World’s smallest programmable robots open new possibilities

Complete robot next to the year on a penny for scale. Photo: Kyle Skelil, University of Pennsylvania

The world’s ‘smallest fully programmable, autonomous swimming robots’, which have debuted at the University of Pennsylvania (Penn) and feature a ‘brain’ developed at the University of Michigan (U-M), can independently sense and respond to their surroundings, operate for months — and cost ‘mere pennies each’. Barely visible to the naked eye, each robot is about 0.2 x 0.3 x 0.05mm, meaning they can operate at the scale of many microorganisms. However, they can be programmed to move in complex patterns, sense local temperatures, and adjust their paths in response.

Marc Miskin, assistant professor in electrical and systems engineering at Penn and senior author of a pair of studies published in Science Robotics and the Proceedings of the National Academy of Sciences, said these light-powered robots, developed with primary support from the US National Science Foundation, could advance medicine by monitoring the health of individual cells and aid manufacturing by helping construct microscale devices.

He said: “The robots can move in complex patterns and even travel in coordinated groups, much like a school of fish; and because their propulsion system has no moving parts, the robots are extremely durable; they are also easy to transfer with a micropipette and capable of swimming for months.”

Mr Miskin added that for decades, electronics have been made ever smaller, as epitomised by the record-setting ‘sub-millimetre’ computers developed in the lab of David Blaauw and Dennis Sylvester, professors of electrical and computer engineering at U-M. Yet robots have struggled to keep pace, in part because independent motion is exceptionally difficult for microscale devices — a problem Miskin says has stalled the field for 40 years, until now.

Swimming robots
Professor Blaauw, a senior author of the Science Robotics study, said: “We saw that Penn Engineering’s propulsion system and our tiny computers were just made for each other. Operating at the microscale in water, drag and viscosity are so large that Mr Miskin says it is like moving the robot through tar. His team’s propulsion design gets around this by turning the problem around, so instead of trying to move themselves, these robots ‘move the water’ by generating an electrical field that nudges ions in the surrounding liquid, and in turn these push on nearby water molecules, generating force to move the robot.”

On the computing side, Professor Blaauw’s team needed to run the robot’s program on 75 nanowatts of power, which he says is 100,000 times less than a smart watch requires. “To get even that tiny amount of power, the solar panels take up most of the robot and we to totally rethink the computer program instructions, condensing what conventionally would require many instructions for propulsion control into a single, special instruction.”

Mr Miskin concluded: “This is just the first chapter. We have shown that you can put a brain, a sensor and a motor into something almost too small to see, and have it survive and work for months. Once you have that foundation, you can layer on all kinds of intelligence and functionality and open the door to a whole new future for robotics at the micro-scale.”