Patent Publication Number: US-2016228269-A1

Title: Low profile stent with flexible link

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a division of U.S. Ser. No. 13/782,302 filed Mar. 1, 2013, which is a division of U.S. Ser. No. 12/400,079 filed Mar. 9, 2009 now U.S. Pat. No. 8,388,675, which is a division of U.S. Ser. No. 09/894,984 filed Jun. 28, 2001 now U.S. Pat. No. 7,520,892, all of which are incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to a device for repairing body lumens and more particularly, to a design for stents that provides desired flexibility while still allowing the stent to be crimped to a small profile for delivery to the implant site. 
     Stents conventionally repair blood vessels that are diseased. Stents are generally hollow and cylindrical in shape and have terminal ends that are generally perpendicular to their longitudinal axis. In use, the conventional stent is positioned at the diseased area of a vessel and, after deployment, the stent provides an unobstructed pathway for blood flow. 
     Repair of vessels that are diseased can be particularly challenging since the stent must be precisely positioned, provide adequate coverage of the disease and maintain vessel patency in order to allow adequate blood flow. Therefore, the stent must provide adequate coverage to the diseased portion of the vessel, without compromising blood flow, and extend to a point within and beyond the diseased portion. Unopposed stent elements may promote lumen compromise during neointimal formation and healing, producing restenosis and requiring further procedures. Moreover, by extending into the vessel lumen at a bifurcation, the stent may block access for further interventional procedures. 
     Recently, the art has taught the use of stents having a cylindrical body with rings aligned along a longitudinal axis, where each ring has a delivered diameter in which it is crimped or compressed tightly onto a catheter, and an implanted diameter where the stent is implanted in a vessel. Each ring includes a number of first peaks and one or more second peaks, with at least one second peak of each ring connected to a second peak of the adjacent ring by a link, the rings and links being made of struts. The first peaks are configured to spread apart to permit the rings to be expanded outwardly or to be compressed radially inwardly onto a balloon portion of a delivery catheter. The second peaks and links provide longitudinal connection points between the rings. 
     By varying the number of rings and first peaks, the outward expansion of the various sections of the implanted stent can be customized and, thereby providing additional support provided at selected areas of the patient&#39; s lumen. Moreover, by varying the length and shapes of the links which connect the rings, the expandability, flexibility and degree of compression attainable may be varied. Flexibility of a stent is important with regard to both the ability of the stent to conform to the curvature of a tortuous artery after expansion and to the ability to maneuver the compressed stent through anatomy for delivery to the implant site. In particular, non-linear links may have undulating portions which are directed generally perpendicular to a longitudinal axis of the stent and which act as a hinge to enhance stent flexibility. Although the undulating portions provide desired stent flexibility, they also limit the extent of compression that may be achieved in the stent and therefore, result in increasing the delivery profile. Because the undulating portions extend perpendicular to the axis of the stent, in certain designs, they will contact the adjacent first peaks when the stent is compressed, thereby limiting the degree of compression achievable. 
     It may therefore be desirable for a stent to embody structure which not only provides additional support to a body lumen but also permits the stent to be compressed radially to a relatively high degree while maintaining necessary flexibility. Such a stent would be capable of being delivered through tortuous vasculature as well as being well suited for treating disease. The present invention endeavors to satisfy these needs. 
     SUMMARY OF THE INVENTION 
     The invention provides an improved ring design for cylindrical stents used to repair a vessel. Stents embodying the improved ring design are contemplated to provide required support in the repair of vasculature as well as to include structure providing the stent with desired flexibility and crimpability. 
     In one aspect, the stent of the present invention has rings with first peaks and second peaks, the second peaks of longitudinally adjacent rings being connected by links. The stent design of the present invention incorporates non-linear links and rings with first peaks defined by struts having different lengths or otherwise occupying staggered longitudinal positions along the stent, such structure being configured such that desired stent flexibility is achieved without sacrificing stent compression for delivery. 
