Molecular Dynamics Study of the Interactions between Polyethylene Nanoplastic Particles and Lipid Membranes

Plastic wastes can break down into micro and nano-sized particles, which can enter biological tissues and potentially impact human health. The interactions of micro and nano-plastics with biological systems, such as cell membranes, however, are not well understood. In this work, we investigate the interactions between polyethylene (PE) nanoplastic particles and model POPC lipid bilayers in water using all-atom (CHARMM36 force field) and coarse-grained (MARTINI) molecular dynamics (MD) simulations. We show that atomistic resolution is critical for quantifying the polymer-membrane interactions. The all-atom PE nanoparticle is semicrystalline with crystalline surfaces exposed to water. The MARTINI polymer nanoparticle, however, is a spherical liquid droplet. The distinct morphologies give rise to different nanoplastic-membrane interactions. We compute the potentials of the mean force of both model systems and show their differences throughout the intermolecular distance between the PE nanoplastic particle and the POPC lipid bilayer. While the interaction between a PE particle and the lipid bilayer is purely repulsive in the all-atom simulations, the coarse-grained PE particle can penetrate the lipid membrane and dissolve in the hydrophobic core of POPC. We speculate that the crystallinity of nanoplastics plays an important role in the polymer-membrane interactions.