A FUTURISTIC programme to make tiny, implantable 鈥渂iofuel鈥� cells has hit a stumbling block. The first living creatures to be fitted with the devices died shortly after tests began.
The military is keen to use such fuel cells so soldiers need not carry as many batteries. The miniature power sources are being developed in the US for the Defense Advanced Research Projects Agency (DARPA), the central research and development wing of the US Department of Defense.
The fuel cells are intended to sit beneath the skin and convert glucose and oxygen from body fluids into small, but useful amounts of electricity. They could then be used to power miniature sensors worn by soldiers to monitor their vital signs and warn if they are suffering from fatigue or extreme temperatures, say.
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Biofuel cells are made from a pair of ultra-thin carbon fibre electrodes, each 7 microns wide and 2 centimetres long. One electrode is coated with an enzyme called glucose oxidase that strips electrons out of any glucose molecules it comes into contact with. These electrons then pass round a circuit, which would contain the sensor, to the second electrode, where they are taken up by oxygen molecules dissolved in the body鈥檚 fluids.
The only by-products of the process are water and gluconolactone, which is produced in the body anyway as glucose is broken down.
In previous lab tests Adam Heller and his team of biochemical engineers at the University of Texas in Austin immersed biofuel cells in a glucose solution. They produced about 2 microwatts of power 鈥� just enough to power a watch. Subsequent tests showed the fuel cells also worked when implanted into grapes and green peppers.
But getting the fuel cells to work in living creatures was a different matter. Heller鈥檚 student Nicolas Mano recently tried them out in two grasshoppers. Although they survived the implant procedure, they died about 15 minutes later, before Mano was able to extract any power from the fuel cells. They are still trying to find out what went wrong. 鈥淲e don鈥檛 know why they died,鈥� he said. More tests are planned for early this year.