JP2018082726A - Medical implant composed of zinc alloy, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medical implant with a controlled corrosion rate, and excellent mechanical properties (particularly ductility).SOLUTION: A medical implant is composed of a zinc alloy obtained by the extrusion of a sintered body containing zinc and magnesium.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a medical implant made of a zinc-based alloy and a manufacturing method thereof.

  Conventionally, ischemic heart diseases such as angina pectoris and myocardial infarction are performed by percutaneous transluminal coronary angioplasty (PTCA) for the stenosis of the coronary artery, and ischemic diseases of the femoral artery and the carotid artery are percutaneous through the stenosis. Treatment is performed by tubular angioplasty (PTA) or the like. Each of these treatment methods is a technique for securing and resuming blood flow by dilating a blood vessel that has been narrowed or occluded by using a catheter having a balloon that is small folded at the tip. These therapies have the advantage of being less invasive because they require a smaller wound than when the body is cut open.

  In the treatment using a catheter, a metal stent may be placed to ensure the patency of the blood vessel in order to prevent the dilated blood vessel from restenosis or occlusion. Stents include those cut out from a single metal pipe, meshes made of metal wires, coils, and the like, all of which have a tubular structure that can be reduced in diameter. The stent is inserted into a blood vessel by a catheter in a reduced diameter state, and is expanded and placed so as to mechanically support the blood vessel lumen in the stenosis.

  The stent needs a radial force (radial strength) sufficient to keep the lumen of the blood vessel for a certain period after vasodilation. However, when a state where the expanded state of the blood vessel can be maintained without the stent after the predetermined period has elapsed, the radial force by the stent is not necessary. Therefore, it is desirable to gradually disassemble medical implants such as stents that have finished their role in the medium to long term.

  For example, as a material for manufacturing the above biodegradable medical implant typified by a stent, a corrosive metal such as magnesium is used. For example, Patent Document 1 describes a stent formed by casting from magnesium or a magnesium alloy.

US Patent Application Publication No. 2013/0261735

  Since the magnesium alloy described in Patent Document 1 has a very high corrosion rate, the corrosion rate is adjusted by applying a biodegradable polymer to the surface of the magnesium alloy to form a coat layer or the like. However, the coat layer made of a biodegradable polymer may be peeled off from the stent body at the time of insertion or indwelling, or may not be able to follow the elongation of the metal at the time of implant expansion and may break. In this case, there is a possibility that the decomposition rate cannot be adjusted by the coat layer, which causes a problem in use.

  Zinc is known as a corrosive metal other than magnesium. Patent Document 1 discloses a stent using a strut in which a core made of a magnesium alloy having a high corrosion rate is covered with a shell made of zinc having a low corrosion rate, as a scaffold for the stent. However, zinc alone has a problem that the corrosion rate is excessively slow.

  Furthermore, in order to increase the corrosion rate, it is conceivable to use an alloy of zinc and magnesium, but the magnesium-containing zinc-based alloy formed by the general casting method has sufficient mechanical properties (particularly ductility). The present inventors have found that there is a problem that it is not.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a medical implant that can control the corrosion rate and is excellent in mechanical properties (particularly ductility).

  As a result of intensive studies to solve the above problems, the present inventors have used a zinc-based alloy obtained by extruding a sintered body containing zinc and magnesium for a medical implant. The present inventors have found that the above problems can be solved, and have completed the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the medical implant which can control a corrosion rate and was excellent in mechanical characteristics (especially ductility) is provided.

It is a mimetic diagram of a stent concerning one embodiment of the present invention. It is an electron microscope image of the molten metal powder (FIG. 2A), sintered body (FIG. 2B), and zinc-based alloy (FIG. 2C) in Example 4.

  Embodiments of the present invention will be described below. In addition, this invention is not limited only to the following embodiment.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”, and unless otherwise specified, measurement of operation and physical properties is performed at room temperature (20 to 25 ° C.) / Relative humidity of 40 to 50%. Measure under conditions.

