It is often said that engineers take ideas from nature and turn them into technology. However, copying nature is one of the hardest tasks an engineer can face. Making replacement body parts such as implants and prostheses is difficult as the anatomical processes are often poorly understood.
So building a prosthetic hand is a real achievement, which is why the i-Limb Hand, launched last year by Scottish company Touch Bionics, has made such a stir, winning the MacRobert Award, the Royal Academy of Engineering’s highest award for innovation.
The company claims it is the world’s first commercially available fully-articulated hand.
Hugh Gill, Touch Bionics’ director of technology and operations, in charge of developing it into the next generation, says the product has a great deal of potential.
‘When I joined the company 15 months ago, the product was just at the end of the prototyping stage,’ he said. ‘Over the past 12 months, I’ve changed the design significantly.’
Gill’s background is in product design and manufacturing. After 11 years developing products and setting up manufacturing lines for Polaroid, he founded his own consultancy, called WideBlue, which specialised in taking high-tech products from concept to manufacturing. ‘I worked to support about 30 companies, quite a few of which were in the biomedical engineering sector.’
Joining Touch Bionics, Gill realised that the i-Limb Hand was too realistic for its own good. Users were treating it as though it was flesh and blood rather than machinery, and that sometimes took it beyond its capabilities.
‘People were climbing ropes with it; someone got a finger caught in a mesh and ripped it off. Someone else came off his motorbike — he survived, the hand didn’t. People were lifting heavy settees with it, dropping them and crushing the hand. People were trying to fire bows and arrows; even trying to do handstands. So I’ve been putting lots of changes in to make it more robust.’
The i-Limb Hand is a chassis for the five digits, which contain their own batteries and motors. ‘There’s no electrical hard-wiring in there,’ said Gill. ‘It’s all done with direct-contact cotter pins, which are spring-loaded. You can just screw in a new digit and it engages with the electrical contacts and away you go.’
So making the hand stronger and more durable is not just a matter of more powerful motors. ‘One of the problems is that there’s a tendon inside each of the digits, which has to handle huge forces. I’ve been researching many different technologies and materials to come up with something that would be very strong but when it got to a certain force level there would be a certain percentage stress in it. But that’s just one of many challenges.’
Gill stressed that the machinery and electronics of the hand is not the only challenge: the covering of the prosthetic, known as a cosmesis, is just as hard.
There are two types of cosmesis, he explained, a ‘robotic’ one, which is mostly transparent and shows off the technology of the hand; and a human-form one, which is opaque, skin-toned, and makes the hand look as natural as possible.
‘These have to function well without losing any power in the hand, and they have to be durable,’ said Gill. ‘When the hand closes, the elastic stiffness of the cosmesis is a factor in how much power is transmitted by its motors.’
For the robotic hand, for example, the cosmesis contains a liner that reduces friction between the machinery and the injection-moulded ‘glove’. ‘There are lots of features to make sure it grips where it should grip and slips where it should slip,’ he said.
Although it is a medical device, Gill’s work does not bring him into contact with many medics.
‘The product is non-invasive; you don’t need any surgery done,’ he explained. ‘It operates through myoelectric sensors, which are in contact in the skin of the remaining limb and pick up the microvolt signals from the muscles just beneath. So the folks I work with are occupational therapists and prosthetists; I don’t need to work directly with surgeons.’
Above left: the clear cosmesis that covers the prosthetic. Right: a variety of different grips are possible with the artificial hand
Translating the myoelectric signals into hand movements is a major part of the i-Limb Hand technology. ‘The software is the heart and lungs of the project,’ said Gill. This is because the control strategy varies from person to person. Since every individual has different residual muscles, the hand’s control system must be tailored so that it responds to the signals each person is capable of generating.
‘The holy grail for our technology is something called pattern recognition,’ said Gill. ‘That’s to pick up the pattern of signals from the muscle which represents the movement of the digits. They’re very small, discrete signals and difficult to pick up; we’re working on it, along with many other companies. Nobody’s got a solution yet.’
So until then, the prosthetists must work with what they have. This often involves using the phenomenon known as phantom limb syndrome, where an amputee can feel their missing limbs.
Each i-Limb Hand user has a special socket made for them, vacuum-formed onto their remaining limb, into which the myoelectric contacts are placed. With the hand clicked onto the electronic wrist mount, the prosthetist will ask the patient to flex their ‘phantom’ hand, which will cause the muscles of the remaining limb to contract and generate a signal. It is then a case of telling the hand what to do when it receives that signal.
‘The new generation of i-Limb Hands will have a smaller circuit-board than the current one, but it’ll have more functionality,’ said Gill. ‘It has Bluetooth technology, which communicates with a graphical user interface (GUI) on the prosthetist’s computer. That will allow the prosthetist to develop the different movements the hand is capable of, map them to the myoelectric signals, and send that control strategy over to the unit wirelessly.
‘The chap with the hand can then say whether he’s happy with that, or if he’d like something changed. We can programme in features that allow the digits to move independently of each other, we can make a fist and then bring the thumb and forefinger into play for precision work.’
Gill is even working on restoring the expressiveness of body language. ‘We can programme some gestures in. You can imagine what they might be. That’s a fun side of it, but it’s very important to people to be able to do that. The GUI will make that much easier.’
The individually powered and controlled digits are helping the company towards its next launch, which will cater for people who have lost fingers or part of their hands. ‘We’ll manufacture a chassis to support as many replacement fingers as a person needs, which will contain motors and electrical contacts and a small control system, then position sensors in the palm of the hand to pick up those signals. It’s an important market for us, because nobody’s supporting those patients at the moment.’
For Gill, the ease of use of the systems is the most important factor. ‘You don’t need surgery. There’s a lot of work going on to implant metal probes to carry the nerve signals, but you can pick up strong skin signals at the moment and use those to give the patient back a lot of the movement they had before without any surgery.
‘I’ve had a patient come over from Africa, lost his hand five years ago, never had a prosthesis. He walked away three days later — and he shook my hand.’