JP5008181B2 - Stent - Google Patents

Description

  The present invention relates to a stent made of a shape memory alloy used as a treatment instrument for stenosis of tubular organs of the human body such as blood vessels, biliary tract and urethra.

  Stent treatment is a new technology that has been rapidly used in recent years. A stent is a mesh-like metal pipe that is placed in the body in order to prevent restenosis after expansion of a stenosis part such as a blood vessel. The stent having a reduced diameter and housed in the distal end portion of the catheter is attached to the inner wall of a blood vessel or the like by release / expansion operation from the catheter after introduction into the stenosis portion. In the case of PTCA (percutaneous coronary angioplasty), the stent is expanded with a vasodilation operation by inflation of a balloon combined with the inner wall of the storage. This is called a balloon-expandable type, and stainless steel, tantalum, or cobalt chromium alloy is used as the metal material.

  On the other hand, as a method for preventing rupture of an aneurysm that causes subarachnoid hemorrhage or the like, there is to stop blood flow to the aneurysm. As an example, there is an embolization technique in which a metal coil, such as platinum, is packed in a knob to form a thrombus. However, there is a concern that a part of the thrombus is detached from the metal and flows to the periphery along with the blood flow to block the blood vessel. As a countermeasure, a covered stent technique for embolizing an aneurysm with an artificial blood vessel has been studied. The stent of the covered stent technology is released from the catheter and expands with its own springiness to press the artificial blood vessel against the blood vessel wall. A so-called self-expandable material that has excellent spring characteristics is required.

Next, shape memory alloys such as Ti—Ni alloys are known as alloys having excellent spring characteristics. Shape memory alloys undergo martensitic transformation from a parent phase, which is a high-temperature phase, to a martensitic phase, which is a low-temperature phase, by cooling. In addition, it exhibits spontaneous shape recovery by performing martensite reverse transformation (hereinafter also referred to as reverse transformation) to the parent phase due to temperature rise from the martensite phase, and also exhibits a superelastic effect (so-called shape memory) in the parent phase temperature range. It is a superelastic effect found in alloys, and is also referred to as superelasticity hereinafter) and exhibits excellent spring characteristics.
The superelastic property is noticeable in Ti—Ni alloys and Ti—Ni—X alloys (X = V, Cr, Co, Nb, etc.) among many shape memory alloys. The shape memory effect of Ti—Ni alloy is shown in Patent Document 1 below, and the superelastic effect is shown in Patent Document 2. The shape memory effect and the superelastic effect of the Ti—Ni—X alloy are described in, for example, Patent Document 3 and Patent Document 4 regarding the Ti—Ni—V alloy, and Patent Document 5 regarding the Ti—Ni—Nb alloy. Yes.
The Ti—Ni—Nb alloy according to the present invention has been put to practical use in a reactor pipe joint or the like in order to show the feature that the temperature hysteresis can be widened by applying stress compared to the Ti—Ni alloy.

The feature of Ti-Ni shape memory alloy is that it starts at the reverse transformation temperature start temperature (As temperature) of the alloy and is higher than the reverse transformation end temperature (Af temperature). It is restored to its shape, and the recovery amount reaches about 7% in elongation strain. As temperature means start temperature for shape recovery, and Af temperature means end temperature for shape recovery (temperature for shape recovery). In the case of stent use, a hoop-shaped stent formed slightly larger than the indwelling lumen is spontaneously restored to its original diameter immediately after being released from the reduced-diameter mount catheter into the catheter, and is in close contact with the lumen.
That is, the Af temperature of the alloy is set to a living body temperature (around 37 ° C.) or lower. Along with the above features, superelastic stents have the disadvantages of vascular wall damage due to spontaneous shape restoration, indwelling positioning misalignment, lack of delivery, etc., so that they can be used in vascular systems that require delicate expansion and placement such as coronary arteries. Is difficult to use.

  The material of the PTCA stent is preferably a metal material with low elasticity that is difficult to damage blood vessels and has excellent delivery properties (meaning that delivery means the intravascular transport of the stent). The pressing force (expansion force) is weak. As a solution, a stent using a shape memory alloy has been proposed. Patent Document 6 describes the application of a Ti-Ni-Nb alloy stent according to the present invention. Characteristic features include: "Low Young's modulus during shape recovery of Ti-Ni-Nb shape memory alloy, and high Young's modulus stent during shape deformation due to external force. The ratio of the stress at the point to the stress at the inflection point when not loaded is at least 2.5: 1 ”. However, this technique exhibits a superelastic effect at the living body temperature after being released from the catheter, and does not sufficiently solve the problems required for PTCA (positioning optionality, etc.).

