Patent Publication Number: US-8974515-B2

Title: Stent with flexible hinges

Description:
RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 11/582,818, filed on Oct. 18, 2006, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND AND SUMMARY 
     The present application relates to expandable stents and, more particularly, to expandable stents with flexible hinges. 
     It is desirable to provide flexibility in stents to facilitate introduction of the stent into vessels that are difficult to reach. Often, however, characteristics of the stent that provide longitudinal flexibility that is desirable when introducing the stent into the vessel can be disadvantageous in terms of keeping the stent in an expanded condition. For example, stents formed from interconnected rings with closed cell structures or generally diamond-shaped cells are typically less flexible than stents formed from one or more helices, but are usually more uniformly and consistently expandable than helical stents. It is desirable to provide a stent with substantial flexibility that is adapted to be expanded in a uniform and consistent fashion. 
     In WO 03/015664, which is incorporated by reference, a stent having interconnected struts with openings for drug delivery is disclosed. However, elements for bridging the stents are generally thinner and spaced further apart than the struts. Thus, for such drug-eluting stents, the bridging element can provide an area of reduced or less consistent drug delivery. It is desirable to provide a drug-eluting stent in which areas of reduced or less consistent drug delivery can be reduced. 
     In accordance with an aspect of the present invention, a helical stent comprises at least one helical winding, each helical winding comprising a plurality of alternating long struts and short struts, ends of at least some of the long struts being joined to an end of an adjacent short strut by a flexible hinge arrangement, the struts being substantially rigid, and at least one interconnection member connecting a hinge arrangement on one turn of the at least one winding with a hinge arrangement on an adjacent turn of the at least one winding, wherein fewer than all hinge arrangements on the at least one helical winding are connected to other hinge arrangements by an interconnection member. 
     In accordance with another aspect of the present invention, a helical stent comprises at least one helical winding, each helical winding comprising a plurality of struts, ends of the struts being joined to an end of an adjacent strut by a flexible hinge arrangement, the struts being substantially rigid, and at least one interconnection member connecting a hinge arrangement on one turn of the at least one winding with a hinge arrangement on an adjacent turn of the at least one winding, wherein fewer than all hinge arrangements on the at least one helical winding are connected to other hinge arrangements by an interconnection member. 
     In accordance with another aspect of the present invention, a helical stent comprises at least one helical winding, each helical winding comprising a plurality of pairs of long struts and short struts, the struts being substantially rigid, and a plurality of flexible hinge arrangements, ends of at least some of the long struts being joined to an end of an adjacent short strut by the hinge arrangements, each of the plurality of flexible hinge arrangements comprising a substantially rigid connecting member and a first flexible hinge between the connecting member and a long strut and a second flexible hinge between the connecting member and a short strut. 
     In accordance with another aspect of the present invention, a helical stent comprises at least one helical winding, each helical winding comprising a plurality of pairs of long strut assemblies and short strut assemblies, the struts being substantially rigid, the long strut assembly comprising at least two struts and being longer than the short strut assembly, and a plurality of flexible hinge arrangements, ends of at least some of the long strut assemblies being joined to an end of an adjacent short strut assembly by the hinge arrangements, each of the plurality of flexible hinge arrangements comprising a substantially rigid connecting member and a first flexible hinge between the connecting member and a long strut assembly and a second flexible hinge between the connecting member and a short strut assembly. 
     In accordance with another aspect of the present invention, an expandable stent includes a plurality of expandable cells having at least eight sides and formed by a plurality of alternating long and short, substantially non-deforming struts interconnected by deformable hinges. 
     In accordance with a further aspect of the present invention, an expandable stent includes a plurality of struts extending substantially longitudinally along an axis of the stent in an unexpanded configuration and a plurality of hinges interconnecting the struts. The plurality of hinges each have a straight active portion which extends substantially circumferentially around the stent in the unexpanded configuration and two curved portions interconnecting the active portion to adjacent ones of the plurality of struts. 
