We have the technology

An Irishman, Prof Richard Weir, is driving American research that will make bionic technology a reality, creating tiny devices that can translate thought into mechanical movement, writes DICK AHLSTROM

THE BIONIC AGE has arrived, when human and machine merge and biology controls advanced artificial limbs. Mechanical hands and arms are now being built, animated by the power of thought alone.

A Dubliner finds himself in the middle of all this science fiction-like research. Prof Richard Weir is based in Chicago and is involved in a research group that built a mechanical hand featuring on a recent cover of National Geographic.

He describes his work as director of the biomechatronics laboratory at the world famous Rehabilitation Institute of Chicago (RIC) in the simplest of terms. “I design hands and have been doing that for a while now,” he says.

Also professor of biomedical engineering and physical medicine and rehabilitation at Northwestern University, he is part of a team developing the next generation of prosthetic limbs.

The main support for the project, which is led by the applied physics Lab at Johns Hopkins University in Maryland, comes via Darpa, the US’s Defence Advanced Research Projects Agency. Subcontracted researchers include the RIC and Otto Bock Healthcare among others.

Its goal is to see completely new kinds of prosthetic limbs emerging for use by soldiers injured in Iraq and Afghanistan. An early prototype, Proto 1 featured in the National Geographic report, and a more advanced version, Proto 2 has just been completed.

Weir’s interest in this area has a long history. He received a Bachelor’s degree at Trinity College Dublin in microelectronics and electrical engineering in 1983, then an MSc in biomedical engineering in 1989 before heading for the US.

His interest in biomedicine was sparked in part by a traumatic event in his own family, he says. “My twin sister lost her hand when she was five.”

It seemed too that he was destined to become involved in this advanced area of medicine. “I came from a medical family,” he says. “I like to make things and have always been interested in science fiction and robotics.”

With this kind of background it was clear where he would head next, to Chicago and Northwestern University where advanced work was under way in the area of biomedical engineering. “One of the leading labs in the field was there,” he says.

He completed a PhD in 1995 and remained there, now sharing his time between Northwestern and the RIC, a leader in the field of biomedical engineering.

The RIC won the contract to work with Johns Hopkins on the new advanced arm replacement, and Weir has been involved in several areas including the development of the hand.

“Our role on that hand was to build all the drives for all the fingers and the thumb and lead the development of the index and middle fingers,” he says.

The amazing thing about the two Proto arms however is the approach used to control their movement. It is based on both electronics and a surgical technique developed at the RIC called “targeted muscle re-innervation”.

It is based on using the remnant nerves that formerly controlled hand and arm movements left behind after amputation, and co-opting these as a way to control the replacement limb.

Dr Todd Kuiken of the RIC devised the surgical approach that allows messages coming down along the nerves to be translated into readable signals by the electronics developed by Weir. This means that when the subject uses the old familiar thought processes to pivot the wrist or close fingers together, the mechanical limb responds in like fashion.

Weir stresses that this is a new technology and one still under development. It will be some time before they become available as a matter of routine. “Mechanically, we can build this arm with a high degree of freedom of movement, the issue is how will we control it,” he says.

Even so, work on Proto 2 shows that the approach works and that thought can be used to control limb movement. The challenge is to locate the residual nerve endings and then “rewire” them for use in this new approach.

Its success depends very much on what nerves can be found and the availability of remnant muscle tissue used for the re-innervation, he says. “Basically you use whatever you can.”

It does mean however that the notion of a bionic person is no longer quite so far-fetched.

'The muscle acts like a biological amplifier'

THE NEXT Generation of artificial limbs will be controlled using only the power of thought. Wearers will be able to manipulate a hand, arm or leg using the same thought patterns as used with the original limbs. We won’t have to wait years for these new limbs, they already exist. And their level of sophistication is growing rapidly.

Dublin scientist Prof Richard Weir is deeply involved in this work, designing some of the hardware used in artificial hands and arms, but also developing the tiny electronic devices that can translate thought into mechanical movement.

While researchers at other centres are reporting success in placing electronic sensors directly into the motor cortex, the areas of the brain responsible for limb movement, he and the group of collaborators in the US reject this method.

Instead, their approach is based on “targeted muscle re-innervation”, a technique pioneered by Weir’s colleague at the Rehabilitation Institute of Chicago, Dr Todd Kuiken. “He calls it rewiring,” Weir says of his colleague’s approach.

The method involves searching for the nerves that originally controlled hand and arm movement. Although now truncated like cut wires, the remnant nerves remain in the upper limb and are still directly wired to the brain.

A careful search isolates these nerves, picking up the faint electrical signals the nerves release as the person thinks about hand movements. The electrical signals from these nerves are very weak, but Kuiken’s technique involves greatly boosting the signal by reconnecting these nerve endings to muscle cells in what remains of the limb.

“The muscle acts like a biological amplifier,” Weir says.

Thinking about a hand movement sends a signal down the nerve to stimulate the rewired muscle tissue. This in turn releases a much stronger signal that is picked up by a special implantable electronic device developed by Weir and his team called “injectable myoelectric sensors”.

These are surgically implanted in the muscle and pick up the signal. The sensor then passes this message to a receiver and more electronics placed above it on the skin’s surface.

This interprets the signal and triggers motors in the artificial limb allowing it to move simply by thinking about what used to be a natural hand- movement.The person quickly adapts to controlling the prosthesis, given the system relies on using the nerves originally used by the brain to control the limb, Weir says.

The human arm offers 22 “degrees” of movement. The old-style artificial arm provides just three, but Proto 1 the initial version of the new arm gives seven degrees, controlled by about 10 implanted electrodes, he explains.

The goal however is to go much further. The approach potentially could be developed over time to deliver 22 degrees of movement again, provided the correct nerve-endings can be found and then wired up to remaining muscle.

Weir does not underestimate the challenge, pointing out we use 18 muscles to control the hand and wrist alone. They are still a “long way away” from being fitted to the people who need them. He believes, however, that their approach offers the possibility of developing permanent limb replacements.

Early efforts to connect nerve endings directly to wires and electronics lasted only a short time before the death of the nerve cells. This approach however does not damage the nerve tissue, and Weir believes these connections will last in the body for decades. “We are thinking of a lifetime – that they will last the lifetime of the individual. Two years is not good enough,” he says.

Dick Ahlstrom is on Twitter: @dickahlstrom