Bionic arm

Bionic devices, including bionic arms, have been in the realm of science fiction for quite some time. So, we have used to the idea that lost limb replacement should be possible and as easily accessible as a cough treatment.

From time to time we can read popular science publications that claim that thought controlled prosthetic arms are just around the corner. Arms so nimble that it is possible to play the piano with them. In reality, things are a bit different.

Credit: Johns Hopkins University Applied Physics Laboratory

We've read articles like that for fifty years now, but a real, working, accessible, and functional bionic arm is nowhere near for most people who'd need one. Don't get too depressed though, the research efforts have been quite remarkable, especially, in the past five years.

So, you wonder why the development of bionic arms lags behind that of bionic knees? The answer is quite simple - a human arm is much more sophisticated than a leg, and the desired general functions of an artificial arm are not as straightforward as those of legs - walking and running.

Now, don't get me wrong, I'm not saying that bionic legs are "simple" to make or design. What I mean is - it is possible to make software that figures out the desired response from an artificial knee by monitoring values like acceleration, speed, applied load, or by mimicking the sound leg.

It is not possible, however, in case of an arm; voluntary control is an essential requirement to achieve the functionality sought. So, in order to design a functional bionic arm one has to solve the difficult neural control problem as well.

Today, there are myoelectric arms with their pros and cons, and other control solutions are being researched. These include brain-computer interfaces, innovative manual control methods, as well as the most promising method - targeted muscle reinnervation.

Myoelectric arms

Myoelectric arms pick up and interpret signals from voluntarily contracted muscles in a residual limb. These devices are usually used for upper-limb, below-elbow amputees, as muscle signals can be picked up in these cases. Functionality level provided depends on the specific condition.

The idea itself is far from new. Actually, it's the very opposite - the idea is more than 50 years old, and the first commercially available myoelectric hand was available in 1964. These prostheses haven't managed to push out body-controlled prostheses from the market.

Some heavy criticism has been directed to this type of prostheses, they are often regarded as impractical, inconvenient, unreliable and too expensive for the benefits they provide. At the end, around one third of the upper-limb amputees don't use prostheses at all.

However, I'll shortly discuss some myoelectric arms' manufacturers and arm models manufactured by them.

Otto bock

Otto Bock is one of the oldest and largest prosthetics companies in the world. They have a wide selection of prosthetic arms - either myoelectric, body-powered, cosmetic or hybrid. Since myoelectric arms are in the scope of this article, I'll further discuss them.

There are numerous myoelectric devices manufactured by Otto bock that are tailored to different types of amputation and to different purposes. The interesting thing about Otto bock's myoelectric arms is their Dynamic Mode Control, which controls the grip speed and force in accordance to the muscle signal.

Liberating Technologies

Liberating Technologies is a company that's best known because of their Boston digital arm system. Boston digital arm system is an upper-limb prosthetics control platform. So, it includes an artificial, microprocessor-controlled elbow that can control other compatible devices such as hands, grippers and wrist rotators.

Although I list this device under myoelectric arms, this is only partially true. Devices connected to Boston Digital Arm System can be controlled using numerous different input methods, such as myoelectrodes, touch pads, servo controls and switches.

Liberating Technologies also separately offer numerous electric hands, grippers, wrists, elbows and other hardware such as batteries and the controller used in the above mentioned bionic arm system.

Touch bionics

Photo courtesy of Touch Bionics. ©Touch Bionics

Touch bionics is often regarded as one of the leading upper-limb bionic prosthetics manufacturers. Their product line includes a myoelectric hand - i-LIMB and ProDigits - powered digits for people with one or more fingers amputated.

The i-LIMB, as other myoelectric hands, utilizes a control system with two myoelectrodes that pick up muscle signals from remaining muscles in the residual limb. While this is common with other devices of the same kind there's something that singles out this one.

