BIOCOMPATIBLE ALLOY AND MEDICAL PRODUCT

Abstract

Provided is a biocompatible alloy having low magnetic susceptibility and excellent mechanical properties. The biocompatible alloy according to the present invention contains: Zr as a main component; Nb of not less than 0.1% by mass and not greater than 25% by mass; Mo of not less than 0.1% by mass and not greater than 25% by mass; and Ta of not less than 0.1% by mass and not greater than 25% by mass. A total content of Nb, Mo, and Ta in the biocompatible alloy is not less than 2% by mass and not greater than 50% by mass. The biocompatible alloy has a mass susceptibility of not greater than 1.5010.sup.6 cm.sup.3/g. The biocompatible alloy has a Young's Modulus of not greater than 100 GPa. Various biocompatible implants and medical devices can be manufactured from the biocompatible alloy.

Claims

1. A biocompatible alloy comprising: Zr as a main component; Nb of not less than 0.1% by mass and not greater than 25% by mass; Mo of not less than 0.1% by mass and not greater than 25% by mass; and Ta of not less than 0.1% by mass and not greater than 25% by mass.

2. The biocompatible alloy according to claim 1, wherein a total content of Nb, Mo, and Ta is not less than 2% by mass and not greater than 50% by mass.

3. The biocompatible alloy according to claim 1, wherein the Nb content is not less than 0.5% by mass and not greater than 25% by mass, the Mo content is not less than 0.1% by mass and not greater than by mass, and the Ta content is not less than 1.0% by mass and not greater than 15% by mass.

4. The biocompatible alloy according to claim 1, wherein the Nb content is not less than 12% by mass and not greater than 16% by mass, the Mo content is not less than 0.5% by mass and not greater than 5% by mass, and the Ta content is not less than 3% by mass and not greater than 12% by mass.

5. The biocompatible alloy according to claim 1, wherein a ratio (PMo/PTa) of PMo, which is the Mo content (% by mass), to PTa, which is the Ta content (% by mass), is not less than 1/20 and not greater than 1/3.

6. The biocompatible alloy according to claim 1, wherein the biocompatible alloy has a mass susceptibility of not greater than 1.5010.sup.6 cm.sup.3/g.

7. The biocompatible alloy according to claim 1, wherein the biocompatible alloy has a Young's Modulus of not greater than 100 GPa.

8. A medical product made of the biocompatible alloy according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a graph showing the results of a study, in which the compositions of Zr-based alloys were studied by using the d-electron alloy design theory.

[0018] FIG. 2 is a front view of a test piece used in a tensile test.

[0019] FIG. 3 is a front view of an ingot for Vickers hardness measurement.

[0020] FIG. 4 is a graph showing XRD results.

DESCRIPTION OF EMBODIMENTS

[0021] Hereinafter, the present invention is described in detail based on preferred embodiments with reference to the drawings as necessar.

[0022] A medical product according to the present invention is made of a biocompatible alloy. The biocompatible alloy contains Zr, Nb, Mo, and Ta. Preferably, the rest of the alloy is made up of inevitable impurities.

[0023] The inventors of the present invention studied the compositions of Zr-based alloys by using the d-electron alloy design theory. The d-electron alloy design theory is a method in which parameters indicating the properties of alloy elements are obtained, and the parameters are used to study alloy compositions. Based on this theory, an alloy composition having intended mechanical properties can be determined.

[0024] FIG. 1 is a graph showing the results of the study, in which the compositions of Zr-based alloys were studied by using the d-electron alloy design theory. In the graph, the directions of arrows contribute to phase determination, and the lengths of the arrows contribute to phase stability. It is clear from the graph that Nb, Mo, and Ta contribute to phase formation of a Zr alloy.

[0025] Zr is a main component of the biocompatible alloy according to the present invention. Among the content rates of all the elements in the alloy, the Zr content is the highest in the alloy. Zr has low cytotoxicity. In addition, Zr has excellent corrosion resistance. Therefore, a medical product in which the alloy is used is excellent in terms of durability in a living body. In the alloy, the Zr content is preferably not less than 40% by mass, and particularly preferably not less than 50% by mass.

