Mariam Saleh | Staff Writer
In our current world, people are defined by the work produced by their hands or legs. So, our limbs play a critical role in shaping our future and value in society. But despite that, the USA and several countries in Europe witness around 295,000 amputations each year, with approximately 3.18 million amputees in total, posing critical psychological distress and health risks to these patients, and threatening to lose their occupations and positions in The workplace or even their independence. Prostheses have been there for a long time, enabling these patients with at least some compensation for their lost limbs. However, despite the significant advantages of prosthetic limbs, they are still lacking in terms of patient control and sensation. This called for the development of more refined technology with almost natural motor and sensory limb functions and thus an “active and sensorized prosthetic device,” the bionic limb.
The term bionics comes from the combination of biology and electronics, implying the connection between the individual’s nervous or muscular system and electronic devices. But for this connection to be successful, three interfaces must be considered. The first mechanical interface has to do with how the bionic limbs are attached to the body. Our tissues across our bodies are variable in terms of surface, stiffness, and compliance. To achieve proper mirroring of the prosthetic limb and the biological limb, the former must be attached via synthetic skins with varying stiffness, developed using a mathematical model of the biological limb and imaging tools. This skin can also be embedded with sensory and smart materials, enabling greater control and maneuverability. When considering these factors, bionic limbs can become so comfortable.
The second interface that must be considered is dynamic, meaning how the bionic limb moves like flesh and bone. To construct this, it is important to first understand human motions, such as standing, walking, running, or any type of motion that the limb must perform. It is important to understand what the muscles are doing and how they are controlled by the spinal cord, then study the forces and powers to carry out each stage of each motion, including heel-strike, mid-stance, and walking stride as some examples. This allows for stiffness modulation and positive power assist.
The third interface is electrical, and it covers how bionic limbs communicate with the nervous system. This occurs in what is known as bidirectional control: electrodes are attached to the residual limb above the level of amputation to measure the electrical pulse of the muscles, which corresponds to the motor neuronal signals carrying messages from the brain to the muscle, and communicated to the bionic limb. In turn, devices implanted in the artificial limb are connected to the remaining nerves or muscles above the amputated part and can deliver sensory feedback to the nervous system. For this to happen, the signals must be converted to electrical impulses to be received and interpreted by the brain; this was achieved by the construction of artificial nociceptors, which are receptors that detect harmful stimuli. These will allow the flow of natural sensation between the person and the artificial limb, making the bionic limb close to real flesh and bone.
We are rapidly moving towards a future where bionic limbs don’t only move like normal limbs, but also feel like our own flesh and bone. However, it is important to understand that there may be certain limitations associated with such technology. Bionics is rather an emerging field, and the long-term research surrounding it, about the behavior of the electrodes in the body and their safety and functionality, is still not known and under investigation in clinical trials. Not only that, but the presence of these microelectrodes inside our bodies makes them susceptible to stress-induced mechanical failure, which can lead to errors and malfunctioning. The consequences of this are still unknown and may require additional research and continuously advanced treatments. One other risk is that the nociceptors found in the bionic limbs may be prone to degradation by UV radiation. But this could be solved by attaching UV-damage sensing nociceptors, which imitate the same behaviors of a major nociceptor in terms of threshold, relaxation, and sensitization, and which implies that external stimuli under a certain threshold will not elicit a response to maximize efficiency when exposed to risk.
However, the field of bionics does not escape ethical concerns. It is true that such technologies overcome the gaps between disability and ability, and that they help disabled people, specifically amputees, regain their limb control and thus achieve higher quality of life. However, with this rapid development in technology, one cannot help but wonder about the boundaries of expanding beyond natural limitations and relying too much on a technology that might reflect in a beneficial way or an extremely dangerous way. Another ethical issue is the idea of invading a person’s privacy by placing microelectrodes inside their bodies. And that’s why the patient must be informed about the risks and effects of incorporating such devices, and they must consent. An alternative to these concerns can include tissue engineering and limb regeneration. Tissue engineering is an interdisciplinary field that combines biological, chemical, and engineering principles to repair or regenerate tissues, including human limbs. This field provides a lot of promise in treating tissue damage across the body, however, it still requires a lot of research before it can be utilized and integrated into treatment.
I presented here only an overview of bionic limbs and their huge potential to transcend disability, giving individuals with limb loss hope and a chance to move like normal, but it is also important to understand the risks behind such technology and the ethical concerns around it. It is both terrifying and astounding how technology can be used, and there is only a fine line between when technology is beneficial and when it is dangerous, and we must be able to recognize it. Otherwise, where is the limit to advancing such technologies? Would this lead us to build full human cyborgs and lead our steps toward the abyss?
Sources:
Bumbaširević, M., Lesic, A., Palibrk, T., Milovanovic, D., Zoka, M., Kravić-Stevović, T., & Raspopovic, S. (2020). The current state of bionic limbs from the surgeon’s viewpoint. EFORT open reviews, 5(2), 65-72. DOI: https://doi.org/10.1302/2058-5241.5.180038
Herr, Hugh. “New bionics let us run, climb and dance.” TED. YouTube. 29 Mar, 2014, New bionics let us run, climb and dance | Hugh Herr | TED (youtube.com)
Laurencin, C. T., & Nair, L. S. (2016). The Quest toward limb regeneration: a regenerative engineering approach. Regenerative biomaterials, 3(2), 123-125. DOI: 10.1093/rb/rbw002
Pasluosta, C., Kiele, P., Čvančara, P., Micera, S., Aszmann, O. C., & Stieglitz, T. (2022). Bidirectional bionic limbs: A perspective bridging technology and physiology. Journal of Neural Engineering, 19(1), 013001. DOI: 10.1088/1741-2552/ac4bff