Jellyfish-inspired multilayered responsive hydrogels via micelle-confined photopolymerization for underwater communication and emergency rescue.

Hydrogels offer considerable promise as flexible sensors. However, maintaining their stable performance in complex underwater environments characterized by high pressure, high salinity, and temperature fluctuations remains a significant challenge. Inspired by the dynamic adaptive capabilities of jellyfish, this study reports a biomimetic composite conductive hydrogel with multi-level environmental responsiveness, synthesized via the copolymerization of N-isopropylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and octadecyl methacrylate (OMA), incorporating color-changing microcapsules through a cetyltrimethylammonium bromide (CTAB) micelle-confined polymerization strategy. The long alkyl chains of OMA promote hydrophobic association networks inside CTAB micelles, endowing the hydrogel with both high strength and exceptional stretchability (fracture strength of 690 kPa; elongation at break 1370%). This hydrogel achieves multi-parameter, synchronized responses to complex marine conditions: strong temperature sensitivity (-15.344%/°C), an electrical response to water-depth pressure (7.13 kPa-1, corresponding to 0-500 m water depth), stable tensile responsiveness, and reversible color changes visible to the naked eye. Building on these capabilities, the hydrogel can monitor human motion in conventional settings and also enable underwater sensing and Morse-code-based information transmission, demonstrating substantial potential for applications for underwater communication and emergency rescue applications.