Barriers between organs and fluid systems exist throughout the body to selectively regulate the movement of compounds through membranes. One example is the blood-brain barrier, which modulates what molecules and compounds can travel from the bloodstream to the brain through layers of epithelial cells, endothelial cells, pericytes, and astrocytes. The intestine barrier allows the microbiome of the gut to absorb and process nutrients while not leaking into the blood or other organs.
Selectivity across physiological barriers is crucial to assess for applications like drug delivery since therapeutics have to cross several barriers to reach target sites effectively. Culturing cells on microfluidic chips with dynamic flow promote cells to perform in vivo-like functionalities, which in turn allow accurate, translatable measurements of parameters like transepithelial/transendothelial resistance (TEER).