiting, and all sections may have different physical portions between them. Both the open slop  903  and the pass-through slot  904  are discussed in further detail above, and recessed section  905  is further discussed below. 
     In some embodiments, the circumferentially adjacent backbones, such as those shown in  FIG. 21 , can have each of the three sections described above at the same longitudinal position, where each backbone has a different section. For example, as shown in  FIG. 21 , backbone A can have the open bond slot  903 , and circumferentially adjacent backbone B can have the closed pass-through slot  904  at the same longitudinal position. In certain variants, adjacent backbone C can have the recessed section  905  at the same longitudinal position as the open bond slot  903  of backbone A and the pass-through slot  904  of backbone B. Moving around the stent circumferentially, these three sections, or others, can repeat in various combinations, although the order of the sections is not limiting. 
       FIGS. 22A, 22B and 22C  illustrate cross sections of example portions of the structural backbones of the stent assembly shown in  FIG. 21 , cut along the backbone extent and showing the sections of adjacent rail members.  FIGS. 22A-C  aligned vertically to demonstrate the longitudinal alignment of features in adjacent backbone portions. 
       FIG. 23  illustrates a cross-section perpendicular to those of  FIGS. 22A-C , cut along the circumferential extent of a rail member, showing its engagement with each adjacent backbone member. As shown, the U rail member  902 . 1  can be attached to open bond slot  903 , can pass through the pass-through slot  904 , and can bend to rest atop the recessed portion  905 . One advantage shown is that the bend in the U rail member  902  is less substantially than if the recess portion  905  was not on the stent, thereby putting less stress on the U rail member  902 . 
       FIGS. 22A-C  and  23  show detail views of the arrangement of the each recessed portion  905  in circumferential alignment with the closed pass-through slot  904  of an adjacent backbone, so as to engage the distal rail portion  908  of member  902 . As seen in  FIGS. 22A-C  and  23 , like the embodiment  780  of  FIG. 12A , the backbones  901  of stent  900  can include, as a longitudinal array, a plurality of circumferential slots. The slots include open bonding slots  903  to which the proximal tips of the “U” rails are bonded, and closed pass-through slots, each engaged by a rail of a U member  902 . 
     However, unlike the embodiment  780  of  FIG. 12A , each of the backbones  902  of stent  900  can include a recessed (also called “nesting”) portion  905 . These recessed portions  905  can be configured to allow for a portion of the U members  902  to rest upon them, or at least have the U members  902  substantially adjacent to the recessed portion  905  while not physically in contact. Additionally, as shown in  FIGS. 22A-C , the recessed portions  905  can form a generally step down structure to the backbone of the stents. The stent backbone can have its peak thickness when surrounding the member  902  or an adjacent stent, can have an intermediate thickness of the recessed portion  905 , and can have the smallest thickness at the bonding slots  903 . This allows for a reduction in the overall thickness of the stent assembly, as further described below. The thickness changes between the respective sections,  904 / 905 / 903 , can be relatively sharp, as shown in  FIGS. 22A-C , or can have relatively smooth transitions between thicknesses. 
     The overall arrangement of recessed portions  905  with respect to slots  903  and  904  of adjacent backbones  901  may best be seen in  FIGS. 24A and 24B  which illustrate the full longitudinal backbone feature alignment of the stent of  FIG. 21 .  FIG. 24A  illustrates a top view of a first backbone, shown in respective alignment with three adjacent side elevation views of  FIG. 24B  comprising the first backbone along with two adjacent backbones, and showing schematically the alignment of interconnecting circumferentially-directed U rail members  902 . Arrows in  FIG. 24A  illustrate the direction of the extension of the U rail members  902 . 
     The bond slots  903  on each backbone ( FIG. 24A  shows backbone  901 A) can be arranged (in this example) in pairs, corresponding to the twin rail tips  907  of each rail member  902 . Adjacent pairs of bond slots  903  of a given backbone  901  can correspond to oppositely sensed rail members  902  included in adjacent rail modules, each module having one rail member  902  bonded to a different backbone. 
     As seen in  FIG. 24B , the each bond slot  903  can lie circumferentially-adjacent to a corresponding closed pass-through slot  904  on an adjacent backbone, interconnected by a rail  908  of a rail member  902 . The corresponding recessed portion  905  can lie further distally adjacent the slot  904  on the next adjacent backbone. 
       FIGS. 25 and 26  illustrate comparison side elevations of portions of each of a backbone of the stent of  FIG. 12  with similar portions of backbone of the stent of  FIG. 21 , illustrating the relative thicknesses of backbone and rail member profile features of the two stent embodiments, indicating illustrative examples of dimensions of each in microns. These figures depict a representative portion of a backbone of the corresponding stents  780  and  900 , in which the relative positions of the rail members  784  and  902  represent the stent in a compacted stent configuration (as mounted on a balloon catheter prior to deployment). The dimensions (in micron) are for purposes of illustration only (actual dimensions may be more or less), although the dimensions shown provide a reasonable basis for comparison between the two stent embodiments  780  and  900 . 
       FIG. 25  shows a portion of a backbone of assembly  780  showing the backbone/slot/rail geometry (see  FIGS. 20A  thought  20 D) at three longitudinally spaced apart cross sections, as follows:
         (1) The first section point (indicated as cross section 1 or XS1) is positioned at an open bonding slot  786 . Here the total thickness of the assembly  780  is the sum of the backbone at the open slot portion, together with two thickness of the rail  784 , depicting an example configuration in which the rail wrapping around the circumference to overlap slot a second time;   (2) At the second section, XS2, the total thickness of the assembly  780  is the sum of the backbone at an intermediate portion between slots  786  and  787 , together with one thickness of the rail  784 , depicting an example configuration in which the rail only overlaps the backbone once. In this configuration, rail  784  on line XS2 is approximately directly on top of rail  784  of line XS1, as shown by the dashed rail  784 ; and   (3) At the third section, XS3, the total thickness of the assembly is that of the backbone at the closed slot location 782.1, depicting an example configuration in which the rail only passes through the closed slot and does not overlaps the backbone.       

