Untangling perturbations to lipid membrane hydration induced by polystyrene nanoplastics through multiscale simulation and experiment

Understanding the impact of anthropogenic nanoparticles on the phase behavior, dynamics, and stability of biological membranes has been a longstanding area of interest within chemical and biological physics. In particular, it has been of recent interest to understand how nano-sized plastic particles (nanoplastics), which originate from the breakdown of microplastics, drive changes in the membrane structure and dynamics. Using uncrosslinked polystyrene nanoparticles as a model for nanoplastic particles, Laurdan fluorescence spectroscopy experiments have observed a concentration dependent blue shift that would typically be interpreted as a fluid to gel membrane phase transition for traditional nano-bio interactions. In the present work, we demonstrate using multi-scale molecular dynamics simulations that this does not appear to be the case; it instead appears that the flexible, hydrophobic nature, of polystyrene nanoparticles allows them to penetrate and dissolve into the membrane interior leading to a dehydration of Laurdan probe molecules that confounds traditional interpretation of Laurdan fluorescence. Specifically, using coarse-grained molecular dynamics simulations we demonstrate that polystyrene nanoplastic particles are able to rapidly penetrate into lipid membranes and dissolve into the hydrophobic interior of the membrane. Then, using all-atom molecular dynamics simulations, we show that this process results in a dehydration of both the membrane and the Laurdan fluorescent probe. Lastly, using QM/MM calculations we demonstrate that this dehydration, rather than membrane phase change, induces a spectroscopic blue shift of Laurdan probe molecules incorporated within the membrane. These results will then be discussed in the context of nano-bio interactions, and their implications for understanding the biological impact of these nanoparticles.<!-- notionvc: 427600a5-4c0c-444a-a8b0-89bbea65855f -->