Protonation-mediated multifunctional silk fibroin hydrogel adhesives for epidermal interface sensing

Silk fibroin (SF)-based hydrogels have attracted significant interest in biological interface applications, especially for epidermal sensing and tissue/cell scaffolds, due to their exceptional natural properties. However, achieving multifunctionality in SF-based hydrogels, such as mechanical robustness, interfacial adhesion, electronic conductivity, and long-term stability, often requires chemical modification or functional doping, which may compromise the innate biological activity of silk materials. Developing SF-based hydrogels that retain their natural advantages while gaining tailored functionalities remains a critical challenge, hindering their broader application in biological interfaces. Here, we present a protonation-mediated SF-based multifunctional hydrogel adhesive for biological epidermal interfaces. By blending SF and polyvinyl alcohol (PVA), we constructed a physically cross-linked hydrogel network governed solely by molecular interactions. Phosphoric acid (H3PO4) was introduced as a protonation agent to modulate hydrogen bonding within the system, enabling precise control over adhesion, mechanical strength, and electronic conductivity while preserving high biocompatibility. Furthermore, incorporating glycerol (Gly) as a moisturizing agent significantly enhanced the hydrogel’s long-term stability for skin-surface applications. The resulting protonation-mediated SF hydrogel adhesive demonstrates excellent performance in monitoring electrophysiological signals (e.g., electrocardiogram (ECG), electromyograms (EMG), and electroencephalogram (EEG)), offering a promising platform for advanced biological interface applications.