US20090036974A1 - Expandable stent and method for delivery of same - Google Patents

Abstract

An expandable stent having a proximal end and a distal end in communication with one another, and a tubular wall disposed between the proximal end and the distal end. The tubular wall has a longitudinal axis and a porous surface defined by a plurality of intersecting members comprising a series of longitudinal struts disposed substantially parallel to the longitudinal axis of the stent. Each longitudinal strut in the series comprises flexure members for substantially complementary extension and compression of a diametrically opposed pair of the longitudinal struts upon flexure of the stent. The flexure members may comprise first and second curved sections which are of a different size. At least one of the curved sections may comprise an arc of greater than about 180°.

Description

• This is a continuation application of application Ser. No. 11/831,693, filed Jul. 31, 2007, which is a continuation application of application Ser. No. 11/419,895, filed May 23, 2006 (abandoned), which is a continuation application of application Ser. No. 10/849,990 (now U.S. Pat. No. 7,094,255, issued Aug. 22, 2006), filed May 21, 2004, which is a continuation of application Ser. No. 09/672,768 (now U.S. Pat. No. 6,758,860, issued Jul. 6, 2004), which is a continuation of application Ser. No. 09/142,509, filed Feb. 18, 1999 (now U.S. Pat. No. 6,183,506, issued Feb. 6, 2001), which is a 371 of PCT/CA97/00152), filed Mar. 5, 1997 (designating the U.S.; and published in English as WO 97/32544 on Sep. 12, 1997), which claims benefit of (i) CA 2,171,047, filed Mar. 5, 1996, (ii) CA 2,175,722, filed May 3, 1996, (iii) CA 2,185,740, filed Sep. 17, 1996, and (iv) CA 2,192,520, filed Dec. 10, 1996, the contents of which are incorporated herein by reference.
TECHNICAL FIELD
• The present invention relates to an expandable stent.
BACKGROUND ART
• Stents are generally known. Indeed, the term “stent” has been used interchangeably with terms such as “intraluminal vascular graft” and “expansible prosthesis”. As used throughout this specification the term “stent” is intended to have a broad meaning and encompasses any expandable prosthetic device for implantation in a body passageway (e.g. a lumen or artery).
• In the past six to eight years, the use of stents has attracted an increasing amount of attention due the potential of these devices to be used, in certain cases, as an alternative to surgery. Generally, a stent is used to obtain and maintain the patency of the body passageway while maintaining the integrity of the passageway. As used in this specification, the term “body passageway” is intended to have a broad meaning and encompasses any duct (e.g. natural or iatrogenic) within the human body and can include a member selected from the group comprising: blood vessels, respiratory ducts, gastrointestinal ducts and the like.
• Initial stents were self-expanding, spring-like devices which were inserted in the body passageway in a contracted state. When released, the stent would automatically expand and increase to a final diameter dependent on the size of the stent and the elasticity of the body passageway. An example of such a stent is known in the art as the Wallstent™.
• The self-expanding stents were found by some investigators to be deficient since, when deployed, they could place undue, permanent stress on the walls of the body passageway. Further, upon expansion, the stent would shorten in length in an unpredictable fashion thereby reducing the reliability of the stent. This led to the development of various stents which were controllably expandable at the target body passageway so that only sufficient force to maintain the patency of the body passageway was applied in expanding the stent.
• Generally, in these later systems, a stent, in association with a balloon, is delivered to the target area of the body passageway by a catheter system. Once the stent has been properly located (for example, for intravascular implantation the target area of the vessel can be filled with a contrast medium to facilitate visualization during fluoroscopy), the balloon is expanded thereby expanding the stent by plastic deformation so that the latter is urged in place against the body passageway. As indicated above, the amount of force applied is at least that necessary to maintain the patency of the body passageway. At this point, the balloon is deflated and withdrawn within the catheter, and subsequently removed. Ideally, the stent will remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).
• A stent which has gained some notoriety in the art is known as the Palmaz-Schatz™ Balloon Expandable Stent (hereinafter referred to as “the Palmaz-Schatz stent”). This stent is discussed in a number of patents including U.S. Pat. Nos. 4,733,665, 4,739,762, 5,102,417 and 5,316,023, the contents of each of which are hereby incorporated by reference.
• Another stent which has gained some notoriety in the art is known as the Gianturco-Roubin Flex-Stent™ (hereinafter referred to as “the Gianturco-Roubin stent”). This stent is discussed in a number of patents, including U.S. Pat. Nos. 4,800,882, 4,907,336 and 5,041,126, the contents of each of which are hereby incorporated by reference.
• Other types of stents are disclosed in the following patents:
• U.S. Pat. No. 5,035,706 (Gianturco et al.),
• U.S. Pat. No. 5,037,392 (Hillstead),
• U.S. Pat. No. 5,147,385 (Beck et al.),
• U.S. Pat. No. 5,282,824 (Gianturco),
• Canadian patent 1,239,755 (Wallsten), and
• Canadian patent 1,245,527 (Gianturco et al.), the contents of each of which are hereby incorporated by reference.
• While these prior art stents have achieved a varying degree of success, the art is constantly in need of new stents having improved flexibility and stability while being able to be readily implanted with little or no trauma to the target lumen.
