Drug discovery is a lengthy and costly endeavor. In fact, the cost of drug development has been rising year after year as a result of a lack of physiological models that can accurately predict the effect of a drug in humans. Therefore, risky drugs may enter human clinical trials while promising drugs might be eliminated at early stages; both scenarios lead to a sizable financial loss. Organ-on-a-chip devices have emerged to combat this, and are poised to fill this gap where the conventional cell-based assays and animal testing fail1,2. These technologies build on sophisticated microfluidic systems to culture human cells in a precisely controlled microenvironment to coordinate cells to work together and to recapitulate organ-level function that would otherwise be difficult to mimic in a traditional monolayer culture environment. The ultimate goal is to accurately model human physiology for precision drug testing.