Alloy for medical use and method of producing the same

Abstract

The present invention is an alloy for medical use including an AuPt alloy, containing 34 to 36 mass % of Pt with the balance being Au, and having an -phase single structure in which a ratio of a peak intensity (X) of a Pt (111) plane to a peak intensity (Y) of an Au (111) plane (X/Y) is 0.01 or less in an X-ray diffraction analysis. The alloy can be produced in such a manner that after the AuPt alloy ingot is molten and cast, cold working and a heat treatment for homogenization are performed at least two times on the molten and cast alloy. The alloy of the present invention is an artifact-free material that exhibits excellent compatibility with a magnetic field environment such as an MRI and has magnetic susceptibility of 4 ppm with respect to that of water.

Claims

1. An alloy for medical use comprising an AuPt alloy, wherein the alloy contains 34 to 36 mass % of Pt with the balance being Au, and has an -phase single structure in which a ratio of a peak intensity (X) of a Pt (111) plane to a peak intensity (Y) of an Au (111) plane (X/Y) is 0.01 or less in an X-ray diffraction analysis, and wherein the alloy has a volume magnetic susceptibility of from 13 ppm to 5 ppm.

2. A method of producing an alloy for medical use, the alloy defined in claim 1, comprising the steps of: melting and casting an alloy ingot comprising an AuPt alloy containing 34 to 36 mass % of Pt with the balance being Au; and performing, at least twice, a homogenizing treatment including a cold working process of the alloy ingot and a heat treatment process of heating the cold-worked alloy ingot to 1150 to 1250 C. and then rapidly cooling the heated alloy ingot.

3. The method of producing the alloy for medical use according to claim 2, wherein the cold working of the homogenizing treatment sets a working ratio to be 30% or more.

4. The method of producing the alloy for medical use according to claim 2, wherein the heat treatment process of the homogenizing treatment effects heating the alloy ingot to 1150 to 1250 C. for at least one hour and then rapidly cooling the heated alloy ingot.

5. The method of producing the alloy for medical use according to claim 2, wherein the molten and cast alloy ingot is subjected to hot forging before the homogenizing treatment.

6. The method of producing the alloy for medical use according to claim 3, wherein the heat treatment process of the homogenizing treatment effects heating the alloy ingot to 1150 to 1250 C. for at least one hour and then rapidly cooling the heated alloy ingot.

7. The method of producing the alloy for medical use according to claim 3, wherein the molten and cast alloy ingot is subjected to hot forging before the homogenizing treatment.

8. The method of producing the alloy for medical use according to claim 4, wherein the molten and cast alloy ingot is subjected to hot forging before the homogenizing treatment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a phase diagram of an AuPt alloy.

(2) FIG. 2 is a diagram illustrating XRD pattern of each of AuPt alloy samples.

(3) FIG. 3 is a diagram illustrating an XRD pattern of an AuPt alloy which is subjected to homogenizing treatment only once.

(4) FIG. 4 is a diagram illustrating measurement results of magnetic susceptibility of each of AuPt alloy samples.

(5) FIG. 5 shows imaging results of each of AuPt alloy samples by an MRI apparatus.

DESCRIPTION OF EMBODIMENTS

(6) An embodiment of the present invention will be described below. In the present invention, magnetic susceptibility measurement and probability of artifact occurrence were examined after producing an AuPt alloy with varying Pt concentration and confirming a phase structure and composition distribution of the AuPt alloy. A process of producing the AuPt alloy is as follows.

(7) Pure Au and pure Pt (both having purity of 99.99%: produced by Tanaka Kikinzoku Kogyo K. K.) were weighed to be a target composition and were subjected to high-frequency melting, whereby an alloy ingot was cast. The alloy ingot of about 60 g was produced. The molten and cast alloy ingot was subjected to hot forging. The hot forging was performed at 1000 C.

(8) Subsequently, the alloy ingot was subjected to a homogenizing treatment. As the homogenizing treatment, first, the alloy ingot was subjected to cold groove rolling and then to cold working (working ratio: 40%). Then, the alloy ingot was heated for one hour at 1200 C. Thereafter, the alloy was introduced into ice water to be rapidly cooled. The homogenizing treatment, which was a combination of the cold working and the heat treatment, was performed three times in the present embodiment. The homogenized alloy was thus subjected to groove rolling to produce an AuPt alloy wire. In the present embodiment, the AuPt alloy wire having Pt concentration of 24 to 36 mass % was produced.

(9) In the present embodiment, the AuPt alloy was produced even in production conditions in which precipitates could occur. That is, the molten and cast alloy ingot was subjected to homogenizing treatment only once in the production process, and then worked into the wire. The comparison samples were also produced for AuPt alloys having multiple compositions.

