When ‘smart’ donor nerves are surgically reconnected to a muscle, more diverse and intensive neuromuscular connections are created. A team led by Oskar Aszmann, head of the Center for Bionic Limb Reconstruction at the Medical University of Vienna, showed in animal experiments that this could help improve communication between the nervous system and prosthetics after amputations. They report on this in the journal ‘Science Advances’.
According to the researchers, the idea behind the approach is to essentially rewire the nerves in patients who have lost an arm or hand, for example. The central nerve structures – brain, brain stem, spinal cord – and the nerves that control the missing limbs are still there and can be used to move a prosthesis. “To do this, we take a nerve and transfer it to a muscle that is still present in the amputation stump, such as the biceps,” Aszmann explains.
This muscle is no longer functional when the elbow movement it controlled no longer exists. So you could transfer the ulnar nerve, which is specifically responsible for the hand when you play the piano or type on the keyboard, to the ‘dumb’ biceps. This makes the muscle more intelligent and functional. “When the patient then thinks about more complex movements of his hand, the biceps plays the piano, as it were,” says the researcher.
“Smart” nerve on “dumb” muscle
This complexity of the movement also becomes visible because – as documented in the work of Aszmann’s team led by first author Vlad Tereshenko – the composition of the muscle fibers changes. These are actually tailored in detail to the respective requirements: turning elbows or playing the piano. But when a motor “smart” nerve is applied to a “dumb” muscle, the muscle changes composition depending on the nerve’s needs. This also affects innervation density, i.e. the supply of nerve fibers to the skeletal muscles to control muscle movements. This makes the muscle more intelligent in terms of the complexity of the movement manifested there.
In particular, the animal experiment used the facial nerve next to the ulnar nerve – “a nerve that controls the entire facial movement and has the highest information density known in the human organism,” Aszmann explains. The study found that when the facial nerve was used as a bronzing nerve, information transfer to the muscle increased fifteenfold. This is evident from the fact that, compared to the original nerve, more nerve fibers have found functional contact in this muscle.
Translator of neural information
The muscle becomes a translator of neural information and speaks a language that is also understandable to the mechatronics engineer who has to control the prosthetic hand. To date, no signals can be meaningfully derived directly from the nerve – unlike the muscle. “With our work, we have shown that it is possible to translate signals in such a way that a variety of signals are created that can then be used for reliable prosthetic control,” said Aszmann.
With modern prostheses it is currently only possible to close and open the hands due to the lack of control signals. “These nerve transmissions allow us to present a solid control system that makes the interface between people, the biosignals and the machine so fluid that individual finger movements are also possible,” says the expert. In a few years, it will be possible to use biosignals to control other technical devices, apart from prosthetics, in a way that “cannot be foreseen today.”
Source: Krone
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