WO1999011197A1

WO1999011197A1 - Expandable stent

Info

Publication number: WO1999011197A1
Application number: PCT/CA1998/000835
Authority: WO
Inventors: Donald R. Ricci; Ian M. Penn
Original assignee: Divysio Solutions Ulc
Priority date: 1997-09-04
Filing date: 1998-09-04
Publication date: 1999-03-11
Also published as: CA2214627A1; AU8969698A

Abstract

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 arranged to define a first repeating pattern comprised of a polygon having a pair of side walls substantially parallel to the longitudinal axis, each side wall comprising first and second flexure means of the same phase with respect 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.

Description

EXPANPAm ,F, ,STF,NT

TFCHMCAI. FTF.TI) 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 "intralummal vascular graft" and "expansible prosthesis" As used throughout this specification the term "stent" is intended to have a broad meaning and encompasses any expendable prosthetic device for implantation in a body passageway (e.g. a lumen or artery)

In the past eight to ten 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 latrogenic) within the human body and can include a member selected from the group compπsmg: blood vessels, respiratory ducts, gastrointestinal ducts and the like

Initial stents were self-expanding, sprmg-hke de\ ices w hich were inserted in the body passageway in a contracted state

In the case of self-expanding, sprmg-hke devices, 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 an 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 Fuπher, upon expansion, the stent would shorten in length m 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, m the balloon-deployable 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 mtravascular implantation the target area of the vessel can be filled with a contrast medium to facilitate visualization duπng 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 w ill remain in place and maintain the target area of the body passageway substantially free of blockage (or narrowing).

A stent which has gained some notoπetv m 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 United States patents 4.733.665, 4,739.762, 5.102.41 7 and 5.316,023. the contents of each of which are hereby incorporated by reierence.

Another stent which has gained some notonen in the art is known as the

Gianturco-Roubin Flex-Stent™ (hereinafter reterred to as "the Gianturco-Roubm stent") This stent is discussed in a number ol patents, including United States patents 4.800.882. 4.907.336 and 5.041.126. the contents oi each of which are hereby incorporated by reference

Other types of stents are disclosed in the follow ing patents

United States patent 5,035.706 (Gianturco et al ). United States patent 5.037.392 (Hillstead )

United States patent 5.147.385 (Beck et al. ). United States patent 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 pπor 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. An improved expendable stent is descπbed in the following copending patent applications.

Canadian patent application number 2.134.997 (filed November 3, 1994), Canadian patent application number 2,171.047 (filed March 5, 1996), Canadian patent application number 2.175.722 (filed May 3, 1996),

Canadian patent application number 2.185.740 (filed September 17. 1996),

Canadian patent application number 2,192.520 (filed December 10, 1996), International patent application PCT/CA97/00151 (filed March 5, 1997), and

International patent application PCT/CA97/00152 (filed March 5, 1997),

the contents of each of which are hereby incorporated b\ reterence (hereinafter collectively referred to as "the Divysio applications" ) Generally, the stent illustrated in the Divysio patent applications comprises a tubular wall disposed between the proximal end and the distal end The tubular w all 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 w all connect the side walls The stent is expendable from a first, contracted position to a second, expanded position upon the application of a radially outward force exerted on the stent. In the field of stent design, there is an ongoing need to develop a stent which has a combination of the the following properties (i) flexibility in the unexpanded state of the stent to facilitate delivery of the stent via tortuous pathway (if necessary) to the the target lumen: (ii) radial rigidity of the stent in the expanded (i.e.. deployed) state to mitigate against the occurrence of collapse or recoil of the stent; and (in) relative ease of expansion of the stent from the unexpanded state to the expanded state to reduce the likelihood of injuring the target lumen duπng expansion.

The stent illustrated in the Divysio applications provides an desirable combination of these features Notwithstanding this, it would be desirable to further improve feature (in), l e . the ease of expansion of the stent.

