Wearable technologies represent the new frontier of vital signs monitoring in different
applications, from fitness to health. With the progressive miniaturization of the electronic
components, enabling the implementation of portable and hand-held acquisition and recording
devices, the research focus has shifted toward the development of effective and unobtrusive
textile electrodes. This work deals with the study, development and characterization of
organic-polymer-based electrodes for biopotentials.
After an overview of the main materials and fabrication technologies presented so far in
the scientific literature, the possibility to use these electrodes as an alternative to the Ag/AgCl
disposable gelled electrodes usually adopted in clinical practice was tested. For this purpose,
several textile electrode realization techniques were studied and optimized, in order to create
electrodes with adequate features to detect two fundamental physiological signals: the electrocardiogram
(ECG) and the electromyogram (EMG). The electrodes were obtained by depositing
on the fabric the organic bio-compatible polymer poly(3,4-ethylenedioxythiophene)
doped with poly(4-styrenesulfonate) (PEDOT:PSS) with three deposition procedures: dipcoating,
ink-jet printing and screen printing. The physical\u2013chemical properties of the polymer
solution were varied for each procedure to obtain an optimal and reproducible result. For
what concerns the ECG signal, the research activity focused on screen-printed textile electrodes
and their performance was first assessed by benchtop measurements and then by
human trials. The first tests demonstrated that, by adding solid or liquid electrolytes the
electrodes, the largest part of the characteristics required by the ANSI/AAMI EC12:2000
standard for gelled ECG electrodes can be achieved. Tests performed in different conditions
showed that the skin contact impedance and the ECG morphological features are highly
similar to those obtainable with disposable gelled Ag/AgCl electrodes (\u3c1 > 0.99). A trial
with ten subjects revealed also the capability of the proposed electrodes to accurately capture
with clinical instruments an ECG morphology with performance comparable to off-the-shelf
disposable electrodes. Furthermore, the proposed textile electrodes preserve their electrical
properties and functionality even after several mild washing cycles, while they suffered
physical stretching.
Similar tests were performed on screen-printed textile electrodes fabricated in two different
sizes to test them as EMG sensors, with and without electrolytes. After a series of
controlled acquisitions performed by electro-stimulating the muscles in order to analyze the
waveform morphologu of the M-wave, the statistical analysis showed a high similarity in
terms of rms of the noise and electrode-skin impedance between conventional and textile
electrodes with the addition of solid hydrogel and saline solution. Furthermore, the M-wave
recorded on the tibialis anterior muscle during the stimulation of the peroneal nerve was
comparatively analyzed between conventional and textile electrodes. The comparison provided
an R2 value higher than 97% in all measurement conditions. These results opened their
use in smart garments for real application scenarios and for this purpose were developed a
couple of smart shirts able to detect the EGC and the EMG signal. The results indicated that
this approach could be adopted in the future for the development of smart garments able to
comfortably detect physiological signals