     In accordance with another further aspect of the present invention, an expandable stent includes a plurality of struts extending substantially longitudinally along an axis of the stent in an unexpended configuration and a plurality of hinge arrangements interconnecting the struts. Each of the hinge arrangements includes a central portion and four tapered hinges each connected at one end to the central portion and at another end to one of the plurality of struts. Each of the tapered hinges has a smallest width closer to the struts and a largest width closer to the central portion. 
     In accordance with another aspect of the present invention, an expandable stent includes a plurality of struts extending substantially longitudinally along an axis of the stent in an unexpected configuration, a plurality of first hinges interconnecting the struts, and a plurality of interconnecting hinge arrangements interconnecting the stents. The plurality of hinges each have a straight active portion which extends substantially circumferentially around the stent in the unexpanded configuration interconnected to adjacent ones of the plurality of struts. Each of the interconnecting hinge arrangements includes a central portion and four second hinges each connected at one end to the central portion and at another end to one of the plurality of struts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which: 
         FIG. 1  is a view of a stent according to an embodiment of the present invention shown in partly expanded form, cut along a line parallel to a longitudinal axis of the stent, and unrolled; 
         FIGS. 2A and 2B  are views of a stent according to another embodiment of the present invention shown in unexpanded and expanded form, cut along a line parallel to a longitudinal axis of the stent, and unrolled; 
         FIG. 3  is a view of a stent according to another embodiment of the present invention shown in partly expanded form, cut along a line parallel to a longitudinal axis of the stent, and unrolled; 
         FIGS. 4A and 4B  are views of a portion of a stent according to an embodiment of the present invention shown in unexpanded and expanded form; 
         FIG. 5  is a schematic view of a portion of an end ring for a stent according to an embodiment of the present invention; 
         FIG. 6  is a schematic view of a portion of a helical winding according to another embodiment of the present invention; 
         FIG. 7  is a view of a stent according to yet another embodiment of the present invention shown in partly expanded form, cut along a line parallel to a longitudinal axis of the stent, and unrolled. 
         FIG. 8  is an enlarged view of one of the hinge arrangements from  FIG. 7 ; and 
         FIG. 9  is an enlarged view of one of the interconnection hinge arrangements from  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     A helical stent  21  according to an embodiment of the present invention is shown in  FIG. 1 . The stent  21  is shown in  FIG. 1  as it would appear if the stent were in an at least partially expanded condition and cut along its length. More particularly, the stent  21  shown in  FIG. 1  is shown in the form in which it would appear if it were cut along its length and the cut article was laid out flat. The stent  21  can be formed in any suitable manner, such as by being laser cut from a tube made of a suitable material including cobalt chromium alloys, stainless steel alloys or nickel titanium alloys. In an “as cut” version of the stent  21 , top and bottom edges  23  and  25  would ordinarily be joined together.  FIGS. 2A and 2B  show another embodiment of a stent  121  in an unexpended and an at least partially expanded condition, respectively, and cut along its length. The present invention will be described as a vascular stent, such as a coronary or peripheral stent. However, the stent structure described can also take the form of other known stents. In practice, while a laser cut tubular coronary stent might have a diameter of approximately 2 mm when it is cut from a metal tube, it is ordinarily subsequently crimped to a more compressed condition (such as is shown in  FIG. 2A ), to, for example, a diameter of approximately 1 mm and, upon expansion, such as by a balloon catheter, the expanded stent might have a diameter of approximately 2-4 mm, i.e., the components of the “expanded” stent would be more expanded than they appear in the illustrated “as cut” version. Other types of stents would have other diameters corresponding to their application. 
     The stent  21  includes at least one helical winding  27 . The stent  21  in  FIG. 1  includes one helical winding  27 . The stent  121  shown in  FIG. 2B  and the stent  221  shown in  FIG. 3  each include two helical windings  127 ′ and  127 ″, and  227 ′ and  227 ″, respectively. If desired, the stent can have more than two helical windings. Ordinarily, each helical winding  27  will have multiple winding turns, usually at least three turns. 
