Abstract:
Segmented articulatable stent of open structure comprised of end-connected struts of first and second lengths making up first and second segments with angular interconnects between adjacent first and second segments.

Description:
[0001]    This application is a Continuation-in-Part of application Ser. No. 08/511,076, filed Aug. 3, 1995, the disclosure of which is hereby incorporated by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to an endoprosthesis device for implantation within a body vessel, typically a blood vessel. More specifically, it relates to a tubular expandable stent of improved longitudinal flexibility.  
         BACKGROUND OF THE INVENTION  
         [0003]    Stents are placed or implanted within a blood vessel for treating stenoses, strictures or aneurysms therein. They are implanted to reinforce collapsing, partially occluded, weakened, or dilated sections of a blood vessel. They have also been implanted in the urinary tract and in bile ducts.  
           [0004]    Typically, a stent will have an unexpanded (closed) diameter for placement and an expanded (opened) diameter after placement in the vessel or the duct. Some stents are self-expanding and some are expanded mechanically with radial outward force from within the stent, as by inflation of a balloon.  
           [0005]    An example of the latter type is shown in U.S. Pat. No. 4,733,665 to Palmaz, which issued Mar. 29, 1988, and discloses a number of stent configurations for implantation with the aid of a catheter. The catheter includes an arrangement wherein a balloon inside the stent is inflated to expand the stent by plastically deforming it, after positioning it within a blood vessel.  
           [0006]    A type of self-expanding stent is described in U.S. Pat. No. 4,503,569 to Dotter which issued Mar. 12, 1985, and discloses a shape memory stent which expands to an implanted configuration with a change in temperature. Other types of self-expanding stents not made of shape memory material are also known.  
           [0007]    This invention is directed to stents of all these types when configured so as to be longitudinally flexible as described in detail hereinbelow. Flexibility is a desirable feature in a stent so as to conform to bends in a vessel. Such stents are known in the prior art. Examples are shown in U.S. Pat. No. 4,856,516 to Hillstead; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 4,994,071 to MacGregor; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,195,984 to Schatz; U.S. Pat. No. 5,135,536 to Hillstead; U.S. Pat. No. 5,354,309 to Shepp-Pesch et al.; EPO Patent Application 0 540 290 A2 to Lau; EPO Patent Application No. 0 364 787 B1 to Schatz, and PCT Application WO 94/17754 (also identified as German Patent Application 43 03 181).  
           [0008]    Generally speaking, these kinds of stents are articulated and are usually formed of a plurality of aligned, expandable, relatively inflexible, circular segments which are interconnected by flexible elements to form a generally tubular body which is capable of a degree of articulation or bending. Unfortunately, a problem with such stents is that binding, overlapping or interference can occur between adjacent segments on the inside of a bend due to the segments moving toward each other and into contact or on the outside of a bend the segments can move away from each other, leaving large gaps. This can lead to improper vessel support, vessel trauma, flow disturbance, kinking, balloon burst during expansion, and difficult recross for devices to be installed through already implanted devices and to unsupported regions of vessel.  
           [0009]    A diamond configuration with diagonal connections between each and every diamond of each segment is also known but such closed configurations lack flexibility.  
           [0010]    It is an object of this invention to provide a longitudinally flexible stent of open configuration that avoids these problems and exhibits improved flexibility (radially and longitudinally) in the stent body segments thereof rather than in flexible joints between the segments.  
           [0011]    It is a further object of the present invention to provide a stent that is flexible yet also allows for side branch access.  
         SUMMARY OF THE INVENTION  
         [0012]    It is a goal of the present invention to provide a flexible stent formed of interconnected bands which provides for side branch access and which further avoids the problem of pinching or overlap between adjacent bands. Pinching or overlap is avoided where peaks and troughs of adjacent bands are circumferentially displaced relative to each other. The stents of the present invention accomplish this goal by having different bands characterized by different wavelengths over the length of the stent and/or disposing the interconnecting members in such a way that after expansion of the stent, the phase relationship between adjacent bands is altered with the peaks and troughs displaced circumferentially relative to each other.  
           [0013]    The inventive expandable stents are formed of a plurality of interconnected band-like elements characterized by alternating peaks and troughs. The ends of the interconnecting members which join adjacent bands are circumferentially offset and optionally, longitudinally offset. Peaks and troughs in adjacent bands are circumferentially offset as well so that the stent, in an expanded state, will have minimal overlap of peaks and troughs.  
