Application of a flexible electrode in wearable devices

Abstract

The present invention belongs to the field of flexible reference electrode applications, and discloses an application of a flexible electrode in wearable devices. The present invention provides the application of a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl flexible reference electrode in wearable products for EEG, ECG and EMG monitoring. The conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl flexible reference electrode prepared by the present invention has the characteristics of high stability, long storage period and high sensitivity. The electrode has good flexibility and air permeability, and its performance is comparable to that of commercial reference electrodes, but its wearing comfort is significantly higher than that of commercial electrodes.

Description

Technical Field

[0001] The invention belongs to the application field of flexible reference electrodes, and relates to the application of a flexible electrode in wearable devices. Background Art

[0002] As living standards improve, the chronic diseases people suffer from are becoming more and more complicated. In order to monitor patients' daily health conditions in real time so that patients can receive faster and more accurate treatment, more and more researchers are devoted to manufacturing wearable devices. [1] . Patients wearing wearable devices can monitor their heart rate, muscles and EEG status under different conditions. When manufacturing wearable devices, flexible sensors are an indispensable part. Wearable devices need to be worn for a long time, so their comfort and lightness are extremely important, and flexible materials can solve this problem. The high ductility and high fit of flexible materials ensure that their performance will not change under high-intensity tests, so they can be widely used as the core raw materials of sensors. The flexible wearable devices made are mostly used in the medical field and have the advantages of comfortable wearing, high sensitivity, high stability, and good biocompatibility. [2] Among the flexible sensors manufactured, metal nanoparticles, nanowires, and conductive polymers are currently the most commonly used flexible conductive materials, but these materials have poor stability and mechanical properties, and their stretchability is often limited.

[0003] The reference electrode is an extremely important part in the preparation of flexible sensors and an indispensable component in electrochemical analysis. The reference electrode is a type of electrode used as a reference when measuring the electrode potential of the electrochemical system. It has a simple structure, stable performance, can be used multiple times, and has high reusability. When comparing the performance of the reference electrode, its stability, polarization resistance, reaction rate, repeatability, and life span are the key points to judge the quality of a reference electrode. The sheet reference electrodes composed of metal nanomaterials as the substrate in the existing field still need to be improved in these properties. At present, the commonly used reference electrodes mainly include calomel electrode (Hg / Hg2Cl2) with internal reference solution and Ag / AgCl reference electrode, but the calomel electrode is difficult to miniaturize and contains toxic mercury, which has certain limitations in electrode monitoring. Summary of the invention

[0004] In order to overcome the rigidity of existing reference electrodes and the performance deficiencies of sheet-like metal nanoparticle reference electrodes, the present invention provides an application of flexible electrodes in wearable devices. The present invention first prepares a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl flexible reference electrode with high stability, long storage period and high sensitivity, and applies the flexible reference electrode to wearable devices for EEG, ECG and EMG monitoring.

[0005] The above object of the present invention is achieved through the following technical solutions:

[0006] A flexible electrode is used in wearable devices. The electrode is a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode. Specifically, the electrode is used as a skin surface adhesive electrode in electromyography monitoring.

[0007] A flexible electrode is used in wearable devices. The electrode is a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode. Specifically, the electrode is used as an electrical lead electrode sheet in electrocardiogram monitoring.

[0008] A flexible electrode is used in wearable devices. The electrode is a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode. The application of the flexible electrode in wearable devices is specific to electroencephalogram (EEG) monitoring.

[0009] The above-mentioned conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode is prepared by using a conductive tape / carbon nanotube as a substrate of the reference electrode by an electrochemical method, and coating the conductive hydrogel on the outer layer of the reference electrode, then using a chronoamperometry method to deposit nanosilver particles, and finally using an electrochemical chlorination method to chlorinate the nanosilver particles to generate Ag / AgCl, thereby obtaining a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0010] The specific preparation method of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode is as follows:

[0011] Step 1. Preparation of carbon nanotube / conductive tape flexible substrate: Use conductive tape as the electrode substrate, take an appropriate amount of carbon nanotubes and dissolve them in ultrapure water, ultrasonicate for 20 minutes to completely dissolve them, take an appropriate amount of carbon nanotube solution and evenly apply it on the conductive tape, and store it in a dry room temperature environment for one day.

