Nanofabbed bots are small enough to be delivered via syringe, raising all sorts of fantastic voyage possibilities. Nick Carne reports. How do you build a very big army of very small robots? Start with a 10-centimetre silicon wafer. That’s what engineers from the University of Pennsylvania in the US did to create a million of them in just a few weeks using nanofabrication techniques borrowed from the semiconductor industry. Each robot is wirelessly powered, able to walk and survive harsh environments, and tiny enough to be injected through an ordinary hypodermic needle, which opens up all manner of possibilities. "When...