The original skin electrodes for transcutaneous electrical nerve stimulation (TENS) in the 1860s consisted of rollers and brushes.
The Electreat device manufactured during WWI used saline soaked pads and sponges. When TENS became a high volume therapy in the 1970s more efficient means of conducting electrical stimulation across the skin were sought.
The first of the modern TENS skin electrodes were conductive silicone pads taped to the skin over a conductive gel. These were easily dislodged and the gel would tend to dry out.
A truly innovative TENS electrode was the Medtronic “Epiductive” skin electrode. It consisted of a microparticle imprgnated conductive tape activated by a solvent which allowed microparticles to enter the epidermis and make a highly efficient electrical contact. Further research into Epiductive and its use in pattern displays on skin were not pursued by Medtronic.
Shown here is a 3M Corporation compound skin electrode utilizing a contained gel on its skin surface. The hardy and effective design serves well for TENS as well as external stimulation for bone growth devices and different types of skin monitoring, particularly for cardiologic purposes.
Skin electrodes are more practical today but it is clear that the technology remains in its infancy when compared to more sophisticated applications of transcutaneous drug delivery, pattern stimulation and other, more advanced applications.