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It is an object of the present invention to provide a novel expandable stent. Accordingly, the present invention provides an expandable stent composing 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 ot a polygon having a pair of side walls substantially parallel to the longitudinal axis, each side wall compπsmg first and second flexure means of the same phase with respect 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 w all 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. Thus, we have now discovered that, of the vaπous flexure means disclosed in International patent applications PCT CA97/00151 and PCT/CA97/00152 (both filed March 5. 1997). the use of a specific subset thereof m the side walls of the polygon of the first repeating pattern leads to a surpπsmg and unexpected reduction m the expansive forces needed to transform the stent from the unexpanded state to the expanded state The enhancement of this property can be achieved without compromising the desirable flexibility and radial πgidity propeπies of stent discussed above (l e , features (1) and (n), respectively) Generally, the specific subset is the combination of first and second flexure means of the same phase with respect to the longitudinal axis of the tubular wall of the stent As used throughout this specification, the term "first and second flexure means of the same phase" is intended to mean that each flexure means compπses a lateral section in the side wall (this term is used throughout this specification with the term longitudinal strut") with the proviso that, for a given longitudinal strut the lateral section of each flexure means departs from the longitudinal axis of the strut in the same direction By "lateral section" is meant a section of the longitudinal strut hich is bowed in or out of (l e . radially from) the strut Other than this, the specific shape of the first and second flexure means disposed in the longitudinal strut is not particularly restπcted The apex of the lateral section mav be pointed, rounded or substantially flat

Of course, the first and second flexure means should act to confer lateral flexibilitv to the unexpanded stent bv allowing diametπcallv opposed pairs of the longitudinal struts to undergo substantialh complementary extension and compression The term "diametπcallv opposed pairs of the longitudinal struts". as used m this specification, is intended to ha\ e a broad meaning Thus, the "pair" can include opposed struts in the same hoπzontal plane (e g . the same πng of polygons) or in different hoπzontal planes (e g , one strut in a first πng of polygons and the other diametπcallv opposed strut m a second πng of polygons above or below the first πng)

In a given longitudinal strut, the first and second flexure means may be symmetπc or asymmetπc (in the case of asvmmetπc this includes two sections of the same shape but different size and two sections of different and size)

As descπbed m vaπous of the Divysio patent applications, practically, the flexure means confers lateral flexibilitv 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 diametπcally 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, m most cases, the first longitudinal strut w ill 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 oπginal lengths of the first longitudinal strut and the second longitudinal strut.

Preferably, for a given circumferential πng of polygons in the first repeating pattern, the first and second flexure means are in the same phase with respect to the longitudinal axis of the tubular wall More preferably, phase of the first and second flexure means is reversed with respect to adjacent circumferential πngs of polygons m the tubular wall - this is illustrated in Figure 1 of the present application. In one preferred embodiment, one or both ol the first and second flexure means used in a given longitudinal strut is designed to hav e a curved section with an arc of about 180° - i.e., this is illustrated in Figure 1 of the present application. The term "arc" denotes the angle from one end of the

ed section to the other about the radial point of the curved section. In another preferred embodiment, one or both of the first and second flexure means used in a given longitudinal strut is designed to have a curved section wherein each curved section has an arc of greater than 180° - i.e.. the shape of the curved section is m the form of an omega design. Further, the pair of the first and second flexure means used in a given longitudinal strut can be of the same size or of diffeπng size (this is illustrated in Figure 1 of the present application), the latter being the most preferred embodiment. In one preferred embodiment, the series of longitudinal struts, each containing the first and second flexure means, comprise all substantially longitudinal struts which define to polygon of the repeating pattern defined hereinabove. 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. As will be readily apparent, the first apex (i.e., of the concave-shaped first wall) is directed into the polygon hereas the second apex (i.e., of the convex-shaped second wall) is directed away from the polygon.

