Liquid silicone rubber (LSR)-based dry bioelectrodes: The effect of surface micropillar structuring and silver coating on contact impedance

• We produced and tested liquid silicone rubber based dry bioelectrodes.
• We used smooth and micropatterned, uncoated and silver coated electrodes in the measurements.
• Our aim was to achieve as low contact impedance modulus as possible.
• The electrical impedance spectroscopy measurements were conducted using a skin model (gelatin gel).
• The results indicate that micropatterning and/or silver coating improve the electrode performance significantly.

Bioelectrode–skin contact impedances need to be minimized to enable high quality recordings of biopotentials. Low contact impedances can be achieved with large, effective bioelectrode–skin contact areas. In this study, novel dry microstructured electrodes based on electrically conductive liquid silicone rubber (LSR) were developed and characterized with electrical impedance spectroscopy (EIS) measurements. Two different micropillar structures with inter-pillar distances of 20 μm and 100 μm, respectively, were compared with smooth LSR electrodes, as such or coated with silver (Ag). A gelatin gel based skin model was used in EIS measurements to overcome the problems associated with real skin measurements. Both microstructurings were found to significantly decrease the contact impedance modulus. In addition, the Ag coating caused highly significant (p < 0.01) decrease in impedance modulus for each surface topography, e.g. for smooth electrodes the impedance drop was roughly from 140 ± 30 kΩ to 50 ± 10 kΩ at 1 Hz. The Ag coating combined with microstructuring expectedly revealed the most superior electrical characteristics as the contact impedance declined even as low as 10 ± 2 kΩ at 1 Hz. Instead, no statistically significant differences in impedance values were detected between the two microstructurings in the uncoated or Ag-coated electrodes. However, more sparse microstructuring (100) seemed to offer lower variation, i.e. more reproducible results. In conclusion, present microstructured electrodes that do not pierce any layer of skin but improve the contact to skin might be a good alternative to conventional wet electrodes.