A hydrogel electrode with adhesion and anti-sweat properties and its preparation method and application

Abstract

The application discloses a kind of hydrogel electrode with adhesion and anti-sweat characteristics and preparation method and application thereof, belong to flexible hydrogel sensing material technical field.The electrode is formed by dissolving acrylic acid, hydrophobic modified tannic acid, initiator, polyethyleneimine and conductive substance in deionized water to form a precursor solution, and is prepared by pouring into mould and then carrying out ultraviolet light polymerization.The hydrogel electrode prepared by the application has good mechanical strength, excellent skin adhesion, significant anti-sweat interference ability, high conductivity and low contact impedance.The electrode can be directly attached to the skin and used as a strain sensor or to collect various bioelectric signals, and has the comprehensive advantages of high stability, good detection accuracy, low interface impedance, excellent biocompatibility, easy-to-obtain material and simple process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of flexible hydrogel sensing materials, and particularly relates to a hydrogel electrode with adhesion and sweat resistance and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of science and technology, human beings have entered the intelligent era. At present, flexible electronic devices based on artificial intelligence technology have attracted much attention due to their great application potential in emerging fields such as wearable devices and electronic skin. As a functional material, conductive hydrogel has inherent flexibility, high water content and excellent conductivity. It is usually composed of a hydrophilic polymer network and a conductive component (such as conductive polymer, carbon-based material, metal nano-filler or ionic salt, etc.). With good biocompatibility, adjustable mechanical properties and biological activity, conductive hydrogel shows important application value in the field of flexible electronic devices, especially in the field of biological electrical signal sensing.

[0003] Biological electrical signals, such as electrocardiogram (ECG) and electromyogram (EMG), are key indicators reflecting the physiological state and motor function of the human body, 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 arrhythmias and myocardial ischemia; EMG signals are helpful for diagnosing neuromuscular disorders, assessing muscle function and guiding rehabilitation training. The epidermal electrode for detecting biological electrical signals not only needs to output high signal-to-noise ratio signals, but also needs to meet the following key performance requirements: skin-matched electrical conductivity to reduce electrode-skin interface impedance and reduce environmental noise interference; excellent adhesion to ensure tight and stable adhesion to the skin without additional auxiliary fixation; good sweat resistance to maintain long-term stable adhesion and avoid slipping or falling under the condition of skin sweating; excellent biocompatibility to ensure the comfort and safety of long-term wear. In addition, with the advancement of sensing technology and signal processing algorithms, the monitoring of biological electrical signals is developing towards portability, real-time and intelligence, which puts forward higher requirements for the quality of signal acquisition, anti-interference ability and feature extraction accuracy.

[0004] At present, hydrogel electrodes play an important role in biological electrical signal monitoring, but still face many challenges in actual application: first, insufficient adhesion: the bonding force between the electrode and the skin is weak, often relying on additional fixation devices (such as adhesive tape or bandage), increasing the complexity of use; second, poor motion stability: skin sweating easily leads to electrode slipping or falling, affecting the continuity and reliability of signal acquisition; third, poor comfort for long-term wear: some materials may cause skin redness, allergy and other adverse reactions; fourth, interface impedance problem: the electrode-skin interface impedance is high, which easily introduces environmental noise and reduces the signal-to-noise ratio.

[0005] The above limitations significantly restrict the practical application of hydrogel electrodes in wearable devices such as health monitoring and motion recognition. Therefore, in order to meet the demand for high-precision bioelectric signal acquisition, it is particularly urgent to develop a new type of hydrogel electrode that can effectively overcome the limitations of existing technologies. SUMMARY

[0006] The first technical problem to be solved by the present application is to provide a hydrogel electrode with adhesion and sweat resistance, which can closely adhere to the human skin and flexible substrate, maintain high-precision and high signal-to-noise ratio physiological signal acquisition in a sweat environment, and has a repeatable pasting property. The second technical problem to be solved by the present application is to provide a preparation method of a hydrogel electrode with adhesion and sweat resistance, which has simple and efficient preparation process, easily available raw materials, short cycle and is suitable for large-scale production. The third technical problem to be solved by the present application is to provide the application of the hydrogel electrode in strain sensors and bioelectric signals.

