Ionic microsphere-reinforced multifunctional conductive hydrogel sensors for human motion monitoring

Abstract

Hydrogel-based flexible sensors are attractive for wearable electronics because of their softness, conformability, and tissue-like mechanics. Nevertheless, integrating high toughness, robust adhesion, self-healing ability, anti-freezing capability, and reliable strain sensitivity into a single hydrogel remains challenging. Here, we report a multifunctional conductive hydrogel in which ionic liquid-functionalized microspheres (MS) are introduced into an oxidized xanthan gum/chitosan (OXG/CS) matrix to serve as reinforcing nodes, dynamic physical crosslinking sites, and sacrificial energydissipation units. The microspheres interact strongly with the surrounding polymer chains through hydrogen bonding and electrostatic interactions, while the OXG/CS network provides reversible imine bonds. This hybrid dynamic network markedly improves the mechanical performance of the hydrogel, yielding an elongation at break of more than 970%, a toughness of 320 kJ m⁻³, and strong interfacial adhesion, while retaining excellent self-healing behavior. The incorporation of ionic species also endows the hydrogel with high conductivity (4.1 S m⁻¹) and excellent anti-freezing performance. As a strain sensor, the hydrogel exhibits high sensitivity, with a gauge factor of 6.70 in the 100-600% strain range, and can reliably detect subtle physiological signals such as pulse waves and vocal-cord vibrations. These results demonstrate that ionic microsphere reinforcement is an effective strategy for constructing multifunctional hydrogel sensors for use in complex environments.