Creation of lumen structures in layered cell sheets. (a) Illustration of the process of creating the lumen structure in layered cell sheets. (b) Top view of the layered cell sheets and the layered cell sheets with the wire. The white arrow denotes the titanium wire (scale bars, 5 mm). (c) Phase contrast microscopy images before and after the wire were removed from the stacked cell sheets (scale bars, 100 μm). (d) Electron microscopy images before insertion and after the extracting of the wire from the laminated cell sheet (scale bars, 20 μm). (e) Performance of Live/Dead staining after removing the titanium wire (scale bars, 100 μm).