The implant is made of a flexible material called nitinol, which is also used in bra underwires and eyeglass frames. (Credit: University of Melbourne)

brains

Thought-controlled exoskeleton could let paralyzed people walk

A device the size of a matchstick implanted in the brain may help a group of paralyzed people walk using only their thoughts and a robotic exoskeleton.

In 2017, researchers will choose a select group of paralyzed people from Australia to receive the implant, called a stentrode. If the trial succeeds, the technology could become commercially available in as little as six years.

The stentrode, crafted from a space-age alloy called nitinol, could also benefit people with Parkinson’s disease, motor neuron disease, obsessive compulsive disorder, and depression. It could even predict and manage seizures in epileptic patients.

exoskeleton
An exoskeleton, similar to this one, will be used by patients implanted with a stentrode. (Credit: Rex Bionics)

It will be inserted into the blood vessel with a catheter fed up through the groin—the same approach that has been used for years for cardiology and removing stroke clots.

“This technology is really exciting. It’s the first time that we’ve been able to demonstrate and develop a device that can be implanted without the need for a big operation, to chronically record brain activity,” says Terry O’Brien from the Royal Melbourne Hospital and the University of Melbourne’s Medicine, Dentistry and Health Sciences Faculty.

“The most obvious benefit is for people who are paralyzed following a stroke or spinal cord injury. It is simple and non-invasive and much safer for patients.”

No dangerous surgery required

The stentrode is inserted into a blood vessel that sits over the motor cortex. The device is delivered through a small catheter, and when in position, the catheter is removed, deploying the stentrode.

The stentrode expands to press the electrodes against the vessel wall close to the brain where it can record neural information and translate these signals into commands that can be used to control an exoskeleton.

When the catheter is inserted into the blood vessel in the brain, it leaves a small cigar-shaped “basket,” wired with electrodes, that can record the brainwave activity.

“There is no craniotomy, no risk of infection; it’s all run through the groin and passed inside the body up into the brain,” says O’Brien.

“This has been the Holy Grail for research in bionics—a device that can record brainwave activity over long periods. Inside the blood vessel, it’s protected—it doesn’t damage the brain vessel and can stay there forever.”

Tested in living sheep

Clive May from the Florey Institute of Neuroscience and Mental Health is behind trials of the technology in the brains of healthy living sheep.

He recorded this seamless integration of technology and biology, with the device reading electronic brain signals from the motor cortex loud and clear. The sheep seemed unaffected by the painless and simple operation and were walking and eating within an hour.

[Watch a paralyzed man move a robotic arm with his thoughts]

“As the device absorbed into the vein wall after nine or so days, the electrical signals continued to become clearer and stronger, up to 190 hertz, as strong as signals previously recorded with intricate invasive brain surgery,” says May.

These signals act as the electrical messengers that provoke intricate muscle movements and can, theoretically, be coded into software that links to an external skeleton.

“Personally, the fact that our device can record signals up to 190 hertz is the most exciting finding in our Nature Biotechnology paper,” says Thomas Oxley, a neurologist at the University of Melbourne, who designed the device. “The data between 70 to 200 hertz is the most useful for brain machine interfacing.

“Very smart people told us that we would have big problems with blood creating so much noise it would interfere with the signal, but we showed this isn’t true.”

People and machines

The chief engineer behind the device is the University of Melbourne’s Nick Opie, a senior research fellow and co-head of the Vascular Bionics Laboratory at the Royal Melbourne Hospital.

He and Oxley cofounded SmartStent, the company that will translate this research into reality.

“I’ve always been fascinated by the integration of man and machine, and the ways that people and machines could function together. Fortunately, I was born in the time to do this,” Opie says.

His challenge: to engineer a tiny net-like device that could be fitted with electrode receivers. It needed the ability to collapse to a tiny few millimeters in diameter and spring back into shape to act as a scaffold to maintain the flow of blood and permanently settle into the vein. Crucially, the device needed to be biocompatible.

“The first iteration was pretty horrible,” he admits. “I don’t want to count how many we’ve made. It required a lot of microscope work and very steady hands.”

Hundreds of iterations later, Opie and his team produced the winning design using a flexible material called nitinol, also used in bra underwires and for modern glasses frames.

It is fitted with tiny recording discs, called electrodes, which sit on the wall of the blood vessel, right next to the brain tissue.

Each disc records electrical activity fired by some 10,000 neurons, which is delivered via delicate wires that run out of the brain, into the neck, and emerge into the chest into a wireless transmission system.

How to walk with an exoskeleton

The researchers say this transmission can be coded into signals that control an exoskeleton. The first patient will work hard to “code” each of these unique signals to their exoskeleton.

Much like the process of learning to walk or speak again, the process will take many months, until finally, the movement becomes as effortless as driving a car, touch-typing, or writing your name on a form.

“With our device, you’ve essentially connected an electronic limb to the patient’s brain, but they have to learn how to use it.”

“Imagine someone bought a piano for you and you didn’t know how to play,” Oxley explains.

“You know that your hands are physically capable of playing it, but you don’t understand the sequence in which the keys have to be struck. It will take time to use your hands to learn how to play the piano.

“With our device, you’ve essentially connected an electronic limb to the patient’s brain, but they have to learn how to use it.”

How they’ll choose patients

The first patients will most likely be young people who have suffered a traumatic spinal cord injury around six months to a year earlier, who are suitable for exoskeleton legs.

Their level of determination and physiology will be important factors, says Opie, who will guide the first patients through the process.

Oxley says it will be a matter of years before people with paralysis will be able to ask for this treatment.

“The process for getting commercial approval for new medical devices is a long process, so realistically, it could be another five to seven years away,” he says. “And during that five years, we’d have to do a broader clinical trial of closer to 30 to 40 people.

“So we are hopeful this will be on the market by 2022.”

Source: University of Melbourne

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