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Everything You Need To Know About Bionic Limbs

What if you were told that our brains can speak to artificial limbs (fitted to amputees) and that these limbs can respond to the instructions of the brain by mimicking what the human body would do if the natural limb had been in place. Many would put this statement aside considering it to be a science-fiction fantasy, but the truth is that the business of creating stand-ins for missing body parts is not something entirely new but something that is growing and gaining popularity rapidly. The entire process of making this possible revolves around the designing and implementation of bionics.

Till almost the last decade, people were attempting to replace lost body parts with the use of man-made materials. However, the latest technologies enable you to connect these prostheses to the brain. Going by the technical definition, bionics is a terminology that refers to the flow of concepts from engineering to biology and vice versa [1] . It can be a complicated understanding for the common man.

However, in simple terms, the working methodology of bionic limbs can be understood as electrical impulses from the brain that reach the base of the leg wherein a pair of sensors are embedded in the muscle tissues connecting the neural dots and then wirelessly transmitting the signal to the bionic foot [2] .

Read on to gain more insight about bionic limbs.

What Are Bionic Limbs?

Bionic limbs have been created with the general rule that they should begin to work as soon as you think they need to, and quite literally so because they operate on the electrical signals sent from your brain. The bionic limb has wireless transmitted implanted in the muscles around them, so as soon as your brain has the idea to move your arm, the bionic prosthetic gets into action and makes it happen [3] .

Under normal circumstances, your brain controls the muscles in your limbs by sending down electrical commands through the spinal cord and then through peripheral nerves to the muscles. However, when a limb is amputated, the signals when sent out from the nerve endings reach a dead end (that is where the limb once was). This is where bionic prosthetics get its developmental idea. It has been developed with the idea of receiving signals (not letting them reach a dead end) and also reacting to these signals [4] .

The Technology Behind Bionic Limbs

The replication of the interaction between thought, action and response, which is otherwise quite obvious with a natural limb, is what makes researchers strive hard to achieve and implement the perfect bionic prosthesis.

Although several forms of techniques have been used (some still under research) to create the best bionic prosthesis, the most used one is a procedure called Targeted Muscle Reinnervation (TMR). In this procedure, the amputated nerves are reattached to a healthy, functioning muscle [5] . For example, in the case of an amputated arm, the nerve endings are attached to the chest muscle. The bionic arm is designed to respond to the chest muscle's movement. This creates a pathway between the brain signals and the newly created bionic limb.

High-end prosthetics are made using advanced plastics and carbon-fibre composites [6] . The materials used are lightweight and far more conductive in the interaction with the human body. The bionic limbs are carefully crafted so that they can perform more subtle motions associated with human mobility. The high-limbs are developed such that they are capable of automatically adapting their functionality during different tasks, such as walking or gripping.

Special sensors are surgically inserted into the muscles around the amputated region. This helps the prosthetic limb to receive the brain's signals. Apart from being connected to the neural pathways, these sensors also wirelessly transmit the brain's signals to the prostheses [7] . One would wonder how a muscle contraction is not experienced by the wearer at this stage. Well, it is so because the signals reach the prosthetic limb even before the muscles are able to register that the brain had sent a signal. The entire process perfectly replicates a natural brain-to-limb movement [8] .

What Is Targeted Muscle Reinnervation (TMR)?

TMR is a surgical procedure that uses nerves that remain after an amputation to use the impulses from the brain to control how the artificial limb works. The surgical procedure involves reattaching nerves that control the joints from the missing area of the limb into muscle tissue in the residual limb. This procedure allows for a more natural thought process and enables the prosthesis to be controlled quite similar to myoelectric control [9] . The brain impulses get linked to a computer in the prosthesis that in turn directs motors to move the limb.

Recent Advances In The Creation Of Bionic Limbs

  • Myoelectric limbs

Myoelectric limbs [10] are externally powered (using a battery and an electronic system) to control movement unlike the traditional technique of using cables and harnesses to attach the prosthesis onto the human body. Suction technology is used to attach the custom-made prosthesis to the residual limb [11] . Electronic sensors exist that can detect even the slightest muscle, nerve or electrical activity in the remaining limb. This activity is then transmitted to the surface of the skin where it undergoes amplification and is then sent to microprocessors.

