Abstract

As oxygen is inhaled it has to first cross a very thin layered membrane, lung surfactant, before it can enter the bloodstream. This lung surfactant membrane is composed of saturated and unsaturated phospholipids and membrane proteins which serve to reduce the surface tension at the air-liquid interface of the alveoli preventing alveolar collapse. To maintain this function through repetitive compression-expansion cycles, the film employs a mechanism of reversible reservoir formation and exhibits a high degree of fluidity. The inhalation of nanoparticulate may interfere with the functional properties of pulmonary surfactant including lowering the film collapse, altering viscoelastic properties and modifying lipid reservoir formation. This study aims to determine the degree to which nanoparticles interfere with the phase structure, compressibility, and viscoelastic properties when they deposit on the lipid membrane. The lung surfactant films are modelled using monolayers comprising either lipid-only mixtures or a natural membrane extract, namely Infasurf (a clinical formulation containing both extracted lipids and proteins). Surface pressure-area isotherms, Brewster angle microscopy, rheological measurements and grazing incidence x-ray diffraction data of films in the absence and presence of cationic and anionic silica nanoparticles are presented and discussed. The charge was found to play an important role with cationic nanoparticles having a greater impact on structural properties while anionic nanoparticles affect the viscoelastic properties of the films.