In vitro release characteristics of bioactive molecules from dextran dialdehyde cross-linked gelatin hydrogel films

Hydrogel films, prepared by cross-linking of gelatin with dextran dialdehydes (weight ratio 2:1), and containing either fluorescein isothiocyanate-dextran (MW 70 000) or polypeptides were evaluated in terms of their release characteristics and mechanical properties upon increasing storage time at 4°C. Important changes in release kinetics and mechanical properties of the cross-linked gelatin films were observed, especially during the first week after the hydrogel production. Rheological and NMR measurements showed that the mechanical properties of the gelatin hydrogel films were improved with increasing storage time. It appeared that the process of chemical cross-linking and physical structuring of the gelatin hydrogel matrix did not occur instantaneously and substantially influenced the polypeptide release patterns. Cross-linked gelatin hydrogels were found to be appropriate release systems for medium-term sustained delivery of biologically active epidermal growth factor (EGF), but release characteristics were strongly dependent on the nature of the protein which was incorporated.