Medical Pt alloy wire and medical Pt alloy coil

Abstract

The present invention is drawn to a medical Pt alloy wire, made of a Pt—W alloy containing 10% by mass or more and 15% by mass or less of W, a balance of Pt, and inevitable impurities. The Pt alloy wire has Vickers hardness of 400 Hv or more and 600 Hv or less, and has hardness and strength superior to those of a conventional Pt alloy wire having the same composition. The Pt alloy wire of the present invention has properties preferable as a coil applied to an embolic coil or a guide wire or the like, and is also good in workability in secondary processing for producing such a medical tool.

Claims

1. A medical Pt alloy wire, comprising a Pt—W alloy containing 10% by mass or more and 14% by mass or less of W, a balance of Pt, and inevitable impurities, wherein Vickers hardness of the medical Pt alloy wire is 400 Hv or more and 600 Hv or less; and a tensile strength of the medical Pt alloy wire is 2500 MPa or more and 3500 MPa or less.

2. The medical Pt alloy wire according to claim 1, wherein an average aspect ratio of crystal grains is 30 or more in a material structure of the wire in an arbitrary cross section in a lengthwise direction.

3. A Pt alloy coil for a medical tool, formed by winding of the medical Pt alloy wire defined in claim 1.

4. An embolic coil or a guide wire, comprising the Pt alloy coil for a medical tool defined in claim 3.

5. A Pt alloy coil for a medical tool, formed by winding of the medical Pt alloy wire defined in claim 2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows photographs of a disconnection state obtained through coiling processing of Pt alloy wires having a W concentration of 12% by mass (with process annealing performed/not performed) and a W concentration of 16% by mass (with process annealing performed); and

(2) FIG. 2 shows an SEM photograph of a material structure, in a cross section in a lengthwise direction, of a Pt alloy wire having a W concentration of 12% by mass.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) A preferred embodiment of the present invention will now be described. In the present embodiment, Pt—W alloy wires having different W concentrations were produced to measure their mechanical properties and evaluate their workability.

(4) [Production of Pt Alloy Wires]

(5) First, Pt metal (purity of 99.98%) and W (purity of 99.9%) were weighed and mixed to obtain a prescribed composition, and the resultant mixture was subjected to arc melting to produce a mother alloy. The mother alloy was vacuum melted to produce a Pt—W alloy ingot in the shape of a round bar (with a diameter of 10 mm). In the present embodiment, Pt—W alloys respectively having W concentrations of 8% by mass, 10% by mass, 12% by mass, 13% by mass, 14% by mass, 15% by mass, and 16% by mass were produced to produce Pt alloy wires having respective compositions.

(6) Next, the bar-shaped Pt alloy ingot was processed into a crude wire through a hot working step. In the hot working step, the bar-shaped Pt alloy ingot was heated at 700° C. for 10 minutes, and then appropriately subjected to hot swaging and hot groove rolling, and thus, a crude wire having a wire diameter of 3.5 to 7.4 mm was formed. In this hot working step, a total area reduction rate was set to 45% or more.

(7) After the hot working step, the crude wire was subjected to cold groove rolling and cold wire drawing at room temperature, and thus processed into a diameter of 0.5 mm. Then, the resultant was subjected to a process annealing treatment by heating at 800° C. for 60 minutes in a nitrogen atmosphere to release a plastic strain.

(8) After the process annealing treatment, the resultant crude wire was subjected to cold wire drawing at room temperature, and further subjected to continuous wire drawing, and thus, the crude wire was processed into a Pt alloy wire having a wire diameter of 28 As a result of the cold working performed after the process annealing, an equivalent strain of the alloy wire was 5.8 (No. 1 to No. 4, and No. 6 to No. 9). Thereafter, the resultant was washed, and cut into samples having a length suitable for various measurements and evaluation.

(9) In the present embodiment, a sample (No. 5) of a Pt alloy wire produced from the Pt alloy having a W concentration of 12% by mass without performing the process annealing was also produced for comparison. Although this sample was not subjected to the process annealing of the present invention, a heat treatment (at 700° C. for 10 minutes) performed before the hot working corresponds to an annealing treatment. Therefore, the diameter (10 mm) of the bar-shaped alloy ingot at the time of this heat treatment corresponds to a reference in calculating an equivalent strain, and the equivalent strain is 10.4.

(10) Production conditions for the Pt alloy wires produced in the present embodiment are listed together in Table 1.

(11) TABLE-US-00001 TABLE 1 Hot Working Step Hot Swaging 1 Wire Total Area Cold Working Step Alloy Pass Area Hot Diameter Reduction Cold Cold Composition Reduction Groove after Hot Rate by Hot Process Groove Wire Wire Equivalent No. Pt W Rate Rolling Working Working Annealing Rolling Drawing Diameter Strain 1 92  8 25%, 12% — 7.4 mm 45% 800° C. 12% 15%, 12%, 28 μm  5.8 2 90 10 6% 3 88 12 6.3 mm 60% 4 5.0 mm 75% 5 — 10.4 6 87 13 12% 3.5 mm 88% 800° C.  5.8 7 86 14 8 85 15 9 84 16 * Heating is performed at 700°C for 10 minutes at the beginning of the hot working step.

(12) [Measurement of Mechanical Properties]

(13) Each of the alloy wires (having a wire diameter of 28 μm, and a sample length of 200 mm) produced as described above was measured for Vickers hardness. As a preparation for the measurement, the alloy wire was cut into a length of 15 mm or less, and the cut wires were bundled, and embedded in and fixed with a resin with the lengthwise direction set to be vertical to the bottom of the resin. The resultant resin was polished with waterproof abrasive paper and diamond slurry for exposing/polishing a measurement surface. The measurement was performed with a Vickers hardness measuring device (product name: HM-200, manufactured by Mitutoyo Corporation) under a load of 50 gf.

