There are a lot of people who lose any limb and live on it. In spite of using prosthetics, these men are limited in their day-to-day life. But science brought us new branch of science – Brain Controlled Prosthetic Limbs.
The first bionic prosthetic hand has been set by scientists Rehabilitation Institute of Chicago in 2002 to electric from Tennessee, Jesse Sullivan. As an electrician, he accidentally touched an active cable that contained 7,000-7,500 volts of electricity. In May 2001, he had to have both his arms amputated at the shoulder. Seven weeks after the amputation, Jesse Sullivan received matching bionic prostheses from Dr. Todd Kuiken of the Institute. Originally, they were operated from neural signals at the amputation sites, but Jesse Sullivan developed hyper-sensitivity from his skin grafts, causing great discomfort in those areas. Jesse Sullivan underwent neural surgery to graft nerves, which originally led to his arm, to his chest. The sensors for his bionic arms have been moved to the left side of his chest to receive signals from the newly grafted nerve endings. Scientists at the Johns Hopkins University Applied Physics Laboratory (APL) were awarded no less than $34.5 million by the DARPA (Defense Advanced Research Projects Agency − the Pentagon’s research division) to continue their outstanding work in the field of prosthetic limb testing.
Six years later their new Modular Prosthetic Limb (MPL) system was just about ready to be tested on human subjects, as it has proved successful with monkeys. In order for a robotic prosthetic limb to work, it must have several components to integrate it into the body’s function: Biosensors detect signals from the user’s nervous or muscular systems. It then relays this information to a controller located inside the device, and processes feedback from the limb and actuator (e.g., position, force) and sends it to the controller. Examples include wires that detect electrical activity on the skin, needle electrodes implanted in muscle, or solid-state electrode arrays with nerves growing through them. Mechanical sensors process aspects affecting the device (e.g., limb position, applied force, load) and relay this information to the biosensor or controller. Examples include force meters and accelerometers. The controller is connected to the user’s nerve and muscular systems and the device itself. It sends intention commands from the user to the actuators of the device, and interprets feedback from the mechanical and biosensors to the user. The controller is also responsible for the monitoring and control of the movements of the device. An actuator mimics the actions of a muscle in producing force and movement. Examples include a motor that aids or replaces original muscle tissue.
The robotic arm itself weighs nine pounds, which is about as much as a real limb, and provides just as much dexterity too. Besides tasks like moving each individual finger and rotating the wrist, it is capable of 22 degrees of freedom, and reacts with speed and agility to the user’s commands and can allow patients a level of freedom they never thought they’d have again. The arm allows movement in five axes and allows the arm to be programmed for a more customized feel.
Recently, robotic limbs have improved in their ability to take signals from the human brain and translate those signals into motion in the artificial limb. DARPA is working to make even more advancements in this area. Initially, the design will be used on people with spinal-cord injuries, who have lost nearly all movement and would benefit the most from using the robotic limb.
Transradial and transtibial prostheses typically cost between US $6,000 and $8,000. Transfemoral and transhumeral prosthetics cost approximately twice as much with a range of $10,000 to $15,000 and can sometimes reach costs of $35,000. The cost of an artificial limb does recur because artificial limbs are usually replaced every 3-4 years due to wear and tear. In addition, if the socket has fit issues, the socket must be replaced within several months.
The end result would be a prosthetic that acts as a veritable extension of one’s own body. And a platform capable of accurately distinguishing between, and interpreting, different sensory signals − temperature, pressure, motion − would “allow the incorporation of the limb into the sense-of-self” and offer unprecedented freedom of movement for a prosthetic wear.
The agency also wants an ultra-reliable platform, with an error rate of less than 0.1 percent and a lifespan of around 70 years. By comparison, current neural-recording interfaces last around two years before they need to be replaced. Sounds far-fetched, but Darpa’s already got one major lead. The agency’s new Neurophotonics Research Center will investigate fiber-optic prosthetic interfaces that can incorporate thousands of sensors into a single filament.