Synergistic Reinforcement of Composite Hydrogels via Dual Cross-Linking and Supramolecular Filler

The weak mechanical properties of hydrogels limit their applicability in load-bearing environments. Here, tough composite hydrogels with dual supramolecular cross-linking via host–guest (HG) interactions were developed to enhance the mechanical properties. Primary HG cross-linking between β-cyclodextrin (β-CD) and adamantane (Ad) provided structural integrity and self-recovery, while secondary cross-linking at the filler/matrix interface improved energy dissipation. Adamantane-modified cellulose nanocrystals (Ad-CNCs) enabled secondary cross-linking with β-CD grafted onto the matrix. The synergistic effect of dual cross-linking led to remarkable improvements in strength and toughness, surpassing those of single cross-linking systems. In situ small- and wide-angle X-ray scattering (SWAXS) and multiscale finite element analysis (FEA) revealed that primary cross-linking governs alignment of CNCs and energy dissipation, while secondary cross-linking enhances filler connectivity for efficient stress transfer, leading to improved toughness and Young’s modulus. The proposed design strategy contributes to the fundamental understanding and development of tough hydrogels.