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 CO 2 . The CO 2 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 CO 2 enables the use of traditional organic solvents with no risk of explosion.