     As seen, for example, in  FIG. 1 , each helical winding  27  comprises a plurality of alternating long struts  29  and short struts  31 . Ends  33  of at least some of the long struts  29  are joined to an end  35  of an adjacent short strut  31  by a flexible hinge arraignment  37 . The struts  29  and  31  are substantially rigid compared to the hinge arrangement  37  and ordinarily do not substantially bend or deform during expansion of the stent  21  from an unexpanded condition to an expanded condition. The hinge arrangements  37  account for substantially all deformation or bending of components of the stent  21 . During expansion of the stent from an unexpanded condition to an open or expanded condition, substantially all deformation occurs in the hinge arrangements, which are designed to facilitate uniform and consistent expansion of the stent, and which can facilitate retaining the stent in an expanded condition. Stents with ductile hinges connecting more rigid components such as struts are disclosed in U.S. Pat. No. 6,241,762, which is incorporated by reference. 
     Periodically, the alternating pattern of long and short struts  29  and  31  connected by hinge arrangements is interrupted by an interconnection hinge arrangement  39 . The interconnection hinge arrangement  39  connects one turn  41   a  of the at least one winding  27  with an adjacent turn  41   b  of the at least one winding. Fewer than all bends of the winding  27  are connected to other bends by an interconnection hinge arrangement  39 . The interconnection hinge arrangements  39  have a rigid central portion and four deformable hinge portions connecting to four adjacent struts (two short and two long struts). 
     Ordinarily, a plurality of interconnection hinge arrangements  39 , i.e., at least two, are provided. Each interconnection hinge arrangement  39  replaces the hinge arrangement  37  on one turn  41   a  of the at least one winding  27  and the hinge arrangement on the adjacent turn  41   b  of the at least one winding. In this way, two successive (in the direction of the helix) interconnection hinge arrangements  39  delimit a cell  43  defined by long and short struts  29  and  31  and hinge arrangements  37  between the successive interconnection members. 
     Ordinarily, the long and short struts  29  and  31  are substantially straight, although they can be other shapes, such as curved, etc. When the struts are substantially straight, as can be seen in  FIG. 1 , the cell  43  can be multi-sided.  FIG. 1  shows a cell with 16 sides (hexadecahedron) formed by 8 short and 8 long struts, however, cells with different numbers of sides can be provided (e.g., 4, 8, 12, 16, 20 . . . ). By linking only some of the bends with interconnections  39  between adjacent turns  41   a  and  41   b  of the helical winding  27 , i.e., by providing fewer interconnections than pairs of hinge arrangements, the stent  21  can have substantial flexibility, while retaining even coverage upon expansion. 
     As seen in  FIGS. 4A and 4B , the hinge arrangement  37  can comprise a first portion  45  connected to a long strut  29  and a second portion  47  connected to an adjacent short strut  31 . The first portion  45  and the second portion  47  can have different cross-sectional shapes or other structural or other differences. For example, the second portion  47  of the hinge arrangement  37  can be provided with a smaller cross-sectional shape than the first portion  45  of the hinge arrangement, which can tend to make it easier to bend the second portion of the hinge arrangement. By providing an appropriate combination of characteristics for the first and second portions  45  and  47  of the hinge assembly  37 , characteristics of the stent during expansion from an unexpanded condition to an expanded condition can be controlled. For example, the stent shown in  FIGS. 1 ,  2 A and  2 B are approximately the same length in the unexpanded position as in the open position. In other words, the stent does not significantly shorten upon expansion. In  FIG. 2A , it will be seen that the overall length of the stent  121  is largely a function of the lengths of the struts  129  and  131  in the longitudinal direction of the stent. In  FIG. 2A , it will be seen that the overall length of the stent  121  is largely a function of the lengths of those same struts  129  and  131 , as well as a function of the angle with which those struts  129  and  131  make with the longitudinal axis of the stent. 
