Epithelial tissue is comprised of layers of epithelial cells that form a protective barrier between the body and the external environment.This is achieved through the polarised expression of proteins including tight junctions, which are intercellular protein complexes selectively permeable to ions and macromolecules.In the lung, formation of these physical barriers along with chemical and immunological barriers maintains tissue homeostasis.A lab-on-a-chip platform has been developed for the continuous monitoring of an in-vitro epithelial cell culture barrier model under constant perfusion conditions.