JP4654361B2 - Stent - Google Patents

Description

The present invention relates to a stent used for improving stenosis occurring in a living body such as a blood vessel, and particularly to a stent having excellent durability.

In recent years, a stent treatment method that rapidly expands the affected arterial lesion that has been narrowed due to the progression of arteriosclerosis with a balloon catheter and restores blood flow by placing a metal stent in the lumen of the artery has rapidly spread. It has become.
A stent used for such treatment 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. Or to the constriction. Thus, the stent must be flexible in order to pass through the narrow and tortuous artery. Secondly, the expanded stent has sufficient strength to support the incised arterial wall and keep the stenosis open, as well as repeated radial expansion and contraction due to the heartbeat. It must be durable enough to withstand bending.

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 planned by the doctor's treatment plan. Therefore, it is desirable that the stent does not shorten the length after expansion.

As a result of thorough examination of the conventional stent design, the inventors of the present invention disclosed the designs disclosed in Patent Documents 1 to 3, that is, a plurality of cells (6) were connected vertically, and the cells (6) were connected to the stent. A plurality of the tubular units (4) are arranged by surrounding the central axis (C1) of (1), and the adjacent tubular units (4) are connected to each other by at least one connection portion (5), The end of the bend (8) is connected to the left or right end of the cell (6), and the stent is uniform in flexibility and has sufficient strength to maintain the open state of the stenosis. Although it is an ideal design, it has been surprisingly found as a result of animal tests that a case where a bent portion forming a connecting portion is cut occurs. In stent treatment, such disconnection must be avoided. As a result of various investigations on the cause of disconnection of the connecting portion, the present inventors have generated a force that repeatedly bends the stent inserted into the blood vessel due to the heartbeat, and there is a problem with the durability of the connecting portion against this bending. I found. Durability can be easily improved by increasing the thickness of the connecting part, but flexibility and expansion, which are the characteristics of a stent with a structure in which adjacent tubular units (4) are connected by a connecting part (5), It is not easy to provide a stent that meets all three requirements.
JP 11-501551 A Patent No. 3654627 Patent No. 3663192

Accordingly, it is an object of the present invention to provide a flexible stent that can be easily delivered through a slender, narrow artery.

Another object of the present invention is to provide a stent that has sufficient strength to support the artery and maintain the open state of the stenosis when the stent is expanded, and to withstand repeated bending of the artery caused by the heartbeat. It is.

Furthermore, an object of the present invention is to provide a stent that substantially prevents the overall length from being shortened when expanded.

As a result of detailed examination of the fracture site of the stent in order to solve the above problems, the present inventors have found that the fracture occurs at the top of the arc of the bent portion forming the connecting portion, and the width of the top of the arc that is the fracture site. It has been found that if the width is made wider than the width of the straight portion, the durability against bending stress is drastically improved, and the present invention has been achieved. That is,

(1) The present invention is a stent (1) made of a cobalt chromium alloy that is formed in a substantially tubular body and is expandable in the radial direction from the inside of the tubular body by expansion of a balloon, and comprises a plurality of cells (6). The tubular unit (4) is configured by connecting a plurality of the cells (6) so as to surround the central axis (C1) of the stent (1), and the plurality of the tubular units (4) are connected to the stent (1). 1) is arranged in the axial direction, and the adjacent tubular units (4) are connected to each other by at least one connection portion (5), and the connection portion (5) includes at least one bent portion (8). The bent portion (8) is formed of an arc and a substantially straight portion (7) continuous with the bent portion (8), and the end of the bent portion (8) is located on the left side of the cell (6). or is connected to the right end portion, the coupling portion and the cell, the thickness is constant, the width of the connecting portion is narrower than the width of the cell, configure front Symbol bent portion (8) The width of the top of the arc is 1.4 to 1.6 times the width of the substantially straight portion (7), and the width from the substantially straight portion (7) toward the top of the arc constituting the bent portion (8). Is a stent characterized by increasing gradually.

