materials Communication
Washable and Reliable Textile Electrodes Embedded into Underwear Fabric for Electrocardiography (ECG) Monitoring Amale Ankhili 1,2,3, *, Xuyuan Tao 1,2 , Cédric Cochrane 1,2 , David Coulon 3 and Vladan Koncar 1,2 1
2 3
*
École Nationale Supérieure des Arts et Industries Textiles/Génie et Matériaux Textiles Laboratory (ENSAIT/GEMTEX), 2 Allée Louis et Victor Champier, F-59100 Roubaix, France;
[email protected] (X.T.);
[email protected] (C.C.);
[email protected] (V.K.) GEMTEX, University of Lille, Cité Scientifique, F-59650 Villeneuve d’Ascq, France @HEALTH, Europarc de Pichaury, 1330 Rue Jean René Guillibert Gauthier de la Lauzière, F-13290 Aix-en-Provence, France;
[email protected] Correspondence:
[email protected]; Tel.: +33-320-258-694
Received: 14 December 2017; Accepted: 5 February 2018; Published: 7 February 2018
Abstract: A medical quality electrocardiogram (ECG) signal is necessary for permanent monitoring, and an accurate heart examination can be obtained from instrumented underwear only if it is equipped with high-quality, flexible, textile-based electrodes guaranteeing low contact resistance with the skin. The main objective of this article is to develop reliable and washable ECG monitoring underwear able to record and wirelessly send an ECG signal in real time to a smart phone and further to a cloud. The article focuses on textile electrode design and production guaranteeing optimal contact impedance. Therefore, different types of textile fabrics were coated with modified poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in order to develop and manufacture reliable and washable textile electrodes assembled to female underwear (bras), by sewing using commercially available conductive yarns. Washability tests of connected underwear containing textile electrodes and conductive threads were carried out up to 50 washing cycles. The influence of standardized washing cycles on the quality of ECG signals and the electrical properties of the textile electrodes were investigated and characterized. Keywords: textile electrodes; ECG; electrical properties; washability
1. Introduction The improvement of human health is an important objective that remains a relevant aim of research. Currently, cardiovascular diseases are the first cause of lethal issues worldwide. The “@Health” company has been created to improve health conditions by revolutionizing the way in which cardiovascular problems are diagnosed. The purpose of the company’s approach is not only to meet the needs for pre-diagnostic development linked to diseases whose symptoms only appear too late (or not at all), but also to increase economic requirements, as well as the need for mass prevention policy design. As cardiovascular diseases provoke 30% of deaths worldwide, @Health is developing custom medical monitoring solutions to anticipate the onset of symptoms and to implement as quickly as possible a treatment that will increase the chance of recovery. Analysis and alerting using real-time electrocardiogram (ECG) signals could be considered as a possible solution to decrease the death toll caused by heart diseases. The ECG signal quality is essential for permanent and accurate heart monitoring. It can be obtained from high-quality, flexible, textile-based electrodes embedded into underwear [1]. These electrodes should guarantee permanent contact with the skin, optimal reliability, washability, and acceptable lifetime.
