Hydrogen-bonded network enables polyelectrolyte complex hydrogels with high stretchability, excellent fatigue resistance and self-healability for human motion detection

Polyelectrolyte complex hydrogel (PECH) is an emerging ion conductive hydrogel made from non-covalent interacted oppositely charged polyelectrolytes in water. However, the construction of PECH with high stretchability, excellent fatigue resistance and self-healability is heavily demanded while remaining a profound challenge. Herein, a hydrogen-bonded network densification strategy is presented for preparing a highly stretchable and deformation-tolerant PECH hydrogel (Fe/CS/PAA), which is composed of an anionic Fe3+-coordinated polyacrylic acid network (Fe-PAA) and cationic Fe3+-coordinated chitosan network (Fe-CS). Benefiting from the formation of dense hydrogen-bonded network between the Fe-PAA and Fe-CS networks activated by salt impregnation, the resultant densified hydrogen-bonded Fe/CS/PAA hydrogel (DHB-Fe/CS/PAA) exhibits large tensile strength (~0.34 MPa), high stretchability (~1370%), low-temperature resistance to −25 °C, and heat-accelerated self-healability. Due to its high stretchability, excellent fatigue resistance and high ionic conductivity, the DHB-Fe/CS/PAA can readily work as a stretchable ionic conductor for skin-inspired ionic strain sensor, displaying high sensitivity in a wide strain range (0.5%–500%), fast response time (<180 ms) and excellent durability for 500 cycles at a 100% strain. Besides, the as-assembled ionic sensor is capable of maintaining high ionic conductivity and mechanical robustness at a sub-zero temperature of −25 °C ascribing to the presence of high-concentration charged functional groups and impregnated salts. As a demonstration, a wearable DHB-Fe/CS/PAA ionic sensor in a resistive mode is assembled, demonstrating high sensitivity, wide response range and excellent cyclability in detecting and distinguishing complex human motions rapidly and in real-time.