JP2016059506A - Stent which can be properly placed to lesioned part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stent which can be placed to a lesioned part which has vasoconstriction without deviation.SOLUTION: A stent 1 is configured so that, annular units formed by connecting plural cells having a substantially linear part and substantially arc part and having a substantially U-shape opening to one end side along an axial direction, are arranged in the axial direction and connected by connection parts, for forming a tubular body, the tubular body can expand from its inside to a radial direction. First annular units 3 formed of a first cell group formed by connecting the plural first cells 2 in a peripheral direction, and second annular units 3' formed of a second cell group formed by connecting the plural second cells 2' in the peripheral direction, are alternately disposed to surround a stent center shaft. The shapes of the first cells and second cells are symmetric to a stent shaft direction with the connection parts as a center, and only some of cells, out of plural relative cells of the adjacent first and second annular units, are connected by the connection parts.SELECTED DRAWING: Figure 1

Description

The present invention relates to a stent used for improving narrowing of an opening in a living body such as a blood vessel.

Stents are used to treat various diseases caused by stenosis or occlusion of blood vessels or other in-vivo lumens, to expand the stenosis or occlusion site and to maintain the size of the lumen. Is a medical device. A stent is a coil made of a single linear metal or polymer material, a metal tube cut out and processed by a laser, a linear member welded and assembled by a laser, a plurality of linear shapes There are things made by weaving metal.

These stents can be classified into those that are expanded by a balloon (balloon expanding type) and those that expand themselves by removing a member that suppresses expansion from the outside (self-expanding type). The balloon expand type is attached to the balloon portion (balloon catheter) in which an expandable member such as a balloon is attached near the distal end of the intravascular catheter (balloon catheter) (mounting process), and the catheter is moved to the treatment site in the body lumen of the patient. The balloon is inflated at the treatment site, and the stent is expanded and placed. The balloon is then deflated and the catheter is removed. When the balloon is expanded, the expansion pressure is adjusted according to the state of the tubular tissue to be expanded and the mechanical strength of the stent.

In the stent, the strength not to be defeated by the tubular tissue to be expanded, the flexibility that can be advanced without difficulty to the target site by proceeding in the severely bent tubular tissue, when placed in and after placement in the tubular tissue, Post-expansion flexibility to prevent damage to the tubular tissue as much as possible, expansion uniformity to cover the tubular tissue more uniformly and fineness of the design, the operator confirms the position by X-ray during placement Various performances such as X-ray opacity are required. A number of stent designs have been provided to meet these requirements. These are disclosed in Patent Document 1 and Patent Document 2, for example.

In recent years, these stents have been frequently used especially for angioplasty of the heart and carotid artery, and it has been shown that the frequency of restenosis is significantly reduced by stent placement, At present, restenosis is still caused with a high probability. For example, regarding the cardiac coronary artery, even when stenting is performed, the occurrence of restenosis has been reported with a frequency of about 20 to 30%. This restenosis may be induced from biological vascular injury or vascular injury due to stent placement. It is considered that typical vascular stenosis and restenosis induced by vascular injury is caused by proliferation of intimal smooth muscle cells. First, smooth muscle cells start to grow following vascular injury, and then the smooth muscle cells migrate to the intima. Smooth muscle cells in the intima then proliferate with matrix deposition resulting in intimal thickening.

For example, Patent Document 3 proposes an attempt to reduce the restenosis rate by covering a stent with a drug that restricts occlusion. There are many drugs that limit obstruction, such as anticoagulants, antiplatelet substances, antispasmodics, antibacterial drugs, antitumor drugs, antimicrobial agents, anti-inflammatory agents, antimetabolite drugs, and immunosuppressants. It is being considered. With regard to immunosuppressive agents, attempts have been proposed to reduce restenosis by coating stents with cyclosporine, tacrolimus (FK-506), sirolimus (rapamycin), mycophenolate mofetil, and their analogs. As a specific example, for example, Patent Document 4 discloses a stent coated with sirolimus (rapamycin), which is known as an immunosuppressive agent, and Patent Document 5 discloses a stent coated with taxol (paclitaxel), which is an antitumor agent. ing. For example, Patent Document 6 and Patent Document 7 disclose a stent coated with tacrolimus (FK-506). However, even with these drug-coated stents, restenosis after stent placement has occurred at a certain rate, and in order to further reduce the restenosis rate, optimization of the base stent design Is currently required.

As a conventionally known stent structure, there is a structure shown in FIG. 7 (the structure described in FIG. 1 of Patent Documents 8 and 9). In the stents disclosed in Patent Documents 8 and 9, a plurality of cells 11 are connected in the circumferential direction, a plurality of the cells 11 are arranged so as to surround the central axis C1 of the stent 15, and the annular unit 12 is configured. The opposing cells 11, 11 'of the matching annular units 12, 12' are connected by a substantially S-shaped connecting portion 14, respectively.

As another stent structure, the structure shown in FIGS. 3 and 5 (the structure described in FIGS. 1 and 3 of Patent Document 10) is known. In this stent, a first annular unit 8 composed of a first cell group in which a plurality of first cells 7 are connected in the circumferential direction, and a second cell in which a plurality of second cells 7 ′ are connected in the circumferential direction. A group of second annular units 8 'are alternately arranged so as to surround the central axis C1 of the stent 6, and a part of the adjacent first and second annular units 8, 8' in the opposed cells. Are connected by a connecting portion 9, and the shapes of the first cell 7 and the second cell 7 ′ are symmetrical with respect to the axial direction of the stent 6 around the connecting portion 9, and the cells of the connecting portion 9 are It is slightly longer than the unconnected cell.

