Stent

Abstract

Provided is a stent for a cerebral aneurysm, said stent being formed of a material absorbable in vivo. One embodiment of the present invention pertains to a stent 10 that has self-expandability and, therefore, is crimped to blood vessel wall and placed so as to straddle a cerebral aneurysm. The stent 10 has bioabsorbable properties and comprises a magnesium alloy containing 90 at% or more of Mg or pure magnesium.

Description

Technical Field

[0001] The present invention relates to a stent for cerebral aneurysms having bioabsorbability and a method for manufacturing the same.

Background Art

[0002] A cerebral aneurysm is a part of a cerebral artery that bulges like a bump. The bump is usually formed by a branch of a major blood vessel distributed in the brain being pushed by cerebral blood flow and gradually swelling. Since a cerebral aneurysm ruptures to cause subarachnoid hemorrhage, it is a very terrible disease. In order to prevent subarachnoid hemorrhage, it is necessary to treat the cerebral aneurysm before rupture. The treatment methods are either a craniotomy clipping operation that opens the skull or a surgical treatment such as endovascular treatment using a stent for cerebral aneurysms. The treatment method using a stent for cerebral aneurysms is as follows. A doctor inserts a tube from an artery at the base of the leg, guides it to the cerebral aneurysm, and a stent for a flow diverter is deployed from a catheter so as to straddle the cerebral aneurysm, and the stent for the flow diverter is placed in the blood vessel. As a result, the blood flow to the cerebral aneurysm becomes gentle, and the cerebral aneurysm gradually thromboses. Then, as the thrombus is absorbed, the cerebral aneurysm gradually becomes smaller, and eventually the cerebral aneurysm is completely cured. Patent Document 1 discloses a flow diverter stent made of a NiTi alloy as the above-described stent for cerebral aneurysms. Since the above-described flow diverter stent is made of a NiTi alloy, it is not absorbed by the living body even after the cerebral aneurysm is completely cured. Therefore, there is a problem that the stent remains in the cerebral blood vessel, and the subsequent burden on the patient is large. That is, when a stent remains in the cerebral blood vessel, in order to prevent side effects therefrom, the patient has to continue taking medicine thereafter, and the burden on the patient becomes extremely large. Therefore, if a stent for cerebral aneurysms is placed in a cerebral artery and the stent is made of a material that is absorbed by the living body after the treatment of the cerebral aneurysm is completed, the subsequent burden on the patient can be reduced.

Prior Art Documents

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One aspect of the present invention is to provide a stent for cerebral aneurysm formed of a material absorbed by a living body.

Means for Solving the Problems

[0005] Various aspects of the present invention are as follows. [1] A stent that has self-expandability and is placed so as to be pressed against the blood vessel wall to straddle a cerebral aneurysm, has bioabsorbability, and is characterized by being made of a magnesium alloy containing 90 atomic% or more of Mg or pure magnesium. [2] In the above [1], the stent is composed of a tubular braid knitted with a wire made of the magnesium alloy or the pure magnesium, or is formed by cross-coiling, parallel-coiling, or coiling the wire, and is characterized by being a stent. [3] In the above [1], the stent is composed of a tubular braid knitted with two or more types of wires including a wire made of a magnesium alloy containing 90 atomic% or more of Mg or pure magnesium and a wire made of a magnesium alloy having a composition different from that of the magnesium alloy or the pure magnesium and containing 90 atomic% or more of Mg, or is formed by cross-coiling, parallel-coiling, or coiling the two or more types of wires, and is characterized by being a stent. [4] In the above [1], The stent is composed of a tubular braided body woven from two or more types of wire materials, including a wire made of a magnesium alloy containing 90 atomic% or more of Mg or pure magnesium, and a wire made of a material different from the magnesium alloy or the pure magnesium, or is formed by cross-coiling, parallel-coiling, or coiling the two or more types of wire materials. [5] In the above [4], The stent is characterized in that the material is one material selected from the group consisting of a bioabsorbable polymer, W, Ta, Pt, and Au. [6] In any one of the above [2] to [5], 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 [2] to [6], The stent is a stent for a flow diverter or a stent for a coil embolization. [8] In the above [7], The surface coverage rate of the stent for a flow diverter is 30% or more (preferably 35% or more), and the number density of its holes is 14 or more per mm 2 (preferably 15 or more per mm 2 or more), The surface coverage rate of the stent for a coil embolization is 5% or more (preferably 10% or more), and the number density of its holes is 0.2 or more per mm 2 (preferably 0.4 or more per mm 2 or more), The angle formed by the wires in the braided body is 10° or more and 70° or less. [9] In the above [7] or [8], The bioabsorption rate of the stent for a flow diverter is 12 months or more and 36 months or less, The bioabsorption rate of the stent for a coil embolization is 1 month or more and 3 months or less.

[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 in that.

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

[11] , 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 in that.

[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 stacking structure phase, and the stent is characterized in that.

[14] A method for manufacturing a stent that is self-expanding and is placed so as to be crimped to the blood vessel wall to straddle a cerebral aneurysm, It has a step (a) of knitting using a wire rod with 8 or more (preferably 16 or more) strokes, The wire rod 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 rod is 100 μm or less (preferably 80 μm or less), and the method for manufacturing a stent is characterized in that.

[15] In the above

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

[16] In the above

[14] or

[15] , Before the step (a), it has a step (b) of subjecting the wire rod to surface treatment or coating, or after the step (a), it has a step (c) of subjecting the stent to surface treatment or coating, and the method for manufacturing a stent is characterized in that.

[17] In the above

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

[18] In any one of the above

[14] to

[17] , before the step (a), there is a step (d) of manufacturing the wire, the step (d) includes a step (e) of rapidly solidifying a molten magnesium alloy or pure magnesium containing 90 atomic% or more of Mg to produce a plurality of rapidly solidified products, a step (f) of producing a billet by filling and enclosing the plurality of rapidly solidified products in a copper can, and producing a solidified molded product by extrusion molding the billet, a step (g) of producing a magnesium alloy base wire by extruding the solidified molded product, and a step (h) of producing a wire of a magnesium alloy having an α-Mg phase or a long-period stacked structure phase by performing multiple drawing processes on the magnesium alloy base wire, and a method for manufacturing a stent is characterized in that the inner surface of the can is subjected to a chromium coating treatment. By applying one aspect of the present invention, a stent for a cerebral aneurysm formed of a material absorbed by a living body can be provided.

