JP2002537064A - Stent with customized flexibility - Google Patents

Abstract

SUMMARY An expandable stent is disclosed for implantation in a body lumen, such as an artery. The stent includes a plurality of radially expandable cylindrical elements aligned along a common longitudinal stent axis, and one or more interconnects arranged such that the stent is longitudinally flexible. And a member. At least one of the ends of the stent has a smaller number of interconnects than the central portion of the stent to provide localized flexibility in selected areas of the stent.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to an expandable indwelling device, known as a stent, designed to be implanted within a body lumen of a patient, such as a blood vessel, to maintain its patency. About. These devices are useful for vascularization after stenosis is compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or after removal by atherectomy or other means. It is particularly useful for the treatment and repair of

BACKGROUND OF THE INVENTION This application is a continuation-in-part of application Ser. No. 09/008366, filed Jan. 16, 1998, which is a pending parent application, the entire contents of which are hereby incorporated by reference. Incorporated in

[0003] A stent is a generally cylindrically shaped device that has the function of retaining and often expanding a vessel or other lumen, such as a portion of the coronary artery. Stents are suitable for use to support the lumen or retain the lining of an incised artery capable of occluding a fluid passage therethrough.

[0004] Various devices used in the prior art as stents are well known, including balloon-expandable stents; coiled in various patterns that are deployed on a lumen and then expanded on a balloon catheter. Spiral wound coil springs made of expandable, heat-sensitive metal; and self-expanding stents formed in a zig-zag pattern, inserted under compression. One of the problems encountered when using prior art stents is that while maintaining the radial stiffness required to maintain a body lumen open,
The purpose is to maintain the longitudinal flexibility of the stent to facilitate its delivery and adapt to the path of often tortuous body lumens.

[0005] Another problem area has been the limited range of scalability. Some prior art stents do not expand to a limited extent due to uneven stresses created on the stent during radial expansion. This necessitates the provision of stents having different diameters, thus increasing manufacturing costs. In addition, providing the stent with a wider range of expandability allows the physician to re-expand the stent when the native dimensions of the vessel are misrepresented.

Another problem with prior art stents has been that as the stent expands radially, the stent shortens along its longitudinal axis. This creates placement problems within the artery during dilatation.

Various means for delivering and implanting a stent have been described. One method that has often been described for delivering a stent to a desired location within a lumen is to use an expandable member provided on the distal end of a catheter in the vessel, such as an expandable stent on a balloon. Attaching and advancing the catheter to the desired location within the patient's body lumen, inflating the balloon on the catheter to expand the stent to a permanently expanded state, and then deflating the balloon to remove the catheter.

What has been needed is a method for easily advancing through tortuous passages and expanding radially over a wider range of diameters with minimal longitudinal contraction to provide a larger range of vessel diameters A stent with enhanced flexibility that can be adapted to The expanded stent must, of course, have the appropriate structural strength (hoop strength) to keep the body lumen in which it is expanded open. The present invention fulfills this need.

SUMMARY OF THE INVENTION [0009] The present invention provides enhanced flexibility in the longitudinal direction, as well as the ability of a stent to radially expand to accommodate vessels having both larger and smaller diameters than previously possible. To a stent that is configured to allow The stents of the present invention also have greater flexibility along the longitudinal axis to facilitate delivery through tortuous body lumens, but are very stable when radially expanded, Maintains the patency of body lumens such as arteries or other blood vessels when implanted therein. The unique pattern of the stent of the present invention results in greater longitudinal flexibility and enhanced radial expandability and stability compared to prior art stents.

[0010] Different embodiments of the stent of the present invention each include a plurality of adjacent cylindrical elements that are generally radially expandable and arranged along the longitudinal stent axis. The cylindrical element is formed in various meandering wavy patterns perpendicular to the longitudinal axis and has a plurality of alternating peaks and valleys. At least one interconnecting member extends between adjacent cylindrical elements;
And connect the cylindrical elements to one another. These interconnecting members ensure that longitudinal contraction during radial expansion of the stent within the body vessel is minimized. The serpentine pattern has varying degrees of flexion in the top and valley regions, and the radial expansion of the cylindrical element is generally cylindrical when the stent transitions from the collapsed state to the expanded state. It is configured to be uniform around the periphery of the element.

The resulting stent structure is spaced sufficiently close in the longitudinal direction that small incisions in the lumen wall of the body are pressed into the lumen wall and return to position. A series of radially expandable cylindrical elements that compromise the longitudinal flexibility of the stent both when crossing a body lumen without the stent expanding and when the stent expands into place. These are not very close. The serpentine pattern provides a uniform expansion around the outer circumference, as described by the relative differences in stresses created by the radial expansion of the cylindrical element. Each individual cylindrical element rotates slightly with respect to its adjacent cylindrical element without significant deformation, providing incrementally a stent that is flexible along its length and about a longitudinal axis. However, it is very stable in the radial direction to resist collapse after expansion.

[0012] Each of the stents of the present invention can be mounted on an expandable member of a delivery catheter, such as a balloon, and easily passed through the body lumen to the implantation site through the body lumen to facilitate intraluminal insertion. It can be supplied to a desired position.
Various means can be used to secure the stent to the expandable member of the catheter for delivery to a desired location. Currently, it is preferred to compress or swage the stent onto an unexpanded balloon. Other means of securing the stent to the balloon include providing ridges or collars on the inflatable member to limit lateral movement and using a temporary bioabsorbable adhesive Or adding a retractable covering to cover the stent during delivery through a body lumen.

