US20080294244A1 - Stent having helical elements - Google Patents

Abstract

An expandable stent comprised of a plurality of helical segments is disclosed. In one embodiment, the stent is generally cylindrical in shape having a cylindrical axis, and comprises a first and second set of helical segments. The helical segments in the first set are substantially parallel and have a first pitch forming a first helical angle with respect to the cylindrical axis. The helical segments in the second set are also generally parallel to each other and form a second pitch that differs from the first pitch, thereby forming a second helical angle with respect to the cylindrical axis. In an alternative embodiment, the stent comprises one set of helical segments and a plurality of circumferential elements that are joined together by the helical segments to form a plurality of cylindrical elements which are joined together to form a stent body. The stent may also have endzones.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application is a continuation of U.S. patent application Ser. No. 12/027,382, filed on Feb. 7, 2008, which application is a continuation of U.S. patent application Ser. No. 10/014,705, filed on Dec. 11, 2001, now issued U.S. Pat. No. 7,329,277, which application claims the benefit of U.S. Provisional Application No. 60/254,688, filed on Dec. 11, 2000, all of which are hereby incorporated in their entirety by reference. U.S. patent application Ser. No. 10/014,705 is also continuation-in-part of U.S. patent application Ser. No. 09/511,481, filed on Feb. 23, 2000, now U.S. Pat. No. 7,108,714, which is a continuation of U.S. patent application Ser. No. 09/094,402, filed Jun. 10, 1998, now U.S. Pat. No. 6,117,165, all of which are hereby incorporated in their entirety by reference.
FIELD OF THE INVENTION
• The present invention relates to prosthetic stents. In particular, the present invention relates to stents having helical elements and to methods for manufacturing the stents of the present invention.
BACKGROUND OF THE INVENTION
• Stents are prosthetic devices that are implanted in the lumen of a vessel inside the body to provide support for the vessel's wall. Structural support from stents is particularly important in angioplasty procedures. Typically, stents are implanted within a vessel system to reinforce vessels that are partially occluded, collapsing, weakened, or abnormally dilated. More generally, stents can be used inside any physiological conduit or duct including, for example, arteries, veins, bile ducts, the urinary tract, alimentary tracts, the tracheobronchial tree, a cerebral aqueduct or the genitourinary system. Stents may be used in both humans and animals.
• There are typically two types of stents: self expanding stents and balloon expandable stents. Self expanding stents automatically expand once they are released and assume a deployed, expanded state. A balloon expandable stent is expanded using an inflatable balloon catheter. The balloon is inflated to plastically deform the stent. Balloon expandable stents may be implanted by mounting the stent in an unexpanded or crimped state on a balloon segment of a catheter. The catheter, after having the crimped stent placed thereon, is inserted through a puncture in a vessel wall and moved through the vessel until it is positioned in the portion of the vessel that is in need of repair. The stent is then expanded by inflating the balloon catheter against the inside wall of the vessel. Specifically, the stent is plastically deformed by inflating the balloon so that the diameter of the stent is increased and remains at an increased state. In some situations, the vessel in which the stent is implanted may be dilated by the stent itself when the stent is expanded.
• The Palmaz-Schatz™ stent, which is disclosed in the Handbook of Coronary Stents by Patrick W. Serruys et al. (Martin Dunitz, LTD 1998), is an example of a balloon expandable stent that had been implanted in hundreds of thousands of patients. The Palmaz-Schatz™ stent, like other known stents, has certain limitations. These include, but are not limited to: (i) low stent-to-vessel ratio uniformity, (ii) comparative rigidity of the stent in a crimped as well as deployed state, and (iii) limited flexibility making delivery and placement in narrow vessels difficult. Stent-to-vessel ratio generally refers to the degree that the vessel wall is supported by the stent in its expanded state and preferably should be uniform throughout the length of the stent. Furthermore because the Palmaz-Schatz™ stent consists of one or more bridges that connect a number of consecutively slotted tubes, there are a number of bare areas in the vessel after the expansion of the stent. These shortfalls are common to many stents. Id. at36.
SUMMARY OF THE INVENTION
• The present invention is directed to expandable stents that have relatively uniform stent-to-vessel ratios when expanded and other desirable properties, as well as methods for making these stents. The stents of the present invention comprise a generally cylindrically shaped main body having a plurality of expandable helical segments. The main body is comprised of a plurality of cylindrical main body elements that are joined together by the helical segments. The cylindrical elements have cylindrical axes that are collinear with the cylindrical axis of the main body. The cylindrical elements are formed from a plurality of circumferential elements that are joined together by the expandable helical segments. In some embodiments, the stent may comprise endzones that straddle the main body.