[2] The present invention is further that the width of the front SL cells 90～110Myuemu, thicknesses of and the connecting portion of the cell at 60 to 80 m, a width of 30~50μm der Turkey of the substantially straight portions (7) The stent according to [1] characterized by the above.
[3] In the present invention, the connecting part (5) is also arranged between cells of one part among a plurality of cells (6) of adjacent tubular units (4) of the stent (1). The stent according to [1] or [2], wherein

[4] The present invention, said cell (6), a stent according to the connecting portion through (5), characterized in that formed symmetrically to the stent axis direction [1] or [2].
[5] The stent according to [1] or [2] , wherein the cell (6) is further arranged in the same direction and at the same height in the axial direction of the stent (1).

[6] The stent according to [1] or [2] , wherein the present invention is coated with a diamond-like thin film.

The stent of the present invention is flexible by setting the width of the fractured part to a specific width while keeping the design of the conventional stent composed of cells and connecting portions excellent in flexibility and expandability. The durability against bending can be improved without impairing the resistance.

FIG. 1 is a plan view of a stent of the present invention (FIG. 2 is an enlarged view of FIG. 1 and FIG. 3 is an enlarged view showing a state of the stent of the present invention after expansion).
The stent is formed in a substantially tubular body and is radially expandable from the inside of the tubular body, and connects a plurality of cells (6) up and down and surrounds the central axis (C1) of the stent (1). By arranging a plurality of the annular units (4) as described above, at least one of the plurality of the annular units (4) is connected by the connecting portion (5).

In the present invention, the cell (6) means one structural unit of the pattern constituting the surface of the stent (1), and has a bent portion (12) having at least one acute angle (X) as shown in FIG. And includes substantially all the forms configured by connecting the substantially straight line portion (11) and the curved line portion (13) through the same. The cell (6) is configured by connecting the substantially straight portion (11) and the curved portion (13) via the bent portion (12), and the curved portion (13) is a small bent portion having an obtuse angle (Y) ( It is preferable to form two or more 14).

The bent portion 13 (substantially S-shaped portion) comprising the substantially straight portion 11 and the bent portion 12 and the small bent portion 14 constituting the cell 6 is closer to perpendicular to the central axis C1 after expansion of the stent. Increases radiation support. As a result, it has been found that the radiation support force of the stent increases as the angle θ after expansion of the bent portion 12 approaches 180 °. That is, in the design of the stent, the angle θ after expansion of the bent portion 12 is preferably designed to be at least 30 ° or more when expanded to at least φ2.5 mm.

In addition, since these relate to the number of cells 6 arranged, the number of cells 6 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. Also, 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, eg, φ3.0, φ4.0) is reached, for example, as described above Further, the angle θ after expansion of the bent portion 12 is designed to be at least 30 ° or more, usually 45 ° to 140 °, preferably 45 ° to 120 °.

Designing to exceed 140 ° in the target diameter is effective for the radial support force of the stent, but the amount of deformation of the bent portion 12 becomes large, causing problems, and shortening the total length of the stent due to expansion (four shortening) ) Is increased, which causes problems such as difficulty in positioning during stent placement, which is not preferable.

In addition, the strut shape of the cell 6 is relatively asymmetrical as shown in Fig. 4 (b) rather than symmetrically as shown in Fig. 4 (a) with respect to the center line C2 in the stent axial direction. (For example, when comparing FIGS. 4 (a) and 4 (b), 2a <c + d is always satisfied), the expandability of the stent itself can be improved and the effect of suppressing for shortening can be enhanced.

The bent portion has at least one bent portion. For example, in the stent 1, the bent portion 8 is configured by connecting the bent portions 8 to both sides of the substantially straight portion 7 at the center, and the end of the bent portion 8 is connected via the connecting portion 9. Are connected to the end portions of the cells 6 constituting the different annular units 4, respectively. The connecting portion 5 is asymmetrically connected to both ends of the cell 6. The connecting part 5 is likely to be improved in flexibility as the total length of the straight line part 7 and the bent part 8 combined is 1 mm or longer, and the longer the connecting part 5, the larger the proportionally S-shaped connecting part 5 becomes. When the stent is mounted on the balloon catheter (the diameter of the stent may be slightly reduced on the balloon catheter) or when the stent is bent along the blood vessel when passing through the bent portion of the blood vessel, the upper and lower connecting portions 5 are Interference, and conversely, flexibility is lost. Therefore, the total length is preferably 1 mm or more, usually 1 to 2 mm. Further, the R (radius) of the arc constituting the bent portion 8 is preferably set to R = 0.05 mm or more, usually 0.05 to 0.2 mm for the above-described reason.
Further, in the present invention, if the ratio of the length 6L of the cell 6 in the stent axial direction to the length direction 5L of the connecting portion 5 in the stent axial direction 5 is 6L, 5L is formed to be 50-100. Although preferable, it is good to form 50-90 on account of design. As a result, it is possible to suppress the flare phenomenon after expansion of the stent or during delivery and to impart flexibility to the stent itself.