As described in vaπous of the Divysio applications, the use of the first repeating pattern including at least one of the first apex and second apex being substantially flat 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 duπng 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 conca\ e-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: (1) endolum al 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 all 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

1 1 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 w ill 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 abov e 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 descπbed and illustrated m more detail in vaπous of the Divysio applications). In one preferred embodiment, 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. In another preferred embodiment, the connecting strut compπses a third flexure means. The discussion above with respect to the design of the first and second flexure means applies equally here with respect to the design of the third flexure means. Preferably, for a given polygon in the repeating pattern, the third flexure means is in the same phase has the first and second flexure means disposed in the pair of side walls (or longitudinal struts) compπsed in the polygon. This feature improves the lateral flexibility of the stent thereby facilitating implantation thereof. In some cases, 15 the curvature may be designed to compπse 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.

The stent of the present invention may be mono-tubular or bifurcated. Preferably, the present stent is monotubular The stent of the present invention (bifurcated or mono-tubular) can further compπse coating mateπal thereon The coating mateπal can be disposed continuously or discontinuously on the surface of the stent. Further, the coating may be disposed on the mteπor and'or the exteπor surface(s ) of the stent. The coating mateπal can be one or more of a biologically inert mateπal (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 coating, 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 polymeπc mateπal. which is generally provided by applying to the stent a solution or dispersion of preformed polymer m a solvent and removing the solvent. Non-polymeπc coating mateπal may alternatively be used. Suitable coating mateπals. for instance polymers, may be polytetraflouroethylene or sihcone rubbers, or polyurethanes which are known to be biocompatible. Preferably however the polymer has zwitteπomc 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 unfavourable 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 mateπal 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, secuπng of the stent to the existing endoluminal prosthesis or biological mateπal may be facilitated by designing the stent such that an end of the stent compπses an annular row of the above-mentioned polygons is having a convex-shaped wall with a flat apex.

Embodiments of the present invention will be descπbed with reference to the accompanying drawing, in which:

Figure 1 illustrates a two dimensional representation of a preferred embodiment of a repeating pattern useful in the stent of the present invention.

With reference to Figure 1. there is illustrated a preferred embodiment of a two dimensional representation of a repeating pattern useful in the present stent. The repeating pattern is manifested in a wall 10 disposed between the proximal end and the distal end of the stent (not shown). As illustrated, tubular wall 10 is porous. The porosity of tubular wall 10 is defined by a plurality of intersecting members 15. Intersecting members 15 define a first repeating pattern designated A m Figure 1.

As illustrated and with further reference to Figure 1. repeating pattern A is a polygon compπsing a pair of side walls 35.40. Side walls 35,40 are substantially parallel to a longitudinal access of the stent and thus, side walls 35.40 may be considered to be longitudinal struts Side walls 35,40 are connected by a concave-shaped wall 50 and a convex-shaped wall 60. Further, side walls 35,40 include a pair of curved sections 36,41. It should be noted that each curved section 36.41 in Figure 1 has an arc of about 180°. Further, as illustrated, concave-shaped wall 50 and concave-shaped wall 60 are not equidistance along an access normal to the longitudinal access of the stent (not shown)

As illustrated, concav e-shaped wall 50 is made up of a tπo of segments 52.^4,56 In the illustrated embodiment, segment 54 is the apex of concave-shaped wall 50 As is evident, segment 54 is a flat apex and result m the provision of a pair of substantially rounded shoulders 57,58 Convex-shaped wall 60 is made up of a tπo of segments 62,64.66. In the illustrated embodiment, segment 64 is apex of convex-shaped wall 60 and compπses a pair of rounded shoulders 67.68 It will be appreciated by those of skill in the art that the provision of first repeating pattern A. as illustrated, necessaπly defines and prov ides 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 access (not shown) substantially normal to the longitudinal access of the stent. Thus, m the illustrated embodiment, adjacent row s of repeating pattern A and repeating pattern B may be considered to be interlocking polygons (or "arrowheads")

