The advent of double network (DN) hydrogel-based strain sensors has attracted immense research interest in artificial intelligence, wearable devices, and health-monitoring systems. However, the integration of the synergistic characteristics of good mechanical properties, self-adhesiveness, self-healing capability and high strain sensitivity for fabricating hydrogel-based strain sensors is still a challenge. Here, three multifunctional hydrogels (CTA-1, CTA-2 and CTA-3) composed of a Chitosan (CS)/ Tetraethylene glycol (TEG)/ Polyacrylic acid (PAA) hybrid network are fabricated by varying the cross-linker terepthaldehyde, sodium hydroxide and sodium chloride. The PAA network is covalently cross-linked by N, N- methylenebisacrylamide, and the CS network is covalently and ionically cross-linked in CTA-1, CTA-2 and CTA-3. These two networks are further interlocked by physical entanglement and hydrogen bond interactions. The obtained three hydrogels show unique behaviour in mechanical strength, conductivity and self-healing capability. The rheology study shows excellent self-healing behaviour up to 6-7 cycles between the oscillation strain of 1 and 1500%. Moreover, the hydrogels exhibit self-adhesive behaviour on various materials, including metal, plastic, polytetrafluoroethylene, copper, wood, glass, aluminium, rubber and skin. The antibacterial property, originating from chitosan, made the hydrogels non-toxic to skin. Further, the DN hydrogel CTA-2 shows self-adhesive nature towards metal, glass and skin, in presence of water. Notably, the hydrogels can be applied as soft human-motion sensors for real-time and accurate detection of small human activities like joint motion. This work provides a new prospect for the design of the biocompatible chitosan-based hydrogels with stretchable, self-adhesive, self-healing, and strain-sensitive properties for potential applications in wearable electronic sensors and healthcare monitoring.

Comparative study of mechanical, self-adhesive, self-healable properties of a hybrid hydrogel based on chitosan, tetraethylene glycol and polyacrylic acid

ACS Spring 2022

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