Preparation of triple-network CS-QCH-TA/PAA hydrogels with enhanced mechanical properties for flexible sensors

Hydrogels typically exhibit significant swelling in aqueous environments and fail to maintain stable mechanical properties underwater, which severely limits their practical applications. To address this critical challenge, we herein report the incorporation of tannic acid (TA) as a multifunctional crosslinker and the adoption of a facile one-pot synthesis method for the fabrication of chitosan-chitosan quaternary ammonium salt-tannic acid/poly(acrylic acid) (CS-QCH-TA/PAA) triple-network hydrogels. The optimized hydrogel (with 5% TA) demonstrates exceptional mechanical performance, including a tensile strength of ∼1900 kPa and a compressive strength of ∼6913 kPa, which outperforms previously reported dual-network hydrogels. Benefiting from multiple dynamic crosslinking interactions, the hydrogel can autonomously repair damage and retain mechanical strength even after swelling. As a proof-of-concept, flexible strain sensors fabricated from this hydrogel exhibit clear and repeatable signals when monitoring human finger and wrist movements. Furthermore, the reduced water swelling behavior of the hydrogel ensures stable performance under wet conditions. This work provides a novel strategy for preparing robust, self-healing hydrogels with enhanced water stability, thereby paving the way for their potential applications in wearable sensors, biomedical devices, and other fields requiring hydrogels to withstand aqueous environments.