[0007] To solve the above technical problems, the technical solutions adopted by the present application are as follows:

[0008] A preparation method of a hydrogel electrode with adhesion and sweat resistance, comprising the following steps:

[0009] (1) Preparation of hydrophobically modified tannic acid: dissolve tannic acid in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to alkaline solution is 1:20-1:30; then, dissolve benzalkonium chloride in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water is 1:20-1:30; finally, mix and stir the tannic acid solution and the benzalkonium chloride aqueous solution to obtain a white precipitate, wash, filter and dry to obtain hydrophobically modified tannic acid;

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

[0011] (3) Mould pouring and ultraviolet polymerization: pour the precursor solution obtained in step (2) into an electrode mould, then place the electrode mould in an ultraviolet lamp for photopolymerization reaction to obtain a hydrogel electrode.

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

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

[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; and 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 1.5-3 h; in step (2), the stirring time is 0.5-2 h; and in step (3), the photopolymerization time is 0.5-2 h.

[0016] A hydrogel electrode with adhesion and anti-sweat properties.

[0017] Further, the thickness of the hydrogel electrode is 0.4-0.7 mm.

[0018] Further, the hydrogel electrode with adhesion and anti-sweat properties is applied in strain sensors and bioelectric signals.

[0019] Further, a resistance strain sensor is obtained by attaching copper wires to both ends of the hydrogel electrode, and the strain sensor is connected to a digital multimeter for motion sensing.

[0020] Further, the hydrogel electrode is attached to the skin and connected to an electrocardio collection device for measuring electrocardio signals, and the hydrogel electrode is attached to the skin and connected to an electromyography collection device for measuring electromyography signals.

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

[0022] (1) The hydrogel electrode prepared by the present application has improved signal collection stability, and the electrode can be closely attached to human skin and a flexible substrate, can still maintain high-precision and high-signal-to-noise-ratio physiological signal collection in a sweat environment, and has a repeatable pasting property.

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

[0024] (3) The present application can realize enhanced application compatibility, the electrode is suitable for various wearable devices, has stable operation, low operation threshold, and strong universality, and is easy to promote in clinical and consumer fields.

[0025] (4) The application provides a preparation method of the hydrogel electrode with adhesion and sweat resistance, which is simple and efficient, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A flowchart for preparing the hydrogel electrode of the application;

[0027] Figure 2 An assembly schematic diagram of a strain sensor of the hydrogel electrode prepared in the application;

[0028] Figure 3 A test schematic diagram of the hydrogel electrode prepared in the application, wherein a is a shear adhesion test schematic diagram; and b is a "T" type adhesion test schematic diagram;

[0029] Figure 4 A tensile stress-strain curve diagram of the hydrogel electrode prepared in the application example 1 and the comparative example 2;

[0030] Figure 5 Optical photographs of the hydrogel electrode prepared in the application example 1 in bending and torsion states;

[0031] Figure 6 Adhesion photographs of the hydrogel electrode prepared in the application example 1 and different substrates;

[0032] Figure 7 An underwater adhesion test diagram of the hydrogel electrode prepared in the application example 1;

[0033] Figure 8 A relative resistance change curve diagram of the hydrogel electrode prepared in the application example 1 under the action of stretching;

[0034] Figure 9 An electromyographic signal acquisition diagram of the hydrogel electrode prepared in the application example 1 and a commercial gel electrode;

[0035] Figure 10 An electrocardiographic signal acquisition diagram of the hydrogel electrode prepared in the application example 1 and a commercial gel electrode;

[0036] Figure 11 A contrast optical photograph of the hydrogel electrode prepared in the application example 1 and a commercial gel electrode after being worn on the forearm skin of a volunteer for 48 hours. DETAILED DESCRIPTION

[0037] The following examples are intended to illustrate the application in more detail, but not to limit the scope of the application. Any modification or replacement made by those skilled in the art based on the concept of the application shall be considered to fall within the protection scope of the application.

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

[0039] Figure 1 A schematic diagram of the process for preparing the hydrogel electrode with adhesion and sweat resistance includes the following three steps:

[0040] (1) Preparation of hydrophobically modified tannic acid: dissolve tannic acid in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to alkaline solution is 1:20-1:30; then, dissolve benzalkonium chloride in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water is 1:20-1:30; finally, mix and stir the tannic acid solution and the benzalkonium chloride aqueous solution to obtain a white precipitate, wash, filter, and dry to obtain hydrophobically modified tannic acid;

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

[0042] (3) Mould pouring and ultraviolet polymerization: pour the precursor solution obtained in step (2) into an electrode mould, then place the electrode mould in a UV lamp for photopolymerization to obtain a hydrogel electrode.

