Polystyrene-Induced Dehydration of Lipid Membranes: Insights from Atomistic Simulations

Nanoplastics, small plastic particles smaller than microplastics, have been suggested to have a wide-range of unique interactions when they encounter lipid membranes. Recent studies have demonstrated that the smaller size of nanoplastic particles may allow them to penetrate and dissolve in lipid membranes. Following this penetration, however, there is not yet a clear picture of how such particles impact the local lipid environment. A recent study by the present authors found that when lipid vesicles that included laurdan, a fluorescent dye molecule typically thought to report on the membrane phase, were exposed to polystyrene nanoparticles, they exhibited a concentration-dependent blue shift consistent with a fluid-to-gel phase transition. However, coarse-grained simulations suggested that no such transition was taking place; instead, the simulations observed that polymer chains from the polystyrene nanoparticles penetrated into the liposome membrane. In the present work, we use all-atom molecular dynamics simulations to demonstrate that the inclusion of polystyrene within a lipid membrane causes significant changes to the local hydration and structure of that membrane while maintaining the membrane phase. Specifically, through the explicit incorporation of laurdan within the present simulations, we demonstrate that the local hydration environment of the dye molecule changes significantly but continuously as membranes are exposed to polystyrene, thus suggesting a possible explanation for the previously reported experimental observation. The present results provide a picture of the complex heterogeneity generated within polymer-containing membranes.