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I am sure you have seen or heard of artificial hand or artificial leg especially in Paralympic games. This artificial replacement of missing body parts such as teeth, legs, arms etc. is regarded as prosthetics.
Below are some key points about prosthetics. More details can be found in the main article
The latest advancement in prostheses are the myoelectric prosthetic limbs which give amputees control over their artificial hands or legs through the muscle signal in the remaining part of that missing hand or leg.
Prosthetic devices are custom made and can last 2-5 years depending on activity level, growth and age. There is a need for yearly replacement when it is used on children due to their body growth.
Modern prostheses are commonly made from tough yet lightweight plastic materials (polyethylene, polyurethane, and polypropylene), carbon fiber and metals like titanium and aluminum.
The residual body part needs to heal completely before prosthesis can be used.
Direct bone attachment, stump-socket and the suspension mechanism are the common methods used for attaching prosthetic devices to the human body
Man has been improvising since time immemorial. The use of prosthesis dates back to the 15th century but at that time most of the devices were just for cosmetic purposes. Functional prostheses is believed to have started by a man named Ambroise Pare who introduced the socket mechanism which is still in use till date.
Nowadays, prostheses are made from lightweight materials instead of the traditional heavy metals and woods. Technological advancements such as biometrics, bionic implants, 3D printing etc. have also contributed greatly to the manufacture and use of these devices.
The recent improvements in prostheses include: myoelectric prostheses, i-limbs which enable the wearers change hand grips and carry certain weights, the Power Foot and many more.
Now that you have a little penetration into what prosthetics entail, let us talk about the types of prosthesis and their working principles.
Interestingly, modern cosmetic prosthetic limbs are equipped with features such as veins, hairs, freckles and even tattoos. They are made to match the skin tone of the wearer. It is also worthy to note that some of these passive prostheses still offer some basic functions such as pushing and light grasping.
myoelectric is the term for electric properties of muscles.
Is there anything electric in the human body? Yes and you can read more about the human body as an electrical system in this post by 
Myoelectric prosthesis involves the use of electrical signals generated from the muscle in the residual body part to control the artificial limbs. This device at its most basic consists of some electrodes, an amplifier circuit and a relay system. The electrodes are used to detect the Electromyographic (EMG) signals (electrical signals generated by muscle activity) from the residual limb. These signals are then amplified and conveyed by the amplifier circuit to the relay system which controls the electric motors that drive the robotic hand or leg. These components are battery-powered and are concealed within the artificial part.
wikimedia creative commons: Myoelectric control of ankle exoskeleton
A major challenge of this arrangement is that it does not allow simultaneous movement of joints and ineffective when the level of amputation is high
How are these devices interfaced with the human body? Let’s find out
This method simply involves fastening socket to the residual limbs through straps, sleeves or belts. A silicone liner or co polymer material is usually worn on the stump to reduce the friction and heat between the socket and the skin.
Ossoeintegration obviously eliminates the adverse effect inherent in the use of stump-socket method but it sure leaves its own trail. The implant used sometimes cause different skin infections.
Like most tech devices, work is still ongoing to improve the current prosthetic devices. Despite the recent advancement in prosthetic limb, one common feedback from its users is that they feel as though they are wearing a tool and would not know when somebody touches their artificial part without them looking. As a result of this, many neuroscientists and biomedical engineers have developed prototypes of prosthetic limbs with a sense of touch. Wow, right? Yeah.
One of such prototypes is the near-natural bionic hand developed by the Defense Advanced Research Projects Agency [DARPA] in 2015. In their demonstration, the prosthetic hand was wired directly to the sensory cortex (the section of the brain that identifies sensation) of a 28 years old paralyzed volunteer. With his eyes closed, the volunteer was able to say the exact finger touched within seconds. The researchers concluded that this was just alpha testing and a better version will be fully developed within few years.Similarly, a company known as Rewalk recently brought to the market, a wearable robotic suit prototype called Restore that can help people with paralysis to stand up and walk.
The Restore transmits power to key joints of the legs with cable technologies powered with software
We cannot explore it all. Let me draw the curtain here.
The truth is that missing body parts can never be fully replaced but anyone missing one part or the other would agree that this seeming half bread is better than none. Prosthetic devices have really saved a lot of people from the crushing weight of amputation.Despite some of the challenges highlighted above, many amputees would still prefer to get one. The prosthetic revolution has begun and one can say with certitude that the coming years will be brighter.
In this article, we have seen the different types of prosthetic devices and the methods of attaching them to the human body
Thank you for taking time to read this article
See you next time.
Prosthetics
Myoelectric Prosthetics 101
What is osseointegration
Harnessing thought to defeat paralysis
Bionic hand can feed physical sensations directly to the brain
Jonathan T., Kerstin H., Lars H. & Rickard B. (2010). Osseointegrated Titanium implants for limb Prostheses Attachments: Infectious Complications. Clinical Orthopedics and Related Research. 468(10): 2781-2788
Elaine A.,Biddiss & Tom T.C. (2007). Upper limb prosthesis use and abandonment: A survey of the last 25 years. Prosthetics and Orthotics International. 31(3): 236-257
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