     In another aspect, the stent of the present invention includes rings aligned along a longitudinal axis, where each ring has a first diameter in which it is crimped or compressed tightly, and a second diameter when the stent is implanted in a vessel. Each ring includes a number of first peaks and one or more second peaks, with at least one second peak of each ring connected to a second peak of a longitudinally adjacent ring by a link. The first peaks are configured to spread apart to permit the rings to be expanded outwardly or to be compressed radially inwardly onto a delivery catheter. 
     Additionally, at least some of the links which connect the second peaks are non-linear and have struts defining undulating portions, the struts being generally perpendicular to a longitudinal axis of the stent. These undulating portions act to enhance stent flexibility as well as vessel coverage. Furthermore, struts defining certain of the first peaks immediately adjacent each non-linear link have different lengths. The different lengths of these first peaks allow the undulating portions to be imbedded or nested within a ring width and thereby facilitate greater compression of the stent for delivery. 
     In one embodiment, struts defining one of the first peaks adjacent to each undulating link are shortened. The resulting space in the ring accommodates about one half of a perpendicular or circumferentially extending portion as well as a longitudinal length of the undulating link, thereby facilitating greater compression of the stent. 
     In an alternate embodiment, struts defining one of the first peaks adjacent to each undulating link is shortened and struts defining the other first peak adjacent each undulating link is lengthened. Lengthening the struts of the adjacent first peaks provides additional space to accommodate the entire generally perpendicular or circumferentially extending portion of the undulating link with a smaller decrease in the unsupported surface area of the expanded stent. Moreover, the lengthened first peaks may be adapted to facilitate accommodating undulating portions with additional perpendicular or circumferentially extending transitions. 
     In another alternate embodiment, the generally perpendicular transitions of the undulating portions are asymmetrical, the transitions longer in the direction of a shortened first peak. The longer perpendicular transitions can be adapted to customize the flexibility of the stent. 
     In yet another alternate embodiment, not all the links in each ring have undulating portions, with only the struts of certain of the adjacent first peaks being shortened. Selective placement of the undulating links allows the flexibility of portions of the stent to be tailored to the vessel in which it is implanted. 
     The basic concept of the ring design of the present invention may be incorporated into stents having various link shapes and lengths as well as stents having sections with different link configurations. It is contemplated that the ring design of the present invention may be applied whenever it is desired to increase the flexibility of a stent while maintaining desired crimpability, by incorporating undulating portions into the links and embedding or nesting the links within stent rings. 
     Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic view of a prior art ring design in which every link has an undulating portion; 
         FIG. 1B  is a flattened elevation view depicting a prior art stent in which every link has an undulating portion; 
         FIG. 2A  is a schematic view of a prior art ring design in which not all the links have an undulating portion; 
         FIG. 2B  is a flattened elevation view depicting a prior art stent in which not all the links have an undulating portion; 
         FIG. 3A  is a perspective view depicting a preferred embodiment of the stent of the present invention in an unexpanded configuration; 
         FIG. 3B  is a flattened elevation view depicting a preferred embodiment of the stent of the present invention; 
         FIG. 3C  is a an enlarged view of the portion of the stent in  FIG. 3B  indicated by the dotted line; 
         FIG. 4A  is a schematic view of a preferred embodiment of the ring design of the present invention in which struts defining one first peak adjacent to each undulating link are shortened; 
         FIG. 4B  is a schematic view of an embodiment of the ring design of the present invention in which struts defining one first peak adjacent to each undulating link are shortened and the other first peak adjacent to each undulating link embody relatively longer struts; 
         FIG. 4C  is a schematic view of an embodiment of the ring design of the present invention in which each undulating link has three perpendicular transitions; 
         FIG. 4D  is a schematic view of an embodiment of the ring design of the present invention in which the perpendicular transitions of each undulating link are asymmetrical; and 
         FIG. 4E  is a schematic view of an embodiment of the ring design of the present invention in which not all links have an undulating portion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The stent ring design of the present invention incorporates non-linear links with undulating portions extending generally perpendicularly or circumferentially with respect to a longitudinal axis of the stent and adjacent first peaks certain of which are defined by struts with different lengths such that stent flexibility is enhanced without sacrificing stent compression for delivery. Prior art attempts at increasing the flexibility of stents by incorporating undulating portions in the links have been developed. For example,  FIGS. 1 and 2  depict prior stents which include undulating portions in links that connect longitudinally arranged rings characterized by having first  11  and second  12  peaks.  FIGS. 1A and 1B  depict a stent  10  having an undulating portion  15  in each link  13  between second peaks  12 .  FIGS. 2A and 2B  depict a stent  110  in which only certain selected links  13  between second peaks  12  have an undulating portion  15 . Note that each first peak  14  of a selected ring terminates at the same longitudinal position along the stent  10 ,  110 . Note also that the undulating portions  15  are generally perpendicular to a longitudinal axis of the stent  10 ,  110  and, therefore, occupy a space that is wider than a cross-section of an individual link  13 . The undulating portions  15  provide the stent with desired flexibility. However, the undulating portions  15  can interfere with the adjacent first peaks  11  when the stent is compressed for delivery, thereby decreasing the degree of compressibility achievable. 
