Abstract: Vascularizing cell aggregates or tissue segments in a microfluidic device by filling a chamber within the device with a matrix that allows for endothelial sprouting; creating at least three voids within the matrix, of which at least two outer voids are lumenally connected to separate perfusion paths within the device and at least one additional void is positioned in between the at least two outer voids; endothelializing the at least two outer voids; introducing at least one cell type, matrix material, tissue segment, or combinations thereof into the void between the two outer voids; and using vascular growth factors to induce the endothelial cells to sprout into the matrix until the at least three voids are interconnected by endothelial sprouts.