In a groundbreaking development, researchers from the University of Pennsylvania and the University of Michigan have unveiled the world’s smallest fully programmable and autonomous robots. These microscopic swimming machines, barely visible to the naked eye, can independently sense and respond to their surroundings, operate for months, and cost just a penny each. Measuring approximately 200 by 300 by 50 micrometers, these robots are smaller than a grain of salt and operate at the scale of many biological microorganisms.
The potential applications for these tiny robots are vast. In medicine, they could revolutionize health monitoring at the cellular level, while in manufacturing, they could assist in constructing microscale devices. Powered by light, these robots are equipped with microscopic computers and can be programmed to move in complex patterns, sense local temperatures, and adjust their paths accordingly.
Breaking the Sub-Millimeter Barrier
The announcement comes as a significant leap in the field of robotics, which has long struggled to create autonomous machines at such a small scale. According to Marc Miskin, Assistant Professor in Electrical and Systems Engineering at Penn Engineering and the senior author of the study, “We’ve made autonomous robots 10,000 times smaller. That opens up an entirely new scale for programmable robots.”
For decades, while electronics have consistently shrunk in size, robots have faced challenges in keeping pace, particularly below the one-millimeter mark. “Building robots that operate independently at sizes below one millimeter is incredibly difficult,” Miskin explains. “The field has essentially been stuck on this problem for 40 years.”
At the microscale, forces tied to surface area, like drag and viscosity, dominate. “If you’re small enough, pushing on water is like pushing through tar,” Miskin adds. This necessitated the design of a new propulsion system that works with the unique physics of the microscopic realm.
Making the Robots Swim
Unlike larger aquatic creatures that propel themselves by pushing water behind them, these new robots generate an electrical field to nudge ions in the surrounding solution. This movement, in turn, animates the water around the robot’s body, creating a self-propelled effect. “It’s as if the robot is in a moving river,” says Miskin, “but the robot is also causing the river to move.”
The robots can adjust the electrical field to move in complex patterns and even travel in coordinated groups, akin to a school of fish, at speeds of up to one body length per second. The durability of these robots is notable, as they can be transferred between samples using a micropipette without damage. Charged by the glow of an LED, they can continue operating for months.
Giving the Robots Brains
For true autonomy, these robots require a computer to make decisions, sensors to perceive their environment, and tiny solar panels for power. This is where David Blaauw’s team at the University of Michigan played a crucial role. Blaauw’s lab, known for creating the world’s smallest computer, collaborated with Miskin’s team to integrate these technologies into the robots.
“The key challenge for the electronics,” Blaauw notes, “is that the solar panels are tiny and produce only 75 nanowatts of power. That is over 100,000 times less power than what a smartwatch consumes.” To address this, the Michigan team developed circuits that operate at extremely low voltages, reducing the computer’s power consumption significantly.
The solar panels occupy most of the robot’s space, leaving minimal room for the processor and memory. “We had to totally rethink the computer program instructions,” says Blaauw, “condensing what conventionally would require many instructions for propulsion control into a single, special instruction.”
Robots that Sense, Remember and React
The resulting innovation is the first sub-millimeter robot capable of independent thought. These robots can sense temperature changes to within a third of a degree Celsius, allowing them to move towards warmer areas or report temperature as a proxy for cellular activity. This capability enables them to monitor the health of individual cells.
“To report out their temperature measurements, we designed a special computer instruction that encodes a value, such as the measured temperature, in the wiggles of a little dance the robot performs,” explains Blaauw.
Programmed by light pulses, each robot has a unique address, enabling researchers to load different programs onto each one. “This opens up a host of possibilities,” adds Blaauw, “with each robot potentially performing a different role in a larger, joint task.”
Only the Beginning
This development represents just the beginning of what could be a new era in microscale robotics. Future iterations of these robots could store more complex programs, move faster, integrate new sensors, or operate in more challenging environments. The current design serves as a general platform, offering seamless integration of propulsion and electronics, cost-effective fabrication, and the potential for expanded capabilities.
“This is really just the first chapter,” says Miskin. “We’ve 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.”
The studies were conducted at the University of Pennsylvania School of Engineering and Applied Science, Penn School of Arts & Sciences, and the University of Michigan’s Department of Electrical Engineering and Computer Science. They were supported by various institutions, including the National Science Foundation, the Air Force Office of Scientific Research, and the Army Research Office.
The research team included Maya M. Lassiter, Kyle Skelil, Lucas C. Hanson, Scott Shrager, William H. Reinhardt, Tarunyaa Sivakumar, and Mark Yim from the University of Pennsylvania, along with Dennis Sylvester, Li Xu, and Jungho Lee from the University of Michigan.