           [0014]    To this end, the invention provides a tubular, flexible, expandable stent, comprising a plurality of undulating band-like elements of a selected wavelength or wavelengths. The band-like elements have peaks and troughs and are aligned on a common longitudinal axis to define a generally tubular stent body. The peaks and troughs take a generally longitudinal direction along the stent body. Adjacent band-like elements may be in phase or out of phase with each other. The inventive stents further comprise a plurality of interconnecting elements having first ends and second ends. The first and second ends extend from adjacent band-like elements and are displaced from one another in a longitudinal direction and in a radial direction along the stent. Desirably, upon expansion of the stent, at least some of the peaks and troughs of a given band-like element are displaced relative to each other about the periphery of the stent to accommodate longitudinal flexing of the stent within the band-like elements and without interference between adjacent band-like elements.  
           [0015]    In one embodiment, two different types of band-like elements are present in the stent, first band-like elements with a first selected wavelength and second band- like elements with a second selected wavelength exceeding the first selected wavelength. The first and second band-like elements preferably alternate over the length of the stent. Although the terminology of ‘first band-like element’ and ‘second band-like element’ is used, it is not intended to convey the relative order of appearance of the elements in the inventive stents.  
           [0016]    In another embodiment, two different types of band-like elements are present, first and second band-like elements, each of which has peaks and troughs. The first band-like elements have more peaks (or troughs) than the second band-like elements. Similarly, the invention is also directed to embodiments having first and second band-like elements with peaks and troughs where the peaks (or troughs) of the first band-like elements are spaced closer together than the peaks (or troughs) of the second band-like elements.  
           [0017]    In another embodiment in which band-like elements of only one wavelength are present, adjacent bands are about 180° out of phase with one another. Interconnecting elements extend at an oblique angle relative to the longitudinal axis from a peak to a trough on an adjacent band.  
           [0018]    In another embodiment in which band-like elements of only one wavelength are present, peaks from which interconnecting elements emanate are elongated relative to the peaks which are not connected to troughs and similarly, the troughs from which interconnectors emanate are elongated relative to troughs which are not connected to peaks. Further, each interconnecting element extends from the side of a peak to the side of a trough on an adjacent band.  
           [0019]    In yet another embodiment in which band-like elements of only one wavelength are present, adjacent bands are about 90° out of phase with one another. Each interconnecting element extends between a peak and a trough and the ends of the interconnecting member are circumferentially offset from one another and, optionally, longitudinally offset.  
           [0020]    The invention further provides a tubular, flexible, expandable stent having a longitudinal axis, comprising one or more cylindrical shaped first segments having first struts, the first segment being defined by a member formed in an undulating pattern of interconnected paired first struts and in which adjacent pairs of first struts in a given first segment are interconnected at opposite ends and one or more cylindrical shaped second segments defined by a member formed in an undulating pattern of interconnected paired second struts and in which adjacent pairs of second struts in a given second segment are interconnected at opposite ends. The first struts are shorter than the second struts. The first segments are formed of a number of first struts and the second segments are formed of a number of second struts with the number of first struts in a first segment exceeding the number of second struts in a second segment. The first and second segments, present and desirably alternating along the stent body, are aligned on a common longitudinal axis to define a generally tubular stent body. Adjacent first and second segments are connected by a plurality of interconnecting elements, each interconnecting element extending from an end of paired first struts on a first segment to an end of paired second struts on an adjacent second segment. The ends of interconnecting elements are circumferentially offset relative to each other, and optionally, longitudinally offset. Desirably, upon expansion of the stent, the paired struts of the adjacent segments are displaced relative to each other about the periphery of the stent body to accommodate longitudinal flexing of the stent within the segments and without interference between adjacent segments. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0021]    [0021]FIG. 1 a  shows a band-like element used in the inventive stents.  
         [0022]    [0022]FIG. 1 b  shows a schematic of a peak region which contains a double peak and a trough region containing a double trough.  
         [0023]    [0023]FIG. 2 shows a flat view of a stent configuration according to the invention.  
         [0024]    [0024]FIG. 3 shows the pattern of FIG. 2 in a tubular stent.  
         [0025]    [0025]FIG. 4 a  shows a flat view of a stent configuration according to the invention.  
         [0026]    [0026]FIG. 4 b  shows a flat view of a stent configuration according to the invention.  
         [0027]    [0027]FIG. 5 a  shows a flat view of a stent configuration according to the invention.  
         [0028]    [0028]FIG. 5 b  shows a flat view of a stent configuration according to the invention.  