[Medical implant]
The 1st side surface of this invention is related with the medical implant which consists of a zinc-type alloy obtained by the extrusion process of the sintered compact containing zinc and magnesium. In the present specification, the “zinc-based alloy” refers to an alloy component having the highest zinc content by measurement using an analytical instrument such as ICP-MS and ICP-AES described in Examples. Preferably, in the present specification, the “zinc-based alloy” means that the zinc content in the alloy exceeds 50% by weight by measurement using an analytical instrument such as ICP-MS and ICP-AES described in Examples. Say. The zinc-based alloy used for the medical implant according to the present invention is also referred to as “zinc-based alloy according to the present invention”.

  As described above, a medical implant such as a stent requires a radial force that keeps the lumen of the blood vessel for a certain period after vascular dilation, but an intima is formed on the stent surface. Once done, radial force is no longer needed. Therefore, it is desirable to gradually disassemble a stent that has finished its role in the medium to long term. In the present invention, this decomposition is performed by corrosion of a zinc-based alloy.

  The mechanism presumed in the present invention will be described below.

  For the medical implant according to the present invention, a zinc-based alloy containing zinc as a main component is used. For this reason, the corrosion rate does not increase excessively as much as an alloy containing magnesium as a main component. On the other hand, the zinc-based alloy, which is the material for the medical implant according to the present invention, contains magnesium in addition to zinc, and therefore has a higher corrosion rate than a medical implant made of zinc alone. Therefore, the medical implant according to the present invention can control the corrosion rate by adjusting the contents of zinc and magnesium. That is, the medical implant according to the present invention can control the corrosion rate without a polymer coat layer for adjusting the corrosion rate.

  Furthermore, the medical implant which concerns on this invention can improve mechanical strength (tensile strength) by setting it as the zinc-type alloy containing magnesium compared with the case of zinc alone. This is considered to be because dislocation is suppressed by solid solution of magnesium atoms in the zinc crystal lattice. Due to the high mechanical strength (tensile strength) of the medical implant material, the radial force can be maintained even if the medical implant is thin. In addition, it is considered that a polycrystalline metal such as a zinc-magnesium alloy easily slips (deforms) within crystal grains and stops at the crystal grain boundaries according to the Hall-Petch equation. For this reason, when the crystal grains are fine, the slip distance within the crystal grains is limited, and the resistance to deformation increases. Therefore, it is guessed that the zinc-type alloy which concerns on this invention can obtain the outstanding tensile strength.

  The present inventors have also found a problem that a magnesium-containing zinc-based alloy obtained by a conventional casting method has poor mechanical properties, particularly ductility. If the ductility of the medical implant material is low, for example, when the medical implant is expanded with a balloon and is left in the body, the medical implant may be broken due to expansion (and overexpansion) by the balloon.

The inventors surprisingly found that a zinc-based alloy obtained by extruding a sintered body of zinc and magnesium is a magnesium-containing zinc-based material obtained by extruding a cast material composed of zinc and magnesium. It has also been found that mechanical properties, particularly ductility, are superior to those of alloys. When a magnesium-containing zinc-based alloy is produced by a casting method, a highly brittle intermetallic compound phase such as Mg ₂ Zn ₁₁ or MgZn ₂ is formed at the crystal grain boundary of the alloy. On the other hand, when a zinc-based alloy is produced by extruding a sintered body of zinc and magnesium as in the present invention, since the fine powder is used as a raw material, the crystal grain size of the zinc-based alloy is reduced. As a result, the intermetallic compound existing at the crystal grain boundary is dispersed, and is less likely to be a starting point of fracture. For this reason, it is presumed that the zinc-based alloy according to the present invention has excellent ductility.

  The above mechanism is speculation and does not limit the technical scope of the present invention.

  Examples of the medical implant according to the present invention include a stent and a stent graft.

