Standard Practice for Maintaining Oxidative Capacity of Test Solutions for Degradation Screening of Non-Absorbable Polymers

Abstract

4.1 This standard practice summarizes a method to maintain the oxidative capacity of test solutions, in line with the recommendations of ISO 10993-13. The approach outlined in this standard practice is applicable for ongoing monitoring and maintenance of hydrogen peroxide (H2O2) concentrations in aqueous test solutions, ensuring consistency for oxidative degradation screening of non-absorbable polymers at both ambient and elevated temperatures over extended durations. The system outlined in this standard practice utilizes the electrochemical activity of H2O2 for continuous detection and monitoring of H2O2 concentration and an integrated feedback loop, activated by a microcomputer when the H2O2 concentration in the test solution drops below a predefined threshold. The electrodes facilitate the oxidation and reduction reactions of H2O2, and the resulting current serves as a measurable indicator of its electrochemical activity. This current is employed as a benchmark for H2O2 concentration, determined through a calibration against a set of test solutions with known H2O2 concentrations. 4.2 While this standard practice can be used for in vitro oxidative degradation screening of non-absorbable polymers as per ISO 10993-13, it does not make clinical predictions due to the potential disparity in simulating the in vivo conditions of a polymeric medical device post-implantation. Users are recommended to assess the applicability of this practice to their specific device or material. This methodology considers polymer degradation through hydrolytic and oxidative chemical pathways of the finalized polymeric device. It does not account for degradation induced during the device's intended use by mechanical stress, wear, electromagnetic radiation, or biological factors such as enzymes, other proteins, or cellular activity. 4.3 An illustrative example of a test system is described in this standard practice, which employs open-source components and a two-electrode setup comprising a platinum (Pt) microelectrode as the working electrode and a graphite rod serving as the counter and reference electrode. Furthermore, an exemplar protocol is offered, delineating electrochemical parameters utilized for the measurement of H2O2 concentration in aqueous test solution. As electrochemical systems are inherently sensitive to test conditions, users are advised that optimization of electrochemical parameters may be necessary, contingent on the type of electrodes, potentiostats, or other components integrated into their respective system. Users are recommended to document the range of H2O2 concentrations within which reliable monitoring is feasible, contingent upon the observed linear relationship between the current generated by the electrodes of the chosen electrochemical setup and H2O2 concentration in the test solution. 4.4 Users have the flexibility to adopt the provided example test system, inclusive of the specified electrochemistry parameters, should their components mirror those in this practice. However, if alternative components are employed, users are recommended to optimize the electrochemistry parameters to ensure the accuracy and reliability of their results.