Structure of engineered tissues under static conditions. Representative longitudinal hematoxylin and eosin micrographs: (A) RAEC-only, (B) RMSC-only, and (C) RAEC-RMSC coculture after 3 days. More spreading and networking of cells were observed after 7 days of culture in (D) RAEC-only, (E) RMSC-only, and (F) RAEC-RMSC coculture. Cross-sectional hematoxylin and eosin micrographs of (G) RAEC-only, (H) RMSC-only, and (I) RAEC-RMSC coculture after 7 days demonstrating vascular lumens only in the coculture indicated by the arrows in panel (I). Scale bar = 50 μm. RAEC, rat aortic endothelial cell; RMSC, rat mesenchymal stem cell. Color images available online at www.liebertonline.com/ten.