Fig. 1

Study design and uptake of fluorescently labeled polystyrene NMP in skin cells. a After homogenization of murine skin tissue, skin cells (i.e., mix of primary keratinocytes and dermal fibroblasts) were cultivated and incubated with NMP over several weeks; at the end of every week (d7, d14, d21, d28), downstream analyses were performed including determination of NMP uptake, secretion profiling, gene and protein expression of selected targets. Representative images show skin cells in the brightfield channel. b Study scheme and dynamic light scattering size verification of several polystyrene NMP with fluorescent labeling ranging from 0.2 µm to 6 µm. c Flow cytometry analysis of cells incubated with NMP and quantification of side-scatter signals from individual cells (SSC). d Algorithm-based image analysis and calculation of NMP uptake. e 50 z-stack maximum intensity projection of murine skin cells with fluorescent membrane label (blue) and fluorescent particles inside as well as outside of the cell. All data were normalized to control cells (i.e., 1.0) non-exposed to NMP. Statistical analysis was done by unpaired, two-tailed Student's t test (n > 3) with *p ≤ 0.05 and ***p ≤ 0.001. Scale bars are 100 µm (a) and 50 µm (e)