Patent Publication Number: US-2011054592-A1

Title: Flexible expandable stent and methods of deployment

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/613,443 filed Dec. 20, 2006, which is a continuation-in-part of U.S. patent application Ser. No. 29/252,668 filed Jan. 25, 2006, issued as U.S. Pat. No. D553,746 and U.S. application Ser. No. 29/252,669 filed Jan. 25, 2006, issued as U.S. Pat. No. D553,747, the contents of each of which are herein incorporated by reference in their entirety. This application claims the benefit of U.S. patent application Ser. No. 61/013,246 filed on Dec. 12, 2007, the contents of which are incorporated herein by reference in its entirety. This application is related to U.S. patent application Ser. No. 11/843,376 filed on Aug. 22, 2007, U.S. patent application Ser. No. 11/843,402 filed on Aug. 22, 2007, U.S. patent application Ser. No. 60/823,692 filed on Aug. 28, 2006, U.S. patent application Ser. No. 60/825,434 filed on Sep. 13, 2006, U.S. patent application Ser. No. 60/895,924 filed on Mar. 20, 2007, U.S. patent application Ser. No. 60/941,813 filed on Jun. 4, 2007, U.S. patent application Ser. No. 60/975,383, filed Sep. 26, 2007, and World International Property Organization (WIPO) International Patent Application Number PCT/US08/77871 filed on Sep. 26, 2008, the contents of each of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention relate to medical stents which are implantable devices for propping open and maintaining the patency of vessels and ducts in the vasculature of a human being. 
     2. Description of the Related Art 
     Stents are implantable prosthesis used to maintain and/or reinforce vascular and endoluminal ducts in order to treat and/or prevent a variety of medical conditions. Typical uses include maintaining and supporting coronary arteries after they are opened and unclogged by a medical procedure, such as through an angioplasty operation. A stent is typically deployed in an unexpanded or crimped state using a catheter and, after being properly positioned within a vessel, is then expanded into place. 
     As a foreign object inserted into a vessel, a stent can potentially impede the flow of blood through the vessel. This effect can also be exacerbated by the undesired growth of tissue on and around the stent, potentially leading to complications including thrombosis and restenosis. Thus, stents are manufactured to minimize impedance of blood flow through a vessel while being capable of effectively maintaining the expanded state of the vessel. Typical stents have the basic form of an open-ended tubular element supported by a mesh of thin struts with openings formed thereinbetween. Such stent designs require excessive amounts of material and excessive strut-to-tissue contact that can increase the likelihood of the above-described complications. These problems can be particular apparent with multiple-stent applications in which the stents overlap each other (e.g., bifurcation procedures). 
     Thus, many stent designs have been produced to minimize the amount of material used and reduce the level of stent-to-vessel contact percentage, i.e., the percentage of direct strut surface contact relative to the surface area defined by the inner vessel wall along the extent of the stent. Reducing the level of contact reduces the likelihood and level of damage during deployment and adverse reactions caused by implanted materials. Stent designs with insufficient amounts of material, however, and/or with poorly distributed support and expansion profiles can result in complications such as a partial or complete collapse of the struts, and consequently, collapse of portions of the vessel which they support. 
     For example, some designs included in a category known as “open stent” designs (e.g., having areas of struts with relatively few connecting points) can provide substantial flexibility but may have inadequate support in certain areas of the stent, particularly when placed across hard lesions such as calcified vessels. After an angioplasty balloon is deflated, the stented vessel area will have a tendency to return to its naturally curved state and exert forces on the stent correspondingly. With typical “open” stent designs, the flexing of the stent in response to these forces will generally occur around or pivot about these “open” areas along the limited connecting points, thus potentially opening these “open” areas even further and substantially reducing vessel support about them. 
     These types of “open” designs are also typified by high proportions of strut deformation, separation, and movement in relatively focused areas of the stent, thus potentially causing high levels of abrasion to adjacent tissue and creating large open unsupported areas across the expanded stent. 
     Although “open” stent designs can also provide the advantage of reduced strut-to-vessel contact percentage, improvements are needed toward lowering the typical percentage of around 15 percent or more by better distribution of contact along the vessel. 
     Stents with poorly distributed expansion profiles (e.g., that result in uneven expansion or movement of struts) can potentially cause excessive damage and complicate healing after deployment, increasing the likelihood of restenosis and risky revascularization procedures. For example, a design which is the subject of U.S. Pat. No. 6,432,133 issued Aug. 13, 2002, entitled “Expandable Stents and Method for Making Same,” incorporated herein by reference in its entirety, proposes generally independently expandable radial components with substantially straight longitudinal segments that, during expansion, pivot almost exclusively about a limited set of connecting bends. Thus, the deformation of these stents during expansion would occur almost exclusively by the pivoting and rotation of these straight segments, causing significant movement and abrasion about the adjacent vasculature during expansion. 
     In addition to strut patterns, the surface profile of a stent strut during and after deployment can impact the level of incidental damage caused to a vessel and effect complications during recovery, including inflammation, restenosis, thrombosis, and the speed of healing about the stent. Particularly sharp or angular strut surfaces that may be adopted to minimize overall stent material can, however, increase the likelihood of adverse complications by causing too much stress and abrasion to the tissue in which the strut surfaces contact. Thus, better optimized strut patterns and strut surface profiles are needed for providing both effective overall support, limiting damage to the tissue during and after deployment, and promoting effective healing. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention relate to medical stent assemblies comprised of elongated tubular patterns of metal capable of expanding and propping open a vessel or duct within a living, human being. 
