(219c) Association and Adsorption of Mucins to the Air Interface in Human Airway Mucus

The airway surface layer lines the respiratory tract, simultaneously trapping inhaled particulates and facilitating their removal from the lung. Secreted gel-forming mucins, which possess both hydrophilic glycosylated domains and hydrophobic globular domains, interact with a wide range of proteins and nucleic acids and are responsible for the characteristic biophysical properties of mucus. The mucin hydrophobic domains promote: 1) self-association in the bulk phase; and 2) strong adsorption at the air-mucus interface with formation of a thin, viscoelastic skin layer that effectively separates the mucus layer itself into two distinct sublayers. Measuring the modulus of mucus using multiple rheometric geometries with varying surface-to-volume ratios, we measure different apparent viscosities with different contributions of surface to bulk. A simple model deconvolutes these contributions, permitting assessment of the bulk and surface properties. Surfactants are shown to reduce the associative interactions of mucins, lowering the degree of association/adsorption and overall viscoelastic modulus. Understanding of the structural organization of mucus in the airway and resultant mechanical properties will enable the development of therapeutic approaches to improve mucus clearance in muco-obstructive lung diseases.