How MIT’s glucose-based fuel cell uses the brain to power bioelectric devices
Technology could one day be used to power implantable systems for restoring movement in people with spinal cord injuries
I suppose if you were to have a fuel cell implanted within your brain or spinal cord as a means for powering an implant that could help you overcome paralysis, the group you’d most likely trust to create this source of power would be engineers from MIT.
In the June 12 edition of the journal PLoS ONE , a group from the distinguished tech school published an article that details how they created a fuel cell on silicon capable of stripping electrons from the body’s glucose molecules for the purpose of creating a small electric current. Since the fuel cell is entirely synthetic, it is highly compatible with the existing circuitry found in most bioelectronics devices.
Silicon wafer consists of glucose fuel cells of varying sizes, with the largest being 64 by 64 mm. (Image: Sarpeshkar Lab)
Research was led by Rahul Sarpeshkar, an associate professor of electrical engineering and computer science at MIT. The group’s hope is that the glucose fuel cell could one day be used to power bioelectronics devices like brain implants for people with spinal injuries, giving them the ability to move their arms and legs again without having to be hooked up to an external power source.
Not a new concept . . .
Back in the 1970s, scientists proved that a pacemaker could be powered with a glucose fuel cell. The idea was abandoned, however, in favor of lithium-ion batteries, which proved capable of providing more power per unit area than the former solution.
Another problem that scientists found with these glucose fuel cells was that they used enzymes to extract electrons from the glucose molecules. This proved impractical for long-term implementation in the body as they eventually ceased to function efficiently.
. . . but a different approach
What Sarpeshkar and the folks at MIT did here is they created the fuel cell using absolutely no biological components whatsoever. For starters, they used the same technology manufacturers use to create semiconductor chips: They fabricated the fuel cell on silicon. They also opted to include a platinum catalyst to strip electrons from glucose. The element does an excellent job mimicking the activity of the body’s cellular enzymes, which break down glucose to generate adenosine triphosphate, the cell’s energy currency.
On a side note, platinum has a well-documented record of long-term biocompatibility within the body, making it an excellent choice for this technology. It’s not only capable of doing the job, it’ll keep doing it for a long, long time.
With their new approach in place, the fuel cell proved in numerous tests to efficiently generate up to hundreds of microwatts without any external assistance. That much electricity is more than 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 Sarpeshkar’s lab. He is also the first author on the new MIT study.
If the fuel cell is in the brain, where exactly is it getting the glucose?
The group theorizes that the fuel cell could get all the glucose it needs from the cerebrospinal fluid (CSF) that surrounds the spinal cord and brain. You see, there are very few cells in the CSF (most notably white blood cells), so it’s unlikely that an implant located there would provoke any sort of immune / rejection response. There is, however, a TON of glucose in the CSF, all of which does not normally get used by the body. And since just a small amount of the available power would actually be used by the glucose fuel cell, its impact on the overall brain’s functionality would be pretty small (translation: the fuel cell using glucose from the CSF surrounding one’s brain will not impact one’s thinking / ability to function).
Karim Oweiss, an associate professor of electrical engineering, computer science, and neuroscience at Michigan State University, notes that the work being done by Sarpeshkar and the rest of the MIT team is an excellent first step toward the development of implantable medical devices that don’t require external power sources (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; these implants, however, had to be plugged into a wall outlet).
“It’s a proof of concept that they can generate enough power to meet the requirements,” says Oweiss. She adds the next step for the team would be to demonstrate that the glucose fuel cell can work in a living animal.
Using microelectronics to mimic human biology
Sarpeshkar’s group is widely considered to be at the forefront when it comes to ultra-low-power electronics that mimic human biology. They’ve already pioneered designs for cochlear implants and brain implants, but the excitement surrounding their glucose fuel cell is because it presents perhaps the most possibility for all bioelectronics devices. “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.
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 adds.
While his team has just begun bringing ultra-low-power and medical technology to market, Sarpeshkar is quick to point out that glucose fuel cells are still a long way away from real-life implementation. ■
Story and image via: MIT
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