Bioprinting of liver tissues. (A) Layout of typical structural units of the hepatic lobule. In cross-sectional views, the microstructures appear as a hexagonal lattice, with the hepatic artery, bile duct, and portal vein triads placed at the hexagon vertices. Reproduced with permission from Ref. 82, copyright 2011 John Wiley & Sons. (B-D) Bioprinted liver tissue constructs with similar arrangement of the hepatic lobules to native liver tissues and tissue-like cellular density and tight intercellular junctions, using human primary hepatocytes, endothelial cells, and hepatic stellate cells. (B, C) Photographs showing the liver organoids immediately after bioprinting. (D) Fluorescence micrograph of the planar cross-section after tissue maturation, highlighting the compartmentalization of the non-parenchymal cells relative to the hepatocytes. The hepatic stellate cells and endothelial cells were pre-labeled in green and red, respectively, while the nuclei of all cells were stained in blue. Adapted with permission from Ref. 103, copyright 2015 OrganovoTM.