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A number of more or less flexible and rarely stretchable electrodes already exist on the market or as prototypes in research laboratories. However, they are not yet adapted to reliable and washable underwear for ECG monitoring in real time able to generate a medical quality signal. The most-used electrodes are based on silver–silver chloride (Ag/AgCl). They consist of a silver base with an ionic compound silver chloride layer on its surface [2,3]. Nevertheless, they can provoke cutaneous reactions in combination with the hydrogel that is used to improve the contact impedance, after prolonged contact with the skin [4]. Furthermore, after repeated use, the silver chloride film can be damaged due to mechanical stresses. This type of electrode can be used for short-term diagnostic recording such as taking a clinical electrocardiogram in the hospital [3]. The basic metal plate (inflexible and non-stretchable) electrode is also used for ECG measurement. It contains a metallic conductor with a thin layer of electrolyte gel between the metal and the skin to insure a good contact with the skin and to decrease the contact resistance [3]. These electrodes could also be made of metallic foils. Sometimes they are produced in the form of a suction electrode. Metals used for this type of electrode include silver, gold, platinum, and nickel-silver alloys [3]. Thin-film flexible electrodes are basically the same as metallic plate electrodes; the only difference is the thickness of the metal, which is less than a micron. These metal films are usually supported on a flexible plastic substrate, such as polyester or polyimide plate [1,3]. Textile substrates intended to be used within underwear are expected to be lightweight, flexible, stretchable, conformable, washable, and long-lasting [5,6]. Conductive patterns on textiles can be achieved by micro-contact embedded electrodes, inkjet printing, and screen printing [1]. Thin stainless steel, copper, or other metal wires are employed to sew conductive patterns on textile fabrics by embroidery [7]. On the other side, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has exhibited growing potential, not only in flexible electronics, but also in biomedical devices, due to its excellent electrical properties, environmental stability, and decent biocompatibility [8, 9]. Electrodes made of PEDOT:PSS have already been successfully used in ECG measurements [6]. In this study, the fabrication of fully wearable electrodes using dip-coating technology of conducting polymer PEDOT:PSS on a commercial knitted fabric is reported. Knitted fabrics were chosen as substrates because of their high level of stretchability, allowing a good contact with the skin. Textile fabrics coated with PEDOT:PSS were assembled into textiles structures, such as bras, by sewing with conductive yarn, then textile electrodes were connected to ab ECG measurement device and high-quality ECG signals were successfully recorded. Washability tests of connected underwear were carried out up to 50 washing cycles, and ECG data, recorded from a healthy volunteer, were found to be stable. This experiment paves the way for the fabrication of low cost electrodes for cutaneous electrophysiology. The influence of the encapsulation process on the electrical properties of electronic modules during washing tests is under development in our laboratory [10] and will be investigated and analyzed later on. 2. Materials and Methods Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), also called PEDOT:PSS, type Clevios was purchased from Heraeus Conductive Polymers Division (Hanau, Germany). The conductive thread employed (Shieldtex 234/34-2 ply HCB) is silver-coated polyamide yarn, which is used for signal transmission. The linear resistance is less than 100 Ω/m, which is acceptable for sensing an ECG signal in a low energy consumption system. For the electrical surface resistance measurements, a Keithley 8009 device (Keithley Instruments Sarl, Les Ulis, France) was used. The washing tests were performed according to the standard ISO 6330 [11]. The washing test laboratory machine was a Datacolor AHIBA IR (Paris, France). For ECG measurements, an ambulatory device “Colson CardiPocket 2” (Cuers, France) was connected to textile-based PEDOT:PSS electrodes in order to determine the quality of the ECG signal. Three textile electrodes were manufactured by dip-coating. Polyamide, polyester, and cotton knitted fabrics were soaked in a chemically modified PEDOT:PSS solution and then dried at 110 ◦ C
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for 1 h. The electrodes have a solid circle shape with a diameter of 11 cm. These circular electrodes are cut to small electrodes (15 cm2 ) for integration into bras for women. The commercially available PEDOT:PSS solution had to be chemically modified in order to make it suitable for each textile fabric for the dip-coating process, particularly to guarantee optimal washing behavior. The nature of the chemical modification cannot be revealed in this article because of confidentiality issues. After drying, electrodes were rinsed in distillated water to eliminate all remaining particles. 3. Results and Discussion 3.1. PEDOT:PSS Absorption Textile fabrics exhibit various features depending on the structure and type of fibers. For this reason, three different knitted fabrics were selected to make ECG electrodes. Textiles need to be coated not only on the surface of the knitted structure, but also inside, providing continuous contact between the yarns during its mechanical deformation. The viscoelastic properties of PEDOT:PSS formulation allows a homogeneous coating of flexible knitted textiles, in our case, cotton, polyamide, and polyester. Table 1 shows that the cotton electrode absorbs more PEDOT:PSS than the polyamide or polyester electrodes. This is probably due to different adhesions in the function of the substrate material, particularly for polyester. This will be verified in our future studies. Table 1. Mass weight percentage of PEDOT:PSS after dip-coating. Textile Electrodes
Percentage of Absorbed PEDOT:PSS after Drying (wt %)
Cotton Polyamide Polyester
6% 4.4% 3.2%
3.2. Electrical Characterization The experimental characterization was realized according to ASTM D 257-99 [12] and IEC 61340-5-1 Standards [13]. Surface resistivity is defined as the electrical resistance of the surface of the material. It is measured from electrode to electrode along the surface of the sample. Surface resistivity measurement is carried out by a KEITHLEY 8009 resistivity test fixture (Figure 1). The sample was placed between two concentric ring electrodes. Its resistance was measured by sourcing a known voltage, and measuring the resulting current using Ohm’s Law. From the resistance measurement, the resistivity was determined based on the physical dimensions of the test sample (Equation (1)). A lower value of surface resistivity allows a good acquisition of the ECG signal, even if it is not directly related to the contact impedance between the electrode and the skin. ρs = 53.4
V I
(1)
where ρs is the surface resistivity of the sample, V is the applied voltage from the electrometer, and I is the current reading from the electrometer. Table 2 shows that the average surface resistivity of the cotton electrode (21.02 kΩ) is lower than that of the other electrodes. The difference in electrical conductivity between these electrodes seems to result from the PEDOT:PSS coating. As more PEDOT:PSS was absorbed by cotton, the cotton electrode consequently has the best electrical properties, followed by the polyamide and finally the polyester electrodes. To improve the absorption of PEDOT:PSS by hydrophobic substrates, the fabric surface could be treated by atmospheric plasma. In our case, there was not any surface preparation.