  Patent Document 7 proposes a stent as an invention by the present inventors. That is, it is a proposal of a stent that exhibits a shape memory effect at a living body temperature at the time of insertion into the body and a superelastic effect after shape restoration by a balloon. In the examples, it is described that the recovery temperature is increased by strongly deforming a stent made of a Ti—Ni alloy and a Ti—Ni—X alloy (X = Cr, V, Cu, Fe, Co, etc.). However, the addition of strain is only a strong deformation by housing the slot-processed stent in the catheter, and a sufficient effect cannot be obtained depending on the slot shape. In addition, there is no mention of Ti-Ni-Nb alloy, which has a large temperature rise to restore shape due to strain addition, and the attachment to the balloon is insufficient, and the necessity of restraining from the outside with a catheter is described. Yes.

Patent Document 8 proposes that the stiffness of a material is partially changed by heat treatment in a stent using a Ti—Ni alloy or a Ti—Ni—X alloy. Specifically, the super-elastic part having relatively high rigidity and the plastic deformation part having low rigidity (the part in which the super-elasticity is broken in the specification) are alternately linked by the heat treatment change, and the intended purpose of the present invention Is different from the means. In addition, it is problematic in terms of reproducibility and cost to perform different heat treatments on complicated shapes such as stents.
In Patent Document 9, a stent using a Ti—Ni—Nb alloy was proposed. In Patent Document 9, the temperature at which shape recovery is performed before the balloon is expanded and indwelled is equal to or higher than the living body temperature. Proposes a stent that exhibits a superelastic effect at temperature.
US Patent 3,174,851 JP 58-161753 A JP-A-63-171844 JP-A-63-14834 U.S. Pat. No. 4,770,725 JP-A-11-42283 Japanese Patent Laid-Open No. 11-099207 Special table 2003-505194 gazette JP 2005-245848 A

The required functions for stents are delivery (intravascular transportability), optional placement (easy placement at the required location), and restenosis prevention (strong expansion force and flexible shape following after placement). is there. Along with the rapid increase in stent treatment cases in recent years, there are problems such as restenosis after stent placement and displacement from the initial placement position. This occurs particularly when balloon expansion is currently performed, such as in coronary arteries where it is difficult to use a stent having a superelastic effect as described above.
In order to solve these problems, the problem of the present invention is to solve the problems of the Ti-Ni-Nb stent proposed by the present inventors, and to achieve good delivery properties without heating in the body. It is to provide a stent that has both indwellability and anti-restenosis and is difficult to displace from the initial placement position.

TI-Ni-Nb alloys are known to have various characteristic characteristics compared to Ti-Ni alloys and other Ti-Ni-X alloys. For example, the increase range of the reverse transformation temperature due to the strain addition is larger, and the width of the reverse transformation start temperature and the reverse transformation end temperature is rapidly reduced before and after the strain addition. A 46.4Ti-47.6Ni-6Nb wire having a final cold working rate of 30% was subjected to heat treatment at 400 ° C. for 1 hour, and then subjected to a tensile test at room temperature. FIG. 9 shows the stress strain curve. Unloading and pulling were repeated by increasing the strain amount by 1% to 14%.
When the amount of strain is small, it shows a superelastic effect, but as the amount of strain increases, the transformation temperature rises, the residual strain increases and does not return to its original length, and the superelastic effect also decreases and eventually lost. . Moreover, the yield stress decreased and softened with increasing strain. These characteristics are remarkable as compared with Ti-Ni alloys and other Ti-Ni-X alloys. Further, elements such as V, Cr, Co, and Fe may be added to such an extent that these characteristics are not impaired. Similar to other Ti—Ni—X alloys and Ti—Ni binary alloys, the Ti—Ni—Nb alloy can appropriately change these properties by selecting the composition, the final cold work rate, and the heat treatment conditions. In the present invention, a stent was produced using the mechanical properties of this Ti—Ni—Nb alloy.

