We all remember that image of a rat with a human ear growing on its back. But researchers at Princeton University have gone one step further by creating a 3D printed ear that can pick up signals beyond the range of human hearing. Researchers printed a gel made up of calf cells on to a frame that resembled the shape of an ear. As it's printed, the cells bond to create living tissue, which is then coated with silver nano particles that allow the ear to pick up signals. While no attempt has been made to attach one of these to anyone, we can't imagine it's too far off.