'Edible' Electronics Can Be Powered by Melanin

Medical devices are becoming smaller and more advanced, with researchers inventing tiny nano-scale devices that can even be ingested for internal monitoring or medication release. These devices wil,l of course, require power sources that also are safe for ingestion or implantation, and engineers are eyeing new forms of batteries and energy-harvesting methods to solve this problem.

One of the latest solutions comes from researchers at Carnegie Mellon University, who have discovered that melanin—a natural pigment found in the human skin—demonstrates a chemical structure well-suited to creating batteries based on natural melanin pigments. These batteries could become future power sources for a new class of medical devices called “edible electronics,” said Chris Bettinger, Carnegie Mellon associate professor and one of the researchers on the project.

“Edible electronics represents a class of electronically active medical devices that can be deployed orally, reside in the gastrointestinal tract temporarily, and eventually pass through the body harmlessly [as waste],” he said. “Edible electronics would have far-reaching diagnostic and therapeutic applications including devices for in vivo bio-sensing and controlled release of biologically active macromolecules.”

Melanin is best known as the pigment that dictates human skin tone, but it also is naturally found in the brain and in hair, as well as other places. But researchers don’t know much about what forms melanin pigments, which are at the center of the team’s research.

A diagram shows the structure of a melanin-based battery designed by researchers at Carnegie Mellon University that could be used to power edible, ingestible medical devices.
(Source: Carnegie Mellon University)

In their work, researchers assembled the different structures within melanin into what they surmised were the most stable arrangements, with each having a different function depending on its chemical structure. The molecules bound together formed a macromolecular structure, or a polymer, that could be arranged to create a potential battery material.

By using melanin as a battery cathode, their research led them to discover that a tetramer structure—a four-membered ring composed of larger molecules—was consistent with the structural model of melanin macromolecules. At the same time, they also learned that melanin exhibits a two-voltage plateau characteristic of normal battery materials, while outputting a surprisingly high voltage, said Venkat Viswanathan, an assistant professor of mechanical engineering at Carnegie Mellon and another of the researchers on the team.

“The voltage we got out was high; comparable to what you would get for the best sodium-based cathode materials we would use in a battery,” he said. “So this was surprising to us, that we could take this material from biology, and it could function potentially as a very good cathode material.”

The cathode in the battery is comprised of 8-10 milligrams of manganese oxide, which is about the daily-recommended dose for humans of the chemical, Bettinger said. The team is eyeing the battery for use as a bio-compatible source of power for emerging devices, such as biosensors, controlled release systems, and tissue-stimulation devices, that could be ingested and

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