Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, Maryland, 20993, USA.
J Biomed Mater Res B Appl Biomater. 2021 Aug;109(8):1188-1197. doi: 10.1002/jbm.b.34781. Epub 2020 Dec 19.
Nitinol exhibits unique (thermo)mechanical properties that make it central to the design of many medical devices. However, nitinol nominally contains 50 atomic percent nickel, which if released in sufficient quantities, can lead to adverse health effects. While nickel release from nitinol devices is typically characterized using in vitro immersion tests, these evaluations require lengthy time periods. We have explored elevated temperature as a potential method to expedite this testing. Nickel release was characterized in nitinol materials with surface oxide thickness ranging from 12 to 1564 nm at four different temperatures from 310 to 360 K. We found that for three of the materials with relatively thin oxide layers, ≤ 87 nm nickel release exhibited Arrhenius behavior over the entire temperature range with activation energies of 80 to 85 kJ/mol. Conversely, the fourth ''black-oxide'' material, with a much thicker, complex oxide layer, was not well characterized by an Arrhenius relationship. Power law release profiles were observed in all four materials; however, the exponent from the thin oxide materials was approximately 1/4 compared with 3/4 for the black-oxide material. To illustrate the potential benefit of using elevated temperature to abbreviate nickel release testing, we demonstrated that a > 50 day 310 K release profile could be accurately recovered by testing for less than 1 week at 340 K. However, because the materials explored in this study were limited, additional testing and mechanistic insight are needed to establish a protective temperature scaling that can be applied to all nitinol medical device components.
镍钛诺具有独特的（热）力学性能，这使其成为许多医疗器械设计的核心。然而，镍钛诺的名义上含有 50%的原子镍，如果释放量足够大，可能会对健康产生不利影响。虽然通常使用体外浸泡试验来表征镍钛诺器械的镍释放，但这些评估需要很长的时间。我们已经探讨了升高温度作为加速这种测试的潜在方法。在四个不同温度（310 至 360 K）下，研究了表面氧化层厚度从 12 至 1564nm 的四种镍钛诺材料中的镍释放情况。结果发现，对于三个氧化层相对较薄的材料，≤87nm 的镍释放表现出整个温度范围内的 Arrhenius 行为，激活能为 80 至 85kJ/mol。相反，第四个“黑氧化物”材料，具有更厚、更复杂的氧化层，不能用 Arrhenius 关系很好地描述。在所有四种材料中都观察到幂律释放曲线；然而，与黑氧化物材料的 3/4 相比，薄氧化层材料的指数约为 1/4。为了说明使用高温缩短镍释放测试的潜在好处，我们证明了在 340 K 下测试不到 1 周即可准确恢复 >50 天 310 K 的释放曲线。然而，由于本研究中所研究的材料有限，需要进行更多的测试和机理研究，以建立可应用于所有镍钛诺医疗器械部件的保护温度缩放。
