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Intuitive Prosthetics

INTRODUCTION

As the human race progresses, so does our curiosity. We invent new mechanical devices

to make our lives easier; or we synthesize new medicines to prolong our health. These advances

open new doors and opportunities and ultimately allow us to explore our own capabilities.

Arguably the most important fields of study are those which affect us, human beings,

directly; fields pertaining to human biology and chemistry. By learning more about the biology

of humans we are able to improve our bodies more so than natural mutations would allow for.

For example, LASIK eye surgery, which was only optimized for commercial world-wide use in

the late 1990’s, uses laser surgery to reshape the eye’s cornea and effectively repair damaged

vision. LASIK is a permanent alternative to other vision-correcting methods such as glasses or

contacts. It has improved the quality of life for millions of visually impaired individuals all over

the world, and has paved the way for further research in the field.

LASIK surgery is only a simple manipulation of our bodies, and yet it positively affects

millions of impaired. How else can we use the study of our bodies and medicine to help

ourselves as human beings? In order for us to answer this question we must consider problems

which affect the human race as a whole.

Perhaps one of humanity’s greatest traits, besides of course the abilities of our brains and

minds, is our possession of developed limbs. Our limbs allow us to function as living creatures,

and humans have particularly well developed limbs which allow us to take part in a wide variety

of activities. Metaphorically, our limbs are the paintbrush that allows the artist (our brains) to

paint. Of course without our limbs we would be extremely limited in what we could accomplish.

It is obvious then that limbs are truly one of our greatest features. But all that glitters isn’t

gold. Our limbs, because they protrude so far from our bodies, have proven to be very

vulnerable. Most likely for as long as humans have had limbs have we also lost them due to

trauma, amputation or other health related issues. According to Douglas G. Smith, MD, there is

estimated to be over 1.6 million people in the U.S. that have some type of limb loss, excluding

fingers and toes. Limb loss of course can occur as a result of trauma or injury to a limb, a

medical condition that affects the limb, a medical amputation of the limb, or even genetic or birth

defects. However, to combat the problems we face in losing our limbs, humans have created

prosthetic limbs.

BACKGROUND

Prosthetic limbs have been mentioned and referred to throughout history, as far back as

even 1000 B.C.E. We have found preserved prosthetics from Ancient Egypt. And from then up

until the 20th century, prosthetic limbs have been simple in design and have lacked any

immersive features. They were only as advanced as our technology has allowed them to be, often

times being simple constructions of wood or metal. Today, however, we have a much more

advanced understanding of the human body and, thus, a much more developed variety of

prosthetic limbs.

Modern prosthetics are designed to be as unobtrusive as possible. We can make them

extremely life-like for average citizens or we can make them ultra-lightweight for athletes. But at

the end of the day they are still prosthetics and we cannot make them as useful as we can our

natural limbs. And so in this paper we will explore the future of prosthetics and how we can

further advance the technology to benefit those who utilize it.

Currently there are prosthetics that use mechanical methods of movement, electronic

methods of movement, and of course there are those that are static; they do not use movement.

Mechanical methods include cable controlled limbs which grant immediate, physical feedback,

but are limited in their variety of movement. Electronic methods include myoelectric limbs, and

computer controlled limbs.

MECHANICALLY OPERATED PROSTHETICS

As mentioned, mechanically operated prosthetics typically involve cables. They are

implemented in arm prosthetics and are body powered; in other words, the motions generated by

your body are used to operate the cables (Figure 1). The tension created by the cables causes the

hand prosthetic to grasp whatever objects the user wishes. For the majority of the 20th century,

this was as advanced as our prosthetic limbs could get. The system was very inefficient,

however. Lawrence E. Carlson Deng, a professor of mechanical engineering at the University of

Colorado at Boulder, conducted a study on the efficiency of upper-limb cable prosthetics and

concluded that even with different cable housing materials, the system showed a marginally high

loss in energy due to friction. Though they are clearly limited in their functionality, they allow

amputees to get by and perform simple everyday tasks that they otherwise would not be able to

complete. The ingenious design of a prosthetic that used the power of your body to create motion

had perhaps paved the path for the generations that followed to create a better system.

Figure 1: Illustrates the operation of a body powered cable prosthetic.

(The illustration in Figure 1 belongs to www.wired.com)

MYOELECTRIC PROSTHESES

Because of the advances that have been made in science in the last few generations, we

have been able to commercialize myoelectric prostheses. Myoelectric prostheses detect and

interpret the action potentials that are produced by the voluntary contraction of our muscles, and

then act accordingly. Although the technology was initially invented in the 1960’s it was not

very functional; however continuous research into the technology has allowed it to become much

more useful. Myoelectric prostheses are much more common today than cable controlled limbs.

They can aid the extension of elbows, the rotation of your wrists, or the opening and closing of

your fingers.

There is a lot of hardware that goes into making a myoelectric limb functional. First, a set

of electronic sensors is required on the muscles to detect the action potentials that will be

produced upon contraction. The signals then must be transmitted to a computer that will interpret

the signals. Once the signals are interpreted and translated into a language that the prosthetic

controller can understand, the prosthetic completes the action (Figure 2).

