Laser cutters use lasers to cut shapes into existing material, but Rice University scientists have figured out how to make one build objects instead of cut them. The result is the $2,000 3D printer that you see above, constructing the blood vessel network inside a mouse liver. If we want to maximize the usefulness of 3D printers, we have to maximize the number of materials they can work with, while minimizing the cost. That was the goal of the Rice scientists, when they devised a way to make a 3D printer with a couple of days, a couple of thousand...