  Preferably, the medical implant according to the present invention is a stent. For example, the stent is a balloon-expandable stent (balloon expandable stent), similar to a conventionally used stent. The shape of the stent is not particularly limited, and a conventionally known shape can be adopted. For example, what formed the fiber by knitting a fiber, what provided the opening part in the pipe (tubular body), etc. are mentioned.

  As an embodiment of the present invention, the shape of a stent is illustrated in FIG.

  In the embodiment shown in FIG. 1, the stent 1 is made of a zinc-based alloy 2 and has a substantially rhombic element 21 having a notch therein as a basic unit. A plurality of substantially rhombic elements 21 are continuously arranged in the minor axis direction and joined to form an annular unit 22. The annular unit 22 is connected to an adjacent annular unit via a linear connecting member 23. Thus, the plurality of annular units 22 are continuously arranged in the axial direction in a partially coupled state. With such a configuration, the stent 1 has a cylindrical body that is open at both ends and extends between the ends in the longitudinal direction. The stent 1 has a substantially diamond-shaped notch, and has a structure that can be expanded and contracted in the radial direction of the cylindrical body by deforming the notch.

  However, in the present invention, the shape of the stent is not limited to the illustrated embodiment. The structure includes a large number of notches communicating with the side surface and the inner surface, and a structure that can expand and contract in the radial direction of the cylindrical body by deforming the notches. The cross-sectional shape of the zinc-based alloy constituting the stent is not particularly limited, and examples thereof include a rectangle, a circle, an ellipse, and a polygon other than a rectangle.

  The thickness of the medical implant can be a conventional one. For example, taking a stent as an example, the thickness of the zinc-based alloy is, for example, about 5 to 1000 μm, preferably about 20 to 500 μm, more preferably about 50 to 200 μm, from the relationship between supportability and placement time. Since the zinc-based alloy according to the present invention has excellent tensile strength, the implant can be made thin.

  The size of the medical implant is also appropriately adjusted according to its purpose and function. Taking a stent as an example, the outer diameter of the stent before expansion is preferably about 0.3 to 5 mm, more preferably about 0.4 to 4.5 mm, and particularly preferably about 0.5 to 1.6 mm.

  Further, the length of the medical implant is not particularly limited, and can be appropriately selected depending on the disease to be treated. For example, taking a stent as an example, the length is preferably about 5 to 100 mm, more preferably about 6 to 50 mm. Alternatively, the length of the stent is preferably about 1.5 to 4 mm, and more preferably about 2 to 3 mm.

<Zinc-based alloy>
The medical implant which concerns on this invention consists of a zinc-type alloy obtained by the extrusion process of the sintered compact containing zinc and magnesium. The zinc-based alloy according to the present invention essentially contains magnesium, and in one embodiment, the zinc content exceeds 50% by weight. In addition, in this specification, an elemental composition is the value measured by the measurement using ICP-MS or ICP-AES as described in an Example.

  Since the zinc-based alloy, which is the material for the medical implant according to the present invention, contains magnesium in addition to zinc, the corrosion rate is higher than that of the medical implant made of zinc alone. Furthermore, mechanical strength (tensile strength) can be improved by using a zinc-based alloy containing magnesium as compared with the case of zinc alone.

  One embodiment of the present invention consists of more than 50 wt.% And less than 100 wt.% Zinc, more than 0 wt.% And less than 50 wt.% Magnesium, and the balance unavoidable impurities. Preferably, the zinc-based alloy according to the present invention comprises 97% by weight or more and less than 100% by weight of zinc, more than 0% by weight of 3% by weight or less of magnesium, and the balance of inevitable impurities. More preferably, the zinc-based alloy according to the present invention is composed of 99% by weight or more and less than 100% by weight zinc, more than 0% by weight and 1% by weight magnesium or less, and the balance of inevitable impurities. More preferably, the zinc-based alloy according to the present invention comprises 99.3% by weight to 99.95% by weight of zinc, 0.05% by weight to 0.7% by weight of magnesium, and the balance of inevitable impurities. .

