Researchers in Australia have built an implantable brain-machine interface (BMI) that may give people with spinal cord injuries the ability to walk again using the power of their own thoughts. Consisting of a stent-based electrode, known as a "stentrode", implanted within a blood vessel of a patient's brain, along with a power supply and transmitter inserted under the skin in front of the shoulder, the new system creates a minimally invasive BMI that is capable of translating thoughts into action.

The bionic device does this by sensing certain types of neural activity and transmitting these to a processor, which then supplies signals to move the recipient's own limbs though the use of an exoskeleton or to control powered artificial arms or legs. Roughly the size of an ordinary paperclip, the stentrode is able to be implanted in a person's brain without the need for major surgery – instead, it is fed into the head using a catheter snaking up through an artery starting in the leg.

"This technology is really exciting," says Professor Terry O'Brien, head of Melbourne University's Department of Medicine at the Royal Melbourne Hospital. "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. 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."

Constructed from nitinol – a modern alloy of nickel and titanium – the device is scheduled to be implanted in the first human trial at The Royal Melbourne Hospital some time in 2017, with firm hopes that the new device will be highly bio-compatible. In pre-clinical trials using sheep, the device was shown as capable of capturing high-quality, machine-usable signals from the brain's motor cortex, and rather than being rejected by living tissue, melded into the recipient's veins.

"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," said Professor Clive May, from the Florey Institute of Neuroscience and Mental Health who conducted the clinical trials on sheep.

Each stentrode picks up electrical activity fired from some 10,000 individual neurons, and then delivers these signals through wires that trail out of the brain, down through the neck and into a wireless transmission system implanted on the upper chest in front of the shoulder. The resulting transmission can then be turned into control signals for an exoskeleton or prosthesis.

In this way, the recipients will gain the ability to walk or move once more by training their thoughts to match the actions of the devices under their wireless command, that eventually – it is hoped – will result in the movements becoming as natural and effortless as someone with full use of their own limbs.

According to the researchers, the first human recipients of the new device will probably be younger people with severe spinal cord injuries sustained about six months to a year prior to implantation, and who are also suitable candidates for exoskeleton legs. This group of people has likely been chosen because they are most able to cope with surgery, have faster recovery times, and are generally quicker to respond to treatment. They will also be chosen for their determination, their resolve and their physiology, according to biomedical engineer Dr Nicholas Opie of Melbourne University.

As for widespread commercial release, however, it may be some years before people afflicted with paralysis will be able to specifically ask for this procedure.

"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," said Dr Thomas Oxley Neurologist at the University of Melbourne, Florey Institute and the Royal Melbourne Hospital, and current endovascular neurosurgery fellow at Mount Sinai Hospital. "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."

The device is the result of a collaboration between researchers from the University of Melbourne, the Royal Melbourne Hospital and the Florey Institute of Neuroscience and Mental Health. The results of their research were recently published in the journal Nature Biotechnology.

The short video below is of biomedical engineer Dr Nicholas Opie explaining more about how the device was developed.

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