         [0029]    [0029]FIG. 6 shows a flat view of a stent configuration according to the invention.  
         [0030]    [0030]FIG. 7 shows a flat view of a stent configuration according to the invention.  
         [0031]    [0031]FIG. 8 shows a flat view of a stent configuration according to the invention.  
         [0032]    [0032]FIG. 9 shows a flat view of a stent configuration according to the invention.  
         [0033]    [0033]FIG. 10 shows a flat view of a stent configuration according to the invention.  
         [0034]    [0034]FIG. 11 shows a flat view of a stent configuration according to the invention.  
         [0035]    [0035]FIG. 12 shows a flat view of a stent configuration according to the invention.  
         [0036]    [0036]FIG. 13 shows the pattern of FIG. 12 in a tubular stent.  
         [0037]    [0037]FIG. 14 shows an expanded stent of the configuration shown in FIG. 12.  
         [0038]    [0038]FIG. 15 shows a flat view of an alternate stent configuration according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.  
         [0040]    For the sake of consistency, the terms ‘peak’ and ‘trough’ shall be defined with respect to the proximal and distal ends of the stent. Each of the stents has a proximal end  91  and a distal end  93  and a longitudinal axis  95 , as seen in FIG. 1 a . Peaks  36  are generally concave relative to the proximal end of the stent and generally convex relative to the distal end of the stent. Troughs  40 , on the other hand, are generally convex relative to the proximal end of the stent and generally concave relative to the distal end of the stent. Notwithstanding this definition, the term peak is also intended to extend to regions  48  that are generally peak-like which may, nevertheless, contain trough-like regions within the peak-like region as seen in FIG. 1 b . Similarly the term trough is also intended to extend to regions  52  that are generally trough-like which may, nevertheless, contain peak-like regions within the trough-like region as seen in FIG. 1 b.    
         [0041]    Corresponding to each peak  36  is an inner diameter peak  38  where the inner diameter of the band-like element reaches its peak. The set of points on a given band-like element which are distal to inner diameter peak  38  is denoted peak region  48 . Similarly, corresponding to each trough  40  is an inner diameter trough  42  where the inner diameter of the band-like element reaches its trough. The set of points on a given band-like element which are proximal to inner diameter trough  42  is denoted trough region  52 . For the sake of clarity, unless otherwise indicated, analogous portions of stents will be similarly labeled, using three digit reference numerals to distinguish among the various embodiments shown.  
         [0042]    Also included within this definition of peak regions and trough regions are peak regions which are comprised of multiple peaks as well as trough regions which are comprised of multiple troughs such as those shown schematically in FIG. 1 b . Peak  36  is seen to consist of two sub-peaks  36   a,b  and trough  40  is similarly seen to consist of two sub-troughs  40   a,b . In the case of peaks containing sub-peak and troughs containing sub-troughs, the peak region  48  includes all of the points along the band-like element between the sub-peaks that make up the peak and similarly, the trough region  52  includes all of the points along the band-like element between the sub-troughs that make up the trough.  
         [0043]    The inventive stents may incorporate one or more bands of a chosen wavelength. In some embodiments, the inventive stents include one or more small amplitude, short wavelength bands to provide for flexibility and one or more large amplitude, long wavelength bands to give side branch access or to provide for sections of alternative strengths such as soft and/or stiff sections.  
         [0044]    Turning to the Figures, FIG. 2 shows a flat view of a stent configuration and FIG. 3 shows the stent of FIG. 2 in tubular form. That is, the stent is shown for clarity in FIG. 2 in the flat and may be made from a flat pattern  110  (FIG. 2) which is formed into a tubular shape by rolling the pattern so as to bring edges  112  and  114  together (FIG. 2). The edges may then joined as by welding or the like to provide a cylindrical configuration such as that shown generally at  115  in FIG. 3.  
         [0045]    A more preferred method of manufacture begins with a thin walled tube which is then laser cut to provide the desired configuration. It may also be chemically etched or EDM&#39;d (electrical discharge machined) to form an appropriate configuration.  
         [0046]    The configuration can be seen in these Figures to be made up of one or more spaced first band-like elements  120 . First band-like elements have a generally serpentine configuration to provide continuous waves to the first band-like elements. The waves are characterized by a plurality of peaks  124  and troughs  128  taking a generally longitudinal direction along the cylinder such that the waves in first band-like elements  120  open as the stent is expanded from an unexpanded state having a first diameter to an expanded state having a second diameter.  