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Figure 1. Photo of KEITHLEY 8009 resistivity test fixture. Figure 1. Photo of KEITHLEY 8009 resistivity test fixture. Table 2. Surface resistivity (kΩ) as a function of the type of the substrate coated by PEDOT:PSS. Table 2. Surface resistivity (kΩ) as a function of the type of the substrate coated by PEDOT:PSS.
Textile Electrodes Textile Electrodes Cotton
Polyamide Cotton Polyamide Polyester Polyester
Surface Resistivity (kΩ) Surface Resistivity 21.02 (kΩ)
Standard Deviation (kΩ) Standard Deviation (kΩ) 0.64
34.26 21.02 34.26 36.31
0.74 0.64 0.74 0.84
36.31
0.84
The washability issue is always an obstacle in terms of application, reducing the reliability of wearable electrodes,issue and therefore making them not ready for the market and use in real Due to of The washability is always an obstacle in terms of application, reducing the life. reliability the capillary effect, textile substrates absorb water and the mechanical stresses provoked by the wearable electrodes, and therefore making them not ready for the market and use in real life. Due to the washing process may destroy the electrical contacts between the conductive threads. As a result, the capillary effect, textile substrates absorb water and the mechanical stresses provoked by the washing electrical resistance becomes uncontrollable after several washing cycles and the wearable electrodes process may destroy the electrical contacts between the conductive threads. As a result, the electrical become unstable and, in some cases, stop functioning. resistance becomes uncontrollable after several washing cycles and the wearable electrodes become To evaluate the electrical performance of our textile electrodes in a wearable configuration for unstable and, in some cases, stop functioning. long-term monitoring, 50 washing cycles at 40 °C for 30 min were realized according to ISO 6330 To The evaluate the standards electrical performance textile electrodes in a for wearable configuration [11]. washing offer a varietyofofour water temperature levels different applications,for ◦ long-term washing cyclesthe at 40 C forspeed 30 min realized according toisISO 6330 [11]. ranging monitoring, from 30 to 9250 °C. In this study, rotation is were 30 rpm. Surface resistivity measured The washing standards offer a variety of water temperature levels for different applications, ranging after every washing cycle. Then ratio Ri/R0 is calculated, where R0 is the surface resistance before ◦ from 30 to 92 study, the rotation speed 30washing rpm. Surface washing andC. RiIn is this the surface resistance after the is i-th cycle. resistivity is measured after every washing cycle.2 Then Ri /R0 is calculated, where R0 values is the surface resistance before washing and Figure showsratio the evolution of surface resistance of textile electrodes during washing Ri tests. is theFor surface resistance after the i-th washing cycle. cotton- and polyamide-based electrodes, the resistance increases linearly with the number 2 shows the evolution surfacecycle, resistance values of washing of Figure washing cycle. After the 50th of washing this increase fortextile cottonelectrodes electrodesduring (4.9 times) is slower that forpolyamide-based polyamide (9.2 times) or polyester ones (59 increases times). This result with can be tests. For than cottonand electrodes, the resistance linearly theexplained number of by the fact that polyester doeswashing not absorb PEDOT:PSS as well cottonelectrodes or polyamide. we washing cycle. After the 50th cycle, this increase forascotton (4.9 Otherwise, times) is slower can assume that polyester will exhibit the same linear behavior but with a different slope. At the than that for polyamide (9.2 times) or polyester ones (59 times). This result can be explained by the fact same time, does we can assume the remaining quantity PEDOT:PSS Otherwise, after 40 cycles leads to that polyester notalso absorb PEDOT:PSS as well as cotton of or polyamide. we can assume improper conduction, hence a sudden R i measurement increase, which indicates that PEDOT:PSS is that polyester will exhibit the same linear behavior but with a different slope. At the same time, we coveredthe onremaining the surfacequantity and consumed faster during washing cyclesto forimproper polyesterconduction, than for canevenly also assume of PEDOT:PSS after 40 cycles leads cotton or polyamide because of the poor adhesion of PEDOT:PSS to polyester. It should be mentioned hence a sudden Ri measurement increase, which indicates that PEDOT:PSS is evenly covered on the that this failure of the coating derives from the mechanical movement (bending, friction, etc.) during surface and consumed faster during washing cycles for polyester than for cotton or polyamide because the washing. of the poor adhesion of PEDOT:PSS to polyester. It should be mentioned that this failure of the coating derives from the mechanical movement (bending, friction, etc.) during the washing.