A presently preferred structure for the expandable cylindrical element forming the stent of the present invention comprises a circumferential serpentine pattern having a plurality of alternating peaks and valleys. The degree of curvature along adjacent peaks and valleys is designed to compensate for the stresses created during expansion of the stent such that the expansion of each peak and valley is uniform with each other. This new structure allows the stent to expand radially from a smaller first diameter to a much larger second diameter as the stress is more uniformly distributed along the cylindrical element. The uniformity of this stress distribution is
It reduces the tendency for fatigue failure in one particular area and provides a high expansion rate.

[0014] Different embodiments of the stent also allow the stent to expand from small to large diameters and to different sized body vessels without compromising the radial strength and limited reduction in longitudinal length. Allow to adapt to the cavity. The open network of the stent results in a low mass device. It also allows for blood perfusion over a large portion of the wall of the artery and can improve the healing and recovery of the lining of the damaged artery.

In one presently preferred embodiment, the ability of the stent to treat larger diameter vessels is such that the starting compressed diameter is greater than in prior art devices. This is caused by increasing the number of units in the repeating pattern. When expanded, the stent of this embodiment adequately covers the lumen wall and maintains its structural integrity due to the forces exerted by the lumen wall and resisting collapse.

[0016] The serpentine pattern of the cylindrical elements can have different degrees of bending at adjacent peaks and valleys to supplement the expansion characteristics of the peaks and valleys. In addition, the degree of flexion along the peak can be set differently in adjacent regions to compensate for the expansion characteristics of the valley adjacent to it. The more uniform radial expansion in this design results in a stent that is expandable to accommodate larger diameters with minimal out-of-plane twist. This is because the high stress is not concentrated on any one particular area of the pattern and is more evenly distributed between the peaks and valleys, allowing the peaks and valleys to expand uniformly. . Reducing the amount of out-of-plane twist minimizes the potential for thrombus formation.

The meandering curve pattern of the individual cylindrical elements can be phased with other meandering patterns to reduce stent contraction with expansion along the length of the stent. The cylindrical element of the stent is plastically deformed when expanded so that the stent remains expanded and therefore sufficiently rigid when expanded to prevent collapse during use. Do (nickel titanium (NiTi)
Except for alloys).

When the stent is formed from a superelastic NiTi alloy, expansion occurs when the compressive stress is removed. This allows a martensite to austenite phase transition to occur, resulting in stent expansion

As the stent expands, some peaks and / or valleys lean out, but not necessarily, into the vessel wall. Thus, after expansion, the stent does not have a smooth outer wall surface. Rather, it has small protrusions that fit into the vessel wall and hold the stent in place in the vessel. The outwardly projecting tip and strut twist are primarily due to struts having a high aspect ratio. In one preferred embodiment, the stent has a thickness of about 0.0889 mm (0.0035).
Inches) and a width of about 0.0559 mm (0.0022 inches).
It has an aspect ratio of 6. An aspect ratio of 1.0 results in less tilt and twist.

The interconnecting members interconnecting adjacent cylindrical elements must have a cross-sectional shape similar to the transverse dimension of the undulating elements of the expandable cylindrical member. The interconnecting member may be formed in one piece with an expandable cylindrical element formed from the same intermediate product, e.g., a tubular element, or the interconnecting member may be formed separately and between the expandable cylindrical element Mechanically fixed to

[0021] Preferably, the number and location of the interconnect members can be varied to provide the desired longitudinal flexibility in the stent structure in both the expanded and unexpanded states. These properties are important to minimize the alteration of the intrinsic physiology of the body lumen in which the stent is implanted and to maintain the flexibility of the body lumen in which the stent is supported. is there. Generally, the longitudinal direction of the stent, especially when the implantation site is in a curved portion of the body lumen, such as in the coronary arteries or surrounding vessels, and when the body lumen is a saphenous vein or other larger vessel. The greater the flexibility of the stent, the easier and more secure the stent can be delivered to the implantation site.

According to the foregoing claims, generally, the more interconnecting members between the contiguous cylindrical elements of the stent, the less longitudinal flexibility of the stent. More interconnect members reduce flexibility but increase vessel wall coverage and help prevent tissue prolapse between stent struts. Thus, it is possible to customize the number of connections for flexibility when it is needed most and for coverage when coverage is needed most.

In a preferred embodiment, the present invention is directed to a stent that is longitudinally flexible and expandable from a reduced condition to an expanded condition for implantation in a body lumen, the stent comprising a longitudinal stent. A plurality of adjacent cylindrical elements each having an outer periphery extending about an axis, the cylindrical elements being disposed cylindrically along a longitudinal stent axis to form a generally tubular member; The generally tubular member has a first end, a second end, and a central portion therebetween; a central portion such that the first and second portions are relatively more flexible than the central portion. And adjacent cylindrical elements are connected by n interconnect members, and adjacent cylindrical elements are connected by nk interconnect members at at least one of the first end and the second end. Sa K is a number selected from the group consisting of 1, 2, 3, 4 or 5; and is directed to a stent characterized by n> k.

In the structure of this preferred embodiment, the first and second ends are connected by a number of interconnect members that is always less than the number of members that interconnect the central portion of the cylindrical element of the stent. Thus, in the design of the present invention, it is flexible at at least one end and optionally flexible at both ends, but rigid at the center. In other words, in one embodiment one end is flexible but the central portion and the opposite end are relatively rigid; in another embodiment the central portion is relatively rigid but Both ends are flexible.

[0025] Stents of this kind work well for diseases that are located in the curvature of blood vessels. The strongest part can be located on the heaviest plaque mass. This area has minimal clearance and slope between the cylindrical elements, thus minimizing tissue prolapse. On the other hand, the flexible end of the stent minimizes the length of the arteries that are forced to follow the vessel and otherwise straighten by the otherwise rigid stent. The softer end is located closer to the normal part of the artery where tilt is a minor factor. This means that the stent has sufficient length to cover the disease and extends from the normal part of the blood vessel to other normal parts.