Brief Description of the Drawings

[0006] FIG. 1 is a view showing a stent for a cerebral aneurysm composed of a tubular braided body in which a wire according to one aspect of the present invention is braided. FIG. 2 is a view showing a stent for a cerebral aneurysm configured by coiling a wire according to one aspect of the present invention. FIG. 3 is a view showing a stent for a cerebral aneurysm configured by parallel coiling a wire according to one aspect of the present invention. FIG. 4 is a view showing a stent for a flow diverter according to one aspect of the present invention. FIG. 5 is a diagram schematically showing a state in which the stent 20 for a flow diverter shown in FIG. 4 is placed in a blood vessel 22 so as to straddle a cerebral aneurysm 21. FIG. 6 is a diagram showing a stent for coil embolization according to one aspect of the present invention. FIG. 7 is a diagram schematically showing a state in which the coil embolization stent 30 shown in FIG. 6 is placed in a blood vessel 32 so as to straddle a cerebral aneurysm 31. FIG. 8 is a diagram schematically showing a method for manufacturing a wire of a magnesium alloy according to one aspect of the present invention. FIG. 9 is an external appearance photograph (SEM photograph) of each of the wire rods (wires) of Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5 according to Example 1. FIG. 10 is a diagram showing the results of measuring the yield stress (0.2% proof stress) of each of the wire rods of Samples 1 to 5 shown in FIG. 9. FIG. 11 is a diagram showing the results of measuring the Young's modulus (longitudinal elastic modulus) of each of the wire rods of Samples 1 to 5 shown in FIG. 9. FIG. 12 is an external appearance photograph showing a stent for a cerebral aneurysm according to Example 2. FIG. 13(A) is a diagram showing the immersion time dependence of the corrosion rate of each of Samples 1 and 2 of the comparative example in a simulated body fluid, and FIG. 13(B) is a diagram showing the immersion time dependence of the corrosion rate of each of the sample of Example 3 and Sample 1 of the comparative example in a simulated body fluid. FIG. 14 is a diagram showing a stent for a cerebral aneurysm formed by cross-coiling a wire rod according to one aspect of the present invention. FIG. 15 is an external appearance photograph showing a stent for a cerebral aneurysm according to Example 3.

MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that the form and details thereof can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments shown below. (Embodiment 1) FIG. 1 is a diagram showing a stent composed of a tubular braided body in which a wire is braided according to one embodiment of the present invention. This stent 10 is used for the treatment of cerebral aneurysms and has self-expanding properties, so that it is pressed against the blood vessel wall and implanted. However, the "stent" in this specification is different from a general stent. A general stent is implanted at a stenotic or occluded site to treat diseases caused by stenosis or occlusion of a blood vessel or other in-vivo lumens (such as trachea, lymphatic vessels, ureters, etc.), in order to expand the stenotic or occluded site and secure its lumen. Therefore, it is common to have a stent that expands at the stenotic or occluded site to increase its outer diameter and maintains the lumen as it is. However, the "stent" in this specification is used for the treatment of cerebral aneurysms in which a part of the cerebral artery bulges like a bump, and is implanted in a cerebral artery that is not stenotic or occluded. Therefore, it does not require an expansion function as much as a general stent, and it only needs to have self-expanding properties to the extent that it can be pressed against the blood vessel wall of the cerebral artery. And it is sufficient if it can ensure the blood flow in the implanted blood vessel and has the effect of restricting the blood flow flowing into the aneurysm. Here, having self-expanding properties means that the outer diameter after expansion is 4 times or more and 12 times or less the outer diameter before expansion of the stent in the atmosphere. The stent 10 shown in FIG. 1 is composed of a tubular braided body braided with a plurality of wires 11a, 11b made of a magnesium alloy or pure magnesium having bioabsorbability and having an α-Mg phase or a long-period stacking ordered structure phase. The stent 10 also has a cylindrical body. Magnesium is preferred because it has excellent biocompatibility and is harmless even if it is absorbed by the living body during or after treatment. Here, the magnesium alloy is an alloy containing 90 atomic% or more of Mg. The plurality of wires 11a, 11b constituting the stent 10 may be made of wires having two or more different compositions. For example, magnesium alloys having two or more different compositions may be used, or pure magnesium and a magnesium alloy may be used. In addition, the plurality of wire materials 11a and 11b constituting the stent 10 may be made of two or more types of wire materials including a wire material made of a magnesium alloy or pure magnesium and a wire material made of a material different from that of the wire material. This different material may be a material selected from the group of bioabsorbable polymers, W, Ta, Pt, and Au. Note that W, Ta, Pt, and Au have visibility, and thus are useful for confirming the position of the stent when the stent is placed in the blood vessel of the cerebral artery. Further, in order to ensure visibility, markers (not shown) formed of a material selected from the group of W, Ta, Pt, and Au may be attached to both ends of the stent 10. The visibility referred to here means that since the stent made of a magnesium alloy transmits X-rays, the position of the stent cannot be confirmed by an X-ray fluoroscope used during the stent placement surgery. However, by attaching a wire material or a marker made of W, Ta, Pt, and Au that does not transmit X-rays to the stent, the position can be confirmed by the X-ray fluoroscope. As the bioabsorbable polymer, for example, any one of polyglycolic acid (PGA), a copolymer of glycolic acid and L-lactic acid (PGLA), a copolymer of glycolic acid and DL-lactic acid (PGDLLA), poly-L-lactic acid (PLLA), poly-D-lactic acid (PDLA), poly-DL-lactic acid (PDLLA), a copolymer of L-lactic acid and ε-caprolactone (LCL), and poly-p-dioxanone (PDO) can be used. The method for manufacturing a wire material using a bioabsorbable polymer is manufactured by melt spinning, wet spinning, dry spinning, gel spinning, or the like, and these wire materials may be appropriately strengthened by processes such as hot stretching, cold rolling, and heat treatment. In addition, the angle 18 formed by the wire 11a and the wire 11b is preferably 10° or more and 70° or less. Further, the cross-sectional shapes of the wires 11a and 11b may be circular, elliptical, or rectangular, and the aspect ratio of the elliptical or rectangular wire is preferably 1 or more and 5 or less. Also, the diameter of the stent 10 is preferably 2 to 6 mm, and the length of the stent 10 is preferably 10 to 50 mm. Also, the wires 11a and 11b are preferably subjected to surface treatment or coating. Specifically, a polymer bond or polymer coating may be applied to the surfaces of the wires 11a and 11b, or a hydrofluoric acid treatment, an anodizing treatment, or a DLC (Diamond Like Carbon) film-forming treatment may be performed on the surfaces of the wires 11a and 11b. Oxides, fluorides, etc. may be formed on the surfaces of the wires 11a and 11b by the surface treatment. Further, the stent 10 is preferably subjected to surface treatment or coating. Specifically, a hydrofluoric acid treatment, an anodizing treatment, or a DLC film-forming treatment is preferably performed on the stent 10. Oxides, fluorides, etc. may be formed on the surface of the stent 10 by the surface treatment. DLC is preferable because it has excellent biocompatibility and is harmless even if it is absorbed by the living body during or after treatment. By performing such surface treatment or coating, the timing at which the stent 10 is absorbed by the living body can be controlled. According to the present embodiment, since the stent 10 is manufactured