Bioinspired Low-Friction and High-Stability Hydrophilic Coatings for Capsule Endoscopy Surfaces

Polycarbonate (PC)-based capsule endoscopes (CEs) face significant challenges such as high friction against gastrointestinal mucosa, susceptibility to biofouling (including protein adsorption and bacterial adhesion), and inadequate stability of surface modifications, all of which impair clinical performance and patient safety. To overcome these limitations, this study introduces a bioinspired composite coating based on polydopamine (PDA) and zwitterionic polymers. A one-step oxidative codeposition approach was utilized to graft poly(sulfobetaine methacrylate) (PSBMA), along with control polymers using sulfopropyl methacrylate (SPMA) and 2-methacryloxyethyl phosphorylcholine (MPC), onto PC substrates via a PDA interlayer, resulting in robust PC-PDA&PSB and related composite coatings. Comprehensive characterization─including XPS, SEM, and AFM─verified successful coating deposition and revealed that the incorporation of zwitterionic polymers transformed the initially coarse PDA aggregates into uniform and continuous structures. Then, the composite coatings demonstrated synergistic functional improvements: the PC-PDA&PSB coating achieved a water contact angle of 14.3 ± 3.1°, an ultralow coefficient of friction (<0.05) in different aqueous conditions, over 80% suppression of BSA/BFG adsorption, and sustained stability after 14 days in pH 1.5 PBS. Finally, in vitro cytocompatibility assessments (CCK-8 and Live/Dead staining) confirmed noncytotoxicity, with cell viability exceeding 80%, in compliance with ISO 10993-5. This strategy effectively addresses the poor adhesion often associated with zwitterionic polymer coatings alone and provides a scalable surface modification platform for enhancing the safety and functionality of CEs. It also holds considerable promise for other biomedical devices requiring slippery and antifouling properties.