Electric field-induced hydrogel, electrode and preparation method and application thereof

Abstract

The application discloses a preparation method of an electric field-induced hydrogel electrode and application thereof. The method mainly uses polyvinyl alcohol as a base material, combines conductive media (PEDOT:PSS, NaCl or CaCl), a chemical crosslinking agent (glutaraldehyde) and a reversible coordination crosslinking agent (sodium tetraborate decahydrate), and introduces tannic acid to improve adhesion. The core of the method is that the electric field-induced hydrogel is added dropwise to the surface of an electrode to be grown, a redox reaction is induced in a cathode area by applying an electric field, the pH value of a solution is rapidly increased, the coordination crosslinking of sodium tetraborate is activated, and the hydrogel is rapidly and in-situ solidified on the surface of the electrode. The hydrogel electrode prepared by the method has high tensile property, high conductivity and self-repairing characteristics, has low contact impedance and high signal-to-noise ratio, and can be used as a high-performance flexible electrode and applied to detection of electrocardiosignal and other electrophysiological signals, and has obvious advantages compared with commercial electrodes.

Description

Technical Field

[0001] This invention belongs to the field of electric field induced hydrogel technology, specifically relating to an electric field induced hydrogel, an electrode, its preparation method, and its application. Background Technology

[0002] With technological advancements, the pace of life has accelerated, and work pressure has increased, leading to a year-on-year rise in the incidence of cardiovascular diseases. Electrode patches, as an important tool for detecting electrophysiological signals, are widely used in the analysis of abnormal electrocardiograms (ECGs). Currently, conventional ECG electrodes mainly consist of a protective film, medical gel, carbon film (coated with silver or silver chloride), and lead connectors. During use, the electrode patch directly contacts the skin, and the lead connector connects to the ECG monitor. However, the medical gel, as the part that directly contacts the body and collects electrical signals, still suffers from problems such as high contact impedance and long preparation cycles.

[0003] Hydrogels possess excellent flexibility and biocompatibility, and their modulus is similar to that of skin tissue; however, their mechanical properties are typically poor, and their preparation time is relatively long. Therefore, developing electric field-induced hydrogels that are simple to prepare, reliable, durable, and highly tensile are crucial for the fabrication of reliable electrocardiogram (ECG) electrodes. Currently, commonly used hydrogel preparation methods include cyclic freeze-thaw cycles, photoinitiation, and thermosetting. Traditional cyclic freeze-thaw methods for preparing polyvinyl alcohol (PVA) hydrogels usually require more than three cycles to form a sufficient number of microcrystals in the polymer matrix, thereby achieving gelation and improving matrix strength. The entire process is time-consuming and cumbersome, and it is difficult to quickly achieve customized patterning of the hydrogel.

[0004] Therefore, it is essential to provide a novel electric field-induced hydrogel and its preparation method. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a hydrogel electrode that is fast to prepare, simple to process, and easy to pattern and customize, as well as its preparation method and application.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: The first aspect of this invention provides an electric field-induced hydrogel, comprising the following raw materials in parts by weight: 5-12.5 wt% polyvinyl alcohol; 1.5-3.0 wt% sodium chloride or calcium chloride; 0.10-1.00 wt% PEDOT:PSS; 0.10-0.80 wt% sodium tetraborate decahydrate; 0.10-0.60 wt% tannic acid; 5-25 wt% hydrochloric acid solution with pH=1-4; 0.005-0.10 wt% glutaraldehyde; and the balance being deionized water. The total mass of all raw materials is 100 parts by weight, and the balance being deionized water includes the deionized water used to prepare the polyvinyl alcohol aqueous solution, as well as the water carried in each aqueous solution / dispersion (including the pH=1-4 hydrochloric acid solution, PEDOT:PSS dispersion, glutaraldehyde solution, etc.).

[0007] It is understood that the amounts of PEDOT:PSS and glutaraldehyde are based on the active ingredient. The preferred amount of polyvinyl alcohol is 10 wt%. Furthermore, the electric field-induced hydrogel is cross-linked and cured by means of an electric field; wherein the voltage of the electric field is 1-5V and the application time is 60-300 seconds.