[0012] Step 2. Deposition of silver by chronoamperometry: The carbon nanotube / conductive tape flexible substrate is used as the working electrode, the saturated calomel electrode is used as the reference electrode, and the platinum wire is used as the counter electrode. A three-electrode system is used for the deposition reaction. The electrode is placed in a mixed solution of 0.005-0.015 mol / L AgNO3 and 0.05-0.15 mol / L NaNO3. The constant deposition potential is set to -0.4 V. Nanosilver particles are deposited by chronoamperometry to obtain an Ag-carbon nanotube / conductive tape electrode.

[0013] Step 3. Chlorination of Ag-carbon nanotube / conductive tape electrode: Using Ag-carbon nanotube / conductive tape electrode as working electrode, saturated calomel electrode as reference electrode, platinum wire as counter electrode, adopting three-electrode system for chlorination reaction, placing three electrodes in 0.05-0.15 mol / L HCl solution, using electrochemical chlorination method, chlorinating Ag-carbon nanotube / conductive tape electrode at a potential higher than open circuit potential by 250 mV, to prepare Ag / AgCl-carbon nanotube / conductive tape electrode.

[0014] Step 4. Prepare a conductive hydrogel / carbon nanotube / conductive tape Ag / AgCl reference electrode: Weigh an appropriate amount of polyvinyl alcohol conductive hydrogel, dissolve it in a saturated KCl solution, and evenly apply the conductive hydrogel on the Ag / AgCl-carbon nanotube / conductive tape electrode to form a flat hydrogel film, which is placed in a vacuum oven to dry and cure completely to obtain a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0015] The present invention uses conductive tape and carbon nanotubes in carbon materials to prepare Ag / AgCl reference electrode substrates. Carbon nanotubes also serve as conductive layers. Carbon nanotubes have better flexibility and stability than metal nanomaterials. [3] In order to prevent the carbon nanotubes and silver nanoparticles from falling off easily and ensure that the surface of the Ag / AgCl reference electrode has good adhesion and conductivity to the skin, the present invention also applies a conductive hydrogel to the substrate. [4] This also makes the substrate more conductive and more sensitive. Compared with the more common PDMS substrate, the present invention simplifies the experimental steps and has high repeatability.

[0016] The beneficial effects of the present invention compared with the prior art are:

[0017] The present invention mainly studies the application and practicability of the prepared flexible electrodes in wearable products. Wearable devices are currently commonly used in the medical field, especially in real-time monitoring of patient health conditions, for patient health monitoring, safety monitoring, home rehabilitation and efficacy evaluation. The most important point is that when patients wear wearable medical devices, the disease can be discovered in time and contained in the early stages. The substrate used in the present invention is carbon nanotubes and flexible conductive tapes, which have high conductivity, sensitivity and excellent stability, and good flexibility and air permeability. The performance of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode prepared by the present invention is comparable to that of a commercial reference electrode, and the flexible electrode can be used in wearable products for EEG, ECG and EMG monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1This is a scanning electron microscope image of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0019] Figure 2 The OCP curves of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode and the commercial hard glass Ag / AgCl reference electrode.

[0020] Figure 3 Figure 3. Human EEG monitoring graph for the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0021] Figure 4 Human electrocardiogram for conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0022] Figure 5 Figure 3. Human electromyography monitoring graph for the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode. DETAILED DESCRIPTION

[0023] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0024] The specific preparation method of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode involved in the embodiment is as follows: nanosilver particles are deposited on the carbon nanotube / conductive tape by electrochemical deposition, and a conductive hydrogel is coated on the outer layer.

[0025] S1. Preparation of carbon nanotube / conductive tape flexible substrate: prepare a conductive tape of appropriate size as the substrate of the electrode, prepare 0.3-0.8 mg of carbon nanotubes, dissolve the carbon nanotubes in ultrapure water, and put them in an ultrasonic machine for 20 minutes to completely dissolve them, take an appropriate amount of carbon nanotube solution and drop it on the conductive tape to make it evenly coated, and store it at room temperature in a dry environment for one day.

