The principle of prosthesis is a concept which has been around since the Ancient Egyptian times, with a mummified Egyptian wearing a prosthetic toe made of leather and wood. During recent years, however, prosthetics has been outshined by bionics: the idea of creating parts that will function and assist the user with their missing body part, instead of just replacing it. The idea of men with hooks for hands has the potential to be replaced with the half-man, half-machine idea, which has only previously been seen in science fiction. Sadly, this article is less about building your own Terminator, but more about how technology has been integrated with people to assist those who are unfortunate enough not to be as physically whole as others.
The most recent breakout in prosthetic technology is called ‘targeted muscle reinnervation’, allowing for people to wear bionic arms that only need to be fitted snugly, with sensors attached to the skin, which let a motorised arm be controlled by the brain.
Your muscles are controlled by your brain, which sends electrical impulses through the nervous system. When limbs have been severed, the information sent from the brain cannot reach the muscles in the lost limb. However, the commands still get passed down the remaining nerves, but can’t get any further than that which is severed. Therefore surgeons can rewire these split nerves to another muscle (preferably a portion of the chest), such that when the brain signals the lost muscles to contract, present chest muscle would contract. The process of re-networking these nerves is not a simple procedure. The surgeons need to find the stumped nerve endings that would have controlled the movements of the lost arm joints and reroute them to a functioning muscle group, all without damaging them.
The time taken for the rewired nerves to become part of the new muscle takes several months, but afterwards the patient should be functional enough to be fitted with the prosthetic limb. Electrodes which can be placed on the skin to interpret the electrical activity caused by these muscle contractions, uses the data collected to provide information for the movement in the joints in the prosthetic limb. So by only imagining moving the amputated arm, the user can command the prosthetic arm to move.
Whilst all of this is ground-breaking progress with creating an arm, creating a bionic leg has its complications, since walking has stability issues and the prosthetic limbs are essentially just tools. They lack feeling, essentially leading to patients walking with a constant dead leg. This problem is being tackled literally one step at a time, with the Rehabilitation Institute of Chicago creating a thought-controlled leg using targeted muscle reinnervation. According to Levi Hargrove, the lead scientist of this research, their developped leg “learns and performs activities unprecedented for any leg amputee, including seamless transitions between sitting, walking, ascending and descending stairs and ramps and repositioning the leg while seated”. This can show the capabilities of bionic limbs which adapt to the situation they are in. As far as the the problem of obtaining feeling in a lost limb goes, nerves need to be rerouted closer to the skin’s surface. This is because sensors can be placed around the base of the prosthetic foot, to measure pressure in different areas of the foot. These pressure signals are processed by micro-controllers which send signals to stimulators in the leg close to the stumped leg, which vibrate to stimulate the repositioned nerve endings, relaying signals to the brain. This sensation is somewhat far from the genuine feeling in a limb, but it can give people a sense of what they are stepping on.
Not only can prosthetic limbs be controlled by targeted muscle reinnervation, but it can be taken one step further. If you are using the nerves’ electrical signals to provide information for the bionic limbs, then why not simply just collect the data from the source, like the brain? Well, at Duke University, Dr Miguel Nicolelis was able to demonstrate neural interfacing by using a monkey. This monkey would play a simple game with a joystick and was incentivised with a reward every time she completed the game. The intention was to have this monkey play the game over again, and the brain movement for every arm motion was recorded until they have sufficient data from the monkey so that they could use the brain signals of the monkey thinking about moving her arm, and the joystick could be remotely controlled and this monkey essentially had a functioning third limb, although it was not directly connect to her.
This was in 2003, and if they could do this with a robotic arm, surely they could make a whole version of a robotic monkey that could be controlled. Roughly four years later, at Duke University in the USA, they had a monkey moving on a treadmill, providing the brain signals for movement, which was being processed and sent to Kyoto in Japan, where this information was being used to give the commands for a robotic version of a monkey to walk. The surprising thing was that information was being received 20 milliseconds faster than it would have taken for the signals from the brain to reach the muscles of the monkey.
By using this information, you could put a person in this robot and they could move it from inside. This seems pretty trivial, but it could have important consequences in the medical profession. Serious accidents can leave people with intense spinal injuries, preventing the brain to send signals to the muscles through the central nervous system. Now you can take the signals which cause the muscles to move straight from the brain, and this time you would not necessarily need to use prosthetics, but a mechanical exoskeleton to provide supportive movement to the paralysed patients.
We have seen Dr Miguel Nicolelis’ work come into motion at the 2014 Brazil FIFA World Cup as a paraplegic man, wearing an exoskeletal suit performed the opening kick. However, they have still only scratched the surface because this technology can progress to be made more efficient, lighter, and can be used in other fields such as in the military to assist soldiers. Perhaps this will lead to a new generation of soldiers akin to those in the latest instalments of the Call of Duty franchise.
As with other fields of technology, the main constraint is that the current know-how is limited in its ability to produce worthwhile assistive machinery on a commercial scale. However, the ideas are there and when there are technological breakthroughs, the concepts will be ready and waiting.
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