Biological validation of thiolated food grade secondary oil in water nanoemulsions with enhanced mucus-adhesion properties in Intestine-on-a-chip model

Recently, oral delivery systems have gained more and more attention and among them oil in water nano-emulsions (O/W NEs) are of particular interest for their capability of loading and delivering lipophilic compounds, improving their pharmacokinetic. Few years ago, our group developed a method to stabilize O/W NEs by adding a polymeric shell on the oil core, using pharma grade formulations. To effectively exploit this formulation as food supplement we tried to enhance muco-adhesion properties of the polymer shell, namely chitosan (Ct) towards the intestinal barrier. However, in the field of food supplements, food grade materials should be used, because of both their safety and cost effectiveness. Therefore, in this work, we first have replaced pharma grade (PG) materials with food grade (FG) ones for the preparation of the polymer coated O/W NEs, namely secondary O/W NEs, performing a comparative study between the two formulations. Then we have modified Ct by adding thiol groups via a simple non-covalent procedure based on N-acetylcysteine (NAC) salification, which is compliant with food supplement formulations. PG and FG formulations were prepared and physio-chemically characterized using different techniques, including DLS, 1H-NMR, ITC, obtaining comparable results. We validated these systems in terms of physiological behaviour. Very importantly, we assessed mucus-adhesion properties of the two polymeric coatings (Ct and Ct-NAC) within a microfluidic device in the shape of an intestine-on-chip device capable of mimicking the in-vivo intestinal microenvironment, verifying a significant enhancement in the mucus-adhesive properties of Ct-NAC with respect to Ct due to the presence of thiol groups, as expected. Nonetheless, in-vivo assays are required as a final assessment for the proposed system to be commercialized.