Fabrication and Characterization of Inkjet Printed Flexible Dry ECG Electrodes

Commercial gel ECG electrodes have a limited lifetime of operation and metal dry electrodes are rigid and noisy. In this study, we developed flexible dry ECG electrodes in different shapes and sizes using an inkjet printing (IJP) technology. As an additive manufacturing technique, IJP provides the flexibility to personalize the shape and size of electrodes with rapid prototyping. IJP ECG electrodes were fabricated on flexible polyimide substrates using silver nanoparticle inks for the conductive layer and a custom polymer ink of poly(4-vinylphenol) (PVP) for the insulator layer. The maximum and minimum diameters of the electrodes were 21 and 9 mm, respectively. The thickness of IJP electrodes was 2 ± 0.5
$\mu \text{m}$
. Various tests were performed for feasibility, including changing electrode position, and subject’s activity such as resting, standing, and walking using IJP ECG electrodes simultaneous with clinical standard gel electrodes, which provides an accurate comparison. Compared to the gel electrode, the circular shape IJP electrode was more promising than rectangular and square shapes as it showed more coherence to the gel electrode. IJP electrodes with different diameters were compared along with the gel electrode and the result demonstrated that the IJP electrode with a diameter of 21, 19, and 16 mm shows almost similar performance as the gel electrode. Considering ECG signal quality, IJP electrode with a diameter of 19 mm was the optimal size. These IJP dry electrodes can be usable in ECG wearable as it is flexible, reusable, and can be used for a long time.