by a cylindrical body formed of wires 11a and 11b made of a magnesium alloy or pure magnesium having an α-Mg phase or a long-period stacked structure phase, a stent for cerebral aneurysm that is absorbed by the living body can be realized. In the present embodiment, a stent for cerebral aneurysm having a cylindrical braided body braided with wires is described. However, any stent for cerebral aneurysm having bioabsorbability can be implemented with the following modifications. The stent 12 for cerebral aneurysm shown in FIG. 2 is configured by coiling a wire 13. That is, this stent 12 is a coil formed by winding the wire 13 in a circular or spiral shape. In addition, the stent 14 for cerebral aneurysm shown in Fig. 3 is formed by parallel coiling of wire materials 15 and 16. That is, this stent 14 is produced by arranging in parallel a coiled shape obtained by winding the wire material 15 in a circular or spiral shape and a coiled shape obtained by winding the wire material 16 in a circular or spiral shape. Also, it may be formed by parallel coiling of three or more wire materials. In addition, the stent 19 for cerebral aneurysm shown in Fig. 14 is formed by cross coiling of wire materials 17a and 17b. That is, this stent 19 is produced by overlapping a coiled shape obtained by winding the wire material 17a in a circular or spiral shape and a coiled shape obtained by winding the wire material 17b in a circular or spiral shape. Also, it may be formed by cross coiling of three or more wire materials. Also, the plurality of wire materials constituting the stents 14 and 19 may be wire materials 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. Also, the plurality of wire materials 15, 16, 17a, 17b constituting the stents 14 and 19 may be two or more wire materials including a wire material made of a magnesium alloy or pure magnesium and a wire material made of a material different from that wire material. These stents 12, 14, 19 are preferably applied to the coil embolization stent described later. In addition, as another example of a stent for cerebral aneurysm (not shown), it is produced through a process of processing a thin tube made of a magnesium alloy or pure magnesium from the outer periphery with laser light. As this different material, it may be a material selected from the group of bioabsorbable polymers, W, Ta, Pt, and Au. Note that W, Ta, Pt, and Au have visibility, and thus are useful for confirming the position of the stent when the stent is placed in the blood vessel of the cerebral artery. (Embodiment 2) Fig. 4 is a diagram showing a stent for a flow diverter according to an aspect of the present invention. This stent 20 for a flow diverter is a stent for a cerebral aneurysm and is composed of a tubular braided body braided with 48 wires. The stent 20 for a flow diverter can have the same configuration as the stent 10 shown in FIG. 1, except that the number of wires braided is larger. FIG. 5 is a diagram schematically showing a state in which the stent 20 for a flow diverter shown in FIG. 4 is placed in a blood vessel 22 so as to straddle a cerebral aneurysm 21. A doctor guides a catheter through the femoral artery at the root of the leg to the intracranial region, and the stent 20 for a flow diverter is inserted into the blood vessel 22 from the catheter so as to straddle the cerebral aneurysm 21, and is deployed in a form that presses against the blood vessel wall by having self-expandability. When the stent 20 for a flow diverter is placed in the parent blood vessel 22 where the cerebral aneurysm 21 exists, the blood flow (not shown) flowing into the cerebral aneurysm 21 is restricted by the mesh structure on the surface of the stent 20 for a flow diverter, and internal thrombosis is gradually promoted, and the neck portion of the aneurysm 21 is covered with the stent neointima. After several months, the cerebral aneurysm 21 is completely occluded, and moreover, the stent 20 for a flow diverter itself is gradually decomposed over several months and finally disappears without leaving foreign substances. However, when a wire or the like having no bioabsorbability is used for a part of the stent 20 for a flow diverter in order to ensure visibility, it may remain without disappearing. The surface coverage rate of the stent 20 for a flow diverter is 30% or more (preferably 35% or more), and the number density of its holes is 14 holes / mm 2 or more (preferably 15 holes / mm 2 or more). The reason for setting it within such a range is that if the surface coverage rate is less than 30% or the number density of the holes is less than 14 holes / mm 2 as shown in FIG. 5, even if the stent 20 for a flow diverter is deployed so as to straddle the cerebral aneurysm 21, the effect of restricting the blood flow flowing into the cerebral aneurysm 21 becomes insufficient. The bioabsorption rate of the stent 20 for a flow diverter is preferably 12 months or more and 36 months or less. That is, this is for leaving the stent 20 for a flow diverter in the parent vessel 22 where the aneurysm 21 exists during the period from when the stent 20 for a flow diverter is placed in the parent vessel 22 until the cerebral aneurysm 21 is completely occluded. In this embodiment as well, the same effects as those in Embodiment 1 can be obtained. (Embodiment 3) FIG. 6 is a diagram showing a stent for coil embolization according to one aspect of the present invention. This stent 30 for coil embolization is a stent for a cerebral aneurysm and is composed of a cylindrical braided body braided with 16 wires. The stent 30 for coil embolization can have the same configuration except that the number of wires braided is less than that of the stent 20 for a flow diverter shown in FIG. 4. Note that the stent 10 for a cerebral aneurysm shown in FIG. 1 can be used for both the stent for a flow diverter and the stent for coil embolization. FIG. 7 is a diagram schematically showing a state where the stent 30 for coil embolization shown in FIG. 6 is 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 root of the leg to the inside of the skull, and through this, the stent 30 for coil embolization is inserted into the blood vessel 32 so as to firmly cover the front and back of the entrance of the cerebral aneurysm 31 from a thin treatment catheter, and is deployed 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 treatment catheter through the catheter, and several coils are added until almost no blood flow enters the cerebral aneurysm 31. After that, the catheter is removed. Note that as the coil 33 used here, a wire having the same bioabsorbability as the wires of the stent 30 for coil embolization is preferably used. While inserting the coil embolization stent 30 into the parent 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, the internal thrombosis is gradually promoted, the neck portion of the cerebral aneurysm 31 is covered with the stent neointima, and after one to several months, the cerebral aneurysm 31 is completely occluded. Moreover, the coil embolization stent 30 and the coil 33 itself are gradually decomposed over one to several months and finally disappear, leaving no foreign substances. However, when a wire 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. 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 holes / mm 2 or more (preferably 0.4 holes / 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 holes / mm 2 even if the coil embolization stent 30 is deployed so as to straddle the cerebral aneurysm 31 as shown in Fig. 7, the coil 33 cannot be stably placed in the cerebral aneurysm 31, and the effect of suppressing the inflowing blood flow becomes insufficient. The bioabsorption rate of the coil embolization stent 30 is preferably one month or more and three months or less. That is, it is for the purpose of leaving the coil embolization stent 30 in the vessel 32 during the period from when the coil 33 is placed in the cerebral aneurysm 31 while the coil embolization stent 30 is placed in the parent vessel 32 where the cerebral aneurysm 31 exists until the cerebral aneurysm 31 is completely occluded. In this embodiment, the same effects as those of Embodiment 1 can be obtained. The magnesium alloy applied to the wire used in Embodiments 1 to 3 may be any of the following alloys [1] to

