Bioinspired Antiswelling Hydrogel Sensors with High Strength and Rapid Self-Recovery for Underwater Information Transmission

Hydrogel-based sensors typically demonstrate conspicuous swelling behavior in aqueous environments, which can severely compromise the mechanical integrity and distort sensing signals, thereby considerably constraining their widespread applicability. Drawing inspiration from the multilevel heterogeneous structures in biological tissues, an antiswelling hydrogel sensor endowed with high strength, rapid self-recovery, and low swelling ratio was fabricated through a water-induced phase separation and coordination cross-linking strategy. A dense heterogeneous architecture was developed by the integration of "rigid" quadridentate carboxyl-Zr⁴⁺ coordination bonds and "soft" hydrophobic unit-rich regions featuring π-π stacking and cation-π interactions into the hydrogels. This unique structural design facilitated the progressive breaking of cross-links within the hydrogel network from "soft" to "rigid" under external loads, effectively dissipating energy and thereby imparting the hydrogels with exceptional mechanical characteristics, evidenced by a strength of 1.42 MPa, and complete self-recovery within 3 min. Simultaneously, the "rigid" and "soft" dynamic interactions synergistically conferred augmented elastic retractive forces on the hydrogel network by enhancing cross-linking density, thereby providing the hydrogels with prominent antiswelling capabilities in water (with a swelling ratio of only -2.49%), in solutions with diverse pH (1-9), and in seawater. Moreover, the hydrogels manifested favorable strain-sensitivity (gauge factor up to 2.45) and frequency response by virtue of the collaborative contribution of dynamic ions (Cl^- and Zr⁴⁺). Consequently, the hydrogels were utilized to assemble underwater sensors with the capacity to transmit information using Morse code. This bioinspired design methodology achieved the desired integration of the mechanical, swelling-resistant, and sensing performance within the hydrogels, thereby contributing innovative insights toward the advancement of underwater sensor technology.