The Role of the Size and Surface Chemistry of Polystyrene Micro- and Nanobeads in the Interaction with an Advanced In Vitro Tri-Culture Intestinal Barrier Model

Micro- and nanoplastics represent ubiquitous environmental contaminants with emerging concerns regarding their impact on human health. The gastrointestinal tract is the primary site of contact, where micro- and nanoplastics may interact with the intestinal epithelium, potentially disrupting barrier integrity, altering microbiota composition, and triggering inflammatory or oxidative stress responses. Moreover, variability in particle size, shape, chemical composition, and surface modifications adds complexity to assessing their health impact. Findings remain inconsistent, and the mechanisms of toxicity are not yet fully elucidated. This study developed a tri-culture in vitro intestinal barrier model incorporating Caco-2 enterocytes, HT29-MTX mucus-secreting cells, and Raji B-induced M-like cells to mimic the structural and functional features of the human gut epithelium. Polystyrene beads of different sizes (40 nm and 200 nm) and surface functionalization (carboxylated and aminated) were characterized and exposed to the model to examine their effects on barrier integrity, cellular uptake, and cytotoxicity. The results showed that size and surface chemistry play key roles in particle interaction dynamics with the intestinal barrier, affecting cellular internalization and toxicological outcomes. This validated in vitro model provides a valuable tool for investigating micro- and nanoplastic behavior upon oral exposure, contributing to more accurate health risk assessments associated with plastic pollution.