Pt-Co BASED ALLOY FOR MEDICAL USE

Abstract

The present invention relates to an alloy for medical use, including Pt, Co, Cr, Ni, and Mo. The alloy includes 10 atom % or more and 30 atom % or less of Pt, 20 atom % or more and 31 atom % or less of Cr, 5 atom % or more and 24 atom % or less of Ni, 4 atom % or more and 8 atom % or less of Mo, the balance Co, and unavoidable impurities, and a ratio of the Ni content (C.sub.Ni) to the Pt content (C.sub.Pt), C.sub.Ni/C.sub.Pt is 1.5 or less. The present invention can be applied to various kinds of devices for medical use, such as catheter, embolic coils, and guide wires, in addition to stents such as flow-diverter stents.

Claims

1. An alloy for medical use, comprising Pt, Co, Cr, Ni, and Mo, wherein the alloy comprises 10 atom % or more and 30 atom % or less of Pt, 20 atom % or more and 31 atom % or less of Cr, 5 atom % or more and 24 atom % or less of Ni, 4 atom % or more and 8 atom % or less of Mo, the balance Co, and unavoidable impurities, and C.sub.Ni/C.sub.Pt, which is a ratio of the Ni content (C.sub.Ni) to the Pt content (C.sub.Pt), is 1.5 or less.

2. The alloy for medical use according to claim 1, wherein the Pt content is 14 atom % or more and 30 atom % or less.

3. The alloy for medical use according to claim 1, wherein the alloy comprises W, and the W content and the Mo content is 4 atom % or more and 8 atom % or less in total.

4. The alloy for medical use according to claim 1, wherein the alloy further comprises at least any one of Ti, V, Mn, Fe, Zr, Nb, and Ta, and a total content of these elements is 10 atom % or less.

5. The alloy for medical use according to claim 1, wherein the alloy has an elastic modulus of 240 GPa or more, and a yield stress of 1680 MPa or more.

6. A stent, a catheter, a coil, a guide wire, a delivery wire, dental braces, a clasp, an artificial dental root, a clip, a staple, a bone plate, a nerve stimulation electrode, a lead for a pacemaker, or a radiation marker, comprising the medical alloy defined in claim 1.

7. A component of a medical device, comprising the medical alloy defined in claim 1.

8. The alloy for medical use according to claim 2, wherein the alloy comprises W, and the W content and the Mo content is 4 atom % or more and 8 atom % or less in total.

9. The alloy for medical use according to claim 2, wherein the alloy further comprises at least any one of Ti, V, Mn, Fe, Zr, Nb, and Ta, and a total content of these elements is 10 atom % or less.

10. The alloy for medical use according to claim 3, wherein the alloy further comprises at least any one of Ti, V, Mn, Fe, Zr, Nb, and Ta, and a total content of these elements is 10 atom % or less.

11. The alloy for medical use according to claim 2, wherein the alloy has an elastic modulus of 240 GPa or more, and a yield stress of 1680 MPa or more.

12. The alloy for medical use according to claim 3, wherein the alloy has an elastic modulus of 240 GPa or more, and a yield stress of 1680 MPa or more.

13. The alloy for medical use according to claim 4, wherein the alloy has an elastic modulus of 240 GPa or more, and a yield stress of 1680 MPa or more.

14. A stent, a catheter, a coil, a guide wire, a delivery wire, dental braces, a clasp, an artificial dental root, a clip, a staple, a bone plate, a nerve stimulation electrode, a lead for a pacemaker, or a radiation marker, comprising the medical alloy defined in claim 2.

15. A stent, a catheter, a coil, a guide wire, a delivery wire, dental braces, a clasp, an artificial dental root, a clip, a staple, a bone plate, a nerve stimulation electrode, a lead for a pacemaker, or a radiation marker, comprising the medical alloy defined in claim 3.

16. A stent, a catheter, a coil, a guide wire, a delivery wire, dental braces, a clasp, an artificial dental root, a clip, a staple, a bone plate, a nerve stimulation electrode, a lead for a pacemaker, or a radiation marker, comprising the medical alloy defined in claim 4.

