Tag Archives: prosthethic

Grafted mini muscles enable amputees to control robot hand with their minds

Joe Hamilton of Flint, Mich. intuitively controls a DEKA prosthetic hand—made by Mobius Bionics and called the “LUKE Arm. Credit: Evan Dougherty/University of Michigan Engineering.

You might have already seen prosthetic robot hands controlled by an amputees’ thoughts. These are amazing but, since the technology is still in its infancy, they’re also plagued by many limitations. Biomedical engineers at the University of Michigan have made an important contribution to the field by demonstrating a new method that uses muscle grafts to produce a more sensitive response, allowing prosthetic users to make more natural movements with their robot hand.

Other prosthetic robot hands offer amputees control by measuring nerve activity in the residual limb. The problem is that this signal is very faint, so control over the robot hand is very clunky. This negates the value of having highly flexible prosthetics with many joints and a high degree of freedom. The bottleneck lies in the ‘control software’ rather than the hardware.

Writing in the journal Science Translational Medicine, researchers led by Paul Cederna have described a clever workaround. In order to amplify the control signal, the researchers surgically grafted small pieces of muscle onto nerve endings of the residual limb.

When an amputee loses a body part, such as their arm from the elbow down, nerves start growing on the residual forearm. Patients typically end up with a big ball of nerves called a neuroma which can be very painful when it’s touched, preventing them from wearing their prosthesis. Patients sometimes refer to this uncomfortable sensation as phantom pain.

However, for this study, the neuroma is useful. Instead of interfering with daily life, the ball of nerves wrapped around the muscle tissue harvested from the thigh, amplifying the electrical signal.

Credit: University of Michigan.

In order to control the robotic hand, electrodes were implanted in the muscle, which now detected a signal 100 times more powerful than before the nerves grew into the mini-muscles.

In experiments with three subjects, the nerves that control the thumb interacted with the grafted muscle just as they would if the person still had their real thumb intact.

This intent is powerful enough to send an electric signal to move the thumb of the robotic hand, called DEKA. However, the researchers like to call the prosthetic ‘Luke’s hand’, after Luke Skywalker from Star Wars.

The prosthetic is comprised of a semitransparent sheath that covers a mechanical skeleton that is attached to the residual limb through a custom-designed socket.

One of the patients involved in the study had an amputation up near the shoulder, but even in his case, the signal of the contracting muscle was strong enough to discern between different intended movements, such as flexing pointer finger while keeping the thumb isolated.

Using a computer algorithm that learned to translate the electrical signal into intended contractions, the participants were able to perform very precise coordinated movements, such as stacking a set of small wooden blocks or manipulating variously shaped objects.

Unfortunately, this technology is still in its early days. The entire setup is very cumbersome, requiring wires tethered to the participants. But, eventually, the researchers plan on developing a more compact version that the amputees can use in their day-to-day lives.

Photo: Georgia Tech

Robot prosthetic helps drummer play like a three-armed cyborg

Photo:  Georgia Tech

Photo: Georgia Tech

A freak accident left Jason Barnes without his left arm below the elbow – a disheartening matter by all means, made worse when considering he also used to be a drummer. The young man did not despair, however, and as an Atlanta Institute of Music and Media student he sought to fill in his missing arm as best as he could. He built his own prosthetic device shortly after the accident, and could  bang the drums by moving his elbow up and down. His prosthetic, however, was a cruel joke compared to his old hand which he used to bang his kit.

Georgia Tech Professor Gil Weinberg entered the scene and built an amazing robotic prosthetic for Barnes, one that essentially turned him into a cyborg drummer. How so? Well, his new arm primarily features two motors that control two drum sticks. While one of the sticks is controlled both physically by the musicians’ arms and electronically using electromyography (EMG) muscle sensors, the other is autonomous, listening to the rhythm played by the first stick, and improvising on the way. Yeah, a drummer who plays with three sticks, and the third stick has a mind of its own.

“Jason can pull the robotic stick away from the drum when he wants to be fully in control,” says Weinberg. “Or he can allow it to play on its own and be surprised and inspired by his own arm responding to his drumming.”

Besides allowing him to perform again on his kit, Barnes can now perform a couple of tricks that were impossible before he lost his arm, by virtue of brute machine force.

“Music is very time sensitive. You can hear the difference between two strokes, even if they are a few milliseconds apart,” said Weinberg. “If we are able to use machine learning from Jason’s muscles (and in future steps, from his brain activity) to determine when he intends to drum and have the stick hit at that moment, both arms can be synchronized.”

Because an embedded chip can control the speed of the drumsticks, the prosthesis can be programmed to play two sticks at a different rhythm. It can also move the sticks faster than humanly possible.

“I’ll bet a lot of metal drummers might be jealous of what I can do now,” he said. “Speed is good. Faster is always better.”