A method for preparing and applying a highly conductive hydrogel

Abstract

This application discloses a method for preparing and applying a highly conductive hydrogel. The first aspect of this application provides a method for preparing a highly conductive hydrogel material, comprising the following steps: forming a pattern of highly conductive ink on a hydrogel substrate using a mask; and heat-treating the highly conductive ink to form a conductive permeation layer, thereby obtaining a highly conductive hydrogel. This preparation method is simple and easy to implement. During the preparation process, heat treatment accelerates the ion exchange between the highly conductive ink and the hydrogel substrate, promoting the penetration of conductive substances from the highly conductive ink into the hydrogel substrate, forming a tightly bonded and uniform conductive permeation layer. This novel structure combines the highly conductive ink coating and the hydrogel substrate, with a tight bond and no obvious boundary between them, retaining the ultra-high conductivity of the highly conductive ink and the flexibility and biocompatibility of the hydrogel, providing a new approach for developing highly conductive flexible hydrogel electrodes with novel structures.

Description

Technical Field

[0001] This application relates to the field of hydrogel technology, and in particular to a method for preparing and applying a highly conductive hydrogel. Background Technology

[0002] Hydrogels are polymeric materials with a three-dimensional polymer network and a large internal water content. The three-dimensional polymer network endows them with solid properties, while the aqueous phase gives them liquid-like transport characteristics. The good biocompatibility, low Young's modulus, and water content similar to the tissue environment of hydrogel materials make them perfect candidates for drug delivery materials, medical dressings, tissue scaffolds, and implantable bioelectrodes. In recent years, conductive hydrogels have proven to be effective interfacial bridging media between biological systems and artificial bioelectronics. Due to the ionic conductivity of hydrogels, water-rich conductive hydrogels have the potential to achieve better signals than dry electrodes.

[0003] There are generally two approaches to improve the conductivity of hydrogels. One is to mix conductive polymers (providing conductivity) with conventional insulating polymer matrices (providing structural support and water absorption), but poor processability and mechanical brittleness limit their application in bioengineering. The other approach uses inorganic conductive fillers, such as carbon-based materials, transition metal carbides / nitrides, and liquid metals, which provide efficient electron transport channels through the polymer matrix via covalent / non-covalent interactions with the polymer chains, thereby improving the conductivity of the hydrogel. However, these composite conductive hydrogels suffer from drawbacks such as unstable additive binding and in vivo toxicity, limiting their application in the biomedical field. Therefore, it is necessary to prepare hydrogel materials with non-toxicity, stable binding, and excellent conductivity using simple methods. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a method for preparing and applying a highly conductive hydrogel material. This method can prepare a non-toxic, highly conductive composite hydrogel material with stable bonding between additives and the hydrogel in a simple manner.

[0005] A first aspect of this application provides a method for preparing a highly conductive hydrogel material, comprising the following steps:

[0006] Patterns of highly conductive ink are formed on a hydrogel substrate using a mask;

[0007] Heat treatment of highly conductive ink forms a conductive permeation layer, resulting in a highly conductive hydrogel.

[0008] The preparation method according to the embodiments of this application has at least the following beneficial effects:

[0009] The preparation method provided in this application is simple and easy to implement. By adjusting the shape of the mask, the pattern shape of the final highly conductive hydrogel can be flexibly controlled. Simultaneously, heat treatment during the preparation process accelerates ion exchange between the highly conductive ink and the hydrogel substrate, promoting the penetration of conductive substances from the highly conductive ink into the hydrogel substrate, forming a tightly bonded and uniform conductive permeation layer. This novel structure combines the highly conductive ink coating and the hydrogel substrate, with a tight bond and no obvious boundary, preserving the ultra-high conductivity of the highly conductive ink and the flexibility and biocompatibility of the hydrogel. This provides a new approach for developing highly conductive flexible hydrogel electrodes with novel structures.

[0010] Highly conductive inks typically consist of a system comprising conductive materials, solvents, and / or dispersants. The pattern of a highly conductive ink refers to the pattern formed by the highly conductive ink penetrating a cutout portion of a mask onto a hydrogel substrate. It can be understood that this pattern can refer to the shape of the highly conductive ink in its liquid state, or it can refer to the conductive pattern formed after further evaporation of the solvent in the ink. Furthermore, in the embodiments of this application, the heat treatment step allows the highly conductive ink to not only form a separate conductive pattern layer on the hydrogel surface, but also to exchange with the hydrogel substrate, causing this conductive pattern to extend into the hydrogel substrate to form an interpenetrating conductive permeation layer. Therefore, the conductive pattern of the highly conductive ink, the interpenetrating conductive permeation layer, and the hydrogel substrate are not clearly defined, forming a complete highly conductive hydrogel structure.