     In an aspect of the invention, a flexible, expandable, elongated stent assembly is provided having a pattern of interconnected along a curvilinear path, the struts defining a generally cylindrically shaped channel, the channel having a plurality of openings and a longitudinal axis. The struts include a plurality of circumferential arrays of webs or bends of material, each circumferential array connected to an adjacent circumferential array by fewer than 4 cross-links, wherein each circumferential array extending from a first side of a circumferential array of the plurality of circumferential arrays is substantially circumferentially offset from every cross-link extending from an opposite side of the same circumferential array. In a cross-section generally normal to the curvilinear path of the strut and normal to a center of curvature of the channel, the struts have a surface width that is at least one and a half times that of a surface height of the strut. 
     In an embodiment, the flexible, each circumferential array is connected to an adjacent array by two cross-links. 
     In an embodiment, the cross-links are arranged such that, upon expansion of said stent assembly from a first position in an unexpanded state to a second position in an unexpanded state, the cross-links are re-oriented or pivoted with respect to the longitudinal axis. 
     In an embodiment, each of the cross-links is attached to a bend of a circumferential array such that any bending or pivoting of the each of the cross-links is directly and substantially coupled with a bending or pivoting of the attached circumferential array. 
     In an embodiment, each of the cross-links extends from a mid-portion of a longitudinally extending curved section of a first bend of a first array to a tip portion of a first bend of a longitudinally adjacent second array. In an embodiment, each cross-link connects diagonally positioned bends of said circumferential arrays of bends or webs to each other. 
     In an embodiment, wherein each cross-link extending from the first side of each circumferential array is substantially is substantially circumferentially offset by at least about 60 degrees from said every cross-link extending from an opposite side of the same circumferential array. In an embodiment, each of the cross-links extending from the first side of each circumferential array is offset by about 90 degrees from said every cross-link extending from an opposite side of the same circumferential array. 
     In an embodiment, a circumferential gap or open cell is arranged between circumferentially adjacent cross-links, the circumferential gap extending along about a half-circumference of the stent. 
     In an embodiment, the surface width is greater than about 90 microns. In an embodiment, the surface width is between about 90 and 130 microns. In an embodiment, the surface width is about 120 microns. 
     In an embodiment, the strut surface width is of about twice that of the strut surface height. 
     In an embodiment, the stent assembly is manufactured such that upon having an expanded diameter of between about 2.75 mm and 4 mm in a vessel, the stent assembly has less than about 10.5% to 13.5% of strut-to-vessel contact over an area encompassing an entire periphery of the channel. 
     In an embodiment, the circumferential arrays include arcuately shaped, generally hairpin-like smoothly curved webs or bends. In an embodiment, a substantial portion of each of the arcuately shaped, generally hairpin-like curved webs or bends form arcs of generally the same orientation with respect to the circumference of said stent assembly. 
     In an embodiment, each of the circumferential arrays of webs or bends comprises a first pattern of lengthwise-sized bends and a second pattern of lengthwise-elongatedly-sized bends at regular intervals on each circumferential array. 
     In an embodiment, wherein a first stent assembly of the flexible, expandable stent assembly is combined with a second stent assembly that extends at least partway through an opening of the first stent assembly. In an embodiment, the second stent assembly extends at least partway through a generally circumferentially disposed opening of the first stent assembly. In an embodiment, the second stent assembly extends through a generally longitudinally disposed opening of the first stent assembly. In an embodiment, the second stent assembly is of at least one of a smaller length and a smaller diameter than that of the first stent assembly. 
     In an embodiment, the plurality of circumferential arrays of webs or bends of material is metal. 
     In an aspect of the invention, a method for expanding and supporting the vasculature of a patient is provided, the method including the step of placing a first stent assembly into a vessel of the patient. The stent assembly includes a pattern of interconnected struts along a curvilinear path, the struts defining a generally cylindrically shaped channel that extends along a longitudinal axis, the channel having a plurality of openings, the struts including a plurality of circumferential arrays of webs or bends of a material, wherein each cross-link extending from one side of a circumferential array of the plurality of circumferential arrays is substantially circumferentially offset from every cross-link extending from an opposite side of the same circumferential array, each circumferential array connected to an adjacent circumferential array by fewer than four cross-links. Each strut has, in a cross-section generally normal to the curvilinear path of the strut and normal to to a center of curvature of the channel, a strut surface width of at least one and a half times that of a strut surface height of the strut. 
     In an embodiment, the fewer than four cross-links consists of two cross-links. 
     In an embodiment, a circumferential gap or open cell is arranged between circumferentially adjacent cross-links, the circumferential gap extending along about a half-circumference of the stent assembly. 
     In an embodiment, the method further includes the step of expanding the first stent assembly. 
     In an embodiment, the step of expanding the first stent includes re-orienting or pivoting the cross-links with respect to said longitudinal axis. 
     In an embodiment, each one of the cross-links is fixed to a bend of a circumferentially array such that the re-orienting or pivoting of the each one of the cross-links is directly and substantially coupled with a bending or pivoting of said bend of a circumferential array. 
