Hierarchical anisotropic self-repairing conductive hydrogel electrode material, preparation method and application

Abstract

The invention discloses a hierarchical anisotropic self-repairing conductive hydrogel electrode material, a preparation method and application, and belongs to the technical field of electrode materials. The hydrogel takes a polyacrylamide-polyacrylic acid-polyaniline copolymerization network formed by polymerization as a core skeleton, contains a covalent-dynamic non-covalent double cross-linked network, is doped with carbon nanotubes, constructs a synergistic conductive system by combining polyaniline in the copolymerization network, and is prepared by directional freeze casting, low-temperature polymerization and KCl ion strengthening treatment. The hierarchical anisotropic microstructure is composed of micron channels parallel to the freezing direction and interconnected nano porous structures uniformly distributed in the walls of the channels and in a polymer network. By means of the structural design and the synergistic conductive system, collaborative optimization and improvement of mechanical, conductive, adhesion, biocompatibility and self-repairing multi-dimensional performance are achieved through the synergistic effect of ion strengthening, the process is simple and repeatable, the application requirements in the fields of flexible wearable bioelectric electrodes and the like are perfectly met, and the application prospect is wide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a hierarchical anisotropic self-repairing conductive hydrogel electrode material, a preparation method and application. BACKGROUND

[0002] Brain-computer interface (BCI) technology breaks the physiological limitations of neural signal transmission by building a direct communication bridge between the nervous system and external devices, and shows application potential in many frontier fields such as neural rehabilitation, auxiliary medical treatment and human-computer interaction, and has become a research hotspot in recent years. As the core key component for signal acquisition and transmission in the brain-computer interface system, the mechanical properties, electrical properties, biocompatibility and long-term stability of the electrode directly determine the quality of the acquired electroencephalogram signal and the reliability of the system operation, and are the key to the application of BCI technology from the laboratory to the clinical practice.

[0003] At present, the traditional rigid electrode widely used in the field of brain-computer interface has a huge difference in mechanical modulus with the human brain tissue and skin soft tissue, and has poor biocompatibility, is prone to inflammatory reaction in long-term wearing, and has insufficient signal acquisition stability, which is difficult to meet the actual needs of high-precision and long-term wearable brain-computer interface, and seriously limits the expansion of application scenarios and performance improvement of BCI technology.

[0004] In order to solve the inherent defects of the traditional rigid electrode, the flexible hydrogel electrode has become an ideal candidate material for the next generation of brain-computer interface electrode due to its high mechanical performance matching with human tissue, excellent biocompatibility, good flexible fitting and controllable physicochemical properties, and has attracted extensive attention and research. However, the existing flexible hydrogel electrode material generally has an inherent technical contradiction that is difficult to break through: in order to improve the electrical conductivity of the electrode, a large amount of conductive filler is often added, and the introduction of the conductive filler will significantly destroy the polymer network structure of the hydrogel, resulting in the decrease of mechanical strength, the deterioration of toughness, the easy breakage, and the possible decrease of biocompatibility of the material, which cannot realize the synergistic optimization of electrical conductivity, mechanical properties and biocompatibility, and is difficult to meet the comprehensive requirements of the brain-computer interface electrode on multiple dimensional properties.

[0005] In recent years, freeze casting technology provides a new technical idea for solving the performance contradiction of hydrogel electrodes because it can construct materials with directional pore structures and is widely used in the collaborative optimization of hydrogel structure and function. For example, Chinese Patent CN202310737759.7 discloses a high-strength hydrogel based on freeze casting and in-situ polymerization. This technology uses polyvinyl alcohol (PVA) to construct a rigid skeleton. Through solvent replacement and low-temperature volatilization process, a freeze-cast PVA skeleton is first prepared, and then a polyacrylic acid-polyacrylamide (PAA-PAM) flexible network is introduced into the skeleton through photo-induced in-situ polymerization, finally forming a PVA-PAA-co-PAM double network structure, which focuses on improving the mechanical strength of the hydrogel. However, this existing technology still has obvious defects: first, the prepared hydrogel is isotropic structure, which cannot be optimized by structural regulation to further optimize the electrical conductivity; second, although the tensile strength of the hydrogel is improved to 11.2 MPa, the rigid skeleton and high-density cross-linking design used to achieve high tensile strength will result in a significant increase in the mechanical modulus of the hydrogel, making it difficult to match the modulus of the human skin soft tissue, and the flexibility is insufficient, which cannot achieve non-inductive adhesion, and does not meet the core requirements of brain-computer interface flexibility; third, this technology only focuses on improving the overall mechanical strength of the hydrogel, and does not design self-repairing performance. The hydrogel is easily damaged and fails after mechanical damage, and the long-term stability is insufficient, which still cannot meet the comprehensive requirements of high electrical conductivity, excellent mechanical properties, self-repairing ability, and long-term stability of brain-computer interface electrodes.

[0006] In summary, in the current field of brain-computer interface electrode materials, whether it is a traditional rigid electrode, an existing flexible hydrogel electrode, or an improved hydrogel based on freeze casting technology, each has its own technical defects, especially the inability to achieve high electronic conductivity and ionic conductivity, excellent mechanical properties, self-repairing performance, and long-term stability. It is difficult to meet the actual application requirements of high-precision, long-term wearable brain-computer interfaces. Therefore, the development of a hydrogel electrode material that can break through the above technical bottlenecks and simultaneously achieve multi-dimensional performance collaborative optimization is of great significance for promoting the development and clinical application of brain-computer interface technology, and has become a technical problem urgently to be solved in the current field. SUMMARY

[0007] The present application aims to solve the problem that the existing hydrogel electrode material is difficult to coordinate multiple performances, and through the synergistic regulation of multiple technical means such as covalent-dynamic non-covalent bond double crosslinking network construction, hierarchical anisotropic structure regulation of directional freeze casting process, carbon nanotube and polyaniline synergistic conductive system doping and potassium chloride ion strengthening post-processing, a hierarchical anisotropic self-repairing conductive hydrogel is prepared, which realizes the synergistic optimization and improvement of mechanical, conductive, adhesive, biocompatibility and self-repairing multidimensional performance, has the innovation of structural design and the feasibility of practical application, and can be widely applied to the technical field of flexible electronics, biomedical electrodes and the like, especially in the high-fidelity acquisition scene of brain-computer interface, electroencephalogram / electrocardiogram and the like.

