Extracting pulmonary surfactants to form inverse micelles on suspended graphene nanosheets

The increasing risk of human exposure to emerging nanoparticles (NPs) has created a wide concern about their inhalation toxicity. Once NPs are inhaled, they get through the branching airway to deposit in the alveoli, where a thin pulmonary surfactant (PS) layer acts as the first barrier against them entering the deep lung. However, in terms of the inhalation toxicity of NPs, the mechanisms by which inhaled NPs interact with the PS layer and how the morphological change of NPs due to the PS layer interactions influences the subsequent fate of NPs are still elusive. By using molecular dynamics simulations, we investigate the interactions between graphene nanosheets (GNs) and the PS layer. It is found that when GNs suspend above or slowly penetrate the PS layer, PS molecules can spontaneously be extracted from the layer and made to form inverse micelles via cooperative molecular motion and rearrangement on the GN surfaces. We demonstrate that the PS layer tension and GN properties like size, oxidation ratio and curvature significantly affect the extraction dynamics. Notably, for curved GNs, only the concave surface can vigorously extract PS molecules, showing that the dispersive adhesion between GN and PS dominates the extracting and rearranging process. Our results propose new mechanisims for the experimental findings on the inhalation toxicity of graphene-family nanomaterials. Moreover, bearing in mind that the surface properties of GNs have been masked by adsorbed PS molecules, the newly formed structure may act like a corona that influences the biological identity of GNs. Therefore, anyone either evaluating inhalation toxicity or promoting biomedical applications of GNs should consider the first contact with PS at the air–water interface in alveoli.