Robotic Limb Replacement

The field of robotics is becoming more and more advanced. A very exciting application of robotics is in the field of medicine, more specifically in the development of robotic limb replacement. Limb replacement involves using some type of prosthetic to take the place of a part of the body that was amputated or lost due to injury or illness. With advances in technology and with a better understanding of how the brain controls movement, limb replacements are becoming more sophisticated and lifelike.

Significance

• The goal of robotic limb replacement is to develop prosthetics that look, act and feel like the limb that they are replacing. It is no longer enough to just replace the limb, it must now function as a fully operational limb. This involves not only building very specialized artificial limbs but also in understanding how the brain controls movement. The challenge is how to connect the robotic limb so that the patient can control its movement, just as if it were a normal limb. Currently, most artificial limbs are controlled by muscular contractions initiated by the patient versus neuronal signals from the brain, as occurs in natural movement.

Function

• Every movement that the body makes begins with a thought. As soon as a thought such as I need to take a step forward, or I need to pick up my coffee cup occurs, the brain triggers a series of complex reactions to make that movement happen. The brain must figure out what muscles to contract and relax along with how much force is needed to accomplish the task. With lightening speed, the brain sends signals through the spinal cord and along the nervous pathways to coordinate and recruit the necessary muscles. When there is a loss of a limb, there is also a loss of the nerves that connected that limb to the signals sent by the brain.

Types

• Common prosthetics used today do not connect the artificial limb with the nervous system. The prosthesis is made up of the artificial limb and cables that connect to an area of the body where the muscles are functioning. For example a hand prosthesis would connect to the shoulder muscles. The patient must then contract the shoulder muscles in very precise ways in order to pull on the cables, which in turn makes the hand prosthesis move. There are also externally powered prosthetic limbs. In this case the limb is moved with a battery powered motor. In this case switches must be moved to make the limb move. Both require a lot of time and training on the part of the patient. Both also leave a lot to be desired when it comes to looking lifelike and in replicating natural movement. Hence the need for robotic limb replacement which will allow the brain and the artificial limb to interact directly with one another.

Considerations

• To make robotic limbs work properly scientists must figure out how to get the signals sent by the brain to interact with the artificial limb. The goal is to develop computerized systems that can interpret the signals from the brain and then translate them to the robotic limb so it can respond accordingly. It is almost a case of developing an artificial nervous system. Science is getting closer with the development of utilizing computer chips which can be programmed to control a prosthesis. The prosthesis which contains the chip, monitors the patient as he or she moves. This information is then evaluated by an external computer program. Next, the prosthesis is programmed to mimic the patients natural movements. The chip acts as a brain and automatically reacts to changes in speed and direction. This information is then preprogrammed into the prosthesis, so the artificial limb is better matched with the patients unique way of moving through their daily life activities.

Potential

• As exciting as programmable limbs are, they are still have their limitations. They only allow for a small number, usually ten, programmable modes. Since they operate on battery power they must be recharged. Efforts are currently being made to allow the battery to operate for up to fifty hours.
  Here is where the science of robotic limb replacement offers promise. The goal is to somehow "wire" the artificial limb directly to the nervous system so the brain controls its every move naturally. First an electrode must be surgically placed in the brain. Then computers contained in the prosthesis would be programmed to interpret the signals sent by the brain to initiate movement. In addition the computer in the artificial limb needs to send information back to the brain as movement occurs, so adjustments can be made. Scientists are now experimenting with the best places to attach the electrodes and on improving the computerized signals between the prosthesis and the brain. While we are still a ways from making this a reality in humans, research in rats and monkeys has been successful. See the links below for more information.