[0011] In some embodiments of this application, the highly conductive ink is configured to have a conductivity of 1000–8000 S / cm when forming a conductive pattern individually, for example, 1000 S / cm, 1500 S / cm, 2000 S / cm, 2500 S / cm, 3000 S / cm, 3500 S / cm, 4000 S / cm, 4500 S / cm, 5000 S / cm, 5500 S / cm, 6000 S / cm, 6500 S / cm, 7000 S / cm, 7500 S / cm, or 8000 S / cm. In some embodiments, the highly conductive ink is configured to have a conductivity of 2000–6000 S / cm, 3000–6000 S / cm, 4000–6000 S / cm, or 5000–6000 S / cm when forming a patterned electrode individually.

[0012] In some embodiments of this application, the highly conductive ink is configured to have a resistivity of 1–30 kΩ@100 Hz when forming a conductive pattern individually, for example, 1 kΩ@100 Hz, 2 kΩ@100 Hz, 5 kΩ@100 Hz, 8 kΩ@100 Hz, 10 kΩ@100 Hz, 12 kΩ@100 Hz, 15 kΩ@100 Hz, 18 kΩ@100 Hz, 20 kΩ@100 Hz, 25 kΩ@100 Hz, or 30 kΩ@100 Hz. In some other embodiments, the highly conductive ink is configured to have a resistivity of 1–20 kΩ@100 Hz, 1–10 kΩ@100 Hz, 2–8 kΩ@100 Hz, or 4–6 kΩ@100 Hz when forming a conductive pattern individually.

[0013] In some embodiments of this application, the conductive material in the highly conductive ink includes a highly conductive polymer. In some embodiments, the highly conductive polymer is incorporated such that the highly conductive ink is configured to have a conductivity of 1000–8000 S / cm when forming a conductive pattern on its own.

[0014] In some embodiments of this application, the highly conductive polymer includes PEDOT:PSS.

[0015] In some embodiments of this application, the highly conductive ink further includes at least one of ethylene glycol (EG) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0016] In some embodiments of this application, the highly conductive ink further includes ethylene glycol and lithium bis(trifluoromethanesulfonyl)imide.

[0017] In some embodiments of this application, the mass of ethylene glycol is 1 to 10 wt% of the PEDOT:PSS solution, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%. In some embodiments, the mass of ethylene glycol is 2 to 10 wt% or 5 to 10 wt% of the PEDOT:PSS solution.

[0018] In some embodiments of this application, the mass of LiTFSI is 5–50 wt% of the solid content of the PEDOT:PSS solution, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%. In some embodiments, the mass of LiTFSI is 10–48 wt%, 10–46 wt%, 10–45.5 wt%, 15–45.5 wt%, 20–45.5 wt%, 30–45.5 wt%, or 40–45.5 wt% of the solid content of the PEDOT:PSS solution.

[0019] By adding EG or LiTFSI to the PEDOT:PSS system and controlling the corresponding ratio, especially by adding EG and LiTFSI simultaneously, it is possible to achieve a significant and simultaneous improvement in conductivity and tensile properties.

[0020] In some embodiments of this application, the viscosity of the highly conductive ink is 1 to 1000 cP.

[0021] In some embodiments of this application, the surface tension of the highly conductive ink is 30–40 mN / m.

[0022] In some embodiments of this application, the heat treatment temperature is 25–150°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, or 150°C. In some embodiments, the heat treatment temperature is 40–120°C, 50–120°C, 60–120°C, 70–120°C, 40–90°C, 50–90°C, 60–90°C, or 70–90°C.

[0023] In some embodiments of this application, the heat treatment is performed by heating the mask or heating the hydrogel substrate. This heat treatment accelerates the evaporation of the solvent in the highly conductive ink, speeds up the ion exchange between the highly conductive ink and the hydrogel substrate, and promotes the penetration of conductive substances in the highly conductive ink into the hydrogel substrate, forming a tightly bonded and uniform conductive penetration layer. This increases the adhesion between the conductive pattern formed by the highly conductive ink and the hydrogel substrate, and shortens the preparation time of the highly conductive hydrogel.

[0024] In some embodiments of this application, the hydrogel substrate material is selected from at least one of polyvinyl alcohol, polyacrylic acid, polyacrylate, polyacrylamide, polyurethane, polyhydroxyethyl methacrylate, polyethylene oxide, poly(N-isopropylacrylamide), polyethylene glycol diacrylate, polyethylene glycol methacrylate, gelatin, alginate, hyaluronic acid, agarose, chitosan, and collagen.

