Conductive silver paste biological binder and preparation method and application thereof

Abstract

The preparation method comprises the following steps: adding a cross-linking agent into polylipoic acid to carry out covalent cross-linking reaction, adding a stabilizer and a solvent, mixing to obtain a polymer binding phase solution, finally adding micron-sized flake silver powder, and fully mixing to obtain the conductive silver paste biological binding agent. The prepared conductive silver paste biological binder is suitable for a skin environment and is naturally dried and cured. Meanwhile, high conductivity, excellent skin adhesion, biocompatibility and environmental stability are realized.

Description

Technical Field

[0001] This invention relates to a technology in the field of flexible materials, specifically a conductive silver paste bio-adhesive, its preparation method, and its application. Background Technology

[0002] Existing wearable devices cannot effectively conform to highly curved or dynamic joint areas; their adhesion to the skin is weak, and the flexible substrate lacks breathability, resulting in low data acquisition reliability in practical applications and impacting user comfort. In-situ fabricated bioelectronic devices utilize bioconductive silver paste to directly fabricate electronic components on the skin, enabling them to spontaneously conform to the skin's micro- and nano-scale features and achieve mechanical compatibility with the epidermis. However, existing conductive silver pastes suffer from difficulties in balancing excellent conductivity and adhesion, poor biocompatibility, limited application in skin environments, poor electromechanical stability, significantly increased resistance after stretching, difficulty adapting to skin deformation, and inability to meet the application requirements of wearable devices. Summary of the Invention

[0003] This invention addresses the problems of insufficient biocompatibility in existing technologies, which prevent prolonged skin contact; mechanical incompatibility, making it difficult to adapt to the complex morphology and dynamic changes of the skin; and poor long-term stability, which makes it prone to performance degradation due to environmental factors. It proposes a conductive silver paste bio-adhesive, its preparation method, and its application. The polymer chain is formed through thermally initiated free radical ring-opening polymerization of thioctic acid (LA). 1,3-Diisopropenebenzene (DIB) enhances the network strength through covalent cross-linking, and citric acid (CA) further strengthens the network structure through hydrogen bonding and coordination. The resulting bio-adhesive simultaneously achieves high conductivity, strong skin adhesion, and biocompatibility.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for preparing a conductive silver paste bio-adhesive, which involves adding a crosslinking agent to polythioctic acid to carry out a covalent crosslinking reaction, then adding a stabilizer and a solvent to mix and obtain a polymer binder phase solution, and finally adding micron-sized flake silver powder and mixing thoroughly to obtain the final product.

[0006] The polythioctic acid is obtained by heating thioctic acid to 80-120℃ to initiate a free radical ring-opening polymerization reaction.

[0007] The crosslinking agent is 1,3-diisopropenebenzene (DIB) and / or N,N'-methylenebisacrylamide, preferably 1,3-diisopropenebenzene.

[0008] The mass ratio of the crosslinking agent to the silver powder is (0.02~0.06):1, preferably 0.04:1.

[0009] The stabilizer is citric acid (CA), malic acid, tannic acid, or a combination thereof, preferably citric acid.

[0010] The mass ratio of the stabilizer to the silver powder is (0.02~0.05):1, preferably 0.05:1.

[0011] The solvent used may be, but is not limited to, ethanol (EtOH) or glycerol, with ethanol being preferred.

[0012] The mass ratio of the solvent to silver powder is (0.25~0.65):1, preferably 0.52:1.

[0013] The mass ratio of the silver powder, polythioctic acid, stabilizer, crosslinking agent and solvent is 1:(0.1~0.25):(0.02~0.05):(0.02~0.06):(0.25~0.65), preferably 1:0.2:0.04:0.05:0.52.

[0014] The silver powder has a particle size range of 1-20 μm, preferably 4-8 μm.

[0015] This invention relates to a conductive silver paste bio-binder prepared by the above method, with a solid content of 77%~89% and an appearance of silver paste. The composition is a mixture of silver powder and a biocompatible polymer binder phase. The silver powder interacts with the polymer binder phase through Ag-S and Ag-COOH to form a stable conductive binder.

[0016] This invention relates to the application of the above-mentioned conductive silver paste bio-binder, for the preparation of low-impedance bioelectrodes, for monitoring electrocardiogram (ECG) and electrical skin activity (EDA) signals without motion artifacts, or for the preparation of in-situ assembled PPG circuits.