• In one embodiment of the present invention, the stent may comprise a first non-helical endzone and a second non-helical endzone that straddle the main body. The main body is generally cylindrically shaped and has a cylindrical axis. A plurality of adjacent main body cylindrical elements are connected together to form the main body of the stent. Each main body cylindrical element may be comprised of a plurality of expandable first and second circumferential elements. In some embodiments, the second circumferential elements have a circumferential dimension less than the circumferential dimension of the first circumferential elements. In yet other embodiments, the first and second circumferential elements have the same circumferential dimensions and are substantially identical except that, with respect to the cylindrical axis of the stent, they are oriented differently. Each second circumferential segment in each main body cylindrical element is connected to two first circumferential segments. In addition, each second circumferential segment in each main body cylindrical element is connected to a second circumferential segment in an adjoining main body cylindrical element thereby forming a plurality of helixes in the main body of the stent.
• In one embodiment, the main body may be comprised of a plurality of first helical segments each having a substantially identical first pitch and a plurality of second helical segments, each having a substantially identical second pitch. The first and second pitches are generally different. In at least one embodiment, the second pitch is twice that of the first, and at least one first helical segment crosses one of the second helical segments.
• The stents of the present invention may be manufactured from a tubular member by removing material from the tube to form a first endzone region, a second endzone region, and a middle region. By removing material from the middle region a plurality of parallel helical segments will remain and a plurality of circumferential segments will remain connecting the helical segments. Alternatively, the stent may be formed from a tube by removing material such that at least two sets of helical segments remain with each set having a different pitch.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a three dimensional view of one embodiment of a stent according to the present invention in its unexpanded state.
• FIG. 2 is planar view of a flattened portion of the circumference of the stent inFIG. 1.
• FIG. 3 is an enlarged portion ofFIG. 2.
• FIG. 4 is another planar view of a flattened portion of the circumference of a stent according to the present invention in its unexpanded state.
• FIG. 5 is an enlarged view of a portion ofFIG. 4 showing a first circumferential element of the stent.
• FIG. 6 is an enlarged view of a portion ofFIG. 4 showing a second circumferential element of the stent.
• FIG. 7 is a planar view of a flattened portion of the stent inFIG. 1 showing a plurality of sets of helical segments propagating through the stent's body.
• FIG. 8 is a planar view of a flattened endzone that may be employed in a stent of the present invention.
• FIG. 9 is a planar view of a flattened portion of part of the endzone shown inFIG. 8.
• FIG. 10 is a planar view of a flattened portion of an expandable stent according to the present invention, after the stent has been deployed in a lumen.
• FIG. 11 is three dimensional view of an alternative embodiment of the present invention.
• FIG. 12 is a three dimensional view of an another stent according to the present invention.
• FIG. 13 is a planar view of the stent shown in12.
• FIG. 14 is a detailed view of a portion ofFIG. 13.
• FIG. 15 is a detailed view of another portion ofFIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
• The present invention is directed to an expandable stent, as well as a method of manufacturing the stent. In one embodiment, as is shown inFIGS. 1 and 2, the stent comprises a generally cylindrical shapedmain body section11 having acylindrical axis5 and awall thickness103. Thewall thickness103 may optionally be uniform throughout the stent. Themain body section11 is comprised of a plurality ofhelical segments30 and40 and a plurality of main bodycylindrical elements100, each having cylindrical axes (not shown) that are collinear with the main bodycylindrical axis5. The main bodycylindrical elements100 are each comprised ofcircumferential elements50 that are joined together by thehelical segments30 and40 to formindividual cylinders100.
• The stent may also have afirst endzone10 and asecond endzone20 that straddle thebody section11. In some embodiments, such as the one shown inFIG. 1, theendzones10 and20 may advantageously provide the stent with squareouter edges8. The stent may be manufactured from stainless steel, or other suitable materials. In most embodiments, it is desirable that the material, or a portion of the material, be radiopaque and that the various segments that form the stent be contiguous. Although, in some embodiments, the various segments that make up the stent can be distinct elements that are joined together.
• Themain body11, shown inFIGS. 1 and 2, may be formed in numerous ways. For example, thebody11 may contain two or more firsthelical segment30 and40 that are generally parallel to each other. In some embodiments they may be opposite each other by 180.degree. In general, the firsthelical segments30 and40 will be spaced equidistant along thecircumference110 of themain body11. The firsthelical segments30 and40 are joined by a plurality ofcircumferential segments50 to form a plurality of main bodycylindrical elements100, which may be only generally cylindrically shaped. In one embodiment, thecircumferential segments50 make up a majority of thecircumference110 of eachcylindrical element100. In addition to joining thecircumferential elements50 to formcylindrical elements100, thehelical segments30 and40 connect eachcylindrical element100 to an adjacentcylindrical element100 to form themain body11.
