Silk fibroin enhanced double-network hydrogels with extreme stretchability, self-adhesive and biocompatibility for ultrasensitive strain sensors

Wearable devices based on hydrogels have numerous application prospects. However, developing hydrogels with outstanding stretchability, high sensitivity, and multifunctional properties is challenging. Herein, a one-pot method for preparing double network (DN) hydrogels was proposed. The first network of hydrogel was formed by physical crosslinking of silk fibroin (SF) and polyvinyl alcohol (PVA), and the covalently crosslinked polyacrylamide (PAM) network was used as the second network. Excellent mechanical properties of hydrogels were obtained by adjusting the content of β-sheet in SF. The tensile strength, elongation, compressive strength, and toughness of the hydrogel increased to 76.2 kPa, 735%, 384.5 kPa and 389.78 kJ/m3, respectively. In addition, 34.9% of the initial toughness was recovered after resting the hydrogel for 1 min, and incorporating CaCl2 into the hydrogel resulted in an ionic conductivity of 6.13 mS/m. Notably, the hydrogel exhibited the ability to rapidly self-repair its mechanical and electrical properties. Moreover, it exhibited self-adhesion to different materials and human skin. The fabricated DN hydrogel exhibited good biocompatibility, and could be assembled into a strain sensor for monitoring body movements as well as recognizing other information such as throat chewing. Demonstrated its potential application in wearable devices.