       FIG. 26  shows a portion of a backbone of assembly  900  showing the backbone/slot/rail geometry at the same three longitudinally spaced apart cross sections as in  FIG. 25 , as follows:
         (1) At XS1, the total thickness of the assembly  900  is the sum of the backbone portion at slot  903  together with twice the thickness of rail  902 , however the backbone is depicted as somewhat thinner at this section (see polymer discussion below);   (2) At XS2, the total thickness of the assembly  900  is the sum of the backbone at an recessed portion  905 , together with one thickness of the rail  902  (depicted in the example configuration of  FIG. 25 ). As shown, the overall thickness of the assembly  900  is less in  FIG. 26  than the same portion in  FIG. 25 , and rail  902  on line XS2 would not fall directly on top of rail  902  on line XS1, but would instead be partially encompassed, as shown by the dashed rail  902 ; and   (3) At XS3, the total thickness of the assembly  900  is that of the backbone at the closed slot location 904 (depicted in the example configuration of  FIG. 25 )2       

     TABLE 1 includes an illustrative summary of the dimensions indicated in  FIGS. 26-26  along with total thickness at three longitudinal points for each backbone, thereby providing a comparison of the effective profile thickness contributions for each stent. It may be seen that the total thicknesses at XS1 and at XS3 are substantially less for the Stent  900  than the stent  780 , which can be due to, for example, a combination of polymer thickness as well as the use of the recessed portion  905 . The overall average at all three sections is shown to be about 15% less for stent  900  than stent  780 . 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Thickness Comparison of the Stent Assemblies  
               
               
                 According to FIGS. 25 and 26 
               
               
                 Illustrative example dimensions (microns) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 XS 1 
                 XS 2 
                 XS 3 
                 Average 
               
               
                   
                   
               
               
                   
                 FIG. 25 
                   
                   
                   
                   
               
               
                   
                 Surface 
                 150 
                 300 
                 300 
                   
               
               
                   
                 U-1 
                 130 
                 130 
                   
                   
               
               
                   
                 U-2 
                 130 
                   
                   
                   
               
               
                   
                 Totals 
                 410 
                 430 
                 300 
                 380 
               
               
                   
                 FIG. 26 
                   
                   
                   
                   
               
               
                   
                 Surface 
                 105 
                 195 
                 285 
                   
               
               
                   
                 U-1 
                 130 
                 130 
                   
                   
               
               
                   
                 U-2 
                 130 
                   
                   
                   
               
               
                   
                 Totals 
                 365 
                 325 
                 285 
                 325 
               
               
                   
                   
               
            
           
         
       
