Will cyborgs be made from melanin? The discovery of a pigment allows a biocompatible electronics

In a landmark study published in Frontiers in ChemistryItalian researchers have subtly altered the structure of eumelanin by heating it under vacuum.

"Our process has multiplied by one billion the electrical conductivity of eumelanin," say lead authors of the study, Alessandro Pezzella of the University of Naples Federico II and Dr. Paolo Tassini of the University of Naples. 39; Italian National Agency for New Technologies, Energy and Sustainable Economic Development. "This makes possible the long-awaited design of melanin-based electronics, which can be used for implanted devices because of the biocompatibility of the pigment."

Eumelanin is a biocompatible driver

A young Pezzella had not even gone back to school when scientists discovered that a type of melanin could drive electricity. The discovery quickly gained excitement as eumelanin – the dark brown pigment found in hair, skin and eyes – is fully biocompatible.

"Melanins are naturally present in almost all life forms and are non-toxic and do not cause immune responses," explains Pezzella. "Out of the environment, they are also completely biodegradable."

Decades later, and despite extensive research on the structure of melanin, no one has been able to exploit its potential in implantable electronics.

"Until now, the conductivity of synthetic as well as natural eumelanin has been far too low for valuable applications," he adds.

Some researchers have tried to increase the conductivity of eumelanin by combining it with metals or overheating it to make it a graphene-like material – but what they had left was not really the promised biocompatible conductive material.

Determined to find the real deal, the Neapolitan group examined the structure of eumelanin.

"All the chemical and physical analyzes of eumelanin paint the same picture: stacked electron-sharing molecular leaves." The answer seemed obvious: clean the batteries and align the sheets so that they could all share electrons – then electricity flow. "

Heat treatment straightens the hair pigment

This process, called annealing, is already used to increase electrical conductivity and other properties in materials such as metals.

For the first time, researchers carried out a high-vacuum annealing of synthetic eumelanin films, a bit like a hair straightener, but with only the pigment.

"We heated these eumelanin films – not thicker than a bacteria – under vacuum, from 30 min to 6 hours," Tassini describes. "We call the resulting material annealed Eumelanin high vacuum, HVAE."

The annealing did wonders for eumelanin: the films were thinned by more than half and took a real tan.

"The HVAE films were now dark brown and about as thick as a virus," reports Tassini.

Crucially, the films had not just been burned to ashes.

"All our analyzes confirm that these modifications reflect the reorganization of eumelanin molecules from a random orientation to a uniform electron-sharing stack." The annealing temperatures were too low to break down the loci. eumelanin and we did not detect any elemental carbon combustion. "

Increased conductivity of a billion times

After achieving the desired structural changes for eumelanin, the researchers proved their hypothesis dramatically.

"The conductivity of the films has been multiplied by a billion, reaching an unprecedented value of more than 300 S / cm, after annealing at 600 ° C for 2 hours," confirms Pezzella.

Although most metal conductors are far from most metal conductors – the conductivity of copper is about 6 x 107 S / cm – this discovery makes it possible to launch eumelanin in a useful range for bioelectronics.

In addition, the conductivity of HVAE was adjustable depending on the annealing conditions.

"The conductivity of the films has increased with the increase in temperature, from 1000 times to 200 ° C. This opens the possibility of adapting eumelanin to a wide range of applications in electronics. organic and bioelectronic.It also allows to conclude with the structural analysis that the annealing reorganized the films, rather than burn them ".

There is a potential damper: the immersion of the films in the water causes a marked decrease in the conductivity.

"This contrasts with untreated eumelanin which, although in a much lower range, becomes more conductive with hydration (moisture) as it conducts electricity via ions as well as electrons. Further research is needed to fully understand the ionic and electronic contributions of eumelanin conductivity, which could explain the practical use of eumelanin in implantable electronics. "Concludes Pezzella.

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More information:
Ludovico Migliaccio et al, Evidence of unprecedented high electronic conductivity in mammalian pigments-based mammalian thin films after vacuum thermal annealing, Frontiers in Chemistry (2019). DOI: 10.3389 / fchem.2019.00162