Fabrication of Mechanically Enhanced Self-Healing Hydrogels Based on the Synergistic Effect of Curcumin and CMC-Na for Strain-Sensing Applications

Abstract

In practical applications, hydrogel sensors are required to withstand continuous tensile deformation and are highly susceptible to external mechanical damage such as puncture. These issues often lead to irreversible degradation of sensing performance, thereby limiting their further application. In this study, a self-healing hydrogel was fabricated for strain sensors by combining Schiff base reactions with metal coordination interactions. Sodium carboxymethyl cellulose (CMC-Na) was introduced as a functional reinforcement phase, and an optimal CMC-Na content of 1.0 wt % was found to simultaneously enhance both the electrical conductivity and mechanical properties. The resulting PAA/PEI/CMC-Na–Cur–Al³⁺ hydrogel exhibits an ionic conductivity of 1.07 S/m and a tensile strength of 77.12 kPa, yielding an approximately 5-fold enhancement compared to the hydrogel without CMC-Na. The hydrogel sensor also demonstrates a gauge factor of 2.15 and stable sensing performance over 2500 s of cyclic stretching. It is capable of detecting human joint movements and can be applied as a stylus. These superior properties demonstrate that the PAA/PEI/CMC-Na–Cur–Al³⁺ hydrogel is an ideal candidate material for flexible strain sensors.