17. A stent, a catheter, a coil, a guide wire, a delivery wire, dental braces, a clasp, an artificial dental root, a clip, a staple, a bone plate, a nerve stimulation electrode, a lead for a pacemaker, or a radiation marker, comprising the medical alloy defined in claim 5.

18. A component of a medical device, comprising the medical alloy defined in claim 2.

19. A component of a medical device, comprising the medical alloy defined in claim 3.

20. A component of a medical device, comprising the medical alloy defined in claim 4.

Description

DESCRIPTION OF EMBODIMENTS

[0068] Hereinafter, the embodiment of the present invention will be described. In the present embodiment, a plurality of Pt—Co based alloys (Pt—Co—Cr—Ni—Mo alloys) each having adjusted contents of Pt, Co, Cr, Ni, and Mo were produced. Subsequently, the mechanical properties (elastic modulus, elastic strain limit, and yield stress) of each alloy were measured, and further the X-ray visibility was evaluated.

[Alloy Production]

[0069] In the production of a Pt—Co based alloy, high-purity raw materials of respective metals were weighed and mixed with each other, and the mixture was melted and cast by argon arc melting to prepare an alloy ingot. Subsequently, the alloy ingot was heated at 1200° C. for 12 hours for homogenization treatment. After the homogenization heat treatment, a wire rod having a diameter of 3 mm was produced by hot swaging processing. With the use of this wire rod as a base material, a sample for a tensile test, a sample for measurement of an elastic modulus, and a sample for evaluation of X-ray visibility were produced.

[0070] In addition, the various kinds of alloys produced above were subjected to quantitative analysis in order to accurately grasp the alloy composition. In this analysis, a specimen having a length of 1 mm was collected from an alloy wire rod having a diameter of 0.5 mm in the middle of the processing, and was quantitatively analyzed by Spark ICP (trade name of device: RIGAKU SPECTRO-SASSY/CIROS-MarkII). The microscopic observation of the crystal structure was performed by the SEM-EDX analysis on cross sections of various kinds of alloy wires. The measurement points of the EDX analysis were set to 3 points or more for each sample. In all the samples, the difference between the ICP analysis value and the SEM-EDX analysis value was within ±20%, and local segregation and the like were not observed.

[Elastic Modulus Measurement]

[0071] The above-produced base material having a diameter of 3 mm was rolled to prepare a plate material (60 mm×10 mm, having a thickness of 1 mm), and the plate material was subjected to heat treatment for stress relief, and thus a sample for elastic modulus measurement was prepared. The heat treatment for stress relief was performed by the heating at 1200° C. for 4 hours in a vacuum electric furnace. The elastic modulus measurement was performed by a free resonance method under the room-temperature atmosphere with a room-temperature elastic modulus measuring device, JE-RT.

[Workability Evaluation and Tensile Test (Yield Stress Measurement)]

[0072] The above-produced base material having a diameter of 3 mm was subjected to cold wire drawing with a cemented carbide die to a diameter of 0.6 mm, and was further subjected to cold wire drawing with a diamond die to a diameter of 0.25 mm. In these cold wire-drawing workings, a carbon-based lubricant was used as a lubricant. In the working on this wire rod, the same step was repeatedly performed three times, and when the alloy cracked or broke even once during the working, the alloy was determined to have workability “defective (x)”. Further, in all of the three workings, the alloy on which the cold wire-drawing working was successfully performed to a diameter of 0.25 mm was determined to have workability “good (∘)”.

[0073] A tensile test was conducted using the alloy wire rod produced by the above cold wire-drawing working as a sample for the tensile test. The tensile test was conducted with the use of a tensile testing machine for extra-fine wire (STROGRAPH E3-S manufactured by Toyo Seiki Seisaku-sho, Ltd.). The test conditions were set to be a gauge length of 150 mm, and a crosshead speed of 10 mm/min. In this tensile test, the yield stress was measured. Further, the elastic strain limit and the rupture stress were also measured at the same time.

