Stent manufacturing method

Abstract

To provide a stent for cerebral aneurysm that is formed of a material to be absorbed by an organism.SOLUTION: A stent 10 has self-expanding property and is placed so as to stride across a cerebral aneurysm while being crimped to a vessel wall. The stent includes a magnesium alloy having bioabsorbable property and including 90 atom% or more Mg of or pure magnesium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bioabsorbable stent for cerebral aneurysms and a method for manufacturing the same. [Background technology]

[0002] A cerebral aneurysm is a bulge that forms in a part of an artery in the brain. The bulge usually forms when a branch of a large blood vessel supplying the brain is compressed by cerebral blood flow, causing it to gradually expand. A ruptured cerebral aneurysm can lead to a subarachnoid hemorrhage, making it a very dangerous condition. To prevent subarachnoid hemorrhage, it is necessary to treat cerebral aneurysms before they rupture. Treatment options include surgical procedures such as open-cranial clipping surgery or endovascular treatment using a cerebral aneurysm stent.

[0003] The treatment method using a cerebral aneurysm stent is as follows: A physician inserts a tube into an artery in the groin and guides it to the cerebral aneurysm. A flow diverter stent is then deployed from the catheter to straddle the aneurysm and placed in the blood vessel. This slows down blood flow to the aneurysm, causing it to gradually clot. Subsequently, as the clot is absorbed, the aneurysm gradually shrinks, and eventually the aneurysm is cured. Patent Document 1 discloses a flow diverter stent made of NiTi alloy as the stent for cerebral aneurysms mentioned above.

[0004] Because the flow diverter stents described above are made of NiTi alloy, they are not absorbed by the body even after the cerebral aneurysm has healed. Therefore, a problem arises in that the stent remains in the blood vessels of the brain, placing a significant burden on the patient afterward. In other words, if a stent remains in the blood vessels of the brain, the patient must continue taking medication to prevent side effects, resulting in an extremely heavy burden on the patient.

[0005] Therefore, if a stent for a cerebral aneurysm is placed in a cerebral artery and the stent is made from a material that can be absorbed by the body after the treatment for the cerebral aneurysm is completed, the burden on the patient afterward can be reduced. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-135794 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] One aspect of the present invention aims to provide a stent for cerebral aneurysms made of a bioabsorbable material. [Means for solving the problem]

[0008] Various embodiments of the present invention are as follows. [1] A stent that is self-expanding and is placed to be compressed against the blood vessel wall and straddle a cerebral aneurysm, It is bioabsorbable, A stent characterized by being made of a magnesium alloy or pure magnesium containing 90 atomic percent or more of Mg. [2] In the above [1], The stent is characterized in that it is composed of a tubular braided body woven from wires made of the magnesium alloy or pure magnesium, or is composed of wires cross-coiled, parallel coiled, or coiled. [3] In the above [1], The stent is characterized in that it is composed of a tubular braided body woven with two or more types of wires, including a wire made of a magnesium alloy containing 90 atomic percent or more of Mg or pure magnesium, and a wire made of a magnesium alloy having a different composition from the magnesium alloy or pure magnesium and containing 90 atomic percent or more of Mg, or it is composed of the two or more types of wires cross-coiled, parallel coiled, or coiled. [4] In the above [1], The stent is characterized in that it is composed of a tubular braided body woven with two or more types of wires, including a wire made of a magnesium alloy containing 90 atomic percent or more of Mg or pure magnesium, and a wire made of a material different from the magnesium alloy or pure magnesium, or is composed of the two or more types of wires cross-coiled, parallel coiled, or coiled. [5] In the above [4], The stent is characterized in that the material is a single material selected from the group consisting of bioabsorbable polymers, W, Ta, Pt, and Au. [6] In any one of the above paragraphs [2] through [5], A stent characterized in that the cross-sectional shape of the wire is round, elliptical, or square, and the aspect ratio of the elliptical or square wire is 1 or more and 5 or less. [7] In any one of the above paragraphs [2] through [6], The stent is characterized in that it is a stent for a flow diverter or a stent for coil embolization. [8] In the above [7], The stent for the flow diverter has a surface coverage of 30% or more (preferably 35% or more) and a number density of 14 holes / mm². 2 (preferably 15 pieces / mm) 2 (The above) The coil embolization stent has a surface coverage of 5% or more (preferably 10% or more) and a number density of holes of 0.2 holes / mm². 2 (preferably 0.4 pieces / mm) 2 (The above) The angle formed by the wire materials in the above assembly is 10° or more and 70° or less, and the stent is characterized by this. [9] In the above [7] or [8], The bioabsorption rate of the stent for the flow diverter is 12 months or more and 36 months or less, The bioabsorption rate of the stent for the coil plug is 1 month or more and 3 months or less, and the stent is characterized by this.

[10] In the above [9], The stent is characterized in that it is subjected to surface treatment or coating.

[11] In any one of the above [7] to

[10] , The diameter of the stent is 2 to 6 mm, and the length of the stent is 10 to 50 mm, and the stent is characterized by this.

[12] In any one of the above [1] to

[11] , Having the self-expanding property means that the outer diameter after expansion of the stent in the atmosphere is 4 times or more and 12 times or less the outer diameter before expansion, and the stent is characterized by this.

[13] In any one of the above [1] to

[12] , The magnesium alloy is an alloy having a crystal structure with an α-Mg phase or a long-period stacked structure phase, and the stent is characterized by this.

[14] A method for manufacturing a stent that is self-expanding and is placed so as to press against the blood vessel wall and straddle a cerebral aneurysm, It has a step (a) of knitting using wire materials with 8 or more stitches (preferably 16 or more stitches), The wire material is made of a magnesium alloy containing 90 atomic% or more of Mg or pure magnesium, and has a yield stress (0.2% proof stress) of 300 MPa or more (preferably 500 MPa or more) and a Young's modulus (longitudinal elastic modulus) of 50 GPa or less, The diameter of the wire material is 100 μm or less (preferably 80 μm or less), and the method for manufacturing the stent is characterized by this.

[15] In the above

[14] , The stent is a stent for a flow diverter, The number of hits is 24 or more (preferably 48 or more), A method for manufacturing a stent, characterized in that the diameter of the wire is 50 μm or less (preferably 30 μm or less).

[16] In the above

[14] or

[15] , A method for manufacturing a stent, characterized by having a step (b) of applying a surface treatment or coating to the wire before step (a), or a step (c) of applying a surface treatment or coating to the stent after step (a).

[17] In the above

[16] , Step (b) is to perform polymer bonding or polymer coating on the surface of the wire, or to perform hydrofluoric acid treatment, anodic oxidation treatment or DLC film formation treatment on the surface of the wire. The method for manufacturing a stent is characterized in that step (c) is to perform hydrofluoric acid treatment, anodic oxidation treatment, or DLC film deposition treatment on the stent.

[18] In any one of the above paragraphs

[14] through

[17] , The process includes, prior to step (a), a step (d) for manufacturing the wire, The process (d) comprises: (e) rapidly cooling and solidifying a magnesium alloy containing 90 atomic percent or more of Mg or pure magnesium to produce a plurality of rapidly solidified products; (f) filling and sealing the plurality of rapidly solidified products into a copper can to produce a billet, and extruding the billet to produce a solidified molded product; (g) extruding the solidified molded product to produce a magnesium alloy base wire; and (h) subjecting the magnesium alloy base wire to multiple drawing processes to produce a magnesium alloy wire having an α-Mg phase or a long-period layered structure phase. A method for manufacturing a stent, characterized in that the inner surface of the can is treated with a chrome coating.

