Incorporation of Oligo(Styrene), Oligo(Butadiene), Oligo(Methyl Methacrylate), and Oligo( tert -Butyl Acrylate) Droplets in Giant Unilamellar Vesicles

Abstract

In the environment, microplastics fragment and degrade into plastic oligomers, posing potential risks to ecosystems and human health. In the present study, the interactions between giant unilamellar vesicles (GUVs) and liquid droplets of oligo(styrene), oligo(butadiene), oligo(methyl methacrylate), and oligo(tert-butyl acrylate) were investigated using fluorescence microscopy. GUVs were used in a homogeneous fluid state or in a phase-separated state consisting of either a liquid-disordered (Ld) phase and a solid-ordered (So) phase, or a Ld phase and a liquid-ordered (Lo) phase. The effects of plastic oligomers on membrane structures vary depending on the oligomer type. Oligo(styrene), oligo(butadiene), and oligo(tert-butyl acrylate) droplets were homogeneously embedded between the monolayer leaflets, whereas the oligo(methyl methacrylate) droplets were bound to the bilayers through inhomogeneous membrane structures, regardless of the lipid composition. The bilayer phase separations were retained after oligomer incorporation, except for the Ld/So phase-separated bilayer exposed to oligo(tert-butyl acrylate). In this exceptional case, no domain structures were visible in the fluorescence images. In the Ld/So phase-separated bilayer, the oligo(styrene) and oligo(butadiene) droplets were distributed exclusively in the Ld phase, and were all pinned at the domain boundaries. In the Ld/Lo phase-separated bilayer, the oligo(styrene), oligo(butadiene), and oligo(tert-butyl acrylate) droplets invariably localized to the Ld phase, with approximately half anchored to domain boundaries. The data also suggested that in the Ld/So bilayer, oligo(methyl methacrylate) molecules were predominantly partitioned into the Ld phase, whereas in the Ld/Lo bilayer, they were slightly more soluble in the Ld phase than in the Lo phase. Furthermore, the slight solubility of oligo(methyl methacrylate) in water enabled its incorporation into homogeneous fluid bilayers via two pathways: transfer from an in-bilayer droplet to the matrix bilayer and transfer from aqueous solution.