Microencapsulation of proteins by rapid expansion of supercritical solution with a nonsolvent

A new method-rapid expansion from supercritical solution with a nonsolvent (RESS-N) - is reported for forming polymer microparticles containing protei ns such as lysozyme (from chicken egg white) and lipase (from Pseudomonas c epacia). A suspension of protein in CO2 containing a cosolvent and dissolve d polymer is sprayed through a nozzle to atmospheric pressure. The polymers are poly(ethylene glycol) (PEG4000; MW = 3,000 PEG6000; MW = 7,500, PEG200 00; MW = 20,000) poly(methyl methacrylate) (PMMA; MW = 15,000), poly(L-lact ic acid) (PLA; MW = 5,000), poly(DL-lactide-co-glycolide) (PGLA; MW = 5, 00 0) and PEG - poly(propylene glycol) (PPG) - PEC triblock copolymer (MW = 13 ,000). The solubilities of these polymers in CO2 increase significantly wit h low-molecular-weight alcohols as cosolvents. The particles do not tend to agglomerate after expansion, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of the microcapsules were investi gated by TEM, SEM, and optical microscopy. The thickness of the polymer coa ting about the protein, as well as the mean particle diameter and particle- size distribution could be controlled by changing the feed composition of t he polymer.