2.10 Cell culture
Human umbilical vein endothelial cells (HUVECs, Lonza, MD, USA) were cultured in EGM-2 (Lonza, USA) and smooth muscle cells (SMCs, Lonza, MD, USA) were cultured in smooth muscle cell growth medium 2 (Promocell, USA). Both media were added with 1% v/v penicillin and streptomycin antibody and the cells were cultured at 37 ℃, 5% CO2, and 95% relative humidity. 1:1 EGM-2 and smooth muscle cell growth medium were mixed for culturing the printed vascular structure, and the mixed medium was changed every two days. HUVECs and SMCs used in all experiments were in 4 to 8 generations.