While 3D-printed organs sound like a great idea -- imagine no longer waiting around for a transplant -- a major hurdle for printing internal ones thus far have been creating intricate blood vessels and ventricles that are required for the organ to actually, you know, work. Now, a collaboration between scientists from the University of Sydney, Harvard, Stanford and MIT have discovered a way to do just that. The team used an advanced bioprinter to create tiny interconnected fibers, and then coated them in human endothelial cells and a protein-based material, which hardens under light. They then removed the fibers, and voilà -- a network of capillaries was born.