Multi-scale modelling of powder dispersion in a carrier-based inhalation system

Purpose: Carrier-based dry powder inhalers (DPIs) are widely used for rapid and convenient delivery of drug to the site of action. This work aimed to predict powder aerosolisation in DPIs through numerical modelling. Methods: A multi-scale modelling technique based on the combined computational fluid dynamics (CFD) and discrete element method (DEM) approach was developed. Results: The simulation results of the detachments of the drug particles from single carrier under different impact velocities and angles were comparable with those measured in the experiments in terms of fine particle fraction FPF_loaded. Empirical equations were developed to link the detachment performance with impact velocity and impact angle. Then the dynamics of the carrier particles in Aerolizer® was simulated. The results indicated that the carrier-wall impaction was the dominant mechanism for drug aerosolisation performance. By linking the empirical equations with the carrier-wall impact energy, the predictions showed that for a given formulation mass with a fixed carrier/drug ratio, the inhaler performance decreased with carrier size and increased with air flow rate. Device empty efficiency, however, was independent with carrier size and flow rate. Conclusions: The multi-scale model was able to provide quantitative information to better understand the aerosolisation mechanisms of carrier-based formulation.