It's no longer a rare feat to 3D print blood vessels. Printing vessels that act like the real deal, however, has been tricky... until now. Lawrence Livermore researchers have successfully 3D printed blood vessels that deliver nutrients and self-assemble like they would in a human body. The key is to print an initial structure out of cells and other organic material, and then to augment it with bio ink and other body-friendly materials. With enough time, everything joins up and behaves naturally.