[0008] The technical solution of the present application is a hierarchical anisotropic self-repairing conductive hydrogel electrode material, which is prepared by using acrylamide, acrylic acid and aniline hydrochloride as ternary comonomers, polymerizing to form a polyacrylamide-polyacrylic acid-polyaniline copolymer network as a core framework, doping carbon nanotubes (CNT) and combining polyaniline (PANI) in the copolymer network to construct a synergistic conductive system, and then performing directional freeze casting, low-temperature polymerization and potassium chloride (KCl) ion strengthening post-processing.

[0009] The preparation method of the above-mentioned hierarchical anisotropic self-repairing conductive hydrogel electrode material is as follows: 1) Dissolve acrylamide monomer, aniline hydrochloride monomer, acrylic acid monomer, reducing agent and crosslinking agent in deionized water, stir until all components are dissolved, then add antifreeze and continue to stir evenly to obtain a clear and transparent solution A; 2) Disperse carbon nanotubes (CNT) in deionized water, grind for 25-35 min to form a uniform and stable suspension, and record it as solution B; 3) Mix solution B and solution A in proportion, stir uniformly, and then perform ultrasonic defoaming treatment to obtain a composite precursor solution which is uniformly dispersed and has no obvious bubbles; 4) Prepare an initiator aqueous solution; 5) Put the composite precursor solution into the tubular mold, add a certain amount of initiator aqueous solution, mix well, then gently contact the bottom of the mold with the surface of liquid nitrogen (the initial immersion depth of the mold is about 0.5 cm), and use the low-temperature effect of liquid nitrogen to initiate the solution to freeze rapidly along the axial direction of the mold. The ice crystals grow from the bottom to the top in one direction, forming a regular and continuous columnar structure. At this time, the polymer or solute particles are excluded by the growth front of the ice crystals and are concentrated in the gap between the ice crystals. After the top of the solution is completely frozen, the morphology of the ice crystals determines the template of the final porous structure. Then, the mold is removed from the surface of liquid nitrogen and immediately transferred to an environment of-30~-20℃ for continuous freezing for 48~96 h. In this low-temperature environment, the ternary monomers concentrated in the unfrozen liquid phase channels undergo free radical copolymerization under the initiation of the initiator-reducing agent redox system, forming a stable polyacrylamide-polyacrylic acid-polyaniline copolymer network, and finally forming a hydrogel with a hierarchical anisotropic network structure; 6) Take the polymerized hydrogel out of the mold and immerse it in a potassium chloride aqueous solution. This process allows K + and Cl - to diffuse into the hydrogel network, which not only significantly improves the ionic conductivity of the hydrogel, but also further strengthens the dynamic non-covalent cross-linking within the polymer network through ionic interactions, thereby synergistically optimizing the mechanical and electrical properties of the material. After soaking is completed, take out, wash and dry to obtain a hierarchical anisotropic self-healing hydrogel electrode material.

[0010] Further, in step 1), the crosslinking agent is selected from at least one of N,N'-methylenebisacrylamide (MBAAm), ethylene glycol bisacrylate (EGDA), diethylene glycol bisacrylate (DEGDA), and N,N'-methylenebismethacrylamide, preferably N,N'-methylenebisacrylamide; the reducing agent is selected from at least one of ascorbic acid, sodium ascorbate, sodium pyrosulfite, sodium bisulfite, and sodium thiosulfate, preferably ascorbic acid; and the antifreeze agent is selected from at least one of glycerol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, and polyethylene glycol, preferably glycerol.

[0011] Further, in step 1), the molar ratio of acrylamide, aniline hydrochloride, and acrylic acid is 6~10:1.5~5:1, and the molar ratio of the crosslinking agent to aniline hydrochloride monomer is 1:80~130; the amount of the reducing agent is 2.5%~5% of the total moles of the ternary monomers of acrylamide, aniline hydrochloride, and acrylic acid; and the volume ratio of the antifreeze agent to deionized water is 1:8~10.

[0012] Further, in step 2), the concentration of carbon nanotubes in solution B is 40~70 mg / mL.

[0013] Further, in step 3), the volume ratio of solution B to solution A is 1:10-25, and the ultrasonic treatment time is 15-25 min.

[0014] Further, in step 4), the initiator is at least one of ammonium persulfate, potassium persulfate and sodium persulfate, and preferably ammonium persulfate; the concentration of the aqueous initiator solution is 0.70-0.80 g / mL.

[0015] Further, in step 5), the volume ratio of the composite precursor solution to the aqueous initiator solution is 60-70:1.

[0016] Further, in step 6), the concentration of the aqueous potassium chloride solution is 0.5-1.5 mol / L, and the soaking time is 8-12 min.

[0017] The above hierarchical anisotropic self-repairing conductive hydrogel electrode material can be widely applied to the preparation of flexible wearable electronic devices and biomedical devices, and is particularly suitable for the preparation of flexible wearable bioelectric electrodes, including at least one of electrodes for brain-computer interfaces, electrocardiogram electrodes and electromyogram electrodes; and can also be applied to the preparation of flexible conductive sensors and tissue engineering scaffolds, and is suitable for human body contact, dynamic deformation and long-term use scenarios.

