High-conductivity conductive hydrogel and preparation method thereof

Abstract

The invention discloses a high-conductivity conductive hydrogel which is prepared by the following steps: blending a conductive polymer dispersion liquid, a dopant and a second component, drying to remove the dopant, and rehydrating. The obtained hydrogel is high in conductivity, good in mechanical property, excellent in flexibility and free of organic small molecule residues. The conductive hydrogel can be used for rapid transmission and collection of electric signals, and can be used as a spinal cord electrical stimulation electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive materials, and in particular to a conductive hydrogel with high electrical conductivity and a preparation method thereof. Background Art

[0002] Spinal cord stimulation (SCS) is a method of pain relief that utilizes neural regulation. Stimulating electrodes are implanted in the epidural space of the corresponding spinal cord segment, stimulating the spinal cord with electrical pulses, blocking pain signal transmission and thus eliminating pain. Traditional SCS systems primarily consist of an electrical pulse generator, stimulating electrodes, and extension leads. The stimulating electrodes are often made of metal materials, such as platinum-iridium alloys. While the high electrical conductivity of metal electrodes meets the electrical conductivity requirements for electrical stimulation, the modulus of the metal material is mismatched with tissue, causing abnormal sensations in patients. Furthermore, the expensive precious metals used for electrodes, and the high cost of electrode equipment, lead to high surgical costs, making them unaffordable for the general public. Furthermore, the mismatch between the mechanical properties of traditional rigid electrode materials and soft tissue is a key factor in the development of chronic inflammation and fibrous capsule thickening. Therefore, the interface mismatch between implantable materials and living systems has become a major issue in current bioelectronic devices. Furthermore, while lower electrical conductivity can meet the requirements of applications such as sensors, higher conductivity for bioelectrodes facilitates the complete transmission and recording of pulses, reducing the risk of distortion and other issues.

[0003] Hydrogel is a hydrophilic gel with a three-dimensional network structure. Conductive hydrogel, as a type of hydrogel, not only has electrical conductivity, but also its mechanical properties can be adjusted by means of crosslinking density or adding different components, so that it can be modulo-matched with different biological tissues, which provides a good solution to the interface mismatch problem. However, the electrical conductivity of ion-conductive hydrogel is low (below 10S / m), and its electrical conductivity is usually strongly dependent on ion concentration, and excessive ion concentration may cause tissue damage risk. Electronic conductive hydrogels include metal-based conductive hydrogels, carbon-based conductive hydrogels and conductive polymer-based conductive hydrogels. Among them, metal-based conductive hydrogels and carbon-based conductive hydrogels are obtained by adding metal nanomaterials or carbon-based nanomaterials as conductive media to the organic polymer hydrogel skeleton. However, these nanomaterials are difficult to disperse in the hydrogel and are prone to aggregation and sedimentation in the hydrogel, resulting in unstable structure and conductive properties of the hydrogel. In addition, hydrogels generated by in-situ polymerization of monomers often have the problem of incomplete reaction, resulting in residual toxic small molecules in the hydrogel.

[0004] In response to the problems of current conductive hydrogels, such as low conductivity, poor mechanical properties, and residual organic small molecules in in-situ polymerized hydrogels, the present invention provides a high-conductivity conductive hydrogel and a preparation method thereof. Summary of the Invention

[0005] To solve the above problems, the inventors have discovered that by using a conductive polymer aqueous dispersion obtained from poly(3,4-ethylenedioxythiophene) with excellent conductivity and poly(styrene) sulfonate with sulfonic acid groups to enhance its conductivity and dispersibility, and compounding it with a dopant that can further improve the conductivity and a second component that improves the mechanical properties, and after mixing and drying, a high-conductivity polymer hydrogel is obtained, which has ideal high conductivity, high strength and flexibility, thereby completing the present invention.

[0006] The present invention aims to provide a high-conductivity conductive hydrogel, which is prepared by mixing a conductive polymer aqueous dispersion obtained from poly(3,4-ethylenedioxythiophene) with excellent conductivity and a poly(styrene)sulfonate with sulfonic acid groups to enhance its conductivity and dispersibility, with a dopant that can further improve the conductivity and a second component that improves the mechanical properties.

[0007] In a preferred embodiment, as a conductive polymer aqueous dispersion having excellent conductivity, it is preferred to use any one or more selected from poly(3,4-ethylenedioxythiophene):sodium polyethylene sulfonate (PEDOT:PVSNa), poly(3,4-ethylenedioxythiophene):potassium polyethylene sulfonate (PEDOT:PVSK), and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS).

