The Evolution of Prosthetics

DO WE BECOME WHAT WE DO, OR DO WHAT WE ARE?

Technological advancement has driven our adaptive nature, subsequently allowing us to adapt nature to our means and desires. Analyzing this progression from archaeological discoveries into modern innovations, the trend appears: technology approaches closer to us until inevitably manifesting within us. I have collected prosthetic hands, portraying how technology attempts to close the gap, replacing the natural. We must acknowledge that nature still remains well beyond our comprehension and before altering our implicit memory forged by it, we must fully appreciate its value.

I began by examining prosthetic arms and observed their technological progression. Initially, functionality replicates the natural form. Having produced an acceptable replacement, newer designs pursue ornateness while retaining the same performance. Some later designs even seek to minimalize the arm to is simplest function, an appendage for gripping. As prosthetics shift to modern technologies and manufacturing, it is interesting to note how their mechanics have advanced. At the moment, all the designs which mimic the human arm fail to deliver the same range of motion in their joints, especially at the knuckles, as their biological inspiration. The lack of biomechanics in their design inevitably prevents the same interaction with our world as a natural limb.

Some scientists have opted for biomimetic designs which offer far more mobility and associative function with the existing anatomy. While they are rare and currently prototypes, they are gaining traction in their respective fields. One such example that carried forward my project was Zhe Xu and Emmanuel Todorov’s prosthetic arm which they built at the University of Washington. Bones are 3D-printed to softened versions of their biological curvatures. They considered the biomechanics of these geometries to understand how the joints work. While some bones are conjoined for simplicity, the overall function retains accuracy to a real arm. Muscles and tendons are also simplified but, in this case, can perform the same motions as their biological counterparts. By doing this, Xu and Todorov iteratively discovered the shortcomings of existing prosthetics, “During this process, we first identified two crucial constraints that have been limiting the development of anthropomorphic robotic hands: the lack of properly translated engineering knowledge of the human hand and the restrictions caused by conventional mechanical joints.”

1 The arm was then mechanized using electromyographical measurements which were translated to electronic controls through a computer.2

Furthering my admiration of the human hand, I studied how humans had descended through lineages of evolving species. It is evident how this trend was not linear and how nature had several periods of experimentation and adaptation to culminate at the form we take on today: The evolution of modern planning capabilities can be investigated by analyzing the decision steps used to produce ancient tools. There are, for example, many different ways of making stone artifacts. Over the last 200,000 years a variety of reduction techniques in different combinations were used to make stone tools. This resulted in different techno-complexes, but all with the same degree of complexity.3

Various iterations of technological advancement likely enabled cultural traditions and in turn a strengthened relationship between the mind and the hand. Additionally, these practices may have also driven a heightened intelligence to generate further technology, “When considering when and how modern behavior developed, it is essential to take into account how the brain could have evolved to support modern capabilities...Evolutionary biology and neuroscience studies suggest that hominin symbolic com- municative capabilities co-evolved with the brain, resulting in some parts of the brain becoming proportionally larger.”4 Cultural processes such as tool-making likely allowed more efficient expenditure of energy and therefore more time to create better tools. This positive feedback may have contributed to increased dexterity and intelligence. In order to familiarize myself with the arm’s natural mechanics, I first studied several x-rays and images from anatomical diagrams. From here, I analyzed digital models and traced over them to consolidate the general contours of the arm bones, revealing the function behind their form. Using my newfound insight, I carved anatomically accurate bones at a 1:1 scale from wood. Conveniently, this manual learning corresponded well with my project just as it had for Xu and Todorov:

Although there is still no consensus about the definition of human hand dexterity, the biological variations found in length of bones, branching of tendons, and insertion of muscles all suggest that dexterity is a highly personal property that is not only shaped by individual’s motor control ability, but also inherently bonded to the unique biomechanical characteristics of its very owner, and therefore can not be generalized without considering the biological difference.5

I started to appreciate what I was able to do and create with my own hands and how significant our dexterity and precision enables us to build the world we live in.

A model arm, while anatomically functional, needs power and control to operate as a prosthetic. To control the prosthetic by the user’s own intent, there must be a correlation of mind to body. Electroencephalography (EEG) and electromyography (EMG) have existed for a several decades but only relatively recently are being used in prosthetics, whereby neurological measurements are translated into electronic controls through computers. These electronic controls correspond to mechanical actuators in an advanced prosthetic.

Amputees often note the presence of a phantom limb, the vague memory of an arm of leg that was lost yet still feels as if it was there when they think of moving it. This strongly relates to implicit memory, “Examples of implicit memory are: perceiving a picture or a face more quickly after it was seen, though the person may deny that the face or word was familiar (perceptual priming); learning a repeated, complex motor sequence, even though the individual may not be aware of the sequence or that it was repeated (procedural memory).”6 This implicit memory may still prove valuable though, because existing neurons can be connected to a prosthetic with EMG and possibly sup- port by EEG, providing motor control comparable to the natural limb.

Altogether, I used my research to create my final drawings based on the past versus present and dystopian versus utopian futures for humanity as technology continues to shape us. “As a result, technologies will vary according to the task at hand, the possible solutions known to the population, the cost of failure, as well as myriad other factors. In turn, and of great interest to the archaeologist, technologies will often reflect aspects of the biology and/or culture of their creators.”7 The future beyond the natural is only possible through appreciating how far it has brought us, or it will be our undoing.

1. Zhe Xu and Emmanuel Todorov, “Design of a highly biomimetic anthropomorphic robotic hand towards artificial limb regeneration,” IEEE International Conference on Robotics and Automation (ICRA) (2016): 8, accessed May 3, 2020, https://homes.cs.washington.edu/~todorov/ papers/XuICRA16.pdf

2. Ibid., 2.

3. Sarah Wurz, “The Transition to Modern Behaviour,” Nature Education Knowledge 3, no. 10 (2012): 15, accessed May 3, 2020, https://www. nature.com/scitable/knowledge/library/the-transition-to-modern-behavior-86614339/

4. Joseph V. Ferraro, “A Primer on Paleolithic Technology,” Nature Education Knowledge 4, no. 2 (2012): 9, accessed May 3, 2020, https:// www.nature.com/scitable/knowledge/library/a-primer-on-paleolithic-technology-83034489/.

5. Xu and Todorov, “Design of a highly biomimetic anthropomorphic robotic hand towards artificial limb regeneration,” 1.

6. Morris Moscovitch et. al., “Functional neuroanatomy of remote episodic, semantic and spatial memory: a unified account based on multiple trace theory,” Journal of Anatomy 207, no. 1 (2005): 40, accessed May 3, 2020, https://www.ncbi.nlm.nih.gov/pmc/articles/ PMC1571502/

7 .Ferraro, “A Primer on Paleolithic Technology,” 9.