Printed soft skin electrodes for seamless bio-impedance measurements

Abstract

Bio-impedance measurements are widely used to assess various physiological parameters.
Contemporary skin electrodes for bio-impedance measurements are cumbersome and novel
electrode designs are needed to allow fast and easy placement, long-term stability and user
comfort. This investigation introduces dry, printed, bio-compatible electrode arrays, made
of screen-printed carbon and inkjet-printed PEDOT:PSS that measure bio-impedance noninvasively
and stably. Two contact impedance measurements yield the lowest normalized
values of soft electrodes reported to date. Four contact bio-impedance measurements
from the radial, ulnar, common carotid and superficial temporal arteries were performed,
demonstrating the ability to capture blood pulsation in different areas with small form
factor. Owing to the unique properties of the printed electrodes reported here, we were
able to demonstrate for the first time blood pulsation in the face, continuous blood pulsation
measurement during simultaneous muscle activation and signal stability over many hours.

Soft electrodes for simultaneous bio-potential and bio-impedance study of the face

“…As clearly seen in figure 1(a1) and 1(a2), IPG records blood pulsation that can be readily seen when the electrodes are positioned in close proximity to an artery (ulnar artery in the forearm or superficial temporal artery in the face). As we recently demonstrated in [30], IPG recordings with soft-printed dry electrodes are characterized by high-quality signals and good stability, even under muscle activation.…”

“…Soft and dry electrodes were used for simultaneous IPG and sEMG measurements, to study how muscle activation affects the diameter of the superficial temporal artery in the face. We used unique screenprinted dry carbon electrodes which were extensively validated previously for bio-potential [29] and bioimpedance [30] measurements. As a reference, we also performed similar measurements on the forearm.…”

“…Foremost, we observe that the pulse shape differs between the forearm and face, with the secondary notch (the dicrotic notch [31]) being less pronounced at the face. Indeed pulse shape has a strong association with the electrode location [30,32]. Additionally, from the extremal points (corresponding to the pulsation itself), we can extract the pulse amplitude (ΔZ) and duration (Δt) (see figure 1(a1)), which characterize blood flow.…”

Bio-potential noise of dry printed electrodes: physiology versus the skin-electrode impedance

“…A fabrication process for inkjet-printed electrodes was used as described previously (Levit et al 2023). In short, a PixDro LP50 inkjet printer was used to fabricate silver-poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) dry electrodes on TPU substrates.…”

“…Kappel et al measured the impedance at two different areas of the ear and demonstrated a significant change in impedance values (Kappel et al 2019). Skin electrodes also tend to show a process of time-dependent stabilization (Levit et al 2023). Previous investigations showed that impedance values in the scalp were 15-50 kΩ • cm 2 before stabilization and after 15 min, the impedance was reduced to 5-15 kΩ • cm 2 .…”