US20080177376A1 - Stent With Improved Flexibility and Method for Making Same - Google Patents

Abstract

A stent and a method for manufacturing a stent are provided. The stent includes a first ring having a plurality of peaks and a plurality of valleys, a second ring having a plurality of peaks and a plurality of valleys, and a connector that connects one of the peaks of the first ring to one of the valleys of the second ring. The connected peak of the first ring includes a deformed portion that extends towards the connected valley of the second ring. The method includes forming a first ring having a plurality of peaks and a plurality of valleys, forming a second ring having a plurality of peaks and a plurality of valleys, deforming a portion of at least one of the peaks of the first ring, and connecting the deformed portion of the peak of the first ring to one of the valleys of the second ring.

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates generally to a stent with improved flexibility. More specifically, the present invention relates to a welded stent having increased flexibility at the welded connections.
• 2. Description of Related Art
• A stent is a prosthesis that is inserted into a body lumen and used, for example, for treating stenoses, strictures, and/or aneurysms therein. In the event of a stenosed vessel, a stent may be used to prop open the vessel after an angioplasty procedure. Once opened, the stent forms to the inner wall of the vessel, remains in place, and may help prevent restenosis. Additionally, in the event of an aneurysm or weakened vessel wall, stents may be used to provide support to, and reinforce the vessel wall.
• To perform such functions, stents in the past have included many different structures. For example, previously disclosed stents include coiled stainless steel springs, helical wound springs, and generally serpentine configurations with continuous waves of generally sinusoidal character. Some of these stents self deploy when placed in the vessel, whereby stent expansion is primarily achieved by removing a restraint mechanism holding the stent in a constricted state. Other types of stents rely on alternate means to deploy, for example, use of a balloon catheter system, whereby balloon dilation expands and deploys the stent.
• One of the major complications associated with using stents has been thrombosis. This complication is caused by clotting in the vicinity of the stent and is associated with high morbidity and mortality. It has been shown that the better the stent apposition against the vessel wall and the larger the lumen, the less likely that this complication will occur. A further complication is restenosis, which is caused by tissue proliferation around the angioplasty site. To minimize the potential for restenosis, the stent should cover the lesion and not leave any significant gaps in which restenosis may occur. The stent should also adhere to the inner wall of the vessel as much as possible.
• Accordingly, when a stent deploys in a restricted vessel, adequate radial strength is required to overcome the strictures and ensure apposition of the stent to the vessel wall. Radial strength is a force produced by the stent acting at all points on the vessel wall in an outwardly direction perpendicular to the vessel wall. Stents are designed with circumferential rings to provide most of the radial strength needed to overcome radial forces pushing inwardly against the stent as the stent expands.
• Many stents also include longitudinal links that primarily act to attach longitudinally adjacent circumferential rings, but also add radial strength and stent stability. Once the stent is fully deployed, in addition to providing adequate radial strength, the stent must provide adequate vessel wall coverage, hereinafter referred to as scaffolding affect. Scaffolding affect is defined as the amount of area of the vessel wall covered by the stent, once the stent is fully deployed. The circumferential rings and longitudinal links connecting the circumferential rings have traditionally provided the needed scaffolding affect. Other stents include welded connections between longitudinally adjacent circumferential rings.
• Further, to meet the demands of adequate radial strength and scaffolding affect, conventional stents have been designed with circumferential rings manufactured with adequate ring width, which were then continuously connected at each peak and valley or trough by longitudinal links. However, such conventional stents suffer from predilation stent longitudinal rigidity. Predilation or crimped stent longitudinal rigidity is a resistance to movement and decreased flexibility of the stent along the stent's longitudinal axis. Accordingly, predilation longitudinal stent rigidity makes it much harder and oftentimes even impossible to thread the stent through long tortuous vessels and past constrictions and lesions.
• Past attempts have been made to overcome predilation stent longitudinal rigidity. Such attempts have included designs with decreased ring width, often referred to as decreased wire gauge, which resulted in increased longitudinal flexibility but decreased radial strength. These conventional designs have resulted in inadequate stent apposition and/or inadequate vessel wall support. Additionally, past attempts to increase longitudinal flexibility have included designs where longitudinal links are not attached to each peak and valley of the circumferential ring. Thus, only some of the peaks and valleys of adjacent circumferential rings are connected by longitudinal links. This increases longitudinal flexibility but decreases the scaffolding affect of the stent. The decreased scaffolding affect creates areas where the vessel wall is not adequately covered by the stent, which may lead to thrombosis and/or restenosis.