• As is shown inFIGS. 2 and 3, the body of thestent11 may comprise a plurality of main bodycylindrical elements100 formed from firstcircumferential segments50 that are joined with secondcircumferential segments60. The secondcircumferential segments60 of eachcylindrical element100 may be joined with secondcircumferential segments60 of adjacentcylindrical elements100 to form a plurality of firsthelical segments30 and40 in themain body11. (SeeFIG. 2). Each firstcircumferential segment50 may have acircumferential dimension55 and each secondcircumferential segments60 may have a circumferential dimension66′ (SeeFIG. 3). In some embodiments, it may be desirable for thecircumferential dimension55 of the firstexpandable element50 to be larger than the circumferential dimension66′ of the secondexpandable element60.
• Thefirst circumferential segment50 may be an expandable segment formed from plurality of segments joined together to form a pattern. The pattern, such as the one shown in theFIGS. 1-3, may be a repeating pattern that resembles a square wave form having curved peaks and valleys. Other patterns, both repeating and non-repeating, may be used. For example, and without limitation, the firstcircumferential segments50 may resemble a triangle wave form, a sinusoidal wave form, other repetitious patterns, or any pattern that enables the segment to expand when a radial force is exerted on the stent from the inside or collapse radially when an external crimping force is applied.
• The firstcircumferential elements50 may have a filament width420 (seeFIG. 4). In one embodiment, the filament width may vary between 0.002 inches and 0.007 inches, but is preferably about 0.0050 inches. Other filament widths may be used depending on the parameters of the stent.
• In the embodiment shown inFIGS. 1-5, the firstcircumferential elements50 compriselinear portions320 andcurved portions328 that join thelinear portions320 together to form a repeating pattern. In some, but not all, embodiments, thelinear portion320 may be parallel to the cylindrical axis of the stent. In other embodiments, thelinear portion320 lies at an angle of between 0-45 degrees with respect to the cylindrical axis. Thefirst circumferential segment50 has anamplitude350 and aperiod380. In one embodiment the amplitude may range from 0.5 mm to 2.0 mm and the period may range from 0.5 mm to 2.0 mm. In some embodiments, the amplitude is less than the period. Other amplitudes and periods may be used depending on the overall stent design and performance constraints.
• The secondcircumferential element60, which may be joined together in a helical pattern to form one or morehelical segments30 or40, may also take numerous forms, in addition to the form shown inFIG. 6. In the embodiment shown inFIG. 6, the secondcircumferential element60 compriseslinear portions412 andcurved portions414 having afilament width407, and resembles generally an S-shaped structure. In addition, the secondelement circumferential segment60 may have an angledportion417 attached to thelinear portion412 at an end opposite that of thecurved portion414. The angled portion may be oriented to form an angle .alpha. relative to the cylindrical axis of thestent5 in the range of 0-45 degrees. In at least one embodiment, the preferable angle .alpha. is about 10 degrees. In some embodiments, thelinear portions412 of the secondcircumferential element60 lies at an angle .OMEGA. relative to the cylindrical axis of the stent, wherein .OMEGA. preferably ranges from 0 to 45 degrees. When viewed in a planar fashion as inFIG. 2, thelinear portions412 may, in some embodiments, form an angle .OMEGA., relative to the cylindrical axis of the stent. In some embodiments, .OMEGA. may be approximately equal to the helical angle of the firsthelical segments30 and40. In one embodiment, the secondcircumferential elements60 may have an amplitude300 (seeFIGS. 3,4, and6) ranging from 0.5 mm to 2.0 mm and aperiod310 ranging from 0.5 mm to 2.0 mm. Other ranges may be used depending on the particular stent size and design being employed. In one embodiment, the preferred period is about 0.82 mm and the preferred length of thelinear portion412 is about 0.5 mm and theamplitude300 is about 0.38 mm. The amplitude of the secondcircumferential element60 may be greater than, equal to, or less than the amplitude of the firstcircumferential element50. In one embodiment, the circumferential contributions of the firstcircumferential elements50 to the overall circumference of themain body11 is greater than the circumferential contribution of the secondcircumferential element60, in terms of either circumferential length or circumferential cylindrical surface area. In one embodiment, the stent may have an overall outer surface area of about 0.029 square inches.
• As is shown inFIG. 7, the stent may have amain body11 comprised of two or more firsthelical segments30 and40, as well as two or more secondhelical segments200 and210. The first and secondhelical segments30,40 and200,210, respectively, are joined together to form a generally cylindrically shapedbody11. In some, but not all embodiments, the first and second helical segments may share a common connectingelement250. In some embodiments, the common connectingelement250 may be H-shaped and the two generally parallel linear portions of the H-shaped connectingsegment250 may form an angle .delta. relative to theaxis5. (SeeFIG. 6). .delta. may, in one embodiment, be about 14 degrees. As is shown inFIG. 7, the firsthelical segments30 and40 and secondhelical segments200 and210 may have different pitches, i.e. number of spirals per unit length, which results in the first and second helical segments as having different helical angles (.theta. and .beta., respectively) i.e. the angle of the helical segment relative to thecylindrical axis5 of the stent. In one embodiment, the secondhelical segments200 and210 have a pitch approximately twice that of the first helical segments. In one embodiment .theta. may vary from 0 to 45 degrees and is preferably about 40 degrees and .beta. is preferably about twice .theta. In other embodiments the angle .theta. may range from 0 to 90 degrees. to thecircumference110 of eachcylindrical element100.
