Hydrogel electrode with adhesiveness and sweat resistance and preparation method and application thereof

Abstract

The invention discloses a hydrogel electrode with adhesiveness and sweat resistance as well as a preparation method and application of the hydrogel electrode, and belongs to the technical field of flexible hydrogel sensing materials. The electrode is prepared by dissolving acrylic acid, hydrophobic modified tannic acid, an initiator, polyethyleneimine and a conductive substance in deionized water to form a precursor solution, casting the precursor solution through a mold and then carrying out ultraviolet polymerization. The hydrogel electrode prepared by the invention has good mechanical strength, excellent skin adhesion, remarkable sweat interference resistance, high conductivity and low contact resistance. The electrode can be directly attached to the skin, is used as a strain sensor or is used for collecting various bio-electricity signals, and has the comprehensive advantages of high stability, good detection precision, low interface impedance, excellent biocompatibility, easily available materials, simple and convenient process and the like.

Description

Technical Field

[0001] This invention belongs to the field of flexible hydrogel sensing materials technology, specifically relating to a hydrogel electrode with adhesive and sweat-resistant properties, its preparation method, and its application. Background Technology

[0002] With the rapid development of science and technology, humanity has entered the intelligent era. Currently, flexible electronic devices based on artificial intelligence technology are attracting much attention due to their enormous application potential in emerging fields such as wearable devices and electronic skin. Conductive hydrogels, as a functional material, combine the inherent flexibility, high water content, and excellent conductivity of hydrogels. They are typically composed of a hydrophilic polymer network and conductive components (such as conductive polymers, carbon-based materials, metal nanofillers, or ionic salts). With their good biocompatibility, tunable mechanical properties, and bioactivity, conductive hydrogels demonstrate significant application value in the field of flexible electronic devices, especially in bioelectrical signal sensing.

[0003] Bioelectrical signals, such as electrocardiograms (ECG) and electromyograms (EMG), are key indicators reflecting human physiological state and motor function, providing core evidence for clinical diagnosis, rehabilitation assessment, human-computer interaction, and basic life science research. For example, ECG signal analysis can be used to identify cardiac diseases such as arrhythmias and myocardial ischemia; EMG signals help diagnose neuromuscular diseases, assess muscle function, and guide rehabilitation training. Epidermal electrodes used to detect bioelectrical signals not only need to output high signal-to-noise ratio signals but also need to meet the following key performance requirements: conductivity matching human skin to reduce electrode-skin interface impedance and minimize environmental noise interference; excellent adhesion to ensure a tight and stable fit without additional fixation; good sweat resistance to maintain stable adhesion even under sweating conditions, preventing slippage or detachment; and excellent biocompatibility to ensure long-term comfort and user safety. Furthermore, with advancements in sensing technology and signal processing algorithms, bioelectrical signal monitoring is moving towards portability, real-time monitoring, and intelligence, which places higher demands on signal acquisition quality, anti-interference capabilities, and feature extraction accuracy.

[0004] Currently, hydrogel electrodes play an important role in bioelectrical signal monitoring, but their practical application still faces many challenges: First, insufficient adhesion: the bonding force between the electrode and the skin is weak, often requiring additional fixing devices (such as tape or straps), increasing the complexity of use; Second, poor motion stability: sweating can easily cause the electrode to slip or fall off, affecting the continuity and reliability of signal acquisition; Third, poor comfort during long-term wear: some materials may cause adverse reactions such as skin redness and allergies; Fourth, interface impedance issues: the electrode-skin interface impedance is high, which can easily introduce environmental noise and reduce the signal-to-noise ratio.

[0005] The aforementioned limitations significantly restrict the practical application of hydrogel electrodes in wearable devices such as health monitoring and motion recognition. Therefore, to meet the demand for high-precision bioelectrical signal acquisition, it is particularly urgent to develop novel hydrogel electrodes that can effectively overcome the limitations of existing technologies. Summary of the Invention

[0006] The first technical problem to be solved by this invention is to provide a hydrogel electrode with adhesive and sweat-resistant properties. This electrode can adhere closely to human skin and flexible substrates, maintain high precision and high signal-to-noise ratio physiological signal acquisition even in sweaty environments, and has the characteristic of being re-attached. The second technical problem to be solved by this invention is to provide a method for preparing a hydrogel electrode with adhesive and sweat-resistant properties. This method is simple and efficient, uses readily available raw materials, has a short cycle, and is suitable for large-scale production. The third technical problem to be solved by this invention is to provide the application of this hydrogel electrode in strain sensors and bioelectrical signals.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a hydrogel electrode with adhesive and sweat-resistant properties includes the following steps:

