Abstract:
Luminal prostheses comprise adjacent expansible segments, typically serpentine ring segments joined by sigmoidal links. By properly orienting the sigmoidal links and aligning hinge regions on adjacent serpentine rings, enhanced performance can be obtained.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to medical devices and methods using the same. More particularly, the present invention relates to the structure of radially expansible luminal prostheses, including stents and grafts.  
           [0002]    Luminal prostheses are provided for a variety of medical purposes. For example, luminal stents can be placed in various body lumens, such as blood vessels, the ureter, the urethra, biliary tract, and gastrointestinal tract, for maintaining patency. Luminal stents are particularly useful for placement in pre-dilated atherosclerotic sites in blood vessels. Luminal grafts can be placed in blood vessels to provide support in diseased regions, such as aortic abdominal, and other aneurysms.  
           [0003]    Both stent and graft prostheses must meet certain mechanical criteria to function successfully. In particular, such prostheses should be at least partly flexible or articulated (such as rigid sections that articulate relative to one another) over their lengths so that they may be advanced through tortuous body lumens, such as those of the coronary vasculature. In addition, the prostheses should preferably maintain their original length or foreshorten minimally when the prostheses assume an expanded configuration. Further such prostheses must have sufficient mechanical strength, particularly hoop strength, in order to mechanically augment the luminal wall strength and thus assure lumen patency. The ability to meet these requirements is severely limited in the case of cylindrical endoluminal prostheses which are delivered in a radially constrained or collapsed configuration. Such prostheses must radially expand at a target site within the body lumen, so any adaptations which are intended to enhance flexibility will not interfere with the ability to radially expand or to maintain strength once expanded.  
           [0004]    Such prostheses, including stents, can suffer from a variety of performance limitations including fishscaling, poor tracking, flaring, and unwanted twisting upon deployment. Fishscaling is a phenomena which occurs when the prosthesis is flexed or articulated during delivery or tracking, resulting in the expanded prosthesis having unwanted outward protrusion of portions of the prosthesis from its surface, thereby increasing the likelihood that the prosthesis will dig into or otherwise engage the wall of the body lumen during delivery and even arrest the progress of the prosthesis and its delivery system to the diseased region (or target site). Poor tracking performance may be exhibited when the prosthesis&#39; ability to pass smoothly through tortuous pathways is below the desired level. Flaring is a phenomena which occurs when the distal or proximal end of the prosthesis are bent outward, assuming a crown-like configuration due to bending forces placed on these elements as the prosthesis passes through tortuous body passageways, often resulting in the same deleterious effects as the previously described fishscaling phenomenon, injuring or traumatizing the blood vessel wall as the prosthesis is delivered or tracked within the blood vessel. A common problem with many of the current devices is their being twisted upon or after deployment in the lumen, resulting in unwanted deformation. The unwanted twisting may occur during the deployment of the device. Often, the devices, when for example deployed by an expandable member such as a balloon, is first expanded at its two ends with the midsection, usually at the center, of the device exhibiting an inward crease with its peak pointing inward in the luminal direction. Such inwardly facing peaks then result in a smaller local inner diameter of the device, leading to obstruction of the lumen.  
           [0005]    Accordingly, it would be a significant advance to provide improved devices and methods using the same. This invention satisfies at least some of these and other needs.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    The present invention provides improved luminal prostheses suitable for endoluminal placement within body lumens, particularly blood vessels, and most particularly coronary and peripheral arteries. The luminal prostheses may be in the form of stents, intended for maintaining luminal patency, or may be in the form of grafts, intended for protecting or enhancing the strength of a luminal wall. Generally, the term “stent” will be used to denote a vascular or other scaffold structure comprising expansible components, such as ring segments, which when expanded form an open lattice or framework which is disposed against the luminal wall. In contrast, the term “graft” will generally denote such as luminal scaffold which is covered by a liner, membrane, or other permeable or impermeable layer which covers at least a portion of the scaffold. The drawings included herein are generally directed at stent structures, but it will be appreciated that corresponding graft structures could be provided by incorporating a liner, membrane, or the like, on either the outer or inner surfaces of the stent.  
           [0007]    The prostheses are preferably placed endoluminally. As used herein, “endoluminally” will mean placement through a body opening or by percutaneous or cutdown procedures, wherein the prosthesis is transluminally advanced through the body lumen from a remote location to a target site in the lumen. In vascular procedures, the prostheses will typically be introduced “endovascularly” using a catheter over a guidewire under fluoroscopic guidance. The catheters and guidewires may be introduced through conventional access sites to the vascular system, such as through the femoral artery, or brachial, subclavian or radial arteries, for access to the coronary arteries.  
           [0008]    A luminal prosthesis according to the present invention will usually comprise at least two radially expansible, usually cylindrical, ring segments. Typically, the prostheses will have at least four, and often five, six, seven, eight, ten, or more ring segments. At least some of the ring segments will be adjacent to each other but others may be separated by other non-ring structures.  