The implementation of this technology into prosthetic limbs has improved the quality of

life for affected amputees exponentially. Myoelectric limbs allow for a much more natural

appearing and much more functional prosthetic, which is ultimately the goal for the majority of

the prosthetic wearing population.

There are, however, drawbacks to the myoelectric limbs. When using a body powered

prosthetic that is operated with cables, the user can experience immediate tactile feedback from

the system. Because the myoelectric method is operated by receiving the action potentials that

are sent out by your muscles, it is only natural that there will be a physical lag during operation.

The receptors must wait until they receive the electric signal and then must interpret the signal to

perform movement.

Not only is there a lag when using myoelectric methods, but it is also very daunting to

learn to use the technology effectively. Amputees require hundreds of hours’ worth of

rehabilitation and physical therapy to train for effective use of these limbs.

These drawbacks leave us plenty of room to advance the technology. But what’s next?

Figure 2: Some of the components required for an operational myoelectric prosthetic limb.

(The illustration in Figure 2 belongs to electronicproducts.com)

IMMERSIVE PROSTHETICS

Of course the ultimate goal for those in the field is to design a fully immersive prosthetic

that functions as naturally as a biological limb would. This means that it would have to be

controlled completely by your mind and with as little effort as your natural limbs require. There

have recently been breakthroughs in the research on this technology, and we are steps closer to

unlocking the true capabilities of prosthetic limbs.

The problem with myoelectric limbs is that the external sensors only provide the limb

with a small range of movements. Of course our real limbs have a range of hundreds of different

complex movements, all possible because of the many signal receptors in our arms that receive

the signals being sent from the motor neurons in our brains. So, in order to make a prosthetic as

capable as our natural limbs, we need to emulate this system. This requires internally implanting

electrodes to receive the signals from the brain. According to Dr. Rickard Brånemark of the

Sahlgrenska University Hospital, internal electrodes combined with a prosthetic that is directly

anchored to the stump will allow for a prosthetic to be capable of almost all of the natural ranges

of motion for a limb. Dr. Brånemark has implemented this technology in at least one amputee,

and claims that it has improved the patient’s experience marginally.

So if we have the technology to create essentially “bionic” limbs, why are we not

implementing it? Truthfully, the process is far from refined. The human body does not react well

to foreign objects, hence why we have an immune system. Internal implants within the brain

could cause many health problems, which, according to Andrew B. Schwartz in his research

journal, include “neuronal death due to insertion injury; or chronic inflammation and neuronal

exclusion by the glial sheath.” Inserting a processing chip into the brain could potentially

damage the surrounding tissues.

Externally, there could also be health issues regarding the permanent anchoring of a

prosthetic to skin and bone. Infection is likely to occur if the body rejects the prosthetic or if the

anchoring is not done correctly (See Feedback Loop).

So before we can implement mind controlled prosthetics, we must learn how to work

around the protective systems that our bodies naturally implement. Unlocking the true potential

of prosthetic limbs could be humanity’s greatest achievement. The quality of millions of lives

could be improved exponentially if we were able to replace cognitive movements that have been

lost through amputation. The technology will be even more helpful once a cheap and affordable

method is implemented.

CONCLUSION

This is why funding to research in human biology is so important; it is a field in which

allows us to improve ourselves. Many believe that we are playing God when we enhance our

capabilities through the use of technology; however, the way I see it, we are only utilizing our

own capabilities which God has given to us.

REFERENCES:

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Seniors." InMotion: Prosthetic Rehabilitation and Technology, Options and Advances for Seniors.

InMotion, 18 Aug. 2014. Web. 27 Apr. 2015.

Schwartz, A., X. Cui, D. Weber, and D. Moran. "Brain-Controlled Interfaces: Movement Restoration

with Neural Prosthetics." Neuron 52.1 (2006): 205-20. Web. 26 Apr. 2015.

"A Brief Review of the History of Amputations and Prostheses Earl E. Vanderwerker, Jr., M.D.

JACPOC 1976 Vol 15, Num 5" Web 26 Apr. 2015.

Allen E. Buchanan, Beyond Humanity?: The Ethics of Biomedical Enhancement, Oxford Scholarship

Online. Sep. 2011. Web, 27 Apr. 2015.

Carlson, Lawrence E., Bradley D. Veatch, and Daniel D. Frey. "Efficiency of Prosthetic Cable and

Housing." JPO Journal of Prosthetics and Orthotics 7.3 (1995): 96-99. Web. 27 Apr. 2015.

Fougner A, Kyberd PJ, Losier YG, Parker PA, Stavdahl Ø: Control of upper limb prostheses:

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Chorost, Michael. "A True Bionic Limb Remains Far Out of Reach | WIRED."Wired.com. Conde Nast

Digital, 227 Apr. 2015. Web. 27 Apr. 2015.

Chalmers University of Technology. "World premiere of muscle and nerve controlled arm

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Abate, Tom. "STANFORD RESEARCHERS REVEAL MORE ABOUT HOW OUR BRAINS

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Sobuh, MMD, LPJ Kenney, AJ Galpin, SB Thies, J. McLaughlin, J. Kulkarni, and P. Kyberd.

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