Flexible hydrogel brain electrode structure, preparation method and device thereof, and brain-computer interface system

Abstract

The application discloses a flexible hydrogel brain electrode structure, a preparation method and device thereof, and a brain-computer interface system. The flexible hydrogel brain electrode structure comprises a flexible cap-shaped fitting base, a conductive hydrogel structure comprising a conductive hydrogel main body and a comb-shaped microcolumn structure, the top of the conductive hydrogel main body is combined with the bottom of the flexible cap-shaped fitting base, the comb-shaped microcolumn structure comprises a plurality of conductive hydrogel microcolumns which are vertically combined on the bottom surface of the conductive hydrogel main body and are arranged at intervals, and a water storage and controlled release structure is formed in the conductive hydrogel structure and comprises a three-dimensional interconnected micropore structure formed by a plurality of interconnected micropores, and the three-dimensional interconnected micropore structure is filled with a hydrophilic substance. The flexible hydrogel brain electrode structure can effectively penetrate hair, maintain stable low impedance contact with the scalp, has long-term moisturizing, signal stability, structure adaptability, and is matched with a high-precision and universal preparation device to realize large-scale and consistent production.

Description

Technical Field

[0001] This invention belongs to the fields of bioelectronics, brain-computer interface, or electroencephalogram (EEG) signal acquisition technology, specifically relating to a flexible hydrogel brain electrode structure, its preparation method, preparation device, and brain-computer interface system. Background Technology

[0002] Electroencephalography (EEG) electrodes are an important component of non-implantable brain-computer interface (BCI) systems, widely used in fields such as BCI, sleep monitoring, neurorehabilitation, and cognitive state assessment. Existing EEG electrodes are mainly classified into three categories: dry electrodes, wet electrodes, and semi-dry electrodes. Dry electrodes face difficulties in penetrating hair and maintaining stable contact, often resulting in high contact impedance and signal quality fluctuations, while also offering poor wearing comfort. Wet electrodes, although providing high signal quality, typically rely on conductive gel or saline solution, making operation cumbersome, prone to contamination, and prone to drying and failure of the conductive medium during prolonged use, thus failing to meet long-term monitoring requirements. Semi-dry electrodes combine the advantages of both dry and wet electrodes, but still face challenges such as high structural rigidity, difficulty in precisely controlling electrolyte release, and hair hindering full contact between the electrode and scalp.

[0003] In recent years, flexible conductive hydrogel materials have been introduced into brain electrode design due to their excellent skin-friendliness, conformability, and conductivity. However, existing hydrogel brain electrodes mostly adopt planar contact structures, which are insufficient in terms of penetrating hair and maintaining comfort; the interface size and fixing method of EEG caps from different brands are inconsistent, lacking a universal electrode design, which affects device compatibility and ease of use. On the other hand, existing electrode molding molds still have shortcomings in terms of structural precision, dimensional consistency, adaptability, and one-time molding capability, resulting in low mass production efficiency and poor product consistency of hydrogel electrodes, further limiting their commercialization and large-scale application.

[0004] In summary, the existing technologies mainly have the following technical problems: (1) The contact impedance between the brain electrode and the scalp is high and unstable, resulting in poor signal quality; (2) Hair blockage leads to insufficient effective contact area, which easily causes contact failure; (3) Hydrogel electrodes are prone to water loss and drying, and their conductivity decays rapidly over time; (4) High addition of conductive fillers leads to increased material rigidity and decreased biocompatibility; (5) The structure is uncontrollable, making it difficult to balance hair penetration, stable conductivity, and comfortable wear; (6) The brain electrode preparation process lacks standardization, making it difficult to achieve consistent mass production.

[0005] Therefore, there is an urgent need for a flexible hydrogel brain electrode structure that can effectively penetrate hair, maintain stable low-impedance contact with the scalp, and has long-lasting moisturizing and signal stability, along with a high-precision and universal preparation device to achieve large-scale and standardized production of the flexible hydrogel brain electrode structure. Summary of the Invention

[0006] The main objective of this invention is to provide a flexible hydrogel brain electrode structure, its preparation method, preparation device, and brain-computer interface system to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the present invention employs the following technical solution.

[0008] The first aspect of the present invention provides a flexible hydrogel brain electrode structure comprising: A flexible cap-shaped adhesive base is used to cooperate with the EEG acquisition cap interface and conduct electrical signals. The flexible cap-shaped adhesive base contains a flexible conductive pathway layer. A conductive hydrogel structure includes a conductive hydrogel body and a comb-shaped micropillar structure. The top of the conductive hydrogel body is bonded to the bottom of a flexible cap-shaped adhesive substrate. The comb-shaped micropillar structure includes multiple conductive hydrogel micropillars, which are vertically bonded to the bottom surface of the conductive hydrogel body and spaced apart from each other. A water-storage controlled-release structure is formed in a conductive hydrogel structure, including a three-dimensional interconnected microporous structure formed by multiple interconnected micropores, wherein the three-dimensional interconnected microporous structure is filled with an aqueous ion electrolyte system. The flexible cap-shaped adhesive substrate and the conductive hydrogel structure are both integrally molded from conductive hydrogel. The raw materials of the conductive hydrogel include 0.5~5.0 wt% natural polymer, 5.0~12.0 wt% synthetic polymer, 2~10 wt% humectant, 0.1~1 wt% electrolyte, 0.5~5 wt% crosslinking regulator, 0.05~5 wt% conductive reinforcing material, and 0.5~3 wt% antibacterial component, with the remainder being water.

[0009] A second aspect of the present invention provides a method for preparing the flexible hydrogel brain electrode structure, comprising: A hydrogel precursor solution is provided, the hydrogel precursor solution comprising 0.5-5.0 wt% natural polymer, 5.0-12.0 wt% synthetic polymer, 2-10 wt% humectant, 0.1-1 wt% electrolyte, 0.5-5 wt% crosslinking regulator, 0.05-5 wt% conductive reinforcing material, and 0.5-3 wt% antibacterial component, the remainder comprising water; The hydrogel precursor fluid is filled into a mold cavity having a shape that matches the flexible hydrogel brain electrode structure, and then pre-freezing and freeze-thaw cycles are performed to obtain the flexible hydrogel brain electrode structure. The pre-freezing includes freezing at -10℃ to -20℃ for 0.5 to 2 hours, and the freeze-thaw cycle includes freezing at -80℃ to -20℃ for 4 to 6 hours, thawing at room temperature for 3 to 4 hours, and repeating the cycle 4 to 5 times.

[0010] A third aspect of the invention provides an apparatus for fabricating the flexible hydrogel brain electrode structure, comprising a mold, the mold cavity having a shape matching the flexible hydrogel brain electrode structure, and including: The first mold cavity has a shape that matches the flexible cap-shaped substrate; The second mold cavity is connected to the first mold cavity and has a shape that matches the conductive hydrogel body; The third mold cavity is connected to the second mold cavity and has a shape that matches the comb-like micropillar structure.

[0011] A fourth aspect of the present invention provides the application of the flexible hydrogel brain electrode structure in the field of brain access ports.

[0012] A fifth aspect of the present invention provides a non-implantable brain-computer interface system, including an electroencephalogram (EEG) acquisition device, the EEG acquisition device including the flexible hydrogel brain electrode structure.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The flexible hydrogel brain electrode structure provided by the present invention significantly reduces the contact impedance between the brain electrode and the scalp and improves the signal-to-noise ratio while ensuring flexibility and wearing comfort.

[0014] (2) The flexible hydrogel brain electrode structure provided by the present invention can achieve conductivity stability and moisture retention for more than 70 hours, and has obvious advantages in water loss resistance compared with single system of the same composition.

[0015] (3) The flexible hydrogel brain electrode structure provided by the present invention, through the comb-shaped micropillar structure and the microcavity controlled release structure, avoids channel short circuit while penetrating hair and has a steady-state release capability, that is, the release rate can be maintained in a window range that is conducive to the infiltration of the stratum corneum but does not cause short circuit.

[0016] (4) The conductive enhancement material doped in the flexible hydrogel brain electrode structure provided by the present invention is a nanomaterial. Through low doping, a connected electronic / ionic dual conduction pathway is formed, thereby improving conductivity and flexibility at the same time with a nanomaterial dosage far lower than that of traditional conductive paste, and reducing biocompatibility risk.

