World's Smallest Autonomous Robots Built: Penny-Machine That Swim, Sense and Decide
Microscopic Robots Achieve Full Autonomy for the First Time
Researchers from the University of Pennsylvania and the University of Michigan have developed the smallest fully programmable autonomous robots ever built—microscopic machines that swim, sense their surroundings and react without human intervention. Remarkably, each robot costs only a penny and can function for months.
So small they are barely visible, the robots measure just 200 by 300 by 50 micrometers, placing them below the size of a grain of salt. Operating on the same scale as many microorganisms, they hold promise for applications ranging from single-cell health monitoring to the construction of tiny engineered systems.
The light-powered devices contain microscopic computing units and can be programmed to navigate complex paths, measure temperature variations and adjust their movement accordingly.
According to reports published in Science Robotics and the Proceedings of the National Academy of Sciences (PNAS), the robots move and function without tethers, magnetic fields or external controllers. This milestone establishes them as the first genuinely autonomous, programmable robots of their size.
"We've created autonomous robots that are 10,000 times smaller than anything before," said Marc Miskin, an assistant professor at Penn Engineering and the studies' senior author. "It opens the door to programming robots on a completely new scale."
More coverage on emerging robotics and frontier science is available at FSNews365.
Breaking the Sub-Millimeter Barrier in Robotics
While electronic devices have steadily shrunk over the decades, robotics has struggled to follow the same trajectory. Building robots that can operate independently at sizes below one millimeter remains an enormous challenge, according to Marc Miskin, who notes that the field has effectively been grapping with this obstacle for more than 40 years.
At such tiny scales, the physical rules change dramatically. Forces familiar in everyday life, such as gravity and inertia, become far less important, while surface-related forces like drag and viscosity dominate. As Miskin explains, moving through water at this scale is more like pushing through tar.
As a result, conventional movement strategies used by larger robots, including limbs, tend to fail at the microscale. Delicate legs and arms are not only extremely difficult to manufacture, but also prone to breaking.
As a result, the team was forced to rethink movement from the ground up, developing a completely new propulsion system designed to work in harmony with the unusual physics that govern motion at microscopic scales.
Making the Robots Swim Without Moving Parts
Large aquatic animals, such as fish, propel themselves by pushing water backwards. Under Newton's Third Law, this backward force produces an equal and opposite reaction, driving the animal forward.
The newly developed robots operate very differently. Instead of bending or flexing their bodies, they create an electrical field that gently shifts ions in the surrounding fluid. These ions then push against nearby water molecules, setting the water around the robot in motion.
"It's as though the robot is travelling in a flowing river," Miskin explains, "While at the same time generating that flow itself."
By finely tuning the electrical field that drives their motion, the robots can follow intricate paths and even move together in coordinated groups, resembling a school of fish, at speeds of up to one body length per second.
Because the electrodes that create this field contain no moving parts, the robots are exceptionally robust. "They can be transferred again and again between samples using a micropipette without suffering damage," Miskin explains. Powered by the light of an LED, the robots are capable of swimming continuously for months.
Research on how physical systems interact with extreme environments is also explored at Earth Day Harsh Reality.
Giving the Robots Brains at the Microscale
For a robot to operate independently, it must carry a computer to make decisions, sensors to interpret its environment, electronics to control movement and miniature solar cells to supply power— all compressed onto a chip measuring only a fraction of a millimeter. This challenge is where David Blaauw's team at the University of Michigan stepped in.
Blaauw's laboratory holds the world record for the smallest computer ever built. When Marc Miskin and Blaauw first crossed paths at a DARPA-hosted presentation five years ago, they quickly recognized that their technologies were ideally suited to work together.
"We realized that Penn Engineering's propulsion system and our ultra-compact computers were a natural fit," Blaauw said. Even so, it took five years of intensive effort from both teams to produce their first fully functioning robot.
"The main hurdle for the electronics," Blasuw explained, "is that the solar panels are minuscule and generate just 75 nanowatts of power—more than 100,000 times less than a typical smartwatch consumes."
To make the robot's computer function on such limited energy, the Michigan team designed specialized circuits that operate at ultra-low voltages, cutting power consumption by over a thousandfold.
However, the solar panels take up most of the robot's surface area, leaving very little room for the processor and memory. As a result, the team had to radically redesign the computer's instructions.
"We compressed what would normally require multiple propulsion commands into a single, custom instruction," Blaauw said, "so the entire programme could fit within the robot's tiny memory."
Robots That Sense, Remember and React
These advances have delivered the first sub-millimeter robot capable of genuine decision-making. To the researchers' knowledge, no one has previously integrated a complete computer—combining a processor, memory and sensors— into a robot of this size. This milestone marks the first microscopic robots able to independently sense their surroundings and take action.
Equipped with electronic temperature sensors accurate to within a third of a degree Celsius, the robots can move towards warmer regions or relay temperature data. Because temperature serves as a proxy for cellular activity, this capability allows the robots to monitor the health or individual cells.
To communicate temperature readings, the team devised a bespoke computer instruction that encodes values such as measured heat into subtle movements, or "wiggles", performed by the robot. These movements are recorded through a microscope-mounted camera and decoded to reveal the data, a method Blaauw likens to the waggle dance used by honey bees to communicate.
The robots are programmed using pulses of light, which also serve as their power source. Each robot carries a unique address, enabling researchers to upload different programmes to individual units. According to Blaauw, this flexibility opens the door to a wide range of applications, with each robot potentially taking on a distinct role with a coordinated task.
Insights into cellular monitoring and human health implications are also covered at Human Health Issues.
Only the Beginning for Microscale Robotics
Future generations of the robots could carry more sophisticated software, move at higher speeds, incorporate additional sensors or operate in far harsher conditions. At its core, the current design serves as a flexible platform: its propulsion system integrates smoothly with electronics, its circuits can be mass-produced at low cost, and its architecture allows new capabilities to be added with ease.
"This is only the opening chapter," Miskin said. "We've demonstrated that it's possible to place a brain, a sensor and a motor into something almost invisible, and have it function reliably for months. With that foundation in place, layers of intelligence and functionality can be added, opening an entirely new future for microscale robotics."
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