Science in Popular Culture is a column by contributor Jae Bailey. In this column, Jae explores the science and technology of bionic limbs, arc reactors, and Death Stars in popular culture.
Welcome back to Part Three of the Science in Popular Culture series!
In Part One, I wrote about what it might be like for Iron Man to live with an arc reactor in his chest. This time I’ll focus on what life with a metal limb might be like for Edward Elric from Full Metal Alchemist, Marvel’s Deathlok (Mike Peterson from Agents of Shield), Bucky Barnes from Captain America: The Winter Soldier and Luke Skywalker from Star Wars.
Bionic arms and legs are currently more science fiction than science fact. Fine finger control and being able to simultaneously receive feedback from different parts of the limb is currently near impossible. However, scientists and engineers have established the basics of brain-machine interfaces and robotic limbs.
A bionic prosthetic limb has to communicate with the brain, which generates neural signals. These brain signals contain information about the intended movement. To read these signals, an array of electrodes has to be implanted into the relevant part of the brain. For movement, this is generally the primary motor cortex. Then the signals have to be decoded by a computer which then sends the translated signals to the correct motor within the limb. At the same time, sensors on the bionic limbs collect data (has the bionic hand come into contact with anything?) and transmit it into a computer. The data is translated into signals the brain can understand, and those are then fed back into the brain via a different array of electrodes implanted into sensory brain areas such as the primary somatosensory cortex.
It is reasonable to assume that all characters except Edward Elric would have had brain surgery. The largest challenge in having a bionic limb act and feel natural is understanding what brain signals trigger which movement and making sure the data from sensors is translated correctly into “brain language” and sent to the exact right place in the brain. On top of that, each brain is unique and will make its own adjustments in order to control a robotic limb which doesn’t mimic the way a human one works perfectly. However, if such challenges are overcome, the feedback from the limb shouldn’t feel too unnatural (if the computer interprets and translates the signals correctly). The number and type of sensors would dictate how likely the limb is to notice touch, heat, or cold. Since a hand numbed by anesthetics can’t keep hold of a glass of water, touch sensors would always be included in bionic hands. Temperature sensors might not be, however.
Since none of these characters are hooked up to an external computer, it is also safe to say that they have a computer implanted somewhere in their body. Most likely this computer would be located within the bionic limb, but it could theoretically be implanted anywhere.
Apart from probably housing a computer, the bionic limbs will also need to accommodate the many motor modules required for even basic movements. For the kind of fine control required for a bionic hand, an even larger number of motors is necessary. Additionally, these motors need to be powered—and for the Winter Soldier, aka Bucky Barnes, and Mike Peterson, the power those motors need to supply has to exceed standard human strength many times over. To simulate normal human strength in the shoulder/upper arm area, a bionic arm requires about eight motors—each with a peak power of ca. 1000 watts or 1.3 horsepower. For comparison, a desktop computer uses only about 65 watts; as you can imagine, the heat output and the weight of a bionic arm with super-human strength will soar out of control quickly.
The use of metal as the material of choice for super-human bionic limbs is therefore not only to provide stability and durability; metal is an exceptionally good heat conductor. The heat generated by those motors can be conducted toward the surface, where the surrounding air can cool the limb.
Bucky and Luke’s bionic arms and Mike’s bionic leg will be cool to the touch when they’re at rest but will heat up considerably when they’re fighting or doing any heavy lifting. This could cause some significant discomfort where the limb joins their body. For Luke Skywalker, it is possible that some additional heating or cooling units were installed to keep the flesh adjoining parts roughly at body temperature, but it is unlikely that Hydra’s scientists would have cared about comfort.
Additionally, the amount of power the bionic limbs require, especially for battle, means that each limb will also need to come equipped with batteries. Since lightsabers in the Star Wars universe never seem to run out of battery power, it’s safe to say that battery technology in that universe is significantly more advanced than currently on Earth. However, Mike and Bucky would need to have powerful and long-lived batteries to supply all the motors in their limbs with enough power—think of the kind of batteries that power electric bikes, except better. Even if we assume their batteries are as advanced as their cybernetics, it’s likely they might need to charge or exchange the batteries in their limbs eventually.
The technology in Edward Elric’s times (alternate early twentieth century) is less advanced than modern day. Most importantly, there are no computers. However, it is also highly unlikely that Ed had brain surgery—in the Full Metal Alchemist universe the prosthetic limbs hooks up directly to the nerve ending in people’s stumps. The computer is unnecessary, as the brain can send the signals to the arm directly. Batteries are available in this universe, and although early twentieth century high-power batteries were large, we can assume in the Full Metal Alchemist universe they are considerably smaller.
Ed’s leg and arm are both made of metal and it is mentioned that the arm is heavier than a flesh arm would be. Mike and Bucky’s prosthetic limbs are equally likely to be far heavier than if they were made out of flesh. Since they both have versions of super-soldier serum it is likely that their bodies were able to adjust through strengthening their muscles elsewhere. Additionally, some of their bones may have been strengthened to cope with additional load from the metal limbs. In contrast, Ed doesn’t have that advantage. He had to train his muscles the old fashioned way and would likely still suffer muscle pain and soreness due to the additional weight of the arm in particular. Meanwhile, Luke’s arm is the one most likely to have been optimized for comfort.
I believe all of them would likely appreciate the occasional back and/or hip massage though.