Self-Healing and Highly Stretchable Gelatin Hydrogel for Self-Powered Strain Sensor

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