Electrostatic charge effects on pharmaceutical aerosol deposition in human nasal-laryngeal airways

Abstract

Electrostatic charging occurs in most aerosol generation processes and can significantly influence subsequent particle deposition rates and patterns in the respiratory tract through the image and space forces. The behavior of inhaled aerosols with charge is expected to be most affected in the upper airways, where particles come in close proximity to the narrow turbinate surface, and before charge dissipation occurs as a result of high humidity. The objective of this study was to quantitatively evaluate the deposition of charged aerosols in an MRI-based nasal-laryngeal airway model. Particle sizes of 5 nm-30 µm and charge levels ranging from neutralized to ten times the saturation limit were considered. A well-validated low Reynolds number (LRN) k-ω turbulence model and a discrete Lagrangian tracking approach that accounted for electrostatic image force were employed to simulate the nasal airflow and aerosol dynamics. For ultrafine aerosols, electrostatic charge was observed to exert a discernible but insignificant effect. In contrast, remarkably enhanced depositions were observed for micrometer particles with charge, which could be one order of magnitude larger than no-charge depositions. The deposition hot spots shifted towards the anterior part of the upper airway as the charge level increased. Results of this study have important implications for evaluating nasal drug delivery devices and for assessing doses received from pollutants, which often carry a certain level of electric charges.

Figure 1

(a) Surface geometry and inner anatomy of the nasal airway of an adult; (b) Computational mesh. SM, superior meatus; MM, middle meatus; IM, inferior meatus; MP, median passage; ST, superior turbinate; MT, middle turbinate; IT, inferior turbinate.

Figure 2

Comparison of numerically predicted aerosol deposition due to the image force with the analytic expression of Chen and Yu [11] for fully developed laminar flow in a tube.

Figure 3

Inhalation airflow inside the nasal airway under normal breathing conditions: (a) velocity field; (b) turbulent viscosity ratio; (c) streamlines (right passage); and (d) flow pattern visualized with mass-less fluid particles at various instants.

Figure 4

Surface deposition of monodisperse aerosols with different charge levels and particle sizes.

Figure 5

Comparison of deposition fraction as a function of particle size under different charge levels.

Figure 6

Sub-regional deposition of monodisperse aerosols with different charge levels for particle size of (a) 3 µm, and (b) 10 µm. For 10 µm particles, deposition shifted to front of the nasal cavity as charge level increased.