one preferred embodiment of the invention is illustrated in fig1 - 8 . it comprises a metal tube - like structure 10 as best shown in fig3 and 4 , such as nitinol or stainless steel , which has been etched or laser cut to the configuration shown in the plan view of fig1 and 2 and in a short version as shown in fig4 . 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 fig2 . 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 fig4 - 8 . it can be seen from fig4 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 fig8 . more specifically the cells are of two kinds as shown in fig8 . 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 fig1 - 4 undergoes expansion , such as from the embodiment of fig4 it will appear as shown in fig5 in the fully expanded condition . fig5 shows the stent in perspective . the unwinding action which the coil elements 16 undergo upon stent expansion is best seen in fig6 - 8 which show only the front side surface of the stent for simplicity and clarity . as radial expansion begins ( seen in fig6 ) 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 fig6 . upon further expansion ( seen in fig7 ), spirals 16 undergo further unwinding , i . e ., elements 13 undergo further straightening . finally in fig8 substantial full expansion provides substantially straightened elements 13 which in that condition limit stent recoil and increase the resistance to compression of the stent . fig9 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 . fig1 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 fig9 . in fig1 , 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 fig8 . other embodiments are shown in subsequent figures with different spiral arrangements . for example , the embodiment of fig1 - 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 . fig1 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 . fig1 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 fig1 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 fig1 , 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 fig1 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 . fig1 - 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 . fig2 shows segments 12 in a configuration other than the annular serpentine configuration of previous figures . fig3 shows alternate segments 12 in serpentine annular configuration interconnected by double rows of interconnected coil configurations 16 . fig3 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 .
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 .