In the stent 1, the thickness of the cell 6 and the connecting portion 5 is usually constant. In the stent made of a cobalt chromium alloy, the cell width is 90 to 110 μm, the connecting portion width is 40 to 80 μm, the thickness of the cell 6 and the connecting portion 5 is 60 to 90 μm. In the stent made of stainless steel, the cell width is 70 to 150 μm, the width of the connecting portion is 60 to 100 μm, and the thickness of the cell 6 and the thickness of the connecting portion 5 are 100 to 150 μm. In such a conventional stent, it was observed in the animal test that the connecting portion 5 was broken. Further, from the test results described later, the top of the arc of the connecting portion where bending stress is concentrated breaks and cannot be put to practical use. In the present invention, as shown in enlarged views of the connecting portion 5 in FIGS. 10-1 and 11, the width t2 of the top of the arc is set to t2 = (1.4 to 1.6) × t1 with respect to the width t1 of the straight portion 7. ing. The width gradually decreases from the top of the arc toward the straight portion 7. When the width t2 of the top of the arc is 1.4 × t1 or less, durability against bending is low. On the other hand, when t2 exceeds 1.6 × t1, rigidity of the stent increases and flexibility is impaired. In a stent made of a cobalt chromium alloy, the width t1 is usually 30 to 50 μm, preferably 40 μm, whereas the top width of the arc is usually 42 to 80 μm, preferably 60 μm. Further, when the width is changed suddenly, the stress concentrates on the changed portion, so the width needs to be gradually reduced from the top of the arc to the straight portion. In the present invention, only by increasing the width of the top of the arc of the connecting portion where stress is concentrated, there is no decrease in flexibility and expandability, and the durability can be drastically improved. There is an advantage that the stent pattern can be adopted as it is.

In the stent pattern of the present invention, the cells 6 are arranged non-target in the axial direction of the stent via the connecting portion 5, but may be arranged in the same direction and at the same height in the stent axial direction. The cells 6 in the stent axial direction are arranged so as to overlap each other when viewed from the nth column to the (n + 1) th column in the stent axial direction. Further, the connecting portions 5 in the same row are also arranged in the same direction in the stent circumferential direction so as to overlap each other when they are slid up or down in the same row. The width of the struts constituting the cell 6 is shifted to a position higher than the width of the struts constituting the connecting portion 5.

The stent 1 of the present invention includes an angle θ after expansion of the bent portion 12, a ratio of the length 6L of the cell 6 in the stent axial direction to the length 5L in the stent axial direction, the form of the connecting portion 5 and the cell 6, and the connection When the diameter of the stent 1 is reduced as shown in FIG. 5 due to the circumferential and axial arrangement (pattern) of the stent of the portion 5 and the cell 6, the cell 6 and the connecting portion 5 are respectively The stents are formed so as not to overlap each other in the circumferential direction of the stent and to fit in the space S between the stents in the circumferential direction.

6 and 8 are plan views showing other embodiments of the stent of the present invention (FIGS. 7 and 9 are partially enlarged plan views of FIGS. 6 and 8).
The stent 1A of FIG. 6 (FIG. 7) is compared with the stent 1 of FIG. 1 in that (a) the cell 6A bends a substantially straight portion 11A having an acute angle X with respect to the axial center line C2 of the stent 1A. It is configured by connecting to the curved portion 13A via 12A (the stent 1 is arranged such that the cell 6 is arranged substantially horizontally (substantially parallel) with respect to the axial center line C2 of the stent 1), (b) The cells 6A are arranged symmetrically in the axial direction of the stent 1A via the connecting portion 5A, and (c) the cells 6A in the axial direction of the stent 1A are temporarily arranged in every nth row in the axis of the stent 1A. When viewed in the direction, the difference is that they are arranged so as to overlap each other.