         [0047]    The stent further comprises a plurality of spaced second band-like elements  132  having a generally serpentine configuration to provide continuous waves to the second band-like elements. The waves are characterized by a plurality of peaks  136  and troughs  140  taking a generally longitudinal direction along the cylinder such that the waves in the second band-like elements open as the stent is expanded from an unexpanded state having a first diameter to an expanded state having a second diameter. First and second band-like elements are characterized by respective wavelengths and amplitudes with the wavelength and amplitude of the second band-like elements exceeding the wavelength and amplitude of the first band-like elements.  
         [0048]    Adjacent first band-like elements  120  and second band-like elements  132  are interconnected via a plurality of interconnecting elements  144 . The ends of interconnecting element are circumferentially offset from each other.  
         [0049]    In an embodiment, as shown in FIGS. 2 and 3, first band-like elements  120  and second band-like elements  132  alternate over the length of the stent. Optionally, as shown in FIGS. 2 and 3, each end  152  of the stent may terminate in a first band-like element. The invention also, however, contemplates each end terminating in a second band-like element, or further, one end terminating in a first band-like element and the other end terminating in a second band-like element.  
         [0050]    While a minimum of one connecting element is required to join adjacent band-like elements, two or more interconnecting elements are preferred. In one embodiment, as shown in FIGS. 2 and 3, adjacent first and second band-like elements  120  and  132  are connected with three interconnecting elements  144 . Further, in one embodiment, adjacent interconnecting elements  144  extending from peaks  136  on a first band-like element  120  are spaced five peaks apart on the first band-like element while adjacent interconnecting elements  144  extending from troughs  140  on a second band- like element  132  are spaced three troughs apart on the second band-like element.  
         [0051]    It is a further feature of the present invention that peaks  124  on first band-like elements  120  are circumferentially displaced on the periphery of the stent from troughs  140  on adjacent second band-like elements  132 . It is desirable that peaks and troughs be displaced in the expanded state of the stent to minimize the possibility of pinching or overlap between adjacent band-like elements.  
         [0052]    Although the stent of FIG. 2 is comprised of two different wavelength band-like elements, the invention contemplates stents with a plurality of different wavelength band-like elements. As such, other stents may have three, four or more different wavelength band-like elements.  
         [0053]    In another embodiment, the inventive stent is comprised of band-like elements of a single wavelength, interconnected by interconnecting elements. Turning to FIGS. 4 a  and  4   b , band-like elements  220   a,b  are interconnected by interconnecting elements  244   a,b . Adjacent band-like elements  220   a,b  are 180° out of phase with one another. In the compressed state, the band-like elements consist of a plurality of peaks  236   a,b  and troughs  240   a,b . Peak region  248   a,b  and trough region  252   a,b  have been shaded in one instance for illustrative purposes.  
         [0054]    In the embodiment shown in FIG. 4 a , each interconnecting element  244   a  extends between a peak region  248   a  and a trough region  252   a . Rectilinear interconnecting elements  244   a  consist of a first shank  280   a , a second shank  284   a  and a link  288   a  disposed in-between the first and second shanks  280   a  and  284   a . First shank  280   a  extends in a longitudinal direction from peak region  248   a  and is substantially perpendicular to link  288   a . Second shank  284   a  extends in a longitudinal direction from trough region  252   a  and is perpendicular to link  288   a.    
         [0055]    In the embodiment shown in FIG. 4 b , the stent differs from the embodiment of FIG. 4 a  in that interconnecting element  244   b  extending between a peak region  248   b  and a trough region  252   b  is curvilinear rather than rectilinear.  
         [0056]    In both FIGS. 4 a  and  4   b , the interconnecting elements are seen to emanate from the middle of the peak and trough regions.  
         [0057]    In another embodiment, as shown in FIG. 5 a , the inventive stent is comprised of band-like elements  320   a  of a single wavelength, interconnected by interconnecting elements  344   a . Adjacent band-like elements  320   a  are 180° out of phase with one another. The band-like elements consist of a plurality of peaks  336   a  and troughs  340   a . Interconnecting elements  344   a  extend between a peak region  348   a  and a trough region  352   a . The peak regions  348   a  and trough regions  352   a  from which interconnecting elements  344   a  emanate on a given band-like element  320   a  are seen to extend longitudinally beyond adjacent peak regions  348   a ′ and trough regions  352   a ′ from which no interconnecting elements extend. The extension is such that at least a portion of peak regions  348   a  overlap longitudinally along the stent with at least a portion of trough region  352   a  on an adjacent band-like element  320   a ′. Of course, the overlap is limited to the longitudinal direction and not to the circumferential direction.  
