A double-layer hydrogel material for bioelectric signal detection and a preparation method thereof

Abstract

The application relates to a double-layer hydrogel material for bioelectric signal detection and a preparation method thereof, and belongs to the technical field of flexible electronic materials. By constructing a synergistically working double-layer structure, performance decoupling is realized in space: the lower layer is a high-efficiency mixed conductive layer, an ion / electron mixed conductive network is constructed by utilizing the synergistic effect of PEDOT:PSS and ions in the hydrogel, and low impedance and high charge transmission efficiency are ensured; the upper layer is a body temperature response interface layer, which is designed to trigger phase change by body temperature after being in contact with the skin, so that the skin topography is actively adapted, and stable, self-adapting and comfortable non-adhesive physical adhesion is realized. The application can realize high-fidelity bioelectric signal acquisition and long-term reliable wearing stability.

Description

Technical Field

[0001] This invention relates to a bilayer hydrogel material for bioelectric signal detection and its preparation method, belonging to the field of flexible electronic materials technology. Background Technology

[0002] In recent years, advancements in flexible electronics and wearable technology have been driving health monitoring towards continuous and personalized approaches. Against this backdrop, achieving high-quality acquisition of physiological signals such as electroencephalograms (EEGs) and electromyograms (EMGs) has become crucial for supporting precision medicine and intelligent human-computer interaction. This urgently requires the development of flexible electrode materials that can form stable and comfortable contact interfaces with human soft tissues to ensure high-fidelity and long-term signal stability.

[0003] Currently, conductive hydrogels are considered promising materials for constructing ideal electrode-skin interfaces due to their advantages such as modulus close to that of skin, good biocompatibility, and the ability to conduct electricity through ions. Researchers mainly optimize performance in two aspects: first, by introducing conductive polymers (such as polyaniline), constructing interpenetrating networks, or adding nano-conductive fillers (such as silver nanowires) to improve conductivity; second, by introducing functional components such as polymers containing carboxyl and amino groups or tannic acid, utilizing multiple hydrogen bonding interactions to enhance adhesion to the skin and improve adhesion stability.

[0004] However, existing conductive hydrogel systems for wearable bioelectrical sensing face a fundamental contradiction: their homogeneous monolayer structure makes it difficult to simultaneously achieve efficient charge transport and dynamically adaptive skin adhesion. Introducing high-content rigid fillers or dense conductive networks to pursue high conductivity often sacrifices material flexibility and mechanical comfort; while functional designs focusing on interfacial adhesion may hinder ion migration or occupy conductive pathways, leading to a decline in electrical signal quality. This irreconcilable performance conflict within a single material system makes it difficult for existing solutions to simultaneously achieve high signal-to-noise ratio signal acquisition and a stable, comfortable wearing experience during long-term, dynamic monitoring. This limits the practical application of conductive hydrogels in scenarios requiring long-term, dynamic, and high signal-to-noise ratio bioelectrical sensing. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a bilayer hydrogel material for bioelectrical signal detection and its preparation method. This invention achieves spatial performance decoupling by constructing a synergistic bilayer structure: the lower layer serves as a highly efficient hybrid conductive layer, utilizing the synergistic effect of PEDOT:PSS and ions in the hydrogel to construct an ion / electron hybrid conductive network, ensuring low impedance and high charge transport efficiency; the upper layer serves as a body temperature-responsive interface layer, designed to trigger a phase transition upon contact with skin based on body temperature, thereby actively adapting to the skin morphology and achieving a stable, adaptive, and comfortable non-adhesive physical fit. This invention can uniformly achieve high-fidelity bioelectrical signal acquisition and long-term reliable wearing stability.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for preparing a bilayer hydrogel material for bioelectric signal detection, comprising the following steps:

[0008] (1) Preparation of modified PEDOT:PSS solution: Sorbitol and conductive reinforcing filler were added to poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) solution (PEDOT:PSS) and stirred overnight to obtain modified PEDOT:PSS solution; (2) Preparation of monomer solution: Sodium alginate (SA), acrylamide (AM) and LiCl are dissolved in deionized water and heated to dissolve, thus obtaining monomer solution; (3) Preparation of the lower layer of highly conductive hydrogel: Add crosslinking agent N,N'-methylenebisacrylamide (MBAA) and CaCl2 to the monomer solution, then add the modified PEDOT:PSS solution and glycerol, mix evenly, and then add initiator ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED) to form a precursor solution. The precursor solution is introduced into the mold and irradiated in the UV curing chamber at a power of 240-300W for 300-320s to obtain the initially crosslinked lower layer hydrogel in the mold; (4) Preparation of upper precursor solution: Pluronic F127, gelatin, LiCl and sodium alginate (SA) were added to deionized water, heated to dissolve and cooled to room temperature. Acrylamide (AM), crosslinking agent N,N'-methylenebisacrylamide (MBAA) and initiator ammonium persulfate (APS) were added in sequence, stirred and ultrasonically degassed. Finally, initiator N,N,N',N'-tetramethylethylenediamine (TEMED) was added to obtain upper precursor solution. (5) Preparation of bilayer composite hydrogel: CaCl2 solution is uniformly coated on the surface of the lower layer hydrogel in the mold, and then the upper layer precursor solution is poured in. The mixture is cured at 37-42℃ for 45-60 minutes to obtain a bilayer hydrogel material for bioelectric signal detection.

