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German engineers develop 3D printed bionic hand with muscles made from 'smart' wires
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By Alec | 3ders.org

While 3D printing has already proved itself in the field of mechanical hand prostheses with very basic or no functions, the field of bionics has proven more challenging. To be sure, there are a number of very promising ongoing projects out there (such as the British Open Bionics), but all reach the same obstacle: how do you make a bionic cheap, functional and lightweight at the same time? Well, it looks like a team of German engineers from Saarland University have come up with an ingenious solution: a bionic hand that relies on a bundle of smart wires and an electric charge instead of bulky motors and electronics.

This bionic and very lightweight prosthetic was designed and 3D printed by a team from the Saarland University, led by Professor Stefan Seelecke (also of the Center for Mechatronics and Automation (ZeMA)). Key are these bundles of very thin muscle-like fibers that have been made from nickel-titaninum wire, each as thin as a human hear. These wires are known as shape-memory alloys, and are some of the best actuation mechanisms in the world for featuring the highest energy density out of all competitors. This, in short, enables very powerful movements in minuscule spaces.

As professor Seelecke explains, this is the secret behind this particularly lightweight system. ‘And the fact that they come in the form of wires enables us to use them as artificial muscles, or artificial tendons. So we can build systems with those that can be like bio-inspired, look-to-nature for a successful prototype, and that's what we realized with this first prototype of a robotic hand using shape-memory alloy wires,’ he explained to reporters.

– Stefan Seelecke

While conventional bionics are filled with motors that govern the opening and closing movements of a prosthetic, these wires have an ability called ‘shape memory’. This enables them to return to their original shape after being deformed, meaning that the ‘off-mode’ can be an open hand, and a single electric charge is all that is needed to close it. When turned off, the wire efficiently returns to the open mode without using energy. To test this very efficient use of electricity, the German team prototyped a basic bat capable of beating its wings through these shape memory strands.

As Filomena Simone, one of the PhD students working on the project explained, each of the bundle has been designed to copy the structure of a human muscle. To do so, all the fine wires have been grouped into bundles, just like muscle fibers. Each bundle is capable of undergoing rapid contractions and releases, just like your own hand muscles are capable of.

‘The movement of the hand is done by the wire. This wire, when activated, they contract. And we are able to exploit this contraction to make the finger move. And we can move each phalanx independently,’ she explained.

– Filomena Simone

She went on to explain the shape of the wires themselves is controlled by a single semiconductor chip, which functions on electrical resistance. This means that no external sensors are needed, as the material itself has sensory properties that govern movement very precisely. This is especially useful for picking up objects.

‘We can monitor the position of the finger without adding any other sensor; only exploiting this embedded feature of the wire. This helps us to always preserve a very lightweight structure. This is a big deal because normally prostheses until now are very heavy,’ Simone explained.

– Filomena Simone

Unfortunately, this prosthetic is still in its prototyping stage, but the team is very hopeful about the results and envision prosthetic limbs that function and feel like regular arms and hands. Especially the removal of bulky motors and pneumatics means that they can also be easily worn by everyone.

Taking things even further, professor Seelecke even speculated about the possibility of integrating these smart strands into a person’s own neurological system.

‘I think if you look down the road to future prostheses generations, you'd like to see this integrated with the human body in a way that you can actually sense the nerve stimuli and then can feed that into a micro-controller which there will be translated to a corresponding signal to activate the muscle,’ he speculated. ‘So, eventually you need to couple nerves with proper electrodes and combine that with the actuation of the muscles so you can create some integrated, biologically inspired actuation system for prostheses.’

– Stefan Seelecke

While that is a very distant future for now, it is absolutely amazing to see what 3D printing can achieve.

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