Furthermore, regarding the other company stent 1 (S-Stent) shown in FIG. 8 that is currently on the market, the cells 16, 16 ′ are partially connected by the connecting portion 17, and the length of the cell is a constant value. The length of the connecting portion 17 is about 0.2 mm. In the case of the other company stent 2 (Driver) shown in FIG. 9 which is currently on the market, the cells 18 and 18 ′ are formed by bending a CoCr alloy wire in a zigzag shape, and the connection portion 19 is partially connected by welding. Yes.

In recent years, a stent treatment method has been rapidly popularized to restore blood flow by mechanically dilating an arterial lesion that has been narrowed due to the progression of arteriosclerosis using a balloon catheter, and placing a metal stent in the lumen of the affected area. It has become. A stent used for such a therapy needs to satisfy the following three requirements. First, the closed stent is placed on a balloon attached to the distal end portion of the balloon catheter, and passed through the patient's tortuous artery along a guide wire that has been inserted into the artery in advance. Transport to the constriction. Thus, the stent must be flexible in order to pass through the narrow and tortuous artery. Second, the expanded stent must be durable enough to withstand repeated bending loads caused by the heartbeat, with sufficient strength to support the arterial wall or keep the stenosis open. . Third, when the stent is expanded by inflating the balloon of the balloon catheter, the total length of the expanded stent becomes shorter than the length of the closed state. If the length of the expanded stent is shortened, the lesion may not be covered as per the doctor's treatment plan. Therefore, it is desirable that the stent before and after expansion has a small dimensional change.

As a result of thorough examination of conventional stent designs, the present inventors have found that the stents disclosed in Patent Documents 8 and 9 are uniform in flexibility and have sufficient strength to maintain the open state of the stenosis. As a result of finite element analysis, when the stent is subjected to a bending load, the maximum stress is generated at the top of the bending portion 13 constituting the S-shaped connecting portion, and the bending durability is determined as a result of the fatigue durability test. It was found that the bending durability of the top portion of 13 is inferior to the bending durability at the substantially straight portions constituting the opposing cells 11, 11 'and the S-shaped connecting portion. In stent treatment, when the stent is subjected to a very complicated deformation such as bending or twisting in a blood vessel, it is necessary to avoid excessive stress from being generated at the top of the arc constituting the bent portion 13 in terms of durability. In this respect, the stents disclosed in Patent Documents 8 and 9 have a problem.

The stent described in Patent Document 10 has sufficient bending durability when subjected to a bending load as a result of the physical property evaluation, but the standard expansion pressure at the time of stent expansion is disclosed in Patent Documents 8 and 9. It was found to be higher than 7 stents and difficult to open. Therefore, the stent disclosed in Patent Document 10 has a problem in terms of expandability. Further, the other stents shown in FIGS. 8 and 9 that are currently on the market also have difficulty in terms of expandability, similar to the stent disclosed in Patent Document 10.

Expansion uniformity is one of the performance requirements of a stent. The stent is always expanded uniformly, and it is required to receive and distribute the force from the in-vivo lumen. When the stent is expanded non-uniformly, problems such as breakage or breakage of the stent due to concentration of load, damage to the biological tissue caused by non-uniform contact with the biological tissue, and the like arise. These problems have a major impact on restenosis after stent placement. In the case of drug-coated stents, it is important that the drug be uniformly transferred to the lumen in the body, so that the expansion uniformity of the stent is increasingly important.

In general, stent designs often consist of a series of basic units and are designed to be uniformly expanded. However, in actual use, it is often expanded non-uniformly due to severe bending of the in-vivo luminal region, and there is a need for a stent design that can be expanded even at the bent part. It is.

In addition, the stent is required to have high flexibility. In many cases, a stent is placed in a finely bent blood vessel. In such a case, the flexibility of the stent is particularly important. When the stent is inflexible, a large force is always applied to the blood vessel portion in which the stent is placed due to the pulsation of the heart or the like. Conversely, if the stent is flexible, it is possible to minimize such vascular irritation. However, there are limits to reducing the number of axial links to increase the flexibility of the stent or increasing the flexibility by making the links thinner. If the number of links is reduced, the uniformity when the stent is expanded is lowered, and if the links are made thinner, the risk of breakage due to metal fatigue and breakage of the link portion is increased.

In addition, when the stent was mounted on a balloon catheter and crimped, dog bones were formed at both ends of the balloon catheter, and the stent was shortened when the stent was expanded due to the influence.
Japanese Patent Application Publication No. JP-A-2-174859 Japanese Patent Application Publication No. 6-181993 Japanese Patent Application Publication No. 5-502179 Japanese Patent Application Publication No. 6-9390 Japanese Patent Application Publication No. 9-503488 International Publication No. WO02 / 065947 Specification European Patent Publication No. 12554674 Japanese Patent No. 3654627 Specification Japanese Patent No. 3663192 Specification Japanese Utility Model Registration No. 3145720 Specification

Accordingly, the objects of the present invention are as follows: (1) It has a high flexibility that can be easily transported through a meandering thin artery, has excellent extensibility during stent expansion, supports the artery wall, and opens the stenosis. Providing a stent that has sufficient strength to maintain the state and has excellent durability to withstand repeated bending loads on arteries caused by heartbeat, (2) Uniform expansion even at the bending portion of the body lumen Is to provide a stent for living indwelling that is superior to the above, to provide a stent for living indwelling with a low restenosis rate after stent placement, and (3) a vessel diameter retaining force that maintains the patency of the lumen diameter Excellent, flexible stent with excellent expandability and excellent followability to lumens (thus allowing passage through three-dimensionally meandering lumens), no shortening, and capable of forming lateral holes in the stent. Offer To be to provide a (4) also occurred dogbone balloon catheter scalable uniformity stent.

