Force control and powder dispersibility of spray dried particles for inhalation

This study aims towards a deeper understanding of the correlation between particle morphology, cohesion forces, and aerosol performance of spray dried powders for inhalation. Therefore, forces affecting cohesion and dispersion are considered and some novel contact models are introduced to explain the improved powder dispersibility of corrugated particles. Particles with different degrees of corrugation are prepared by spray drying and characterized. Powder dispersibility is measured by positioning a dry powder inhaler in front of the laser diffraction device. The particle sizes of all powders are in the range of x50 = 2.11 ± 0.15 µm. The ratio of mass specific surface area Sm to volume specific surface area SV rises from 0.54 cm3/g (spherical particles) to 0.83 cm3/g (most corrugation). The fine particle fraction (FPF) rises significantly with increasing corrugation at 24 L/min which can be explained by a distinct difference in powder dispersibility. From theoretical models a reduction in cohesion up to 90% can be estimated for corrugated particles compared to spherical particles. Advantages in powder dispersibility can be expected for particles having a lower density and smaller radius of curvature in the contact zone. Both characteristics are given in case of corrugated particles and can be optimized to a certain degree of corrugation. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:303-316, 2010