(14) Besides, a tensile testing machine for extra fine wires (Strograph E3-S: Toyo Seiki Seisaku-sho, Ltd.) was used to perform a tensile test on each alloy wire. Test conditions were a gauge length of 100 mm, and a cross-head speed of 10 mm/min. By this tensile test, tensile strength (UTS) was measured.

(15) Furthermore, a modulus of elasticity and a modulus of rigidity were measured by a free resonance method. As a tester, a free resonance type Young's modulus/rigidity measuring device (JE-RT, JG-RT: Nihon Techno-Plus Co., Ltd.) was used to perform the measurement at room temperature. Then, based on a resonance frequency thus measured, a modulus of elasticity and a modulus of rigidity were calculated.

(16) [Evaluation of Workability]

(17) Workability was evaluated by subjecting each wire sample to coiling processing, and determining whether or not the wire was disconnected during the processing. The coiling processing was performed with a coil index (D/d) set to 4 and by winding the wire sample around a core material (with a diameter of 0.1 mm). When an alloy wire with a length of 10 m could be processed to the last through the coiling processing, this sample was determined to have good workability (good). When a wire was disconnected during the processing, the processing was terminated at that point, and this sample was determined to have poor workability (poor). The measurement results (at room temperature) of the mechanical properties, and the evaluation results of the workability are shown in Table 2.

(18) TABLE-US-00002 TABLE 2 Alloy Mechanical Properties Evaluation Composition Process Equivalent Hardness Tensile Modulus of Modulus of of No. Pt W Annealing Strain (Hv) Strength (Mpa) Elasticity (Gpa) Rigidity (Gpa) Workability 1 92  8 800° C.  5.8 368 2450 228.3 86 good 2 90 10 455 2783 245.1 91.6 good 3 88 12 498 2996 259.1 96.6 good 4 485 2978 258.8 95.8 good 5 — 10.4 610 3056 260.1 96.8 poor 6 87 13 800° C.  5.8 518 3025 262.7 98.4 good 7 86 14 536 3149 272.7 102.1 good 8 85 15 550 3159 269.8 101.5 good 9 84 16 605 3359 280.4 103.9 poor

(19) Referring to Table 2, the Pt alloy wires having a W concentration falling in the range of the present invention (8% by mass or more and 15% by mass or less: No. 2 to No. 8) exhibit Vickers hardness of 400 Hv or more and tensile strength of 2500 MPa or more. Besides, it is understood that the hardness and the tensile strength of a Pt alloy wire increase in accordance with the increase of the W concentration. This is probably owing to strength increase of the Pt alloy by increase of the W concentration, and appropriate work strengthening by setting an equivalent strain in the cold working step.

(20) The reduction of area was measured based on the tensile test results of the Pt alloy wires No. 2 to No. 8, and as a result, the wire No. 2 (having a W concentration of 10% by mass) had reduction of area of 65%, which was the maximum value, and the wire No. 8 (having a W concentration of 15% by mass) had reduction of area of 35%, which was the minimum value.

(21) The Pt alloy wire (No. 9) having a W concentration of 16% by mass had hardness beyond 600 Hv. This Pt alloy wire was found to be poor in the workability because disconnection was caused through the secondary processing (coiling processing). Regarding the workability evaluation, FIG. 1 illustrates a disconnection state of coils obtained through the coiling processing of the Pt alloy wires having a W concentration of 12% by mass and a W concentration of 16% by mass. It is deemed, based on this result, that the hardness and the tensile strength of these Pt alloy wires are favorable, but the upper limit of the W concentration should be 15% by mass in consideration of the workability.

(22) Alternatively, in the Pt alloy wire (No. 5) obtained from the wire having a W concentration of 12% by mass without performing the process annealing to adjust an equivalent strain to 10.4, the hardness was beyond 600 Hv, and disconnection was caused in the coiling processing. Considering that the Pt alloy wires (Nos. 3 and 4) having the same W concentration and subjected to the process annealing to adjust an equivalent strain to 5.8 were good in workability, it is understood that the equivalent strain is preferably controlled to improve the mechanical properties and to ensure the workability.

(23) FIG. 2 shows an SEM photograph of a material structure, in a cross section in the lengthwise direction, of the Pt alloy wire (No. 4) having a W concentration of 12% by mass. As is understood from FIG. 2, the material structure of this Pt alloy wire contained laterally long crystal grains having a high aspect ratio. A needle structure having a very small minor axis length got into this material structure. The aspect ratios of a plurality of crystal grains measured in FIG. 2 were all 30 or more.

(24) Regarding the Pt alloy wire (No. 1) having a W concentration of 8% by mass, the tensile strength of a Pt alloy wire having the same composition described in Patent Document 1 of the conventional technique was 1850 MPa. Therefore, the Pt alloy wire of the present embodiment has strength higher than that obtained by the conventional technique even when the W concentration is 8% by mass. In the present invention, when strength increase by 50% or more as compared with that obtained by the conventional technique is set as a target value, the lower limit of the W concentration is suitably 10% by mass.

(25) Industrial Applicability

(26) A Pt alloy wire of a medical Pt—W alloy of the present invention has preferable mechanical properties and good workability. The present invention can be expected to be applied to a medical tool in the shape of a coil such as an embolic coil or a guide wire.