Many of us take the simple act of picking up an object for granted, but for those people who use prostheses, it can be a pretty frustrating exercise. In spite of their obvious potential, brain-operated bionic arms, whether invasive or non-invasive, still belong in the lab. Can a new prosthetic arm that is able to detect signals emitted by spinal nerve cells push researchers closer to designing an artificial limb that looks like the real thing?
The biggest problem with robotic arms that are controlled by muscles is that they depend on jerks from amputated limbs whose fibers are usually damaged.
Dario Farina, a bioengineering professor at the Imperial College of London explains that in case an arm gets amputated, the muscles and nerve fibers are also cut off. This makes it very hard to get significant signals from them in a manner that would make using a prosthetic viable.
According to Farina, this restricts the number of tasks that can be performed using an artificial limb. It also explains why almost half of all the users of artificial limbs eventually ditch them out of frustration. But what if it was possible for the prosthetic to utilize the nervous system such that the signals transmitted by the motor neurons (which are responsible for controlling the movement of muscles) are deciphered more distinctly? Might this result in the development of robotic arms that are more intuitive? This are the questions that Farina and his team sought to answer.
In order to test their hypothesis, they designed a sensor that utilizes the electrical signals transmitted by spinal motor neurons in form of commands and engaged six amputees who would test it. So as to amplify the signals and make them easily detectable by the sensor, the nerves linked with arm and hand movements on the test subjects were surgically redirected to healthy muscles in their biceps or chest. After that the research team decoded and then mapped the information in the signals transmitted by the nerves. Next the signals were compared to those given off by healthy patients. The thinking was that once they decoded the meaning of the signals transmitted by these motor neurons, they could finally create a complete suite of commands for hand and arm functions in the prosthetic limb to enable it to work like an actual limb.
In this study, the research team encoded, as commands, particular motor neuron signals into the prosthetic’s design. Afterwards, they put a sensor patch on the operated muscle, and this was then attached to the prosthetic.
The results of the tests were encouraging, and this was reported by the researchers in their study. The team worked with physiotherapists in order to know how the device could be controlled. It involved visualizing themselves controlling a make-believe arm and thinking of simple actions. The amputees were able to carry out a wider variety of movements when compared to those who used the regular robotic muscle-controlled prosthetics. The actions consisted of raising their arms upwards and downwards and twisting their wrists from side to side.
To some analysts, what is unique about the research study is that prosthetic limbs could, in future, be controlled using computer algorithms. Because the sensor is not implanted in a person’s body, it is not necessary to have additional surgery, unlike brain-controlled prostheses where invasive brain implants must be used.
Levi Hargrove, a researcher at Chicago’s Rehabilitation Institute Center for Bionic Medicine and a non-participant in the study, notes that one does not require a sensor to be inserted in the body to know what the nerves are doing.
The endeavor to build artificial limbs that can implement the commands of the brain goes back several decades. There are 185,000 amputations in the United States alone each year, with vascular diseases accounting for most of them. War is also a contributing factor to this statistic. By 2012, the wounded US combatants in Iraq and Afghanistan included over 1500 amputees. Since the year 2006, DARPA (or Defense Advanced Research Projects Agency) has used US$153 million on a program known as Revolutionizing Prosthetics. However, in spite of creating innovative products such as the Luke Arm, there is still much to do in this area.
After achieving proof-of-concept with their research study, the next goal for Farina and his team is to utilize the technology in a more extensive clinical trial and subject it to stringent testing. If everything goes as planned, the researchers predict that it could be introduced into the market in three years.