The pigment in our skin could be used to make electrical body implants
by Frank Swain / 26 March 2019
“Bionic implants could one day be built with melanin, the pigment that gives skin and hair its 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 films made of the material 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 it.
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. Because we naturally produce the pigment, it is unlikely to elicit an immune reaction. 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.”
Melanin conducts enough electricity to enable implantable electronics
by Robby Berman / 29 March, 2019
“We are electrical creatures. Defibrillators jump-start us, for one thing, and electricity plays a part in how we work, down to a cellular level. Eumelanin, a dark pigment from which we get our eye, hair, and skin color, has been understood for nearly 50 years to conduct electricity. For almost as long, scientists have been looking for ways to take advantage of this trait, but eumelanin’s conductivity has been too weak to serve any practical purpose beyond its biological role.
Now, however, a multi-discipline team of scientists from Italy — their findings were published in Frontiers in Chemistry on March 26 — have figured out how to boost that conductivity to the point that it may become usable as a coating for medical implants and other devices that human bodies won’t reject. “This is the first [stepping] stone of a long process that now can start,” said chemist and lead author Alessandro Pezzella. What’s been holding eumelanin’s conductivity back?
Other teams have attempted to boost the conductivity of eumelanin by combining it with metals or super-heating it with graphene have helped increase it, but required adding metals and other chemicals the human body would reject. Pezzella’s team wondered if the problem was that the natural molecular structure of eumelanin was too chaotic, and too loosely packed to maintain a strong current. Says Pezzella, “All of the chemical and physical analyses of eumelanin paint the same picture — of electron-sharing molecular sheets, stacked messily together. The answer seemed obvious: Neaten the stacks and align the sheets, so they can all share electrons — then the electricity will flow.”
They decided to try and achieve this, says co-author and electrical engineer Paolo Tassini, through “basically, heating in a vacuum” to tighten up eumelanin by getting rid of its water and vapor molecules. While water is often an aid to conductivity, in the case or eumelanin, it was suspected it might be holding it back. The process they employed isn’t new — it’s called “annealing” — and has been used before to boost conductivity in other materials. Clumps of eumelanin were sealed in a high vacuum and heated to 600° C. Says Tassini, “We heated these eumelanin films — no thicker than a bacterium — under vacuum conditions, from 30 min up to 6 hours. We call the resulting material High Vacuum Annealed Eumelanin, or HVAE. The HVAE films were now dark brown and about as thick as a virus,” he says. Pezzella tells phys.org, “The conductivity of the films increased billion-fold to an unprecedented value of over 300 S/cm, after annealing at 600°C for 2 hours.” This is still far less than conductivity in metals, but it’s now within a useful range.
The process Pezzella’s team came up with is simple enough that it will be easy to boost eumelanin’s conductivity going forward, but that’s just a beginning. He hopes to architect a simple-to-handle version of HVAE, perhaps a sheet of it, that will allow others to begin experimenting with using it as a coating for implantable technology. “Further research is needed to fully understand the ionic vs. electronic contributions in eumelanin conductivity,” says Pezzella, “which could be key to how eumelanin is used practically in implantable electronics.”
Your skin’s melanin can conduct electricity
by Kat Eschner / March 27, 2019
“Researchers have known for a long time that eumelanin—the pigment that colors human skin, hair, and eyes—can conduct electricity. But eumelanin in its natural form isn’t conductive enough to be very useful, and nobody could figure out how to give it a boost. This week, that changed. In a paper published this week in the journal Frontiers in Chemistry, an interdisciplinary team of Italian scientists describe a breakthrough process that dramatically enhances eumelanin’s conductivity. “This is the first [stepping] stone of a long process that now can start,” says study author Alessandro Pezzella, a University of Naples Federico II organic chemist. Humans and other organisms don’t react to eumelanin, which means it could be used to coat medical implants or other devices meant to go inside the human body.
But Eumelanin in its natural form is too untidy on a molecular level to conduct electricity with much efficiency. Previous work failed to improve that without the addition of metals or other chemicals an organism’s body would treat as foreign. In order to make eumelanin more conductive without adding outside agents, Pezzella and his colleagues developed a process that organized the molecules so electricity could flow from electron to electron. The process is “basically heating in a vacuum,” says coauthor Paolo Tassini, an electrical engineer from the Italian National Agency for New Technologies, Energy and Sustainable Economic Development. “In this way you completely remove oxygen and water vapor.” Absent the extra molecules, the eumelanin is much better able to conduct. The process turns eumelanin “into a real conductor,” Tassini says, by enhancing its conductivity by more than nine orders of magnitude. The researchers call their result High Vacuum Annealed Eumelanin (HVAE.) However, eumelanin is still a pigment. “Metals have a completely different range of conductivity,” says Pezzella, and HVAE is much weaker.
