Innovative microfluidic model for investigating the intestinal mucus barrier: numerical and experimental perspectives

The intestinal mucus layer serves as a critical first line of defense against external agents, functioning as a barrier to the absorption of drugs, food, and pathogens. While numerous in vitro studies have explored the role of mucus in preventing particle penetration, the effects of flowing luminal material, dislodging of mucus because of induced shear rate by lumen material and interfacial phenomena remain poorly understood. This study introduces a microfluidic approach to simulate the interaction between flowing luminal material and the mucus layer. The approach successfully measures both particle penetration into the mucus layer and the rate of mucus dislodgement by flowing luminal material. A biosimilar mucus model (BSM) and Hank's Balanced Salt Solution (HBSS) were employed as mimics of human intestinal mucus and luminal fluid, respectively. To investigate the effect of viscosity on the particle penetration pattern, two variants of the mucus model were used: BSM-1, representing a low-viscosity mucus model, and BSM-2, representing a high-viscosity mucus model. The velocity fields in the mucus and luminal material were extracted by tracking fluorescent particles. The results revealed significant differences between BSM-1 and BSM-2, attributed to their rheological properties. These findings were further confirmed through an assessment of the viscoelastic properties of the BSM models. The study utilized COMSOL Multiphysics for numerical simulations, successfully predicting experimental outcomes by solving fluid flow equations. Physicochemical characterizations of BSM and HBSS were performed to link the experimental results with numerical simulations, including flow sweep tests, the application of the power-law model for viscosity, and measurements of mucus density and wettability. This study proposes a microfluidic platform for examining mucus dislodgement and particle penetration in both low- and high-viscosity mucus models. The findings offer valuable insights into the intestinal mucus barrier's response to shear stress. The validated numerical approach and physicochemical characterizations provide a foundation for future studies on mucus dislodgement rates and penetration in more complex intestinal geometries and diverse flow conditions.