Nanoparticle-induced structural changes in lung surfactant membranes: an X-ray scattering study

The effect of low concentration (0.001 wt%) of charged silica nanoparticles (NPs) on the molecular structure of lung surfactant monolayers was investigated at the air/water interface using grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR). The lipid systems investigated included 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), mixtures of DPPC and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), and Infasurf (a clinical lung surfactant formulation). In all cases, the anionic silica NPs interacted with the films but induced only small structural changes. By contrast, the cationic NPs induced a significant reduction of the alkyl chain tilt angle when anionic lipid was present. This appears to be associated with a condensation of the POPG lipids that would alter the ratio of liquid-expanded and condensed phases. Thus, this study reveals that low concentrations of cationic NPs can induce structural changes that could impact film mechanical properties that are important for pulmonary function.