If we can harvest energy from within the body, we may spur the development of a new generation of implantable devices that can work as long as the patient is alive and not require bulky batteries, a typical stumbling block for biomedical engineers. Researchers at Case Western Reserve University managed to generate electricity from naturally occurring chemicals within the abdomen of the false death’s head cockroach.
The researchers envision sensor-enabled roaches to perform odd jobs, but we’re instinctively terrified of the possibility of roaches controlled externally by a real human. We prefer to see this kind of technology powering an implantable defibrillator that doesn’t have to be changed every ten or so years.
From the announcement:
The key to converting the chemical energy is using enzymes in series at the anode.
The first enzyme breaks the sugar, trehalose, which a cockroach constantly produces from its food, into two simpler sugars, called monosaccharides. The second enzyme oxidizes the monosaccharides, releasing electrons.
The current flows as 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 solutions, prototype electrodes were inserted in a blood sinus in the abdomen of a female cockroach, away from critical internal organs.
“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.”
The researchers found the cockroaches suffered no long-term damage, which bodes well for long-term use.
To determine the output of the fuel cell, the group used an instrument called a potentiostat. Maximum power density reached nearly 100 microwatts per square centimeter at 0.2 volts. Maximum current density was about 450 microamps per square centimeter.
The study was five years in the making. Progress stalled for nearly a year due to difficulties with trehalase – the first enzyme used in the series.
Lee suggested they have the trehalase gene chemically synthesized to generate an expression plasmid, which is a DNA molecule separate from chromosomal DNA, to allow the production of large quantities of purified enzyme from Escherichia coli. “Michelle then began collecting enzyme that proved to have much higher specific activities than those obtained from commercial sources,” Lee said. “The new enzyme led to success.”
Abstract in Journal of the American Chemical Society: An Implantable Biofuel Cell for a Live Insect