06 February 2014

Bionic hand with sense of touch

Nine years ago, Dane Dennis Aabo Sorensen had to amputate his left arm after an accident. Of course, he didn't think for a minute when he was offered to volunteer in a clinical trial of a new bionic hand that allows not only to perform movements, but also to touch objects.

The Lifehand 2 prosthesis was developed by a group of bioengineers from the Swiss Federal Polytechnic School in Lausanne (Ecole Polytechnique Federale de Lausanne, EPFL) and the Italian School of Advanced Studies named after St. Anna (Scuola Superiore Sant'Anna) under the leadership of Silvestro Micera. Work on the prototype of the "Living Hand – 2" began in 2009, but it was finalized for four years before the first clinical trial.

In particular, it turned out that sensors measuring tension in artificial tendons controlling finger movements generate electrical signals too strong for nerves to perceive – we had to develop a special computer program that weakened the signal intensity to a level close to nerve impulses passing through the processes of neurons.

On January 26, 2013, a group of surgeons and neurologists led by Paolo Maria Rossini, at the Gemelli Hospital in Rome, implanted ultrathin transneural electrodes developed by the Thomas Stieglitz research group from the University of Freiburg (Germany) into the ulnar and median bundles of brachial nerves that control finger movements. According to the principle of biofeedback, the tension of the tendons allows you to touch objects – even if not as well as with a live hand.

After 19 days of preliminary testing, the electrodes were attached to the prosthesis, and for a week Sorensen practiced using it daily.

The developers feared that after nine years of inactivity, the sensitivity of the patient's nerves would decrease, but the tests of the prosthesis were more than successful.

As Sorensen himself said, "Sensory feedback worked just incredibly. I have regained the sensations that I had been deprived of for nine years. During the test, they put a blindfold on my eyes and put earplugs in my ears to leave only touch, but I really felt a round object I was holding in my hand or rectangular, soft or hard. There were no problems with the capture either."

Unfortunately, a month later, the electrodes had to be removed from Sorensen's hand – in accordance with the rules of clinical research, although scientists are sure that without harm to the patient, both implants and a prosthesis could be left in place for many years.

The next step is to miniaturize the sensors, which will reduce the size of the prostheses. In addition, scientists intend to improve the technology to increase the sensitivity of the system.

The authors of the work note that the technology of sensory feedback has a huge potential. Its modifications can be used to return almost any sense – for example, hearing. Michera and his colleagues are already working on expanding the technology, and commercialization of the new bionic prosthesis will begin in the coming years.

Article by Stanisa Raspopovic et al. Restoring Natural Sensory Feedback in Real-Time Bidirectional Hand Prostheses is published in the latest issue of the journal Science Translational Medicine.

Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on EPFL Materials: Amputee Feels in Real-Time with Bionic Hand06.02.2014

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