• As is shown inFIGS. 2,3,4, and6, thehelical segments30,40 are circumferentially expandable (i.e. they expand along the circumference of the stent) and may be formed from a plurality ofcircumferential elements60 that in turn are made up of linear412 and/or curved414 segments (seeFIG. 6) that each have a filament width407 (seeFIG. 6) that is less than the circumferential dimension66 of the circumferential element60 (seeFIG. 3). In some embodiments, eachhelical segment30 or40 will make a total contribution to the circumference of eachcylindrical element100 that is greater than thefilament width407. The circumferential contribution of eachhelical segment30 or40 to the overall circumference of the stent (110 inFIG. 1 or105 inFIG. 11) may be greater than the circumferential contribution of thefilament widths407 of the segments (e.g.412 and414) making up thecircumferential elements60 that in turn make up the helical segments. (I.e., In some embodiments the circumferential contribution of thehelical segments30 and40 to thecircumference110 of eachcylindrical element100 is more than just a function of thefilament width407, e.g., it may be a function of the geometry of theelement60.) For the embodiment shown inFIGS. 1 and 11, this is the case when the stent is in both the unexpanded and expanded state. The geometry of thehelical segments30 and40 are a factor in determining their expandability.
• Likewise, thehelical segments200,210 are circumferentially expandable and may be comprised of othercircumferential elements50 that are in turn comprised of linear320 and/or curved segments328 (seeFIGS. 3 and 5) that have a filament width420 (seeFIG. 4). The contribution of thehelical segments200,210 to the overallcircumferential dimension110 of eachcylindrical element100 is greater than just the contribution of the filament widths420 of theindividual segments320 and328 that make up theelements50 that in turn make up thehelical segments200,210. The geometry of theelements50 making up thehelical segments200,210 may be a more important factor in determining the circumferential contribution of thehelical segments200 and210 to the overall stent circumference than the filament width420. Thus, in one embodiment of the present invention, the circumference of thestent110 in its unexpanded state and thecircumference105 when the stent is expanded are primarily functions of the geometry of theelements50 and60 that make up thehelical segments30,40 and200,210, respectively.
• Some, but not all embodiments, of the present invention may employendzones10 and20. (SeeFIGS. 1,2, and11). Stents that employ endzones will generally have two endzone regions straddling a central zone in the middle of the stent. The stents may also have a transition region between the endzone and the central zone. The transition region serves to help smoothly transition between the expanded middle region and portions of the end of the stent that remain unexpanded after the stent is implanted. The size and characteristics of the transition region are a function of the material and geometry of the stent. For example, the transition range properties vary as a function of, among other things, the helical angle of the first helical segments, the number of curved segments located in the endzones, and the angle .epsilon. of the linear portions of the segments forming the endzones. (See e.g.FIG. 8).
• Theendzones10 and20 may take numerous forms. In some embodiments, the endzones may be comprised of one or more rings17. (SeeFIG. 8). Therings17 may be generally cylindrically shaped, and in some embodiments, right cylindrically shaped. In one embodiment, the rings are formed fromlinear segments28 joined together bycurved segments29 to form a pattern. The pattern, which is preferably—but not necessarily—a repeating pattern may take numerous forms, including the one shown. Theendzones10 and20 may be comprised of a plurality ofrings17 attached together.Struts15 may be used to attach the rings together to form the endzone and to attach the endzone to themain body11. The struts, in some embodiments, act as cantilever springs and there stiffness, which is a function of their width and thickness, may define bending properties of the stent along itscylindrical axis5.
• In the embodiment shown inFIGS. 1,7,8, and9, which is exemplary only, thelinear segments28 in theendzone10, are oriented at an angle .epsilon. relative to the cylindrical axis of the stent. In one embodiment, the angle .epsilon. is greater than 0 degrees. In another embodiment, .epsilon. may range from 0 to 45 degrees and in still another embodiment is preferably about 10 degrees. The segments of the endzone may have afilament width13 of between 0.002 and 0.007 inches. In one embodiment, the repeating pattern of the endzone has aperiod2 of about 0.027 inches and anamplitude21 of about 0.043 inches. Other values may be used. As is shown inFIG. 1, thestruts15, which are but one way to attach theendzones10 and20 to themain body11, may, in one embodiment have a width of between 0.002 inches and 0.08 inches and preferably the width does not exceed the wall thickness, which typically—but not necessarily ranges from about 0.002 to 0.008 inches.
