Tiny microbots swimming through liquid invariably conjures up images of Isaac Asimov's sci-fi classic Fantastic Voyage.But while microbots exist, and they can be made to swim, it's getting them to change direction that has been tricky so far - a bit of an issue if you're even planning on sticking them in a human body, for instance.Now a system used to propel swimming microbots without the need for on-board fuel has brought this idea one step closer. Researchers at North Carolina State University have coaxed their bots to perform U-turns on command.