Microencapsulation of proteins with polymer-blend by rapid expansion of supercritical carbon dioxide

A new polymer-blend microencapsulation, rapid expansion from supercritical solution with a nonsolvent (RESS-N), is reported for forming polymeric microparticles containing proteins, in this case lipase (from Pseudomonas cepacia) and lysozyme (from chicken egg white). A suspension of protein in carbon dioxide (CO2) containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. The polymers are poly (ethylene glycol) (PEG 4000;M. W. = 3,000, PEG 6000; IM. W.=7,500, PEG 20000; MT. W.=20,000), poly (methyl methacrylate) (PMMA; M. W.=15,000), poly (L-lactic acid) (PLLA; M. W.=5,000), poly (DL-lactide-co-glycolide) (PGLA; M. W.=5,000) and PEG-poly (propylene glycol) (PPG)-PEG triblock copolymer (PEG-PPG- PEG; M. W. = 13,000). The solubilities of these polymers in CO2 increase significantly with the use of low molecular weight alcohols as cosolvents. After expansion, the particles do not tend to agglomerate, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of the microcapsules were investigated by TEM, SEM with EPMA, laser-diffraction particle-size analysis, and optical microscopy. The thickness of the polymer coating about the protein, and likewise, the mean particle diameter and particle size distribution could be controlled by changing the feed composition of the polymer.