Production of Irregularly Shaped True-To-Life Microplastics with Embedded Optical Labels and Exemplary Application in an Ex Vivo Model

Ubiquitous in the environment, microplastics (MPs) are also taken up by all organisms. Possible implications are increasingly being studied, yet research is often limited by the use of idealized, spherical MPs. To better mimic MPs found in the environment, we demonstrate electrospun microfibers (MFs) as a possible precursor material, allowing for direct embedding of labels and simplified production of irregular microplastic (MP) fragments and fibers. Specifically, using polystyrene as a model polymer, MFs are doped with either organic (9,10-diphenylanthracene, DPA) or inorganic (upconversion nanoparticles, UCNPs) luminophores. Those optical labels allow for imaging under UV/vis or NIR excitation, respectively. Stable embedding is proven with minimal leaching over 35 days (DPA: 0.0023 wt %, UCNPs: 0.2 wt %). Mechanical disruption yielded MP fragments of (4 ± 3) μm in diameter for ball milling and fibers of (20 ± 20) μm in length for shear force exfoliation. While fibrous MPs were still too long for biological studies, the milled MPs are successfully applied ex vivo in mouse kidneys and are readily imaged in the tissue. Future studies on the biological impact will benefit from this approach, which offers a standardized method to produce traceable MPs that better resemble environmentally occurring MPs.