Highly stretchable and nonvolatile gelatin-supported deep eutectic solvent gel electrolyte-based ionic skins for strain and pressure sensing

There is a growing demand for devices that exhibit human skin-like sensory capabilities due to their broad applications in soft robotics and healthcare. Ionically conductive hydrogels have long been studied for wearable, flexible sensor applications; however, the volatility of water inevitably leads to dehydration issues that can limit the long-term use of hydrogel-based devices. In this report, highly stretchable, gelatin biopolymer-supported deep eutectic solvent (DES) gel electrolytes are presented as a promising nonvolatile alternative to hydrogels for ionic skin applications. The DES gel containing 22 wt% gelatin exhibited high stretchability (fracture strain 4 300%) and a room temperature ionic conductivity of 2.5 mS cm(-1). Capacitive-type pressure and strain sensors fabricated using gelatin-supported DES gel electrolytes provided linear responses over a wide range; an applied pressure as low as 1 kPa could be detected using a 1 V bias. A 3 x 3 sensor array was also constructed, which exhibited excellent performance for identifying the (multi) touch location(s) of applied pressure. These characteristics not only demonstrate the suitability of gelatin-supported DES gels for ionic skin applications, but also present a new class of materials for developing future nonvolatile sensors.