  In the present specification, “inevitable impurities” refers to zinc-based alloys that are present in the raw material or are inevitably mixed in the manufacturing process. The inevitable impurities are originally unnecessary impurities, but are a very small amount and do not affect the characteristics of the zinc-based alloy, and thus are allowable impurities. For example, silicon (Si) is 0.01% by weight or less, aluminum (Al) is 0.01% by weight or less, and titanium (Ti) is 0.0% by weight as unavoidable impurities. 005 wt% or less, iron (Fe) 0.005 wt% or less, nickel (Ni) 0.005 wt% or less, copper (Cu) 0.005 wt% or less, manganese (Mn) 0.005 wt% % Or less, lead (Pb) 0.01% by weight or less, and cadmium (Cd) 0.01% by weight or less.

  In one preferred embodiment of the present invention, the zinc-based alloy is represented by the following formula (1).

  In the formula (1), A is an unavoidable impurity, x, y, and a represent weight percent, where 97 ≦ x <100, 0 <y ≦ 3, and 0 ≦ a <y, x + y + a = 100.

  The zinc-based alloy represented by the formula (1) contains 97% by weight or more of zinc and magnesium of more than 0 and 3% by weight or less based on the whole alloy. When the magnesium content is 3% by weight or less, there is an advantage that high ductility can be obtained.

  From the viewpoint of adjusting the corrosion rate and giving the stent the necessary mechanical properties (ductility and tensile strength), in formula (1), 99 ≦ x <100, 0 <y ≦ 1, and 0 ≦ a < y, preferably x + y + a = 100, and in Formula (1), 99.3 ≦ x ≦ 99.95, 0.05 ≦ y ≦ 0.7, and 0 ≦ a <y, and x + y + a = More preferably, it is 100. In the formula (1), the range of a is, for example, 0 ≦ a ≦ 0.01, and preferably 0 ≦ a <0.005.

  The zinc-based alloy according to the present invention has high ductility. Therefore, by using the zinc-based alloy according to the present invention for medical implants, the medical implant can be prevented from being expanded (and over-expanded) and from being bent, twisted, or pulsated before and after placement. it can. In addition, since the zinc-based alloy has high ductility, there is an advantage that the degree of freedom of the stent structure is increased. The zinc-based alloy according to the present invention is also excellent in tensile strength. Therefore, by using the zinc-based alloy according to the present invention for a medical implant, the medical implant can be made thin while maintaining a high radial force.

  Preferably, the medical implant according to the present invention is made of a zinc-based alloy having a tensile strength of 200 MPa or more and an elongation rate exceeding 5% in a tensile test under the following conditions. That is, in one embodiment of the present invention, a medical implant is provided in which the tensile strength of the zinc-based alloy is 200 MPa or more and the elongation percentage exceeds 5%. In this specification, the tensile test for calculating and measuring the tensile strength and the elongation rate is performed under the following conditions. Here, the tensile strength is calculated by dividing the maximum tensile force required to break the test piece by the sectional area of the test piece when the following test piece is pulled until it breaks under the following conditions. . Moreover, when the elongation rate of the following test piece is pulled until it breaks under the following conditions, the maximum elongation rate at the time of breaking the test piece is measured.

(Tension test conditions)
Shape of test piece: Round bar Diameter of test piece: 3 mm
Test piece length: 40 mm
Test piece parallel part length: 15mm
Strain rate: 5 × 10 ⁻⁴ s ⁻¹ .

  The tensile strength of the zinc-based alloy is more preferably 230 MPa or more, and further preferably 250 MPa or more. At this time, the elongation percentage of the zinc-based alloy is more preferably 10% or more, and further preferably 15% or more. The upper limit of the tensile strength and elongation rate is not particularly limited, but substantially the tensile strength is 330 MPa or less and the elongation rate is 30% or less.

  The above tensile test is measured at room temperature (25 ° C.).