[48] . [1] The magnesium alloy contains a atomic % of Zn, b atomic % of Y, and the balance consists of Mg and inevitable impurities, and a and b satisfy the following (Formula 11) to (Formula 13) or (Formula 14) to (Formula 16), and it is preferably composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacking 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 contains a atomic % of Zn, b atomic % of Y, and the balance consists of Mg and inevitable impurities, and a and b satisfy the following (Formula 11’), (Formula 12), and (Formula 13), and it is preferably composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacking 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 further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and c preferably satisfies the following (Formula 17) and (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm (mischmetal), and Gd, and c preferably satisfies the following (Formula 19) and (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, and c preferably satisfies the following (Formula 20) and (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, and c preferably satisfies the following (Formula 22) and (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, and c and d preferably satisfy the following (Formula 14) to (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, and c and d preferably satisfy the following (Formula 16) and (Formula 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 further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Tb, Sm, and Nd, and a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, Mm, and Gd, and c and d preferably satisfy the following (Formula 18) to (Formula 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 according to 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 a total amount of more than 0 atomic % and 2.5 atomic % or less.

[11] The magnesium alloy contains a atomic % of Zn and a total of b atomic % of at least one element selected from the group consisting of Dy, Ho, and Er, and the balance consists of Mg and inevitable impurities, where a and b satisfy the following (Equation 21) to (Equation 23) or (Equation 24) to (Equation 26), and it is preferably composed of an alloy having a crystal structure having an α-Mg phase or a long-period stacking structure phase. (Equation 21) 0.1 ≦ a ≦ 5.0 (Equation 22) 0.1 ≦ b ≦ 5.0 (Equation 23) 0.5a - 0.5 ≦ b (Equation 24) 0.1 ≦ a ≦ 3.0 (Equation 25) 0.1 ≦ b ≦ 5.0 (Equation 26) 2a - 3 ≦ b

[12] The magnesium alloy contains a atomic % of Zn and a total of b atomic % of at least one element selected from the group consisting of Dy, Ho, and Er, and the balance consists of Mg and inevitable impurities, where a and b satisfy the following (Equation 21’), (Equation 22’), and (Equation 23) or (Equation 24’), (Equation 25’), and (Equation 26), and it is preferably composed of an alloy having a crystal structure having an α-Mg phase or a long-period stacking structure phase. (Equation 21’) 0.2 ≦ a ≦ 5.0 (Equation 22’) 0.2 ≦ b ≦ 5.0 (Equation 23) 0.5a - 0.5 ≦ b (Equation 24’) 0.2 ≦ a ≦ 3.0 (Equation 25’) 0.2 ≦ b ≦ 5.0 (Equation 26) 2a - 3 ≦ b

[13] The magnesium alloy according to

[11] or

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

[14] The magnesium alloy described in the above

[11] or

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

[15] The magnesium alloy described in the above

[11] or

[12] further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Sm, and Nd, and a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, and c and d preferably satisfy the following (Formula 31) to (Formula 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 the above

[11] to

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

[17] The magnesium alloy described in any one of the above

[11] to

[16] further contains more than 0 atomic % and 2.5 atomic % or less in total of 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.

[18] At least a part of the long-period stacked structure phase of the magnesium alloy described in any one of the above

[11] to

[17] is preferably curved or bent.

[19] The magnesium alloy contains a atomic % of Zn, a total of b atomic % of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, and the balance consists of Mg and inevitable impurities, where a and b satisfy the following (Equation 41) to (Equation 43) or (Equation 44) to (Equation 46), and it may be composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase. (Equation 41) 0.1 ≦ a ≦ 5.0 (Equation 42) 0.25 ≦ b ≦ 5.0 (Equation 43) 0.5a - 0.5 ≦ b (Equation 44) 0.1 ≦ a ≦ 3.0 (Equation 45) 0.25 ≦ b ≦ 5.0 (Equation 46) 2a - 3 ≦ b

[20] The magnesium alloy contains a atomic % of Zn, a total of b atomic % of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, and the balance consists of Mg and inevitable impurities, where a and b satisfy the following (Equation 41’), (Equation 42’), and (Equation 43) or (Equation 44’), (Equation 45’), and (Equation 46), and it may be composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase. (Equation 41’) 0.2 ≦ a ≦ 5.0 (Equation 42’) 0.5 ≦ b ≦ 5.0 (Equation 43) 0.5a - 0.5 ≦ b (Equation 44’) 0.2 ≦ a ≦ 3.0 (Equation 45’) 0.5 ≦ b ≦ 5.0 (Equation 46) 2a - 3 ≦ b

[21] The magnesium alloy described in the above

[19] or

[20] further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Sm, and Nd, and c preferably satisfies the following (Equation 47) and (Equation 48). (Equation 47) 0 ≦ c ≦ 3.0 (Equation 48) 0.25(0.5) ≦ b + c ≦ 6.0

[22] The magnesium alloy described in the above

[19] or

[20] further contains a total of c atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, and c preferably satisfies the following (Equation 49) and (Equation 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 further contains a total of c atomic % of at least one element selected from the group consisting of Yb, Sm, and Nd, and a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Eu, and Mm, and c and d may satisfy the following (Formula 51) to (Formula 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 more than 0 atomic % and 1.5 atomic % or less in total of at least one element selected from the group consisting of Dy, Ho, and Er.

[25] The magnesium alloy described in any one of

[19] to

[23] above may further contain more than 0 atomic % and 1.0 atomic % or less of Y.

[26] The magnesium alloy described in any one of

[19] to

[25] above may further contain less than 3 atomic % 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 more than 0 atomic % and 2.5 atomic % or less in total of 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.

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

[19] to

[27] above may be curved or bent.

[29] The magnesium alloy contains a total of a atomic % of at least one metal among Cu, Ni, and Co, and a total of b atomic % of at least one element selected from the group consisting of Y, Dy, Er, Ho, Gd, Tb, and Tm, with the balance being composed of Mg and inevitable impurities, where a and b satisfy the following (Equation 61) to (Equation 63), and is characterized by being composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase. (Equation 61) 0.2 ≤ a ≤ 10 (Equation 62) 0.2 ≤ b ≤ 10 (Equation 63) 2 / 3a - 2 / 3 < b

[30] The magnesium alloy described in the above

[29] may further contain c atomic % of Zn, and a and c preferably satisfy the following (Equation 64). (Equation 64) 0.2 < a + c ≤ 15

[31] In the above

[30] , a and c preferably further satisfy the following (Equation 65). (Equation 65) c / a ≤ 1 / 2

[32] The magnesium alloy described in any one of the above

[29] to

[31] may further contain a total of d atomic % of at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Yb, and Lu, and b and d preferably satisfy the following (Equation 66). (Equation 66) 0.2 < b + d ≤ 15

[33] In the above

[32] , b and d preferably further satisfy the following (Equation 67). (Equation 67) d / b ≤ 1 / 2

[34] The magnesium alloy described in any one of the above

[29] to

[33] may further contain a total of e atomic % 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, and e preferably satisfies the following (Equation 68). (Equation 68) 0 < e ≤ 2.5

[35] In the above

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

[36] The magnesium alloy contains a atomic % of Zn, a total of b atomic % of at least one element selected from Y, Dy, Ho, and Er, a total of c atomic % of at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Gd, Tb, and Yb, and the balance consists of Mg and inevitable impurities, where a, b, and c satisfy the following (Equation 71) to (Equation 74), and it is preferably made of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase. (Equation 71) 0.2 ≤ a ≤ 5.0 (Equation 72) 0.2 ≤ b ≤ 5.0 (Equation 73) 2a - 3 ≤ b (Equation 74) 0.05b ≤ c < 0.75b

[37] The magnesium alloy described in

[36] above preferably further contains d atomic % of Al and satisfies the following (Equation 75). (Equation 75) 0.05b ≤ d < 0.75b

[38] The magnesium alloy described in

[36] or

[37] above preferably contains a total of b atomic % of at least two elements selected from the group consisting of Y, Dy, Ho, and Er.

[39] The magnesium alloy contains a atomic % of Zn, a total of b atomic % of at least one element selected from Gd and Tb, a total of c atomic % of at least one element selected from the group consisting of Al, Y, La, Ce, Pr, Nd, Sm, Dy, Ho, Er, Tm, and Yb, and the balance consists of Mg and inevitable impurities, where a, b, and c satisfy the following (Equation 81) to (Equation 84), and it is preferably made of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase. (Equation 81) 0.2 ≤ a ≤ 5.0 (Equation 82) 0.2 ≤ b ≤ 5.0 (Equation 83) 2a - 3 ≤ b (Equation 84) 0.05b ≤ c < 0.75b

[40] The magnesium alloy contains a atomic % of Al and b atomic % of Gd, and the balance consists of Mg and inevitable impurities, where a and b satisfy the following (Equation 91) and (Equation 92), and it is preferably made of an alloy having a crystal structure with an α-Mg phase or a long-period stacking structure phase or a phase containing a close-packed atomic plane area defect. (Formula 91) 0.01 ≤ a ≤ 2.0 (Formula 92) 0.2 ≤ b ≤ 5.0 In the present specification, the close-packed atomic plane layer defect means a layer in which zinc and rare earth elements, which are solute atoms, are concentrated in two consecutive atomic layers along the close-packed atomic plane in the stacking direction (solute atom-concentrated two-atomic layer), and the case where the solute atom-concentrated two-atomic layer does not have periodicity in the stacking direction over a long distance.

