Conductive hydrogel and preparation method and application thereof

Abstract

The application belongs to the field of flexible electronic materials, and specifically discloses a conductive hydrogel as well as a preparation method and application thereof. The conductive hydrogel is composed of a double-network polymer matrix and hybrid conductive nanofillers; the double-network contains polyvinyl alcohol and poly(sulfobetaine methacrylate-co-N-hydroxyethyl acrylamide), and the hybrid conductive nanofillers are composed of silver nanoparticle-loaded MXene nanosheets and poly(3,4-ethylenedioxythiophene) / poly(styrene sulfonic acid) composites. Through the synergistic effect among the components and the hydrogen bonding and electrostatic interaction between the polymer networks, the hydrogel has high conductivity, excellent mechanical properties and electrocatalytic activity. The hydrogel exhibits good stability and application potential in human motion monitoring and real-time detection of sweat ascorbic acid, can realize continuous monitoring of the change of epidermal sweat ascorbic acid after taking vitamin C, and has important value in the biomedical field.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic materials, specifically to a conductive hydrogel, its preparation method and application, and more specifically to a conductive hydrogel that can be used for both strain sensing and sweat ascorbic acid detection, and its preparation method. Background Technology

[0002] Flexible wearable sensors based on conductive hydrogels have shown broad application prospects in personalized health monitoring and human-computer interaction due to their excellent flexibility, stretchability, and biocompatibility. By incorporating conductive nanomaterials into a hydrogel matrix to construct nanocomposite conductive hydrogels, electrical response functions can be imparted while maintaining the material's softness, and these sensors have been widely used for real-time monitoring of macroscopic human movement and subtle physiological signals. However, most current flexible sensors based on nanocomposite hydrogels are mainly limited to the detection of physical deformation or electrophysiological signals, making it difficult to obtain biochemical information directly related to human physiological states at the molecular level. This significantly restricts the depth and breadth of their application in complex scenarios such as comprehensive health assessments.

[0003] Epidermal sweat, as a non-invasive biofluid, contains abundant electrolytes, metabolites, and nutrients, among other biomarkers. Ascorbic acid, a key nutrient for maintaining immune function and antioxidant balance, exhibits concentration fluctuations closely related to nutritional status and oxidative stress levels. Accurate monitoring of ascorbic acid in sweat is of significant clinical importance. Current electrochemical detection techniques typically rely on rigid or semi-rigid nanocomposite electrodes to achieve high-sensitivity analysis. However, these electrodes are prone to structural damage during repeated deformation, leading to decreased detection stability and difficulty in performance recovery. While combining the flexibility of hydrogels with the electrochemical activity of nanomaterials is considered a feasible direction for improving the skin adaptability of sweat sensors, existing nanocomposite hydrogels often suffer from significant deficiencies in mechanical strength, toughness, and structural stability. They struggle to maintain a stable electrochemical interface while withstanding substantial mechanical deformation, making reliable synergy between physical signal sensing and molecular-level chemical detection difficult on the same material platform.

[0004] Therefore, there is an urgent need in this field to develop novel multifunctional conductive hydrogel materials to overcome the technical bottleneck of the difficulty in simultaneously achieving mechanical, conductive, and electrochemical properties. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a conductive hydrogel, its preparation method, and its applications. This invention designs the specific composition of the conductive hydrogel, utilizing the synergistic effect of a first network of polyvinyl alcohol and a second network of polysulfonated betaine methacrylate and N-hydroxyethyl acrylamide copolymer, and the synergistic effect of a hybrid conductive nanofiller composed of MXene nanosheets loaded with silver nanoparticles and a composite of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid). This results in a conductive hydrogel with excellent mechanical properties, high conductivity, and excellent electrocatalytic properties, enabling wide-range, highly sensitive detection of strain signals and trace electrochemical detection of ascorbic acid in human sweat.

[0006] To achieve the above and other related objectives, in a first aspect, the present invention provides a conductive hydrogel, comprising a polymer matrix and a conductive filler dispersed in the polymer matrix, wherein, The polymer matrix is ​​a dual-network polymer matrix, which is composed of a first network and a second network that interpenetrate and crosslink. The first crosslinking network is a network formed by crosslinking polyvinyl alcohol, and the second network is poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide). The conductive filler is a hybrid conductive nanofiller, which includes MXene nanosheets loaded with silver nanoparticles and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) composite (PEDOT:PSS).