• The stent of the present invention may, after insertion into a vessel, be expanded such that it plastically deforms from the unexpanded state to an expanded state having a diameter increase of about 400 to 500%, which results in alarger circumference105. (SeeFIG. 11).FIG. 11 depicts the stent shown inFIG. 1 in an expanded state. Upon expansion the stent's outer diameter in one particular embodiment increases from 1.0 mm to 3.00 mm and maintains a stent-to-vessel ratio in the expanded state that is greater than on average 16%.
• Whileendzones10 and20 may be used to provide square edge, not all stents according to the present invention require endzones.FIGS. 12-15 depict an endzoneless stent. Like the stent shown inFIG. 19, the stent ofFIGS. 12-15 comprises a plurality of adjacentcylindrical elements100. Thecylindrical elements100 are formed from a plurality of firstcircumferential elements50′ and secondcircumferential elements60. The firstcircumferential elements50′ of the stent inFIGS. 12-15 are substantially identical to the secondcircumferential element60 except that they are rotated to have a different orientation. The circumferential elements may be generally S-shaped having alinear portion412, acurved portion414 having a radius R, and anangled portion417. R may vary widely depending on overall stent characteristics and in one embodiment varies between 0.001 and 0.02 inches and is preferably about 0.0083 inches. Theangled portion417 is spaced adistance499 from the linear portion. In one particular embodiment, thedistance499 may vary from 0.002 to 0.020 inches and is preferably about 0.007 inches. Thefilament width407 of the elements may, in one embodiment, be about 0.13 mm. The circumferential elements depicted inFIG. 14 and the expansion elements depicted inFIG. 15 are positioned about thecylindrical axis5 as defined by angle K and may be generally S-shaped having alinear portion412, acurved portion414 having a radius R, and anangled portion417. The angle K may vary widely depending on overall stent characteristics and range of radial compression or expansion about theaxis5.
• Adjacentcylindrical elements100 are joined together by connecting firstcircumferential elements50′ in eachcylindrical element100 with firstcircumferential elements50′ in an adjacentcylindrical element100, such that the firstcircumferential elements50′ in adjacentcylindrical elements100 form helixes through the stent and such that second circumferential elements form helixes through the stent having an angle .theta. relative to theaxis5. In some embodiments, a connecting segment250 (seeFIG. 7) is used to connect first circumferential elements in adjacentcylindrical elements100 and to connect secondcircumferential elements60 in adjacentcylindrical elements100. In addition, the connecting segment, connects firstcircumferential elements50′ in eachcylindrical element100 with two secondcircumferential elements60 in eachcylindrical element100. In one embodiment, the individualcylindrical elements100 are adjacent to each other and are located adistance666 apart. In one embodiment, the preferred may range between 0.002 and 0.020 inches, and is preferably about 0.009 inches.
• The above description of the stent of the present invention is illustrative and not exhaustive. Various modifications may be made to the stent to change its overall characteristics without deviating from the scope and spirit of the invention as defined by the claims. For example and without limitation, the increasing the length of the linear segments and or increasing the arc of the secondcircumferential elements60 will decrease the amount of radial force required to expand each circular section and will increase flexibility. Increasing the angle .OMEGA. of the secondcircumferential element60 will: (i) increase the amount of radial force required for expansion, (ii) increase surface area, and (iii) decrease flexibility. Likewise, various modifications may be made to thestruts15. (SeeFIG. 2). Increasing strut width and wall thickness will: (i) increase surface area, (ii) increase radial strength, (iii) increase pressure required to expand the stent radially, (iv) decrease flexibility, and, in the case of increased wall thickness, (v) increase radiopacity.
• The stent of the present invention may be manufactured in numerous ways. The stent may be formed from a metallic tube by removing various portions of the tube's wall to form the patterns described herein. The resulting stent will thus be formed from a single contiguous piece of material, eliminating the need for connecting various segments together. Material from the tube wall may be removed using various techniques including laser (YAG laser for example), electrical discharge, chemical etching, metal cutting, a combination of these techniques, or other well known techniques. See e.g. U.S. Pat. No. 5,879,381 to Moriuchi et al. and U.S. Pat. No. 6,117,165 to Becker, which are hereby incorporated in their entirety by reference. Forming stents in this manner allows for creation of a substantially stress-free structure where the helical segments are integral with the circumferential elements. In one embodiment, the tube from which the stent is formed may have an internal diameter of about 3.0 mm, a wall thickness of about 1.0 mm and a length of about 30 mm. Tubes having other dimensions may be used. In particular, the length may be adapted to that of the diseased part of the lumen in which the stent is to be placed. This may avoid using separate stents to cover the total diseased area.
• Those skilled in the art will recognize that the stent and manufacturing method described above are illustrative and not exhaustive of the present invention and that modifications and variations may be made without deviating from the scope and spirit of the invention as defined by the following claims.

