Silk fibroin-based hydrogels with low hysteresis, self-adhesion, and tunable ionic conductivity for wearable devices

Silk Fibroin (SF) hydrogels are easy to functionalize and possess biocompatibility, making them highly promising for the development of flexible electronic devices and wearable equipment. However, fabricating SF-based hydrogels with multiple functions such as low hysteresis, self-adhesion, and high elasticity, while constructing flexible wearable electronic devices with high sensitivity and fidelity, remains a challenge to date. To address these issues, this work reports a one-step preparation of a fully polymer-based triple-network hydrogel through precursor solution pH pre-regulation, with polyacrylamide (PAM) as a brittle network, methyl cellulose (MC) as a tough network, and SF as a zwitterionic macromolecule. The introduction of MC effectively regulate the network aperture of the hydrogel, so as to improve the ion transport capacity and realize the high conductivity of the hydrogel. Through the regulation of the precursor solution pH, the cross-linking degree of the PAM network, the hydrogen bonding interactions between the triple networks, and the interfacial properties were simultaneously modulated, resulting in a reduction in hysteresis of the hydrogel from 21.4 % to 7.2 %, an increase in conductivity from 0.34 S·m^-1 to 0.57 S·m^-1, an increase in elastic modulus from 18.6 kPa to 58.9 kPa, and an improvement in interfacial adhesion from 4.5 kPa to 15.48 kPa. The prepared SF-based hydrogel was assembled into flexible electronic patches and adhered to different parts of the human body, enabling self-adhesive, multi-channel, wireless detection of human multi-scale movements. The hydrogel prepared in this work also demonstrates exceptional potential in fields such as electrocardiogram monitoring, electromyogram detection, information encryption, and self-powered devices. The method reported in this paper provides new insights for the synergistic enhancement of mechanics, electricity, and adhesion in natural polymer-based hydrogels.