[X-Ray Visibility Evaluation]

[0074] The above-produced base material having a diameter of 3 mm was rolled to prepare a plate material (10 mm×10 mm, having a thickness of 0.3 mm), and the plate material was used as a sample for X-ray visibility evaluation. This sample was subjected to an X-ray transmission test under the condition of 63 kv×2.4 mA using a mobile C-arm X-ray system (Siemens Japan GEN2). The evaluation for X-ray visibility was based on the Gray-Scale value of 35NLT (No. 12 in the following Table 1), which is a conventional alloy. Alloys having a value lower than that of 35NLT was determined to have X-ray visibility “good (∘)”, and alloys having a value higher than that of 35NLT was determined to have X-ray visibility “poor (x)”.

[0075] The results of the evaluation tests conducted on the alloys, which have various kinds of compositions and produced in the present embodiment, are shown in Table 1. The evaluation test was also conducted on the 35NLT alloy being a conventional medical alloy.

TABLE-US-00001 TABLE 1 Mechanical property Elastic Yield Elastic Rupture Composition (at %) modulus stress strain stress X-Ray No. Pt Cr Ni Mo Co W C.sub.Ni/C.sub.Pt (GPa) (MPa) limit (%) (MPa)*.sup.1 visibility Workability Category 1 29.98 23.94 5.24 5.82 Balance — 0.17 242 2360 1.0% 2411 ◯ ◯ Example 2 27.00 23.91 8.22 5.83 Balance — 0.30 251 2325 0.9% 2415 ◯ ◯ 3 20.35 23.85 14.87 5.79 Balance — 0.73 282 2295 0.8% 2385 ◯ ◯ 4 17.61 23.88 17.61 5.88 Balance — 1.00 275 2159 0.8% 2244 ◯ ◯ 5 14.84 23.82 20.38 5.94 Balance — 1.37 270 2099 0.8% 2171 ◯ ◯ 6 15.95 20.20 18.80 5.88 Balance — 1.18 243 1965 0.8% 2015 ◯ ◯ 7 15.11 30.58 18.12 5.88 Balance — 1.20 253 2235 0.9% 2281 ◯ ◯ 8 14.80 22.95 20.10 4.10 Balance — 1.36 257 2085 0.8% 2245 ◯ ◯ 9 14.20 22.90 19.30 7.90 Balance — 1.36 249 2254 0.9% 2298 ◯ ◯ 10 8.90 27.90 14.90 7.60 Balance — 1.67 218 2120 1.0% 2230 ◯ ◯ Comparative 11 35.22 23.83 — 5.78 Balance — — NA*.sup.2 ◯ X Example 12 33.20 23.81 4.35 5.88 Balance — 0.13 231 2354 1.0% 2369 ◯ ◯ 13 15.63 18.24 18.32 5.88 Balance — 1.17 238 2010 0.8% 2198 ◯ ◯ 14 15.67 33.53 19.22 5.88 Balance — 1.23 214 2311 1.1% 2344 ◯ ◯ 15 14.66 22.85 19.83 3.10 Balance — 1.35 221 2085 0.9% 2245 ◯ ◯ 16 14.80 22.89 20.10 8.28 Balance — 1.36 211 2310 1.1% 2398 ◯ ◯ 17 11.82 23.91 23.40 5.83 Balance — 1.98 237 2013 0.8% 2185 ◯ ◯ 18 10.21 23.85 25.01 5.85 Balance — 2.45 231 1945 0.8% 2007 ◯ ◯ 19 14.20 22.99 19.30 4.88 Balance 1.00 1.36 241 2052 0.9% 2154 ◯ ◯ Example 20 14.20 22.94 19.30 4.00 Balance 4.00 1.36 242 2020 0.8% 2088 ◯ ◯ 21 — 22.90 33.50 6.20 Balance — — 232 2068 0.9% 2275 X ◯ Conventional Example *.sup.1Measurement value after cold working *.sup.2A sample for tensile test could not be produced due to the breaking of wire during cold wire-drawing working.

