In vitro generation of micro/nano-plastics for biological tests

Abstract

Micro/nanoplastics (MPs/NPs) in the environment exhibit various effects on ecosystems as well as living organisms, such as immune system toxicity. To understand the effects of MPs/NPs experimentally, preparing synthetic MPs/NPs with their geometrical morphology closely similar to the MPs/NPs present in natural environments and with specific material composition is necessary. A pin-on-disc method with plastic pins and micro-textured glass discs has been employed to generate MPs/NPs with defined composition for biological tests. However, these previous studies did not clarify the repeated elastic deformation and stress distribution inside the pin causing the fatigue of degraded areas. Accordingly, in this study, MPs/NPs were generated using a pin-on-disc method, and the interfacial pressure of the pin and disc and the micro-texture pattern were assessed as factors that could change the elastic deformation and the stress distribution inside the pin; additionally, how these factors affect the MP/NP geometrical morphology were investigated. Polyethylene, polypropylene, polyvinyl chloride, polystyrene, and polyethylene terephthalate were used as test materials. Almost all the MPs/NPs of these materials had a fragmented morphology. Further, these MPs/NPs were compared to those identified and they showed almost the same geometrical morphology as the fragmented MPs/NPs in the environment. The equivalent circle diameters of the generated MPs/NPs were suggested to be affected by micro-textures on the discs, which promoted fatigue failure. Additionally, by increasing the interfacial pressure, the stress was distributed deeper inside the pin depending on the plastic materials, which accelerated the crack propagation and generated a large amount of MPs/NPs. From these results, the fragmented morphology of MP/NP which is similar to those present in environments is expected to be generated with defined morphology and material composition for application to biological tests.

Keywords

• microplastics
• nanoplastics
• ultraviolet
• hydrolysis
• fatigue failure
• elastic deformation
• surface texture