Slide-Ring Hydrogel Networks Cross-Linked by Movable Cucurbit[8]uril/Macromer Host-Guest Complexes

For traditional covalently cross-linked hydrogels, achieving both stiffness and toughness is generally difficult, owing to the fixed cross-linking points and the lack of dynamic response. Introducing movable cross-linking points into the network has proven to be an effective strategy to overcome this limitation. However, most existing approaches rely on pseudopolyrotaxane architectures based on cyclodextrin (CD) and polyethylene glycol (PEG), which require complicated synthesis. In this study, slide-ring hydrogels were conveniently synthesized via free radical polymerization of acrylamide (AM) and acrylic acid (AA) monomers, employing a supramolecular complex of azobenzene guest-modified telechelic macromers (Acr-Azo-PEG20K-Azo-Acr) and cucurbit[8]uril (CB[8]) as movable cross-linkers. Benefiting from the introduction of dynamic host-guest cross-linking, these hydrogels possess movable cross-linking points that can effectively dissipate energy and distribute stress during deformation, thereby significantly enhancing the mechanical properties through the pulley effect. By tuning the cross-linker content, solid content, and monomer structure, the material properties could be precisely optimized. Furthermore, posttreatment with ferric citrate (FeCA) allowed the introduction of Fe3+ dynamic coordination cross-linking into the acrylic-based slide-ring hydrogels, achieving a simultaneous 3-fold increase in tensile strength and an approximately 4-fold increase in toughness while maintaining high ductility and excellent fatigue resistance. The use of macromer/CB[8] complexes as movable cross-linkers offers a new strategy for high-performance hydrogels and lays a solid foundation for their future applications.