[0009] (1) Preparation of hydrophobically modified tannic acid: Tannic acid was dissolved in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to alkaline solution was 1:20~1:30; then, benzalkonium chloride was dissolved in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water was 1:20~1:30; finally, the tannic acid solution and the benzalkonium chloride aqueous solution were mixed and stirred to obtain a white precipitate, which was washed, filtered, and dried to obtain hydrophobically modified tannic acid;

[0010] (2) Preparation of precursor solution for hydrogel electrode: Add hydrophobic modified tannic acid, acrylic acid, polyethyleneimine and conductive components obtained in step (1) to deionized water, add photoinitiator, stir to dissolve, and obtain precursor solution;

[0011] (3) Mold casting and ultraviolet light polymerization: The precursor solution obtained in step (2) is injected into the electrode mold, and then the electrode mold is placed in an ultraviolet lamp to carry out photopolymerization reaction to obtain a hydrogel electrode.

[0012] Further, in step (1), the mass ratio of tannic acid solution to benzalkonium chloride aqueous solution is 1:1 to 1:1.5; the pH of alkaline solution is 9 to 12; the freeze-drying temperature is -20 ℃ to -80 ℃; and the drying time is 48 to 72 h.

[0013] Further, in step (2), the mass ratio of acrylic acid to hydrophobically modified tannic acid is 8:1 to 80:1; the mass ratio of acrylic acid to polyethyleneimine is 10:1 to 100:1; the mass ratio of acrylic acid to conductive component is 80:1 to 8:1; and the mass ratio of acrylic acid to photoinitiator is 20:1 to 100:1.

[0014] Further, in step (2), the photoinitiator is selected from one of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone; the conductive component is selected from one or more of sodium chloride, lithium chloride, and potassium chloride.

[0015] Further, in step (1), the stirring time is 1.5~3h; in step (2), the stirring time is 0.5~2h; in step (3), the photopolymerization time is 0.5~2h.

[0016] A hydrogel electrode with adhesive and sweat-resistant properties.

[0017] Furthermore, the thickness of the hydrogel electrode is 0.4~0.7 mm.

[0018] Furthermore, the aforementioned hydrogel electrode with adhesive and sweat-resistant properties is used in strain sensors and bioelectrical signals.

[0019] Furthermore, copper wires are attached to both ends of the hydrogel electrode to obtain a resistive strain sensor, which is then connected to a digital multimeter for motion sensing.

[0020] Furthermore, hydrogel electrodes are attached to the skin and connected to an electrocardiogram (ECG) acquisition device to measure ECG signals; hydrogel electrodes are also attached to the skin and connected to an electromyography (EMG) acquisition device to measure EMG signals.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) The hydrogel electrode prepared by the present invention improves the stability of signal acquisition. The electrode can be closely attached to human skin and flexible substrate. It can still maintain high precision and high signal-to-noise ratio physiological signal acquisition in sweat environment, and has the characteristic of being re-attached.

[0023] (2) The wearable strain sensor based on the present invention can capture human movement in real time and sensitively, and has the advantages of convenient operation and lightweight device.

[0024] (3) The present invention can achieve enhanced application compatibility, the electrode is compatible with a variety of wearable devices, the operation is stable, the operation threshold is low, the versatility is strong, and it is easy to promote in the clinical and consumer fields.

[0025] (4) The present invention proposes a method for preparing a hydrogel electrode with adhesive and anti-sweat properties. The preparation process is simple and efficient, the raw materials are readily available, the cycle is short, and it is suitable for large-scale production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process for preparing the hydrogel electrode in this application;

[0027] Figure 2 This is a schematic diagram of the assembly of the strain sensor based on the hydrogel electrode prepared in this application;

[0028] Figure 3 The diagram shows the test results of the hydrogel electrode prepared in this application, where a is a schematic diagram of shear adhesion test; b is a schematic diagram of "T" type adhesion test.

[0029] Figure 4 The tensile stress-strain curves of the hydrogel electrodes prepared in Example 1 and Comparative Example 2 of this application are shown.

[0030] Figure 5 Optical photographs of the hydrogel electrode prepared in Example 1 of this application under bending and twisting states;

[0031] Figure 6 These are actual images showing the adhesion of the hydrogel electrode prepared in Example 1 of this application to different substrates;

[0032] Figure 7 This is a diagram of an underwater adhesion test of the hydrogel electrode prepared in Example 1 of this application;

[0033] Figure 8 This is a graph showing the relative resistance change of the hydrogel electrode prepared in Example 1 of this application under tensile stress.

