Bionic Limbs, The End of Disability

By: Amrutha Tummala, Tech Blog Editor

Image by stepintofuture - Pixabay

In 2012, a drummer named Jason Barnes was cleaning the exhaust vent of a restaurant when 22,000 volts of electricity shot through him. The next thing he remembered was waking up in the hospital with burns all over his body. After half a dozen surgeries, Jason ruefully agreed with the doctors that his right hand needed to be amputated--one of the worst things that can happen to a musician.

It should have been the end of his musical career, but Barnes was determined to continue playing the drums and even made his own prosthetic arm. Intrigued with Jason’s accomplishments, Eric Sanders, his music teacher, showed Jason a video of some work done by Gil Weinberg, an engineer from the Georgia Institute for Robotics and Intelligent Machines. Weinberg had been developing robot musicians which listened to the music being played and improvised an accompaniment to go with it. Jason decided to email Weinberg to see if they could work together. Weinberg agreed.

The product of their collaboration was a robotic drumming arm. It was a myoelectric unit that relied on Jason’s muscles and grip but also listened to the music being played and accompanied it. The arm would hold two drumming sticks, one controlled by Barnes and the other controlled by the arm itself. What seemed like the end of Jason Barnes’s musical career might have only been the beginning.

Overview

Prostheses, or artificial limbs, are used to replace missing limbs. The types of prostheses a person can use depends on a variety of factors, including the cause of the amputation or limb loss and the location of the missing body part.

People have been using basic artificial limbs for centuries. Wooden legs, hooks for hands…. These replacements gave back basic movement and function but were often uncomfortable, difficult to use, and simply unattractive. Now, researchers are working to develop better options that are lighter, smaller, easier to control, and more affordable and lifelike. The new generation of prosthetics unites with bionic technology and diverse fields of study such as biotechnology, medicine, electronics, and computing. This field, which integrates mechanical devices with biological organisms, is known as biomechatronics.

It may be tempting to imagine that bionic limbs give the wearer superhuman abilities like the Terminator, but as of now, scientists are only working to mimic the functionality and movement characteristic of a healthy human limb. It sounds simple--after all, a task such as picking up a glass is trivial for us. But pause for a moment and think about the underlying processes that happen when you pick up a glass. First, you bend your elbow so that your forearm is in the correct position close to the glass. Then, you rotate your forearm and wrist at the correct angle so that your hand can actually reach the glass. After that, you need to wrap your fingers around the glass, putting enough pressure so that you have a firm Image by Hwee Quek - Unsplash

grip, but not so much pressure that the glass cracks within your grip. A robotic arm needs to accomplish all of this easily and quickly. It is the interaction between the brain and the body that researchers around the world are trying to mimic in their bionic technology. There are a number of bionic technologies that are beginning to replicate the functionality of the original limb. Others are still in the research and development stages but show great promise.

Myoelectric Limbs

Upper-body prostheses used to be body-powered, using cables to attach to the body and relying on body movements to move the cables that controlled the artificial limb. It was tiring and unnatural. Myoelectric limbs are powered by batteries and use an electronic system to control the movement of the limb. The prosthesis is custom-made and attaches to the residual limb with suction technology. Electric sensors detect even the slightest muscle, nerve, and electrical action in the limb. After the muscle activity is transmitted to the surface of the skin, it is amplified and sent to microprocessors. They process the information and then control the movements of the bionic limb. The user can control the prosthesis much like an ordinary limb, varying the intensity of their muscle movements to control strength, speed, and grip. Anything that cannot be controlled by muscle movements can be controlled with switches. Sensors and motorized controls are also implemented into the bionic limb, allowing for better dexterity.

Two advantages of myoelectric limbs are the auto-grasp function and its ability to mimic the looks of a natural limb. The auto-grasp function automatically changes the tension when it detects changes in the circumstance, such as holding a glass as it is being filled with water. The cons of this technology are that the battery and motor inside make the bionic limb heavy, it is expensive, and there is a slight delay between the wearer sending a command and the computer inside the limb processing it and performing the action.

Osseointegration

Osseointegration involves direct contact between the bone and the surface of a synthetic implant, usually titanium-based. A skeletally integrated titanium implant is connected through an opening in the residual limb to an external prosthetic limb. Because of this direct connection between the bone and the prosthesis, the limb provides better stability and control, uses less energy, is more comfortable because it does not use suction, and puts the weight on other bones, reducing the risk of degeneration and atrophy.

Image by ThisIsEngineering - Pexels

The procedure involves two surgeries. The first operation includes the insertion of titanium implants into the bone. Often, extensive revision of soft-tissue is also needed. The second operation happens six to eight weeks later, involving refinement of the stoma (the opening in the residual limb) and the attachment of the hardware that connects the titanium implants to the prosthetic. Over time, muscle and bone will grow around the implanted titanium. The external prosthetic limb can be attached or removed in a matter of seconds. The bionic limb has a greater range of movement and control because it is attached directly to the bone. In some cases, it has allowed the wearer to distinguish between surfaces, such as the difference between carpet and wood.

Many recipients of osseointegration technology have been up and walking within weeks of the operation and have regained much of their old quality of life. They say that it almost feels like a real limb.

The disadvantages of osseointegration technology are that it is expensive and incompatible with many amputees.

Mind-controlled Bionic Limbs

Mind-controlled bionic limbs are highly advanced because they can be integrated with body tissues including the nervous system. They can respond to commands from the central nervous system and therefore can closely replicate normal movement and functionality and instantly trigger movements with little delay. There are several different procedures and technologies that are in the research and development phase.

Targeted muscle reinnervation is a surgery that uses nerves remaining after amputation and impulses from the brain to control the artificial limb. During the procedure, nerves that control the joints from the missing part of a limb are transplanted into muscle tissue in the residual limb, allowing for a more natural thought process when controlling the prosthetic limb. Brain impulses are linked to a computer inside the prosthesis that directs motors to move the limb. Some patients who undergo this surgery can not only move their new limb but also feel some sensations with it.

Implanted myoelectric sensor technology involves implanting sensors directly into the limb muscles but does not transplant nerve tissue from one part of the body to another. The implantation requires only a fifteen-minute operation in which the sensors are placed into the tissue via small incisions one centimeter long. The sensors do not need to be replaced after being implanted unless they are damaged. Implanted myoelectric sensor technology does not require complex surgery, functions well in real-life scenarios, and can work for an extended period of time.

Some mind-controlled bionic technologies implant tiny sensors into parts of the brain that control movement and feeling, thus allowing the user to know when their hand is opened or closed without looking or being able to tell when their finger is being touched. Dr. Paul Marasco, a biomedical engineering researcher at Cleveland Clinic, devised a system with his team that restored the feeling of movement by having the bionic limb send signals to a computerized control system outside of the body. It then made a small robot worn on the residual limb send vibrations to the muscle, telling the brain what the bionic limb is doing.

Though the methods by which bionic limbs achieve their goals may be different, one thing is clear: bionic technology has already accomplished so much, and it is just the beginning. Scientists are still yet to achieve the same level of functionality that normal human limbs have with bionic limbs, but when they do, we can be sure that it will be the end of physical disability.