[0018] In the application, acrylamide (AM), acrylic acid (AA) and aniline hydrochloride (AN) are used as ternary comonomers, N,N'-methylenebisacrylamide (MBAAm) is used as a chemical crosslinking agent, and ammonium persulfate (APS) is used as a free radical initiator, and a stable covalent crosslinked three-dimensional network is constructed through free radical copolymerization and chemical crosslinking reaction, thereby providing rigid support and basic structural stability for the hydrogel. At the same time, the negative carboxylate (-COO - ) formed by dissociation of the carboxyl groups in the polyacrylic acid (PAA) molecular chain of the copolymer and the positive protonated amino group (-NH3 +The hydrogel forms dynamic and reversible ionic bonds, and the numerous polar functional groups such as amide groups (-CONH2), carboxyl groups (-COOH), amino groups (-NH2), and hydroxyl groups (-OH) on the molecular chain spontaneously form extensive intermolecular hydrogen bonds. These two groups constitute a dynamic non-covalent network entangled in the covalent backbone. These non-covalent bonds can be reversibly broken and rebuilt under external forces and molecular thermal motion, endowing the hydrogel with ultra-high elasticity and plasticity (such as 581% elongation at break and 0.11 MPa tensile stress at break) and self-healing ability. The covalent cross-linked network prevents the non-covalent network from excessively deforming and collapsing. The non-covalent network can absorb external forces and protect the covalent backbone. When the external forces disappear, the broken non-covalent bonds can be quickly rebuilt, allowing the hydrogel to return to its initial shape, providing the core mechanism for subsequent self-healing performance. The synergistic effect of these two factors constitutes the core structural source of the hydrogel's excellent mechanical strength, high toughness, and self-healing properties. Simultaneously, by combining the CNT-PANI synergistic conductive system and KCl ion enhancement treatment, the conductive, mechanical, and self-healing properties are synergistically optimized, perfectly meeting the application requirements of flexible wearable bioelectric electrodes.

[0019] The beneficial effects of this invention are as follows: 1. This application successfully prepared a hierarchical anisotropic conductive hydrogel by synergistically designing four core technologies: covalent cross-linking and dynamic non-covalent dual cross-linking network construction, hierarchical anisotropic structure regulation by directional freeze casting process, doping of carbon nanotube and polyaniline synergistic conductive system, and potassium chloride ion strengthening post-treatment. This achieved synergistic improvement and optimization of multiple dimensions of performance, including mechanical, conductive, adhesive, biocompatibility, and self-healing properties. 2. This application uses a ternary monomer system of acrylamide, acrylic acid, and aniline hydrochloride in conjunction with a crosslinking agent to first form a dual crosslinking network with the dual effects of covalent crosslinking and dynamic non-covalent bonds. Then, ice crystal formation is induced by directional freeze casting technology, driving phase separation and monomer concentration enrichment of the system. Subsequent low-temperature polymerization generates a high-density stacked polymer phase. Compared with the loose entangled network formed by non-directional freezing, this method effectively enhances intermolecular interactions and constructs a multi-scale structural framework. The final hydrogel has a compressive modulus of approximately 39 kPa, which perfectly matches the modulus of human skin soft tissue, enabling imperceptible and close skin adhesion. It also has excellent elasticity and plasticity, with an elongation at break of up to 581% and a tensile stress at break of up to 0.11 MPa. It can withstand complex deformations such as knotting, and its mechanical strength and toughness are synergistically enhanced, making it suitable for the actual use conditions of wearable electrodes. 3. This application introduces carbon nanotubes into the hydrogel framework, enabling them to form auxiliary conductive pathways and be tightly connected with the polyaniline conductive network, effectively reducing the overall resistance of the hydrogel. At the same time, the parallel-arranged micron channels generated during the directional freeze-casting process serve as efficient and low-impedance charge transport paths, maximizing the ion mobility within the system. Combined with further optimization through potassium chloride ion-enhanced post-treatment, the final hydrogel obtained has a conductivity as high as 2.8 S / m, which is significantly better than traditional wet electrodes and various dry electrodes, enabling low-noise, high-quality bioelectric signal acquisition and transmission. 4. The hydrogel disclosed in this application contains a carboxyl (-COOH) polar functional group in its polymer chain, which can form extensive hydrogen bonding with hydroxyl (-OH) and amino (-NH2) groups on the surface of substrates such as skin. This allows it to adhere firmly to different substrate surfaces and has good adhesion to irregular surfaces such as human skin. It does not have problems such as adhesion deviation or detachment, effectively solving the problem of unstable signal transmission caused by poor adhesion of traditional electrodes and improving the accuracy of bioelectric signal acquisition. 5. This application uses bio-friendly ternary copolymer monomers and green preparation processes to produce hydrogels without toxic or harmful leachates or component leaching. In vitro cell experiments using the MTT assay and live / dead cell fluorescence staining method have verified that the hydrogel is non-cytotoxic and does not inhibit cell proliferation in any way. Furthermore, after being firmly attached to human skin for 10 hours, it did not cause any irritation. Both in vitro cell experiments and human skin contact tests have confirmed the reliability of the material when applied to human skin, providing a reliable biosafety guarantee for its clinical and civilian applications as a biomedical electrode. 6. The hydrogel prepared in this application has multiple dynamic reversible non-covalent interactions within the polymer network as its core self-healing mechanism. The dynamic reversible ionic bonds formed by the carboxyl groups in the polyacrylic acid molecular chain and the protonated amino groups in polyaniline, combined with extensive intermolecular hydrogen bonds within the network, enable efficient self-repair. After repair, the hydrogel reconnects tightly at the original cut to form a whole, which can stably withstand tensile stress and restore most of its mechanical properties. At the same time, the conductive pathway is reconstructed, and the conductivity is restored to the original level, achieving dual self-repair of mechanical and conductive properties. This effectively solves the limitations of existing hydrogel bioelectric electrodes, which are susceptible to mechanical damage and have a short service life. 7. This application uses potassium chloride ion strengthening for hydrogel post-treatment, which can not only further optimize the ion transport environment of the hydrogel and help improve its conductivity, but also strengthen the dynamic interaction within the polymer network, providing support for the realization of self-healing performance. At the same time, it can moderately densify the hierarchical anisotropic network structure of the hydrogel, which plays an auxiliary role in enhancing the stability of mechanical properties, avoiding the problem of other performance degradation caused by single performance optimization, and realizing the mutual enhancement of the mechanical, conductive and self-healing properties of the hydrogel. Attached Figure Description

