PRESS your ear against your biceps, bend your arm and listen. The gurgling murmurs you can hear, made by muscle fibres as they move against each other, could provide a way for people to control prosthetic hands more easily.
In a lab at Imperial College London, PhD student Sam Wilson straps two matchbox-sized listening devices to my arm just below the elbow. I clench my hand and the robotic hand resting on the table makes a fist. I try using it to grab a soft cube. It escapes the hand’s grip on my first few attempts, but with a bit of practice it’s easy.
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Wilson and his supervisor are designing new ways for the human body to control prostheses. Typically, these use electrodes on the surface of the skin to pick up electrical activity in the arm muscles, called myoelectricity.
Vaidyanathan had the idea to develop different sensors for controlling prostheses when a colleague told him about a man who split his time between India and the UK, and claimed that his prosthetic hand knew when it was in India and stopped working. His doctors were baffled. Eventually they realised that the warmer Indian climate was the culprit: sweat was interfering with the electrodes that sense his muscle movements. It’s a common problem with such prostheses: they don’t work consistently for long periods.
“We wondered if there was a more robust way of detecting muscle activity and harnessing it for robotic control,” says Vaidyanathan.
He had been using accelerometers to sense muscle movements, but found that the gurgling muscle fibres were interfering with the signal. Using the sound input on its own is similarly noisy, but by combining inputs from a microphone and an accelerometer in one device, any unwanted signal can be reduced. “We can filter it out and make them feed off each other,” he says.
Vaidyanathan and Wilson, whose PhD is sponsored by the US Office of Naval Research Global, are working with Alex Lewis to develop the technology. Lewis lost all of his limbs two years ago when a streptococcus infection developed into toxic shock, septicaemia and necrotising fasciitis, also known as flesh-eating bacteria. He has a prosthesis, where two metal hooks open and close based on electrical readings from his arm muscles, but finds it cumbersome to use.
“The weight is at the end of the socket, so it’s very, very heavy,” he says. “Trying to open and close the hook and rotate the wrist, it really works your muscle quite hard. It’s an aggressive motion. You could only use it for maybe 3 or 4 hours at best.”
Lewis is impressed with what Wilson has made. “It’s incredibly easy to use. With the myoelectric split hook that I’ve got, I have to really force it to open and close. With this, it’s a very, very slight movement. It’s something I could probably use for 14, 16 hours and not feel worn out doing it.”
“It’s incredibly easy to use. It’s something I could probably use for 16 hours and not feel worn out”
Listening to our muscles’ sounds makes it easier to get signals out of the body. But the devices those signals control are important, too. The hand Lewis and I are controlling is a Bebionic 2, manufactured by British firm RSL Steeper. Each digit has its own motor, and the user can choose between 14 grip patterns. While it looks impressive, inviting comparisons with Luke Skywalker’s bionic hand in Star Wars, it isn’t necessarily more useful than simple split hook prostheses, which have barely changed from a design patented in 1912.
Price drop
“That hand is amazing, how it works, but the practicality of it is not that good,” says Lewis. Choosing the desired grip pattern isn’t trivial – the user has to press a button on the back of the hand to cycle through the options – and it’s quite heavy. “I think long-term use is out of the question because of the weight,” he says. At a cost of around £30,000, advanced bionic hands like Bebionic and the Deka Arm System are also prohibitively expensive for most people.
Vaidyanathan hopes his research will help make these devices more accessible. The sensor package they are working with costs less than £100. “I think the technology has been developing at such a rate that people haven’t focused on the price as much yet,” he says. “That’s one of the niches I hope this interface can help with.” Lewis has a to raise money for prostheses and other rehabilitation costs.
Vaidyanathan’s team has already made the hand a bit simpler for Lewis to use by rigging the sensors to allow him to switch grips with an exaggerated upward movement of his arm. Another of his students is working on using a camera under the hand’s wrist to detect objects and automatically choose the most suitable grip.
Lewis is an interior designer, and one of his biggest daily challenges is holding a stylus to work on a computer for hours at a time. Rather than his heavy myoelectric prosthesis, he mainly uses body-powered split hooks, which rely on cables to transmit force from his shoulders to close the grip. They are easier to use, but put a lot of strain on his shoulders over time.
Nor would the Bebionic 2 help. “Although the hand’s nice to look at, I probably would only use a thumb, index finger and middle finger,” says Lewis. Vaidyanathan is planning to design a modified split hook prosthesis with a small motor controlled by their new sensor interface, to help Lewis hold a stylus more easily.
They are also thinking about what other functions around the house it would be useful to control with the sensor, like light switches or the TV. It’s less glamorous than developing bionic hands that can be controlled effortlessly, but more likely to be of use for people.
“Engineers like to build things, but they have to be going in the right direction,” says Vaidyanathan. “Otherwise we just end up with toys.”
(Images: Dave Stock for żěè¶ĚĘÓƵ)
This article appeared in print under the headline “A helping hand”
