Generation of Nano/Microplastics for Immunological Assessments

Abstract

This study aimed to develop a method to generate nano/microplastics (NPs/MPs), whose morphology and constituents are clarified for various biological tests. NPs/MPs were generated using a pin-on-disc machine, where a pin made of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), or polyethylene terephthalate (PET) was pressed onto a quartz glass disc. Relative motion between the pin and disc was then applied in a saline solution. An ultraviolet lamp (UV-B) was used to irradiate the frictional surfaces through a quartz glass disc to investigate the degradation of the plastic materials. A microtextured glass surface was used to induce fatigue failure of plastic materials and adjust the crack propagation of plastic materials. UV degradation was confirmed for all the plastic materials and UV irradiation increased the equivalent circle diameter (D) of PE, PVC, and PET but decreased the equivalent circle diameter (D) of PP. However, it was thought that UV irradiation did not affect the aspect ratio (R) and complexity (C) of all plastic materials. The physical degradation mechanism of using the microtextured glass surface may increase the generation of NPs/MPs, and the surface profile of microtextured glass may adjust the crack propagation of plastic material surfaces. Notably, almost all the NPs/MPs generated were fragment-shaped. The NPs/MPs were compared to the particles found in the environment or generated by milling, cutting or chemical degradation in vitro. It was concluded that the fragment-shaped NPs/MPs were similar to the particles found in the environment or generated by milling in vitro, through visual inspection, aspect ratios, and complexity. As the presence of NPs/MPs in the human body can pose a serious health risk, a microchamber device capable of both quantitative and time-dependent assessments of inflammatory cytokine (TNF-α) secretion from human monocyte-derived macrophages (HMDMs) was proposed. The microchamber was constructed with a height of 200 μm and a diameter of 15 mm. This configuration enabled the NPs/MPs to pass near the HMDM, which is important in the phagocytosis of NPs/MPs and contributes to quantitative assessment. Although approximately the same morphological aspects of NPs/MPs were administered, the secretion of TNF-α differed depending on the plastic material.