Here, by controlling the temperature at which the stent of Ti—Ni—Nb alloy is locally distorted to restore the shape, the present inventors can store the balloon, and have superelasticity or high elasticity after expansion. It has been found that it is possible to apply a high expansion force without heating (including that which has a large amount of elastic deformation strain in the original sense and includes those which do not exhibit a superelastic effect).
That is, according to the stent of the present invention, which has a link portion connecting the annular strut and the strut forming a bent portion having a deformable holder at the bent portions, Ti-Ni based shape memory alloy containing Nb a tubular stent consisting of a temperature of shape recovery of the deformable retaining portion across biological temperature, temperature of shape recovery of the portion other than the modified form of holder is to be the following biological temperature.
The stent has a structure in which the deformable holding portion of the bent portion is selectively distorted and the temperature for restoring the shape of the deformable holding portion is increased compared to other portions. ing.
In the stent, the composition of the Ti—Ni-based shape memory alloy containing Nb is a ratio of Ti 46.4 to 47.2 at%, Ni 47.6 to 47.8 at%, Nb 5 to 6 at%, and the heat treatment temperature is 450. A temperature of ˜500 ° C. can be applied.
The above-mentioned stent has a temperature at which only the deformable holding part of the bent part recovers the shape above the living body temperature, and the other part has a temperature at which the shape recovers below the living body temperature. It was made to have.
In addition, the stent has a structure in which the temperature at which the shape recovery is performed is higher than that of other portions, and the bent portion is an annular strut formed continuously in a wave shape, and the bent portion is formed on the strut. It arrange | positions toward an axial direction and it was made to connect between the bending parts of the struts adjacent to this axial direction by the said link part.

  In the present invention, since the temperature at which the shape is restored is higher than other parts due to the strain applied to the cell bent part, the balloon can be expanded, and the expansion force partially having superelasticity or high elasticity is highly deformed. It is possible to supply a stent having a good recovery from the above. It is possible to provide a stent that has both delivery, arbitrary placement, and restenosis prevention, and that is difficult to be displaced from the initial placement position. A stent with high expansion force and good recovery from deformation can be obtained without heating to eliminate the added strain, so the system can be configured simply, and it can be applied to conditions where heating is difficult it can. The force necessary for stent expansion, shape recovery, and expansion force can be set in a wider range than before.

Hereinafter, a stent according to an embodiment of the present invention will be described with reference to the drawings.
1 and 2 illustrate a preferred embodiment of a stent made of a shape memory alloy constructed in accordance with the present invention. The first stent is generally designated by the numeral 11, the second stent is generally designated by the numeral 21, and the first and second stents 11 and 21 each have a cylindrical shape that is entirely reticulated. FIG. 1 and FIG. 2 show a flat development.
The stents 11 and 21 are produced by producing a Ti-Ni-Nb alloy by frequency melting and forming a tubular precursor by hot working and cold working. The cold working rate is 10% or more and 60% or less at which mechanical fracture can occur. Preferably, it is 20% or more at which good mechanical properties can be obtained, and 50% or less capable of stable machining. is there. In this embodiment, the dimensions of the tube are approximately the outer diameter of 2.45 mm and the wall thickness of 0.19 mm. The final cold working rate of the tube at this time was about 30% in terms of the area reduction of the cross-sectional area.

Next, the tube was cut and processed with the Nd: YAG laser device except for the required part. Specifically, the tube was cut into a pre-programmed shape while the irradiated laser beam was scanned and the tube was also rotated and moved in the longitudinal direction. In this embodiment, it cut | disconnected in the shape shown in FIG.2 and FIG.4. 2 and 4 are views in which a cut product is added to the plane. In order to expand these to a predetermined outer diameter, a round bar having a conical tip was inserted into the stent and heat treatment was performed. In this embodiment, the extended heat treatment was performed so that the outer diameter of the stent was 5 mm. 3 was expanded to produce the stent 11 of FIG. 1, and the cut product 4 of FIG. 4 was expanded to produce the stent 21 of FIG. The heat treatment temperature is 300 ° C. to 600 ° C., preferably 400 ° C. to 500 ° C.
In addition, the surface of the stents 11 and 21 can be provided with an appropriate synthetic resin coating having biocompatibility, if necessary, and a required drug can be applied.

