US20010047200A1 - Non-foreshortening intraluminal prosthesis - Google Patents

Abstract

A stent has a plurality of cells disposed about the circumference of the stent, with at least one cell having a plurality of struts that are connected together to form the cell. At least one strut has a portion that compensates for foreshortening of the struts during expansion of the stent.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention[0001]
• The present invention relates to intraluminal prostheses for implantation into a mammalian vessel, and in particular, to intraluminal stents that do not experience foreshortening in the longitudinal direction when the stent is deployed to an expanded state.[0002]
• 2. Description of the Prior Art[0003]
• Intraluminal prosthesis, such as stents, are commonly used in the repair of aneurysms, as liners for vessels, or to provide mechanical support to prevent the collapse of stenosed or occluded vessels. These stents are typically delivered in a compressed state to a specific location inside the lumen of a vessel or other tubular structures, and then deployed at that location of the lumen to an expanded state. These stents have a diameter in their expanded state which is several times larger than the diameter of the stents in the compressed state. These stents are also frequently deployed in the treatment of atherosclerotic stenosis in blood vessels, especially after percutaneous transluminal coronary angioplasty (PTCA) procedures, to improve the results of the procedure and to reduce the likelihood of restenosis.[0004]
• U.S. Pat. Nos. 5,733,303 (Israel et al.) and 5,827,321 (Roubin et al.) describe the problems associated with the foreshortening of intraluminal stents when such stents are expanded. In addition, U.S. Pat. No. 5,733,303 (Israel et al.) describes stents that have struts whose longitudinal length decreases when the stent expands, thereby causing the overall longitudinal length of the stent to foreshorten. These struts are connected by flexible connecting members, each having an area of inflection that functions to compensate for the foreshortening experienced by the struts during expansion of the stent.[0005]
• Unfortunately, there are certain drawbacks associated with providing flexible connecting members that have areas of inflection. First, to accommodate the areas of inflection, these connecting members often create segments within the stent where the aperture or opening defined by these connecting members have a large size. Such increased aperture size may allow increased ingrowth of tissue (also known as “in-stent restenosis”). Second, curved areas of inflection on these connecting members may cause distortion of the lumen of the stent when the stent is twisted or experiences angulation in the longitudinal direction. Third, the connecting members form an area of weakness in the stent structure which may encourage kink of the stent at the site with flexion or angulation, or which in extreme circumstances may lead to stent breakage after experiencing repetitive stress. In other words, the provision of the connecting members decreases the amount of support that the stent can enjoy.[0006]
• Thus, there still remains a need for an intraluminal prosthesis that maintains a consistent length in both its fully compressed and fully expanded states, while avoiding the disadvantages set forth above. There also remains a need for a stent which can accommodate body vessels having varying lumen diameters, different anatomies, and different disease states.[0007]
SUMMARY OF THE DISCLOSURE
• It is an object of the present invention to provide an intraluminal prosthesis that maintains a consistent length in both its fully compressed and fully expanded states.[0008]
• It is another object of the present invention to provide an intraluminal prosthesis that provides increased support throughout the prosthesis while minimizing the potential for stent kink or breakage at certain regions along the stent.[0009]
• It is yet another object of the present invention to provide an intraluminal prosthesis that minimizes the potential for in-stent restenosis.[0010]
• In order to accomplish the objects of the present invention, there is provided a stent having a plurality of cells disposed about the circumference of the stent, with at least one cell having a plurality of struts that are connected together to form the cell. At least one strut has a portion that compensates for foreshortening of the struts during expansion of the stent.[0011]
• In another embodiment, the present invention provides a stent having a plurality of cells disposed about the circumference of the stent, with at least one cell having a plurality of double-struts that are connected together to form the cell.[0012]
