Interaction of Polystyrene Nanoplastic with Lipid Membranes

As demonstrated in in vitro studies, polystyrene nanoplastics (PSNPs) are effectively internalized by various cells. All known mechanisms of PSNP internalization involve the initial step of their interaction with the cell membrane, highlighting the importance of understanding such interactions at the molecular level. Here we consider the effects of PSNPs obtained from disposable food packaging on zwitterionic lipid membranes, used as a model system for protein-free cell membranes. We combined microscopic imaging and unbiased atomistic molecular dynamics (MD) to investigate the behavior of PSNPs on the surface and inside the lipid membrane. Our results show that PSNPs are hydrated and have a high negative surface charge when dispersed in an aqueous media. The penetration of PS nanoparticles into the lipid bilayer requires the removal of water molecules at the nanoparticle-membrane interface, which is an effective barrier to the entry of PSNPs into its hydrophobic region. Overcoming this energy barrier by slightly inserting the PS nanoparticle into the polar region of the membrane leads to its rapid penetration into the center of the bilayer and coating its surface with lipid molecules. PS nanoplastics do not disaggregate after penetrating the lipid membrane, which affects the molecular structure of the bilayer. In addition, our MD simulations demonstrated that small-molecule additives (e.g., unreacted monomers) present in nanoplastics can be released into lipid membranes if they are located close to the nanoparticle surface. The outcomes of this study are important for understanding the passive uptake of nanoplastics by cells.