[0026] Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, which proceeds with reference to the accompanying illustrative figures.

Prior art stent designs, such as Advan, Santa Clara, California
ced Cardiovascular Systems, Inc. In the MultiLink Stent (registered trademark) manufactured by the Company, a plurality of cylindrical rings are connected by three connecting members between adjacent cylindrical rings. Each cylindrical ring is formed from a repeating pattern of U, Y and W shaped members, typically having three repeating patterns forming each cylindrical ring.
For a more detailed discussion of the shape of the MultiLink Stent®, see US Pat. No. 5,569,295 (Lam) and US Pat.
154 (Lau et al.).

The ability to provide a very flexible stent suitable for insertion into larger vessels and to provide better coverage of the lumen wall without sacrificing radial strength or flexibility In order to have, the stent of the present invention has U,
Optionally, at least another repeating pattern of Y and W shaped members is added. In addition, a pair of connecting members, spaced 180 degrees between adjacent cylindrical rings, provides increased flexibility to prior art stents, which is a result of the serpentine anatomical features of the present stents. It is essential for feeding through structural tissue and implanting in curved sections of blood vessels.

FIG. 1 illustrates a first embodiment of a stent 10 incorporating features of the present invention mounted on a delivery catheter 11. The stent includes a plurality of radially expandable cylindrical elements 12 that are disposed substantially coaxially and interconnect members 13 disposed between adjacent cylindrical elements 12. Interconnected by The delivery catheter 11 includes an expandable portion or balloon 1 to expand the stent 10 within an artery 15 or other blood vessel.
Four. The artery 15, as shown in FIG. 1, has a dissected or separated inner layer 16 that blocks a portion of the arterial passage.

The delivery catheter 11 to which the stent 10 is essentially attached is the same as a normal balloon dilatation catheter for an angioplasty procedure. Balloon 14 may be made of any suitable material, such as polyethylene, polyethylene terephthalate, polyvinyl chloride, nylon, and E. coli. I. Manufactured from ionomer manufactured under the trade name SURLYN by the Polymer Products Division of duPont de Nemours. Other polymers can also be used.

The stent 10 is compressed or crimped onto the balloon 14 so that the stent 10 remains in position on the balloon 14 during delivery to the site of injury in the artery 15.
To ensure that the stent 10 remains in place on the balloon 14 of the delivery catheter 11 and prevents wear of the body lumen by the open surface of the stent 10 during delivery to the desired arterial location. Is provided with a retractable protective supply sleeve 20. Other means can also be used to secure the stent 10 on the balloon 14, such as providing a collar or ridge on the end of the working portion, ie, the cylindrical portion of the balloon 14. The radially expandable cylindrical elements 12 of the stent 10 each expand independently. Accordingly, balloon 14 may be provided with a non-cylindrical, eg, tapered, inflated shape to facilitate implantation of stent 10 into various shaped body lumens.

In a preferred embodiment, delivery of the stent 10 is accomplished in the following manner. The stent 10 is first mounted on an inflatable balloon 14 on the distal end of a delivery catheter 11. Stent 10 can be used with balloon 1 to obtain a small profile.
4 is crimped. The catheter-stent assembly is introduced into the patient's vasculature by conventional percutaneous vascular catheterization via a guide catheter (not shown). A guidewire 18 is placed through a portion of the damaged artery having a detached or dissected inner layer 16. The catheter-stent assembly is then advanced over the guidewire 18 in the artery 15 until the stent 10 is just below the separated inner layer 16. The balloon 14 of the catheter 11 expands or expands, causing the stent 10 to expand inside the artery 15, as shown in FIG. Although not shown in the drawings, the artery 15 is preferably slightly expanded by expansion of the stent 10 to attach or fit the stent 10 to prevent movement. Indeed, in some situations during the treatment of a stenotic portion of an artery, the artery must be significantly dilated to facilitate the passage of blood or other liquids.

FIGS. 1-3 depict a blood vessel with a separated inner layer 16, but with the stent 1
0 is used for purposes other than treating the inner lining. For those other purposes,
For example, supporting a blood vessel, reducing the likelihood of restenosis, or assisting in the attachment of a vascular graft (not shown) when treating an aneurysm ventral to the aorta.

Generally, the stent 10 serves to keep the artery 15 open after the catheter 11 has been withdrawn, as shown in FIG. Due to the configuration of the stent 10 from the elongate tubular member, when the stent 10 is expanded, the cylindrical element 12 is pressed against the wall of the artery 15 so that the blood flow through the artery 15 is not obstructed. The undulating element of the cylindrical element is relatively flat in cross section. Artery 15
The cylindrical element 12 of the stent 10 pressed against the wall of the stent is eventually covered by endothelial cell growth to minimize turbulence in blood flow. The serpentine pattern of the cylindrical element 12 provides good cohesive properties to prevent stent movement within the artery.
In addition, the closely spaced cylindrical elements 12 at regular intervals provide uniform support to the wall of the artery 15 and, as shown in FIGS. It is well configured to hold adhesively to small flaps or incisions in the wall.

In one preferred embodiment of the stent 10, as shown in FIGS. 4 and 5, the stress associated with expansion from a small profile to an expanded profile is such that the stress at each different top and valley of the stent 10 is different. More evenly distributed between them. As shown in FIG.
Some cylindrical elements 12 of the stent 10 embody a serpentine pattern having a plurality of peaks and valleys that assist in uniform distribution of the expansion force. In this first embodiment, the interconnecting members 13 serve to connect adjacent tops and valleys of each adjacent cylindrical element 12 as described above. Each crest and valley has a generally repeating pattern of U, Y, and W shapes, forming a cylindrical element 12.

