Abstract:
The invention is directed to an expandable stent which is longitudinally flexible in both the unexpanded and expanded conditions. The stent includes spiral structures which at least partially unwind upon expansion of the stent to limit stent recoil. Regions of low strain in the stent during expansion are provided by the spiral structures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of U.S. application Ser. No. 09/954,364, filed Sep. 17, 2001, which is a Continuation of U.S. application Ser. No. 09/389,832, filed Sep. 3, 1999, issued as U.S. Pat. No. 6,334,870 on Jan. 1, 2002, which is a Continuation of U.S. application Ser. No. 08/846,164, filed Apr. 25, 1997, issued as U.S. Pat. No. 6,033,433 on Mar. 7, 2000, the contents of which are hereby incorporated by reference 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to stents of improved configuration which incorporate spiral articulations which unwind to form bracing structures or scaffolding upon expansion. 
     2. Brief Description of the Prior Art 
     Stents are radially expandable endoprosthesis which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. They have also been implanted in urinary tracts and bile ducts. They are used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon. 
     In the past, stents have assumed many configurations and been made of many materials, including metals and plastic. Ordinary metals such as stainless steel have been used as have shape memory metals such as nitinol and the like. Stents have also been made of biodegradable plastic materials. They have been formed from wire, tube stock, etc. 
     SUMMARY OF THE INVENTION 
     This invention provides a new configuration for stents which may be adapted by all of the various types of prior art stents referred to hereinabove. There are numerous advantages to the new configuration. It limits recoil and adds resistance to compression for the expanded stent, among other things. It is longitudinally flexible in both the unexpanded and expanded conditions. It has several embodiments. 
     An important part of the new configuration includes a spiral or spiral-like structure comprised of joined elements which are coiled or bent and which unwind, uncoil or unbend to a more or less straightened condition on expansion of the stent. Such structures are hereinafter referred to collectively as spirals, spirals or spiral-like structures. These structures provide regions of low strain in the stent during expansion. These elements may be joined to each other or to any radially expansive members of any kind, annular serpentine members being preferred. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a flat view of one pattern embodiment of a stent configuration of the invention (unexpanded); 
         FIG. 2  is a detail of a portion of  FIG. 1 ; 
         FIG. 3  is an end view of a stent of the  FIG. 1  pattern according to the invention showing it in tubular configuration; 
         FIG. 4  is a showing of a stent in the embodiment of the preceding Figures in perspective and in an unexpanded configuration; 
         FIG. 5  is a showing of the stent of  FIG. 4  fully expanded with details of the front and rear of the stent; 
         FIGS. 6 ,  7  and  8  are showings of the stent of  FIG. 4  in various stages of expansion with only details of the front of the stent shown for simplicity; 
         FIG. 9  is a plan view showing another embodiment of the invention; 
         FIG. 10  is a showing of a modified embodiment; 
         FIG. 11  is a showing of another embodiment; 
         FIG. 12  is a detail of a portion of  FIG. 11 ; 
         FIG. 13  is a showing of the stent of  FIGS. 11 and 12  in an expanded configuration; 
         FIG. 14  is a showing of another embodiment; 
         FIG. 15  is a showing of still another embodiment; 
         FIG. 16  is a showing of yet another embodiment; 
         FIG. 17  is a showing of still another embodiment; 
         FIGS. 18-28  show various spiral-like arrangements of the invention; 
         FIG. 29  shows another embodiment of the invention; 
         FIG. 30  shows yet another embodiment; and 
         FIG. 31  shows still another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One preferred embodiment of the invention is illustrated in  FIGS. 1-8 . It comprises a metal tube-like structure  10  as best shown in  FIGS. 3 and 4 , such as nitinol or stainless steel, which has been etched or laser cut to the configuration shown in the plan view of  FIGS. 1 and 2  and in a short version as shown in  FIG. 4 . The configuration is made up of a series of serpentine annular expandable elements or segments  12  which form loops  14  to allow for radial annular expansion. Segments  12  may be other configurations but serpentine is preferred. Elements  12  are interconnected by pairs of elongated members  13   a  and  13   b  which are attached at one end to successive loops  14  of a segment  12  and which are joined at their other ends to adjacent pairs of elongated members  13   a  and  13   b , as best seen in detail in  FIG. 2 . Members  13   a  and  13   b  are preferably of narrower gauge than members  12  and are joined together in a coiled or spiral arrangement as shown generally at  16 . Spiral  16  forms a structure about which members  13  may uncoil or unwind in a counterclockwise direction or clockwise direction to a substantially straight condition, depending on the spiral winding direction, upon radial expansion of members  12 . In this embodiment spirals  16  are formed in alternate wound structures so that some unwind in one direction and some in the other direction. Of course, in any embodiment the spirals can be formed so that they all unwind in one direction, either clockwise or counterclockwise and they may have more or fewer members  13 . Also, more or less spirals may be included between the segments. The unwinding is accompanied by a straightening action with respect to members  13  as is described in more detail in connection with  FIGS. 4-8 . It can be seen from  FIGS. 4 through 8  that the resultant configuration in an expanded stent of this configuration is comprised of a plurality of cells, the perimeter of each of which is defined by a pair of members or struts defined by the loop portion  14  of segment  12  and a pair of members or struts  13 . The cells are joined at  16  as best seen in  FIG. 8 . More specifically the cells are of two kinds as shown in  FIG. 8 . A first pair of cells are A and B made up of a segment  12  and two struts  13   a  for cell A or  13   b  for cell B. A second pair of cells are C and D made up of an inward loop portion  14  of segment  12  and a strut  13   a  and a strut  13   b  for cells C and D. 