But for the first time, it is in the range where it can be useful for bioelectronics. “I think the work is very important,” says Phillip Messersmith, a UC Berkeley materials scientist who was not involved with the study. But there are still lots of unresolved questions and challenges, he says. A big one: eumelanin loses its conductivity when exposed to water, and the HVAE also became much less conductive under these conditions. That will pose a problem in the human body, since we’re mostly water, but further research could make the pigment more resilient. “I don’t think it’s an insurmountable challenge,” Messersmith says. Pezzella says the next step for their work is to create “a very simple architecture,” made out of HVAE, “such as a thin film.” The film could pave the way for applications like coating electrical devices intended for use in humans, but that’s a long way off yet. When the researchers tried heating eumelanine in a vacuum environment, they didn’t know what would happen. The heat, which was in the range of 1000 degrees Fahrenheit, could have simply burnt up the pigment. Instead, it served to make it denser, in a process that Pezzella compares to crumpling up a ball of aluminum foil tighter and tighter. “We were very happy about what we found,” says Tassini.
Will cyborgs be made from melanin? Pigment breakthrough enables biocompatible electronics
“The dark brown melanin pigment, eumelanin, colors hair and eyes, and protects our skin from sun damage. It has also long been known to conduct electricity, but too little for any useful application—until now. In a landmark study published in Frontiers in Chemistry, Italian researchers subtly modified the structure of eumelanin by heating it in a vacuum. “Our process produced a billion-fold increase in the electrical conductivity of eumelanin,” say study senior authors Dr. Alessandro Pezzella of University of Naples Federico II and Dr. Paolo Tassini of Italian National Agency for New Technologies, Energy and Sustainable Economic Development. “This makes possible the long-anticipated design of melanin-based electronics, which can be used for implanted devices due to the pigment’s biocompatibility.”
A young Pezzella had not even begun school when scientists first discovered that a type of melanin can conduct electricity. Excitement quickly rose around the discovery because eumelanin—the dark brown pigment found in hair, skin and eyes—is fully biocompatible. “Melanins occur naturally in virtually all forms of life. They are non-toxic and do not elicit an immune reaction,” explains Pezzella. “Out in the environment, they are also completely biodegradable.” Decades later, and despite extensive research on the structure of melanin, nobody has managed to harness its potential in implantable electronics. “To date, conductivity of synthetic as well as natural eumelanin has been far too low for valuable applications,” he adds. Some researchers tried to increase the conductivity of eumelanin by combining it with metals, or super-heating it into a graphene-like material—but what they were left with was not truly the biocompatible conducting material promised. Determined to find the real deal, the Neapolitan group considered the structure of eumelanin. “All of the chemical and physical analyses of eumelanin paint the same picture—of electron-sharing molecular sheets, stacked messily together. The answer seemed obvious: neaten the stacks and align the sheets, so they can all share electrons—then the electricity will flow.”
This process, called annealing, is used already to increase electrical conductivity and other properties in materials such as metals. For the first time, the researchers put films of synthetic eumelanin through an annealing process under high vacuum to neaten them up—a little like hair straightening, but with only the pigment. “We heated these eumelanin films—no thicker than a bacterium—under vacuum conditions, from 30 min up to 6 hours,” describes Tassini. “We call the resulting material High Vacuum Annealed Eumelanin, HVAE.” The annealing worked wonders for eumelanin: the films slimmed down by more than half, and picked up quite a tan. “The HVAE films were now dark brown and about as thick as a virus,” Tassini reports. Crucially, the films had not simply been burnt to a crisp. “All our various analyses agree that these changes reflect reorganization of eumelanin molecules from a random orientation to a uniform, electron-sharing stack. The annealing temperatures were too low to break up the eumelanin, and we detected no combustion to elemental carbon.” Having achieved the intended structural changes to eumelanin, the researchers proved their hypothesis in spectacular fashion.
“The conductivity of the films increased billion-fold to an unprecedented value of over 300 S/cm, after annealing at 600°C for 2 hours,” Pezzella confirms. Although well short of most metal conductors—copper has a conductivity of around 6 x 107 S/cm—this finding launches eumelanin well into a useful range for bioelectronics. What’s more, the conductivity of HVAE was tunable according to the annealing conditions. “The conductivity of the films increased with increasing temperature, from 1000-fold at 200°C. This opens the possibility of tailoring eumelanin for a wide range of applications in organic electronics and bioelectronics. It also strongly supports the conclusion from structural analysis that annealing reorganized the films, rather than burning them.”
There is one potential dampener: immersion of the films in water results in a marked decrease in conductivity. “This contrasts with untreated eumelanin which, albeit in a much lower range, becomes more conductive with hydration (humidity) because it conducts electricity via ions as well as electrons. Further research is needed to fully understand the ionic vs. electronic contributions in eumelanin conductivity, which could be key to how eumelanin is used practically in implantable electronics.” concludes Pezzella.”
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