Efficient handling and transport of fine-particle powders can be difficult because of the highly cohesive nature of the bulk powder mass. It is well reported in the literature that the application of nanosized guest dry powder coatings, such as silicon dioxide, onto the surfaces of these cohesive host particles can effectively reduce the attractive forces between them (1–5). The fine nanoparticles increase the spacing between the host particles and increase the apparent surface roughness, which decreases the host particle cohesive van der Waals attractions (5, 6). After dry powder coating, the bulk powder exhibits increased bulk density, improved powder flow performance, and easy fluidization behavior, all of which can significantly improve manufacturing performance (1–5). This result is of significant benefit to pharmaceutical powder processing because the easy transport of large bulk quantities of powder through unit operations is necessary to manufacture solid dosage forms such as capsules and tablets.
It was recently demonstrated that conventional pharmaceutical processing equipment, namely a comil, can effectively apply dry powder coatings of silicon dioxide onto active pharmaceutical ingredients (APIs) and excipients without causing attrition of the host's primary particles (1). This discovery is important because comils can be operated in a continuous manufacturing process and are commonly available at pharmaceutical product manufacturing sites. Although the comil is a simple, effective, and scalable unit operation for applying dry powder coatings, the systematic study of the process operational design space, such as screen size and impeller speed, may be required to optimize the coating performance. This iterative method may not be possible in early drug product development because of the limited available quantities of API (often less than 50 g) and the potential for improved performance after dry powder coating may be overlooked, especially as API synthesis, isolation, and sizing processes change often. Therefore, alternative (or complementary) methods for applying dry powder coatings would be desirable during early product development.