Note: Descriptions are shown in the official language in which they were submitted.
PRINTED ECG ELECTRODE AND METHOD
BACKGROUND OF THE INVENTION
[0001] Cardiovascular disease (CVD) is a major cause of death.
Electrocardiogram (ECG) is one of the most frequently used techniques for
monitoring the heart's electrical signals to investigate and diagnose symptoms
related to heart problems. Even though wet Ag/AgCI electrodes are widely used
for monitoring ECG signals and have good signal stability, it has drawbacks
such
as requiring skin preparation and using conductive gels that often causes
irritation or allergies of the skin. In addition, motion artifacts reduce the
performance of wet electrodes due to relative motion of electrodes with the
body
as well as drying of the conductive gel.
[0002] Several research groups have reported on the use of dry electrodes
such
as nanofiber web textile dry electrodes, silver nanowire dry electrode,
conductive
fabric textile dry electrode and circular ring electrode for ECG measurements.
These dry electrodes can be applied for long-term ECG monitoring and used
multiple times without the use of conductive gel. However, the fabrication of
these dry electrodes may require the use of metallic electrodes as well as
metal
or rigid substrates, which are not conformal enough and may cause damage to
the skin. Several studies have
reported on the development of conductive polymers by coating, dispersing or
encapsulating metallic electrode surfaces with materials such as
polyvinylidene
fluoride
(PVDF), polydimethylsiloxane (PDMS) and conductive polymer foam. In addition,
traditional printing processes such as gravure, screen and inkjet have also
been
employed for the development of low cost, lightweight, biocompatible and
flexible
electronic devices.
[0003] In this work, screen printing process was used to fabricate dry ECG
electrodes by depositing silver (Ag) ink on flexible polyethylene
terephthalate
(PET) substrate. A multi-walled carbon nanotube (MWCNT)/
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polydimethylsiloxane (PDMS) composite was developed as a conductive polymer
and was bar coated on the screen printed electrode. The response of the dry
ECG electrodes, with three different radii, for monitoring ECG signals without
the
use of conductive gels or skin preparation was investigated.
BRIEF SUMMARY OF THE INVENTION
[0003a] According to an aspect of the invention, there is provided a method
of
fabricating a dry electrocardiogram (ECG) electrode, the method comprising:
printing conductive ink onto a polymer substrate to form a conductive
layer; and
coating at least a portion of the conductive layer with a composite material
comprising conductive carbon nanoparticles and a polymer material adherable to
a patient's skin.
[0003b] Preferred embodiments are presented below.
[0004] A flexible dry electrode comprises a multi-walled carbon nanotube
(MWCNT)/polydimethylsiloxane (PDMS) composite. The flexible dry electrode
may be utilized for monitoring electrocardiogram (ECG) signals. The dry ECG
electrode may be fabricated by screenprinting silver (Ag) ink on flexible
polyethylene terephthalate (PET) substrate, followed by bar coating of a
MWCNT/PDMS composite.
[0005] Another aspect of the present disclosure is a method of fabricating
a dry
ECG electrode includes printing conductive ink such as silver onto a polymer
substrate to form a conductive layer. At least a portion of the conductive
layer is
coated with a composite material comprising carbon nanoparticles disposed in a
polymer matrix material. The carbon nanoparticles may comprise multiwall
carbon nanotubes (MWCNTs), and the polymer matrix may comprise
polydimethylsiloxane.
[0006] These and other features, advantages, and objects of the present
invention will be further understood and appreciated by those skilled in the
art by
reference to the following specification, claims, and appended drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIGS. 1A, 1B, and 1C show screen printed dry ECG electrodes having
radii of 8 mm, 12 mm, and 16 mm, respectively;
[0008] FIG. 1D is a schematic cross sectional view of the ECG electrode of
FIG.
1C;
[0009] FIG. 2 is a perspective view of an ECG electrode test setup;
[0010] FIG. 3 is a graph showing ECG signal intensity for three different
dry
electrodes;
[0011] FIG. 4A is a graph showing the correlation between traditional wet
Ag/AgCL electrode and printed dry ECG electrode for a first electrode;
[0012] FIG. 4B is a graph showing the correlation between traditional wet
Ag/AgCL electrode and printed dry ECG electrode for a second electrode
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CA 02930837 2016-05-20
[0013] FIG. 4C is a graph showing the correlation between traditional wet
Ag/AgCL
electrode and printed dry ECG electrode for a third electrode;
[0014] FIG. 5A shows ECG signal measurements for a wet Ag/AgCL electrode
while the
body is in motion;
[0015] FIG. 5B shows ECG signal measurements for a wet Ag/AgCL first
electrode while
the body is in motion;
[0016] FIG. 5C shows ECG signal measurements for a wet Ag/AgCL second
electrode
while the body is in motion; and
[0017] FIG. 5D shows ECG signal measurements for a wet Ag/AgCL third
electrode while
the body is in motion.
