Bionic hand allows amputee to feel again

A Danish man who lost his left hand in an accident nearly a decade ago has become the first to receive a bionic hand that feels in real time.

The prosthetic hand was wired to the nerves in his upper arm. It has helped Dennis Aabo Sorensen grasp objects intuitively and identify what he was touching while being blind folded.

"The sensory feedback was incredible," said the 36 year-old amputee from Denmark. "I could feel things that I hadn't been able to feel in over nine years."

In a laboratory setting wearing a blindfold and earplugs, Sorensen was able to detect how strongly he was grasping, as well as the shape and consistency of different objects he picked up with his prosthetic.

"When I held an object, I could feel if it was soft or hard, round or square," Sorensen said.

This, experts say, is the first sensory-enhanced artificial limb.

Initially, scientists were worried about reduced sensitivity in Dennis' nerves since they hadn't been used in over nine years. These concerns faded away as the scientists successfully reactivated Sorensen's sense of touch.

The clinical study therefore provides the first step towards a bionic hand. The next step involves miniaturizing the sensory feedback electronics for a portable prosthetic. In addition, the scientists will fine-tune the sensory technology for better touch resolution and increased awareness about the angular movement of fingers.

The electrodes were removed from Sorensen's arm after one month due to safety restrictions imposed on clinical trials, although the scientists are optimistic that they could remain implanted and functional without damage to the nervous system for many years.

Sorensen lost his left hand while handling fireworks during a family holiday. He was rushed to the hospital where his hand was immediately amputated. Since then, he has been wearing a commercial prosthetic that detects muscle movement in his stump, allowing him to open and close his hand, and hold onto objects.

Created by Silvestro Micera and his team at EPFL (Switzerland) and SSSA (Italy), a prototype of this bionic technology was tested in February 2013 during a clinical trial in Rome under the supervision of Paolo Maria Rossini at Gemelli Hospital (Italy).

Sorensen underwent surgery in Rome at Gemelli Hospital on January 26. A specialized group of surgeons and neurologists, led by Paolo Maria Rossini, implanted transneural electrodes into the ulnar and median nerves of Sorensen's left arm.

After 19 days of preliminary tests, Micera and his team connected their prosthetic to the electrodes - and to Sorensen - every day for an entire week.

The ultra-thin, ultra-precise electrodes, developed by Thomas Stieglitz's research group at Freiburg University (Germany), made it possible to relay extremely weak electrical signals directly into the nervous system. A tremendous amount of preliminary research was done to ensure that the electrodes would continue to work even after the formation of post-surgery scar tissue. It is also the first time that such electrodes have been transversally implanted into the peripheral nervous system of an amputee.

So what exactly did the team do?

Micera and his team enhanced the artificial hand with sensors that detect information about touch. This was done by measuring the tension in artificial tendons that control finger movement and turning this measurement into an electrical current. But this electrical signal is too coarse to be understood by the nervous system. Using computer algorithms, the scientists transformed the electrical signal into an impulse that sensory nerves can interpret. The sense of touch was achieved by sending the digitally refined signal through wires into four electrodes that were surgically implanted into what remains of Sorensen's upper arm nerves.

"This is the first time in neuro-prosthetics that sensory feedback has been restored and used by an amputee in real-time to control an artificial limb," says Micera.

"It works like a brake on a motorbike," explains Sorensen about the conventional prosthetic he usually wears. "When you squeeze the brake, the hand closes. When you relax, the hand opens."