• Additionally, in order to meet the requirements of drug eluting stents, conventional stent substrates have been designed with circumferential elements manufactured with adequate ring/strut/apex width, which were then continuously connected at each peak and valley by longitudinal links. However, such conventional stents may suffer from abrasion or damage due to adjacent apexes (i.e., peaks and valleys) interacting during crimping and tracking, which may be caused by the close proximity of adjacent apexes coming into contact with one another due to links or weld not providing adequate clearance. This interaction may cause abrasion or damage during the coating of the stent with a drug and/or polymer or during tracking of the stent through the anatomy.
• Accordingly, there arises the need for a stent, which provides adequate radial strength, scaffolding affect, with increased apex spacing and longitudinal flexibility. It is among the objects of the present invention to provide a stent that overcomes the foregoing shortcomings and meets the needs discussed above.
SUMMARY OF THE INVENTION
• One aspect of the present invention provides a stent having improved longitudinal flexibility and minimal apex to apex (i.e., peak to valley) interaction between adjacent rings.
• In an embodiment of the present invention, a stent is provided. The stent includes a first ring having a plurality of peaks and a plurality of valleys, a second ring having a plurality of peaks and a plurality of valleys, and a connector connecting one of the peaks of the first ring to one of the valleys of the second ring. The connected peak of the first ring includes a deformed portion that extends towards the connected valley of the second ring.
• Another aspect of the present invention provides a method for manufacturing a stent with improved longitudinal flexibility and increased apex to apex spacing between adjacent rings.
• In an embodiment of the present invention, a method for manufacturing a stent is provided. The method includes forming a first ring having a plurality of peaks and a plurality of valleys, forming a second ring having a plurality of peaks and a plurality of valleys, deforming a portion of at least one of the peaks of the first ring, and connecting the deformed portion to one of the valleys of the second ring.
• In another embodiment of the present invention, a method for manufacturing a stent is provided. The method includes forming a first ring having a plurality of peaks and a plurality of valleys, forming a second ring having a plurality of peaks and a plurality of valleys, connecting one of the peaks of the first ring to one of the valleys of the second ring, and deforming a portion of the connected peak of the first ring.
• The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
• FIG. 1 illustrates a stent in accordance with an embodiment of the invention;
• FIG. 2 illustrates a detailed view of a connection between two adjacent rings of a conventional welded stent;
• FIG. 3 is a cross-sectional view taken along line3-3 inFIG. 2;
• FIG. 4 illustrates a detailed view of a connection between two adjacent rings of a stent according to an embodiment of the invention;
• FIG. 5 is a cross-sectional view taken along line5-5 inFIG. 4;
• FIG. 6 is a perspective view of a distal end of an embodiment of a tool used to manufacture the stent ofFIG. 1;
• FIG. 7 is a side view of the tool ofFIG. 6 just before it is applied to one of the rings ofFIG. 4 in accordance with an embodiment of the invention;
• FIG. 8 is a side view of the tool ofFIG. 6 just after it has been applied to the ring ofFIG. 7;
• FIG. 9 is a side view of a portion of an apparatus used to manufacturing the stent ofFIG. 1 according to another embodiment of the invention; and
• FIG. 10 is a perspective view of a distal end of a tool of the apparatus ofFIG. 9.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
• The foregoing and other features and advantages of the invention will be apparent from the following, more detailed description of the preferred embodiment of the invention, as illustrated with reference to the Figures. While specific embodiments are discussed in detail, it should be understood that this is done for illustrative purposes only. A person skilled in the art will recognize that other embodiments can be used without departing from the spirit and scope of the invention.
• FIG. 1 illustrates astent10 according to an embodiment of the invention. As illustrated, thestent10 includes a plurality of circumferential rings12 that are each in the shape of a sinusoid. Eachring12 includes a plurality ofpeaks14 and a plurality ofvalleys15 that are connected to each other by a plurality ofsegments16. Aproximal end18 of the sinusoid has been arbitrarily labeled “peak” and adistal end20 of the sinusoid has been arbitrarily labeled “valley.” It would be understood by one of ordinary skill in the art that thepeaks14 andvalleys15 have been labeled for illustrative purposes and ease of understanding and that the terms may be switched.
