(625d) Transport Modeling of Micro- and Nanometer-Sized Particles in a Human Lung Geometry

Micro- and nanoparticles are well recognized for their inherent suitability in biomedical applications, due in part to their high surface area to volume ratio. Significant research efforts have been directed towards the use of micro- and nanoparticles for drug delivery to specific organs in the human body. One common approach is inhaled drug delivery via deposition and absorption at the lung epithelium. For example, drugs such as DNAase and insulin are currently delivered via particulate inhalation mechanisms. Conversely, many environmental micro- and nanoparticles represent potential health hazards due to inhalation exposure, such as diesel exhaust particles and coal dust. Numerical modeling approaches to predict the transport and deposition of inhaled particles represent key enabling technologies for the development of improved drug delivery methods and for the mitigation of detrimental health effects.

Recent efforts in particle transport modeling in the lung airway have focused on three-dimensional computational fluid dynamics (CFD) simulations. Typically, the airflow in the lung is obtained from numerical solution of the single-phase Navier-Stokes equations, with the particles treated as a passive phase in a dilute mixture. For microparticles, transport is almost always simulated using a Lagrangian approach in which individual particle trajectories are computed via the solution of the governing ordinary differential equations. Statistical measures of particle transport and fate are obtained by averaging over a large number of trajectories. Nanoparticles, on the other hand, are often treated using a one-fluid Eulerian approach, in which a concentration equation is solved for the particle phase, and the phase (bulk) velocity is assumed to be equal to the air velocity.

This paper examines a unified, two-fluid Eulerian modeling approach, in which a concentration equation is solved for both micro- and/or nano-sized particles. In addition, a particle phase momentum equation is solved to determine the particle bulk velocities, separate from the air velocity. Results are compared to the more traditional approaches mentioned above to evaluate the performance of the unified method. Steady state flow in two geometries is considered: flow through a 90° elbow and flow through a representative lung airway model based on the Weibel morphology. Simulations are performed using the commercial CFD code FLUENT, and the particle phase equations are incorporated using User-Defined Function subroutines. The effects of mesh resolution and numerical method (discretization scheme) are evaluated. Results suggest that the unified Eulerian method is an effective approach for particle transport simulations in the human lung airway.