     In an embodiment, the direct and substantial coupling is provided by a cross-link directly connected between a mid-portion of a longitudinally extending curved section of a bend of a first circumferential array and the tip portion of a bend of a second circumferential array that is adjacent to the first circumferential array. 
     In an embodiment, the stent is expanded to a diameter between about 2.75 millimeters and 4 millimeters and provides an overall strut-to-vessel contact percentage of less than about 10.5% to 13.5% of vessel area encompassing the periphery of the channel. 
     In an embodiment, the stent conforms to curves in the vessel of the patient by generally concentrating abending of the stent about the longitudinal axis over portions of the stent where the circumferential position of the cross-links substantially corresponds to apexes of the curves in the vessel. 
     In an embodiment, wherein each cross-link extending from the first side of each circumferential array is substantially circumferentially offset from every cross-link extending from the opposite side of the circumferential array. 
     In an embodiment, each cross-link extending from the one side of each circumferential array is offset by about 90 degrees from every cross-link extending from the opposite side of the circumferential array. 
     In an embodiment, the strut surface width of the stent assembly is greater than about 90 microns. In an embodiment, the strut surface width is between about 90 and 130 microns. In an embodiment, the strut surface width is about 120 microns. In an embodiment, the strut surface width is of about twice that of the strut surface height. 
     In an embodiment, the stent assembly includes circumferential arrays of switchback webs or bends, wherein the circumferential arrays are connected to one another by an arrangement of cross-links, wherein each of the cross-links comprises a path of curvature that continuously extends a path of curvature of at least one of said bends. 
     In an embodiment, a substantial portion of each of the webs or bends of the stent assembly form arcs of generally the same orientation with respect to the circumference of the stent assembly. 
     In an embodiment, each of the circumferential arrays of webs or bends of the stent assembly includes a first pattern of lengthwise sized bends and a second pattern of lengthwise-elongatedly sized bends at regular intervals on each circumferential array. 
     In an embodiment, the first stent assembly is placed across a first arm of a bifurcated vessel and the method further includes a step of placing a second stent assembly at least partway through a side wall opening of the first stent assembly and into a second arm of the vessel bifurcation. 
     In an embodiment, the second stent assembly is defined by a pattern of struts essentially equivalent to that of the first stent assembly. 
     In an embodiment, the method further includes the step of extending the first stent assembly by placing a second stent assembly at least partway through a longitudinal end opening of the first stent assembly. 
     In an embodiment, the second stent assembly is defined by a pattern of struts essentially equivalent to that of the first stent assembly. In an embodiment, the second stent assembly is of a smaller diameter than that of the first stent assembly. 
     In an embodiment, the second stent assembly is of a shorter length than that of the first stent assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and advantages of the present invention will become more apparent when viewed in conjunction with the following drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  is an illustrative longitudinal presentation, in a flat or “planar” array, of an unexpanded stent assembly in accordance with embodiments of the invention. 
         FIG. 2  is a side elevational view of a stent assembly in an embodiment of the present invention in a cylindrical configuration in accordance with embodiments of the invention. 
         FIG. 3A  is an enlarged illustrative view, in plan, of a portion of a circumferential array of arcuately shaped hairpin-like bends of the stent assembly shown in  FIG. 1  in accordance with embodiments of the invention. 
         FIG. 3B  is an illustrative side perspective view of a strut section of the assembly shown in  FIG. 3A . 
         FIG. 3C  is an illustrative cross-sectional view across lines I-I′ of an embodiment of the stent strut section shown in  FIGS. 3A and 3B . 
         FIG. 4A  is an illustrative cross-sectional view of a typical square-shaped stent strut abutting a vessel wall. 
         FIG. 4B  is an illustrative cross-sectional view of a stent strut in accordance with an embodiment of the invention abutting a vessel wall in accordance with embodiments of the invention. 
         FIG. 5  is a perspective illustrative view of two expanded stent assemblies in accordance with an embodiment of the present invention shown interdigitated in a vessel bifurcation in accordance with embodiments of the invention. 
         FIG. 6  is a view of an enlarged flattened illustrative pattern of the stent of  FIGS. 1 and 2  shown after balloon expansion in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The accompanying drawings are described below, in which example embodiments in accordance with the present invention are shown. Specific structural and functional details disclosed herein are merely representative. This invention may be embodied in many alternate forms and should not be construed as limited to example embodiments set forth herein. 
     Accordingly, specific embodiments are shown by way of example in the drawings. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the claims. Like numbers refer to like elements throughout the description of the figures. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that “adjacent” does not necessarily imply contact but may connote an absence of the same type of element(s) therein between “adjacent” elements. 
     It will be understood that when an element is referred to as being “on,” “connected to,” or “coupled to” another element, it can be directly on, connected to or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element, there are no intervening elements present. Also, when an element is referred to as being “attached to” or “affixed to” another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). 
     The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” “comprising,” “include,” “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Referring now to the drawings in detail, and particularly to  FIG. 1 , a medical stent assembly  10  in accordance with an embodiment of the present invention is represented in a flat or planar configuration for ease of understanding. The medical stent assembly  10  is comprised of an elongated tubular pattern of metal capable of expanding and propping open a vessel or duct within a living being, as represented in its cylindrical form, in  FIG. 2 . The stent assembly  10  comprises a plurality of web-like, circumferential arrays  12 ,  12 A, . . .  12 H of switchback bends or loops or loops  14 , generally in the manner of an arcuately shaped “hairpin-like” curve, as indicated within the dashed rectangle “X” shown in  FIG. 1  and  FIG. 3A . 
