Dynamic Covalent-Crosslinked Natural Polymer Hydrogels: Construction Strategies, Property Trade-Offs, and Oral Drug Delivery and Tissue Repair

Introducing reversible covalent linkages, such as Schiff base bonds and disulfide bonds, into natural polymer networks like chitosan and hyaluronic acid has become an important research direction in the hydrogel field. This strategy seeks to reconcile the limited strength of physically crosslinked gels with the poor adaptability of permanently crosslinked gels. Although dynamic covalent networks, self-healing natural-polymer hydrogels, and injectable oral or periodontal materials have each been reviewed, these topics are often treated separately. The unresolved question addressed here is how to select dynamic bonds and regulate their exchange kinetics under the coupled constraints of the oral cavity, including salivary washout, masticatory friction, local pH/ROS/glucose fluctuations, required retention and degradation periods, and manufacturability. This review therefore focuses on dynamic covalent-crosslinked hydrogels built from natural polymer backbones and evaluates three mainstream bond types: Schiff base bonds, disulfide bonds, and boronic ester bonds. Following an oral-specific design framework of “pathological signals—bond response—property trade-offs—scenario fit—translation bottlenecks”, it examines local drug delivery and tissue-repair applications in periodontitis and oral ulcers and discusses dentin hypersensitivity and pulp protection only as potential extension directions. Diagnostic sensing, molecular imaging, and receptor-mediated targeting are outside the evidence base of this review and are not claimed as established applications. The review summarizes trade-off rules between mechanical performance and dynamic functions and identifies bottlenecks in multi-network regulation, sterilization, and clinical translation. Its added value lies in linking bond chemistry to oral-specific design constraints, rather than cataloguing hydrogel examples alone.