As described above, according to the present invention, the Ti-Ni-Nb alloy stent is locally strained to control the temperature at which the shape is restored, so that it can be stored in the balloon and can be super-elastic or highly elastic after expansion. Adds high expansion force without heating. Hereinafter, a stent-shaped structure that can be locally strained will be described.
The first stent 11 is arranged in the vertical direction shown in FIG. 1 in the longitudinal direction (axial direction of the stent), and a plurality of links disposed between each of the plurality of annular struts 13 and the adjacent struts 13. 16 is included. The struts 13 have a wave shape (or a zigzag shape or a corrugated shape) and extend in the circumferential direction, that is, in the left-right direction in FIG. More specifically, the strut 13 includes an inclined straight strut portion 13a and a curved strut portion 13b inclined to the opposite side, and the straight strut portions 13a and the curved strut portions 13b are alternately arranged in the circumferential direction. The curved strut 13b has a curved shape having inflection points 14a and 14b at two locations, and in this embodiment, the angle of the inner angle is made to coincide. In the strut 13, the inflection points 14 a and 14 b are formed only in one curved strut 13 b, but the inflection points may be formed in the straight strut portion 13 a in the same manner.
A connecting portion between one end of the straight strut portion 13a and one end of the curved strut portion 13b is connected via a bent portion 12 having a substantially semicircular arc shape (or a square shape). That is, the bent portion 12 is provided at both end positions of the straight strut portion 13a and both end positions of the curved strut portion 13b. Such a strut 11 forms one cell by a combination of a pair of straight strut portions 13 a, curved strut portions 13 b, and bent portions 12. An annular strut 13 is formed by arranging a plurality of these cells in the circumferential direction.

The links 16 are arranged at intervals in the circumferential direction, in the left-right direction in FIG. Each of the links 16 extends in a Z shape (or a mirror image S shape in which the S shape is reflected in a mirror) in the longitudinal direction of the stent 11. The link 16 has two bent portions 17a and 17b. The bent portions 17a and 17b need to be arranged in the circumferential direction of the stent 11.
Each of the links 16 is disposed between each of the bent portions 12 and 12 that are positioned opposite to each other in the axial direction of the stent 11, and one end and the other end of the link 16 are connected between the bent portions 12 and 12. . In this embodiment, the cross-sectional area of the link 16 is smaller than the cross-sectional areas of the straight struts 13a and the curved struts 13b, but the cross-sectional areas may be the same. The link 16 is disposed at all the bent portions 12 except for both ends in the longitudinal direction of the stent 11.
The stent 11 may form a link in a mirror image Z shape instead of the link 16 extending in the Z shape in the longitudinal direction.

  The second stent 21 includes a plurality of links 26 disposed between adjacent struts 23 and a plurality of annular struts 23 arranged in the longitudinal direction (axial direction of the stent), that is, the vertical direction in FIG. Contains. In the present embodiment, the number of links 26 is less than that of the first stent 11 when five bent portions 22 are arranged in the circumferential direction of the stent 21. The link 26b connecting the lower strut 23 having the link 26a is shifted in the circumferential direction with respect to the upper links 26a and 26a so as to be positioned between the links 26a and 26a.

  The strut 23 has a wave shape (or a zigzag shape or a corrugated shape) and extends in the circumferential direction, that is, in the left-right direction in FIG. More specifically, the strut 23 includes a plurality of straight strut portions 23 a and 23 b, and the straight strut portions 23 a and 23 b are alternately arranged in the circumferential direction of the annular strut 23. The connecting portion between one end of the straight strut portion 23a and one end of the straight strut portion 23b is connected via a bent portion 22 having a substantially semicircular arc shape (or a square shape). That is, the bending part 22 exists in the both end position of the linear strut parts 23a and 23b. Such a stent 21 forms one cell by a combination of a pair of straight strut portions 23 a and 23 b and a bent portion 22. The shape of the link 26 is formed in a substantially square shape, and the cross-sectional area of the link 26 is smaller than the cross-sectional area of the straight struts 23a and 23b, but may have the same cross-sectional shape.

Next, the operation of the stent of this embodiment will be described.
The stents 11 and 21 shown in FIGS. 1 and 2 were reduced in diameter and applied with strain. Using a dedicated jig, the outer diameter was gradually reduced in a form that was suppressed from the outside of the stents 11 and 21 by an external force, and the outer diameter was reduced from 5 mm to 2.5 mm in a substantially concentric shape while maintaining a circular shape. . Thereafter, the restraint from the outside by the jig was released, and the external force on the stents 11 and 21 was eliminated. The basic shapes of the stents 11 and 21 when the diameter was reduced to 2.5 mm were the same as in the cut state (FIGS. 3 and 4).
At this time, the struts 13 and 23 are narrowed only at the angles of the bent portions 12 and 23, the shape of the straight struts 13a, the curved struts 13b and the straight struts 23a and 23b is not changed, and the links 16 and 26 are also shaped. There was no change. This is because the positions of the apexes of the bent portions 12 and 22 are directed in the axial direction, so that when the force in the reduced diameter direction is applied to the stents 11 and 21, the stress is applied to the bent portions 12 and 22. Thus, substantial stress is not applied to the straight struts 13a, the curved struts 13b, and the straight struts 23a located between the bent portions 12 and 22, respectively. On the other hand, when the bent portions 12 and 22 adjacent to each other in the circumferential direction (left and right direction in FIGS. 1 and 2) approach each other as the stents 11 and 21 are reduced in diameter, the links 16 and 26 are adjacent to each other. Were moved in parallel with each other, and no substantial stress was applied, and the shape did not change. In this way, it is possible to manufacture the stents 11 and 21 having the deformable holding portions of the bent portions 12 and 22, which are portions where the bent portions 12 and 22 are distorted to increase the temperature for shape recovery.