[0009] By applying one aspect of the present invention, a stent for cerebral aneurysms made of a bioabsorbable material can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a stent for a cerebral aneurysm, which is made of a tubular braided body in which wires are woven together, according to one aspect of the present invention. [Figure 2] This figure shows a stent for a cerebral aneurysm constructed by coiling wires according to one aspect of the present invention. [Figure 3] This figure shows a stent for a cerebral aneurysm constructed by parallel coiling wires according to one aspect of the present invention. [Figure 4] This figure shows a stent for a flow diverter according to one aspect of the present invention. [Figure 5] Figure 4 schematically shows a flow diverter stent 20 placed in a blood vessel 22 so as to straddle a cerebral aneurysm 21. [Figure 6] This figure shows a coil embolization stent according to one aspect of the present invention. [Figure 7] Figure 6 schematically shows a coil embolization stent 30 placed in a blood vessel 32 so as to straddle a cerebral aneurysm 31. [Figure 8] This is a schematic diagram illustrating a method for manufacturing a magnesium alloy wire according to one aspect of the present invention. [Figure 9] These are SEM images of the wire samples 1, 2, 3, 4, and 5 from Example 1. [Figure 10] Figure 9 shows the results of measuring the yield stress (0.2% proof stress) of each wire material from samples 1 to 5. [Figure 11] Figure 9 shows the results of measuring the Young's modulus (longitudinal elastic modulus) of each wire material from samples 1 to 5. [Figure 12] This is a photograph showing the external appearance of a stent for a cerebral aneurysm according to Example 2. [Figure 13] (A) is a figure showing the dependence of the corrosion rate on immersion time in the simulated bodily fluid for each of the comparative examples, Sample 1 and Sample 2, and (B) is a figure showing the dependence of the corrosion rate on immersion time in the simulated bodily fluid for each of the sample from Example 3 and Sample 1 from the comparative example. [Figure 14] This figure shows a stent for a cerebral aneurysm constructed by cross-coiling wires according to one aspect of the present invention. [Figure 15] This is a photograph showing the external appearance of a stent for a cerebral aneurysm according to Example 3. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and that its form and details can be modified in various ways without departing from the spirit and scope of the present invention. Accordingly, the present invention shall not be interpreted as being limited to the descriptions of the embodiments shown below.

[0012] (Embodiment 1) Figure 1 shows a stent composed of a tubular braided body in which wires are woven together, according to one aspect of the present invention. This stent 10 is used in the treatment of cerebral aneurysms and is self-expanding, allowing it to be compressed against the blood vessel wall for placement. However, the term "stent" as used herein differs from that of a general stent.

[0013] A typical stent is placed in a location to treat diseases caused by narrowing or obstruction of blood vessels or other internal lumens (such as the trachea, lymphatic vessels, or ureters) by expanding the narrowed or obstructed area and securing the lumen. Therefore, stents that expand at the narrowed or obstructed site to increase their outer diameter while maintaining the lumen are common. However, the term "stent" in this specification refers to a cerebral aneurysm, a bulge in a cerebral artery, which is placed in a cerebral artery that is not narrowed or blocked. Therefore, it does not require the same level of expansion as a typical stent; it only needs to have enough self-expandability to conform to the wall of the cerebral artery. It should also ensure blood flow within the vessel where it is placed and restrict blood flow into the aneurysm. Self-expandability, as used herein, means that the outer diameter after expansion is between 4 and 12 times the outer diameter before expansion in the atmosphere.

[0014] The stent 10 shown in Figure 1 is bioabsorbable and consists of a tubular braided body woven from multiple wires 11a, 11b made of a magnesium alloy or pure magnesium having an α-Mg phase or a long-period stacking ordered structure phase. The stent 10 also has a tubular body. Magnesium is preferred because it has excellent biocompatibility and does not cause harm even if absorbed by the body during or after treatment. The magnesium alloy referred to here is an alloy containing 90 atomic percent or more of Mg. The multiple wires 11a and 11b constituting the stent 10 may be made of two or more different compositions. For example, magnesium alloys of two or more different compositions may be used, or pure magnesium and a magnesium alloy may be used.

[0015] Furthermore, the multiple wires 11a and 11b constituting the stent 10 may consist of two or more types of wires, including wires made of magnesium alloy or pure magnesium and wires made of a different material. This different material may be one material selected from the group consisting of bioabsorbable polymer, W, Ta, Pt, and Au. Note that W, Ta, Pt, and Au are visible and are useful for confirming the position of the stent when placing it in a cerebral artery. In addition, to ensure visibility, markers (not shown) made of one material selected from the group consisting of W, Ta, Pt, and Au may be attached to both ends of the stent 10. Visibility here refers to the fact that stents made of magnesium alloy are transparent to X-rays, making it impossible to confirm the position of the stent with an X-ray fluoroscopy device used during stent placement surgery. However, by attaching wires or markers made of W, Ta, Pt, and Au, which do not transmit X-rays, to the stent, it becomes possible to confirm its position with an X-ray fluoroscopy device.

[0016] Furthermore, bioabsorbable polymers include, for example, polyglycolic acid (PGA), copolymer of glycolic acid and L-lactic acid (PGLA; Poly(glycolide-co-L-lactide)), copolymer of glycolic acid and DL-lactic acid (PGDLLA; Poly(glycolide-co-DL-lactide)), poly-L-lactic acid (PLLA; Poly-L-lactide), poly-D-lactic acid (PDLA; Poly-D-lactide), and poly-DL-lactic acid (PDLLA; Any of the following can be used: poly-DL-lactide, a copolymer of L-lactic acid and ε-caprolactone (LCL:Poly(L-lactide-co-ε-caprolactone), or polydioxanone (PDO:Poly-p-dioxanone). The wires using bioabsorbable polymers can be manufactured by melt spinning, wet spinning, dry spinning, gel spinning, etc., and these wires may be appropriately strengthened by treatments such as hot stretching, cold stretching, and heat treatment.

[0017] Furthermore, the angle 18 formed by wires 11a and 11b should be between 10° and 70°. The cross-sectional shapes of wires 11a and 11b may be round, elliptical, or square, and the aspect ratio of elliptical or square wires should be between 1 and 5. The diameter of the stent 10 should be between 2 and 6 mm, and the length of the stent 10 should be between 10 and 50 mm. Furthermore, the wires 11a and 11b may be surface-treated or coated. Specifically, polymer bonding or polymer coating may be applied to the surfaces of the wires 11a and 11b, or hydrofluoric acid treatment, anodizing treatment, or DLC (Diamond Like Carbon) film deposition treatment may be applied to the surfaces of the wires 11a and 11b. Oxides or fluorides may be formed on the surfaces of the wires 11a and 11b by the surface treatment. Furthermore, the stent 10 may be surface-treated or coated. Specifically, the stent 10 may be hydrofluoric acid treatment, anodizing treatment, or DLC film deposition treatment. Oxides or fluorides may be formed on the surface of the stent 10 by the surface treatment.

[0018] DLC is preferred because it has excellent biocompatibility and does not cause harm even if it is absorbed by the body during or after treatment. By applying such a surface treatment or coating, the timing of absorption of the stent 10 by the body can be controlled.

[0019] According to this embodiment, since the stent 10 is made of a tubular body formed from wires 11a and 11b made of a magnesium alloy having an α-Mg phase or a long-period stacked structure phase, or pure magnesium, it is possible to realize a stent for cerebral aneurysms that can be absorbed by the body.

[0020] In this embodiment, a stent for cerebral aneurysms having a tubular braided body woven with wire is described, but any bioabsorbable stent for cerebral aneurysms can be implemented with the following modifications.

[0021] The stent 12 for cerebral aneurysms shown in Figure 2 is constructed by coiling wire 13. In other words, this stent 12 is a coil-like structure made by winding wire 13 in a circular or spiral shape.

[0022] Furthermore, the stent 14 for cerebral aneurysms shown in Figure 3 is constructed by parallel coiling of wires 15 and 16. In other words, this stent 14 is made by arranging in parallel a coil-shaped wire 15 wound in a circular or spiral shape and a coil-shaped wire 16 wound in a circular or spiral shape. Alternatively, parallel coiling may be performed using three or more wires.