[0025] In some embodiments of this application, the hydrogel substrate is a peelable ultrathin hydrogel.

[0026] In some embodiments of this application, at least one side of the hydrogel substrate has a release film, and a pattern of highly conductive ink is formed on the other side of the hydrogel substrate opposite the release film using a mask.

[0027] In some embodiments of this application, a release film is provided on both opposite surfaces of the hydrogel substrate.

[0028] In some embodiments of this application, the release film is hydrophobically modified.

[0029] In some embodiments of this application, the hydrogel substrate is prepared by coating a one-step reactive hydrogel stock solution onto a release film and pressing it to obtain the hydrogel substrate.

[0030] In some embodiments of this application, the hydrogel substrate is prepared by applying a one-step reactive hydrogel stock solution between two release films and pressing it with two rollers to obtain the hydrogel substrate. In some embodiments, one release film is peeled off to expose one side of the hydrogel substrate, allowing it to adhere to a photomask and form a pattern therein with highly conductive ink to prepare a highly conductive hydrogel; while the other release film, which is not peeled off, serves to fix the shape of the hydrogel during the ink patterning process.

[0031] In some embodiments of this application, the pattern cut out on the photomask is achieved by laser lithography. Using laser lithography technology is advantageous for obtaining photomasks with sharper edges, more precise shapes, and easier adjustment.

[0032] In some embodiments of this application, the photomask has a hydrophobic surface. A photomask with a hydrophobic surface can better confine the highly conductive ink within the shape of the photomask and the exposed area of ​​the hydrogel, rather than spreading it across the photomask surface. Simultaneously, it facilitates separation from the hydrogel substrate after the highly conductive hydrogel has been molded. It is understood that the hydrophobic surface can be obtained by forming a hydrophobic coating on the surface or by physical and / or chemical modification, which will not be elaborated further here.

[0033] In some embodiments of this application, the mask template has high flexibility. Selecting a mask template with high flexibility allows the mask to be easily peeled off from the hydrogel substrate after the highly conductive hydrogel is molded, without damaging the surface morphology and structure of the hydrogel substrate.

[0034] Since pattern formation depends on the adhesion between the hydrogel substrate and the mask, in some embodiments of this application, the mask and the hydrogel substrate can be seamlessly adhered, thereby ensuring that ink does not penetrate between the mask and the hydrogel substrate during the pattern formation process, which helps to create a highly conductive hydrogel with precise shape and sharp edges.

[0035] In some embodiments of this application, the mask is at least one of polyethylene terephthalate (PET), polyimide (PI), and polydimethylsiloxane (PDMS).

[0036] In some embodiments of this application, the mask is a PDMS.

[0037] In some embodiments of this application, after obtaining the highly conductive hydrogel, the mask is peeled off, and the release film on the side where the hydrogel forms the pattern is re-covered on the original side of the highly conductive hydrogel. By re-covering with the release film, moisture loss during storage is prevented, thus maintaining the performance of the highly conductive hydrogel.

[0038] In some embodiments of this application, the method for forming a pattern of highly conductive ink on the cutout portion of a photomask involves drop-coating the highly conductive ink therein. Through the photomask drop-coating process, the shape of the highly conductive hydrogel can be flexibly varied, and the highly conductive ink can be better confined within the shape of the photomask and the exposed area of ​​the hydrogel during drop-coating, rather than spreading on the surface of the photomask. Furthermore, it is easier to separate the highly conductive hydrogel from the hydrogel substrate after molding. The heat-treated photomask drop-coating method can accelerate the evaporation of solvents in the highly conductive ink, accelerate ion exchange between the highly conductive ink and the hydrogel substrate, and promote the penetration of conductive substances in the highly conductive ink into the hydrogel substrate, forming a tightly bonded and uniform conductive penetration layer. This increases the adhesion between the conductive ink coating and the hydrogel substrate and shortens the preparation time of the highly conductive hydrogel.

[0039] A second aspect of this application provides a highly conductive hydrogel, which is prepared according to any of the aforementioned preparation methods.

[0040] In some embodiments of this application, the conductivity of the highly conductive hydrogel is 1000–3000 S / cm. In some other embodiments, the conductivity of the highly conductive hydrogel is 1500–3000 S / cm, 2000–3000 S / cm, or 2500–3000 S / cm. In some other embodiments, the conductivity of the highly conductive hydrogel is 2778 S / cm.

