Caco-2 cells were plated into black opaque 96-well plates at a density of 5 x 104 cells per well in 300 µL of culture medium. The cells were allowed to attach for 24 hours before treatment. Subsequently, culture medium was replaced by 100 µL particle suspensions in six replicates per treatment and incubated for 24 hours (at 37 °C, 10% CO2). Positive controls were prepared by diluting 10% (w/v) sodium dodecyl sulfate (SDS) in water to achieve a final concentration of 0.22% (v/v) SDS in the cell culture medium. Culture medium was used as negative control. The water content in all treatments was kept at or below 2%. Finally, the viability of Caco-2 cells was evaluated with the CellTiter-Glo Luminescent Cell Viability Assay (Promega, USA). The luminescent signal from each well was determined with a plate reader (Tecan, Switzerland). A two-way analysis of variance (ANOVA) using Tukey's multiple comparisons test was used to compare the groups. Data analysis was performed using GraphPad Prism 9.0 software (La Jolla, CA, USA). p values were calculated as 0.1234 (ns), 0.0332 (*), 0.0021 (**), 0.0002 (***), and <0.0001 (****).