[0020] Figure 1 In the image, a is a cross-sectional scanning electron microscope (SEM) image of the hydrogel electrode material prepared in Example 1 after longitudinal cutting along the directional freezing axis; b is a cross-sectional SEM image of the hydrogel electrode material prepared in Comparative Example 1; c is a cross-sectional SEM image of the hydrogel electrode material prepared in Comparative Example 2. Figure 2 The compressive stress-strain curves of the hydrogel electrode materials prepared in Example 1 and Comparative Examples 1-2 are shown. Figure 3 The tensile stress-strain curves of the hydrogel electrode materials prepared in Example 1 and Comparative Examples 1-2 are shown. Figure 4 The adhesion performance test results of the hydrogel electrode material prepared in Example 1 on the surface of pigskin after 20 peels; Figure 5 The results of MTT assay are for the hydrogel electrode material prepared in Example 1. Figure 6 The results of live / dead cell fluorescence staining of the hydrogel electrode material prepared in Example 1; Figure 7 This is a schematic diagram of the self-healing process of the hydrogel electrode material prepared in Example 1; Figure 8 The graph shows the conductivity test results of the hydrogel electrode materials prepared in Example 1 and Comparative Examples 1-4. Detailed Implementation

[0021] To better understand the content of this invention patent, the technical solution of this invention is further illustrated below through specific embodiments and accompanying drawings. However, these examples do not limit the invention. Modifications and substitutions made to the methods, steps, or conditions of this invention without departing from the essence of this invention are all within the scope of this invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0022] Example 1

[0023] This embodiment discloses a method for preparing a hydrogel (HAC) electrode material, the specific process of which is as follows:

[0024] 1) Take a 20 mL glass bottle and add 5.4 mL of deionized water. Weigh out 2.4 g acrylamide (AM, 33.76 mmol), 0.015 g N,N'-methylenebisacrylamide (MBAAm, 97.30 μmol), 1.44 g aniline hydrochloride (AN, 11.11 mmol), and 0.25 g ascorbic acid (1.42 mmol). Then, measure 300 μL of acrylic acid (AA, 4.38 mmol) and add it to the glass bottle. Stir thoroughly at room temperature until all components are completely dissolved. Then add 0.6 mL of glycerol and continue stirring until the mixture is homogeneous. Finally, a clear and transparent solution is obtained, which is denoted as solution A (glycerol can act as a humectant and antifreeze agent, improving the compatibility of the system and the flexibility of the subsequent hydrogel).

[0025] 2) Take 0.5 g of carbon nanotubes (CNTs) and add them to 10 mL of deionized water. Grind the mixture for 30 min to ensure that the carbon nanotubes are fully dispersed and do not agglomerate, so that a uniform and stable suspension is formed. This suspension is denoted as solution B.

[0026] 3) Measure 500 μL of solution B and add it to solution A. First, stir magnetically for 10-15 min to initially and uniformly disperse carbon nanotubes in solution A. Then, sonicate the mixture (200W) for 20 min. This can further promote the uniformity of CNT dispersion and completely eliminate residual small bubbles in the solution, avoiding defects such as pores and cracks during subsequent gelation and polymerization. Finally, a composite precursor solution with uniform dispersion and no obvious bubbles is obtained.

[0027] 4) Weigh 1.5 g of ammonium persulfate (APS), dissolve it in 2 mL of deionized water, stir until completely dissolved, and prepare an APS aqueous solution with a concentration of 0.75 g / mL as an oxidative initiator for low-temperature free radical polymerization;

[0028] 5) Measure 2 mL of the composite precursor solution and inject it into the tubular mold (in this embodiment, the tubular mold is a standard 10 mL centrifuge tube used in the laboratory). Then add 30 μL of APS aqueous solution and stir until the mixture is uniform. Gently touch the bottom of the mold to the surface of liquid nitrogen (the initial immersion depth of the mold is about 0.5 cm). Utilize the low temperature effect of liquid nitrogen to initiate the rapid axial freezing of the solution along the mold. After the top of the solution is completely frozen, quickly remove the mold from the liquid nitrogen surface and immediately transfer it to a -20℃ freezer to continue freezing for 48 h. This allows the system to stably complete the free radical polymerization reaction under low temperature conditions, forming a hydrogel with an anisotropic network structure.

[0029] 6) After freeze polymerization for 48 h, the hydrogel is removed from the tubular mold and immersed in a 1.0 mol / L potassium chloride (KCl) aqueous solution for 10 min. The conductivity and self-healing properties of the hydrogel are optimized by ion strengthening treatment. After immersion, excess KCl on the surface of the hydrogel can be rinsed with deionized water and then dried to constant weight to finally obtain a self-healing hydrogel electrode material.

[0030] Example 2

[0031] The only difference between this embodiment and Example 1 is the concentration of aniline hydrochloride in solution A. The rest of the preparation steps, components and parameters are completely the same as in Example 1.

[0032] 1) Take a 20 mL glass bottle and add 5.4 mL of deionized water. Weigh out 2.4 g of acrylamide (AM, 33.76 mmol), 0.015 g of N,N'-methylenebisacrylamide (MBAAm, 97.30 μmol), 1.92 g of aniline hydrochloride (AN, 14.82 mmol), and 0.25 g of ascorbic acid (1.42 mmol). Then, measure out 300 μL of acrylic acid (AA, 4.38 mmol) and add it to the glass bottle. Stir thoroughly at room temperature until all components are completely dissolved. Then add 0.6 mL of glycerol and continue stirring until the mixture is homogeneous. The final clear and transparent solution is denoted as solution A.

[0033] 2)-6): Same as steps 2)-6 in Example 1.

[0034] Example 3

[0035] The only difference between this embodiment and Example 1 is the concentration of aniline hydrochloride in solution A. The rest of the preparation steps, components and parameters are completely the same as in Example 1.

