Robotic surgery is no longer the stuff of science fiction. However, these robots can't really feel their way around -- the need for super-small mechanisms rules out existing approaches to touch. That's where Harvard researchers might come to save the day. They've developed a pop-up sensor whose four layers collapse to a tiny footprint (just a tenth of an inch) when necessary, but expand into a 3D sensor thanks to a built-in spring. The design is extremely sensitive, too, with a light intensity sensor that can detected mere millinewtons of force.