Water behavior, thermal, structural, and viscoelastic properties of physically cross-linked chitosan hydrogels produced by NaHCO3 as a crosslinking agent

In this study, we prepared chitosan hydrogels using two chitosan concentrations (1.5 and 2.0 wt%) and two molecular weights of chitosan (low and medium molecular weight) by a physical crosslinking process using sodium bicarbonate (NaHCO 3 ). A two-step process was used to produce four different hydrogels: (1) freeze-drying of the chitosan solutions and (2) crosslinking by coagulation bath with NaHCO 3 . Thermal stability (TGA), chemical structure (FT-IR), microstructure (SEM), water state (DSC analysis), water sorption (GAB model), and viscoelastic properties (oscillatory test) of the chitosan hydrogels were evaluated. The physicochemical properties of the hydrogels depended on the concentration and molecular weight of chitosan. The chitosan hydrogels showed high hydrophilicity, predominantly solid-viscoelastic behavior, highly porous, and interconnected structures with average pore diameters from 131 ± 17 to 239 ± 35 µm. Chitosan hydrogels could be excellent candidates as polymer scaffolds for biomedical applications. Graphical abstract