Force Spectroscopy by Atomic Force Microscopy as Indicator for Cellular Microplastic Uptake

Concentrations of microplastic particles (MPs) in the environment are low, and cellular uptake is difficult to measure. Cancer tissue accumulates more MPs than normal tissue. This study aims to determine whether cellular stiffness measurements by atomic force microscopy could indicate whether cells ingested MPs. In this study, spheroids with different compositions were exposed to MPs, and Young's moduli were compared to fluorescent readings of MP uptake in monolayer cultures. The tested cancer cell lines differed in their basal Young's modulus and in the increases observed upon MP exposure, both in monolayer and spheroid culture. Young's moduli of the THP-1-containing spheroids were higher than those of spheroids without macrophages and were higher after MP exposure than before. In monolayer culture, softer cells showed larger increases in Young's modulus after MP exposure than did stiffer cells. The Young's moduli of the cell monolayers under static and dynamic conditions were positively correlated. Young's modulus could serve as a parameter for MP uptake and can differentiate MP-containing spheroids from non-exposed spheroids. In monolayer culture, Young's modulus can identify cell lines that ingested MPs. However, complicated use and low throughput limit the broad application of atomic force microscopy in biological evaluation.