Tough and Conductive Hydrogels Fabricated via Dehydration and Solvent Displacement as Flexible Strain Sensors and Self-Powered Devices

Abstract

Conductive hydrogels are highly promising candidates for fabricating flexible wearable devices due to their superior biocompatibility and mechanical flexibility. However, the inferior mechanical properties and poor conductivity of conventional hydrogels greatly constrain their sensing capabilities. Herein, a tough conductive hydrogel with a semi-interpenetrating network structure was developed utilizing a two-step process involving initial drying, followed by solvent displacement with an acidic solution. Crystalline regions, multiple hydrogen bonds, and electrostatic interactions are established in hydrogels during the processes, significantly enhancing the hydrogel's mechanical properties. The resulting hydrogels have high tensile strength and high toughness yet skin-like low modulus. The unique network structure gives this gel low hysteresis and excellent fatigue resistance in the low strain range. The presence of abundant free ions within the network results in a suitable conductivity, enabling their application as resistivetype strain sensors that demonstrate high sensitivity, excellent linear responsiveness, broad sensing window, and favorable durability, thereby showcasing significant potential for monitoring human motions. The acidic environment inside the hydrogels is conducive to their use in self-powered devices with an adequate output voltage. Sufficient output voltages can be realized by connecting multiple hydrogels in series, and a self-powered sensor is proposed that is capable of responding to strain signals through changes in output voltage without the need for an external power source. This work provides a strategy for fabricating tough conductive hydrogels with considerable promise in the fields of flexible electronics and self-powered devices.