     
     The substantially smaller thicknesses of the backbone portions at both slot  903  and recessed portion  905  of backbone  901  of stent  900 , when compared to the corresponding portions  786  and  782 . 2  of stent  780 , may result in higher forces and moments, such as bending moments, in a given medical application, such as a coronary artery stent deployment. Such forces and moments depend on a number of different design aspects as well as the particular stent deployment operation itself (e.g., balloon pressure, nature and size of lesion, etc). However, medical polymer structures providing both biodegradability and radiopacity, combined with high strength and fatigue resistance, are enabled by the polymeric materials, monomers and processes disclosed in U.S. Pat. No. 8,252,887, and in pending U.S. patent application Ser. No. 13/757,752 filed Feb. 2, 2013 (not yet published), both assigned to Rutgers State University. Both of these patent disclosures are incorporated herein by reference in their entirety. Such materials of high strength and fatigue resistance may support stent designs having substantially smaller dimensions, such as those shown for the example stent  900 . 
       FIGS. 27A-B  and  28 A-B show comparative photographic representations of stent assemblies generally similar to, and/or according to, the embodiments of  FIGS. 12 and 21 , shown compacted and mounted on a balloon delivery catheter. For each figure, subfigure A illustrates an oblique perspective and subfigure B illustrates an inset shown a side view. 
     As shown in  FIGS. 27A-B , one result of the thinner backbone structure  901  of stent  900 , as well as the effect of the recessed “nesting” portion  905 , is a thinner overall stent profile in the compacted configuration, which facilitates vascular insertion and deployment in smaller arteries and difficult vascular geometry. For example, it has been demonstrated that stent/catheter package of 7 French gauge (e.g., about 2.3 mm in diameter) may be reduced to 6 French gauge (e.g., about 2.0 mm in diameter) through the use of embodiments of stent  900 . A comparison of the side elevation of the mounted stent depicted in  FIG. 27A  (generally similar to stent  780 ) with the  FIG. 28B  mounted stent depicted in  FIG. 27B  (generally similar to stent  900 ) demonstrates the substantial reduction in profile. As shown in  FIGS. 27 and 28B , the thickness profile of stent  900  can be significantly smaller than that of stent  780 . For example, as indicated by the scales in  FIGS. 27 and 28B , the thickness (e.g., diameter) of the stent  900  can be approximately ⅕ less than that of stent  780 . 
     A surprising and unexpected result of the compact profile of stent  900 , including the longitudinal interlocking effect of the nested profile, is much improved retention of the stent as mounted and compacted on a balloon catheter in a clinical product. This unexpected result has now been shown to permit elimination of the retractable protective sheath covering the stent as during vascular insertion (shown as sheath  802  in  FIG. 13A ). As shown in  FIG. 27A , the use of sheath  802  may require the use of a mating cap  805  on catheter  804 , which may impede vascular insertion. The elimination of the sheath  802  provides a much thinner profile than the same stent with the sheath, and improves the flexibility of the stent/catheter product, further facilitating vascular insertion. In some implementations, not including the sheath  802 , and its respective components, allows for a much simpler stent assembly. 
       FIG. 29  shows a high-resolution micro-X-ray-tomography scan of a cross-section of a stent generally similar to that of  FIG. 21  in compacted configuration about a central support, such as a catheter, the cross-section generally aligned with a rail member, so as to show its engagement with each circumferentially-adjacent backbone member, and also indicating chamfered backbone edges, and tapered proximal tips and distal tails of the circumferential rail members. 
       FIG. 30  comprises a three-view depiction of a detail portion of a backbone such as in  FIG. 21 , showing chamfered edges of the recessed portion, which facilitate reduced profile in the compacted stent configuration and can be desirable to help improve engagement of the stent. 
       FIG. 31  illustrates a top and side section depiction of a detail portion of a rail member such as in  FIG. 21 , showing tapered proximal tips and distal tails. 
     It should be noted that the taper angles and particular dimensions of the tapers  910 ,  911  and  912  are exemplary, and may vary. Likewise a curved or smoothed profile may be substituted for angular tapers. These tapered or chamfered feature serve to assist and promote compaction of the stent assembly during mounting as a clinical package. 
     Reference is made to  FIGS. 18 through 20  of the present application, and to  FIGS. 45 through 47  of co-owned U.S. Pat. No. 7,947,071, which discloses related subject matter. Available methods of assembly include the assembly of the components of stent  900  in a compacted, or nearly-fully compacted configuration. This may include pre-forming complexly curved shapes of components such as backbones  901  and “U” rail members  902 . Further forming operations, for example employing “iris” type compaction devices, with or without heat, fluid pressure or other assist factors, may be used to produce a final mounted configuration on a balloon catheter as a clinical product. 
       FIG. 32  comprises a set of nine micro-CT scans, indicated as a-j, similar to the scan of  FIG. 29 , taken at longitudinally adjacent sections (labeled a though j) of a compacted stent similar to the stent shown in  FIG. 21 . For purposes of illustration, the sub-images a though j include phantom reference circles approximating the size of an internal support (e.g., balloon catheter body or assembly mandrel), and approximating a 2 millimeter reference diameter (representative of a 6 French sized clinical package). 
       FIG. 33  illustrates a photographic side view of stent such as in  FIG. 32 , showing section lines generally representative of the scans a though j of  FIG. 32 . It is notable that, for sections crossing the rail tooth array of a U member  902  (see  FIG. 11A-B ), the rail appears in a CT image to be “broken up” into small segments. Similarly, the cross members  909  of U members  902  appear to be floating unattached in these discrete sectional images. Overall, the series of nine images give a fair picture of the compact form of stent  900  in its mounted clinical form. 
     Testing Data of Stent Embodiments Compared to Prior Art Stents 
     As discussed herein, embodiments of the helical slide-and-lock stents can provide superior flexibility and stiffness compared to prior polymer stents. In this regard, various tests have shown that the stiffness of embodiments disclosed herein is greater than that of prior art polymer stents. Indeed, the structural properties, such as the stiffness, of embodiments disclosed herein more closely mimics the structural properties of metal stents. 
     Accordingly, embodiments of the stents disclosed herein represent a significant advance in stent technology which allows a polymer and/or composite material to be used in a configuration that provides structural properties that can approach and/or replicate the structural properties of a metal stent. Metal stents have the disadvantage of not being as bioresorbable as polymer stents; however, metal stents have long provided superior structural properties that may be needed for severe lesions, such as rigidity, stiffness, and crush strength. In contrast, prior polymer stents could provide resorbability and other benefits not available with metal stents; however, prior polymer stent were not as stiff, rigid, or strong as the metal counterparts. One of the solutions and advances made by embodiments of the stent of the present application is the provision of a manner of achieving bioresorbability and the other benefits of polymers while exhibiting superior structural properties similar to metal stents. Indeed, the unique features and configurations of the helical slide-and-lock polymer stents disclosed herein enable one of skill to obtain the benefits of polymer and metal stents. Further, the present disclosure also provides for a variety of stents having a composite material structure which can incorporate advantages of various materials. 
     Lamination Manufacturing Process Embodiments 
     Stents in accordance with embodiments can be fabricated or created using a wide variety of manufacturing methods, techniques and procedures. These include, but are not limited to, laser processing, milling, stamping, forming, casting, molding, bonding, welding, adhesively fixing, and the like, among others. 
     In some embodiments, stent features and mechanisms can be created in a generally two dimensional geometry and further processed, for example by utilizing, but not limited to, bonding, lamination and the like, into three dimensional designs and features. In other embodiments, stent features and mechanisms can be directly created into three dimensional shapes, for example by utilizing, but not limited to, processes such as injection molding and the like. 
     In certain embodiments, stents can be fabricated by using an injection molding process, technique or method. For example, an injection molding process or the like, among others, can be used to form stent rows as integral units. The axially extending rows can then be connected and rolled into a tubular form in the collapsed state. 
