Medical Device Corrosion Testing per ASTM F2129

人体及其免疫和炎症机制可以为金属植入物创造一个具有侵略性的环境，导致植入物排斥和失败(吉尔伯特), Corrosion, 2017;73(12):1478-1495). 小型植入物的体外测试通常根据ASTM F2129进行，以减轻这些风险. 虽然这种测试有助于确定植入物对腐蚀的敏感性, it does not take into account the effects of cells, proteins, 以及植入物在体内会经历的其他生物效应.

Despite its limitations, ASTM F2129自2001年最初出版以来经历了几次修订，以更好地帮助医疗器械制造商评估其小型植入物对点蚀和缝隙腐蚀的抵抗力. 该标准提供了一种测试方法，用于在整个设备的最终形状和成品上进行循环(正向和反向)动电位极化测量.

In the sections below, we describe the test methods, apparatus, results and acceptance criteria used in vitro corrosion testing of small implants.  

Test Apparatus  

采用典型的多通道电化学试验池进行试验. 有氮气和热水循环的进/出口, ports for the reference, graphite counter and working/sample electrodes, and an inner chamber for the saline bath.  

Additional components include potentiostat, computer, pH meter, nitrogen tank, water pump, conductive epoxy with UV lamp and mask for curing, and stainless steel wire for sample attachment. 磷酸盐缓冲盐水等试剂用于洗浴, 和异丙醇和II型试剂级水用于样品冲洗. 光学和电子扫描显微镜用于测试前后的检查.   

Test Method 

Table 1 provides a brief terminology summary; for further details consult the ASTM F2129 standard.

简单地说，将植入物置于37±1°C的生理盐水中，初始pH值为7.4±0.2 in the setup shown on the right. 在植入物和参考电极之间引入电位，并上升到上述生理电位. 击穿通常会导致电流密度迅速增加, as evidenced by the output plot of potential vs. log current density. 需要计算或估计暴露在溶液中的样品的总表面积，以便确定样品产生的电流密度.

样品准备测试和彻底检查. 任何预处理都应该进行，因为它会影响植入物的行为. 导电环氧树脂用作与样品的接口(试样支架根据设备类型而变化), connected to a potentiostat through a wire, and resistance is checked to ensure a good connection. The test cell is filled with saline (minimum of 500 mL, typically 1L), heated to the target temperature, and nitrogen gas flow at 150 mL/min is initiated. 氮气流用于使溶液脱氧和降低溶解氧浓度，以降低氧化和还原电流相等时的电位. 

Temperature, pH, and nitrogen gas flow time (30 min minimum) are recorded, 然后将该装置冲洗干净，用导线插入测试单元. Saline is added into the reference electrode holder, 电极插入距离样品5mm或更小, but not in contact with the sample. The nitrogen purge is continued throughout the test. The open circuit test is initiated, and E_r is recorded after 1 hour. 然后，设置E，以1 mV/s的扫描速率启动循环极化测试_i and E_f to E_r. The cyclic polarization is closely monitored; if a current density increase larger than two decades occurs, voltage is reversed. 

试验完成后，最终温度、pH值、E_r, E_b, Ef, and E_p are recorded. The sample is removed from the test and rinsed, the wire is clipped ~1 inch above the sample, 样品被储存起来，以备进一步的测试后检查. 而标准并没有规定需要检测多少样品, we typically see 3-8 samples per surface finish.   

Test Results

记录每个样品的测试条件:氮气流动时间, initial temperature, initial pH, final temperature, and final pH. 样本测试结果通常以表格和图形格式提供. 还提供了试验前后的观察和检查结果. 

上图显示了镍钛诺装置8个样品的腐蚀测试结果，用电位(mV) vs. log current (A). Results show consistency between the 8 samples; the purple data set with the increase in current density is an example of a breakdown potential.

Acceptance Criteria 

ASTM F2129没有定义验收标准，但确定了E_b 作为坑形核和生长的关键数据点. Therefore, the higher the E_b 是不是金属越耐点蚀. It is also recommended that E_b 作为参考，将值与在体内表现出良好耐腐蚀性的谓词装置的值进行比较. 器械制造商为其植入物定义可接受标准. In our experience, acceptable E_b 值通常设置在300mv以上，它们通常设置在更高的阈值. 

Consultation

We often perform corrosion testing 在医疗设备上表征其腐蚀电位. If you would like more information about our medical device corrosion testing 服务，或协助您的设备的腐蚀和/或疲劳测试， contact our Engaged Experts to discuss how we can help.

Element提供最广泛的医疗设备测试, so if you are looking for services such as package testing, microbiological analysis, accelerated aging-shelf life testing，或EMC/EMI测试，请im体育APP以连接合适的实验室.