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Rehabilitation Institute of Chicago – RIC has unveiled to the public the woman with an artificial, bionic arm. Her arm was amputated at the shoulder, in a traffic accident. Today, after installing the bionic prosthesis, she can, for example, open the closet with her thoughts. She can control the number of complex movements, and it opens many opportunities for those who have lost limbs. All this is achievable symbiosis surgery and technology.

Technology of "bionic arm" is possible because of two facts. The first is the existence of a motor center in the brain (the area that controls voluntary muscle movements), which always sends control signals, even in the event when there are no muscles that can be controlled. Another factor is based on the fact that, during the amputation, not all the nerves that control the movements of the hand are removed. According to that, when the arm is amputated, the nerve endings remain alive, ending in the shoulder, and they simply have no place to send the information. If these nerve endings are diverted to the active muscle groups, then the person thinks of command "open closet" and sends the appropriate signals to the nerves that are supposed to communicate with the hand. These signals then end of active muscle groups instead on the part that is, relatively speaking, dead.

The procedure is simple redirection. Therefore, the developed procedure called targeted muscle reinnervation - TMR.

Muscles and electrodes

Basically, the surgeons access the nerve endings that are found in the shoulder, and control arm movements. Then, without nerve damage, the nerve endings are diverted to the active muscle group. In the described of bionic arm, surgeons from RIC connect nerve endings to the chest muscle group. It takes several months for the nerves to connect to these muscles and become an integrated unit. The end result is a reversal of control signals: motor center in the brain sends signals to the hand through nerve pathways, as it always was. But, instead ending in the shoulder, the signals end at the chest.

In order to use these signals to control the bionic arm, electrodes are placed on the surface of the chest muscles. Each electrode controls one of the six motors that move the joints of the prosthesis. When you think of the command "open hand", the brain sends a signal to "open hand" to the appropriate nerve which is now located on the chest. When the nerve endings receive the signal, the chest muscle is activated which results in its contraction.

When the chest muscle contracts, the electrode on the muscle is activated to detect and forward the command to the appropriate motor to open the hand prosthesis. Since every nerve ending is integrated in different part of chest muscle, a person with a bionic prosthesis can run all six engines at the same time which produces quite accurate movements of the prosthesis. The disadvantage is the fact that the prosthesis is heavy as a result of additional engines that allow greater freedom of movement.

An interesting fact is that if you touch the skin of the chest where the redirected nerves the arm, one feels like his hand is touched!
Nearly natural movements

The next step is to develop ways to get the signals from the prosthetic fingers to the nerves in the chest and further, to the brain so you can feel the pressure, cold or heat.

Besides the already mentioned prosthesis, another patient had prototype bionic arm, which was later additionally improved. Artificial hand project was made by order of the Defense Advanced Research Projects Agency (DARPA), by the name of “Revolutionizing Prosthetics 2009-RP”. A team of scientists has produced the first integrated prosthetic arm that can be controlled in a natural way, which provides sensory feedback and provides eight direction movements, which is now far better then the latest prosthetic limbs.

Engineering center mentioned has completed a system of artificial limbs, which includes training for patients using this limbs (the virtual environment), as well as the system of recording movements and control signals during clinical trials. All this has led to improvements in functional verification, such as the possibility of repositioning the finger during various operations - for example, taking a credit card out of pocket and free movement of limbs close to natural gait.

This natural behavior and integrated sensory feedback have been achieved by using TMR method described above. You need to know that this method is based on the transfer of the remaining nerves from an amputated arm to the unused part of the muscle around the injury. With TMR technique, nerves are transferred from shoulders to the patient's chest. Using the electrodes on reinnervated sites the natural control of the prosthesis is enabled. This gives a much more natural way to control the prosthesis and natural sense of touch and grip strength.

The above advanced systems will be greatly enhanced by using IMES devices. Scientists are now working on the next generation prototype called PROTO 2, which will have more than 26 stages of movement and the strength and speed of movement will be approximate to capabilities of the human hand. This is combined with more than 80 individual sensory elements used as a feedback for touch, temperature and position of the hands. We should also mention the construction of a new unit for the shoulder and wrist movements, all of which should be integrated into the new prosthesis.

DARPA is an ambitious effort to create the most complex medical and rehabilitative technologies for the benefit of people. Doctors and scientists included in this projects are excited to be part of a team that has the ability to positively affect the quality of life of those who, by coincidence, have lost an arm or hand.