     In some embodiments, a lamination stack can used to fabricate the stent rows by a lamination process in accordance with one embodiment. The axially extending rows can then be connected and rolled into a tubular form in the collapsed state. 
     The lamination stack, in some embodiments, generally can comprise three sheets or pallets which can have the desired features formed thereon, for example, by laser cutting, etching and the like. The pallets can be aligned and joined, for example, by bonding, welding and the like to form a unit. The excess material (e.g., side and end rails) can be removed to form the stent rows. The pallets can include various circumferentially nesting features such as male and female articulating and/or ratcheting designs to control and limit the diameter in collapsed and fully deployed states. 
     Stent Materials Generally 
     The stent can be fabricated from at least one or more materials. These materials include metals, polymers, composites, and shape-memory materials. In another optional embodiment, the stent further can comprise a tubular member formed from a biocompatible and preferably, bioresorbable polymer, such as those disclosed in co-pending U.S. application Ser. No. 10/952,202, the disclosure of which is incorporated herein in its entirety by reference. It is also understood that the various polymer formulae employed can include homopolymers and heteropolymers, which can include stereoisomerism, composites, filled materials, etc. Homopolymer is used herein to designate a polymer comprised of all the same type of monomers. Heteropolymer is used herein to designate a polymer comprised of two or more different types of monomer which is also called a co-polymer. A heteropolymer or copolymer can be of a kind known as block, random and alternating. Further with respect to the presentation of the various polymer formulae, products according to embodiments can be comprised of a homopolymer, heteropolymer and/or a blend of such polymers. 
     The term “bioresorbable” is used herein to designate polymers that undergo biodegradation (through the action of water and/or enzymes to be chemically degraded) and at least some of the degradation products can be eliminated and/or absorbed by the body. The term “radiopaque” is used herein to designate an object or material comprising the object visible by in vivo analysis techniques for imaging such as, but not limited to, methods such as x-ray radiography, fluoroscopy, other forms of radiation, MRI, electromagnetic energy, structural imaging (such as computed or computerized tomography), and functional imaging (such as ultrasonography). The term “inherently radiopaque” is used herein to designate polymer that is intrinsically radiopaque due to the covalent bonding of halogen species to the polymer. Accordingly, the term does encompass a polymer which is simply blended with a halogenated species or other radiopacifying agents such as metals and their complexes. 
     In another optional variation, the stent further can comprise an amount of a therapeutic agent (for example, a pharmaceutical agent and/or a biologic agent) sufficient to exert a selected therapeutic effect. The term “pharmaceutical agent”, as used herein, encompasses a substance intended for mitigation, treatment, or prevention of disease that stimulates a specific physiologic (metabolic) response. The term “biological agent”, as used herein, encompasses any substance that possesses structural and/or functional activity in a biological system, including without limitation, organ, tissue or cell based derivatives, cells, viruses, vectors, nucleic acids (animal, plant, microbial, and viral) that can be natural and recombinant and synthetic in origin and of any sequence and size, antibodies, polynucleotides, oligonucleotides, cDNA&#39;s, oncogenes, proteins, peptides, amino acids, lipoproteins, glycoproteins, lipids, carbohydrates, polysaccharides, lipids, liposomes, or other cellular components or organelles for instance receptors and ligands. Further the term “biological agent”, as used herein, can include virus, serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product, or analogous product, or arsphenamine or its derivatives (or any trivalent organic arsenic compound) applicable to the prevention, treatment, or cure of diseases or injuries of man (per Section 351(a) of the Public Health Service Act (42 USC 262(a)). Further the term “biological agent” can include 1) “biomolecule”, as used herein, encompassing a biologically active peptide, protein, carbohydrate, vitamin, lipid, or nucleic acid produced by and purified from naturally occurring or recombinant organisms, tissues or cell lines or synthetic analogs of such molecules, including antibodies, growth factors, interleukins and interferons; 2) “genetic material” as used herein, encompassing nucleic acid (either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), genetic element, gene, factor, allele, operon, structural gene, regulator gene, operator gene, gene complement, genome, genetic code, codon, anticodon, messenger RNA (mRNA), transfer RNA (tRNA), ribosomal extrachromosomal genetic element, plasmagene, plasmid, transposon, gene mutation, gene sequence, exon, intron, and, 3) “processed biologics”, as used herein, such as cells, tissues or organs that have undergone manipulation. The therapeutic agent can also include vitamin or mineral substances or other natural elements. 
     In some embodiments, the design features of the axially or circumferentially offset elements can be varied to customize the functional features of strength, compliance, radius of curvature at deployment and expansion ratio. In some embodiments, the stent can comprise a resorbable material and vanishes when its job is done. In some embodiments, the stent serves as a therapeutic delivery platform. 
     Some aspects are also disclosed in co-pending U.S. patent application Ser. Nos. 11/016,269, 60/601,526, 10/655,338, 10/773,756, and Ser. No. 10/897,235, the disclosures of each of which are incorporated herein in their entirety by reference thereto. 
     Some features and arrangements of embodiments of stents are disclosed in U.S. Pat. Nos. 6,033,436, 6,224,626, and 6,623,521, each issued to Steinke, the disclosures of each of which are hereby incorporated in their entirety by reference thereto. 
     Advantageously, the stent design elements and interlocks can be varied to customize the functional features of strength, compliance, radius of curvature at deployment and expansion ratio. In some embodiments, the stent can comprise a resorbable material and vanishes when its job is done. In some embodiments, the stent serves as a delivery platform for therapeutic agents such as pharmaceutical compounds or biological materials. 
     Metal Stents and Methods of Manufacturing 
     Possible materials for making the stents in accordance with some embodiments include cobalt chrome, 316 stainless steel, tantalum, titanium, tungsten, gold, platinum, iridium, rhodium and alloys thereof or pyrolytic carbon. In still other alternative embodiments, the stents can be formed of a corrodible material, for instance, a magnesium alloy. Although various stent embodiments have been described as being conventional balloon expandable stents, those skilled in the art will appreciate that stent constructions according to embodiments can also be formed from a variety of other materials to make a stent crush-recoverable. For example, in alternative embodiments, such as self expandable stents, shape memory alloys that allow for such, such as Nitinol and Elastinite®, can be used in accordance with embodiments. 
     Various methods of forming the individual elements from metal sheets can comprise laser cutting, laser ablation, die-cutting, chemical etching, plasma etching and stamping and water jet cutting of either tube or flat sheet material or other methods known in the art which are capable of producing high-resolution components. The method of manufacture, in some embodiments, depends on the material used to form the stent. Chemical etching provides high-resolution components at relatively low price, particularly in comparison to high cost of competitive product laser cutting. Some methods allow for different front and back etch artwork, which could result in chamfered edges, which can be desirable to help improve engagements of lockouts. Further one can use plasma etching or other methods known in the art which are capable of producing high-resolution and polished components. The embodiments disclosed herein are not limited to the means by which stent or stent elements can be fabricated. 
     Once the base geometry is achieved, the elements can be assembled numerous ways. Tack-welding, adhesives, mechanical attachment (snap-together and/or weave together), and other art-recognized methods of attachment, can be used to fasten the individual elements. Some methods allow for different front and back etch artwork, which could result in chamfered edges, which can be desirable to help improve engagements of lockouts. In an advantageous method of manufacture, the components of the stent can be heat set at various desired curvatures. For example, the stent can be set to have a diameter equal to that of the deflated balloon, as deployed, at a maximum diameter, or greater than the maximum diameter. In yet another example, elements can be electropolished and then assembled, or electropolished, coated, and then assembled, or assembled and then electropolished. 
     Polymeric Stents 
