Development of a Low-cost Epimysial Electromyography Electrode: A Simplified Workflow for Fabrication and Testing

We seek to understand the neuromuscular and electrical physiological consequences of ACL injury using a preclinical rodent model. Our current experiments use implantable epimysial EMG electrodes to investigate how non-invasive ACL injury alters quadriceps activation. Although fundamental resources exist detailing the considerations for electrode fabrication and testing, we aim to provide an updated, easy-to-follow guide to epimysial electrode fabrication and testing for the modern electrophysiology laboratory.

Our goal was to streamline the epimysial EMG fabrication and testing process, facilitating the broader use of epimysial electrodes in the advancement of neuromuscular research. To begin, use tape to secure the silicone base on the cutting jig. Perforate the silicone with cutting jig guides and an X-ACTO Knife for placement of the contact foils.

Using the folding jig, bend the biocompatible precut platinum or radium contact foils into a U-shape. Insert the foils into the perforated slots in the silicone base to construct the contact surfaces of the electrode, ensuring proper spacing between electrodes. Place a piece of surgical tape over the contact surfaces to hold the foils in place.

Remove the silicone base from the cutting jig. Flip the silicone base to expose U-shaped foil arms. Hold one arm of each U-shaped foil flush with the silicone base.

Cut the perfluoroalkoxy coated stainless steel wire to a desired length. Using a lighter, denude one end of the wire. Position the denuded end of the wire on the inside of the unfolded arm of the foil and weld it using a micro TIG welder.

To test the wire foil connection, apply tension to the stainless steel wire. If the connection holds, fold the foil arm down, flush with the silicone base, and remove the tape bordering of the silicone sheet. Next, mix biocompatible liquid silicone with toluene until desired thinner or syrup-like consistency is achieved.

Drop up the mixture using an 18-gauge blunt-tip syringe, and apply it to the back of the welded electrodes to seal it. After 72 hours, use scissors to cut the silicone base into individual electrodes. After electrode fabrication, pin each electrode lead wire to a channel on an electrode interface board.

Connect the industry standard electrode to the same board for comparison. Now connect the electrode interface board to a data acquisition platform via a magnetic tethered cable system. Denude one end of a perfluoroalkoxy coated stainless steel wire, and spot weld it to a grounding source.

Pin the ground lead wire to the designated ground position on the board. In a 250-milliliter glass beaker, add 180 milliliters of 0.9%sterile saline. Submerge both custom-fabricated and industry standard epimysial electrodes in the saline bath and secure them in a stable position.

Then place the grounding source in the saline bath and secure its position. Submerge two stimulating needle electrodes in the saline bath, and connect them to the signal generator. On a signal generator, set the voltage to 0.1 volts and frequency to five hertz.

Deliver repeated waveforms into the saline bath to compare recorded signals between the custom-fabricated and industry standard electrodes. Assess performance informally and visually in real time to evaluate signal variation between electrodes. The intraclass correlations revealed high levels of agreement between the custom-fabricated and industry standard electrodes across all wave forms.

The sine wave forms showed an intraclass correlation of 0.993, square wave forms of 0.995, and triangle wave forms of 0.958. Bland-Altman plots also indicated a high degree of signal agreement between the electrodes. Similarly, Pearson correlations demonstrated strong positive correlations between the custom-fabricated and industry standard electrodes.