[0026] S2. Silver deposition by chronoamperometry: The carbon nanotube / conductive tape flexible substrate prepared above was used as the working electrode, the saturated calomel electrode was used as the reference electrode, the platinum wire was used as the counter electrode, and the deposition reaction was carried out using the three-electrode system of CHI660E electrochemical system. The electrode was placed in a mixed solution of 0.005-0.015 mol / L AgNO3 and 0.05-0.15 mol / L NaNO3, and the constant deposition potential was set to -0.4 V. Nanosilver particles were deposited by chronoamperometry to obtain Ag-carbon nanotube / conductive tape electrode.

[0027] S3. Chlorination of Ag-carbon nanotube / conductive tape electrode: The Ag-carbon nanotube / conductive tape electrode prepared above is used as the working electrode, the saturated calomel electrode is used as the reference electrode, and the platinum wire is used as the counter electrode. The three-electrode system of CHI660E electrochemical system is used for chlorination reaction. The three electrodes are placed in 0.05-0.15 mol / L HCl solution. The electrochemical chlorination method is used to chlorinate the Ag-carbon nanotube / conductive tape electrode at a potential 250 mV higher than the open circuit potential. The chlorination time is 3000s-4500s. Finally, the Ag / AgCl-carbon nanotube / conductive tape electrode is prepared and placed at room temperature to dry completely.

[0028] S4. Prepare a conductive hydrogel / carbon nanotube / conductive tape Ag / AgCl reference electrode: weigh 2-4g of polyvinyl alcohol conductive hydrogel, dissolve it in a saturated KCl solution, and evenly apply the hydrogel on the above-obtained Ag / AgCl-carbon nanotube / conductive tape electrode to form a flat hydrogel film, put it into a vacuum oven, and bake it at 50-80℃ for 2-2.5h to completely dry and solidify it, thereby obtaining a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode.

[0029] Example 1

[0030] In order to further study the performance of the reference electrode, the performance of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode was compared with that of the commercial hard glass Ag / AgCl reference electrode;

[0031] In order to compare whether the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode prepared by the present invention reaches the performance standard of the commercial hard glass Ag / AgCl reference electrode, a three-electrode system of a CHI660E electrochemical system was used, with a glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, and a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode as the reference electrode. The stability of the reference electrode prepared by the present invention and the commercial hard glass Ag / AgCl reference electrode was compared by the open circuit potential method at an open circuit potential of 600s. Figure 2 It can be obtained that the OCP (open circuit potential) test curves of the electrode prepared by the present invention and the commercial hard glass Ag / AgCl reference electrode are relatively stable, and there is no obvious difference between the two. It can be seen that in terms of stability, the prepared conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode is comparable to the commercial hard glass Ag / AgCl reference electrode.

[0032] Example 2

[0033] Conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode as a flexible sensor for human EEG, ECG and EMG monitoring

[0034] Simply put, an EEG is an image obtained by recording the discharge of cells. When the EEG cap is put on the head, the electrical signals generated by brain cells are received and collected, and then transmitted to the computer. After processing, a wave-like image is obtained. The electrical signals are generated because the brain nerve cells are converted through chemical signals when they are working and transmitting information. At present, EEG is mainly used for the diagnosis and treatment of localized or diffuse pathological manifestations caused by epilepsy, tumors, neurological diseases and degenerative diseases. It also has diagnostic value for changes in the central nervous system caused by extracerebral diseases such as metabolic and endocrine disorders and poisoning. However, while it plays an important role in diagnosis and treatment, it also has certain limitations, such as low sensitivity and low specificity.

[0035] According to whether the electrodes are placed inside or outside the skull, EEG can be divided into scalp electrode EEG and intracranial electrode EEG. The electrodes provided by the present invention are used in EEG detection applications as scalp point electrode EEG. The conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode is placed on a fixed part of the scalp surface according to the international 10-20 system electrode placement method. A chemical reaction occurs between the ions in the conductive gel and the reference electrode to form a primary cell, which significantly reduces the contact resistance compared to the traditional electrode resistance. Figure 3 As shown, it can be observed that its frequency and amplitude are relatively stable, which illustrates the practicability of applying the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode to EEG monitoring and its ability to accurately reflect the sensitivity of the EEG.