[0008] A second aspect of the present invention provides a method for preparing the above-described electric field-induced hydrogel, the method comprising: S1: Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; S2: Take sodium chloride, tannic acid and sodium tetraborate decahydrate, add hydrochloric acid solution and glutaraldehyde, mix well to obtain NaCl-TA-GA solution; S3: Add PEDOT:PSS and polyvinyl alcohol solution to the NaCl-TA-GA solution, mix well and remove air bubbles in the solution to obtain the electric field induced hydrogel.

[0009] Furthermore, S1 specifically includes: dissolving polyvinyl alcohol in deionized water, heating at 80-90°C and stirring magnetically for 1-2 hours to obtain a polyvinyl alcohol aqueous solution.

[0010] Further, S3 specifically includes: adding PEDOT:PSS and polyvinyl alcohol solution to the NaCl-TA-GA solution, sonicating for 30 minutes to mix evenly and remove air bubbles from the solution, to obtain the electric field-induced hydrogel. The preferred ultrasonic power is 240 W.

[0011] Furthermore, S4 includes: the electric field-induced hydrogel can be stored at room temperature; if it is not used for a long time and then reused, it needs to be ultrasonically homogenized again. The cured hydrogel, if not used in the short term, needs to be sealed with release paper and stored at low temperature.

[0012] A third aspect of the present invention provides a hydrogel electrode, comprising: an electrode, and the above-described electric field-induced hydrogel.

[0013] The fourth aspect of the present invention provides a method for preparing the above-mentioned hydrogel electrode, characterized in that the method includes: injecting the electric field-induced hydrogel onto the surface of the electrode, inducing a redox reaction by applying an electric field of 1-5V and then solidifying it to obtain the hydrogel electrode.

[0014] The fifth aspect of the present invention provides the application of the above-described hydrogel electrode as an electrocardiogram electrode.

[0015] Furthermore, the specific method of using hydrogel silver electrodes as electrocardiogram electrodes includes: printing silver electrode patterns on PDMS using a dispensing method, and curing and growing the electric field-induced hydrogel on the silver electrode patterns to obtain the hydrogel silver electrodes. The hydrogel silver electrode was attached to the chest and connected to the ad8232 module for measuring electrocardiogram signals.

[0016] Specifically, this invention provides a rapid and simple method for preparing electric field-induced hydrogels, comprising the following steps: Weigh a certain amount of polyvinyl alcohol granules into a beaker, and weigh a certain volume of deionized water using a graduated cylinder to prepare a polyvinyl alcohol solution with a mass fraction of 5-12.5 wt%. After adding a polytetrafluoroethylene stir bar, seal the mouth of the beaker and place it in a water bath at 80-90℃. Heat and stir for 1-2 hours until the granules are completely dissolved to obtain a polyvinyl alcohol aqueous solution.

[0017] Take a centrifuge tube and first add solid reagents such as sodium chloride, tannic acid, and sodium tetraborate decahydrate. Then add hydrochloric acid solution with pH=1-4 and a certain amount of glutaraldehyde, and mix well.

[0018] Add a polyvinyl alcohol aqueous solution, and finally add a certain amount of PEDOT:PSS. Stir thoroughly and then sonicate for 30 minutes to allow the solute to diffuse evenly and remove air bubbles from the solution, thus obtaining an electric field-induced hydrogel.

[0019] This invention uses polyvinyl alcohol as the base material, selects the polythiophene derivative PEDOT:PSS, and NaCl or CaCl as the conductive medium to construct dual electronic and ionic conductive channels within the material. A flexible electric field-induced hydrogel with high tensile strength, high conductivity, and self-healing properties is developed through a chemical and coordination dual crosslinking strategy. Glutaraldehyde acts as a chemical crosslinking agent in the system, which can condense with hydroxyl groups under acidic conditions to form COC acetal bonds. The chemical crosslinking sites enable the PVA molecular chains to form a three-dimensional network structure, giving the hydrogel water absorption and anti-swelling properties, and improving the tensile strength of the material. Sodium tetraborate decahydrate releases borate ions in water. The four empty orbitals on the boron atom can accommodate the lone pair electrons of the hydroxyl oxygen, forming coordination crosslinks with PVA. Coordination crosslinking has a significant impact on the viscosity of the system. Under alkaline conditions, a small amount of borate ions can crosslink the PVA solution into a solid. By finely controlling the solution pH and the molar ratio of borate ions to hydroxyl groups, a viscoelastic PVA can be obtained, exhibiting both the fluidity and plasticity of a fluid and the mechanical strength of a solid.