[0017] (5) The flexible hydrogel brain electrode structure provided by the present invention takes into account structural adaptability, wearing comfort, high-fidelity signal transmission and long-term stability, and can be used for long-term brain signal acquisition in fields such as medical diagnosis, rehabilitation training, sleep monitoring, and driving fatigue detection. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a modular precision mold according to one embodiment of the present invention; Figure 2 This is a physical diagram of a flexible hydrogel brain electrode structure according to one embodiment of the present invention; Figure 3 This is a microstructure morphology diagram of the flexible hydrogel brain electrode of Embodiment 1 of the present invention at 50 μm. Figure 4 This is a microstructure morphology diagram of the flexible hydrogel brain electrode of Embodiment 1 of the present invention at 20 μm. Figure 5 This is a microstructure morphology diagram of the flexible hydrogel brain electrode of Comparative Example 1 of the present invention at 100 μm. Figure 6 This is a microstructure morphology diagram of the flexible hydrogel brain electrode of Comparative Example 1 of the present invention at 20 μm. Figure 7 This is a tensile stress-strain curve of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 8 This is a tensile stress-strain curve of the flexible hydrogel brain electrode of Comparative Example 1 of the present invention. Figure 9 This is the electrochemical impedance Nyquist plot of the flexible hydrogel brain electrode of Example 1 of the present invention; Figure 10 This is the electrochemical impedance spectroscopy (EI) Bode plot of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 11 This is the electrochemical impedance Nyquist plot of the flexible hydrogel brain electrode of Comparative Example 1 of the present invention. Figure 12 This is the electrochemical impedance spectroscopy (EIS) Bode plot of the flexible hydrogel brain electrode of Comparative Example 1 of the present invention. Figure 13 This is a diagram of the square wave-sine wave signal transmission waveform of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 14 This is a sinusoidal-square wave signal transmission waveform of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 15 These are antibacterial experimental diagrams of the flexible hydrogel brain electrodes of Example 6 and Comparative Example 6 of the present invention. Figure 16This is a cellular biosafety diagram of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 17 This is a signal acquisition diagram of the flexible hydrogel brain electrode of Embodiment 1 of the present invention; Figure 18 This is a magnified view of the local electroencephalogram (EEG) signal of the flexible hydrogel brain electrode of Embodiment 1 of the present invention. Detailed Implementation

[0020] In view of the problems existing in the above-mentioned prior art, after in-depth research, a flexible hydrogel brain electrode structure, its preparation method, preparation device and brain-computer interface system are provided.

[0021] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0022] The first aspect of the present invention provides a flexible hydrogel brain electrode structure comprising: A flexible cap-shaped adhesive base is used to cooperate with the EEG acquisition cap interface and conduct electrical signals. The flexible cap-shaped adhesive base contains a flexible conductive pathway layer. A conductive hydrogel structure includes a conductive hydrogel body and a comb-shaped micropillar structure. The top of the conductive hydrogel body is bonded to the bottom of a flexible cap-shaped adhesive substrate. The comb-shaped micropillar structure includes multiple conductive hydrogel micropillars, which are vertically bonded to the bottom surface of the conductive hydrogel body and spaced apart from each other. A water-storage controlled-release structure is formed in a conductive hydrogel structure, including a three-dimensional interconnected microporous structure formed by multiple interconnected micropores, wherein the three-dimensional interconnected microporous structure is filled with an aqueous ion electrolyte system. The flexible cap-shaped adhesive substrate and the conductive hydrogel structure are both integrally molded from conductive hydrogel. The raw materials of the conductive hydrogel include 0.5~5.0 wt% natural polymer, 5.0~12.0 wt% synthetic polymer, 2~10 wt% humectant, 0.1~1 wt% electrolyte, 0.5~5 wt% crosslinking regulator, 0.05~5 wt% conductive reinforcing material, and 0.5~3 wt% antibacterial component, with the remainder being water.

[0023] In this invention, the aqueous ionic electrolyte system uses purified water as the dispersion medium and contains basic conductive electrolytes sodium chloride and potassium chloride, providing a large amount of free Na+. + K +This improves the ionic conductivity of the hydrogel, reduces the electrode-scalp interface impedance, and ensures efficient transmission of EEG signals. The water-storage controlled-release structure forms a stable porous framework through freeze-thaw cycles and freeze-drying, and the pore size is further controlled by a cross-linking regulator. The water-storage controlled-release structure is a three-dimensional framework of the hydrogel phase network structure, which has a water-storage capacity similar to a sponge and is a porous structure.

[0024] In some embodiments, the natural polymer includes one or more combinations of sodium alginate, gelatin, and chitosan, but is not limited thereto.

[0025] In some embodiments, the synthetic polymer includes, but is not limited to, one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS).

[0026] In some embodiments, the moisturizer includes glycerin and sodium pyrrolidone carboxylate.

[0027] In some implementations, the electrolyte includes NaCl and KCl.

[0028] In some embodiments, the crosslinking regulator includes CaCl2 and FeCl3.

[0029] In some embodiments, the conductive enhancement material includes MXene and silver nanowires.

[0030] In some embodiments, the antibacterial component includes chitosan quaternary ammonium salt or ε-polylysine.

[0031] In some implementations, the pore size of the micropores is 10~80μm.

[0032] In some implementations, the pore volume of the three-dimensional interconnected microporous structure accounts for 50-70% of the total volume of the conductive hydrogel structure.

[0033] In some embodiments, the comb-like micropillar structure comprises 4 to 16 conductive hydrogel micropillars.

[0034] In some embodiments, the conductive hydrogel micropillars are biomimetic structures with a gradually changing diameter. The diameter of the top end adjacent to the bottom surface of the conductive hydrogel body is 0.5~2 mm, the diameter of the bottom end is 1~4 mm, the height is 3–8 mm, and the spacing between adjacent conductive hydrogel micropillars is 0.5~1.5 mm.

[0035] In some embodiments, the conductive hydrogel body and the comb-like micropillar structure are integrally formed.

[0036] In some embodiments, the flexible cap-shaped bonding substrate is formed of conductive hydrogel and is integrally disposed with the conductive hydrogel structure.

[0037] In some embodiments, the diameter of the flexible cap-shaped adhesive substrate is 8-12 mm and the height is 1.5-2.5 mm.

[0038] In some embodiments, the conductive hydrogel body has a diameter of 5-15 mm and a height of 8-12 mm.

[0039] In some embodiments, the natural polymer comprises 1.0–3.0 wt% sodium alginate, 2.0–4.0 wt% gelatin, and 0–2 wt% chitosan. The sodium alginate forms an ionic cross-linked porous network, serving as a reservoir phase; the gelatin improves biocompatibility and adhesion, and enhances interfacial wetting; and the chitosan improves adhesion and antibacterial properties.

[0040] In some embodiments, the synthetic polymer comprises 6-10 wt% polyvinyl alcohol, 0-3 wt% polyvinylpyrrolidone, 0-2 wt% polyethylene glycol, and 0.5-1.5 wt% poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The polyvinyl alcohol forms a physically cross-linked backbone, controlling elasticity and resilience; if the mass fraction is too low, mechanical properties are weakened, while if the mass fraction is too high, rigidity increases, causing scalp discomfort. PEDOT:PSS provides a continuous ionic-electronic conductive phase, and the polyvinylpyrrolidone and polyethylene glycol can modulate viscosity / pore formation.

[0041] In some embodiments, the crosslinking regulator comprises 0.5–5 wt% CaCl2 and 0.05–2 wt% FeCl3. The FeCl3 can form metal coordination sites, improving the adhesion and viscoelasticity of the flexible hydrogel. The CaCl2 can induce the formation of a porous framework from the sodium alginate network. That is, Ca²⁺ + With Fe³ + In synergy, it forms an "ionic crosslinking-coordination crosslinking" dual network with sodium alginate and polyvinyl alcohol / gelatin / chitosan, respectively, which improves the porosity, adhesion, water loss resistance and viscoelastic recovery of the flexible hydrogel electrode.