[41] The magnesium alloy contains a atomic % of Zn, a total of b atomic % of at least one element selected from the group consisting of Y, Dy, Ho, Er, Gd, Tb, and Tm, c atomic % of Al, and the balance consists of Mg and unavoidable impurities. a, b, and c satisfy the following (Formula 101) to (Formula 104), and it is preferably an alloy having a crystal structure including an α-Mg phase or a long-period stacking structure phase or a phase containing a close-packed atomic plane layer defect. (Formula 101) 0.2 ≤ a ≤ 5.0 (Formula 102) 0.2 ≤ b ≤ 5.0 (Formula 103) 2a - 3 ≤ b (Formula 104) 0.05b ≤ c < 0.75b

[42] The magnesium alloy described in the above

[41] further contains a total of d atomic % 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, and d preferably satisfies the following (Formula 105). (Formula 105) 0 ≤ d ≤ b / 2

[43] The magnesium alloy preferably consists of any one of the following chemical components (A) to (G). (A) By mass, Al: 0.1 to 12.0%, Mn: 0.1 to 1.0%, and the balance consists of Mg and impurities (B) By mass, Al: 0.1 to 12.0%, Mn: 0.1 to 1.0%, further containing one or more elements selected from Zn: 0.5 to 2.0% and Si: 0.3 to 2.0%, and the balance consists of Mg and impurities (C) By mass, Zn: 1.0 to 10.0%, Zr: 0.4 to 2.0%, and the balance consists of Mg and impurities (D) By mass, containing Zn: 1.0 - 10.0%, Zr: 0.4 - 2.0%, Mn: 0.5 - 2.0%, with the balance being Mg and impurities (E) By mass, containing Zn: 1.0 - 10.0%, rare earth element: 1.0 - 3.0%, with the balance being Mg and impurities (F) By mass, containing Zr: 0.4 - 2.0%, rare earth element: 1.0 - 3.0%, with the balance being Mg and impurities (G) By mass, containing Zn: 1.0 - 10.0%, Mn: 0.1 - 1.0, Cu: 0.5 - 2.0%, with the balance being Mg and impurities

[44] The magnesium alloy contains a atomic % of Zn and b atomic % of Y, where a and b satisfy the following (Equation 11) - (Equation 13) or (Equation 14) - (Equation 16), and is preferably composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacked structure phase. (Equation 11) 0.25 ≤ a < 5.0 (Equation 12) 0.5 < b < 5.0 (Equation 13) 2 / 3a - 5 / 6 ≤ b (Equation 14) 0.25 ≤ a ≤ 5.0 (Equation 15) 0.5 ≤ b ≤ 5.0 (Equation 16) 0.5a ≤ b

[45] The magnesium alloy contains a atomic % of Zn and a total of b atomic % of at least one element selected from the group consisting of Dy, Ho, and Er, where a and b satisfy the following (Equation 21) - (Equation 23) or (Equation 24) - (Equation 26), and is preferably composed of an alloy having a crystal structure with an α-Mg phase or a long-period stacked structure phase. (Equation 21) 0.1 ≤ a ≤ 5.0 (Equation 22) 0.1 ≤ b ≤ 5.0 (Equation 23) 0.5a - 0.5 ≤ b (Equation 24) 0.1 ≤ a ≤ 3.0 (Equation 25) 0.1 ≤ b ≤ 5.0 (Equation 26) 2a - 3 ≤ b

[46] The magnesium alloy contains a atomic % of Zn and a total of b atomic % of at least one element selected from the group consisting of Gd, Tb, Tm, and Lu, and a and b satisfy the following (Formula 41) to (Formula 43) or (Formula 44) to (Formula 46), and it is preferably made of an alloy having a crystal structure having an α-Mg phase or a long-period stacking 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 contains a atomic % of at least one metal selected from Cu, Ni, and Co in total, and a total of b atomic % of at least one element selected from the group consisting of Y, Dy, Er, Ho, Gd, Tb, and Tm, and a and b satisfy the following (Formula 61) to (Formula 63), and it is preferably made of an alloy having a crystal structure having an α-Mg phase or a long-period stacking structure phase. (Formula 61) 0.2 ≦ a ≦ 10 (Formula 62) 0.2 ≦ b ≦ 10 (Formula 63) 2 / 3a - 2 / 3 < b

[48] The magnesium alloy contains a atomic % of Al and b atomic % of Gd, and a and b satisfy the following (Formula 91) and (Formula 92), and it is preferably made of an alloy having a crystal structure having an α-Mg phase or a long-period stacking structure phase. (Formula 91) 0.01 ≦ a ≦ 2.0 (Formula 92) 0.2 ≦ b ≦ 5.0 (Embodiment 4) A method for manufacturing a stent according to an aspect of the present invention will be described. This stent is a stent for cerebral aneurysm shown in FIG. 1. <Method for manufacturing a wire> First, a magnesium alloy base material wire having a small average crystal grain size of the α-Mg phase is produced. Specifically, a molten magnesium alloy containing 90 atomic % or more of Mg is rapidly solidified to produce a plurality of rapidly solidified products. The cooling rate at this time is preferably faster than 1000 K / second (preferably 10000 K / second). The plurality of rapidly solidified products are, for example, powders produced by the RS-P / M method (or thin flakes, ribbons or wires produced by the RS-P / M method, wires produced by the melt extraction method). Next, a solidified molded product is produced by hot extruding the plurality of rapidly solidified products. Specifically, a billet can be produced by filling a powder (or thin flake, ribbon or wire) into a copper can and vacuum-sealing it, and a solidified molded product can be produced by extruding it. As another method of solidification molding, there is a method of rolling the powder with grooved rolls. Note that it is preferable that the inner surface of the above-mentioned copper can is subjected to a chromium coating treatment (for example, Cr plating). Thereby, the diffusion of copper into the magnesium alloy can be suppressed, and as a result, the corrosion resistance of the produced wire can be improved. In other words, when the magnesium alloy contains about 100 ppm of copper, the corrosion resistance deteriorates. However, by subjecting the inner surface of the copper can to a chromium coating treatment, the diffusion of copper into the magnesium alloy can be suppressed, and as a result, the original corrosion resistance of the magnesium alloy can be obtained. Next, by extruding the solidified molded product, a magnesium alloy base wire having a small average crystal grain size of the α-Mg phase is produced. In this embodiment, a magnesium alloy base wire having a small average crystal grain size of the α-Mg phase is produced by the rapid solidification powder metallurgy (RS-P / M) method. However, from a magnesium alloy billet produced by a casting method, a magnesium alloy base wire having a small average crystal grain size of the α-Mg phase may be produced by a method in which a large strain is applied to the material, such as the equal-channel-angular-extrusion (ECAE) processing method. The equal-channel angular extrusion (ECAE) process is a method of rotating the sample by 90° in the longitudinal direction of the sample for each pass in order to introduce uniform strain into the sample. Specifically, a magnesium alloy casting, which is a forming material, is forced into the forming hole of a forming die having a forming hole with an L-shaped cross-section, and stress is applied to the magnesium alloy casting particularly at the portion bent at 90° of the L-shaped forming hole to obtain a formed body. The number of ECAE passes is preferably plural. The temperature during ECAE processing is preferably, for example, 250°C or higher and 500°C or lower. After producing the above-described magnesium alloy base wire, a wire of a magnesium alloy having an 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 means a wire after multiple drawing processes have been completed. A magnesium alloy base wire means a wire before multiple drawing processes and a wire during multiple drawing processes. That is, a magnesium alloy base wire means all wires before multiple drawing processes are completed. For example, in the case where the processing step shown in FIG. 8 is the last drawing process in which multiple drawing processes are completed, the wire before this last drawing process is the magnesium alloy base wire 41, and the wire after the drawing process is the magnesium alloy wire 42. Further, in the case where the processing step shown in FIG. 8 is a drawing process during multiple drawing processes, the wire before this intermediate drawing process is the magnesium alloy base wire 41, and the wire after the drawing process is also the magnesium alloy base wire 42. The above-described magnesium alloy base wire is preferably formed of a magnesium alloy in which grain growth does not occur (or hardly occurs) during heat treatment at a temperature of 300°C, and may be a general-purpose magnesium alloy, an LPSO (Long-Period Stacking Ordered) type alloy, pure magnesium, etc., and may be formed of any of the above alloys [1] to

