In Situ Displacement Reaction Enables a Conductive Metallized Hydrogel Interface for Smart Underwater Flexible Electronics

Underwater wearable sensing is severely hampered by the intrinsic drawbacks of conventional materials, including water absorption, swelling, and electrical drift during long-term immersion. Here, we develop an anti-swelling hydrogel with a surface-metallized layer, which achieves strong stability of both mechanical structure and electrical conductivity during long-term underwater immersion. The precise regulation of hydrophilic acrylamide and hydrophobic butyl acrylate enables anti-swelling performance, while an in-situ displacement reaction conveniently and readily constructs an interfacial silver layer on the hydrogel. The hydrogel exhibits remarkable mechanical sensing performance, including high pressure sensitivity, fast response/recovery times, and a broad tensile sensing range. The sensor is integrated into an electronic skin for motion and physiological monitoring (joint bending, respiration, electromyography, and electrocardiography). With AI assistance, this electronic skin achieves 93.75% accuracy in handwriting recognition via a ProbSparse Transformer model. More importantly, a waterproof multichannel sensing system is constructed for real-time monitoring of underwater finger movements and gesture-associated resistance responses. This hydrogel sensor thus serves as a simple, robust, and amphibious platform for healthcare and human-machine interfaces in both air and water.