[0036] Electrocardiogram is a graph of the changes in electrical activity produced by each cardiac cycle of the heart recorded from the body surface by an electrocardiograph. In each cardiac cycle, the pacemaker, atrium, and ventricle are excited successively, accompanied by changes in bioelectricity, and various forms of potential changes are drawn from the body surface through the electrocardiograph. Electrocardiogram is one of the most commonly used clinical examinations. It can be used to record the electrical activity of the normal human heart, help diagnose arrhythmias, diagnose myocardial ischemia, myocardial infarction and its location, and determine the status of artificial heart pacing. Electrocardiograms are divided into single-lead and multi-lead types, including 3-lead, 6-lead, and 12-lead. The most commonly used electrocardiogram in clinical practice is 12-lead, which can be used for routine electrocardiogram monitoring and 24-hour dynamic electrocardiogram monitoring.

[0037] The electrode provided by the present invention adopts 12 leads in the application of ECG detection. The electrode sheet of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode replaces the lead ball, is pasted on the patient, and connected to the electrocardiograph to record the ECG changes. This installation can prevent the lead ball from falling off, and the monitoring is more convenient. Figure 4As shown, it can be concluded that a complete P wave, QRS complex, T wave and U wave appear accurately in one cardiac cycle, which shows the practicality of using the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode in ECG monitoring.

[0038] Surface electromyography, also known as dynamic electromyography, is a bioelectric signal of neuromuscular system activity that is guided and recorded from the muscle surface through electrodes. It has varying degrees of correlation with the activity and functional state of the muscle, and can therefore reflect neuromuscular activity to a certain extent. The bioelectricity generated during muscle movement generates a potential difference through two measuring electrodes. After the differential amplifier detects the signal, it is amplified and recorded to obtain a graph. In clinical practice, electromyography can be used for the diagnosis of neuromuscular diseases, sports systems, fatigue determination, sports technology analysis, and prediction of the non-damage of muscle fibers. It is of great significance in evaluating whether muscles are normal, such as the diagnosis of the cause of pain, numbness, atrophy or weakness.

[0039] At present, when measuring surface electromyography, most of the electrodes used are nano-Ag / AgCl reference electrodes, but this type of reference electrode is costly and has poor sensitivity. The surface electromyography electrode of the present invention uses a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode. The electrode has low production cost and high sensitivity, which is more conducive to data collection and disease diagnosis. When the test electrode is placed at different positions on the muscle belly, the electromyographic signal results obtained are also different. The present invention monitors the electromyographic morphology of the ulnar nerve, tibial nerve, median nerve and common peroneal nerve. The electromyographic signal is as follows: Figure 5 As shown in the figure, we can see that its amplitude, time limit, and percentage of multiphase waves are consistent with the pattern of normal electromyography. Therefore, the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode can be used for electromyography detection and shows high sensitivity.

[0040] Comparative Example

[0041] The flexible electrode of the present invention uses conductive tape / carbon nanotubes as the base of the reference electrode, and a layer of conductive hydrogel is coated on the outer layer of the reference electrode. The production of this base combines the advantages of conductive tape and carbon nanotubes, and the conductive hydrogel on the outer layer greatly improves the conductivity, flexibility and stability of the reference electrode. The differences between the present invention and other research groups are shown in Table 1 below:

[0042] Table 1. Differences between the solution of the present invention and that developed by other research groups

[0043]

[0044] In summary, the present invention takes a different approach, using a new type of conductive tape and carbon nanotubes to make the substrate, and improves the performance of the reference electrode, which has not been reported in other documents and patents. The present invention simplifies the experimental steps, has high repeatability, and the flexible electrode produced has higher conductivity, stronger sensitivity and stability. The electrode product can be comparable to commercial reference electrodes, and the electrode is highly sensitive in EEG, ECG and EMG monitoring, and is practical in wearable products.

[0045] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

[0046] References

[0047] [1] Jia Zhenyu, Wang Wei, Wang Chen, et al. Application and development of wearable devices in the medical field [J]. China Medical Equipment, 2017, 2(32): 96-99.

[0048] [2] He Zijun, Zeng Qing, Gong Ze. Application of wearable devices based on flexible sensors in rehabilitation field [J]. Journal of Rehabilitation, 2021, 3(31): 258-264.

[0049] [3] Zhao Liduan, Liu Liyan, He Yin, et al. Research and development of wearable flexible sensors based on carbon nanotubes [J]. Knitting Industry, 2021, 2, 87-91.

