Insights into Schiff-base crosslinking in chitosan porous scaffolds: the role of dialdehyde polysaccharide ionic nature and bioactive functionalization.

This study introduces a systematic framework for fabricating chitosan porous scaffolds using five green dialdehyde polysaccharides (DAPs: chitosan, dextran, gellan, xanthan, and furcellaran) as sustainable click-chemistry-inspired crosslinkers. For the first time we demonstrated that scaffold properties are governed by the DAP's ionic character and acid strength. The covalent Schiff base formation dominates in porous scaffolds crosslinked with non-ionic oxidized dextran, ensuring the highest porosity and lowest degradation rate. Conversely, the use of anionic DAPs introduces competitive polyelectrolyte complexation (PEC) effects. We demonstrated that the acid strength of the anionic group is critical: the highly acidic sulfate groups of furcellaran cause the rapid destabilization of the PEC via competitive ion-exchange in PBS, resulting in the high rate of degradation despite creating the most compact structure - lowest swelling and porosity. Meanwhile, the highly rigid and high-molecular-weight oxidized xanthan gum proves to be an effective anionic DAP in achieving superior mechanical properties. Integration of bioactive modifiers (gelatin, Sr-doped sol-gel-derived bioactive glass, rosmarinic acid) further tunes the microarchitecture, mineralization, and mechanical behaviour. While these additives had minimal effect on the materials swelling and stability in vitro, gelatin notably reduced scaffold porosity and pore size, while bioactive glass promoted mineralization in PBS and significantly enhanced scaffold mechanical performance. In vitro studies confirmed that all formulations exhibit composition-dependent modulation of human fibroblast proliferation, while maintaining superior cytocompatibility. These findings establish critical guidelines for the rational design of multifunctional, ionically-tailored scaffolds, positioning DAPs as versatile tools for precisely engineered biomimetic matrices in advanced regenerative medicine.