[0042] In this invention, the humectant reduces evaporation and improves wearing comfort. The electrolyte provides electrolytes and regulates permeability. The conductive reinforcing material is a nanomaterial that can form electronic pathways and maintain the flexibility of the flexible hydrogel. In this invention, the conductive reinforcing material can form electronic conduction paths even with extremely low doping levels. Through synergy with the PEDOT:PSS ion-conducting network, it establishes a low-impedance conduction system with ion-electron coupling, thereby improving the signal-to-noise ratio of the EEG signal while maintaining flexibility.

[0043] Furthermore, the mass ratio of glycerol to sodium pyrrolidone carboxylate is 1 to 3:1.

[0044] Furthermore, the mass ratio of NaCl to KCl is 2~4:1.

[0045] Furthermore, the mass ratio of MXene to silver nanowires is 1:1 to 3:1.

[0046] Furthermore, the silver nanowires have a length of 50~200μm and a diameter of 50~100nm.

[0047] Furthermore, after continuous use at room temperature for 12 hours, the contact resistance of the flexible hydrogel brain electrode structure increases by ≤20%, and the antibacterial rate against Escherichia coli and Staphylococcus aureus is ≥90%.

[0048] A second aspect of the present invention provides a method for preparing the flexible hydrogel brain electrode structure, comprising: A hydrogel precursor solution is provided, the hydrogel precursor solution comprising 0.5-5.0 wt% natural polymer, 5.0-12.0 wt% synthetic polymer, 2-10 wt% humectant, 0.1-1 wt% electrolyte, 0.5-5 wt% crosslinking regulator, 0.05-5 wt% conductive reinforcing material, and 0.5-3 wt% antibacterial component, the remainder comprising water; The hydrogel precursor fluid is filled into a mold cavity having a shape that matches the flexible hydrogel brain electrode structure, and then pre-freezing and freeze-thaw cycles are performed to obtain the flexible hydrogel brain electrode structure. The pre-freezing includes freezing at -10℃ to -20℃ for 0.5 to 2 hours, and the freeze-thaw cycle includes freezing at -80℃ to -20℃ for 4 to 6 hours, thawing at room temperature for 3 to 4 hours, and repeating the cycle 4 to 5 times.

[0049] In some embodiments, the method for preparing the flexible hydrogel brain electrode structure specifically includes: The natural polymer is completely dissolved in deionized water to form a first mixed solution; The synthetic polymer, moisturizer, and electrolyte are added sequentially to deionized water and mixed evenly at 70-100°C. The mixture is then cooled to room temperature, and the conductive reinforcing material and antibacterial component are added. After ultrasonic dispersion, a second mixed solution is formed. The first and second mixed solutions are mixed, the crosslinking regulator is added, and the mixture is magnetically stirred and degassed under vacuum to obtain the hydrogel precursor solution.

[0050] In some embodiments, the preparation method of the flexible hydrogel brain electrode structure specifically includes: before filling the mold cavity with the hydrogel precursor liquid, providing a mold for plasma treatment for 30~60s, wherein the surface contact angle of the mold cavity is ≤15°, at least to improve the wettability of the hydrogel precursor liquid.

[0051] In some embodiments, the preparation method of the flexible hydrogel brain electrode structure specifically includes a post-processing stage: immersing the molded product after the freeze-thaw cycle in a sodium chloride solution containing 3-5 wt% glycerol for 2-4 hours, followed by surface modification and ultraviolet ozone treatment for 10-15 minutes to obtain the flexible hydrogel brain electrode structure. In the above steps, immersing the flexible hydrogel brain electrode structure in a moisturizing solution can replenish the initial water content of the flexible hydrogel brain electrode structure to 80-85 wt%, enhancing its initial conductivity.

[0052] Furthermore, the ultrasonic dispersion power is 50~400W, the frequency is 20~100kHz, and the time is 20~30min. After ultrasonic dispersion, it can be ensured that the conductive reinforcing material is uniformly dispersed without agglomerated particles with a particle size ≥5μm.

[0053] Furthermore, the magnetic stirring time is 15-20 minutes, and the vacuum degassing time is 5-10 minutes.

[0054] In this invention, the pre-freezing allows for control of the pore size distribution of the three-dimensional interconnected micropores.

[0055] Specifically, in this invention, the specific mechanisms of each substance are as follows: (1) Fe³ + As a trivalent cation, it can form polydentate coordination bonds with PVA, carboxylated polysaccharides (such as partially modified alginate), and protein groups. These coordination bonds act as additional cross-linking points under static conditions, reducing chain slippage and improving viscosity and adhesion. Under dynamic stress (wearing, friction), the coordination bonds can undergo reversible breakage and recombination, thus exhibiting excellent viscoelastic recovery, which is beneficial for maintaining a proper fit during prolonged wear. + Linear ionic cross-linking is formed between the alginate and the alginate chain, resulting in a stable porous framework. The pore size distribution can be adjusted by controlling the degree of cross-linking, thereby controlling the wetting rate and the water / electrolyte release rate. Fe³ + With Ca² + Both participate simultaneously, working synergistically to achieve a superior combination of adhesion / water storage / mechanical properties compared to single metal ions, enhancing adhesion, water loss tolerance, and ion conduction stability.

[0056] (2) The crystalline region of PVA grows during repeated cold and thaw cycles, forming a strong network of physical cross-links, which significantly improves the elastic modulus and compressive recovery ability of the gel; natural polysaccharides form a hydrophilic porous network; the two are separated by induced phase to obtain a two-phase structure of "high-strength skeleton + high-porosity liquid reservoir phase", which takes into account both strength and porosity, ensuring mechanical rebound and providing controllable pore size for steady-state release.

[0057] (3) Under the premise of ensuring flexibility, the conductive reinforcement material forms an electronic conduction path, which works in conjunction with the PEDOT:PSS plasma conductive network to generate a low impedance conduction path of ion-electron coupling, significantly reducing contact impedance without sacrificing flexibility, improving conductivity and suppressing the rigidity side effect brought by nanomaterials.

[0058] (4) Evaporation inhibition and osmotic regulation of humectant (glycerin) and electrolyte: Humectant reduces evaporation rate by forming a strong hydrogen bond network with water while maintaining gel flexibility; electrolyte increases local osmotic pressure and promotes electrolyte migration at the interface between the stratum corneum and the electrode, thereby achieving sufficient stratum corneum hydration and low impedance window duration at a low total water content.

[0059] (5) The Fe³ + With Ca² + The dual-ion crosslinking system and multiple polymer networks work synergistically to form a composite ion-electron conductive structure; after freeze-induced phase separation, the internal pore size of the hydrogel is distributed in the range of 10~80 μm, thus constructing a steady-state water storage and controlled release network.

[0060] Therefore, through the synergistic effect of the above mechanisms, the flexible hydrogel brain electrode structure provided by the present invention can effectively penetrate hair, maintain stable low-impedance contact with the scalp, and has long-lasting moisturizing and signal stability.

[0061] Furthermore, the non-implantable brain-computer interface system provided by this invention specifically includes: (1) Bionic hierarchical structure design The conductive hydrogel adopts a hierarchical configuration of "conductive hydrogel body - comb-shaped micropillar structure": the conductive hydrogel body provides structural support and water storage; the comb-shaped micropillar structure is a biomimetic structure with a gradually changing diameter (sharp at the top and thick at the bottom), which can effectively part the hair and form multi-point contact with the scalp. The number of micropillars (4~16) and the spacing (0.8~1.5mm) are optimized according to the human scalp hair density (approximately 100~300 hairs / cm²) to ensure stable contact when not shaving.

[0062] (2) Dual-network conductive hydrogel system This invention employs a dual-network design combining physical cross-linking of natural polymers and chemical cross-linking of synthetic polymers. The natural network provides biocompatibility, moisture retention, and ion conductivity pathways; the synthetic network enhances mechanical strength and electronic conductivity; Ca²⁺…+ It forms an ionic cross-linking network with sodium alginate, Fe³ + It forms coordination crosslinks with polymer chain segments to achieve a balance between mechanical strength and adhesion; the conductive reinforcing material forms a "electronic conductivity-ionic conductivity" synergistic pathway, which significantly reduces contact resistance (≤500Ω).

