CFD-DEM investigation of the dispersion of elongated particles in the Turbuhaler® aerosol device

Elongated drug particles have the potential to be superior to spherical drug particles for delivery to the deep lung due to their increased ability to align with the airflow. However, the performance of elongated particles within dry powder inhalers (DPIs) has been largely unexplored. This paper presented a CFD-DEM study to simulate the dispersion of elongated active pharmaceutical ingredient (API) particles with equivalent sizes of 1.55–5.53 μm in a commercial DPI device Turbuhaler®. The model, which adopted a multi-sphere approach to mimic the shape of elongated spherocylindrical particles, was validated by comparing experimental data of fluidized beds. The model was then utilized to simulate the dispersion of powders with different aspect ratios in Turbuhaler. Findings revealed that the depositions of elongated particles in the chamber and the mouthpiece were significantly higher than those of spherical particles, and the depositions increased with higher aspect ratios. The higher deposition of the elongated particles was due to much stronger inter-particle cohesion when particles were in flat contact with particles or wall surfaces. Similar to spherical particles, both emitted dose and fine particle fraction (FPF, % mass of particles below 5 μm) of elongated particles increased with flow rates due to intensified particle-wall collisions. On the other hand, the FPF of elongated particles in the device decreased more significantly with increasing cohesion than spherical particles. Results indicated that while elongated particles are preferred for drug delivery to deeper lungs, their poor dispersion in inhalers due to higher deposition needs to be considered.