[48] , for example. As shown in Fig. 8, a magnesium alloy base material wire 41 with a wire diameter of more than 1 mm and 3 mm or less, for example, is drawn at a drawing speed of 0.1 m / min or more and 1000 m / min or less (preferably 0.1 m / min or more and 100 m / min or less, more preferably 0.5 m / min or more and 100 m / min or less) in the direction of the arrow using a die 43 to form a magnesium alloy wire (or a magnesium alloy base material wire in the case of during multiple drawing processes) 42. The temperature of the magnesium alloy base material wire 41 during the drawing process (i.e., the temperature of the magnesium alloy base material 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 or higher and 350°C or lower, or higher than 200°C and 300°C or lower. The reason for such a temperature range is that the magnesium alloy base material wire is less likely to break during the drawing process, and also to reduce the temperature or time of the heat treatment for removing strain after the drawing process. The reason for reducing the temperature or time of the heat treatment is that it can suppress the grain growth of the α-Mg phase when it is small. In this specification, the wire diameter of the magnesium alloy base material wire means, for example, the wire diameter d3 of the magnesium alloy base material wire 41 shown in Fig. 8. When the cross-sectional shape of the magnesium alloy base material wire is not circular, it means the maximum outer diameter of the cross-section of the magnesium alloy base material wire. When the first drawing process is performed on the magnesium alloy base material wire 41 at room temperature, considering that heat due to friction between the die 43 and the magnesium alloy base material wire 41 is applied to the magnesium alloy base material wire 42 after drawing when passing through the die 43, the temperature of the die 43 is controlled. For example, the temperature of the die 43 is controlled to be 200°C or higher and 300°C or lower. Thereby, the temperature of the magnesium alloy base material wire 41 during the drawing process can be made within the above range. When performing the second drawing process, the temperature of the magnesium alloy base material wire 41 is returned to room temperature, and the magnesium alloy base material wire 41 at room temperature is passed through a die 43 with controlled temperature for drawing. Such drawing 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. When the average crystal grain size of the α-Mg phase observed in the cross-section cut in the longitudinal direction of the magnesium alloy wire 42 is L (not shown), and the average crystal grain size of the α-Mg phase observed in the cross-section cut in the direction perpendicular to the longitudinal direction is d (not shown), it is preferably to satisfy the following (Equation 42) and (Equation 43). (Equation 41) 5μm ≦ D ≦ 50μm (Equation 42) d ≦ 1μm (preferably, d ≦ 0.5μm, more preferably, d ≦ 0.3μm, still more preferably d ≦ 0.19μm, even more preferably d ≦ 0.12μm, and even more preferably d ≦ 0.1μm) (Equation 43) 10 ≦ L / d (preferably 43 ≦ L / d, more preferably 54 ≦ L / d, still more preferably 70 ≦ L / d, even more preferably 90 ≦ L / d) When performing each of the above multiple drawing processes, it is preferable to supply a non-silicon-based oil as a lubricating oil to the die 43, for example, edible oil. Thereby, the frictional heat between the die 43 and the magnesium alloy base material wire 41 can be reduced, and the breakage of the wire during the drawing process can be suppressed. The cross-sectional reduction rate RA when performing each of the above multiple drawing processes preferably satisfies the following (Equation 45), more preferably satisfies the following (Equation 45'), and still more preferably satisfies the following (Equation 45''). (Equation 45) 1% ≦ RA ≦ 30% (Equation 45') 3% ≦ RA ≦ 15% (Equation 45'') 5% ≦ RA ≦ 12% Note that the cross-sectional reduction rate means a value of (1 - (D / d3)) × 100, where d3 is the wire diameter before the drawing process and D is the wire diameter after the drawing process. 2 ) × 100. Also, as the magnesium alloy base material wire 41 is subjected to multiple drawing processes, the wire diameter of the magnesium alloy base material wire 41 gradually decreases. Heat treatment is performed on the magnesium alloy base material wire 42 after at least one of the multiple drawing processes. The temperature of this heat treatment is preferably 50°C or more and 450°C or less, or 50 degrees or more and 400°C or less higher than the temperature of the magnesium alloy base material wire 42 immediately after the drawing process immediately before the heat treatment, and the heat treatment time is preferably 10 seconds or more and 12 hours or less. As the timing for performing the heat treatment, it is when the average crystal grain size of the α-Mg phase of the magnesium alloy base material wire 42 after multiple drawing processes becomes significantly smaller than the average crystal grain size of the α-Mg phase of the magnesium alloy base material wire 41 before multiple drawing processes. Also, the number of times of performing the heat treatment may be multiple times and may be adjusted as appropriate. For example, heat treatment may be performed after each drawing process, or not after each drawing process, and there may be times when heat treatment is performed and times when it is not performed after the drawing process. Also, for example, if the heat treatment temperature is 350°C and the heat treatment time is 30 minutes, even when the heat treatment is performed in an air atmosphere, the formation of an oxide film on the surface of the magnesium alloy wire 42 can be reduced. That is, even when heat treatment is performed, the formation of the oxide film is reduced. In this way, a magnesium alloy wire 42 with a wire diameter D of 5 μm or more and 100 μm or less 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) can be manufactured. In this case, the wire diameter D and the average crystal grain size d preferably satisfy the following (Equation 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, and more preferably d / D ≦ 1 / 500) The above-mentioned magnesium alloy wire 42 corresponds to the wire materials of Embodiments 1 to 3, and the Young's modulus (longitudinal elastic modulus) of this wire material is preferably 50 GPa or less. In addition, the wire diameter of the wire for manufacturing the flow diverter stent is preferably 50 μm or less, more preferably 30 μm or less. Further, the wire diameter of the wire for manufacturing the coil plug stent is preferably 100 μm or less, more preferably 80 μm or less. Also, the yield stress (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, still more preferably 600 MPa or more, and even more preferably 700 MPa or more. According to the above embodiment, a magnesium alloy base wire 41 having a small crystal grain size is produced by the rapid solidification powder metallurgy method, and then the drawing process and heat treatment process of the magnesium alloy base wire 41 that suppress recrystallization and grain growth as much as possible are repeated, so that the average crystal grain size of the α-Mg phase can be made 1 μm or less at a predetermined wire diameter. Thereby, a wire 42 of a magnesium alloy having high strength or high corrosion resistance can be realized. Moreover, even if 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 not easily broken can be realized. Next, it is preferable to perform surface treatment or coating on the wire manufactured by the above method. This is for adjusting the period until the stent is decomposed or the bioabsorption rate after the stent is placed in the blood vessel. As described above, the required bioabsorption rates are different for the flow diverter stent and the coil plug stent, and it is considered that the required bioabsorption rates also differ depending on the size and condition of the cerebral aneurysm. Specific examples of the surface treatment of the wire include performing hydrofluoric acid treatment or anodic oxidation treatment on the surface of the wire. Oxides, fluorides, etc. are formed on the surface of the wire by the surface treatment. Specific examples of the coating of the wire include performing a polymer bond or a polymer coating on the surface of the wire, or performing DLC film formation treatment. <Wire weaving process> Next, using the above-described wire, the wire is woven with 8 or more stitches (preferably 16 or more stitches) by a braider (braiding machine) to produce a stent 10 composed of the tubular braided body shown in FIG. 1. The braided body is formed by alternately crossing wires and braiding them into a tubular shape. When weaving, it is preferable that the twist of the wire is 1 rotation or less per 10 cm of the wire length. To reduce the twist, it is advisable to increase the diameter of the bobbin of the braider or to use a vertical bobbin. Here, when manufacturing the stent 30 for a coil plug, it is preferable that the wire is woven with 8 or more wires, and more preferably, the wire is woven with 16 or more wires. Also, when manufacturing the stent 20 for a flow diverter, it is preferable that the wire is woven with 24 or more wires, and more preferably, the wire is woven with 48 or more wires. Further, it is preferable that the stent composed of the above-described braided body has a constant outer diameter over its entire length. Also, it is preferable that the density of the braided body is uniform throughout. Next, the stent woven by the above method may be subjected to surface treatment or coating. In this case, it is better not to perform surface treatment or coating in the state of the wire. By performing such surface treatment or coating, it is possible to adjust the period until the stent is decomposed after being placed in the blood vessel or the bioabsorption rate. Specific examples of the surface treatment of the stent are to perform hydrofluoric acid treatment or anodic oxidation treatment on the surface of the stent. Oxides, fluorides, etc. are formed on the surface of the stent by the surface treatment. Also, specific examples of the coating of the stent are to perform a polymer bond or a polymer coating on the surface of the stent, or to perform DLC film formation treatment. Next, in order to fix the shape of the stent, the stent may be heat-treated. The heat treatment conditions at this time are preferably in the range where the temperature is higher than room temperature and 400 ° C or lower, and the treatment time is 1 second or more and 12 hours or less. Also, the shape of the stent during heat treatment is preferably in a state with a larger diameter than when placed in the blood vessel. This larger diameter is equal to the outer shape after expansion, and it is used by stretching it in the length direction during insertion. Note that the heat treatment and the surface treatment or coating of the stent may be performed in a swapped order. Note that the above-described Embodiments 1 to 4 can be implemented in appropriate combination with each other.