Examples of the stent of the present invention will be described below.
[Production of stent according to Example]
In this example, the expansion heat treatment was performed so that the outer diameter of the stent was 5 mm according to the composition of the stent described below. The stent 11 of FIG. 1 is expanded by expanding the cut product of FIG. 3, or the stent 21 of FIG. 2 is expanded by expanding the cut product of FIG. 4 as Examples 1 to 3 and Comparative Examples 1 and 2 shown in Table 1. did.

表１に示すように、実施例１（Ｎｏ．１：46.4Ti-47.6Ni-6Nb）のステントでは、Ｔｉ４６．４ａｔ％、Ｎｉ４７．６ａｔ％、Ｎｂ６％の合金組成とし、熱処理条件を５００℃の温度で施して、ステントを作製した。ステントの形状は、図２に示すステント２１と同じである。
実施例２（Ｎｏ．２：46.4Ti-47.6Ni-6Nb）のステントでは、Ｔｉ４６．４ａｔ％、Ｎｉ４７．６ａｔ％、Ｎｂ６％ａｔの合金組成とし、ステントの組成は実施例１と同じ条件とし、熱処理条件を４５０℃の温度で施したことが異なる。ステントの形状は、図１に示すステント１２と同じである。
実施例３（Ｎｏ．３：47.2Ti-47.8Ni-5Nb）のステントでは、Ｔｉ４７．２ａｔ％、Ｎｉ４７．８ａｔ％、Ｎｂ５％ａｔの合金組成とし、熱処理条件を４５０℃の温度で施して、ステントを作製している。形状は、図２に示すステント２１と同じである。
比較例１（Ｎｏ．４：49.4Ti-50.6Ni）のステントでは、Ｔｉ４９．４ａｔ％、Ｎｉ５０．６％ａｔの合金組成とし、熱処理条件を５００℃の温度で施して、ステントを作製した。形状は、図１に示すステント１２と同じである。
比較例２（Ｎｏ．５：50Ti-50Ni）のステントでは、Ｔｉ５０ａｔ％、Ｎｉ５０％ａｔの合金組成とし、熱処理条件を５００℃の温度で施して、ステントを作製した。形状は、図１に示すステント１２と同じ形状である。 [Table 1]

As shown in Table 1, the stent of Example 1 (No. 1: 46.4Ti-47.6Ni-6Nb) has an alloy composition of Ti 46.4 at%, Ni 47.6 at%, Nb 6%, and heat treatment conditions of 500 ° C. A stent was made by applying at temperature. The shape of the stent is the same as that of the stent 21 shown in FIG.
In the stent of Example 2 (No. 2: 46.4Ti-47.6Ni-6Nb), the alloy composition of Ti 46.4 at%, Ni 47.6 at%, and Nb 6% at was set, and the composition of the stent was the same as in Example 1. The difference is that the heat treatment was performed at a temperature of 450 ° C. The shape of the stent is the same as that of the stent 12 shown in FIG.
In the stent of Example 3 (No. 3: 47.2Ti-47.8Ni-5Nb), an alloy composition of Ti 47.2 at%, Ni 47.8 at%, and Nb 5% at was used, and heat treatment conditions were applied at a temperature of 450 ° C. Is making. The shape is the same as the stent 21 shown in FIG.
In the stent of Comparative Example 1 (No. 4: 49.4Ti-50.6Ni), an alloy composition of Ti 49.4 at% and Ni 50.6% at was used, and the heat treatment was performed at a temperature of 500 ° C. to produce the stent. The shape is the same as the stent 12 shown in FIG.
In the stent of Comparative Example 2 (No. 5: 50Ti-50Ni), an alloy composition of Ti50at% and Ni50% at was used, and the heat treatment was performed at a temperature of 500 ° C to produce the stent. The shape is the same as that of the stent 12 shown in FIG.

