Co²⁺-Mediated Hydrogels with Enhanced Mechanical Properties for Flexible Sensing

Flexible artificial skin sensors have been a hot research topic over the past 20 years due to their remarkable prospects in the fabrication of smart wearable devices. Normally, electronic skin sensors transmit signals via stretchy electrical conductors, and the manufacturing processes are more complicated, involving multiple steps. For the first time, this work reports a facile one-step fabrication of poly(sodium methacrylate-co-vinylimidazole)-Co2+ hydrogels with high mechanical strength, good elasticity, and excellent sensitivity that can be used as ionic skins (I-skins). In addition, mechanical analysis indicates that the designed hydrogels have enhanced strain and tensile strength due to hydrogen bonding and metal–ligand bonding interactions, and these two types of dynamic noncovalent interactions are explored in detail. Simultaneously, the developed hydrogels also display superior conductivity and self-healing qualities with restored sensing properties. Furthermore, the proposed hydrogel with good sensitivity and stable strain range is suitable to fabricate a wearable strain sensor, and this hydrogel sensor was demonstrated to be effective in monitoring human motion, including joint flexion, pulse, vocal cord vibration, and respiration. In addition, a pressure distribution sensor array was developed by this hydrogel and was used to construct the model of plantar pressure distribution in normal subjects and flatfoot patients, offering a strategy for the early detection and clinical diagnosis of numerous foot-related disorders. Hence, this research may offer a promising approach for generating biocompatible hydrogels with integrated mechanical characteristics, and these hydrogels present development potentials in multifunctional ionic skins.