Blood may become the power source of choice for small implantable medical devices, writes Dick Ahlstrom
Your own blood supply could be the energy source of the future when it comes to powering small, implantable medical devices. Blood already has everything needed to keep a tiny fuel cell operating provided you can make a fuel-cell small enough.
This is the goal of an EU funded research project co-ordinated by NUI Galway's Dr Donal Leech. A lecturer in chemistry based in Galway's Environmental Change Institute, he leads an international group that is building a new type of fuel-cell driven by the oxygen and sugar readily available inside the body.
"If you can get the sugar to give electrons to oxygen they can power a device," says Leech. Even a tiny amount of power is enough to drive sophisticated electronics, something that gives the project such huge potential.
The research has two goals, to deliver a functioning fuel cell type power source and also a new type of biosensor, Leech explains.
Fuel cells are much different than batteries. Batteries deliver electricity given off by reactions between chemicals stored inside. Fuel cells as the name implies require a fuel source which supports an ongoing chemical reaction capable of producing electricity. In the case of the devices being studied by Leech's consortium, it is a fuel cell powered by biological sources.
"With fuel cells, if you have a fuel you can take electrons from it and give them to another electrode. Our idea is not to compete in providing electricity for transport or large electrical generation but use fuels in vivo, for example glucose or sugar."
Being able to do this is based on the use of biocatalysts and specialised metal electrodes, he explains. "The beauty of nature is it has designed biological catalysts, enzymes, that will only react with oxygen."
Enzymes are highly specific in their action, making them easier to control. "The project looks at research trying to optimise the interaction between biocatalysts and electrodes. Only a few people worldwide are using enzymes in fuel cells," he says.
There are a number of advantages to this approach. The body uses enzymes as catalysts to drive many different biochemical reactions. They are a natural part of our biochemistry.
Batteries are small containers of chemical substances. Some of the best small batteries are based on chemicals that are toxic, yet they still have to be relatively large to deliver useable power.
Size is not an issue if you use enzymes as biocatalysts to drive fuel cells, says Leech. "You can miniaturise the fuel-cell much smaller than a battery. The main advantage of using the biocatalysts is you can miniaturise it and miniaturise it."
The fuel-cell has several elements, an enzyme that will act as a catalyst in supporting an oxygen reaction, a specialised electrode that will accept the flow of electrons, in other words electricity, and a "mediator", explains Leech.
The mediator is essential in that it shuttles the electrons from the fuel source to the electrode.
Sugar in the form of glucose and oxygen are readily available in the bloodstream. Developing a fuel cell that can exploit these delivers two things, a source of renewable energy and also an exquisitely sensitive sensor.
"One of the goals of the general research around this area is to try and develop an integrated self-powered feed-back system," Leech explains.
One use would be in diabetic patients whose pancreases are unable to produce the insulin needed to control sugar levels in the blood.
The device would provide the energy needed to drive a sensor able to respond to sugar levels and also an implanted insulin pump. This "artificial pancreas" would continuously measure blood sugar, introducing insulin only when needed.
NUI Galway is working on the mediators needed to shuttle the electrons. These are inorganic complexes making use of metals from the transition group as described by the periodic table of the elements. "We are looking at what parameters are important for these mediators," explains Leech.