As a result of various studies focusing on the substantially arc portion of the cell with regard to the bending durability, the present inventors have found that the maximum stress in the approximately arc portion of the cell is repeated due to the heartbeat after stent expansion by the balloon and after placement of the stent. The maximum stress caused by bending load greatly depends on the structure of the cell connection part. Particularly, the optimization of the structure of the connection part between the opposing cells makes a breakthrough in bending durability without impairing expandability. Has been found to improve.

As a result of further investigations, the inventors have made the radius of curvature of the top of the arc constituting the substantially arc portion of the cell larger than the radius of curvature of the tangential circle formed at the arc-side end of the substantially linear portion of the cell. As a result, when the stent is subjected to a bending load, the stress and strain are almost uniformly distributed, the load applied to the cell is reduced most, and the bending durability is excellent, and the standard expansion pressure is lowered and the expansion uniformity is also reduced. After confirming that it was excellent and flexible, the present invention was achieved.

That is, according to the present invention, an annular unit formed by connecting a plurality of cells each having a substantially U-shaped shape having a substantially straight portion and a substantially arc portion and opened to one end along the axial direction is provided in the axial direction. A tubular body is formed by arranging a plurality of parts and being connected by a connecting portion, and the tubular body is a stent that is radially expandable from the inside thereof,
A first annular unit consisting of a first cell group connecting a plurality of first cells in the circumferential direction, and a second annular unit consisting of a second cell group connecting a plurality of second cells in the circumferential direction. Are alternately arranged so as to surround the central axis of the stent, and the shapes of the first cell and the second cell are symmetrical with respect to the axial direction of the stent around the connecting portion, and the adjacent first and second cells In the stent formed by connecting only a part of the cells in the plurality of opposing cells of the second annular unit by a connecting portion, and the connecting portion is formed by connecting the substantially arc portions of the opposing cells. ,
The curvature radius of the apex of the arc forming the substantially arc portion of the cell in substantially all cells constituting the stent is 1.1 to 1.5 times the radius of curvature of the tangential circle of the substantially straight portion of the cell. The stent is characterized in that a misalignment prevention portion is provided at the center of the stent that can be placed without being displaced at the lesion site. The stent has a first end portion, a second end portion, and a misalignment prevention portion. The first end portion and the second end portion are 1 to 3 annular units from both ends of the stent, and the misalignment prevention portion is The stent is composed of 1 to 3 annular units in the center of the stent. The stent is characterized in that the first end portion, the second end portion, and the misalignment prevention portion have the same strength. In addition, it is preferable that the first end portion, the second end portion, and the misregistration prevention portion have higher strength than other portions.
Here, the strength refers to the difficulty of deformation in the major axis direction and the rigidity against compression in the radial direction.

  In the stent, it is preferable that the radius of curvature of the arc of the substantially arc portion of the cell is in a range of 1.2 to 1.4 times the radius of curvature of the tangential circle of the substantially straight portion of the cell.

  In the above-mentioned stent, it is preferable that the lengths of the substantially straight portions of both cells connected by the connecting portion are the same and slightly longer than the length of the substantially straight portion of the cells of the non-connecting portion. . In general, the substantially straight line portion of the cells connected by the connecting portion is approximately 10 to 25% longer than the substantially straight line portion of the non-connected portion cell. .About 1 to 0.3 mm.

  In the stent, each of the annular units includes 6 to 10 cells, and the first end, the second end, and the misalignment prevention unit include 3 to 5 cells. It is preferable that the annular unit is a stent in which 1 to 3 cells form a connecting portion between the cells.

  In the above stent, the connecting portion may be constituted by a short linear object between the substantially arc portions of the opposed cells and the substantially arc portions, but the substantially arc portions and the substantially arc portions of the opposed cells are directly connected. It is preferable that the connecting portion is constituted by this, and it is particularly preferable that the connecting portion has a structure in which the apexes of the central arcs of the substantially arc portions of the opposing cells share each other. It is preferable that the width and thickness of the cell and the connecting portion are constant.

  In the above stent, the material forming the stent is preferably a cobalt chromium alloy or stainless steel, and a material made of a biodegradable metal or a biodegradable polymer is preferable. As the biodegradable metal, pure magnesium, magnesium alloy, pure iron or iron alloy is preferable.