[0008] Typical conductive polymers, such as polypyrrole, polyaniline, polythiophene, and polyacetylene, are difficult to prepare directly into hydrogels due to their rigid backbones and poor hydrophilicity. The inventors have discovered that aqueous dispersions of poly(styrene) sulfonate-dispersed poly(3,4-ethylenedioxythiophene) offer a promising approach for preparing conductive hydrogels.

[0009] In the present invention, as a conductive polymer aqueous dispersion, it provides extremely excellent conductivity for the hydrogel to be prepared, and as an aqueous dispersion, it does not contain toxic organic small molecules, ensuring the high quality of the obtained hydrogel.

[0010] In a further preferred embodiment, the mass percentage of the conductive polymer in the conductive polymer aqueous dispersion is 1%-5%, and more preferably, the mass percentage of the conductive polymer in the conductive polymer aqueous dispersion is 1%-1.3%.

[0011] In a preferred embodiment, as the dopant, one or more selected from dimethyl sulfoxide, polyethylene glycol, tetrahydrofuran, glycerol, sulfuric acid and hydrochloric acid are preferably used, and dimethyl sulfoxide is more preferably used.

[0012] The inventors have discovered that the use of dopants can further enhance the conductivity of the resulting hydrogel and, to a certain extent, improve its mechanical properties. Specifically, the conductivity of the resulting hydrogel, obtained by drying and rehydrating an aqueous dispersion of poly(3,4-ethylenedioxythiophene) dispersed in poly(styrene) sulfonate doped with dimethyl sulfoxide (DMSO), can reach over 1000 S / m.

[0013] In the present invention, there is no particular limitation on the amount of the conductive polymer aqueous dispersion and the dopant, but the volume ratio of the conductive polymer aqueous dispersion to the dopant is preferably (8-10):(0-2), more preferably (9.3-9.7):(0.3-0.7).

[0014] In the present invention, as the second component, it further improves the mechanical properties of the hydrogel and gives it good flexibility. It can also be used as a low molecular weight component to adjust the modulus of the hydrogel by dosage, thereby solving the interface mismatch problem.

[0015] In a preferred embodiment of the present invention, as the second component, one or more selected from polyvinyl alcohol (PVA), polyacryloyl glycinamide (PNAGA), polyethylene glycol (PEG), etc. are preferably used, and polyvinyl alcohol is more preferably used.

[0016] Polyvinyl alcohol, as a polymer with good biocompatibility and high chemical stability, contains abundant hydroxyl groups and has abundant hydrogen bonding interactions, which can improve the mechanical properties of hydrogels. In addition, the hydroxyl groups on polyvinyl alcohol can also form hydrogen bonds with the benzenesulfonic acid groups of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid, which is conducive to the phase separation between poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, and helps to improve the conductivity of the hydrogel.

[0017] In a further preferred embodiment, the number average molecular weight of the polyvinyl alcohol is 8,000-130,000 g / mol, more preferably 60,000-110,000 g / mol, and even more preferably 70,000-80,000 g / mol. Studies have found that if the molecular weight of PVA is too low, the mechanical properties of the hydrogel deteriorate; if the molecular weight of PVA is too high, the polymer becomes difficult to dissolve, the degree of cross-linking in the hydrogel increases, and the conductivity decreases.

[0018] Preferably, the alcoholysis degree of the polyvinyl alcohol is 98%-100%, more preferably 99%. A higher alcoholysis degree ensures abundant hydroxyl groups, which is conducive to the formation of intermolecular crosslinks and hydrogen bonds.

[0019] Preferably, the concentration of the polyethanol solution is 5-20 wt %, preferably 8-15 wt %, more preferably 9-11 wt %.

[0020] In the present invention, since different polyethylene glycols can be used to adjust the modulus of the resulting hydrogel to match the modulus requirements of different application scenarios, those skilled in the art can determine the amount of polyethylene glycol used according to actual needs, and no special limitation is made here.

[0021] In another preferred embodiment of the high-conductivity conductive hydrogel provided by the present invention, it is prepared from an aqueous dispersion of a conductive polymer obtained from poly(3,4-ethylenedioxythiophene) having excellent conductivity and a poly(styrene) sulfonate having sulfonic acid groups to enhance its conductivity and dispersibility, combined with a dopant that can further improve conductivity, a second component that improves mechanical properties, and a cross-linking agent that further improves mechanical properties.

