Abrasion and ion elution of implantable metallic electrode in bending-rotating fatigue testing

作为FES（功能性电刺激）电极应用的基础研究，通过旋转弯曲试验研究了不锈钢钢丝绳和钛丝在310 K模拟体液中的疲劳特性。(1)在较低的最大弯曲应力水平下，新型不锈钢（Fe-22Cr-10Ni-6Mn-2Mo-0.4N）钢丝绳比SUS3 16L型钢丝绳具有更高的疲劳强度和耐磨损腐蚀性能。(2)随着疲劳试验循环次数的增加，乳酸溶液中的金属离子浓度呈上升趋势，这与不锈钢的化学成分一致。另一方面，在Hanks溶液中，它们在低水平被抑制，离子洗脱量的顺序为Ni>Cr>Fe。(3)疲劳试验过程中，在Hanks溶液中形成了铁氧氢氧化物（β-FeOOH）作为腐蚀产物，这可能使Hanks溶液中的铁和铬离子保持在低浓度。(1)新型β型钛合金Ti-14Mo-3Nb-1.5Zr丝与cpp ti丝相比，具有优异的疲劳强度。(2) cpp ti丝的疲劳极限σ_f与抗拉强度σ_U之比小于30%，这可能是由于冷加工过程中引入的表面缺陷所致。(3)类金刚石碳（DLC）涂层的cpp ti丝的σ_f/ σ_U值较高。结果表明，优化DLC涂层工艺可以提高钛丝的疲劳寿命。

The fatigue properties of stainless steel wire ropes and titanium wires in simulated body fluids at 310 K were investigated in rotating-bending testing as a fundamental study for applications to the FES (Functional Electrical Stimulation) electrode.1.Stainless steel wire rope(1)The new stainless steel (Fe-22Cr-10Ni-6Mn-2Mo-0.4N) wire rope exhibited the higher fatigue strength and wear corrosion resistance than the type SUS3 16L stainless steel wire rope under low maximum bending stress level.(2)The metal ion concentrations in the lactic acid solution increased with increasing of number of cycles in fatigue testing, which agreed with the chemical composition of the stainless steels. On the other hand, in Hanks' solution, they are suppressed at the low level, and the order of the amounts of ion elution was Ni>Cr>Fe.(3)The ferric oxyhydroxides (β-FeOOH) was formed in Hanks' solution as corrosion products during fatigue testing, which might keep iron and chromium ions at low concentration in Hanks' solution.2.Titanium wires(1)The wire made of the new β-type titanium alloy, Ti-14Mo-3Nb-1.5Zr, had excellent fatigue strength compared with the C.P.Ti wire.(2)The ratio of fatigue limit (σ_f) to tensile strength (σ_U) of the C.P.Ti wire was less than 30 percent, which might be caused by the surface flaws introduced during the cold working process.(3)The C.P.Ti wire with diamond like carbon (DLC) coating exhibited the relatively high value of σ_f/ σ_U. This result suggests that the fatigue life of the titanium wire can be improved by the optimization of the DLC coating process.