[0007] The present invention achieves excellent mechanical properties and high conductivity in conductive hydrogels by using polyvinyl alcohol and poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide) as a dual-network polymer matrix, combined with MXene nanosheets loaded with silver nanoparticles and a composite of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) as hybrid conductive nanofillers. The dual-network structure of polyvinyl alcohol and poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide) endows the hydrogel with good mechanical properties, enabling it to withstand large tensile stresses. The introduction of MXene nanosheets and PEDOT:PSS significantly improves the conductivity and sensing performance of the hydrogel, resulting in excellent performance in stress sensing and ascorbic acid detection.

[0008] In some implementations, silver nanoparticles are loaded onto the surface of MXene nanosheets.

[0009] Preferably, the average diameter of the silver nanoparticles is between 50 nm and 90 nm.

[0010] If the average diameter of the silver nanoparticles is less than 50 nm, the surface energy of the particles is too high, making them prone to aggregation on the MXene surface and resulting in uneven construction of conductive pathways. If the average diameter is greater than 90 nm, the loading stability of the silver nanoparticles on the MXene surface decreases, and they are prone to detaching from the MXene surface during hydrogel stretching, affecting mechanical stability and the continuity of the conductive network. Therefore, controlling the average diameter of the silver nanoparticles within the range of 50 nm to 90 nm can maintain a stable conductive network while ensuring uniform loading.

[0011] In some embodiments, the conductive hydrogel has a tensile strength of 1 MPa to 2.5 MPa, an elongation at break of 800% to 1300%, and a toughness of 5 KJ / m. 3 ~15KJ / m 3 The elastic modulus is 0.1 MPa to 0.3 MPa; the electrical conductivity is 0.6 mS / cm to 3 mS / cm.

[0012] Preferably, when the mass of the MXene nanosheets loaded with silver nanoparticles is 1 mg to 4 mg, the tensile strength of the conductive hydrogel is 1.3 MPa to 2.2 MPa; the elongation at break is 900% to 1200%; and the toughness is 7 KJ / m. -3 ~14.5KJ m -3 The elastic modulus is 0.13 MPa to 0.22 MPa; the electrical conductivity is 1.0 mS / cm to 2.8 mS / cm.

[0013] The synergistic improvement in mechanical and electrical properties mentioned above is mainly due to the synergistic effect between the energy dissipation mechanism provided by the dual-network polymer matrix and the highly efficient conductive network constructed by the hybrid conductive nanofiller.

[0014] In some embodiments, the conductive hydrogel has a strain sensitivity coefficient of 1.5 to 8.0 in the tensile strain range of 0% to 1000%.

[0015] Preferably, the strain sensitivity coefficient of the conductive hydrogel is 1.0 to 2.0 in the tensile strain range of 0% to 100%, 2.0 to 4.0 in the tensile strain range of 100% to 500%, and 4.0 to 8.0 in the tensile strain range of 500% to 1000%.

[0016] This segmented sensitivity characteristic enables the hydrogel to have suitable response capabilities in different strain ranges, ensuring stability under small strains and achieving high-sensitivity monitoring under large strains.

[0017] In some embodiments, the conductive hydrogel has a response time of no more than 120 ms and a recovery time of no more than 100 ms under 50% tensile strain.

[0018] The rapid response and recovery capabilities ensure that the sensor accurately captures dynamic human motion signals in real time.

[0019] Secondly, the present invention provides a method for preparing a conductive hydrogel, comprising the following steps: MXene was dispersed in deionized water to obtain an MXene dispersion; AgNO3 solution was added dropwise to the MXene dispersion under stirring to reduce AgNO3 to silver nanoparticles. After dispersion and freeze-drying, MXene nanosheets loaded with silver nanoparticles were obtained. The MXene nanosheets loaded with silver nanoparticles were dispersed in deionized water and mixed with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composite to obtain a hybrid conductive nanofiller mixture. The hybrid conductive nanofiller mixture was mixed evenly with polyvinyl alcohol, a second network monomer and a photoinitiator, transferred to a mold, and photopolymerized by ultraviolet irradiation to obtain a conductive hydrogel. The second network monomer is a mixture of methacrylic acid sulfobetaine and N-hydroxyethyl acrylamide.

[0020] In some embodiments, the MXene is prepared as follows: LiF at a mass-to-volume ratio of 1:(18~22) g / mL was mixed with 9M HCl solution and stirred. Ti3AlC2 block was added and reacted at 37℃~39℃ for 46h~50h to obtain the MXene.

