The brain controls the tactile prosthesis! NEJM's man-machine integration era has arrived.

Everyone's childhood impression of "prosthetic limbs" should be the hook hand of Captain Hook in the movie Peter Pan, right? This kind of prosthesis has almost only decorative function. Feeling or doing complicated actions is an idiotic dream. But recently, the research and development results reported in the New England Journal of Medicine (NEJM) have made prostheses that can give instructions and even feel!

According to this report, three patients now use this kind of prosthesis. Due to the improvement of prosthetic function, patient 1 has resumed full-time work, and can also ski, fish under the ice and ride snowmobiles. Patient 2 has been able to take part in the car rally and repair the car with artificial limbs. Patient 3 can use artificial limbs for field orientation, canoeing and skiing.

All patients said that after receiving treatment, they trusted the prosthesis more, and they already thought the prosthesis was a part of themselves. They also said that artificial limbs have a positive impact on their self-esteem, self-image and social relations.

The lack of "feeling" of prosthetic limbs is the main problem. To understand how this pioneering invention of "man-machine integration" was realized, we should first review the biology class in junior high school. For example, if you want to pick up a wallet that has fallen to the ground, the instructions given by your brain will be conveyed through your nerves. When you touch your wallet, your fingertips will give feedback and tell your brain to "touch it", and then your brain will give instructions to "grab it".

This process happens instantly in normal people, and it is a piece of cake. However, the prosthetic technology has not been broken through, mainly due to the lack of intuitive control and sensory feedback system for prosthetic limbs.

Researchers from several Swedish universities and MIT Media Lab have cooperated with Integrum AB for several years. They invented a simulated artificial limb, which is intuitively controlled by the brain and has a tactile experience. This prosthesis is connected to the nerves, muscles and bones of the user at the same time. Four amputees have been fitted with this prosthesis and have been using it for three to seven years.

The research team broke through five major scientific and technological problems. The research team always has five things to break through: nerve transplantation, bone integration, man-machine connection, prosthetic control system and sensory feedback.

Nerve transplantation

The biggest challenge to improve the function of artificial limb is that during amputation, the arm nerve loses control of the muscles it controls, thus cutting off the bridge between the brain center and the muscles. In 2006, Dr Todd Kuiken and Dr Gregory Dumanian of Northwest University developed a targeted neuromuscular reinnervation (TMR). Even if the patient's arm was amputated more than ten years ago, the residual arm nerve can be transferred to other muscle parts through surgery to re-establish innervation.

Osteointegration

Our impression of prosthetic limbs is often "detachable", but this kind of prosthetic limbs, including bones, need to be integrated. In this regard, dental technology has been used, and dental implants have started very early. The team referred to related operations. The prosthesis consists of arms, elbows and hands, which are connected with joints.

Man-machine connection

The implant system used by the team for man-machine interface is called e-OPRA, and the implant system is connected with the residual limb through bone integration technology. The prosthesis is directly connected to the bone, thus providing mechanical stability. Nerves and muscles are also connected to the control system of the prosthesis through neuromuscular electrodes, and signals are sent in both directions between the prosthesis and the brain.

Prosthetic control system

The prosthetic controller is designed as an independent wearable component, which can decode the exercise will and provide direct sensory feedback. Prosthetics do not need external batteries, wires or equipment to maintain their functions, but are controlled by epicardial electrodes.

Prosthetic control and communication unit is the core module of prosthetic controller, which can use digital and analog signals to control prosthetic devices. Neurotransmitters can provide direct signal feedback to the input nervous system according to the sensory signals transmitted by prosthetic hands.

Sensory feedback

It is very difficult for an amputee to make the prosthesis feel physically. In this study, the electricity that causes tactile sensation is coupled to the pressure sensor on the thumb of the prosthetic hand, so that the patient can feel the real tactile sensation from the prosthetic hand, and the patient can feel when to touch the object, the characteristics of the object and the strength of pressing the object. Ideally, the number of sensors in the prosthetic hand should match the resolution of the interface, so that the patient can feel all the parts that the sensors in the prosthetic hand can detect.

? Three users have proved that man-machine integration is expected to be realized. In daily life, patients can effectively use artificial limbs without guidance. After 3~7 years of use, the neuromuscular interface of 3 patients maintained normal function (another 1 patient did not participate in the follow-up, but had a record of using neuromuscular prosthesis in daily life for 2.5 years). During the follow-up period, the patient did not have any serious adverse events, infection, bleeding or stopped using prosthetic limbs due to implantation adverse events.

The current research is aimed at amputees above the elbow, and the research team is also developing man-machine docking and leg prosthesis for amputees below the elbow. In the future, it seems that the picture of "man-machine integration" will no longer be just the plot in science fiction movies.