Figure 4.

An ideal in vitro model of the microbiota‐immunity‐CNS network crosstalk. This schematic representation highlights the main physical and biological features that may be implemented with the most advanced state‐of‐the‐art engineering systems. From top to bottom: anaerobic gut bacteria are cultured in dynamic conditions, under the effects of physiological levels of shear stress. Controlled anaerobic culture medium flow conveys the secreted bacterial molecules, which diffuse across the intestinal barrier, recreated by a mucin‐based bi‐layered mucus on top of the intestinal epithelium. A tuned oxygen gradient is maintained across the barrier. The microbial activity recruits from the “blood channel” the immune cells in the interstitial space, represented by a perfused micro‐channel. The immune cells in the interstitial space start secreting inflammatory mediators that are free to diffuse back across the intestinal barrier. On the other hand, the bacterial molecules and immune system cytokines can reach the CNS thanks to the bloodstream. At the BBB interface, a selective permeability porous membrane regulates fluid extravasation and molecule diffusion. The final compartment is composed by a multi‐culture of CNS‐resident cells within a biomimetic 3D matrix, resembling the ECM inside the brain. (Image created with BioRender.com.)