As is apparent from the above description, according to the present invention, the following effects can be expected. That is, (1) In a conventional stent in which cells are connected by a substantially S-shaped connecting portion (the connecting portion 14 in FIG. 7), the cells in the adjacent annular units are opposed to each other without the substantially S-shaped connecting portion. The curvature radius of the apex of the arc forming the substantially arc portion of the cell in substantially all the cells constituting the stent by connecting only some of the cells to each other is set to the arc side of the substantially straight portion of the cell. -By making it larger than the radius of curvature of the tangential circle formed at the end, the stress and strain applied to the cell are uniformly distributed, and the durability against bending load can be improved without sacrificing flexibility. it can. (2) Since only a part of the opposing cells is connected and the substantially arc shape of the cell in the connecting portion is as described above, the standard expansion pressure is lowered, so that the bending load described above is not impaired without impairing expandability. It is possible to drastically improve the durability against. (3) By gradually increasing the number of connecting portions from the center of the stent toward both ends, the stent can be expanded uniformly. Moreover, since it is easy to expand between adjacent annular members, a horizontal hole can be formed.

It is a top view which shows an example of the stent of this invention. It is the elements on larger scale of FIG. It is a top view which shows an example of the conventional open cell stent. FIG. 4 is an enlarged view of FIG. 3. It is a top view which shows another example of the conventional open cell stent. FIG. 6 is an enlarged view of FIG. 5. It is a top view of the conventional closed cell stent. It is a schematic plan view which shows the connection between the annular units of another company's stent. It is a schematic plan view which shows the connection between the annular units of another company's stent. It is a conceptual diagram of the strut which comprises a cell. It is the schematic which shows the sample for a bending test. It is a graph which shows the maximum distortion about the stent of an Example and a comparative example. It is a schematic plan view of the tangent circle formed in the circular arc side edge part of the linear part of a cell. It is a top view which shows another example of an open cell stent. It is a top view which shows another example of an open cell stent. It is a top view which shows another example of an open cell stent.

(Basic shape of stent)
Hereinafter, specific embodiments of the stent of the present invention will be described in detail with reference to the drawings. FIG.
These are top views which show an example of the stent 1 of this invention. FIG. 2 is an enlarged view showing a connecting portion of the stent 1 shown in FIG. As shown in FIG. 1, in the stent 1 of the present invention, the circumferential direction is such that the cells 2, 2 ′ having a substantially U-shape opened to one end along the axial direction surround the central axis C <b> 1 of the stent 1. Are connected to each other to form an annular unit 3, 3 ′.
A plurality of 3's are arranged in the axial direction and connected by a connecting part 4 to form a tubular body. The tubular body can be extended in the radial direction from the inside thereof, and the U-shaped cell is composed of a substantially linear portion and a substantially arc portion 5.

In the stent of the present invention, a first annular unit 3 composed of a first cell group in which a plurality of first cells 2 are connected in the circumferential direction and a second ring unit in which a plurality of second cells 2 ′ are connected in the circumferential direction. A tubular body is formed by alternately connecting the second annular units 3 ′ composed of cell groups, and the first cell 2 and the second cell 2 ′ are symmetrical with respect to the connecting portion 4. doing. Annular unit 3, 3 '
Only a part of a plurality of cells facing each other is connected by a connecting portion 4 (open cell type). Since only some of the cells are connected, the flexibility of the stent can be obtained compared to the case where all the cells are connected (closed cell type). The connecting portion 4 connecting the first annular unit 3 and the second annular unit 3 ′ and the connecting portion 4 ′ connecting the adjacent annular units 3 ″, 3 ′ ″ are along the axial direction C1. Therefore, it is preferable to arrange them in a row a, a ′ because cell expansion during stent expansion tends to be less likely to be unbalanced in the axial direction. In the present invention, the connection structure in the connection portion 4 may be such that the tops of the substantially arc portions of the opposing cells may be connected with a short non-bent linear object of 0.1 to 0.3 mm. The substantially straight line portions of the cells connected by the portion 4 are slightly longer than the substantially straight line portions of the cells of the non-connected portion, and the top of the substantially arc portion 5 of one cell is the substantially arc portion of the other cell. 5 is preferably in direct contact with 5. When connected via a short linear object, when subjected to a bending load, maximum stress may be generated at the center of the linear connecting part, which may be disadvantageous in terms of bending durability. In the case of connection, the maximum stress is generated at four locations around the connecting portion (see reference numeral 22 in FIG. 2), the level of the maximum stress can be reduced, and the bending durability can be improved. In this case, it is particularly preferable from the viewpoint of uniformity of expansion that the substantially straight line portions of both cells are equal and slightly longer. By making the substantially straight line portions of the cells equal, the cells open at the same angle and the blood vessels can be supported uniformly. Therefore, among the opposing cells 2 and 2 ′, the cells 2 and 2 ′ connected by the connecting portion 4 are connected to each other, so there is no gap between the opposing cells. As shown in FIG. 1, a gap is formed between the cells 2 and 2 'between the substantially arc portions of the cells, and the substantially straight portion of the cell of the connecting portion is not a distance corresponding to the gap. It is slightly longer than the substantially straight part of the cell of the connection part. The presence of this slight gap in the unconnected portion prevents cells from overlapping when the stent is bent or contracted, and the opposing cells when the stent is bent. Will not win. Usually, the substantially straight part of the cells connected by the connecting part is approximately 10 to 25% longer than the substantially straight part of the cells of the non-connected part. If it is less than 10%, the gap between the cells 2 and 2 'in the unconnected portion is too small to sufficiently obtain the above effect, and if it exceeds 25%, the space becomes large and blood vessels are uniformly supported. In addition, it is disadvantageous in terms of expansion uniformity if the length of the cell of the connecting portion is longer than the length of the cell of the non-connecting portion, and stress is easily applied to the connecting portion.

