Neurally-controlled Prosthetic Ankle Helps Correct Balance
Most existing lower-limb prosthetic devices aren’t equipped to allow for mind-controlled balance or posture correction, increasing a prosthetic user’s chances of falling or making walking difficult. To solve this issue, the National Institute of Biomedical Imaging and Bioengineering (NIBIB) funded researchers to work on a prosthetic ankle that can be controlled by a user’s residual muscles—and the electrical signals they generate.
This prosthetic ankle is controlled by directly mapping the electrical activity generated from the user’s residual muscles.
Unlike passive prosthetic limbs, which store and return energy when walking, and most robotic prostheses, which require external sensors to help anticipate the user’s movement, this prosthetic ankle is controlled by directly mapping the electrical activity generated from the user’s muscles.
Helen Huang, Ph.D., a professor in biomedical engineering at both North Carolina State University and the University of North Carolina at Chapel Hill, leads a research group working on a lower-limb prosthetic device that operates using the body’s electrical signals. That signaling ability can be seen in the muscles in the residual limb, which can still receive electrical signals from the brain, resulting in the contraction of muscle fibers, which enables movement. The concept that uses the body’s signals to direct prosthetic device movement is known as direct electromyographic (dEMG) control.
The research team recently tested their dEMG-controlled prosthetic device on an individual with below-knee amputation. Surface electrodes were placed on the tester’s residual limb to detect electrical signals from the muscles. The case study found that when the user contracts their residual muscles, intending to flex the foot, the electrodes collected and processed the associated EMG activity. The EMG signal is used to drive pneumatic artificial muscles by using pressurized air to contract or extend. This allows the user to control the movement of the prosthetic limb continuously.
We use our muscles differently when a part of a limb is removed.
However, it’s important to note that prosthetic users can only operate the device after training with a physical therapist. This is because we use our muscles differently when a part of a limb is removed.
In Huang’s research group’s case study, the physical training for the tester lasted three weeks. Training included daily life activities that require postural control, such as picking up a heavy object and transitioning from standing to sitting and vice versa.
After the physical training, the researchers evaluated the participant’s stability while performing specific tasks on a passive prosthetic ankle and the dEMG-controlled device. The researchers found that his stability markedly improved when using the latter, even when the tests challenged his postural control, like standing on a foam surface or performing tasks with his eyes closed, which tests balance.
The study also investigated the synchronization between the participant’s sound side leg and prosthetic limb; they found that synchronization was far higher when the tester was wearing the dEMG-controlled device than his passive prosthesis.
According to Huang, this case study shows the “feasibility of developing a device that allows the user to adjust their posture intuitively, which could greatly increase their quality of life.”
The team is currently investigating using the prototype dEMG prosthetic ankle among other individuals with below-knee limb loss. They will also evaluate the effectiveness of the device in more tasks.