Three-dimensional printing has been used to make a jawbone, a functioning bladder, as well as a model kidney, and there have been successful experiments in printing tissue such as skin cells for burn treatments and even the external part of an ear. Now scientists at Princeton University have, for the first time, printed not only the tissue for an ear but also the electronic components that would make an artificial sensory organ work. It's the first step toward printing organs that behave like the real thing.Heart Cells Beat in a Lab DishMichael McAlpine, an assistant professor of mechanical and aerospace engineering, and his colleagues used a commercially available 3-D printer to do the work. The "inks" consisted of hydrogels mixed with calf cells and silver nanoparticles. Layer-by-layer, the ink was laid down onto a surface, building up the three-dimensional structure of the ear and embedded electronics. Because it's the first attempt, the electronics are just a simple antenna. But if it were connected to a receiver that in turn could be connected to a person's auditory nerve with electrodes, it would allow a deaf person to hear.McAlpine has experimented with tissue-compatible electronics before: last year, he and his team created "tattoos" for teeth that were sophisticated electronic sensors.