Bionic implants could one day be built with melanin, the substance that gives skin and hair its dark colour. A new process boosts the substance’s electrical conductivity a billion-fold, making it suitable for use in implantable devices.
Clumps of eumelanin, a type of melanin, are typically made up of millions of disordered sheets layered on top of one another. By heating samples in a vacuum, Paolo Tassini at the Laboratory for Nanomaterials and Devices in Italy and his colleagues found that the sheets reordered themselves into a parallel arrangement.
The process also shrank the films and dramatically improved their conductivity. This procedure is called annealing, and is more commonly used in industries such as metallurgy. It isn’t fully understood why it works.
Previous efforts using heat to alter eumelanin often destroyed the pigment.
A conductive version of eumelanin could one day replace metals in bioelectronics and tissue interfaces, such as the brain implants used to treat epilepsy or Parkinson’s. The pigment, being something produced by our bodies, is unlikely to elicit an immune reaction, and can be broken down by the body without issue.
There are still some hurdles to overcome. Despite the boost in conductivity, the modified melanin is still half a billion times less conductive than copper.
What’s more, its conductivity drops when immersed in water, which isn’t an ideal property for an implantable electronic that will often get wet.