     While metal stents possess certain desirable characteristics, the useful lifespan of a stent is estimated to be in the range of about 6 to 9 months, the time at which in-stent restenosis stabilizes and healing plateaus. In contrast to a metal stent, a bioresorbable stent cannot outlive its usefulness within the vessel. Moreover, a bioresorbable stent could potentially be used to deliver a greater dose of a therapeutic agent, deliver multiple therapeutic agents at the same time or at various times of its life cycle, to treat specific aspects or events of vascular disease. Additionally, a bioresorbable stent can also allow for repeat treatment of the same approximate region of the blood vessel. Accordingly, there remains an important unmet need to develop temporary (i.e., bioresorbable and/or radiopaque) stents, wherein the polymeric materials used to fabricate these stents can have the desirable qualities of metal (e.g., sufficient radial strength and radiopacity, etc.), while circumventing or alleviating the many disadvantages or limitations associated with the use of permanent metal stents. 
     In some embodiments, the stent can be formed from biocompatible polymers that are bio-resorbable (e.g., bio-erodible or bio-degradable). Bio-resorbable materials can be preferably selected from the group consisting of any hydrolytically degradable and/or enzymatically degradable biomaterial. Examples of suitable degradable polymers include, but are not limited to, polyhydroxybutyrate/polyhydroxyvalerate copolymers (PHV/PHB), polyesteramides, polylactic acid, polyglycolic acid, lactone based polymers, polycaprolactone, poly(propylene fumarate-co-ethylene glycol) copolymer (aka fumarate anhydrides), polyamides, polyanhydride esters, polyanhydrides, polylactic acid/polyglycolic acid with a calcium phosphate glass, polyorthesters, silk-elastin polymers, polyphosphazenes, copolymers of polylactic acid and polyglycolic acid and polycaprolactone, aliphatic polyurethanes, polyhydroxy acids, polyether esters, polyesters, polydepsidpetides, polysaccharides, polyhydroxyalkanoates, and copolymers thereof. For additional information, see U.S. Pat. Nos. 4,980,449, 5,140,094, and 5,264,537, the disclosures of each of which are incorporated by reference herein. 
     In one mode, the degradable materials can be selected from the group consisting of poly(glycolide-trimethylene carbonate), poly(alkylene oxalates), polyaspartimic acid, polyglutarunic acid polymer, poly-p-dioxanone, poly-.beta.-dioxanone, asymmetrically 3,6-substituted poly-1,4-dioxane-2,5-diones, polyalkyl-2-cyanoacrylates, polydepsipeptides (glycine-DL-lactide copolymer), polydihydropyranes, polyalkyl-2-cyanoacrylates, poly-.beta.-maleic acid (PMLA), polyalkanotes and poly-.beta.-alkanoic acids. There are many other degradable materials known in the art. (See e.g., Biomaterials Science: An Introduction to Materials in Medicine (29 Jul. 2004) Ratner, Hoffman, Schoen, and Lemons; and Atala, A., Mooney, D. Synthetic Biodegradable Polymer Scaffolds. 1997 Birkhauser, Boston; each of which are incorporated herein by reference). 
     Further still, in another embodiment, the stents can be formed of a polycarbonate material, such as, for example, tyrosine-derived polycarbonates, tyrosine-derived polyarylates, tyrosine-derived diphenol monomers, iodinated and/or brominated tyrosine-derived polycarbonates, iodinated and/or brominated tyrosine-derived polyarylates. For additional information, see U.S. Pat. Nos. 5,099,060, 5,198,507, 5,587,507, which was resiussed in U.S. Pat. Nos. RE37,160, 5,670,602, which was resiussed in U.S. Pat. Nos. RE37,795, 5,658,995, 6,048,521, 6,120,491, 6,319,492, 6,475,477, 5,317,077, and 5,216,115, and U.S. application Ser. No. 09/350,423, the disclosures of each of which are incorporated by reference herein. In yet another embodiment, the polymer can be any of the biocompatible, bioabsorbable, radiopaque polymers disclosed in: U.S. Patent Application Nos. 60/852,513, 60/852,471, 60/601,526, 60/586,796, 60/866,281, 60/885,600, 10/952,202, 11/176,638, 11/335,771, 11/200,656, 11/024,355, 10/691,749, 11/418,943, and Ser. No. 11/873,362; U.S. Patent Publication No. US26115449A1; U.S. Pat. Nos. 6,852,308 and 7,056,493; and PCT Application Nos. PCT/US2005/024289, PCT/US2005/028228, PCT/US07/01011, and PCT/US07/81571, the disclosures of each of which are incorporated herein by reference thereto. 
     Natural polymers (biopolymers) include any protein or peptide. Biopolymers can be selected from the group consisting of alginate, cellulose and ester, chitosan, collagen, dextran, elastin, fibrin, gelatin, hyaluronic acid, hydroxyapatite, spider silk, cotton, other polypeptides and proteins, and any combinations thereof. 
     In yet another alternative embodiment, shape-shifting polymers can be used to fabricate stents constructed according to embodiments. Suitable shape-shifting polymers can be selected from the group consisting of polyhydroxy acids, polyorthoesters, polyether esters, polyesters, polyamides, polyesteramides, polydepsidpetides, aliphatic polyurethanes, polysaccharides, polyhydroxyalkanoates, and copolymers thereof. For addition disclosure on bio-degradable shape-shifting polymers, see U.S. Pat. Nos. 6,160,084 and 6,284,862, the disclosures of each of which are incorporated by reference herein. For additional disclosure on shape memory polymers, see U.S. Pat. Nos. 6,388,043 and 6,720,402, the disclosures of each of which are incorporated by reference herein. Further the transition temperature can be set such that the stent can be in a collapsed condition at a normal body temperature. However, with the application of heat during stent placement and delivery, such as via a hot balloon catheter or a hot liquid (e.g., saline) perfusion system, the stent can expand to assume its final diameter in the body lumen. When a thermal memory material is used, it can provide a crush-recoverable structure. 
     Further still, stents can be formed from biocompatible polymers that are biostable (e.g., non-degrading and non-erodible). Examples of suitable non-degrading materials include, but are not limited to, polyurethane, Delrin, high density polyethylene, polypropylene, and poly(dimethyl siloxane). 
     In some embodiments, the layers can comprise or contain any example of thermoplastics, such as the following, among others: fluorinated ethylene-propylene, poly(2-hydroxyethyl methacrylate) (aka pHEMA), poly(ethylene terephthalate) fiber (aka Dacron®) or film (Mylar®), poly(methyl methacrylate) (aka PMMA), Poly(tetraflouroethylene) (aka PTFE and ePTFE and Gore-Tex®), poly(vinyl chloride), polyacrylates and polyacrylonitrile (PAN), polyamides (aka Nylon), polycarbonates and polycarbonate urethanes, polyethylene and poly(ethylene-co-vinyl acetate), polypropylene, polystyrene, polysulphone, polyurethane and polyetherurethane elastomers such as Pellethane® and Estane®, Silicone rubbers, Siloxane, polydimethylsiloxane (aka PDMS), Silastic®, Siliconized Polyurethane. 
     Finally, the polymer(s) utilized in embodiments of the stent can be fabricated according to any variety of processes, such as those discussed in U.S. Patent Application Nos. 60/852,471 and 60/852,513, and U.S. Pat. Nos. 5,194,570, 5,242,997, 6,359,102, 6,620,356, and 6,916,868, the disclosures of each of which are incorporated by reference herein. 
     Methods of Manufacturing and Assembling Polymeric Stents 
     Where plastic and/or degradable materials are used, the elements can be made using laser ablation with a screen, stencil or mask; solvent casting; forming by stamping, embossing, compression molding, centripetal spin casting and molding; extrusion and cutting, three-dimensional rapid prototyping using solid free-form fabrication technology, stereolithography, selective laser sintering, or the like; etching techniques comprising plasma etching; textile manufacturing methods comprising felting, knitting, or weaving; molding techniques comprising fused deposition modeling, injection molding, room temperature vulcanized molding, or silicone rubber molding; casting techniques comprising casting with solvents, direct shell production casting, investment casting, pressure die casting, resin injection, resin processing electroforming, or injection molding or reaction injection molding. Certain embodiments with the disclosed polymers can be shaped into stents via combinations of two or more thereof, and the like. 
     Such processes can further include two-dimensional methods of fabrication such as cutting extruded sheets of polymer, via laser cutting, etching, mechanical cutting, or other methods, and assembling the resulting cut portions into stents, or similar methods of three-dimensional fabrication of devices from solid forms. For additional information, see U.S. patent application Ser. No. 10/655,338, the disclosure of which is incorporated by reference herein. 
     Stents of some of the embodiments can be manufactured with elements prepared in full stent lengths or in partial lengths of which two or more are then connected or attached. If using partial lengths, two or more can be connected or attached to comprise a full length stent. In this arrangement the parts can be assembled to give rise to a central opening. The assembled full or partial length parts and/or modules can be assembled by inter-weaving them in various states, from a collapsed state, to a partially expanded state, to an expanded state. 
     Further, elements can be connected or attached by solvent or thermal bonding, or by mechanical attachment. If bonding, advantageous methods of bonding comprise the use of ultrasonic, radiofrequency or other thermal methods, and by solvents or adhesives or ultraviolet curing processes or photoreactive processes. The elements can be rolled by thermal forming, cold forming, solvent weakening forming and evaporation, or by preforming parts before linking. 
