Linking Polysaccharide Structure, Gelation Kinetics, and Function in Dynamic Acylhydrazone Hydrogels

Dynamic covalent hydrogels created via reversible acylhydrazone crosslinking have become promising injectable biomaterials. However, the relationship between their macromolecular structure, gelation kinetics, material properties, and cellular responses remains poorly understood. To address this knowledge gap, researchers constructed an acylhydrazone hydrogel library using alginate adipohydrazide crosslinked with oxidized alginate (OxA) or oxidized dextran (OxD).

These two reactive aldehyde-bearing polymers share comparable chemical functionality but possess distinct backbone structures.

By varying polysaccharide type, oxidation degree, and reaction pH, the researchers were able to separate the effects of chemical functionality from macromolecular structure. This allowed them to establish quantitative relationships between structure, gelation kinetics, material properties, and function. The findings revealed that OxD-based hydrogels exhibit rapid gelation that is largely pH-independent.

In contrast, OxA-based systems display pronounced pH-dependent kinetics with delayed network formation at physiological pH.

These differences in gelation kinetics directly influence hydrogel mechanics. OxA hydrogels display higher stiffness, greater stress relaxation, reduced stability, less injectability, and slower post-injection recovery compared to OxD hydrogels. Furthermore, these kinetics variations impact cell-matrix interactions during three-dimensional cell culture.

Slowly forming OxA hydrogels preserve rounded chondrocyte shapes, while rapidly gelling OxD networks lead to transient cell elongation. Importantly, mesenchymal stem cells maintain similar shapes regardless of gelation kinetics, revealing cell-type-specific responses to matrix formation dynamics.