• In our Canadian patent application number 2,134,997 (Penn et al.), the contents of which are hereby incorporated by reference, there is described an improved expandable stent. The stent comprises a tubular wall disposed between the proximal end and the distal end. The tubular wall has a longitudinal axis and a porous surface defined by a plurality intersecting members arranged to define a first repeating pattern. The first repeating pattern comprises a polygon having a pair of side walls substantially parallel to the longitudinal axis. A first concave-shaped wall and a second convex-shaped wall connect the side walls. The first wall and the second wall are equidistant along an axis which is parallel to the longitudinal axis. The stent is expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent.
• As disclosed in the '997 application, the first repeating pattern can be implemented in, inter alia, a mono-tubular expandable stent and a bifurcated expandable stent.
• While the stent disclosed in the '997 application is an advance in the art, in certain cases, a significant force is required to achieve expansion in the target body passageway. Further, implantation of the stent disclosed in the '997 application can be difficult in certain situations where the unexpanded stent must travel through a significantly curved pathway to the target body passageway.
• Accordingly, it would be desirable to have an improved stent which overcomes these disadvantages. It would be further desirable if the improved stent could be readily adapted, inter alia, to mono-tubular expandable stents and bifurcated expandable stents. The latter type of stents would be useful in treating aneurysms, blockages and other ailments. It would also be desirable if such a stent was relatively easy to implant. It would be further desirable if such a stent were capable of being uniformly expanded at relatively low pressure while obviating or mitigating longitudinal shrinkage thereof. It would be further desirable if such a stent were not susceptible to asymmetric internal coverage of the body passageway, a problem associated with “coil”-type stents—see, for example. U.S. Pat. No. 5,282,824 (Gianturco). It would be further desirable if such a stent was not susceptible to movement along the longitudinal axis of the body passageway during or after implantation. It would be further desirable if such a stent was characterized by a desirable balance of lateral flexibility in the unexpanded state and radial rigidity in the expanded state.
DISCLOSURE OF THE INVENTION
• It is an object of the present invention to provide a novel expandable stent which obviates or mitigates at least one of the above-mentioned disadvantages of the prior art.
• Accordingly, in one of its aspects, the present invention provides an expandable stent comprising a proximal end and a distal end in communication with one another, a tubular wall disposed between the proximal end and the distal end, the tubular wall having a longitudinal axis and a porous surface defined by a plurality of intersecting members comprising a series of longitudinal struts disposed substantially parallel to the longitudinal axis of the stent, each of the longitudinal struts comprising flexure means for substantially complementary extension and compression of a diametrically opposed pair of the longitudinal struts upon flexure of the stent, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force on the stent.
• Thus, in this aspect of the present invention, we have now discovered that the use of flexure means in the series of longitudinal struts leads to a very desirable balance of lateral flexibility of the unexpanded stent and radial rigidity of the expanded stent. Practically, the flexure means confers lateral flexibility to the unexpanded stent by allowing diametrically opposed pairs of the longitudinal struts to undergo substantially complementary extension and compression. If one considers a stent in a flexed state, a first longitudinal strut disposed at the tangent of the bend (i.e. in two dimensions) will expand in response to the bending moment. In contrast, a second longitudinal strut disposed diametrically opposite (this can mean above, below or in the same radial plane as) the first longitudinal strut will compress in response to the bending bend moment. Generally, the degree of extension and compression will be substantially complementary. In other words, in most cases, the first longitudinal strut will expand and lengthen a first distance and the second longitudinal strut will compress and shorten a second distance. Preferably, the first distance is greater than the second distance and most preferably, the sum of the first distance and the second distance is substantially equal to the sum of the original lengths of the first longitudinal strut and the second longitudinal strut.
• The specific shape of the flexure means disposed in the longitudinal strut is not particularly restricted provided that it confers lateral flexibility to the unexpanded stent by allowing diametrically opposed pairs of the longitudinal struts to undergo substantially complementary extension and compression. The term “diametrically opposed pairs of the longitudinal struts”, as used in this specification, is intended to have a broad meaning. Thus, the “pair” can include opposed struts in the same horizontal plane (i.e. the same ring of polygons) or in different horizontal planes (e.g. one strut in a first ring of polygons and the other diametrically opposed strut in a second ring of polygons above or below the first ring). Preferably, the flexure means comprises at least one lateral section disposed in the longitudinal strut, more preferably at least a first lateral section and a second lateral section disposed in the longitudinal strut. By “lateral section” is meant a section of the longitudinal strut which is bowed in or out of (i.e. radially from) the strut. The apex of the lateral section may be pointed, rounded or substantially flat. When the flexure means comprises a first lateral section and a second lateral section, the two sections may be symmetric or asymmetric (in the case of asymmetric this includes two sections of the same shape but different size and two sections of different and size). Further, when the flexure means comprises a first lateral section and a section lateral section, the sections may be bowed in the same or opposite direction.
• A particularly preferred embodiment of the flexure means comprises a sinusoidal or S-shaped section (various examples of such a section are illustrated herein and discussed below). Preferably, the sinusoidal or S-shaped section is adjacent the second apex of the polygon and the remaining portion of the strut is substantially straight. This feature improves the lateral flexibility of the stent thereby facilitating implantation thereof and may further mitigate longitudinal shortening of the stent upon expansion.