DETAILED DESCRIPTION
[0018] For purposes of description herein, the terms "upper," "lower,"
"right," "left,"
"rear," "front," "vertical," "horizontal," and derivatives thereof shall
relate to the
disclosure as oriented in FIG. 1. However, it is to be understood that the
invention may
assume various alternative orientations and step sequences, except where
expressly
specified to the contrary. It is also to be understood that the specific
devices and
processes illustrated in the attached drawings, and described in the following
specification, are simply exemplary embodiments of the inventive concepts
defined in
the appended claims. Hence, specific dimensions and other physical
characteristics
relating to the embodiments disclosed herein are not to be considered as
limiting,
unless the claims expressly state otherwise.
[0019] As discussed in more detail below, a printed, flexible dry ECG
electrode 1 (FIGS.
1A-1C) according to the present disclosure comprises a multi-walled carbon
nanotube
(MWCNT)/polydimethylsiloxane (PDMS) composite layer 2 (FIG. 1D) that is
disposed on
a conductive layer 4 utilizing a bar coating process. The conductive layer 4
may be
formed by screen printing a suitable conductive ink such as silver (Ag) onto a
flexible
substrate 6. Flexible substrate 6 may comprise a suitable polymer material
such as a
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,
polyethylene terephthalate (PET). In use, the composite layer 2 is placed in
contact with
a patient's body (e.g. skin), and electrical signals produced by the patient's
body (e.g.
ECG signals) may be measured and processed utilizing known ECG
equipment/instruments.
[0020] As also discussed below, the performance of ECG electrodes
fabricated utilizing
the process were investigated by measuring ECG signals using printed dry
electrodes 1A,
13, 1C (FIGS. 1A, 1B, 1C) with radii varying from 8 mm to 16 mm, respectively.
The
electrodes may be circular, oval, or other suitable shape. The results were
compared
with a traditional wet Ag/AgCI ECG electrode (T716). It was observed that the
dry ECG
electrode 1C with the largest area (FIG. 1C), demonstrated better performance,
in terms
of signal intensity and correlation, when compared to the traditional wet ECG
electrode.
The response of the dry ECG electrodes 1A, 13, 1C are analyzed in more detail
below.
[0021] The flexible dry ECG electrode 1 may be printed with
conductive ink (e.g. silver)
on a thin polymer substrate and bar coated with PDMS that is doped with multi-
walled
carbon nanotubes (MWCNT). The PDMS sticks to human skin well, and the MWCNT
provides conductance of ECG signals to the electrode. The bar coating and
screen
printing may be accomplished utilizing known processes.
Example
The following is an example of a specific process utilized to fabricate an ECG
electrode.
It will be understood that the present invention is not limited to this
example.
A. Chemicals and Materials
[0022] PDMS, which was used to prepare the conductive polymer, was
purchased as a
two-part heat curable silicone elastomer kit (Sylgard 184) from Dow Corning.
High
purity MWCNTs (about 95%) were purchased from US Researchers Nanomaterial,
Inc.
with outer diameter of 20-30 nm, inner diameter of 5-10 nm and electrical
conductivity
>100 s/cm. Ag ink (Electrodag 479SS, Henkel) was used for metallization of the
dry
flexible ECG electrode. Flexible PET (Melinex 51506 PET, DuPont Teijin Films)
was used
as the substrate. Toluene solvent (Sigma Aldrich Chemical Company) was used to
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facilitate mixing and dispersion of both the PDMS and MWCNTs. Wet Ag/AgCI ECG
electrode (T716) was purchased from Bio-Protech Inc.
B. Conductive MWCNT/PDMS Composite Preparation
[0023] The composite polymer was developed by mixing conductive MWCNTs with
non-
conductive PDMS. In order to reduce the agglomeration due to Van der Waals
forces
and achieve a good dispersion, magnetic stirring was used in all steps.
SYLGARD6' 184
consisted of polymer base resin (Part-A) and curing agent (Part-B). First, a
MWCNT/Toluene dispersion was prepared by dispersing MWCNT in toluene (1:15
w/w)
and a PDMS Part-A/Toluene dispersion was prepared by dispersing PDMS Part-A in
toluene (1:3 w/w). Both the solutions were magnetically stirred for 1 hour at
room
temperature. Next, the MWCNT/Toluene dispersion was added to the PDMS Part-A
/Toluene dispersion and was mixed for 1 hour at room temperature using
magnetic
stirring. After this, the mixture was again magnetically stirred for 3 hours
on a hot plate
at 70 C to form the homogeneous MWCNT/PDMS composite with about 8% MWCNT by
weight. The solution was then sonicated for 30 minutes. Finally, PDMS Part-B
was added
to the solution (1:10 w/w) and magnetically stirred for 30 minutes at room
temperature.
