Chalmers University of Technology,
Gothenburg, Sweden

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 advanced 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.

Fig. 1 – Max Ortiz Catalan demonstrates how the system works with the aid of electrodes, which capture bio-electric signals from the surface of the arm. (Credit: Oscar Mattsson)

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.

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 1)

“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.”

To see a video of Max Ortiz Catalan demonstrating the hand, please visit: .