Understanding the motion of rotating hard shell capsules in dry powder inhalers 

Benedict Benque¹ & Johannes Khinast¹

¹Institute of Process and Particle Engineering, Graz University of Technology, Inffeldgasse 13, Graz 8010, Austria

Summary

In certain dry powder inhalers (DPI), the discharge and dispersion of carrier-based or carrier-free formulations from a pierced and rotating capsule is crucial for the delivery of small drug particles to the patient’s peripheral airways. The dispersion of drug particles depends on turbulence and on particle collisions in the inhaler. The present study examined the three-dimensional motion and the resulting wall collisions of a size three capsule in an Aerolizer® inhaler using high-speed photography. A correlation between the capsule-wall collision rate and the capsule’s rotation was observed. The capsule collided predominantly with the mouthpiece grid, frequently in a bouncing motion.

Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) simulations were used to investigate how this motion affects the powder behavior and powder release from the capsule. The CFD simulations were conducted using ANSYS Fluent and neglected the lateral and vertical displacement of the capsule. The transient air flow through the pierced capsule was shown to be the dominant force on small drug particles, while the motion of the larger carrier particles was governed by inertial forces.

DEM simulations were conducted using XPS® (eXtended Particle Simulation) to study the influence of capsule-wall collisions on the discharge of cohesive and non-cohesive powder from the rotating capsule. The collisions were found to increase the powder release of non-cohesive and slightly cohesive material, while decreasing it in the case of highly cohesive materials.