An Ion-Conductive Honeycomb Hydrogel with Triple Network Structures for 3D Tactile Sensing and Interaction

Abstract

Ion-conductive hydrogels possess great potential in the field of flexible sensing due to their unique mechanical characteristics and internal ionic conduction. However, one of the primary challenges lies in the difficulty of balancing both superior mechanical strength and conductivity, which hampers their broader use in practical applications. In this study, we present a PVA/PAANa ion-conductive composite hydrogel with dual improvement in both properties, featuring a macroscopic honeycomb-like pore structure and a microscopic triple network (TN) configuration. Specifically, hydrogen bond-enriched networks are initially formed within the PVA and PAANa chains through a process involving thermal polymerization and a combined freeze-thaw approach. Subsequently, the conductive percolation network is incorporated through the addition of silver nanowires, to further boost the overall conductivity. Then, Na+ ions are introduced through a salting-out effect, enhancing electrostatic interactions with COO- groups in the hydrogel and creating an additional electrostatic network, which improves both the mechanical properties and ion retention capability. When implemented as a pressure-sensitive tactile sensor, the composite hydrogel exhibited a pressure sensitivity of 0.189 kPa-1 (pressure range: 0.797- 2.171 kPa) with a response time of 143 ms, and an exceptional fatigue resistance over 1500 compression cycles. Lastly, a 3x3 tactile sensor array based on P/P/A-NaCl hydrogels was designed for multidimensional sensing and pressure distribution mapping, showcasing its potential in applications such as health monitoring, sports tracking, and interactive 3D soft robotics.