Development of Polypyrrole Textile Electrodes for Electromyography
S. Rodrigues, R. Miguel, J. Lucas, C. Gaiolas
Textile Science and Technology Department, Textile and Paper Materials R&D Unit, University of Beira Interior
Rua Marquês d’Ávila e Bolama, Covilhã, Portugal
P. Araújo
Computer Science Department, University of Beira Interior, Covilhã, Portugal
N. Reis
Biosurfit S.A., Lisbon, Portugal
Keywords: Wearable Technologies, Electromyography, Smart Structures Monitoring, Textile Electrodes, Polypyrrole
Conducting Polymer.
Abstract: Following the work already done, in particular the “textile arm" by the authors, incorporating metallic
filaments in the fabric during the weaving process with the aim of capturing surface electromyography
signals, we concluded that there was a need to maximise the area of contact with skin to improve the
obtained electrodes signals. The main objective of this work is the development of electrodes embedded into
textile materials able to capture electromyography signals, using the polypyrrole conducting polymer, both
in coating of electrodes directly into the textile fabric and preparing a conductor yarn with this polymer to
obtain a knit structure. This work allowed developing wearable technology textile structures for muscle
activity monitoring, through the measurement of electromyography signals, keeping simultaneously comfort
and easy-care textile characteristics. The signals obtained with this approach had a good definition
compared with commercial electrodes and with the great advantage of this procedure can be applied in
industrial production.
Through times, many have been the fields of science
and technology that progressed in separate ways.
During the last years, a considerable convergence
appeared among some of these fields, with
surprising results. The smart technology for
materials and structures is one of these results
(Lucas, 2007).
1.1 Wearable Technology
The smart textiles concept was firstly defined in
Japan in 1989 (Langenhove, 2007). With the
discovery of shape memory materials in 19600 and
intelligent polymeric gels in the 1970 decade, it was
accepted the birth of really smart materials. These
have been introduced in textiles only in the 90´s
(Langenhove, et al., 2006). Smart textiles can be
described as textiles that can feel stimuli from
environment, react and adapt themselves to them by
integrating functionalities in the textile structure
(Langenhove, et al., 2006).
The stimulus, as well as the response may be
electrical, thermal, chemical, magnetic or of other
kind. The degree of intelligence can be divided into
three subgroups:
Passive smart textiles that only feel, being
Active smart textiles that perceive external
stimuli and react to them, besides being
sensors, they act also as actuators;
Rodrigues S., Miguel R., Lucas J., Gaiolas C., Araújo P. and Reis N. (2009).
WEARABLE TECHNOLOGY - Development of Polypyrrole Textile Electrodes for Electromyography.
In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 402-409
DOI: 10.5220/0001548904020409
Truly smart textiles, being one step ahead
and able to adapt its behavior to the
circumstances (Zhang, 2001).
It would be wonderful to have clothes like our
skin, which is a smart material layer. Our skin has
sensors to detect pressure, pain, heat, etc. and,
together with the brain, can work in a smart manner
with environmental stimuli, generating large
amounts of perspiration to cool our body when in a
hot surrounding and stimulating blood circulation
when it is cool. It changes colour when exposed to a
high sun radiation level, in order to protect the body,
It is breathable and allows moisture penetration,
avoids the entry of undesired species, it can be
damaged, repaired and regenerate itself. Thus, to
study and develop a smart material like our skin is a
big challenge (Boczkowska, Leonowics, 2006).
To Bonato (2005), when looking for a better way
of life, more and more solutions have been
investigated to contribute to a comfort improvement
and well-being. The research field is going on and
several research groups have already demonstrated a
relevant application and the potential impact of this
technology is remarkable in clinic practices
concerning physical and rehabilitation treatments.
Presently, the main use of clinic techniques resides
on methods that embed devices into smart clothes on
in the patient’s body. The wearable technology has
a large potential to redirect these techniques into
functioning during the normal day life (Bonato,
The development of small size sensors that can
be connected to the body or can be a part of clothes,
embed elements into cloth fabrics, open a large
number of possibilities to monitor patients during
long periods of time. This is of particular relevance
to the practice of physical and rehabilitation
treatment. The wearable technology allows to
clinical staff the treatment of data, acquired at home
or by direct observations relating to the impact of
clinic interventions in mobility, thus reaching a
higher independence level and a better quality of
(Bonato, 2005).
