First thought-controlled prosthetic arm to be implanted in patients
12 December 2012
The world’s first robotic arm controlled by
thoughts is due to be implanted in the first patient this winter by
Chalmers University of Technology in Sweden.
The prosthetic arm will be anchored directly to the skeleton and
electrodes connected to nerves and muscles will transfer signals
from the brain to the arm and also provide feedback to the brain.
Problems with current systems
Ever since the 1960s, amputees have been able to use prostheses
controlled by electrical impulses in the muscles. Unfortunately,
however, the technology for controlling these prostheses has not
evolved to any great extent since then.
For example, very advanced
electric hand prostheses are available, but their functionality is
limited because they are difficult to control. "All movements must by pre-programmed,"
said researcher Max Ortiz Catalan.
"It’s like having a Ferrari without a steering wheel. Therefore, we
have developed a new bidirectional interface with the human body,
together with a natural and intuitive control system."
Today’s standard socket prostheses, which are attached to the
body using a socket tightly fitted on the amputated stump, are so
uncomfortable and limiting that only 50% of arm amputees are
willing to use one at all.
Robotic arm controlled by skin electrodes
Currently, in order to pick up the electrical signals to control
the prosthesis, electrodes are placed over the skin. The problem is
that the signals change when the skin moves, since the electrodes
are moved to a different position. Additionally, the signals are
also affected when we sweat, since the resistance on the interface
In existing prostheses, amputees use only visual or auditory
feedback. This means, for example, that you have to look at or hear
the motors in the prosthesis in order to estimate the grip force
applied to a cup if you want to move it around.
The new technique
This research project is using a Brånemark
titanium implant (OPRA Implant System), which anchors the
prosthesis directly to the skeleton through what is known as osseointegration.
Osseointegration was developed in the 1960s by Professor Per-Ingvar
Brånemark. He discovered that titanium is not rejected by the body,
but is integrated into the surrounding bone tissue. The method is
used for tooth implants and for leg, arm and face prostheses as well
as for anchoring hearing aids.
The researchers are planning to implant the
electrodes directly on the nerves and remaining muscles.
Since the electrodes are closer to the source and the body acts as
protection, the bio-electric signals become much more stable.
Osseointegration enables the signals inside the body to
reach the prosthesis. The electrical impulses from the nerves in the
arm stump are captured by a neural interface, which sends them to
the prostheses through the titanium implant. These are then decoded
by sophisticated algorithms that allow the patient to control the
prosthesis using his or her own thoughts.
How the new system will work
With the new method,
patients receive feedback too, as the electrodes stimulate the neural
pathways to the patient’s brain, in the same way as the
physiological system. This means that the patient can control their prosthesis in a more natural and intuitive way. This has not
been possible previously.
Giving more control to amputees
Max Ortiz Catalan, doctoral student at Chalmers University of
Technology said, “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. Osseointegration
is vital to our success. We are now using the technology to gain
permanent access to the electrodes that we will attach directly to
nerves and muscles.
"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. 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
“By testing the method on a few patients, we can show that the
technology works and then hopefully get more grants to continue
clinical studies and develop the technology further. This technology
can then become a reality for lots of people. 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