[0022] Specifically, a conductive polymer aqueous dispersion obtained from poly(3,4-ethylenedioxythiophene) with excellent conductivity and poly(styrene)sulfonate with sulfonic acid groups to enhance its conductivity and dispersibility is immersed in a crosslinker solution with a hydrogel made of a dopant and a second component to further enhance its mechanical properties.

[0023] Another object of the present invention is to provide a method for preparing the above-mentioned high-conductivity conductive hydrogel, which comprises uniformly mixing a conductive polymer aqueous dispersion, a dopant, and a second component, drying to remove the dopant, and then hydrating to obtain a high-conductivity conductive hydrogel.

[0024] The method for preparing the high-conductivity conductive hydrogel provided by the present invention preferably comprises the following steps:

[0025] (1) preparing a conductive polymer composite aqueous dispersion: mixing the conductive polymer aqueous dispersion and a dopant, and then mixing with a second component to obtain a conductive polymer composite aqueous dispersion;

[0026] (2) preparing a conductive film: coating the obtained conductive polymer composite aqueous dispersion on a substrate, drying, and volatilizing the dopant to obtain a conductive film;

[0027] (3) Preparation of conductive hydrogel: The conductive film was swelled in deionized water and subjected to multiple freeze-thaw cycles to prepare the conductive hydrogel;

[0028] and optionally (4) preparing a strong and tough conductive hydrogel: soaking the obtained conductive hydrogel in a room temperature crosslinking agent solution for further crosslinking to prepare a strong and tough conductive hydrogel with higher mechanical properties.

[0029] The preparation method provided by the present invention has a simple preparation process, and the obtained conductive hydrogel has desired high electrical conductivity and mechanical properties.

[0030] In the present invention, borax is preferably used as the cross-linking agent, more preferably one or more selected from sodium tetraborate, borax pentahydrate, anhydrous borax, and sodium tetraborate decahydrate, and most preferably anhydrous borax.

[0031] In step (1), regarding the method of adding the second component, if polyvinyl alcohol is used, the polyvinyl alcohol can be prepared into a polyvinyl alcohol solution for use, or the polyvinyl alcohol can be added to the polymer composite aqueous dispersion and completely dissolved evenly under high temperature stirring conditions; if acrylyl glycinamide is used, it needs to be prepared into polyacryloyl glycinamide for use, so that the polyacryloyl glycinamide is fully dissolved in the conductive polymer composite aqueous dispersion.

[0032] In step (2), as a coating method, methods such as drop coating, coating, inkjet printing, etc. can be used to coat and dry on a substrate such as polytetrafluoroethylene, polypropylene or polyethylene terephthalate to obtain a conductive film.

[0033] Preferably, in step (2), the drying is to dry the polymer solution at room temperature, and the drying temperature is 0-35°C, preferably 15-30°C, and more preferably 22.5-27.5°C.

[0034] Preferably, in step (2), the drying time is 24h-144h, preferably 72h-144h.

[0035] Preferably, in step (2), the substrate comprises any one of glass, polyethylene terephthalate, polypropylene, polytetrafluoroethylene, and polydimethylsiloxane.

[0036] In step (3), the conductive film is swollen in deionized water to form a conductive hydrogel, and the swollen conductive hydrogel is subjected to multiple freeze-thaw cycles, such as freezing at -18°C for 24 hours and thawing at room temperature for 3 hours, to promote further physical cross-linking, thereby improving the mechanical properties of the hydrogel.

[0037] Step (4) is an optional step, i.e., the conductive hydrogel can be immersed in a borax solution. In step (4), borate ester bonds are formed between the borax and the second component, further enhancing the mechanical properties of the hydrogel.

[0038] Preferably, the concentration of borax is 1.5-10 wt %, preferably 3-6 wt %, of the amount of polyvinyl alcohol added.

[0039] Borax and polyvinyl alcohol can form dynamic borate ester bonds, and borax is relatively low in toxicity. Introducing a small amount of borax can further enhance the mechanical properties of the hydrogel. Furthermore, because the conductive hydrogel is prepared via a drying-rehydration method, the conductive pathways within the hydrogel are already interconnected. Therefore, the conductivity reduction achieved by borax soaking is higher than that achieved by directly mixing boric acid with the raw materials.