[0020] The unique feature of the dual crosslinking strategy employed in this invention lies in the rapid and reversible interaction between sodium tetraborate decahydrate and the hydroxyl groups. The crosslinking effect is highly sensitive to the solution pH and the crosslinking agent content; under alkaline conditions, even trace amounts of sodium tetraborate can significantly alter the solution viscosity. In the formulation design of this invention, the hydrogel solution contains a large number of hydrogen ions. By controlling the pH of the solution, the coordination crosslinking effect of the hydrogel can be regulated. Simultaneously, the tannic acid in the solution also contains a large number of hydrogen bonds, which can provide a certain degree of viscosity after the hydrogel solidifies, thus improving the electrode performance.

[0021] This invention uses an electrochemical reduction method to control the pH of the solution. In practical use, the conductor to which the hydrogel needs to be grown is immersed in the hydrogel solution. A graphite rod is used as the anode, and the conductor is used as the cathode, connected to an electrochemical workstation for energization. A redox reaction occurs in the solution; the carbon in the graphite rod loses electrons to become carbon ions, and the hydrogen ions in the solution gain electrons and are reduced to hydrogen gas. The pH of the solution rises, and in an alkaline environment, sodium tetraborate rapidly solidifies the hydrogel.

[0022] In this invention, the mass ratio of polyvinyl alcohol to deionized water is 1:7 to 1:19, the heating temperature is 80-90℃, and the stirring time is 1-2 hours.

[0023] In this invention, the crosslinking density of polyvinyl alcohol and sodium tetraborate decahydrate is 0.09-1.85 mol, and the crosslinking density of polyvinyl alcohol and glutaraldehyde is 0.018-0.88 mol.

[0024] In this invention, the volume ratio of polyvinyl alcohol solution to hydrochloric acid solution with pH=2 is 3:1 to 5:1.

[0025] In this invention, PEDOT:PSS accounts for 1-3 wt% of the system mass fraction, and NaCl accounts for 1.5-3 wt% of the system mass fraction.

[0026] In this invention, the mass ratio of tannic acid to polyvinyl alcohol (based on polyvinyl alcohol solids) is 1:30 to 1:35.

[0027] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages: This invention provides an electric field-induced hydrogel, an electrode, a method for its preparation, and an application of the method. In the formulation of the electric field-induced hydrogel, polyvinyl alcohol is used as the base material, combined with a conductive medium (PEDOT: PSS, and NaCl or CaCl), a chemical crosslinking agent (glutaraldehyde), and a reversible coordination crosslinking agent (sodium tetraborate decahydrate), and tannic acid is introduced to improve adhesion. The core of the process is: the electric field-induced hydrogel is drop-added onto the surface of the electrode to be grown; by applying an electric field, a redox reaction is induced in the cathode region, causing the pH value of the solution to rise rapidly, thereby activating the coordination crosslinking of sodium tetraborate, achieving rapid, in-situ solidification of the hydrogel on the electrode surface. The hydrogel electrode prepared by this invention has high tensile strength, high conductivity, and self-healing properties; it has low contact impedance and a high signal-to-noise ratio, and can be used as a high-performance flexible electrode for the detection of electrophysiological signals such as electrocardiogram (ECG) signals, showing significant advantages over commercial electrodes. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation process of the electric field-induced hydrogel in this invention; Figure 2 This is a schematic diagram of the hydrogel electrode prepared in this invention; Figure 3 This is an electron microscope image of the hydrogel prepared in this invention; Figure 4 This is the infrared spectrum of the hydrogel in this invention; Figure 5 This is a cyclic voltammetry curve of the precursor solution of the hydrogel in this invention; Figure 6 This is an Ampere current curve of the precursor solution of the hydrogel in this invention; Figure 7 This is a contact impedance diagram of different polyvinyl alcohol concentration gradients in the hydrogel of this invention. Figure 8 This is a contact impedance diagram of the hydrogel with different tannic acid concentration gradients in this invention; Figure 9 This is a comparison diagram of the electrocardiogram signals of the hydrogel electrode in this invention and commercial electrodes. Detailed Implementation