The information is then used to control the movements of the artificial limb. Varying the intensity of the movement of the existing functional muscles allow the wearer to control various aspects of the bionic limb such as strength, grip and speed. Myoelectric limbs can be replicated to look like a natural limb.

However, the battery and motor present inside myoelectric limbs make them heavy and expensive. Research also shows that there could be a slight delay in the process of the user sending a command followed by the computer processing it and turning into action [12] .

  • Osseointegration

This procedure involves creating direct contact between living bone and the surface of a synthetic implant [13] . The following are some of the advantages of a direct connection between the prosthesis and bone:

  • Greater stability and control

  • Reduction in the amount of energy expended
  • Does not require suction for suspension
  • Weight-bearing is balanced such that there is no degeneration

Procedure [14] : The first step is the insertion of titanium implants into the bone. The second stage includes the refinement of the stoma and the attachment of the hardware that connects the implant to the external prosthetic leg. When bone and muscle begin to grow around the implanted titanium on the bone end, a functional bionic leg is created. The prosthesis created this way has a greater range of movement and control.

However, these are quite expensive and also not suitable for many types of amputees.

  • Mind-controlled Bionic Limbs

Mind-controlled bionic limbs are those that can be integrated with the body tissues (including the nervous system) [15] . They are the most advanced form of bionic limbs such that they are capable of responding to commands from the central nervous system. This feature has made these bionic limbs closely replicate normal movement and functionality. It can also trigger the desired movement with far less lag time. Research is still underway to attain advanced information about this form of bionic limbs.

  • Implanted myoelectric sensor technology

Researchers have created a mind-controlled prosthetic leg that makes use of implanted myoelectric sensor (IMES) technology. The sensors are implanted directly into the patient's limb muscles [16] . This does not require transplantation of the nerve tissue from one part of the body to another. The sensors are placed into the tissue via incisions that are just 1 centimetre long. The user will no longer need to be consciously alert about his or her movements as their unconscious reflexes are automatically converted into myoelectric impulses that control their bionic prosthesis.

In this procedure, an array of electrodes are clinically implanted onto the man's sensory cortex (region of the brain responsible for identifying tactile sensations such as texture and pressure). Arrays are also placed on the person's motor cortex (part of the brain that directs body movements). Wires from these arrays are connected externally to a mechanical limb. The limb contains complex torque sensors that are capable of detecting pressure and converting the sensations to electrical signals. These signals are routed back to the arrays on the patient's brain, thus stimulating the sensory neurons in the brain, eventually allowing the sensation and feeling of each finger to be felt by the patient.

Cosmetic Improvements For Bionic Limbs

With technology being uplifted on a daily basis, artificial limbs are gaining an all-new look. The emergence of computer-aided design, along with 3D printing, has paved the path for the creation of limbs that are a perfect fit for the wearer. Also, with time, these are said to become more affordable.

Most of the present day bionics have a look that is more fictional than real. Researchers are working towards the creation of more realistic appliances. If the results of current research are to be observed, it can be seen that the prosthesis made are anatomically of the perfect shape and mirror the form of the wearer. Such prosthesis is also designed to match the skin colour, freckles, birthmarks, tattoos, fingerprints, fingernails, veins and hair. These life-like creations are made using a range of silicones [17] . The prosthetic limbs are covered using a variety of methods such as stretchable skins, suction, adhesive, form-fitting or a skin sleeve.

On A Final Note...

Although we are uncertain about how the future would look at the differential lines between human and machine, at least the present day bionic limbs are just medical devices that are designed to restore function and provide the amputees with a better quality of life. In spite of being impressively futuristic, bionic limbs are yet to be able to fully replicate the complexity, functionality and range of movement of a normal human limb.