[0023] Furthermore, the cerebral aneurysm stent 19 shown in Figure 14 is constructed by cross-coiling wires 17a and 17b. In other words, this stent 19 is made by overlapping a coil-shaped wire 17a wound in a circular or spiral shape with a coil-shaped wire 17b wound in a circular or spiral shape. Cross-coiling may also be performed using three or more wires. In addition, the multiple wires constituting the stents 14 and 19 may consist of two or more different compositions. For example, two or more magnesium alloys with different compositions may be used, or pure magnesium and a magnesium alloy may be used. In addition, the multiple wires 15, 16, 17a, and 17b constituting the stents 14 and 19 may consist of two or more types of wires, including wires made of magnesium alloy or pure magnesium and wires made of a different material. These stents 12, 14, and 19 are preferably used with the coil embolization stents described later.

[0024] Furthermore, other examples of stents for cerebral aneurysms (not shown) are manufactured by processing a tubular structure made of magnesium alloy or pure magnesium from the outside using laser light. This different material may be a single material selected from the group consisting of bioabsorbable polymers, W, Ta, Pt, and Au. W, Ta, Pt, and Au are visible, which is useful for confirming the stent's position when placing it in a cerebral artery.

[0025] (Embodiment 2) Figure 4 shows a stent for a flow diverter according to one aspect of the present invention. This flow diverter stent 20 is a stent for cerebral aneurysms and is composed of a tubular braided body woven with 48 wires. The flow diverter stent 20 can be constructed in the same way as the stent 10 shown in Figure 1, except that it has a larger number of woven wires.

[0026] Figure 5 schematically shows the flow diverter stent 20 shown in Figure 4 being placed in a blood vessel 22 so as to straddle a cerebral aneurysm 21. A physician guides a catheter through the femoral artery in the groin into the cranial cavity, and a flow diverter stent 20 is inserted into a blood vessel 22 from the catheter so as to straddle the cerebral aneurysm 21. Due to its self-expanding properties, it expands by compressing against the blood vessel wall. When the flow diverter stent 20 is placed in the parent blood vessel 22 where the cerebral aneurysm 21 is located, the mesh structure on the surface of the flow diverter stent 20 restricts the blood flow (not shown) into the cerebral aneurysm 21, gradually promoting thrombosis inside the aneurysm, and the neck portion of the aneurysm 21 is covered with neointimal tissue of the stent, leading to complete occlusion of the cerebral aneurysm 21 after several months. Furthermore, the flow diverter stent 20 itself gradually decomposes over several months and eventually disappears, leaving no foreign body behind. However, if a non-biodesorbable wire or similar material is used in part of the flow diverter stent 20 to ensure visibility, that part may remain and not disappear.

[0027] The flow diverter stent 20 has a surface coverage of 30% or more (preferably 35% or more) and a hole number density of 14 holes / mm². 2 (preferably 15 pieces / mm) 2 (The above) The reason for this range is that the surface coverage is less than 30% or the number density of holes is 14 / mm 2If the value is less than this, even if the flow diverter stent 20 is deployed across the cerebral aneurysm 21 as shown in Figure 5, the effect of restricting blood flow into the cerebral aneurysm 21 will be insufficient. The bioresorption rate of the flow diverter stent 20 is preferably between 12 and 36 months. In other words, the flow diverter stent 20 is to remain in the vessel 22 where the aneurysm 21 is located for the period from the time the flow diverter stent 20 is placed in the vessel 22 where the aneurysm 21 is located until the cerebral aneurysm 21 is completely occluded.

[0028] In this embodiment, the same effects as in Embodiment 1 can be obtained.

[0029] (Embodiment 3) Figure 6 shows a coil embolization stent according to one embodiment of the present invention. This coil embolization stent 30 is a stent for cerebral aneurysms and is composed of a tubular braided body woven with 16 wires. The coil embolization stent 30 can be constructed similarly to the flow diverter stent 20 shown in Figure 4, except that it has fewer woven wires. The cerebral aneurysm stent 10 shown in Figure 1 can be used as both a flow diverter stent and a coil embolization stent.

[0030] Figure 7 schematically shows the coil embolization stent 30 shown in Figure 6 being placed in a blood vessel 32 so as to straddle a cerebral aneurysm 31. A doctor guides a catheter through the femoral artery at the groin of the leg to the intracranial region, and through it, a coil embolization stent 30 is inserted into the blood vessel 32 from a thin therapeutic catheter so as to firmly cover the vicinity of the entrance of the cerebral aneurysm 31. It is expanded in a form that presses against the blood vessel wall by having self-expanding properties. Then, a coil 33 is inserted into the cerebral aneurysm 31 from another thin therapeutic catheter passed through the catheter, and several additional coils are added until blood flow hardly enters the cerebral aneurysm 31. Thereafter, the catheter is removed. Note that for the coil 33 used here, a wire material having the same bioabsorbability as the wire material of the coil embolization stent 30 may be used.

[0031] In this way, while placing the coil embolization stent 30 in the parent blood vessel 32 so as to cover the neck portion of the cerebral aneurysm 31, the coil 33 is inserted into the cerebral aneurysm 31. As a result, the blood flow (not shown) flowing into the cerebral aneurysm 31 is suppressed, internal thrombosis is gradually promoted, and the neck portion of the cerebral aneurysm 31 is covered with a stent neointima, leading to complete occlusion of the cerebral aneurysm 31 one to several months later. Moreover, the coil embolization stent 30 and the coil 33 themselves are gradually decomposed over one to several months and finally disappear, leaving no foreign substances. However, when a wire material or the like having no bioabsorbability is used for a part of the coil embolization stent 30 to ensure visibility, it may remain without disappearing.

[0032] The surface coverage rate of the coil embolization stent 30 is 5% or more (preferably 10% or more), and the number density of its holes is 0.2 pieces / mm 2 or more (preferably 0.4 pieces / mm 2 or more). The reason for setting it within such a range is that if the surface coverage rate is less than 5% or the number density of the holes is less than 0.2 pieces / mm 2 as shown in FIG. 7, even if the coil embolization stent 30 is deployed so as to straddle the cerebral aneurysm 31, the coil 33 cannot be stably placed in the cerebral aneurysm 31, and the effect of suppressing the inflowing blood flow becomes insufficient.

[0033] The bioabsorption rate of the coil embolization stent 30 is preferably between one and three months. In other words, the coil embolization stent 30 is placed in the parent vessel 32 where the cerebral aneurysm 31 is located, and the coil 33 is placed inside the cerebral aneurysm 31. The coil embolization stent 30 is kept in the vessel 32 from the time of placement until the cerebral aneurysm 31 is completely occluded.

[0034] In this embodiment, the same effects as in Embodiment 1 can be obtained.

[0035] The magnesium alloy used in the wires of Embodiments 1 to 3 may be one of the following alloys [1] to

[48] .