Further, the stent 1B of FIG. 8 (FIG. 9) is compared with the stents 1 and 1A of FIG. 1 and FIG. 6 (FIG. 7), (a) the cell 6B is relative to the axial center line C2 of the stent 1B. It is configured by connecting a substantially straight portion 11B having an acute angle X to a substantially straight portion 13B disposed substantially horizontally (substantially parallel) with respect to the axial center line C2 of the stent 1 via a bent portion 12B. (Stents 1 and 1A are configured by connecting cells 6 and 6A to substantially curved portions 13 and 13A through substantially straight portions 11 and 11A via bent portions 12.) (B) the cells 6B are arranged symmetrically in the axial direction of the stent 1B via the connecting portion 5B, and (c) the cells 6B in the axial direction of the stent 1B are temporarily arranged from the nth column to the (n + 2) th column. When viewed in the axial direction of the stent 1B every other row, the stents 1B are substantially the same as the stent 1A, unlike the stent 1 in that they are arranged so as to overlap each other.

In the stents 1, 1A, 1B illustrated in FIGS. 1, 6, 8 of the present invention, the connecting portions 5, 5A, 5B of the cells 6, 6A, 6B constituting the annular units 4, 4A, 4B are as follows: Stents 1, 1A, 1B are continuously arranged in the radial direction without gaps, but are arranged with at least one space in the radial direction (placed with one or two or two spaces) As a result, the stents 1, 1A, and 1B as a whole become more flexible, improve delivery to the branched blood vessels, and distribute the stress to the arc part forming the connection part, so that the connection part continues without gaps. Durability is improved as compared with a stent placed in the same manner.

The stent of the present invention, the cobalt chromium alloys or Ranaru metal pipe, for example, formed by a laser processing method or the like.

Next, the manufacturing process of the stent of the present invention will be described. FIG. 12 shows a stent processing step. Based on the shape data of the designed stent (FIG. 12-1), a tool path (FIG. 12-2) in laser processing is created using CAM. The tool path is set in consideration of the fact that the stent shape can be maintained after laser cutting and that no chips remain. Next, laser processing is performed on the metal thin-film meat tube. Select machining conditions with the goal of high-speed and high-quality machining by suppressing the generation of burrs.

After the mesh shape is formed by laser cutting (Fig. 12-3), the surface is made glossy using electropolishing and the edge is finished to a smooth shape (Fig. 12-4). In the process of processing a stent made of cobalt chrome alloy, a 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, the stent, stainless steel, and other metal plates are immersed in the electrolyte, and the two are connected via a DC power source. Abrasion effect is obtained by dissolving the stent on the anode side by applying voltage with the stent side as the anode and the metal plate side as the cathode. In order to obtain an appropriate polishing effect, it is necessary to examine the composition of the electrolyte and electrical conditions in detail.

Next, an example explains the present invention. The stent used in the example shown in FIG. 13 has a length of 17.4 mm, an inner diameter of 1.0 mm when contracted, an inner diameter of 3.0 mm when expanded, the width of the straight portion forming the connecting portion is 40 μm, and the width of the top of the arc Is a full-link type stent made of a cobalt chromium alloy with a width gradually reduced from the top toward the straight part at 60μ (Example 1), and a partial link type stent provided with connecting parts every other place as shown in FIG. 14 (Example) A linear link forming the connecting portion shown in FIG. 15 and an all-link stent made of a cobalt chromium alloy having an arc width of 40 μ were used as comparative examples.
Each of the above stents was recoiled into a 3.0 mm inner diameter and 4.0 mm outer diameter silicon tube, the inner diameter was expanded to 3.0 mm, and physiological saline was injected into the tube to obtain an environment of 37 degrees. Also, as shown in the schematic diagram of the bending test apparatus in FIG. 16, both ends of the tube are fixed, a wire is attached to the center of the silicon tube, the end of the wire is fixed to the cam, and the cam is operated by rotating the motor. The wire endurance test was performed by reciprocating the wire so that the stroke was 4.0 mm (2.0 mm on one side), bending the center of the silicon tube, and repeatedly bending the center of the stent inserted into the tube.