     The stent ring design of the present invention incorporates non-linear links with undulating portions extending generally perpendicularly or circumferentially with respect to a longitudinal axis of the stent and adjacent first peaks certain of which are defined by struts with different lengths such that stent flexibility is enhanced without sacrificing stent compression for delivery. Prior art attempts at increasing the flexibility of stents by incorporating undulating portions in the links have been developed. For example,  FIGS. 1 and 2  depict prior stents which include undulating portions in links that connect longitudinally arranged rings characterized by having first  11  and second  12  peaks.  FIGS. 1A and 1B  depict a stent  10  having an undulating portion  15  in each link  13  between second peaks  12 .  FIGS. 2A and 2B  depict a stent  110  in which only certain selected links  13  between second peaks  12  have an undulating portion  15 . Note that each first peak  14  of a selected ring terminates at the same longitudinal position along the stent  10 ,  110 . Note also that the undulating portions  15  are generally perpendicular to a longitudinal axis of the stent  10 ,  110  and, therefore, occupy a space that is wider than a cross-section of an individual link  13 . The undulating portions  15  provide the stent with desired flexibility. However, the undulating portions  15  can interfere with the adjacent first peaks  11  when the stent is compressed for delivery, thereby decreasing the degree of compressibility achievable. 
     Referring to  FIGS. 3A-C  and  4 A-E, the stent of the present invention is shown. The design of the stent of the present invention provides the flexibility desired as well as enhances compressibility. By incorporating first peaks a selection of which being defined by struts having different lengths, the undulating portion of the links can be embedded or nested within a ring of the stent when placed in a compressed configuration. 
     With reference to  FIGS. 3A-C  there is shown a preferred embodiment of the present invention. The depicted stent  120  has a cylindrical body  121  that includes a proximal end  122  and a distal end  123 . The stent  120  has an outer surface  124  which contacts vasculature or other body lumens into which it is placed when implanted and an inner surface  125  which accommodates blood flow. The stent  120  can be described as having a plurality of connected rings  130  aligned along a common longitudinal axis of the stent  120 . In one aspect, each ring  130  embodies struts defining a generally serpentine pattern of alternating peaks. As such, each ring  130  includes a plurality of first peaks directed in a first longitudinal direction and a plurality of second peaks directed in a second, opposite longitudinal direction. In one preferred embodiment, a ring  130  has six second peaks  112  and has six first peaks defined by struts of various lengths thereby creating three long first peaks  111  and three short first peaks  116 . The struts of the first peaks  111 ,  116  are configured to be spread apart to permit the stent  120  to be expanded to a larger diameter or compressed tightly toward each other to a smaller diameter for placement onto a catheter. The alignment of any two adjacent rings  130  is such that only three second peaks  112  of adjacent rings  130  are aligned or in phase. The aligned second peaks  112  of adjacent rings  130  are connected by a link  113 . 
