Oxidative Degradation Alters the Interactions of Polystyrene Nanoparticles with Lung Surfactant Monolayers: A Reactive and Classical Molecular Dynamics Study

Abstract We investigated how oxidative degradation of polystyrene (PS) nanoparticles affects their interactions with lung surfactant (LS) monolayers using reactive and classical all-atom molecular dynamics. Oxidation was modeled with ReaxFF in molecular oxygen, using shock compression to accelerate reactions, and yielded hydroxyl, carbonyl, aldehyde, ether, and peroxide groups plus crosslinking. The oxidized nanoparticles were then placed on realistic LS monolayers to study adsorption, penetration, energetics, and surface tension. Unlike pristine PS nanoparticles, which remained hydrophobic near the interface, oxidized nanoparticles penetrated deeply into the lipid layer and interacted more strongly electrostatically with the surfactant molecules. Steered molecular dynamics showed lower translocation forces and smaller membrane perturbations for oxidized particles. They also altered the monolayers’ mechanical response and markedly reduced the surface tension. Environmental aging thus substantially alters the behavior of PS nanoplastics at pulmonary interfaces and should be considered when assessing the respiratory impact of airborne nanoplastics.