[0036] [1] The magnesium alloy is an alloy containing a atomic percent of Zn, b atomic percent of Y, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (Equation 11) to (Equation 13) or (Equation 14) to (Equation 16), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 11) 0.25≦a<5.0 (Formula 12)0.5 <b<5.0 (Formula 13)2 / 3a-5 / 6≦b (Formula 14)0.25≦a≦5.0 (Formula 15)0.5≦b≦5.0 (Formula 16)0.5a≦b [2] The magnesium alloy is an alloy containing a atomic percent of Zn, b atomic percent of Y, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (Equation 11'), (Equation 12), and (Equation 13), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 11')0.5≦a<5.0 (Formula 12)0.5 <b<5.0 (Formula 13)2 / 3a-5 / 6≦b [3] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, wherein c satisfies the following equations (17) and (18). (Formula 17)0≦c≦3.0 (Formula 18)0.1(0.2)≦b+c≦6.0 [4] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm (mischmetal), and Gd, wherein c satisfies the following equations (19) and (20). (Formula 19)0≦c<2.0 (Formula 20)0.2≦b+c≦6.0 [5] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, wherein c satisfies the following equations (20) and (21). (Formula 20)0.2≦b+c≦6.0 (Formula 21)c / b≦1.5 [6] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, wherein c satisfies the following equations (22) and (23). (Formula 22)0≦c≦3.0 (Formula 23)0.1≦b+c≦6.0 [7] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, wherein c and d satisfy the following equations (14) to (16). (Formula 14)0≦c≦3.0 (Formula 15)0≦d<2.0 (Formula 16)0.2≦b+c+d≦6.0 [8] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, wherein c and d satisfy the following equations (16) and (17). (Formula 16)0.2≦b+c+d≦6.0 (Formula 17) d / b≦1.5 [9] The magnesium alloy described in [1] or [2] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, wherein c and d satisfy the following equations (18) to (20). (Formula 18)0≦c≦3.0 (Formula 19)0≦d≦3.0 (Formula 20)0.1≦b+c+d≦6.0

[10] The magnesium alloy described in any one of [1] to [9] above may further contain at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B, C, Sn, Au, Ba, Ge, Bi, Ga, In, Ir, Li, Pd, Sb, and V in total amount of more than 0 atomic% and less than or equal to 2.5 atomic%.

[11] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element selected from the group consisting of Dy, Ho and Er, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (21) to (23) or (24) to (26), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 21)0.1≦a≦5.0 (Formula 22)0.1≦b≦5.0 (Formula 23)0.5a-0.5≦b (Formula 24)0.1≦a≦3.0 (Formula 25)0.1≦b≦5.0 (Formula 26)2a-3≦b

[12] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element selected from the group consisting of Dy, Ho, and Er, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (Equation 21'), (Equation 22'), and (Equation 23) or (Equation 24'), (Equation 25'), and (Equation 26), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 21')0.2≦a≦5.0 (Formula 22')0.2≦b≦5.0 (Formula 23)0.5a-0.5≦b (Formula 24')0.2≦a≦3.0 (Formula 25')0.2≦b≦5.0 (Formula 26)2a-3≦b

[13] The magnesium alloys described in

[11] or

[12] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Sm, and Nd, wherein c satisfies the following equations (27) and (28). (Formula 27)0≦c≦3.0 (Formula 28)0.1(0.2)≦b+c≦6.0

[14] The magnesium alloys described in

[11] or

[12] above may further contain a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, wherein c satisfies the following equations (29) and (30). (Formula 29)0≦c≦3.0 (Formula 30)0.1(0.2)≦b+c≦6.0

[15] The magnesium alloy described in

[11] or

[12] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Sm, and Nd, and a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, wherein c and d satisfy the following equations (31) to (33). (Formula 31)0≦c≦3.0 (Formula 32)0≦d≦3.0 (Formula 33)0.1(0.2)≦b+c+d≦6.0

[16] The magnesium alloy described in any one of

[11] to

[15] above further contains a total of y atomic percent of at least one of Y and Gd, wherein y satisfies the following equations (34) and (35). (Formula 34)0≦y≦4.9 (Formula 35)0.1≦b+y≦5.0

[17] The magnesium alloy described in any one of

[11] to

[16] above may further contain at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B, C, Sn, Au, Ba, Ge, Bi, Ga, In, Ir, Li, Pd, Sb, and V in total amount of more than 0 atomic% and less than or equal to 2.5 atomic%.

[18] At least a portion of the long-period layered structure phase of the magnesium alloy described in any one of

[11] to

[17] above is curved or bent.

[19] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (41) to (43) or (44) to (46), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 41)0.1≦a≦5.0 (Formula 42)0.25≦b≦5.0 (Formula 43)0.5a-0.5≦b (Formula 44)0.1≦a≦3.0 (Formula 45)0.25≦b≦5.0 (Formula 46)2a-3≦b

[20] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following (Formula 41'), (Formula 42'), and (Formula 43) or (Formula 44'), (Formula 45'), and (Formula 46), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 41')0.2≦a≦5.0 (Formula 42')0.5≦b≦5.0 (Formula 43)0.5a-0.5≦b (Formula 44')0.2≦a≦3.0 (Formula 45')0.5≦b≦5.0 (Formula 46)2a-3≦b

[21] The magnesium alloys described in

[19] or

[20] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Sm, and Nd, wherein c satisfies the following equations (47) and (48). (Formula 47)0≦c≦3.0 (Formula 48)0.25(0.5)≦b+c≦6.0

[22] The magnesium alloys described in

[19] or

[20] above may further contain a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, wherein c satisfies the following equations (49) and (50). (Formula 49)0≦c≦2.0 (Formula 50)0.25(0.5)≦b+c≦6.0

[23] The magnesium alloy described in

[19] or

[20] above may further contain a total of c atomic percent of at least one element selected from the group consisting of Yb, Sm, and Nd, and a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, wherein c and d satisfy the following equations (51) to (53). (Formula 51)0≦c≦3.0 (Formula 52)0≦d≦2.0 (Formula 53)0.25(0.5)≦b+c+d≦6.0

[24] The magnesium alloy described in any one of

[19] to

[23] above may further contain at least one element selected from the group consisting of Dy, Ho, and Er in total amount of more than 0 atomic% and 1.5 atomic% or less.

[25] The magnesium alloy described in any one of

[19] to

[23] above may further contain Y in an amount greater than 0 atomic% and less than or equal to 1.0 atomic%.

[26] The magnesium alloy described in any one of

[19] to

[25] above may further contain less than 3 atomic percent in total of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu.

[27] The magnesium alloy described in any one of

[19] to

[26] above may further contain at least one element selected from the group consisting of Al, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B, and C in total amount of more than 0 atomic% and 2.5 atomic% or less.

[28] At least a portion of the long-period layered structure phase of the magnesium alloy described in any one of

[19] to

[27] above may be curved or bent.

[29] A magnesium alloy is characterized in that it contains a total of a atomic percent of at least one metal of Cu, Ni, and Co, and a total of b atomic percent of at least one element selected from the group consisting of Y, Dy, Er, Ho, Gd, Tb, and Tm, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following formulas (61) to (63), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 61)0.2≦a≦10 (Formula 62)0.2≦b≦10 (Formula 63)2 / 3a-2 / 3

[30] The magnesium alloy described in

[29] above may further contain c atomic percent of Zn, wherein a and c satisfy the following equation (64). (Formula 64)0.2 <a+c≦15

[31] In the above

[30] , a and c may further satisfy the following (Equation 65). (Formula 65)c / a≦1 / 2

[32] The magnesium alloy described in any one of

[29] to

[31] above further contains a total of d atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Yb, and Lu, wherein b and d satisfy the following formula (66). (Formula 66)0.2 <b+d≦15 ​

[33] In the above

[32] , b and d may further satisfy the following (Equation 67). (Formula 67)d / b≦1 / 2

[34] The magnesium alloy described in any one of

[29] to

[33] above further contains a total of e atomic percent of at least one element selected from the group consisting of Zr, Ti, Mn, Al, Ag, Sc, Sr, Ca, Si, Hf, Nb, B, C, Sn, Au, Ba, Ge, Bi, Ga, In, Ir, Li, Pd, Sb, V, Fe, Cr, and Mo, where e satisfies the following formula (68). (Formula 68)0 <e≦2.5

[35] In the above

[34] , e, a, b, and d may further satisfy the following (Equation 69). (Formula 69)e / (a+b+c+d)≦1 / 2

[36] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element from Y, Dy, Ho, and Er, a total of c atomic percent of at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Gd, Tb, and Yb, with the remainder being Mg and unavoidable impurities, wherein a, b, and c satisfy the following equations (71) to (74), and the alloy has a crystalline structure having an α-Mg phase or a long-period layered structure phase. (Formula 71)0.2≦a≦5.0 (Formula 72)0.2≦b≦5.0 (Formula 73)2a-3≦b (Equation 74) 0.05b ≤ c < 0.75b

[37] The magnesium alloy described in

[36] above may further contain d atomic percent of Al and satisfy the following formula (75). (Equation 75) 0.05b ≤ d < 0.75b

[38] The magnesium alloy described in

[36] or

[37] above may contain a total of b atomic percent of at least two of the elements Y, Dy, Ho, and Er.