[0009] Preferably, in step (1), the conductive reinforcing filler includes ethylene glycol, 3-glycidyl etheroxypropyltrimethoxysilane (GOPS), and dodecylbenzenesulfonic acid (DBSA).

[0010] Preferably, in step (1), the modified PEDOT:PSS solution contains 1-1.3 wt% PEDOT:PSS, 5-6 vol% sorbitol, 4-6 vol% ethylene glycol, 0.40-0.55 vol% 3-glycidyl etheroxypropyltrimethoxysilane, and 0.123-0.126 vol% dodecylbenzenesulfonic acid.

[0011] Preferably, in step (2), the monomer solution contains sodium alginate at a mass fraction of 0.63-0.65 wt%, acrylamide at a mass fraction of 12-13 wt%, and LiCl at a mass fraction of 3.40-3.50 wt%.

[0012] Preferably, in step (2), the heating temperature is 50-55℃.

[0013] Preferably, in step (3), the amount of N,N'-methylenebisacrylamide added is 0.0158-0.0161 wt% of the monomer solution mass, and the amount of CaCl2 added is 0.053-0.054 wt% of the monomer solution mass.

[0014] Preferably, in step (3), the volume ratio of monomer solution, modified PEDOT:PSS solution, glycerol, and N,N,N',N'-tetramethylethylenediamine in the precursor solution is 10:2.8-3.3:1.8-2.2:0.014-0.016, and the mass fraction of ammonium persulfate is 0.026-0.027 wt%.

[0015] Preferably, in step (4), the heating temperature is 50-55℃.

[0016] Preferably, in step (4), the upper precursor solution contains 0.72-0.73 wt% Pluronic F127, 4.2-4.4 wt% gelatin, 4.3-4.4 wt% LiCl, 0.57-0.59 wt% sodium alginate, 17.2-17.5 wt% acrylamide, 0.0215-0.0219 wt% N,N'-methylenebisacrylamide, 0.0361-0.0365 wt% ammonium persulfate, and the volume ratio of deionized water to N,N,N',N'-tetramethylethylenediamine is 10:0.006-0.008.

[0017] Preferably, in step (5), the volume ratio of the precursor solution, CaCl2 solution and upper precursor solution used to prepare the lower hydrogel is 120:10-12:80-90, and the mass fraction of the CaCl2 solution is 1-2%.

[0018] Beneficial effects 1) This invention fundamentally solves the problem of the mutual constraint between conductivity and flexible adhesion in a single hydrogel system through a functionally partitioned double-layer structure design. The lower hydrogel serves as the conductive functional layer, utilizing small-molecule modified PEDOT:PSS and electrolyte ions (Li... + A highly efficient ion / electron hybrid conductive network was constructed, ensuring excellent bulk conductivity and low interfacial impedance, providing a foundation for high-fidelity bioelectric signal acquisition.

[0019] (2) The upper hydrogel serves as an interface functional layer. By introducing the thermosensitive block copolymer Pluronic F127 and the biocompatible gelatin, the upper hydrogel possesses unique body temperature response characteristics: after contact with the skin, the human body temperature triggers the material to undergo a reversible phase change or modulus softening, thereby dynamically and adaptively conforming to the micro-contour of the skin, achieving a stable, comfortable and non-irritating physical fit, significantly improving wearing comfort and long-term interface stability.

[0020] (3) By performing secondary cross-linking and curing between the two layers after applying CaCl2 solution, a strong bond between the two layers is achieved, avoiding the risk of delamination during use. This preparation method is controllable and the raw materials are readily available. The resulting bilayer hydrogel material has excellent comprehensive performance, providing an effective material solution for the development of a new generation of highly comfortable and reliable wearable bioelectric sensing electrodes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the principle of the thermodynamic phase transition of the bilayer hydrogel of the present invention.

[0022] Figure 2 This is a comparison of the adsorption strength of the bilayer hydrogel of the present invention and Comparative Example 1 at different temperatures.

