Researchers have created a hair-thin battery that can power robots larger than the dot at the end of this sentence.
An air-zinc battery draws oxygen from its environment and emits a small amount of zinc, a reaction of about 1 volt. This energy can then power things like sensors or a small robotic arm that can raise and lower to deliver a load – say, insulin directly to the cells of a diabetic.
Although cell-sized robots have been proposed to deliver drugs to specific areas of the body, powering them has been difficult. Most current designs are solar powered, meaning they must be exposed to sunlight or controlled by a laser. But it does not penetrate far from the body, limiting how such robots, called “marionettes,” because they must stay connected to this light source like a puppet string, can move.
“Marionette systems don’t need a battery because they get all the power they need from outside,” learns the senior author. Michael Strangechemical engineer at MIT, said to a statement. “But if you want a small robot to be able to get into places you wouldn’t otherwise be able to get to, it needs to have a greater level of autonomy. A battery is essential for something that can’t locked up in the outside world.”
The new battery is among the smallest ever invented. In 2022, German researchers described a millimeter sized battery that can fit into a microchip. Strano and his team’s battery is about 10 times smaller, at 0.1 mm long and 0.002 mm thick. An average human hair is about 0.1 millimeter thick.
A battery has two parts, a zinc electrode and a platinum electrode. These are encapsulated in a polymer called SU-8. When zinc comes into contact with oxygen from the air, it causes an oxidation reaction that releases electrons. These electrons flow to the platinum electrode.
The batteries are made using a process called photolithography, which uses a photosensitive material to transfer nanometer-sized patterns onto silicon wafers. This method is often used to make semiconductors. It can quickly “print” 10,000 batteries from a single silicon, Strano and his colleagues reported Aug.14 in the journal. Scientific Robots.
In a new study, the researchers used wires to connect these itsy-bitsy batteries to cell-sized robots, which Strano’s lab is reproducing. They tested the battery’s ability to power a memristor, a circuit that changes resistance based on the amount of charge flowing through it; these memristors can store memories of events based on responsible changes.
They also used batteries to power a clock circuit, enable robots to tell time, and power two nano-sized sensors, one made of carbon nanotubes and the other of molybdenum disulfide. Microsensors like these could be installed in pipes or other hard-to-reach places to detect leaks, according to the researchers.
“We’re building the building blocks to create jobs at the cellular level,” Strano said.
The team also used these batteries to power an arm on one of their tiny robots, about the size of a human egg cell. These small forces can allow medical robots that work inside the body to release drugs at a specific time or place.
In the future, the team hopes to ditch the wires, and build their own batteries into their tiny robots.
“This will be the basis of many of our robotics efforts,” says Strano. “You can build a robot around a power source, just like you can build an electric car around a battery.”
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