All-Starch-Based Hydrogel for Flexible Electronics: Strain-Sensitive Batteries and Self-Powered Sensors

Natural biopolymers are biodegradable and biocompatible and thus have huge potential for the development of biomedical or transient systems. Herein, we report an entirely starch-based hydrogel for flexible electronics including strain-sensitive batteries and self-powered (SP) wearable sensors. This biodegradable hydrogel is only based on natural high-amylose starch, CaCl2, and glycerol, and the preparation method is green and facile (namely, stirring at 70 °C for 1 h). This hydrogel is highly stretchable, flexible, reprocessable, and self-healable. Based on this hydrogel, we developed a galvanic cell-type Zn-Cu battery (composed of one starch-based hydrogel additionally incorporated with zinc powder and the other with CuCl2 and copper powder), which has a voltage of 0.81 V and its output current positively correlated with compression deformation. Based on this Zn-Cu battery, a self-powered (SP) wearable sensor was further constructed, which has a high sensitivity (1.5371 kPa-1) even under weak compression stress. This SP sensor can be used to detect human activities involving small strain such as wrist pulse and throat vibration, for which the signals are strong, clear, and stable. Considering the easy processability, cost-effectiveness, high strain sensitivity, robustness, and greenness of the starch-based hydrogel and electronics, their brilliant application prospect is foreseen.