Fragmentation Behavior and Surface Characteristics of Different Plastics: Influence on the Potential Toxicity to Macrophages and Angiogenesis

The production and waste of plastics are increasing rapidly, and there is a growing interest in investigating the impact of microplastics (MPs) smaller than 5mm on human beings as pollutants. Previous research has primarily focused on the toxicity of engineered plastic particles with a spherical shape, overlooking the fact that microplastics tend to fragment under environmental conditions, resulting in various morphological characteristics and sizes. This fragmentation behavior has not been adequately considered in toxicity analysis. Therefore, it is crucial to comprehend the fragmentation behavior of different plastics and analyze the surface characteristics of each microplastic to gain a better understanding of their potential toxicity.<br/>In this study, we conducted a comprehensive investigation into the fragmentation patterns of plastics, specifically focusing on polypropylene (PP), acrylonitrile butadiene styrene copolymer (ABS), and polyethylene terephthalate (PET) as representative plastics. To simulate the fragmentation of each plastic, we employed a ball-milling process, which resembles the physical fragmentation process that occurs during plastic weathering.<br/>After the fragmentation process, we characterized the surface of the microplastics using scanning electron microscopy (SEM), FT-IR, Raman spectroscopy, and x-ray photoelectron spectroscopy. We also examined the change in crystalline structure using a differential scanning calorimeter (DSC). Considering that the micronization behavior of plastics is highly dependent on the amorphous structure, we confirmed the crystalline and amorphous parts and their respective crystallinity. Additionally, we conducted size and shape analysis of the microplastics to investigate cellular uptake and toxicity.<br/>Macrophages were selected as representative immune cells due to their ability to recognize infectious agents and remove toxicants through phagocytosis. We studied the cellular uptake of each microplastic and observed cellular reactions such as ROS generation in the macrophage cytosol, polarization, and immune-cytokine secretion. Furthermore, we investigated the complex cellular reactions by co-culturing macrophages with human umbilical vein endothelial cells (HUVECs). As HUVECs possess angiogenic abilities, we analyzed <i>in vitro</i> tube formation under co-culture conditions and quantified the amount of angiogenic growth factors after exposing macrophages to microplastics.<br/>Our findings revealed three significant points in understanding the potential toxicity of microplastics:<br/>The characteristics of fragmented microplastics differ significantly from engineered microplastics.<br/>The fragmentation behavior and properties of each microplastic should be considered to understand their potential toxicity.<br/>Depending on the composition of the microplastics, the reaction of macrophages and subsequent effects on angiogenesis vary.