Starch/polyvinyl alcohol with ionic liquid/graphene oxide enabled highly tough, conductive and freezing-resistance hydrogels for multimodal wearable sensors.

With ever-growing demand for eco-friendly materials for wearable electronics, biopolymer-based hydrogels have drawn significant attention. As one of the most abundant and biodegradable biopolymers, starch-based hydrogels have a great potential for wearable electronics. However, mechanical fragility, low conductivity and subzero freeze restrict their applications. Here, a multifunctional hydrogel was facilely fabricated by integrating ionic liquid and graphene oxide into potato starch/polyvinyl alcohol skeleton via a green physical-crosslinking method. The abundant hydrogen-bond and electrostatic interactions endowed the hydrogel with excellent stretchability (657.5 %), strength (0.64 MPa), high conductivity (1.98 S·m) and good anti-freezing property (< -20 °C). Multiple characterizations and theoretical simulation (DFT) were combined to understand and confirm the interactions among different components. Taking advantage of these properties, multimodal wearable sensors were constructed for sensing tension (gauge factor: 6.04), compression (gauge factor: 3.27) and temperature (sensitivity: 0.71 %/°C), which are applied for monitoring human motion, daily-life pressure and body temperature. The sensor had a good anti-fatigue property with stable signals during 2000 cycles. Moreover, the sensor can effectively recognize handwriting and perform human-computer interaction. This work provides a promising route to develop sustainable and multifunctional biopolymer hydrogels for wearable sensors with versatile applications in human health, exercise monitors and soft robots.