A robust and transparent nanosilica-filled silicone rubber coating with synergistically enhanced mechanical properties and barrier performance

Implantable electronic devices (IEDs) are widely used by human beings to achieve medical treatment and diagnosis nowadays. However, ideal encapsulation of IEDs is still far from perfect as full prevention of body fluid diffusion into the coating remains unsolved. Herein, we develop a high-performance composite coating for IED encapsulation by introducing SiO2 nanoparticles into silicone rubber, which synergistically enhances mechanical properties and improves barrier performance. By fabricating composite coatings with different nanosilica contents, 3% nanosilica is proved to be an optimal additive content with an excellent combination of improved fracture strength (from 2.5 MPa to 4.5 MPa), increased coating resistance (from 104 to 109 Ω cm2) and ideal coating uniformity. Mechanical and electrochemical characterizations subsequently confirm substantially enhanced mechanical properties and barrier performance of the composite coating, which effectively resist crack propagation and impede penetrations of water and chloride ions through the coating. Theoretical calculations further uncover that modified SiO2 particles with enriched methyl groups endow a strong bridging effect to interact with silicone rubber monomer, which, together with anti-agglomeration property of methyl groups, contributes to a pronounced improvement in mechanical performance of nanosilica-filled silicone rubber. Benefitting from the enhanced mechanical and barrier properties, the as-fabricated nanosilica-filled silicone rubber demonstrates superior protection for the encapsulated circuits with a significantly improved lifetime (709.1 h) compared to that of circuits coated by pure silicone rubber (472.8 h) and bare circuit boards (1 h), which offers great values for packaging material design in future IED encapsulation.