Effects of Nanoplastics on Lipid Membranes and Vice Versa: Insights from All-Atom Molecular Dynamics Simulations.

We compute the potential of mean force (PMF) between semicrystalline polyethylene (PE) nanoplastics (NPLs) and model POPC and DPPC bilayers, which approximate in vivo membranes, using atomistic simulations. Our work shows that atomistic resolution is required to characterize the NPL and lipid interactions. By analyzing the PMF, we demonstrate that the mechanical properties of membranes, rather than NPL semicrystalline morphologies, govern NPL-membrane interactions. Resistance to NPL penetration arises from the elastic energy of the membrane deformation. The flexible POPC membranes resist NPL translocation, and the brittle DPPC membranes fracture under stress. Using an elastic free energy model, we approximate effective repulsions between lipid membranes and NPLs of various sizes. Our mean first-passage time analysis shows that even small, bare NPLs cannot easily penetrate brittle lipid membranes via passive diffusion, even at high concentrations. However, eco-coronas or other mechanisms, such as endocytosis, may still facilitate the cellular uptake of NPLs and MPLs. While semicrystalline morphologies do not directly impact NPL translocation, they do influence NPL behavior within lipid membranes upon translocation. Semicrystalline NPLs remain intact within lipid membranes, whereas amorphous NPLs can dissolve into the hydrophobic core and alter the elastic properties of the membrane.