A tiny battery designed by MIT engineers could enable the deployment of cell-sized autonomous robots for delivering drugs inside the human body, as well as other applications such as locating leaks in gas pipelines.
The new battery, which is 0.1 millimeters long and 0.002 millimeters thick (about the thickness of a human hair), can capture oxygen from the air and use it to oxidize zinc, creating a current with a potential of up to 1 volt. That’s enough to power a small circuit, sensor or actuator, the researchers demonstrated.
“We think this will be very beneficial for robotics,” said Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and senior author of the paper. “We’re building robotic functions into the battery and starting to put these components together to form devices.”
Ge Zhang, PhD ’22, and MIT graduate student Sungyun Yang are the lead authors of the paper, which appears in Scientific robotics.
Battery operated
For several years, Strano’s lab has been working on tiny robots that can sense and respond to stimuli in their environment. One of the main challenges in developing such small robots is making sure they have enough power.
Other researchers have shown that they can power microscale devices using solar energy, but the limitation of that approach is that the robots must have a laser or other light source pointed at them at all times. These devices are known as “puppets” because they are controlled by an external power source. Placing a power source, such as a battery, inside these tiny devices could free them to move much farther.
“Puppet systems don’t really need a battery because they get all the power they need from the outside,” Strano says. “But if you want a small robot to be able to get into spaces you wouldn’t otherwise be able to access, it needs to have a higher level of autonomy. A battery is essential for something that’s not going to be tethered to the outside world.”
To create robots that could become more autonomous, Strano’s lab decided to use a type of battery known as a zinc-air battery. These batteries, which have a longer lifespan than many other types of batteries due to their high energy density, are often used in hearing aids.
The battery they designed consists of a zinc electrode connected to a platinum electrode, embedded in a strip of a polymer called SU-8, which is commonly used in microelectronics. When these electrodes interact with oxygen molecules in the air, the zinc oxidizes and releases electrons that flow toward the platinum electrode, creating a current.
In this study, the researchers showed that this battery could provide enough energy to power an actuator — in this case, a robotic arm that can be raised and lowered. The battery could also power a memristor, an electrical component that can store memories of events by changing its electrical resistance, and a clock circuit, which allows robotic devices to keep track of time.
The battery also provides enough power to run two different types of sensors that change their electrical resistance when they come into contact with chemicals in the environment. One of the sensors is made of atomically thin molybdenum disulfide and the other is made of carbon nanotubes.
“We’re making the building blocks for cellular level function,” Strano says.
Robotic swarms
In this study, the researchers used a cable to connect their battery to an external device, but in future work they plan to build robots in which the battery is built into a device.
“This is going to be at the core of a lot of our efforts in robotics,” Strano said. “You can build a robot around a power source, just like you can build an electric car around a battery.”
One such effort revolves around designing tiny robots that could be injected into the human body, where they could seek out a target site and then release a drug such as insulin. For use in the human body, researchers envision the devices would be made of biocompatible materials that would disintegrate once they were no longer needed.
Researchers are also working to increase the battery voltage, which could enable additional applications.
The research was funded by the U.S. Army Research Office, the U.S. Department of Energy, the National Science Foundation, and a MathWorks Engineering Fellowship.