[0017] Technical effect

[0018] This invention uses non-toxic and harmless polythioctic acid as the binder phase of conductive silver paste, along with a specific combination of crosslinking agents, stabilizers, and solvents, to form a stable supramolecular conductive network when mixed with sheet-like silver flakes. The conductive silver paste bio-adhesive prepared by this invention is suitable for epidermal environments and cures naturally. It simultaneously achieves high conductivity, excellent skin adhesion, biocompatibility, and environmental stability. Attached Figure Description

[0019] Figure 1 The diagram shows the effect of electrodes or circuits printed on different substrates using the conductive silver paste obtained in Example 3 of the present invention.

[0020] Figure a shows an electrode fabricated on the skin of an arm, and figure b shows an optical photograph of a circuit printed on pigskin.

[0021] Figure 2 This is a scanning electron microscope image of the conductive silver paste obtained in Example 3 of the present invention;

[0022] Figure 3 Tissue section of mouse back skin after 14 days of application of the present invention. Detailed Implementation Example 1

[0023] This embodiment relates to a method for preparing a conductive silver paste bio-adhesive, comprising: adding 3 g of thioctic acid powder to a sample vial, heating to 80 degrees Celsius, and stirring for 10 minutes to obtain a pale yellow transparent liquid polythioctic acid. Then, 0.6 g of 1,3-diisopropylbenzene (DIB) is added, and the mixture is reacted for 10 minutes under magnetic stirring. After adding 10 mL of ethanol, stirring is continued and the mixture is cooled to room temperature. Subsequently, 14.56 g of flake silver powder is added, and the mixture is homogenized using a high-speed mixer (2500 rpm, 3 minutes) to obtain the conductive silver paste bio-adhesive. Example 2

[0024] This embodiment relates to a method for preparing a conductive silver paste bio-adhesive, comprising: adding 3 g of thioctic acid powder to a sample vial, heating to 80 degrees Celsius, and stirring for 10 minutes to obtain a pale yellow transparent liquid polythioctic acid. After adding 10 mL of ethanol, stirring is continued and the mixture is cooled to room temperature. Then, 0.75 g of citric acid (CA) is added, and the mixture is magnetically stirred for 1 hour. Subsequently, 14.56 g of flake silver powder is added, and the mixture is homogenized using a high-speed mixer (2500 rpm, 3 minutes) to obtain the conductive silver paste bio-adhesive. Example 3

[0025] This embodiment relates to a method for preparing a conductive silver paste bio-adhesive, comprising: adding 3 g of thioctic acid powder to a sample vial, heating to 80 degrees Celsius, and stirring for 10 minutes to obtain a pale yellow transparent liquid polythioctic acid. Then, 0.6 g of 1,3-diisopropylbenzene (DIB) is added, and the mixture is reacted for 10 minutes under magnetic stirring. After adding 10 mL of ethanol, stirring is continued and the mixture is cooled to room temperature. Next, 0.75 g of citric acid (CA) is added, and the mixture is magnetically stirred for 1 hour. Subsequently, 14.56 g of flake silver powder is added, and the mixture is homogenized using a high-speed mixer (2500 rpm, 3 minutes) to obtain the conductive silver paste bio-adhesive. Example 4

[0026] This embodiment relates to a method for preparing conductive silver paste bio-adhesives, including: except for changing the mass of flake silver powder, the remaining steps and conditions are the same as in Example 3, resulting in different conductive silver paste binders. The numbers, components, and contents of the obtained conductive silver paste bio-adhesives are shown in Table 1.

[0027] Table 1 Raw material usage in different embodiments

[0028] The conductive silver paste bio-adhesive of this invention, when applied to the skin, forms electrodes or circuits of different shapes and, after natural drying, appears silvery-white, such as... Figure 1 As shown.

[0029] After being coated onto glass and dried, the sample was subjected to scanning electron microscopy (SEM). The resulting SEM image is shown below. Figure 2 As shown.

[0030] Performance testing: The conductive silver paste bio-adhesives prepared in Examples 1-5 were subjected to the following tests:

[0031] Test 1. The conductive silver paste bio-adhesive prepared in Examples 1-3 was coated onto a polyurethane elastomer substrate to prepare a 5mm×20mm rectangular circuit. The maximum elongation and resistance change of the circuit under different tensile deformations were measured using a Keithley source meter and the four-probe method. The test results are shown in Table 2.

[0032] Table 2

[0033] Test 2. The conductive silver paste bio-adhesive prepared in Examples 3-5 was coated onto a glass substrate to prepare the circuit. The resistance of the circuit in this example was measured using a Keithley source meter and the four-probe method. The length and width of the circuit were measured using a ruler, and the film thickness was measured using a film thickness gauge. Finally, the conductivity was calculated.

