Childhood brain tumors have few treatment options available since drugs cannot traverse the vessels and spaces in the brain to reach the tumor. To develop nanoparticles that can carry drugs to tumors, the Hammond and Straehla labs use self-assembling, 3D microscale models of blood vessels, as shown in this image. Because this organ-on-a-chip system faithfully replicates human brain vasculature, researchers can screen and test for more clinically promising nanoparticle formulations and drug delivery strategies.