• Thus, the stent according to the present invention maintains a consistent length in both its fully compressed and fully expanded states, and in all states between its fully compressed and fully expanded states. As a result, the stent according to the present invention facilitates accurate sizing and deployment, thereby simplifying, and possibly reducing the time needed for, the medical procedure.[0013]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of a stent according to one embodiment of the present invention;[0014]
• FIG. 2A is a side elevational view of a portion of the stent of FIG. 1 in its expanded state;[0015]
• FIG. 2B is a side elevational view of the portion of FIG. 2A in its compressed state;[0016]
• FIG. 3A is an enlarged side elevational view of a cell of the portion of FIG. 2A;[0017]
• FIG. 3B illustrates the longitudinal component of a strut and its compensating portion of FIG. 3A when the stent is in its expanded state;[0018]
• FIG. 3C illustrates the longitudinal component of a strut and its compensating portion of FIG. 3A when the stent is in its compressed state;[0019]
• FIG. 4 illustrates a modification to the cell pattern of the stent of FIGS. 1 and 2A;[0020]
• FIG. 5 is an enlarged side elevational view of a cell of portion of a stent according to another embodiment of the present invention;[0021]
• FIG. 6A is a side elevational view of a portion of a stent according to another embodiment of the present invention;[0022]
• FIG. 6B is a side elevational view of the portion of FIG. 6A in its compressed state;[0023]
• FIG. 6C illustrates the longitudinal component of a strut and its compensating portion of FIG. 6A when the stent is in its expanded state;[0024]
• FIG. 6D illustrates the longitudinal component of a strut and its compensating portion of FIG. 6A when the stent is in its compressed state;[0025]
• FIGS.[0026]7-9 are side elevational views of portions of stents according to other embodiments of the present invention;
• FIG. 10 is an enlarged side elevational view of a cell of portion of a stent according to another embodiment of the present invention;[0027]
• FIGS.[0028]11-14 are side elevational views of portions of stents according to other embodiments of the present invention; and
• FIG. 15A is a side elevational view of a portions of a stent according to another embodiments of the present invention;[0029]
• FIG. 15B is a side elevational view of the portion of FIG. 15A in its compressed state; and[0030]
• FIGS.[0031]16-18 illustrate modifications to the cell pattern of the stent of FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. The scope of the invention is best defined by the appended claims.[0032]
• The intraluminal prosthesis according to the present invention is a stent, although the principles of the present invention are also applicable to other prosthesis such as liners and filters. The stent is delivered to a desired location in the lumen of a body vessel in a compressed state, and is then deployed by expanding it to its expanded state. The stent maintains substantially the same length in both its fully compressed and fully expanded states.[0033]
• The stent according to the present invention can be a self-expanding stent, or a stent that is radially expandable by inflating a balloon or expanded by an expansion member, or a stent that is expanded by the use of radio frequency which provides heat to cause the stent to change its size. The stent may also be coated with coverings of PTFE, dacron, or other biocompatible materials to form a combined stent-graft or endovascular prosthesis. The vessels in which the stent of the present invention can be deployed include but are not limited to natural body vessels such as ducts, arteries, trachea, veins, ureters and the esophagus, and artificial vessels such as grafts.[0034]
• A stent[0035]20 according to the present invention is illustrated in FIGS. 1, 2A and3A in its expanded state. Referring to FIG. 1, the stent20 has a tubular configuration and is made up of a plurality of cells that are comprised of generally V-shaped struts connected at their apices. FIGS. 2A and 2B illustrate a portion of the stent20 in greater detail, and FIG. 3A illustrates onecell22. Eachcell22 has afirst strut24 having afirst end26 and asecond end28, asecond strut30 having afirst end32 and asecond end34, athird strut36 having afirst end38 and asecond end40, and afourth strut42 having afirst end44 and asecond end46. The first ends26 and32 of the first andsecond struts24 and30, respectively, are connected at afirst apex48, and the first ends38 and44 of the third andfourth struts36 and42, respectively, are connected at asecond apex50. The second ends28 and40 of the first andthird struts24 and36, respectively, are connected to form athird apex52, and the second ends34 and46 of the second andfourth struts30 and42, respectively, are connected to form afourth apex54, so that the four struts24,30,36 and42 together form an aperture oropen space56.