[39] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element from Gd and Tb, a total of c atomic percent of at least one element selected from the group consisting of Al, Y, La, Ce, Pr, Nd, Sm, Dy, Ho, Er, Tm and Yb, with the remainder being Mg and unavoidable impurities, wherein a, b and c satisfy the following equations (81) to (84), and the alloy has a crystalline structure having an α-Mg phase or a long-period layered structure phase. (Formula 81)0.2≦a≦5.0 (Formula 82)0.2≦b≦5.0 (Formula 83)2a-3≦b (Equation 84) 0.05b ≤ c < 0.75b

[40] The magnesium alloy is preferably an alloy containing a atomic percent of Al, b atomic percent of Gd, with the remainder being Mg and unavoidable impurities, wherein a and b satisfy the following equations (91) and (92), and the alloy has a crystalline structure having an α-Mg phase, a long-period stacked structure phase, or a phase containing close-packed atomic area layer defects. (Formula 91)0.01≦a≦2.0 (Formula 92)0.2≦b≦5.0 In this specification, a close-packed atomic area layer defect refers to a layer containing a concentrated diatomic layer (solute atom-enriched diatomic layer) in which solute atoms, namely zinc and rare earth elements, are continuous in the stacking direction along the close-packed atomic plane, and in which the solute atom-enriched diatomic layer does not have periodicity in the stacking direction over long distances.

[41] The magnesium alloy is an alloy containing a atomic percent of Zn, a total of b atomic percent of at least one element selected from the group consisting of Y, Dy, Ho, Er, Gd, Tb, and Tm, a atomic percent of Al, and the remainder being Mg and unavoidable impurities, wherein a, b, and c satisfy the following equations (Equations 101) to (Equations 104), and the alloy has a crystalline structure having an α-Mg phase, a long-period stacked structure phase, or a phase containing close-packed atomic area layer defects. (Formula 101)0.2≦a≦5.0 (Formula 102)0.2≦b≦5.0 (Formula 103)2a-3≦b (Equation 104) 0.05b ≤ c < 0.75b

[42] The magnesium alloy described in

[41] above further contains a total of d atomic percent of at least one element selected from the group consisting of Li, Sn, Di, La, Ce, Pr, Nd, Sm, Eu, Mm, Yb, Th, Ca, Si, Mn, Zr, Ti, Hf, Nb, Ag, Sr, Sc, B, C, Ga, and Ge, where d satisfies the following equation (105). (Formula 105)0≦d≦b / 2

[43] The magnesium alloy may consist of one of the following chemical components (A) to (G). (A) By mass%, it contains Al: 0.1-12.0%, Mn: 0.1-1.0%, with the remainder being Mg and impurities. (B) By mass%, it contains Al: 0.1-12.0%, Mn: 0.1-1.0%, and one or more elements selected from Zn: 0.5-2.0% and Si: 0.3-2.0%, with the remainder being Mg and impurities. (C) By mass%, it contains Zn: 1.0-10.0%, Zr: 0.4-2.0%, with the remainder being Mg and impurities. (D) By mass%, it contains Zn: 1.0-10.0%, Zr: 0.4-2.0%, Mn: 0.5-2.0%, with the remainder being Mg and impurities. (E) By mass%, it contains Zn: 1.0-10.0%, rare earth elements: 1.0-3.0%, with the remainder being Mg and impurities. (F) By mass%, it contains Zr: 0.4-2.0%, rare earth elements: 1.0-3.0%, with the remainder being Mg and impurities. (G) In mass%, Zn: 1.0~10.0%, Mn: 0.1~1.0%, Cu: 0.5~ It contains 2.0%, with the remainder being Mg and impurities.

[44] The magnesium alloy may be an alloy containing a atomic percent of Zn and b atomic percent of Y, wherein a and b satisfy the following equations (Equation 11) to (Equation 13) or (Equation 14) to (Equation 16), and having a crystalline structure with an α-Mg phase or a long-period stacked structure phase. (Formula 11) 0.25≦a<5.0 (Formula 12)0.5 <b<5.0 (Formula 13)2 / 3a-5 / 6≦b (Formula 14)0.25≦a≦5.0 (Formula 15)0.5≦b≦5.0 (Formula 16)0.5a≦b

[45] The magnesium alloy may be an alloy containing a atomic percent of Zn and a total of b atomic percent of at least one element selected from the group consisting of Dy, Ho, and Er, wherein a and b satisfy the following equations (21) to (23) or (24) to (26), and which has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 21)0.1≦a≦5.0 (Formula 22)0.1≦b≦5.0 (Formula 23)0.5a-0.5≦b (Formula 24)0.1≦a≦3.0 (Formula 25)0.1≦b≦5.0 (Formula 26)2a-3≦b

[46] The magnesium alloy may be an alloy containing a atomic percent of Zn and a total of b atomic percent of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, wherein a and b satisfy the following equations (41) to (43) or (44) to (46), and which has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 41)0.1≦a≦5.0 (Formula 42)0.25≦b≦5.0 (Formula 43)0.5a-0.5≦b (Formula 44)0.1≦a≦3.0 (Formula 45)0.25≦b≦5.0 (Formula 46)2a-3≦b

[47] The magnesium alloy may be an alloy containing a total of a atomic percent of at least one metal, Cu, Ni, and Co, and a total of b atomic percent of at least one element selected from the group consisting of Y, Dy, Er, Ho, Gd, Tb, and Tm, wherein a and b satisfy the following equations (61) to (63), and the alloy has a crystalline structure having an α-Mg phase or a long-period stacked structure phase. (Formula 61)0.2≦a≦10 (Formula 62)0.2≦b≦10 (Formula 63)2 / 3a-2 / 3 ​

[48] ​​The magnesium alloy may be an alloy having a crystalline structure containing a atomic percent of Al and b atomic percent of Gd, where a and b satisfy the following equations (91) and (92), and having an α-Mg phase or a long-period stacked structure phase. (Formula 91)0.01≦a≦2.0 (Formula 92)0.2≦b≦5.0

[0037] (Embodiment 4) A method for manufacturing a stent according to one aspect of the present invention will be described. This stent is a cerebral aneurysm stent as shown in Figure 1.

[0038] <Method of manufacturing wire> First, a magnesium alloy base wire with a small average grain size of the α-Mg phase is fabricated. In detail, a molten magnesium alloy containing 90 atomic percent or more of Mg is rapidly cooled and solidified to produce multiple rapidly solidified products. The cooling rate in this case should be faster than 1000 K / second (preferably 10000 K / second). The multiple rapidly solidified products are, for example, powders produced by the RS-P / M method (or thin flakes, thin strips or fine wires produced by the RS-P / M method, or fine wires produced by the molten metal extraction method).

[0039] Next, a solidified molded product is produced by hot extrusion of multiple rapidly solidified materials. Specifically, a billet can be produced by filling a copper can with powder (or flakes, strips, or fine wires) and vacuum sealing it, and then extruding the billet to produce a solidified molded product. Another method of solidification is to roll the powder using grooved rolls.

[0040] Furthermore, it is preferable that the copper cans mentioned above have a chrome coating (e.g., Cr plating) applied to their inner surface. This suppresses the diffusion of copper into the magnesium alloy, thereby improving the corrosion resistance of the resulting wire. In other words, while the corrosion resistance of a magnesium alloy deteriorates when it contains around 100 ppm of copper, applying a chrome coating to the inner surface of the copper can suppresses the diffusion of copper into the magnesium alloy, thereby restoring the original corrosion resistance of the magnesium alloy.