     Rolling of the flat series of module(s) to form a tubular member can be accomplished by any means known in the art, including rolling between two plates, which can be each padded on the side in contact with the stent elements. One plate can be held immobile and the other can move laterally with respect to the other. Thus, the stent elements sandwiched between the plates can be rolled about a mandrel by the movement of the plates relative to one another. Alternatively, 3-way spindle methods known in the art can also be used to roll the tubular member. Other rolling methods that can be used in accordance with certain embodiments include those used for “jelly-roll” designs, as disclosed for example, in U.S. Pat. Nos. 5,421,955, 5,441,515, 5,618,299, 5,443,500, 5,649,977, 5,643,314 and 5,735,872, the disclosures of each of which are incorporated herein in their entireties by reference thereto. 
     The construction of the slide-and-lock stents in these fashions can provide a great deal of benefit over the prior art. The construction of the locking mechanism can be largely material-independent. This allows the structure of the stent to comprise high strength materials, not possible with designs that require deformation of the material to complete the locking mechanism. The incorporation of these materials will allow the thickness required of the material to decrease, while retaining the strength characteristics of thicker stents. In some embodiments, the frequency of catches, stops or teeth present on selected circumferential elements can prevent unnecessary recoil of the stent subsequent to expansion. 
     Radiopacity 
     Traditional methods for adding radiopacity to a medical product include the use of metal bands, inserts and/or markers, electrochemical deposition (i.e., electroplating), or coatings. The addition of radiopacifiers (i.e., radiopaque materials) to facilitate tracking and positioning of the stent could be accommodated by adding such an element in any fabrication method, by absorbing into or spraying onto the surface of part or all of the device. The degree of radiopacity contrast can be altered by element content. 
     For plastics and coatings, radiopacity can be imparted by use of monomers or polymers comprising iodine or other radiopaque elements, i.e., inherently radiopaque materials. Common radiopaque materials include barium sulfate, bismuth subcarbonate, and zirconium dioxide. Other radiopaque elements include: cadmium, tungsten, gold, tantalum, bismuth, platinum, iridium, and rhodium. In some embodiments, a halogen such as iodine and/or bromine can be employed for its radiopacity and antimicrobial properties. 
     Multi-Material Vascular Prosthesis 
     In still other alternative embodiments, various materials (e.g., metals, polymers, ceramics, and therapeutic agents) can be used to fabricate stent embodiments. The embodiments can comprise: 1) differentially layered materials (through stacking in the vertical or radial axis) to create a stack of materials (materials can be stacked in any configuration, e.g., parallel, staggered, etc.); 2) spatially localized materials which can vary along the long axis and/or thickness of the stent body; 3) materials that are mixed or fused to create a composite stent body (e.g., whereby a therapeutic agent(s) is within the stent body with a polymer); 4) embodiments whereby a material can be laminated (or coated) on the surface of the stent body (see Stent Surface Coatings with Functional Properties as well as see Therapeutic Agents Delivered by Stents); and, 5) stents comprised of 2 or more parts where at least one part can be materially distinct from a second part, or any combination thereof. 
     The fashioning of a slide-and-lock multi-material stent can have between two or more materials. Thickness of each material can vary relative to other materials. This approach as needed or desired allows an overall structural member to be built with each material having one or more functions contributing towards enabling prosthesis function which can include, but is not limited to: 1) enabling mechanical properties for stent performance as defined by ultimate tensile strength, yield strength, Young&#39;s modulus, elongation at yield, elongation at break, and Poisson&#39;s ratio; 2) enabling the thickness of the substrate, geometrical shape (e.g., bifurcated, variable surface coverage); 3) enabling chemical properties of the material that bear relevance to the materials performance and physical state such as rate of degradation and resorption (which can impact therapeutic delivery), glass transition temperature, melting temperature, molecular weight; 4) enabling radiopacity or other forms of visibility and detection; 5) enabling radiation emission; 6) enabling delivery of a therapeutic agent (see Therapeutic Agents Delivered by Stents); and 7) enabling stent retention and/or other functional properties (see Stent Surface Coatings with Functional Properties). 
     In some embodiments, the materials can comprise load-bearing properties, elastomeric properties, mechanical strength that can be specific to a direction or orientation e.g., parallel to another material and/or to the long axis of the stent, or perpendicular or uniform strength to another material and/or stent. The materials can comprise stiffeners, such as the following, boron or carbon fibers, pyrolytic carbon. Further, stents can be comprised of at least one re-enforcement such a fibers, nanoparticles or the like. 
     In another implementation of some embodiments, the stent can be made, at least in part, from a polymeric material, which can be degradable. The motivation for using a degradable stent can be that the mechanical support of a stent can only be necessary for several weeks. In some embodiments, bioresorbable materials with varying rates of resorption can be employed. For additional information, see U.S. patent application Ser. Nos. 10/952,202 and 60/601,526, the disclosures of each of which are incorporated by reference herein. Degradable polymeric stent materials can be particularly useful if it also controls restenosis and thrombosis by delivering pharmacologic agents. Degradable materials can be well suited for therapeutic delivery (see Therapeutic Agents Delivered by Stents). 
     In some embodiments, the materials can comprise or contain any class of degradable polymer as previously defined. Along with variation in the time of degradation and/or resorption the degradable polymer can have other qualities that are desirable. For example, in some embodiments the materials can comprise or contain any example of natural polymers (biopolymers) and/or those that degrade by hydrolytic and/or enzymatic action. In some embodiments, the material can comprise or contain any example of hydrogels that can or cannot be thermally reversible hydrogels, or any example of a light or energy curable material, or magnetically stimulateable (responding) material. Each of these responses can provide for a specific functionality. 
     In some embodiments, the materials can comprise or be made from or with constituents which can have some radiopaque material alternatively, a clinically visible material which can be visible by x-ray, fluoroscopy, ultrasound, MRI, or Imatron Electron Beam Tomography (EBT). 
     In some embodiments, one or more of the materials can emit predetermined or prescribed levels of therapeutic radiation. In an embodiment, the material can be charged with beta radiation. In another embodiment, the material can be charged with Gamma radiation. In yet another embodiment, the material can be charged with a combination of both Beta and Gamma radiation. Stent radioisotopes that can be used include, but are not limited to, 103Pd and 32P (phosphorus-32) and two neutron-activated examples, 65Cu and 87Rb2O, (90)Sr, tungsten-188 (188). 
     In some embodiments, one or more of the materials can comprise or contain a therapeutic agent. The therapeutic agents can have unique, delivery kinetics, mode of action, dose, half-life, purpose, et cetera. In some embodiments, one or more of the materials comprise an agent which provides a mode and site of action for therapy for example by a mode of action in the extracellular space, cell membrane, cytoplasm, nucleus and/or other intracellular organelle. Additionally an agent that serves as a chemoattractant for specific cell types to influence tissue formation and cellular responses for example host-biomaterial interactions, including anti-cancer effects. In some embodiments, one or more of the materials deliver cells in any form or state of development or origin. These could for example be encapsulated in a degradable microsphere, or mixed directly with polymer, or hydrogel and serve as vehicle for pharmaceutical delivery. Living cells could be used to continuously deliver pharmaceutical type molecules, for instance, cytokines and growth factors. Nonliving cells can serve as a limited release system. For additional concepts of therapeutic delivery, see the section entitled: Therapeutic Agents Delivered by Stents. 
     Therapeutic Agents Delivered by Stents 
     In another implementation, the stent further can comprise an amount of a therapeutic agent (as previously defined for a pharmaceutical agent and/or a biologic agent) sufficient to exert a selected therapeutic effect. The material of at least a portion of the stent itself can comprise at least one therapeutic agent, or at least one therapeutic agent can be added to the stent in a subsequent forming process or step. In some embodiments of the stent (e.g., polymer stents and multi-material stents), the therapeutic agent can be contained within the stent as the agent is blended with the polymer or admixed by other means known to those skilled in the art. 