• As shown in FIG. 2A, the[0036]first apex48 of eachcell22 is connected to thesecond apex50 of a longitudinallyadjacent cell22, and thethird apex52 of eachcell22 is connected to thefourth apex54 of a transverselyadjacent cell22. For purposes of the present invention,cells22 can be provided in longitudinal rows and transverse columns. Therefore, the first andsecond apices48 and50 ofadjacent cells22 are connected to form a row R ofcells22, while the third andfourth apices52 and54 ofadjacent cells22 are connected to form a column C ofcells22.
• The[0037]struts24,30,36 and42 would normally experience foreshortening when the stent20 is expanded. Therefore, any of thestruts24,30,36 and42 can be provided with a compensatingportion60 that functions to compensate for the foreshortening experienced by thestruts24,30,36 and42 during expansion of the stent20. As shown in greater detail in FIG. 3A, each compensatingportion60 has at least one point of inflection. In the non-limiting example shown in FIG. 3A, the compensatingportion60 has three points ofinflection62 and64 that are inflected in directions opposite to each other. One point ofinflection62 can be considered to be an external point of inflection since it extends outside the confines of thecell22 as defined by thestruts24,30,36 and42. Similarly, each of the other two points ofinflection64 can be considered to be an internal point of inflection since it extends into theaperture56. Each compensatingportion60 can be provided along any portion of thestrut36 and42, and slopes downwardly from one end of thestrut36 and42 to an internal point ofinflection64, at which point it slopes upwardly to the external point ofinflection62, then slopes downwardly to the other internal point ofinflection64, before sloping upwardly again towards the other end of thestrut36 or42. Thus, each compensatingportion60 has a plurality of alternating segments that are defined by the points ofinflection62 and64.
• As best shown in FIG. 2A, the pattern of[0038]cells22 can define a second pattern ofcells22xthat have about the same configuration as thecells22, but reversed about a vertical axis defined byapices52 and54 to form a substantial mirror image of thecells22. Each of thesecond cells22xis defined by a separate strut from fourseparate cells22. Like thecells22, thesesecond cells22xare also arranged to form rows and columns ofcells22x.
• Referring to FIG. 2B, when the stent[0039]20 is in the compressed state, the internal points ofinflection64 are adjacent to each other. However, it is possible to position the compensatingportions60 along the third andfourth struts36 and42 so that the points ofinflection62,64 can be nested within each other when the stent20 is compressed. In such a case, when the stent20 is compressed, an internal point ofinflection64 of thethird strut36 can be nested or fitted inside the space defined by an external point ofinflection62 of thefourth strut42, and an internal point ofinflection64 of thefourth strut42 can nested or fitted inside the space defined by an external point ofinflection62 of thethird strut36.
• As another example, it is possible to also provide the compensating[0040]portions60 for the first andsecond struts24 and30, in addition to or in lieu of the compensatingportions60 for the third andfourth struts36 and42. For example, FIG. 10 illustrates acell22 where eachstrut24,30,36 and42 has a compensatingportion60.
• The compensating[0041]portions60 function to compensate for the longitudinal foreshortening experienced by thestruts24,30,36,42, thereby maintaining the stent20 at substantially the same length at all times. This is accomplished by providing the compensatingportions60 with a natural bias and a springy nature, which together with its alternating segments, combine to shorten its length l₁(see FIG. 3B) when compressed (i.e.,1₂in FIG. 3C is less than l₁). When allowed to expand, each compensatingportion60 is biased to return to its natural or original position, which increases its length from l₂to l₁to compensate for the foreshortening experienced by the longitudinal component of eachstrut24,30,36,42.