[0063] (3) Intelligent water storage and controlled release mechanism The three-dimensional interconnected microporous structure is formed through a gradient freeze-thaw process, with the pores filled with a complex system of glycerin-pyrrolidone sodium carboxylate moisturizer and electrolyte. This structure achieves "initial rapid wetting followed by long-lasting slow release," releasing moisture to wet the scalp stratum corneum and establish ion channels in the initial stage, and then slowly releasing water through hydrogen bonding of hydrophilic substances to ensure a moisturizing effect of ≥70 hours.

[0064] (4) Modular precision manufacturing device The mold consists of a first sub-mold, a second sub-mold, and a base. The comb-shaped micropillars of the second sub-mold are replaceable modules to adapt to the hair characteristics of different groups of people. It integrates vacuum infusion and programmed temperature control units to achieve high-precision electrode production (dimensional error ≤0.05mm) and large-scale production.

[0065] Therefore, this invention constructs a high-performance, non-implantable, flexible hydrogel brain electrode system through the synergistic design of structural biomimicry, material composites, and device innovation.

[0066] The third aspect of the present invention provides an apparatus for fabricating the flexible hydrogel brain electrode structure, comprising a mold, wherein the mold cavity has a shape matching the flexible hydrogel brain electrode structure, and includes: The first mold cavity has a shape that matches the flexible cap-shaped fitting base; The second mold cavity is connected to the first mold cavity and has a shape that matches the conductive hydrogel body; The third mold cavity is connected to the second mold cavity and has a shape that matches the comb-like micropillar structure.

[0067] In some embodiments, the mold includes a first sub-mold and a second sub-mold, the first mold cavity and the second mold cavity being disposed within the first sub-mold, and the third mold cavity being disposed within the second sub-mold, the third mold cavity including a plurality of cylindrical channels formed within the second sub-mold.

[0068] Furthermore, a groove is formed on one side surface of the first sub-mold that can be interference-fitted with the second sub-mold. When the second sub-mold is inserted into the groove, the third mold cavity communicates with the first mold cavity and the second mold cavity and cooperates to form the mold cavity of the mold.

[0069] Furthermore, a positioning groove symmetrically distributed on both sides of the slot is also provided on one side surface of the first sub-mold.

[0070] Furthermore, a micro vent is provided at the bottom of the first mold cavity, which penetrates the first sub-mold to connect the first mold cavity with the outside. The diameter of the micro vent is 0.1~0.5mm.

[0071] Furthermore, the material of the mold includes at least one of medical-grade polylactic acid, medical-grade polycarbonate, and medical-grade silicone, but is not limited to these.

[0072] In a typical embodiment of the present invention, a schematic diagram of the flexible hydrogel brain electrode structure is shown below. Figure 1 As shown, the first sub-mold (part 1) is rectangular in shape, with a first mold cavity at the top that matches the flexible cap-shaped base, and a molding groove with a concave-convex interlocking structure at the bottom of the first mold cavity; The second sub-mold (component 2) consists of multiple detachable parts, including a flexible cap-shaped substrate molding part, a conductive hydrogel main body molding part, and a comb-shaped micro-pillar molding part. Each part is precisely matched by positioning pins to form a second mold cavity that matches the structure of the conductive hydrogel. The second sub-mold also includes a mold base (component 3), which has the third mold cavity, including multiple cylindrical channels formed in the second sub-mold; the three are precisely assembled through interference fit and positioning groove, with a fit error ≤0.05mm.

[0073] The mold is also equipped with a micro vent and a vacuum injection interface to ensure that no air bubbles remain during the injection of the precursor fluid.

[0074] A fourth aspect of the present invention provides the application of the flexible hydrogel brain electrode structure in the field of brain access ports.

[0075] A fifth aspect of the present invention provides a non-implantable brain-computer interface system, including brain electrodes, the brain electrodes including the flexible hydrogel brain electrode structure.

[0076] In summary, this invention, through the synergistic design of the material system (natural and synthetic polymers + bimetallic ion coordination + conductive reinforcing materials + moisturizers + antibacterial components) and structural process (comb-shaped micropillars + microporous structure + one-time molding), enables the flexible hydrogel brain electrode structure to effectively penetrate hair, maintain stable low-impedance contact with the scalp, and possess long-lasting moisturizing, signal stability, and structural adaptability. Furthermore, the accompanying high-precision, universal molding mold enables large-scale, standardized production.

[0077] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should all be covered within the protection scope of this invention.

[0078] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0079] For example, the specifications of each raw material in the embodiments and comparative examples of this invention are shown in Table 1: Table 1. Specifications of raw materials in the examples and comparative examples.

[0080] Mold Design and Printing A mold suitable for molding flexible hydrogel brain electrodes with comb-like micropillar structures: (1) Mold design The mold structure was designed using SolidWorks 3D modeling software. The mold includes a top cap-shaped cavity and a bottom comb-shaped cylindrical channel. The diameter and height of the top cap-shaped cavity, as well as the number, diameter, height, and center distance of the bottom comb-shaped cylindrical channels, were designed according to the requirements of the flexible hydrogel brain electrode structure.

[0081] The cap-shaped cavity and the comb-shaped cylindrical channel are connected by an interference fit. The bottom of the cap-shaped cavity is provided with a micro vent hole with a diameter of 0.3 mm to prevent air bubbles from being trapped during the glue injection process.

[0082] The mold shell is equipped with symmetrical positioning grooves to ensure precise assembly of the mold after 3D printing or injection molding.

[0083] (2) Mold printing The upper and lower parts of the mold were prepared using medical-grade polylactic acid (PLA) filament and an FDM 3D printer (layer thickness 0.1 mm, infill density 100%, printing temperature 210 ℃).

[0084] After printing, the product is initially disinfected by soaking in 75% ethanol for 30 minutes, and residual dust is removed in an ultrasonic cleaner.

[0085] After the final mold assembly, the dimensional accuracy is checked using mechanical measuring tools (vernier calipers, accuracy 0.02 mm), and the deviation does not exceed ±0.05 mm.

[0086] Example 1 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, as detailed below: (1) Material proportions: Natural polymers: Sodium alginate (SA) 2 wt%, Gelatin 3 wt%; Synthetic polymer: Polyvinyl alcohol (PVA) 8 wt%, PEDOT:PSS 1 wt%; Crosslinking regulator: 0.8 wt% calcium chloride (CaCl2), 0.1 wt% ferric chloride (FeCl3·6H2O); Moisturizer: 1 wt% glycerin, 1 wt% sodium pyrrolidone carboxylate, with a mass ratio of 1:1 between glycerin and sodium pyrrolidone carboxylate; Electrolytes: NaCl 0.5 wt%, KCl 0.5 wt%, with a mass ratio of NaCl to KCl of 1:1; Conductive enhancement material: 0.5wt% silver nanowires + 0.5wt% MXene (composite system); Antibacterial component: 1.0 wt% chitosan quaternary ammonium salt; The remainder is deionized water.

[0087] (2) Preparation process of hydrogel precursor solution: A. Sodium alginate and gelatin are added to deionized water and stirred at 55°C for 30 minutes until dissolved to obtain aqueous phase A.

[0088] B. Polyvinyl alcohol, poly(3,4-ethylenedioxythiophene): polystyrene sulfonate, glycerol, NaCl were added to deionized water and stirred at 75°C for 40 min. After cooling, silver nanowires, MXene, and chitosan quaternary ammonium salt were added and ultrasonically dispersed at 250 W for 25 min to obtain aqueous phase B.

[0089] C. Mix aqueous phases A and B, add CaCl2 and FeCl3, stir magnetically for 18 min, and degas under vacuum for 8 min to obtain hydrogel precursor solution.

