Self-Adhesive, Anti-Freezing Multifunctional Zwitterionic Hydrogels with Lignin-Promoted Rapid Gelation for Flexible Strain Sensors

Hydrogel holds great promise as a strain sensor for flexible electronics. However, traditional hydrogel polymerization processes are hindered by extensive time and energy demands. Additionally, the inadequate adhesion of hydrogel sensors to human skin in extreme conditions often results in signal instability and inaccuracy. To address these challenges, herein, a novel lignin-assisted self-catalytic system (lignin-Fe3+) has been developed to rapidly fabricate self-adhesive and antifreezing multifunctional zwitterionic hydrogels (L-Fe@HE-AA/DMAPS hydrogels) in a water (H2O)–ethylene glycol (EG) solution. The incorporation of EG and zwitterionic [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide (DMAPS) endows the hydrogels with remarkable anti-freezing property over a wide temperature range from −60 to 60 °C, enhanced non-drying properties (73.7% retention), excellent self-adhesion (110.0 ± 3.1 kPa on paper), and excellent mechanical properties (236.15 kPa fracture stress, 556.8% fracture elongation). Leveraging the comprehensive integration of these properties, the zwitterionic hydrogels were assembled as strain sensors, exhibiting high sensitivity (Gauge factor = 6.044), fast response (198 ms), and impressive signal stability. The design of L-Fe@HE-AA/DMAPS hydrogels via a lignin-Fe3+ self-catalytic system and zwitterionic DMAPS presents a promising strategy for practical applications in skin strain sensors.