• This effect is illustrated in FIGS. 2A, 2B,[0042]3A,3B and3C. When the stent20 is in its compressed state, the compensatingportion60 has an actual length which is less than its actual length when the compensatingportion60 is in its expanded state. When the compensatingportion60 is in the compressed state, its alternating segments have a higher amplitude and a smaller wavelength than when it is in the expanded state (compare FIGS. 3B and 3C). Thus, this difference between the actual lengths of the compensatingportion60 in its two compressed and expanded states compensates for the difference between l₁and l₂of thestruts36 and42, so that the longitudinal lengths L₁and L₂of the strut (e.g.,36) are the same in both the compressed and expanded states. The lines70 and72 in FIGS. 2A and 2B also show that the relevant portion of the stent20 does not experience any foreshortening.
• FIG. 4 illustrates a modification to the cell pattern for stent[0043]20 shown in FIG. 2A. In particular, the cell pattern20ain FIG. 4 provides a plurality of straight connectingmembers80 that connect the first andsecond apices48 and50, respectively, ofadjacent cells22 in a longitudinal row R. These straight connectingmembers80 can increase the flexibility of the stent, primarily in the longitudinal direction, but also to a small degree in the radial direction. In addition, one or more of these straight connectingmembers80 can be omitted, either randomly or in a pattern (e.g., in a spiral pattern) to increase the flexibility of the stent at desired locations.
• Although the compensating[0044]portions60 have been described in FIGS.1-3 as assuming a particular configuration, it will be appreciated by those skilled in the art that the compensatingportions60 can assume other configurations without departing from the spirit and scope of the present invention. For example, the compensatingportion60 can be modified so that each has two points of inflection. This is illustrated in FIG. 5, where thethird strut36 has a compensatingportion60athat has one external point of inflection62aand one internal point ofinflection64a,and thefourth strut42 has a compensatingportion60athat has one external point of inflection62aand one internal point ofinflection64a.
• FIGS.[0045]6-9 illustrate another type of compensatingportion90 according to the present invention which is configured to be a generally incomplete or C-shaped circle provided at one or more apices of the cells. For example, referring to FIG. 6A, each cell22bis essentially the same ascell22 in FIG. 3A, except that the compensatingportions60 have been replaced by compensatingportions90bthat are provided at the location of the first andsecond apices48 and50 in such a manner that the first andsecond apices48 and50 are replaced by these compensatingportions90b.Each compensatingportion90bhas a generally incomplete circular or C-shaped configuration, extending from thefirst end26b,32b,38bor44bof one of thestruts24b,32b,36bor42b,respectively, then curling around in a circular fashion to thefirst end26b,32b,38bor44bof theadjacent strut24b,32b,36bor42b,respectively. The elements of the cell22bthat are the same as the elements of thecell22 in FIG. 3A are provided with the same numeral designations except that a “b” has been added to the numeral designations in FIG. 6A.
• Each compensating[0046]portion90bof each cell22bis longitudinally (i.e., along a row) connected to a compensatingportion90bof an adjacent cell22bby a straight connecting member80b.The compensatingportions90bfunction in the same manner as the compensatingportions60 to compensate for the longitudinal foreshortening experienced by thestruts24b,30b,36b,42b.In this regard, the generally circular curved configuration of the compensatingportions90bhas one area of inflection95 so that each compensatingportion90bhas a shortened longitudinal length L2 when compressed, but has an increased longitudinal length L1 when allowed to expand so as to compensate for the foreshortening experienced by the longitudinal component of eachstrut24b,30b,36b,42b.This effect is illustrated in FIGS. 6B, 6C and6D.
• FIG. 7 illustrates a stent pattern in which each cell[0047]22cis essentially the same as cell22bin FIG. 6A, except that the compensating portions90care now provided at the third andfourth apices52 and54, respectively, in such a manner that the third andfourth apices52 and54 are replaced by these compensating portions90c.Each compensating portion90chas the same configuration as compensatingportion90b.The elements of the cell22cthat are the same as the elements of the cell22bin FIG. 6A are provided with the same numeral designations except that a “c” has been added to the numeral designations in FIG. 7. Each compensating portion90cof each cell22ccan be transversely (i.e., along a column) connected to a compensating portion90cof an adjacent cell22cby a straight connecting member80c.