     Each link  113  between second peaks  112  is further defined by an undulating portion  115  with two generally perpendicular or circumferentially extending transitions. This undulating portion  115  provides desired flexibility to the stent  120 . The long and short first peaks  111 ,  116  alternate around the circumference of each ring  130  such that each undulating portion  115  is adjacent one long first peak  111  and one short first peak  116  and further, is embedded or nested within a width or longitudinal length of a ring  130 . With the undulating portion  115  imbedded in the ring width, the stent maintains optimum compressibility for delivery within vasculature. 
     The stent typically is made from a metal alloy such as stainless steel, titanium, nickel-titanium (NiTi or nitinol of the shape memory or superelastic types), tantalum, cobalt-chromium, cobalt-chromium-vanadium, cobalt-chromium-tungsten, gold, silver, platinum, platinum-iridium or any combination of the foregoing metals and metal alloys. However, it is contemplated that the stent may be made from any material and fabricated by any process known in the art. 
     Turning now to  FIGS. 4A-E , there is depicted alternative embodiments of stent ring designs. It is contemplated that any of the designs may be incorporated into the stent of the present invention. 
       FIG. 4A  depicts a preferred embodiment of a ring design in which one of the first peaks  216  adjacent to each link  213  undulating portion  215  is shorter than the other first peak  211  adjacent the same undulating portion  215 . Note that the number of generally perpendicular or circumferential transitions in the undulating portion  215  is reduced to two from the three transitions in the prior art ring design shown in  FIGS. 1 and 2 . When the stent is compressed for delivery, the undulating portion  215  occupies the space created by the shortened first peak  216 , thereby allowing greater compression. 
       FIG. 4B  depicts an alternate embodiment of a ring design in which one of the first peaks  316  adjacent to each undulating portion  315  is shorter than the other first peak  311  adjacent the same undulating portion  315 , the other first peak  311  being longer than corresponding structures of the prior art design shown in  FIGS. 1 and 2 . The lengthened first peak  311  provides additional space to accommodate the undulating portion  315  when the stent is compressed for delivery. 
       FIG. 4C  depicts another alternate embodiment of the ring design incorporating the shortened first peaks  416 , lengthened first peaks  411 , and undulating portions  415  having three generally perpendicular or circumferential transitions. By sacrificing some of the compressibility of the embodiment shown in  FIG. 4B , additional flexibility is gained by the additional generally perpendicular transitions of the undulating portions  415 . 
       FIG. 4D  depicts another alternate embodiment of the ring design incorporating the shortened first peaks  516 , lengthened first peaks  511 , and undulating portions  515  having non-symmetrical generally perpendicular or circumferential transitions. By sacrificing some of the compressibility of the embodiment shown in  FIG. 4C , additional vessel coverage and flexibility is gained by the larger perpendicular transitions of the undulating portions  515 . 
       FIG. 4E  depicts yet another alternate embodiment of the ring design in which not all the links  613  have undulating portions  615  and adjacent short first links  616 . The first peaks  611  adjacent links without undulating portions  613  are not shortened. 
     It is contemplated that the number of first and second peaks per ring may be varied depending upon the application and the type of vessel to be treated. The stent of the present invention may contain separate sections, each section having a different ring design chosen for the particular requirements of the vessel in which it is implanted. The peaks are spaced on the rings in such a fashion as to provide uniformity after final expansion inside the vessel. 
     It is also contemplated any number of links may be provided between second peaks of each ring. Each of the rings can have at least one second peak connected to a link. Longer links may be provided, as well as links of different shapes, as a way of increasing the expandability and diameter of the rings. 
     Additionally, the stent may have rings and links with variable thickness or variable width struts in order to customize the radial strength of the stent  120 , provide higher radiopacity under fluoroscopy, and vary flexibility. The portions where the stent  120  has the thinnest struts will be the most flexible. Variable thickness struts or variable width struts may be more radiopaque and may be positioned along the stent to help the physician position the stent during delivery and implantation in the vessel. 
     While particular forms of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications can be made without departing from the scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.