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60 50
Ri/Ro
40 30
Cotton
20
Polyester
10
Polyamide
0 0
10
20
30
40
50
washing cycle Figure 2. The evolution of Ri /R0 versus washing cycle. Figure 2. The evolution of Ri/R0 versus washing cycle.
3.3. Evaluation Evaluation of of Textile Textile Electrodes Electrodes in 3.3. in ECG ECG Monitoring Monitoring An ECG ECG signal signal of of medical medical quality quality is is necessary necessary for for permanent permanent monitoring, monitoring, and and accurate accurate heart heart An examining can be obtained from instrumented underwear only if it is equipped with high-quality, examining can be obtained from instrumented underwear only if it is equipped with high-quality, flexible, textile-based low contact impedance withwith the skin. In order to assess flexible, textile-basedelectrodes electrodesguaranteeing guaranteeing low contact impedance the skin. In order to the performance of our developed textile electrodes in biomedical monitoring in depth, we investigated assess the performance of our developed textile electrodes in biomedical monitoring in depth, we electrocardiography recordings before and after washing as well as during motion. investigated electrocardiography recordings before and after washing as well as during motion. Figure 33 shows shows the the schematic schematic representation representation of of aa normal normal ECG. ECG. The The P P wave wave represents represents atrial atrial Figure depolarization; the QRS (QRS complex corresponds to a specific part of the ECG considering Q, R, R, depolarization; the QRS (QRS complex corresponds to a specific part of the ECG considering Q, and SS waves; waves; It It corresponds corresponds to to the the depolarization depolarization of of the the right right and and left left ventricles ventricles of of the the human human heart) heart) and complex represents ventricular depolarization, and the T wave represents ventricular repolarization. Materials 2018, 11, x FORventricular PEER REVIEW 6 of 11 complex represents depolarization, and the T wave represents ventricular repolarization.
ECGs are normally printed on a grid. The horizontal axis represents time and the vertical axis represents voltage. In an ECG signal, Leads I, II, and III are called the limb leads. The electrodes that form these signals are located on the limbs—one on each arm and one on the left leg [14–16]. The limb leads form the points of what is known as Einthoven’s triangle [17]: Lead I: the voltage between the left arm (LA) electrode and right arm (RA) electrode. Lead II: the voltage between the left leg (LL) electrode and the right arm (RA) electrode. Lead III: the voltage between the left leg (LL) electrode and the left arm (LA) electrode. Textile electrodes were sewn into bras with conductive yarns, in order to connect them to the ECG device by using snap fastener buttons with crocodile clips (Figure 4). The distance between the electrodes is 14 cm. The size of electrodes is 15 cm2 per electrode. When wearing the bra, the right arm is replaced by the right chest and the left arm by the left chest. In the right and left leg, we connect metallic medical electrodes; therefore, the performance of textile electrodes is more relevant in the first lead (lead I) because it represents the voltage between two sewn textile electrodes.
