A team of researchers at Chalmers
University of Technology in
Gothenburg, Sweden, say that
they have created the world’s first
implantable robotic arm controlled by
thoughts. Prosthetic leg technology has
ad vanced rapidly in the past
decade, but prosthetic arms
have been much slower to
catch up. Since the 1960s,
upper limb amputees have
been taught to use prostheses
that are controlled by electrical
impulses in the muscles.
Many still have hooks for
“hands.” And, the technology
for controlling these prostheses
really has not evolved to
any great extent since then.
There are, to be sure, some
advanced electric hand prostheses
available, but their
movements must be preprogrammed.
Rehabilitation is
slow and frustrating. And,
since there’s no sensory feedback,
the sense of touch is a
greatly missed.
Most standard socket prostheses are
attached to the body using a socket tightly
fitted on the amputated stump. Many
users say that these are uncomfortable
and limiting. In order to pick up electrical
signals to control a prosthetic arm,
electrodes are placed over the skin. The
problem is that the signals can change
when the skin moves, since the electrodes
move to a different position. Signals can
also be affected when users sweat, since
the resistance on the interface changes.
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| Max Ortiz Catalan demonstrates how the system works with the aid of
electrodes, which capture bio-electric signals from the surface of the
arm. |
How It Works:
In this research project, the researchers plan to implant the electrodes directly
onto the nerves and remaining muscles
instead. Since the electrodes are closer to
the source and the body acts as protection,
the bio-electric signals should
become much more stable. By incorporating
“osseointegration,” they will
anchor the prosthesis directly to the
skeleton. This method for anchoring the
prosthesis directly to bone, also called the
OPRA Implant System, was first developed
by Swedish Professor Per-Ingvar
Brånemark in the 1960s when he discovered
that titanium is not rejected by the
body but instead integrates with the surrounding
bone tissue.
Osseointegration enables the electrical
impulses from the nerves in the arm
stump to be captured by a neural interface,
sending them to the prosthesis
through the titanium implant. These are
then decoded by sophisticated algorithms
that allow the patient to control
the prosthesis using his or her thoughts.
In most prostheses, amputees have
only visual or auditory feedback. This
means, for example, that users must look
at or hear the motors in the prosthesis in
order to estimate grip force applied to
objects, such as a cup. With the new
method, patients receive neural feedback
as the electrodes stimulate the neural
pathways to the patient’s brain, in the
same way as the physiological system.
This should allow users to control the
prosthesis in a more natural and intuitive
way than has been previously possible.
Max Ortiz Catalan, an industrial doctoral
student at Chalmers, said, “We have
developed a new bidirectional interface
with the human body, together with a
natural and intuitive control system. Our
technology helps amputees to control
an artificial limb, in much the
same way as their own biological
hand or arm, via the person’s
own nerves and remaining
muscles. This is a huge
benefit for both the individual
and to society.” (See Figure )
“Many of the patients that we
work with have been amputees
for more than 10 years, and have
almost never thought about
moving their missing hand during
this time”, explained
Catalan. “When they arrived
here, they got to test our virtual
reality environment or our more
advanced prostheses in order to
evaluate the decoding algorithms.
We placed electrodes on
their amputation stumps, and
after a few minutes, they were
able to control the artificial limbs in ways
that they didn’t know they could, most of
the times. This made the patients very
excited and enthusiastic.”
What’s Next:
After testing the method on a few
patients, the researchers expect that
they will prove that the technology works
and then hope to get enough grants to
continue clinical studies and further
develop the technology.
Catalan said, “We want to leave the lab
and become part of the patients’ everyday
life. If the first operations this winter
are successful, we will be the first
research group in the world to make
‘thought-controlled prostheses’ a reality
for patients to use in their daily activities,
and not only inside research labs.”
Video of Max Ortiz Catalan demonstrating the hand