     There are, for example, a plurality of circumferential arrays of switchback loops or hairpin-like curves  12 ,  12 A,  12 B,  12 C,  12 D,  12 E,  12 F,  12 G, and  12 H spaced apart from one another along the longitudinal axis “L” of the stent assembly  10 , as shown in  FIGS. 1 and 2 . The loops or bends  14  at a first end  16  of the stent assembly  10  in the first circumferential array  12  thereat are all generally in peripheral alignment with one another, as indicated by their edge in alignment with a border identified by a dashed line  11 . In an embodiment, elongated loops  18  on the inwardly directed side of the first or leftmost circumferential array  12  of every third of the switchbacks or hairpin-like curves or loops  14  extend longitudinally beyond a peripheral border  15 , while remaining loops  14  of the first or leftmost circumferential array  12  do not extend inwardly beyond the peripheral border  15 . Further, the elongated loops  18  in each of the circumferential arrays  12 ,  12 A etc. comprising, in an embodiment, at least every third of the switchbacks or hairpin-like curves or loops  14  can extend longitudinally beyond one or more of their peripheral border alignments, as indicated by dashed lines  15  and  21  of their adjacent bends, in an exemplary manner, for the two leftmost arrays  12  and  12 A. 
     In an embodiment, a plurality of preferably smoothly curved, arcuate cross-links  50  are arranged so as to connect diagonally adjacent elongated loops  18  between longitudinally adjacent arrays  12 ,  12 A, etc., of bends or curves  14 . Those elongated loops  18  preferably comprise every third loop  14  as most easily seen in  FIG. 1 . 
     Loops (also referred to as curves)  14  are shown in an enlarged representation in  FIG. 3A  in an embodiment of the invention. The arcuately shaped “hairpin-like” curves  14  have a smoothly curved concave side  17  and a smoothly curved convex side  19 . Thus, the concave and convex sides  17  and  19  of each curve  14  are configured to be curved circumferentially, that is, curved in the “same direction” or orientation, in their definition of each individual loop or curve  14 . 
     In an embodiment, the second and successive circumferential arrays  12 A,  12 B etc, of switchback or hairpin-like curves or loops  14  are in generally corresponding longitudinal alignment with the switchback or hairpin-like curves or loops  14  of the first circumferential array  12  of loops  14  (shown in  FIG. 1  as the leftmost array) at the first end  16  of the stent assembly  10 , as indicated by dashed line CA, shown in  FIG. 1  passing through the tips of the loops  14 , which may be called “fronds” in conforming with a “Palm Tree” shape, described herein in greater detail. That is, a switchback or loop  14  of an Nth circumferential array  12 N, for example, circumferential array  12 D, is generally aligned according to a predetermined displacement, if any, with respect to loops  14  in the N+1 circumferential array  12 N+1 of switchback or hairpin-like curves or loops  14 , for example, circumferential array  12 E. For example, beginning with array  12 A, loops  14  are generally closely correspondingly aligned with loops  14  of alternating subsequent arrays  12 B,  12 D, etc. . . . , and offset (or out of phase) with respect to loops  14  of alternating subsequent arrays  12 A,  12 C, etc, thus providing a “Palm Tree” shape. 
     In an embodiment, each adjacent circumferential array  12 ,  12 A, . . .  12 H of loops or arcuately shaped hairpin-like curves  14  is joined to its longitudinally adjacent circumferential array  12 A,  12 B etc. . . . of loops or hairpin-like curves  14  by at least two smoothly curved arcuate cross-links  50 . Each cross-link  50  extends from a mid-portion  52  of a curved section of an arch of an elongated switchback loop  18  to the tip portion  56  of the curved hairpin-like curve or bend  14  on a generally diagonally adjacent elongated curved switchback loop  18 , as best represented in  FIG. 1 , and which is also illustrated in  FIGS. 2 ,  5 , and  6 . Furthermore, each circumferential array is directly connected to each adjacent circumferential array by a cross-link  50  between a mid-portion  52  of an elongated curved switchback loop  18   a  of a first circumferential array, for example, array  12 G and a tip portion  56  of an elongated curved switchback loop  18   b,  of an adjacent second circumferential array, for example, array  12 F, that generally extends the arcuate curvature of the bend  18   b  leading to the tip portion  56 . The direct connection by a cross-link  50  to a mid-portion  52  of a bend of a circumferential array promotes substantial coupling between any re-orienting, pivoting, and bending of a cross-link  50  with re-orienting, pivoting, and bending of that linked circumferential array, resulting in each circumferential array not generally being independently expandable with respect to an adjacent circumferential array and promoting even expansion across the stent assembly. Those cross-links  50  extending from tip portions  56  are on the same longitudinal end of a circumferential array  12 ,  12 A etc and those cross-links that extend from a mid-portion  52  are on the opposite longitudinal end of the circumferential array, which can also help promote uniform expansion of the stent. 
