Self-Healable Hydrogel–Liquid Metal Composite Platform Enabled by a 3D Printed Stamp for a Multimodular Sensor System

Hydrogels and liquid metals have been emerging as potential materials for use in self-healing electronics. This paper presents a simple fabrication procedure for a custom-designed hydrogel-liquid metal composite and its various applications. The hydrogel is patterned using three-dimensional printed molds for creating an electrical pathway, which is subsequently filled with liquid metal. The lifetime and self-healing property of the hydrogel improve drastically through coating of its surface with a moisture protectant layer and via the formation of an oxidized layer of liquid metal, respectively. Three joined units of the resulting hydrogel-liquid metal composite are successfully applied as self-healable electrodes in a customizable multimodular sensor system consisting of a photoresistor, a thermistor, and a tilt switch. The composite is also used as an electrode for biosignal (electromyogram, electrocardiogram, and electrodermal activity) detection, and its sensing ability is found to be comparable to that of a conventional Ag/AgCl electrode. The demonstrated hydrogel-liquid metal composite provides wide scope for researchers to achieve practical advances in self-healing electronics.