[0021] Specifically, the mass-to-volume ratio of the LiF to the HCl solution is 1 g: (18~22) mL, and the concentration of the HCl solution is 8~10 M.

[0022] Specifically, the mass ratio of LiF to Ti3AlC2 is 1:(0.9~1.1).

[0023] Specifically, after the reaction is completed, the obtained product is washed with deionized water and centrifuged until the pH of the supernatant is 4-6. The precipitate is dispersed in deionized water, sonicated, and centrifuged. The supernatant is collected and freeze-dried.

[0024] The above etching conditions ensure that the Al layer is fully etched without damaging the layered structure of MXene. If the temperature is below 37°C or the time is less than 46 hours, the etching will be incomplete. If the temperature is above 39°C or the time is more than 50 hours, the MXene sheets are prone to breakage, affecting the subsequent loading of silver nanoparticles and the construction of conductive networks.

[0025] In some embodiments, when preparing MXene nanosheets loaded with silver nanoparticles, the mass ratio of MXene to AgNO3 is (2~14):(2~5).

[0026] In the preparation of MXene nanosheets loaded with silver nanoparticles, the mass ratio of MXene to AgNO3 was controlled at (2~14):(2~5), which was designed based on the balance between the chemical reduction active sites on the MXene surface and the growth kinetics of silver nanoparticles. The surface of MXene nanosheets is rich in end groups such as hydroxyl, oxygen, and fluorine groups. These groups can not only adsorb silver ions through electrostatic interactions, but also act as reduction sites to reduce them into silver nanoparticles. When the proportion of MXene is too high and AgNO3 is relatively insufficient, the number of silver nanoparticles generated by reduction is too small and their distribution is sparse, resulting in insufficient electrocatalytic active sites and making it difficult to achieve highly sensitive detection of ascorbic acid. Conversely, if the proportion of AgNO3 is too high, the reduction and growth of silver ions on the MXene surface will be out of control, easily causing excessive growth, uneven size, or even aggregation of silver nanoparticles. This will not only block the layered structure of MXene and reduce its specific surface area, but also destroy the conductive scaffold function and dispersion stability of the MXene nanosheets. This ratio range enables uniform anchoring and controllable growth of silver nanoparticles on the MXene surface, maintaining the particle size within a suitable range. This ensures a rich electrocatalytic active interface while preserving the high conductivity and nano-enhancing effect of MXene.

[0027] When preparing hybrid conductive nanofillers, the mass ratio of the MXene nanosheets loaded with silver nanoparticles to the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composite (PEDOT:PSS) is (1~4):(0.7~2.8).

[0028] In the preparation of hybrid conductive nanofillers, the mass ratio of MXene nanosheets loaded with silver nanoparticles to poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composites (PEDOT:PSS) was (1~4):(0.7~2.8), reflecting the synergistic design concept between the conductive polymer matrix and the inorganic nanofunctional phase. PEDOT:PSS mainly acts as a conductive binder and a bridge between the continuous phases in this system. Its high proportion is beneficial for constructing a continuous three-dimensional conductive network within the hydrogel, ensuring the continuity of the charge transport path. If the proportion of MXene-AgNPs is too high, the inorganic nanosheets are prone to stacking and agglomeration in the polymer matrix, leading to increased interfacial impedance and stress concentration, thereby compromising the film-forming continuity of PEDOT:PSS and the flexibility of the hydrogel. Conversely, if the proportion of MXene-AgNPs is too low, the inorganic filler cannot form effective functional nodes in the polymer network, making it difficult to demonstrate electrocatalytic activity and nano-reinforcement effects. This ratio range allows a small amount of MXene-AgNPs to be uniformly dispersed in the PEDOT:PSS matrix. With the help of the encapsulation and bridging effect of PEDOT:PSS, the aggregation and deactivation of inorganic nanomaterials are avoided, while the electrocatalytic function of silver nanoparticles and the conductivity enhancement effect of MXene are fully utilized. At the same time, the good processing adaptability and interfacial compatibility of the hybrid filler are maintained.

[0029] When preparing the conductive hydrogel, the mass ratio of the hybrid conductive nanofiller, polyvinyl alcohol, methacrylate sulfobetaine and N-hydroxyethyl acrylamide is (3.1~7.1):(50~150):(264~528):(1280~3200).

