Wall collision and drug-carrier detachment in dry powder inhalers: Using DEM to devise a sub-scale model for CFD calculations

In this work, the Discrete Element Method (DEM) is used to simulate the dispersion process of Active Pharmaceutical Ingredients (API) after a wall collision in dry powders inhaler used for lung delivery. Any fluid dynamic effects are neglected in this analysis at the moment. A three-dimensional model is implemented with one carrier particle (diameter 100 μm) and 882 drug particles (diameter 5 μm). The effect of the impact velocity (varied between 1 and 20 m s⁻¹), angle of impact (between 5° and 90°) and the carrier rotation (±100,000 rad s⁻¹) are investigated for both elastic and sticky walls. The dispersion process shows a preferential area of drug detachment located in the southern hemisphere of the carrier. The angle of impact with the highest dispersion is 90° for the velocities over 9 m s⁻¹ and between 30° and 45° for lower velocities. The rotation of the carrier before the impact, on the other hand, for velocities higher than 7 m s⁻¹, plays a little role on the dispersion performance. The DEM results are finally “distilled” into a simplified analytic model that could be introduced as a sub-scale model in Euler/Lagrange CFD calculations linking fluid dynamics with the detachment probability of APIs in the inhaler.