Tissue-adhesive, silk-based conductive hydrogel with high stretchable, transparent, healable and degradable properties for real-time, precise monitoring of tissue motions and electrocardiogram under sweaty condition.

Developing bioelectronic sensors with exceptional physicochemical properties, such as strong adhesion to wet biological tissues, high mechanical strength and stretchability, transparency, self-healing ability, biocompatibility, and degradability remains a significant challenge in meeting the complex requirements of monitoring biological tissues. In this study, a novel silk fibroin/polyacrylamide/ferric ion (PAM-SF/Fe) double network hydrogel was developed by a self-assembly cross-linking strategy to address this challenge. Benefiting from the double network structure, reinforcement of random coils of SF, a large number of metal chelation and hydrogen bond interactions among SF, PAM, and Fe, the hydrogel demonstrates exceptional mechanical properties, including a maximum tensile strength of 71 kPa, elongation at break exceeding 1442 %, compressive stress over 0.66 MPa, Young's modulus of approximately 10 kPa, light transmittance of about 90 %, instant robust adhesion to various wet biological tissues even underwater, and excellent self-healing capability at room temperature. To the best of our knowledge, this is the highest stretchability and mechanical strength among the reported silk-based conductive hydrogels while simultaneously achieving adhesive performance on wet biological tissues. Additionally, the PAM-SF/Fe hydrogel also exhibits good biocompatibility and degradability, enabling direct adhesion to wet biological tissue surfaces, such as pig lung and rat bladder, for real-time and reliable monitoring of their contractile movements. Furthermore, it serves as flexible conductive gel electrodes for long-term continuous monitoring of ECG signals under sweaty conditions and displays promising applications in implantable sensors, wearable devices, and personal healthcare and human-machine interfaces.