[0034] Figure 9 Electromyography (EMG) signal acquisition images of the hydrogel electrode prepared in Example 1 of this application and a commercially available gel electrode;

[0035] Figure 10 These are electrocardiogram (ECG) images of the hydrogel electrode prepared in Example 1 of this application and a commercially available gel electrode.

[0036] Figure 11 Comparative optical photographs of the hydrogel electrode prepared for Example 1 of this application and a commercially available gel electrode worn on the skin of a volunteer's forearm for 48 hours. Detailed Implementation

[0037] The following embodiments are intended to illustrate the present invention in more detail, but are not intended to limit the scope of the invention. Any modifications or substitutions made by those skilled in the art based on the inventive concept should be considered to fall within the protection scope of the present invention.

[0038] The thickness of the hydrogel electrodes prepared in the following examples is 0.4~0.7 mm.

[0039] Figure 1 A schematic diagram of the process for fabricating a hydrogel electrode with adhesive and sweat-resistant properties includes the following three steps:

[0040] (1) Preparation of hydrophobically modified tannic acid: Tannic acid was dissolved in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to alkaline solution was 1:20~1:30; then, benzalkonium chloride was dissolved in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water was 1:20~1:30; finally, the tannic acid solution and the benzalkonium chloride aqueous solution were mixed and stirred to obtain a white precipitate, which was washed, filtered, and dried to obtain hydrophobically modified tannic acid;

[0041] (2) Preparation of precursor solution for hydrogel electrode: Add hydrophobic modified tannic acid, acrylic acid, polyethyleneimine and conductive components obtained in step (1) to deionized water, add photoinitiator, stir to dissolve, and obtain precursor solution;

[0042] (3) Mold casting and ultraviolet light polymerization: The precursor solution obtained in step (2) is injected into the electrode mold, and then the electrode mold is placed in an ultraviolet lamp to carry out photopolymerization reaction to obtain a hydrogel electrode.

[0043] Example 1

[0044] A method for preparing a hydrogel electrode with adhesive and sweat-resistant properties includes the following steps:

[0045] (1) Preparation of hydrophobic modified tannic acid: 4 g of tannic acid was dissolved in 100 g of sodium hydroxide aqueous solution (pH=10) to obtain tannic acid solution; 4 g of benzalkonium chloride was dissolved in 100 g of deionized water to obtain benzalkonium chloride aqueous solution; the tannic acid solution and benzalkonium chloride aqueous solution were mixed at a ratio of 1:1 for 2 h to obtain a white precipitate; the white precipitate was washed three times with deionized water, vacuum filtered, and freeze-dried at -20 ℃ for 48 h to obtain hydrophobic modified tannic acid.

[0046] (2) Preparation of precursor solution for gel synthesis: Acrylic acid, polyethyleneimine, hydrophobically modified tannic acid, and conductive component were added to 2 g of deionized water, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide was added. The mixture was stirred magnetically for 1 h at room temperature to fully dissolve the precursor solution. The specific parameters of each raw material are shown in Table 1.

[0047] (3) Pour the precursor solution obtained in step (2) into the electrode mold separated by a polytetrafluoroethylene membrane, and then place the electrode mold into a UV lamp for photopolymerization reaction for 1 h to obtain a hydrogel electrode.

[0048] The difference between Examples 2-16 and Example 1 lies in the different mass ratios of acrylic acid to polyethyleneimine, hydrophobically modified tannic acid, conductive components, or photoinitiators in steps (2) or (3), or the different types of conductive components or photopolymerization times, resulting in hydrogel electrodes. Specific parameters for each raw material are shown in Table 1.

[0049] Comparative Example 1

[0050] The difference from Example 1 is that in step (2), hydrophobic modified tannic acid is not added to prepare the hydrogel electrode.

[0051] Comparative Example 2

[0052] The difference from Example 1 is that in step (2), polyethyleneimine is not added to prepare the hydrogel electrode.

[0053] Table 1. Preparation parameters of Examples 1-16 and Comparative Examples 1-2

[0054]

[0055] The hydrogel electrodes prepared in Examples 1-16 and Comparative Examples 1-2 were tested for conductivity, stress, strain, shear adhesion strength and peel adhesion strength.

[0056] Conductivity testing: The prepared hydrogel electrode was removed from the mold and assembled into a strain sensor, i.e., cut into strips of 30 mm × 6 mm. Silver paste was applied to both ends of the strips, which were then wrapped with copper sheets. Copper wires were then connected to the copper sheets. Figure 2 As shown in Table 2, the resistance of the hydrogel was measured using a digital multimeter, and the conductivity of the sample was calculated using the formula σ=L / RS, where L, S, and R represent the length, cross-sectional area, and resistance of the sample, respectively.