     For various embodiments of the invention, the general pattern can be adapted for differently sized stents or stents of different strengths varied according to need. For example, the frequency or number of circumferential arrays may be varied and the number of hairpin-like curves or loops may be varied as necessary for each circumferential array. For example, embodiments of the pattern with six hairpin-like loops for each circumferential array can provide for a stent length of about 9 mm with four columns of circumferential arrays, a length of about 18 mm with 9 columns of circumferential arrays, a length of about 28 mm with 12 columns of circumferential arrays. These embodiments can have, for example, initial outer diameters of about 2 mm, crimped inner diameters of about 0.7 mm, and deployed outer diameters of about 2.75 mm, 3.0 mm, 3.5 mm, or 4.0 mm. 
     In other embodiments, the elongated switchback loops  18  in every series of peripherally adjacent bends of adjacent circumferential arrays extend longitudinally beyond the bends or tips of their circumferentially adjacent hairpin-like curves  14 , as indicated by the dashed lines  15 ,  21 , and  42 , shown in  FIG. 1 . 
     In an embodiment, a generally semi-circumferentially extending annular, circumferentially elongated gap or space  30  between array  12  and longitudinally adjacent array  12 A defined by their respective circumferential loops  14  and the arcuate cross-links  50  resembles the aforementioned branched “Palm Tree” configuration, most conspicuously shown in  FIG. 1 . 
     In an embodiment, the last circumferential array  12 H of the stent assembly  10  has an edge array of bends  14  thereon which are generally in peripheral alignment with one another, as indicated by their common alignment with dashed line  40 , as shown in  FIG. 1 . The last or rightmost circumferential array  12 H at the second end  32  of the stent assembly  10  also has elongated bends or elongated switchback loops  18  that extend longitudinally beyond the peripheral edge of the adjacent switchback loops or hairpin-like curves  14  on that particular circumferential array  12 H, as indicated by their extension in a longitudinal direction, “inwardly” beyond the dashed line  42 , also shown in  FIG. 1 . 
     Thus, there are annular gaps  30  between adjacent circumferential arrays  12 ,  12 A etc. of switchback loops or hairpin-like curves  14  comprising about 180 degrees (as represented by circumferential offset identifiers  64 ) of the peripheral space of the stent assembly  10  at that particular longitudinal location between adjacent arrays  12 ,  12 A etc. The 180 degree clear, open, circumferentially disposed, “Palm Tree” shaped “open cell” space  30  between adjacent circumferential arrays  12 ,  12 A etc. generally comprises a “half periphery” of the stent assembly  10 , permitting a second stent assembly  10 ′ (see  FIG. 5 ) to be passed therethrough and expanded outwardly as in a vessel bifurcation, because of the multiple longitudinally-dispersed, half-circumference “open cell” structure of each particular stent assembly  10 , thereby allowing such multiple stent assembly interdigitation to be provided. Further embodiments within the scope of this invention can include more than two annular “open cell” spaces or gaps  30  between circumferential arrays  12 ,  12 A etc of loops  14 , depending upon the number of cross-links  50  dividing up each annular space between adjacent arrays  12 ,  12 A etc. For example, one embodiment may extend the general pattern of open spaces  30  to comprise three annular “open spaces” or gaps  30 , each one of which spans about a third of the periphery (about 120 degrees) of the stent assembly  10 . In a further embodiment, a varying number (e.g. 2, 3 or more) of cross-links  50  may be disposed between adjacent arrays  12 ,  12 A etc. is contemplated, to provide any particular desired variation in bending and/or in receptability to through-wall penetration by several stein assemblies  10 ,  10 ′ etc. 
     After the insertion of such a stent assembly  10  of the present invention in a vessel and upon expansion of the adjacent circumferential loops  14  of each array  12 ,  12 A etc., each of the cross-links  50  between adjacent circumferential arrays  12 ,  12 A, etc. may in an embodiment, be re-oriented slightly or pivoted, as viewed radially inwardly, indicated by the arrow “P” in  FIG. 1 . In an embodiment, as a stent assembly  10  expands from an unexpanded state such as shown in  FIG. 1  to an expanded state (such as shown in  FIG. 6 ), the cross-links  50  can rotate, pivot, and/or bend relative to the longitudinal axis “L” of the strut assembly so to be repositioned from an oblique orientation with respect to its alignment with the longitudinal axis “L” of the stent assembly  10  to an orientation which is more parallel to the longitudinal axis “L” of the stent assembly  10 . Such a movement of these cross-links  50  assists in forestalling any shortening of the length of the stent assembly  10  as it expands within the vasculature of a patient. Such annular or circumferential disposition of the semi-circumferential gaps or spacings  30  during expansion of the stent assembly  10 , and the rotation of the cross-links  50 , however, remain in general circumferential disposed alignment with respect to the longitudinal axis of the stent assembly  10 , and not obliquely angled with respect thereto. Such a stent assembly  10  foreshortening during expansion thereof can be, however, primarily prevented by the expansive common circumferential and longitudinally directed deformation of the curves or bends  14  due to their unique curvilinear configuration, which comprises the structure being moved radially outwardly. 
