- D3.518 - Environmentally relevant irregular polystyrene particles exert stronger biological effects than spherical model particles in human bronchial smooth muscle cells

Plastic degradation releases micro- and nanoplastics detected in air and lung tissue, raising concerns about respiratory health. Plastics undergo physical and chemical degradation processes that lead to the formation of particles with irregular shapes, rough surfaces, and heterogeneous sizes, rather than smooth spherical structures. However, most in vitro studies use spherical particles. This study aimed to compare the effects of spherical polystyrene particles (PS) with irregular PS particles on human bronchial smooth muscle cells (hBSMC).

Healthy hBSMC were cultured under standard conditions and exposed to spherical PS of Ø25 nm and irregular PS <0.22 µm in size (at the same mass concentration, 100 µg/mL). Commercially purchased spherical PS and irregular PS generated from disposable polystyrene cutlery by cryogenic milling and suspended in PBS were used. Intracellular localization of PS in hBSMC were visualized with holotomographic microscopy. Changes in hBSMC morphology and behavior were monitored using holographic microscopy. Cellular responses were compared between groups to assess whether PS type influences the biological effects.

Imaging showed that irregular PS penetrated hBSMC, indicating cellular internalization. After exposure, irregular PS fragments caused a greater reduction in hBSMC confluence and cell number than spherical PS particles. Compared with control cells, confluence decreased by approximately 19% after exposure to irregular PS and by approximately 9% after exposure to spherical PS, while cell number decreased by approximately 20% and 13%, respectively. Morphological analysis revealed that the most pronounced difference was observed in optical thickness. After exposure to irregular PS, cell thickness reached approximately 20–25 µm, whereas control cells and cells exposed to spherical PS remained lower at 5–7 µm, and irregular PS exposure was associated with a broader optical volume distribution and an altered cell irregularity profile.

Environmentally relevant irregular PS particles exert stronger biological effects on hBSMC than conventional spherical particles. Irregular PS were internalized by the cells, caused a greater reduction in cell growth, and induced more pronounced morphological changes. This suggests that particle morphology is an important determinant of cellular responses and that the use of irregular particles may improve the biological relevance of in vitro models and better reflect real-life exposure to micro- and nanoplastics.