A minuscule battery designed by MIT engineers could enable autonomous cell-sized robots to deliver drugs to the human body, as well as other applications such as locating leaks in gas pipelines.
The fresh battery, which is 0.1 millimeters long and 0.002 millimeters broad — about the width of a human hair — can capture oxygen from the air and employ it to oxidize zinc, creating a current of up to 1 volt. That’s enough to power a tiny circuit, sensor or actuator, researchers have shown.
“We think this will be very helpful for robotics,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and senior author of the study. “We’re building robotic functions on batteries and starting to connect those components into devices.”
Ge Zhang, a 2022 PhD candidate, and Sungyun Yang, a postgraduate student at MIT, are the lead authors paperwhich appears in .
Battery powered
For several years, Strano’s lab has been working on minuscule robots that can sense and respond to stimuli in their environment. One of the main challenges in developing such minuscule robots is providing them with enough power.
Other researchers have shown that they can power microscale devices using solar energy, but the limitation of this approach is that the robots must have a laser or other delicate source pointed at them at all times. Such devices are known as “puppets” because they are controlled by an external power source. Putting a power source, such as a battery, inside these minuscule devices could allow them to travel much farther.
“Puppet systems don’t really need batteries because they get all the power they need from the outside,” Strano says. “But if you want a little robot to be able to get into spaces that you wouldn’t be able to get to otherwise, 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 employ 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, commonly used in microelectronics. When these electrodes interact with oxygen molecules in the air, the zinc oxidizes and releases electrons that flow to the platinum electrode, creating electricity.
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 that allows robotic devices to keep track of time.
The battery also provides enough power to power two different types of sensors that change their electrical resistance when they encounter chemicals in the environment. One of the sensors is made of atomically slim molybdenum disulfide, the other of carbon nanotubes.
“We’re creating the basic building blocks to build function at the cellular level,” Strano says.
Robot swarms
In this study, the researchers used a wire to connect the battery to an external device, but in future work they plan to build robots in which the battery is built into the device.
“This is going to be the core of a lot of our robotic efforts,” Strano says. “You can build a robot around an energy source, just like you can build an electric car around a battery.”
One of these efforts focuses on designing minuscule 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. Scientists envision that for employ in the human body, the devices would be made of biocompatible materials that would disintegrate when no longer needed.
Scientists are also working to augment the battery voltage, which could enable additional applications.
The research was funded by the U.S. Army Office of Research, the U.S. Department of Energy, the National Science Foundation and a MathWorks Engineering Fellowship.