(E-187) 3D Printed Dry Electrodes

Introduction:: Electrodes are small, electrically conductive devices that measure muscle, brain, or heart electrical signals when applied to the skin. An ECG(Electrocardiogram) is a graphical display of heart signals. ECGs are useful for quickly and painlessly monitoring heart health. Traditional electrodes use a conductive gel to reduce the electrical impedance between the skin and the electrode surface. Reducing electrode-skin impedance limits signal attenuation, power line interference, and movement noise. These traditional "wet electrodes" take a long time to apply, leaving gel residue on the skin and other surfaces, and the gel tends to dry after a few hours, increasing impedance[1]. Dry electrodes eliminate these problems by forgoing the gel[2], [3] and can also be manufactured for cheaper and in less time using a standard 3D printer. This experiment investigates if cheap, 3D-printed dry electrodes can produce similar-looking ECGs to traditional wet electrodes.

Materials and Methods:: All of the dry electrodes were printed from the same two 3D object files: The conductive electrode body and the TPU(Thermoplastic polyurethane) shield to block interference. Electrode bodies were quality controlled for smooth contact surfaces. A smooth surface decreases skin-electrode impedance(The bottom layer's smoothness tends to depend on bed temperature, nozzle temperature, and nozzle height). This experiment investigates a conductive PLA(Polylactic Acid) blend, a conductive ABS(Acrylonitrile Butadiene Styrene) blend, and a silver conductive paint that can be applied to an electrode of any filament. The ECGs were digitized using National Instrument hardware and software. MATLAB post-processing was used to denoise the dry-electrode ECGs. The filters applied are a 60 Hz notch filter for transmission line interference, a Chebyshev II lowpass filter for high-frequency muscle contraction noise, and a Chebyshev II highpass filter for DC and baseline wander.

Results, Conclusions, and Discussions:: The quality of the ECGs was dependent on the electrode's impedance. The silver-painted electrodes had impedances of around 10 ohms and therefore produced ECGs similar to the wet electrode ECGs. The PLA and ABS electrodes had impedances around 5k ohms and around 25k ohms, respectively. They both produced ECGs that needed denoising to produce similar-looking ECGs to the wet electrode ECGs. The cost estimation of a 3D-printed dry electrode is about 25% of a commercial wet electrode.
This experiment showed that 3D-printed dry electrodes could produce similar-looking ECGs to traditional wet electrodes with DSP denoising.
Future work in this subject could be on ways to maximize signal integrity through filtering. Once a dry electrode prototype reaches comparable signal integrity to wet electrodes, new manufacturing techniques could be utilized to measure commercial viability. 3D printing is a great tool for prototyping new technology but is slow and costly compared to injection molding.

Acknowledgements (Optional): :

References (Optional): : [1] Ask, P., Öderg, P. Å., Ödman, S., Tenland, T., & Skogh, M. (1979). ECG Electrodes: A Study of Electrical and Mechanical Long‐term Properties. Acta Anaesthesiologica Scandinavica, 23(2), 189-206.
[2] Gruetzmann, A., Hansen, S., & Müller, J. (2007). Novel dry electrodes for ECG monitoring. Physiological measurement, 28(11), 1375.
[3] Salvo, P., Raedt, R., Carrette, E., Schaubroeck, D., Vanfleteren, J., & Cardon, L. (2012). A 3D printed dry electrode for ECG/EEG recording. Sensors and Actuators A: Physical, 174, 96-102.