[0041] In some embodiments of this application, the elongation at break of the highly conductive hydrogel is 30-100%. In some embodiments, the elongation at break of the highly conductive hydrogel is 40-100%, 50-100%, 60-100%, 70-100%, or 80-100%. In some embodiments, the elongation at break of the highly conductive hydrogel is 89%.

[0042] In some embodiments of this application, the Young's modulus of the highly conductive hydrogel is 1–60 MPa. In some other embodiments, the Young's modulus of the highly conductive hydrogel is 1–50 MPa, 1–40 MPa, 1–20 MPa, 1–10 MPa, or 1–8 MPa. In some other embodiments, the Young's modulus of the highly conductive hydrogel is 4.95 MPa.

[0043] In some embodiments of this application, the impedance of the highly conductive hydrogel in PBS solution is 1–100 Ω @ 1000 kHz. In some other embodiments, the impedance of the highly conductive hydrogel in PBS solution is 1–80 Ω @ 1000 kHz, 1–50 Ω @ 1000 kHz, 1–40 Ω @ 1000 kHz, 1–30 Ω @ 1000 kHz, or 1–20 Ω @ 1000 kHz. More preferably, in some other embodiments, the impedance of the highly conductive hydrogel in PBS solution is 15.6 Ω @ 1000 kHz.

[0044] A third aspect of this application provides a medical device comprising the aforementioned highly conductive hydrogel.

[0045] In some embodiments of this application, medical devices include, but are not limited to, drug delivery materials or drug delivery devices or systems containing drug delivery materials, medical dressings or medical devices or equipment containing medical dressings, tissue engineering scaffolds or other materials, devices or equipment required for interventional treatments, implantable bioelectrodes or monitoring or treatment-related medical devices or equipment containing them.

[0046] In some embodiments of this application, the medical device includes an implantable bioelectrode. The highly conductive hydrogel prepared using the above method serves as a highly conductive flexible electrode that conformally adheres to the epidermis, thereby enabling precise monitoring of important physiological signals such as electrocardiograms and electromyograms, and as an implantable bioelectrode with extremely low impedance, thereby monitoring important physiological electrical signals of the cerebral cortex.

[0047] The method for preparing a highly conductive hydrogel provided in this application is simple to operate, requires minimal equipment, and allows for flexible control of the hydrogel's shape by adjusting the mask shape. Furthermore, by applying additional heat during the preparation process, ion exchange between the highly conductive ink and the hydrogel substrate is accelerated, promoting the penetration of conductive substances from the highly conductive ink into the hydrogel substrate, forming a tightly bonded and uniform conductive permeation layer. This novel structure combines a tightly bonded, seamlessly integrated highly conductive ink coating with a hydrogel substrate, preserving the ultra-high conductivity of the highly conductive ink and the flexibility and biocompatibility of the hydrogel, providing a new approach for developing highly conductive flexible hydrogel electrodes with novel structures.

[0048] In addition, since the thickness of the hydrogel substrate and the mask can be flexibly varied, highly conductive hydrogels with adjustable thickness (10-150 μm) can be prepared.

[0049] The highly conductive hydrogel provided in this application possesses ultra-high conductivity (1000–3000 S / cm). Within a 90% strain range, its resistance initially decreases and then increases, but the change range does not exceed 2%, demonstrating extremely high tensile stability. Furthermore, after 1000 cycles under a 30% strain tensile condition, the rate of change in resistance does not exceed 4%. Additionally, the highly conductive hydrogel prepared using the above method can achieve a relatively thin thickness (15 μm), while its low Young's modulus (1–60 MPa) and extremely low flexural stiffness (0.1–10 pN / m) allow it to conformally adhere to tissue texture as a wearable and implantable bioelectrode. Moreover, in vitro cytotoxicity tests were conducted using mouse hippocampal neurons (HT-22), confirming the low cytotoxicity of the highly conductive hydrogel to neurons.

[0050] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0051] Figure 1 The highly conductive hydrogel prepared in Example 1. In the image, a is a photograph showing the adhesion of a PDMS mask to a hydrogel substrate with a PET release film on one side; b is a photograph of the highly conductive hydrogel with PET release films on both sides after the PDMS mask has been peeled off and the release film has been reapplied; c is a photograph of the completely peeled-off highly conductive hydrogel.

[0052] Figure 2 The image shows the SEM image (top left) and elemental distribution diagram of the highly conductive hydrogel in Example 1.

[0053] Figure 3 The results are the shear strength test results of the highly conductive hydrogel in Example 1.

[0054] Figure 4 The results of tensile (a) and conductivity (b) tests on the highly conductive hydrogel in Example 1 are shown.

