Tough and Conductive\nHydrogels Fabricated via Dehydration\nand Solvent Displacement as Flexible Strain Sensors and Self-Powered\nDevices

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