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| Melanin could be used for more than tanning (Image: Shelbi Lynn Awabdy/Getty) |
Your body may use it to catch a tan, but now the skin pigment melanin has been repurposed for the first time to make batteries. These may one day offer a safer way to power electronic devices that can be swallowed or inserted into the human body for drug delivery or internal monitoring.
Rechargeable lithium-ion batteries are widely used in electronics because they are very efficient and can hold their charge for long periods. But because they contain lithium, these batteries are potentially toxic if used long-term inside the body. So Christopher Bettinger at Carnegie Mellon University in Pittsburgh, Pennsylvania, wanted to find a way to build batteries from biological materials.
"If we could safely ingest devices, then we could overcome a lot of the issues we have with current implanted devices, such as infection and inflammation," says Bettinger. "So we started with substances that are biologically derived and occur in the human body naturally, like sodium, water and melanin."
Skin power
To make the bio-battery, Bettinger and his team engineered positively charged anodes out of a mixture containing high levels of melanin, the substance that creates pigment in humans and many other animals. They then introduced sodium ions and loaded the anodes into a steel mesh structure. Melanin's uniform chemical structure means it can pack in plenty of ions, which is key to determining how much charge a battery can hold. This battery could discharge for up to 5 hours, although at a lower power output than standard batteries.
Other biomaterials such as plant matter have been tested as potential electrodes, but they require extra chemical modifications to hold a charge. By contrast, melanin can be used in its natural form, and it is very possible that it could be simply harvested from human skin, says Bettinger. However, using a source with a much higher density of the pigment – the ink sac of a squid, for example – would be more efficient.
"This paper describes a really clever route to producing batteries out of biodegradable materials," says John Rogers at the University of Illinois at Urbana-Champaign. Although the current version isn't fully biodegradable, it shows how batteries could one day be made to dissolve harmlessly in the body.
"The idea is that such technologies could be used as power sources for systems that go into the body, monitor a wound-healing process, deliver therapy as necessary and then naturally disappear after the wound is completely healed. Similar sorts of systems might be designed to treat cancerous tumours, or to treat bone fractures or torn ligaments."
The researchers also found that natural melanin is better at holding charge than synthetic versions. But the melanin battery is not as efficient as the lithium-ion variety, partly because natural melanin is usually found in very dense granules, says Bettinger. Finding a way to make it spongy would help it soak up more sodium ions and pack in even more charge.
Journal reference: PNAS, DOI: 10.1073/pnas.1314345110
ORIGINAL: New Scientist
Rechargeable lithium-ion batteries are widely used in electronics because they are very efficient and can hold their charge for long periods. But because they contain lithium, these batteries are potentially toxic if used long-term inside the body. So Christopher Bettinger at Carnegie Mellon University in Pittsburgh, Pennsylvania, wanted to find a way to build batteries from biological materials.
"If we could safely ingest devices, then we could overcome a lot of the issues we have with current implanted devices, such as infection and inflammation," says Bettinger. "So we started with substances that are biologically derived and occur in the human body naturally, like sodium, water and melanin."
Skin power
To make the bio-battery, Bettinger and his team engineered positively charged anodes out of a mixture containing high levels of melanin, the substance that creates pigment in humans and many other animals. They then introduced sodium ions and loaded the anodes into a steel mesh structure. Melanin's uniform chemical structure means it can pack in plenty of ions, which is key to determining how much charge a battery can hold. This battery could discharge for up to 5 hours, although at a lower power output than standard batteries.
Other biomaterials such as plant matter have been tested as potential electrodes, but they require extra chemical modifications to hold a charge. By contrast, melanin can be used in its natural form, and it is very possible that it could be simply harvested from human skin, says Bettinger. However, using a source with a much higher density of the pigment – the ink sac of a squid, for example – would be more efficient.
"This paper describes a really clever route to producing batteries out of biodegradable materials," says John Rogers at the University of Illinois at Urbana-Champaign. Although the current version isn't fully biodegradable, it shows how batteries could one day be made to dissolve harmlessly in the body.
"The idea is that such technologies could be used as power sources for systems that go into the body, monitor a wound-healing process, deliver therapy as necessary and then naturally disappear after the wound is completely healed. Similar sorts of systems might be designed to treat cancerous tumours, or to treat bone fractures or torn ligaments."
The researchers also found that natural melanin is better at holding charge than synthetic versions. But the melanin battery is not as efficient as the lithium-ion variety, partly because natural melanin is usually found in very dense granules, says Bettinger. Finding a way to make it spongy would help it soak up more sodium ions and pack in even more charge.
Journal reference: PNAS, DOI: 10.1073/pnas.1314345110
ORIGINAL: New Scientist
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