As will be apparent with reference to Figure 1. the phase of curved sections 36.41 in a circumferential πng of repeating pattern A is the same within the πng. and is reversed with respect to the phase of curved sections 36,41 in an adjacent circumferential πng of repeating pattern B With further reference to repeating pattern A m Figure 1 , a strut 70 has been added to connect segment 54 of concave-shaped wall 50 and segment 64 of 15 convex-shaped w all 60 - this may be regarded as a "closed design" Further, strut 70 includes a curved section 71 along the length thereof Thus, strut 70 may be considered as a relatively thin retention segment which reconciles the need for retaining flexibility in the strut w ith mitigating lifting of rounded shoulders 57.58 when the strut is delivered to the target for a passageway through a relatively tortuous route As will be apparent to those of skill in the art. the provision of strut 70 is optional and mav be omitted When strut 70 is omitted from repeatmg pattern A and/or repeating pattern B, the design may be regarded as an "open design" Thus, the terms "closed design" and "open design" are used in a relative sense

It should be noted that curved sections 36 and 71 are of the same size and differ in size from curved section 41 A distinct advantage of the interspersion of curved sections 36,41 ,71 in repeatmg pattern A and or repeatmg pattern B is that substantially umformal radial expansion of all segments in the stent will occur without specific regard to the expansion forces generated by the balloon or other means used to deploy the stent Further, a specific design illustrated herein minimizes the force (e g , pressure from a balloon) required to expand the stent As will be further apparent to those of skill in the an. curved sections 36 and 41 are offset with respect to one another in a plane noπzontal to the longitudinal axis of tubular wall 10 The offset nature of these curved sections serves to increase the bending points m the stent allow ing the stent to bend while avoiding bucking thereof Thus, the staged distπbution of curved portions over a large portion of the surface area of the stent serves to improv e the flexibility of the stent

It will be further appreciated by those of skill in the art that the shape of concave-shaped wall 50 and/or con ex-shaped wall 60 can be modified without departing from the function and performance of the stent provided that at least one of concave-shaped w all 50 and convex-shaped w all 60 retain a substantially flat apex For example, the tπo of segments can be replaced by a suitable curved or arcuate wall Alternatively, more than t o segments can be used to define concave-shaped wall 50 and/or convex-shaped wall 60 Other modifications will be apparent to those of skill m the art

It will be further appreciated by those of skill in the art that vaπous 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 spiπt and scope of the invention For example, it is possible to omit one or both of side walls 35,40 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 of segment 62.64.66 at selected points along the body of the stent with a view to improving the lateral flexibilitv of stent

Still further, the design depicted in Figure 1 can be modified to omit, on a selected basis, first repeating pattern A and or second repeating pattern B with a view to improving flexibility of the stent and to allow access to other structures (e g , side branches/arteπes) outside the bounds of the stent As discussed above, the use of flexure means, such as the curved sections referred to in Figure 1, 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 to bend to compress w hile concurrently allowing the outer stent surface adjacent to bend to extend all while maintaining substantially mtact the mtπcal strength of the stent and avoiding buckling of the stent

The manner by which the present stent is manufactured is not particularly restπcted Preferably, the stent is produced by laser cutting techniques applied to a tubular starting mateπal Thus, the starting mateπal could be a thm tube of a metal or alloy (non-hmitmg 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 abov e Thus, the preferred design of the present stent is one of a tubular wall which is distinct from pπor art wire mesh designs wherein wire is conformed to the desired shape and welded m place The preferred tubular wall design of the present stent facilitates production and improves quality control by avoidmg 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-(tπmethylammonιum ethyl) phosphate inner salt with lauryl methaciylate m ethanol (as descπbed in Example 2 of International patent application WO-A-93/01221 ) as follows The non-expanded stent may be placed m a tube having a slightly larger diameter than the stent The tube may then be filled with coating solution and the solution allowed to dram 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°C for a peπod 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-(tπrnethvlammonιum ethvl) phosphate inner salt, 47 mole % lauryl methaciylate, 5 mole % γtπmethoxvsilylpropyl methaciylate and 25 mole % of γhydroxypropyl methacrylate This may be apphed to the sent by the above descπbed technique from a 5mg/ml ethanoic solution The solution may be dπed as descπbed above and then cured by heating at 70 to 75°C for a peπod of at least about 1 hour, for instance overnight This cuπng generally results in substantially complete reaction of the methoxv silyl groups, either with other methoxylsily groups or with hvdroxv groups deπved from the hydroxypropyl methacrylate monomer, dπving off methanol In one preferred embodiment the crosslmkable coating is applied to the cleared stent, cured and then a further coating of the lauryl methacrylate copolvmer descπbed above is applied The coated stent may be steπhsed by ethvlene oxide, gamma radiation or electron beam and subsequently mounted onto a balloon catheter for delivery

