Hydrogel-to-Emulsion Gel Transformation Enabled by Dynamic Schiff Base Network Reconstruction

Dynamic emulsion gels with self-healing and injectable properties have attracted growing interest in food structuring and soft material design; however, facile strategies for directly converting preformed hydrogels into emulsion gels remain largely unexplored. In this study, a facile hydrogel-to-emulsion gel transformation strategy was developed based on dynamic Schiff base cross-linking between carboxymethyl chitosan (CMCS) and oxidized sodium alginate (OSA). CMCS-OSA hydrogels were first rapidly formed through reversible imine bonds between amino and aldehyde groups and subsequently converted into oil-in-water emulsion gels via high-speed homogenization with sunflower oil. During homogenization, the bulk hydrogel was converted into a pregel solution that underwent gelation at the oil–water interface and subsequently reconnected through dynamic covalent interactions, thereby rebuilding a continuous gel network. Increasing OSA concentration enhanced cross-linking density, leading to stronger mechanical properties, denser network structures, reduced pore size, and lower water mobility while prolonging self-healing time. The introduction of oil droplets transformed the hydrogel into an emulsion gel in which the droplets acted as active fillers, reinforcing the gel matrix. However, excessive oil volume fractions increased structural heterogeneity and weakened self-healing performance. Both hydrogels and emulsion gels exhibited solid-like viscoelastic behavior, pronounced shear-thinning, injectability, and autonomous structural recovery. These findings demonstrate that dynamic covalent hydrogels can undergo shear-induced conversion into a pregel solution and network reconstruction during emulsification, enabling the formation of stable emulsion gels. This work provides mechanistic insight into hydrogel-to-emulsion gel transformation and offers a simple strategy for designing dynamic polysaccharide-based soft materials for food and related applications.