As a result of the above test, the durability of the partial link stent (Example 2) is greater than that of the entire link stent (Example 1). The reason is that the cell space of the partial link is deformed, so that the load applied to the link is reduced, and it is estimated that the bending durability is superior to that of the all link stent.

Next, in the all-link type stent having the structure of Example 1, the width of the top of the arc forming the connecting portion is 1.2 times (48 μm) the width of the straight portion of 40 μm. The stent of 60 μm) was compared with Example 3 and the 1.8 times (72 μm) stent of Comparative Example 3, and the bending strength and the like were measured in the same manner as in Example 1.

As a result of the above test, the width of the top part of the arc forming the connecting part is 1.4 to 1.6 times the width of the straight part with respect to the width of the straight part of 40 μm, and the bending durability is excellent, and the foreshortening value is the same as the conventional stent It was a stent with an excellent balance between durability and performance.

Plan view of the stent of the present invention Enlarged view of Figure 1 Enlarged view showing the state of the stent after expansion Conceptual diagram of struts constituting a cell Enlarged view of stent diameter reduced during delivery to blood vessel The top view which shows the other Example of the stent of this invention Partially enlarged plan view of FIG. The top view which shows the other Example of the stent of this invention Partially enlarged plan view of FIG. Plan view of stent connection part of comparative example Plan view of the stent connection part of the embodiment Enlarged view of the bent part of the stent shown in Fig. 10-2 Explanatory drawing showing the stent creation process All link stents used in Example 1 Partial link stent used in Example 2 All link stents used in the comparative examples Schematic diagram of bending test equipment

Explanation of symbols

1, 1A, 1B stent
4, 4A, 4B ring unit
5, 5A, 5B connecting part
6, 6A, 6B cells
7 Substantially straight section
8, 8A, 8B Bend
9 Connection
11, 11A, 11B, 13B Substantially straight section
12, 12A, 12B Bend
13, 13A Curve
14, 14A Small bend
15 Substantially straight section
17 Roughly <shaped cell ・ Roughly S-shaped cell ・ Components in Stents A and B

Claims (5)

A stent (1) formed of a cobalt-chromium alloy formed in a substantially tubular body and expandable in the radial direction from the inside of the tubular body by expansion of a balloon, and a plurality of cells (6) are vertically connected to each other. A plurality of (6) are arranged so as to surround the central axis (C1) of the stent (1) to form a tubular unit (4), and the plurality of tubular units (4) are arranged in the axial direction of the stent (1). The adjacent tubular units (4) are connected to each other by at least one connection portion (5), and the connection portion (5) includes at least one bent portion (8) and the bent portion (8). And an end portion of the bent portion (8) is connected to the left or right end portion of the cell (6), and an arc that constitutes the bent portion (8). the coupling portion and the cell, the thickness is constant, the width of the connecting portion is narrower than the width of the cell, the width of the top of the arc constituting the bent portion (8) The width is approximately 1.4 to 1.6 times the width of the substantially straight portion (7), and the width gradually increases from the substantially straight portion (7) toward the top of the arc constituting the bent portion (8). A stent characterized by Before SL width of the cell is 90～110Myuemu, thicknesses of and the connecting portion of the cell at 60 to 80 m, to claim 1 where the width of the substantially straight portions (7) characterized the 30~50μm der Turkey The described stent. The said connection part (5) has been arrange | positioned between the cells of one part in the several cells (6 ) of the adjacent tubular units (4) of a stent (1), The 1 or 2 characterized by the above-mentioned. the stent according to. 3. The stent according to claim 1, wherein the cells (6) are formed symmetrically in the stent axial direction via the connecting portion (5). 3. The stent according to claim 1, wherein the cells (6) are arranged in the same direction and at the same height in the axial direction of the stent (1).