• Eachring12 may be formed from a single piece of material, such as a metal wire, or each ring/element12 may be cut from a metal tube. Forrings12 that are formed from a single wire, the ends of the wire may be welded together so as to form a continuous ring. The material used to fabricate therings12 can be made of an inert, biocompatible material with high corrosion resistance that can be plastically deformed at low-moderate stress levels such as tantalum, or moderate to high stress levels such as L605, MP35N, or any other high work hardening rate material. Other acceptable materials include, but are not limited to, nickel titanium, stainless steel, titanium ASTM F63-83 Grade 1, niobium, cobalt-chromium (Co—Cr) alloys, and other cobalt-based alloys. A self-expanding device can be made by the use of superelastic NiTi, such as nitinol. As discussed in further detail below, a single ring may be connected to an adjacent ring with aconnector22, such as aweld24, so as to form a flexible connection between the rings.
• FIGS. 2 and 3 illustrate a conventional connection betweenadjacent rings12a′,12b′ of astent10′. As illustrated, therings12a′,12b′ may be connected with aconnector22′. In the illustrated embodiment, theconnector22′ is aweld24′. During the manufacturing process, theadjacent rings12a′,12b′ are placed in contact with each other so that a peak14a′ of onering12a′ contacts avalley15b′ of anadjacent ring12b′. Theweld24′ is then created at the contact point of the peak14a′ andvalley15b′ so as to form theconnector22′. Theweld24′ may be created by conventional welding techniques, including but not limited to butt welding, resistance welding, and/or laser welding. As shown inFIG. 2, the resultingweld24′ has a length of d₁. Such a configuration may provide a connection with limited flexibility, because the peak14a′ andvalley15b′ are abutted against each other, and the length d₁of theweld24′ is relatively short. In order to increase the length of the weld, thepeaks14a′ and thevalley15b′ of theadjacent rings12a′,12b′ would have to be spaced further apart before theweld24′ is created, which may lead to inconsistent weld lengths and/or weaker connections.
• FIGS. 4 and 5 illustrate a connection betweenadjacent rings12a,12baccording to an embodiment of the invention. As illustrated, a peak14aof one of therings12aincludes adeformed portion26aandnon-deformed portions28athat are on opposite sides of thedeformed portion26a. Similarly, avalley15bof theadjacent ring12bincludes adeformed portion26bandnon-deformed portions28bthat are on opposite sides of thedeformed portion26b. Thedeformed portions26a,26bmay be created by methods discussed in further detail below. In the illustrated embodiment, therings12a,12bare connected with aconnector22 in the form of aweld24.
• As shown in greater detail inFIG. 5, thedeformed portions26a,26beach include arecess30a,30b, respectively, that are recessed from the respectivenon-deformed portions28a,28bof the peak14aand thevalley15b, respectively. As discussed in further detail below, as eachrecess30a,30bis created, at least oneextension32a,32b, respectively, is also created, due to the displacement of the material. In an embodiment, one of theextensions32aof therecess30aextends in a direction that is toward thevalley15bof theadjacent ring12b, as shown inFIG. 6, and theother extension32aextends in a direction that is away from thevalley15bof theadjacent ring12b. Although twoextensions32aare illustrated, in some embodiments, therecess30amay only include a single extension that extends towards thevalley15bof theadjacent ring12b. The illustrated embodiment is not intended to be limiting in any way.
• As discussed in further detail below, thedeformed portions26a,26bmay be created by work hardening (e.g., cold-working) the material in the peak14aand thevalley15b, respectively, such that the material plastically deforms, thereby creating therecesses30a,30band theextensions32a,32b. As a result of work hardening the material, thedeformed portions26a,26bmay have a hardness that is greater than the hardness of thenon-deformed portions28a,28bof the peak14aand thevalley15b, respectively.
• In an embodiment, the material in thedeformed portions26a,26bhave a hardness that is at least about 20%, and preferably between about 20% and about 40%, higher than the hardness of the material in thenon-deformed portions28a,28bdue to the work hardening of the material. For example, in an embodiment, thering12amay be made from annealed stainless steel, or Co—Cr alloy having a Vickers hardness of about 220 HV, while the hardness of the material of thedeformed portion26athat has been work-hardened may be about 300 HV, which is an increase of about 36%.
• Of course, the actual amount of increase in hardness of the material in thedeformed portion26awill depend on the material, the degree of deformation, the working temperature, and the amount and duration of pressure that is applied to the material. The same considerations apply to the deformation of thevalley15bof theadjacent ring12b, if applicable. In some embodiments, only the peak of one ring is deformed and is connected to a non-deformed valley of an adjacent ring. The illustrated embodiment is not intended to be limiting in any way.
