Shape-Dependent Interactions of Manganese Oxide Nanomaterials with Lipid Bilayer Vesicles

Interactions of transition-metal-oxide nanomaterials with biological membranes have important environmental implications and applications in ecotoxicity and life-cycle assessment analysis. In this study, we quantitatively assess the impact of MnO₂ nanomaterial morphology-one-dimensional (1D) nanowires, 2D nanosheets, and 3D nanoflowers-on their interaction with phospholipid vesicles as a model for biological membranes. Confocal microscopy suggests visual evidence for the interaction of undisrupted vesicles with dispersed MnO₂ nanomaterials of different morphologies, and it further supports the observation that minimal dye leakage of the vesicle inner solution was detected during the interaction with MnO₂ nanomaterials during the dye leakage assay. Upon titration of vesicles to dispersions of MnO₂ nanowires, nanosheets, and nanoflowers, each roughly 10 times larger than the vesicles, dynamic light scattering reveals two diffusive time scales associated with aggregates in the mixture. While the longer time scale corresponds to the dispersed MnO₂ control population, the appearance of a shorter timescale with vesicle addition indicates interaction between the dispersed metal oxide nanomaterials and the vesicles. The interaction is shape-dependent, being more pronounced for MnO₂ nanowires than for nanosheets and nanoflowers. Furthermore, the shorter diffusive time scale is intermediate between the vesicle and nanomaterial controls, which may suggest a degree of metal oxide aggregate breakup. Vesicle adsorption isotherms and zeta potential measurements during titration corroborate vesicle attachment on the nanomaterials. Our results suggest that the dispersed nanomaterial shape plays an important role in mediating nondestructive vesicle-nanomaterial interactions and that lipid vesicles act as efficient surfactants for MnO₂ nanomaterials.