Effect of porous structure on the degradation of freeze-dried gelatin hydrogels

Abstract

Porous biodegradable hydrogels were prepared by glutaraldehyde crosslinking of acidic gelatin with an isoelectric point of 5.0, followed by freeze-drying. The inner structures of the freeze-dried hydrogels were strongly dependent on the preliminary freezing temperatures prior to freeze-drying. As the freezing temperature was raised, the pore size of the freeze-dried hydrogels increased while their wall thickness decreased. The hydrogels frozen at -20°C swell more rapidly in water than those at -80° and -196°C. In vivo and in vitro degradations of freeze-dried hydrogels with different inner structures were evaluated subcutis in mice and in a collagenase aqueous solution, respectively. The hydrogels prepared at -20°C were more rapidly degraded both in vitro and in vivo, compared to those at -80° and -196°C. The hydrogels freeze-dried at -196°C had the smallest pore size, thickest gelatin walls, and required a longer time for complete degradation. Basic fibroblast growth factor (bFGF) was impregnated into the gelatin hydrogels and the in vitro bFGF release was evaluated. No influence by the inner structure on the release profile of bFGF was observed. Since bFGF is ionically complexed with acidic gelatin, it is possible that it was released from these gelatin hydrogels in a similar fashion, irrespective of the hydrogel inner structure.