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 energy-dissipation 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.