• In another preferred embodiment, at least one, more preferably both, of the side walls (i.e. longitudinal struts) of the polygon comprises the sinusoidal or S-shaped section. Preferably, the sinusoidal or S-shaped section is disposed at an end of the side wall. This feature improves the lateral flexibility of the stent thereby facilitating implantation thereof and may further mitigate longitudinal shortening of the stent upon expansion.
• When a sinusoidal or S-shaped portion is disposed in the side walls and/or the strut connecting the first apex and the second apex (if present), the precise shape of the portion is not particularly restricted and generally takes the form of an “S”. Thus, the sinusoidal or S-shaped portion may be comprised of a pair of joined curved sections wherein each curved section has an arc of about 180 degrees—i.e. this is illustrated inFIG. 8 of the present application. The term “arc” denotes the angle from one end of the curved section to the other about the radical point of the curved section. Alternatively, the sinusoidal or S-shaped portion may be comprised of a pair of joined curved sections wherein each curved section has an arc of greater than 180 degrees—this is illustrated inFIG. 9 of the present application.
• Further, the pair of joined curved sections can be of the same size (this is illustrated inFIGS. 8 and 9 of the present application) or of differing size (this is illustrated inFIG. 10 of the present application), the latter being the most preferred embodiment.
• Preferably, the series of longitudinal struts containing the flexure means comprises all substantially longitudinal struts comprised in the plurality of intersecting members making up the porous surface of the stent.
• Preferably, for this aspect of the present invention, the intersecting members are arranged to define a first repeating pattern comprised of a polygon having a pair of side walls substantially parallel to the longitudinal axis (i.e. a pair of the above-mentioned longitudinal struts comprising flexure means), a concave-shaped first wall having a first apex and a convex-shaped second wall having a second apex connecting the side walls. As used throughout this specification, the terms “concave-shaped” and “convex-shaped” are intended to have a broad meaning and a shape having apex. Thus, the first wall has a first apex and the second wall has a second apex. Thus, the first apex (i.e. of the concave-shaped first wall) is directed into the polygon whereas the second apex (i.e. of the convex-shaped second wall) is directed away from the polygon.
• In another of its aspects, the present invention provides an expandable stent comprising a proximal end and a distal end in communication with one another, a tubular wall disposed between the proximal end and the distal end, the tubular wall having a longitudinal axis and a porous surface defined by a plurality intersecting members arranged to define a first repeating pattern comprised of a polygon having a pair of side walls substantially parallel to the longitudinal axis, a concave-shaped first wall having a first apex and a convex-shaped second wall having a second apex, the first wall and the second wall connecting the side walls, at least one of the first apex and the second apex being substantially flat, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force on the stent.
• In this aspect of the invention, it is has been discovered that the use of such a first repeating pattern (including at least one of the first apex and second apex being substantially flat), with or without the flexure means present in the side walls of the polygon in the first repeating pattern, results in an improved stent. The advantages associated with the use of such a such a first repeating pattern include the following: 1. the force required to expand the stent is substantially reduced; 2. the stent is subjected to less traumatic stress during expansion; 3. plastic deformation of the stent during expansion is facilitated; 4. construction of the stent is facilitated; and 5. upon expansion of the stent, warpage of the first apex and the second apex is obviated or mitigated.
• The provision of at least one of the first apex and the second apex being substantially flat usually results in the apex of the concave-shaped first wall and/or the convex-shaped second wall having a pair of shoulders. Preferably, these shoulders are rounded. The provision of such round shoulders results in the following additional advantages: 6. mitigation of potential trauma to the target body passageway from: (i) endoluminal contents within the passageway, and (ii) the contours of the passageway; 7. the resulting expanded stent is more stream-lined and flow-directed which mitigates potential trauma to the target body passageway; 8. further reduction in the force required to expand the stent; 9. an improved stent expansion ratio is achieved (i.e. ratio of expanded stent diameter at maximum expansion to unexpanded stent diameter); 10. upon expansion of the stent, the concave-shaped first wall and the convex-shaped second wall are in a substantially orthogonal relationship to the longitudinal axis thereby improving the rigidity of the stent (this is very important to mitigate the occurrence of stent recoil); and 11. the pattern of the expanded stent improves the rheology of fluid flow in the body passageway.
• When the stent of the present invention includes the above-mentioned first repeating pattern, it is preferred to provide a connecting strut between the first apex and the second apex. Generally, the connecting strut will be substantially longitudinal (i.e. it will be parallel to the longitudinal axis of the stent). This feature mitigates lifting of the shoulders referred to above as the stent is flexed, for example, when passing the stent through a curved body passageway. The result of this is that potential trauma to the body passageway is mitigated since scraping of the body passageway by the shoulders is mitigated.
• In a preferred embodiment, the connecting strut is curved with respect to the longitudinal axis (this is described and illustrated hereinbelow). Preferably, the strut is sufficiently curved to have a length of up to about 35%, more preferably up to about 15%, even more preferably in the range of from about 2% to about 8%, most preferably in the range of from about 3% to about 7%, greater than the distance between the first apex and the second apex. This feature improves the lateral flexibility of the stent thereby facilitating implantation thereof. In some cases, the curvature may be designed to comprise the flexure means discussed above. In other words, the shape of the curvature may be designed substantially complementary extension and compression of the connecting strut upon flexure of the stent.
