Study On New Alginate-Gelatin Hydrogels

Alginate and gelatin are both natural biomaterials, they have been widely used in tissue engineering and other relative fields because of their low price and good biocompatibility. 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. Besides,at room temperature the starting gelatin is not soluble in water unless the temperature is raised above 37℃, because it has intermolecular physical cross-linkages. To circumvent these problems,we modified both alginate and gelatin to change their physical or chemical properties. In this paper, partially oxidized sodium alginate was covalently cross-linked with aminated gelatin via Schiff's base formation to prepare a novel injectable hydrogel.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 higher in water-ethanol than pure water system. Oxidation in water-ethanol system has the advantage of generating large quantities of the oxidized alginate in higher yield using less solvent. Oxidized sodium alginate had a controllable biodegradability under physiological condition.Gelatin was modified with ethylenediamine in the presence of EDC to convert the carboxyl groups in original gelatin into amino groups. Additionally, amino contents were measured using TNBS. The amino contents enhanced along with the increasing amounts of added ED. The introduction of amino groups in gelatin improved its solubility and facilitated gelatin dissolving in water at room temperature.Oxidized sodium alginate reacted with aminated gelatin to form covalently cross-linked hydrogels. IR analysis confirmed the characteristic peak of Schiff's base group in the hydrogel. By increasing the OD, amino content and concentration of reactants, gelation time could be controlled from 30s to 250s. The dynamic shear modulus and compressive modulus of the hydrogels could be modulated by the gelling conditions. The degradability of hydrogels was dependent on oxidized alginate and had a suitable biodegradability under physiological condition. Cytotoxicity evaluation using L929 fibroblasts as model system showed that the covalently cross-linked alginate-gelatin hydrogels were nontoxic in proper compositions.