Biomimetic phase-separated bilayer gel sensors with robust interfacial adhesion for high-humidity and underwater communication

Traditional hydrogel-based flexible sensors suffer from structural instability and severe electrical fluctuations in high-humidity or underwater environments due to their single-layer networks and poor water resistance. Inspired by the multi-layered structure of biological surfaces, this research develops a biomimetic, phase-separated bilayer flexible material (DAC-Gel-PAM-BA-50IL) comprising a skin-conforming hydrogel substrate and a hydrophobic outer ionogel layer. The inner dialdehyde cellulose (DAC)/gelatin/polyacrylamide dual-network hydrogel provides exceptional biological tissue adhesion (0.08 MPa on pigskin) and stretchability, while the outer fluorinated ionogel serves as a robust waterproof barrier to isolate environmental humidity. Benefiting from the synergistic interfacial hydrogen bonding and ion-dipole interactions, the bilayer gel demonstrates a stable mechanical interlocking with an impressive fracture strain of 408%. Remarkably, the integrated sensor exhibits reliable ionic conductivity across a wide temperature range (-20 °C to 30 °C) and humidity range, alongside a fast response time (217 ms) and outstanding cyclic stability (800 cycles). Leveraging these superior electromechanical and waterproof properties, the skin-attachable device is successfully applied to real-time human motion monitoring and accurate underwater Morse code communication. This study offers a simple, scalable, and innovative structural design strategy for multi-phasic flexible sensors in wearable healthcare and smart underwater electronics.