Longevity Expectations for Polymers in Medical Devices Demand New Approaches to Evaluating Their Biostability

Ten years after a new poly(dimethylsiloxane)urethane material was introduced as part of a long-term medical device implant, an unexpectedly high rate of in-service degradation was observed. The chemical signatures of molecular degradation in the materials were not identified during the comparatively short preclinical assessment of biostability. This outcome highlights the need to transform the assessment of biostability for new materials used in long-term implanted medical devices to protocols that rely more heavily on accelerated in vitro testing. The industry has over-relied on in vivo exposure to assess the stability of a material due to the perceived complexities associated with the accurate simulation of the biological environment. Strategically designed accelerated in vitro testing can provide important insights into the long-term biostability of materials: insights that cannot be readily gleaned through the in vivo studies that dominate current regulatory guidelines. Real-time validation of previously published accelerated data combined with clinical observations substantiates the accelerated approach and creates a compelling case for shifting the emphases in biostability assessment, especially for devices that have anticipated lifespans that exceed a decade.