       FIGS. 4A and 4B  show a single pair of adjacent long and short struts  29  and  31  in a closed and an open position, respectively. It will be seen that the combined length of a long and a short strut and is equal to “L” when they lie substantially along the axis of the stent in the closed state, where the long strut&#39;s length is equal to “L” and the short strut&#39;s length is equal to “L-Z”, and the long strut completely overlaps the short strut. For each zig-zag of such a strut pair along the helical winding, the helix will advance a length “Z”. If the stent is opened such that, as in  FIG. 4B  the long strut forms an angle of Θ 1  with the longitudinal axis of the stent, it&#39;s length along the axis will be equal to L cos (Θ 1 ), which will be shorter than the length L. However, if the component of the short strut&#39;s  31  length along the longitudinal axis is shorter by the same amount, the helix will still advance a length “Z” for each zig-zag. This can be accomplished, for example, where the short strut  31  forms a certain angle Θ 2  with the longitudinal axis greater than the angle Θ 1  formed by the long strut  29 . 
     Cells  43  in  FIG. 1  defined by connected long and short struts  29  and  31  have long axes x that are skewed or at an angle with respect to a circumference of the generally cylindrical stent. Axes of individual, generally diamond shaped portions of a cell extending from hinge to hinge can extend generally parallel to the axis of the stent. 
     As seen in  FIG. 1 , the stent  21  can comprise first and second flexible end rings  49  and  51  hingedly joined to opposite ends  53  and  55 , respectively, of the at least one helical winding  27 . The end rings  49  and  51  can take a variety of suitable shapes. In the embodiment of  FIG. 1 , each end ring  49  and  51  can comprise two ring halves  49   a  and  49   b , and  51   a  and  51   b . Each ring half can comprise a plurality of end ring struts  57  joined to each other at ends  59  thereof by flexible end ring hinge arrangements  60  and interconnecting hinge arrangements  61  that define alternating left- and right-pointing bends, which may be in the form of gentle, round curves, or sharper, more angular curves, in a zig-zag or accordion fashion. 
     If each left-pointing bend to left-pointing bend or right-pointing bend to right-pointing bend “wave” is considered as defining 360°, then the two ring halves  49   a  and  49   b  and  51   a  and  51   b  of each ring  49  and  51  are 180° out of phase with each other and joined by interconnection hinge arrangements  61  to define a plurality of diamond shaped end ring cells  63 . The interconnection hinge arrangements  61  include a rigid central portion  65  and four hinges like the interconnection hinge arrangements  39  and may be substantially identical to them. 
     In the embodiment of  FIG. 1 , all of the left-pointing bends of the first end ring halves  49   a  and  51   a  are joined to corresponding right-pointing bends of the second end ring halves  49   b  and  51   b  to form the closed diamond shaped cells  63 . Although in this embodiment, the end ring struts  57  are substantially straight and the cells  63  are substantially diamond-shaped. However, other arrangements, including open cell configurations such as where every other pair of left-pointing bends are attached, can be provided. 
     The long and short struts  29  and  31  and the flexible hinge arrangements  37  of the at least one helical winding  27  typically also define alternating left-pointing bends P and right-pointing bends T. An end strut  67  at the first end  53  of the helical winding  27  can be disposed at a left-pointing bend and can be connected to an end ring hinge arrangement  61  at a right-pointing bend of the first end ring half  49   a  of the first end ring  49 . Similarly, an end strut  69  at the second end  55  of the helical winding  27  can be disposed at a right-pointing bend and can be connected to an end ring hinge arrangement  61  at a left-pointing bend of the second end ring half  51   b  of the second end ring  51 . The end struts  67  and  69  at the first and second ends  53  and  55  of the helical winding  27  can be connected to the end ring hinge arrangement  60  at the right-pointing bend of the first end ring half  49   a  of the first end ring  49  and at the left-pointing bend of the second end ring half  51   b  of the second end ring  51 , respectively, by a flexible end hinge arrangement  71 . This provides for freedom of motion of the end strut for expansion while maintaining even strut distribution on expansion. 