C. Dry ECG Electrode Fabrication
[0024] A HMI MSP-485 high precision screen printer was used to print the Ag
ink on the
flexible PET substrate 6 (FIG. 1D). A 325 stainless steel mesh count screen
(Microscreen) with 28 [tm wire diameter, 22.5 angle and 12.7 m thick MS-22
emulsions was used. The printed Ag (layer 4, FIG. 1D) was cured in a VWR oven
at 120 C
for 20 minutes. The prepared MWCNT/PDMS composite was then bar coated on the
printed Ag layer 4 to form composite layer 2. Electrodes 1A, 1B, and 16 (FIGS.
1A, 1B,
1C, respectively) were formed with radii of 8 mm, 12 mm, and 16 mm,
respectively. The
electrodes 1A, 1B, and 1C include leads 8A, 8B, 8C, respectively. Electrodes
8A, 8B, and
8C may comprise a bare portion of conductive layer 4 disposed on flexible
substrate 6
that is not coated with composite layer 2. Finally, the ECG electrodes 1A, 1B,
and 1C
CA 02930837 2016-05-20
were again cured in a VWR oven at 120 C for 20 minutes to form the dry ECG
electrodes
1A, 1B, 1C, with three different radii of 8 mm (1A), 12 mm (1B) and 16 mm
(1C).
D. Experiment Setup
[0025] The performance of the fabricated dry ECG electrodes 1A, 1B, and 1C
was
investigated by monitoring ECG signals and comparing it against the response
of a wet
Ag/AgCI electrode. The experiment setup is shown in FIG. 2. It includes of a
power
supply 20 (Tektronix, PS280 DC power supply), digital oscilloscope 22
(Tektronix,
TDS510B Digital Phosphor Oscilloscope), printed dry ECG electrodes 1A, 1B, 1C
and an
ECG data acquisition electronic circuit 24. All measurements were conducted at
room
temperature. Three dry electrodes (1A or 1B or 1C), with similar radius, were
placed on
the body 26 of a healthy volunteer at three positions: left forearm 28, right
forearm 30
and right leg (not shown), without shaving the hair and with no skin
preparation. The
ECG electrodes 1A, 1B, 1C were retained via straps 32A, 32B with the composite
layer 2
in contact with the patient's skin. No conductive (wet) gel or other
conductive material
was positioned between the composite layer 2 and patient's skin. The
electrodes 1A,
1B, 1C were connected to the digital oscilloscope 22 for visualizing and
recording the
ECG signals. The ECG data acquisition electronic circuit 24 of this example
includes a
front end amplifier circuit, instrumentation amplifier, a driven right leg
(DRL) circuit, and
an active filter. The front end amplifier circuit contains a buffer amplifier
to ensure high
input impedance, and an AC coupler. The instrumentation amplifier is an Analog
Devices
INA 2128 chip with input impedance of 10 GO. The DRL circuit was used to
reduce the
common mode voltage in the biopotential amplifiers. The active filter consists
of a notch
filter, used to reduce 60 Hz base line interference, a Sallen Key low pass
filter, with a
cut-off frequency 150 Hz, and high pass filter, with cut-off frequency of 0.05
Hz.
[0026] The performance of the ECG signal measurements were recorded in both
the
relaxed sitting position and while the body is in motion. It is known that the
electrode-
skin impedance is dependent on the electrode contact area on the skin. Hence,
initially,
the influence of the dry ECG electrodes 1A, 1B, 1C area on the ECG signal
intensity was
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analyzed, in the relaxed position. It was observed that the peak-to-peak
amplitude of
the ECG signal was directly proportional to the area of the dry electrodes,
with a
maximum intensity for electrode 1C (FIG. 3). These results demonstrated that a
better
electrode performance is achieved by using the electrode (1C), which has a
bigger
electrode-skin interface area, for monitoring ECG signals.
[0027] The signal quality of the ECG signal, obtained using the printed dry
ECG
electrodes 1A, 1B, 1C, was then compared to that of the wet Ag/AgCI electrode,
in the
relaxed position (FIG. 4). In the ECG signals, a specific electrical event
during the heart
activity triggers different waves. In the results obtained, it was possible to
identify the
typical ECG characteristic wave components, which include the P wave, QRS
complex
and the T-wave. The QRS complex occurs as the ventricles in the heart
depolarize. The P
wave and the T-wave occur before and after the QRS complex, respectively. A
correlation of 0.85 (FIG. 4(A)), 0.93 (FIG. 4(B)) and 0.97 (FIG. 4(C)) was
calculated
between the wet Ag/AgCI electrode sensor and the dry ECG electrodes 1A, 1B,
and 1C,
respectively. The results obtained demonstrated that dry ECG electrode with
larger area
(1C) has a better correlation and hence a better electrode performance.