[0040] It's important to note that borax crosslinking is optional. High-conductivity flexible conductive hydrogels have already been prepared and are suitable for use. Borax crosslinking further enhances mechanical properties due to the resulting crosslinking, but conductivity decreases. Whether or not to perform borax crosslinking is determined based on performance requirements.

[0041] The mechanism of the present invention is hypothesized as follows: the dopant can induce phase separation between the conductive phase and the auxiliary dispersed phase in the conductive polymer, forming highly conductive polymer-rich domains and mechanically enriched domains that facilitate bonding. The polyacryloyl glycinamide or polyvinyl alcohol present in the polymer composite aqueous dispersion can form hydrogen bonds with the mechanically enriched domains. These hydrogen bonding interactions further promote phase separation, constructing a stable, high-strength hydrogel network structure and achieving excellent flexibility and mechanical strength. However, the above mechanism is merely speculative and the present invention is not limited thereto.

[0042] The present invention has the following beneficial effects:

[0043] (1) High conductivity of hydrogel: By introducing dopants, the conductive phase and auxiliary dispersed phase in the conductive polymer are induced to separate during the drying process, forming a conductive polymer-rich domain with high conductivity, thereby improving the conductivity of the hydrogel;

[0044] (2) High hydrogel strength: The strength of the hydrogel can be improved by introducing a second component polymer network and even optionally introducing dynamic borate bonds;

[0045] (3) Modulus matching: by introducing low molecular weight polyethylene glycol, the modulus of the hydrogel can be controlled within a certain range;

[0046] (4) The preparation process is simple and environmentally friendly: it is prepared by blending, drying and rehydrating the polymer aqueous dispersion, without the need for complex chemical processes and without the problem of organic small molecule residues.

[0047] The high-conductivity conductive hydrogel prepared by the present invention first uses a dopant to separate the conductive phase and the mechanical phase, thereby increasing the conductivity while preliminarily improving the mechanical properties; then, a second component is mixed in to further improve the mechanical properties, and the material is given good flexibility. The modulus can also be adjusted by a low-molecular-weight component; during the drying process, the dopant can be removed by volatilization to avoid its residual toxicity.

[0048] The conductive polymer hydrogel prepared by this invention achieves a high electrical conductivity of 3884 S / m, excellent flexibility that allows it to be folded arbitrarily without damage, and a modulus of 30 kPa. This allows for the rapid and accurate transmission and collection of electrical signals, and its excellent toughness allows it to withstand long-term use without damage. Furthermore, the materials used exhibit excellent biocompatibility. Experiments with spinal cord electrical stimulation in rats have demonstrated its excellent ability to conduct and record electrical pulses. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 SEM images of cross sections of the conductive hydrogels of Examples 1-4 of the present invention. (a) PVA 10, (b) PVA 15, (c) PVA 20, and (d) PVA 10 soaked in boric acid.

[0050] Figure 2 SEM images of cross sections of the conductive hydrogels of Examples 5-8 of the present invention (a) for PEG-1, (b) for PEG-4, (c) for PEG-7, and (d) for PEG-10;

[0051] Figure 3 Graphs showing the elastic modulus and loss modulus of the conductive hydrogels of Examples 5-8 of the present invention;

[0052] Figure 4 Graphs showing the elastic modulus and loss modulus of the conductive hydrogels of Examples 1-3 of the present invention;

[0053] Figure 5 This is a test graph of the elastic modulus and loss modulus of the conductive hydrogel according to Example 4 of the present invention;

[0054] Figure 6 1 is a comparison chart of the electrical conductivities of the conductive hydrogels of Examples 1-8 of the present invention;

[0055] Figure 7 Graphs showing the temporal variation of electrical signals collected from a rat spinal cord electrical stimulation experiment using the conductive hydrogel electrodes of Examples 2, 4, and 6 of the present invention and the electrodes of the control group, (a) PEDOT:PSS / PVA@platinum-iridium alloy electrode (ECAPT=70μA), (b) PEDOT:PSS / PVA / Borax@platinum-iridium alloy electrode (ECAPT=100μA), (c) PEDOT:PSS / PNAGA / PEG@platinum-iridium alloy electrode (ECAPT=200μA), and (d) platinum-iridium alloy electrode (ECAPT=70μA). DETAILED DESCRIPTION

[0056] The present invention will be further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become more clear and distinct. Wherein, although various aspects of the embodiments are shown in the accompanying drawings, unless otherwise specified, the drawings are not necessarily drawn to scale.