[0023] Figure 3 This is a comparison chart of the adsorption strength of the bilayer hydrogel of the present invention and Comparative Example 2 and Example 2-32 at 25℃ and 37℃.

[0024] Figure 4 This is a structural diagram showing the distribution of conductive ions and conductive polymers in the bilayer hydrogel of this invention.

[0025] Figure 5 This is a comparison of the electrochemical impedance spectroscopy curves of the bilayer hydrogel of the present invention and Comparative Examples 3, 4-5 at 0.1-1MHz.

[0026] Figure 6 This is a comparison of the electrochemical impedance spectroscopy curves of the bilayer hydrogel of the present invention and Comparative Examples 4, 6-7 at 0.1-1MHz.

[0027] Figure 7 This is a comparison of the time-domain signals and power spectral density of EEG signals measured by the bilayer hydrogel of this invention and commercial Ag / AgCl electrodes.

[0028] Figure 8 The image shows the effect of EEG signals collected by placing the double-layer hydrogel of this invention at three sampling positions (FP1, FP2, and FPZ) for three mental states (distracted attention, focused attention, and fatigue).

[0029] Figure 9 This is a bar chart comparing the noise power and signal-to-noise ratio of EEG signals measured by the bilayer hydrogel of this invention and commercial Ag / AgCl electrodes.

[0030] Figure 10 This is a comparison of electromyographic signals measured by the bilayer hydrogel of this invention and commercial Ag / AgCl electrodes. Figure 11 This is a bar chart comparing the signal-to-noise ratio of electromyographic signals measured by the bilayer hydrogel of this invention and those measured by commercial Ag / AgCl electrodes. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to specific embodiments.

[0032] Example 1 (1) Customize cylindrical plastic film with a thickness of 10mm and a radius of 5mm.

[0033] (2) Spray the film with DS608 fluorine release agent.

[0034] (3) Add 5 vol% sorbitol, 5 vol% ethylene glycol, 0.5 vol% GOPS and 0.125 vol% DBSA to 4 mL of original PEDOT:PSS and stir overnight to obtain a modified PEDOT:PSS solution. Dissolve 0.12 g SA, 2.4 g AM and 0.65 g LiCl in 10 mL of deionized water and prepare a monomer solution at 50 °C. Add 0.003 g MBAA and 0.01 g CaCl2 to the monomer solution and sonicate to dissolve. Then add 3 mL of modified PEDOT:PSS solution and 2 mL of glycerol and mix rapidly. Finally, add 0.005 g APS and 15 μL TEMED. Pour the obtained precursor solution into a mold and irradiate at 100% power for 300 s in a UV curing chamber to obtain the bottom hydrogel.

[0035] (4) Dissolve 0.1g Pluronic F127, 0.6g gelatin, 0.6g LiCl and 0.08g SA in 10mL of deionized water and stir in a 50℃ water bath until clear. After cooling to room temperature, degas by sonication, add 2.4g AM and stir until homogeneous. Then add 0.003g MBAA and 0.005g APS, stir to dissolve and degas by sonication again. Finally, add 8μL TEMED to obtain the precursor solution for the upper hydrogel. After coating the surface of the lower hydrogel with 1% CaCl2 solution, quickly drop the upper hydrogel precursor solution onto it and place it in a 37℃ oven for 45 minutes to obtain a complete bilayer hydrogel.

[0036] Example 2-3 The preparation method is similar to that in Example 1, except that the gelatin content in step (4) is adjusted to 0.578g and 0.608g respectively.

[0037] Examples 4-5 The preparation method is similar to that in Example 1, except that the concentration of lithium chloride in step (4) is adjusted to 1.39M and 1.43M respectively.

[0038] Examples 6-7 The preparation method is similar to that in Example 1, except that the amount of PEDOT:PSS in step (3) is adjusted to 2.8 mL and 3.3 mL respectively.

[0039] Comparative Example 1 The preparation method is similar to that in Example 1, except that Pluronic F127 is not added in step (4). Comparative Example 2 The preparation method is similar to that in Example 1, except that the gelatin content in step (4) is adjusted to 0g.

[0040] Comparative Example 3 The preparation method is similar to that in Example 1, except that the concentration of lithium chloride in step (4) is adjusted to 0.4M.

[0041] Comparative Example 4 The preparation method is similar to that in Example 1, except that the amount of PEDOT:PSS in step (3) is adjusted to 1 mL.