[0028] The ECG signal quality, while the body is in motion, was then
analyzed and
compared between the wet Ag/AgCI electrode and the printed dry ECG electrodes
1A,
1B, 1C. The responses of the wet and dry electrodes are shown in FIG. 5. It
was observed
that ECG signals obtained from the wet Ag/AgCI electrode and the printed dry
ECG
electrodes (1A and 1B) were less stable and noisier (FIG. 5(A), (B) and (C)).
Therefore,
the QRS complexes, P-wave and T-wave could not be observed clearly. It is
worth noting
that the QRS complexes are used to define and detect the R-R Interval (RRI)
length,
which is used to calculate the interval between neighboring QRS complexes and
can
reflect the information of the heart rate. It was difficult to observe and
distinguish the
R-peak for the wet Ag/AgCI electrode and the printed dry ECG electrodes (1A
and 1B),
due to the effect of motion artifacts. However, the response of the printed
dry ECG
electrode (1C) was better, in terms of identifying the typical ECG
characteristic
components: the P-wave, QRS complex and the 1-wave (FIG. 5(D)). The results
obtained
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demonstrate the capability of the fabricated printed dry electrode ECG sensor
(1C) to
detect the RRI and perform better than the wet Ag/AgCI sensor electrode and
the
printed dry electrodes (1A and 1B), while in motion.
Summary
[0029] Flexible dry ECG electrodes according to the present disclosure may
be
fabricated by integrating MWCNT/PDMS composite conductive polymers with a
screen
printing process. In the example discussed above, three different sizes of
electrodes
(1A, 1B, 1C) were fabricated by screen printing Ag ink on flexible PET
substrate 6 (FIG.
10) and MWCNT/PDMS was then bar coated on the printed Ag4 to form composite
outer layer 2. The capability of the flexible dry ECG electrodes 1A, 1B, 1C
for monitoring
ECG signals, without the use of any conductive gels or skin preparation, was
investigated
in both the relaxed sitting position and while the body is in motion. The
electrode
performance was analyzed by comparing the responses of the fabricated
electrodes 1A,
1B, 1C to that of a wet Ag/AgCI electrode. It was observed that the printed
dry ECG
electrode (1C), with the largest electrode-skin interface area, had a better
electrode
performance in terms of peak-to-peak signal intensity and correlation when
compared
to the wet Ag/AgCI electrode, in the relaxed position. Moreover, the typical
ECG
characteristic components were better distinguishable in the printed dry
electrode (1C)
when compared to the wet Ag/AgCI electrode and the printed dry electrodes (1A
and
1B), while in motion.
[0030] It is to be understood that variations and modifications can be made
on the
aforementioned structure without departing from the concepts of the present
invention, and further it is to be understood that such concepts are intended
to be
covered by the following claims unless these claims by their language
expressly state
otherwise. Specifically, the layers 2, 4, and 6 are not necessarily limited to
the specific
materials described herein. For example, spherical or approximately spherical
carbon
nanoparticles and/or carbon nanotubes (CNTs) could be utilized instead of (or
in
combination with) WMCNTs. Other suitable polymers could be utilized instead of
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PDMS. Also, the composite layer 2 could be formed using processes other than
bar
coating. Examples includes inkjet, screen, gravure, or flexo printing.
Similarly, the
conductive layer 4 may be formed using various conductive materials/inks (e.g.
silver,
gold, copper, etc.) that are applied using additive deposition processes such
as inkjet,
screen, gravure, and flexo printing.
[0031] The flexible substrate 6 could comprise other suitable materials
such as
Polyethylene napthalate (PEN), polyimide (Kapton ), or thermoplastic
polyurethanes
(TPUS). Although polymer materials are preferred for flexible substrate 6,
virtually any
non-conductive material having sufficient flexibility to conform to a body
part may be
utilized. Furthermore, the weight percentage of MWCNTs of the composite layer
2 may
be about 8% as described above, or other weight percentages (e.g. at least
about 2%,
4%, 6%, or ranges of about 6%40%, 4%-20%, or 1%-50%) may also be utilized. In
general, any weight % of CNTs or MWCNTs providing sufficient electrical
conductivity to
permit accurate ECG readings may be utilized. Still further, other types of
conductive
particles (e.g. carbon flakes) may also be utilized in the composite layer 2.
[0032] The thickness of composite layer 2, conductive layer 4, and flexible
substrate 6
are not limited to a specific range. However, substrate 6 may have a thickness
of about
50 pm to about 1000 m, conductive layer 4 may have a thickness of about 300
nm to
about 60 prn, and composite layer 2 may have a thickness of about 500 nm to
about
1000 m.
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