[0057] Unless otherwise specified, the components used in the present invention are all commercially available products. The experimental test conditions are not otherwise specified and are all conventional technical operations in the art. TM .

[0058] Example

[0059] Example 1

[0060] (1) Preparation of polymer composite aqueous dispersion:

[0061] Using a pipette, 9.5 mL of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (Heraeus Clevios TM , the conductive polymer mass content is 1-1.3%), 0.5 mL of dopant dimethyl sulfoxide, stirred at 1500 rpm for 24 hours to mix uniformly, and obtained a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide.

[0062] 5 g of polyvinyl alcohol was dissolved in 45 g of deionized water to prepare a 10 wt % polyvinyl alcohol solution.

[0063] 250 μL of a 10 wt% polyvinyl alcohol solution (average molecular weight of polyvinyl alcohol: 80,000 g / mol), 250 μL of deionized water, and 2000 μL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid and dimethyl sulfoxide were mixed and stirred at 1500 rpm for 24 h to obtain a conductive polymer composite aqueous dispersion.

[0064] (2) Preparation of conductive film:

[0065] The prepared polymer composite aqueous dispersion droplets were coated on a polytetrafluoroethylene mold and dried at room temperature for 144 hours to fully volatilize the dimethyl sulfoxide to obtain a conductive polymer film.

[0066] (3) Preparation of conductive hydrogel:

[0067] The conductive film was swollen in deionized water to form a conductive hydrogel, and the swollen conductive hydrogel was then subjected to three freeze-thaw cycles (freezing at -18°C for 24 hours and thawing at room temperature for 3 hours) to promote further physical cross-linking of PVA to obtain a conductive hydrogel.

[0068] The microstructure of hydrogel is a composite structure of macropores and micropores, such as Figure 1 As shown in (a).

[0069] (4) Hydrogel swelling test:

[0070] The mass of the dry film of the hydrogel was weighed using an electronic analytical balance, and then it was immersed in deionized water. The film was taken out at intervals and the surface was gently wiped with filter paper to fully absorb the surface moisture. The mass of the hydrogel was weighed again using an electronic analytical balance until the mass of the hydrogel did not change after multiple tests. The swelling degree SR of the hydrogel was calculated according to the following formula:

[0071]

[0072] SR—hydrogel swelling ratio, %;

[0073] M1—mass of hydrogel after dry film absorbs water, mg;

[0074] M2—dry film mass, mg.

[0075] Three samples were weighed in each experiment, and the average value was taken to measure the swelling ratio SR, which was about 720%.

[0076] (5) Hydrogel mechanical properties test:

[0077] Rheological tests were performed using a flat plate rheometer to characterize the mechanical properties: the hydrogel sample was made into a cylindrical specimen with a diameter of about 20 mm and a thickness of 1-2 mm. The test temperature was room temperature, the test conditions were a fixed strain of 1%, and the frequency sweep range was 1-100 rad / s. The measured elastic modulus was 30 kPa.

[0078] (6) Hydrogel conductivity test:

[0079] Conductivity was tested using a digital four-probe conductivity meter: the hydrogel was removed from the mold and cut into 8 x 8 mm blocks. The thickness was measured using a flat-head thickness gauge. The measurement parameters of the multifunctional digital four-probe conductivity meter were modified according to the size of the hydrogel. The four probes of the digital four-probe conductivity meter were gently touched to the surface of the hydrogel. Once the reading stabilized, the test results were recorded. The data read by the four-probe tester is the resistivity ρ, and the conductivity σ data can be obtained according to the following formula:

[0080]

[0081] σ——conductivity, S×m -1 ;

[0082] ρ——resistivity, mΩ×cm.

[0083] Each sample was measured three times and the average value was taken. The measured conductivity was 6480 S / m.

