Importance of Wall Collisions for Particle-Particle Detachment in Dry Powder Inhalers, and Advanced Wall Collision Models

This work presents tools for estimating Fine Particle Fractions generated inside Dry Powder Inhalers, by analysing detachment of drug particles from carrier particles. The trajectories of carrier particles through an inhaler are simulated using the FLUENT software for Computational Fluid Dynamics. These are analysed, by evaluating the forces that may break carrier/drug bonds. These forces, from impacts with inhaler walls or from fluid effects, are compared with carrier/drug bond strengths, measured by Atomic Force Microscopy. The comparison is in terms of torque, which is the probable mechanism for detachment. Impact torques greatly exceed fluid-based torques. This demonstrates the importance of wall collisions; several collision models are considered, including effects of spin, inelasticity and particle shape. The results show that commonly-used wall collision models are unsuitable.