Anti-Swelling Dual-Network Zwitterionic Conductive Hydrogels for Flexible Human Activity Sensing

Conventional conductive hydrogels are susceptible to swelling in aquatic environments; which compromises their mechanical integrity; a limitation that poses a potential challenge to their long-term stability and application. In this study, a zwitterionic ion-conductive hydrogel was fabricated from polyvinyl alcohol (PVA), acrylic acid (AA), and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SMBA), forming a dual-network structure. A copolymer of zwitterionic SBMA and AA formed the first network, and PVA formed the second network by repeated freeze-thawing. The equilibrium state of zwitterionic SBMA was modulated by AA to protonate the SBMA, which resulted in the conversion of -SO₃^- to -SO₃H; thus, hydrogels had the anti-swelling property driven by electrostatic repulsion. In addition, the prepared hydrogels possessed excellent mechanical properties (tensile strength of 0.76 MPa, elongation at break of 322%, and compressive strength of 0.97 MPa at 75% compressive strain) and remarkable anti-swelling properties (80% swelling after 120 h of immersion). Owing to the zwitterionic nature of SBMA, the hydrogel also showed inherent antimicrobial properties and high electrical conductivity, which could be capable of monitoring human movement and physiological signals. This work provides a facile strategy for designing hydrogels with remarkable mechanical properties and anti-swelling characteristics, expanding the application environment of hydrogels in flexible sensing.