Powering insect cyborgs with an implantable biofuel cell
Research into developing insect cyborgs for use as first responders or super stealthy spies has been going on for a while now. Most research has focused on using batteries, tiny solar cells or piezoelectric generators to harvest kinetic energy from the movement of an insect's wings to power the electronics attached to the insects. Now a group of researchers at Case Western Reserve University have created a power supply that relies just on the insect's normal feeding.
Recognizing that using a real insect is much easier than starting from scratch to create a device that works like an insect, Case Western Reserve chemistry professor teamed up with graduate student Michelle Rasmussen, biology professor Roy E. Ritzmann, chemistry professor Irene Lee and biology research assistant Alan J. Pollack to develop an implantable biofuel cell to provide usable power for the various sensors, recording devices, or electronics used to control an insect cyborg.
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To convert chemical energy harvested from the insect and turn it into electricity, the team used two enzymes in series to create the anode. The first enzyme breaks down the sugar trehalose, which a cockroach constantly produces from its food, into two simpler sugars, called monosaccarides, while the second enzyme oxidizes the monosaccarides to release electrons. A current them flows as the electrons are drawn to the cathode, where oxygen from air takes up the electrons and is reduced to water.
After testing the system using trehalose solution, the team inserted prototype electrodes in a blood sinus away from critical organs in the abdomen of a female cockroach. The cockroaches suffered no long-term damage, which the researchers say bodes well for long-term use.
"Insects have an open circulatory system so the blood is not under much pressure," Ritzmann explained. "So, unlike say a vertebrate, where if you pushed a probe into a vein or worse an artery (which is very high pressure) blood does not come out at any pressure. So, basically, this is really pretty benign. In fact, it is not unusual for the insect to right itself and walk or run away afterward."
Using an instrument called a potentiostat, the team determined the maximum power density of the fuel cell reached nearly 100 microwatts per square centimeter at 0.2 volts, with a maximum current density of about 450 microamps per square centimeter.
The researchers are now working to miniaturize the fuel cell so that it can be fully implanted into an insect while still allowing it to run or fly normally and examining which materials might last for a long time inside an insect. They are also working with other researchers to develop a signal transmitter that can run on little energy and also exploring how to add a lightweight rechargeable battery to the system.
"It's possible the system could be used intermittently," Scherson said. "An insect equipped with a sensor could measure the amount of noxious gas in a room, broadcast the finding, shut down and recharge for an hour, then take a new measurement and broadcast again."