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For the first time, people with arm amputations can experience touch sensations in a mind-controlled arm prosthesis that they use in everyday life. A study in New England Journal of Medicine reports on three Swedish patients who have lived for several years with this new technology, one of the world’s most integrated human-machine interfaces.
The breakthrough is unique: Patients have worn a mind-controlled prosthesis in their daily lives for up to seven years. For the past few years, they have also lived with a new function: sensations of touch in the prosthetic hand. This is a new concept for artificial limbs, which are called neuromusculoskeletal prostheses, since they are connected to the user’s nerves, muscles and skeleton.
The research was led by Max Ortiz-Catalan, associate professor at Chalmers University of Technology, in collaboration with Sahlgrenska University Hospital, Gothenburg University and Integrum AB, all in Gothenburg, Sweden. Researchers from the Vienna University of Medicine in Austria and the Massachusetts Institute of Technology in the United States also participated.
“Our study shows that a prosthetic hand, attached to the bone and controlled by electrodes implanted in nerves and muscles, can operate much more precisely than conventional prosthetic hands. We further improve the use of prosthetics by integrating the tactile sensory feedback they use. patients to mediate how difficult it is to grip or squeeze an object. Over time, patients’ ability to discern smaller changes in sensation intensity has improved, “says Ortiz-Catalan.
“The most important contribution of this study was to demonstrate that this new type of prosthesis is a clinically viable replacement for a lost arm. No matter how sophisticated the neural interface is, it can only provide real benefit to patients if the connection between the patient and the prosthesis is safe and reliable in the long term. Our results are the product of many years of work, and now we can finally present the first bionic arm prosthesis that can be reliably controlled using implanted electrodes, while transmitting sensations to the user. in everyday life, “continues Ortiz-Catalan.
Since receiving their prostheses, patients have used them daily in all their professional and personal activities.
The new concept of neuromusculoskeletal prosthetics is unique in that it offers several different features that have not been brought together in any other prosthetic technology in the world:
- It has a direct connection to a person’s nerves, muscles, and skeleton.
- It is mentally controlled and offers sensations that the user perceives as a result of the missing hand.
- It is autonomous; All the necessary electronic components are contained within the prosthesis, so patients do not need to carry additional equipment or batteries.
- It is safe and stable in the long term; The technology has been used without interruption by patients during their daily activities, without the supervision of researchers, and is not limited to confined or controlled environments.
The newest part of technology, the feeling of touch, is made possible by stimulating the nerves that used to be connected to the biological hand before amputation. Force sensors located on the thumb of the prosthesis measure the contact and pressure applied to an object while holding it. This information is transmitted to the nerves of the patients that lead to their brains. In this way, patients can feel when they touch an object, its characteristics and how hard they press it, which is crucial to imitate a biological hand.
“Currently, sensors are not the obstacle to restore sensation,” says Ortiz-Catalan. “The challenge is to create neural interfaces that can seamlessly transmit large amounts of artificially collected information to the nervous system, so that the user can experience sensations naturally and effortlessly.”
The implementation of this new technology took place at the Sahlgrenska University Hospital, directed by Professor Rickard Brånemark and Dr. Paolo Sassu. More than a million people worldwide suffer from limb loss, and the ultimate goal of the research team, in collaboration with Integrum AB, is to develop a widely available product suitable for as many people as possible.
“Right now, patients in Sweden are participating in the clinical validation of this new prosthetic technology for arm amputation,” says Ortiz-Catalan. “We hope that this system will be available outside of Sweden in a couple of years, and we are also making considerable progress with similar technology for leg prostheses, which we plan to implant in a first patient later this year.”
How the technology works
The implant system for the prosthetic arm is called e-OPRA and is based on the OPRA implant system created by Integrum AB. The implant system anchors the prosthesis to the skeleton in the stump of the amputated limb, through a process called osseointegration (osseo = bone). The electrodes are implanted into the muscles and nerves within the amputation stump, and the e-OPRA system sends signals in both directions between the prosthesis and the brain, just like in a biological arm.
The prosthesis is controlled mentally, through the electrical signals from the muscles and nerves sent through the stump of the arm and captured by the electrodes. Signals pass to the implant, which passes through the skin and connects to the prosthesis. The signals are then interpreted by an integrated control system developed by the researchers. The control system is small enough to fit inside the prosthesis and processes the signals using sophisticated artificial intelligence algorithms, resulting in control signals for the movements of the prosthetic hand.
Tactile sensations arise from force sensors on the prosthetic thumb. The prosthesis control system converts the signals from the sensors into electrical signals that are sent to stimulate a nerve in the stump of the arm. The nerve leads to the brain, which then senses the levels of pressure against the hand.
The neuromusculoskeletal implant can be connected to any arm prosthesis available on the market, allowing them to operate more effectively.
How the artificial sensation is experienced
People who lose an arm or a leg often experience phantom sensations, as if the missing part of the body remains even if it is not physically present. When the force sensors on the prosthetic thumb react, the patients in the study feel that the sensation comes from their phantom hand. Precisely in which part of the phantom hand varies between patients, depending on which nerves in the stump receive the signals. The lowest level of pressure can be compared to touching the skin with the tip of a pencil. As the pressure increases, the sensation becomes stronger and more “electric”.
Reference
Ortiz-Catalan et al. (2020). Self-contained neuromusculoskeletal arm prostheses. NEJM. DOI: https://doi.org/10.1056/NEJMoa1917537
This article has been reissued from the following materials. Note: the material may have been edited for length and content. For more information, contact the source cited.
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