[0036] 1) Take a 20 mL glass bottle and add 5.4 mL of deionized water. Weigh out 2.4 g of acrylamide (AM, 33.76 mmol), 0.015 g of N,N'-methylenebisacrylamide (MBAAm, 97.30 μmol), 0.96 g of aniline hydrochloride (AN, 7.41 mmol), and 0.25 g of ascorbic acid (1.42 mmol). Then, measure out 300 μL of acrylic acid (AA, 4.38 mmol) and add it to the glass bottle. Stir thoroughly at room temperature until all components are completely dissolved. Then add 0.6 mL of glycerol and continue stirring until the mixture is homogeneous. The final clear and transparent solution is denoted as solution A.

[0037] 2)-6): Same as steps 2)-6 in Example 1.

[0038] Comparative Example 1

[0039] This comparative example is used to compare the effect of directional freezing technology on the performance of hydrogel electrode materials. The core difference between this example and Example 1 is that the hydrogel is prepared by direct room temperature polymerization instead of directional freezing polymerization. The other preparation steps, components and parameters are completely consistent with those in Example 1.

[0040] 1)-4): Same as steps 1)-4) of Example 1, to prepare a clear and transparent solution A, a carbon nanotube suspension (solution B), a uniformly dispersed and bubble-free composite precursor solution, and an aqueous solution of APS oxidation initiator with a concentration of 0.75 g / mL.

[0041] 5) Measure 2 mL of the composite precursor liquid and inject it into the tubular mold. Then add 30 μL of APS aqueous solution, stir until the mixture is uniform, and place it at room temperature (25±2℃) for static polymerization until the system is completely gelled to obtain a hydrogel with no orientation structure.

[0042] 6) Remove the hydrogel from the tubular mold and immerse it in a 1.0 mol / L KCl aqueous solution for 10 min. After immersion, rinse the surface of the hydrogel with deionized water to remove excess KCl, and then dry it to constant weight to obtain the hydrogel electrode material.

[0043] Comparative Example 2

[0044] This comparative example is used to compare the effects of directional freezing technology and conventional freezing process on the performance of hydrogel electrode materials. The core difference between this example and Example 1 is that the directional freezing polymerization process of "instant contact between the bottom of the mold and liquid nitrogen" is not used. Instead, the conventional freezing polymerization process of "the entire mold is immersed in liquid nitrogen" is used. All other preparation steps, components and parameters are completely consistent with Example 1.

[0045] 1)-4): Same as steps 1)-4) of Example 1, to prepare a clear and transparent solution A, a carbon nanotube suspension (solution B), a uniformly dispersed and bubble-free composite precursor solution, and an aqueous solution of APS oxidation initiator with a concentration of 0.75 g / mL.

[0046] 5) Measure 2 mL of the composite precursor solution and inject it into the tubular mold. Then add 30 μL of APS aqueous solution and stir until the mixture is uniform. Then immerse the entire tubular mold directly into liquid nitrogen (ensure that the top surface of the liquid nitrogen is above the top surface of the liquid inside the tube). After the solution inside the mold is completely frozen, quickly remove the mold from the liquid nitrogen and immediately transfer it to a -20℃ freezer for 48 h to allow the system to complete the free radical polymerization reaction stably under low temperature conditions, and finally form a hydrogel with a non-directional porous structure.

[0047] 6) After freeze polymerization for 48 h, the hydrogel was removed from the tubular mold and immersed in a 1.0 mol / L KCl aqueous solution for 10 min. After immersion, excess KCl on the surface of the hydrogel was rinsed with deionized water and then dried to constant weight to obtain the hydrogel electrode material.

[0048] Comparative Example 3

[0049] This comparative example is used to compare the effects of potassium chloride (KCl) ion-strengthening post-treatment on the performance and self-healing properties of hydrogel electrode materials. The core difference between this example and Example 1 is that the ion-strengthening post-treatment step of soaking in potassium chloride aqueous solution is not performed. All other preparation steps, components and parameters are completely consistent with Example 1.

[0050] 1)-5): Following the steps 1)-5) of Example 1, a clear and transparent solution A, a carbon nanotube suspension (solution B), a uniformly dispersed and bubble-free composite precursor solution, and an aqueous solution of APS oxidation initiator with a concentration of 0.75 g / mL were prepared sequentially. Then, the solution was subjected to a directional freezing process in which the bottom of the mold was brought into instantaneous contact with liquid nitrogen, and then transferred to a -20°C freezer for continuous freezing for 48 h to complete low-temperature free radical polymerization and form a hydrogel with a directional anisotropic network structure.

[0051] 6) Remove the polymerized hydrogel from the tubular mold to obtain a hydrogel sample without ion strengthening treatment. This sample is then compared with the hydrogel electrode material strengthened by potassium chloride ions in Example 1 to determine the effect of ion strengthening treatment on the conductivity and self-healing properties of the material.

[0052] Comparative Example 4

[0053] This comparative example is used to compare the effect of carbon nanotube addition on the performance of hydrogel electrode materials. The specific steps are as follows:

[0054] 1) Same as step 1) of Example 1.

[0055] 2) Weigh 1.5 g of ammonium persulfate (APS), dissolve it in 2 mL of deionized water, stir until completely dissolved, and prepare an APS aqueous solution with a concentration of 0.75 g / mL as an oxidative initiator for low-temperature free radical polymerization;

[0056] 3) Measure 2 mL of solution A and inject it into the tubular mold. Then add 30 μL of APS aqueous solution and stir until the mixture is uniform. Gently contact the bottom of the mold with the liquid nitrogen surface and use the low temperature effect of liquid nitrogen to initiate the rapid axial freezing of the solution along the mold. After the top of the solution is completely frozen, quickly remove the mold from the liquid nitrogen surface and immediately transfer it to a -20℃ freezer for 48 h to allow the system to stably complete the free radical polymerization reaction in a low temperature environment and form a hydrogel with an anisotropic network structure.

[0057] 4) After freeze polymerization for 48 h, the hydrogel was removed from the tubular mold and immersed in 1.0 mol / L KCl aqueous solution for 10 min to obtain the hydrogel electrode material.

