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Assessing the MartiniForce Field for Modeling PolyolefinNanoplastics near Lipid Membranes
Summary
Scientists trying to computer-model how plastic nanoparticles interact with our cell membranes found that current simulation tools don't work well—the virtual plastic particles behave unrealistically, dissolving into membranes rather than staying intact like real plastic would. This matters because understanding how nanoplastics actually interact with our cells is a key step toward figuring out their health risks, and this study shows we need better computer models before we can trust those predictions.
We present an improved Martini-type coarse-grained (CG) model for polyethylene (PE) nanoplastics and benchmark its performance against three existing Martini PE models from the Martini 2 and Martini 3 force fields. While current Martini models reproduce conformational statistics for molten PE, the PE chains do not crystallize below experimental melting temperatures. With improved bonded interactions, our CG PE chains exhibit melt properties and semicrystalline morphologies consistent with all-atom (AA) simulations and experimental data. Using our improved model, we generate semicrystalline PE nanoplastics (NPLs) at body temperature (310 K) in agreement with the AA reference, whereas NPLs from current Martini PE models remain amorphous. We further investigate the interaction of semicrystalline PE NPLs with a POPC lipid membrane in the Martini framework. The membrane exhibits unphysical behavior similar to that observed for amorphous NPLs, bending toward and mixing with the nanoplastic. When embedded within the membrane core, the semicrystalline Martini-type NPL spreads laterally and dissolves, losing its crystalline domains, whereas the all-atom NPL remains intact, with alkane–membrane interactions promoting further crystallization. These results indicate that improving the PE model alone is insufficient and that refining the membrane model is also required to accurately describe polyolefin nanoplastic–membrane interactions in the Martini force field.