Anti-Freezing and High-Strength Chitosan-Based Conductive Hydrogels for Flexible Sensors

Chitosan-based conductive hydrogels have attracted considerable attention as promising platforms in health monitoring and flexible wearable electronics due to their distinctive properties. In this study, an anti-freezing chitosan/poly(acrylic acid) (CS/PAA) hydrogel with excellent mechanical performance was first synthesized via in situ polymerization. Subsequent immersion in a glycerol/lithium chloride (Gly/LiCl) mixed solution promoted chitosan chain cross-linking and yielded a chitosan/poly(acrylic acid)/lithium (CS/PAA/Li) conductive hydrogel that integrated high mechanical strength, anti-freezing capability, and water retention. Within the Gly/LiCl aqueous system, a synergistic salt-soaking effect combined with electrostatic shielding promoted chitosan chain aggregation and intermolecular entanglement, significantly enhancing the hydrogel’s mechanical performance. The optimized CS/PAA/Li hydrogel exhibited a fracture stress of 11.27 MPa, an elongation at break of 937%, and a fracture toughness of 48.26 MJ/m 3, comparable to the mechanical properties of biomimetic muscle hydrogels. Moreover, it retained structural integrity and flexibility across a broad temperature range (–18 to 25 °C), demonstrating exceptional cryostability. Electromechanical evaluation of the CS/PAA/Li hydrogel-based strain sensor revealed a linear relationship between the relative resistance change and applied strain, indicating its potential for accurate strain quantification. Structural analyses confirmed that the hydrogel network was stabilized by reversible physical cross-linking, involving chitosan nanofiber entanglement, hydrogen bonding, and electrostatic interactions between chitosan nanofibers and PAA chains. This dynamic architecture imparted remarkable cyclic stability to the strain sensor. Comprehensive physiological monitoring trials validated the sensor’s practical utility by reliably detecting both low-frequency joint motions (e.g., finger, elbow, wrist, and knee flexion) and high-frequency, high-intensity activities such as running. These findings highlight the significance of this work in advancing high-performance chitosan-based conductive hydrogels and strain sensors. The simple and effective methodology provides a viable framework for the scalable fabrication of advanced physiological monitoring devices and is particularly relevant to the future deployment of wearable sensor technologies in healthcare and biomedical applications.