View Article References
  1. [1] Dickinson M. H. (1999). Bionics: biological insight into mechanical design.Proceedings of the National Academy of Sciences of the United States of America,96(25), 14208–14209.
  2. [2] Sensky T. (1980). A consumer's guide to "bionic arms".British medical journal,281(6233), 126–127.
  3. [3] James, R., & Laurencin, C. T. (2015). Regenerative engineering and bionic limbs.Rare metals,34(3), 143-155.
  4. [4] Dickinson M. H. (1999). Bionics: biological insight into mechanical design.Proceedings of the National Academy of Sciences of the United States of America,96(25), 14208–14209.
  5. [5] Zuo, K. J., Willand, M. P., Ho, E. S., Ramdial, S., & Borschel, G. H. (2018). Targeted Muscle Reinnervation: Considerations for Future Implementation in Adolescents and Younger Children.Plastic and reconstructive surgery,141(6), 1447-1458.
  6. [6] Thesleff, A., Brånemark, R., Håkansson, B., & Ortiz-Catalan, M. (2018). Biomechanical Characterisation of Bone-anchored Implant Systems for Amputation Limb Prostheses: A Systematic Review.Annals of biomedical engineering,46(3), 377–391.
  7. [7] Weir, R. F., Troyk, P. R., DeMichele, G. A., Kerns, D. A., Schorsch, J. F., & Maas, H. (2009). Implantable myoelectric sensors (IMESs) for intramuscular electromyogram recording.IEEE transactions on bio-medical engineering,56(1), 159–171.
  8. [8] Ciancio, A. L., Cordella, F., Barone, R., Romeo, R. A., Bellingegni, A. D., Sacchetti, R., … Zollo, L. (2016). Control of Prosthetic Hands via the Peripheral Nervous System.Frontiers in neuroscience,10, 116.
  9. [9] Kuiken, T. A., Barlow, A. K., Hargrove, L., & Dumanian, G. A. (2017). Targeted Muscle Reinnervation for the Upper and Lower Extremity.Techniques in orthopaedics (Rockville, Md.),32(2), 109–116.
  10. [10] Chadwell, A., Kenney, L., Thies, S., Galpin, A., & Head, J. (2016). The Reality of Myoelectric Prostheses: Understanding What Makes These Devices Difficult for Some Users to Control.Frontiers in neurorobotics,10, 7.
  11. [11] Sanders, J. E., Harrison, D. S., Myers, T. R., & Allyn, K. J. (2011). Effects of elevated vacuum on in-socket residual limb fluid volume: case study results using bioimpedance analysis.Journal of rehabilitation research and development,48(10), 1231–1248.
  12. [12] Carey, S. L., Lura, D. J., & Highsmith, M. J. (2015). Differences in myoelectric and body-powered upper-limb prostheses: Systematic literature review.Journal of Rehabilitation Research & Development,52(3).
  13. [13] Al Muderis, M., Lu, W., & Li, J. J. (2017). Osseointegrated Prosthetic Limb for the treatment of lower limb amputations.Der Unfallchirurg,120(4), 306-311.
  14. [14] Tillander, J., Hagberg, K., Hagberg, L., & Brånemark, R. (2010). Osseointegrated titanium implants for limb prostheses attachments: infectious complications.Clinical orthopaedics and related research,468(10), 2781–2788.
  15. [15] James, R., & Laurencin, C. T. (2015). Regenerative Engineering and Bionic Limbs.Rare metals,34(3), 143–155.
  16. [16] Pasquina, P. F., Evangelista, M., Carvalho, A. J., Lockhart, J., Griffin, S., Nanos, G., … Hankin, D. (2014). First-in-man demonstration of a fully implanted myoelectric sensors system to control an advanced electromechanical prosthetic hand.Journal of neuroscience methods,244, 85–93.
  17. [17] Lucarotti, C., Oddo, C. M., Vitiello, N., & Carrozza, M. C. (2013). Synthetic and bio-artificial tactile sensing: a review.Sensors (Basel, Switzerland),13(2), 1435–1466.

    Read more about: limbs prosthetics
    Story first published: Wednesday, May 8, 2019, 13:30 [IST]
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