content: Ohhh, think about this. We can already 3D print prosthesis. What if we just mount a surface to some dude's arm, with some electrodes and whatnot connecting the nervous system. Then 3D print whatever new design right onto there. Then if he wants to change out, just chop the thing off and print something else. I mean, all you need is to keep the nerve-prosthesis interface the same between transitions.