     For example, one or more therapeutic agents can be delivered through a multi-material vascular prosthesis. In some embodiments, the entire stent can be formed from materials comprising one or more therapeutic agents. In other embodiments, portions of the stent, such as individual components thereof, can comprise materials comprising one or more therapeutic agents. In such embodiments, it is contemplated that the therapeutic agent(s) can be released as the stent material degrades. 
     For example, the therapeutic agent can be embedded or impregnated into the film by means of a combination of solvent casting and thermal pressing. In such a method, the film can be formed from a mixture of the polymer and the therapeutic agent (20% solids polymer, for example poly(90% DTE-co-10% DT carbonate), which can be made with 1% rapamycin in dichloromethane). Once this mixture is prepared, the film can be cast using a doctor blade. Alternatively, the film can be formed by using a mechanical reverse roll coater or other solvent-based film caster. Once the film is cast, the solvent can be evaporated off using a vacuum oven, e.g., for a period of time and at a temperature suitable for the polymer and drug, such as at 40° C. for at least 20 hours. Once the film is dried, it can be thermally pressed, e.g., at a temperature of 100° C. between two heated platens of a hydraulic press. This allows the potency of the drug to be retained. 
     In addition, the therapeutic agent can be embedded or impregnated into the film using only a solvent or by spin casting. Once a therapeutic agent is selected, one needs to determine if the solvent is compatible with the agent and the polymer chosen. The objective is to prepare a suitable sprayable suspension. Additionally, the stability of the drug can be measured such that the therapeutic agent can remain active while in the coating as well under physiological conditions once released from the film. This can be determined by those skilled in the art who conduct standard in vitro elution studies (see Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel, The AAPS Journal, 6 (3) Article 27 (2004), http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent, Trends in Biomaterials &amp; Artificial Organs, Vol. 19(2), 88-92 (2006), http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf) of agent embedded films and through the use of analytical methods such as HPLC methods (see Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent) to detect the purity of the drug. 
     In other embodiments, at least one therapeutic agent can be added to the stent and/or its components after the formation of the stent and/or its components. For example, at least one therapeutic agent can be added to individual stent components, through a coating process or otherwise. The addition of at least one therapeutic agent can occur before or after cutting or lasing of the stent components. In another example, at least one therapeutic agent can also be added to at least a portion of the stent after partial or full assembly thereof, through a coating process or otherwise. In some embodiments of the stent, the therapeutic agent can be delivered from a polymer coating on the stent surface. In other embodiments of the stent, a therapeutic agent can be localized in or around a specific structural aspect of the device. 
     For example, the therapeutic agent can be delivered from a polymer coating on the stent surface. Thus, the stent can be made by applying the therapeutic agent to a stent component before the stent is assembled or formed. In this regard, the stent component can be created from a polymer sheet, such as a flat polymer film. Thus, at least one stent component can be separated from a remainder or excess portion of the film either before or after the therapeutic agent has been applied to the stent component and/or film. After the therapeutic agent is applied and the stent component is separated from the film, the stent component can be assembled (and in some embodiments, with other stent components) to form a stent therefrom. 
     In some embodiments, the stent can be prepared with the following preparation method. The stent can be initially prepared by creating a pattern of a stent component on a flat polymer film. The creation of the pattern on the film can occur before or after application of a therapeutic agent thereto, as discussed below. The pattern of the stent component can be created on the film such that the stent component can be detached from the film when desired. In some embodiments, the pattern can be created using a laser to lase the pattern onto the film. Additionally, the lased pattern can be of any given stent component design, such as that used in a slide and lock stent design. After the pattern is created on the film, the entire film can be cleaned. For example, if the therapeutic agent has not yet been applied to the film, the entire lased film can be immersed into a cleaning solution that is compatible with the specific type of polymer from which the film is made. The cleaned film can then be dried, for example, by being blown and oven dried. 
     A coating formulation can be prepared by dissolving or dispersing the polymer and the therapeutic agent(s) of choice and solvent(s) or other compatible excipient(s) using a calculated amount of each component to achieve the desired concentration. The coating formulation can then be applied to the lased polymer film using one or more coating methods. For example, the film may be coated by means of spraying, dipping, or other coating methods. Additionally cross-linking reagents may also be used to prepare a coating. 
     In a spraying coating method, the lased polymer films can be coated with the coating formulation by first mounting the cleaned dried films into a spray apparatus. The coating formulation can then be sprayed onto the film, and the film can be rotated 180 degrees such that the other side can be coated if desired. This method can allow for coating of one or both sides of the stent component(s). This method can also allow one to apply different therapeutic agents per side of the lased film and/or stent component and to selectively coat regions thereof. The method can further allow one to coat multiple drugs per film and/or stent component. Alternative coating methods can allow for other similar benefits. 
     For example, a therapeutic agent can be coated onto a film or stent component as in the following illustration. First, the therapeutic agent in this example is a Polymer-Paclitaxel Formulation, such as a 0.5% [25% Paclitaxel/75% Poly(86.75% I2DTE-co-10%12DT-co-3.25% PEG2000 carbonate)] in tetrahydrofuran (THF), which can be prepared using an analytical balance. In order to do so, one must first weigh 0.0150 g of Paclitaxel into a tared vial. Then weigh 0.0450 g of polymer into another vial. Next, weigh 11.940 g of THF into each vial. Shake the vials on a laboratory shaker, such as a Roto-genie, for at least one hour. In this example, coating can be achieved using a spray gun apparatus, such as an air brush (see Westedt, U., Biodegradable Paclitaxel-loaded Nanoparticles and Stent Coatings as Local Delivery Systems for the Prevention of Restenosis—Dissertation, Marburg/Lahn (2004), http://deposit.ddb.de/cgi-bin/dokserv?idn=972868100&amp;dokvar=d1&amp;dokext=pdf&amp;filename=972868100.pdf; and Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-Eluting Stents, Medical Device Technology (2006), http://www.devicelink.com/mdt/archive/06/11/004.html). Typically, the spray gun apparatus should first be cleaned with THE In order to do so, a syringe can be filled with at least 10 ml of THF. The syringe can then be attached to a spray line attached to the spray gun. Gradually, the 10 ml of THF can be pushed from the syringe into the spray gun without N2 pressure. This can be repeated as necessary to ensure that the line is washed clean. The syringe pump can then be set up with the syringe containing the Polymer-Paclitaxel Formulation. 
     Next, a film, which can be either lased or unlased, can be placed into a hooded environment and mounted or clipped into a holder. If necessary, the surfaces of the film can be cleaned of lint and dust using a pure air or gas source or equivalent. For consistent coating quality, the film can be programmed to move at a set rate (distance and speed) relative to a spray stream by integrating the film holder apparatus with a motion control system. Manual coating without the motion control can also be used to achieve a coating. The spray gun can also be set to direct the spray to only a given location to control coating distribution. 
     In some embodiments, to coat both sides of the film uniformly, the spray cycle can start with the spray hitting at the bottom corner of the film, and the motion control should move the film incrementally as it traverses back and forth in front of the spray nozzle. The system can then move the film back to the start position so the spray is directed at the bottom. The film holder can be turned 180 degrees and the cycle can be repeated to coat the second side. After coating, the film holder can be removed with the film and the film can be dried in a vacuum oven at a temperature suitable for the drug and polymer, e.g., 25°±5° C. for at least 20 hours. 
