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Bowen, James; Cheneler, David and Andrews, James W.
(2015).
URL: http://aerosol-soc.com/?q=annual-aerosol-society-c...
Abstract
The effect of particle size and wettability on the interaction between micro/nanoparticles and lung lining fluid (LLF) is considered theoretically. The conditions under which particles will float, sink, or become submerged are investigated.
Lung lining fluid (LLF) is a thin aqueous film which coats the surface of alveoli and is essential to lung function, contributing primarily to gaseous exchange. LLF contains of a variety of dissolved species, including proteins and phospholipids, and the film has approximate thickness 100-200 nm. The interaction of airborne particles with LLF will generally correspond to one of the following three categories:
1. Floating
2. Wall Supported
3. Submerged
For Floating particles the possibility exists that they could be removed from the LLF, perhaps by vibrations induced via coughing. For Wall Supported and Submerged particles, their removal is less likely due to the increased force required to separate them from the liquid film. These particles will remain in the LLF unless removed by dissolution or through the action of alveolar macrophages. Particles which remain in contact with the epithelial cell wall for prolonged periods of time could become internalised within the lungs, enhancing their toxic potential [1].
This work presents a tool for predicting which of the above categories an inhaled particle interacting with LLF will correspond to. Research areas which will benefit from this work include (i) studies utilising airborne particles for drug delivery, and (ii) studies investigating respiratory illnesses caused by airborne contaminants.
It is well established that particles larger than PM10 are more likely to be captured higher up in the respiratory tract. Here we consider spherical particles of diameters in the range 1 nm to 10 µm for their ability to enter the pulmonary region of the lungs. i.e. PM2.5 and PM10 are both considered. The particle mass is considered by varying the density of the particle material. The wettability of the particle surface is explored by varying the contact angle, θ, of the three phase line created between the LLF and the particle in the range 0 < θ < 180o. A force balance which includes the particle buoyancy and capillary forces is constructed, which includes the Laplace-Young equation [2]. The force balance is solved numerically for each combination of particle diameter, mass, and contact angle. The LLF is assumed to have constant thickness, density, and surface tension for all calculations.
The maximum particle diameter and mass which was predicted to float on the LLF was a function of the wettability of the particle surface. For those particle which could not float, the likelihood that they would become submerged by LLF was also strongly dependent on the wettability of the particle surface.
Surface wettability is a crucial parameter for the determination of whether a particle making contact with lung lining fluid will float, sink, or become submerged. This is particularly important for particles in the PM2.5 regime.
[1] Geiser, M.; Rothen-Rutishauser, B.; Kapp, N.; Shürch, S.; Kreyling, W.; Schulz, H.; Semmler, M.; Im Hof, V.; Heyder, J.; Gehr, P.; Ultrafine particles cross cellular membranes by nonphagocytic mechanisms in lungs and in cultured cells, Environ. Health Perspect. 2009, 113, 1555-1560.
[2] Young, T.; An essay on the cohesion of fluids, Trans. Phil. Roy. Soc. Lond. 1805, 95, 65-87.
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