The stent of the present invention shown in FIG. 1 is an annular unit that is formed by connecting a plurality of cells each having a substantially U-shape that is open at one end along the axial direction, and that has a substantially straight portion and a substantially arc portion. Are arranged in the axial direction and connected by a connecting portion to form a tubular body, and the tubular body is a stent that can expand radially from the inside thereof,
A first annular unit consisting of a first cell group connecting a plurality of first cells in the circumferential direction, and a second annular unit consisting of a second cell group connecting a plurality of second cells in the circumferential direction. Are alternately arranged so as to surround the central axis of the stent, and the shapes of the first cell and the second cell are symmetrical with respect to the axial direction of the stent around the connecting portion, and the adjacent first and second cells In the stent formed by connecting only a part of the cells in the plurality of opposing cells of the second annular unit by a connecting portion, and the connecting portion is formed by connecting the substantially arc portions of the opposing cells. ,
The curvature radius of the apex of the arc forming the substantially arc portion of the cell in substantially all cells constituting the stent is 1.1 to 1.5 times the radius of curvature of the tangential circle of the substantially straight portion of the cell. The stent is characterized in that a misalignment prevention portion is provided at the center of the stent that can be placed without being displaced at the lesion site. The stent has a first end portion, a second end portion, and a misalignment prevention portion. The first end portion and the second end portion are 1 to 3 annular units from both ends of the stent, and the misalignment prevention portion is The stent is composed of 1 to 3 annular units in the center of the stent. The stent is characterized in that the first end portion, the second end portion, and the misalignment prevention portion have the same strength. The first end portion, the second end portion, and the misregistration prevention portion are stronger than the other portions. By adopting such a configuration, the present invention improves the expansion uniformity of the stent.

(General arc shape of the cell)
In the stent of the present invention, the radius of curvature of the top of the arc constituting the substantially arc portion 5 of the cell constituting the stent is a tangent circle 2 formed at the arc-side ends of the two substantially straight portions of the cells 2 and 2 ′.
It is in the range of 1.1 to 1.5 times the radius of curvature of 1,21 ′, preferably in the range of 1.2 to 1.4 (see FIG. 13). As a result, the level of the maximum stress generated at the top of the substantially arc portion due to the bending load is reduced, the durability against repeated bending loads is improved, and the stress and strain are evenly distributed during expansion, so that the expansion uniformity is improved. As a result, the standard expansion pressure is lower than that of the conventional stent, and the safety factor of the expansion operation is improved. If the radius of curvature is less than 1.1 times the radius of curvature, it is difficult to reduce the level of the maximum stress generated at the top of the substantially arc portion, and if the radius of curvature exceeds 1.5 times the radius of curvature, Stress is generated at the boundary with the substantially arc portion, and the durability improvement effect cannot be obtained. On the other hand, if the ratio exceeds 1.5 times, the top of the arc becomes too large, and the arcs may interfere with each other when crimping the stent, which is not preferable. The cells 2 and 2 'have a greater radial support force when the stent is expanded at an obtuse angle with respect to the central axis C1. As the angle θ formed by the two substantially linear portions of the expanded cell approaches 120 °, the radial support force of the stent increases. That is, in the design of the stent, when the cell is expanded to at least φ2.5 mm, the angle θ after cell expansion is preferably designed to be at least 50 ° or more.

(Stent dimensions)
In the present invention, the size of the stent (the length when the stent is not expanded, the diameter when the stent is not expanded) is not particularly limited, and may be the same as a conventionally used stent.
It is preferably about 9 to 40 mm, and the diameter when not expanded is about 0.8 to 2 mm. The length of one annular unit of the stent is preferably about 0.5 to 3.0 mm. The length of one connecting portion (the length of the gap in the axial direction between the cells of the non-connecting portion) is preferably about 0.05 to 1 mm, more preferably 0.1 to 0.3 mm.
The number of cells 2, 2 ′ arranged in the circumferential direction is preferably 4 or more. Further, when the diameter after expansion is φ3.0 mm or more, it is preferable to arrange 6 or more, usually 6 to 12 pieces. In addition, it is preferable that the annular units 3 and 3 ′ are arranged in a total of 6 or more, usually 6 to 12, in the stent axial direction by combining both annular units. Further, in the stent axial direction, 3 or more per 10 mm, usually 4 to 8 are arranged, and when the target diameter for stent expansion (standard diameter, for example, φ3.0, φ4.0) is reached, for example, as described above In addition, the angle θ after cell expansion is preferably designed to be at least 50 ° or more, usually 60 ° to 120 °. Designing to exceed 120 ° in the target diameter is effective for the radiation support force of the stent, but there is a problem that the deformation amount of the substantially circular arc portion 5 becomes large. In addition, the shortening of the total length (four shortening) of the stent accompanying expansion becomes large, which causes problems such as difficulty in positioning during stent placement, which is not preferable.

The struts (two straight portions) of the cells 2 and 2 ′ are preferably formed in a radially symmetrical shape as shown in FIG. 10 with respect to the center line C1 in the stent axial direction. Further, in the stent 1, the thickness of the cell 2 is usually constant. Generally, in the stent 1 made of a cobalt chromium alloy, the width of the cell 2 is usually 70 to 110 μm, and the thickness is 45 to 90 μm. In the stent 1 made of stainless steel, the width of the cell 2 is usually 80 to 150 μm and the thickness is 100 to 150 μm. In this invention, it is preferable that the width | variety and thickness of the cell 2 in the cyclic | annular unit 3 and the connection part 4 are constant. The constant width and thickness make it easy to control the dimensions during processing and polishing, and the constant width and thickness means that the cross-sectional area is constant and the bending moment in the same direction at any position. Tend to be the same, and the flexibility of the stent tends not to be affected by the direction. In particular, it is preferable that the cells are directly connected to each other, and the vertices of the center arc portions 20 and 20 'of the cells facing each other at the connecting portion overlap to make the thickness and width constant, thereby enhancing expansion uniformity (see FIG. 2).

