Zwitterionic polyurethane thin films enabling wet conformal adhesion to dynamic tissues

Abstract

Achieving conformal adhesion on dynamically deformable tissues in vivo remains a major challenge. Conventional polymer thin films, owing to their intrinsically low bending stiffness, have been widely used in epidermal electronics; however, their performance in vivo remains unsatisfactory. Here, zwitterionic polyurethane (ZWPU) is synthesized by grafting sultone onto the tertiary amine units of the polyurethane backbone and processed into large-area thin films with a thickness of 200–1200 nm using bar coating. ZWPU thin films retain the elasticity of elastomers, exhibiting elongation at break exceeding 500%. The incorporation of zwitterionic groups imparts excellent antifouling capability for in vivo applications and, more importantly, promotes the formation of a hydration layer. This hydration layer would enable synergistic “liquid bridge” and “molecular bridge” effects that significantly enhance frictional interactions with wet tissue surfaces. In case studies, transferring ZWPU thin films onto edematous mouse brains and expanded rabbit lungs demonstrates unprecedented wet conformal adhesion to dynamic tissues, sustaining stretch ratios up to 150% without slippage or fracture. These findings establish ZWPU thin films as a promising material for implantable bioelectronics and advanced biointerfaces.