Figure 3. Schematic representation of a normal electrocardiogram (ECG). P, Q, R, S, T are graphical Figure 3. Schematic representation of a normal electrocardiogram (ECG). P, Q, R, S, T are graphical deflections of a typical electrocardiogram. They express depolarization and repolarization of the deflections of a typical electrocardiogram. They express depolarization and repolarization of the human heart. human heart.
ECGs are normally printed on a grid. The horizontal axis represents time and the vertical axis represents voltage. In an ECG signal, Leads I, II, and III are called the limb leads. The electrodes that
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form these signals are located on the limbs—one on each arm and one on the left leg [14–16]. The limb leads form the points of what is known as Einthoven’s triangle [17]: Lead I: the voltage between the left arm (LA) electrode and right arm (RA) electrode. Lead II: the voltage between the left leg (LL) electrode and the right arm (RA) electrode. Lead III: the voltage between the left leg (LL) electrode and the left arm (LA) electrode. Textile electrodes were sewn into bras with conductive yarns, in order to connect them to the ECG device by using snap fastener buttons with crocodile clips (Figure 4). The distance between the electrodes is 14 cm. The size of electrodes is 15 cm2 per electrode. When wearing the bra, the right arm is replaced by the right chest and the left arm by the left chest. In the right and left leg, we connect Figure 3. Schematic representation of a normal electrocardiogram (ECG). P, Q, R, S, T are graphical metallic medical electrodes; therefore, the performance of textile electrodes is more relevant in the first deflections of a typical electrocardiogram. They express depolarization and repolarization of the lead (lead I) because it represents the voltage between two sewn textile electrodes. human heart.
(a)
(b) Figure into bras; bras; (b) (b) Polyamide Polyamide electrodes electrodes sewn sewn into into bras. bras. Figure 4. 4. (a) (a) Cotton Cotton electrodes electrodes sewn sewn into
In order to reduce muscle movements and respiratory artifacts, as a first measurement, the In order reduce muscle and respiratory artifacts, assignals a first that measurement, volunteer wastositting at rest. Thismovements position allows obtaining high-quality can be usedthe to volunteer was sitting at rest. This position allows obtaining high-quality signals that can be used to detect heart function anomalies. The above ECG measurement tests conducted for static postures detect heart function anomalies. conducted static postures were were recorded successfully withThe noabove prior ECG skin measurement preparation ortests application of for conductive gels. With recorded successfully with no prior skin preparation or application of conductive gels. With the cotton and polyamide electrodes, decent ECG signals were obtained for medical analysis. Figures 5 and 6 show that before and after 50 washing cycles, the P and Q wave and QRS complex corresponding to the different phases of polarization and depolarization of cardiac cells were easily observed in the signals recorded using both the cotton and polyamide electrodes. The ST (the ST segment is the interval between S and T waves; it is important to have a clear view of it to track ischemic issues) segment was also observed, which is very important for myocardial ischemia and ventricular arrhythmias detection.
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the cotton and polyamide electrodes, decent ECG signals were obtained for medical analysis. the cotton and6 show polyamide electrodes, decent ECG signals for and medical Figures 5 and that before and after 50 washing cycles,were the P obtained and Q wave QRS analysis. complex Figures 5 and 6 show that before and after 50 washing cycles, the P and Q wave and QRS complex corresponding to the different phases of polarization and depolarization of cardiac cells were easily corresponding the different phases of both polarization andand depolarization cardiac cells easily observed in thetosignals recorded using the cotton polyamide of electrodes. Thewere ST (the ST Materials 2018, 11, 256 7ST of 11 observed theinterval signals between recorded Susing the cotton and polyamide The (the segment isinthe and Tboth waves; it is important to have electrodes. a clear view of ST it to track segment the interval between S and T waves; it isis important to have clear view ischemia of it to track ischemic is issues) segment was also observed, which very important foramyocardial and ischemic issues) segmentdetection. was also observed, very importantPEDOT:PSS-coated for myocardial ischemia and ventricular arrhythmias However, which for theispolyester-based electrodes However, for the polyester-based PEDOT:PSS-coated electrodes (Figure 7), P, QRS, and T waves were ventricular arrhythmias However, for the polyester-based PEDOT:PSS-coated (Figure 7), P, QRS, and detection. T waves were not recognizable; therefore, the acquired signalselectrodes from the not(Figure recognizable; therefore, the acquired signals from the polyester electrodes weresignals not acceptable 7), P, QRS, and T waves were not recognizable; therefore, the acquired from thefor polyester electrodes were not acceptable for our application. This failure is due not only to the lower ourpolyester application. This failure is due not onlyfor toour the application. lower quantity offailure PEDOT:PSS absorbed electrodes wereabsorbed not acceptable This is due not only between toby thepolyester, lower quantity of PEDOT:PSS by polyester, but also to the high contact impedance the butquantity also to the high contact impedance between the skin and the polyester electrode. absorbed by polyester, but also to the high contact impedance between the skin and of thePEDOT:PSS polyester electrode. skin and the polyester electrode.
