Biomass-based multifunctional hydrogel fabricated using lignin-Li+ self-catalytic system with high mechanical strength and ionic conductivity for flexible sensor.

Conductive hydrogels derived from natural biomass have attracted considerable attention owing to their excellent flexibility and electrochemical performance. However, simultaneously achieving high mechanical strength, high electrical conductivity, and multifunctional integration remains a notable challenge. Herein, we propose a facile strategy to obtain bamboo cellulose nanofiber (BF) as the reinforcing phase using hydrated multi-carboxylic acid deep eutectic solvent and construct a multifunctional polyacrylamide-lignin/LiCl-BF (PAM-LLi-BF) hydrogel through free radical polymerization reaction induced by LLi catalytic system. The PAM-LLi-BF hydrogel leverages the uniform dispersion and permeation of BF throughout its network, as well as the dual effects of the LLi system in promoting rapid hydrogel polymerization and enhancing conductivity, which exhibits satisfactory compressive performance (615.27 kPa), tensile properties (strain of 1260.67%), and fatigue resistance. In addition, it possesses excellent conductivity, adhesion, and antifreezing capabilities. Moreover, the fabricated hydrogel-based flexible sensor simultaneously serves as a strain sensor (GF = 3.89, working range of 0-500%) and a pressure sensor (response time of 231 ms, stable sensing after 1000 compression cycles). Combined with a deep-learning algorithm, the PAM-LLi-BF hydrogel is integrated into an intelligent seat cushion and successfully applied to monitor human sitting posture in real time (with an identification accuracy rate of 95.1%).