• By creating thedeformed portions26a,26bin the peak14aand thevalley15b, respectively, by work hardening the material, not only are theextensions32a,32bcreated, but the strength of theextensions32a,32bmay be increased. This may allow the connection between the peak14aand thevalley15bto be more flexible, yet stronger. Increased flexibility may be achieved by allowing thenon-deformed portions28a,28bof the peak14aand thevalley15bin theadjacent rings12a,12b, respectively, to be spaced apart at a greater distance than other connected peaks and valleys, such as the peak14a′ andvalley15b′ illustrated inFIGS. 2 and 3 and discussed above.
• For example, as discussed above, in the conventional weldedstent10′, theweld24′ has a length of d₁. However, in the embodiment illustrated inFIG. 4, theweld24 of thestent10 has a length d₂, which is greater than d₁due to the presence of theextensions32a,32bof thedeformed portions26a,26bof the peak14a, and thevalley15b, respectively. The longer weld24 (as compared to theweld24′ illustrated inFIGS. 2 and 3) may improve the flexibility of theconnector22, while the work hardened material in thedeformed portions26a,26bmay increase the strength of theconnector22. In other words, the presence of theextensions32a,32bwithin theweld24 may increase the strength of the connection between theadjacent rings12a,12b, and at the same time provide a more flexible connection.
• Theweld24 may be created by conventional welding techniques, including but not limited to butt welding, resistance welding, and/or laser welding. In addition, it is contemplated that theconnector22 may not be in the form of a weld per say, and may be created by soldering or brazing.
• In an embodiment, heat may be generated at the peak14aand thevalley15bwith a laser, so as to cause the material in the peak14aand thevalley15bto flow together, thereby creating theweld24. As theweld24 is created, an inert gas, such as argon or helium, may be used to flood the weld area at a sufficient flow rate to prevent oxidation so that theweld24 does not become brittle. Of course, other welding techniques may be used, and the above-described method should not be considered to be limiting in any way.
• FIG. 6 shows an embodiment of atool40 that may be used to create thedeformed portion26aof the peak14aof thering12adescribed above. Of course, thesame tool40 may be used to create thedeformed portion26bof thevalley15bof thering12bas well. Thetool40 is preferably fabricated from a material having a greater hardness than the material used to form thering12a. In the embodiment illustrated inFIG. 6, thetool40 includes apunch42 that has a circular cross-section and adistal end44 that is flat. Of course, thepunch42 may have other cross-sectional shapes, such as ellipsoid, rectangular, etc. The illustrated embodiment of thepunch42 is not intended to be limiting in any way.
• Asupport46 may be placed inside thering12 so that it contacts aninside surface48 of the peak14a, as shown inFIG. 7. Thesupport46 may be a mandrel, or any other structure that is configured to support thering12aas thepunch42 is used to create thedeformed portion26aof the peak14a. After thering12ahas been properly positioned on thesupport46, thepunch42 may engage anoutside surface50 of the peak14aat a location of the peak14awhere thedeformed portion26ashould be created. With the peak14apositioned between thesupport46 and thepunch42, suitable pressure may be applied to thepunch42 until the desired amount of deformation takes place, as shown inFIG. 8. The suitable pressure should be enough pressure to cause the material of the peak14ato flow, yet not too great to cause the material at the peak14ato fracture. As would be appreciated by one of ordinary skill in the art, the stress-strain curve of the material used to form therings12 may be used to select the suitable pressure. After the desired amount of deformation has taken place, thepunch42 may be removed from the peak14a, thereby leaving thedeformed portion26abehind.
• In another embodiment, thedeformed portions26a,26bmay be formed simultaneously by using anapparatus52 illustrated inFIG. 9. As illustrated, theapparatus52 includes amandrel54 on which therings12 of thestent10 are placed. Theapparatus52 also includes a plurality oftools40 that are aligned along themandrel54 such that thetools40 are axially aligned with thepeaks14 of therings12. In an embodiment, illustrated in greater detail inFIG. 10, thetool40 includes aroller56 at a distal end thereof. Themandrel54 may be rotated and thetools40 may be moved towards the mandrel so that eachroller56 may engage theouter surfaces46 of thepeaks14. As shown, asingle roller56 may engage apeak14 of one ring and avalley15 of anadjacent ring12 at the same time. Of course, other arrangements may be used. For example, if deformed portions26 are to be created in onlycertain peaks14 and/orvalleys15, rather than all of thepeaks14 andvalley15, themandrel54 and therollers56 may be indexed so that therollers56 only contact thepeaks14 in which the deformed portions26 are to be created. The illustrated embodiment is not intended to be limiting in any way.
• In another embodiment, that peak14aand thevalley15bofadjacent rings12a,12bmay first be welded together, as shown inFIG. 2, and the tool40 (either with thepunch48 ofFIG. 6 or theroller56 ofFIG. 10) may then be used to create thedeformed portions26a,26bof the peak14aand thevalley15b, respectively, in the manner discussed above. Both methods are contemplated as being within embodiments of the present invention.
• While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims (38)