[0026] Nb is a phase-stabilized element. Nb contributes to the lowering of the magnetic susceptibility of the alloy. This alloy is capable of suppressing artifacts in diagnostic MRI. Nb is capable of forming an all proportional solid solution together with Zr. Therefore, Nb can be uniformly distributed in the alloy. This alloy has excellent mechanical properties. In addition, Nb has low cytotoxicity.

[0027] The Nb content in the alloy is preferably not less than 0.1% by mass and not greater than 25% by mass. The alloy in which the Nb content is not less than 0.1% by mass is capable of suppressing artifacts. In addition, the alloy in which the Nb content is not less than 0.1% by mass is capable of contributing to the mechanical properties of a medical product. In light of these, the Nb content in the alloy is more preferably not less than 0.5% by mass, and particularly preferably not less than 12% by mass. The alloy in which the Nb content is not greater than 25% by mass is capable of suppressing artifacts. In light of this, the Nb content in the alloy is more preferably not greater than 20% by mass, and particularly preferably not greater than 16% by mass.

[0028] Mo is a phase-stabilized element. Mo contributes to the lowering of the magnetic susceptibility of the alloy. This alloy is capable of suppressing artifacts in diagnostic MRI. Mo contributes to the mechanical properties of the alloy. In addition, Mo has low cytotoxicity.

[0029] The Mo content in the alloy is preferably not less than 0.1% by mass and not greater than 25% by mass. The alloy in which the Mo content is not less than 0.1% by mass is capable of suppressing artifacts. In addition, the alloy in which the Mo content is not less than 0.1% by mass is capable of contributing to the mechanical properties of a medical product. In light of these, the Mo content in the alloy is more preferably not less than 0.8% by mass, and particularly preferably not less than 1.0% by mass. The alloy in which the Mo content is not greater than 25% by mass is capable of suppressing artifacts. In light of this, the Mo content in the alloy is more preferably not greater than 10% by mass, and particularly preferably not greater than 5% by mass.

[0030] Ta is a phase-stabilized element. Ta also facilitates an phase formation. Ta contributes to the lowering of the magnetic susceptibility of the alloy. This alloy is capable of suppressing artifacts in diagnostic MRI. Ta is capable of forming an all proportional solid solution together with Zr. Therefore, Ta can be uniformly distributed in the alloy. This alloy has excellent mechanical properties. In addition, Ta has low cytotoxicity.

[0031] The Ta content in the alloy is preferably not less than 0.1% by mass and not greater than 25% by mass. The alloy in which the Ta content is not less than 0.1% by mass is capable of suppressing artifacts. In addition, the alloy in which the Ta content is not less than 0.1% by mass is capable of contributing to the mechanical properties of a medical product. In light of these, the Ta content in the alloy is more preferably not less than 1.0% by mass, and particularly preferably not less than 3% by mass. The alloy in which the Ta content is not greater than 25% by mass is capable of suppressing artifacts. In light of this, the Ta content in the alloy is more preferably not greater than 15% by mass, and particularly preferably not greater than 12% by mass.

[0032] In the alloy, the total content of Nb, Mo, and Ta is preferably not less than 2% by mass and not greater than 50% by mass. The alloy in which the total content of Nb, Mo, and Ta is within this range achieves all of the following advantages: high tensile strength; high breaking elongation; low Young's Modulus; and low magnetic susceptibility. In light of this, the total content of Nb, Mo, and Ta is more preferably not less than 10% by mass, and particularly preferably not less than 15% by mass. The total content of Nb, Mo, and Ta is more preferably not greater than 40% by mass, and particularly preferably not greater than 35% by mass.