[0029] In view of the prior art, this invention develops an electric field-induced hydrogel and a technique for preparing hydrogel electrodes, enabling the rapid fabrication of hydrogel electrodes on any conductive material, including metal electrodes. The prepared hydrogel electrodes can completely cover and firmly adhere to the surface of the conductive material, while also exhibiting good adhesion to human skin. When used for electrophysiological signal monitoring, they demonstrate excellent performance such as low contact impedance and high signal-to-noise ratio. This preparation method is simple and rapid, and the resulting hydrogel electrodes exhibit superior performance.

[0030] The present invention will now be described in detail with reference to specific embodiments.

[0031] like Figures 1 to 9 As shown, the preparation method and performance characterization of the electric field-induced hydrogel are described, and the specific preparation steps are as follows.

[0032] Figure 1 The preferred preparation steps for the electric field-induced hydrogel in this invention are as follows: Step 1: Prepare a 10wt% PVA solution. The specific method is as follows: add polyvinyl alcohol to deionized water and heat it to above 80°C while stirring magnetically to fully dissolve it and obtain the PVA solution.

[0033] Step 2, prepare NaCl-TA-GA solution. The specific method is as follows: weigh sodium chloride, tannic acid and sodium tetraborate decahydrate, add hydrochloric acid with pH=1-4 and glutaraldehyde to obtain NaCl-TA-GA solution. Step 3: Mix the PVA solution obtained in Step 1 with the NaCl-TA-GA solution and add the polythiophene derivative PEDOT:PSS. Then, treat the mixture with ultrasound for 30 minutes to achieve uniform mixing.

[0034] Example 1 Step 1: Add 5g of polyvinyl alcohol to 45mL of deionized water, heat to 90℃ and stir magnetically for 30min to dissolve it completely, to obtain a 10wt% PVA solution.

[0035] Step 2: Add 0.25g NaCl, 0.025g tannic acid (3.125wt% of PVA), 0.032g sodium tetraborate decahydrate, and 200μL glutaraldehyde solution (concentration 10000μg / mL) to 2mL hydrochloric acid solution with pH=2.

[0036] Mix the solutions obtained in step 1 and step 2, and add 1.7 g of the polythiophene derivative PEDOT:PSS (concentrated). (1.5% concentration) was ultrasonically mixed.

[0037] Example 2 Step 1: Prepare an 8% (w / w) Dextron solution. Add this solution dropwise to a 7cm plasma-treated solution. The solution was spin-coated onto a 7 cm glass slide at a speed of 800 rpm. Subsequently, the coated glass slide was placed at 60°C for 5 min to allow the Dextron solution to form a film, serving as a soluble sacrificial layer.

[0038] Step 2: Use stretchable conductive silver paste (model: LY-50) as ink. Utilize dispensing printing technology to precisely print a specific electrode pattern onto the sacrificial layer prepared in Step 1. After printing, cure the pattern at 80°C for 10 minutes to ensure complete evaporation of the solvent in the ink, forming a conductive circuit.

[0039] Step 3: Mix PDMS component A and component B at a mass ratio of 10:1 until homogeneous, and stir for 10 minutes. Then, perform a 30-minute vacuum extraction to degas the mixture. Spin-coat the degassed PDMS mixture onto the conductive pattern from Step 2 at 800 rpm for 30 seconds to form a substrate layer. After spin-coating, cure the structure at 80°C for 30 minutes. Finally, place the cured PDMS film underwater for peeling, thereby transferring the conductive circuit from the glass sheet to the PDMS substrate film, obtaining a flexible circuit substrate.

[0040] Step 4: Prepare the PDMS encapsulation layer using the same method as in Step 3 (mixing components A and B in a 10:1 ratio, degassing, spin coating, and curing). The difference is that the encapsulation layer needs to be cut into a customized shape using a dicing machine to expose the electrode connection area. Precisely align the flexible circuit substrate, FPC connection board, and the prepared PDMS encapsulation layer obtained in Step 3. Finally, place the three-layer structure into an MK-TH30 mold. In a 38-inch hot press, the flexible electrode is hot-pressed at 120°C for 2 minutes to complete the final encapsulation.

