Can a MARTINI-like coarse-grained model describe nanoplastic-lipid membrane interactions?

Microplastics (MPLs) and nanoplastics (NPLs) pose potential health risks. To fully assess their impact on human health, it is crucial to investigate their interactions with plasma membranes using molecular simulations. While atomistic simulations can accurately describe the properties and behaviors of polymers and lipid membranes, they are limited to small systems. To model larger NPLs, coarse-grained (CG) models are necessary. However, existing CG models may not accurately describe the properties of commodity polymers and their interactions with lipid bilayers. For instance, although the MARTINI model is widely used for lipid membrane simulations, it can predict wrong NPL morphologies and artificial interactions between NPLs and membranes. Here, we developed a MARTINI-type model for studying polyethylene (PE) NPLs near lipid membranes. Our CG model reproduces the density, stiffness, and chain dimensions of PE observed in atomistic simulations across a range of temperatures. Moreover, the new CG model allows the PE NPLs to develop semicrystalline morphologies below the crystal melting temperatures. Despite these improvements, simulations of bare PE NPLs interacting with POPC membranes still exhibit unphysical mixing, indicating that further refinement of the CG lipid model is necessary to accurately describe NPL–membrane interactions.