University of Washington bioengineers have developed the first structure to grow small human blood vessels, creating a 3-D test bed that offers a better way to study disease, test drugs and perhaps grow human tissue. Ying Zheng, a UW research assistant professor, first built the structure out of collagen while working as a postdoc at Cornell University. She created tiny channels and injected them with human endothelial cells, which line blood vessels. Over two weeks, the cells grew and formed tubes through the mold's rectangular channels. When brain cells were injected into surrounding gel, they released chemicals that prompted the engineered vessels to sprout new branches, extending the network. After joining the UW, Zheng explored how this research platform would transport real blood. The engineered vessels transported blood smoothly and developed clots when inflamed, like real vessels. These vessels could be used to study a variety of conditions, from cancer to malaria.