Printing of self-healable gelatin conductors engineered for improving physical and electrical functions: Exploring potential application in soft actuators and sensors

Novel gelatin-based composite system is engineered for preparing self-healable and printable conductors suitable for dielectric elastomer actuators and strain sensors. Organogel networks consisting of gelatin and tannic acid in the choline chloride deep eutectic solvents exhibit good mechanical/electrical performances with self-healing capabilities. With electrohydrodynamic printing of the gelatin-based composites, dielectric elastomer actuators and strain sensors are fabricated, showing high performances and good self healing properties. • Novel gelatin system is engineered for preparing self-healable/printable conductors. • Gelatin-tannic acid gels show mechanical/electrical properties with good self-healing. • High-performance dielectric elastomer actuators are fabricated with EHD-printed gels. • The printed gels also detect wrist and finger joint movements instantly. Significant efforts have been devoted to developing dielectric elastomer actuators owing to their mechanical flexibilities, silent operation, and muscle-like performances. However, it still remains a challenge to demonstrate the actuators that maintain function when subjected to damage because most soft materials constituting such devices are vulnerable to mechanical stresses during repeated operation. Here, self-healable electrodes suitable for dielectric elastomer actuators were prepared from an eco-friendly gelatin-based composite including conductive ions and hydrogen bonds. Electrohydrodynamic printing was used to reproducibly fabricate a custom-made electrode with desired geometry. The printed gelatin-based electrodes were attached onto elastomers to fabricate dielectric elastomer actuators. The devices exhibited good actuator operation and, owing to the self-healing capability of the gelatin-based electrodes, almost fully recovered their performances with an efficiency of up to 96.8% even after the electrodes were damaged. Furthermore, the potential application of the gelatin-based electrode was explored by using them as a strain sensor; this sensor showed a sensitive dependence of electrical resistance on external joint movements. We believe this work provides a useful guideline for designing self-healable conductive composites that can be effectively used to make printed actuators and sensors endowed with good ionic conductivity and useful mechanical properties.