Molecular engineering of backbone rotation in an energy-dissipative hydrogel for combining ultra-high stiffness and toughness

, compared to the corresponding chemically cross-linked hydrogel. It is further elucidated that the Hofmeister effect immobilizes the polymer segmental motion by restricting backbone rotation, utilizing the hydrophobic pendant methyl groups, while the secondary cross-links function as energy-dissipating elements. The synergistic stress transfer from the primary network to the secondary cross-links effectively integrates these typically opposing mechanical traits. Additionally, we applied the HARD strategy to a double-network hydrogel system, demonstrating its versatility and broad applicability. The dynamic and highly tunable mechanical enhancement makes this strategy a powerful tool for advancing hydrogel design across various applications, as demonstrated by case studies on shape recovery and anti-freezing properties.