[0084] (7) Spinal cord electrical stimulation application test:

[0085] The prepared conductive polymer composite aqueous dispersion was transferred to the platinum-iridium alloy electrode sheet (1.5uL for a single electrode) of the rat spinal cord electrical stimulation electrode lead fixed on the surface of a 50°C metal heating platform using a pipette, so that the aqueous dispersion evenly covered the platinum-iridium alloy electrode sheet, and the composite aqueous dispersion dried to form a conductive film. Repeat the previous operation until the eight electrode contacts of the electrode lead were covered with a conductive film. The electrode lead was soaked in deionized water to obtain a PEDOT:PSS / PVA hydrogel electrode lead. Subsequently, a small animal anesthesia machine (Shenzhen Ruiwode) was used to anesthetize the rat with isoflurane (2.5% oxygen) in the anesthesia chamber (oxygen flow rate of 2L / min), and anesthesia was maintained using a nose cone (isoflurane of 2.0%) (oxygen flow rate of 1.5L / min). The hair on the back was then shaved, and the area was approximately 3×5cm. 2 , disinfected alternately with iodine and alcohol three times. Then, the skin and fascia were cut longitudinally along the midline, and the parapyramidal muscles were bluntly separated using tools to expose the vertebral lamina. The vertebral lamina of the target segment was removed with bone rongeurs to expose the dorsal surface of the spinal cord. During this period, normal saline was used to continuously flush the surgical field to keep the tissue moist. Finally, the test electrode was inserted into the epidural space of the rat's spinal cord, and the rat was stimulated with different currents using a physiological recorder and stimulator. The ECAP signal of the rat was collected, and the muscle tremor of the rat was observed. In this paper, the stimulation frequency was set to 0.5 Hz and the stimulation pulse width was set to 200 μs.

[0086] Example 1 can observe clear ECAP potential, such as Figure 7 As shown in (b), at the minimum current threshold (ECAPT) of 70 μA at which the ECAP potential is observed, the ECAP is approximately 0.086 mV. In contrast, at the minimum current threshold (ECAPT) of 70 μA at which the ECAP potential is observed, the ECAP of the Pt-Ir alloy electrode is approximately 0.114 mV.

[0087] Example 2

[0088] A hydrogel was prepared according to the method of Example 1, except that 375 μL of polyvinyl alcohol solution, 125 μL of deionized water, and 2000 μL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid and dimethyl sulfoxide were mixed together.

[0089] The conductivity of the hydrogel obtained in Example 2 was 4288 S / m, the elastic modulus was 32 kPa, and the microscopic morphology was compared with that in Example 1, and the pore size was significantly smaller.

[0090] Example 3

[0091] A hydrogel was prepared according to the method of Example 1, except that 500 μL of polyvinyl alcohol solution and 2000 μL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid and dimethyl sulfoxide were mixed together.

[0092] The conductivity of the hydrogel obtained in Example 3 is 3698 S / m, the elastic modulus is 40 kPa, and the microscopic morphology is further reduced in pore size compared with Example 2. Figure 1 (c) shown.

[0093] Example 4

[0094] A hydrogel was prepared according to the method in Example 1, except that 250 uL of polyvinyl alcohol solution, 250 uL of deionized water, and 2000 uL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide were mixed together, freeze-thawed to prepare a conductive hydrogel, and then soaked in 5 wt% boric acid (Borax) at room temperature.

[0095] The resulting hydrogel in Example 4 exhibited a conductivity of 2419 S / m and an elastic modulus of 150 kPa. Compared to Example 2, which contained the same PVA content, the microstructure showed a significantly smaller pore size due to the further crosslinking of borate bonds. A clear ECAP potential was observed, approximately 0.032 mV at a minimum current threshold (ECAPT) of 100 μA, where the ECAP potential is observed. In comparison, the ECAP potential of the platinum-iridium alloy electrode was approximately 0.114 mV at a minimum current threshold (ECAPT) of 70 μA, where the ECAP potential is observed.

[0096] Example 5

[0097] (1) Preparation of conductive polymer composite aqueous dispersion:

[0098] Using a pipette, 9.5 mL of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid) and 0.5 mL of dopant dimethyl sulfoxide were weighed and stirred at 1500 rpm for 24 h to mix them evenly.

[0099] Take 20mg of polyacryloyl glycinamide powder, mix it with 25uL polyethylene glycol-400, 475uL deionized water and 2000uL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide, and stir it at 1500rpm for 24h to mix it evenly to obtain a conductive polymer composite aqueous dispersion.

[0100] (2) Preparation of conductive film:

[0101] The prepared polymer composite aqueous dispersion droplets were coated on a polytetrafluoroethylene mold and dried at room temperature for 144 hours to fully volatilize the dimethyl sulfoxide to obtain a conductive polymer film.

[0102] (3) Preparation of conductive hydrogel:

[0103] The conductive hydrogel was prepared by swelling the conductive polymer film in deionized water for 3 h.

