These hollow tubesmade of polydimethylsiloxane (PDMS) could be readily popu-lated with a monolayer of endothelial cells on their interiorsurfaces, and the oxygen permeability of PDMS would facili-tate the long-term viability and functionality of the endothelia.These endothelialized PDMS tubes, when further used to linkthe different organ-on-a-chip components, could then accuratelymimic the vascular interconnections between the various tis-sues with desired biological activities as they do in the humanbody, to facilitate drug testing on these tubular vascular models.