Ultratough, Stretchable Silk Protein Fibrous Membranes for Robust and Permeable Epidermal Bioelectronic Sensors

ABSTRACT Epidermal bioelectronics hinges critically on the skin‐adaptive and robust device‐epidermal interface, creating a high demand for soft functional polymers. Natural biopolymers like silk are ideal interfacing materials due to their biocompatibility and sustainability, yet engineering them into tough, thin, and permeable membranes adapting to skin remains a challenge. To overcome this, we report an ultratough and stretchable silk protein fibrous membrane (SPFM). Through a combined strategy of electrospinning and hygroscopicity‐driven crystallization, ionic‐conductive SPFM is engineered with a hierarchical architecture composing of aligned microfibers and a randomly entangled peptide network sparsely crosslinked by β ‐sheet nanocrystals, overcoming the intrinsic brittleness of natural silk. The resulting SPFM with a thickness of ≈19 µm, exhibits a fracture strain of 220%, a fracture stress of 9.88 MPa, a toughness of 14.97 MJ m −3 , and an ultrahigh fracture energy of 98.18 kJ m −2 based on special crack deflection mechanism. As skin‐adaptive and permeable sensors, SPFM reliably monitors body motions and bioelectric signals with high fidelity, achieving electromyographic recording with a high signal‐to‐noise ratio (>45 dB) during dynamic movements. Dual‐channel electromyographic recording assisted by machine learning, demonstrates 98.91% accuracy in gesture recognition, highlighting the potential of high‐performance biopolymer epidermal electronics for human‐machine interaction applications.