By growing rat tissue onto a microscopic silicon chip, scientists have created tiny robots that can move using their own muscle power. The robots, which are less than a millimetre long, are the first to include such living cells as complex as muscle tissue. The self-assembling cells were melded onto a tiny robotic frame, resulting in a device that could move like primitive legs without an external power source. In one experiment, the team fed a glucose solution to rat heart cells in a culture mimicking a living system. Muscle contractions propelled the tiny structure to shuffle along. The technique involved growing the muscle tissue onto the silicon structure, instead of dissecting muscle from a living animal. The versatile system may lead to the integration of cells and tissue with a variety of other microstructures, they added. Microscopic devices like mini electrical generators could power computer chips. Someday, the system could also have medical applications, such as a muscle-based way to stimulate nerves, allowing people who are paralysed to breathe without a ventilator.