<b>Supplemental Videos S1-S5</b>

<b>Supplemental Video S1.</b> Characterization of 3D endothelium. Human umbilical vein endothelial cells (HUVECs) were cultured in two-lane Organoplates (Mimetas), forming 3D tubular structures within 4–5 days. The 3D HUVECs were stained for CD31 (green), F-actin (red), and nuclei (blue). The 3D architecture was visualized using Z-plane images captured at 8-μM intervals in confocal mode with the Opera Phenix High-Content Screening System.<br><b>Supplemental Video S2 and S3. </b>Comparisons of heparan sulfate (HS) expression between 2D endothelial cell cultures and 3D endothelium. Human umbilical vein endothelial cells (HUVECs) were cultured in <b>(</b><b>S2</b><b>) </b>24-well plates until 95% confluency or <b>(</b><b>S3</b><b>)</b> two-lane Organoplates to generate 3D endothelium. They were stained for HS (green) and nuclei (blue). Images were captured using Z-plane images at 8-μM intervals in confocal mode via the Opera Phenix High-Content Screening System.<br><b>Supplemental Video S4 and S5. </b>Comparisons of wheat germ agglutinin (WGA) staining between 2D endothelial cell cultures and 3D endothelium. Human umbilical vein endothelial cells (HUVECs) were cultured in <b>(</b><b>S4</b><b>)</b> 24-well plates until 95% confluency or <b>(</b><b>S5</b><b>)</b> two-lane Organoplates to generate 3D endothelium. They were stained with WGA (green) and nuclei (blue). Images were captured using Z-plane images at 8-μM intervals in confocal mode via the Opera Phenix High-Content Screening System.