[Addition of strain to stent and change in transformation point]
Next, the above No. 1-5 stents were reduced in diameter and added with strain. The strain was reduced gradually from the outside of the stent by an external force using a special jig, and the outer diameter was reduced gradually, and the outer diameter was reduced from 5 mm to 2.5 mm in a substantially concentric shape while maintaining a circular shape. Thereafter, the restraint from the outside by the jig was released, and the external force on the stent was eliminated.
The shape of the stent when the diameter was reduced to 2.5 mm was the same as in the cut state (FIGS. 3 and 4). A comparison between the expanded state and the reduced diameter state in one unit of the stent is shown in FIGS. The shape change due to the diameter reduction of the stent was mainly a change in the cell bending portion, and almost no change was observed in the other portions of the cell and the shape of the link.
Therefore, it was found that the strain due to the reduced diameter from 5 mm to 2.5 mm was not added to the cells and links other than the cell bent portion, but was mainly added to the cell bent portion. From the change in the shape of the cell bent portion, the added strain amount was 8% in the stent 21 of FIG. 2 and 7% in the stent 12 of FIG.

  Next, the reverse transformation start temperature and reverse transformation end temperature of the cell bent portion to which strain was imparted by the diameter reduction and the martensite of the other portion to which strain was not imparted were measured. The reverse transformation start temperature is a temperature at which shape recovery starts, and the reverse transformation end temperature is a temperature at which shape recovery is completed. Specifically, in each of the stents in Table 1, the linear or curved portion between the cell bent portion and the cell bent portion in the cell is further released from the jig after being reduced in diameter by the jig. The approximately central part was cut so as not to be distorted and analyzed by DSC (differential scanning calorimetry). Table 1 shows the measurement results of the reverse transformation start temperature and reverse transformation end temperature. No. 1-No. In No. 3, an increase in the reverse transformation temperature of the cell bent portion was observed as compared with the portion between the cell bent portions to which the strain was not applied. In any case, the reverse transformation end temperature of the cell bent portion is much higher than the living body temperature. 1 and no. 3, the reverse transformation start temperature was also higher than the living body temperature. That is, the cell bent portion did not exhibit high elasticity or superelasticity, and was in a state of small springiness in which deformation remained easily. On the other hand, the portion between the cell bent portions is No. 1-No. In any of the compositions of No. 3, it was found that the reverse transformation temperature was not higher than the living body temperature and high elasticity or superelasticity appeared.

No. 4 and no. In the comparative example of Ti-Ni binary alloy No. 5, the increase in the reverse transformation temperature of the cell bent portion is small, and a large difference in mechanical properties between the cell bent portion and the portion between the cell bent portions cannot be given. It was. No. In No. 4, the reverse transformation temperature of the part between the cell bent part and the cell bent part is equal to or lower than the living body temperature, and it was found that the superelastic effect appears in any part. No. In No. 5, the reverse transformation temperature of the cell bent portion and the link portion was equal to or higher than the living body temperature, and neither portion exhibited superelasticity or high elasticity.
The yield stress of Ti-Ni shape memory alloys including Ti-Ni-Nb depends on the relative temperature difference between the transformation temperature and the service temperature. For example, in superelasticity and high elasticity at living body temperature, the lower the temperature at which the shape is restored, the higher the yield stress and the greater the expansion force in the stent shape. Ti-Ni-Nb alloy has a large range of increase in transformation temperature due to strain addition. Therefore, by controlling the amount of strain at the cell bends in various ways, not only the values in this example but also cell bends in stents and other It is easy to add various different transformation temperatures and associated mechanical properties to the part.

[Storability in balloon]
Next, the above-mentioned No. 1 to No. In stents up to 5, the outer diameter was reduced from 5 mm to 2.5 mm, and then the change in the stent diameter when the restraint from the outside by the jig was released was examined. Table 2 shows the results at 37 ° C.

バルーン拡張型ステントでは、体内へのデリバリーの際に、ステントを小さな径でバルーンに密着させるため、拡張以前は小径に維持されることが重要である。すなわち、本実施例では２．５ｍｍ縮径後の解放時に、なるべく小さい径であること、いわゆる、スプリングバックが小さいことが望ましい。本実施例では、Ti-Ni-Nb合金のステントＮｏ．１〜Ｎｏ．３において、セル屈曲部の変態温度が高いためスプリングバックが小さく変形に対する戻りが小さく、縮径後の径保持性の良いことがわかった。一方、比較例のＮｏ．４では、縮径後もセル屈曲部の変態温度が生体温度以下であるため、超弾性効果を発現し縮径前の外径に回復した。つまりバルーンへの格納性が悪くバルーン拡張には適さないことがわかった。さらに、比較例のＮｏ．５では、縮径前後ともセル屈曲部の変態温度が生体温度以下であるため、縮径後の径保持性は比較的良好であった。 [Table 2]