1.2 Conductive Polymers
The firs conductive polymer was discovered
accidentally by Hideki Shirakawa in 1971
(Shirakawa, Ikeda, 1971) during a reaction with
acetylene. From this, it began research to understand
the charge transfer mechanisms in these (Neto,
The key to get a conductive polymer is the
presence of conjugate double bonds in the polymer
main chain. During conjugation, links between
carbon atoms are alternately single and double
bonds. Each double bond has a localized bond that
gives a strong attraction (σ bond) and a weaker one
(π bond). The electrical conductivity in polymers is
an effect due to π electron displacement in alternate
sequence of single and double bonds (Lucas, 2007),
as seen in Figure 1.
Figure 1: Illustration of π electrons displacement in
alternate sequence – electrical conduction (Lucas, 2007).
Conjugation is not enough to assure conduction
in a polymer. The doping function is now of an
agent seen as polymer charge carrier, as extra or
“missing” electrons (hole). One of these holes can be
filled by an electron jumping from a neighbor
position, creating a new hole and, thus, successively,
allowing a moving charge through a long (Lucas,
Polypyrrole is one of the most studied
conductive polymers due to its high conductivity,
good environmental stability, harmless and easy to
synthesize. Consequently, polypyrrole has
advantages in real applications in microelectronics,
informatics industry and biomedical information.
However, polypyrrole is not soluble in water and in
organic solvents, due to the strong intermolecular
and intramolecular interaction and crossed polymer
chains. For this reason, to overcome the non
solubility issue of polypyrrole, many research works
have been done (Pires, 2007).
Recently, soluble polypyrrole was synthesized
with large dope agents, such as dodecyl-benzene-
sulphonate acid (DBSA) and naphtale-sulphonate
(Lim, et al., 2005).
According to Dall’Acqua, L. et al. (2006), the
affinity of different types of fibers, yarns and fabrics
with doped polymers allows production of textile
composites having improved electrical properties.
Following the study of Lim., H. K. et al. (2005),
a new soluble and conductive polypyrrole, doped
with DBSA and combined with a polymeric agent,
the poly (ethylene glycol) (PEG).
WEARABLE TECHNOLOGY - Development of Polypyrrole Textile Electrodes for Electromyography
1.3 Electromyography Signal
According to J. Basmajian e C. De Luca (1985)
electromyography measures the electric activity
resulting from skeletal muscle activation, these
being responsible by the support and movement of
According to the Hospital Sant Pere Claver
Electromyography Unit at Barcelona,
electromyography is an electrophysiological study of
neuromuscular system; it is not a complementary
proof but an extension of a neurological study. This
basis of all electrophysiological research is the
registration of excitable cells potentials.
Electromyography deals with registering of such
potentials, self acting in the muscle and
electroneurography of evoked potentials, both on the
muscle and on nerve branches, by generally
electrical stimulation of nerves having anatomic
connection with the registering area. The electrical
properties of excitable nervous and muscle fibers
derive from a semi permeable membrane that
separates intracellular and extracellular fluids having
different ionic concentration origination a
transmembrane potential.
When measuring electromyography signals
(EMG’s) electrodes can be used placed inside the
muscle (deep electromyography) or electrodes
placed on the skin (surface electromyography)
(Sousa et al., 2007).
According to the type of acquisition, electrodes
may be invasive or not. When an electrode becomes
into contact with the body fluid is called invasive,
which can be of the yarn or needle type and presents
characteristics such as low electrical impedance, this
is, it does not need of conductive gel, it acquires
larger amplitudes and its power spectrum goes up to
10KHz (Ricciotti, 2006). They are most indicated
for clinical analysis, where it is possible to detect the
acting potential of a moving unit, as well as
exploring an isolated of a deep muscle. The invasive
electrodes have several drawbacks, being among
them excellent sterilization, the danger of breakage
of yarns inside the muscle and, after all, the patient´s
(Ricciotti, 2006).
According to Jacquelin Perry (1998), from the
28 main muscles that control each lower member,
most of them are surface muscles, being possible to
monitor their activity using surface
electromyography. During the last years, surface
electromyography (sEMG) has become very
frequent when studying and treating several muscle
dysfunctions, due to the fact that it is a secure
technique, easy to use and non-invasive. Most of
knowledge fields use EMG signals as starting point
to several human muscle system function and
dysfunction analysis. Recent studies relate the
muscle fatigue process to a displacement of signal
spectral contents. Other investigations emphasized
the importance of these signals in neuromuscular
reeducation of patients having hyperactive muscles
by electromyography biofeedback (Sartori et al.,
There several ways to configure EMG signal
acquisition through electrodes, the most common
being those requiring one (monopolar) and two
(bipolar) capturing points. The monopolar
configuration deals with the potential difference
between two points (a capturing and a reference
point). The bipolar configuration is characterized by
the potential difference between to acquisition
points, measured respecting to a third point
(reference). Electrodes are normally made of silver
coated with silver chloride (Ag-AgCl), since it is a
non polarizable noble metal.