     For at least some of the alternating left-pointing bends and right-pointing bends of a helical winding  27 , in a center portion of the stent, all the short struts are of the same length and all the long struts are of the same length. By contrast, in some parts of the helical winding such as the ends of the helical winding as seen at “A” in  FIG. 1 , the strut lengths are varied according to the available space and to achieve uniformity of strut coverage after expansion. Often, as seen in  FIGS. 1 and 3 , but not always, several strut pairs in a row will have struts of the same length. 
     In addition to or instead of connecting the winding  27  to the end rings  49  and  51  by the end hinge arrangements  71  at ends  53  and  55  of the winding, at least one interconnection hinge arrangement  73  can be used. As seen in  FIG. 1 , the first right-pointing bend at which the flexible end hinge arrangement  71  joins the end strut  67  of the winding  27  to the first end ring  49  and the second right-pointing bend at which the interconnection hinge arrangement  73  joins the winding to the first end ring can be non-successive, which can enhance flexibility of the stent  21 . The interconnections  73  typically include a rigid portion of four hinges like the interconnections  39  and may be substantially identical to them. 
       FIGS. 2A-2B  and  FIG. 3  show other forms of end-rings  149  and  151 , and  249  and  251 , respectively, than of the type shown in  FIG. 1 . Referring to  FIG. 2B , in the end rings  149  and  151 , each end ring comprises a plurality of end ring struts  157  joined to each other at ends thereof by flexible end ring hinge arrangements  161  that define alternating left-pointing bends and light-pointing bends. There are not two end ring halves, as in the embodiment of  FIG. 1 . The end rings  149 ,  151 ,  249 , and  251  can otherwise be similar to the end rings  49  and  51 , particularly in terms of how they are connected to the helical winding(s) of the stent. In  FIGS. 2A-2B , the end ring struts  157  are shown as substantially straight struts such that, when the stent is in the expanded state ( FIG. 2B ), the end ring struts  157  and hinge arrangements  161  define a substantial Z-shape. As seen in  FIG. 5 , if the end ring struts  557  are some other shape, such as curved or S-shaped, other shapes can be formed, such as substantial S-shapes, upon expansion of the stent. 
     The end-rings  249  and  251  of  FIG. 3  include a combination of diamond shaped portions and z-shaped portions. Additionally, while the end ring struts  57  in the embodiment of  FIG. 1 , as well as the end ring struts  157  in  FIG. 2B , are all the same length, it is not necessary that they be the same length and, as seen in  FIG. 3 , some end ring struts  257   a  may be longer than other end ring struts  257   b.    
     Referring again to  FIG. 1 , while the helical winding  27  can have alternating long and short struts  29  and  31  along its entire length, it may be desirable to provide additional struts  75  having lengths other than the lengths of the long and short struts, particularly in the area of the transition from the end rings  49  and  51  to the helical winding toward the ends  53  and  55  of the winding. These additional, transitional struts  75  may be at the ends  53  and  55 , or near the ends, and are sized to ensure, inter alia, substantially even stent coverage while preventing overlap between a left-pointing bend of a series of zig-zag struts of the winding  27  and a right-pointing bend of a series of zig-zag struts of an end ring. 
     The helix is formed with an odd number of struts in each 360 degree turn of the helix which results in a configuration in which the hinge arrangements  39  are lined up with hinge arrangements in adjacent turns. This is sometimes called an 180 degree out of phase construction. 
     Some or all of the struts  29 ,  31 ,  57 , and  75  can comprise at least one opening  77  for receiving a drug. WO 03/015664, which is incorporated by reference, describes a non-coated drug-eluting stent with openings for receiving a drug. In addition to having openings  77  in the struts  29 ,  31 ,  57 , and  75 , openings for drugs can be provided in the interconnection  39 , in the end ring interconnection  65 , in the end interconnection  73 , in the hinge arrangement (see, for example, openings  77  in the rigid portions of the hinge assemblies  137  and  237  in  FIGS. 2A-2B  and  3 ). Although the examples of stents shows herein include openings for beneficial agents, these openings and the beneficial agents may be omitted. Where the openings are omitted, an agent may be incorporated into the stent in other ways, such as a coating or a polymer stent containing drug. 
