While melanin is best known as the pigment that protects our skin from being damaged by the sun’s ultraviolet light, it's also found deep inside the brain. Located in the substantia nigra which, as its name implies, is darkly pigmented, the melanin there is thought to play a role in sieving toxic metals from the blood such that they do not accumulate and harm neurons. This sieving property proved alluring to a team of engineers who wondered if if melanin could potentially be used as a nontoxic material to house the sorts of ions that are traditionally used in batteries. Keen to find out, they ran an experiment with melanin inside test batteries filled with different ion solutions and found that there is a real potential to create non-toxic batteries with it for future ingestible medical devices. You can read more in The Economist article that I wrote on this here.