Flexible chitosan sensing hydrogel enabled by phytic acid coordination effect with high-conductivity and ultra-sensitivity for self-powered handwriting recognition and multimodal sensors

Chitosan hydrogel has garnered significant interest for its potential to confer excellent biocompatibility, degradability, and renewability upon flexible electronics. Nonetheless, its inherent mechanical weaknesses have necessitated compromises in terms of flexibility, conductivity, and sensing sensitivity, thereby limiting its applicability. In this study, we present a flexible chitosan sensing hydrogel with remarkable properties, including high-conductivity (9.96 S/m) and ultra-sensitivity (gauge factor=11.83), achieved through the coordination effect of phytic acid (PA). A novel protective cross-linking strategy was employed, balancing the strong complexing ability of PA through the regulation of carboxylated cellulose nanofiber (CCNF) to establish a moderate cross-linked network between chitosan (CS) and polyethyleneimine (PEI). CCNF not only forms hydrogen bonds with CS and PEI, occupying some active sites that could chelate with PA, but also repels adjoining PA via electrostatic repulsion, thereby preventing excessive coordination. Consequently, the resulting hydrogel exhibits superior properties, including excellent flexibility, deformability, conductivity and GF, while simultaneously possessing high sensing sensitivity and energy harvesting capacity. Remarkably, the hydrogel-assembled sensors demonstrate outstanding performance in monitoring subtle facial expression changes, throat motion, and various limb movements. Even more impressively, the hydrogel-based triboelectric nanogenerator (TENG) exhibits exceptional energy harvesting capacity (1070.8 mW/m2) and high accuracy (98%) for handwriting recognition. This study presents a promising approach for constructing biomass-based multifunctional hydrogels with enhanced sensing capabilities and energy harvesting abilities, paving the way for their utilization in high-performance self-powered devices and intelligent handwriting recognition systems.