The vascular endothelium defines the interface between blood and tissue, forming a semi-permeable barrier that controls the exchange of nutrients. Dysfunction in the endothelial barrier is associated with numerous blood disorders and inflammatory diseases, such as sickle-cell disease and malaria, but the underlying mechanisms remain unknown. To address this gap in knowledge, researchers recently developed a microvasculature-on-a-chip that recapitulates endothelial barrier function and enables the real-time, high-resolution, long-term visualization of blood vessel obstruction and endothelial permeability under continuous flow conditions. According to the authors, this system demonstrates significant promise for drug discovery and for investigating how molecular and cellular interactions directly mediate endothelial barrier dysfunction in a wide spectrum of diseases. The study, published in Nature Biomedical Engineering, was partly funded by NHLBI.