The same cells electric eels use to shock predators and prey can be engineered to power implanted biomedical devices, say researchers from Yale University and the National Institute of Standards and Technology (NIST).
"We now understand how the natural electric eel cells work," said David LaVan of NIST. "Now we can think about how we can use those cells to power medical devices."
Natural electric eel cells generate and release electric pulses of more than 500 volts with eight different channels and pumps.
By pumping positively charged potassium and sodium ions out of the cell, the number of negatively charged ions inside the cells rises. Opening certain channels causes electrons to flood out of the cell, producing enough electricity to stun the eel's victim.
Using computer models, the scientists experimented with different combinations of those eight pumps and channels. A cell with four pumps and channels was easier to make but only about four percent as efficient at converting sugar to electricity.
Surprisingly, by eliminating one pump (an "evolutionary leftover," as LaVan calls it) and adjusting the ratio of the other pumps and channels, the scientists designed a cell that was both powerful and energy efficient.
"It's like having a Ferrari that is also the most fuel-efficient car in the world," said LaVan. Natural electric eel cells are about 14 percent efficient at converting sugar into electricity, compared to 19 percent for the engineered cells.
The pumps and channels are powered by the same fuel that drives every human cell: adenosine triphosphate, or ATP. Stripping off one phosphate group drives cellular activities and in the process turns ATP into adenosine diphosphate, or ADP. Sugar helps recycle ADP back into ATP.
Scientists would divert the sugar naturally produced in the body into the implanted electrical generator. Each individual cell would produce an estimate 150 millivolts.
Lining up those cells and sandwiching them between an insulting material, a four-millimeter cube could produce three volts of electricity, enough to power a retinal implants, for example. A typical TV remote battery produces about 1.5 volts.
Sugar is plentiful. Sunlight is even more plentiful. Eventually, the researchers want to use photosynthesis, the process plants use to turn sunlight into sugar, instead of using the body's own supply.
"Those pieces [that plants use for photosynthesis] exist, but we will have to sit down and rework them," said LaVan. "That's still an open question."
Another open question is whether these cells can actually be built; so far the powerful and efficient cellular powerhouses are only present in virtual reality.
Actually creating them can be done in two ways, said Atul Parikh, a scientist at the University of California, Davis.
One way is top-down — essentially breeding live electric eels, harvesting their cells, and reconfiguring them to power implanted devices.
The other way is to engineer the cells from the bottom up, growing them into a designed configuration. The bottom-up method will likely be harder, but it would produce power more efficiently, said Parikh.
However the cells are created, Parikh said they could be used not only to power biomedical devices, but also energy outside the body.
"This could be a new way to make solar panels more efficient or bring us closer to a hydrogen economy," he said.
Basic prototypes could be developed within a couple of years, and an actual device could be implanted in as little as five years, if everything goes smoothly.
"The practical implications of this are huge," said Parikh. "The notion of biobatteries is very real."