During expansion, the double curved portion (W) 34 located in the region of the valley to which the interconnecting members 13 are connected has the most mass, and thus is the most rigid during deformation. No. In contrast, the top (U) 36 is least rigid and the valley (Y) 30 is medium stiffness. In the exemplary embodiment of FIG. 4, there are four repeating patterns of tops and valleys within each cylindrical element 12.

The preferred embodiment of the stent 10 has a pair of portions, as seen in FIG. That is, the first and second ends 31A and 31B. As shown, the first ends 31A each have a double curved portion (W) 34 with an interconnect member 1A.
3 thereby providing maximum support to the ends of the stent. First
End 31A can optionally include a central portion in a theoretical sense.
However, the theoretical center portion has the same number of interconnect members and first ends 31
This central portion is not separated because it has the same cylindrical element design as A, but will be perceived as a separate portion for purposes of describing this embodiment. If not, one would think that in the embodiment shown in FIG. 4, the central part has been completely omitted.

To improve flexibility and uniform expansion at the second end 31 B, the members 3
Every other portion of the cylindrical element 12 indicated by 7 has every other interconnecting member 13 removed. Where the interconnect member 13 has been removed from the member 37, it has less local mass and therefore less local stiffness, yielding a more flexible and uniform expansion. The remaining interconnect members 13 are preferably 180
Degrees apart. Thus, at the second end 31B, adjacent cylindrical elements 12 are connected by only a pair of interconnecting members 13.

Due to the mass associated with the stent design of the present invention, the double curved portion 34 is the stiffest structure and the top 36 is the least stiff structure, resulting in different stresses during expansion. Is explained. Also, the top portion 36, which is the least rigid structure, is disposed between the double curved portion 34 and the valley portion 30, which are relatively rigid structures. To equalize the stress, the top 36 has a different curvature in the regions 32 and 33 as shown in FIG. Region 33 has a larger radius than region 32 and expands more easily. Since the region 32 is adjacent to the stiffer region, the double curved portion 34, the region 32 and the double curved portion 34 expand more evenly and distribute the expanding stress more uniformly. In addition, the valleys 30 and the double bends 34 have different diameters to equalize the expansion force with respect to the top 36. The new structure described above avoids the disadvantages of the prior art, including out-of-plane twisting of the metal. Different degrees of bending along top 36 result in a more uniform expansion of cylindrical element 12 as a whole.

The stent 10 of FIGS. 2-5 can be moved from a crimped state to an expanded state by about one.
. It has an expansion ratio in the range of 0-5.0, but maintains its structural integrity when expanded. As shown in FIG. 6, after expansion of the stent 10, each cylindrical element 12
Part turns outward to form a small protrusion 38 that fits into the vessel wall. More precisely, the tip 39 of the apex 36 tilts outward sufficiently in response to expansion of the stent 10 and cuts into the vessel wall to help secure the stent 10 when implanted. Upon expansion, protrusion 38 creates a non-smooth outer wall surface on stent 10.
Protrusions 38, on the other hand, help secure stent 10 within the vessel, but the protrusions are not sharp enough to cause trauma or damage to the vessel wall.

The outwardly projecting tip 39 and the torsion of the strut are primarily due to the strut having a high aspect ratio. In one preferred embodiment, the width of the strut is about 0.055
9 mm (0.0022 inch) with a thickness of about 0.0889 mm (0.0035 inch)
Inches), resulting in an aspect ratio of 1.6. The aspect ratio of 1.0 is
Produces less tilt and twist.

FIG. 7 shows another embodiment of the stent of the present invention. More specifically, FIG. 7 is a plan view of a flattened portion of a stent 40 having first and second flexible end portions 41A, 41B and a relatively rigid central portion. In this exemplary embodiment, the central portion 42 preferably comprises four interconnected portions that connect a double curved portion (W) 44 of one cylindrical element 12 to a valley (Y) 43 of an adjacent cylindrical element 12. It has a connection member 13. In the exemplary embodiment shown in FIG. 7, the interconnect members 13 in the central portion 42 are spaced 90 degrees apart.

Each cylindrical element 12 has a valley (Y) 43, a top (U) 46 and a double curved portion (
W) 44, consisting of repeating portions of four meandering waveform patterns. The valleys 43 and the tops 46 each have a generally single radius of curvature. Each valley 4
3 is connected to the interconnecting member 13 and bridged to the top 46. All of the structures described above are preferably in central portion 42. First and second ends 4
In 1A and 41B, every other interconnect has been removed to increase flexibility in that area. Thus, members 47 are interspersed between interconnect members 13 at first end 31A and second end 31B. Within the first and second ends 41A, 41B, the interconnect members 13 are spaced 180 degrees apart.

The cylindrical element 48 found in the first and second ends 41 A, 41 B has a serpentine pattern having a valley (Y) 43, a top (U) 46 and a double curved portion (W) 44. However, the difference from the above is that the interconnection member 13 for connecting the member 47 to the adjacent valley 43 is omitted. Thus, in the exemplary embodiment depicted in FIG. 7, the first end 41A comprises three cylindrical elements 48 having three pairs of interconnecting members 13. The same structure applies to the second end 41B. The central portion 42, however, preferably has four interconnecting members 1
It comprises four cylindrical elements 12 having four sets of three.

The interconnecting members 13, as shown in FIG. 7, comprise every other cylindrical element 12, 4
At 8 they are axially aligned or they are staggered according to the bending requirements of the particular stent. Indeed, the present invention controls the flexibility of the stent by using interconnecting members between the cylindrical elements of the stent. Generally speaking, the more interconnecting members between the cylindrical elements of the stent, the less longitudinal flexibility of the stent. Thus, more interconnecting members decrease flexibility but increase stent coverage on the vessel wall, which helps prevent tissue prolapse between stent struts.