(a) (a)
(b) (b)
Figure 5. Electrocardiography at rest from the cotton electrode (a) before washing, and (b) after Figure 5. Electrocardiography at rest from the cotton electrode (a) before washing; and (b) after Figure 5. Electrocardiography at rest from the cotton electrode (a) before washing, and (b) after 50 washing cycles. 50 washing cycles. 50 washing cycles.
(a) (a)
(b) (b) Figure 6. Electrocardiography at rest from the polyamide electrode (a) before washing, and (b) after Figure 6. Electrocardiography at rest from the polyamide electrode (a) before washing, and (b) after 50 washing cycles. Figure 6. Electrocardiography at rest from the polyamide electrode (a) before washing; and (b) after 50 washing cycles. 50 washing cycles.
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(a)
(b) Figure 7. Electrocardiography at rest from the polyester electrode (a) before washing, and (b) after Figure 7. Electrocardiography at rest from the polyester electrode (a) before washing; and (b) after 50 washing cycles. 50 washing cycles.
ECG signals were evaluated after 50 washing cycles, captured by the cotton and polyamide ECG signals were evaluated after 50 washing cycles, captured by the cotton and polyamide electrodes in motion to investigate if these electrodes are proper for long-term monitoring where no electrodes in motion to these proper for long-term no skin preparation is investigate allowed andif no gelelectrodes is added. are ECG measurements weremonitoring conducted where in three skindifferent preparation is allowed and no gel is added. ECG measurements were conducted in three different postures: sitting on a chair with arms on a desk, walking, and climbing stairs. Good-quality postures: onbea obtained chair with arms on a desk, walking, and climbingtextile stairs.electrodes Good-quality signalssitting should from a woman wearing a bra containing as shesignals goes through her daily routine. should be obtained from a woman wearing a bra containing textile electrodes as she goes through her In ECG measurement, the quality of ECG signals depends on the contact impedance between daily routine. the body the wearable electrodes. contact is liable to drop of a impedance change in motion or In ECG and measurement, the quality ofThis ECG signals depends on because the contact between posture. Figures 8 and 9, there are three ECGissignals recorded (a) at rest, walking, and (c) the body andInthe wearable electrodes. This contact liable to drop because of a (b) change in motion or climbing stairs. In all of the cases, lead I is relative to the signal recorded from the two chest posture. In Figures 8 and 9, there are three ECG signals recorded (a) at rest, (b) walking, and (c) climbing electrodes, leadcases, II between right chest electrode and the left leg the electrode, andelectrodes, lead III between stairs. In all of the lead Ithe is relative to the signal recorded from two chest lead II the left chest electrode and the left leg electrode. It is obvious that the signal quality is best when between the right chest electrode and the left leg electrode, and lead III between the left chest electrode only the two chest electrodes are used, particularly in motion. This case is the best for our and the left leg electrode. It is obvious that the signal quality is best when only the two chest electrodes application, as the ECG signal should be recorded only using the underwear. As it can be seen from are used, particularly in motion. This case is the best for our application, as the ECG signal should Figure 8, using polyamide electrodes subjected to 50 washing cycles, the lead I of ECGs taken with be recorded only using the underwear. As it can be seen from Figure 8, using polyamide electrodes the polyamide electrodes have stable P, R, and T wave amplitudes, indicating that the influence of subjected to 50 washing cycles, the lead I of ECGs taken with the polyamide electrodes have stable P, R, motion is significantly lower on the recordings of these electrodes. Leads II and III exhibit some and variation T wave amplitudes, indicating the influence of by motion significantly on the in amplitudes and arethat more contaminated noiseisbecause, whilelower walking andrecordings climbing of these electrodes. Leads II and III exhibit some variation in amplitudes and are more contaminated by stairs, the crocodile clip connected to the metallic medical electrodes on the legs tends to move. noise because, while walking and climbing stairs, the crocodile clip connected to the metallic medical However, P, QRS, and T waves are still recognizable in lead I. Thus, the acquired signals are electrodes on the to move. However, P, QRS, and the T waves still recognizable in lead acceptable for legs our tends application. Figure 9 shows