Example

[0008] FIG. 9 is an external appearance photograph (SEM photograph) of the wire materials (wires) of Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5 according to Example 1. Sample 1 is a wire (wire material) of a magnesium alloy with a wire diameter of 95.5 μm obtained by solidifying and molding a powder, a thin sheet, a thin strip, or a thin wire produced by the RS-P / M method, subjecting the solidified molded product to extrusion processing, and then performing multiple drawing processes and heat treatments. The alloy composition thereof is Mg 97.94 -Zn 0.56 -Y 1.5 Sample 2 is a wire material with a wire diameter of 73 μm obtained by further performing multiple drawing processes and heat treatments on Sample 1. Sample 3 is a wire material with a wire diameter of 49.2 μm obtained by further performing multiple drawing processes and heat treatments on Sample 2. Sample 4 is a wire material with a wire diameter of 32 μm obtained by further performing multiple drawing processes and heat treatments on Sample 3. Sample 5 is a wire material with a wire diameter of 29.7 μm obtained by further performing drawing processes and heat treatments on Sample 4. Note that the wire diameter of the wire material was measured using a high-precision digital micrometer (MDH-25MB manufactured by Mitutoyo Corporation). The method for producing 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 in an argon gas atmosphere and cooled at a cooling rate of about 2×10 5 K / sec to produce alloy powder. Next, the alloy powder is preformed at a pressure of 60 to 170 MPa and vacuum degassed at a temperature of 250° C. for 2 hours to produce a billet. Next, the die and the container are fixed, and the billet is pressed against the die to perform extrusion processing. At this time, the extrusion processing conditions are as follows. Extrusion speed: 2.5 mm / min Temperatures of the container, die, and billet: 350 °C Extrusion ratio: 15 In this example, a cooling rate of about 2×10 5 K / sec is used, but a cooling rate in the range of 1×10 5 K / sec or more and 2×10 5 K / sec or less can also be used. The method for producing Sample 1 is as follows. Temperature during the drawing process of the magnesium alloy base material wire 41: 300 °C until the wire diameter of the magnesium alloy base material wire 41 reaches 1.08 mm, and 225 °C for wire diameters less than that Drawing speed: 0.1 - 1.0 m / min Heat treatment temperature: 350 °C Heat treatment time: 10 minutes Frequency of heat treatment: For wire diameters of the magnesium alloy base material wire 41 up to 1.65 mm, it is carried out for each drawing process; for wire diameters less than that, it is carried out once for every two drawing processes Material of the die: Cemented carbide die until the wire diameter of the magnesium alloy base material wire 41 reaches 2.13 mm, and diamond die for wire diameters less than that Die temperature: 300 °C until the wire diameter of the magnesium alloy base material wire 41 reaches 1.08 mm, and 225 °C for wire diameters less than that Lubricant for the die: Edible oil Drawing direction: Two directions Wire diameter of the wire of Sample 1: 95.5 μm Note that the drawing direction means the direction of the arrow shown in Fig. 8. Having two drawing directions means that when one direction is the direction of the arrow shown in Fig. 8, the other direction means the drawing direction in which the direction of the magnesium alloy base material wire 41 is rotated 180° and arranged in the opposite direction. The method for producing Sample 2 is as follows. Temperature during the drawing process of the magnesium alloy base material wire 41: 225 °C Drawing speed: 1.0 m / min Heat treatment temperature: 350 °C Heat treatment time: 10 minutes Frequency of heat treatment: Performed once in 2 - 4 processing steps Material of the die: Diamond die Temperature of the die: 225°C Lubricant for the die: Edible oil Drawing direction: Two directions Wire diameter of the wire for Sample 2: 73μm The manufacturing method of Sample 3 is as follows. Temperature during the drawing process of the magnesium alloy base wire 41: 225°C Drawing speed: 1.0 - 5.0 m / min Temperature of heat treatment: 350°C Heat treatment time: 10 minutes Frequency of heat treatment: Performed once in 3 - 10 processing steps Material of the die: Use diamond die Temperature of the die: 225°C Lubricant for the die: Edible oil Drawing direction: Two directions Wire diameter of the wire for Sample 3: 49.2μm The manufacturing method of Sample 4 is as follows. Temperature during the drawing process of the magnesium alloy base wire 41: 225°C Drawing speed: 1.0 - 5.0 m / min Temperature of heat treatment: 350°C Heat treatment time: 10 minutes Frequency of heat treatment: Performed once in 12 or more processing steps Material of the die: Use diamond die Temperature of the die: 225°C Lubricant for the die: Edible oil Drawing direction: Two directions Wire diameter of the wire for Sample 4: 32μm The manufacturing method of Sample 5 is as follows. Temperature during the drawing process of the magnesium alloy base wire 41: 225°C Drawing speed: 1.0 - 5.0 m / min Heat treatment temperature: 350 °C Heat treatment time: 10 minutes Frequency of heat treatment: Performed once in 12 or more processing steps Die material: Use diamond die Die temperature: 225 °C Die lubricant: Edible oil Drawing direction: Two directions Wire diameter of the wire for Sample 5: 29.7 μm Figure 10 is a diagram showing the results of measuring the yield stress (0.2% proof stress) of the wires of 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. Figure 11 is a diagram showing the results of measuring the Young's modulus (longitudinal elastic modulus) of the wires of 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.