     The stent  21  can be configured with left-pointing bends and right-pointing bends of strut pairs of struts  29  and  31  on successive turns of the helical winding  27  being relatively close to each other such that, although an interconnection member  39  with a drug opening  77  may not be disposed between each left-pointing bend and right-pointing bend, drug delivery from openings on the stent will be substantially consistent, i.e., there are no particularly large spaces between drug openings. 
     The helical stent according to the present invention will ordinarily, as in the embodiment of  FIG. 1 , comprise a plurality of alternating long and short struts  29  and  31  so that the resulting zig-zag shape will form a helix  27  when disposed around a longitudinal axis. The helix may, however, be formed in other ways. For example, as seen in  FIG. 6 , all of the struts  629  forming the helix might be of the same length SL, while the hinge  637  might have legs  637   a  and  637   b , of different lengths such that the resulting shape of the struts with the hinges with different length legs forms a helix. 
       FIG. 3  shows an embodiment of a helical stent  221  comprising two helical windings  227 ′ and  227 ″. The helical windings  227 ′ and  227 ″ comprise a plurality of pairs of long struts  229  and short struts  231  and a plurality of flexible hinge arrangements  261 . In addition, the helical windings  227 ′ and  227 ″ comprise an additional strut  275  between two pairs of struts. The additional strut  275  is connected, via an additional hinge arrangement  261 ′, at a first end  275   a  to an end  233  of a long strut  229  of a first strut pair and is connected, via a hinge arrangement  261 , at a second end  275   b  to an end  235  of a short strut  231  of a second strut pair. The additional hinge arrangement  261 ′ may be of a type similar to the hinge arrangement  261 . The hinge arrangements  261  and  261 ′ shown in  FIG. 3  both comprise a substantially rigid connecting member  265  and  265 ′ and a first and a second flexible hinge  267 ,  269  and  267 ′ and  269 ′ between the connecting member and the strut. 
     With reference to  FIG. 3 , it is, of course, not necessary that the struts  229  be longer than the struts  231  and a helical winding can, instead, comprise a plurality of pairs of long strut assemblies and short strut assemblies. The long strut assembly can comprise at least two struts  229  and  275  and can be longer than the short strut assembly, which can comprise one strut  231  or multiple struts, like the long strut assembly. The struts  229 ,  275 , and  231  may all be the same length. 
       FIG. 7  shows another embodiment of a stent  721  similar in many respects to the embodiment of the stent  21  shown in  FIG. 1 . Differences between the stent  721  and the stent  21  include that the stent  721  can comprise hinge arrangements  737  having a somewhat more recti-linear shape than the hinge arrangements  37  in the stent  21  in  FIG. 1  which are curved or substantially semi-circular. In the stent  721 , interconnection  739 , end ring interconnection  765 , and end interconnection  773  can be more compact to reduce spacing between windings than corresponding structures in the stent  21  of  FIG. 1 . Further, at least one end ring interconnection  765 ′ can be elongated relative to other end ring elongated members  765  and can extend around a greater portion of the circumference of the stent. An end hinge arrangement  771  on the stent  721  can be longer and more curved, such as substantially S-shaped, than the end hinge arrangement  71  provided on the stent  21 . On the stent  21 , a majority of the long and short struts  29  and  31  have five and four drug receiving openings  77 , respectively, a majority of the long and short struts  729  and  731  in the stent  721  can have four and three drug receiving openings  777 , respectively. The features of the stent  721  including more squared hinge arrangements  737 , thinner interconnections  739 ,  765 , and  773 , an elongated end ring interconnecting member  765 ′, and a more elongated and curved end hinge arrangement  771  can facilitate, inter alia, flexibility of bending portions of the stent as well as improved uniformity upon expansion. 
