Self-Healing and Highly Stretchable Gelatin Hydrogel\nfor Self-Powered Strain Sensor

Abstract

Hydrogels that electronically respond to mechanical changes\ncan be used as strain sensors. However, these systems usually require\nexternal power to convert changes in strain into electrical signals.\nHere, a self-powered strain sensor is developed based on a gelatin-based\nhydrogel and a galvanic cell. In the hydrogel matrix, hydrophobic\ninteractions and hydrogen bonding between tannic acid and gelatin\ngive the prepared hydrogel great potential for elongation (1600%).\nThe hydrogel also has a rapid self-healing ability (within 0.65 s)\nand high self-healing efficiency (95%). The hydrogel operates as an\nefficient electrolyte material and forms a hydrogel battery when assembled\nwith a thin layer of zinc and an air electrode. This device had excellent\ntolerance to large compressional strain without sacrificing open-circuit\nvoltage. On the basis of this hydrogel battery, we fabricated a self-powered\nstrain sensor by connecting the hydrogel battery to a fixed resistor\nto form a closed loop. By converting its chemical energy into electrical\nenergy, the self-powered sensor efficiently converted resistance changes,\ncaused by stretching or compression of the hydrogel, into changes\nin the voltage output signals without external power. Owing to the\nstretchability of the hydrogel, the self-powered sensor exhibited\ngood response and flexibility. Self-healing and continuous cycling\ntests confirmed the long-term stability of the device. These properties\nsuggest that our self-powered sensor has a potential for applications\nto portable and wearable electronic devices.