[0030] In the preparation of conductive hydrogels, the mass ratio of hybrid conductive nanofiller, polyvinyl alcohol, sulfobetaine methacrylate, and N-hydroxyethyl acrylamide was (3.1~7.1):(50~150):(264~528):(1280~3200), based on the consideration of synergistic optimization of mechanical load-bearing capacity and functional conduction in dual-network hydrogels. The mechanical properties of the hydrogel mainly depend on the structural integrity of the polymer dual-network. Among them, P(SBMA-co-HEAA), as the main network with the highest mass proportion, endows the hydrogel with extremely high toughness, elongation at break, and fatigue resistance. PVA, as the first network, provides hydrogen bond cross-linking points through abundant hydroxyl groups, forming multiple physical cross-links with the second network. If the proportion of conductive filler is too high, it will disrupt the continuity of the polymer network, leading to hydrogel embrittlement, decreased elasticity, and easy agglomeration of filler, causing stress concentration and breakage of conductive pathways. If the proportion of filler is too low, it is difficult to form an effective percolating conductive network, and the conductivity and electrocatalytic performance cannot meet the sensing and detection requirements. This ratio range ensures that the polymer dual network dominates as a continuous matrix of the hydrogel, maintaining excellent mechanical properties such as an elongation at break of 1180% and a tensile strength of 2.12 MPa. At the same time, through the uniform embedding of an appropriate amount of hybrid conductive nanofiller, a stable conductive and electrocatalytic channel is constructed within the polymer network, achieving the integration of high conductivity, high sensitivity strain response, and trace detection of ascorbic acid in sweat.

[0031] It should be noted that the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composite is a commercially available substance.

[0032] Preferably, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

[0033] The choice of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone as the photoinitiator is primarily based on the requirements of the aqueous photopolymerization process of the hydrogel system in this invention. This hydrogel uses polyvinyl alcohol aqueous solution as a base and incorporates betaine-type zwitterionic monomers and hydrophilic monomers such as N-hydroxyethylacrylamide. The entire preparation process is completed in an aqueous environment. The photoinitiator's molecular structure contains hydroxyethoxy groups, giving it excellent water dispersibility and hydrophilicity, allowing it to dissolve or disperse uniformly in the aqueous reaction system. This eliminates the need for additional organic solvents, achieving a highly efficient photoinitiation process, which aligns perfectly with the green and mild preparation route of this invention. From a photochemical perspective, this initiator undergoes a highly efficient homolytic cleavage reaction under ultraviolet light irradiation, generating highly reactive free radical species, thereby rapidly initiating the opening of double bonds in vinyl monomers and initiating chain polymerization. Its maximum absorption wavelength matches well with the output band of conventional ultraviolet light sources, enabling in-situ polymerization of the first network with lower photoinitiator dosage and shorter irradiation time, effectively improving preparation efficiency and reducing energy consumption. The advantages of this photoinitiator also lie in its excellent biocompatibility and low cytotoxicity. Since the hydrogel of this invention is intended for wearable sensing and bioelectrochemical detection applications, it will inevitably come into contact with human skin or bodily fluids. This initiator and its photolysis products are relatively mild, with low residue levels and minimal irritation to the human body, significantly improving the safety of the material in biosensing applications. Furthermore, its highly efficient initiation properties help form a polymer network with a uniform structure and moderate crosslinking density, reducing network defects caused by uneven initiator dispersion, thereby facilitating the acquisition of a high-quality dual-network hydrogel with synergistically enhanced mechanical properties and conductivity.

[0034] Preferably, the ultraviolet irradiation time is 2 min to 4 min, the wavelength of the ultraviolet light is 365 nm, and the power is 40 W.