     The minimal number of cross-links  50  between longitudinally adjacent circumferential arrays  12 ,  12 A etc of loops  14  adds to the stent assembly&#39;s flexibility and adaptability of that stent assembly  10  in the curved vasculature of a patient. Similarly, the untethered adjacent bends  14  in the respective circumferential arrays  12 ,  12 A etc. allows for substantially uniform radial strength over the length of the stent assembly  10 , permitting substantially uniform expansion and helps reduce or avoid such effects as “dog boning” or the foreshortening of the stent assembly  10  within a patient. In an embodiment, each of the cross-links  50  extending from a circumferential array  12 A,  12 B, . . . ,  12 E, is substantially circumferentially offset from each cross-link  50  extending from the same circumferential array on its longitudinally opposite side, thus providing flexibility and adaptability of that stent assembly  10  in the curved vasculature of a patient. In an embodiment, the circumferential offset is about 90 degrees as shown by circumferential offsets  54  between cross-links  50 . 
     In an embodiment, the dimensions and geometry of the stent strut cross-sections, their relative orientation combined with the strut pattern, and the strut surface profile are designed to promote flexibility, to promote support of the vasculature, to minimize surface contact and damaging abrasion therefrom. 
       FIG. 3A  is an enlarged illustrative view, in plan, of a portion of a circumferential array of arcuately shaped hairpin-like bends of the stent assembly shown in  FIG. 1 .  FIG. 3B  is an illustrative side perspective view of a strut section  100  of the assembly shown in  FIG. 3A .  FIG. 3C  is an illustrative cross-sectional view across lines I-I′ of an embodiment of the stent strut section  100  shown in  FIG. 3A .  FIG. 4B  is an illustrative cross-sectional view of a stent strut in accordance with an embodiment of the invention abutting a vessel wall  105 . In an embodiment, a cross-sectional dimension  110  (defined herein as strut “surface width”) is generally planar relative to a targeted vessel surface and, in an embodiment, longer than its normal dimension  120  (defined herein as “strut height”). In contrast,  FIG. 4A  provides an illustrative cross-sectional view of a substantially square-shaped stent strut  150  abutting a vessel wall  105 . The elongated dimension  110  as shown in  FIGS. 3C and 4B  provides a flatter, less angular, surface profile of the strut against a vessel wall than a more square profile such as of the strut  150  shown in  FIG. 4A , thus reducing the potential for damage during stent expansion while retaining the necessary strength and flexibility to meet various biomechanical requirements of an expandable stent. In an embodiment of the invention, dimension  110  of the stent strut  100  is between about 90 to about 130 microns and dimension  120  of the stent strut  100  is between about 50 to about 80 microns and suitable, for example, for smaller vessels (i.e., less than 3 mm in diameter). In an embodiment, dimension  110  averages about  115  microns across stent  10  and dimension  120  averages about 65 microns across the struts of stent  10 . In an embodiment of the invention, dimension  120  of the struts  100  is of a thickness of between about 60 and 100 microns which can be suitable, for example, for medium sized vessels (i.e., from 3 mm to less than 4 mm in diameter). In an embodiment, dimension  110  is at least about one and a half times that of dimension  120  and, in an embodiment, about twice or more than that of dimension  120 . 
     Referring now to  FIG. 5 , the interdigitation of a second stent assembly  10 ′ (extending along axis  300 ) through a first stent assembly  10 ″ (extending along axis  350 ) within a bifurcated body vessel B is shown in an embodiment of the invention. Such a multiple stenting is made easier by virtue of the expansive circumferential “Palm Tree” shaped open cell spaces  30 , such as described herein with regard to the embodiments illustrated in  FIG. 1 . A minimal number of cross-links  50  (e.g., two cross-links) between adjacent arrays  12 ,  12 A, etc of hairpin-like curves  14  promotes the curvature of each stent  10 ′ and  10 ″ for accommodating one another, and wherein a first stent  10 ′ can be penetrated by another stent  10 ′ without significant interference, which is highly beneficial to a patient needing such a bifurcation procedure. This double stenting at a bifurcated vessel B can be achieved one stent at a time, with the second stent assembly  10 ′ being directed though the longitudinal opening of the first stent assembly  10 ″ then angularly directed through such a “Palm Tree” shaped side opening  30  which is in alignment with vessel V 1  of the bifurcated vessel B being stented. Further, the second stent assembly  10 ′ in a bifurcation procedure of the present invention may be of shorter length or of smaller diameter to facilitate the stenting of a bifurcation B, or to accommodate only a relatively short or narrow branch requiring stenting extending from the parent vessel V 2 , to minimize any unnecessary overlap between the first and second stent assemblies  10 ″ and  10 ′. 
     In addition, the limited number of cross-links  50 , their distribution, and the “flat” strut profile (such as that illustrated in  FIGS. 3C and 4B ) provides adequate vessel support and also provides longitudinal flexibility in a highly curved area such as bifurcating vessel V 1 . The “flat” strut profile shown in  FIG. 3C  reduces the tendency of struts, including cross-links  50 , to bend along the  110  dimension and rather promotes bending along the narrower  120  dimension, and helps limit a further longitudinal widening of already “open” areas  30  along areas of high vascular curvature. In an embodiment, each cross-link  50  has a “flat” profile and is substantially circumferentially offset from every other cross-link  50  extending from the opposite side of the circumferential array. In an embodiment, the offset is about 90 degrees, as shown in the assembly of  FIGS. 1 and 2 . 
