(A) A schematic illustration of 3D bioprinting of lattice scaffolds using HUVECs- and CMs/CFs-laden MeTro/GelMA bioinks. Green and red food colors were used to distinguish the HUVECs- and CMs/CFs-laden inks, respectively, only for imaging experiments. (B) Immunostaining of the lattice structure against sarcomeric α-actinin (red), CD31 (green), and DAPI (blue) at day 7 post bioprinting. Printed CMs/CFs and HUVECs are marked with red and green boxes, respectively. (C) A schematic to describe 3D bioprinting vascularized cardiac constructs with HUVECs-laden MeTro/GelMA bioink and CMs/CFs/HUVECs-laden GelMA bioink. (D) A vascularized cardiac construct in the support bath right after printing process and (E) the construct after the photocrosslinking and washing steps. Green and red food colors were used to distinguish the MeTro/GelMA and GelMA bioinks, respectively, only for imaging experiments. (F) A cross-sectional fluorescence image of the vascularized cardiac construct. Fluorescein and rhodamine dyes were added to the MeTro/GelMA and GelMA bioinks, respectively. (G) Viability of HUVECs (in MeTro/GelMA bioink) and CMs/CFs/HUVECs (in GelMA bioink) within vascularized cardiac tissue constructs. (H) Live/dead staining of the vascularized cardiac construct at day 10 post bioprinting. (I) Immunostaining of the vascularized cardiac construct against sarcomeric α-actinin (red), CD31 (green), and DAPI (blue) at day 10 post bioprinting. HUVECs (in MeTro/GelMA bioink) and CMs/CFs/HUVECs (in GelMA bioink) are marked with green and red boxes, respectively.