  The corrosion rate of the zinc-based alloy according to the present invention is faster than when zinc is used alone, and is slower than when magnesium is used alone. Since the corrosion rate of zinc-based alloys varies depending on the medical implant used, it cannot be generally stated.

<Manufacturing method>
The zinc-based alloy according to the present invention is obtained by extrusion of a sintered body containing zinc and magnesium. That is, the second aspect of the present invention is a medical use comprising a step of sintering a metal powder containing zinc and magnesium to obtain a sintered body; and a step of extruding the sintered body to obtain a zinc-based alloy. The present invention relates to a method for manufacturing an implant.

  Hereinafter, the manufacturing method of the zinc-type alloy and medical implant which concern on this invention is demonstrated in detail.

1. Providing Metal Powder Containing Zinc and Magnesium In the production of the zinc-based alloy according to the present invention, metal powder containing zinc and magnesium is used as a raw material. By adjusting the weight ratio of zinc and magnesium in the raw material powder, the contents of zinc and magnesium in the alloy can be arbitrarily set.

  Zinc used as a raw material is preferably highly pure, and the better the content of contained inevitable impurities. The purity of the raw material zinc is, for example, 99.99% by weight or more (the upper limit is 100% by weight).

  Magnesium used as a raw material is also preferably highly pure, and the lower the content of inevitable impurities contained, the better. The purity of the raw material magnesium is, for example, 99.9% by weight or more (the upper limit is 100% by weight).

  From the viewpoint of suppressing the formation of intermetallic compounds, the powder particle size of zinc used as a raw material is preferably small, for example, 200 μm or less, and preferably 150 μm or less. The lower limit of the particle size of the powder is not particularly limited, but for example, 1 μm or more. In the present specification, the metal powder particle size is a value measured by a sieving method.

  The powder particle diameter of magnesium used as a raw material is also preferably small from the viewpoint of suppressing the formation of intermetallic compounds, for example, 200 μm or less, and preferably 150 μm or less. Although the minimum of a particle size is not restrict | limited in particular, For example, it is 1 micrometer or more.

  In the method for producing a zinc-based alloy according to the present invention, a mixture obtained by mixing zinc powder and magnesium powder in a powder state may be sintered. In this case, raw material zinc and raw material magnesium are mixed and sintered so as to be uniform. As a mixing method, it can carry out by conventionally well-known methods, such as a powder mill, for example.

  On the other hand, when there is a difference in particle size between the zinc powder and the magnesium powder, uniform mixing may be difficult. In this case, a metal powder having a uniform particle size can be obtained by preparing a metal powder from zinc and magnesium by melting. In a preferred embodiment of the present invention, in the step of obtaining a sintered body, a molten metal powder containing zinc and magnesium is sintered.

  Zinc and magnesium used for the preparation of the melted metal powder may be powder as described above or ingot.

  These raw materials are heated and melted to form a molten metal and powdered. The method for obtaining the molten metal powder is not particularly limited as long as it is a method capable of obtaining a powder having a small particle diameter, and a conventionally known method such as a centrifugal spray method, a water spray method, a gas spray method, etc. can be employed. It is preferable to carry out by a centrifugal spray method. In the centrifugal spraying method, the molten metal is rapidly cooled, so that the formation of highly brittle intermetallic compounds can be suppressed. Further, the centrifugal spray method has an advantage that particles having a sharp particle size distribution can be obtained.

  The melting temperature of the raw material in producing the molten metal powder is not particularly limited as long as it is equal to or higher than the melting point of the raw material, but is 400 ° C. or higher, for example. Moreover, it is preferable that a melting temperature is 500 degrees C or less from a viewpoint of preventing evaporation of zinc.

  The particle size of the melted metal powder is preferably small from the viewpoint of suppressing the formation of intermetallic compounds, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less. Although the minimum of a particle size is not restrict | limited in particular, For example, it is 1 micrometer or more. For example, the particle size can be arbitrarily controlled by adjusting the rotational speed of the disk in the case of the centrifugal spraying method, and adjusting the gas pressure in the case of the gas spraying method.

