Shown here are two intramuscular electrodes formed by winding single strand and multistrand wire into a helical configuration. The stimulating electrode and the lead are a single unit. The electrodes are loaded into hypodermic needles, one with single strand wire (bottom) and one with a multistranded lead wire (top) are shown in this vignette.
The single strand helically wound electrode was a percutaneous structure connecting to an external pulse generator. A surprising features of the structure was the lack on infections when left traversing the skin for weeks. As time went on we were conducting experiments that required mechanical stability greater that what could be achieved from the single strand helix. The multistrand, helical electrodes, have proven to be much more robust under similar loading conditions. The coiled structure can better withstand torsional and bending forces during movement. The bent tip at the terminal part of the electrode provides a means for unloading it from the hypodermic needle after insertion into a muscle. The deinsulated region is the electroactive surface for transferring electrical charge to the tissue to be activated.