In the stent 1 of the present invention, by configuring the connecting portion 4 as described above, since stress is not concentrated on the connecting portion 4, durability can be dramatically improved, and flexibility and expandability can be improved. There is an advantage that there is no decrease. In addition, since the connecting portions 4 are not provided in all of the individual cells 2 and 2 '(open cell type), the cells 2 and 2' are respectively provided even when the diameter of the stent 1 is reduced during delivery to the blood vessel. They do not overlap with each other in the radial direction of the stent.

  In the stent 1 of the present invention illustrated in FIGS. 1 and 2, at least one connection portion 4 of the cells 2, 2 ′ constituting each annular unit 3, 3 ′ needs to be formed in the circumferential direction of the stent 1. . As described above, since the number of cells arranged in the circumferential direction varies depending on the diameter of the stent, the number of connecting portions is selected according to the number of cells. Usually, the stent has a diameter of 2 to 6 mm and the number of cells of 6 to 10 It is preferable that the number of the connection parts in the case of a piece is 1-3. In the present invention, a connecting portion is formed only in a part between a plurality of opposing cells 2 and 2 ′, and the remaining cells 2 and 2 ′ are not connected but form a non-connecting portion. Due to the presence of the non-connecting portion, the entire stent 1 becomes more flexible, the delivery performance to the branched blood vessel is improved, and the stress on the arc portion forming the connecting portion is dispersed, so that the connecting portion is continuous without a gap. Thus, the durability is improved as compared with the stent disposed in the same manner.

(Stent material)
The stent of the present invention is manufactured from a metal pipe made of stainless steel such as SUS316, shape memory alloy such as Ni—Ti alloy, Cu—Al—Mn alloy, titanium alloy, tantalum alloy, cobalt chromium alloy and the like.
In addition, the stent of the present invention may be manufactured from a metal (biodegradable metal) that can be decomposed in vivo. Examples of the biodegradable metal include pure magnesium, magnesium alloy, pure iron, and iron alloy. Magnesium alloys include magnesium as the main component, Zr, Y, T
Those containing at least one element selected from the biocompatible element group consisting of i, Ta, Nd, Nb, Zn, Ca, Al, Li, and Mn are preferable. For example, magnesium is 50 to 98%, lithium (Li) is 0 to 40%, iron is 0 to 5%, and other metals or rare earth elements (cerium, lanthanum, neodymium, praseodymium, etc.) are 0 to 5% Can be mentioned. Iron alloys include iron as the main component, Mn, Co, Ni, Cr, Cu
, Cd, Pb, Sn, Th, Zr, Ag, Au, Pd, Pt, Re, Si, Ca, Li,
Those containing at least one element selected from the biocompatible element group consisting of Al, Zn, Fe, C, and S are preferred. For example 88-99.8% iron, 0.1-7% chromium and 0
Examples include -3.5% nickel as well as less than 5% other metals.
Furthermore, the stent of the present invention comprises a biodegradable polymer such as polylactic acid, polyglycolic acid, poly (lactic acid-glycolic acid), poly (lactic acid-ε-caprolactone), poly (glycolic acid-ε-caprolactone), poly ( A biodegradable high toughness polymer such as butylene succinate) may be made of a composite biodegradable polymer dispersed in a biodegradable matrix polymer such as polylactic acid. These biodegradable polymers may be stretched and oriented. Furthermore, a biodegradable polymer may be coated on a metal that can be decomposed in vivo.

The stent of the present invention has a shape having the above-described characteristics, but the stent having such a shape can be integrally manufactured by laser processing. The manufacturing process by laser processing will be described. First, a tool path in laser processing is created using CAM based on the shape data of the designed stent. The tool path is set in consideration of the fact that the stent shape can be maintained after laser processing and that no chips remain. Next, laser processing is performed on the thin tube made of metal or polymer. Control the generation of burrs and select machining conditions with the goal of high speed and high quality machining.

After the mesh shape is formed by laser cutting, the surface is finished glossy by electropolishing and the edge portion is finished in a smooth shape. In the processing process of the cobalt-chromium alloy stent, the post-processing process after laser cutting is important. In the stent after laser cutting, the oxide on the metal cut surface is first dissolved with an acid solution, and then electropolishing is performed. In electropolishing, a metal plate such as a stent and stentless is immersed in an electrolytic solution, and the two metals are connected via a DC power source. By applying voltage with the stent side as the anode and the metal plate side as the cathode, the stent on the anode side is dissolved to obtain a polishing effect. In order to obtain an appropriate polishing effect, it is necessary to examine the composition of the electrolytic solution and the applied current conditions.

The stent manufactured by the above laser processing method can form a network structure as designed, so that high flexibility and radiation support force are sufficiently secured, vasodilatability is enhanced, and foreshortening and flare phenomenon are suppressed. It is possible to provide a stent that does not cut cells or the like during use.

