Mucus matters: entrapment of inhaled aerosols in lung airways

Abstract

The air we inhale brings along a variety of harmful aerosols, which if deposited on the wall of the airways can cause severe respiratory illness. The lung's primary defense against airborne particles is provided by a film of mucus which lines the airway walls. This film is continuously transported, upward and out of the lungs, by a carpet of wall-attached cilia; thus, harmful particles are evacuated provided they deposit on the mucus. In this talk, I will show that particles can manage to avoid the mucus and deposit on the exposed airway wall. The fate of particles depends on their size—which sets the strength of Brownian or inertial forces—as well as the coupled flow of air and mucus. The Rayleigh-Plateau instability of the annular inter-fluid interface plays a key role, by controlling the morphology of the mucus film, and ultimately leads to a counter-intuitive result: More mucus does not imply more trapping; instead, more particles—allergens, pathogens, and hopefully aerosolised drugs—are able to reach the wall.