The surface electrodes allow capturing signals
representing the activity of a muscle as a whole or a
group of muscles in a global manner and can be
subdivided into passive and active electrodes
(Barros, 2005 in: Ricciotti, 2006). The passive
electrode is constituted by a metal disk (in general,
Ag-AgCl), that must be placed over the skin (Figure
2). To decrease the contact impedance between
electrode and skin, it may be required a tricotomy
(pile removal from the region where the electrode
will be placed), the use of conductive abrasives and
gel or paste (Ricciotti, 2006).
a) Adhesive for electrode fixation;
b) Reusable electrodes;
c) Reusable electrodes detail;
d) Reusable electrodes rear view;
e) Reusable electrodes front view.
Figure 2: Examples of commercial passive electrodes
(Ricciotti, 2006).
BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices
The active electrodes have a magnifying circuit
encapsulated near the electrode acquisition place.
Generally, these are bipolar electrodes, this meaning
that the amplifier used is of differential type. The
active electrodes, since they are made of a
differential amplifier, require a reference electrode
placed ion an inactive region to avoid measurement
interference (Basmajian, De Luca, 1985). Such
electrodes are also called dry electrodes, since
generally do not need to use conducting gel, paste,
abrasives or pile (Ricciotti, 2006).
The textile support represents the first
functionality level of a wearable technology
architectures system, since it comprises the infra-
structure to embed the basic functions as energy and
data transmission or the sensorial (Rodrigues et al.,
Following work already done, namely the
“textile arm” (Rodrigues et al., 2008), where
conductive metallic yarns are incorporated into the
fabric during weaving with the aim to acquire
surface electromyography signals, it was observed
the need to optimise the contact region with the skin
to improve electrode signal acquisition. Aiming to
contribute to problem solving, it is studied now the
applicability of polypyrrole as a conductive polymer.
2.1 Printed Polypyrrole Electrodes
2.1.1 Textile Substrate
As textile substrate the dobby fabric developed in
the “textile arm” research work was used (Rodrigues
et al., 2008), having a compound weave based on
heavy twill 3 (Figure 3).
The main fabric characteristics are:
Cover Factor: 95.3%;
Weft density (DT): 19 yarns/cm;
Warp density (DB): 24 yarns/cm;
Warp yarn – 2/36Nm (45WO/53PES/2EA)
Weft yarn – 2/50Nm (45WO/55PES)
2.1.2 Reagent Preparation
The pyrrole solution was prepared with: 9% of
DBSA – doping agent that reduces inter and intra
interactions in polypyrrole chains, improving pyrrole
solubility in organic solvents; 9% of PEG –
polymeric additive and 82% distilled water.
These reagents are mixed at room temperature
with slow stirring (10-15minutes). After, pyrrole is
added on a 0.11ml/g ration of the prepared solution.
After dissolving completely, the resulting solution
was isolated from air. Due to the need of a viscous
solution, for coating, a printing paste with only a
thickener (6% Sodium Alginate) in water was
Figure 3: Compound weave module based on 2/1 twill 3
with metallic yarn (Rodrigues et al., 2008).
Since the pyrrole solution is quite unstable, the
oxidizing solution must be prepared before, which is
more stable. The oxidizing solution was prepared
with 20% of APS – oxidizing agent and 80%
distilled water.
2.1.3 Electrode Coating Methods
Following, the sodium alginate thickener was added
to the pyrrole solution on a 1/1 proportion. After a
complete mixing, the resulting paste was isolated
from air and kept at low temperature.
The fabric was pre-scoured in a bath containing
1g/l of Invadine LU (CIBA) – wetting agent, at 40ºC
during 20 minutes.
For electrode coating the respective area was
delimited and, to achieve a good electrode area
definition, the liquid oxidising solution was applied
first in excess followed by the pyrrole solution
thickened with sodium alginate (Figure 4). The
coated fabric was kept at room temperature for 15 to
30 minutes and then placed in a woven during 2
WEARABLE TECHNOLOGY - Development of Polypyrrole Textile Electrodes for Electromyography
Figure 4: Electrode coating device.
minutes at 100ºC.