[0090] (3) One-piece molding of mold (e.g.) Figure 1 (As shown) S1. Mold assembly: The first sub-mold and the second sub-mold (5 comb-shaped micro-pillars, 2mm in diameter, 5mm in height, and 1mm in spacing) are assembled with the base; S2. Vacuum infusion: Precursor fluid is injected into the plasma treatment mold at a pressure of -0.07MPa; S3. Freeze-thaw cycle: Pre-cool at -20℃ for 1 hour, freeze at -80℃ for 5 hours, thaw at room temperature for 3.5 hours, repeat 4 times; S4. Post-treatment: Immerse in 4wt% glycerol-sodium chloride solution for 3 hours, then treat with ultraviolet ozone for 12 minutes. After demolding, a flexible hydrogel brain electrode with a comb-like micropillar structure is obtained. Its structural diagram is shown below. Figure 2 As shown.

[0091] In the flexible hydrogel brain electrode structure prepared in this embodiment, the diameter of the flexible cap-shaped bonding substrate is approximately 5 mm and the height is approximately 1 mm. The conductive hydrogel body has a diameter of approximately 10 mm and a height of approximately 5 mm. The comb-shaped micropillar structure consists of 5 pillars, each with a top diameter of approximately 2 mm, a bottom diameter of approximately 1 mm, and a height of approximately 5 mm.

[0092] Comparative Example 1 The method for preparing a flexible hydrogel brain electrode structure provided in this comparative example differs from that in Example 1 only in that: (1) Material proportions: Conductive enhancement material: 1.0 wt% silver nanowires (without MXene), the rest is the same as in Example 1.

[0093] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0094] (3) One-piece molding The molding process is the same as that in Example 1.

[0095] Example 2 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Water storage controlled-release regulator: CaCl2 0.6wt% + FeCl3 0.3wt% (bimetallic ion synergy), the rest is the same as in Example 1.

[0096] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0097] (3) One-piece molding The molding process is the same as that in Example 1.

[0098] Comparative Example 2 The method for preparing a flexible hydrogel brain electrode structure provided in this comparative example differs from that in Example 2 only in that: (1) Material proportions: Water storage controlled-release regulator: CaCl2 0.9wt% (no FeCl3), the rest is the same as in Example 2.

[0099] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 2.

[0100] (3) One-piece molding The molding process is the same as that in Example 2.

[0101] Example 3 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Moisturizer: 3.0 wt% glycerin + 2.0 wt% sodium pyrrolidone carboxylate (compound system), the rest is the same as in Example 1.

[0102] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0103] (3) One-piece molding The molding process is the same as that in Example 1.

[0104] Comparative Example 3 The method for preparing a flexible hydrogel brain electrode structure provided in this comparative example differs from that in Example 3 only in that: (1) Material proportions: Moisturizer: 5.0 wt% glycerin (without hyaluronic acid), the rest is the same as in Example 3.

[0105] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 3.

[0106] (3) One-piece molding The molding process is the same as that in Example 3.

[0107] Example 4 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Consistent with Example 1.

[0108] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0109] (3) One-piece molding S1. Same as step S1 in Example 1.

[0110] S2. Same as step S2 in Example 1.

[0111] S3. The freeze-thaw cycle was used (pre-cooling at -20°C for 1 hour, freezing at -80°C for 5 hours, thawing at room temperature for 3.5 hours, and repeating 4 times), and the rest was the same as in Example 1.

[0112] S4. Same as step S4 in Example 1.

[0113] Comparative Example 4 This comparative example provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Example 4 in that: (1) Material proportions: Consistent with Example 4.

[0114] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 4.

[0115] (3) One-piece molding S1. Same as step S1 in Example 4.

[0116] S2. Same as step S2 in Example 4.

[0117] S3. The freeze-thaw cycle was used (pre-cooling at -20°C for 1 hour, freezing at -40°C for 5 hours, thawing at room temperature for 3.5 hours, and repeating 4 times), and the rest was the same as in Example 4.

[0118] S4. Same as step S4 in Example 4.

[0119] Example 5 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Consistent with Example 1.

[0120] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0121] (3) One-piece molding S1. Same as step S1 in Example 1, except that the mold specifications are: the comb-shaped micropillar molding part has 10 channels (diameter 0.5 mm, height 5 mm, spacing 0.5 mm), and the rest is the same as in Example 1.

[0122] S2. Same as step S2 in Example 1.

[0123] S3. Same as step S3 in Example 1.

[0124] S4. Same as step S4 in Example 1.

[0125] Comparative Example 5 This comparative example provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Example 1 in that: (1) Material proportions: Consistent with Example 5.

[0126] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 5.

[0127] (3) One-piece molding S1. Same as step S1 in Example 5, the mold specifications are: the comb-shaped micro-pillar molding part has 3 channels (diameter 2mm, height 5mm, spacing 2mm), the rest is the same as in Example 5.

[0128] S2. Same as step S2 in Example 5.

[0129] S3. Same as step S3 in Example 5.

[0130] S4. Same as step S4 in Example 5.

[0131] Example 6 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Antibacterial component: 1.2 wt% chitosan quaternary ammonium salt, the rest is the same as in Example 1.

[0132] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0133] (3) One-piece molding The molding process is the same as that in Example 1.

[0134] Comparative Example 6 This comparative example provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Example 6 in that: (1) Material proportions: No chitosan quaternary ammonium salt was used; otherwise, it was the same as in Example 6.

[0135] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 6.

[0136] (3) One-piece molding The molding process is the same as that in Example 6.

[0137] Example 7 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Synthetic polymer: 10.0 wt% polyvinyl alcohol, 1.5 wt% poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, the remainder being the same as in Example 1.

[0138] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0139] (3) One-piece molding The molding process is the same as that in Example 1.

[0140] Comparative Example 7 This comparative example provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Example 7 in that: (1) Material proportions: Synthetic polymer: 5.0 wt% polyvinyl alcohol, 0.5 wt% poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, the remainder being the same as in Example 7.

[0141] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 7.

[0142] (3) One-piece molding The molding process is the same as that in Example 7.

[0143] Example 8 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Electrolytes: NaCl 0.5wt% and KCl 0.5wt%, the rest are the same as in Example 1.

[0144] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0145] (3) One-piece molding The molding process is the same as that in Example 1.

[0146] Comparative Example 8 This comparative example provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Example 8 in that: (1) Material proportions: Electrolyte: NaCl 0.5wt%, the rest is the same as in Example 8.

[0147] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 8.

[0148] (3) One-piece molding The molding process is the same as that in Example 8.

[0149] Example 9 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Natural polymers: Sodium alginate (SA) 1 wt%, gelatin 2 wt%, chitosan 2 wt%; Synthetic polymers: Polyvinyl alcohol (PVA) 6 wt%, polyvinylpyrrolidone 1 wt%, polyethylene glycol 1 wt%, PEDOT:PSS 0.5 wt%; Crosslinking regulator: Calcium chloride (CaCl2) 5 wt%, Ferric chloride (FeCl3·6H2O) 2 wt%; Moisturizer: 6 wt% glycerin, 4 wt% sodium pyrrolidone carboxylate, with a mass ratio of glycerin to sodium pyrrolidone carboxylate of 2:1; Electrolytes: NaCl 0.6 wt%, KCl 0.3 wt%, with a NaCl to KCl mass ratio of 2:1; Conductive enhancement material: 2.5wt% silver nanowires + 2.5wt% MXene (composite system); Antibacterial component: 0.5 wt% chitosan quaternary ammonium salt; The remainder is deionized water.

[0150] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0151] (3) One-piece molding The molding process is the same as that in Example 1.

[0152] Example 10 This embodiment provides a flexible hydrogel brain electrode structure and its preparation method, which differs from Embodiment 1 in that: (1) Material proportions: Natural polymers: Sodium alginate (SA) 3 wt%, gelatin 4 wt%, chitosan 0.5 wt%; Synthetic polymers: Polyvinyl alcohol (PVA) 10 wt%, polyvinylpyrrolidone 3 wt%, polyethylene glycol 2 wt%, PEDOT:PSS 1.5 wt%; Crosslinking regulator: 0.5 wt% calcium chloride (CaCl2), 0.05 wt% ferric chloride (FeCl3·6H2O); Moisturizer: 3 wt% glycerin, 1 wt% sodium pyrrolidone carboxylate, with a mass ratio of 3:1 for glycerin to sodium pyrrolidone carboxylate; Electrolytes: NaCl 0.8 wt%, KCl 0.2 wt%, with a NaCl to KCl mass ratio of 4:1; Conductive enhancement material: 0.05wt% silver nanowires + 0.05wt% MXene (composite system); Antibacterial component: ε-polylysine 3wt%; The remainder is deionized water.