1. A method for manufacturing a stent, the method comprising:

forming a first ring having a plurality of peaks and a plurality of valleys;

forming a second ring having a plurality of peaks and a plurality of valleys;

deforming a portion of at least one of the peaks of the first ring; and

connecting the deformed portion to one of the valleys of the second ring.

2. The method according toclaim 1, wherein the first ring is formed from a first continuous wire.

3. The method according toclaim 2, wherein the second ring is formed from a second continuous wire.

4. The method according toclaim 1, wherein said deforming comprises work hardening the portion.

5. The method according toclaim 4, wherein the Vicker hardness value of the deformed portion of the peak increases by at least about 20% during said work hardening.

6. The method according toclaim 5, wherein the Vicker hardness value of the deformed portion of the peak increases by about 20% to about 40% during said work hardening

7. The method according toclaim 1, further comprising deforming a portion of at least one of the valleys of the second ring, and wherein said connecting comprises connecting the deformed portion of the at least one peak of the first ring to the deformed portion of the at least one valley of the second ring.

8. The method according toclaim 7, wherein said deforming the portion of the at least one valley of the second ring comprises work hardening the portion of the at least one valley.

9. The method according toclaim 8, wherein the Vicker hardness value of the deformed portion of the valley of the second ring increases by at least about 20% during said work hardening.