           [0009]    The luminal prostheses of the present invention are radially expansible. “Radially expansible” as used here in, refers to a prosthesis that can be converted from a small diameter configuration (used for endoluminal placement) to a radially expanded, usually cylindrical, configuration which is achieved when the prosthesis is implanted at the desired target site.  
           [0010]    The prosthesis may be minimally resilient, e.g., malleable, thus requiring the application of an internal force to expand and set it at the target site. Typically, the expansive force can be provided by a balloon, such as the balloon of an angioplasty catheter for vascular procedures.  
           [0011]    In an embodiment, usually by the application of a radially outward internal force to expand a minimally resilient (usually malleable) prosthesis structure. Such radially outward internal force will usually be provided by an inflatable balloon, and such balloon expansible stents are well-known in the art and described in the background references which have been cited above and are incorporated herein by reference.  
           [0012]    Alternatively, at least some of the radially expansible luminal prostheses of the present invention may be self-expanding. By fabricating the prostheses from a resilient material, usually a metal, such as spring stainless steel, a nickel-titanium alloy (such as Nitinol® alloy), or the like, the prosthesis can be designed to have a large (fully expanded) diameter in an unconstrained state. The diameter of the prosthesis can be reduced by applying a radial constraint, e.g., by placing the prosthesis within a sleeve, tube, or other constraining structure. In that way, the self-expanding prosthesis can be delivered while constrained and deployed by releasing the constraint at the target site within the body lumen. The general principles of constructing self-expanding stents and other luminal prostheses are also well-known in the art and described in at least some of the background references which have previously been incorporated herein.  
           [0013]    In an embodiment, a radially expansible luminal prosthesis comprises a plurality of unit segments, usually serpentine ring segments, including struts regions connected by hinge regions.  
           [0014]    In an embodiment, the hinge regions are usually formed by a short curved, normally a C- or U-shaped region which permits the connected struts to reverse direction in order to define the serpentine ring pattern. In an embodiment, the hinge region includes an apex portion with side potions extending on either side of the apex, the side portions transforming into the strut region of the ring.  
           [0015]    In an embodiment at least some, usually all of the hinge regions are radially off set from one another. In another embodiment, at least some, usually all of the hinge regions are radially aligned with one another.  
           [0016]    At least some of the longitudinally adjacent serpentine rings are joined by links which may be malleable or elastically deformable in order to allow the adjacent segments to flex relative to each other during prosthesis delivery and expansion.  
           [0017]    The links connect at least some of the hinge regions of one ring to at least some of the hinge regions of another ring which is longitudinally offset and adjacent to the one ring. In an embodiment, the connected ring segments are longitudinally immediately adjacent one another, with the connecting links forming a tubular column comprising a plurality of links which are radially offset from one another.  
           [0018]    The links can extend from any portion of the hinge region, such as the apex or the side portions, or somewhere in between. In an embodiment, at least some, preferably all, of the links extend laterally from each hinge region, typically from a point where the hinge region transforms into the strut.  
           [0019]    In an embodiment, the links generally have a smooth, multi (usually double) curvature shape, usually in a sigmoidal shape, normally an “S” shape. In an embodiment, the links are configured to provide both expansion and contraction between adjacent unit segments.  
           [0020]    In an embodiment, a double curvature link includes two curved portions and a straight portion therebetween. In one embodiment, the connecting links within the same connecting link column are oriented in the same direction, the direction being generally different than the direction of an adjacent connecting link column.  
           [0021]    In an embodiment, at least some, usually all of the straight portions of links within the same column form an oblique angle, normally either an acute or an obtuse angle with an imaginary longitudinal axis of the prosthesis. In one embodiment, at least some, usually all, of the straight portions of the connecting links of an adjacent column are inclined at a supplementary angle, with the longitudinal axis of the prosthesis, to that of its adjacent connecting column. Supplementary angle, as used herein, refers to two or more angles which together form a 180 degree angle with an axis.  
           [0022]    The use of such sigmoidal links is beneficial since it permits the longitudinal expansion or contraction of the prosthesis to accommodate length changes as the prosthesis is expanded. Such links further permit bending of the prosthesis since they allow differential motion of adjacent serpentine rings. Such flexibility is particularly advantageous since it allows improved tracking of the prosthesis as it is delivered to an endoluminal location. The sigmoidal links also improve the conformability of the expanded prosthesis when placed in a native vessel, artificial graft, or other body lumen location. In the embodiments where the links attach away from the apex of the hinge region, stress at the apex is reduced and uniform expansion of each ring segment is enhanced.  
