Anti-swelling Zwitterionic Gels with High Stretchability, Conductivity for Wireless Underwater Strain Sensing

Gel-based flexible wearable sensors have attracted considerable interest in aquatic environments. However, the development of underwater conductive gel sensors with outstanding anti-swelling, mechanical, and sensing capabilities faces significant challenges. The aim of this study is to develop anti-swelling and conductive zwitterionic gels and investigate their applications in wireless underwater strain sensing. Multi-functional zwitterionic gels were fabricated by copolymerizing [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) and acrylic acid (AA) in a mixed solution of aluminum chloride (AlCl 3 ) and poly(vinyl alcohol) (PVA) under ultraviolet light (360 nm). PSBMA was switched from a neutral polymer to a positively charged polymer because of the combination of Al 3+ with the negative groups SO 3 − . The water molecules were eliminated because of electrostatic repulsion. The gels exhibited anti-swelling properties (swelling ratio <11%), high stretchability (600% strain), and toughness (2451 kJ/m 3 ). The PPAS-Al 3+ gel was integrated with a wireless Bluetooth system to construct underwater wearable strain sensors that could accurately capture the signals caused by human joint movements and speech recognition even in water. Antibacterial activity (>98.9% inhibition) and stable wireless sensing have potential applications in the fields of wearable sensors, underwater communication, and intelligent healthcare.