The diameter, length, material, and the like of the stent described above are merely examples, and do not limit the present invention.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention should not be limited by an Example. In the following examples and comparative examples, the expansion pressure, bending durability time, flexibility, for shortening value, recoil value, and maximum strain are those measured by the following methods.

(Measurement of expansion pressure)
A 3.0 mm diameter stent was inserted into a silicon tube having an inner diameter of 3.0 mm and an outer diameter of 4.0 mm, and the expansion pressure was measured when the inner diameter of the stent was expanded to 3 mm with a balloon through physiological saline.

(Measurement of bending endurance time)
As shown in FIG. 11, the both ends of the tube are fixed, the left end of the silicon tube is fixed to the stage, the right end is fixed to the cam, and the cam is operated by the rotation of the motor. It was reciprocated so that it bends 0 mm, the center part of the silicon tube was bent, and the durability time until it was broken by repeatedly bending the center of the stent inserted into the tube was measured.

(Evaluation of flexibility)
The bending strength was measured by a four-point bending method, and the flexibility was evaluated based on this value.

(For shortening value measurement)
The stent was inserted into a silicon tube having an inner diameter of 3.0 mm and an outer diameter of 4.0 mm, and the inner diameter of the stent was expanded to 3 mm through physiological saline. The length of the stent after expansion was measured, and the reduction ratio with respect to the length of the stent before expansion was calculated to obtain a for shortening value.

(Calculation of recoil value)
The stent was inserted into a silicon tube having an inner diameter of 3.0 mm and an outer diameter of 4.0 mm, and the inner diameter of the stent was expanded to 3 mm with a balloon through physiological saline. Thereafter, the balloon was removed, the inner diameter of the stent after the balloon was removed, and the recoil value was calculated by the following equation (1).

(Maximum strain measurement)
In order to evaluate the strain generated in each part of the stent from the viewpoint of material strength in the series of processes from the diameter reduction by the crimper to the placement by balloon expansion into the blood vessel, it was analyzed by computer simulation. Build a stent finite element model, enter appropriate material properties and characteristics, expand the stent to an inner diameter of 3.0 mm, then expand the stent to an inner diameter of 3.0 mm, and place it in the blood vessel. The maximum distortion that occurred was calculated.

The stent shown in the following (Example 1) was used as the stent of the present invention, compared with the stents of Comparative Examples 1 to 4 shown below, and the results are shown in Table 1 and FIG. Each of the stents used in Example 1 and Comparative Examples 1 to 4 has a length of 17.4 mm, an inner diameter of 1.0 mm when contracted, and an inner diameter of 3.0 mm when expanded. 4 has a constant width of 100 μm and a constant thickness of 70 μm, both of which are stents made of cobalt chromium alloy.

Example 1
The curvature radius of the top of the arc constituting the substantially arc portion 5 of all the cells of the connected portion and the non-connected portion of the stent shown in FIG. 1 is set to the radius of curvature R0.15 μ of the tangential arc of the substantially straight portion 2. On the other hand, the curvature radius is 1.3 times R0.20 μ (FIG. 2).
(The length of the cell in the unconnected portion: 1.2 mm, the length of one cell in the connected portion: 1.3 mm, the number of cells in one annular unit: 8)

(Comparative Example 1)
The conventional stent (closed cell stent) of Comparative Example 1 shown in FIG. 7 includes a first annular unit 12 composed of a first cell group in which a plurality of first cells 11 are connected in the circumferential direction, and the first cell. And second annular units 12 ′ composed of a plurality of second cells 11 ′ having a symmetric shape when viewed from the radial direction are alternately arranged, and all the opposing cells are connected to form a substantially tubular body. . The adjacent annular units 12 and 12 'are all connected by a connecting portion 14, can be extended in the circumferential direction from the inside of the tubular body, and connect a plurality of cells 11 in the circumferential direction. Are arranged so as to surround the central axis C1.
(Length of one cell: 1.2 mm, length of connecting portion: 0.6 mm, number of cells in one annular unit: 6)

(Comparative Example 2)
The radius of curvature of the top of the arc constituting the cell arc 10 of the stent of Comparative Example 2 shown in FIG. 3 is R0.15 μ (FIG. 4).
(Length of one cell: 1.2 mm, length of one cell in the connecting portion: 1.3 mm, number of cells in one annular unit: 6)

(Comparative Example 3)
The radius of curvature of the top of the arc constituting the cell arc 10 of the stent of Comparative Example 3 shown in FIG. 5 is R0.20 μ (FIG. 6).
(Length of one cell in the unconnected portion: 1.2 mm, length of one cell in the connected portion: 1.3 mm, number of cells in one annular unit: 6)

(Comparative Example 4)
The stent of Comparative Example 4 shown in FIG. 14 is similar to the conventional stent of Comparative Example 1 shown in FIG. 7. The opposed cells 11, 11 ′ of the annular units 12, 12 ′ are connected by a substantially S-shaped connecting part 14. Instead of the closed cell type connecting portion, an open cell type in which every other connecting portion is provided.

