What's Next for Mind-Controlled Prosthesis Allowing Patients to Feel?

Prof. Max Jair Ortiz Catalan, a researcher who developed a mind-controlled arm prosthesis allowing patients to feel, hopes this invention will be widely available in the next few years. Meanwhile, augmented reality treatment could help patients experiencing phantom pains after amputation.

In 2020, a study by Prof. Ortiz Catalan and his colleagues was published in the New England Journal of Medicine. It describes cases of three patients living with mind-controlled arm prostheses. For the first time, patients with amputations could experience a sensation of touch.

"What we are trying to do is to replace a lost biological limb with an artificial one," Dr. Max Ortiz Catalan, Professor at the Chalmers University of Technology in Sweden, said in an interview for Healthnews.

Connecting to bone, nerves, and muscles

Mechanical prostheses that resemble hooks have been used for over a century. However, challenges on how to control them, feel with them, and attach them to the body remain, Prof. Ortiz Catalan explains.

The conventional way of attaching a mechanical prosthesis is through a prosthetic socket, a device that suspends the prosthesis onto the residual limb. But, according to Prof. Ortiz Catalan, wearing the prosthetic socket can be very uncomfortable and painful due to pressure on the limb.

"There are many robotic devices that can be used as hands. But connecting them to the body and allowing people to control them has been the major challenge for the past 10-20 years," he says.

To overcome the challenge, Prof. Ortiz Catalan and his team developed a neuromusculoskeletal implant system that enables patients to control their prosthetic arm using their minds. Researchers applied a technology called osseointegration, which allows the introduction of an implant inside the bone.

Then, the bone grows tightly around the implant and integrates it, or, as Prof. Ortiz Catalan puts it, becomes an extension of the skeleton.

Using electrodes implanted in muscles and nerves inside the residual limb, the neuromusculoskeletal interface sends signals in both directions between the prosthesis and the brain.

"This is a highly integrated human-machine interface, a connection to the skeleton, nerves, and muscles. Using this technology, we translate the biological control system into a robotic one. We do not make the arm itself, but we make the connection between the person and the prosthesis, so patients can use the arm or hand the way they want it," Prof. Ortiz Catalan said to Healthnews.

Less sophisticated but reliable

According to Prof. Ortiz Catalan, patients can usually use a prosthetic arm immediately after the surgery, even if it works with limited function. However, it takes time for the patient to remember how to make certain movements; therefore, performing more demanding functions may take longer.

The researcher says it is impossible to compare a prosthetic limb to a biological hand in terms of motor skills. But even if it is less sophisticated, the mind-controlled prosthetic limb is reliable.

"It can help you to grasp and move things and make many other movements with intuitive and reliable control," Prof. Ortiz Catalan says.

At this stage, the mind-controlled prosthesis allows one to feel touch. It "tells" the patient how much force to use when they grab an object.

As with any other surgical procedure, prosthesis implantation does not come without risks. It requires anesthesia, which can cause complications, and implants carry risks of infection. Prof. Ortiz-Catalan says that people with cardiovascular diseases are not eligible for a such implant.

Nevertheless, at least seven people currently live with the mind-controlled bionic limbs developed at the Chalmers University of Technology, the Sahlgrenska University Hospital, and Integrum AB. Prof. Ortiz Catalan hopes the prostheses will be widely available in the next few years. But being such sophisticated technology, it may be costly.

"There are many other research groups worldwide working on cheaper solutions that may be less functional but more widely available. These kinds of devices are very important because they provide a solution for many people today. Our technology is experimental, and we hope that once it becomes more common and established, it will be cheaper and more accessible," he said.

Modern treatment for phantom pains

An estimated 8 out of 10 people who lose a limb experience some degree of phantom pain — a sensation as if the missing limb was there. Prof. Ortiz Catalan says that scientists still do not know precisely why it happens, but there are several hypotheses.

One is related to the areas of the human brain dedicated to processing information that comes from different body parts. Even when the limb is missing, the sensation may still be represented in this sensory map, and the brain can continue to create the experience.

Prof. Ortiz Catalan says that in many cases, phantom pain diminishes when a person starts wearing a prosthetic limb. "The more functional and the better integrated the prosthesis is, the less likely patients are to feel phantom limb pain," he explains.

While not everyone is eligible or has access to a prosthesis, researchers are looking for alternative treatments for phantom pains. Prof. Ortiz Catalan and his team developed a new method called phantom motor execution, which consists of using muscle signals from the amputated limb to control augmented and virtual environments.

The method brings the perceived phantom arm to life through a virtual representation that the patient can see and control on a screen. In this way, the patient reactivates areas of the brain that were used to move the arm before it was amputated, which might be why the phantom limb pain decreases.

"This is very useful for patients who do not have prostheses because they are not always easy to access. Instead, we create a virtual reality environment and allow patients to control a virtual prosthesis. Studies have shown that it helps to reduce phantom pain," Prof. Ortiz Catalan said to Healthnews.

Asked if the future for people with amputations looks promising, as researchers are developing modern technologies like bionic limbs or exoskeletons, Prof. Ortiz Catalan says it definitely looks better than it is now.

"But we're still far from a perfect artificial replacement for a biological limb. So I would say the future looks good, but we should also be realistic," he said.