[0104] The conductivity of Example 5 is 3950 S / m, the elastic modulus is 177 kPa, and the microstructure is a three-dimensional porous network structure. Figure 2 As shown in (a).

[0105] Example 6

[0106] A hydrogel was prepared according to the method of Example 5, except that 20 mg of polyacryloyl glycinamide powder was mixed with 100 μL of polyethylene glycol-400, 400 μL of deionized water, and 2000 μL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide.

[0107] The conductivity of the hydrogel obtained in Example 6 is 2804 S / m, the elastic modulus is 100 kPa, and the micromorphology is more inclined to generate a discontinuous macroporous structure compared with Example 5 due to the increase in the PEG-400 content, such as Figure 2 (b) A clear ECAP potential is observed, approximately 0.046 mV at the minimum current threshold (ECAPT) of 200 μA. In contrast, the ECAP potential of the Pt-Ir alloy electrode is approximately 0.114 mV at the minimum current threshold (ECAPT) of 70 μA.

[0108] Example 7

[0109] A hydrogel was prepared according to the method of Example 5, except that 20 mg of polyacryloyl glycinamide powder was mixed with 175 uL of polyethylene glycol-400, 325 uL of deionized water, and 2000 uL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide.

[0110] The conductivity of the hydrogel obtained in Example 7 is 1737 S / m, the elastic modulus is 49 kPa, and the microstructure is a discontinuous macroporous structure, such as Figure 2 (c) shown.

[0111] Example 8

[0112] A high conductivity conductive polymer hydrogel was prepared according to the method of Example 5, except that 20 mg of polyacryloyl glycinamide powder was mixed with 250 uL of polyethylene glycol-400, 250 uL of deionized water, and 2000 uL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid and dimethyl sulfoxide.

[0113] The conductivity of the hydrogel obtained in Example 8 is 1386 S / m, the elastic modulus is 37 kPa, and the microstructure is a discontinuous macroporous structure, such as Figure 2 (d) shown.

[0114] Comparative Example 1

[0115] (1) Preparation of conductive polymer composite aqueous dispersion:

[0116] Using a pipette, 9.5 mL of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid) and 0.5 mL of dopant dimethyl sulfoxide were weighed and stirred at 1500 rpm for 24 h to mix them evenly.

[0117] 500 μL of deionized water was mixed with 2000 μL of a mixed solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid and dimethyl sulfoxide, and stirred at 1500 rpm for 24 h to mix uniformly to obtain a conductive polymer composite aqueous dispersion.

[0118] (2) Preparation of conductive film:

[0119] The polymer composite aqueous dispersion prepared in step (1) was dropwise coated on a polytetrafluoroethylene mold and dried at room temperature for 144 hours to obtain a conductive polymer film.

[0120] (3) Preparation of conductive hydrogel:

[0121] The conductive hydrogel was prepared by swelling the conductive polymer film in deionized water for 3 h.

[0122] Experimental Example 1

[0123] The cross section of the conductive hydrogel obtained in Example 1-8 was subjected to scanning electron microscopy test, and the scanning electron microscopy images thereof are shown in FIG. Figure 1 、 Figure 2 shown.

[0124] from Figure 1 It can be seen that with the increase of PVA content, the network structure of the hydrogel becomes denser. Moreover, after the addition of boric acid, due to further cross-linking, the network structure of the hydrogel is even denser than before the addition of boric acid.

[0125] Experimental Example 2

[0126] The elastic modulus (Gˋ) and loss modulus (Gˋˋ) of the conductive hydrogels of Examples 1-8 were tested. The test results are as follows: Figure 3 、 Figure 4 、 Figure 5 shown.

[0127] Experimental Example 3

[0128] The hydrogel was removed from the mold and cut into 8ˊ8mm hydrogel blocks. The thickness was measured with a flat-head thickness gauge. The measurement parameters of the multifunctional digital four-probe tester were modified according to the size of the hydrogel. The four probes were lightly touched on the surface of the hydrogel. After the readings stabilized, the test results were recorded. The data read by the four-probe tester is the resistivity ρ. The conductivity σ data can be obtained according to the following formula. The test results are as follows: Figure 6 As shown:

[0129]

[0130] σ——conductivity, S×m -1 ρ is the resistivity, mΩ×cm. Each sample was measured three times and the average value was taken.