[0058] Related performance tests

[0059] 1) Morphological characterization: The hydrogel sample prepared in Example 1 was longitudinally cut along the directional freezing axis, and its cross-sectional morphology was observed using a scanning electron microscope. The observation results are as follows: Figure 1 As shown in Figure a, the hydrogel exhibits a well-organized, continuous, vertical tunnel-like micro-channel structure on a cross-section parallel to the freezing direction. Further observation reveals that interconnected nanoporous structures are uniformly distributed within the pore walls of the micro-channels and throughout the entire polymer network, with the pore walls exhibiting a typical honeycomb morphology. These characteristics fully demonstrate that the hydrogel prepared in Example 1 possesses a highly ordered dual-scale hierarchical anisotropic structure. This structure originates from the unidirectional growth and phase separation effect of ice crystals during the directional freeze-casting process, fully demonstrating the precise control of the microstructure by the process of this invention.

[0060] And observe comparative example 1 ( Figure 1 b) in the example and Comparative Example 2 ( Figure 1 The cross-sectional SEM images of the hydrogel materials prepared in c) show that the cross-sections of the samples prepared in both comparative examples exhibit a disordered and random porous structure. There are no regular micron-sized channels parallel to any specific direction; instead, there are only irregular pores of a single scale, lacking hierarchical anisotropy. This structural difference directly confirms that the directional freeze-casting process is the core key to constructing the hierarchical anisotropic microstructure of this invention.

[0061] 2) Compression mechanical property testing

[0062] Uniaxial compression tests were performed on the hydrogel samples (processed into cylindrical specimens) prepared in Example 1 and Comparative Examples 1-2 using a universal testing machine to obtain their compressive stress-strain curves. Figure 2 As can be seen from the curves, the hydrogel prepared in Example 1 exhibits typical strain hardening characteristics: in the low strain stage (0~60%), the compressive stress increases slowly, demonstrating flexibility and compliance highly matched with biological soft tissues; when the strain exceeds 60%, the stress rises rapidly with increasing strain, demonstrating excellent resistance to compressive deformation. Quantitative analysis shows that the compressive modulus of this hydrogel is approximately 39 kPa, which is highly consistent with the mechanical properties of natural soft tissues such as cartilage; under high strain conditions of 90%, its compressive strength can reach 6.22 MPa, and the sample did not crack, proving that this hydrogel possesses both excellent flexibility and compressive load-bearing capacity, and has the mechanical basis to be used as a biomedical material.

[0063] The hydrogels prepared in Comparative Example 1 and Comparative Example 2 exhibited significantly different mechanical responses: the hydrogel sample prepared in Comparative Example 1 maintained extremely low compressive stress and very slow growth within the strain range of 0-90%, with no obvious strain hardening phenomenon, indicating that its resistance to compressive deformation was weak and it could not withstand loads under high strain. The hydrogel sample prepared in Comparative Example 2 experienced a faster rate of stress increase in the later stage (>75% strain), but this increase only lasted until 80% strain before the sample ruptured and could no longer bear the load. This indicates that although it had a certain initial compressive response, it lacked a stable strain hardening mechanism and anti-rupture ability, and the synergy between its overall flexibility and compressive load-bearing capacity was still significantly weaker than that of Example 1.

[0064] This difference in mechanical properties stems from the fundamental difference in microstructure: the micron channel-nanoporous hierarchical anisotropic structure of Example 1 can absorb energy through the elastic deformation of the nanoporous structure in the low strain stage, maintaining flexibility that matches biological soft tissue; in the high strain stage, it relies on the ordered stacking of micron channels and the rigid support of the pore walls to achieve a sharp increase in stress, thus possessing both flexibility and continuous compressive strength; while the disordered porous structure of Comparative Example 1 cannot effectively bear stress, and the disordered structure of Comparative Example 2 is prone to stress concentration and cracking under high strain. Neither of them can form a hierarchical bearing mechanism, further verifying the effectiveness of the hierarchical anisotropic structure design of the present invention.

[0065] 3) Tensile mechanical property testing

[0066] Using a universal testing machine, the hydrogels prepared in Example 1 and Comparative Examples 1-2 were processed into dumbbell-shaped standard specimens and subjected to uniaxial tensile tests until fracture, obtaining the tensile stress-strain curves of the corresponding specimens. Figure 3 As can be seen, the hydrogel prepared in Example 1 exhibits typical deformation behavior of tough materials: the stress rises rapidly with strain in the initial tensile stage, then enters the strain hardening stage, and the stress increases gradually with strain until the sample fractures. Quantitative test results show that the hydrogel has an elongation at break as high as 581% and a tensile fracture stress of 0.11 MPa. This result indicates that it combines excellent ductility and high toughness, while also possessing good tensile load-bearing capacity. It exhibits excellent mechanical adaptability in applications such as flexible electronics and biomedicine, where material flexibility and mechanical stability are required.

[0067] The tensile responses of the samples prepared in Comparative Example 1 and Comparative Example 2 are significantly different: Although the elongation at break of the sample prepared in Comparative Example 1 is as high as about 800%, the tensile stress is always at an extremely low level (only about 0.045 MPa at break), indicating that although its ductility is good, its tensile load-bearing capacity is extremely weak and cannot meet the mechanical stability requirements in practical applications; The tensile stress growth rate of the sample prepared in Comparative Example 2 is slightly faster than that of Example 1 in the early stage, but it breaks only at about 470% strain. The elongation at break and tensile toughness are significantly lower than those of Example 1, indicating that although it has a certain initial tensile strength, its ductility and toughness are insufficient, and it is prone to brittle fracture under moderate strain.

[0068] This difference in tensile properties also stems from the fundamental difference in microstructure: the anisotropic structure of the micron channel-nanoporous layer in Example 1 can disperse stress during stretching through the elastic deformation of the nanoporous structure, the directional slippage of the micron channel, and the synergistic extension of the molecular chains, ensuring high ductility while maintaining stable stress growth through the synergistic effect of the covalent-dynamic non-covalent double crosslinking network, thus possessing both high elongation and high toughness; in contrast, the disordered porous structure of Comparative Example 1 lacks an effective stress transfer mechanism and relies solely on the weak entanglement of molecular chains to achieve stretching, resulting in weak load-bearing capacity; the disordered structure of Comparative Example 2 is prone to local stress concentration during stretching, leading to premature fracture and failing to achieve synergistic optimization of ductility and load-bearing capacity.

