Towards a gold standard functional readout to characterize In Vitro lung barriers

The development of biomimetic in vitro lung models as an alternative to animal studies is urgent to improve the predictability of the pharmacokinetics of potential new drugs. For pharmacokinetics studies, advanced in vitro lung models such as lung-chips should mimic a functional air-blood barrier. Unlike in vivo conditions, stem/primary cells and cell lines do not necessarily form a functional and tight barrier when cultured in vitro. Here, we explore the two gold standard techniques for monitoring barrier integrity: transepithelial electrical resistance (TEER) and permeability. We discuss the advantages and limitations of these methods, provide recommendations for methodological improvements, and we elude on possible future directions.