2. Sintering The method for producing a medical implant according to the present invention includes a step of sintering a metal powder containing zinc and magnesium to obtain a sintered body. As described above, the metal powder may be a mixture of zinc powder and magnesium powder or the above-mentioned melted metal powder.

  Various methods conventionally used in the field of powder metallurgy can be employed for sintering the metal powder. Specific examples of the sintering method include spark plasma sintering (SPS), hot press sintering, hot isostatic pressing (HIP), millimeter wave sintering, and microwave sintering. From the viewpoint of easy production, the sintering is preferably spark plasma sintering. That is, it is preferable that a sintered body containing zinc and magnesium is obtained by spark plasma sintering.

  Sintering is preferably performed in a vacuum atmosphere or an inert gas atmosphere such as argon gas or nitrogen gas.

  Although sintering temperature is not specifically limited, For example, it is 100-400 degreeC, Preferably it is 300-350 degreeC. Moreover, a temperature increase rate is 1-20 degree-C / min, for example, Preferably it is 5-15 degree-C / min.

  Sintering is preferably performed under pressure, and the conditions at that time are 10 to 100 MPa, preferably 30 to 50 MPa.

  The holding time of sintering is, for example, 10 to 60 minutes, preferably 30 to 40 minutes.

  When sintered by spark plasma sintering (SPS), which is a preferred embodiment, the voltage applied to the metal powder is, for example, 1000 to 3500 V, and the current is, for example, 2.5 to 15 A, although not particularly limited. It is.

  The average crystal grain size of the sintered body after sintering and before extrusion is, for example, 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less. Although the minimum of a particle size is not restrict | limited in particular, For example, it is 0.1 micrometer or more.

3. Extrusion Process The medical implant according to the present invention is characterized by comprising a zinc-based alloy obtained by the extrusion process of the sintered body. Moreover, the manufacturing method of the medical implant which concerns on this invention is characterized by including the process of extruding the said sintered compact and obtaining a zinc-type alloy. A rod is obtained by extruding the sintered body, and a medical implant is manufactured using the rod as a material. The rod shape is not particularly limited, and may be appropriately adjusted according to the purpose. For example, the diameter is 0.05 to 20 cm, and the rod length is, for example, 0.01 to 5 m.

  Note that a pipe may be obtained by extruding the sintered body, and a medical implant may be manufactured using the pipe as a material. Specifically, after extruding the sintered body to create a hollow zinc-based alloy pipe, a stent may be created using the pipe as a material. In this case, a medical implant such as a hollow stent can be more easily manufactured by creating a pipe by extrusion of a sintered body. In one embodiment of the present invention, in the method for producing a medical implant, in the step of obtaining a zinc-based alloy, a sintered body is extruded to create a hollow zinc-based alloy pipe.

  The extrusion process may be any of hot extrusion, cold extrusion, or warm extrusion, but from the viewpoint of processability, hot extrusion is preferably employed. The extrusion ratio in the extrusion process is, for example, 5 to 50, and the extrusion ram speed is 1 to 10 mm / second.

  The conditions for hot extrusion are not particularly limited. For example, the preheating temperature is 100 to 400 ° C., and the preheating time is 1 to 30 minutes.

  The crystal grain size of the zinc-based alloy crystal obtained by the extrusion process is further smaller than that before the extrusion. The average crystal grain size of the zinc-based alloy crystal is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 10 μm or less, and particularly preferably 5 μm or less. By being a small crystal having a zinc-based alloy crystal grain size of 5 μm or less, generation of intermetallic compounds is reduced, and ductility can be improved. Although the minimum of a particle size is not restrict | limited in particular, For example, it is 0.1 micrometer or more.