[0069] 4) Overlap shear strength and adhesion durability test

[0070] To quantitatively characterize the adhesion performance of the hydrogel electrode material prepared in Example 1 to a biological substrate, lap shear strength tests were conducted using pigskin as the adhesion substrate, and repeated adhesive-peel cycle durability tests were performed to examine its adhesion strength, adhesion retention rate, and residue on the substrate surface after adhesion.

[0071] The test results show that ( Figure 4 The hydrogel exhibits an overlap shear adhesion strength of up to 58 kPa on pigskin, demonstrating excellent strong adhesion to biological substrates. After 20 repeated adhesive-peel cycles, the hydrogel-pigskin adhesion system maintains stable adhesion performance with an adhesion strength attenuation rate of less than 15%, and no obvious hydrogel residue is found on the pigskin surface, confirming that the hydrogel possesses both strong adhesion and excellent adhesion durability.

[0072] 5) Cytotoxicity and biocompatibility testing

[0073] To comprehensively evaluate the biocompatibility and biosafety of the hierarchical anisotropic conductive hydrogel prepared in Example 1 and to eliminate its potential risks in human contact scenarios such as biomedical electrodes, cytotoxicity was detected by a combination of MTT assay and live / dead cell fluorescence staining. Simultaneously, human skin contact irritation tests were conducted. The specific test procedures and results are as follows:

[0074] The effects of the hydrogel extract prepared in Example 1 on the cytotoxicity and proliferation of mouse embryonic fibroblasts (NIH 3T3) were evaluated using a combination of MTT assay and live / dead cell fluorescence staining. A 100% concentration hydrogel extract was prepared at a solid-liquid ratio of 0.1 g / mL and then serially diluted to 20%, 40%, 60%, and 80% concentrations. Cell culture medium without extract served as a control (0% concentration). Cells were cultured in the different concentrations of extract for 24 h before detection. MTT assay results (…) Figure 5 The results showed that, within the concentration range of 0% to 100% of the extract, the cell viability of each group remained above 95%, with no significant difference compared to the control group (0% concentration). This indicates that the hydrogel extract is non-cytotoxic and has no inhibitory effect on cell proliferation, and does not affect the normal physiological activity of cells.

[0075] Results of live / dead cell fluorescence staining ( Figure 6 The results showed that cells in both the control group and the 100% concentration hydrogel extract (HAC-Ghydrogel, 0.1 g / mL) treatment group exhibited large areas of green fluorescence (live cell markers), with almost no red fluorescence (dead cell markers). Quantitative analysis showed that the cell viability in the treatment group was >95%, which was highly consistent with the MTT test results, further confirming from a cellular morphology perspective that the hydrogel had no obvious cytotoxicity and excellent biocompatibility.

[0076] To verify the safety of the hydrogel in real-world human contact scenarios, a skin contact irritation test was conducted. Thirty healthy volunteers were selected, and their hands (without skin damage, inflammation, or allergy history) were used as test areas. The hydrogel material was cut to a size suitable for the skin and securely attached to the test area using a medical-grade fixation method. Simulating actual wearing conditions, the material was carefully removed after 10 hours of continuous attachment. The skin condition was observed immediately after removal and continuously monitored for 24 hours, focusing on whether any signs of inflammation or allergy, such as erythema, itching, swelling, or stinging, appeared. The test results showed that all test subjects had no abnormalities in the skin contact area. No hydrogel residue remained on the skin surface upon removal, and no inflammation or allergic reactions occurred during the follow-up observation period. The skin color and texture were consistent with the surrounding normal skin, with no obvious irritation. This confirms that the hydrogel has good compatibility with human skin, is non-irritating and non-sensitizing, and can be safely used in direct skin contact scenarios.

[0077] In summary, the results of both in vivo and in vitro tests consistently demonstrate that the hydrogel electrode material prepared in Example 1 possesses excellent biocompatibility and biosafety, exhibiting no cytotoxicity, skin irritation, or sensitization. This effectively avoids the safety risks associated with the application of biomedical electrode materials in human contact, providing crucial biological evidence and safety assurance for their practical application in tissue engineering, flexible wearable bioelectric electrodes, and other fields.

[0078] 6) Self-healing performance test

[0079] To characterize the self-healing properties of the hydrogel prepared in Example 1, room temperature self-healing and post-healing mechanical recovery tests were conducted: see [link to relevant documentation]. Figure 7 Take the complete hydrogel sample prepared in Example 1, cut it completely along the longitudinal direction with a blade, and then precisely fit the fresh cut surfaces of the two sections together without applying any additional external force. Let it stand at room temperature for 12 hours to complete self-repair. Then, perform a uniaxial tensile test on the repaired hydrogel sample to evaluate its mechanical property recovery.

[0080] Test results show that after 12 hours of self-healing at room temperature, the hydrogel achieves a tight interfacial connection at the original incision site, reforming a complete overall structure. During the stretching process, the sample did not break at the original incision site and can stably withstand a certain tensile stress, indicating that the hydrogel has excellent self-healing ability. After simple cross-section bonding, the mechanical properties can be effectively restored.

[0081] The self-healing performance of Comparative Example 3 (without KCl ion strengthening) was evaluated using the same testing procedures. The results showed that it could not form a tight interfacial bond at the original incision site and fractured directly at the original incision site during stretching, unable to withstand high tensile stress. This result directly confirms that KCl ion strengthening post-treatment is crucial for the realization of hydrogel self-healing ability. It can enhance the reversible breakage and reconstruction ability of dynamic non-covalent bonds within the network through ion interactions, thereby effectively improving the interfacial healing efficiency and mechanical property recovery ability of the hydrogel.

[0082] 7) Conductivity test

[0083] The conductivity of hydrogel samples from Example 1 and Comparative Examples 1 (room temperature polymerization), 2 (overall freezing), 3 (without KCl ion strengthening), and 4 (without CNT doping) was tested using the four-probe method to systematically explore the regulatory effects of component doping, preparation process, and post-treatment on the conductivity of hydrogels.