[0042] Figure 1 This is a schematic diagram illustrating the principle of the thermoresponsive adhesion of the bilayer hydrogel described in this invention. The upper layer of the bilayer hydrogel is the adhesion layer, whose core is composed of thermosensitive polymer gelatin and triblock copolymer Pluronic F127. As shown in the figure, at room temperature (25°C), the gelatin molecular chains mainly exist in a regular helical structure, and the active groups (such as amino and carboxyl groups) on its surface that can be used for adhesion are partially encapsulated; at the same time, Pluronic F127 is dispersed in the aqueous phase in the form of discrete molecular chains. When the adhesion layer comes into contact with the skin and rises to body temperature (37°C), the gelatin undergoes a reversible conformational change, and its helical structure unfolds into random coils, thereby exposing a large number of previously encapsulated polar and nonpolar groups, significantly enhancing the hydrogen bonding, hydrophobic, and van der Waals interactions with the skin surface. Simultaneously, the Pluronic F127 molecules undergo reverse thermogelation, and its hydrophobic segments (PPO) dehydrate and aggregate to form physical cross-linking points, thereby significantly improving the in-situ cohesive strength and structural stability of the adhesion layer. This dual thermosensitive phase change mechanism works synergistically, enabling the upper adhesive layer to quickly and firmly adhere to the skin at body temperature, achieving adaptive strong adhesion. When the temperature drops to room temperature, the above process is reversible: the gelatin restores its helical conformation, the Pluronic F127 micelles dissociate, and the adhesive force is significantly reduced, thus achieving painless and damage-free easy peeling. This intelligent body temperature-triggered adhesion mechanism effectively solves the key problems of insufficient adhesion or discomfort during peeling of traditional electrodes during long-term wear.

[0043] Figure 2This is a comparison of the adsorption strength of the bilayer hydrogel of Example 1 and Comparative Example 1 at different temperatures. In Comparative Example 1, the upper adhesive layer of the bilayer hydrogel did not contain Pluronic F127, and its adhesion strength increased slowly with increasing temperature, from 2.6 kPa at 25°C to 5.7 kPa at 37°C (body temperature), an increase of approximately 119%. This increase is mainly due to the helical-coil conformational transformation of the gelatin component in the system during heating, exposing more active groups. In contrast, the bilayer hydrogel of Example 1 introduced Pluronic F127 into the upper adhesive layer, and its adhesion strength showed a more significant increase with increasing temperature: from 4.75 kPa at 25°C to 11.75 kPa at 37°C, an increase of up to 147%, and the increase was particularly rapid in the key body temperature range of 28°C to 37°C. The data clearly show that, at any given test temperature, the adhesion strength of Example 1 is significantly superior to that of Comparative Example 1, with the most significant difference observed at 37°C, where the adhesion strength of Example 1 is approximately 2.1 times that of Comparative Example 1. This significant performance improvement can be attributed to the dual synergistic mechanism of Pluronic F127: firstly, as an amphiphilic surfactant, its molecules effectively improve the wettability between the hydrogel front and the hydrophobic skin epidermis, expanding the effective contact area and thus enhancing the initial baseline of adhesion; secondly, and more importantly, Pluronic F127 itself possesses significant reverse thermogel properties, where the polyoxypropylene (PPO) segments in its molecules dehydrate and aggregate near body temperature, forming dynamic physical cross-linking points within the gel, significantly enhancing the cohesive strength of the adhesion layer. Simultaneously, this phase transition may lead to stronger hydrophobic interactions at the gel-skin interface. This mechanism, synergistically with the thermosensitive conformational change of gelatin, jointly drives the rapid, intelligent response of adhesion strength near body temperature. Therefore, Figure 2 The data strongly demonstrates that the introduction of Pluronic F127 is key to endowing the bilayer hydrogel of this invention with excellent body temperature-triggered adhesion properties. It not only significantly improves the absolute value of the adhesion strength, but also greatly enhances the material's responsiveness to body temperature, thereby ensuring that the device can automatically form a strong and stable interfacial bond when worn, while maintaining the user-friendly characteristic of easy peeling after cooling.