         [0058]    In another embodiment, as shown in FIG. 5 b , interconnecting elements  344   b  extend between peak region  348   b  and a second closest trough region  352   b  on an adjacent band-like element. Interconnecting elements  344   b  are seen to be perpendicular to the longitudinal axis. As in the stent of FIG. 5 a , peak regions  348   b  from which interconnecting elements  344   b  extend and trough regions  352   b  from which interconnecting elements  344   b  extend may extend beyond adjacent peak regions  348   b ′ and trough regions  352   b ′ from which no interconnecting elements  344   b  emanates.  
         [0059]    In another embodiment, as shown in FIG. 6, adjacent band-like elements  420  are in phase with each other. As in previous Figs, band-like elements  420  are of a single wavelength, interconnected by interconnecting elements  444 . The band-like elements consist of a plurality of peaks  436  and troughs  440 . Interconnecting elements  444  extend at an oblique angle relative to the longitudinal axis of the stent between a peak region  448  and a trough region  452 . As such, ends of interconnecting elements  444  are circumferentially offset relative to each other. The exact angle will, of course, depend on the region from which the interconnecting elements extend, as well as on whether interconnecting elements interconnect nearest peaks and troughs, next nearest peaks and troughs or peaks and troughs that are further separated.  
         [0060]    In FIGS. 5 a ,  5   b  and  6 , the interconnecting elements are seen to emanate from the sides of the peak and trough regions.  
         [0061]    Although for the embodiments of FIGS. 1-6, the interconnecting elements extend from peak regions on band-like elements to trough regions on adjacent band-like elements, the invention further contemplates interconnecting elements extending from a position between a peak region and an adjacent trough region on a band-like element to a position intermediate a trough region and a peak region on an adjacent second band- like element as in FIG. 7.  
         [0062]    In the embodiment of FIG. 7, interconnecting elements are seen to extend from a region between the peak region and the trough region on a band-like element. The stent is formed of adjacent band-like elements  520  which are 180° degrees out of phase with one another. Interconnecting elements  544  extend from a region intermediate a peak region  548  and a trough region  552  on a band-like element to a region intermediate a peak region  548  and a trough region  552  on an adjacent band-like element. Interconnecting elements  544  consist of a first shank  560 , a second shank  564 , and an intermediate member  568  disposed in-between first and second shanks  560  and  564 . First shank  560  and second shank  564  are substantially perpendicular to intermediate member  568  which extends in the longitudinal direction. Although not depicted, the region from which interconnecting elements  544  emanate may be midway between peaks and troughs.  
         [0063]    The embodiment of FIG. 7 also differs from the embodiments of FIGS. 2-6 in the orientation of the interconnecting elements. Whereas the interconnecting elements in FIGS. 2-6 are all similarly oriented, in the embodiment of FIG. 7, the orientation of interconnecting elements alternates between adjacent pairs of adjacent band-like elements. Specifically, second shanks  564 ′ of interconnecting elements  544 ′ are seen to be displaced in a clockwise circumferential direction along the stent relative to first shanks  560 ′, and seconds shank  564 ″ of interconnecting elements  544 ″ are seen to be displaced in a counterclockwise circumferential direction along the stent relative to while first shank  560 ″.  
         [0064]    This feature is also seen in the embodiment of FIG. 8 in which adjacent in-phase band-like elements  620  are interconnected by interconnecting elements  644 . Interconnecting elements  644  extend at an oblique angle relative to the longitudinal axis of the stent between a peak region  648  and a trough region  652 . As in FIG. 7, the orientation of interconnecting elements alternates between adjacent pairs of adjacent band-like elements. Specifically, the distal ends of interconnecting elements  644 ′ are seen to be oriented in a counterclockwise circumferential direction along the stent relative to the proximal end of the interconnecting elements while the distal ends of interconnecting elements  644 ″ are seen to be displaced in a clockwise circumferential direction along the stent relative to the proximal ends.  
         [0065]    Although in the embodiments of FIGS. 2-8, adjacent bands are connected by five interconnecting elements, additional or fewer interconnecting elements may be used. Further, while interconnecting elements are shown spaced three peaks apart and three troughs apart, other separations are contemplated as well.  