To take out polypyrrole in excess from fabric
surface and, thus, to improve washing fastness, a
1g/l Reoklen detergent scouring at 50ºC and during
20 minutes was carried out.
2.2 Embroidered Polypyrrole
2.2.1 Reagent Preparation
A pyrrole solution was prepared having a ratio of
9ml of pyrrole to 100ml of DBSA and PEG in
distilled water, in the same way as described before
in 2.1.2. The oxidising solution used was also the
same as that employed in electrode coating.
2.2.2 Conductive Yarn Preparation
The chemical polymerization was achieved by
making the yarn go through the pyrrole solution and
after, through the oxidising solution, leaving
exposed at room temperature during 15 minutes and
after in a woven at 100ºC during 4 hours. To
eliminate excess of polypyrrole at the knit surface
and improve washing fastness, a detergent scouring
was performed.
2.2.3 Textile Substrate
As textile substrate a jacquard knit was used, being
the polypyrrole conductive yarn inserted into the
knit structure as shown in Figure 5. For knitting, a 3
ply 100% cotton yarn of 2/32Nm count was used. At
the electrode region, a polypyrrole treated 3 ply
100% wool yarn of 2/36Nm count was employed.
Figure 5: Jacquard knit structure showing electrode
In Figures 6 and 7 knit images are shown, being
emphasized conductive yarn and electrodes.
Figure 6: Knit right face with electrodes.
Figure 7: Knit back face with conductive yarns.
BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices
3.1 Electromyography Signal
To acquire surface electromyography signals
(EMG), an experimental system was developed
made by a lap top computer, a differential amplifier
and software for measuring physiological signals
(Elektor Electronics, 2007), as shown in Figure 8.
Figure 8: Experimental system for sEMG signal
To acquire surface electromyography signals
(aEMG), electrodes were placed on the arm and,
when hand squeezing a ball, the stimulated muscle
contracted. At the beginning, commercial electrodes
were used, these being placed on the arm to test the
equipment (Figure 9).
Figure 9: sEMG captured signal using commercial
Figure 10 shows the signal captured in the case
of “textile arm” produced with metallic filament and
embroidered electrodes using conductive yarn
(Rodrigues et al., 2008). In fact, the signal obtained
has a good definition and shows that this method is
adequate and can be used to measure the muscle
Figure 10: sEMG captured signal using hand embroidered
electrodes with metallic yarns (Rodrigues et al., 2008).
activity, for example, in rehabilitation.
However, this method doesn’t show a good
industrial feasibility, mainly because electrodes have
to be hand embroidered. For this reason, it became
necessary to develop embedded electrodes into
textile materials able to capture electromyography
signals and, at the same time, maximise the area of
contact with skin to improve the acquired signals by
electrodes. These signals captured by the “textile
arm” made with printed polypyrrole electrodes are
shown in figure 11. Also, the obtained signals with
the electrodes of the knit structure made with
polypyrrole treated yarns are shown in figure 12.
Figure 11: sEMG captured signal using polypyrrole coated
Figure 12: sEMG captured signal using polypyrrole
knitted electrodes.
WEARABLE TECHNOLOGY - Development of Polypyrrole Textile Electrodes for Electromyography
This data shows that we can obtain good definition
signals with the advantage that may have industrial
In this research work electrodes for wearable
technology were developed, enabling simultaneously
a high level of integration, to keep textile properties,
the conductive polymer properties and the signal
capturing through substrate functionality. Analysing
the clarity of acquired signals it can be concluded
that they are similar, the solutions found presenting,
compared to commercial sensors, the same
advantages than the hand embroidered electrodes in
the “textile arm” (Rodrigues et al., 2008), this is,
textile comfort, mobility, cleanness and
maintenance, etc. Besides these, they also exhibit
advantages at industrial feasibility level.
The acquired results are satisfactory, considering
the possible advantages of these may present sport
and clinical rehabilitation level and even considering
research work on neuromuscular development. Thus,
this work presents the development of textile
solutions that, being improved, both from the textile
point of view, through incorporating electronic
devices, and counting on the informatics
contribution, gather potentialities to perform in
future an important role in people’s quality of life.
The Authors wish to tank to Eduardo Jorge de Jesus,
technician at the Knitting Laboratory of Textile
Science and Technology Department of University
of Beira Interior, for his collaboration concerning
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WEARABLE TECHNOLOGY - Development of Polypyrrole Textile Electrodes for Electromyography