Influence of Microplastic Contaminations on the Barrier Properties of Reconstituted Mucus

There is an invisible but inevitable ingredient that is being served on the tables all around the world: microplastics (MPs). Alarmingly, it is estimated that around 5 g of small sized particles (<1mm) are ingested weekly. These particles can accumulate in the gastrointestinal mucosa, which acts as the first biological barrier encountered by MPs up taken with diet. However, it is yet unknown how the presence of such pollutants affects the physiological functionalities of this highly selective barrier. In this study, a microfluidic setup was used to recreate a MPs contamination at the interface of reconstituted gastric mucus (MUC5AC). For this purpose, 300 nm sized differently charged polystyrene nanoparticles were chosen as a model for natural occurring plastic contamination in the sub-micrometer range. This setup allowed to investigate the penetration of differently charged fluorescent test molecules (4 kDa dextrans) into both the reconstituted pristine and contaminated mucus gel. The hydrodynamic radii of these dextrans were at least two orders of magnitude lower than the mesh size of the mucus gel. Hence, the diffusive penetration of the dextrans was modulated by intermolecular interactions rather than geometric hindrance. By means of fluorescence imaging, it was possible to evaluate and compare the penetration profiles of differently charged dextrans into the mucus gels. The obtained results evidenced that the MPs contamination affects the uptake of the selected test molecules at the mucosal interface, suggesting that its barrier properties are affected by the presence of MPs. This study also suggested that alterations in the barrier properties are driven by electrostatic interactions, along with hydrophobic binding of the tested molecules to the contaminating MPs. Overall, the results of this thesis work provide an advancement in the general understanding of how MPs contamination affects the destiny of ingested substances. Furthermore, these findings on the gastric MUC5AC mucin might be reasonably transferred to other mucin types such as the intestinal MUC2. In the long term, these insights may be relevant for drug delivery applications when drugs are intended to overcome a MPs contaminated mucus barrier.