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New energy source for future medical implants: sugar
Implantable fuel cell built at MIT could power neural prosthetics that help patients regain control of limbs.
MIT engineers have developed a fuel cell that runs on the same sugar that powers human cells: glucose. This glucose fuel cell could be used to drive highly efficient brain implants of the future, which could help paralyzed patients move their arms and legs again.
The fuel cell, described in the June 12 edition of the journal PLoS ONE, strips electrons from glucose molecules to create a small electric current. The researchers, led by Rahul Sarpeshkar, an associate professor of electrical engineering and computer science at MIT, fabricated the fuel cell on a silicon chip, allowing it to be integrated with other circuits that would be needed for a brain implant.
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.
The new twist to the MIT fuel cell described in PLoS ONE is that it is fabricated from silicon, using the same technology used to make semiconductor electronic chips. The fuel cell has no biological components: It consists of a platinum catalyst that strips electrons from glucose, mimicking the activity of cellular enzymes that break down glucose to generate ATP, the cell’s energy currency. (Platinum has a proven record of long-term biocompatibility within the body.) So far, the fuel cell can generate up to hundreds of microwatts — enough to power an ultra-low-power and clinically useful neural implant.
“It will be a few more years into the future before you see people with spinal-cord injuries receive such implantable systems in the context of standard medical care, but those are the sorts of devices you could envision powering from a glucose-based fuel cell,” says Benjamin Rapoport, a former graduate student in the Sarpeshkar lab and the first author on the new MIT study.
Rapoport calculated that in theory, the glucose fuel cell could get all the sugar it needs from the cerebrospinal fluid (CSF) that bathes the brain and protects it from banging into the skull. There are very few cells in the CSF, so it’s highly unlikely that an implant located there would provoke an immune response. There is also significant glucose in the CSF, which does not generally get used by the body. Since only a small fraction of the available power is utilized by the glucose fuel cell, the impact on the brain’s function would likely be small.
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 don’t require external power sources.
“It’s a proof of concept that they can generate enough power to meet the requirements,” says Oweiss, adding that the next step will be to demonstrate that it can work in a living animal.
A team of researchers at Brown University, Massachusetts General Hospital and other institutions recently demonstrated that paralyzed patients could use a brain-machine interface to move a robotic arm; those implants have to be plugged into a wall outlet.
Mimicking biology with microelectronics
Sarpeshkar’s group is a leader in the field of ultra-low-power electronics, having pioneered such designs for cochlear implants and brain implants. “The glucose fuel cell, when combined with such ultra-low-power electronics, can enable brain implants or other implants to be completely self-powered,” says Sarpeshkar, author of the book “Ultra Low Power Bioelectronics.” This book discusses how the combination of ultra-low-power and energy-harvesting design can enable self-powered devices for medical, bio-inspired and portable applications.
Sarpeshkar’s group has worked on all aspects of implantable brain-machine interfaces and neural prosthetics, including recording from nerves, stimulating nerves, decoding nerve signals and communicating wirelessly with implants. One such neural prosthetic is designed to record electrical activity from hundreds of neurons in the brain’s motor cortex, which is responsible for controlling movement. That data is amplified and converted into a digital signal so that computers — or in the Sarpeshkar team’s work, brain-implanted microchips — can analyze it and determine which patterns of brain activity produce movement.
The fabrication of the glucose fuel cell was done in collaboration with Jakub Kedzierski at MIT’s Lincoln Laboratory. “This collaboration with Lincoln Lab helped make a long-term goal of mine — to create glucose-powered bioelectronics — a reality,” Sarpeshkar says. Although he has just begun working on bringing ultra-low-power and medical technology to market, he cautions that glucose-powered implantable medical devices are still many years away.
http://www.extremetech.com/extreme/130923-mit-creates-glucose-fuel-cell-to-power-implanted-brain-computer-interfaces
By Sebastian Anthony
MIT creates glucose fuel cell to power implanted brain-computer interfaces
Neuroengineers at MIT have created a implantable fuel cell that generates electricity from the glucose present in the cerebrospinal fluid that flows around your brain and spinal cord. In theory, this fuel cell could eventually drive low-power sensors and computers that decode your brain activity to interface with prosthetic limbs.
The glucose-powered fuel cell is crafted out of silicon and platinum, using standard semiconductor fabrication processes. The platinum acts as a catalyst, stripping electrons from glucose molecules, similar to how aerobic animal cells (such as our own) strip electrons from glucose with enzymes and oxygen. The glucose fuel cell products hundreds of microwatts (i.e. tenths of a milliwatt), which is a surprisingly large amount — it’s comparable to the solar cell on a calculator, for example. This should be more than enough power to drive complex computers — or perhaps more interestingly, trigger clusters of neurons in the brain. In theory, this glucose fuel cell will actually deprive your brain of some power, though in practice you probably won’t notice (or you might find yourself growing hungry sooner…)
Size-wise,
the MIT engineers have created glucose-powered fuel cells that are as
large as 64x64mm (2.5in), or as small as just a few millimeters. In the
picture above, the large yellow square is a single 64x64mm fuel cell,
and it’s surrounded by a bunch of smaller versions. Presumably the
largest fuel cell produces the most electricity — but at that size, I
don’t think it would fit inside a human brain at least. You could quite
easily implant a few dozen of the smallest fuel cells in your spinal
cord, however.This discovery is exciting for two main reasons: a) The fuel cell is completely synthetic, and b) they can be produced using low-tech, decades-old chip fabrication processes. Glucose fuel cells have been created before, primarily to power pacemakers, but they used biological enzymes (like your own cells) — and enzymes need to be replenished. Platinum, however, will happily strip electrons from glucose indefinitely. Platinum also has the added bonus of being very biocompatible — i.e. your immune system doesn’t try to reject it. Cerebrospinal fluid is almost entirely devoid of cells, too — it’s basically just a glucose-rich fluid that insulates your brain and spine. Because there are no cells, this means there are no white blood cells that can reject the fuel cell.
Ultimately, this fuel cell will hopefully be used to power implanted, ultra-low-power devices that sit inside your skull or spinal cord. In actual fact, MIT’s research into this fuel cell was led by Rahul Sarpeshkar, who happens to be one of the leaders of hybrid digital-biological devices. So far, implanted devices have mostly been tethered to a wall socket — but now, Sarpeshkar’s group can begin work on implants that are completely self-powered.
Now read about a brain-computer interface that bypasses paralyzed limbs, or decoding the brain to integrate a bionic eye
Read more at MIT or download the paper at PLoS ONE (non-paywalled!)
