New edible batteries to power ingestible medical devices

Scientists have developed new non-toxic, edible batteries - made with pigments naturally found in the skin, hair and eyes - which may power ingestible devices for diagnosing and treating diseases in future.
"For decades, people have been envisioning that one day, we would have edible electronic devices to diagnose or treat disease," said Christopher Bettinger from Carnegie Mellon University (CMU) in the US.
"But if you want to take a device every day, you have to think about toxicity issues," said Bettinger.
About 20 years ago, scientists developed a battery-operated ingestible camera as a complementary tool to endoscopies. It can image places in the digestive system that are inaccessible to the traditional endoscope.

It is designed to pass through the body and be excreted. For a single use, the risk that the camera with a conventional battery will get stuck in the gastrointestinal tract is small.
However, the chances of something going wrong would increase unacceptably if doctors wanted to use it more frequently on a single patient, researchers said.

The camera and some implantable devices such as pacemakers run on batteries containing toxic components that are sequestered away from contact with the body.
For low-power, repeat applications such as drug-delivery devices that are meant to be swallowed, non-toxic and degradable batteries would be ideal.

"The beauty is that by definition an ingestible, degradable device is in the body for no longer than 20 hours or so. Even if you have marginal performance, which we do, that is all you need," said Bettinger.
To minimise the potential harm of future ingestible devices, researchers turned to melanins and other naturally occurring compounds.
In our skin, hair and eyes, melanins absorb ultraviolet light to quench free radicals and protect us from damage.
"They also happen to bind and unbind metallic ions. We thought, this is basically a battery," said Bettinger.
Building on this idea, researchers experimented with battery designs that use melanin pigments at either the positive or negative terminals; various electrode materials such as manganese oxide and sodium titanium phosphate; and cations such as copper and iron that the body uses for normal functioning.

Researchers envision using the battery for sensing gut microbiome changes and responding with a release of medicine, or for delivering bursts of a vaccine over several hours before degrading.
They are also making edible batteries with other biomaterials such as pectin, a natural compound from plants used as a gelling agent in jams and jellies.