     Other methods and teachings related to impregnation or coating processes are found in the following references, the entirety of each of which is hereby incorporated by reference herein: Westedt, U., Biodegradable Paclitaxel-loaded Nanoparticles and Stent Coatings as Local Delivery Systems for the Prevention of Restenosis—Dissertation, Marburg/Lahn (2004), http://deposit.ddb.de/cgi-bin/dokserv?idn=972868100&amp;dokvar=d1&amp; dokext=pdf&amp;filename=972868100.pdf; Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-Eluting Stents, Medical Device Technology (2006), http://www.devicelink.com/mdt/archive/06/11/004.html; Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel, The AAPS Journal, 6 (3) Article 27 (2004), http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent, Trends in Biomaterials &amp; Artificial Organs, Vol. 19(2), 88-92 (2006), http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf. 
     After the film is coated using a given coating method, the film can be given time to dry. Once dried, the lased, coated stent component(s) can be separated from the remainder of the film. Care should be taken to not disturb the surfaces of the coated stent component(s) when being detached from the film and assembled or knitted together to form a three-dimensional cylindrical stent. 
     In another variation the therapeutic agent can be delivered by means of a non-polymer coating. In other embodiments of the stent, the therapeutic agent can be delivered from at least one region or one surface of the stent. The therapeutic agent can be chemically bonded to the polymer or carrier used for delivery of the therapeutic from at least one portion of the stent and/or the therapeutic can be chemically bonded to the polymer that can comprise at least one portion of the stent body. In some embodiments, a polymer can be used as a component of the coating formulation. Accordingly, the coating can essentially bond directly to a clean lased film and/or stent component, which can also be comprised of a polymer. Such an embodiment of the method can provide for a seamless interface between the coating and the lased film and/or stent component. Further, in another embodiment, more than one therapeutic agent can be delivered. 
     The amount of the therapeutic agent can be preferably sufficient to inhibit restenosis or thrombosis or to affect some other state of the stented tissue, for instance, heal a vulnerable plaque, and/or prevent rupture or stimulate endothelialization or limit other cell types from proliferating and from producing and depositing extracellular matrix molecules. The agent(s) can be selected from the group consisting of antiproliferative agents, anti-inflammatory, anti-matrix metalloproteinase, and lipid lowering, cholesterol modifying, anti-thrombotic and antiplatelet agents, in accordance with some embodiments. For vascular stent applications, some anti-proliferative agents that improve vascular patency include without limitation paclitaxel, Rapamycin, ABT-578, Biolimus A9, everolimus, dexamethasone, nitric oxide modulating molecules for endothelial function, tacrolimus, estradiol, mycophenolic acid, C6-ceramide, actinomycin-D and epothilones, and derivatives and analogs of each. 
     Some agents act as an antiplatelet agent, antithrombin agent, compounds to address other pathologic events and/or vascular diseases. Various therapeutic agents can be classified in terms of their sites of action in the host: agents that exert their actions extracellularly or at specific membrane receptor sites, those that act on the plasma membrane, within the cytoplasm, and/or the nucleus. 
     In addition to the aforementioned, therapeutic agents can include other pharmaceutical and/or biologic agents intended for purposes of treating body lumens other than arteries and/or veins). Therapeutic agents can be specific for treating nonvascular body lumens such as digestive lumens (e.g., gastrointestinal, duodenum and esophagus, biliary ducts), respiratory lumens (e.g., tracheal and bronchial), and urinary lumens (e.g., urethra). Additionally such embodiments can be useful in lumens of other body systems such as the reproductive, endocrine, hematopoietic and/or the integumentary, musculoskeletal/orthopedic and nervous systems (including auditory and ophthalmic applications); and finally, stent embodiments with therapeutic agents can be useful for expanding an obstructed lumen and for inducing an obstruction (e.g., as in the case of aneurysms). 
     Therapeutic release can occur by controlled release mechanisms, diffusion, interaction with another agent(s) delivered by intravenous injection, aerosolization, or orally. Release can also occur by application of a magnetic field, an electrical field, or use of ultrasound. 
     Stent Surface Coatings with Functional Properties 
     In addition to stents that can deliver a therapeutic agent, for instance delivery of a biological polymer on the stent such as a repellant phosphorylcholine, the stent can be coated with other bioresorbable polymers predetermined to promote biological responses in the body lumen desired for certain clinical effectiveness. Further the coating can be used to mask (temporarily or permanently) the surface properties of the polymer used to comprise the stent embodiment. The coating can be selected from the broad class of any biocompatible bioresorbable polymer which can include any one or combination of halogenated and/or non-halogenated which can or cannot comprise any poly(alkylene glycol). These polymers can include compositional variations including homopolymers and heteropolymers, stereoisomers and/or a blend of such polymers. These polymers can include for example, but are not limited to, polycarbonates, polyarylates, poly(ester amides), poly(amide carbonates), trimethylene carbonate, polycaprolactone, polydioxane, polyhydroxybutyrate, poly-hydroxyvalerate, polyglycolide, polylactides and stereoisomers and copolymers thereof, such as glycolide/lactide copolymers. In an embodiment, the stent can be coated with a polymer that exhibits a negative charge that repels the negatively charged red blood cells&#39; outer membranes thereby reducing the risk of clot formation. In another embodiment, the stent can be coated with a polymer that exhibits an affinity for cells, (e.g., endothelial cells) to promote healing. In yet another embodiment, the stent can be coated with a polymer that repels the attachment and/or proliferation of specific cells, for instance arterial fibroblasts and/or smooth muscle cells in order to lessen restenosis and/or inflammatory cells such as macrophages. 
     Described above are embodiments that can be modified with a coating to achieve functional properties that support biological responses. Such coatings or compositions of material with a therapeutic agent can be formed on stents or applied in the process of making a stent body via techniques such as dipping, spray coating, cross-linking combinations thereof, and the like, as mentioned and described above. Such coatings or compositions of material can also serve purpose other than delivering a therapeutic, such as to enhance stent retention on a balloon when the coating is placed intraluminally on the stent body and/or placed over the entire device after the stent is mounted on the balloon system to keep the stent in a collapsed formation. Other purposes can be envisioned by those skilled in the art when using any polymer material. 
     In accordance with an aspect of certain embodiments, a stent would have a coating applied that can alter the physical characteristics of the stent, such as to provide specific mechanical properties to the stent. The properties can include inter alia thickness, tensile strength, glass transition temperature, and surface finish. The coating can be preferably applied prior to final crimping or application of the stent to the catheter. The stent can then be applied to the catheter and the system can have either heat or pressure or both applied in a compressive manner. In the process, the coating can form frangible bonds with both the catheter and the other stent surfaces. The bonds would enable a reliable method of creating stent retention and of holding the stent crossing profile over time. The bonds would break upon the balloon deployment pressures. The coating would be a lower Tg1 than the substrate to ensure no changes in the substrate. 
     From the foregoing description, it will be appreciated that a novel approach for expanding a lumen has been disclosed. While several components, techniques and aspects have been described with a certain degree of particularity, it is manifest that many changes can be made in the specific designs, constructions and methodology herein above described without departing from the spirit and scope of this disclosure. 
     The methods which are described and illustrated herein are not limited to the sequence of acts described, nor are they necessarily limited to the practice of all of the acts set forth. Other sequences of acts, or less than all of the acts, or simultaneous occurrence of the acts, can be utilized in practicing embodiments. 
     While a number of embodiments and variations thereof have been described in detail, other modifications and methods of using and medical applications for the same will be apparent to those of skill in the art. Accordingly, it should be understood that various applications, modifications, materials, and substitutions can be made of equivalents without departing from the unique and novel last next disclosed herein or the scope of the claims. 
     REFERENCES 
     Some of the references cited herein are listed below, the entirety of each one of which is hereby incorporated by reference herein:
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