Weirdly Interesting

How Do Bionic Prosthetics Work?  

Shanell Mouland
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The science of bionic prosthetics is a little more accessible than you may have thought. In reality, the idea that our brains can speak to artificial limbs, and those limbs can respond by mimicking what the human body would do is no longer a science-fiction fantasy – and you might even be able to understand how this process works. The world of bionics is here, and it's absolutely amazing. 

The business of creating stand-ins for missing body parts isn't a new one. Humans have long been losing parts and attempting to replace them with man-made materials – think glass eyes, dentures, and even toupees. It really isn't a giant leap, almost three thousand years later, to attempt to connect those prostheses to the brain. Put simply, "[bionics] is a term which refers to the flow of concepts from biology to engineering and vice versa." For the scientists among you, this connection may seem rather intuitive, but, for the rest of the population, making sense of the human brain talking to a piece of engineering can be hard to wrap your head around. Erik Sofge of Popular Science explains bionic prostheses best, expounding "[when] the electrical impulse from [the] brain reaches the base of [the] leg, a pair of sensors embedded in [the] muscle tissue connect the neural dots, and wirelessly transmit that signal to the [bionic foot]."

Got it? No? Keep reading for a more detailed explanation.

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Photo: Cpl Richard Cave, RLC/Wikimedia Commons/OGL
It Really Begins With Something As Simple As A Thought

Here's a thing that's surprisingly easy to understand: bionic prosthetics work as soon as you think they need to. To put it more simply, they operate on the electrical signals sent from your brain. As soon as your brain has the idea to move your arm, the bionic prosthetic – through wireless transmitters implanted in muscles – makes it happen. And just like with organic limbs, these signals occur without a whole lot of conscious effort. Think about it: when you reach to grab the milk out of the fridge, you don't think "okay, arm, fetch me that milk"; you just reach for it, and suddenly you possess it. Bionic prosthetics are designed to respond to brain signals just as quickly.

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Bionic Prosthetics Mimic The Things Your Brain And Limbs Already Do

Even without prosthetic limbs, according to Issac Perry Clements of How Stuff Works: "[your] brain controls the muscles in your limbs by sending electrical commands down the spinal cord and then through peripheral nerves to the muscles." 

In the case of an amputated limb, those signals would still be sent out from the nerve endings, only to reach a "dead end" where the limb once was. Scientists have discovered how to create prosthetics that can not only receive those signals but can also react to them. In a procedure called Targeted Muscle Reinnervation (TMR), developed by Dr. Todd Kuiken, these amputated nerves get reattached to a healthy, functioning muscle. For example, in the case of an amputated arm, the nerve endings would get attached to the chest muscle. The prosthetic arm would then be built to respond to the chest muscle's movement, thereby creating a pathway between the brain signals and the new bionic limb.

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Photo: Danie Ware/Wikimedia Commons/CC BY 2.0
They're Built Of Lightweight Plastics That Can Perform Body Movements

Long gone are the heavy and awkward materials of 20th-century prostheses. In fact, today's prosthetics are made of advanced plastics and carbon-fiber composites that are lightweight and far more conducive to interacting with the human body. They're also more carefully crafted to be able to perform the more subtle motions associated with human mobility; they're "even capable of automatically adapting their function during certain tasks, such as gripping or walking." 

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Photo: Ossur
It Involves Wireless Sensors Getting Embedded In A Muscle

In order for a prosthetic limb to be able to receive the brain's signals, special sensors have to be surgically inserted into the muscles near the limb. While these sensors are connected to the neural pathways of the brain, they also wirelessly transmit the brain's signals to the prostheses. The craziest part of this? The signals reach the prosthetic limb before the muscle even registers that the brain sent a signal, so a wearer shouldn't experience a muscle contraction at all, just a natural brain-to-limb movement.