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INNOVATIVE METHODOLOGY

Multichannel thin-film electrode for intramuscular electromyographic recordings

¹Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark; ²Biomedical Engineering Department, Indiana University-Purdue University, Indianapolis, Indianapolis, Indiana; ³Department of Medical Engineering and Neuroprosthetics, Fraunhofer Institute for Biomedical Engineering, St. Ingbert, Germany; and ⁴Laboratory for Biomedical Microtechnology, Department of Microsystems Engineering-IMTEK, University of Freiburg, Freiburg, Germany

Submitted 19 July 2007 ; accepted in final form 21 November 2007

It is currently not possible to record electromyographic (EMG) signals from many locations concurrently inside the muscle in a single wire electrode system. We developed a thin-film wire electrode system for multichannel intramuscular EMG recordings. The system was fabricated using a micromachining process, with a silicon wafer as production platform for polyimide-based electrodes. In the current prototype, the flexible polymer structure is 220 µm wide, 10 µm thick, and 1.5 cm long, and it has eight circular platinum-platinum chloride recording sites of 40-µm diameter distributed along the front and back surfaces with 1,500-µm intersite spacing. The system prototype was tested in six experiments where the electrode was implanted into the medial head of the gastrocnemius muscle of rabbits, perpendicular to the pennation angle of the muscle fibers. Asynchronous motor unit activity was induced by eliciting the withdrawal reflex or sequential crushes of the sciatic nerve using a pair of forceps. Sixty-seven motor units were identified from these recordings. In the bandwidth 200 Hz to 5 kHz, the peak-to-peak amplitude of the action potentials of the detected motor units was 75 ± 12 µV and the root mean square of the noise was 1.6 ± 0.4 µV. The noise level and amplitude of the action potentials were similar for measures separated by up to 40 min. The experimental tests demonstrated that thin film is a promising technology for a new type of flexible-wire intramuscular EMG recording system with multiple detection sites.

motor unit; electromyograph; thin-film technology; spatial sampling