         [0066]    In the embodiment of FIG. 9, each band-like element  720  is seen to comprise peaks  736  of more than one amplitude and troughs  740  of more than one amplitude. Large amplitude peaks  736   a  and small amplitude peaks  736   b  alternate as do large amplitude troughs  740   a  and small amplitude troughs  740   b . As in the previous embodiments, the interconnecting elements are oriented at an oblique angle relative to the longitudinal axis  795  of the stent. More generally, the invention is directed at stents comprising band-like elements whose amplitude varies along the band-like element.  
         [0067]    In another embodiment of the invention, as shown in FIG. 10, each band- like element  820  is seen to comprise peaks  836  of more than one amplitude and troughs  840  of more than one amplitude, however, peaks of the same amplitude are grouped together within a band-like element as are troughs of the same amplitude. It is further noted that in the embodiment of FIG. 10, the location of a group of peaks of given amplitude in a band-like element varies circumferentially along the length of the stent. Interconnecting elements  844  connect peaks  836  and troughs  840  in adjacent band-like elements  820 . Where several peaks of different amplitudes are present in a band-like element, the invention further contemplates the possibility of interconnecting elements extending from the large peaks  836   a  to large troughs  840   a  as in FIG. 9 as well as the possibility of interconnecting elements extending from large peaks to small troughs or from small peaks  836   b  to large troughs  840   a  as in FIG. 10. Further, the interconnecting elements between any two adjacent band-like elements may be of different lengths from one another as seen in FIG. 10 and commence at different longitudinal positions within a band-like element and terminate at different longitudinal positions within a band-like element. Interconnecting element  844   a  is seen to be longer than interconnecting element  844   b . As in the previous embodiments, the interconnecting elements are oriented at an oblique angle relative to the longitudinal axis  895  of the stent. In the embodiment of FIG. 10, interconnecting element  844   a  is seen to be oriented at a smaller oblique angle relative to the longitudinal axis of the stent than interconnecting element  844   b . As is apparent from FIG. 10, the invention is also directed to stents comprised of band-like elements whose wavelength varies along a given band-like element. Region  898  and region  899  of band-like element are characterized by different wavelengths.  
         [0068]    It is also noted that in the embodiment of FIG. 10, all of the troughs  840   a,b  in a given band-like element  820  are aligned longitudinally along the stent and differ only in their circumferential position along the stent.  
         [0069]    It is further noted in the embodiment of FIG. 10, the stent comprises a first group of interconnecting elements  844   a  and a second group of interconnecting elements  844   b . The interconnecting elements of the first group are all parallel to one another and disposed at a different oblique angle relative to the longitudinal axis than the members of the second group which are all parallel to one another. As such, the invention contemplates stents having several different groups of obliquely disposed interconnecting elements where the oblique angle differs from group to group.  
         [0070]    In another embodiment of the invention, as shown in FIG. 11, each band-like element  920  is seen to comprise peaks  936   a,b  of different amplitudes and troughs  940  of different amplitudes, however, peaks of the same amplitude are grouped together within a band-like element as are troughs of the same amplitude. It is further noted that in the embodiment of FIG. 1 Ithe location of groups of peaks of given amplitude in a band-like element varies circumferentially along the length of the stent. Interconnecting elements  944  connect large amplitude peaks  936   a  and small amplitude troughs  940   b  in adjacent band-like elements  920 . Similarly, interconnecting elements  944  also connect small amplitude peaks  936   b  and large amplitude troughs  940   a.    
         [0071]    The invention also contemplates stents similar to that shown in FIG. 11 in which interconnecting elements extend from large peaks  936   a  to large troughs  940   a , as in FIG. 9. Similarly, interconnecting elements may extend from small peaks  936   b  to small troughs  940   b.    
         [0072]    Further, the interconnecting elements between any two adjacent band-like elements may be of different lengths from one another and disposed at different oblique angles.  
         [0073]    As is apparent from FIG. 11, the invention is also directed to stents comprised of band-like elements whose wavelength varies along a given band-like element. Region  998  and region  999  of band-like element  920  are characterized by different wavelengths.  
         [0074]    It is also noted that in the embodiment of FIG. 1 Ithe large amplitude portions  999  of band-like element  920  are symmetrically disposed about the center  1001  of the band-like element as are the small amplitude portions  998 . The center  1001  of the band-like element is defined as a ring that runs along a path that is midway between the large peaks  936   a  and- large-troughs- 940   a  of the band-like element. This-feature may also be seen in the embodiment of FIG. 9.  
