A tiny battery designed by MIT engineers could enable the deployment of cell-sized, autonomous robots to deliver drugs inside the human body, as well as other applications such as detecting leaks in gas pipelines. is
The new battery, which is 0.1 mm long and 0.002 mm thick — about the thickness of a human hair — can capture oxygen from the air and use it to oxidize zinc, producing up to 1 volt. A current is generated. The researchers showed that this is enough to power a small circuit, sensor, or actuator.
“We think it's going to be very applicable to robotics,” says Michael Strano, the Carbon P. Dibbs Professor of Chemical Engineering at MIT and senior author of the study. “We're building robotic functions on the battery and starting to put those components together into devices.”
Jie Zhang, Ph.D. '22, and Sungyun Yang, an MIT graduate student, are lead authors of the paper, which Science 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. A major challenge in developing such small robots is making sure they have enough power.
Other researchers have demonstrated that they can power microscale devices using solar energy, but the limitation of this approach is that the robot must have a laser or other light source on hand at all times. Such devices are known as “marionettes” because they are controlled by an external power source. Putting a power source like a battery inside these tiny devices can free them to roam far.
“Marionette systems don't really need a battery because they're getting all the energy from the outside,” Strano says. “But if you want a small robot to be able to go to places you couldn't otherwise access, it needs a greater level of autonomy. One thing that's essential is a battery. which will not be connected to the outside world.”
To create robots that could be more autonomous, Strano's lab decided to use a type of battery called a zinc-air battery. These batteries, which last longer than many other types of batteries due to their 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 polymer called SU-8, commonly used for microelectronics. When these electrodes interact with oxygen molecules from the air, the zinc oxidizes and releases electrons that flow to the platinum electrode, creating a current.
In this study, the researchers showed that this battery can provide enough energy to power an actuator — in this case, a robotic arm that can be raised and lowered. The battery can 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 monitor time.
The battery also provides enough power to operate two different types of sensors that change their electrical resistance when exposed to chemicals in the environment. One of these sensors is made from atomically thin molybdenum disulfide and the other from carbon nanotubes.
“We're building basic building blocks to enhance functions at the cellular level,” says Strano.
Robotic sheep
In this study, the researchers used a wire to connect their battery to an external device, but in future work they plan to build a robot that incorporates the battery into a device.
“That's going to be the focus of a lot of our robotics efforts,” Strano says. “You can build a robot around an energy source, like you can build an electric car around a battery.”
One of these efforts revolves around designing tiny robots that can be injected into the human body, where they can find a target site and then release a drug like insulin. For use in the human body, researchers envision devices made of biocompatible materials that will break down once they are no longer needed.
Researchers are also working on increasing the battery's voltage, which could enable additional applications.
This research was funded by the US Army Research Office, the US Department of Energy, the National Science Foundation, and a MathWorks Engineering Fellowship.