[0055] Figure 5 The results of the tensile-conductivity cycle test of the highly conductive hydrogel in Example 1 under a strain of 30% are shown. In this figure, a represents the change in tensile properties of the highly conductive hydrogel after 1, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 tensile cycles, and b represents the change in conductivity of the highly conductive hydrogel with different numbers of tensile cycles.

[0056] Figure 6 The impedance spectrum of the highly conductive hydrogel in PBS solution as a function of frequency in Example 1 is shown.

[0057] Figure 7 The graph shows the surface roughness and Young's modulus of the highly conductive hydrogel in Example 1.

[0058] Figure 8 This is an in vitro cytotoxicity test diagram of the highly conductive hydrogel in Example 1.

[0059] Figure 9 The images show the hybrid hydrogel prepared in Comparative Example 1. A through C are photographs of the hydrogel after photocuring, during the peeling off of the PET release film, and after the peeling off of the PET release film, respectively. Detailed Implementation

[0060] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0061] The embodiments of this application are described in detail below. The described embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0062] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0063] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0064] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] Example 1

[0066] This example demonstrates the preparation of a highly conductive hydrogel using a mask drop-casting method. The preparation process is described in [reference needed]. Figure 1 The specific steps are as follows:

[0067] 1. Preparation of hydrogels

[0068] Dissolve 0.1 g of sodium alginate in 6 mL of pure water and stir at room temperature for 4 h until completely dissolved to obtain a sodium alginate solution. Dissolve 0.1 g of acrylamide completely in 1 mL of pure water, then add the sodium alginate solution and stir for 10 min. Immediately add 600 μL of 0.15 wt% N,N′-methylenebisacrylamide crosslinking agent. After stirring at room temperature for 2 h, add 400 μL of 0.2 wt% 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone, continue stirring for 2 h, and allow to stand at room temperature to remove bubbles, obtaining the hydrogel stock solution.

[0069] 2. Preparation of hydrogel substrate

[0070] Two PET release films, each 15cm x 10cm, with a surface release force of 15-20g and thicknesses of 25μm and 75μm respectively, were selected. One side of each PET release film was coated with silicone oil (purchased from Shanghai Huadong Composite Material Filter Cloth Screen Factory). After cutting, the silicone oil-treated side of the 75μm thick PET release film was placed facing upwards. A double-roller coating machine was used to clean the two rollers and adjust the roller spacing to approximately 150μm to ensure that the roller spacing was consistent from left to right.

[0071] Pour approximately 1 mL of the hydrogel stock solution obtained in step 1 onto the surface of the prepared 75 μm thick release film, being careful not to disperse it excessively. Cover the hydrogel with the silicone-treated side of a 25 μm thick PET release film. Insert one end of the two PET release film layers containing the hydrogel mixture into the double rollers of the cold laminator. Rotate the handle to make the rollers roll, and the PET release film will be naturally pressed in. Maintain good flowability of the hydrogel throughout the process. After the hydrogel film is pressed, seal it in a plastic bag and incubate at room temperature overnight.

[0072] 3. Preparation of highly conductive ink

[0073] Add EG (5 wt% of the total system) and LiTFSI (10 wt% of the solid content of PEDOT:PSS) to a PEDOT:PSS aqueous solution (filtered with a 0.45 μm filter head), and stir at 900 rpm for 15 min to obtain a highly conductive ink of PEDOT:PSS / 5 wt% EG / 10 wt% LiTFSI.

[0074] The high conductivity ink was tested to have a viscosity of 23.8 cP using a digital viscometer and a surface tension of 36.7 mN / m using a surface tension meter. The film formed by coating the ink separately into a polytetrafluoroethylene mold and drying it showed a conductivity of 3658 S / cm using a four-probe method.

[0075] 4. Mask preparation

[0076] PDMS material is selected, and a mask is obtained by laser lithography to create a hollow pattern.

[0077] 5. Preparation of highly conductive hydrogels

[0078] Before preparing the highly conductive hydrogel, a 25 μm thick release film was peeled off from both sides of the PET film on the hydrogel substrate to expose the hydrogel. The substrate was then placed on a hot stage, and a patterned, perforated PDMS mask was seamlessly attached to the exposed hydrogel surface. Glass slides were used to press the edges to prevent slight deformation of the hydrogel during heating, which could lead to uneven distribution of the highly conductive ink. Next, a pipette was used to evenly spread the highly conductive ink over the exposed hydrogel area at the perforated portion of the PDMS mask. The hot stage temperature was set to 50 EG. After observing complete formation of the highly conductive ink film, heating was stopped. Once the highly conductive hydrogel cooled to room temperature, the PDMS mask was gently peeled off from the hydrogel.

