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A bionic hand which feels real

A prosthesis capable of sending sensorial signals to the brain has been developed and created by a team of Italian researchers and tested on a patient injured by an exploding firecracker.

September 2014

IMALab A bionic hand which feels real

Grasping, feeling, caressing, expressing, interpreting, activating… the hand is an extraordinary precision instrument at the service of the brain, and its functions are practically uncountable. So it’s obvious how serious a blow it is when someone loses a hand, and why so much research is going on in the quest to develop ever more sophisticated prosthetic substitutes.

The crucial goal for research is to achieve two-way connections between the brain and the artificial hand, that’s to say, that the latter becomes not only capable of forming reliable interpretations of the user’s intended commands but also manages to provide and deliver nearly “natural” sensory feedback to the brain through remnant afferent pathways, simultaneously and in real time. Until this is achieved, the weak point will remain the lack of feedback from hand to brain.

A team from the Scuola Superiore Sant’Anna (Sant’Anna School of Advanced Studies) in Pisa and the Ecole Polytechnique Federale (Swiss Federal Institute of Technology) in Lausanne, directed by Silvestro Micera, have for the first time developed a prosthesis capable of sending sensorial information to the brain which makes it possible for the user to recognize the shape, consistency and texture of an object it is touching.

It enables a person not only to recognize the object but also to “feel” it, and thus to modulate the force necessary to pick it up and use it without damaging it or letting it drop, in this respect simulating the behavior of a natural hand.

The functioning of the prosthesis, which is called “LifeHand2”, was tested on a thirty-six-year-old Danish man whose left hand had been amputated following the explosion of a firecracker.  The result – presented in the February 2014 number of Science Translational Medicine – represents a notable qualitative advance towards the creation of perfectly functional bionic hands.

The team of scientists demonstrated that by stimulating the median and ulnar nerve fascicles using transversal multichannel intrafascicular electrodes, physiologically appropriate (near-natural) sensory information from artificial sensors on a hand prosthesis can be provided to an amputee’s brain during the real-time decoding of different grasping tasks to control a dexterous hand prosthesis.

The application of the prosthesis – carried out at the Policlinico Gemelli hospital in Rome- required a delicate operation to position the electrodes connecting the bionic hand with the nerve fascicles in the arm. The electrodes were developed in the IMTEK Laboratory of Biomedical Microtechnology in the University of Freiburg in Germany, with the aim of maximizing the contact with the nerve fibers at the same time as minimizing their thickness.

The results, evaluated after only eight days of test exercises with the patient, were extremely satisfactory. The blindfolded patient was able to correctly recognize the consistency of hard, intermediate or soft objects in over 78% of his attempts, and in 88% of his attempts he was able to correctly identify the dimensions and shapes of objects such as a baseball ball, a drinking glass or a mandarin orange, and then modulate the correct amount of force to pick them up.

All this was made possible by the team first identifying a series of complex algorithms capable of distributing in the best possible way the tasks to be assigned to the brain and those which could be delegated to the artificial intelligence contained in the prosthesis.

Future studies to improve these algorithms and therefore successfully handle more complex movements and sensations could soon improve the efficacy and “life-like” quality of hand prostheses, resulting in a keystone strategy for the near-natural replacement of missing hands. But they could also be useful for contributing to finding cures for even more serious medical conditions, such as for example movement problems suffered by paraplegic subjects.