The fascinating field of ingestible robotics could potentially allow robot-like machines to probe and diagnose from inside the human body. But a major concern is the safety of such machines, and the toxicity of the materials used to build them. Of particular note are batteries, which are essential parts of any machine, yet often contain harmful chemicals that can kill humans.
That is, until now.
Researchers have created an edible battery. The power source delivers a charge and is eventually flushed out of the body. It even fits in a pill. In a presentation to the National Meeting and Exposition of the American Chemical Society, the researchers described a battery that is derived from melanin, a skin pigment that helps protect the body from UV radiation.
Melanin scoops up charged ions called free radicals, and soaks up metals, like zinc, aluminum, and iron. That basically allows it to act like a battery, making it perfect for this purpose. The battery is made up of melanin as a positive or negative electrode, in addition to manganese oxide, sodium titanium phosphate, copper, and iron, all found naturally in the human body.
This makes for a battery that can give juice to a 5 milliWatt device for up to 18 hours, when using 600 milligrams of active melanin material as a cathode. While this may not seem much, it is enough for an ingestible drug-delivery or sensing device.
This set-up is encased in a digestible 3D-printed shell made of a gelatin material, similar to those used in some food supplements. In case that shell bursts, the melanin and other components could actually be digested or processed by the body, with no side effects.