Bio-inspired, robust, and anti-swelling hydrogel sensors for underwater information transmission

Abstract

Hydrogel-based sensors commonly manifest pronounced swelling in aqueous milieus, a phenomenon that can precipitate deterioration of mechanical performance and distortion in output signals, thereby markedly constraining their expansive applicability. Drawing inspiration from the hierarchical heterogeneous cross-linking architecture inherent in biological tissues, an anti-swelling supramolecular hydrogel with robustness, fast self-recovery, and strain-sensitivity was meticulously engineered through leveraging the principles of multiple dynamic interaction matching. The heterogeneous structure for the hydrogels was constructed by integrating both ‘rigid’ carboxyl-Zr⁴⁺ coordination complexes and ‘soft’ hydrophobic micro-regions mediated by electrostatic interactions into the system. The synergistic interplay between reversible rigid and flexible cross-linking endowed the supramolecular hydrogels with robust mechanical properties, evidenced by a strength of 3.64 MPa, toughness of 6.83 MJ m⁻³, and complete self-recovery within 7 minutes, alongside anti-swelling capabilities in various aqueous environments, including acidic, alkaline, and saline solutions. Moreover, the hydrogels developed desirable sensing properties on account of the contribution of dynamic ions (Br⁻, Cl⁻, and Zr⁴⁺), enabling accurate signal output under diversified frequencies and strains. Consequently, these hydrogels were adapted to construct underwater sensors capable of transmitting information through Morse code. This bio-inspired design strategy achieved the perfect combination of mechanical, anti-swelling, and sensing properties in the hydrogels, offering novel insights into the fabrication of underwater sensors.