• Yet another preferred feature of the stent of the present invention is the provision of one or both of the side walls of the polygon of the repeating pattern being curved. Preferably, both side walls are curved. More preferably the curvature serves as flexure means as described above. Ideally, the curved side wall has length of up to about 35%, more preferably up to about 15%, even more preferably in the range of from about 2% to about 8%, most preferably in the range of from about 3% to about 7%, greater than the distance between the termini of the concave-shaped first wall and the concave-shaped second wall. This feature improves the lateral flexibility of the strut thereby facilitating implantation thereof.
• Preferably, both the strut and the side walls are curved. More preferably, each of the curved members are of substantially the same length.
• Yet another preferred feature of the stent of the present invention is, in addition to the strut and side walls of the polygon being curved, the provision of all longitudinal walls of the polygon of the repeating pattern being curved. Thus, in this embodiment of the invention, the concave-shaped first wall comprises a pair of curved first apex walls connecting the first apex and the side walls of the polygon, and the convex-shaped second wall comprises a pair of curved second apex walls connecting the second apex and the side walls of the polygon. Again, in some cases, the curvature may be designed to comprise the flexure means discussed above. Ideally, the curved first apex walls and the curved second apex walls each have a length of up to about 35%, more preferably up to about 15%, even more preferably in the range of from about 2% to about 8%, most preferably in the range of from about 3% to about 7%, greater than the straight (i.e. non-curved) distance between the first apex and the side walls, and the second apex and the side walls, respectively. In this embodiment, it is further preferred to have substantially all adjacent curved walls in an annular section of the repeating pattern (i.e. of the struts, first apex wall, second apex wall and side walls) are substantially equidistant from one another. This preferred feature of the stent of the present invention even further enhances the lateral flexibility of the stent thereby further facilitating implantation thereof.
• Yet another preferred feature of the stent of the present invention is provision of a porous surface comprising multiple designs. Specifically, in certain cases, it may be desirable to design the stent to varying degrees of relative flexibility and rigidity along the length thereof. Thus, the relatively flexible portion(s) of such a stent would facilitate delivery of the stent to a target body passageway through a relatively tortuous route, while the relatively rigid portion(s) of the stent serves facilitate maintaining the patency of the body passageway. As will be discussed in more detail hereinbelow, this may be achieved by varying the repeating pattern design along the longitudinal length of the stent.
• An aspect of the present invention relates to the provision of an expandable bifurcated stent. As used throughout this specification, the term “bifurcated stent” is intended to have a broad meaning and encompasses any stent having a primary passageway to which is connected at least two secondary passageways. Thus, trifurcated stents are encompassed herein. Further, one of the secondary passageways can be a continuation of the primary passageway with the result that the other secondary passageway is essentially a side branch to the primary passageway.
• The stent of the present invention (bifurcated or mono-tubular) can further comprise coating material thereon. The coating material can be disposed continuously or discontinuously on the surface of the stent. Further, the coating may be disposed on the interior and/or the exterior surface(s) of the stent. The coating material can be one or more of a biologically inert material (e.g. to reduce the thrombogenicity of the stent), a medicinal composition which leaches into the wall of the body passageway after implantation (e.g. to provide anticoagulant action, to deliver a pharmaceutical to the body passageway and the like) and the like.
• The stent is preferably provided with a biocompatible containing, in order of minimize adverse interaction with the walls of the body vessel and/or with the liquid, usually blood, flowing through the vessel. The coating is preferably a polymeric material, which is generally provided by applying to the stent a solution or dispersion of preformed polymer in a solvent and removing the solvent. Non-polymeric coating material may alternatively be used. Suitable coating materials, for instance polymers, may be polytetraflouroethylene or silicone rubbers, or polyurethanes which are known to be biocompatible. Preferably however the polymer has zwitterionic pendant groups, generally ammonium phosphate ester groups, for instance phosphoryl choline groups or analogues thereof. Examples of suitable polymers are described in International application number WO-A-93/16479 and WO-A-93/15775. Polymers described in those specifications are hemo-compatible as well as generally biocompatible and, in addition, are lubricious. It is important to ensure that the surfaces of the stent are completely coated in order to minimize unfavorable interactions, for instance with blood, which might lead to thrombosis.
• This good coating can be achieved by suitable selection of coating conditions, such as coating solution viscosity, coating technique and/or solvent removal step.
• In another embodiment of the invention, the stent may be joined to a polymer material. Specifically, a polymer material may be extruded onto the stent in such a manner that it envelops at least a portion of the stent. This technique may be used to join two or more stents with a flexible polymeric tube. This technique may also be used to join a stent to another prosthetic device such as a tube, a graft and the like. Thus, in this embodiment of the invention, the stent is incorporated into an endoluminal prosthesis.