[0057] Shear adhesion strength and peel adhesion strength tests: The shear adhesion ability of the hydrogel was tested using an lap shear test on a universal electronic testing machine with dimensions of 20×20×0.5 mm. 3 Hydrogel-like patterns are bonded to two pieces measuring 60×60×3 mm. 3 The substrates are pressed together by a 500g weight for 1 minute to achieve close contact, such as... Figure 3 As shown in Figure a, the shear adhesion strength of the sample of this invention was calculated using the formula: Shear Adhesion Strength = F / S, where F and S represent the tested shear force and the contact area of ​​the sample, respectively. The results are shown in Table 2. The peel adhesion ability of the hydrogel was tested using a universal electronic testing machine and a "T"-type adhesion test, with dimensions of 20×60×0.5 mm. 3Hydrogel-like patterns are bonded to two pieces measuring 20×100×3 mm. 3 Between the pigskin, a 500g weight is pressed for 1 minute to ensure close contact, such as... Figure 3 As shown in Figure b; next, a tensile test was conducted at a constant speed of 200 mm / min to obtain the adhesion strength of the sample, and the results are shown in Table 2. The peel adhesion strength of the sample of the present invention was calculated using the formula: peel adhesion strength = 2F / d, where F and d represent the peel force and the contact width of the sample, respectively, and the results are shown in Table 2.

[0058] Tensile property testing: Tensile tests were conducted using strip samples with a length of 30 mm, a width of 6 mm, and a thickness of 0.5 mm. The samples were stretched at a constant speed of 50 mm / min until fracture. Each test was repeated five times, and the average results were recorded. The results are shown in Table 2 and... Figure 4 As shown.

[0059] Table 2 Performance parameters of the hydrogel electrodes prepared in Examples 1-16 and Comparative Examples 1-2

[0060]

[0061] As shown in Table 2, Comparative Example 2, which does not contain polyethyleneimine, exhibits a significantly lower stress compared to Examples 1 and 2-4; Comparative Example 1, which does not contain hydrophobically modified tannic acid, shows a significantly lower shear adhesion strength and peel adhesion strength compared to Examples 1 and 5-7; Examples 1 and 8-10 show increased conductivity of the hydrogel electrode with increasing sodium chloride content; Examples 1 and 11-13 compare the effect of initiator dosage on the mechanical properties of the hydrogel electrode, showing increased fracture stress in the other examples where the initiator dosage was sufficient for complete polymerization compared to the incompletely polymerized hydrogel electrode in Example 14 with insufficient initiator; Examples 1 and 14-16 compare the effect of photopolymerization time on the mechanical properties of the hydrogel electrode, showing increased fracture stress in the fully polymerized hydrogel electrode with a polymerization time of 1 hour or more compared to the incompletely polymerized hydrogel electrode with a photopolymerization time of less than 1 hour; Figure 4 As can be seen from the tensile stress-strain curves of Example 1 and Comparative Example 2 without added polyethyleneimine, the electrostatic interaction and hydrogen bonding between the cationic polymer polyethyleneimine and acrylic acid significantly increased the fracture stress of Example 1.

[0062] Figure 5 The excellent bending and torsional flexibility of the hydrogel electrode prepared in Example 1 is demonstrated.

[0063] Figure 6 The excellent adhesion of the hydrogel electrode prepared in Example 1 to various substrates such as glass, steel, polytetrafluoroethylene (PTFE), and wood is shown.

[0064] Depend on Figure 7 As shown, pigskin with the hydrogel electrode of Example 1 attached was immersed in physiological saline and pre-pressed for 1 minute before adhering to another piece of underwater pigskin. The adhesion was firm even under vigorous shaking, demonstrating its excellent anti-sweat adhesion ability.

[0065] Using a universal testing machine and a digital multimeter together, Figure 8 The results show that Example 1 exhibits sensitive and reversible resistance changes at 80% strain, and good stability after 8 cycles, demonstrating its reliability for real-time strain sensing.

[0066] The hydrogel electrode with adhesive and sweat-resistant properties prepared in Example 1 was used for bioelectrical signal testing. The steps included: cutting the hydrogel electrode into circular electrode pieces with a diameter of 1.5 mm and attaching them to the arm muscles and chest area of ​​the subject, recording electromyographic (EMG) and electrocardiographic (ECG) signals, respectively. The results are shown below. Figure 9-10 .

