Study On Covalently Cross-Linked Alginate-Gelatin Hydrogels

As a natural linear polysaccharide, alginate has been widely used in tissue engineering and other relative fields. However, alginate itself has a very slow degradation rate, and its gels degraded in an uncontrollable manner, releasing high molecular weight strands that may have difficulty being cleared from the body. Simultaneously, ionically cross-linked alginate hydrogels have uncontrollable mechanical properties and disintegration behavior. These drawbacks have limited its use in tissue engineering. In this paper, partially oxidized sodium alginate was covalently cross-linked with gelatin via Schiff's base formation to prepare a novel injectable hydrogel.Guluronic acid-rich high molecular weight sodium alginate was oxidized using sodium periodate. IR analysis confirmed the characteristic peak of aldehyde group in the oxidized alginate. Additionally, the degree of oxidation (OD) or the aldehyde contents were measured by using titration methods. The OD of sodium alginate enhanced along with the increasing amounts of added sodium periodates. The molecular weights of sodium alginate were also declined as reaction temperature rising. Oxidized sodium alginate had a controllable biodegradability at physiological condition.Oxidized sodium alginate was made to react with gelatin A in the presence of sodium tetraborate solution to form covalently cross-linked hydrogels. IR analysis confirmed the characteristic peak of Schiff's base group in the hydrogel. By increasing the OD and concentration of oxidized alginate, gelatin and sodium tetraborate, gelation time could be shortened from ten minutes to one minute. The dynamic shear modulus and compressive modulus of the hydrogels could be modulated by the gelling conditions. The hydrogels also had a suitable biodegradability at physiological condition.Cytotoxicity evaluation using L929 fibroblasts as model system showed that the covalently cross-linked alginate-gelatin hydrogels were nontoxic in proper compositions. Optical and fluorescent photomicrographs showed good morphology of L929 in these hydrogels. MTT assay confirmed that there were no significant differences between the hydrogels and control (TCPS) in cell activity. The results will be helpful for the further research for developing alginate-gelatin hydrogels for tissue engineering.