Neuroprosthetics Powered by the Brain
Powering a neuroprosthetic is a tricky issue. As most of these devices are implanted either on the surface of the brain, or deep inside its folds, it is not a trivial matter to pop it out and change the battery. Every operation does a little more damage to the brain, and even worse, if you move the neuroprosthetic even fractionally during the replacement procedure there is no guarantee it will hook up with active dendrites from the correct brain region in its new position.
One major solution is to incorporate a power receiver under the skull during the first implantation. Power recharges can then be sent via a transmitter affixed to a shaved region of the scalp. However, this is still far from an ideal solution. Ideally a neuroprosthetic would be powered by the body itself; functioning as long as the person is alive.
But, how to do that? Normally such efforts to power prosthetics from the body, rely on piezoelectric power sources. Piezoelectricity is the accumulation of a charge in a solid in response to mechanical stress. In other words, as the body moves, the flesh deforms, and the piezoelectric material deforms along with it. This creates an electrical charge which is used to either power or recharge the prosthetic device.
Unfortunately, the brain is completely encased in the skull. If there is any twisting or deformation, it is not a good thing, and certainly not normal. Piezoelectricity will not work for devices attached to or inside the central nervous system itself.
A group of researchers based at MIT have developed a different approach. If we cannot depend on movement to power the prosthetic, why not use the same power source the cells of the brain use? Why not derive power from the sugars in the blood?
Their prototype glucose fuel cells are tiny; small enough to implant into a silicon wafer. The largest being 64mm by 64mm, the smallest functional cell just 2mm by 2mm.
The fuel cell, described in the June 12 edition of the journal PLoS ONE, strips electrons from glucose molecules to create a small yet continuous electric current proportional to its surface area.
The idea of a glucose fuel cell is not new: In the 1970s, scientists showed
they could power a pacemaker with a glucose fuel cell, but the idea was abandoned
in favor of lithium-ion batteries, which could provide significantly more power
per unit area than glucose fuel cells. These glucose fuel cells also utilized
enzymes that proved to be impractical for long-term implantation in the body,
since they eventually ceased to function efficiently.
So far, the fuel cell can generate up to hundreds of microwatts enough
to power an ultra-low-power and clinically useful neural implant.
Karim Oweiss, an associate professor of electrical engineering, computer science
and neuroscience at Michigan State University, says the work is a good step
toward developing implantable medical devices that dont require external