[0044] Figure 3The figure shows a comparison of the adhesion strength of bilayer hydrogels with different gelatin contents at 25°C and 37°C. The sample with a gelatin content of 4 wt% is designated as Example 1 of this invention, and the samples with contents of 0 wt%, 4.2 wt%, and 4.4 wt% are designated as Comparative Example 2, Example 2, and Example 3, respectively. As shown in the figure, at room temperature (25°C), the adhesion strength first increases and then decreases with increasing gelatin content: Comparative Example 2 (0 wt%) is 2.25 kPa, Example 3 (4.2 wt%) increases to 4.3 kPa, Example 1 (4 wt%) reaches the highest of 4.75 kPa, while Example 4 (4.4 wt%) slightly decreases to 4.25 kPa. When the temperature reached body temperature (37°C), the adhesion strength of all samples significantly increased, exhibiting the same pattern of initial increase followed by decrease: Comparative Example 2 showed 4.75 kPa, Comparative Example 3 increased to 11.3 kPa, Example 1 reached the highest at 11.75 kPa, and Comparative Example 4 decreased to 11.25 kPa. The data indicate that the introduction of gelatin has a crucial impact on adhesion performance. In Comparative Example 2 without added gelatin, the overall strength was low and the temperature-sensitive response was weak. With the increase of gelatin content (Examples 3 to 1), the reversible helical-coil conformational transformation of its molecular chains at body temperature exposed a large number of active groups such as hydroxyl and amino groups, significantly enhancing the dynamic interaction with the skin surface, thereby greatly improving the adhesion strength at 37°C. However, when the gelatin content was too high (Comparative Example 4, 4.4 wt%), the adhesion strength decreased at both temperatures, indicating the existence of an optimal content range. Excessive gelatin may lead to excessively high cross-linking density of the gel network or hindered chain segment movement, reducing the material's adaptability to the skin surface and interfacial contact effect, thus weakening effective adhesion. Example 1 (4 wt% gelatin) exhibited the highest adhesion strength (11.75 kPa) at 37°C, approximately 2.5 times that of Comparative Example 2 without gelatin at the same temperature, and about 4.4% higher than Example 4 with 4.4 wt% gelatin at the same temperature. Appropriate gelatin addition can achieve optimal adhesion performance at body temperature triggering while maintaining suitable mechanical state and interfacial adhesion of the material network.

[0045] Figure 4 This is a schematic diagram of the conductive network structure of the bilayer hydrogel in Embodiment 1 of the present invention, visually demonstrating its layered synergistic conductive mechanism. As shown in the figure, the conductive function of this hydrogel is jointly achieved by the upper and lower layers and the interface coupling structure in the middle. Its core lies in the construction of a spatially ordered charge transport channel that is a mixture of "ions and electrons". The upper layer (adhesion layer) mainly undertakes the ionic conductivity function. A high concentration of lithium chloride (LiCl) is uniformly dispersed in its network structure. + With Cl -Ions can migrate freely within the hydrated network of the hydrogel, forming highly efficient ion conduction pathways. This design allows the upper layer to effectively capture bioelectrical signals from the skin surface through ion coupling when in contact with the skin, and efficiently transfer ion current to the interface. The lower layer (conductive support layer) constructs an electron-ion hybrid conductive network. On one hand, the key component of this invention—the modified conductive polymer poly(3,4-ethylenedioxythiophene) / poly(styrene sulfonate) (PEDOT:PSS)—is interconnected within the layer, forming a through-type electron transport framework, achieving low-resistance electron conduction. On the other hand, lithium chloride (LiCl) is also introduced into this layer, constructing parallel ion conduction pathways. This "hybrid conductivity" mechanism, where electron and ion conduction coexist and synergistically interact, enables this layer to achieve high conductivity (approximately 14.54 S·m). - The core of this invention is the key interface coupling structure located between the upper and lower layers. This invention utilizes the introduction of calcium ions (Ca²⁺). + The alginate (SA) in both the upper and lower layers specifically coordinates with the alginate, forming a stable "egg-box" shaped ion cross-linking network. This structure has a dual function: firstly, it acts as a mechanical anchor point, firmly integrating the upper and lower layers and effectively preventing delamination during use; secondly, it acts as an ion transport bridge, providing a continuous, low-resistance transport path for ion flow between the upper and lower layers, ensuring that the ion current captured by the upper layer can be introduced into the hybrid conductive network of the lower layer without damage. In summary, Figure 4 The core concept of this invention lies in constructing an integrated conductive channel through spatial functional partitioning and ordered structural coupling, which integrates "upper-layer ion capture and transport → interfacial ion bridging → lower-layer mixed conductivity and collection." This design resolves the contradiction between the conductive filler and the adhesive network in traditional homogeneous hydrogels from a physical structural perspective. It is key to achieving a synergistic improvement in high conductivity and strong interfacial adhesion, laying a material foundation for subsequent high-quality bioelectrical signal monitoring.

