Labtimes 2017-06

page 24 Lab Times 6-2017 Analysis Progress has been slow in the field of prosthetics in recent times but with an elegant combination of engineering and biology, researchers are able to give amputees some of their mobility back. A mputations save lives. There’s no doubt about that. For amputees, however, the loss of a limb can seri- ously affect their feeling of independence. What once were simple daily tasks, like ty- ing shoelaces or reading the newspaper, be- come complex and time-consuming chores. To make their lives safer and easier, re- searchers are keen to offer devices with a wide range of functionalities, from the ability to control hand grip to going up and down the stairs without falling. However, this often means complex designs, which can be heavy and difficult to use, increasing the risk of abandonment. It’s not that un- common for prosthetics to end up hidden at the back of the wardrobe or under the bed! Known problems The problem can be aggravated for pa- tients that have used one type of prosthet- ics for a long period and are suddenly faced with a new one. After walking for ten years on the same prosthetic limb, it can be hard to unlearn the old movements and re-learn the new pattern. More often than not, when people get a new system, they continue to use it in the same way as their old one and lose on the extra abilities it can provide. In an attempt to solve some of these is- sues, many research groups are now devel- oping not only more advanced prosthetics from a technical point of view but also more intuitive ones, which are easier to learn how to use. Lab Times explores a few examples. Around since the 1960s, one popular way to control prosthetic devices is by tap- ping into the muscles present in the stump. These are known as myoelectric prosthet- ics and account for most of the upper pros- theses sold today. These prosthetics “work with the current that is provided from each muscle,” explains Oskar Aszmann, from the Medical University of Vienna. “When the muscles contract, they depolarise and pro- vide a current in the area of mV, which can be picked up through the skin and provide a useful control for prosthetics.” For example, sensors placed on the front and back of the arm can be set to open and close the hand. This approach was revolutionary when it was first introduced but, with information limited to two signals, it is starting to be seen as outdated. Using the concept of Targeted Muscle Reinnervation (TMR for short), developed about ten years ago, Aszmann wants to ex- plore the idea of increasing the number of possible control signals. In simple terms, his idea involves relocating peripheral nerves to the muscles in the stump, combined with modern myoelectric, multichannel sensors to disentangle the functions of these nerves. ( Front Neurosci , 2017 11:421). “We can take parts of the muscle in the stump – just sit- ting there without a function – and reroute the nerve into the muscle, and thus provide a new input to the muscle. When the pa- tient thinks about moving his fingers, that muscle will twitch and it will provide in- formation to control a prosthetic device,” says Aszmann. “It makes things a lot easi- er because patients don’t have to re-think the movement, the person can just think of certain motions and they will be the basis of prosthetic control.” Still unpolished At the moment, this is a rather unpol- ished and unpredictable method, as re- searchers don’t fully understand what func- tions are controlled by each nerve. There is still a lot of work to do to decipher this code but Aszmann is confident they will get there eventually. “In the future, we would envision that this signal can provide a very complex interface with prosthetic devices. Modern prosthetics Lend me a Hand Public Domain

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