[0079] During storage, the PET film peeled off in the previous step is re-covered onto the highly conductive hydrogel surface to prevent moisture loss during storage (see reference). Figure 1 (b) When using, peel off the PET release film on both sides, refer to... Figure 1 c yielded a highly conductive hydrogel.

[0080] from Figure 2 Scanning electron microscope images and elemental distribution maps show that during the mask drop-coating process, some penetration occurred between the highly conductive ink and the hydrogel substrate (elements N and S), and even some freely moving ions, such as Na in the hydrogel. + and F in highly conductive ink - Ions underwent a certain degree of displacement, and the highly conductive ink coating and the hydrogel substrate layer no longer had a clear boundary due to the formation of a conductive permeation layer. Therefore, the bonding force between the highly conductive hydrogel, the highly conductive ink layer, and the hydrogel substrate layer was greatly improved due to a certain degree of permeation prepared by mask drop casting. Figure 3 As shown, the bonding force between the two is as high as 79.5 kPa.

[0081] The elongation at break test results of the highly conductive hydrogel are as follows: Figure 4As shown in figure a, it can reach 89%, far exceeding the deformation of skin (0-30%) and the deformation of the cerebral cortex (0-20%). Moreover, this highly conductive hydrogel, while possessing ultra-high conductivity (2778 S / cm), also... Figure 4 The conductivity of b remains essentially unchanged as the strain increases, demonstrating good strain stability.

[0082] To verify the stability of the electrical properties of this highly conductive hydrogel under different cycling conditions, the hydrogel was subjected to 1000 repeated tensile cycles at a strain of 30%. The results are as follows: Figure 5 As shown, with repeated stretching cycles, the resistance of the highly conductive hydrogel exhibits a trend of first decreasing and then increasing, but the change does not exceed 4%, and overall it has very good stability.

[0083] To test whether this highly conductive hydrogel could be applied to implantable bioelectrodes for accurate reading of physiological electrical signals, its electrochemical impedance spectroscopy in PBS solution was measured. Figure 6 As shown, it exhibits extremely low impedance (15.6Ω) at the brain firing frequency (1kHz). Furthermore, during implantation, as... Figure 7 As shown, its smooth surface, as well as its low Young's modulus and bending stiffness (0.33 pN m), ensure that this electrode will not damage the surface of the cerebral cortex.

[0084] The in vitro cytotoxicity test was conducted as follows:

[0085] Rat cortical neurons (Wuhan Procell Biotechnology Co., Ltd.) preserved in rat cortical neuronal cell culture medium were incubated with 0.25% trypsin containing EDTA (Gibco) for 3-5 minutes in a 37°C, 5% CO2 incubator to digest the cells and detach them from the cell wall. To obtain a highly conductive hydrogel culture medium extract, the mixture was prepared at 3cm... 2 Highly conductive hydrogels were precisely cut at a ratio of / mL and immersed in complete culture medium for rat cortical neurons, then placed in a 37°C, 5% CO2 incubator for at least 24 hours. During the extraction process, the detached rat cortical neurons were completely dispersed in the culture medium and seeded into 96-well plates, then incubated at 37°C, 5% CO2 for 24 hours to allow them to adhere. After obtaining the extract, the complete culture medium for rat cortical neurons in the 96-well plates was replaced with the extract, while the complete culture medium for rat cortical neurons in the control group remained unchanged. After incubation at 37°C, 5% CO2 for 1, 3, and 5 days, the cells were characterized by DAPI fluorescence staining. Figure 8As shown, the rat cortical neurons were in good condition, and no cell reduction was observed on the fifth day compared with the control group, proving that the highly conductive hydrogel prepared in Example 1 has good biocompatibility.

[0086] Example 2

[0087] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Example 1 is that polyacrylamide is used as the hydrogel substrate. The specific preparation process is as follows: 0.1 g of acrylamide is completely dissolved in 5 mL of pure water, and then 600 μL of 0.15 wt% N,N′-methylenebisacrylamide crosslinking agent is added. After stirring at room temperature for 2 h, 400 μL of 0.2 wt% 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone is added, and stirring continues for 2 h, followed by standing at room temperature to remove bubbles. The remaining steps for high-conductivity ink and mask drop-coating are the same as in Example 1. The final experimental results show that using polyacrylamide hydrogel as the substrate material for the mask drop-coating process can prepare a highly conductive hydrogel similar to that in Example 1.

