MIT engineers design tiny batteries for powering cell-sized robots

A tiny battery designed by Massachusetts Institute of Technology (MIT) engineers could enable the deployment of cell-sized, autonomous robots for drug delivery within the human body, as well as other applications.

The battery, which is 0.1mm x 0.002mm – roughly the thickness of a human hair – can capture oxygen from air and use it to oxidize zinc, creating a current with a potential up to 1V. That’s enough to power a small circuit, sensor, or actuator.

“We’re building robotic functions onto the battery and starting to put these components together into devices,” says Michael Strano, the Carbon P. Dubbs professor of chemical engineering at MIT and the senior author of the study.

Ge Zhang Ph.D. ’22 and Sungyun Yang, an MIT graduate student, are the lead authors of the paper, which appears in Science Robotics.

Powered by batteries

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 cell-sized robots is making sure they have enough power.

Other researchers have shown they can power microscale devices using solar power, but the limitation is robots must have a laser or another light source pointed at them at all times. These devices are known as marionettes because they’re controlled by an external power source. Putting a power source such as a battery inside these tiny devices could free them to roam much farther.

“The marionette systems don’t really need a battery because they’re getting all the energy they need from outside,” Strano says. “But if you want a small robot to be able to get into spaces you couldn’t access otherwise, it needs to have a greater level of autonomy.”

To create robots that could become more autonomous, Strano’s lab decided to use a zinc-air battery which has a longer lifespan due to its high energy density. The battery they designed consists of a zinc electrode connected to a platinum electrode, embedded into a strip of a SU-8 polymer commonly used for microelectronics. When these electrodes interact with oxygen molecules the zinc becomes oxidized and releases electrons that flow to the platinum electrode, creating a current.

In this study, the researchers showed 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, allowing robotic devices to keep track of time.

The battery also provides enough power to run two different types of sensors changing their electrical resistance when they encounter chemicals in the environment. One of the sensors is made from atomically thin molybdenum disulfide and the other from carbon nanotubes.

Robotic swarms

In this study, the researchers used a wire to connect their battery to an external device, but in future work they plan to build robots with the battery incorporated into a device.

One effort involves designing tiny robots that could be injected into humans where they could seek out a target site and then release a drug, such as insulin.

The researchers are also working on increasing the battery’s voltage, which may enable additional applications.

Massachusetts Institute of Technology
https://www.mit.edu