that with cottonare electrodes put through 50 I. Thus, the acquired acceptable ourHowever, application. Figure 9 shows theare cotton washing cycles, atsignals rest, theare signal is quitefor good. during motion tests,that the with signals not electrodes put through 50complex, washing and cycles, at rest,are thenot signal is quite good. However, during acceptable as P, QRS T waves detectable. This failure is due to themotion poor tests,connection the signalsbetween are not the acceptable as P, QRS complex, and T waves are not detectable. This failure crocodile clips and the ECG device. We can also conclude that the surfaceis due to the poor connection between the crocodile clips and the ECG device. We can also conclude that
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the surface resistivity of the electrode does not play an important role for the ECG recording, because resistivity of the electrode does not play an important role for the ECG recording, because after the after the washing the cotton with lower surface resistivity had worse ECG signals resistivity theprocess, electrode does not electrodes play anwith important for the ECG recording, because the washing of process, the cotton electrodes lower role surface resistivity had worse ECGafter signals compared to the polyamide electrodes. We suppose that the contact impedance between the electrode washing process, cotton electrodes surface resistivity worse ECG signals compared to the the polyamide electrodes.with We lower suppose that the contact had impedance between the and the skin and istoanother factor that impacts the ECG recording. compared the polyamide electrodes. We suppose that recording. the contact impedance between the electrode the skin is another factor that impacts the ECG electrode and the skin is another factor that impacts the ECG recording.
(a) (a)
(b) (b)
(c) (c)
Figure 8. Electrocardiography from the polyamide electrodes after 50 washing cycles (a) at rest, Figure 8. Electrocardiography from the polyamide electrodes after 50 washing cycles (a) at rest; Figure 8. Electrocardiography from the polyamide electrodes after 50 washing cycles (a) at rest, (b) when walking, and (c) when climbing stairs. (b) when walking; and (c) when climbing stairs. (b) when walking, and (c) when climbing stairs.
(a) (a)
(b) (b) Figure 9. Cont.
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(c) Figure 9. Electrocardiography from the cotton electrodes after 50 washing cycles (a) at rest, (b) when Figure 9. Electrocardiography from the cotton electrodes after 50 washing cycles (a) at rest; (b) when walking, and (c) when climbing stairs. walking; and (c) when climbing stairs.
4. Conclusions 4. Conclusions In this paper, a chemical formulation has been developed, based on PEDOT:PSS appropriate for In this paper, a chemical formulation has been developed, based on PEDOT:PSS appropriate the dipping of various textile fabrics (cotton, polyamide, and polyester), making flexible electrodesfor thefor dipping of various textile fabrics (cotton, polyamide, and polyester), making flexible electrodes long-term monitoring as compared to gel electrodes (Ag/AgCl) which are disposable and causefor long-term monitoring compared to gel electrodes which are disposable and cause skin skin irritation. Thereasare three main advantages of (Ag/AgCl) the proposed solution in our paper over other irritation. There are three main advantages ofthose the proposed solutiontextile in ourfabrics, paper over other conductive conductive fabrics. Firstly, compared with non-conductive PEDOT:PSS-coated fabrics. withmechanical those non-conductive PEDOT:PSS-coated textile fabrics textileFirstly, fabricscompared have similar properties, textile such asfabrics, bending, stiffness, and abrasion [18]. (PEDOT:PSS). This is not the case for metallic-based which may be[18]. uncomfortable, such as is have similar mechanical properties, such as bending, electrodes stiffness, and abrasion (PEDOT:PSS). This Ag/AgCl ECG-gel-electrodes andwhich metal may clips.be The wearer found that electrodes notmedical the case for metallic-based electrodes uncomfortable, suchthe as textile medical Ag/AgCl are much more comfortable metallic electrodes. Secondly, compared with traditional organic ECG-gel-electrodes and metalthan clips. The wearer found that the textile electrodes are much more conductor-based conductive fabrics, the main drawbacks of poor washability and aging were solved comfortable than metallic electrodes. Secondly, compared with traditional organic conductor-based within our approach to the PEDOT:PSS-coated fabric. Thirdly, thewere dip-coating technique can be conductive fabrics, the main drawbacks of poor washability and aging solved within our approach easily applied during