Developing and Optimizing the Artificial Limb Prosthesis Based on pH Change at Neuromuscular Junction

Abstract

Until now, the biological information that has been made use for the development of artificial limbs based on electro-mechanical coupling is from EMG signals, EEG signal and/or local signals of neuronal excitation. While all these methodologies are successful experimentally, they also possess few drawbacks such as inability to pick up minute neuronal signals, corrosion of the internal electrode leading to toxicity and aberrant reading of those bio-signals. In humans like any vertebrates, the motor movements of the appendages are commanded by the motor area of cerebral cortex voluntarily when a will to act is generated. This is followed by neuronal excitation that passes through NMJ to excite/contract different group of muscles. The muscle excitation is preceded by action potential development that is initiated, maintained and terminated by sequential ionic movements in and out of the muscle cell. The major ions involved are Na and K. The change in these ionic concentrations can lead to change in pH at the NMJ that can be interpreted as information sent by the brain. Thus it was hypothesized that the changes in the pH can accurately mimic the intended changes in the amputated limb muscles, and therefore can be used to turn the user’s desired motion into actual motion of the limb prosthesis. Briefly, the study utilized a pH-to-voltage converter which converts the pH signals of the neuro-muscular junction into an electrical signal (voltage change). A cut-off voltage was assigned above which the limb moves that exactly simulates the role of action potential in muscle contraction. A high fidelity system thus developed can be projected to the movement of fine moving prosthetics like digits.