[0041] Next, the solidified molded product is extruded to produce a magnesium alloy base wire with a small average crystal grain size of the α-Mg phase. In this embodiment, a magnesium alloy base wire with a small average grain size of the α-Mg phase is fabricated by rapid solidification powder metallurgy (RS-P / M). However, a magnesium alloy base wire with a small average grain size of the α-Mg phase may also be fabricated from a magnesium alloy billet produced by casting using a method that applies large strain to the material, such as the ECAE (equal-channel-angular-extrusion) processing method.

[0042] The ECAE processing method is a method in which the longitudinal direction of the sample is rotated by 90° with each pass in order to introduce uniform strain into the sample. Specifically, it is a method in which a magnesium alloy casting, which is the molding material, is forcibly inserted into a molding hole of a molding die that has an L-shaped molding hole in its cross-section, and stress is applied to the magnesium alloy casting, particularly in the 90° bent portion of the L-shaped molding hole, in order to obtain a molded body. Multiple passes are preferable for ECAE. The processing temperature during ECAE is preferably, for example, 250°C to 500°C.

[0043] After producing the magnesium alloy base wire described above, a magnesium alloy wire containing the α-Mg phase is manufactured by subjecting the magnesium alloy base wire to multiple drawing processes. In this specification, "magnesium alloy base wire" and "magnesium alloy wire" are defined as follows: A magnesium alloy wire refers to the wire after multiple drawing processes have been completed. A magnesium alloy base wire refers to the wire before multiple drawing processes and the wire during multiple drawing processes. In other words, a magnesium alloy base wire refers to all the wire before multiple drawing processes are completed. For example, if the processing step shown in Figure 8 is the final drawing process after multiple drawing processes have been completed, the wire before this final drawing process becomes the magnesium alloy base wire 41, and the wire after drawing becomes the magnesium alloy wire 42. Also, if the processing step shown in Figure 8 is a drawing process in the middle of multiple drawing processes, the wire before this intermediate drawing process becomes the magnesium alloy base wire 41, and the wire after drawing also becomes the magnesium alloy base wire 42.

[0044] The magnesium alloy base wire described above is preferably formed from a magnesium alloy that does not (or does not) undergo grain growth when heat-treated at a temperature of 300°C. This could be a general-purpose magnesium alloy, an LPSO (Long-Period Stacking Ordered) type alloy, pure magnesium, etc. For example, it may be formed from any of the alloys listed in [1] to

[48] above.

[0045] As shown in Figure 8, a magnesium alloy base wire 41 with a diameter of, for example, more than 1 mm and less than or equal to 3 mm is drawn using a die 43 in the direction of the arrow at a drawing speed of 0.1 m / min to 1000 m / min (preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 100 m / min) to form a magnesium alloy wire (or magnesium alloy base wire if multiple drawing processes are in progress) 42. The temperature of the magnesium alloy base wire 41 during the drawing process (i.e., the temperature of the magnesium alloy base wire 41 when passing through the die 43) is preferably in the range of room temperature or higher and 450°C or lower, or 150°C to 350°C or higher and 200°C to 300°C. The reason for such a temperature range is to prevent the magnesium alloy base wire from breaking during the drawing process and to reduce the temperature or time of the heat treatment required to remove strain after the drawing process. The reason for reducing the heat treatment temperature or time is that doing so can suppress grain growth in the α-Mg phase.

[0046] In this specification, the wire diameter of the magnesium alloy base wire refers to, for example, the wire diameter d3 of the magnesium alloy base wire 41 shown in Figure 8, and if the cross-sectional shape of the magnesium alloy base wire is not circular, it refers to the maximum outer diameter of the cross-section of the magnesium alloy base wire.

[0047] When the magnesium alloy base wire 41 is subjected to the first drawing process at room temperature, the temperature of the die 43 is controlled to account for the heat generated by friction between the die 43 and the magnesium alloy base wire 41 as it passes through the die 43, which is then added to the magnesium alloy base wire 42 after drawing. For example, the temperature of the die 43 is controlled to be between 200°C and 300°C. This allows the temperature of the magnesium alloy base wire 41 during the drawing process to be kept within the above range.

[0048] When performing the second drawing process, the magnesium alloy base wire 41 is returned to room temperature, and the room-temperature magnesium alloy base wire 41 is passed through a temperature-controlled die 43 to perform the drawing process. This drawing process is repeated multiple times until the wire diameter D of the magnesium alloy wire 42 satisfies the following equation (41). The magnesium alloy wire 42 that satisfies the following equation (41) has an α-Mg phase, and it is desirable that the following equations (42) and (43) are satisfied when the average grain size of the α-Mg phase observed in a cross-section cut in the longitudinal direction of the magnesium alloy wire 42 is L (not shown), and the average grain size of the α-Mg phase observed in a cross-section cut perpendicular to the longitudinal direction is d (not shown). (Formula 41) 5μm≦D≦50μm (Formula 42) d ≤ 1 μm (preferably d ≤ 0.5 μm, more preferably d ≤ 0.3 μm, even more preferably d ≤ 0.19 μm, even more preferably d ≤ 0.12 μm, and even more preferably d ≤ 0.1 μm) (Formula 43) 10 ≤ L / d (preferably 43 ≤ L / d, more preferably 54 ≤ L / d, even more preferably 70 ≤ L / d, and even more preferably 90 ≤ L / d)

[0049] When performing each of the multiple drawing processes described above, it is advisable to supply a non-silicone type of oil as a lubricant to the die 43, such as edible oil. This reduces the frictional heat between the die 43 and the magnesium alloy base wire 41, thereby preventing the wire from breaking during the drawing process. The cross-sectional reduction rate RA when performing each of the above multiple drawing processes is preferably satisfied with the following (Equation 45), more preferably with the following (Equation 45'), and even more preferably with the following (Equation 45''). (Formula 45) 1%≦RA≦30% (Formula 45')3%≦RA≦15% (Formula 45'')5%≦RA≦12%

[0050] The cross-sectional reduction rate is calculated as follows: (1 - (D / d3)) where d3 is the wire diameter before drawing and D is the wire diameter after drawing.2 This refers to the value of ) × 100. Furthermore, as the magnesium alloy base wire 41 is subjected to multiple drawing processes, the wire diameter of the magnesium alloy base wire 41 gradually decreases. The magnesium alloy base wire 42 is subjected to heat treatment after at least one of the multiple drawing processes. The temperature of this heat treatment is preferably 50°C higher and 450°C or 50°C higher and 400°C or lower than the temperature of the magnesium alloy base wire 42 immediately after the drawing process immediately preceding the heat treatment, and the heat treatment time is preferably 10 seconds to 12 hours.

[0051] The timing for heat treatment is when the average grain size of the α-Mg phase of the magnesium alloy base wire 42 after multiple drawing processes becomes considerably smaller than the average grain size of the α-Mg phase of the magnesium alloy base wire 41 before multiple drawing processes. The number of heat treatments may be multiple and should be adjusted as appropriate.

[0052] For example, heat treatment may be performed after each drawing process, or it may be performed after each drawing process, or it may not be performed at all. Also, for example, if the heat treatment temperature is set to 350°C and the heat treatment time to 30 minutes, the formation of an oxide film on the surface of the magnesium alloy wire 42 can be reduced even when heat treatment is performed in an air atmosphere. In other words, the formation of an oxide film is reduced even when heat treatment is performed.

[0053] In this way, a magnesium alloy wire 42 can be manufactured with a wire diameter D of 5 μm to 100 μm and an average crystal grain size d of the α-Mg phase of 1 μm or less (preferably 0.5 μm or less, more preferably 0.3 μm or less, and even more preferably 0.1 μm or less). In this case, the wire diameter D and average crystal grain size d should satisfy the following equation (formula 44). (Equation 44) d / D ≤ 1 / 100 (preferably 1.15 / 300 or less, more preferably 1.9 / 500 or less, even more preferably d / D ≤ 1 / 300, more preferably d / D ≤ 1 / 500)

[0054] The magnesium alloy wire 42 described above corresponds to the wire material in Embodiments 1 to 3, and it is preferable that the Young's modulus (longitudinal elastic modulus) of this wire material is 50 GPa or less.

