Stentrode: Brain to machine, no surgery

Posted by Sam Maddox in Research News on March 18, 2016 # Research, Assistive Technology

More proof, perhaps, that engineering is moving faster than biology. A group from Australia, funded in part by the U.S. military’s Defense Advanced Research Projects Agency (DARPA), has developed a very cool, non-surgical way to record brain information of the sort that might power brain-machine interface (BMI) devices – prosthetics for paralyzed body parts, for example.

In a typical BMI experiment today, if you are in hopes of using just your thoughts to command your paralyzed arm, as quadriplegic Erik Sorto did last year to reach for a glass of beer, you’ll need a surgeon to open your skull so a sensor or two can be dropped in. Forget about headband sensors, the ones you can buy on the Internet; they can’t pick up the high frequency signals needed for fine motor control.

Erik gladly volunteered to let a group from Rancho Los Amigos in Los Angeles put a pair of chips in his posterior parietal cortex. He did not mind having terminals installed on top of his skull to hook up his chips, and therefore his brain signals, to a computer.

I don’t know about you but I’d call brain surgery and permanent skull terminals an unacceptable downside to the brave bionic future. Implanted circuitry has other issues to. Electrodes wear out in the short term, connections break. The devices have been known to degrade the blood-brain barrier. And, the implants are susceptible to degeneration by way of microglia, the immune army inside the central nervous system. You can’t just swap out new ones; the chips become imbedded in brain tissue.

So how about say no to cranial surgery: In a study just out a couple of weeks ago in Nature Biotechnology, a team from the University of Melbourne has come up with a way to send a brain information sensor deep into brain, snaking it in through a blood vessel in the neck. They use a mesh cage, made of nickel-titanium, about the size of a small paper clip, and looking very much like the stents commonly used to keep blood vessels open.

The “stentrode,” as they call it, is designed to record the type of neural activity that can be fed to a transmitter in the chest, on to a computer and then to an exoskeleton or bionic limb. They tested it in sheep, over a period of six months. The kinds of signals being picked up were the same as the ones the surgical chips picked up.

Have a look at this very cool short video that explains in some nice animations how the stentrode works, from the team in Melbourne.

Said Oxley, via the University of Melbourne:

We have been able to create the world's only minimally invasive device that is implanted into a blood vessel in the brain via a simple day procedure, avoiding the need for high risk open brain surgery.

Our vision, through this device, is to return function and mobility to patients with complete paralysis by recording brain activity and converting the acquired signals into electrical commands, which in turn would lead to movement of the limbs through a mobility assist device like an exoskeleton. In essence this a bionic spinal cord.

From same press release:

The stent itself consists of a three centimeter-long, three millimeter-wide mesh tube made from a nickel alloy called nitinol. Its net-like surface is then covered in an array of electrodes, with each electrode registering the activity of around 10,000 neurons. In the first six days of implantation, the signals sent back by the stentrode were fairly poor, but they then improved over the next few weeks. The group attributes this initial noisiness to the interfering effects of blood flow, which would have been mitigated as the mesh and the surrounding blood vessel began to grow together.

Co-principal investigator and biomedical engineer Nicholas Opie said the concept was similar to an implantable cardiac pacemaker -- electrical interaction with tissue using sensors inserted into a vein, but inside the brain. "Utilizing stent technology, our electrode array self-expands to stick to the inside wall of a vein, enabling us to record local brain activity. By extracting the recorded neural signals, we can use these as commands to control wheelchairs, exoskeletons, prosthetic limbs or computers."

I read in a Melbourne newspaper how neurologist Thomas Oxley cold-called DARPA to pitch for funding his stentrode. You have to appreciate how nimble this part of the military government can be – no study group, minimal bureaucratic friction. Oxley was young, green but passionate. DARPA liked his energy. They said put a team together, we’ll give you $1 million to try.

The Melbourne group, says Opie, is ready to try the device in humans. "In our first-in-human trial, that we anticipate will begin within two years, we are hoping to achieve direct brain control of an exoskeleton for three people with paralysis."

The National Paralysis Resource Center website is supported by the Administration for Community Living (ACL), U.S. Department of Health and Human Services (HHS) as part of a financial assistance award totaling $8,700,000 with 100 percent funding by ACL/HHS. The contents are those of the author(s) and do not necessarily represent the official views of, nor an endorsement, by ACL/HHS, or the U.S. Government.