[0084] Test results ( Figure 8The results show that the CNT-doped hydrogel prepared in Example 1, which underwent directional freeze-casting and KCl ion strengthening treatment, achieved a conductivity of 2.8 S / m, the highest among all samples. Compared to Comparative Example 4 (conductivity 1.72 S / m), which did not have CNT doping, its conductivity increased by 63%, confirming that carbon nanotube doping can introduce electronic conductivity pathways and significantly enhance the electronic conductivity of the hydrogel. Compared to Comparative Example 3 (conductivity approximately 2.2 S / m), which did not undergo KCl ion strengthening, the conductivity of Example 1 increased by approximately 27%, indicating that KCl ion strengthening can further optimize the ionic conductivity of the hydrogel by introducing mobile ions. Compared to Comparative Example 1 (conductivity approximately 1.4 S / m) using a room temperature polymerization process and Comparative Example 2 (conductivity only approximately 0.6 S / m) using an overall freezing process, the conductivity of Example 1 was significantly improved. Compared to the S / m ratio, the conductivity of Example 1 was increased by 100% and 367%, respectively, which fully demonstrates that the hierarchical anisotropic structure constructed by directional freeze casting can significantly improve the conductivity of hydrogels by optimizing the continuity of conductive pathways and ion transport efficiency.

[0085] The above results indicate that the synergistic effect of CNT doping, directional freeze-casting process, and KCl ion enhancement is the core mechanism for achieving the high conductivity of the hydrogel of this invention.

[0086] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A hierarchically anisotropic self-healing conductive hydrogel electrode material, characterized in that, The hydrogel electrode material is prepared by using acrylamide, acrylic acid and aniline hydrochloride as ternary comonomers, polymerizing to form a polyacrylamide-polyacrylic acid-polyaniline copolymer network as a core framework, doping carbon nanotubes and combining polyaniline in the copolymer network to construct a synergistic conductive system, and then performing directional freeze casting, low-temperature polymerization and potassium chloride ion strengthening post-processing.

2. The method of claim 1, wherein the hierarchical anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: The method comprises the following steps: 1) Dissolve acrylamide monomer, aniline hydrochloride monomer, acrylic acid monomer, a reducing agent and a crosslinking agent in deionized water, stir until all components are dissolved, then add an antifreeze agent and continue to stir to obtain a clear and transparent solution A; 2) Disperse carbon nanotubes in deionized water, and grind to form a uniform and stable suspension, denoted as solution B; 3) Mix solution B and solution A in a certain proportion, stir uniformly, and then perform ultrasonic defoaming treatment to obtain a composite precursor solution which is uniformly dispersed and free of obvious bubbles; 4) Prepare an initiator aqueous solution; 5) Place the composite precursor solution in a tubular mold, add a certain amount of initiator aqueous solution, mix uniformly, then gently contact the bottom of the mold with the surface of liquid nitrogen to initiate directional rapid freezing of the solution along the axial direction of the mold, remove the mold from the surface of liquid nitrogen after the top of the solution is completely frozen, immediately transfer the mold into an environment of-30 to-20℃ and continue to freeze for 48 to 96 hours to make the system complete the free radical polymerization reaction in a low-temperature environment, thereby forming a hydrogel with a hierarchical anisotropic network structure; 6) Take out the polymerized hydrogel from the mold, immerse it in a potassium chloride aqueous solution, take it out after soaking, wash and dry to obtain a hierarchical anisotropic self-repairing hydrogel electrode material.

3. The method of claim 2, wherein the layer of the hierarchically anisotropic self-healing conductive hydrogel electrode material is prepared by the steps of: In step 1), the crosslinking agent is at least one selected from N,N'-methylene bisacrylamide, ethylene glycol bisacrylate, diethylene glycol bisacrylate and N,N'-methylene bismethylacrylamide; the reducing agent is at least one selected from ascorbic acid, sodium ascorbate, sodium metabisulfite, sodium bisulfite and sodium thiosulfate; and the antifreezing agent is at least one selected from glycerol, ethylene glycol, 1,2-propanediol, 1,3-propanediol and polyethylene glycol.

4. The method of claim 2, wherein the layer of the hierarchically anisotropic self-healing conductive hydrogel electrode material is prepared by the steps of: In step 1), the molar ratio of acrylamide, aniline hydrochloride and acrylic acid is 6 to 10:1.5 to 5:1, and the molar ratio of the crosslinking agent to the aniline hydrochloride monomer is 1:80 to 130; the amount of the reducing agent is 2.5% to 5% of the total moles of the acrylamide, aniline hydrochloride and acrylic acid ternary monomers; and the volume ratio of the antifreezing agent to deionized water is 1:8 to 10.

5. The method of claim 2, wherein the hierarchical anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: In step 2), the concentration of the carbon nanotubes in solution B is 40 to 70 mg / mL.

6. The method of claim 2, wherein the layer-by-layer anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: In step 3), the volume ratio of solution B to solution A is 1:10 to 25, and the ultrasonic treatment time is 15 to 25 min.

7. The method of claim 2, wherein the hierarchical anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: In step 4), the initiator is at least one selected from ammonium persulfate, potassium persulfate and sodium persulfate, and is preferably ammonium persulfate; and the concentration of the initiator aqueous solution is 0.70 to 0.80 g / mL.

8. The method of claim 2, wherein the hierarchical anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: In step 5), the volume ratio of the composite precursor solution to the initiator aqueous solution is 60-70:

1.

9. The method of claim 2, wherein the hierarchical anisotropically self-healing conductive hydrogel electrode material is prepared by the steps of: In step 6), the concentration of the potassium chloride aqueous solution is 0.5-1.5 mol / L, and the soaking time is 8-12 min.

10. Use of a hierarchically anisotropic self-healing conductive hydrogel electrode material according to claim 1, wherein The hydrogel electrode material is used for preparing flexible wearable electronic devices and biomedical devices.

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