Can a Critical Breakdown Potential Be Established for Electrochemical Corrosion Testing of Medical Devices According to ASTM F2129?

Cyclic potentiodynamic polarization has been widely used to evaluate the corrosion susceptibility of small metallic implantable medical devices. The origination of ASTM F2129 in 2001 has given researchers a platform for attempting to develop clinically relevant standardization of corrosion testing. Currently, there are no studies that establish a clear relationship between the outcomes of this test and the physiologic conditions that drive corrosion in vivo.

One proposal is that a device tested according to ASTM F2129 that exhibits a breakdown potential (EB) greater than 600 mV will have favorable clinical corrosion resistance, while a device with an EB between 300 mV and 600 mV will have marginal clinical corrosion resistance, and a device with an EB below 300 mV will have unacceptable behavior in vivo. However, these proposed limits do not account for variability in results caused by using different formulations of phosphate buffered saline (PBS) as the test solution. Additionally, this proposal does not correlate electrochemical corrosion test results of marketed devices with reported in vivo corrosion behavior.

In this study, the EB of devices tested according to ASTM F2129 in different formulations of PBS is investigated. Also, cyclic potentiodynamic polarization results of US marketed devices with a history of favorable corrosion behavior in vivo are presented. The results demonstrate that results above and below 600 mV can be obtained by varying only the formulation of PBS, and clinically proven devices can have breakdown potentials below 300 mV. Therefore, until a blood analog is developed such that the relationship between clinical corrosion behavior and in vitro electrochemical corrosion testing of medical devices has been established, setting a specific EB as an acceptance criterion is not scientifically valid. ASTM F2129 should only be used to perform statistical comparisons to approved devices with a history of favorable corrosion behavior in vivo.