10th March 2019

Micro robots can be injected through hypodermic needle

Researchers have harnessed the latest nanofabrication techniques to create bug-shaped robots that are wirelessly powered, able to walk, able to survive harsh environments and tiny enough to be injected through an ordinary hypodermic needle.

"When I was a kid, I remember looking in a microscope, and seeing all this crazy stuff going on," said Marc Miskin, Assistant Professor of Electrical and Systems Engineering at the University of Pennsylvania, who is also a member of the Singh Center for Nanotechnology. "Now we're building stuff that's active at that size. We don't just have to watch this world. You can actually play in it."

Miskin developed the new fabrication techniques whilst a post-doc at Cornell University with his colleagues, professors Itai Cohen and Paul McEuen and researcher Alejandro Cortese. This week, he presented his microscopic robot research at the American Physical Society March Meeting in Boston.

Over the past several years, Miskin and research colleagues developed a multi-step nanofabrication technique that turns a 4-inch specialised silicon wafer into a million microscopic robots. Each just 70 microns in length (about the width of a very thin human hair), the robots' bodies are formed from a super-thin rectangular skeleton of glass. This is topped with a thin layer of silicon, onto which the electronics control components are etched, along with either two or four silicon solar cells – the rudimentary equivalent of a brain and organs.

"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," explains Miskin. 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. "It's like painting with atoms," says Miskin. The platinum-titanium layer is then cut into each robot's four 100-atom-thick legs.

"The legs are super strong," says Miskin. "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 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 thus 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 only a centimetre or so into tissue. So Miskin is now looking for alternative energy sources including ultrasound and magnetic fields that would enable these tiny machines to make incredible journeys in the human body. This might one day include tasks 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 adds.

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