[0153] (2) Preparation process of hydrogel precursor solution: The preparation process of the hydrogel precursor solution is the same as in Example 1.

[0154] (3) One-piece molding The molding process is the same as that in Example 1.

[0155] Performance testing The flexible hydrogel brain electrode structures prepared in Examples 1-10 and Comparative Examples 1-9 were subjected to contact impedance testing, moisturizing performance testing, mechanical performance testing, and EEG signal acquisition verification, respectively. The specific test methods are as follows, and the test results are shown in Table 2.

[0156] (1) Hydrogel electrode impedance test: Instrumentation: Electrochemical workstation (e.g., CHI660E), artificial scalp model (simulating the stratum corneum of the scalp, impedance ≈ 10kΩ) cm), standard EEG cap (compatible with electrode cap type substrate), constant temperature and humidity chamber (25℃±2℃, 50% RH±5%).

[0157] Sample preparation: The conductive working area of ​​the hydrogel electrode (8 mm in diameter, with a contact area with the scalp of ≈50 mm²) was cut, and 3 sets of parallel samples (n=3) were prepared according to the hydrogel brain electrode.

[0158] Test procedure: The surface of the artificial scalp model was coated with an equivalent sebum film (0.9% NaCl solution + 0.5% glycerin, simulating scalp secretions). The sample was then fixed on the EEG cap to fit the artificial scalp, and a contact pressure of 0.5 kPa (simulating wearing pressure) was applied. The electrochemical workstation was set to a frequency range of 0.1 Hz to 10 kHz and an AC amplitude of 10 mV, and the test was conducted at an open circuit potential.

[0159] (2) Antibacterial performance test: Instruments and equipment: Biosafety cabinet (level II), constant temperature incubator (37℃±1℃), colony counter, sterile operating table, pipette (100μL / 1mL), petri dish (90mm).

[0160] Test strains and reagents: The test strains were Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC29213). The culture medium used was LB nutrient agar medium and sterile physiological saline (0.9% NaCl).

[0161] Sample preparation: The hydrogel samples were 10 mm in diameter and 2 mm thick, and sterilized with UV light for 30 min. The positive control sample was a hydrogel containing 0.1% benzalkonium chloride, and the negative control sample was a blank hydrogel without antibacterial components.

[0162] Test steps: S1. Strain activation: Inoculate the frozen strain into LB medium, incubate at 37°C for 18 hours, and then dilute to a bacterial concentration of 1×10⁻⁶. 6 CFU / mL; S2. Sample preparation: Place the sample in a petri dish, add 100 μL of bacterial solution, spread it evenly on the sample surface, and let it stand at 37°C for 2 hours (contact stage). S3, Elution Count: Elute the bacteria on the sample surface with 10 mL of sterile physiological saline, serially dilute to 1 × 10³ CFU / mL, and take 100 μL to plate. S4. Culture and count: Incubate at 37℃ for 24 hours and count the number of colonies (CFU). S5. Calculate the antibacterial rate: The rate is calculated using the formula (1 - number of colonies in the sample group / number of colonies in the negative control group) × 100%.

[0163] (3) Biocompatibility test: Instruments and reagents: L929 mouse fibroblasts were used as cells, and MTT assay kit, DMEM medium, fetal bovine serum and trypsin were used as reagents. Microplate reader (490nm) and CO2 incubator (5% CO2, 37℃) were used as instruments.

[0164] Test steps: S1. Preparation of sample extract: Add hydrogel sample (0.1g / mL) to DMEM medium, extract at 37℃ for 24h, and then filter and sterilize. S2, Cell seeding: Seed 1×10⁶ cells per well in a 96-well plate. 4 One L929 mouse fibroblast was cultured for 24 hours. S3. Extraction solution treatment: Discard the culture medium and add different concentrations of extraction solution (25%, 50%, 100%), with 6 replicates per group. Blank culture medium is used as a control. S4. Culture and staining: Incubate at 37℃ for 48 h, add 20 μL MTT solution (5 mg / mL), and continue incubation for 4 h; S5. Discard the supernatant, add 150 μL DMSO, shake for 10 min, and measure the absorbance (OD value) at 490 nm using a microplate reader. S6. Calculate cell viability: Use the formula (OD value of sample group / OD value of control group) × 100%.

[0165] (4) Conductivity test: Instrumentation: Four-probe resistivity meter (e.g., RTS-9, range 10) -4 ~10¹²Ω cm), vernier calipers, and constant temperature and humidity chamber (25℃±2℃, 50% RH±5%).

[0166] Sample preparation: The hydrogel was used to make square samples (20mm×20mm×2mm), with 3 parallel samples per group (n=3), and tested after equilibration for 24 hours.

[0167] Test steps: S1. Measure the sample thickness (d) and side length (a) and record the data; S2. Place the sample on the probe stage of the four-probe tester, ensuring that the probes are in close contact with the sample surface (pressure 0.1 kPa). S3. Set the test current to 1mA (to avoid Joule thermal damage to the sample), and record the volume resistivity (ρ, in Ω). ), calculate conductivity (σ): σ = 1 / ρ (unit: S cm), cm - ¹); Repeat the test 3 times and take the average value.

[0168] (5) Signal input / output performance test: Instruments and equipment: The function signal generator (Keysight 33522B) has a frequency accuracy of ±0.01%, an amplitude range of 0-10Vpp, and supports sine wave / square wave output; Digital oscilloscope (Tektronix MDO3024) with a bandwidth ≥200MHz, sampling rate ≥2GS / s, 4 channels (synchronous acquisition of input / output signals); conductive electrode clamps (copper material, gold-plated surface to prevent oxidation): clamp spacing adjustable, contact pressure 0.2kPa (simulating wearing contact); Constant temperature and humidity chamber (25℃±2℃, 50% RH±5%): to control environmental interference; Vernier calipers (accuracy 0.02mm): used to measure sample dimensions.

[0169] Sample preparation: The hydrogel sample was made into a cuboid transport specimen (20 mm in length, 10 mm in width, and 2 mm in thickness), ensuring that both ends were flat (roughness Ra ≤ 1 μm), and then subjected to conductive pretreatment. A gold film (50 nm thick) was sputtered onto both ends of the sample to increase the conductive contact area and avoid contact impedance interference. Three parallel samples were prepared for each group (n=3), with commercially available conductive silicone rubber (same size) used as a control sample; Before testing, both the sample and the control sample were placed in a constant temperature and humidity chamber for 24 hours to eliminate the moisture gradient.

[0170] Test steps: S1, Circuit Connection Signal path: Signal generator output → Conductive electrode clamp → Hydrogel sample (input end); Synchronous acquisition: Signal generator synchronous output terminal → Oscilloscope channel 1 (reference signal, i.e. "input signal"); Output acquisition: The other end of the hydrogel sample (output end) → Oscilloscope channel 2 (transmitted signal, i.e. "output signal"); Grounding: All equipment shares a common ground to avoid electromagnetic interference (50Hz power frequency filter enabled).

[0171] S2, Sine wave signal test (1Hz) Signal generator settings: waveform is sine wave, frequency is 1Hz, peak-to-peak value (Vpp) is 1V (avoid hydrogel electrolysis, amplitude ≤1V), DC bias is 0V; output impedance is 50Ω (matching test system). Oscilloscope settings: Sampling rate: 10kS / s, sampling duration: 10s (including 10 complete waveforms); Channel 1 / 2 attenuation ratio: 1:1; Coupling mode: DC. Data logging: Saves waveform data of channel 1 (input) and channel 2 (output), and reads key parameters: input amplitude (Vin), output amplitude (Vout), and phase difference (Δφ). Repeated testing: 3 parallel samples, each sample is tested 3 times, and the average value is taken.

