The microscopic robots, which are each just 70 microns long, were produced using a multistep nanofabrication technique that turns a 4-inch specialised silicon wafer into a million microscopic robots in just weeks.
"The really high-level explanation of how we make them is we're taking technology developed by the semiconductor industry and using it to make tiny robots," explained Marc Miskin, assistant professor at the University of Pennsylvania, who developed the techniques whilst a post-doc at Cornell University with his colleagues professors Itai Cohen and Paul McEuen and researcher Alejandro Cortese.
The robots' bodies are formed from a superthin rectangular skeleton of glass topped with a thin layer of silicon into which the researchers etch its electronics control components and either two or four silicon solar cells.
Each of a robot's four legs is formed from a bilayer of platinum and titanium (or alternately, graphene). The platinum is applied using atomic layer deposition and the platinum-titanium layer is then cut into each robot's four 100-atom-thick legs. "The legs are super strong," he said. "Each robot carries a body that's 1,000 times thicker and weighs roughly 8,000 times more than each leg."
The researchers shine a laser on one of a robot's solar cells to power it. This causes the platinum in the leg to expand, while the titanium remains rigid in turn, causing the limb to bend. The robot's gait is generated because each solar cell causes the alternate contraction or relaxing of the front or back legs.
Teams at Cornell and Pennsylvania are now at work on smart versions of the robots with on-board sensors, clocks and controllers.
The current laser power source would limit the robot's control to a fingernail-width into tissue. So Miskin is thinking about new energy sources, including ultrasound and magnetic fields, that would enable these robots to make incredible journeys in the human body for missions such as drug delivery or mapping the brain.
"We found out you can inject them using a syringe and they survive - they're still intact and functional - which is pretty cool," he said.
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