• In yet another embodiment of the invention, the stent may be secured (e.g. by suturing) to an existing endoluminal prosthesis such as Gortex™ material or to biological material such as basilic vein. In this regard, securing of the stent to the existing endoluminal prosthesis or biological material may be facilitated by designing the stent such that an end of the stent comprises an annular row of the above-mentioned polygons is having a convex-shaped wall with a flat apex.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the present invention will be described with reference to the accompanying drawings wherein like numerals designate like parts and in which:
• FIG. 1 illustrates an exploded perspective view of a mono-tubular stent prior to expansion;
• FIG. 1A illustrates an exploded view of a portion of the stent illustrated inFIG. 1;
• FIGS. 2-10 each illustrate a two dimensional representation of various embodiments (not to relative scale) of a repeating pattern useful in the stent of the present invention;
• FIG. 11 illustrates an ostial stenosis to which a preferred embodiment of the invention may be applied; and
• FIGS. 12a-12iillustrate various embodiments of flexure means (in two dimensions) which may be disposed in the longitudinal struts of preferred embodiments of the present stent.
BEST MODE FOR CARRYING OUT THE INVENTION
• With reference toFIG. 1, there is illustrated astent10.Stent10 comprises aproximal end15 and adistal end20. Stent further comprises atubular wall25 disposed betweenproximal end15 anddistal end20. As illustrated,tubular wall25 is porous. The porosity oftubular wall25 is defined by a plurality of intersectingmembers30. Intersectingmembers30 define a first repeating pattern designated A inFIG. 1.
• As illustrated and with further reference toFIG. 1A, repeating pattern A is a polygon comprising a pair ofside walls35,40.Side walls35,40 are substantially parallel to alongitudinal axis45 ofstent10 and thusside walls35,40 may be considered to be longitudinal struts (indeed with reference to each of the drawings, side walls may also be considered to be longitudinal struts).Side walls35,40 are connected by a concave-shapedwall50 and a convex-shapedwall60.
• As illustrated, concave-shapedwall50 is made up of a trio ofsegments52,54,56. In the illustrated embodiment,segment54 is the apex of concave-shapedwall54. As is evident,segment54 is a flat apex and results in the provision of a pair of substantiallysquare shoulders57,58 Convex-shapedwall60 is made up of a trio ofsegments62,64,66. In the illustrated embodiment,segment64 is the apex of convex-shapedwall60.
• It will be appreciated by those of skill in the art that the provision of first repeating pattern A, as illustrated, necessarily defines and provides for a second repeating pattern B. It will also be appreciated by those of skill in the art that second repeating pattern B is a mirror image of first repeating pattern A taken along an axis (not shown) substantially normal tolongitudinal axis45. Thus, in the illustrated embodiments, adjacent rows of repeating pattern A and repeating pattern B may be considered to by interlocking polygons or “arrowheads”.
• It will be further appreciated by those of skill in the art that the shape of concave-shapedwall50 and/or convex-shapedwall60 can be modified without departing from the function and performance of the stent provided that at least one of concave-shapedwall50 and convex-shapedwall60 retain a substantially flat apex. For example, the trio of segments can be replaced by a suitably curved or arcuate wall. Alternatively, more than three segments can be used to define concave-shapedwall50 and/or convex-shapedwall60. Other modifications will be apparent to those of skill in the art.
• It will be further appreciated by those of skill in the art that various walls of first repeating pattern A and second repeating pattern B may be omitted (and even desired) at selected points along the body of the stent without departing from the spirit and scope of the invention. For example, it is possible to omit one or both ofside walls35 and40 at selected points along the body of the stent with a view to improving the longitudinal flexibility of the stent. Further, it is possible to omit one or more ofsegments62,64,66 at selected points along the body of the stent with a view to improving the lateral flexibility of the stent.
• Still further, the stent depicted inFIG. 1 can be modified to omit, on a selected basis, first repeating pattern A and/or second repeating B with a view to improve flexibility of the stent and to allow access to other structures (e.g. side branches/arteries) outside the bounds of the stent.
• With reference toFIGS. 2-10, there are illustrated a number of preferred embodiments of repeating pattern A. For the sake of clarity, numerals inFIGS. 2-8 have the same final two digits as the corresponding numerals inFIG. 1. Thus, for example, the concave-shaped wall is depicted aselement50 inFIG. 1,element150 inFIG. 2,element250 inFIG. 3, etc.
• Thus, as illustrated inFIG. 2, repeating pattern A is comprised of a concave-shapedwall150 and a convex-shapedwall160, the former having a flat apex. Further, as illustrated, concave-shapedwall150 and convex-shapedwall160 are not equidistant along an axis orthogonal to the longitudinal axis of the stent (not shown). Thus, in this embodiment, the flat apex in concave-shapedwall150 has been modified such that it comprises a pair of substantially roundedshoulders157,158.
• With reference toFIG. 3, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 3, the flat apex of concave-shapedwall250 has been modified to provide a pair ofrounded shoulders257,258. Further, astrut270 has been added to connectsegment254 of concave-shapedwall250 andsegment264 of convex-shapedwall260. As illustrated,strut270 is thinner in dimension that any of the segments making up concave-shapedwall250 and convex-shapedwall260. Thus, strut270 may be considered as a relatively thin retention wire which reconciles the need for retaining flexibility in the strut with mitigating lifting ofrounded shoulders257,258 when the stent is delivered to the target body passageway through a relatively tortuous route.