[0172] S1, Square wave signal test (1Hz) Signal generator settings: waveform is square wave, frequency 1Hz, peak-to-peak value 1V, duty cycle 50%, rise time / fall time ≤10ns; other parameters are the same as for sine wave test; Oscilloscope settings: Sampling rate 100kS / s (capturing rising / falling edge details), sampling duration 10s; Data logging: Save input / output waveforms, and read amplitude (Vin / Vout), rise time (tr), fall time (tf), and overshoot (δ). Repeat testing: Same as the sine wave test procedure.

[0173] (6) Microscopic morphology test: Instruments and equipment: Scanning electron microscope (SEM, such as Zeiss Sigma 300, accelerating voltage 5-10kV), freeze dryer (vacuum degree ≤10Pa, temperature ≤-50℃), ion sputtering instrument (gold sputtering thickness 5 nm), cryostat (section thickness 50μm).

[0174] Sample preparation: S1. Sampling: Take samples from the hydrogel matrix and comb-shaped micropillars respectively (volume 1mm×1mm×1mm). S2. Fixation: Fix with 2.5% glutaraldehyde solution at 4℃ for 24h, followed by gradient dehydration (30%, 50%, 70%, 90%, 100% ethanol, 15min each time). S3. Freeze-drying: Place in a freeze dryer and dry at -50℃ for 24 hours to remove moisture (to avoid micropore collapse). S4, Gold Sputtering: Gold sputtering at 5nm using an ion sputtering device to improve conductivity (avoid charging). S5. Section preparation: The hydrogel section was cut using a cryostat and then tested after the same treatment.

[0175] Test steps: S1. Fix the sample on the sample stage and place it in the SEM sample chamber; S2. Set the accelerating voltage to 5kV and the working distance to 8mm, and observe at magnifications of 50×, 500×, and 2000× in sequence. S3. Imaging area: micropillar surface, hydrogel cross section (microporous structure), and conductive enhancer dispersion area; S4. Use the built-in SEM software to measure the pore size of the micropores (randomly select 50 pores and calculate the average value).

[0176] The results of its brain electrode tests are as follows: Figure 3-18 As shown.

[0177] Figure 3 This is a microstructure morphology image of the flexible hydrogel brain electrode in Example 1 at 50 μm. Figure 4 This is a microstructure morphology image of the flexible hydrogel brain electrode in Example 1 at 20 μm. Figure 5 This is a microstructure morphology image of the flexible hydrogel brain electrode in Comparative Example 1 at 100 μm. Figure 6 This is a microstructure morphology image of the flexible hydrogel brain electrode in Comparative Example 1 at 20 μm. From Figures 3 to 6 It can be seen that the conductive hydrogel structure of the present invention includes a three-dimensional interconnected microporous structure formed by multiple interconnected micropores.

[0178] Figure 7 This is a tensile stress-strain curve of the flexible hydrogel brain electrode of Example 1; Figure 8 This is the tensile stress-strain curve of the flexible hydrogel brain electrode in Comparative Example 1. From... Figures 7 to 8 It can be seen that, Figure 7 It includes two cyclic tensile curves: 200% strain cycle and 400% strain cycle; the curves show obvious hysteresis loops, the maximum tensile strain can reach 400%, and the peak tensile stress is about 0.28MPa, indicating that it has a good energy dissipation effect, which is beneficial to structural stability. Figure 8 In a single tensile test, the fracture strain occurred at 380%, with a peak stress of approximately 0.28 MPa. Fracture before reaching 400% indicates poor mechanical properties. The flexible hydrogel brain electrode of this invention can withstand 400% high tensile strain and exhibits stable cyclic elastic recovery, while the comparative sample fractured at only 380% strain. The hydrogel of this invention combines equivalent tensile strength, higher elongation limit, and excellent fatigue viscoelasticity. Under repeated scalp deformation, its structural stability and durability are significantly superior to the comparative sample, ensuring long-term wear of the electrode without damage and stable contact.

[0179] Figure 9 This is the electrochemical impedance Nyquist plot of the flexible hydrogel brain electrode of Example 1; Figure 10 This is the electrochemical impedance spectroscopy (EIS) Bode plot of the flexible hydrogel brain electrode of Example 1; Figure 11 The Nyquist plot of the flexible hydrogel brain electrode in Comparative Example 1 is shown. Figure 12 This is the electrochemical impedance spectroscopy (EI) Bode plot of the flexible hydrogel brain electrode from Comparative Example 1. From... Figures 9 to 12 It can be seen that, Figure 9 The real part curve of the horizontal axis resistance is concentrated in the extremely low real part region; Figure 11 The real part of the horizontal axis resistance is more than ten times that of Example 1. The real part represents the ohmic impedance of the electrode-skin interface, which directly proves that the conductivity of the electrode interface of the present invention is far superior to that of the comparative example. Figure 9 The Nyquist plot of Example 1 exhibits extremely low interfacial real impedance and polarization capacitive arc. Within the core frequency band of EEG acquisition (0.1–100 Hz), the overall impedance modulus of Example 1 is significantly lower than that of the comparative example, and the phase angle is closer to the characteristics of pure resistance. This demonstrates that the flexible hydrogel EEG electrode of this invention, relying on its comb-like micropillar hair-penetrating structure and three-dimensional interconnected microporous aqueous ion electrolyte sustained-release system, significantly reduces the ohmic impedance and polarization resistance at the electrode-scalp interface, resulting in superior charge transfer dynamics. It is well-suited for the high-precision acquisition requirements of weak EEG signals, and its electrical performance is significantly better than that of the comparative sample.

[0180] Figure 13 This is a signal input-output diagram of the flexible hydrogel brain electrode in Example 1; Figure 14 This is a signal input-output diagram of the flexible hydrogel brain electrode from Example 1. From... Figures 13 to 14 It can be seen that regardless of whether the signal is square wave first and then sine wave, or whether the signal form is changed, the hydrogel brain electrode can stably input and output signals.

[0181] Figure 15 These are antibacterial experimental images of the flexible hydrogel brain electrodes of Example 6 and Comparative Example 6. This demonstrates that the brain electrodes of the present invention possess good antibacterial properties.

[0182] Figure 16 This is a cellular biosafety diagram of the flexible hydrogel brain electrode of Example 1, showing that the brain electrode of the present invention is safe and non-toxic.

[0183] Figure 17 This is a signal acquisition diagram of the flexible hydrogel brain electrode in Example 1; Figure 18 This is a detailed diagram of the signal capture phase (5-10 seconds) of the flexible hydrogel brain electrode in Example 1. Figure 17 and Figure 18 It can be seen that the baseline of the electrode in Example 1 is stable and drift-free throughout the 20-second acquisition cycle. Long-term moisturizing and low polarization impedance ensure constant signal state under long-term monitoring conditions. The stimulation-induced EEG rhythm waveform is regular and clear with low noise interference. The multi-channel synchronization is excellent. The comb-like micropillar structure solves the problem of hair obstruction and achieves large-area uniform low-impedance contact with the scalp. The multi-channel acquisition performance is balanced, with no single-point failure or contact difference problems, and it is suitable for large-scale head-mounted acquisition of multi-lead brain-computer interface systems.

[0184] Table 2 Performance test results of the flexible hydrogel brain electrodes prepared in the examples and comparative examples.

[0185] In addition, the present invention has also conducted experiments with other raw materials, process operations and process conditions described in this specification, with reference to the foregoing embodiments, and has obtained relatively ideal results in all cases.