[0088] Example 3

[0089] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Example 1 is that sodium alginate is used as the hydrogel substrate. The specific preparation process is as follows: 0.1 g of sodium alginate is dissolved in 6 mL of pure water and stirred at room temperature for 4 hours until completely dissolved. Then, 600 μL of 0.15 wt% N,N′-methylenebisacrylamide crosslinking agent is added. After stirring at room temperature for 2 hours, 400 μL of 0.2 wt% 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone is added, and stirring continues for 2 hours, followed by standing at room temperature to remove bubbles. The remaining steps for high-conductivity ink and mask coating are the same as in Example 1. Experimental results show that using sodium alginate hydrogel as the substrate material for the mask coating process can produce a highly conductive hydrogel similar to that in Example 1.

[0090] Example 4

[0091] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Example 1 is that hydroxyethyl methacrylate is used as the hydrogel substrate. The specific preparation process is as follows: 3g of hydroxyethyl methacrylate is added and stirred at room temperature for 2 hours to ensure complete dispersion in pure water. Then, 600μL of 0.15wt% N,N′-methylenebisacrylamide crosslinking agent is added. After stirring at room temperature for 2 hours, 400μL of 0.2wt% 2-hydroxy-4-(2-hydroxyethoxy)-2-methylphenylacetone is added, and stirring continues for 2 hours, followed by standing at room temperature to remove bubbles. The remaining steps for high-conductivity ink and mask drop-coating are the same as in Example 1. Experimental results show that using hydroxyethyl methacrylate hydrogel as the substrate material for the mask drop-coating process can prepare a highly conductive hydrogel similar to that in Example 1.

[0092] Example 5

[0093] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Embodiment 1 is that gelatin is used as the hydrogel substrate. The specific preparation process is as follows: 2g of gelatin is soaked in a mixed solvent of 10g of pure water for 12 hours, stirred at 70°C for 2 hours, and then placed in a 90°C oven until all bubbles disappear. The heating switch of the two-roller coater is turned on (heating range 30-90°C), and the two rollers are heated to 90°C until stable. 1mL of the mixed solution is poured hot onto the hydrophobic side of a PET release film, and another layer of PET release film is placed on top. The mixture is then quickly transferred to the laminating machine between the two rollers for pressing and shaping. The sealed hydrogel film is placed in a refrigerator. After the reaction is complete, it is removed to obtain the gelatin hydrogel substrate material. The remaining steps for high-conductivity ink and mask dispensing are the same as in Embodiment 1. Experimental results show that, since gelatin is a thermoplastic hydrogel, the heating temperature of the hot stage recovers a certain degree of fluidity during mask dispensing, thus allowing for better bonding with the high-conductivity ink coating.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing a conductive hydrogel, specifically a polyacrylamide / sodium alginate hydrogel filled with highly conductive ink. The difference between this method and Example 1 is that after the hydrogel stock solution is prepared, highly conductive ink is added at a volume ratio of 1:1. After stirring for 24 hours, the hydrogel substrate is extruded and cured into a film using a two-roller coating machine according to the preparation method of the hydrogel substrate in Example 1.

[0096] The results are as follows Figure 9 As shown, the uneven color distribution of the hydrogel after photocuring indicates that the highly conductive ink cannot be uniformly dispersed in the polyacrylamide / sodium alginate hydrogel during the photocuring process. Furthermore, as... Figure 9As shown in b, when peeling off the PET release film filled with highly conductive ink hydrogel, some areas of the hydrogel could not be photocured, resulting in incomplete peeling. The intact portion of the conductive hydrogel after peeling is shown in Figure b. Figure 9 As shown in Figure c, the electrical properties of the intact hydrogel were tested using a four-probe tester, revealing a conductivity of only 0.01 S / cm. This demonstrates that this filling method cannot yield a hydrogel with a complete conductive pattern, and its conductivity is also far from ideal.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing a conductive hydrogel. The difference between this method and Example 1 is that Ag nanosheets are used to fill the polyacrylamide / sodium alginate hydrogel instead of using a mask to drop-coat the conductive pattern. The specific difference in the preparation process is that after the polyacrylamide / sodium alginate hydrogel is prepared, micron-sized silver flakes accounting for 5% of the hydrogel volume are added to it. After stirring for 2 hours, the hydrogel substrate is extruded and photocured into a film using a two-roller coating machine, following the method for hydrogel substrate in Example 1.

[0099] The electrical properties of this Ag sheet / polyacrylamide / sodium alginate hydrogel were tested using a four-probe tester. The results showed that the conductivity of this Ag sheet / polyacrylamide / sodium alginate hydrogel was only 374 S / cm at most, which is an order of magnitude lower than that of the high conductivity hydrogel prepared in Example 1.

