The role of capsule on the performance of a dry powder inhaler using computational and experimental analyses

Purpose. To study the fundamental effects of the spinning capsule on the overall performance of a dry powder inhaler (Aerolizer(R)). Methods. The capsule motion was visualized using high-speed photography. Computational fluid dynamics (CFD) analysis was performed to determine the flowfield generated in the device with and without the presence of different sized capsules at 60 l min(-1). The inhaler dispersion performance was measured with mannitol powder using a multistage liquid impinger at the same flowrate. Results. The capsule size (3, 4, and 5) was found to make no significant difference to the device flowfield, the particle-device impaction frequency, or the dispersion performance of the inhaler. Reducing the capsule size reduced only the capsule retention by 4%. In contrast, without the presence of the spinning capsule, turbulence levels were increased by 65%, FPFEm (wt% particles <= 6.8 mu m in the aerosol referenced against the amount of powder emitted from the device) increased from 59% to 65%, while particle-mouthpiece impaction decreased by 2.5 times. When the powder was dispersed from within compared to from outside the spinning capsule containing four 0.6 mm holes at each end, the FPFEm was increased significantly from 59% to 76%, and the throat retention was dropped from 14% to 6%. Conclusions. The presence, but not the size, of a capsule has significant effects on the inhaler performance. The results suggested that impaction between the particles and the spinning capsule does not play a major role in powder dispersion. However, the capsule can provide additional strong mechanisms of deagglomeration dependent on the size of the capsule hole.