In a balloon expandable stent, it is important that the stent be maintained in a small diameter before expansion in order to make the stent adhere to the balloon with a small diameter during delivery into the body. That is, in this embodiment, it is desirable that the diameter is as small as possible, that is, the so-called spring back is small when released after the diameter reduction of 2.5 mm. In this example, Ti-Ni-Nb alloy stent No. 1-No. 3, it was found that since the transformation temperature of the cell bent portion was high, the spring back was small, the return to deformation was small, and the diameter retention after shrinking was good. On the other hand, no. In No. 4, since the transformation temperature of the cell bent portion was below the living body temperature even after the diameter reduction, the superelastic effect was exhibited and the outer diameter before the diameter reduction was recovered. In other words, it was found that the storage in the balloon was poor and it was not suitable for balloon expansion. Furthermore, No. of the comparative example. In No. 5, since the transformation temperature of the cell bent portion was below the living body temperature before and after the diameter reduction, the diameter retention after the diameter reduction was relatively good.

[Shape recovery as a stent]
Next, in this embodiment, the above-mentioned No. 1 to No. In up to 5 stents, the shape recoverability of the entire stent including the cell bent portion, the cell, the annular unit, and the link was verified. The stent was expanded to 4.5 mm by expansion and heat treatment, and the stent was pressed and compressed by a compression tester, then unloaded, the amount of residual deformation was measured, and the recovery rate with respect to the outer diameter before compression was verified. As shown in FIG. 6, the push-in is arranged on the base 41 so that the axis of the stent 11 faces in the horizontal direction, and a contact plate 42 is placed on the outer peripheral surface of the stent 11, and the support plate 42 is interposed. The compression was from one direction of the outer diameter. The test was conducted at a temperature of 37 ° C.
Further, as a comparative example, a SUS316L stent and a cobalt chromium alloy stent were similarly verified. These two stents were used as balloon expansion stents, which were manufactured by cutting a 1.55 mm tube with a laser processing machine and mechanically expanding the stent. Assuming the shape and diameter when the balloon is indwelled, it was formed in the shape of FIG. 5 with a diameter of 3 mm. The stent 31 includes an annular strut 33 having a continuous wave shape. The bent portion 32 of the annular adjacent strut 33 is connected to an inverted S-shaped link 36, and the bent portion 32 is a shape that only undergoes distortion. Then, as Comparative Example 3 (No. 6), the above-mentioned SUS316L was used, and as Comparative Example 4 (No. 7), the above-described cobalt chromium alloy was used, and the indentation amount and the residual deformation amount were examined.
In Table 3, the above No. 1 to No. The verification results of 7 types of stents up to 7 are shown.

試験結果として、Ｎｏ．４のTi-Ni２元系の比較例１では、ステント全体が超弾性効果を発現し、高い弾性を有し大変良好な径の回復率を示した。但し、このステントがバルーン拡張に極めて不向きであることは前記のとおりである。Ｎｏ．５の比較例２では、ステント全体の変態温度が３７℃以上であり超弾性効果が表れず弾性が小さいため、残留変形量が大きく径の回復率もＮｏ．４と比較して小さかった。したがって、外力による歪みに対し容易に変形し、一旦変形すると回復し難いことがわかった。 [Table 3]

As a test result, no. In Comparative Example 1 of No. 4 Ti—Ni binary system, the entire stent exhibited a superelastic effect, had high elasticity, and exhibited a very good diameter recovery rate. However, as described above, this stent is extremely unsuitable for balloon expansion. No. In Comparative Example 2 of No. 5, since the transformation temperature of the entire stent was 37 ° C. or higher and the superelastic effect was not exhibited and the elasticity was small, the residual deformation amount was large and the diameter recovery rate was also No. 5. It was small compared with 4. Therefore, it was easily deformed against distortion caused by external force, and it was found that once deformed, it was difficult to recover.

These typical balloon expandable stents, No. 6 and no. In No. 7, since the elasticity was even smaller, it showed a large residual deformation amount, the recovery rate of the diameter was extremely poor, and it was found that the elasticity was extremely weak against deformation from the outside.
On the other hand, no. 1 to No. In the stent No. 3, as described above, the portions other than the cell bent portion show superelasticity or high elasticity, so the residual deformation amount is small, the diameter recovery rate is large, and the stent has a very good elasticity as a balloon expandable stent. It has been found that it has good shape recoverability and expandability.
Thus, also according to the present example, the stents of Examples 1 to 3 containing the Ti—Ni—Nb alloy can be balloon-expanded and partially have superelasticity or high elasticity. Therefore, it is possible to supply a stent that is high and has good recovery from deformation. It is possible to supply a stent that has both deliverability, optional placement, and restenosis prevention.