The exemplary embodiment depicted in FIG. 7 is particularly suitable for diseases on bends.
In the present application, the central portion 42 of the stent 40 is the largest plaque load (p
and the first and second ends 41A, 41A,
41B allows bending around a bend with less supporting plaque.

FIG. 8 is a plan view of a flattened portion of another embodiment of the stent of the present invention. In this alternative embodiment, the stent 50 includes first and second flexible ends 51A, 51B separated by a central portion 52, respectively. First end 5
Within 1A, second end 51B, and central portion 52 are a plurality of cylindrical elements 53, respectively. Each cylindrical element 53 has a meandering pattern of opposed U-shaped curves 54. All of the U-shaped curves 54 have the same radius of curvature to provide a consistent pattern. More precisely, each U-shaped curve 54 has a mouth 55 that is sandwiched and closed by adjacent U-shaped curves 54 to provide a denser strut pattern.

To change the flexibility of the stent 50, the number of interconnecting members 56 is varied along the length of the stent 50. For example, at the first end 51A, there is only one interconnect member 56 between any pair of adjacent cylindrical elements 53.
Similarly, at the second end 51B of the cylindrical element, there is only one interconnection member 56 connecting any pair of adjacent cylindrical elements 53.

In contrast, the central portion 52 preferably has a pair of adjacent cylindrical elements 53 connected by three interconnecting members 56. Both ends of the central portion 52 have a cylindrical element 53 connected to adjacent cylindrical elements 53 in the first and second ends 51A, 51B using three interconnecting members 56. I have. In summary, and with reference to FIG. 8, the stent 50 uses one interconnect member 56 to interconnect adjacent pairs of four cylindrical elements 53 in the first end 51A; And three interconnecting members 56 for interconnecting adjacent pairs of three cylindrical elements 53 at opposing ends; and finally a second end 51
One interconnect member 56 between adjacent pairs of a pair of cylindrical elements 53 in B is used.

FIG. 8 shows that the number and location of interconnect members 56 can be varied based on certain design and flexibility requirements. In practice, the number of interconnects between the cylindrical elements depends on the design shape and the desired flexibility within each area. For example, another embodiment stent (not shown) includes a pair of interconnecting members between a pair of cylindrical elements at a first end, and a pair of interconnecting members between a pair of cylindrical elements in a central portion.
There may be one interconnect member and one interconnect member between the pair of cylindrical elements in the second end. The number of cylindrical elements in the end or middle portion, if any, can be varied to customize the stent for a particular application.
The number of interconnecting members used between any adjacent pairs of cylindrical elements can be varied as needed. Further, the angular position of each interconnect member and the position of each interconnect member relative to each other can be varied as required for flexibility. It is to be understood that the term "interconnect member" as used in the specification of the present application includes not only connecting elements specifically depicted in the drawings but also welds or cylindrical elements between adjacent cylindrical elements. It simply includes the uncut region between them.

The dimensions of any of the foregoing exemplary embodiments can be adjusted to achieve optimal expansion and strength characteristics for a given stent. The number of bends in each cylindrical element can be changed, for example, as shown in FIG.

In many of the drawings, for ease of illustration, the stent is depicted as flat, plan view. All of the examples depicted herein are cylindrically formed stents formed from tubes generally by laser cutting, as described below.

One important feature of all embodiments of the present invention is the ability of the stent to expand from a small diameter to a much larger diameter than previously available, but even in the expanded state. Very flexible while maintaining structural integrity.
With this new structure, using certain compositions of stainless steel, the overall expansion ratio of the stent of the present invention is from about 1.0 to a maximum of 4.0 relative to the original diameter. For example,
The 316L stainless steel stent of the present invention has a diameter of 1.0 unit to about 4.0 mm.
It can be radially expanded to a diameter of 0 units, which deforms the structural member beyond its elastic limit. The stent maintains its structural integrity in the expanded state and serves to keep the vessel in which the stent is implanted open. Materials other than stainless steel (316L) also yield higher and smaller expansion ratios without sacrificing structural integrity.

The present invention contemplates various configurations such as the number of interconnecting members and the location of the interconnecting members within a first end, a central portion, or a second end of the stent. For example, a stent can have a central portion with adjacent cylindrical elements connected by n interconnecting members, and an adjacent cylinder at at least one of a first or second end. The elements are connected by nk interconnect members, where k is a number from 1 to 5 and n> k.

In another embodiment, n is the number of interconnect members in the central portion and k
Is the number of interconnecting members at one of the first or second ends. In this embodiment, the values of n: k are, for example, 1: 2, 1: 3, 1: 4, 1: 5, 1:
6, 1: 7, 1: 8, 1: 9, 1:10, 2: 3, 2: 5, 3: 4 or 3:
5

The stent of the present invention can be manufactured in various ways. However, in a preferred method of manufacturing a stent, a thin walled tubular member, such as stainless steel tubing, is cut, portions of the tubing are removed in the desired pattern for the stent, and relatively intact metal tubing is removed. Leave the portion to form the stent.
Preferably, the tubing is cut into the desired pattern by a machine controlled laser.

The tubing is made from a suitable biocompatible material, such as stainless steel. The alloy type of stainless steel pipe is 316L SS, Special Chemistry
per ASTM F138-92 or ASTM F139-92 gr
ade 2. Special Chemis for surgical implants
try of type 316L per ASTM F138-92 or
The weight percentages of ASTM F139-92 stainless steel are as follows: Carbon (C) Up to 0.03%. Manganese (Mn) Up to 2.00% Phosphorous acid (P) Up to 0.025%. Sulfur (S) Up to 0.010% Silicon (Si) Up to 0.75% Chromium (Cr) from 17.00 to 19.00% Nickel (Ni) from 13.00 to 15.50% Molybdenum (Mo) from 2.00 3.00% Nitrogen (N) Up to 0.10%. Copper (Cu) Up to 0.50% Iron (Fe) Remainder

Since the diameter of the stent is very small, the tubing from which it is made must also or necessarily have a small diameter. Typically, the stent will have an outer diameter of about 1.52 mm (0.06 inches) in the unexpanded state, and the tubing from which it is made will also have the same outer diameter, and .2 inches) or more. The wall thickness of the tubing is 0.076 mm (0.003 inches).