[0041] Step 5: Take the flexible electrode encapsulated in Step 4 and the electric field-induced hydrogel prepared in Example 1. Using a 1mL syringe, take 0.1mL of the precursor solution and drop it onto the exposed silver surface of the flexible electrode. Using a DC power supply, connect a copper foil, gold foil, graphite rod, etc. to the anode, and connect the cathode to the FPC of the flexible electrode. Apply a 2V voltage to the solution. Under the action of the current, a redox reaction is initiated in the solution. Hydrogen ions in the solution gain electrons and become hydrogen gas, undergoing a reduction reaction. The copper foil, gold foil, graphite rod, etc., lose electrons and become ions. As hydrogen ions are reacted, the pH value of the solution rises. In an alkaline environment, a small amount of sodium tetraborate decahydrate can crosslink and solidify the PVA, ultimately forming a... Figure 2 The hydrogel flexible electrode shown.

[0042] like Figure 3 The images shown are cross-sectional electron micrographs of several hydrogels. It can be seen that after soaking in Na2SO4 solution, the hydrogel network structure becomes more uniform and dense due to the Hofmeister effect. The addition of tannic acid can also achieve a similar effect, making the hydrogel network denser and improving its mechanical properties.

[0043] like Figure 4 The images shown are infrared spectra of the hydrogel before and after the addition of tannic acid. The sample without added tannic acid exhibits typical PVA characteristic absorption peaks, including those from approximately 3600 to 3000 cm⁻¹. -1 A broad -OH peak at 2940-2850 cm⁻¹ -1 -CH stretchable and 1260-1000 cm -1 The CO stretching vibration; upon the addition of tannic acid, the -OH peak is significantly broadened and enhanced, and is located at approximately 1600-1510 cm⁻¹. -1 Characteristic peaks of aromatic ring skeletal vibration appear at this location, accompanied by CO region (1260-1000 cm⁻¹). -1 The change in the absorption band indicates that tannic acid was successfully introduced and formed significant hydrogen bonds with PVA, thereby constructing a more stable network structure.

[0044] according to Figure 5 Of the six solutions, PVA, PEDOT:PSS, and their mixtures did not undergo redox reactions, with current values ​​close to zero. Only the two formulations with added NaCl showed significant redox peaks, indicating that sufficient free ions are required to construct a conductive circuit within the solution, supporting the charge transfer generated by the redox reaction. In the positive potential region, the peak current reached its maximum value of approximately 0.049 A at around 0.65 V, revealing that the free ions in the solution had the strongest ability to move towards the electrode at this point. Furthermore, the peak current decreased in the PVA / PEDOT / NaCl solution with added sodium tetraborate decahydrate, indicating that the coordination complexation of sodium tetraborate increased the solution viscosity, slowing down the redox reaction rate in the solution. like Figure 6 As shown, using the presence or absence of NaCl in the solution as a classification criterion, the current curves were divided into red and blue groups. The red group, i.e., the solution with added NaCl, showed a current three orders of magnitude higher than the blue group, clearly demonstrating the crucial role of NaCl in establishing the internal ionic conduction pathway. The red group hydrogel solution exhibited a rapid increase in current after energization, followed by a rapid decrease until reaching equilibrium. This initial surge in current may be attributed to the oxidation reaction of the copper sheet at the anode, which instantaneously stripped away a large amount of Cu. 2+It enters the solution. Once the copper on the surface is completely consumed, the current decreases and tends to stabilize. After adding sodium tetraborate, due to the increased viscosity of the system and impaired ion migration ability, the initial current drops to 2.4 × 10⁻⁶. -2 A. The current value after stabilization is also smaller. In contrast, since the blue group's formulation does not contain NaCl, an effective conductive path cannot be constructed within the system after energizing, hindering the redox reaction. Its initial current is much smaller than that of the red group, and neither curve shows a sudden surge followed by a decrease in current; instead, the current gradually increases until it reaches a stable value.

