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Mind-controlled bionic limbs are shaping the future of prosthetics


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"As humans we are tools users, and every time we invent a new tool, that changes the way we live".

According to Dr. Michael Mcloughlin, Chief Engineer in the Applied Physics Laboratory of John Hopkins University, prosthetic limbs used for patients who have either suffered a loss of one or were born without one simply mark another tool in the history of humans.

From the early stone-age's ancient tools to modern advancements in prosthetics, our innovation never stops and today, by combining already existing artificial body parts with new technologies, we have reached an intersection never seen before. 

What makes a limb bionic?

In his 2011 Ted Talk on prosthetics, Dr. Kulken set the scene of the field of Medical Implants. At the time, prosthetic limbs were widely used by patients with different limb losses but remained relatively unchanged since their inception and refinement in WW1 and WW2.

Discussing upper arms prosthetics, in particular, the two main types available were Body powered and Battery powered prosthetics, each named after the source of their energy.

Body-powered ones relied on antiquated mechanisms akin to bicycle cables and harnesses, whilst the newer one state of the art motorised limbs used myoelectric control. Contracting and relaxing signals from the muscles are picked up and used to trigger movement.

This is when the bionic aspect came into fruition. Physicians and researchers worked to improve prosthetics and take them a step further, allowing them to become not only a tool that can mimic the actions of a hand and arm but rather a sophisticated prosthetic that would connect to the patient's nervous system and communicate with it. This is known as a neural interface.

Nerve signals still exist even in arm loss, but what was needed was a method to record these signals. Microscopic wires that pick up information from individual neurons proved to be impossible to create so a different approach was created.

Targeted Re-innervation

The MPL bionic prototype robot with two bionic arms

Using a "biological amplifier" the muscle signals were amplified thousandfold by shifting the major nerves that normally went down the arm and letting them grow into the chest instead. When you think of closing your hand, a chest section will contract and electrodes will pick up those signals to tell the prosthetic arm to move.

The brain exchanges information through neural circuits, which have receptors to sense a stimulus, report this back to the nervous system and produce an appropriate response via motor neurons which lead to movement.

A touch on the chest would actually lead to the sensation of a touch on the patient's phantom arm, even his missing fingers. Senses of hot, cold, as well as sharpness and dullness were all felt and this provided a way to restore sensation using a prosthetic hand "that feels".

A small microcomputer sits on the patient's back connected to the prosthetic which is trained by the patient's mind to move in specific directions and perform different tasks. This was the first time something like this had ever been done in the US and also the first time that a prosthetic was designed not for the average male user but for the 25th percentile female, being the lightest and smallest arm ever made.

Meanwhile, at the Applied Physics Laboratory (APL) of John Hopkins, a research team developed their own prosthetic limb called a "Modular Prosthetic Limb" (MPL) that communicated with the nerve endings using two armbands.

This project known as the "Revolutionising Prosthetics Programme is funded by DARPA, the US Defense Advanced Research Projects Agency and aims to restore near-natural upper extremity control to military personnel that lost their limbs during their service.

The "myobands" record muscle activity and wirelessly interact with the arm and hand providing improved comfort, aesthetics and motor control. As muscles activate, the prosthetic is told to operate individual fingers without using any invasive skin preparations or implanting electrodes.

The MPL is said to be capable of carrying out almost the entire range of human arm movements using more than 100 sensors in the hand and upper arm and the ultimate goal is to allow patients to feel both temperature and texture as they interact with their environment.

Applications of prosthetics

Johnny using his "osseointegrated prosthetic" with a titanium rod implanted in the bone to attach the prosthetic

Johnny Mattheny was the first person to attach a mind-controlled prosthetic directly to his skeleton after losing his arm to aggressive cancer in 2008 he underwent surgeries to prepare his arm for the MPL prosthetic.

The MPL allowed him to regain an almost complete range of motion. Johnny's goal is for his arm t be "as near natural as a human arm as possible" and noted that training to use such prosthetics is not a quick and easy process and requires continuous hours of mental exercises to perform different grips, bends, rotations etc.

Melissa Loomis, another user of the MPL who lost her arm to an infectious wound, commented on her experience:" You control your hand with your mind naturally, to me I just feel like I have a hand and move it naturally".

Rebekah Marine, the congenital amputee and fashion model known as "The Bionic Model" uses a prosthetic with two electrodes that is connected to an app on her phone.

Rebekah the Bionic Model demonstrating the gesture based prosthetic

With a simple tap, Rebekah can pick different gestures to assist her movement using the I-LIMB hand invented by David How in Bioengineering Centre of the Princess Margaret Rose Hospital in Edinburgh.

Another mind-controlled bionic known as Ipsi-hand allows for faster rehabilitation and recovery of stroke victims using a computer interface to amplify signals. By picking up signals in the left and right hemisphere of the brain which controls the right and left side of the body respectively, using an electrode-fitted headpiece.

Finally, a 53 year old patient paralysed from the neck down due to a high cervical spinal cord injury was able to use a similar neurotechnology-based device to start moving again.

All of these neural implants and smarter prosthetic designs have lead to the overcoming of limb loss and paralysis and have taken us one step closer to our human-machine hybrid fantasy.

With increasing innovation, however, comes an increasing ethical and safety risk. Since these technologies can be hacked and used maliciously, this calls for new laws to evolve concurrently with mind-controlled bionic prosthetics.

As far as Dr McLoughlin is concerned, there is far more to gain from these technologies than there is to fear.

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