The role of water transport in the failure of silicone rubber coating for implantable electronic devices

Abstract

Implantable electronic devices (IEDs) are increasingly used in medical treatment and diagnose for physiological monitoring. However, encapsulation of IEDs still faces significant challenges as full prevention of body fluid penetration into the coating remains unsolved. To enable an extended lifecycle for IEDs, the impact of water transport on the failure mechanism of silicone rubber coating was systematically investigated in this study. Water absorption and morphology characterization firstly illustrate the water diffusion model and demonstrate the presence of cracks inside the silicone rubber coating, respectively. Subsequent electrochemical characterizations further verify a three-step water penetration behavior in the coating/substrate system, and meanwhile quantify the crack growth and evolution. By further experimental and finite element studies, it is proved that crack propagation is responsible for coating failure in IEDs, while a comprehensive failure mechanism of medical silicone rubber coating in simulated body fluid is also uncovered in a detailed manner for the first time. Such a clear elucidation of failure mechanism for silicone rubber coating is greatly beneficial for future packaging material design for IEDs.