SUB-MICROMETER-SIZED BIODEGRADABLE PARTICLES OF POLY(L-LACTIC ACID) VIA THE GAS ANTISOLVENT SPRAY PRECIPITATION PROCESS

Sub-micrometer-sized particles of poly(L-lactic acid) may be formed by using near-critical or supercritical carbon dioxide as an antisolvent to precipitate poly(L-lactic acid) from droplets of methylene chlorid e solution sprayed into a carbon dioxide continuous phase. Particle si zes may be controlled by varying the density of the carbon dioxide; at constant temperature in the supercritical region, higher carbon dioxi de densities yield larger particles. Two methods (one batch and one co ntinuous) for introducing the poly(L-lactic acid) solutions into carbo n dioxide are demonstrated. Although the two methods use very differen t mechanisms for forming the droplets, similar particle sizes are obse rved as a function of carbon dioxide density. We suggest that mass tra nsport, rather than jet breakup and hydrodynamics, controls particle s izes in the near-critical and supercritical regions.