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 But for a while last year he regained his sense of touch after
being attached to a "feeling" bionic hand that allowed him to grasp
and identify objects even when blindfolded.
The prototype device, which was wired to nerves in the 36-year-old
Dane's left arm, blurs the boundary between body and machine and
scientists hope it could one day revolutionize the lives of many
amputees.
There is still work to be done in miniaturizing components and
tidying away trailing cables that mean the robotic hand has so far
only been used in the lab, but Sorensen said the European research
team behind the project had got the basics right.
"It was a great experience. It's amazing to feel something you
haven't been able to feel for so many years," he told Reuters in a
telephone interview. "It was pretty close to having the same feeling
as in my normal hand."
Details of his monthlong use of the bionic hand, including results
from a week of concentrated daily tests, were reported by
researchers from Italy, Switzerland, Germany, Britain and Denmark in
the journal Science Translational Medicine on Wednesday.
Alastair Ritchie, a bioengineering expert at the University of
Nottingham, who was not involved in the research, said the device
was a logical next step but more clinical trials were now needed to
confirm the system's viability.
"It's very exciting preliminary data but it's a one-case study and
we now need to see more cases," he said.
Despite notable advances with prosthetic limbs, current artificial
hands fall down when it comes to providing sensory feedback — a key
element in human dexterity.
In his everyday life Sorensen uses a commercial prosthetic hand that
can detect muscle movement in his stump to open and close his hand,
but provides no sense of touch and requires him to watch constantly
to prevent objects being crushed.
The new so-called LifeHand 2 prosthesis is far more sophisticated in
combining intra-nerve wiring, robotics and computer science to
create life-like feeling.
IMPLANTED ELECTRODES
Ultra-thin electrodes the width of a human hair were surgically
implanted into the ulnar and median nerves of Sorensen's arm before
he was attached to the robotic hand, which is equipped with various
artificial sensors.
These sensors measure the tension in man-made tendons on each finger
to assess the force used to grasp different objects, while computer
algorithms transform this information into an electrical signal that
the nerves can interpret.
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The result is real-time sensation, including a gradation in feelings
that allowed Sorensen in tests to detect both shape and consistency.
In a series of experiments, he was able to recognize the basic
shapes of objects, such as the cylinder of a bottle, and also feel
differences in the stiffness between a mandarin orange and a
baseball.
It is a big advance on an initial LifeHand 1 device unveiled in
2009, which was less refined and was not implanted on the patient
but only connected through electrodes.
There is still a need for further work, however, in order for the
new hand to differentiate between more detailed textures, as well as
between hot and cold.
Silvestro Micera, an engineer at the Ecole Polytechnique Federale de
Lausanne and the Cuola Superiore Sant'Anna in Pisa, said the
challenge now was to ensure the system could remain implanted on
multiple patients for "many months".
"Our final goal is to have this in clinical practice in five, six or
seven years time — but the next step is to show in two to three
years that this can work long-term, not just in one patient but in
several patients," he said.
Assuming further clinical trials go well, the research team is
likely eventually to bring in a commercial partner, although Micera
said this was not on the cards just yet.
One big unknown is cost. The high-tech device will not be cheap, but Micera said the surgery to implant the electrodes was relatively
straightforward, which should limit hospital bills.
(Editing by Alison Williams)
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