[0055] Furthermore, the wire used to fabricate a stent for a flow diverter should have a diameter of 50 μm or less, preferably 30 μm or less. Similarly, the wire used to fabricate a stent for coil embolization should have a diameter of 100 μm or less, preferably 80 μm or less. Furthermore, the yield strength (0.2% proof stress) of the magnesium alloy wire 42 obtained as described above is 300 MPa or more, preferably 400 MPa or more, more preferably 500 MPa or more, even more preferably 600 MPa or more, and even more preferably 700 MPa or more.

[0056] According to the above embodiment, a magnesium alloy base wire 41 with a small grain size is produced by a rapid solidification powder metallurgy method, and then the magnesium alloy base wire 41 is subjected to repeated drawing and heat treatment processes that suppress recrystallization and grain growth as much as possible, thereby making the average grain size of the α-Mg phase 1 μm or less at a predetermined wire diameter. This makes it possible to realize a magnesium alloy wire 42 with high strength or high corrosion resistance.

[0057] Furthermore, even when the wire diameter of the magnesium alloy wire 42 is reduced to 100 μm or less, 50 μm or less, or 30 μm or less, a wire that is less prone to breakage can be achieved.

[0058] Next, the wire manufactured by the above method may be surface-treated or coated. This is to adjust the time until the stent decomposes after it has been placed in the blood vessel, or the rate of bioabsorption. As mentioned above, the required bioabsorption rate differs between flow diverter stents and coil embolization stents, and it is also thought that the required bioabsorption rate differs depending on the size and condition of the cerebral aneurysm.

[0059] Specific examples of wire surface treatment include hydrofluoric acid treatment or anodic oxidation treatment of the wire surface. Surface treatment forms oxides or fluorides on the wire surface. Specific examples of wire coating include polymer bonding or polymer coating of the wire surface, or DLC (Diamond-Like Carbon) film deposition treatment.

[0060] <Wire weaving process> Next, a stent 10 consisting of a tubular braided body as shown in Figure 1 is produced by braiding the above-mentioned wire material with a number of strands of 8 or more (preferably 16 or more) using a blader (braiding machine). The braided body is made by braiding the wire material in a tubular shape by alternately crossing the wire material. It is preferable that the twist of the wire material during braiding be 1 turn or less per 10 cm of wire length. To reduce the twist, it is good to increase the diameter of the blader's bobbin or to use a vertical bobbin.

[0061] In this case, when preparing the coil embolization stent 30, it is preferable to weave together eight or more wires, and more preferably to weave together sixteen or more wires. Furthermore, when manufacturing the stent 20 for the flow diverter, it is preferable to weave together 24 or more wires, and more preferably 48 or more wires. Furthermore, it is preferable that the outer diameter of the stent, which is constructed from the braided material described above, is constant throughout its entire length. It is also preferable that the density of the braided material is uniform throughout.

[0062] Next, the stent woven using the method described above may be subjected to surface treatment or coating. In this case, it is preferable not to apply surface treatment or coating to the wire material. By applying surface treatment or coating in this way, it is possible to adjust the period until the stent decomposes or the rate of bioresorption after the stent has been placed in the blood vessel.

[0063] Specific examples of stent surface treatment include hydrofluoric acid treatment or anodic oxidation treatment of the stent surface. Surface treatment forms oxides or fluorides on the stent surface. Specific examples of stent coating include polymer bonding or polymer coating of the stent surface, or DLC (Diamond-Like Carbon) film deposition treatment.

[0064] Next, the stent may be heat-treated to fix its shape. The heat treatment conditions should be such that the temperature is higher than room temperature but below 400°C, and the treatment time is between 1 second and 12 hours. Furthermore, the stent shape during heat treatment should be larger in diameter than when it is placed in the blood vessel. This larger diameter is equal to the outer diameter after expansion, and it is used by stretching it in the length direction during insertion. The order of heat treatment and surface treatment or coating of the stent may be reversed.

[0065] Furthermore, the above embodiments 1 to 4 can be combined with each other as appropriate. [Examples]

[0066] Figure 9 shows the external appearance (SEM images) of the wires (Sample Microscope) for Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5 according to Example 1.

[0067] Sample 1 is a magnesium alloy wire (wire material) with a diameter of 95.5 μm, obtained by solidifying powder, flakes, strips, or fine wires prepared by the RS-P / M method, extruding the solidified product, and then subjecting it to multiple drawing and heat treatment processes. Its alloy composition is Mg 97.94 -Zn 0.56 -Y 1.5Sample 2 is a wire with a diameter of 73 μm obtained by subjecting Sample 1 to multiple drawing and heat treatment processes. Sample 3 is a wire with a diameter of 49.2 μm obtained by subjecting Sample 2 to multiple drawing and heat treatment processes. Sample 4 is a wire with a diameter of 32 μm obtained by subjecting Sample 3 to multiple drawing and heat treatment processes. Sample 5 is a wire with a diameter of 29.7 μm obtained by subjecting Sample 4 to further drawing and heat treatment processes. The wire diameters were measured using a high-precision digital micrometer (MDH-25MB manufactured by Mitutoyo Corporation).

[0068] The method for manufacturing the magnesium alloy base wire 41 is as follows. Mg 97.94 -Zn 0.56 -Y 1.5 The alloy is melted by gas heating under an argon gas atmosphere, resulting in approximately 2 × 10⁻¹⁰ 5 The alloy powder is prepared by cooling at a cooling rate of K / sec. Next, the alloy powder is pre-formed at a pressure of 60-170 MPa, and a billet is produced by vacuum degassing at a temperature of 250°C for 2 hours. Then, the die and container are fixed, and the billet is pressed against the die to perform extrusion. The extrusion conditions are as follows: Extrusion speed: 2.5 mm / min Container, die, and billet temperature: 350℃ Extrusion ratio: 15

[0069] In this embodiment, approximately 2 × 10 5 A cooling rate of K / sec is used, but 1 × 10 5 K / sec or more 2×10 5 It is also possible to use cooling rates in the range of K / sec or less.

[0070] The method for preparing Sample 1 is as follows: Temperature during drawing of magnesium alloy base wire 41: 300°C for wire diameters up to 1.08 mm, and 225°C for wire diameters smaller than that. Pulling speed: 0.1~1.0 m / min Heat treatment temperature: 350℃ Heat treatment time: 10 minutes Frequency of heat treatment: For magnesium alloy base wire 41, heat treatment is performed after each drawing process for wire diameters up to 1.65 mm, and once every two drawing processes for wire diameters smaller than that. Die material: For wires with a magnesium alloy base, use carbide dies up to 2.13 mm in diameter; for wires with a diameter smaller than that, use diamond dies. Die temperature: 300°C for magnesium alloy base wire 41 up to a wire diameter of 1.08 mm, and 225°C for wire diameters smaller than that. Die lubricant: Edible oil Pull-out direction: Two directions Wire diameter of sample 1: 95.5 μm

[0071] Note that the pull-out direction refers to the direction of the arrow shown in Figure 8. Having two pull-out directions means that if one direction is the direction of the arrow shown in Figure 8, the other direction is the pull-out direction when the magnesium alloy base wire 41 is rotated 180° and positioned in the opposite direction.

