Bioinspired multifunctional conductive hydrogel based on hydroxypropyl methyl cellulose for flexible sensors

Conductive hydrogels based on hydroxypropyl methyl cellulose (HPMC) show great potential in flexible sensors due to their low price and good biocompatibility. Nevertheless, the design of such conductive hydrogels with superior flexible deformability, anti-fracture toughness, notch-insensitiveness, electromechanical performance, antibacterial and self-heal capabilities remains challenging. Herein a multifunctional conductive hydrogel was developed by a simple micellar polymerization of acrylamide (AM) and stearyl methacrylate (SMA) in the presence of HPMC, tunicate cellulose nanocrystals (TCNCs) and silver coated MXene nanosheets. The hydrogels are quite soft and deformable (low modulus of 10.04 kPa, high stretchability of 4520 %), but show excellent anti-fracture toughness (6.128 MJ/m³) and tear resistance. Importantly, the hydrogels exhibit exceptional biocompatibility, self-healing, adhesive, photothermal antibacterial capabilities and conductivity, which serve as strain sensors (gauge factor: 7.57), pressure sensors (pressure sensitivity: 2.96 kPa^-1), and temperature sensors (temperature coefficient of resistance: -2.47 %/^oC). The hydrogel sensor possesses prominent sensitivity and cyclic stability to accurately monitor human motion, writing trajectories, and temperature change during the photothermal therapy in real time. Moreover, a hydrogel-based flexible handwriting keyboard was also fabricated to establish a handwriting recognition intelligent system for deep machine learning. This study provides a potential avenue for multifunctional conductive hydrogels toward environmentally friendly flexible sensors.