[0033] It is clear from the graph of FIG. 1 that Mo contributes to the phase stability to a great degree, whereas Ta contributes to the phase stability to a small degree. Therefore, preferably, in the alloy, the Ta content PTa (% by mass) is greater than the Mo content PMo (% by mass). The ratio (PMo/PTa) is preferably not less than 1/20 and not greater than 1/3, more preferably not less than 1/15 and not greater than 1/4, and particularly preferably not less than 1/10 and not greater than 1/5.

[0034] The alloy may further contain other elements in small amounts. Examples of the other elements include B, C, N, O, Na, Mg, Si, P, S, K, Ca, and Mn. The total content of the other elements in the alloy is preferably not greater than 10% by mass, more preferably not greater than 5% by mass, and particularly preferably not greater than 1.0% by mass.

[0035] The mass susceptibility of the alloy is preferably not greater than 1.5010.sup.6 cm.sup.3/g. The alloy having a mass susceptibility within this range is capable of suppressing artifacts. In light of this, the mass susceptibility of the alloy is more preferably not greater than 1.4510.sup.6 cm.sup.3/g, and particularly preferably not greater than 1.4010.sup.6 cm.sup.3/g. A columnar test piece is used in the measurement of the mass susceptibility. The test piece has a bottom surface diameter of 3 mm and a height of 25 mm. The measurement is performed with a manually operated magnetic balance (MSK-MK1 available from Sherwood Scientific, Ltd.). The applied magnetic field is 0.35 T.

[0036] The Young's Modulus of the alloy is preferably not greater than 100 GPa. Assume that, for example, a fracture fixing device, an artificial joint stem, or the like is obtained from the alloy having a Young's Modulus within this range. In this case, bone resorption caused by stress shielding can be reduced. In light of this, the Young's Modulus of the alloy is more preferably not greater than 80 GPa, and particularly preferably not greater than 70 GPa. The Young's Modulus of the alloy is preferably not less than 10 GPa, and particularly preferably not less than 20 GPa, A columnar test piece is used in the measurement of the Young's Modulus. The test piece has a bottom surface diameter of 3 mm and a height of 52 mm. The measurement is performed with an elastic modulus measuring device of a free vibration type (JE2-C1 available from Nihon Techno-Plus Corp.).

[0037] The tensile strength of the alloy is preferably not less than 600 MPa. A medical product having excellent durability can be obtained from the alloy having a tensile strength of not less than 600 MPa. In light of this, the tensile strength is more preferably not less than 700 MPa, and particularly preferably not less than 750 MPa. The tensile strength is measured by a tensile test. A test piece 2 having a shape shown in FIG. 2 is used in the tensile test. The test piece 2 is obtained by argon arc centrifugal casting. In this casting method, the internal pressure of a chamber is adjusted to be not greater than 1.210.sup.1 Pa, and then argon gas with a purity of not less than 99.9% is injected into the chamber to set the internal pressure to 0.06 MPa. The casting is performed in the chamber. The tensile test is performed with a precision universal testing machine (AG-2000B available from Shimadzu Corporation). The initial strain rate at the test is 1.310.sup.3.

[0038] The 0.2% proof stress of the alloy is preferably not less than 550 MPa. A medical product having excellent durability can be obtained from the alloy having a 0.2% proof stress of not less than 550 MPa. In light of this, the 0.2% proof stress of the alloy is more preferably not less than 650 MPa, and particularly preferably not less than 700 MPa. The 0.2% proof stress is measured by the aforementioned tensile test.

[0039] The breaking elongation of the alloy is preferably not less than 5%. A medical product having excellent durability can be obtained from the alloy having a breaking elongation of not less than 5%. In light of this, the breaking elongation of the alloy is more preferably not less than 8%, and particularly preferably not less than 10%. The breaking elongation is measured by the aforementioned tensile test.