     Referring again to  FIG. 5 , where stent  10 ′ is shown partially inserted into a bifurcated vessel V 1 , the curved arrow  80  is shown generally representing the overall curvature of bifurcating vessel V 1 . The resulting curvature of stent  10 ′ in response to overall curvature  80  of bifurcating vessel V 1  is concentrated more so along the section generally defined by curved arrow  85 , where a cross-link  50  is generally circumferentially oriented with the overall curvature  80 . The “flat” strut profile and alternating nature of the circumferential position of the cross-links  50  helps promote bending in this manner, thereby reducing excessive widening of open areas  30 . Thus, in an embodiment, the bending of a stent in response to the curvature of a vessel tends not to excessively longitudinally widen an open area  30 , further helping prevent a collapse of tissue and preventing bending of the stent by operation of other factors (e.g., calcification) not generally associated with the overall natural shape of a vessel. 
     In embodiments of the invention, various multiple-stent deployments such as in accordance with assembly  FIG. 5  or, for example, a “kissing stent” procedure (in which a first stent is “extended” by placing a second stent at least partway through a longitudinal end of the first stent) are more fully described in co-pending and related U.S. patent application Ser. No. 11/613,443, filed on Dec. 20, 2006 and entitled “Flexible Expandable Stent,” the entire contents of which is incorporated herein by reference in its entirety. The flexible, broadly supportive, and “open” characteristics of a stent assembly  10 , for example, in accordance with an embodiment of the invention is well adapted for placement with one or more other stent assemblies, such as one or more stents in a localized vessel area. 
     While providing substantially evenly distributed support of a vessel wall, an embodiment of the invention provides a strut-to-vessel contact percentage of less than about 14%. 
       FIG. 6  is a view of an enlarged flattened illustrative pattern of the stent  10  of  FIGS. 1 and 2  shown after balloon expansion. In an embodiment, after balloon expansion, the stent  10  is expanded to about twice its original diameter. The expanded pattern illustrates the limited longitudinal widening of open areas  30  which occurs after a stent expansion and deformation of the entire cell  30  and co-dependent expansion between circumferential arrays  12 ,  12 A,  12 B, etc. described further herein. A strut-to-vessel contact ratio is the percentage of strut-to-vessel contact across an area of the vessel surface encompassing the stent and, for example, can be represented in  FIG. 6  as the percentage of the surface area occupied by the struts of stent  10  over the total area represented by box  200 . In an embodiment, a strut-to-vessel contact percentage ranges from about 10.5 percent or less to about 13.5 percent or less, being generally proportional to expansion diameters ranging between about 2.75 and 4 millimeters. In an embodiment, a stent in accordance with the pattern of  FIG. 1  has a strut dimension (or surface width)  110  (described above, for example, in connection with  FIGS. 3B ,  3 C, and  4 B) averaging about 115 microns and, at an expanded diameter of about 3 millimeters, would have a strut-to-vessel contact percentage of about 11%. 
     Various embodiments in accordance with the invention can provide well distributed vessel support combined with well distributed deformation upon expansion, thus helping avoid concentrated abrasion and excessive damage to particular vessel areas. Comparing  FIGS. 1  (an unexpanded stent) and  FIG. 6  (an expanded stent), for example, the struts of stent  10 , including cross-links  50 , will collectively bend, pivot, and deform together to the general orientation as shown in  FIG. 6 . In an embodiment, as stent  10  is expanded, the longitudinal ends of circumferential arrays  12 ,  12 A, etc., generally remain proximal to each adjacent circumferential array  12 ,  12 A, etc., while also substantially avoiding foreshortening. By distributing bending and pivoting over a substantial portion such as over the stent  10  during expansion, excessive movement and abrasion is significantly avoided. 
     Furthermore, when a cross-link  50  is pivoted in a more longitudinal orientation, its direct connection to the mid-portion  52  of a curved section of arch tends to occur in conjunction with a bending of a switchback loop  18  rather than a solely longitudinal widening of an open area  30 . Limiting the further longitudinal opening of these areas generally maintains relatively consistent vessel support around areas  30  and helps avoid excessively large unsupported areas that can be problematic with typical “open” stent designs. 
     Referring again to  FIG. 3A , the direction of loops or curves  14  substantially reverse through bends  60  and  62  in a switchback hairpin-like manner and illustrates exemplary areas  20  and  27  of stent  10  that have, in an unexpanded state, relatively greater (or tighter) degrees of curvature than other areas of the stent. In an embodiment of the invention, a minimal radius of curvature along the entire surface of the unexpanded stent (that is, not expanded beyond a point generally appropriate for deployment), including along those areas of highest curvature, is about 65 microns. In an embodiment of the invention, the minimal radius of curvature is about 80 microns. In an embodiment, the stent has one or more layers of coating material while having a minimal radius of curvature of about 50 microns. 
     The relatively large minimum radius of curvature of the unexpanded stent provides a highly favorable surface over which coating materials can be deposited. Distributing curvature more evenly over the entire stent helps avoid the inclusion of areas of excessively tight curvature that promote the disadvantages of coating prior designs. For example, the overall openness of the curves  14  helps avoid a structural blockage that could prevent a consistent coating over the entire stent surface. A tightly closed area of curvature may more likely receive less material than other areas not similarly closed, thus resulting in insufficient coating about the tightly closed areas. 