         [0075]    The invention is also directed to a tubular, flexible, expandable stent having a longitudinal axis, comprising one or more cylindrical shaped first segments. Cylindrical shaped first segments  20  as seen in FIG. 1, have first struts  23  having first  25  and second  27  ends. First segments  20  are defined by a member formed in an undulating pattern of interconnected paired first struts  23 , in which adjacent pairs of first struts  29 ′ and  29 ″ in a given first segment  20  are interconnected at opposite ends  31 ′ and  31 ″, respectively. Adjacent segments are interconnected.  
         [0076]    The stent may be seen more clearly in FIGS. 2-8. As shown, the stent of FIG. 3, in addition to comprising first segments  120  which are defined by an undulating pattern of interconnected paired first struts  123  in which adjacent pairs of first struts  129 ′ and  129 ″ in a given first segment  120  are interconnected at opposite ends  131 ′ and  131 ″, respectively, the stent further comprises one or more cylindrical shaped second segments  132 , each second segment being defined by a member formed in an undulating pattern of interconnected paired second struts  135  and in which adjacent pairs of second struts  137 ′ and  137 ″ in a given second segment  132  are interconnected at opposite ends  139 ′ and  139 ″, respectively. First struts  123  are shorter than second struts  135 . First segments  120  are formed of a number of first struts  123  and second segments  132  formed of a number of second struts  135 , the number of first struts in a first segment exceeding the number of second struts in a second segment. First and second segments  120  and  132  are aligned on a common longitudinal axis  195  to define a generally tubular stent body, shown generally at  115 . First and second segments  120  and  132  alternate along the stent body. Adjacent first and second segments  120  and  132  are connected by a plurality of interconnecting elements  144 . Each interconnecting element  144  extends from an end  131 ″ of paired first struts on a first segment  120  to an end  139 ″ of paired second struts on an adjacent second segment  132 . The ends of interconnecting elements  144  are circumferentially offset relative to each other.  
         [0077]    Desirably, upon expansion of stent  115 , paired struts  129 ″ and  137 ″ of adjacent segments  120  and  132  are displaced relative to each other about the periphery of the stent body to accommodate longitudinal flexing of the stent within the segments and without interference between adjacent segments.  
         [0078]    In the embodiments as shown in FIGS. 4 a, b , cylindrical shaped segments  220   a,b  are formed of interconnected struts  223   a,b  having first  225  and second  227  ends. Adjacent pairs of struts  229   a,b ′and  229   a,b ″ in a given segment  220   a,b  are interconnected at opposite ends  231   a,b ′ and  231   a,b ″, respectively. Adjacent segments are connected by a plurality of interconnecting elements  244   a,b . Each interconnecting element  244   a,b  extends from an end of paired struts  231  a,b″ on a segment to an end of paired struts  231   a,b ′ on an adjacent segment. First end  245   a,b  and second end  247   a,b  of interconnecting elements  244   a,b  are seen to be circumferentially displaced along the stent.  
         [0079]    Similar structure, denoted by similar reference numerals may be found in the stents of FIGS. 5 a,b , and  6 - 8 .  
         [0080]    In particular, in the embodiment as shown in FIG. 8, cylindrical shaped segments  620  are formed of interconnected struts  623 , having first  625  and second  627  ends. Segments  620  are defined by a member formed in an undulating pattern of interconnected paired struts  623  in which adjacent pairs of struts  629 ′ and  629 ″ in a given segment  620  are interconnected at opposite ends  631 ′ and  631 ″, respectively. Segments  620  are aligned on a common longitudinal axis  695  to define a generally tubular stent body. Adjacent segments are connected by a plurality of interconnecting elements  644  (and  644 ′) having first  645  ( 645 ′) and second  647  ( 647 ′) ends, each interconnecting element  644  ( 644 ′) extending from an end of paired struts  631 ″ on a segment to an end of paired struts  631 ′ on an adjacent segment. First end  645  ( 645 ′) and second end  647  ( 647 ″) are seen to be circumferentially displaced along the stent.  
         [0081]    Additional embodiment of the stents are shown in FIGS. 12-15. FIG. 12 and FIG. 13 show a fragmentary flat view of an unexpanded stent configuration and the actual tubular stent (unexpanded), respectively. That is, the stent is shown for clarity in FIG. 12 in the flat and may be made from a flat pattern  1110  (FIG. 12) which is formed into a tubular shape by rolling the pattern so as to bring edges  1112  and  1114  together (FIG. 12). The edges may then joined as by welding or the like to provide a configuration such as that shown in FIG. 13.  