The vast majority of myoelectric devices have a gripper that is basically a three-fingered clamp with one finger opposing the other two. This clamp is then masked as a hand. As you can understand, in this configuration the ring finger and the pinky finger are both purely cosmetic.

The i-LIMB, on the other hand, has five powered, software controlled digits. The software monitors when each individual finger has sufficient grip on an object and then locks that finger in place until the "open" command is received.

According to Touch Bionics the i-LIMB hand can execute numerous grip patterns. As I understand, this is also done by the software that can determine which pattern is the most appropriate in a given situation (if I'm mistaken - please correct me!).

Previously I also mentioned ProDigits. ProDigits, basically, are powered, artificial fingers - bionic if you will. These myoelectrically controlled digits can be fitted to a patient who is missing 1 to 5 fingers. As far as I'm aware, this is the first such solution that treats this kind of condition.

Motion Control

Motion Control Inc. was established in 1974 by a group of people from the University of Utah to commercialize medical designs developed there. In 1981 they released the Utah Artificial Arm, in 1997 Utah Arm 2 was released and in 2004 - Utah Arm 3 that features microprocessor control.

The Utah Arm is a myoelectric prosthesis for elbow, hand and wrist, so it can be fitted to above-elbow amputees. The third iteration of it - Utah Arm 3 has an improved control system. Other products include ProControl system and a myoelectric hand - ProHand.

As I mentioned, U3 (Utah Arm 3) has an improved control system, namely, it has two microprocessors. This allows simultaneous operation of two devices, for example, an elbow and a wrist, this is a step forward if compared to sequential control.

Numerous control methods such as myoelectrodes, potentiometers, force sensors, touch pads and others can be used, as some of these offer variable input signal, obviously, proportional control is also available.

Of course, it can be discussed whether such devices as all the above mentioned can be regarded as bionic arms, as the functional level is quite low if compared to a natural arm. While with bionic we usually understand something that executes natural functions more or less seamlessly. In my opinion, however, they are purely on the right road, and any development in this field should be welcomed.

Research efforts

One of the main reasons why the development of bionic arms has been relatively slow is the sophisticated nature of such devices. Because of this sophistication it is quite expensive to do research and development in this field. However, there are some really notable achievements, especially in the past 5-10 years. Let me tell you about them.

Targeted reinnervation

Targeted reinnervation is an innovative surgical procedure pioneered by Todd Kuiken - a researcher at Rehabilitation Institute of Chicago. Today, this procedure is being tested and extensively developed. At the moment, it seems that this could be the right answer to many upper-limb prostheses' control issues.

The basic idea goes like this - nerves that used to control the missing limb are still functional although they're cut off. So, it should be possible to relocate them elsewhere, where they could create muscle contractions that could be read using myoelectrodes. Then the prosthesis could be moved by sending the same signals one would naturally send to a sound arm.

Targeted reinnervation is a procedure that does just that - initially, the target muscle (a chest muscle, for example) is denervated (original nerves are cut off) and then nerves that used to control the arm are reinnervated into the target muscle. If this procedure is successful, after several months the target muscle responds with contraction if a patient tries to bend the elbow of the lost arm or do other actions with the "phantom" limb.

The above described procedure is known as targeted muscle reinnervation, but there's another connected technique - targeted sensory reinnervation. With this technique the skin over the target muscle is denervated as well, thus allowing it to be reinnervated by the relocated nerve.

The outcome is even more interesting - the patient is able to feel sensations applied to the target muscle as if they were applied to the missing limb. I suppose you realize what kind of possibilities are opened by invention of such techniques - it is now possible to develop upper-limb prostheses that would act more naturally as well as respond to stimuli, thus allowing direct force control.

Of course, the procedure is still novel and there are some uncertainties. Not all surgeries have been successful, it is not known for sure how long-lasting the effects are, also, phantom limb pain can return and it is not clearly known whether it will go away in all cases.