[0067] Figure 9 The signal-to-noise ratio of the clenched-and-release response signals collected from the same subject's arm muscles by the hydrogel electrode prepared in Example 1 and the commercial gel electrode can be compared with that of the commercial gel electrode. The electrode of the present invention has lower signal noise, higher accuracy and better signal-to-noise ratio.

[0068] Figure 10 The figures show electrocardiogram (ECG) signals generated by the hydrogel electrode prepared in Example 1 and a commercial gel electrode adhered to the chest of the same subject. As can be seen from the figures, compared with the commercial gel electrode, the characteristic waveforms (P wave, QRS complex, etc.) of the electrode of the present invention are clearer and more significant, demonstrating its potential for ECG acquisition.

[0069] Figure 11 To compare the skin condition of the hydrogel electrode prepared in Example 1 with that of a commercially available gel electrode after 48 hours of wear on a volunteer's forearm, the commercially available electrode caused redness and peeling, while the electrode of the present invention only left slight temporary indentations, which disappeared 10 minutes after removal, demonstrating its excellent skin compatibility.

[0070] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A method for preparing a hydrogel electrode with adhesive and sweat-resistant properties, characterized in that, Includes the following steps: (1) Preparation of hydrophobically modified tannic acid: Tannic acid was dissolved in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to alkaline solution was 1:20~1:30; then, benzalkonium chloride was dissolved in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water was 1:20~1:30; finally, the tannic acid solution and the benzalkonium chloride aqueous solution were mixed and stirred to obtain a white precipitate, which was washed, filtered, and dried to obtain hydrophobically modified tannic acid; (2) Preparation of precursor solution for hydrogel electrode: Add hydrophobic modified tannic acid, acrylic acid, polyethyleneimine and conductive components obtained in step (1) to deionized water, add photoinitiator, stir to dissolve, and obtain precursor solution; (3) Mold casting and ultraviolet light polymerization: The precursor solution obtained in step (2) is injected into the electrode mold, and then the electrode mold is placed in an ultraviolet lamp to carry out photopolymerization reaction to obtain a hydrogel electrode.

2. The method for preparing the hydrogel electrode with adhesive and anti-sweat properties according to claim 1, characterized in that: In step (1), the mass ratio of tannic acid solution to benzalkonium chloride aqueous solution is 1:1 to 1:1.5; the pH of alkaline solution is 9 to 12; the freeze-drying temperature is -20 ℃ to -80 ℃; and the drying time is 48 to 72 h.

3. The method for preparing the hydrogel electrode with adhesive and sweat-resistant properties according to claim 1, characterized in that: In step (2), the mass ratio of acrylic acid to hydrophobically modified tannic acid is 8:1 to 80:1; the mass ratio of acrylic acid to polyethyleneimine is 10:1 to 100:1; the mass ratio of acrylic acid to conductive component is 80:1 to 8:1; and the mass ratio of acrylic acid to photoinitiator is 20:1 to 100:

1.

4. The method for preparing the hydrogel electrode with adhesive and anti-sweat properties according to claim 1, characterized in that: In step (2), the photoinitiator is selected from one of 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone; the conductive component is selected from one or more of sodium chloride, lithium chloride, and potassium chloride.

5. The method for preparing a hydrogel electrode with adhesive and sweat-resistant properties according to claim 1, characterized in that: In step (1), the stirring time is 1.5~3h; in step (2), the stirring time is 0.5~2h; in step (3), the photopolymerization time is 0.5~2h.

6. A hydrogel electrode with adhesive and sweat-resistant properties, characterized in that, It is prepared according to any one of the preparation methods described in claims 1 to 5.

7. The hydrogel electrode with adhesive and sweat-resistant properties according to claim 6, characterized in that: The thickness of the hydrogel electrode is 0.4~0.7 mm.

8. The application of the hydrogel electrode with adhesive and sweat-resistant properties as described in claim 6 in strain sensors and bioelectrical signals.

9. The application of the hydrogel electrode with adhesive and sweat-resistant properties according to claim 8 in a strain sensor, characterized in that: A resistive strain sensor is obtained by attaching copper wires to both ends of the hydrogel electrode. The strain sensor is then connected to a digital multimeter for motion sensing.

10. The application of the hydrogel electrode with adhesive and sweat-resistant properties according to claim 8 in bioelectrical signals, characterized in that: Hydrogel electrodes are attached to the skin and connected to an electrocardiogram (ECG) acquisition device to measure ECG signals; hydrogel electrodes are also attached to the skin and connected to an electromyography (EMG) acquisition device to measure EMG signals.

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