• With reference toFIG. 4, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 4, the flat apex of concave-shaped wall350 has been modified to provide a pair ofrounded shoulders357,358. Further, acurved strut370 has been added to connectsegment354 of concave-shaped wall350 andsegment364 of convex-shapedwall360.
• With reference toFIG. 5, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 5, the flat apex of concave-shapedwall450 has been modified to provide a pair ofrounded shoulders457,458. Further, acurved strut470 has been added to connectsegment454 of concave-shapedwall450 andsegment464 of convex-shapedwall460. Further,side walls435,440 are also curved. As discussed above, sinceside walls435,440 are bowed in opposite directions in adjacent rows of repeating pattern A and B, substantially diametric side walls in adjacent rows will function as the flexure means described above.
• With reference toFIG. 6, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 6, concave-shapedwall550 has been modified to have aflat apex554 having a pair ofrounded shoulders557,558 and convex-shapedwall560 has been modified also to have aflat apex564 having a pair ofrounded shoulders567,568. Further, acurved strut570 has been added to connectflat apex554 of concave-shapedwall550 andflat apex564 of convex-shapedwall560. Further,side walls535,540 are also curved.
• With reference toFIG. 7, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 7, concave-shapedwall650 has been modified to have aflat apex654 having a pair ofrounded shoulders657,658 and convex-shapedwall660 has been modified also to have aflat apex664 having a pair ofrounded shoulders667,668. Further, a curved strut670 has been added to connectflat apex654 of concave-shapedwall650 andflat apex664 of convex-shapedwall660. Further,side walls635,640 are also curved. Still further,walls661,662 which connectflat apex664 toside walls635,640, respectively, andwalls651,652 which connectflat apex654 toside walls635,640, respectively, are each curved. It is believed that this design even further enhances the lateral flexibility of the stent.
• With reference toFIG. 8, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 7, concave-shapedwall750 has been modified to have aflat apex754 having a pair ofrounded shoulders757,758 and convex-shaped wall760 has been modified also to have aflat apex764 having a pair ofrounded shoulders767,768. Further, astrut770 has been added to connectflat apex754 of concave-shapedwall750 andflax apex764 of convex-shaped wall760. Further,side walls735,740 have been modified to include a sinusoidal (or S-shaped)portion736,741, respectively, adjacent convex-shaped wall760. Further, strut770 has been modified to include a sinusoidal (or S-shaped)portion771 adjacent flat apex of concave-shapedwall750. This design even further enhances the lateral flexibility of the stent.
• With reference toFIG. 9, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 9, concave-shaped wall850 has been modified to have a flat apex854 having a pair ofrounded shoulders857,858. Further,side walls835,840 have been modified to include a pair of sinusoidal (or S-shaped)portions836,841, respectively, adjacent convex-shapedwall860. This design further enhances the lateral flexibility of the stent illustrated inFIG. 2. It should be noted that each sinusoidal (or S-shaped)portion836,841 inFIG. 9 comprises a pair of adjoined curved sections wherein each curved section has an arc of greater than 180 degrees—another way to conceptualize this is a pair of link omega-shaped sections (cf. with the curved sections of sinusoidal (or S-shaped)portions736,741,771 inFIG. 8).
• With reference toFIG. 10, repeating pattern A is similar to the one illustrated inFIG. 1. InFIG. 10, concave-shaped wall950 has been modified to have aflat apex954 having a pair ofrounded shoulders957,958. Further, astrut970 has been added to connect flat-apex954 of concave-shaped wall950 andsegment964 of convex-shaped wall960. Further,side walls935,940 have been modified to include a pair of sinusoidal (or S-shaped)portions936,941, respectively, adjacent convex-shaped wall960. Further, strut970 has been modified to include sinusoidal (or S-shaped)portion971 adjacent flat apex of concave-shaped wall950. It should be noted that each sinusoidal (or S-shaped)portion936,941,971 inFIG. 10 comprises a pair of adjoined curved sections wherein each curved section has an arc of greater than 180 degrees. Further, the curved sections in sinusoidal (or S-shaped)portions936,941 are of the same size, whereas the curved sections in sinusoidal (or S-shaped)portion971 are of different size. A distinct advantage of the interspersion of sinusoidal (or S-shaped)portions936,941 and sinusoidal (or S-shaped)portion971 is that substantially uniform radial expansion of all segments in this stent will occur without specific regard to the expansion forces generated by the balloon or other means used to deploy the stent. Further, this design minimizes the force (e.g. pressure from a balloon) required to expand the stent. Still further, this design enhances the lateral flexibility of the stent.
• As will be apparent to those of skill in the art, sinusoidal (or S-shaped)portion971 is offset with respect to sinusoidal (or S-shaped)portions936,941 in a panel horizontal to the longitudinal axis of repeating pattern A. The offset nature of these sinusoidal (or S-shaped) portions serves to increase the bending points in the stent allowing the stent to bend while avoiding buckling thereof. Thus, the staged distribution of the sinusoidal (or S-shaped) portions over a large portion of the surface area of the stent serves to improve the flexibility of the stent.
• The advantages of the various alternate embodiments illustrated inFIGS. 2-10 are discussed hereinabove.
