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 -->