Mechanically Enhanced, Antibacterial, and Double-Network Hydrogel Flexible Sensors for Sleep Apnea Monitoring

Despite significant advancements in flexible sensing systems based on conductive hydrogels, these materials continue to face limitations in terms of mechanical properties, sensing performance, and practical applicability. This report describes the preparation of an antibacterial hydrogel sensor from a polyvinyl alcohol (PVA)/silk fibroin (SF) double network, tannic acid-coated liquid metal (TALM), and copper particles, with an ethanol (ET) post-treatment using a multi-level structural regulation strategy. The obtained hydrogel is evaluated in the context of respiratory monitoring. A stepwise impregnation process ensures a spatially ordered distribution of functional components. Specifically, TALM nanodroplets increase dispersion stability; copper ion displacement reactions generate antibacterial copper particles in situ; and the ethanol post-treatment induces a β-sheet conformational transition. The novel hydrogel exhibits excellent overall performance, with a tensile strength of 1.452 MPa (483% greater than that of pure PVA), an elongation at break of 700%, a toughness of 0.483 MJ/cm³, and an electrical conductivity of 0.25 S/m. Antibacterial tests demonstrate that the hydrogel has inhibition zone widths of 2.5 mm for Staphylococcus aureus (S. aureus) and 1.0 mm for Escherichia coli (E. coli). The hydrogel sensor maintains a stable resistance response (ΔR/R₀ fluctuation <5%), even after 1000 stretching cycles, thereby enabling effective respiratory rate monitoring and apnea warning functions. This study provides a new strategy for developing wearable flexible sensors with excellent mechanical performance, electrical conductivity, and antibacterial performance.