Claims (11)

1. An expandable stent having an unexpanded state, the unexpanded stent comprising:

a body defining a cylindrical axis, the body including a helical segment having a substantially H-shaped portion defining two generally parallel linear portions being angled with respect to the cylindrical axis.

2. The stent ofclaim 1, wherein the angle between the H-shaped segment and the cylindrical axis is greater than 0 degrees.

3. The stent ofclaim 2, wherein the angle between the H-shaped segment and the cylindrical axis is less than 90 degrees.

4. An expandable stent having an unexpanded state, the unexpanded stent comprising:

a cylindrical main body defining a cylindrical axis, the main body including a plurality of helical segments, each helical segment including a substantially H-shaped segment defining two generally parallel linear portions being angled with respect to the cylindrical axis.

5. The stent ofclaim 4, wherein the angle between the H-shaped segment and the cylindrical axis is greater than 0 degrees.

6. The stent ofclaim 5, wherein the angle between the H-shaped segment and the cylindrical axis is less than 90 degrees.

7. The stent ofclaim 4, wherein each helical segment includes a substantially S-shaped segment.

8. The stent ofclaim 7, wherein each helical segment includes a plurality of substantially S-shaped segments alternating with a plurality of substantially H-shaped segments.

9. An expandable stent having an unexpanded state, the unexpanded stent comprising:

a main body defining a cylindrical axis, the main body including a helical segment including a substantially S-shaped segment and a substantially H-shaped segment, the H-shaped segment defining two generally parallel linear portions nonparallel to the cylindrical axis.

10. The stent ofclaim 9, the linear portions are not perpendicular to the cylindrical axis.

11. The stent ofclaim 9, wherein each helical segment includes a plurality of substantially S-shaped segments alternating with a plurality of substantially H-shaped segments.

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