[0035] The UV irradiation time was set at 2-4 minutes, primarily based on a balance between photopolymerization kinetics and the structural integrity of the dual-network hydrogel. Within this time range, the 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone photoinitiator can continuously generate sufficient free radicals under UV excitation, allowing N-hydroxyethylacrylamide and betaine-type zwitterionic monomers to undergo sufficient addition polymerization, thus forming a first network with moderate crosslinking density and uniform structure. If the irradiation time is too short, insufficient monomer conversion will lead to incomplete polymer chain growth, increased network defects, and consequently, reduced mechanical strength and structural stability of the hydrogel. Unreacted monomers may also affect the biocompatibility of the material. Conversely, if the irradiation time is too long, excessive crosslinking can easily occur, making the polymer network too rigid, resulting in increased hydrogel brittleness and decreased elongation at break, which is detrimental to obtaining a dual-network structure with high flexibility and toughness. Controlling the irradiation time to 2-4 minutes also helps protect the functional fillers and second network components in the system. Excessive UV irradiation may cause oxidative degradation or destruction of the layered structure of MXene nanosheets, affecting their conductivity and dispersion in the matrix. It may also adversely affect the molecular conformation of PEDOT:PSS and the surface activity of silver nanoparticles. An appropriate irradiation time can maximize the preservation of the inherent electrical properties and electrocatalytic activity of MXene, silver nanoparticles, and the PEDOT:PSS hybrid filler while ensuring sufficient formation of the first network. Furthermore, this time window balances preparation efficiency and process economy. Under these conditions, the photopolymerization reaction can rapidly complete the gelation transition, shortening the production cycle, reducing energy consumption, and ensuring high consistency in the degree of polymerization between batches, thus improving the reproducibility of the hydrogel product quality. The resulting dual-network hydrogel can achieve stable conductive pathway construction while maintaining excellent mechanical properties, providing a reliable structural basis for its subsequent use as a wide-range strain sensor and a high-sensitivity electrochemical sensor.

[0036] Thirdly, the present invention provides the use of a conductive hydrogel as described in the first aspect or a conductive hydrogel prepared by the preparation method described in the second aspect in the preparation of a flexible sensor, the flexible sensor including a strain sensor and an electrochemical sensor.

[0037] Preferably, the strain sensor is used for human motion monitoring; the electrochemical sensor is used to detect ascorbic acid in human sweat.

[0038] Preferably, the electrochemical sensor has a linear detection range of 0.5 μM to 300 μM for ascorbic acid and a limit of detection of 0.352 μM.

[0039] Preferably, the electrochemical sensor has anti-interference selectivity for uric acid, dopamine, and glucose.

[0040] As described above, the conductive hydrogel, its preparation method, and its application provided by the present invention have the following beneficial effects: This invention constructs a dual-network structure consisting of a first network of polyvinyl alcohol and a second network of polysulfonated betaine methacrylate and N-hydroxyethyl acrylamide copolymer. It also introduces a hybrid conductive nanofiller composed of MXene nanosheets loaded with silver nanoparticles, and a composite of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid). This achieves synergistic optimization of mechanical properties, conductivity, and sensing functions. In this system, silver nanoparticles act as an electrocatalyst, endowing the hydrogel with electrocatalytic capabilities, enabling trace detection of ascorbic acid in sweat. MXene, with its large specific surface area, acts as a conductive scaffold, significantly improving the conductivity and mechanical properties of the hydrogel while simultaneously loading silver nanoparticles, utilizing its high conductivity and nano-reinforcing effect. The composite of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonic acid) acts as a conductive bridge to construct a continuous conductive network inside the hydrogel. Furthermore, the end groups on the surface of MXene nanosheets generate strong electrostatic interactions with poly(3,4-ethylenedioxythiophene), promoting the formation of highly conductive quinone-state poly(3,4-ethylenedioxythiophene) structures and further enhancing the conductivity of the hydrogel.

[0041] The polyvinyl alcohol (PVA) network forms hydrogen bonds with poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide) and hybrid nanofillers via hydroxyl groups. The PVA network, in turn, interacts with PVA and hybrid nanofillers through electrostatic interactions and hydrogen bonds, resulting in multiple intermolecular interactions and a multi-layered physically cross-linked double-network structure. The synergistic effect of these electrostatic interactions and hydrogen bonds endows the hydrogel with excellent mechanical properties, exhibiting an elongation at break of 1180%, a tensile strength of 2.12 MPa, and a toughness of 14.34 kJ / m. 3 It has an elastic modulus of 0.21 MPa, an electrical conductivity of 2.1 mS / cm, and excellent electrocatalytic performance.