[0040] The Vickers hardness of the alloy is preferably not less than 160. A medical product having excellent durability can be obtained from the alloy having a Vickers hardness of not less than 160. In light of this, the Vickers hardness of the alloy is more preferably not less than 180, and particularly preferably not less than 200. In the measurement of the Vickers hardness, three discs 6 each having a height of 1.5 mm are cut from an ingot 4 having a shape shown in FIG. 3. The Vickers hardness is measured on the cross section of each disc 6. The measurement is performed at 12 measurement points that are randomly chosen, and the measurement results are averaged. At the time of the measurement, a load of 3 N is applied, and the dwell time of the load is 15 seconds.

[0041] The definition of the medical product according to the present invention includes biocompatible implants and medical devices. Examples of the biocompatible implants include implants such as an artificial bone, an artificial dental root, and an artificial joint. Other examples of the biocompatible implants include a fracture fixing plate, an osteosynthesis nail, an osteosynthesis screw, an intramedullary nail, a ligator (e.g., a clip), a suture instrument (e.g., a stapler), an artificial joint, a blood vessel repairing material (e.g., a stent), and a prosthetic heart valve. Even if a patient having any of these biocompatible implants in their body is subjected to diagnostic MRI, artifacts are less likely to appear in the obtained image.

[0042] Examples of the medical devices include surgical products such as a medical scalpel, medical scissors, medical tweezers, a medical spoon, a medical hook, medical forceps, a medical saw, a medical chisel, a medical raspatory, a medical hammer, a medical file, a medical pry, a medical snare, an injection needle, a puncture needle, a medical puncture instrument, a drill, a perforator, a medical tube with a beak-shaped tip (e.g., a catheter guide wire), and a body fluid induction tube. Even if any of these medical devices is used in diagnostic MRI, artifacts are less likely to appear in the obtained image.

[0043] Examples of a method of manufacturing a medical product from the alloy according to the present invention include plastic working, casting, and sintering. Examples of the plastic working include drawing and extrusion.

[0044] Specific examples of the alloy according to the present invention include Zr-14Nb-1Mo-5Ta and Zr-14Nb-1Mo-10Ta. FIG. 4 is a graph showing XRD results of these alloys. It is clear from this graph that and phases are deposited on Zr-14Nb-1Mo-5Ta, and that , , and phases are deposited on Zr-14Nb-1Mo-10Ta. It is also clear from this graph that the phase decreases, the phase increases, and the co phase increases in accordance with increase in the Ta content.

[0045] Tables 1 and 2 below show the properties of Zr-14Nb-1Mo-5Ta and Zr-14Nb-1Mo-10Ta together with the properties of other alloys.

TABLE-US-00001 TABLE 1 Property Values of Alloys Zr14Nb1Mo5Ta Zr14Nb1Mo10Ta Pure Zr Zr14Nb Vickers Hardness 208 210 129 275 Tensile Strength 796 765 451 784 (MPa) 0.2% Proof Stress 754 717 349 686 (MPa) Breaking Elongation 15 11 13.7 12 (%) Young's Modulus 61 58 95 70 (GPa) Magnetic Susceptibility 1.38 1.35 1.34 1.35 (10.sup.6 cm.sup.3/g)

TABLE-US-00002 TABLE 2 Property Values of Alloys Zr1Mo Ti Ti6Al4V ELI Ti6Al7Nb CoCrMo Vickers Hardness Tensile Strength 970 980 933 980 (MPa) 0.2% Proof Stress 855 920 817 680 (MPa) Breaking Elongation 2.9 14 7 11 (%) Young's Modulus 98 100 100 114 200 (GPa) Magnetic Susceptibility 1.13 2.90 3.17 2.81 7.52 (10.sup.6 cm.sup.3/g)

[0046] As shown in Tables 1 and 2, the alloys according to the present invention achieve strength, low Young's Modulus, and low magnetic susceptibility. These alloys are suitable for use in medical products.

INDUSTRIAL APPLICABILITY

[0047] The alloy according to the present invention is suitable for use in various items that are applied to a living body when performing diagnostic MRI.

REFERENCE SIGNS LIST

[0048] 2 test piece for tensile test [0049] 4 ingot for Vickers hardness measurement [0050] 6 disc for Vickers hardness measurement