[0072] The method for preparing Sample 2 is as follows: Temperature during the drawing process of magnesium alloy base wire 41: 225℃ Pulling speed: 1.0 m / min Heat treatment temperature: 350℃ Heat treatment time: 10 minutes Frequency of heat treatment: Performed once every 2-4 processing steps. Die material: Diamond die Dice temperature: 225℃ Die lubricant: Edible oil Pull-out direction: Two directions Wire diameter of sample 2: 73 μm The method for preparing Sample 3 is as follows: Temperature during the drawing process of magnesium alloy base wire 41: 225℃ Pulling speed: 1.0~5.0 m / min Heat treatment temperature: 350℃ Heat treatment time: 10 minutes Frequency of heat treatment: Performed once every 3 to 10 processing steps. Die material: Diamond dies are used. Dice temperature: 225℃ Die lubricant: Edible oil Pull-out direction: Two directions Wire diameter of sample 3: 49.2 μm The method for preparing Sample 4 is as follows: Temperature during the drawing process of magnesium alloy base wire 41: 225℃ Pulling speed: 1.0~5.0 m / min Heat treatment temperature: 350℃ Heat treatment time: 10 minutes Frequency of heat treatment: Performed once for every 12 or more processing steps. Die material: Diamond dies are used. Dice temperature: 225℃ Die lubricant: Edible oil Pull-out direction: Two directions Wire diameter of sample 4: 32 μm The method for preparing Sample 5 is as follows: Temperature during the drawing process of magnesium alloy base wire 41: 225℃ Pulling speed: 1.0~5.0 m / min Heat treatment temperature: 350℃ Heat treatment time: 10 minutes Frequency of heat treatment: Performed once for every 12 or more processing steps. Die material: Diamond dies are used. Dice temperature: 225℃ Die lubricant: Edible oil Pull-out direction: Two directions Wire diameter of sample 5: 29.7 μm

[0073] Figure 10 shows the results of measuring the yield stress (0.2% proof stress) of each wire material from samples 1 to 5 shown in Figure 9. As shown in Figure 10, the wire of sample 1 has a yield stress of 467.9 MPa, the wire of sample 2 has a yield stress of 482.1 MPa, the wire of sample 3 has a yield stress of 515.7 MPa, the wire of sample 4 has a yield stress of 622.0 MPa, and the wire of sample 5 has a yield stress of 635.4 MPa.

[0074] Figure 11 shows the results of measuring the Young's modulus (longitudinal elastic modulus) of each of the wire samples 1 to 5 shown in Figure 9. As shown in Figure 11, the wire of sample 1 has a Young's modulus of 42.8 GPa, the wire of sample 2 has a Young's modulus of 44.4 GPa, the wire of sample 3 has a Young's modulus of 45.1 GPa, the wire of sample 4 has a Young's modulus of 46.7 GPa, and the wire of sample 5 has a Young's modulus of 48.1 GPa. [Examples]

[0075] Figure 12 is a photograph showing the external appearance of a stent for a cerebral aneurysm according to Example 2. Using a braiding machine designed for round cords (with an even number of braids), the wire material (wire diameter: approximately 50 μm) from Sample 3 of Example 1 was braided with 16 strands to create a stent consisting of a tubular braided body as shown in Figure 12.

[0076] According to Example 2, the outer diameter of the stent could be kept constant along its entire length, and the weaving density could also be made uniform throughout. [Examples]

[0077] The sample for Example 3 was prepared as follows. A billet was produced by filling a copper can with powder, flakes, strips, or wires prepared by rapid solidification powder metallurgy, then vacuum sealing it, and finally extruding the billet. The extruded product was then heat-treated at 738K for 24 hours. The resulting magnesium alloy had the composition Mg 97.25 -Zn0.75 -Y2. The copper can used here has a chromium (Cr) plating on its inner surface.

[0078] Comparative example sample 1 was prepared in the same manner as the sample in Example 3, except that the inner surface of the copper can was not plated with Cr. Furthermore, in comparative example sample 2, an alloy of ASTM (USA) WE43 (a magnesium alloy containing 4 mass% Y and 3 mass% rare earth elements) was cast, and the casting was extruded directly without being placed in a copper can. Therefore, copper was not diffused into comparative example sample 2.

[0079] Figure 13(A) shows the immersion time dependence of the corrosion rate in the simulated body fluid for each of the comparative examples, Sample 1 and Sample 2, and Figure 13(B) shows the immersion time dependence of the corrosion rate in the simulated body fluid for each of the samples from Example 3 and Comparative Example Sample 1. The corrosion rate was measured by immersing the sample from Example 3 and samples 1 and 2 from Comparative Example in a simulated body fluid (HBSS: physiological equilibrium salt solution) adjusted to pH 7.4, and measuring the relationship between immersion time and corrosion rate. The simulated body fluid was kept at a temperature of 310K and exposed to the atmosphere during the measurement.

[0080] When magnesium contains around 100 ppm of copper, its corrosion resistance deteriorates. In comparative example sample 1, which was made using a copper can without chromium plating on the inside, the copper diffuses into the billet material during extrusion, resulting in a deterioration of corrosion resistance. In contrast, the sample of Example 3, which is made using a copper can with Cr plating on the inner surface, prevents Cu from diffusing into the billet material during extrusion, thus achieving its intended corrosion resistance. Therefore, the sample of Example 3 has better corrosion resistance than the comparative example sample 1.

[0081] Furthermore, while Cu is not diffused in comparative example sample 2, the sample from example 3 has better corrosion resistance than comparative example sample 2. [Examples]

[0082] Figure 15 is a photograph showing the external appearance of a stent for a cerebral aneurysm according to Example 4. Using a braiding machine designed for round cords (with an even number of braids), the wire material (wire diameter: approximately 50 μm) from Sample 3 of Example 1 was braided with 48 strands to create a stent consisting of a tubular braided body as shown in Figure 15.

[0083] According to Example 4, the outer diameter of the stent could be kept constant along its entire length, and the weaving density could also be made uniform throughout. [Explanation of symbols]

[0084] 10…Stent for cerebral aneurysm 11a,11b,13,15,16,17a,17b...Wire rod 12, 14, 19… Stents for cerebral aneurysms 18…Angle formed by wire 11a and wire 11b 20…Stent for flow diverter 21, 31… Cerebral aneurysm 22,32…blood vessels 30…Stent for coil embolization 33... Coil 41…Magnesium alloy base wire 42…Magnesium alloy wire 43... Dice d3...Wire diameter of magnesium alloy base wire D...Wire diameter of magnesium alloy wire

Claims

1. A method for manufacturing a stent that is self-expanding and is placed by being compressed against the blood vessel wall to span a cerebral aneurysm, (e) A step of rapidly cooling and solidifying a magnesium alloy or pure magnesium molten metal containing 90 atomic percent or more of Mg to produce multiple rapidly solidified products, The process (f) involves filling and sealing the plurality of rapidly solidified materials into a copper can to produce a billet, and then extruding the billet to produce a solidified molded product. (g) A step of producing a magnesium alloy base wire by extruding the solidified molded product, (h) A step to manufacture a magnesium alloy wire having an α-Mg phase or a long-period layered structure phase by subjecting the magnesium alloy base wire to multiple drawing processes, The process includes (a) weaving the aforementioned wire material with eight or more strands, The aforementioned wire is made of a magnesium alloy or pure magnesium containing 90 atomic percent or more of Mg, and has a yield strength (0.2% proof stress) of 300 MPa or more and a Young's modulus (longitudinal elastic modulus) of 50 GPa or less. The diameter of the aforementioned wire is 100 μm or less. A method for manufacturing a stent, characterized in that the inner surface of the can is treated with a chrome coating.

2. In claim 1, The aforementioned stent is a stent for a flow diverter. The aforementioned number of hits is 24 or more, A method for manufacturing a stent, characterized in that the diameter of the wire is 50 μm or less.

3. In claim 1 or 2, A method for manufacturing a stent, characterized by having a step (b) of applying a surface treatment or coating to the wire before step (a), or a step (c) of applying a surface treatment or coating to the stent after step (a).

4. In claim 3, Step (b) is to perform polymer bonding or polymer coating on the surface of the wire, or to perform hydrofluoric acid treatment, anodic oxidation treatment or DLC film formation treatment on the surface of the wire. The method for manufacturing a stent is characterized in that step (c) is to perform hydrofluoric acid treatment, anodic oxidation treatment, or DLC film deposition treatment on the stent.

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