(10) First, an X-ray diffraction analysis and a composition analysis of a cross-section were performed on the produced AuPt alloy wire. The X-ray diffraction analysis was performed by measuring a measurement plane at a measurement speed of 0.2/sec using a CuK ray (45 kV, 40 mA) as an X-ray source, the measurement plane being a cross-section vertical to a longitudinal direction of the AuPt alloy wire. Additionally, the composition analysis of the cross-section was performed by setting a plurality of measurement points to perform an EDX analysis during SEM observation on the cross-section of the AuPt alloy wire.

(11) Subsequently, the magnetic susceptibility of each alloy was measured. The magnetic susceptibility measurement was performed on each of the alloy samples by use of a magnetic characteristic measuring apparatus (7T-SQUID (superconducting quantum interference element) fluxmeter manufactured by Quantum Design, Inc.). A measurement temperature was 37 C. Additionally, the presence of the artifact was evaluated using an MRI apparatus (Magnetom Sonata 1.5T manufactured by Siemens Inc.). This evaluation was performed by imaging the alloy sample fixed with an agarose gel in a Pyrex (registered trademark) test tube ( 3.5 mm) using the MRI apparatus and visually confirming whether the artifact is present or not. A gradient echo method (TR: 270 ms, TE: 15 ms) and a spin echo method (TR: 500 ms, TE: 20 ms) were used for image taking.

(12) FIG. 2 illustrates XRD patterns of each of the alloy samples. In FIG. 2, a peak of Pt (111) plane was not observed for the AuPt alloy subjected to the proper number of times of homogenizing treatment. An intensity ratio to a peak of Au (111) plane becomes zero. In contrast, FIG. 3 illustrates an XRD pattern of an alloy subjected to only one homogenizing treatment, a peak of Pt (111) plane is observed although it is weak. At this time, a peak intensity ratio was 0.05. The peak of the Pt (111) plane was considered to be due to the fact that the homogenizing treatment was insufficient and thus an .sub.2-phase could not be completely eliminated.

(13) Additionally, Table 1 indicates results obtained by performing an EDX analysis on multiple points toward both ends through the center of the cross-section of each of the alloy samples to analyze Pt concentration and measuring the maximum Pt concentration and the minimum Pt concentration. The alloy sample produced at this time was homogeneous in which no precipitate was observed also from the SEM observation, and the Pt concentration difference was 2 mass % or less. Accordingly, The Pt concentration was found to be substantially uniform over the cross-section for each alloy produced under suitable production conditions of which the homogenizing treatment was repeatedly performed several times.

(14) TABLE-US-00001 TABLE 1 Composition Pt concentration difference (mass %) Au24 Pt 1.78% Au26 Pt 1.05% Au28 Pt 1.69% Au29 Pt 1.22% Au29.5 Pt 1.00% Au30 Pt 1.25% Au31 Pt 1.21% Au32 Pt 1.30% Au33 Pt 1.54% Au34 Pt 1.33% Au35 Pt 1.05% Au36 Pt 1.65%

(15) FIG. 4 illustrates measurement results of magnetic susceptibility of each of the alloy samples. FIG. 4 shows that the magnetic susceptibility monotonously increased to a positive value with an increase of the Pt concentration in AuPt alloy produced by several repetitive homogenizing treatments. When the Pt concentration is 34 to 36 mass %, the magnetic susceptibility is 4 ppm relative to that of water and the magnetic susceptibility of 13 ppm to 5 ppm is confirmed to be exhibited.

(16) Meanwhile, for an alloy with insufficient homogenization, the magnetic susceptibility tends to increase toward the positive value to some extent with the increase of the Pt concentration. However, the value does not monotonously increase, but is jumped and becomes discontinuous in the vicinity of a preferred value. Even when the Pt concentration is 34 to 36 mass %, the magnetic susceptibility does not indicate a preferred value. Accordingly, to control the magnetic susceptibility to the preferred value, it is necessary to optimize the phase structure as well as the composition (Pt concentration).

(17) FIG. 5 shows imaging results of the homogenized AuPt alloy by the MRI apparatus used to confirm the presence or absence of the artifact occurrence. When these results are examined while the above results of the magnetic susceptibility are compared, the artifact is confirmed to have occurred in an alloy having the Pt concentration of 32% or less from spin echo images. Furthermore, the artifact is confirmed to have occurred in an alloy having the Pt concentration of 33% or less from gradient echo images. The artifact is easily observed by the gradient echo method compared to the spin echo method, and this tendency is also seen from the results in FIG. 5. Accordingly, the artifact-free AuPt alloy preferably has the Pt concentration from 34% or more to 36% or less.

INDUSTRIAL APPLICABILITY

(18) An alloy for medical use including an AuPt alloy of the present invention has suitable magnetic susceptibility to suppress an artifact. This alloy has also excellent characteristics such as biocompatibility, corrosion resistance, or workability required for the alloy for medical use. The present invention is useful for a medical appliance such as an embolus treatment coil, a clip, a catheter, a stent, or a guide wire and for a medical appliance to be used in a magnetic field environment such as an MRI.