  The average crystal grain size of the zinc-based alloy or sintered body is as follows: (1) After polishing an arbitrary surface of the zinc-based alloy or sintered body with diamond abrasive grains to make a mirror surface, Etching the surface with hydrochloric acid, (2) Using a scanning electron microscope (SEM) or optical microscope, select an arbitrary place among the etched surfaces, and take an image at a predetermined magnification to obtain an image (3 This image can be obtained by analyzing the image using, for example, image analysis software “Image-Pro Plus” (Media Cybernetics). In addition, any surface of a zinc-based alloy or sintered body is polished using diamond abrasive grains to form a mirror surface, and then crystal analysis is performed by electron beam backscattering analysis (EBSD), and a scanning electron microscope (SEM) ) Etc., it may be confirmed that the crystal grain size of the image obtained by electron beam backscattering analysis (EBSD) matches the crystal grain size of the image obtained by the above method.

  The rod thus produced is optionally processed to produce a desired medical implant. For example, in the case of a stent, the center portion of the rod is drawn out by machining to form a pipe shape. This can be cut into a stent pattern by laser processing, and further subjected to chemical polishing and electrolytic polishing to produce a stent.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

Example 1
Zinc ingot (purity 99.99%) and magnesium ingot (purity 99.9%), which are raw materials of the alloy, were melted in an electric furnace at a ratio of 99.9: 0.1 (weight ratio). Using the obtained molten metal, a melted metal powder having a powder particle size of 5 μm to 150 μm was obtained by centrifugal spraying.

Subsequently, using the obtained molten metal powder, a sintered body was obtained by discharge plasma sintering (device name: discharge plasma sintering apparatus, manufacturer: manufactured by SPS Syntex). The sintering conditions are as follows:
Atmosphere: Vacuum Sintering temperature: 300 ° C
Temperature increase rate: 15 ° C./min Pressure: 30 MPa
Holding time: 30 minutes Voltage: 1100V
Current: 2.5A.

Next, the sintered body is extruded by hot extrusion (equipment name: 2000 kN hydraulically driven molding machine, manufacturer: Shibayama Machine), and is rod-shaped (diameter: 0.7 cm, length: 0.5 m). Alloy 1 was obtained. Extrusion conditions are shown below:
Preheating temperature: 200 ° C
Preheating time: 3 minutes Extrusion ratio: 32
Extrusion ram speed: 3 mm / sec.

The average crystal grain size of the obtained zinc-based alloy 1 was 3 μm.
(Example 2)
An alloy was prepared by the same method as in Example 1 except that the ratio of the zinc ingot and the magnesium ingot as raw materials of the alloy was changed to a ratio of 99.75: 0.25 (weight ratio). Obtained.

(Example 3)
An alloy was prepared by the same method as in Example 1 except that the ratio of the zinc ingot and the magnesium ingot as raw materials of the alloy was changed to a ratio of 99.5: 0.5 (weight ratio). Obtained.

Example 4
An alloy was prepared in the same manner as in Example 1 except that the ratio of the zinc ingot and the magnesium ingot, which were the raw materials of the alloy, was changed to a ratio of 99: 1 (weight ratio), and a zinc-based alloy 4 was obtained. The average crystal grain size of the zinc-based alloy 4 was 3 μm. The average crystal grain size of the sintered body before extrusion in Example 4 was 15 μm. FIG. 2 shows the melting metal powder (FIG. 2A, magnification: 100 times), sintered body (FIG. 2B, magnification: 200 times), and zinc-based alloy 1 (FIG. 2C, magnification: 1000 times) in Example 4. It is an electron microscope image.

(Comparative Example 1)
A zinc ingot and a magnesium ingot were mixed at the same weight ratio as in Example 1, and a comparative metal 1 having a rod shape (diameter: 0.7 cm, length: 0.5 m) was formed by a casting method (melting temperature: 500 ° C.). Obtained. The obtained comparative metal 1 had an average crystal grain size of 20 μm.

(Comparative Example 2)
A zinc ingot and a magnesium ingot were mixed at the same weight ratio as in Example 2, and a comparative metal 2 having a rod shape (diameter: 0.7 cm, length: 0.5 m) was formed by a casting method (melting temperature: 500 ° C.). Obtained.

