The modelling of carrier-wall collision with drug particle detachment for dry powder inhaler applications

The paper proposes a novel particle-wall collision model for calculating temporal changes of particle velocities and forces acting on the particle during the collision between an elastic particle and a plane solid wall. The purpose is to determine the maximum inertia force acting on the particle in connection with an accurate prediction of the transition between the sliding and non-sliding periods. This method is successfully applied to the calculation of drug detachment probability via particle-wall collisions within dry powder inhalers, in which fine drug particles are usually blended with larger carrier particles as one particle cluster for better dispersion. The present novel model is firstly verified in the micro-scale simulation of a single collision between the particle cluster and the wall. The simulation results reveal that the inertia force acting on drug particles is much larger than the fluid dynamic force and dominates the drug detachment. The detachment can occur through lift-off, sliding or rolling. Nearly half of the drug particles on the carrier surface can be detached by lift-off, and most of the remaining drug particles follow up with a sliding or rolling detachment. Based on these studies, a Lagrangian particle tracking algorithm is developed and is used to predict drug detachment probability within an inhaler device through one inhalation. By tracking 1024 particle clusters moving through the inhaler (i.e. the macro-scale simulation), the influence of different flow rates (i.e. 100 l/min and 70 l/min), friction coefficients between the carrier and the wall (i.e. 0.1 and 0.2), and carrier sizes (i.e. 100 μm and 500 μm) on drug detachment are investigated. The improved understanding of particle-wall collision detachment study will be the basis for optimising inhaler design.