Cell coculture system. (a) Schematic diagram of the cell coculture system. (b–e) The confocal images of the cell coculture system containing HepG2 (green), 3T3 (blue), and ECs (red) on day 7 of culture. (f–i) The confocal images of calcein-AM-stained ECs after coculture with HepG2 and both 3T3 and HepG2 for 7 days. White arrows indicate capillary-like structures. The scale bar is 100 μm.