A fluidized-bed coating technology using near-critical carbon dioxide as fluidizing and drying medium

A Wurster-type coater employing near-critical carbon dioxide as the fluidizing medium and antisolvent was developed for pharmaceutical applications. Suitably designed glass inserts housed in a high-pressure chamber allow for the controlled fluidization and circulation of the substrates with dense CO2. The CO2 also removes the solvent from the coating solution sprayed on the substrates, thereby precipitating the coating as a smooth layer. A variety of substrates were successfully coated with thin polymer films for aesthetic/handling purposes or for delayed release applications such as taste masking. The geometry of substrates include glass and microcrystalline cellulose (MCC) beads ranging in diameter from 0.5 to 2 mm, tablets up to 7.9 mm and cylindrical stents up to 20 mm in length. The demonstrated coating process expands the range of substrate/coating combinations possible with the conventional air-fluidized Wurster coater, making it feasible to coat water-soluble substrates with solutes sprayed from organic solutions at near-ambient temperatures wherein degradation of the active pharmaceutical ingredient is avoided. Coating with dense CO2 enables the use of traditional organic solvents with no risk of explosion.