[0131] Experimental Example 4

[0132] The hydrogel was dried and formed onto electrodes used for spinal cord electrical stimulation testing in rats, creating a hydrogel@platinum-iridium alloy electrode. It's worth noting that because the hydrogel completely covered the platinum-iridium alloy electrode, the platinum-iridium alloy in the hydrogel@platinum-iridium alloy electrode no longer functioned as an electrode.

[0133] In the experiment, hydrogel electrodes were inserted into the spinal cord of rats. By adjusting the current of pulse stimulation, the evoked compound action potential (ECAP) of the rats was recorded and the muscle tremors of the rats were observed.

[0134] The ECAP potential diagrams of hydrogel@PtI alloy electrode and PtI alloy electrode are shown in Figure 2. Figure 7 shown.

[0135] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples and the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, and all of these fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A high-conductivity conductive hydrogel, which is prepared by mixing a conductive polymer aqueous dispersion obtained from poly(3,4-ethylenedioxythiophene) with excellent conductivity and poly(styrene)sulfonate with sulfonic acid groups to enhance its conductivity and dispersibility, with a dopant that can further improve conductivity and a second component that improves mechanical properties.

2. The high-conductivity conductive hydrogel according to claim 1, wherein: The conductive polymer aqueous dispersion with excellent conductivity uses any one or more selected from poly(3,4-ethylenedioxythiophene):sodium polyethylene sulfonate (PEDOT:PVSNa), poly(3,4-ethylenedioxythiophene):potassium polyethylene sulfonate (PEDOT:PVSK), and poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid (PEDOT:PSS).

3. The high conductivity conductive hydrogel according to claim 1, wherein: The conductive polymer content in the conductive polymer aqueous dispersion is 1%-5% by mass.

4. The high-conductivity conductive hydrogel according to claim 1, wherein: As the dopant, any one or more selected from dimethyl sulfoxide, polyethylene glycol, tetrahydrofuran, glycerol, sulfuric acid, and hydrochloric acid are used.

5. The high-conductivity conductive hydrogel according to claim 1, wherein: The volume ratio of the conductive polymer aqueous dispersion to the dopant is (8-10):(0-2).

6. The high-conductivity conductive hydrogel according to claim 1, wherein: As the second component, one or more selected from polyvinyl alcohol (PVA), polyacryloyl glycinamide (PNAGA), polyethylene glycol (PEG), and the like are preferably used.

7. The high-conductivity conductive hydrogel according to claim 1 is prepared from an aqueous dispersion of a conductive polymer obtained from poly(3,4-ethylenedioxythiophene) having excellent conductivity and a poly(styrene)sulfonate having sulfonic acid groups to enhance its conductivity and dispersibility, combined with a dopant that further improves conductivity, a second component that improves mechanical properties, and a cross-linking agent that further improves mechanical properties, wherein the cross-linking agent is borax selected from one or more of sodium tetraborate, borax pentahydrate, anhydrous borax, and sodium tetraborate decahydrate.

8. A method for preparing a high-conductivity conductive hydrogel, comprising uniformly mixing a conductive polymer aqueous dispersion, a dopant, and a second component, drying to remove the dopant, and then hydrating to obtain a high-conductivity conductive hydrogel.

9. The preparation method according to claim 8, comprising the steps of: (1) preparing a conductive polymer composite aqueous dispersion: mixing the conductive polymer aqueous dispersion and a dopant, and then mixing with a second component to obtain a conductive polymer composite aqueous dispersion; (2) preparing a conductive film: coating the obtained conductive polymer composite aqueous dispersion on a substrate, drying, and volatilizing the dopant to obtain a conductive film; (3) Preparation of conductive hydrogel: The conductive film was swelled in deionized water and subjected to multiple freeze-thaw cycles to prepare the conductive hydrogel; and optionally (4) preparing a strong and tough conductive hydrogel: soaking the obtained conductive hydrogel in a crosslinking agent solution for further crosslinking to obtain a strong and tough conductive hydrogel with higher mechanical properties.

10. The preparation method according to claim 8, wherein In step (2), drying is carried out at room temperature, high temperature or vacuum oven, wherein the drying time at room temperature is 24-144 hours, the drying time at high temperature is 6-36 hours at 50-100°C, and the drying time in a vacuum oven is 1-3 hours at 50-100°C; In step (3), one freeze-thaw cycle is freezing at -18°C for 24 hours and thawing at room temperature for 3 hours.

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