(Comparative Example 3)
A zinc ingot and a magnesium ingot were mixed at the same weight ratio as in Example 3, and a comparative metal 3 having a rod shape (diameter: 0.7 cm, length: 0.5 m) was formed by a casting method (melting temperature: 500 ° C.). Obtained.

(Comparative Example 4)
A zinc ingot and a magnesium ingot were mixed at the same weight ratio as in Example 4, and a comparative metal 4 having a rod shape (diameter: 0.7 cm, length: 0.5 m) was formed by a casting method (melting temperature: 500 ° C.). Obtained. The average grain size of the obtained comparative metal 4 was 5.5 μm.

(Comparative Example 5)
A comparative metal 5 was obtained by producing a rod by the same method as in Example 1 except that a zinc ingot was used alone as a raw material.

(Comparative Example 6)
A comparative metal 6 was obtained by producing a rod by the same method as in Comparative Example 1 except that a magnesium ingot was used alone as a raw material.

(Tensile test)
Using the above zinc-based alloys 1 to 4 and comparative metals 1 to 6, a tensile test (equipment name: AUTOGRAPH AG-X 50 kN, manufactured by Shimadzu Corporation) was performed at room temperature (25 ° C.) under the following conditions ( n = 3):
Shape of test piece: Round bar Diameter of test piece: 3 mm
Test piece length: 40 mm
Test piece parallel part length: 15mm
Strain rate: 5 × 10 ⁻⁴ s ⁻¹ .

  Table 1 shows the results of the tensile test.

(Corrosion rate)
The corrosion rate was measured by the TAFEL extrapolation method using the above-described zinc-based alloys 1 to 4 and comparative metals 1 to 6. The results are shown in Table 1.

(TAFEL extrapolation method (electrochemical test))
The corrosion rate was calculated from the anode-cathode polarization curve obtained by applying a potential between the sample electrode and the counter electrode.

Equipment used: HZ7000 (Hokuto Denko Corporation)
Electrolyte solution: PBS (pH 7.4)
Reference electrode: Ag / AgCl
Temperature: 37 ° C
Scan speed 20mV / min
Sampling interval 500 ms.

1 stent,
2 Zinc-based alloys,
21 Substantially rhombic elements,
22 annular unit,
23 Connecting member.

Claims (10)

  A medical implant comprising a zinc-based alloy obtained by extrusion of a sintered body containing zinc and magnesium.   The medical implant according to claim 1, wherein the zinc-based alloy has a tensile strength of 200 MPa or more and an elongation rate of more than 5% in a tensile test. The zinc-based alloy has the following formula (1):
In the formula (1), A is an unavoidable impurity, x, y, and a represent weight percent, where 97 ≦ x <100, 0 <y ≦ 3, and 0 ≦ a <y, x + y + a = 100;
The medical implant of Claim 1 or 2 represented by these.   In said Formula (1), it is 99.3 <= x <= 99.95, 0.05 <= y <= 0.7, and 0 <= a <y, The medical use of Claim 3 which is x + y + a = 100 Implant.   The medical implant according to any one of claims 1 to 4, wherein the sintered body is obtained by spark plasma sintering.   The medical implant according to any one of claims 1 to 5, which is a stent. A method for producing a medical implant, comprising: sintering a metal powder containing zinc and magnesium to obtain a sintered body; and extruding the sintered body to obtain a zinc-based alloy.   The manufacturing method of the medical implant of Claim 7 which sinters the molten metal powder containing zinc and magnesium in the process of obtaining the said sintered compact.   The method for manufacturing a medical implant according to claim 7 or 8, wherein the sintering is spark plasma sintering.   The method for producing a medical implant according to any one of claims 7 to 9, wherein, in the step of obtaining the zinc-based alloy, the sintered body is extruded to create a hollow zinc-based alloy pipe. .