Most supercapacitors—electrical components that store energy—are made from aluminum, graphene or various polymers. But the materials list for the new ones being developed at Arizona State University (ASU) could be mistaken for a grocery receipt: cheddar cheese, eggs, gelatin, Gatorade.
Researchers at ASU are using these ingredients to create edible supercapacitors. Foods like cheese and egg white, when placed in the right combinations, can conduct and store electricity. The resulting devices, once swallowed, could one day power medical devices in the stomach or intestinal tract.
“We use food to function like electronics,” says Hanqing Jiang, a professor of mechanical engineering who led the research, heading up a team of students. “And everything works pretty well.”
The steps for making the supercapacitors—the recipe, if you will—go like this: researchers mix a bit of egg white with carbon pellets (activated carbon, sometimes called "activated charcoal," is used in some digestive medicines), then add water and more egg white. They apply the mixture to a bit of edible gold foil. They then layer together a slice of cheese and a sheet of gelatin with the egg-and carbon-covered gold foil. On top of that they add a square of dried seaweed, the type used to roll sushi, which has been soaked with drops of energy drink. They stack more of the same materials together, and seal them in a sealing machine.
“The whole structure is kind of a sandwich,” Jiang says.
The use of the gold leaf was the idea of one of Jiang’s students. “We were trying to think of an edible metal,” Jiang says. “We had one student from India, and he said in India gold is used to decorate cakes and ice cream. So there’s actually edible gold and edible silver.”
The team’s research, published in the journal Advanced Materials Technologies, has shown that currents produced by the edible supercapacitors can kill E. coli, a bacteria that can lead to a variety of ailments.
“The rate [of killing E. coli] is much faster than the current antibiotics,” Jiang says. “The supercapacitor can function as an electronic drug.”
The supercapacitors can power tiny cameras, which could make it easier for doctors to conduct investigative tests of the digestive tract. They can even deliver certain nutrients or medicines to specific areas of the gut.
The edible supercapacitors have the advantage over traditional ingestible electronics in that they are completely nontoxic and don’t need to be passed from the digestive tract. They do have to be swallowed whole though, and as of now, the devices are about the size of a ketchup packet. Gulp?!
Jiang estimates it will be two or three years before they have a functional medical device that is much smaller and 3D printed.