• As discussed above, the use of flexure means, such as the sinusoidal (or S-shaped) portions in the design of the stents illustrated inFIGS. 8-10, in the longitudinal struts in the stent design provides the added benefit of improved flexibility of the stent in the unexpanded state. Specifically, during flexure of the stent, provision of such a feature allows the inner stent surface adjacent the bend to compress while concurrently allowing the outer stent surface adjacent the bend to extend, all while maintain substantially intact the integral strength of stent and avoiding buckling of the stent.
• Accordingly the provision of such flexure means in the longitudinal struts of an otherwise general stent design is another feature of invention. With reference toFIGS. 12a-12ithere are illustrated various alternatives of bowed lateral sections which can be used in place of sinusoidal (or S-shaped)portions736,741,771 inFIG. 8, sinusoidal (or S-shaped)portions836,841 inFIG. 9 and sinusoidal (or S-shaped)portions936,941,971 inFIG. 10. Thus, the flexure means illustrated inFIG. 12amay be considered to be an asymmetric zig-zag whereas that illustrated inFIG. 12bmay be considered to be a symmetric zig-zag and that illustrated inFIG. 12cmay be considered to be an in line symmetric double peak. The flexure means illustrated inFIG. 12dmay be considered to be a single omega, whereas that illustrated inFIG. 12emay be considered to be an inline (and unlinked) double omega and that illustrated inFIG. 12fmay be considered to be an opposed (and unlinked) double omega. The flexure means illustrated inFIG. 12gmay be considered to be an opposed omega (facilitates extension)/Ujoint (facilitates compression). Still further the flexure means illustrated inFIG. 12hmay be considered to be a rail flex whereas that illustrated inFIG. 12imay be considered to be an opposed rail flex. Other specific designs which are with the spirit and scope of the present invention will be apparent to those of skill in the art
• Those of skill in the art will recognize that it is possible to combine various of the alternate embodiments illustrated inFIGS. 2-10 and12 to derive further designs which are still within the spirit and scope of the present invention. Specifically, a preferred embodiment of the present invention involves combining various of the repeating patterns illustrated inFIGS. 2-10 to achieve a stent with relatively flexible and rigid regions, for example, as follows: F-R F-R-F R-F-R wherein F is a relatively flexible region and R is a relatively rigid region. With reference to the embodiments illustrated inFIGS. 1-10, the trackability of the stent through a tortuous pathway is enhanced from the design illustrated inFIG. 1 progressively through to the design illustrated inFIG. 10. For example, an embodiment of the invention is a stent comprising a first section incorporating the design ofFIG. 10 and a second section incorporating the design ofFIG. 9. It is believed that such a multi-sectional design provides a very desirable combination of lateral flexibility (primarily from the design ofFIG. 9) with post-expansion radial rigidity (primarily from the design ofFIG. 10).
• Another technique by which the relative flexibility/rigidity may be varied along the length of the stent involves varying the thickness of the segments making up the polygon discussed hereinabove. Specifically, the thickness of the segments may be varied in the range of from about 0.0015 to about 0.0045 inches, preferably from about 0.0020 to about 0.0040 inches. The lower the thickness in this range, the more flexible the resulting stent design. Conversely, the higher the thickness in this range, the less flexible the resulting stent design. Thus, by judicious selection of segment thickness, the relative flexibility/rigidity of the stent may be varied along its length.
• The provision of a stent with a variable relative flexibility/rigidity along its length is believed to be novel, especially a stent comprising a single relatively flexible portion and a single relatively rigid portion (i.e. the F-R embodiment discussed above). Such a stent would find immediate use in a number of applications. For, example, such a stent would very desirable for implantation in an ostial stenosis (these typically occur in coronary arteries, vein grafts and renal arteries). In this regard, an ostial stenosis is illustrated inFIG. 11 thereof. Thus, there is illustrated a rightcoronary cusp105, a rightcoronary artery110 and anostial segment115 of rightcoronary artery110. As further illustrated astenosis120 presents a narrowing ofostial segment115. Ideally, a stent capable of implantation into such an ostial stenosis must be of sufficient rigidity after expansion to resist the elastic recoil of the ostial blockage (Region Y inFIG. 11). However, a stent of such sufficient rigidity will be deficient since it will either: (i) be retarded in its advance along the artery due to the sharp bend in the right coronary artery (Region X inFIG. 11); or (ii) traverse the sharp bend in the right coronary artery but subsequently straighten Region X of rightcoronary artery110 thereby increasing the likelihood of tearing the artery. Conversely, a stent of sufficiently flexibility to traverse the sharp bend in the right coronary artery (Region X inFIG. 11) is susceptible to recoil in the ostial right coronary artery (Region Y inFIG. 11). Accordingly, to the knowledge of the Applicant, there is no known effective manner by which a stent may be used to treat an ostial stenosis of the type illustrated inFIG. 11. It is believed that a stent having variable relative rigidity/flexibility along its length as discussed above is a novel means by which an ostial stenosis may be treated.FIG. 11 also serves to illustrated the substantially complementary extension and compression of longitudinal members in Region X of the right coronary artery.
