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Biodegradable Microcapsules Via Emulsification/freeze Drying

Weisi Yin and Matt Yates. University of Rochester, Department of Chemical Engineering, 206 Gavett Hall, Rochester, NY 14627

We recently described the factors influencing microcapsule formation in a process we coined “emulsification/freeze drying” (Yin and Yates, Langmuir, 2008). In this simple technique, polymer solution is first emulsified to form an oil-in-water emulsion. Then, the emulsion is rapidly frozen in liquid nitrogen, during which polymer phase separation occurs in the droplets. The solvent-rich phase tends to migrate to the center of the emulsion droplet, surrounded by the polymer rich phase. Upon drying under vacuum, hollow polymer particles are left that have a single hole where the solvent-rich phase was. Subsequently resuspending these particles in water and exposure to a plasticizing solvent results in the hole closing to form microcapsules, in a process first described by Im, et al (Nature Materials, 2005). Here we report the extension of the emulsification/freeze drying technique to form biodegradable microcapsules. Emulsions of poly(lactic acid) and poly(lactic acid-co-glycolic acid) in dichloromethane were freeze dried to generate hollow biodegradable particles with a single opening on the surface. The particle size was strongly influenced by the type of emulsifier and the concentration of solvent used. The dried particles were resuspended in water and exposed to a plasticizing solvent in order to form microcapsules. Procaine hydrochloride, a model water-soluble drug, was encapsulated in the biodegradable microcapsules and drug release kinetics were examined. The results demonstrate the feasibility of using emulsification/solvent evaporation to create biodegradable microcapsules for controlled release.