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

Abstract

Natural biopolymers\nare biodegradable and biocompatible and thus\nhave huge potential for the development of biomedical or transient\nsystems. Herein, we report an entirely starch-based hydrogel for flexible\nelectronics including strain-sensitive batteries and self-powered\n(SP) wearable sensors. This biodegradable hydrogel is only based on\nnatural high-amylose starch, CaCl₂, and glycerol, and the\npreparation method is green and facile (namely, stirring at 70 °C\nfor 1 h). This hydrogel is highly stretchable, flexible, reprocessable,\nand self-healable. Based on this hydrogel, we developed a galvanic\ncell-type Zn–Cu battery (composed of one starch-based hydrogel\nadditionally incorporated with zinc powder and the other with CuCl₂ and copper powder), which has a voltage of 0.81 V and its\noutput current positively correlated with compression deformation.\nBased on this Zn–Cu battery, a self-powered (SP) wearable sensor\nwas further constructed, which has a high sensitivity (1.5371 kPa^–1) even under weak compression stress. This SP sensor\ncan be used to detect human activities involving small strain such\nas wrist pulse and throat vibration, for which the signals are strong,\nclear, and stable. Considering the easy processability, cost-effectiveness,\nhigh strain sensitivity, robustness, and greenness of the starch-based\nhydrogel and electronics, their brilliant application prospect is\nforeseen.