[0043] Example 1

[0044] A method for preparing a hydrogel electrode with adhesion and sweat resistance includes the following steps:

[0045] (1) Preparation of hydrophobically modified tannic acid: dissolve 4 g of tannic acid in 100 g of sodium hydroxide aqueous solution (pH=10) to obtain a tannic acid solution; dissolve 4 g of benzalkonium chloride in 100 g of deionized water to obtain a benzalkonium chloride aqueous solution; mix the tannic acid solution and the benzalkonium chloride aqueous solution 1:1 for 2 h to obtain a white precipitate; wash the white precipitate with deionized water three times, then vacuum filter and freeze-dry at -20 ℃ for 48 h to obtain hydrophobically modified tannic acid.

[0046] (2) Preparation of the precursor solution of the synthesized gel: add acrylic acid, polyethyleneimine, hydrophobically modified tannic acid, and a conductive component to 2 g of deionized water, and add 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, fully dissolve by magnetic stirring at room temperature for 1 h, and obtain a 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 an electrode mould with a polytetrafluoroethylene film, then place the electrode mould in a UV lamp for photopolymerization 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 ensure 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 make 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] Table 2 shows that Comparative Example 2, which does not contain polyethyleneimine, exhibits significantly lower stress compared to Examples 1 and 2-4; Comparative Example 1, which does not contain hydrophobically modified tannic acid, shows 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. Figures 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 having adhesiveness and anti-sweat properties, characterized by, The preparation method comprises the following steps: (1) Preparation of hydrophobically modified tannic acid: tannic acid is dissolved in an alkaline aqueous solution to obtain a tannic acid solution, wherein the mass ratio of tannic acid to the alkaline solution is 1:20-1:30; then, benzalkonium chloride is dissolved in deionized water to obtain a benzalkonium chloride aqueous solution, wherein the mass ratio of benzalkonium chloride to deionized water is 1:20-1:30; finally, the tannic acid solution and the benzalkonium chloride aqueous solution are mixed and stirred to obtain a white precipitate, which is washed, filtered, and dried to obtain hydrophobically modified tannic acid; (2) Preparation of a precursor solution of the hydrogel electrode: the hydrophobically modified tannic acid obtained in step (1) and acrylic acid, polyethyleneimine, and a conductive component are added to deionized water, and a photoinitiator is added, and the mixture is stirred and dissolved to obtain a precursor solution; The conductive component is selected from one or more of sodium chloride, lithium chloride, and potassium chloride; (3) Mould pouring and ultraviolet polymerization: the precursor solution obtained in step (2) is poured into an electrode mould, and then the electrode mould is placed in an ultraviolet lamp for photopolymerization to obtain a hydrogel electrode.

2. The method of claim 1, wherein the method is characterized by: In step (1), the mass ratio of the tannic acid solution to the benzalkonium chloride aqueous solution is 1:1-1:1.5; the pH of the alkaline solution is 9-12; the freeze-drying temperature is -20 ℃-80 ℃; and the drying time is 48-72 h.

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

1.

4. The method of claim 1, wherein the method further comprises: 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.

5. The method of claim 1, wherein the method further comprises: In step (1), the stirring time is 1.5-3 h; in step (2), the stirring time is 0.5-2 h; and in step (3), the photopolymerization time is 0.5-2 h.

6. A hydrogel electrode having adhesiveness and anti-sweat properties, characterized by, The method is prepared according to any one of claims 1-5.

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

8. Application of the hydrogel electrode with adhesion and anti-sweat properties according to claim 6 in strain sensors and bioelectric signals.

9. Use of the hydrogel electrode with adhesion and anti-sweat properties according to claim 8 in a strain sensor, characterized in that: The hydrogel electrode is attached to copper wires at both ends to obtain a resistance strain sensor, and the strain sensor is connected to a digital multimeter for motion sensing.

10. Use of the hydrogel electrode with adhesiveness and anti-sweat properties according to claim 8 in bioelectric signals, characterized in that: The hydrogel electrode is attached to the skin and connected to an electrocardio acquisition device for measuring electrocardio signals; and the hydrogel electrode is attached to the skin and connected to an electromyography acquisition device for measuring electromyography signals. The hydrogel electrode is attached to copper wires at both ends to obtain a resistance strain sensor, and the strain sensor is connected to a digital multimeter for motion sensing. The hydrogel electrode is attached to the skin and connected to an electrocardio acquisition device for measuring electrocardio signals; and the hydrogel electrode is attached to the skin and connected to an electromyography acquisition device for measuring electromyography signals.

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