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How do prosthetic limbs function?

By Joelle Lim


Prosthetic leg, arm, and hands

Have you ever wondered how a cyborg might work? How are scientists able to recreate a machine that replicates the human body? Even though it may seem as if these innovations are purely science fiction, scientists have already invented devices such as prosthetic limbs. They are part of a much larger field known as biomechatronics,which combines biology, machinery, and engineering to develop tools to enhance the lives of many people. According to the World Health Organization, more than 30 million people require the aid of prosthetics.

What are prosthetic limbs?

Prosthetic limbs are artificial devices that can act as substitutes for any part of the body including the toe, finger, ear or even the nose. Although they may appear simple on the outside, these devices are highly complex. Engineers must hold a strong understanding of the processes of the brain in order to create an artificial limb that functions just like a natural limb.

How it works

To fully understand the process behind how prosthetics work, it is essential to know how the brain functions when moving a part of the body. For instance, what is the process behind taking a step? First, the muscles in the leg and foot receive impulses from the motor cortex, the region of the brain responsible for simulating the body’s movements. After receiving these signals, the proper muscles move in a pattern that allows the leg and foot to contract. Muscle spindles, which are also known as sensory receptors, contain neurons that take note of the position of your foot on the floor and send feedback information back to the brain. This allows the brain to deliver signals to your muscles to place your foot back on the ground after lifting it to take a step.

How is this natural process replicated for prosthetic limbs? Engineers have designed biosensors, which collect information that come from the user’s nervous and muscle system. These sensors relay information between the motor cortex of the brain and the prosthetic, which allow the artificial limb to move. For example, if one wanted to move an arm, then biosensors are used to send this information to the brain. Mechanical sensors are then used to collect information, such as the device’s position, that they then send to the biosensor, allowing the device to move as the user wishes. The central feature of the device would be the controller which acts as an interface for the device and the user’s nervous and muscular systems. It sends feedback information to the user from the mechanical biosensors and the actuator, the artificial muscle that acts as a substitute for the user’s natural muscle. These three elements work in harmony to move the desired limb in a way that mimics the motion of a biological limb.


Currently, scientists are working on developing a prosthetic device that more accurately resembles the user’s natural movements. They are looking to incorporate a human phenomenon known as proprioception, which is the ability to know exactly where one’s limbs are without having to look. Engineers want to find a way for the prosthetic limb to move without any conscious thought as well as replicate the user’s sense of touch to create more natural sensations. Additionally, the material used to make the device has been widely debated as the weight of heavy materials could make it more uncomfortable for the user. Therefore, scientists are looking for a resource that weighs the same as a natural limb. One solution could be to use carbon fiber covered with foam padding.

As more research is being done, prosthetic devices are continuously being upgraded to help users function as naturally as possible. One famous example is Terry Fox, an athlete who lost his right leg to cancer but was able to conquer his disability by running a whole marathon across Canada using a prosthetic leg. This comes to show that these bionic limbs may be the key to helping those with disabilities and advancing towards a more STEM based future!

Terry Fox, a Canadian athlete



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