Ca2+/ethanol driven in-situ integration of tough, antifreezing and conductive silk fibroin/polyacrylamide hydrogels for wearable sensors and electronic skin

Abstract

Integrating high strength, flexibility, biocompatibility, adhesion, and freezing resistance into conductive hydrogels for developing wearable electronic devices has consistently posed significant challenges in relevant research fields. Inspired by the silk dissolution behavior, a robust, flexible, antifreezing, and conductive silk fibroin/polyacrylamide (SF/PAM) hydrogel was synthesized in a CaCl2-ethanol–water (Ca2+/E/W) ternary solvent via a one-pot photogelation process. The gelation of SF and AM was enhanced by the ternary solvent, attributed to the inhibitory effects of Ca2+ ions and alcohols on hydrogen bond formation. The SF/PAM hydrogels based on Ca2+/E/W exhibited desirable mechanical properties (stretching: 800 % strain and 120 kPa stress; compression: 80 % strain and 334.0 kPa stress), excellent recoverability after deformation, high ion conductivity (2.4 S·cm−1) and strain sensitivity (gauge factor: ∼2.0), and low-temperature tolerance (−60 °C). These hydrogels were assembled into various wearable electronic devices, such as strain sensors, electronic skin, and electrodes, for detecting multiple physiological parameters, including joint activities, bioelectrical signals, and subtle movements like finger and wrist rotation, heartbeat, and vocal cord vibrations, demonstrating significant potential in flexible electronic applications.