[0050] [4] Jiang Wenjing, Liao Jingwen, Zhang Xuehui, et al. Classification of conductive composite hydrogels and their applications in flexible wearable devices [J]. Journal of Composite Materials, 2022.

[0051] [5] Yin Nana, Li Mingqian, Dai Xin. Preparation and properties of conductive gel-type all-solid-state reference electrode[J]. Chinese Journal of Inorganic Analytical Chemistry, 2018, 3(8): 58-62.

[0052] [6] Huang Fangli, Cao Quanxi, Wei Yunge, et al. Preparation and electrochemical properties of Ag / AgCl electrodes [J]. Electronic Science and Technology, 2010, 6(23): 29-34.

[0053] [7] Sun Jing, Wang Qingxiang, Shen Guijun, et al. A method for preparing a reproducible PDMS-based micro-soft Ag / AgCl electrode and its application [p] CN 108152348 B. 2020-05-19.

[0054] [8] Liu Ruili, Shen Chaochao, Xi Xin, et al. A fibrous flexible solid-state silver / silver chloride reference electrode and its preparation method and application [P] CN113433183A.2021-09-24.

[0055] [9] Zhao Y, Zheng T, Li X, et al. Effect of sintering technology on thestability of solution-filled external pressure balanced reference electrode[J]. Journal of Electroanalytical Chemistry, 2021,902:115813.

Claims

1. A method for preparing a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode, characterized in that: The following steps are involved: S1. Preparation of carbon nanotube / conductive tape flexible substrate: Prepare a conductive tape of appropriate size as the electrode substrate, prepare 0.3-0.8 mg of carbon nanotubes, dissolve the carbon nanotubes in ultrapure water, and ultrasonicate them in an ultrasonic machine for 20 minutes to completely dissolve them, take an appropriate amount of carbon nanotube solution and drop it on the conductive tape to make it evenly coated, and store it at room temperature in a dry environment for one day; S2. Silver deposition by chronoamperometry: The prepared carbon nanotube / conductive tape flexible substrate was used as the working electrode, the saturated calomel electrode was used as the reference electrode, and the platinum wire was used as the counter electrode. The deposition reaction was carried out using the three-electrode system of CHI660E electrochemical system. The electrode was placed in a mixed solution of 0.005-0.015 mol / L AgNO3 and 0.05-0.15 mol / L NaNO3, and the constant deposition potential was set to -0.4 V. Silver nanoparticles were deposited by chronoamperometry to obtain Ag-carbon nanotube / conductive tape electrode. S3. Chlorination of Ag-carbon nanotube / conductive tape electrode: The Ag-carbon nanotube / conductive tape electrode prepared above is used as the working electrode, the saturated calomel electrode is used as the reference electrode, and the platinum wire is used as the counter electrode. The three-electrode system of CHI660E electrochemical system is used for chlorination reaction. The three electrodes are placed in 0.05-0.15 mol / L HCl solution. The Ag-carbon nanotube / conductive tape electrode is chlorinated by electrochemical chlorination method at a potential higher than the open circuit potential by 250 mV. The chlorination time is 3000 s-4500 s. Finally, the Ag / AgCl-carbon nanotube / conductive tape electrode is prepared and placed at room temperature to make it completely dry. S4. Prepare a conductive hydrogel / carbon nanotube / conductive tape Ag / AgCl reference electrode: weigh 2-4 g of polyvinyl alcohol conductive hydrogel, dissolve it in a saturated KCl solution, and evenly apply the hydrogel on the above-obtained Ag / AgCl-carbon nanotube / conductive tape electrode to form a flat hydrogel film. Put it into a vacuum oven and bake it at 50-80 ℃ for 2-2.5h to completely dry and solidify it. Thus, a conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode is obtained.

2. Application of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode prepared by the preparation method according to claim 1 in wearable devices, characterized in that: Specifically, it is used as electrodes attached to the skin surface in electromyography monitoring.

3. Application of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode prepared by the preparation method according to claim 1 in wearable devices, characterized in that: Specifically, it is used as an electrical lead electrode in electrocardiogram monitoring.

4. Application of the conductive hydrogel / carbon nanotube / conductive tape-Ag / AgCl reference electrode prepared by the preparation method according to claim 1 in wearable devices, characterized in that: Specifically, it is used in EEG monitoring.

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