[0046] Figure 5This is a comparison of the electrochemical impedance spectroscopy (EIS) curves of the hydrogels in Examples 1, 4-5, and Comparative Example 3 of this invention in the frequency range of 0.1 Hz to 1 MHz. In Example 1, the upper LiCl concentration was 1.4 M, while the preparation methods for Comparative Examples 3, 4, and 5 were the same as in Example 1, except that the concentration of LiCl in the upper layer was adjusted to 0.4 M, 0.9 M, and 1.9 M, respectively. As shown in the figure, the upper LiCl concentration has a significant and nonlinear effect on the overall impedance of the bilayer hydrogel. Within the test frequency range, except for Comparative Example 3, whose impedance exceeded 7500 Ω in the low-frequency range, the impedance of the other samples remained at a low level (always below 1000 Ω), indicating that the ion-electron hybrid conductive network constructed in this invention possesses excellent basic conductivity at appropriate ion concentrations. Specific analysis shows that the impedance first decreases and then increases with the change in LiCl concentration. Comparative Example 3 (0.4 M) has the highest impedance, mainly due to insufficient ion concentration, allowing freely migrating LiCl particles to move freely within the system. + With Cl - The limited number of ions leads to low ionic conductivity, especially with a sharp increase in impedance in the low-frequency region. As the concentration increases to 0.9 M (Example 4), the impedance decreases significantly, with the low-frequency impedance dropping to approximately 900 Ω. When the concentration reaches 1.4 M (Example 1), the impedance drops to the lowest value among all samples (approximately 660 Ω at low frequencies), demonstrating optimal charge transport performance. However, when the LiCl concentration is further increased to 1.9 M (Example 5), the impedance value does not continue to decrease but instead rebounds, reaching a value similar to that at 0.9 M (approximately 910 Ω at low frequencies). This phenomenon can be attributed to the negative effects of excessively high salt concentrations: on the one hand, excessively high ionic strength may lead to the formation of ion pairs or ion clusters, thus limiting the effective ion mobility; on the other hand, high salt concentrations may alter the swelling state or local microstructure of the polymer network, hindering ion transport pathways. Therefore, Figure 5 The data clearly show that a bilayer hydrogel electrode with an appropriate LiCl concentration in the upper layer can minimize signal attenuation and noise introduction, thus laying a material foundation for high-fidelity monitoring of physiological signals such as EEG and EMG.

[0047] Figure 6The above are comparison charts of the electrochemical impedance spectroscopy (EIS) spectra of the hydrogels in Examples 1, 6-7, and Comparative Example 4 of this invention in the frequency range of 0.1 Hz to 1 MHz, containing a total of four curves. The preparation methods of Comparative Example 4, Example 6, and Example 7 are basically the same as those of Example 1, the only difference being that the amount of PEDOT:PSS in step (3) is adjusted to 1 mL, 2.8 mL, 3.3 mL, and 3 mL respectively. As shown in the figure, the content of PEDOT:PSS has a significant impact on the impedance of the bilayer hydrogel across the entire frequency band, and the change pattern exhibits non-linear characteristics. Except for Comparative Example 4, whose impedance exceeds 4000 Ω in the low-frequency band, the impedance values ​​of the other samples are all below 1000 Ω throughout the entire measurement frequency band, reflecting the "electron" principle of this invention. The design of the "ion-mixed conductive network" exhibits excellent broadband conductivity. The specific variation is as follows: as the amount of PEDOT:PSS increased from 1 mL (Comparative Example 4) to 3 mL (Example 1), the impedance value continuously decreased. Comparative Example 4 (1 mL) showed the highest impedance, mainly because the insufficient PEDOT:PSS content made it difficult to form a continuous and interconnected electron transport pathway in the lower network, resulting in limited electronic conductivity contribution. Especially in the low-frequency region where ion conductivity was dominant, the overall impedance increased sharply. When the amount increased to 2 mL (Example 6), the impedance decreased significantly, indicating improved conductivity of the conductive network, with the low-frequency impedance dropping below 887 Ω. When the amount of PEDOT:PSS reached 3 mL (Example 1), the impedance dropped to its lowest value (low frequency). The impedance value (approximately 663Ω) indicates that a continuous and uniform conductive network has been formed, achieving optimal synergy between electron transport and ion migration. However, when the amount of PEDOT:PSS was further increased to 4 mL (Example 7), the impedance value did not continue to decrease but instead slightly increased (approximately 781Ω at low frequencies), though still better than the 2 mL amount. This phenomenon may stem from two reasons: firstly, excessive PEDOT:PSS particles may agglomerate due to excessively high local concentrations, disrupting the uniformity of the conductive network and slightly hindering ion migration channels; secondly, the introduction of excessive rigid filler may affect the swelling behavior and microstructure of the underlying polymer matrix, thus having a certain adverse effect on charge transport, but compared to insufficient amounts, its overall performance remains at a high level. Therefore, Figure 6 The data clearly show that the appropriate amount of PEDOT:PSS can ensure that the lower layer has both high electronic conductivity and good structural compatibility, thus providing a key material guarantee for the entire electrode to achieve stable, efficient and low-loss bioelectric signal acquisition over a wide frequency range.

