Self-adhesive and tough slide-ring poly(ionic liquid) hydrogel for amphibious motion detection and depth-sensitive...

Although conductive hydrogels have exhibited significant potential as flexible wearable sensors, they also face persistent challenges including mechanical strength, stability and poor performance in complex environments, particularly underwater. In this work, the poly(ionic liquid) based hydrogel (Ir-PR) with slide-ring structure was designed and synthesized via copolymerization of acrylic acid, fluorine-rich imidazolium ionic liquid ([VBIM]Br), N,N-diethylacrylamide (DEAA), and vinyl-functionalized polyrotaxane crosslinkers (PR-AC). The synergistic multiple non-covalent interactions and unique slide-ring based topological structure endow Ir-PR hydrogel with high mechanical performance (0.79 MPa tensile strength, 1168.82% elongation), remarkable toughness (4.023 MJ/m³ fracture energy), anti-swelling performance (19.6% volume increase after 30 days underwater), strong adhesion to diverse substrates, and stable linear gauge factors (GF) in a wide strain-sensing range. Ir-PR hydrogel could detect human motions and monitor electrocardiogram (ECG) signals for health monitoring. Notably, Ir-PR hydrogel exhibits superior capabilities in aquatic scenarios: stable detection of the robotic shark swimming modes (stationary, slow/fast swimming, turns) via resistance signals, underwater Morse code communication, and integration into a depth-sensitive alarm and positioning system for diver safety. This multifunctional hydrogel overcomes critical barriers for reliable operation in variable aquatic environments, opening new avenues for marine exploration and safety systems.