[0045] like Figure 7 The image shows the contact resistance test conducted using PVA solutions with different concentration gradients. It can be seen that the contact resistance effect was best with 12.5 wt% PVA. However, since the 12.5 wt% PVA solution is too viscous and not suitable for use, 10 wt% PVA was ultimately selected as the formulation.

[0046] like Figure 8 The results show the contact impedance tests conducted using tannic acid at different concentration gradients. Adding 3.125, 6.25, and 9.325 wt% tannic acid respectively revealed that the group with 9.4 wt% tannic acid exhibited the best contact impedance. The contact impedances of the hydrogels from different groups were not significantly different. However, excessively high tannic acid concentrations can lead to clumping of the hydrogel induced by the electric field. Therefore, the group with 3.1 wt% tannic acid was subsequently used.

[0047] like Figure 9 The image shows the ECG signals detected using commercial ECG electrodes and electric field-induced hydrogel electrodes, respectively. It can be seen that the signal quality measured by the hydrogel electrode is better than that of the commercial electrode. In addition, according to the signal-to-noise ratio calculation, the signal-to-noise ratio of the hydrogel silver electrode is 8dB higher than that of the commercial electrode. Furthermore, a relatively obvious ECG waveform can still be observed after jogging and wearing it for two hours.

[0048] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An electric field-induced hydrogel, characterized in that, Includes the following raw materials by weight percentage: Polyvinyl alcohol 5-12.5 wt%; Sodium chloride or calcium chloride 1.5-3.0 wt%; PEDOT: PSS 0.10-1.00wt%; Sodium tetraborate decahydrate 0.10-0.80 wt%; Tannic acid 0.10-0.60 wt%; 5-25 wt% hydrochloric acid solution with pH=1-4; Glutaraldehyde 0.005-0.10 wt%; The remainder is deionized water.

2. The electric field-induced hydrogel according to claim 1, characterized in that, The electric field-induced hydrogel is cross-linked and cured by means of an electric field; wherein the voltage of the electric field is 1-5V and the application time is 60-300 seconds.

3. A method for preparing an electric field-induced hydrogel according to claim 1 or 2, characterized in that, The preparation method includes: S1: Dissolve polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; S2: Take sodium chloride, tannic acid and sodium tetraborate decahydrate, add hydrochloric acid solution and glutaraldehyde, mix well to obtain NaCl-TA-GA solution; S3: Add PEDOT:PSS and polyvinyl alcohol solution to the NaCl-TA-GA solution, mix well and remove air bubbles in the solution to obtain the electric field induced hydrogel.

4. The method for preparing an electric field-induced hydrogel according to claim 3, characterized in that, S1 specifically includes: dissolving polyvinyl alcohol in deionized water, heating at 80-90℃ and stirring magnetically for 1-2 hours to obtain a polyvinyl alcohol aqueous solution.

5. The method for preparing an electric field-induced hydrogel according to claim 3, characterized in that, S3 specifically includes: adding PEDOT:PSS and polyvinyl alcohol solution to the NaCl-TA-GA solution, sonicating for 30 minutes to mix evenly and remove air bubbles in the solution, to obtain the electric field induced hydrogel.

6. The method for preparing an electric field-induced hydrogel according to claim 3, characterized in that, It also includes S4: The electric field-induced hydrogel can be stored at room temperature. If it is not used for a long time, it needs to be ultrasonically homogenized again before use.

7. A hydrogel electrode, characterized in that, include: Electrodes, and the electric field-induced hydrogel as described in claim 1.

8. A method for preparing a hydrogel electrode according to claim 7, characterized in that, The preparation method includes: injecting the electric field-induced hydrogel onto the surface of the electrode, inducing a redox reaction by applying an electric field of 1-5V and then solidifying it to obtain the hydrogel electrode.

9. An application of the hydrogel electrode according to claim 7 as an electrocardiogram electrode.

10. The application according to claim 9, characterized in that, The specific method of using hydrogel silver electrodes as electrocardiogram electrodes includes: printing silver electrode patterns on PDMS using a dispensing method, and curing and growing the electric field-induced hydrogel on the silver electrode patterns to obtain the hydrogel silver electrodes. The hydrogel silver electrode was attached to the chest and connected to the ad8232 module for measuring electrocardiogram signals.

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