           [0023]    The dimensions of the luminal prosthesis will depend on its intended use. Typically, the prosthesis will have a length in the range from about 1 to 100 mm, usually being from about 8 to 50 mm for vascular applications; and from about 20 to about 200 mm, usually being from about 50 to about 150 mm for non-vascular applications.  
           [0024]    The small (radially collapsed) diameter of the cylindrical prostheses will typically be in the range from about 0.25 to about 20 mm, usually being from about 0.4 to about 15 mm, and normally from about 0.8 to about 10 mm.  
           [0025]    The small (radially collapsed) diameter of cylindrical prostheses for vascular applications typically range from about 0.25 to about 1.5 mm for coronary and from about 1 to about 4 mm for peripheral applications, usually from about 0.4 to about 1.25 mm for coronary and from about 1.5 to about 3 mm for peripheral applications, and normally from about 0.8 to about 1.2 mm for coronary and from about 1.75 to about 2.5 mm for peripheral applications.  
           [0026]    For nonvascular applications, the prosthesis will typically have a small diameter ranging from about 1.5 to about 20 mm, usually from about 2 to about 15 mm, and normally from about 5 mm to about 10 mm.  
           [0027]    The large (radially enlarged) diameter of the cylindrical prostheses will typically be in the range from about 1 mm to about 100 mm, usually being from about 1.5 mm to about 75 mm, and normally from about 2 to about 50 mm.  
           [0028]    The large (radially enlarged) diameter of cylindrical prostheses for vascular applications typically range from about 1 mm to about 7 mm for coronary and from about 1 mm to about 30 mm for peripheral applications, usually from about 1.5 mm to about 5 mm for coronary and from about 3 mm to about 25 mm for peripheral applications, and normally from about 2 mm to about 4 mm for coronary and from about 5 mm to about 20 mm for peripheral applications.  
           [0029]    For nonvascular applications, the prosthesis will typically have a larger diameter ranging from about 1 mm to about 100 mm, usually from about 5 mm to about 75 mm, and normally from about 10 mm to about 50 mm. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a schematic representation of an exemplary prosthesis embodying features of the present invention in unexpanded configurations.  
         [0031]    [0031]FIGS. 2A and 2B are “rolled out” views of an exemplary embodiment of the prosthesis of FIG. 1.  
         [0032]    [0032]FIGS. 2C and 2D are “rolled out” views of an exemplary embodiment of the prosthesis of FIG. 1, in unexpanded and expanded configurations, respectively.  
         [0033]    [0033]FIG. 3 is a partial “rolled out” view of structure of FIG. 2A with the straight portion of the links forming oblique angles with a longitudinal axis of the prosthesis.  
         [0034]    [0034]FIG. 4A is a partial “rolled out” view of an embodiment of the structure in FIG. 2A showing a straight portion of the hinge portions intersecting the imaginary lines bisecting the curved portions of the links.  
         [0035]    [0035]FIG. 4B is a partial “rolled out” view of an embodiment of the structure in FIG. 2A showing a straight portion of the hinge portions being parallel to imaginary bisecting the curved portions of the links.  
         [0036]    [0036]FIG. 5A is a partial “rolled out” view of an alternate embodiment of the structure of FIG. 2A with the links emerging from the apices.  
         [0037]    [0037]FIG. 5B is a partial “rolled out” view of an alternate embodiment of the structure of FIG. 3 with the hinge regions of the longitudinally adjacent rings being radially aligned with one another. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    [0038]FIG. 1 illustrates a radially expansible luminal prosthesis  10 , such as a stent, generally embodying features of the present invention, and including a frame  13  formed from a plurality of radially expansible ring segments  16 . Although the final shape of the prosthesis  10  will generally be cylindrical, it should be appreciated that the prosthesis may also be conformable to non-cylindrical cross-sectional lumens and may also be conformable to transversely curved lumens.  
         [0039]    An exemplary luminal prosthesis  10  particularly intended for implantation in the vasculature (e.g., coronary or peripheral) comprises from 4 to 50 ring segments  16  (with 7 being illustrated), the segments being joined to a longitudinally set apart adjacent ring segment by at least one link, such as sigmoidal link  19 .  
         [0040]    Now referring to FIGS. 2A through 2D, the ring segments  16 , comprise a plurality of struts  22 , normally linear struts, joined by hinge regions  25 . As shown, the hinge regions  25  have a curved shape and include an apex portion  28  with side potions  31  extending on either side of the apex and transforming into the strut  22 , and trough region  34  opposite the apex  28 .  
         [0041]    The links  19 , connect proximate hinge regions, such as  25 A and  25 B, of adjacent rings, such as  16 A and  16 B. The links connecting adjacent ring segments, as for example  16 A and  16 B, form a radial column  37 . The connecting links  19  generally have a smooth, multi (usually double) curvature shape, usually in a sigmoidal shape, normally an “S” shape.  