[0034] Test 3. The conductive silver paste bio-adhesives prepared in Examples 3-5 were applied to the surface of degreased pigskin, and the shear and peel adhesion strengths of this example were measured using a tensile testing machine. The results of Tests 2-3 are shown in Table 3:

[0035] Table 3 Performance of Examples 3-5

[0036] The biocompatibility of the conductive silver paste bio-adhesive prepared above was tested: the sample was applied to the back skin of mice, and the skin reaction was observed for 14 days. Skin tissue samples from the application site were sectioned for histological analysis of the subcutaneous tissue. At least three samples were tested for each condition, and the average value was taken. No obvious skin irritation or allergic reaction was observed visually. Histological analysis of the subcutaneous tissue showed an intact epidermal structure, normal keratinocyte layering, and well-arranged dermal collagen matrix. The stained tissue sections are shown below. Figure 3 As shown.

[0037] Compared with the prior art, the technical advantages of this invention include:

[0038] High conductivity: By adjusting the silver flake content in the conductive silver paste bio-binder, a conductivity of 2,500-22,000 S / cm can be achieved. -1 In this invention, with a silver solid content of 89%, a 21,700 S cm⁻¹ was achieved. -1 This conductivity is significantly higher than that of existing conductive inks and hydrogel-based materials. In this invention with a silver solid content of 85%, a conductivity of 15050 S / cm is achieved. -1 Furthermore, the resistance only increases by 4 times when subjected to 275% tensile deformation, demonstrating excellent mechanical stability.

[0039] Strong skin adhesion: Adhesion to various skin surfaces exceeds 40 kPa, with a maximum shear adhesion strength reaching 60 kPa, comparable to medical tape, ensuring long-term stability of the device on the skin. Images of the epidermal electrodes and surface circuits fabricated on the skin surface according to this invention are shown below. Figure 1 As shown.

[0040] Biocompatibility: Made from biocompatible monomers, suitable for long-term skin contact, with no toxic side effects.

[0041] Mechanical compatibility: It has good viscoelasticity and mechanical properties, and can adapt to the complex morphology and dynamic changes of the skin.

[0042] Simple and rapid preparation capability: It has a simple and rapid preparation capability, and it dries and cures spontaneously in natural environment without the need for heating and curing process. It is suitable for in-situ manufacturing in the skin environment.

[0043] Multifunctionality: It can be used to manufacture low-impedance bioelectrodes in situ to achieve motion artifact-free electrocardiogram (ECG) and electrical skin activity (EDA) monitoring; it can also be used as a conductive binder for in situ assembly of photoplethysmography (PPG) circuits.

[0044] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for preparing a conductive silver paste bio-adhesive, characterized in that, The polymer binder phase solution is obtained by adding a crosslinking agent to polythioctic acid to carry out a covalent crosslinking reaction, then adding a stabilizer and solvent and mixing. Finally, micron-sized flake silver powder is added and mixed thoroughly.

2. The method for preparing the conductive silver paste bio-adhesive according to claim 1, characterized in that, The polythioctic acid is obtained by heating thioctic acid to 80-120℃ to initiate a free radical ring-opening polymerization reaction.

3. The method for preparing the conductive silver paste bio-adhesive according to claim 1, characterized in that, The crosslinking agent is 1,3-diisopropylbenzene (DIB) and / or N,N'-methylenebisacrylamide.

4. The method for preparing the conductive silver paste bio-adhesive according to claim 1, characterized in that, The stabilizer is citric acid (CA), malic acid, tannic acid, or a combination thereof.

5. The method for preparing the conductive silver paste bio-adhesive according to claim 1 or 3, characterized in that, The mass ratio of the crosslinking agent to the silver powder is (0.02~0.06):

1.

6. The method for preparing the conductive silver paste bio-adhesive according to claim 1 or 4, characterized in that, The mass ratio of the stabilizer to silver powder is (0.02~0.05):

1.

7. The method for preparing the conductive silver paste bio-adhesive according to any one of claims 1-4, characterized in that, The mass ratio of the silver powder, polythioctic acid, stabilizer, crosslinking agent and solvent is 1:(0.1~0.25):(0.02~0.05):(0.02~0.06):(0.25~0.65).

8. The method for preparing the conductive silver paste bio-adhesive according to any one of claims 1-4, characterized in that, The silver powder has a particle size range of 1-20 μm.

9. A conductive silver paste bio-adhesive prepared according to any one of claims 1-8, characterized in that, Specifically, it is a mixture of silver powder and a biocompatible polymer binder phase, wherein the silver powder interacts with the polymer binder phase to form a stable conductive binder.

10. The application of the conductive silver paste bio-adhesive according to claim 9, characterized in that, It can be used to prepare low-impedance bioelectrodes, for motion artifact-free electrocardiogram (ECG) and electrical skin activity (EDA) signal monitoring, or for preparing in-situ assembled PPG circuits.

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