However, I'm pretty optimistic about these procedures, as every surgical procedure faces uncertainties at the beginning but later they are usually cleared. In either case, the R&D efforts regarding targeted reinnervation techniques are pretty active and that's great.

Today, targeted reinnervation is researched mostly in context of a bionic arm for above elbow amputees. However, the technique is promising and could be used to create advanced prostheses for below-elbow and lower-limb amputees as well.

Revolutionizing Prosthetics Program

The modular prosthetic limb (a bionic arm). Photo courtesy of Van Doren designs

Did I mention that R&D in this field is quite expensive? OK, I'll say it again - it is expensive, and who has money? Right, the military. I won't explain here what is DARPA, let's just say that this won't be the last time I mention that organization on this site.

Many technological breakthroughs that have changed our daily lives, like the internet, are rooted in researches carried out by Defense Advanced Research Projects Agency. As robotic technologies and their applications are pretty novel, sometimes significant researches in these fields are funded by DARPA. The bionic arm is not an exception.

So, Revolutionizing Prosthetics Program funded two separate projects - a two-year project Revolutionizing Prosthetics 2007 and a four-year Revolutionizing Prosthetics 2009. The goal of RP 2007 was to develop a prosthetics arm that would adapt existing technologies and facilitate numerous, already-existing, non-invasive control methods.

The goal of the RP 2009, on the other hand, was to develop a bionic arm that would mimic a natural human arm as closely as possible, a bionic arm if you will. RP 2009 posed no limitations on possible control methods, these could range from non-invasive methods to implantable nerve-reading sensors.

The RP 2007 contract was given to DEKA research and development corporation headed by Dean Kamen (the inventor of Segway). They created a prosthetic arm dubbed "the Luke arm" in reference to Luke Skywalker, yeah, Luke actually had a hand prosthesis, but you get the idea.

The Luke arm was created in a way that allows numerous control options, like some of the above mentioned artificial arms. Unlike them, the Luke arm has 18 degrees of freedom, which is great because a human arm has 22 degrees of freedom. Also, it weighs 3.6 kilograms, that's approximately 7.9 pounds.

The RP 2009 project, headed by John Hopkins University Applied Physics Laboratory, with numerous other high-profile partners involved, resulted in a bionic arm design dubbed as the MPL arm. MPL stands for Modular Prosthetic Limb.

As the name suggests it is designed wit modularity in mind to allow different configurations for different conditions. Although numerous control methods, such as brain-computer interface and others, were looked upon, the above mentioned targeted reinnervation is the most promising.

According to DARPA, at the moment both bionic arms are undergoing testing in human clinical trials. The continuity is crucial as the DARPA funding ends, at the moment it seems that in some extent developments from this DARPA program will carry on and eventually better prostheses will be available to people. The Contineo line from Orthocare Innovations is partially derived from this program.

Open Prosthetics

So you read all this and feel like you could do something to make the world a better place as well? Maybe you have an interesting idea regarding arm prostheses haunting you for a while but there's no one with whom to share your ideas?

If we look at some open source successes such as Linux operating systems and other great software, we realize what we can achieve if we work together. Open Prosthetics is a project that strives to utilize this power and apply it in the field of prosthetics.

Not that there's an open sourced bionic arm out there, but the initiative is really compelling. I, personally, admire it, that's why I really felt like I have to tell about it. In either case, if you feel like doing something, check out Open Prosthetics site and look how you can help.


No, I don't mean World of Warcraft, this is my abbreviation of "Words of Wisdom" or "Conclusion".

Of course, there are more in this field than I've written, however, this is enough for you to get the overall idea of what's really out there, what development has been made and what can be expected sooner or later. Sure, a fully working bionic arm that can be implanted and forgotten is still in science fiction.

However, the recent development is quite remarkable, especially, if looked upon in context of what's been around for years in this field. Also, keep in mind that bionic arms are only one solution to this problem. People are searching for other solutions as well - transplantation and limb-regrowing are among those solutions.






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