Independent control of crosslinking density and cell adhesive properties of hydrogels via alginate crosslinker developed by separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to its severely limited solubility in organic solvents. Herein, functional moieties responsible for radical polymerization (methacrylate) and cell adhesion (e.g. RGD peptide, gelatin) were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium ions of alginate in the original form are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent (i.e. dimethyl sulfoxide), followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate (MAlg) was able to not only crosslink different monomers to form hydrogels with varying mechanical properties controlled by the concentration and the degree of methacrylate substitution, but also induce stable cell adhesion to the hydrogels.