Nominally identical microplastic models differ greatly in their particle-cell interactions

Microplastics are an abundant contaminant in all environmental compartments. Due to this ubiquity, organisms frequently interact with these microscopically small plastic particles, which raised concerns about their potentially hazardous effects. In this context, a special focus was set on the cellular interactions of microplastics, as these are a prerequisite for further translocation of the microplastics into tissues. Many studies investigating such cellular interactions and effects of microplastics rely on commercially available polystyrene microspheres. However, even nominally identical model microplastics differ in their physicochemical properties such as the surface charge. This may affect the outcome of studies on the potential hazards of microplastics because their interactions with cells may be altered due to the different surface properties. Here, we show that the physicochemical properties of nominally identical model microplastics from eight different manufacturers were significantly different. Especially the zeta-potential, which characterizes the electrical potential of a particle in a medium, differed by more than one magnitude. We observed that the zeta-potential of the microplastics is additionally altered after environmental exposure and eco-corona formation on their surface. We developed a microfluidic microscopy platform to investigate the binding kinetics and adhesive forces of microplastics to cells in a highly multiplexed single-cell single-particle approach. Our experiments showed that the adhesion strength of microplastics to cells strongly differed between particles from different manufacturers and was determined by their zeta-potential. Using confocal fluorescence microscopy, we showed that the zeta-potential further governed the internalization of microplastics into cells due to the particle-cell adhesion. Therefore, the zeta-potential of microplastics can act as a proxy for microplastic-cell interactions, potentially governing the adverse effects reported in various organisms exposed to microplastics. Also see: https://micro2024.sciencesconf.org/559582/document