     When a stent of the invention, such as that shown in  FIGS. 1-4  undergoes expansion, such as from the embodiment of  FIG. 4 , it will appear as shown in  FIG. 5  in the fully expanded condition.  FIG. 5  shows the stent in perspective. 
     The unwinding action which the coil elements  16  undergo upon stent expansion is best seen in  FIGS. 6-8  which show only the front side surface of the stent for simplicity and clarity. 
     As radial expansion begins (seen in  FIG. 6 ) it can be appreciated that the spiral elements  16  undergo an unwinding or straightening action by a pulling force on all of the members  13 . Specifically, as expansion occurs, elements  13  undergo a straightening action as can be seen in the early stages of expansion in  FIG. 6 . 
     Upon further expansion (seen in  FIG. 7 ), spirals  16  undergo further unwinding, i.e., elements  13  undergo further straightening. 
     Finally in  FIG. 8 , substantial full expansion provides substantially straightened elements  13  which in that condition limit stent recoil and increase the resistance to compression of the stent. 
       FIG. 9  shows a modified embodiment in which elements  13   a  and  13   b  contact segment  12  at the end of its loops  14 . Also note in this embodiment that the spirals  16  are all wound in the same direction. 
       FIG. 10  shows an embodiment of the invention in which the spiral members  13  are more bent and less curvilinear but still form a spiral-like configuration  16 . The remainder of the configuration is similar to that of  FIG. 9 . In  FIG. 10 , elongate members  13  are shown prior to expansion of the stent. When the stent is expanded, members  13  unwind counter-clockwise and straighten somewhat. At full expansion members  13  straighten still further and straighten substantially so as to provide resistance to compression of the stent and low recoil. The expanded configuration displays a cell configuration similar to that seen in  FIG. 8 . 
     Other embodiments are shown in subsequent Figures with different spiral arrangements. For example, the embodiment of  FIGS. 11-13  shows coiled arrangements  16  which are wound in the same direction and elements  13  attached at the end of loops  14  while some adjacent spirals between segments are interconnected by members  15 . 
       FIG. 14  shows some elements  13  in a spiral  16  contacting the end of loops  14  and some contacting segment  12  proper. Also, some adjacent spirals are interconnected by members  17 . 
       FIG. 15  shows a flattened or elongated spiral arrangement  16  and elements  12  are angled with respect to the longitudinal axis of the stent. In previous embodiments, these elements or segments have been arranged parallel to the axis or horizontal. Elongated spirals as in  FIG. 13  and spirals of previous Figures may be mixed together. (Not shown). 
     In the embodiments already discussed, annular expandable segments such as segments  12  are interspersed with spiral arrangements  16 . However, as can be seen in  FIG. 16 , at least a substantial portion or all of the stent body can be merely comprised of spiral arrangements  16  connected to each other. Actually, all of the body may consist of spirals. In this embodiment, the elements  13  interconnect between spirals over substantially the entire body of the stent. Optionally, the ends may include segments  12  as shown. 
     The embodiment shown in  FIG. 17  shows segments  12  alternately angled in opposite directions and with legs thereof of different length and elements  13  contacting the segments at different locations, i.e., as at the loop portion  14  and at the segment portion proper. 
       FIGS. 18-28  demonstrate examples of what is meant by the terms spiral and spiral-like herein. Of course, additional members may be included in the spirals. 
       FIG. 29  shows segments  12  in a configuration other than the annular serpentine configuration of previous Figures. 
       FIG. 30  shows alternate segments  12  in serpentine annular configuration interconnected by double rows of interconnected coil configurations  16 . 
       FIG. 31  is included to demonstrate that spirals  16  may be included on the ends of a stent  10 . 
     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. 
     The above Examples and disclosure are intended to be illustrative and not exhaustive. These examples and 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.