Enhanced spinal cord microstimulation using conducting polymer-coated carbon microfibers

Area of Science:

• Biomedical Engineering
• Neuroscience
• Materials Science

Background:

• Intraspinal microstimulation (ISMS) is a potential therapeutic strategy to restore motor function following spinal cord injury.
• ISMS involves activating spinal motoneurons caudal to the injury site to evoke selective movements.

Purpose of the Study:

• To investigate the safety and effectiveness of conducting polymer (CP)-coated carbon microfibers (CMFs) for ISMS.
• To evaluate electrode performance and motoneuron activation based on microfiber length and polymer coating.

Main Methods:

• 7-µm-diameter CMFs coated with PEDOT:PSS-co-MA were used for current-controlled biphasic electric pulses in anesthetized rats (C7 spinal cord).
• Electrode performance was assessed using voltage transients, cyclic voltammetry, electrochemical impedance spectroscopy, electromyography (EMG), and foreleg kinematics.
• Microfiber length (50 µm vs. 250 µm) and polymer coating presence were varied.

Main Results:

• CP-coated CMFs effectively activated spinal motoneurons with low stimulus thresholds (-28 µA to -46 µA).
• EMG and kinematic thresholds decreased as microfiber tips approached the target motor nucleus (triceps brachii).
• Polymer coating enhanced electrical activity in target fascicles and prevented unsafe overvoltages, though stability decreased over time.

Conclusions:

• CP-coated CMFs offer an effective and minimally invasive electrode for ISMS.
• The polymer coating enhances motoneuron recruitment, but requires optimization for long-term electrical and mechanical stability.
• These microfibers hold potential for developing advanced neuroprosthetic devices for spinal cord injury recovery.