textile manufacturing and is fully compatible with knitted fabrics thanks totextile the to the PEDOT:PSS-coated fabric. Thirdly, the dip-coating technique can be easily applied during rheological properties of PEDOT:PSS. manufacturing and is fully compatible with knitted fabrics thanks to the rheological properties of To evaluate the overall quality of the acquired ECG signals by textile electrodes, washability PEDOT:PSS. tests of underwear equipped with fully textile electrodes (cotton, polyamide, and polyester coated To evaluate the overall quality of the acquired ECG signals by textile electrodes, washability tests with PEDOT:PSS) connected to a “Colson CardiPocket 2” ECG recording device using conductive of underwear equipped with fully textile electrodes (cotton, polyamide, and polyester coated with thread Shieldtex 234/34-2 ply HC+B were carried out up to 50 washing cycles. Several observations, PEDOT:PSS) connected to a “Colson CardiPocket 2” ECG recording device using conductive thread important for smart and connected clothing development, have been noted: (i) the absorption of Shieldtex 234/34-2 ply HC+B were carried out up to 50 washing cycles. Several observations, important PEDOT:PSS depends on the nature of the intrinsic fibers of the textile used as a substrate; (ii) a forcommercially smart and connected have been noted:Clevios (i) the is absorption of PEDOT:PSS availableclothing solutiondevelopment, with dispersed PEDOT:PSS well adapted to the depends on the nature of the intrinsic fibers of the textile used as a substrate; (ii) a commercially dip-coating of textile substrates; (iii) the obtained textile electrodes with cotton and polyamide as available solution with dispersed PEDOT:PSS is well adapted to theadip-coating textile substrates are washable for at least 50 washing Clevios cycles and are able to generate decent ECG of signal, substrates; (iii) the obtained textile electrodes with cotton and polyamide as substrates are washable even in motion in the case of the polyamide electrodes. This may be explained by the partial dyeing forofat the leasttextile 50 washing cycles and are able tosolution, generateas a decent ECG even in highlighting motion in thethe case fibers with the PEDOT:PSS opposed to signal, just a coating, of the polyamide electrodes. This may be explained by the partial dyeing of the textile fibers with the long-term stability of the electrodes. PEDOT:PSS solution, as opposed to justthe a coating, the long-term of the It is very important to underline fact thathighlighting the skin condition will varystability from person toelectrodes. person. The the shape of the ECGthe signal not only on the will surface resistivity of electrodes It quality is very and important to underline factdepends that the skin condition vary from person to person. also on impedance the skin and electrodes. For this reason, of ourelectrodes future Thebut quality andthe thecontact shape of the ECG between signal depends not only on the surface resistivity research work will focus on a novel method to optimize the ECG signal acquired by our electrodes. but also on the contact impedance between the skin and electrodes. For this reason, our future research This method based on minimizing the the contact in order analyze how it varies as work will focus will on abe novel method to optimize ECGimpedance signal acquired by to our electrodes. This method a function type of textile and the skin properties of the wearer. will be basedofonthe minimizing the electrodes contact impedance in order to analyze how it varies as a function of the type of textile electrodes and the skin properties of the wearer. Acknowledgments: Partial funding of this work was obtained from ANRT and @HEALTH Company.
Acknowledgments: Partial funding ofand thisVladan work was obtained ANRTconcept and @HEALTH Company. Author Contributions: David Coulon Koncar definedfrom the general of the study, Cédric Cochrane and Xuyuan Tao contributed to the definition processes and measuring and Amale Ankhili defined Author Contributions: David Coulon andofVladan Koncar definedmethods, the general concept of the study, the materials and their modifications, as well as to performed all of the to the production and Cédric Cochrane and Xuyuan Tao contributed the definition ofprocedures processes related and measuring methods, and characterization of electrodes, and wrote the text of the manuscript. Amale Ankhili defined the materials and their modifications, as well as performed all of the procedures related to the production and characterization of electrodes, and wrote the text of the manuscript. Conflicts of Interest: The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflict of interest.
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