       FIG. 8  shows one of the hinge arrangements  737  interconnecting a long strut  729  having four openings  777  with a short strut  731  having three openings. The hinge arrangements  737  of the embodiment of  FIGS. 7 and 8  each have a straight active portion  780  which accommodates substantially all the bending during expansion of the stent. The active portion  780  is connected to the struts  729  and  731  by curved portions  782 . The curved portions are not significantly deformed during expansion of the stent due to their slightly larger width than the active portion and due to their location in the hinge arrangement. Specifically, the forces applied to the struts due to stent expansion in the direction of the arrows F result in a highest moment applied at a location M on the hinge arrangement. A length of the active portion  780  of the hinge arrangement is selected to be long enough to provide acceptable peak strain while short enough to avoid excessive recoil. If the active portion of the hinge is very long, it will act like a spring. According to one preferred embodiment, the active portion  780  of the hinge has a length to width ratio of between 4:1 and 1:1, preferably about 2:1 and the hinge arrangement is straight over this length. By straight it is meant that both sides of the hinge arrangement are substantially straight in the as-cut configuration. This means that the straight hinges  780  will be slightly curved in the crimped (delivery) configuration and also curved in the expanded configuration. 
     Since the struts within the stent  721  are of differing lengths throughout the stent, the hinge arrangements  737  experience different moments applied by the different length struts. Thus, if the hinge arrangements were designed to be identical, the resulting expansion would be uneven. Some of the hinge arrangements  737  can be modified such as by changing the width or length of the active portion to achieve even expansion. For example, several locations within the stent  721  longer struts are used having five holes. These long five hole struts will exert a greater moment on the adjacent hinge arrangements due to their longer length than the three and four hole struts. Thus, the hinges adjacent the five hole struts can be wider and/or longer to achieve uniform expansion. This same principle applies anywhere there are variations in the lengths or shapes of the struts. To achieve a stent which opens evenly without certain hinges opening before others, the modified hinges are distributed in an uneven pattern on the stent which corresponds to the asymmetric structure of the stent. 
       FIG. 9  shows one of the connection hinge arrangements  739  of the stent of  FIG. 7 . The connection hinge arrangements  739  each include a passive central portion  784  and four active tapered hinge portions  786  connecting to four struts  729  and  731 . Each of the four active hinge portions  786  are tapered with a narrow end connected to the struts and a wider end connected to the passive central portion  784 . This tapered configuration achieves a distribution of the maximum strain along the tapered hinge. This is in contrast to a straight hinge which would result in concentrated strain in the hinge at a location closest to the central portion. According to one preferred embodiment, the active tapered hinge portions  786  have a length to width ratio of between 5:1 and 1:1, preferably about 3:1 where the width measured is the smallest width of the tapered hinge. 
     Stents according to embodiments of the present invention will be provided in a variety of sixes to match the anatomy of the body lumens to be supported. Typical coronary stent lengths are about 8 to 38 mm; circumferences in the closed state are about 1 to 2 mm; and circumferences in the open state are about 2 to 6 mm. Although sizes for coronary stents are described, other types of stents may also be made according to the present invention and their size will depend on their use. 
     The length of a long strut in the embodiments described above is usually about 0.04″ to 0.09″ the length of a short strut is usually about 0.02″ to 0.06″; the length of an end ring strut is usually about 0.02″ to 0.09″. The width of a long strut in the embodiments described above is usually about 0.005″ to 0.01″; the width of a short strut is usually about 0.005″ to 0.01″; the width of an end ring strut is usually about 0.005″ to 0.01″. The length of an interconnection hinge arrangement including four hinges is usually about 0.01″ to 0.06″, and its width at the central portion is usually about 0.005″ to 0.02″. The tubing from which the stent is laser cut, and thus the struts, hinge arrangements, interconnection hinge arrangements, and other features of the stent generally have a thickness which depends on the material used and for cobalt chromium alloys a thickness of about 0.004″ to 0.006″. 
     In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such. 
     While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognised that variations and changes may be made therein without departing from the invention as set forth in the claims.