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Stretching the Boundaries of Computational Fluid Dynamics to Address Deaggregation in DPIs

Kroeger R, Wachtel H.

Respiratory Drug Delivery 2016. Volume 1, 2016: 89-98.

Abstract:

Assuring reproducible aerosol generation inside small portable inhaler devices is challenging. Among the critical parameters of these devices are the air flow resistance, the exit velocity of the aerosol and its particle size distribution as well as the time of release of the drug particles. Computational fluid dynamics (CFD) aids in visualizing and understanding the air flow velocity profiles in a chosen device, e.g., HandiHaler^®. A special user defined function has been developed to account for various particle-particle interactions and applied to model the flow and the deaggregation of powder in the critical air ducts of HandiHaler and Breezhaler^®, two example dry powder inhalers (DPIs) chosen here to illustrate the software. Individual particles are tracked for their position, velocity and rotation in a discrete element model (DEM) manner, coupled to the fluid flow to ensure a real two way coupling during simulated deaggregation within the respective geometries of both inhalers. Van der Waals and capillary, as well as friction forces, are taken into account in the particle-particle as well as particle-wall interactions. All particle agglomerates are detected by their number and size providing a detailed process understanding so that the effects of design changes can be visualized. Based on a simulated model powder, the design space can be explored. While the computer simulation model is highly reproducible, and therefore can explain trends easily, the prediction of minute formulation effects in “real” formulations remains a goal for the future because of the complex (and up-to-now only partly defined) set of parameters describing powder-particle interactions.