[0048] Figure 7 This is a comparison of the time-domain signals and power spectral density of EEG signals measured by the bilayer hydrogel and the commercial Ag / AgCl electrode in Example 1 of this invention. Figure 7This figure compares the time-domain waveforms and power spectral density (PSD) of EEG signals acquired by the bilayer hydrogel electrode of this invention (Example 1) and a commercial Ag / AgCl electrode. As shown, under the same test conditions, the bilayer hydrogel electrode of this invention outperforms the traditional commercial Ag / AgCl electrode in several key EEG signal acquisition indicators. In the time domain, the amplitude of the EEG signal waveform recorded by Example 1 is higher than that of the commercial Ag / AgCl electrode. This indicates that, due to the lower electrode-skin contact impedance and excellent conformal fit of the hydrogel electrode of this invention, it can more effectively capture weak electrophysiological activities on the scalp surface, thereby reducing signal attenuation during transmission. In the frequency domain, power spectral density analysis can further quantify the quality of the signal. The comparison results show that in the key frequency band of 0-10 Hz, which reflects the basic rhythm and slow-wave activity of EEG, the PSD value of Example 1 is also significantly higher than that of the Ag / AgCl electrode. This phenomenon indicates that the electrode of this invention not only improves the overall signal strength but also particularly enhances the ability to capture core EEG features such as low-frequency neural oscillations. This advantage may stem from its stable interface contact, which effectively suppresses low-frequency noise (such as motion artifacts) caused by poor contact or relative motion. Combining the comparison results in the time and frequency domains, Figure 7 This strongly demonstrates that the bilayer hydrogel electrode designed in this invention has significant advantages over traditional commercial electrodes in terms of EEG signal acquisition quality. Its higher signal amplitude and stronger characteristic frequency band power provide a higher quality data foundation for subsequent high-precision EEG monitoring and neural decoding.

[0049] Figure 8 This figure shows a comparison of the time-domain waveforms of typical EEG signals collected by the bilayer hydrogel electrode at three standard sampling locations (FP1, FP2, and FPZ) in Embodiment 1 of this invention, targeting three different cognitive states: distracted attention, focused attention, and fatigue. As shown, the electrode of this invention can clearly capture and present the characteristic EEG activities of the three mental states, with significant and distinguishable pattern differences in their time-domain signals. Specifically, the EEG signal in the distracted attention state exhibits frequent fluctuations without a clear pattern, with relatively random amplitude changes, reflecting the characteristics of neural activity when cognitive resources are not effectively concentrated. The signal collected in the focused attention state shows a significantly different pattern, with a relatively stable and continuous waveform, and visible rhythmic oscillations, consistent with the typical manifestation of enhanced neural synchronicity under focused cognitive tasks. The signal characteristics in the fatigue state are also distinct, with a lower overall amplitude level and the smallest fluctuation amplitude among the three states, exhibiting a certain degree of inhibition and low activity, consistent with the physiological phenomenon of reduced cortical activity in the state of neural fatigue. The results clearly demonstrate that the bilayer hydrogel electrode described in this invention possesses excellent signal sensitivity and stability, and can effectively capture and distinguish subtle brain electrical activities modulated by different cognitive and mental states.

[0050] Figure 9 This is a bar chart comparing the noise power and signal-to-noise ratio (SNR) of the EEG signals measured by the bilayer hydrogel electrode in Example 1 of this invention and the commercial Ag / AgCl electrode. Quantitative analysis further confirms that the electrode of this invention significantly outperforms the traditional commercial electrode in key signal quality indicators. Regarding noise control, the total noise power measured by the bilayer hydrogel electrode of this invention is 80.18 μV. 2 The noise power of commercial Ag / AgCl electrodes is as high as 232.59 μV. 2 This indicates that, thanks to its excellent interfacial adhesion and stable ion-electron hybrid conductivity mechanism, the electrode of this invention can more effectively suppress background electrical noise introduced by poor contact, motion artifacts, and environmental interference. In terms of the core indicator of signal fidelity—the signal-to-noise ratio (SNR)—the electrode of this invention exhibits a significantly superior advantage. Its SNR reaches 36.23 dB, while the SNR of commercial Ag / AgCl electrodes is only 16.99 dB. The SNR of the electrode of this invention is approximately 2.13 times that of commercial electrodes. This significant improvement is directly attributed to its simultaneous achievement of a higher effective signal amplitude (e.g., ...). Figure 7 (As shown) with a lower background noise level.

[0051] Figure 10 This image shows a comparison of the time-domain waveforms of typical electromyographic (EMG) signals collected by the bilayer hydrogel electrode in Embodiment 1 of this invention and a commercial Ag / AgCl electrode at the same muscle location (e.g., forearm muscles). As shown in the figure, under the same muscle contraction conditions, the EMG signal amplitude recorded by the electrode of this invention is significantly higher than that of the commercial Ag / AgCl electrode. This intuitively demonstrates that, thanks to its low-impedance hybrid conductive network and excellent skin-conformal fit, the electrode of this invention can more efficiently capture the electrical signals generated by muscle activity, effectively reducing signal loss at the acquisition interface.