• The principles illustrated in FIGS. 6A and 7 can be combined. For example, FIG. 8 illustrates a stent pattern in which each[0048]cell22dhas compensating portions90dprovided at all fourapieces48,50,52 and54, in such a manner that each of the fourapieces48,50,52 and54 is replaced by a compensating portion90d.Each compensating portion90dof eachcell22dcan be either longitudinally or transversely connected to a compensating portion90dof anadjacent cell22dby a straight connecting member80d.The elements of thecell22dthat are the same as the elements of the cells22band22care provided with the same numeral designations except that a “d” has been added to the numeral designations in FIG. 8.
• In addition, FIG. 9 illustrates a stent pattern which is the same as the stent pattern in FIG. 8, except that the connecting members[0049]80dare omitted. Thus, each compensatingportion90eof eachcell22ein FIG. 9 is directly connected, either longitudinally or transversely, to a compensatingportion90eof anadjacent cell22e.The elements of thecell22ethat are the same as the elements of thecell22dare provided with the same numeral designations except that an “e” has been added to the numeral designations in FIG. 9.
• FIGS. 11 and 12 illustrate different types of compensating portions according to the present invention that embody the underlying principles described in connection with FIGS.[0050]6-9. In FIG. 11, each cell22gshares a compensating portion90gwith each longitudinally adjacent cell22g.In particular, each compensating portion90gis shaped like a sideway “S”, with the top of the “S” coupled to a first cell22gat the location of (and replacing) thefirst apex48, and with the bottom of the “S” coupled to a longitudinally adjacent second cell22gat the location of (and replacing) thesecond apex50 of the second cell22g.Thus, the sideway “S” shape of each compensating portion90gdefines two areas ofinflection100 and102 that function to provide the compensation needed to avoid foreshortening according to the principles set forth in FIGS.2-9 above. Otherwise, the elements of the cell22gin FIG. 11 that are the same as the elements of thecell22 in FIG. 3A are provided with the same numeral designations except that a “g” has been added to the numeral designations in FIG. 11.
• Similarly, in FIG. 12, each[0051]cell22hshares a compensatingportion90hwith each longitudinallyadjacent cell22h.In particular, each compensatingportion90his configured like the compensatingportion90bin FIG. 6, except that afirst end106 of the compensatingportion90his connected to the first end44hof thefourth strut42hof afirst cell22h,with the compensatingportion90hcurling around in a circular fashion to itssecond end108, which is connected to thefirst end32hof thesecond strut30hof a longitudinally adjacentsecond cell22h.Thefirst end38hof the third strut36hof thefirst cell22his connected to the compensatingportion90hbetween the first and second ends106 and108 thereof, and thefirst end26hof thefirst strut24hof thesecond cell22his connected to the compensatingportion90hbetween thesecond end108 and thefirst end38hof the third strut36hof thefirst cell22h.Thus, the compensatingportion90hdefines one area ofinflection110 between two longitudinallyadjacent cells22hthat functions to provide the compensation needed to avoid foreshortening according to the principles set forth in FIGS.2-9 above. Otherwise, the elements of thecell22hin FIG. 12 that are the same as the elements of thecell22 in FIG. 3A are provided with the same numeral designations except that an “h” has been added to the numeral designations in FIG. 12.
• It is not necessary that the[0052]struts24,30,36,42 be straight. In this regard, the present invention provides cells having curved struts that provide at least one area of inflection to provide the compensation needed to avoid foreshortening according to the principles set forth in FIGS.2-10 above. As a non-limiting example, FIG. 13 illustrates a stent pattern in which the cells22iare essentially the same as thecell22 in FIG. 3A, except that eachstrut24i,30i,36iand42iis now completely curved. Otherwise, the elements of the cell22iin FIG. 13 that are the same as the elements of thecell22 in FIG. 3A are provided with the same numeral designations except that an “i” has been added to the numeral designations in FIG. 13.
• The[0053]cells22jin the stent pattern in FIG. 14 borrow from the principles illustrated in FIGS. 3A and 13. Each strut in thecells22jare made up of two strut pieces that have their respective ends connected at theapices48j,50j,52jand54j.In particular, thefirst strut24jhas an accompanying inner strut piece24kwhose ends are also connected to theapices48jand52j,the second strut30jhas an accompanying inner strut piece30kwhose ends are also connected to the apices48jand54j,the third strut36jhas an accompanying inner strut piece36kwhose ends are also connected to theapices50jand52j,and the fourth strut42jhas an accompanying inner strut piece42kwhose ends are also connected to the apices50jand54j.Eachstrut24j,30j,36j,42jand its accompanying inner strut piece24k,30k,36k,42kdefines asmaller cell120,122,124,126, respectively. In this embodiment, the inner strut pieces24k,30k,36k,42kare shorter than eachcorresponding strut24j,30j,36j,42j.