Generally, the tubing is placed in a rotatable collet fixture of a mechanical controller for positioning the tubing with respect to the laser. According to the mechanically encoded instructions, the tubing is then spun and sent longitudinally with respect to the mechanically controlled laser. The laser selectively removes material from the tubing by ablation, and the pattern is cut into the tubing. The tube is thereby cut into individual patterns of the finished stent.

In general, the process of cutting the pattern of the stent into the tubing is automated except for attaching and detaching the entire tubing. For example, a computer numerical control opposition for rotation about the entire axis of the tubing in conjunction with a computer numerical control X / Y table for axially moving the entire tubing with respect to the aforementioned laser that is mechanically controlled. By using a collet fixture, the pattern is cut into the tubing. The entire space between the collets is defined using carbon dioxide, neodymium or the YAG laser setup of the previous embodiment. The program for controlling the device depends on the particular structure used and the pattern to be removed.

Cutting fine structures (web width of 0.0863 mm (0.0034 inch)) requires minimal heat input and the ability to operate the tube accurately. It is necessary to support the tubing so as not to allow the stent structure to distort during the cutting operation. In order to successfully achieve the desired result, the entire system must be very carefully configured. Tubes are 1.52 mm (0.060 inch)
Manufactured from stainless steel having an outer diameter of from 0.10 inches to a wall thickness of 0.002 inches to 0.008 inches. These tubes are fixed under a laser and positioned using computer numerical control to produce very complex and accurate patterns.
The small geometry of the stent pattern, with thin walls and a typical stent width of 0.0035 inch (0.889 mm), allows for very high laser levels such as power level, focal spot size, and precise positioning of the laser cutting path. Need precise control.

To minimize heat input to the stent structure, thereby producing a smooth, debris-free cut, to prevent thermal distortion, uncontrolled burnout of the metal, and metallurgical damage from overheating, Double frequency Q-switched Nd / YAG laser producing a 532 nanometer green beam (Quanton
ix of Hauppauge, a laser typically available from New York) is used. Q-switching is a very short pulse (<100 ns) with high maximum power (kilowatts), low energy pulse (≦ 3 mJ)
) Produces a low energy, high pulse rate (up to 40 kHz). Beam frequency doubling from 1.06 micrometers to 0.532 micrometers allows focusing to a spot size that is twice as small, thereby increasing the power density by a factor of four. All of these parameters allow for cutting narrow, very fine geometries into stainless steel tubing without damaging the smooth, narrow struts that make up the stent structure. Thus, the system of the present invention allows for adjustment of laser parameters to cut narrow kerfs that minimize heat input to the material.

The positioning of the tubular structure requires the use of precision computer numerical control equipment manufactured and sold, for example, by Anorad Corporation. In addition, a unique rotation mechanism is provided that allows the writing of computer programs as if the pattern were cut from a flat sheet. This allows circular and linear interpolation to be used for programming.

An optical system that expands the original laser beam and delivers the beam through the viewhead to focus the beam on the surface of the tube helps to remove debris from the kerfs and allows the beam to interact with the material. And coaxial gas jets and nozzles to cool the area to cut and evaporate metal. As the beam cuts the upper surface of the tube, the beam needs to be blocked to prevent the beam from hitting the opposite surface of the tube along with the metal and debris melted from the cut.

In addition to the laser and computer numerically controlled location equipment, the optical delivery system may include a beam expander to increase the diameter of the laser beam, typically a quarter to remove polarization effects in metal cutting. A circular polarizer in the form of a single wave plate,
It includes a spatial filter facility, a binocular view head and a focusing lens, and a coaxial gas jet surrounding the focused beam and introducing a gas fluid oriented along the beam axis. The coaxial gas jet nozzle is 0.457 mm (0
. 018 inches). The inside diameter (ID) is approximately 0.210 mm (0.010 inch) around the focused beam between the tip of the nozzle and the tubing.
Is centered. The jet is pressurized with 20 psi of oxygen and exits a 0.018 inch diameter nozzle tip and is directed at the tube with a focused laser beam. Oxygen reacts with the metal to aid in thermal cutting as well as oxygen acetylene cutting. The focused laser beam acts as an ignition source and controls the reaction of oxygen with the metal. In this way, it is possible to cut very fine kerfs exactly into the material.

A 0.034 inch diameter stainless steel mandrel is placed inside the tube to prevent burning of the beam and / or molten slag on the wall beyond the tube inner diameter, And it is made to rotate on the bottom of the tube as the pattern is cut. This acts as a beam / debris barrier protecting the wall beyond the inner diameter.

Alternatively, this prophylactic action is to use a second aperture with an aperture to stop excess energy in the beam sent through the kerf with the collected debris emitted from the laser-cut kerf. This is achieved by inserting a tube inside the stent. A vacuum or positive pressure can be introduced into the protective tube to remove the collected debris.

Another technique that can be used to remove debris from the kerfs and cool the surrounding material relies on an inner beam blocking tube as an internal gas jet. By sealing one end of the tube and providing a small hole on its side, and placing it directly under the focused laser beam, gas pressure is applied and the laser cut kerf Creates a small jet that moves debris from inside to outside. This precludes debris from forming or collecting inside the stent structure. It places all debris outward. By using a special protective coating, the resulting debris can be easily removed.

