Highly Sensitive Pressure and Strain Sensors Based on Stretchable and Recoverable Ion-Conductive Physically Cross-Linked Double-Network Hydrogels

Abstract

Ion-conductive hydrogel sensors have attracted great research interests for applications in wearable devices, electronic skins, and implantable sensors, but most such sensors are fragile, with low conductivity and sensitivity. This study reports on novel ion-conductive double network hydrogels with a cross-linked helical structure, hydrophobic association, and metal-ion coordination. The helical κ-carrageenan first network and the second network cross-linked by Pluronic F127 diacrylate micelles and tridentate Fe³⁺-COO^- coordination work synergistically to show the tensile strength of 2.7 MPa, fracture strain of 1400%, and tensile toughness of 9.82 MJ m^-3 and fatigue resistance against cyclic loadings with high strains. The hydrogels show an ion conductivity of 1.15 S m^-1, a strain sensitivity of up to 2.8, and a pressure sensitivity of 0.33 kPa^-1. Sensor arrays fabricated from the conductive hydrogels provide an in-plane detection of pressures less than 200 Pa. Such hydrogel sensors have potential applications to electron skins and implantable sensors.