Role of BSA adsorption in the evolution of polyimide coating performance

Polyimide (PI) encapsulation for implantable electronic devices (IEDs) must resist complex in vivo microenvironments, and its reliability directly determines device service life. However, existing PI coating research has focused primarily on single performance optimization, lacking mechanism-based rational design strategies. To fill this gap, we systematically examined the impact of protein on the degradation behavior of PI encapsulation coatings and the associated interaction mechanisms. The results show that bovine serum albumin (BSA) is capable of forming a dense, stable adsorption layer on the surface of PI. After adsorption, BSA rearranges its conformation and retains stable overall structure. The secondary structure is dominated by α-helix and random coil, and its three tertiary conformations achieve uniform distribution. With a molecular size of 10–20 nm, BSA is much larger than the pore size of PI coatings (the most probable pore size is 3.822 nm). The adsorbed BSA layer seals surface micropores and restricts water penetration, cutting water permeation by 66% and extending coating service life. Notably, BSA adsorption does not alter the intrinsic failure mode of the PI coatings, as coating failure is still dominated by blistering defects caused by the deterioration of interfacial bonding strength.