         [0082]    The configuration can be seen in these Figures to be made up of a plurality of adjacent segments generally indicated at  1116 , each of which is formed in an undulating flexible pattern of substantially parallel struts  1118 . Pairs of struts are interconnected at alternating end portions  1119   a  and  1119   b . As is seen in FIG. 12, the interconnecting end portions  1119   b  of one segment are positioned opposite interconnecting end portions  1119   a  of adjacent segments. The end portions as shown are generally elliptical but may be rounded or square or pointed or the like. Any configuration of end portions is acceptable so long as it provides an undulating pattern, as shown. When the flat form  1110  is formed into an unexpanded tube as shown in FIG. 13, the segments are cylindrical but the end portions  1119  of adjacent segments remain in an opposed position relative to each other.  
         [0083]    A more preferred method of manufacture begins with a thin walled tube which is then laser cut to provide the desired configuration. It may also be chemically etched or EDM&#39;d (electrical discharge machined) to form an appropriate configuration.  
         [0084]    Interconnecting elements  1120  extend from one end portion  1119  of one segment  1116  to another end portion  1119  of another adjacent segment  1116  but not to an oppositely positioned end portion  1119  of an adjacent segment  1116 . There are at least three struts included between the points on each side of a segment  1116  at which an interconnecting element  1120  contacts an end portion  1119 . This results in the interconnecting elements  1120  extending in an angular direction between segments around the periphery of the tubular stent. Interconnecting elements  1120  are preferably of the same length but may vary from one segment to the other. Also, the diagonal direction may reverse from one segment to another extending upwardly in one case and downwardly in another, although all connecting elements between any pair of segments are substantially parallel. FIG. 12, for example shows them extending downwardly, right to left. Upwardly would extend up left to right in this configuration.  
         [0085]    As a result of this angular extension of the interconnecting elements  1120  between adjacent segments and loops, upon expansion of the stent as seen in FIG. 14, the closest adjacent end portions  1119  between segments  1116  are displaced from each other and are no longer opposite each other so as to minimize the possibility of binding or overlapping between segments, i.e., pinching.  
         [0086]    The number of interconnecting elements  1120  may vary depending on circumstances in any particular instance. Three per segment are satisfactory for the configuration shown and at least three will be used typically.  
         [0087]    The alternate design shown in FIG. 15 includes longer struts  1118   a  in the two end segments  1116   a  than in the intermediate segments  1116 . This allows the end segments ( 1116   a ) to have less compression resistance than the intermediate segments ( 1116 ), providing a more gradual transition from the native vessel to the support structure of the stent. Otherwise, the configuration is the same as that shown in FIG. 12.  
         [0088]    As indicated in the Figures, the invention contemplates a variation of interconnecting element shapes ranging from rectilinear to curvilinear. The invention further contemplates embodiments in which all interconnecting elements are similarly oriented as well as embodiments in which adjacent sets of interconnecting elements extending between adjacent pairs of segments are oppositely oriented (e.g., FIGS. 7 and 8). The invention also contemplates the use of interconnecting elements which extend from a range of positions along the segments, ranging from various positions in the area in which paired struts are interconnected to other positions along the struts.  
         [0089]    The invention also contemplates the possibility of interconnecting elements extending at an oblique angle relative to the longitudinal axis of the stent and connecting adjacent peaks and troughs on adjacent segments as well as peaks and troughs on adjacent segments which are separated by one or more peaks and/or troughs.  
         [0090]    The invention also contemplates reversing the orientation of interconnecting elements as shown in FIGS. 7 and 8.  
         [0091]    Finally, there are preferably at least three interconnecting elements joining adjacent first and second segments although fewer or additional interconnecting elements are also contemplated.  
         [0092]    It is understood that the peaks and troughs of the present invention need not be rounded, as shown in the Figures. The peaks and troughs may be bulbous, triangular, square, pointed, or otherwise formed of interconnected straight sections.  
         [0093]    As already indicated, this invention is applicable to self-expanding configurations, mechanically expandable configurations and to a wide variety of materials, including both metal and plastic and any other material capable of functioning as an expandable stent. For example, the stent may be of metal wire or ribbon such as tantalum, stainless steel or the like. It may be thin-walled. It may be-of shape memory - alloy such as Nitinol or the like, etc. The interconnecting elements may be formed integrally with the band-like elements (or segments) or may be bonded thereto via such methods as adhesive bonding, welding or any other known method of bonding.  
         [0094]    The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and this description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.