a solvent exchange method is employed to provide microencapsulated compositions , such as microcapsules of pharmaceutical preparations . the method is based on an exchange of water and a hydrophilic organic solvent , whereby a decline in solvent quality for the organic solvent causes a polymer dissolved therein to be deposited onto an aqueous core . optimal results are rationalized in terms of a balance of water solubility and surface tension for the organic solvent . in a preferred embodiment , microcapsules of selected drugs are formed by contacting microdroplets of an aqueous solution containing the drug with the organic solvent containing a polymer dissolved therein . a preferred method employs biodegradable poly dissolved in acetic acid , ethyl acetate , methyl acetate , or ethyl formate , to form a plga membrane around an aqueous drug core . the method is particularly attractive for encapsulating protein - based drugs without substantial denaturation .