Design, Properties and Applications of Multiple Dynamic Hydrogels.

Hydrogels are highly hydrated polymeric soft materials that closely mimic the mechanical characteristics of biological soft tissues, offering immense promise for biomedical applications such as tissue engineering, drug delivery, flexible electronics, and wound repair. Conventional hydrogels crosslinked by static covalent bonds suffer from irreversible network disruption upon mechanical damage and lack active responsiveness to environmental stimuli, severely limiting their practical use. Incorporating both dynamic covalent bonds and dynamic non-covalent interactions endows hydrogels with intelligent features, including self-healing, injectability, and stimuli responsiveness. A single dynamic crosslinking mode often fails to achieve an optimal balance between mechanical robustness and rapid dynamic reversibility, whereas the synergistic integration of multiple dynamic bonds-exploiting their complementarity in kinetics, energy dissipation, and stimuli-responsiveness-has emerged as a cutting-edge strategy to overcome this limitation. Using dynamic non-covalent interactions as the classification framework, this review systematically summarizes recent advances in hydrogels crosslinked by combinations of dynamic non-covalent interactions with dynamic covalent bonds, covering hydrogen bonds, host-guest interactions, metal-ligand interactions, electrostatic interactions, hydrophobic interactions, π-π stacking interactions, and other emerging multiple dynamic crosslinking systems. The design principles, synergistic mechanisms, multifunctional applications, and key challenges and future directions of each system are discussed and prospected.