• Providing double struts to make up the desired[0054]cells22jcan provide certain benefits. First, the double-strut structure may increase the strength of the stent by providing radial and longitudinal resistance to compression and other changes in shape. Second, the resulting stent may have an increased expansion ratio. Third, the double-strut structure may reduce the tendency of the stent to recoil. Fourth, the resulting stent may have increased stent coverage and cells that have smaller sizes, thereby minimizing tissue in-growth. The double-strut embodiment of FIG. 14 can be especially useful in applications where the prosthesis requires increased support throughout the prosthesis while minimizing the potential for stent kink or breakage at certain regions along the stent.
• FIG. 15A illustrates a stent[0055]20min which thecells22mare essentially the same as the cell22iin FIG. 13, except that eachstrut24m,30m,36mand42mhas less curvature. In fact, eachstrut24m,30m,36mand42mhas one internal point ofinflection64mand one external point ofinflection62m.Otherwise, the elements of thecell22min FIG. 15 that are the same as the elements of the cell22iin FIG. 13 are provided with the same numeral designations except that an “m” has been added to the numeral designations in FIG. 15. Similar to FIG. 2A, the pattern ofcells22mcan define a second pattern of cells22ythat have about the same configuration as thecells22m,but reversed about a horizontal axis defined by the apices48mand50m.Like thecells22m,these second cells22yare also arranged to form rows and columns of cells22y.Each of the second cells22yis defined by a separate strut from fourseparate cells22m.FIG. 15B illustrates the stent20min the compressed state. One difference between thecell22mand theother cells22 herein is that the apex54min eachcell22mis inverted internally into thecell22m,as opposed to extending externally from thecell22m.
• While the embodiments illustrated hereinabove illustrate stent patterns that are made up entirely of[0056]cells22 that have compensatingportions60, it is also possible to intersperse cells that do not have any compensatingportions60. These principles will be illustrated in FIGS.16-18 using thecell pattern22mof FIG. 15. Referring first to FIG. 16, a stent20mis illustrated as having acentral portion150 made up of a plurality of conventional zig-zag struts that do not have any compensating portions, and which form diamond-shapedcells152. The two ends of the stent20mis made up of thecell pattern22millustrated in FIG. 15. This configuration provides more rigidity in thecentral portion150, and is better suited for use, for example, in the carotid arteries where more calcified lesions can be found at about thecentral portion150, and where there is more potential for embolization in thecentral portion150. This is because the diamond-shapedcells152 are better suited to minimize embolization and prevent tissue in-growth.
• FIG. 17 illustrates a[0057]stent20nhaving afirst portion154 made up of a plurality of conventional zig-zag struts that do not have any compensating portions, and which form diamond-shapedcells152, and asecond portion156 that is made up of thecell pattern22millustrated in FIG. 15. Thefirst portion154 can be used to support a body vessel at a location that requires more rigidity, and thesecond portion156 can be used to support a body vessel at a location that requires more flexibility. This configuration is better suited for use, for example, in the iliac arteries where the origin of the iliac arteries might have more calcified lesions where thefirst portion154 would be intended to support.
• FIG. 18 illustrates a stent[0058]20phaving rows158 ofcells22mseparated by one or more rows of the diamond-shapedcells152. Therows158 can be individual rows ofcells22m,or a plurality of rows ofcells22m.This configuration is useful in distributing the radial strength of the stent20pwhile allowing for nonforeshortening and increased flexion at the desired locations (i.e., supported by thecells22m). This configuration is best suited for use, for example, with curved vessels such as external iliac arteries.
• A number of materials can be used to fabricate the stent[0059]20 (including itsstruts24,30,36,42 and connecting members80), depending on its method of deployment. These materials include, but are not limited to, Nitinol (which is a shape memory superelastic metal alloy whose use in stents is well-documented in the literature), stainless steel, tantalum, titanium, elgiloy, gold, platinum, or any other metal or alloy, or polymers or composites, having sufficient biocompatibility, rigidity, flexibility, radial strength, radiopacity and antithrombogenicity.