[0076] From Table 1, all of the Pt—Co based alloys (No. 1 to No. 9, and No. 19 to No. 20), each of which is within the composition range specified in the present invention and has a suitable ratio (C.sub.Ni/C.sub.Pt) of the Ni content (C.sub.Ni) to the Pt content (C.sub.Pt), exhibited a suitable elastic modulus of 240 MPa or more and had favorable X-ray visibility and workability. Further, the elastic strain limit exceeded 0.7%. The measurement samples were alloy wire rods after cold working, and all of which had a rupture stress exceeding 2000 MPa. In this regard, it was also confirmed that the alloy of No. 5 had a rupture stress of 1000 MPa or more when the alloy wire rod was further annealed and a rupture stress was measured.

[0077] The alloys outside the specification of the present invention were inferior to the alloys of the above examples in any one of the properties.

[0078] The alloy of No. 21, which corresponds to the 35NLT alloy being a conventional example, had a low elastic modulus of less than 240 MPa and poor X-ray visibility. The present invention is an alloy having a suitable composition of other constituent elements such as Ni while Pt is added to the Co—Cr based alloy being a conventional alloy. However, the alloy having a low content of Pt even with the addition of Pt, such as the alloy of No. 10, had a clearly low elastic modulus, and the elastic modulus was lower than that of the conventional example (No. 21). Even if Pt is added, a proper amount should be added.

[0079] In addition, with regard to the action of Ni, the alloy (No. 11) without the addition of Ni had poor workability and failed to be processed into a wire rod. It can be deemed it is indispensable for the present inventive medical alloy to be processed into a wire rod or the like, and also deemed that Ni is essential for that purpose. However, even if Ni is added, when the additive amount of Ni is less than 5 atom % as in the alloy of No. 12, the elastic modulus is low even though the workability is improved. Therefore, it is considered that there is a proper range also for the additive amount of Ni.

[0080] In this regard, the ratio (C.sub.Ni/C.sub.Pt) of the Ni content (CN) to the Pt content (C.sub.Pt) will be investigated. This investigation was performed with the comparison of the alloys of No. 1 to No. 5, No. 17, and No. 18, in each of which the contents of additional elements (Cr and Mo) other than Pt and Mo are approximated.

[0081] The alloy of No. 1 is an alloy having a composition in which the Pt content is in the vicinity of the upper limit and the Ni content is in the vicinity of the lower limit, and having the lowest value of C.sub.Ni/C.sub.Pt (C.sub.Ni/C.sub.Pt=0.17). This alloy was evaluated as acceptable in terms of the elastic modulus, the workability, and the like. Further, the elastic modulus increases as the value of C.sub.Ni/C.sub.Pt increases. However, as in the alloys of No. 17 and No. 18, when the C.sub.Ni/C.sub.Pt exceeds the upper limit value (1.5) specified in the present invention and becomes in the vicinity of 2.0 or more, the elastic modulus decreases, and becomes less than 240 MPa. Therefore, the need to make the C.sub.Ni/C.sub.Pt appropriate was confirmed even for an alloy having a composition range of the present invention.

[0082] In the present invention, Mo is also an essential constituent metal, and it can be understood that with the comparison of the alloys of No. 5, No. 8, No. 15, and No. 16, in each of which the contents of constituent elements other than Mo are approximated, the elastic modulus tends to be low regardless of whether the Mo content is high or low. In the Pt—Co based alloy (Pt—Co—Cr—Ni—Mo alloy) of the present invention, it can be confirmed that there is an optimal range of 4 atom % or more and 8 atom % or less for the amount of Mo.

[0083] In addition, in the present invention, W is mentioned as an element having an effect similar to that of Mo, but it was confirmed that even the alloy to which W had been added exhibited favorable strength, workability, and the like, from the results of the alloys of No. 19 and No. 20.

[0084] In addition, from the results of the alloys of No. 13 and No. 14, it was also confirmed that the elastic modulus was less than 240 MPa when the Cr content was outside the specified range of the present invention.

INDUSTRIAL APPLICABILITY

[0085] The medical alloy of the present invention is a Pt—Co based alloy having good mechanical properties, X-ray visibility, and workability. The present invention can be expected to be applied to stents such as flow-diverter stents, or stent retrievers, catheters such as balloon catheters, coils such as embolic coils, and various kinds of medical devices such as guide wires, delivery wires, dental braces, clasps, artificial dental roots, clips, staples, bone plates, nerve stimulation electrodes, leads for pacemakers, and radiation markers.