         [0042]    The links  19  extend from some of the radial hinge regions within the same ring segment  16 , such that not all hinge regions of a ring segment are connected to hinge regions of an adjacent ring, although embodiments connecting all of the proximate hinge regions, or other configurations, are within the scope of the present invention. By way of example, as shown in FIG. 2A, ring segment  16 A and  16 B, comprise hinge regions  25 A and  25 B which are connected to one another by way of link  19 , and hinge regions  25 C and  25 D, which are free from connections to a hinge region on an adjacent ring. The connected hinge regions may alternate with non-connected hinge regions or may have certain repeat patterns. As shown in FIG. 2C, the connected and non-connected hinge regions alternate in the mid-section of the prosthesis with the most distal two link columns at both ends of the prosthesis emerging in a pattern of 3 connected hinge regions followed by a non-connected hinge region.  
         [0043]    Now referring back to FIG. 2A and its enlarged view FIG. 2B, the double curvature links  19  include two curved portions,  40 , such as  40 ′ and  40 ″, and a straight portion  43  disposed therebetween. The connecting links  19  within the same connecting link column  37  are oriented in the same direction with the straight portion  43  of at least some of the links form an oblique angle with an imaginary longitudinal axis  46  of the frame  13 .  
         [0044]    By way of example, the straight portion of the links of two adjacent columns may form similar type of angles with the longitudinal axis, e.g., obtuse or acute. Furthermore, the angles within the same column, even when generally either obtuse or acute, may be similar or different than another angle within the same column.  
         [0045]    As further shown in FIG. 3, the straight portion  43 A of the connecting links  19 A in one column  37 A forms an obtuse angle α with the imaginary longitudinal axis  46  of the frame  13 . The obtuse angle α within each column, independently, ranges from about 95 to about 170, usually from about 100 to about 135, and normally from about 105 to about 130 degrees.  
         [0046]    The straight portion  43 B of the connecting links  19 B of a column  37 B adjacent to column  37 A, forms an acute, angle β with the longitudinal axis  46 . The acute angle β within each column, independently, ranges from about 10 to about 85, usually from about 45 to about 80 and normally from about 50 to about 75 degrees.  
         [0047]    The obtuse and acute angles, α and β, of adjacent rings, preferably, together, form supplementary angles with the longitudinal axis  46 .  
         [0048]    In one embodiment, links  19  have similar dimensions (e.g., the length of the straight portion  43 A is similar, usually the same, as the length of the straight portion  43 B) such that links in adjacent columns are mirror images one another.  
         [0049]    Although the prosthesis as shown includes an even number of connecting columns  37  with the straight portion of the alternating columns forming either obtuse or acute angles, the invention is not limited to such alternating pattern and other configurations and patterns are within the scope of the present invention.  
         [0050]    As can be seen in FIG. 4A, in one embodiment, curved portions  40 ′A and  40 ″A of the multi-curvature link  19 , project in opposite directions such that an imaginary axis  49 A of the straight portion  43 A, at each end intersects one imaginary line which bisects one of the curved portions. As shown, imaginary lines  52 ′A and  52 ″A, each bisects the curved portions,  40 ′A and  40 ″A, respectively. The intersection of the axis  49  of the straight portion with imaginary lines  52 ′A and  52 ″A, respectively, forms angles λ and μ respectively. It should be appreciated that although the intersection of the bisecting lines with the imaginary axis of the straight portion has been described with respect to one link column such as one forming obtuse angle with the longitudinal axis of the prosthesis, intersections may also be formed in adjacent columns which form acute angles with the longitudinal axis of the prosthesis.  
         [0051]    As further can be seen in FIG. 4B, in one embodiment, imaginary lines  59 ′A and  59 ″A bisecting the curved portions  62 ′A and  62 ″A, respectively, of a link  65 A, are parallel with the axis  68 A of the straight portion  71 A.  
         [0052]    In one embodiment, features of which are also shown in FIG. 4B, there is at least one radial plane  74  that intersects both curved portions,  77 ′ and  77 ″, of a given link, 78. It should be appreciated that this feature may be present independent of the other features previously discussed with reference to FIGS. 4A and 4B.  
         [0053]    Now referring to FIG. 5A, in an alternate embodiment, the links  74  generally emerge from apex portion  77  of hinge region  80 , as compared to the side portions described earlier in reference to FIG. 2.  
         [0054]    In one alternate embodiment, features of which are shown in FIG. 5B, the connected hinge regions, such as hinge regions  83 A and  83 B are radially aligned with one another, as compared to the radially offset hinge regions in FIG. 2.  
         [0055]    In operation, the prosthesis of the present invention, may be placed on an expandable portion of a balloon catheter, or within the lumen of a delivery catheter, and delivered to a desired luminal site and disposed therein, as is known in the art.  
         [0056]    Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the true spirit and scope of the invention. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.