• The manner by which the present stent is manufactured is not particularly restricted. Preferably, the stent is produced by laser cutting techniques applied to a tubular starting material. Thus, the starting material could be a thin tube of a metal or alloy (non-limiting examples include stainless steel, titanium, tantalum, nitinol, Elgiloy, NP35N and mixtures thereof) which would then have sections thereof cut out to leave repeating pattern A discussed above. Thus, the preferred design of the present stent is one of a tubular wall which is distinct from prior art wire mesh designs wherein wire is conformed to the desired shape and welded in place. The preferred tubular wall design of the present stent facilitates production and improves quality control by avoiding the use of welds and, instead, utilizing specific cutting techniques.
• Preferably, the stent is coated with a solution of 1:2 (mole) copolymer of (methacryloyloxy ethyl)-2-(trimethylammonium ethyl) phosphate inner salt with lauryl methacrylate in ethanol (as described in Example 2 of International patent application WO-A-93/01221) as follows. The non-expanded stent may be placed in a tube having a slightly larger diameter than the stent. The tube may then be filled with coating solution and the solution allowed to drain steadily from the tube to form a completely coated stent. Immediately thereafter a stream of warm air or nitrogen may be directed through the tube at a linear velocity of 0.1.5 m/s at room temperature to 50 degrees C. for a period of 30 seconds to 5 minutes to dry the coating by evaporation of the ethanol; solvent.
• As an alternative or in addition (on top or underneath) to this coating, a cross-linkable coating may be used consisting of a polymer of 23 mole % (methacryloyloxy ethyl)-2-(trimethylammonium ethyl) phosphate inner salt, 47 mole % lauryl methacrylate, 5 mole % ytrimethoxysilylpropyl methacrylate and 25 mole % of yhydroxypropyl methacrylate. This may be applied to the sent by the above described technique from a 5 mg/ml ethanoic solution. The solution may be dried as described above and then cured by heating at 70 to 75 degrees C. for a period of at least about 1 hour, for instance overnight. This curing generally results in substantially complete reaction of the methoxy silyl groups, either with other methoxylsily groups or with hydroxy groups derived from the hydroxypropyl methacrylate monomer, driving off methanol. In one preferred embodiment the crosslinkable coating is applied to the cleared stent, cured and then a further coating of the lauryl methacrylate copolymer described above is applied.
• The coated stent may be sterilised by ethylene oxide, gamma radiation or electron beam and subsequently mounted onto a balloon catheter for delivery.
• Stent10 can be implanted using a conventional system wherein a guidewire, catheter and balloon can be used to position and expand the stent. Implantation of mono-tubular stents such asstent10 is conventional and within the purview of a person skilled in the art. See, for example, any one of U.S. Pat. Nos. 4,733,665, 4,739,762, 5,035,706, 5,037,392, 5,102,417, 5,147,385, 5,282,824, 5,316,023 and any of the references cited therein or any of the references cited hereinabove. When the present stent is constructed as a bifurcated stent, it may be implanted using the procedure outlined in the '997 patent application incorporated herein by reference. Such a bifurcated stent may be manufactured, inter alia, by any of the methods disclosed in the Canadian patent application number 2,175,720 filed in Applicant's name on May 3, 1996, the contents of which are hereby incorporated by reference.
• It will be apparent to those of skill in the art that implantation ofstent10 can be accomplished by various other means. For example, it is contemplated that the stent can be made of a suitable material which will expand when a certain temperature is reached. In this embodiment, the material may be a metal alloy (e.g. nitinol) capable of self-expansion at a temperature of at least about 30 degrees C., preferably in the range of from about 30 degrees to about 40 degrees C. In this embodiment, the stent could be implanted using a conventional catheter and the radially outward force exerted on the stent would be generated within the stent itself. Further,stent10 can be designed to expand upon the application of mechanical forces other than those applied by a balloon/catheter. For example, it is possible to implantstent10 using a catheter equipped with a resisting sleeve or retaining membrane which may then be removed with the catheter once the stent is in position thereby allowing the stent to expand. Thus, in this example, the stent would be resiliently compressed and would self-expanded once the compressive force (i.e. provided by the sleeve or membrane) is removed.
• As will be appreciated by those of skill in the art, repeating pattern A has been described hereinabove and illustrated inFIG. 1 in respect of a monotubular stent. Repeating pattern A and all of the features relating thereto illustrated in and described with reference toFIGS. 1-10 (including modification to include the flexure means illustrated inFIGS. 12a-12i) is equally applicable to a bifurcated stent such as the one described and illustrated in the '997 application discussed hereinabove, the contents of which are hereby incorporated by reference.
• While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments.

Claims (1)

1. An expandable stent comprising a proximal end and a distal end in communication with one another, a tubular wall disposed between the proximal end and the distal end, the tubular wall having a longitudinal axis and a porous surface defined by a plurality intersecting members arranged to define a first repeating pattern comprised of a polygon having a pair of side walls substantially parallel to the longitudinal axis, a concave-shaped first wall having a first apex and a convex-shaped second wall having a second apex, the first wall and the second wall connecting the side walls, at least one of the first apex and the second apex being substantially flat, the stent being expandable from a first, contracted position to a second, expanded position upon the application of a radially outward force on the stent.

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