  As shown in Table 1, as a result of the test, the durability of the open cell stent (Example 1, Comparative Examples 2, 3, and 4) is greater than that of the closed cell stent (Comparative Example 1). This is presumably because the cell space is deformed in open cells (there are few constraint points and the degree of freedom), so that the load on the link is reduced and the bending durability is better than that of the closed cell stent. In comparison of the open cell stent groups, the durability of Example 1 is greater than that of other open cell stents. The reason for this is presumed that when Example 1 was subjected to a bending load, the maximum strain was reduced (see FIG. 12), the load applied to the cell was most reduced, and the bending durability was excellent. Further, the standard expansion pressure of Example 1 was 8 atm, which was lower than the standard expansion pressure of 9 atm of Comparative Examples 2 and 3, and it was confirmed that the expansion uniformity and flexibility were excellent. Moreover, for shortening, recoil, etc. are equivalent to conventional stents, and are excellent in balance between durability and performance.

In the stent design according to the present invention, first, the maximum stress / strain is minimized, and then the stent has a substantially constant stress / strain at each point along the cell arc portion 5, the cell straight portion and the cell connection portion 4. It is important to have a structure. FIG. 2 is an enlarged view of the arc portion 5 and the connecting portion 4 of the cell of the stent according to the first embodiment. Such a structure is more durable and provides a stent in which the cells are uniformly deformed and the stress and strain of the arc portion 5 and the connecting portion 4 are substantially uniform when subjected to a bending load.

As described above, in the stent of the present invention, the cell arc portion 5 and the connection portion 4 have a relatively low stress compared to the bent portion between the cells of Comparative Example 1 and the arc portion 10 and the connection portion 9 of Comparative Examples 2 and 3. It has a structure subject to strain. Further, the curvature radius of the top of the arc constituting the cell arc portion 5 is determined by the cell 2, 2 ′.
It has a radius of curvature 1.1 to 1.5 times the radius of curvature of the tangential circle formed at the arc-side end of the substantially straight line portion, and the cell is connected at the maximum by the connecting portion 4 Since stress and strain are minimized, the result is excellent bending fatigue durability, bending flexibility, and good expansion uniformity.

Since the present invention greatly contributes to the stent manufacturing technology by providing a stent having a structure excellent in durability against bending load and flexibility, industrial applicability is extremely large. Furthermore, since the stent of the present invention can be manufactured integrally by laser processing, the industrial applicability is great from this point.

Although the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the scope and spirit of the present invention disclosed in the claims. It will be understandable.

1 Stent 2, 2 ′ cell 3, 3 ′, 3 ″, 3 ′ ″ annular unit 4, 4 ′ connection portion 5 cell arc portion 6 Conventional stent (comparative examples 2 and 3)
7, 7 'cell 8, 8' annular unit 9 connecting part 10 arc part 11, 11 'cell 12, 12' annular unit 13 bent part 14 connecting part 15 Conventional stent (Comparative Example 1)
16, 16 'cell 17 connecting portion 18, 18' cell 19 welded portion 20, 20 'central arc 21, 21' tangential circle 22 maximum stress generation point a, a 'connecting portion row C1, ... central axis of stent

Claims (9)

A plurality of annular units formed by connecting a plurality of cells each having a substantially U-shape that opens to one end along the axial direction, each having a substantially straight portion and a substantially arc portion, are arranged in the axial direction. Are connected to form a tubular body, the tubular body being a radially expandable stent from the inside thereof,
A first annular unit consisting of a first cell group connecting a plurality of first cells in the circumferential direction, and a second annular unit consisting of a second cell group connecting a plurality of second cells in the circumferential direction. Are alternately arranged so as to surround the central axis of the stent, and the shapes of the first cell and the second cell are symmetrical with respect to the axial direction of the stent around the connecting portion, and the adjacent first and second cells In the stent formed by connecting only a part of the cells in the plurality of opposing cells of the second annular unit by a connecting portion, and the connecting portion is formed by connecting the substantially arc portions of the opposing cells. ,
The curvature radius of the top of the arc forming the substantially arc portion of the cell in substantially all cells constituting the stent is the radius of curvature of the tangential circle formed at the arc-side end of the substantially straight portion of the cell. The stent which provided the position shift prevention part in the stent center part which exists in the range of 1.1-1.5 times, and can be detained without shifting | deviating to a lesion site | part. The stent has a first end, a second end, and a misalignment prevention unit,
The first end portion and the second end portion are stents having 1 to 3 annular units from both ends of the stent, and the misalignment preventing portion is a stent having 1 to 3 annular units in the center portion of the stent. In the stent, the first end portion, the second end portion, and the misregistration prevention portion have the same strength. The stent according to claim 1, wherein the first end portion, the second end portion, and the misalignment prevention portion are stronger than the other portions.   2. The curvature radius of the apex of the arc constituting the substantially arc portion of the cell according to claim 1, wherein the curvature radius of the tangential circle formed at the substantially arc side end of the substantially straight portion of the cell is 1.2 to 1.. Stent that is 4 times.   In Claim 1, the length of the substantially straight line portion of both cells connected by the connecting portion is the same length, and is slightly longer than the length of the substantially straight line portion of the non-connected portion cell. Stent.   2. The stent according to claim 1, wherein a substantially straight portion of cells connected by the connecting portion is 10 to 25% longer than a substantially straight portion of cells of a non-connecting portion.   In Claim 1, each said cyclic | annular unit is comprised from 6-10 cells, The said 1st end part, the said 2nd end part, and the said position shift prevention part are 3-5 cells, Others In the above-mentioned annular unit, 1 to 3 cells form a connecting portion with the opposite cells. The stent according to claim 1, wherein the cell and the connecting portion have a constant width and thickness.