10. The method according toclaim 9, wherein the Vicker hardness value of the deformed portion of the valley of the second ring increases by about 20% to about 40% during said work hardening.

11. The method according toclaim 7, wherein the deformed portion of the peak of the first ring and the deformed portion of the valley of the second ring contact each other during said connecting so as to space apart non-deformed portions of the peak and non-deformed portions of the valley.

12. The method according toclaim 1, wherein said deforming comprises pressing a tool against the portion.

13. The method according toclaim 12, wherein the tool comprises a punch.

14. The method according toclaim 12, wherein the tool comprises a roller.

15. The method according toclaim 1, wherein said connecting comprises welding.

16. A method for manufacturing a stent, the method comprising:

forming a first ring having a plurality of peaks and a plurality of valleys;

forming a second ring having a plurality of peaks and a plurality of valleys;

connecting one of the peaks of the first ring to one of the valleys of the second ring; and

deforming a portion of the connected peak of the first ring.

17. The method according toclaim 16, further comprising deforming a portion of the connected valley of the second ring.

18. The method according toclaim 17, wherein said deforming the portion of the connected valley of the second ring comprises work hardening.

19. The method according toclaim 18, wherein the Vicker hardness value of the deformed portion of the valley of the second ring increases by at least about 20% during said work hardening.

20. The method according toclaim 19, wherein the Vicker hardness value of the deformed portion of the valley of the second ring increases by about 20% to about 40% during said work hardening.

21. The method according toclaim 16, wherein said deforming comprises work hardening.

22. The method according toclaim 21, wherein the Vicker hardness value of the deformed portion of the peak increases by at least about 20% during said work hardening.

23. The method according toclaim 22, wherein the Vicker hardness value of the deformed portion of the peak increases by about 20% to about 40% during said work hardening.

24. The method according toclaim 16, wherein said deforming comprises pressing a tool against the portion.

25. The method according toclaim 24, wherein the tool comprises a punch.

26. The method according toclaim 24, wherein the tool comprises a roller.

27. The method according toclaim 16, wherein said connecting comprises welding.

28. A stent comprising:

a first ring having a plurality of peaks and a plurality of valleys;

a second ring having a plurality of peaks and a plurality of valleys; and

a connector connecting one of the peaks of the first ring to one of the valleys of the second ring, the connected peak of the first ring comprising a deformed portion that extends towards the connected valley of the second ring.

29. The stent according toclaim 28, wherein the deformed portion of the peak has a Vickers hardness value that is at least about 20% greater than the Vickers hardness value of non-deformed portions of the peak.

30. The stent according toclaim 29, wherein the deformed portion of the peak has a Vickers hardness value that is about 20% to about 40% greater than the Vickers hardness value of non-deformed portions of the peak.

31. The stent according toclaim 28, wherein the connected valley of the second ring comprises a deformed portion that extends towards the connected peak of the first ring.

32. The stent according toclaim 31, wherein the deformed portion of the valley of the second ring has a Vickers hardness value that is at least about 20% greater than the Vickers hardness value of non-deformed portions of the valley of the second ring.

33. The stent according toclaim 32, wherein the deformed portion of the valley of the second ring has a Vickers hardness value that is about 20% to about 40% greater than the Vickers hardness value of non-deformed portions of the valley of the second ring.

34. The stent according toclaim 31, wherein the deformed portion of the peak of the first ring and the deformed portion of the valley of the second ring contact each other so as to space apart the non-deformed portions of the peak and the non-deformed portions of the valley.

35. The stent according toclaim 31, wherein the connector comprises a weld that contacts the deformed portion of the peak of the first ring and the deformed portion of the valley of the second ring.

36. The stent according toclaim 35, wherein the connector comprises a weld that contacts the deformed portion.

37. The stent according toclaim 28, wherein the first ring is formed from a first continuous wire.

38. The stent according toclaim 37, wherein the second ring is formed from a second continuous wire.

Images