• The stent[0060]20 can be made from one of a number of methods, depending on the material of the stent20 and the desired nature of deployment.
• In a non-limiting first preferred method, the stent[0061]20 is fabricated from a solid Nitinol tube with dimensions that are identical to the stent20 when it is in the fully compressed state. The pattern of the stent20 (i.e., its cells22) is programmed into a computer-guided laser cutter which cuts out the segments between the struts and the connecting members (if any) in a manner which closely maintains the outside diameter and wall thickness of the stent20.
• After the cutting step, the stent[0062]20 is progressively expanded until it reaches its fully expanded state. The expansion can be performed by an internal expansion fixture, although other expansion apparatus and methods can be used without departing from the spirit and scope of the present invention. The overall length of the stent20 must be consistently maintained throughout the expansion of the stent20 from its fully compressed to its fully expanded states.
• Once the stent[0063]20 has been expanded to its fully expanded state, it is heat-treated to “set” the shape memory of the Nitinol material so that it will fully return to its expanded dimensions at a temperature that is near body temperature. The stent20 is then cleaned and electro-polished.
• The next step is to compress the stent[0064]20 again into a dimension which allows for delivery into a vessel, either through percutaneous delivery or through minimally invasive surgical procedures. Specifically, the stent20 must be compressed into a smaller state so that it can be delivered by a delivery device to the desired location of the vessel. Any conventional delivery device could be used, such as but not limited to a tube, catheter, or sheath. This compression is accomplished by cooling the stent20 to a low temperature, for example, zero degrees Celcius, and while maintaining this temperature, compressing the stent20 to allow the stent20 to be inserted inside the delivery device. Once inserted inside the delivery device, the stent20 is held by the delivery device in the compressed state until it is released within the lumen of a vessel, at which time the stent will fully re-expand to its “set” dimensions as it equilibrates with body temperature.
• In a non-limiting second preferred method, a balloon-expandable stent[0065]20 can be fabricated by connecting a plurality of wires that have been bent or formed into the desired shapes for thestruts24,30,36,42 and connectingmembers80. The connection can be accomplished by welding, tying, bonding, or any other conventional method. Alternatively, wire electro-discharge machining or a computer guided laser cutter can be used. The wires are capable of experiencing plastic deformation when the stent20 is compressed, and when the stent20 is expanded. Upon plastic deformation of the stent20 to either the compressed or the expanded state, the stent20 remains in this state until another force is applied to plastically deform the stent20 again.
• While certain methods of manufacture have been described above, it will be appreciated by those skilled in the art that other methods of manufacture can be utilized without departing from the spirit and scope of the present invention.[0066]
• The stent[0067]20 can be deployed by a number of delivery systems and delivery methods. These delivery systems and methods will vary depending on whether the stent20 is expanded by self-expansion, radial expansion forces, or radio frequency. These delivery methods are well-known in the art, and shall not be described in greater detail herein.
• Thus, the present invention provides a stent having struts that include portions that compensate for the foreshortening effect. As a result, connecting members can be omitted from the stent designs according to the present invention, leading to at least the following benefits. First, cell sizes can be decreased so as to minimize “in-stent restenosis”, and to provide better support to the vessel. Second, the stent can be provided with a more uniform structure that distributes any angulation or flexion of the stent more evenly along the full length of the stent, so that the stent can experience a more gradual curvature at bends rather than experiencing undesirable kinking at such regions. This further minimizes breakage or other damage to the stent. Of course, connecting members can be optionally added to increase the flexibility of the stent at certain desired areas.[0068]
• While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.[0069]