In most cases, the gas utilized for the jet is reactive or non-reactive (inert). In the case of a reaction gas, oxygen or compressed air is used. In the present application, oxygen is used. This is because it provides more control over the material being removed and itself reduces the thermal effects of the material. Inert gases such as argon, helium or nitrogen are used to eliminate oxidative corrosion of the cut material. The result is a shear cut without oxidative corrosion, but must be removed mechanically or chemically after the cutting operation because there is usually a tail of melt concentrated along the exit side of the gas jet .

[0070] Thermal cutting using a finely focused green beam and oxygen produces very narrow kerfs (approximately 0.0005 inches) and molten slag along the cut. This results in recoagulation. This traps the notch in the pattern, but requires further processing. The cut tube must be immersed in an aqueous hydrochloric acid solution at a temperature of about 55 ° C. for 8 minutes in order to remove slag pieces from the cut portion while removing debris from the remaining stent pattern. Prior to immersion, the tube is placed in a bath of alcohol / water solution and ultrasonically cleaned for about 1 minute to remove any loose debris left by the cutting operation. After immersion, the tubes are ultrasonically cleaned in warm hydrochloric acid for 1-4 minutes depending on the wall thickness. To prevent cracks / cracks in the struts attached to the material left at the pair of ends of the stent pattern due to harmonic vibrations caused by the ultrasonic cleaner, the tubing was removed during the cleaning / debris removal process. A mandrel is placed in the center. When this step is completed, the stent structure is cleaned with water. Here, they are ready for electropolishing.

The stent is preferably made of an acidic aqueous solution, such as ELECTR of Chicago, Ill.
O-GLO Co. , Inc. ELECTRO-GLO sold by
Electrochemically polished with a # 300 aqueous solution, which is a mixture of sulfuric acid, carboxylic acids, phosphates, corrosion inhibitors and biodegradable surfactants. Bath temperature 4 degrees Celsius
It is maintained at 3.3-56.1 degrees (110-133 degrees Fahrenheit) and the current density is about 0
. 0.62 to 0.233 amps / cm (about 0.4 to 1.5 amps / in 2). The area ratio between the cathode and the anode must be at least 2: 1. The stent may be further processed if desired, for example, by applying a biocompatible coating.

Direct laser cutting produces edges that are essentially perpendicular to the axis of the laser cutting beam, whereas chemical etching and the like produces pattern edges that are oriented at an angle. Thus, the laser cutting process of the present invention essentially gives the stent a square or rectangular cross-sectional shape rather than trapezoidal from cut to cut. The resulting stent structure provides superior performance.

The stent tubing is made from a suitable biocompatible material such as, for example, stainless steel, titanium, tantalum, superelastic (nickel-titanium (NiTi)) alloys, and high strength thermoplastic polymers. Since the stent diameter is very small, the tubing from which it is made must necessarily have a small diameter. In percutaneous transluminal coronary angioplasty applications, typically the stent is in an unexpanded state with an outer diameter of about 1.65 mm (0.065 inch), the same outer diameter as the hypo tubing from which it is manufactured. Has a diameter,
And expanded to an outer diameter of 5.08 mm (0.2 inches) or more. The wall thickness of the tubing is approximately 0.076 mm (0.003 inches). Other body implanted stents, for example, in percutaneous transluminal angioplasty applications, have correspondingly larger tubing dimensions. While it is preferred to manufacture the stent by laser cutting the tubing, those skilled in the art will weld the longitudinal edges to form a cylindrical member after laser cutting the flat sheet and roll it into a cylindrical structure. Understand that a stent can be manufactured by this.

If the stent is made of plastic, the implanted stent must be heated within the arterial site where the stent is to be expanded to facilitate expansion of the stent. Once expanded, it is cooled to maintain the expanded state. The stent is conveniently heated by directly heating the fluid within the balloon or the balloon itself by known methods.

Stents are also manufactured from materials such as, for example, superelastic (sometimes called pseudoelastic) NiTi alloys. In this case, the stent is formed to full size,
A smaller diameter is deformed (eg, compressed) on the balloon of the delivery catheter to facilitate intraluminal delivery to the desired intraluminal site. The stress caused by the deformation changes the stent from the martensitic phase to the austenitic phase. Then, once the stent reaches a desired intraluminal location and the force is released, the transformation to a more stable austenite phase results in expansion of the stent. For further details on how NiTi superelastic alloys work, see US Pat.
, 665,906 (Jervis) and 5,067,957 (Jervi).
s Jarvis).

Although the invention has been illustrated and described herein in connection with its use as an intravascular stent, in other cases the stent may be used in all blood vessels in the body. Will be apparent to those skilled in the art. Because the stent of the present invention has the novel feature of preserving its structural integrity while expanding to very large diameters, the stent of the present invention can be used in almost any vessel where such a device is used. Particularly suitable for implantation into. This feature, combined with the limited longitudinal contraction of the stent when the device is radially expanded, provides a very desirable support member for all blood vessels in the body. Other changes and modifications can be made within the scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a cutaway side elevational view depicting a stent embodying features of the present invention mounted on a delivery catheter and positioned within a blood vessel.

FIG. 2 is a fragmentary side elevational view similar to FIG. 1, showing a state in which the stent is expanded in the blood vessel to press the inner layer against the blood vessel wall.

FIG. 3 is a fragmentary side elevational view showing the stent expanded within the blood vessel after withdrawal of the delivery catheter.

FIG. 4 is a plan view of a flattened portion of a stent according to one embodiment of the present invention, showing a serpentine pattern and a varying number of interconnecting members of the stent such that one end is more flexible than the other end.

5 is an enlarged view of a major portion of the stent of FIG. 4, depicting a serpentine pattern along the peaks and valleys that form the cylindrical elements of the stent.

