Changing the Lives of Amputees

Every year, thousands of people across the world lose an arm or a leg. With that in mind, Max Ortiz Catalan, researcher and industrial doctoral student, Chalmers University of Technology, Göteborg, Sweden, is developing the world’s first implantable robotic arm controlled by thoughts.

“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,” Catalan says.

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. Instead, this research project is using the Brånemark titanium implant (OPRA Implant System), which anchors the prosthesis directly to the skeleton through osseointegration.

“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,” Catalan explains.

Controlled by Thought
Currently, in order to pick up the electrical signals to control the prosthesis, electrodes go over the skin. The problem is that the signals change when the skin moves since the electrodes move to a different position. Additionally, when patients sweat there is an effect on the signals since the resistance on the interface changes.

In this project, 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 bioelectric signals become much more stable. The use of osseointegration is to enable the signals inside the body to reach the prosthesis. Captured by a neural interface are the electrical impulses from the nerves in the arm stump, which sends them to the prostheses through the titanium implant. Then, sophisticated algorithms decode these in order to allow the patient to control the prosthesis using his or her own thoughts.

In existing prostheses, amputees use only visual or auditory feedback. With the new method, patients receive feedback 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 his or her prosthesis in a more natural and intuitive way.

From Lab to Patient
“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,” Catalan says. “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 did not know they could, most of the times.

“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 research labs.”

Max Ortiz Catalan
Chalmers University of Technology
maxo@chalmers.se

Professor Bo Ha°kansson
Chalmers University of Technology
boh@chalmers.se

Watch videos from the project at http://bit.ly/V1BtKy.

Photo Credit: Integrum