The present stent can be implanted using a conventional system wherein a guidewire. catheter and balloon can be used to position and expand the stent Implantaion of mono-tubular stents is conventional and with the purview of a person skilled m the art See, for example, any one of United States patents 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 anv of the references cited therein or anv of the references cited heremabove 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 aha, 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 of stent 10 can be accomplished by vaπous other means For example, it is contemplated that the stent can be made of a suitable mateπal which will expand when a certain temperature is reached In this embodiment, the mateπal may be a metal alloy (e g nitmol) capable of self-expansion at a temperature of at least about 30°C, preferably in the range of from about 30° to about 40°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 withm the stent itself Further, stent 10 can be designed to expand upon the application of mechanical forces other than those apphed by a balloon/catheter For example, it is possible to implant stent 10 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 (l e. provided by the sleeve or membrane) is removed

While this invention has been descπbed with reference to illustrative embodiments, this descπption is not intended to be construed m a limiting sense Vaπous 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 descπption It is therefore contemplated that the appended claims will cover any such modifications or embodiments

Claims

What is claimed is:

1 An expandable stent comp╧Çsmg 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 repeatmg pattern comp╧Çsed of a polygon having a pair of side walls substantially parallel to the longitudinal axis, each side wall comp╧Çsmg first and second flexure means of the same phase with respect 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

2. The stent defined in claim 1 , wherein the each of the first and second flexure means comp╧Çse lateral section disposed in each longitudinal strut.

3 The stent defined in claim 2, wherein the lateral section comp╧Çses a pointed apex

4 The stent defined in claim 2. wherein the lateral section comp╧Çses a rounded apex

5. The stent defined in claim 2. wherein the lateral section comp╧Çses a flat apex

6 The stent defined in claim 5, wherein the first flexure means and the second flexure means are symmet╧Çc

7 The stent defined in claim 5, wherein the first flexure means and the second flexure means are asymmet╧Çc

8. The stent defined in claim 7, wherein the first flexure means and the second flexure means have substantially the same shape and differing size.

9. The stent defined in claim 7, wherein the first flexure means and the second flexure means have differing shape and size.

10. The stent defined in any one of claims 6-9, wherein the first lateral section and the second lateral section have substantially the same shape and differing size.

11. The stent defined in any one of claims 1-10, wherein one or both of the first flexure means and the second flexure means comprises a curved section having an arc of greater than 180┬░.

12. The stent defined in any one of claims 1-10, wherein one or both of the first flexure means and the second flexure means comprises a curved section having an arc of about 180┬░.

13. The stent defined in any one of claims 11-12. wherein the curved sections are of substantially the same size.

14. The stent defined in any one of claims 11 -12, wherein the curved sections are of different size.

15. The stent defined in any one of claims 1-14, wherein the stent is constructed of stainless steel.

16. The stent defined in any one of claims 1-14, wherein the stent is constructed of a self-expanding material.

17. The stent defined in claim 16, wherein the self-expanding material is national.

18. The stent defined in claim 16, wherein the self-expanding material expands at a temperature of greater than about 30┬░C.

19. The stent defined in claim 16, wherein the self-expanding material expands at a temperature of in the range of from about 30┬░ to about 40┬░C.