[0052] Figure 11 Further quantitative comparisons were made of the signal-to-noise ratio (SNR), a core quality indicator for electromyography (EMG) signal acquisition, between the two electrodes. Bar chart data show that the SNR of the bilayer hydrogel electrode in Example 1 of this invention is 24 dB, while the SNR of the commercial Ag / AgCl electrode is only 15 dB. The SNR of the electrode of this invention is 60% higher than that of the commercial electrode.

[0053] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing a bilayer hydrogel material for bioelectric signal detection, characterized in that: The method steps include: (1) Preparation of modified PEDOT:PSS solution: Sorbitol and conductive reinforcing filler were added to poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) solution and stirred overnight to obtain modified PEDOT:PSS solution; (2) Preparation of monomer solution: Sodium alginate, acrylamide and LiCl are dissolved in deionized water and heated to dissolve, thus obtaining monomer solution; (3) Preparation of the lower layer of highly conductive hydrogel: Add crosslinking agent N,N'-methylenebisacrylamide and CaCl2 to the monomer solution, then add the modified PEDOT:PSS solution and glycerol, mix evenly, add initiator ammonium persulfate and N,N,N',N'-tetramethylethylenediamine to form a precursor solution, introduce the precursor solution into the mold, and irradiate it in the UV curing chamber at a power of 240-300W for 300-320s to obtain the preliminary crosslinked lower layer hydrogel in the mold; (4) Preparation of upper precursor solution: Pluronic F127, gelatin, LiCl and sodium alginate were added to deionized water, heated to dissolve and cooled to room temperature. Acrylamide, crosslinking agent N,N'-methylenebisacrylamide and initiator ammonium persulfate were added in sequence, stirred and ultrasonically degassed. Finally, initiator N,N,N',N'-tetramethylethylenediamine was added to obtain upper precursor solution. (5) Preparation of bilayer composite hydrogel: CaCl2 solution is uniformly coated on the surface of the lower layer hydrogel in the mold, and then the upper layer precursor solution is poured in. The mixture is cured at 37-42℃ for 45-60 minutes to obtain a bilayer hydrogel material for bioelectric signal detection.

2. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (1), the conductive reinforcing filler includes ethylene glycol, 3-glycidyl etheroxypropyltrimethoxysilane and dodecylbenzenesulfonic acid.

3. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 2, characterized in that: In step (1), the modified PEDOT:PSS solution contains 1-1.3 wt% PEDOT:PSS, 5-6 vol% sorbitol, 4-6 vol% ethylene glycol, 0.40-0.55 vol% 3-glycidyl etheroxypropyltrimethoxysilane, and 0.123-0.126 vol% dodecylbenzenesulfonic acid.

4. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (2), the monomer solution contains sodium alginate at a mass fraction of 0.63-0.65 wt%, acrylamide at a mass fraction of 12-13 wt%, and LiCl at a mass fraction of 3.40-3.50 wt%.

5. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (2), the heating temperature is 50-55℃.

6. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (3), the amount of N,N'-methylenebisacrylamide added is 0.0158-0.0161 wt% of the monomer solution mass, and the amount of CaCl2 added is 0.053-0.054 wt% of the monomer solution mass.

7. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 6, characterized in that: In step (3), the volume ratio of monomer solution, modified PEDOT:PSS solution, glycerol, and N,N,N',N'-tetramethylethylenediamine in the precursor solution is 10:2.8-3.3:1.8-2.2:0.014-0.016, and the mass fraction of ammonium persulfate is 0.026-0.027 wt%.

8. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (4), the heating temperature is 50-55℃.

9. The method for preparing a bilayer hydrogel material for bioelectric signal detection as described in claim 1, characterized in that: In step (4), the upper precursor solution contains 0.72-0.73 wt% Pluronic F127, 4.2-4.4 wt% gelatin, 4.3-4.4 wt% LiCl, 0.57-0.59 wt% sodium alginate, 17.2-17.5 wt% acrylamide, 0.0215-0.0219 wt% N,N'-methylenebisacrylamide, 0.0361-0.0365 wt% ammonium persulfate, and the volume ratio of deionized water to N,N,N',N'-tetramethylethylenediamine is 10:0.006-0.

008.

10. A method for preparing a bilayer hydrogel material for bioelectrical signal detection as described in any one of claims 1 to 9, characterized in that: In step (5), the volume ratio of the precursor solution, CaCl2 solution and upper precursor solution used to prepare the lower hydrogel is 120:10-12:80-90, and the mass fraction of the CaCl2 solution is 1-2%.

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