FIG. 6 is a perspective view showing the stent of FIG. 4 in an expanded state.

FIG. 7 illustrates a flattened portion of another embodiment of a stent according to the present invention, illustrating a serpentine pattern and a varying number of interconnecting members to obtain a flexible end and a relatively rigid central portion. FIG.

FIG. 8 is a plan view of a flattened portion of another embodiment of a stent according to the present invention, wherein the interconnect members have been modified to obtain a flexible end.

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Claims (24)

[Claims] 1. A stent that is longitudinally flexible and expandable from a reduced condition to an expanded condition for implantation in a body lumen, the stent extending about a longitudinal stent axis. A plurality of cylindrical elements, each having an outer periphery, adjacent to each other, wherein the cylindrical elements are disposed cylindrically along a longitudinal stent axis to form a generally tubular member; Have a first end, a second end, the first end and a second end.
And a central portion between the ends of the first and second portions, such that the first and second portions are relatively more flexible than the central portion.
The adjacent cylindrical elements at the central portion are connected by n interconnecting members, and the adjacent cylindrical elements at at least one of the first end and the second end are nk A plurality of interconnected members, wherein k is a number selected from the group consisting of 1, 2, 3, 4 or 5, and n> k. 2. The method of claim 1, wherein both the first and second ends include adjacent cylindrical elements connected by an nk number of the interconnecting members. The stent according to any of the preceding claims. 3. The stent of claim 1, wherein the stent is laser cut from tubing.
A stent according to claim 1. 4. The stent of claim 1, wherein at least one of the first and second ends has n of the interconnect members. 5. The cylindrical element is formed in a meandering wavy pattern extending transverse to the longitudinal axis, and the meandering wavy pattern has a plurality of alternating tops, valleys and double bends. The stent according to claim 1, wherein: 6. The n and nk interconnecting members connect a valley of one cylindrical element to a double curved portion of the cylindrical element adjacent to the cylindrical element. The stent of claim 5. 7. The cylindrical member does not change appreciably the overall length of the stent,
The stent of claim 1, wherein the stent is configured to expand from a first smaller diameter to an expanded diameter range. 8. The stent of claim 5, wherein the apex has an irregular radius of curvature such that the apex expands uniformly and uniformly with expansion. 9. The stent of claim 1, wherein the stent is formed from a flat piece of material.
A stent according to claim 1. 10. The stent is made of stainless steel, tungsten, tantalum, superelastic nickel,
The stent according to claim 1, wherein the stent is formed from a biocompatible material selected from the group consisting of a titanium alloy and a thermoplastic polymer. 11. The stent of claim 1, wherein the stent has a radial expansion ratio of about 1.0 in a contracted state to about 4.0 or more in an expanded state. . 12. The stent of claim 1, wherein the stent is formed from a single piece of tubing.
A stent according to claim 1. 13. A stent that is longitudinally flexible and expandable from a reduced condition to an expanded condition for implantation in a body lumen, the stent extending about a longitudinal stent axis. A plurality of adjacent cylindrical elements having an outer periphery and being substantially independently radially expandable and aligned along a longitudinal stent axis, the plurality of adjacent cylindrical elements being the first cylindrical element; One end,
A second end and a central portion between the first end and the second end, and the cylindrical element meanders extending transverse to the longitudinal axis. It has a valley, a top, and a double curved portion that are formed in a wave pattern and appear alternately,
And a plurality of adjacent cylindrical elements arranged such that the tops of the adjacent cylindrical elements are out of phase with each other; A plurality of interconnecting members connecting the doubly curved portions to each other, wherein the stent has a relatively small number of interconnecting members at at least one of the first and second ends; A stent having a relatively large number of said interconnecting members in said central portion. 14. The stent of claim 13, wherein the serpentine pattern differs in shape and size along adjacent peaks and valleys. 15. The cylindrical element cooperates to define a generally smooth cylindrical surface, and wherein the top forms a projecting edge that projects outwardly from the cylindrical surface as it expands. 14. The stent according to claim 13, wherein: 16. The stent is made of stainless steel, tungsten, tantalum, superelastic nickel,
14. The stent of claim 13, wherein the stent is formed from a biocompatible material selected from the group consisting of a titanium alloy and a thermoplastic polymer. 17. The stent of claim 13, wherein the stent has a radial expansion ratio of about 1.0 in a contracted state to about 4.0 or more in an expanded state. . 18. The stent according to claim 13, wherein said first and second ends have an unequal number of said interconnect members. 19. A stent that is longitudinally flexible and expandable from a reduced condition to an expanded condition for implantation in a body lumen, each stent extending around a longitudinal stent axis. A plurality of adjacent cylindrical elements having an existing perimeter and being substantially independently radially expandable and aligned along the longitudinal stent axis; and extending transverse to the longitudinal axis. A cylindrical element formed in a meandering wavy pattern and having alternating valleys, peaks and double bends, wherein said adjacent cylindrical elements are joined by an interconnect An end, a second end, a central portion between the first end and the second end, and n interconnecting members in the central portion, and k Pieces of the interconnecting members And the second comprises at least one of the ends, n: the ratio of k, 1: 2, 1: 3, 1: 4,1: 5,1: 6,1: 7,1: 8,
A stent selected from the group consisting of 1: 9, 1:10, 2: 3, 2: 5, 3: 4 and 3: 5. 20. The stent of claim 19, including k of said interconnect members in said first and second ends. 21. The stent of claim 20, wherein the doubly curved portions in the first end each include one of the interconnecting members. 22. The stent of claim 21, wherein the doubly curved portions in the second end each include one of the interconnecting members. 23. The stent of claim 20, wherein at least one of the first and second ends includes every other double curved portion. 24. The stent of claim 20, wherein at least one of the first and second ends and the central portion includes an identical number of the interconnect members.