[0042] The prepared hydrogel exhibits outstanding application effects in strain sensing and ascorbic acid detection in sweat. As a strain sensor, the hydrogel has a wide strain response range of 0% to 1000%, with sensitivity coefficients of 1.54, 3.53, and 7.35 in the strain ranges of 0% to 400%, 400% to 700%, and 700% to 1000%, respectively. The response time is 100 ms, and the recovery time is 96 ms. The electrochemical sensor prepared based on this hydrogel has a wide linear range of 0.5 µM to 300 µM for ascorbic acid detection, with a detection limit as low as 0.352 µM. It also exhibits good measurement and storage stability and can successfully monitor changes in ascorbic acid in the epidermal sweat of subjects who have taken vitamin C. Attached Figure Description

[0043] Figure 1 This is a transmission electron microscope image of the MXene-AgNPs composite material prepared in Example 1 of the present invention; Figure 2 This is a particle size distribution diagram of AgNPs in the MXene-AgNPs composite material prepared in Example 1 of the present invention; Figure 3 The tensile stress-strain curves of the conductive hydrogels containing different masses of MXene-AgNPs prepared in Example 2 of the present invention are shown. Figure 4 The diagram shows the toughness and elastic modulus of the conductive hydrogel containing different masses of MXene-AgNPs prepared in Example 2 of the present invention. Figure 5 The conductivity diagram shows the conductivity of the conductive hydrogels containing different masses of MXene-AgNPs prepared in Example 2 of this invention. Figure 6 The strain sensitivity diagram of the conductive hydrogel prepared in Example 2 of the present invention under tensile strain of 0% to 1000% is shown. Figure 7 The response time and recovery time of the conductive hydrogel prepared in Example 2 of the present invention under 50% tensile strain; Figure 8 DPV curves of different electrode materials in 200 μM ascorbic acid solution; Figure 9 The time-ampere response curves of the hydrogel electrochemical sensor in 0–350 μM ascorbic acid solutions are shown. Figure 10 The linearity curve of the hydrogel electrochemical sensor in 0–350 μM ascorbic acid solution is shown. Figure 11 This is a graph showing the selectivity of a hydrogel electrochemical sensor for common coexisting interfering substances in human sweat. Figure 12 Stability diagram of hydrogel electrochemical sensor for measuring ascorbic acid; Figure 13 This is a storage stability diagram of the hydrogel electrochemical sensor; Figure 14 The chronoamperometry response of a hydrogel electrochemical sensor to sweat AA within 60 minutes after a subject takes 1000 mg of vitamin C. Figure 15 The purpose of this study was to use a hydrogel electrochemical sensor to monitor changes in sweat AA concentration within 60 minutes of a subject taking 1000 mg of vitamin C. Detailed Implementation

[0044] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0045] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0046] Unless otherwise specified, all raw materials used in the following examples are commercially available; and all experimental methods used are conventional methods in the art.

[0047] The poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) composite (PEDOT:PSS) used in the following examples is a commercially available substance, model CLEVIOS PH 1000 from HERAEUS, manufacturer: Adamas; solid content is 1.4%; PEDOT:PSS≈1:2.5.

[0048] Example 1 Preparation and characterization of MXene-AgNPs composite materials: LiF was mixed with 9M HCl solution at a mass-to-volume ratio of 1g:20mL and stirred for 30min. Then, Ti3AlC2 blocky material was gradually added to the above solution, with a mass ratio of LiF to Ti3AlC2 blocky material of 1:1. The reaction was carried out at 38℃ for 48h. The resulting product was washed with deionized water and centrifuged repeatedly at 3500 rpm for 10min until the pH of the supernatant was 5. Subsequently, the precipitate was dispersed in 20mL of deionized water, sonicated for 20min, and then centrifuged at 3500 rpm for 3min. The supernatant was carefully collected and freeze-dried for 48h to finally obtain MXene.

[0049] 0.1 g MXene was dispersed in 80 mL of deionized water and sonicated in a water bath for 30 min. Separately, 40 mg AgNO3 was dissolved in 10 mL of deionized water to obtain an AgNO3 solution. Under vigorous stirring, the AgNO3 solution was added dropwise to the above MXene dispersion to reduce AgNO3 to silver nanoparticles (AgNPs) in situ. The resulting composite material was dispersed in an ultrasonic bath for 10 min and then freeze-dried for 48 h to finally obtain MXene nanosheets loaded with silver nanoparticles (denoted as MXene-AgNPs) composite material.

[0050] The prepared MXene-AgNPs were characterized. Their microstructure was studied using transmission electron microscopy, and the results are as follows: Figure 1 As shown, silver nanoparticles are uniformly loaded on the surface of layered MXene nanosheets without obvious aggregation, and the MXene nanosheets maintain a good two-dimensional layered structure. Further statistical analysis of the size of the silver nanoparticles yielded the following results: Figure 2 As shown, the silver nanoparticles have a concentrated particle size distribution with an average diameter of approximately 70 nm.

