Scientists have built microscopic robots equipped with electronic "brains" that are capable of walking autonomously.

A team from Cornell University in the US developed the solar-powered bots as part of research into a new generation of tiny devices that can perform roles ranging from performing microsurgery, to cleaning the inside of arteries.

The microrobots measure just 250 micrometres across – smaller than the head of an ant – and can operate without any external controls.

"Before, we literally had to manipulate these 'strings' in order to get any kind of response from the robot," said Itai Cohen, a professor of physics at Cornell.

"But now that we have these brains on board, it's like taking the strings off the marionette. It's like when Pinocchio gains consciousness."

The breakthrough involves a complementary metal-oxide-semiconductor (CMOS) clock circuit, which can hold thousands of transistors capable of generating frequencies that set the gait of the robot.

The extremely low energy demands of the onboard circuit and platinum-based legs mean that they can be powered by tiny photovoltaic cells.

The system was used on three different types of microrobot: a two-legged version, a four-legged "dogbot", and a six-legged "antbot".

Commands can be sent to control the speed via laser pulse, with Professor Cohen claiming that the onboard "brains" would allow the bots to communicate with researchers and figure out how to carry out the instructions.

"Then we're having a conversation with the robot," he said. "The robot might tell us something about its environment, and then we might react by telling it, 'OK, go over there and try to suss out what's happening.'

"The real fun part is, just like we never really knew what the iPhone was going to be about until we sent it out into the world, what we're hoping is that now that we've shown the recipe for linking CMOS electronics to robotic actuating limbs, we can unleash this and have people design low-power microchips that can do all sorts of things."

The high degree of programmability could lead to a wide range of applications in medicine, according to lead researcher Dr Michael Reynolds, such as identifying good cells and killing bad cells."

A paper detailing the research, titled 'Microscopic robots with onboard digital controls', was published this week in the journal Science Robotics.