Into each mollusc, Katz and his team at Clarkson University in Potsdam, New York, have implanted tiny biofuel cells that extract electrical power from the glucose and oxygen in the snail’s blood. Munching mainly on carrots, the cyborg snails live for around half a year and generate electricity whenever their implanted electrodes are hooked up to an external circuit.
Katz’s snails, for example, produced up to 7.45 microwatts, but after 45 minutes, that power had decreased by 80%. To draw continuous power, Katz’s team had to ramp down the power they extracted to 0.16 microwatts.
Scherson says that he thinks he will be able to get a few hundred microwatts out of cockroaches (his biofuel cells feed on trehalose, a different sugar from glucose). Singhal reports similar results for beetles. Scherson, who is working with a large company to build microelectronics circuits for his cockroaches, points out that power need not be drawn continuously, but could be stored up in capacitors and released in pulses; he has already been able to produce and detect a radio signal from the cockroaches this way
All of these efforts are aimed at helping to create insect (or snail) cyborgs, a concept that has attracted funding from the US Department of Defense. For at least a decade, researchers have been creating battery-powered microcircuits with sensors and radio antennae and implanting them into various bugs and creepy-crawlies so that the creatures could gather information about their surroundings for environmental monitoring or military purposes.
But batteries might be too bulky and short-lived to power prolonged missions — which is where the idea of tapping into the creatures’ own metabolism comes in. Katz has shown that in snails, biofuel cells could provide a steady dribble of power for months. “The truly impressive portion of [Katz’s] work is that the implantation provides such stable potential for such a long period of time,” says Shelley Minteer, who works on biofuel cells at the University of Utah in Salt Lake City.
Philippe Cinquin at the Joseph Fourier University in Grenoble, France, and his colleagues are taking biofuel cells in a different direction — implanting them into rats. Their work, published in 2010, marked the first steps towards using biocompatible fuel cells in humans so that our own blood supply could run low-power medical devices such as pacemakers.
In these cases, the fuel cells must come with biocompatible membranes that ensure the implants aren’t rejected by the body, points out Cinquin. His team has already launched a company to develop artificial urinary sphincters, which require 300–500 microwatts of power and so could draw on glucose fuel from the body. Of course, batteries already exist for such applications — but smaller biofuel cells might, in theory, provide a more convenient, long-lasting way of powering such devices.
Katz says that he aims to move on to animals larger than snails, as their metabolism will provide more power. Next up for him: cyborg lobsters.
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