Claims (22)

What is claimed is:

1. A stent comprising:

a plurality of cells disposed about the circumference of the stent, with at least one cell having a plurality of struts that are connected together to form the cell, with at least one strut having a compensating portion that compensates for foreshortening of the struts during expansion of the stent.

2. The stent of

claim 1

, further including a connecting member for coupling two adjacent cells.

3. The stent of

claim 1

, wherein the compensating portion has at least one area of inflection.

4. The stent of

claim 1

, wherein the compensating portion has an internal area of inflection and an external area of inflection.

5. The stent of

claim 1

, wherein each of the struts has a compensating portion.

6. The stent of

claim 1

, wherein each of the plurality of cells has four struts that define a generally diamond-shaped configuration having four apices, with a compensating portion provided at one of the apices.

7. The stent of

claim 6

, wherein a compensating portion is provided at two of the apices.

8. The stent of

claim 6

, wherein a compensating portion is provided at all the apices.

9. The stent of

claim 6

, wherein the compensating portion is C-shaped.

10. The stent of

claim 6

, wherein the compensating portion is connects apices between two adjacent cells.

11. The stent of

claim 10

, wherein the compensating portion is S-shaped.

12. The stent of

claim 10

, wherein the compensating portion is C-shaped.

13. The stent of

claim 1

, wherein each strut is completely curved.

14. The stent of

claim 1

, wherein the plurality of cells is a first plurality of cells that defines a first plurality of rows and columns, and wherein the stent further includes a second plurality of cells that defines a second plurality of rows and columns.

15. The stent of

claim 14

, wherein the configuration of the first plurality of cells is a substantial mirror image of the second plurality of cells.

16. The stent of

claim 1

, wherein the plurality of cells is a first plurality of cells that is provided along a first length of the stent, and wherein the stent further includes a second plurality of cells that-is provided along a second length of the stent.

17. The stent of

claim 1

, wherein the compensating portion is curved.

18. The stent of

claim 1

, wherein each cell has a plurality of apices that are defined by the plurality of struts, and each of the plurality of struts includes a first strut and a second strut to define a double-strut configuration, with each of the first and second struts having a first end and a second end, wherein the first ends of the first and second struts are connected to a first apex, and the second ends of the first and second struts are connected to a second apex.

19. The stent of

claim 18

, wherein the first and second struts of each of the plurality of struts defines a space therebetween.

20. A stent comprising a plurality of cells disposed about the circumference of the stent, with at least one cell having a plurality of double-struts that are connected together to form the cell.

21. The stent of

claim 20

, wherein each cell has a plurality of apices that are defined by the plurality of double-struts, and with each of double-struts having a first end and a second end, wherein the first ends of the double-struts are connected to a first apex, and the second ends of the double-struts are connected to a second apex.

22. The stent of

claim 21

, wherein each double-strut defines a space therebetween.

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