Hydrogen Bonds Enhance Mechanical and Electrical Properties of Agarose Double-Network Hydrogel for Flexible Sensing

Hydrogels have attracted considerable interest in intelligent sensing owing to their flexibility, versatility, and biocompatibility. However, their practical application remains limited by an insufficient understanding of the intrinsic composition–structure–property relationships. This study takes agarose (agar)-poly(acrylamide-co-acrylic acid) [P(AM-co-AA)] double-network hydrogel as a typical model, elucidating how key variables (agar content, monomer ratio) regulate hydrogel properties to provide theoretical references for the structure–property relationship of analogous systems. The interpenetrating network induces abundant hydrogen bonds, which act as dynamic cross-linking sites and energy dissipation units─the core mechanism governing mechanical and swelling properties. The hydrogen bonds enhance mechanical robustness by dissipating external energy and inhibit water penetration, leading to a 75% lower equilibrium swelling ratio than pure P(AM-co-AA) and over 50% water retention after 24 h ambient incubation. Adjusting the AM/AA ratio modulates the ionization of carboxyl groups in the copolymer chain, thereby regulating the polymer segment flexibility, pH responsiveness, and ionic conductivity. To broaden the applications of hydrogels, MXene (a typical two-dimensional material) was incorporated into the agar/P(AM-co-AA) matrix. Through its surface functional groups, MXene forms hydrogen bonds with the polymer network, without compromising the inherent mechanical properties of the hydrogel, thereby imparting tunable electrical conductivity and photothermal conversion capability. The composite hydrogel enables real-time monitoring of human motion and exhibits photothermal sensing performance. This work clarifies the intrinsic component–structure–property correlations of double-network hydrogels and provides a valuable theoretical basis for the rational design of soft sensing materials, thus advancing their applications in intelligent electronics.