[0186] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A device for preparing a flexible hydrogel brain electrode structure, characterized in that, Includes a mold, the mold cavity having a shape matching the flexible hydrogel brain electrode structure, and includes: The first mold cavity has a shape that matches the flexible cap-shaped substrate; The second mold cavity is connected to the first mold cavity and has a shape that matches the conductive hydrogel body; The third mold cavity is connected to the second mold cavity and has a shape that matches the comb-shaped micropillar structure; The flexible hydrogel brain electrode structure includes: A flexible cap-shaped adhesive base is used to cooperate with the EEG acquisition cap interface and conduct electrical signals. The flexible cap-shaped adhesive base contains a flexible conductive pathway layer. A conductive hydrogel structure includes a conductive hydrogel body and a comb-shaped micropillar structure. The top of the conductive hydrogel body is bonded to the bottom of a flexible cap-shaped adhesive substrate. The comb-shaped micropillar structure includes multiple conductive hydrogel micropillars, which are vertically bonded to the bottom surface of the conductive hydrogel body and spaced apart from each other. A water-storage controlled-release structure is formed in a conductive hydrogel structure, including a three-dimensional interconnected microporous structure formed by multiple interconnected micropores. The three-dimensional interconnected microporous structure is filled with an aqueous ion electrolyte system. The pore volume of the three-dimensional interconnected microporous structure accounts for 50-70% of the total volume of the conductive hydrogel structure. The flexible hydrogel brain electrode structure achieves conductivity stability and moisture retention for more than 70 hours. The flexible cap-shaped bonding substrate is formed of conductive hydrogel and is integrally formed with the conductive hydrogel structure. The conductive hydrogel body and the comb-shaped micropillar structure are integrally formed. The conductive hydrogel comprises 0.5-5.0 wt% natural polymer, 5.0-12.0 wt% synthetic polymer, 2-10 wt% humectant, 0.1-1 wt% electrolyte, 0.5-5 wt% crosslinking regulator, 0.05-5 wt% conductive reinforcing material, and 0.5-3 wt% antibacterial component, with the remainder being water. The natural polymer includes one or more combinations of sodium alginate, gelatin, and chitosan; the synthetic polymer includes one or more combinations of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate; the conductive reinforcing material includes MXene and silver nanowires; the antibacterial component includes chitosan quaternary ammonium salt or ε-polylysine; the humectant includes glycerin and sodium pyrrolidone carboxylate; the crosslinking regulator includes CaCl2 and FeCl3, wherein CaCl2 forms an ionic crosslinking network with the natural polymer, and FeCl3 forms a coordination crosslinking network with the synthetic polymer, and the two synergistically constitute an ionic crosslinking-coordination crosslinking dual-network crosslinking structure.

2. The preparation apparatus according to claim 1, characterized in that: The electrolytes include NaCl and KCl.

3. The preparation apparatus according to claim 1, characterized in that: The pore size of the micropores is 10~80μm.

4. The preparation apparatus according to claim 1, characterized in that: The comb-shaped micropillar structure comprises 4 to 16 conductive hydrogel micropillars.

5. The preparation apparatus according to claim 1, characterized in that: The conductive hydrogel micropillars are biomimetic structures with gradually changing diameters. The top diameter adjacent to the bottom surface of the conductive hydrogel body is 0.5~2mm, the bottom diameter is 1~4mm, the height is 3~8mm, and the spacing between adjacent conductive hydrogel micropillars is 0.5~1.5mm.

6. The preparation apparatus according to claim 1, characterized in that: The diameter of the flexible cap-shaped adhesive base is 8~12mm, and the height is 1.5~2.5mm.

7. The preparation apparatus according to claim 1, characterized in that: The conductive hydrogel body has a diameter of 5-15 mm and a height of 8-12 mm.

8. The preparation apparatus according to claim 1, characterized in that: The natural polymer comprises 1.0-3.0 wt% sodium alginate, 2.0-4.0 wt% gelatin and 0-2 wt% chitosan.

9. The preparation apparatus according to claim 1, characterized in that: The synthetic polymer comprises 6-10 wt% polyvinyl alcohol, 0-3 wt% polyvinylpyrrolidone, 0-2 wt% polyethylene glycol and 0.5-1.5 wt% poly(3,4-ethylenedioxythiophene):polystyrene sulfonate.

10. The preparation apparatus according to claim 1, characterized in that: The crosslinking regulator comprises 0.5-5 wt% CaCl2 and 0.05-2 wt% FeCl3.

11. The preparation apparatus according to claim 1, characterized in that: The mass ratio of glycerol to sodium pyrrolidone carboxylate is 1~3:

1.

12. The preparation apparatus according to claim 2, characterized in that: The mass ratio of NaCl to KCl is 2~4:

1.

13. The preparation apparatus according to claim 1, characterized in that: The mass ratio of MXene to silver nanowires is 1:1 to 3:

1.

14. The preparation apparatus according to claim 1, characterized in that: The silver nanowires have a length of 50~200μm and a diameter of 50~100nm.

15. The preparation apparatus according to claim 1, characterized in that: The contact impedance of the flexible hydrogel brain electrode structure is no greater than 500 Ω at 1 kHz.

16. The preparation apparatus according to claim 1, characterized in that, The method for preparing the flexible hydrogel brain electrode structure includes: A hydrogel precursor solution is provided, comprising 0.5-5.0 wt% natural polymer, 5.0-12.0 wt% synthetic polymer, 2-10 wt% humectant, 0.1-1 wt% electrolyte, 0.5-5 wt% crosslinking regulator, 0.05-5 wt% conductive reinforcing material, and 0.5-3 wt% antibacterial component, with the remainder being water; wherein the natural polymer comprises one or more combinations of sodium alginate, gelatin, and chitosan; the synthetic polymer comprises one or more combinations of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate; the conductive reinforcing material comprises MXene and silver nanowires; the antibacterial component comprises chitosan quaternary ammonium salt or ε-polylysine; the humectant comprises glycerol and sodium pyrrolidone carboxylate; and the crosslinking regulator comprises CaCl2 and FeCl3. The mold providing the mold cavity is subjected to plasma treatment for 30~60s, and the surface contact angle of the mold cavity is ≤15°, which is at least used to improve the wettability of the hydrogel precursor liquid; The hydrogel precursor liquid is filled into a mold cavity with a shape matching the flexible hydrogel brain electrode structure, and then pre-freezing and freeze-thaw cycles are performed. The molded product after the freeze-thaw cycle is immersed in a sodium chloride solution containing 3-5 wt% glycerol for 2-4 hours, and then surface modification is performed. The product is treated with ultraviolet ozone for 10-15 minutes to obtain the flexible hydrogel brain electrode structure. The pre-freezing includes freezing at -10℃ to -20℃ for 0.5 to 2 hours, and the freeze-thaw cycle includes freezing at -80℃ to -20℃ for 4 to 6 hours, thawing at room temperature for 3 to 4 hours, and repeating the cycle 4 to 5 times.

17. The preparation apparatus according to claim 16, characterized in that, The specific method for preparing the flexible hydrogel brain electrode structure includes: The natural polymer is completely dissolved in deionized water to form a first mixed solution; The synthetic polymer, moisturizer, and electrolyte are added sequentially to deionized water and mixed evenly at 70-100°C. The mixture is then cooled to room temperature, and the conductive reinforcing material and antibacterial component are added. After ultrasonic dispersion, a second mixed solution is formed. The first and second mixed solutions are mixed, the crosslinking regulator is added, and the mixture is magnetically stirred and degassed under vacuum to obtain the hydrogel precursor solution.

18. The preparation apparatus according to claim 17, characterized in that: The ultrasonic dispersion power is 50~400W, the frequency is 20~100kHz, and the time is 20~30min.

19. The preparation apparatus according to claim 17, characterized in that: The magnetic stirring time is 15-20 minutes, and the vacuum degassing time is 5-10 minutes.

20. The preparation apparatus according to claim 1, characterized in that: The mold includes a first sub-mold and a second sub-mold, the first mold cavity and the second mold cavity are disposed in the first sub-mold, and the third mold cavity is disposed in the second sub-mold, the third mold cavity including a plurality of cylindrical channels formed in the second sub-mold.

21. The preparation apparatus according to claim 20, characterized in that: A groove is formed on one side surface of the first sub-mold that can be interference-fitted with the second sub-mold. When the second sub-mold is inserted into the groove, the third mold cavity communicates with the first mold cavity and the second mold cavity and cooperates to form the mold cavity of the mold.

22. The preparation apparatus according to claim 20, characterized in that: The first sub-mold also has positioning grooves symmetrically distributed on both sides of the slot on one side surface.

23. The preparation apparatus according to claim 20, characterized in that: The bottom of the first mold cavity is provided with a micro vent hole, which penetrates the first sub-mold and is used to connect the first mold cavity with the outside. The diameter of the micro vent hole is 0.1~0.5mm.

24. The preparation apparatus according to claim 20, characterized in that: The mold is made of at least one of the following materials: medical-grade polylactic acid, medical-grade polycarbonate, and medical-grade silicone.

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