When it comes to tackling the body's internal problems, sometimes the biggest concern isn't treatment, but rather access. Electronic devices that go to work inside the body — like endoscopes and remote drug-delivery systems — need their own power supply, but batteries can pose long term toxicity issues for patients. Now, researchers presenting their work to the American Chemical Society (ACS) say nontoxic, edible batteries could one day power ingestible devices for diagnosing and treating diseases. Progress toward that goal has been made, they say, with batteries made from the melanin pigments naturally found in the skin, hair and eyes.
Dr. Christopher Bettinger leads the team at Carnegie Mellon University (CMU). "For decades, he says, "people have been envisioning that, one day, we would have edible electronic devices to diagnose or treat disease." Scientists did, in fact, develop a battery-operated ingestible camera for endoscopy work about 20 years ago. As was hoped, this device was able to gather images in the digestive system from places that had been inaccessible to the traditional endoscope. This design was considered safe because the apparatus was intended to pass right through the body before being excreted.
Problems arise, however, when such devices need to be taken on a regular — even on a daily — basis. For a single use, the risk that a camera with a conventional battery will get stuck in the gastrointestinal tract is acceptably small. However, the chances of something going wrong would significantly increase if doctors needed to use it more frequently on a single patient.
"That's when we have to think about biologically derived materials that could replace some of these things you might find in a RadioShack," says Bettinger.
Endoscopic cameras and other devices such as implantable pacemakers are traditionally powered by batteries which contain toxic components such as lithium iodide. In such circumstances, the batteries are isolated from the patient's body. For medical conditions that require repeat applications using drug-delivery devices that are meant to be swallowed, isolating the battery is not always the easiest option. In these circumstances, the team reasoned that a better solution would be low-power, nontoxic and degradable batteries.
In many cases, it is not necessary for the device to survive. Like many disposable medical appliances, once it has done its job, it can be disposed of. "The beauty is that, by definition, an ingestible, degradable device is in the body for no longer than 20 hours or so," Bettinger says. "Even if you have marginal performance, which we do, that's all you need."
Bettinger's team realized they could use melanins and other compounds that occur naturally to create a battery that wouldn't pose a threat to health. The melanins in our skin, hair and eyes are complex polymers which determine eye and skin color. They absorb ultraviolet light to neutralize free radicals and protect us from damage. They also happen to bind and unbind metallic ions — negatively or positively charged atoms. This gave Bettinger's team the inspiration they needed: "we thought, this is basically a battery," he says.
The researchers began to experiment with designs that used melanin pigments at either the cathode (positive) or anode (negative) ends of the battery. The team also looked at other substances the body uses naturally such as manganese oxide, sodium titanium phosphate and positively charged ions of copper and iron. "We found basically that they work," says Bettinger's colleague, Dr. Hang-Ah Park. "The exact numbers depend on the configuration, but as an example, we can power a 5 milliWatt device for up to 18 hours using 600 milligrams of active melanin material as a cathode."
Although the capacity of a melanin battery is low compared to that of a standard lithium-ion one, it is still high enough, the scientists say, to power an effective ingestible drug-delivery or sensing device. For example, Bettinger envisions using the battery to power a device able to detect gut microbiome changes and respond with a release of medicine. Similarly, it could be used to deliver multiple doses of a vaccine over several hours before degrading.
In addition to melanin batteries, the team is also researching edible batteries that use other biomaterials such as pectin, the natural compound in plants used as a gelling agent in jams and jellies. The next step is to ensure the new battery design isn't ingested too quickly. They hope to develop packaging materials that will safely deliver the battery to the stomach.