A method for the production of microporous poly(D, L-lactide-co-glycolide) foams containing encapsulated proteins using supercritical carbon dioxide is described. Foams generated as aqueous protein emulsions in a polymer-solvent solution were saturated with carbon dioxide at supercritical conditions, and then suddenly supersaturated at ambient conditions causing bubble nucleation and precipitation of the polymer. Proteins contained in the water phase of the emulsion were encapsulated within the foams, including basic fibroblast growth factor (bFGF), an angiogenic factor of interest in tissue engineering applications. The release and activity of bFGF from these foams was determined in vitro and compared with similar porous scaffolds prepared by traditional solvent casting-salt leaching techniques. Total protein release rate was greater from structures made in CO(2) than those made by the salt leaching technique, however a large initial burst of bFGF was released from the salt leached structures. This initial burst was not observed from the polymer foams processed in CO(2) and active bFGF was released at a relatively constant rate. Residual methylene chloride levels were measured in the foams made with CO(2) and were found to be above the limits imposed by the US Pharmacopoeia implying that further solvent removal would be required prior to in vivo use.
Animals Biocompatible Materials