Polymer and Surface Engineering Laboratory(PolySEL)

http://www2.che.msstate.edu/research/PolySEL/

AcknowledgmentsThis work is supported by the National Science Foundation under Grant EPS-0903787 and the Mississippi State University Bagley College of

Engineering Ph.D. Fellowship.

Health Impacts of Micron-sized Particle Deposition in the Human Tracheobronchial Tree Erick S. Vasquez1, Nicole Stein2, Keisha B. Walters1 and D. Keith Walters2

Dave C. Swalm School of Chemical Engineering1

Mechanical Engineering Department2

Mississippi State University, Mississippi State, MS 39762

Methods-Computational fluid dynamics (CFD) simulations using a physiological realistic bifurcation (PRB) 6-7

-PRB geometry is based on a model by Weibel 8

-Parameters such as branching angle were modified to be more physiologically accurate

-Different levels of refinement (cell number) and two different mesh topologies, tetrahedral (TET) and hybrid (HYB), were analyzed :

IntroductionApplications and prior studies for particle fate/deposition in human lungs include:• drug delivery mechanisms 1

• prediction of dust, diesel or coal particle deposition 2

• particle deposition in bronchial airway bifurcations, which may play a crucial role in lung cancerinduction 3

• relationships between atmospheric pollutant impacts—both natural and anthropogenic sources—and their health impacts 4-5

MotivationExposure to particulates impacts human health. Dust, combustion exhaust, manufacturing toxins (e.g. dioxins), and many other environmental contaminants exist in the form of micron-sized particles. When inhaled, these particles can create health issues such as emphysema and cancer. Conversely, novel biomedical technologies currently include micron-sized particles that are inhaled as a drug delivery vehicle. Unintentional and intentional particle inhalation can result in particles deposited on the mucus lining; these particles can then be taken up and enter the blood stream.

Computational modeling to predict the transport and deposition of inhaled particles represents key enabling technologies for improved drug delivery methods and for the mitigation of detrimental health effects due to pollution.

Methods (continued)

Air flow was solved independently of particle phase (dilute particle assumption).

Particle deposition simulations were performed using (i) an Eulerian modeling approach in which the particles are

represented in terms of an average concentration at each location in the lung airway, and

(ii) a Lagrangian modeling approach in which each particle and its path is tracked within the lung model.

Simulations were completed using these two modeling approaches for 1, 5, 10 and 20 micron particle diameters. Experimental and computational results at 10 microns were compared along with the impact of particle size.

Computational Modeling

Computational fluid dynamics (CFD) simulations were carried out using Fluent (version 12.0.16). Simulation assumptions include:- only drag and gravitational forces are considered - a constant diffusivity value is used - particle volume fraction is zero at the walls - zero velocity at the walls (no slip boundary condition)- second-order discretization for momentum equations;

SIMPLE pressure correction scheme; PRESTO! scheme for pressure discretization

- Lagrangian: 100K randomly distributed particles injected at inlet with velocity equal to air velocity

- Eulerian: particle volume fraction value of 1 E-6 % was utilized as the initial inlet condition for the simulations; first-order and second-order discretization methods are studied for particles deposition analysis

Results and Discussion

Conclusions and Future Work• The level of refinement used for simulations with 1 micron

particle sizes was found to have a high impact on particle deposition data for Lagrangian simulations. The effect of grid refinement is still under investigation for the Eulerian methods.

• For 10 micron particles, the Eulerian method gave a better value for percent total deposition, but worse agreement with the experimental data through the first bifurcation.

• While the Lagrangian method appear to capture better the qualitative deposition pattern, as compared with experimental data, when a parabolic inlet velocity profile is used, the cumulative deposition results are less accurate.

• A high number of cells is required to obtain close agreement with experimental data for Lagrangian simulations.

• Future work will extend these analyses to more complex geometries that better represent human lung airways.

Hybrid (HYB) mesh: hexahedral cells near wall & center tetrahedral cells

Tetrahedral (TET) Mesh:

tetrahedral cells throughout geometry

Physiological Realistic Bifurcation (PRB)

Geometry

Computational results are compared with experimental data obtained by Oldham et al.9 In the experimental study, rectangular microscopic fields (2.05 mm x 1.4 mm) were used along with latex particles (~10 microns; density ~ 1 g/cc):

In the Eulerian simulations, particle phase velocity field differs from air phase due to particle inertia effects, including wall normal component at

bifurcation locations. The particle concentration field is relatively complex.

Example path lines for tracked particles are shown.

Center plane air velocity magnitude for coarse, tetrahedral mesh.

Illustration of qualitative similarity in airway wall deposition patterns between CFD simulations and experimental data for 10 micron particles.

Coarse HYB mesh

• Cumulative percent deposition was studied as a function of distance into the airway through two bifurcations.

• Significant differences were found between the Lagrangian and Eulerian methods for all meshes studied.

• Differences were observed due to mesh topology for smaller particles (less than 10 microns).

• Comparison with experiments (10 micron particle diameter) does not clearly indicate that either method is superior.

Eulerian vs. Lagrangian TET mesh

Results and Discussion (Continued)2nd order Eulerian simulations using different nominal particle sizes showed larger particles

result in higher deposition rates in the PRB geometry.

Particle diameter (microns)

Cumulative deposition (%)

5 31.610 77.320 98.9

References1.Hofmann, W, Journal of Aerosol Medicine 1996, 9(3): 369-388.2.Pope III, CA, et al., Journal of the American Medical Assoc. 2002, 287(9): 1132-1141.3.Balásházy I, et al., Journal of Applied Physiology 2003, 94(5): 1719-25.4.Hesterberg, TW, et al., Critical Reviews in Toxicology 2009, 39(9): 743-781.5.Oldham, MJ, et al., Aerosol Sci. and Tech. 2000, 32(1): 61-71.6.Heistracher, T and W Hofmann, Journal of Aerosol Science 1995. 26(3): 497-509.7.Heistracher, T., and W Hofmann, Annals of Occup. Hygiene 1997, 41 Suppl. 1:537 542.8.Weibel, ER, Morphometry of the Human Lung, 1963, Springer, Berlin.9.Longest, P. W.; Oldham, M. J. Journal of Aerosol Science 2008, 39 (1), 48-70.

Lagrangian and Eulerian simulations conducted for 1 micron (1000 nm) diameter particles showed the mesh topology and

refinement greatly influenced the results obtained for small(er) particles. This effect was not seen for the 10 micron (or larger)

particles.

For the 1 micron particles, Lagrangian simulations began to approach the experimental data when using a Hybrid mesh and

high levels of refinement (8,645,000 cells).

Number of Cells 2,856,292 4,163,830 8,645,075 Experimental9

% Particle Deposition 0.25 0.19 0.13 0.01

5 micron 10 micron 20 micron

Lagrangian simulations were used to track 100K individual particles in each mesh refinement and topology.

Center plane particle phase velocity magnitude shown.

Center plane particle phase velocity magnitude shown.

Experimental Results 5

Computational Results (Eulerian)

Eulerian vs. Lagrangian HYB mesh

TET Mesh