Against this backdrop, researchers in the US have announced the results of a study that accomplishes a 40-year-old challenge. A team of researchers from the University of Pennsylvania and the University of Michigan has developed a new robot that is smaller than a grain of salt, measuring only 200 x 300 x 50 micrometers. At 0.3 mm on its longest side, that's far below the 1-mm threshold. Yet it can sense its surroundings, make decisions on its own, and swim and move in water.