     An inconsistent coating process may prompt thicker layers of material to be applied overall to the stent surface in order to ensure adequate coverage overall. Thicker layers of material, particularly metallic material, can detrimentally effect biomechanical properties of the stent, including flexibility and tissue-to-stent surface contact. In addition, the areas of relatively low curvature help avoid the effect of “webbing,” wherein an area of tight curvature acting as a crevice can essentially be filled in and could cause the coating to stretch apart and/or split during expansion of the stent, including the area of tight curvature. Moreover, areas of tight curvature (with our without coatings) can be subject to greater mechanical stresses when they are opened (such as during expansion), thus increasing the likelihood of metal fatigue, fractures, and/or increased post-expansion recoil. 
     In a further embodiment of the invention, opposing surfaces of a stent (e.g., in accordance with the design of  FIGS. 1 and 2 ) are separated by a minimal distance in order to enhance surface modification processes and help avoid issues such as, for example, uneven coating, webbing, and/or cracking. Referring to  FIG. 3A , exemplary straight-line normal spans  70  are shown between opposing strut surfaces and, in an embodiment, are of at least this minimal distance. In an embodiment, all opposing surfaces of the stent structure are separated by normal straight-line distances (or spans) by a minimal distance of about 130 microns. In another embodiment, all normal straight-line distances (or spans) of opposing surfaces (e.g., normal spans 70) have a minimal distance of about 160 microns. 
     The “open” curvature and/or substantially non-interfering characteristics of various embodiments of the invention promote a structure conducive to various coating technologies including, in particular, those involving streams of coating particles and/or bombarding particles directed at the surface of an embodiment (e.g. the struts of annular arrays  12 ,  12 A etc. and cross-links  50 ) of the stent structure. In an embodiment of the invention, the coating process comprises directing a stream of particles (e.g. coating and/or bombarding atoms or ions) toward the stent structure. In an embodiment of the invention, a coating process comprises at least one of electrochemical deposition, chemical-vapor deposition, electroplating, electro-polishing, ion-assisted deposition, and/or ultrasonic spraying. 
     In an embodiment, the struts are layered with inert biocompatible materials, including gold, silver, platinum, and/or various non-metallic materials. 
     In an embodiment of the invention, one or more layers is provided with an ion-assisted deposition onto the stent structure, such as, for example, through methods which use one or more magnetrons such as described in pending U.S. patent application Ser. No. 09/999,349, filed Nov. 15, 2001, entitled published Sept. 26, 2006 as US Patent Application Publication Number 2002/-0138130A1 and pending U.S. patent application Ser. No. 11/843,376, filed Aug. 22, 2007, and U.S. patent application Ser. No. 11/843,402, filed Aug. 22, 2007, published Sep. 4, 2008, the contents of each of which are incorporated herein by reference in their entirety. Various embodiments of these devices and methods involve actively and/or passively biasing a substrate with electrical charge and thus increasing the attraction of charged coating and/or bombarding atoms or ions, for which various embodiments of the present invention can help improve the uniformity of the magnetic attraction. 
     In an embodiment, the struts of annular arrays  12 ,  12 A, etc. and cross-links  50  are comprised of a highly radiopaque substrate such as, for example, cobalt-chromium material, stainless-steel, and nitinol material. In a further embodiment, such as in accordance with previously cited and incorporated U.S. patent application Ser. No. 11/843,376, gradations of platinum and palladium ions are implanted onto a cobalt chromium base through various embodiments of these methods to produce an adhesion layer of essentially palladium or gold, a transition layer of increasing platinum content and decreasing palladium content and a bio-compatible metal capping layer of essentially platinum or having, at least, a predominance of platinum. In further embodiments of the present invention, the palladium and platinum layers can be from about 100 angstroms and up to about 5,000 angstroms thick, preferably greater than for example, about 500 angstroms thick, and less than about 2,500 angstroms, such that they are optimized to maximize the smoothness and stability of the layers. The thicknesses may depend upon various parameters, including the size and projected expansion of the stent assembly. 
     In an embodiment, the metal capping layer is manufactured with at least one of platinum, platinum-iridium, tantalum, titanium, tin, indium, palladium, gold and alloys thereof. In an embodiment, the metal capping layer and all layers within the metal capping layer (such as, for example, an adhesion layer, or no layers between the substrate and metal capping layer) have a combined thickness of less than about a micron. In an embodiment, the metal capping layer and all layers within the metal capping layer have a combined thickness of less than about 0.5 microns. In an embodiment, the metal capping layer and all layers within the metal capping layer have a combined thickness of less than about 0.25 microns. 
     In an embodiment, surface modifications are applied to struts of annular arrays  12 ,  12 A etc. and cross-links  50  that provide textured surfaces such as in accordance with previously cited and incorporated U.S. patent application Ser. No. 11/843,402. The texturing can improve the surface of the stent for purposes of encouraging healthy endothelial growth upon deployment, providing a more adhesive surface for additional layers such as polymers having drug-eluting properties, and/or improving the retention and avoiding undesired slippage between the surface of the stent and a delivery system (e.g. a balloon catheter) during delivery. 
     It will be understood by those with knowledge in related fields that uses of alternate or varied materials and modifications to the methods disclosed are apparent. This disclosure is intended to cover these and other variations, uses, or other departures from the specific embodiments as come within the art to which the invention pertains.