Concentration-Dependent Impact of Polystyrene Nanoplastic on Lung Surfactant Monolayer in Alveolar Fluid: A Molecular Dynamics Study

Environmentally ubiquitous microplastics (MPs) and nanoplastics (NPs) can be breathed in and travel through the branching air passages to reach the alveoli, where they initially come in contact with the pulmonary/lung surfactant monolayer, the most crucial structure for maintaining optimum respiratory mechanics. Examining the minimum concentration of NPs necessary to impact the physiochemistry of lung surfactant and changes to the typical structure of the surfactant monolayer, as well as how different NP concentrations impact the degree of disruption in lung surfactant structure and function, is an important part of this subject area. The presence of NPs and their detrimental effects on human lung airways have been demonstrated by previous research, but the interaction mechanism with deep lung airways is still mostly unknown. In this study, we employed coarse-grained molecular dynamics simulations to examine the NP interaction and aggregation mechanism of the pulmonary surfactant monolayer. The findings from this investigation revealed that lung surfactant monolayer components spontaneously adsorb onto NPs, endowing the NPs and forming an adsorption layer that can be described as a lipid corona. It is also observed by the structural and compressibility analysis that the increasing concentration of polystyrene NPs progressively reduces the order parameter of monolayer lipids, leading to a more disordered orientation of lipids and impaired monolayer compressibility, which may disrupt the surfactant's capacity to lower surface tension effectively. Furthermore, density map analysis of polystyrene NPs on the surfactant layer shows that with high polystyrene concentrations, NPs dominate the monolayer, causing extensive aggregation and severe structural damage that induces the monolayer to collapse. These structural abnormalities of the monolayer point to potential threats of respiratory dysfunction and alveolar collapse. This research advances our knowledge of the effects of NPs on respiratory health by offering molecular-level insights into how they affect lung surfactant monolayer stability for healthy breathing.