While the embodiments of the present invention have been described above, the present invention can of course be modified or changed in various ways based on the technical idea of the present invention.
Other than the shape of the embodiment of the present invention, the same result can be realized if the amount of strain due to the diameter reduction and expansion is different between the cell bent portion and other portions. Even if strain is introduced into other parts than the cell bent part, if the difference in strain from the cell bent part is large, the same conditions can be obtained by changing the production conditions such as the composition, the cold working rate and the heat treatment condition. The result can be realized.

In the embodiments so far, the case where the cells other than the cell bent portion and the link are superelastic or highly elastic has been described. However, even if the portion does not exhibit superelasticity or high elasticity, a stent different from the conventional one can be provided. For example, it is possible to provide a stent in which the force necessary for balloon expansion, shape recovery, and expansion force are different from those in the past. A large force is required to expand a hardened blood vessel with a balloon as coalification progresses. When performing the vasodilation of the stenosis and the stent placement at the same time, if the force required to expand the stent is small, the vasodilation becomes easier. In such a case, if the method of the present invention is used, the cell bending portion is softly formed, so that the force required for expansion of the conventional SUS or cobalt chrome stent is set smaller, and the recovery from deformation is the same as in the past. Of stents.
In addition, the links 16 and 26 of the first and second stents 11 and 21 have the same shape of the links 16 and 26, respectively, but the shape of the link differs between two or more types in one stent. A link shape may be provided. Furthermore, the shape shown in FIG. 5 may be used.

It is the top view which expand | deployed the stent of the 1st shape in embodiment of this invention on the plane. It is the top view which expand | deployed the stent of the 2nd shape in embodiment of this invention on the plane. FIG. 2 is a plan view in which a cut product obtained by laser processing before expanding the first shape stent of FIG. 1 is developed in a plane. FIG. 3 is a plan view in which a cut product obtained by laser processing before expanding the stent of the second shape in FIG. 2 is developed on a plane. It is a plane development view of a stent of SUS316L as Comparative Example 3 and a cobalt chromium alloy as Comparative Example 4. It is a model side view of the compression test method of the stent performed in the present Example and the comparative example. It is an enlarged plan view which shows the comparison at the time of the diameter reduction in the stent of the 1st shape in embodiment of this invention (a), and the time of expansion (b). It is an enlarged plan view which shows the comparison with the time of diameter reduction (a), the time of expansion, and (b) in the stent of the 2nd shape in embodiment of this invention. It is a diagram which shows the stress strain curve of a Ti-Ni-Nb alloy wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Stent 12 Bent part of stent 13 Annular strut of stent 14a, 14b Inflection point of stent strut 16 Stent link 21 Stent 22 Stent bent part 23 Stent annular strut 26 Stent link

Claims (5)

The annular strut and the strut forming a bent portion having a deformable holding portion and having a link portion connecting with the bending portions, a tubular stent consisting of Ti-Ni based shape memory alloy containing Nb, the stent temperature for shape recovery of the deformable retention portion across biological temperature, temperature of shape recovery of the portion other than the modified form of the holding portion is equal to or less than biological temperature.   The stent according to claim 1, wherein the deformable holding portion of the bent portion is selectively strained and has a structure in which a temperature at which the shape of the deformable holding portion is restored rises compared to other portions. The composition of the Ti—Ni-based shape memory alloy containing Nb is Ti 46.4 to 47.2 at%, Ni 47.6 to 47.8 at%, Nb 5 to 6 at%, and the heat treatment temperature is 450 to 500 ° C. The stent according to claim 1 or 2, which has been subjected to temperature.   Only the deformable holding portion of the bent portion has a superelastic effect at the living body temperature by raising the temperature at which the shape is restored to a temperature above the living body temperature and the other portion has a temperature at which the shape is restored to a temperature below the living body temperature. The stent according to claim 1 or 2, characterized by the above.   The structure in which the temperature at which the shape is restored rises compared to other parts is an annular strut in which a bent portion is continuously formed in a wave shape, and the bent portion is arranged in the axial direction of the strut. The stent according to any one of claims 2 to 4, wherein a bent portion of struts adjacent to each other in the axial direction is connected by the link portion.

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