[0100] Comparative Example 3

[0101] This comparative example uses non-release PET material instead of hydrogel material as the substrate material for the mask drop coating process. Before drop coating using the mask, the PET substrate is treated with oxygen plasma for 5 seconds, and the remaining steps are the same as in Example 1. Experimental results show that because the PET substrate does not have the water-rich environment of hydrogel, it cannot undergo ion exchange with the highly conductive ink, and it does not have the three-dimensional network structure of hydrogel. Therefore, it cannot form a tightly bonded and uniform penetration layer. Thus, after the highly conductive ink is formed, it can still be peeled off from the PET substrate, and there is no bonding force between the two.

[0102] Comparative Example 4

[0103] In this comparative example, hydrophilic PI material was used instead of hydrogel material as the substrate material for the mask drop coating process. Before drop coating using the mask, the PI substrate was treated with oxygen plasma for 5 seconds, and the remaining steps were the same as in Example 1. Experimental results showed that although PI has better hydrophilicity than PET substrate, it cannot undergo ion exchange with highly conductive ink because it lacks the water-rich environment of hydrogel. Furthermore, it lacks the three-dimensional network structure of hydrogel, thus failing to form a tightly bonded and uniform permeation layer. Therefore, after the highly conductive ink is formed, it can still be peeled off from the PI substrate, as there is no bonding force between the two.

[0104] Example 6

[0105] This embodiment provides a method for preparing a highly conductive hydrogel, which differs from Embodiment 1 in that the heating stage temperature is set to 70°C.

[0106] Example 7

[0107] This embodiment provides a method for preparing a highly conductive hydrogel, which differs from Embodiment 1 in that the heating stage temperature is set to 90°C.

[0108] Example 8

[0109] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Embodiment 1 is that EG is omitted in the highly conductive ink.

[0110] Example 9

[0111] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Embodiment 1 is that LiTFSI is omitted in the highly conductive ink.

[0112] Example 10

[0113] This embodiment provides a method for preparing a highly conductive hydrogel. The difference from Embodiment 1 is that the amount of LiTFSI added to the highly conductive ink is 45.5 wt% of the solid content of the PEDOT:PSS solution.

[0114] The properties of the highly conductive inks or highly conductive hydrogels prepared in Examples 6-10 are similar to those in Example 1, and will not be repeated here.

[0115] The present application has been described in detail above with reference to the embodiments. However, the present application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present application. Furthermore, unless otherwise specified, the embodiments and features in the embodiments of the present application can be combined with each other.

Claims

1. A method for preparing a highly conductive hydrogel, characterized in that, Includes the following steps: A photomask is attached to the surface of a hydrogel substrate, and glass plates are pressed around it. Then, a highly conductive ink is evenly spread on the exposed hydrogel area at the cutout of the photomask by drop coating. The highly conductive ink includes PEDOT:PSS and is configured to have a conductivity of 3500-8000 S / m when forming a conductive pattern on its own. Heating the mask and the hydrogel substrate heat-treats the highly conductive ink, promoting the penetration of conductive substances in the highly conductive ink into the hydrogel substrate, forming a conductive permeation layer without obvious boundaries, so that the highly conductive ink pattern layer and the hydrogel substrate are bonded together through the conductive permeation layer to obtain a highly conductive hydrogel. The heat treatment temperature is 40-90℃. Then, after setting the hot stage temperature to 50°C and observing that the highly conductive ink on the surface has completely formed a film, heating was stopped.

2. The preparation method according to claim 1, wherein, The highly conductive ink also includes at least one of ethylene glycol and lithium bis(trifluoromethanesulfonyl)imide.

3. The preparation method according to claim 1, wherein, The hydrogel substrate material is selected from at least one of polyvinyl alcohol, polyacrylic acid, polyacrylate, polyacrylamide, polyurethane, polyhydroxyethyl methacrylate, polyethylene oxide, poly(N-isopropylacrylamide), polyethylene glycol diacrylate, polyethylene glycol methacrylate, gelatin, alginate, hyaluronic acid, agarose, chitosan, and collagen.

4. The preparation method according to claim 1, wherein, At least one side of the hydrogel substrate has a release film, and a pattern of highly conductive ink is formed on the other side of the hydrogel substrate opposite to the release film using a mask.

5. The preparation method according to claim 1, wherein, The mask is at least one of polyethylene terephthalate, polyimide, and polydimethylsiloxane.

6. A highly conductive hydrogel prepared according to any one of claims 1 to 5.

7. A medical device, characterized in that, Including the highly conductive hydrogel as described in claim 6.

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