Example

[0009] Figure 12 is an external photograph showing a stent for cerebral aneurysm according to Example 2. Using the wire (wire diameter: about 50 μm) of Sample 3 of Example 1 with a braider (braiding machine) for round cords (even number of braiding strands), a stent composed of the tubular braided body shown in Figure 12 was produced by braiding 16 strands. According to Example 2, the outer diameter of the stent could be made constant over the entire length, and the braiding density could also be made uniform overall.

Example

[0010] The sample of Example 3 was prepared as follows. Powders, flakes, ribbons or wires produced by rapid solidification powder metallurgy are filled into a copper can, which is then vacuum-sealed to produce a billet, and the billet is extruded. Thereafter, the extruded product was heat-treated at a temperature of 738 K for 24 hours. The composition of the obtained magnesium alloy is Mg 97.25 -Zn 0.75 -Y2. Note that the inner surface of the copper can used here is chromium-plated. The sample 1 of the comparative example was prepared in the same manner as the sample of Example 3 above, except that the inner surface of the copper can was not chromium-plated. Also, the sample 2 of the comparative example was obtained by casting an alloy of ASTM (USA) WE43 (a magnesium alloy containing 4 mass% Y and 3 mass% rare earth elements) and extruding the as-cast material without putting it into a copper can. Therefore, no copper has diffused into the sample 2 of the comparative example. Figure 13(A) is a diagram showing the immersion time dependence of the corrosion rate of each of the samples 1 and 2 of the comparative example in a simulated body fluid, and Figure 13(B) is a diagram showing the immersion time dependence of the corrosion rate of each of the sample of Example 3 and the sample 1 of the comparative example in a simulated body fluid. The method for measuring the corrosion rate was to immerse each of the sample of Example 3 and the samples 1 and 2 of the comparative example in a simulated body fluid (HBSS: physiological balanced salt solution) adjusted to pH 7.4, and measure the relationship between the immersion time and the corrosion rate. The simulated body fluid at the time of this measurement was in a state where the temperature was 310 K and it was open to the atmosphere. When magnesium contains about 100 ppm of Cu, its corrosion resistance deteriorates. In the case of sample 1 of the comparative example prepared using a copper can whose inner surface is not chromium-plated, Cu diffuses into the billet material during extrusion, so the corrosion resistance deteriorates. On the other hand, in the case of the sample of Example 3 prepared using a copper can whose inner surface is chromium-plated, it prevents Cu from diffusing into the billet material during extrusion, so the original corrosion resistance can be obtained. Therefore, the sample of Example 3 has better corrosion resistance than the sample 1 of the comparative example. In addition, although Cu has not diffused in Sample 2 of the comparative example, the sample of Example 3 has better corrosion resistance than Sample 2 of the comparative example.

Example

[0011] FIG. 15 is an external photograph showing a stent for cerebral aneurysm according to Example 4. Using a braider (braiding machine) for round cords (even number of braided strands), the wire (wire diameter: about 50 μm) of Sample 3 of Example 1 was braided 48 times to produce a stent composed of the tubular braided body shown in FIG. 15. According to Example 4, the outer diameter of the stent could be made constant over the entire length, and the braiding density could also be made uniform overall.

Explanation of Signs

[0012] 10… Stent for cerebral aneurysm 11a, 11b, 13, 15, 16, 17a, 17b… Wires 12, 14, 19… Stents for cerebral aneurysm 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 material wire 42… Magnesium alloy wire 43… Die d3… Wire diameter of magnesium alloy base material wire D… Wire diameter of magnesium alloy wire

Claims

1. A stent that has self-expanding properties and is placed so as to be crimped to the blood vessel wall and straddle a cerebral aneurysm, has bioabsorbability, is made of a magnesium alloy containing 90 atomic % or more of Mg or pure magnesium, The stent is composed of a tubular braided body woven from two or more types of wire materials, including a wire material made of a magnesium alloy containing 90 atomic % or more of Mg or pure magnesium and a wire material made of a magnesium alloy having a composition different from that of the magnesium alloy or the pure magnesium and containing 90 atomic % or more of Mg, or is composed of the two or more types of wire materials cross-coiled, parallel-coiled or coiled. A stent characterized by this.

2. In Claim 1, The stent is composed of a tubular braided body woven from a wire material made of the magnesium alloy or the pure magnesium, or is composed of the wire material cross-coiled, parallel-coiled or coiled. A stent characterized by this.

3. In Claim 1, The stent is composed of a tubular braided body woven from two or more types of wire materials, including a wire material made of a magnesium alloy containing 90 atomic % or more of Mg or pure magnesium and a wire material made of a material different from the magnesium alloy or the pure magnesium, or is composed of the two or more types of wire materials cross-coiled, parallel-coiled or coiled. A stent characterized by this.

4. In Claim 3, The material is one material selected from the group of bioabsorbable polymers, W, Ta, Pt and Au. A stent characterized by this.

5. In any one of Claims 1 to 4, The cross-sectional shape of the wire is circular, elliptical or square, and the aspect ratio of the elliptical or square wire is 1 or more and 5 or less. A stent characterized by this.

6. In any one of Claims 1 to 5, The stent is a stent for a coil plug. A stent characterized by this.

7. In any one of Claims 1 to 5, The stent is a stent for a flow diverter. A stent characterized by this.

8. In Claim 6, The stent for a coil plug has a surface coverage rate of 5% or more, a number density of holes of 0.2 pieces / mm ２ or more, The bioabsorption rate of the stent for a coil plug is 1 month or more and 3 months or less, The angle formed by the wires in the braided body is 10° or more and 70° or less. A stent characterized by this.

9. In Claim 7, The stent for a flow diverter has a surface coverage rate of 30% or more, a number density of holes of 14 pieces / mm 2 or more, The bioabsorption rate of the stent for a flow diverter is 12 months or more and 36 months or less. A stent characterized by this.

10. In Claim 9, The stent is characterized in that it is subjected to surface treatment or coating.

11. In any one of Claims 6 to 10, The diameter of the stent is 2 to 6 mm, and the length of the stent is 10 to 50 mm. A stent characterized by this.

12. In any one of Claims 1 to 11, The self-expandability means that the outer diameter of the stent after expansion is 4 times or more and 12 times or less the outer diameter before expansion in the atmosphere, and the stent is characterized by this.

13. In any one of Claims 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.

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