Self-Recoverable, Stretchable, and Sensitive Wearable Sensors Based on Ternary Semi-interpenetrating Ionic Hydrogels

Self-recoverability and stretchability are critical for high-performance hydrogel sensors, but developing hydrogels with combined self-recoverability and stretchability remains a challenge. Here, self-recoverable, stretchable, and sensitive wearable sensors have been achieved based on ternary semi-interpenetrating ionic (TSII) hydrogels. A covalently cross-linked polyacrylamide (PAM) network reinforced by carboxylate cellulose nanofibrils (c-CNF) is designed as the recoverable framework. A ternary semi-interpenetrating network is constructed by simultaneously introducing polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). Because of the ternary semi-interpenetrating structure, the resulting PAM/c-CNF/(PVA-PVP) hydrogels exhibit improved stretchability and self-recoverable properties. Hydrogel strain sensors with a wide sensing range (0–750%), a high gauge factor (GF) of 5.51, low response time (∼140 ms), and excellent stability (>1000 cycles) have been fabricated by utilizing the ionic hydrogels, and wireless strain sensors have also been demonstrated by integrating the sensors into a Bluetooth signal transmission and reception system. Moreover, TSII organohydrogels are further developed by introducing a glycerol/water mixed solvent. The organohydrogels exhibit inherent adhesiveness even at −20 °C and can be applied in sensitive capacitive pressure sensors (GF = 0.97 kPa–1). Finally, various strains and pressures in daily life are monitored by the flexible sensors.