[0051] The above results demonstrate that the present invention successfully prepared MXene nanosheets uniformly loaded with silver nanoparticles via an in-situ reduction method. The silver nanoparticles uniformly distributed on the nanosheet surface serve as spatial isolation sites, inhibiting the stacking and aggregation of MXene nanosheets, and simultaneously providing a good conductive bridge for the subsequent construction of a conductive network.

[0052] Other MXene-AgNPs composite materials prepared using process parameters within the scope of this invention can achieve effects comparable to the aforementioned materials.

[0053] Example 2 Preparation of MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel: 2 mg of MXene-AgNPs prepared in Example 1 was dispersed in 0.1 mL of deionized water and sonicated in a water bath for 10 min. Then it was mixed with 0.15 mL of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) complex (PEDOT:PSS) and stirred vigorously for 2 h to obtain MXene-AgNPs / PEDOT:PSS solution.

[0054] The above MXene-AgNPs / PEDOT:PSS solution was mixed with 1.0 g of 10 wt% polyvinyl alcohol (PVA), 0.88 g of 40 wt% sulfobetaine methacrylate (SBMA), 2.56 g of 98% N-hydroxyethyl acrylamide (HEAA), and 0.5 mg of photoinitiator I 2959. The mixture was magnetically stirred for 5 min until homogeneous, and then transferred to a custom mold (20 mm × 4 mm × 1 mm). Photopolymerization was initiated by ultraviolet irradiation for 2 min. The wavelength of the ultraviolet light irradiation was 365 nm and the power was 40 W, resulting in MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel.

[0055] In this conductive hydrogel, PVA molecular chains form a first physically cross-linked network through hydrogen bonds, and SBMA and HEAA form a second chemically cross-linked network P (SBMA-co-HEAA) through photopolymerization. The two constitute a dual-network polymer matrix. MXene-AgNPs and PEDOT:PSS complex constitute a hybrid conductive nanofiller, which is uniformly dispersed in the dual-network matrix to form a three-dimensional continuous conductive network.

[0056] Example 3 Preparation of MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel: 2.5 mg of MXene-AgNPs prepared in Example 1 was dispersed in 0.1 mL of deionized water and sonicated in a water bath for 10 min. Then it was mixed with 0.15 mL of a poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) complex (PEDOT:PSS, solid content 1.4%) and stirred vigorously for 2 h to obtain an MXene-AgNPs / PEDOT:PSS solution.

[0057] The above MXene-AgNPs / PEDOT:PSS solution was mixed with 0.5g of 10wt% polyvinyl alcohol (PVA), 0.66g of 40wt% sulfobetaine methacrylate (SBMA), 1.31g of 98% N-hydroxyethyl acrylamide (HEAA), and 0.4mg of photoinitiator I 2959. The mixture was magnetically stirred for 5 minutes until homogeneous, and then transferred to a custom mold (20mm×4mm×1mm). Photopolymerization was initiated by ultraviolet irradiation for 2 minutes. The wavelength of the ultraviolet light irradiation was 365nm and the power was 40W, thus obtaining MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel.

[0058] Example 4 Preparation of MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel: 5 mg of MXene-AgNPs prepared in Example 1 was dispersed in 0.1 mL of deionized water and sonicated in a water bath for 10 min. Then it was mixed with 0.15 mL of a poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonic acid) complex (PEDOT:PSS, solid content 1.4%) and stirred vigorously for 2 h to obtain an MXene-AgNPs / PEDOT:PSS solution.

[0059] The above MXene-AgNPs / PEDOT:PSS solution was mixed with 1.5g of 10wt% polyvinyl alcohol (PVA), 1.32g of 40wt% sulfobetaine methacrylate (SBMA), 3.27g of 98% N-hydroxyethyl acrylamide (HEAA), and 1.0mg of photoinitiator I 2959. The mixture was magnetically stirred for 5 minutes until homogeneous, and then transferred to a custom mold (20mm×4mm×1mm). Photopolymerization was initiated by ultraviolet irradiation for 2 minutes. The wavelength of the ultraviolet light irradiation was 365nm and the power was 40W, thus obtaining MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) conductive hydrogel.

[0060] Example 5 Mechanical property testing of conductive hydrogels: The conductive hydrogel prepared in Example 2 was molded into a rectangle measuring 20 mm × 4 mm × 1 mm. Stress-strain tests were performed using an LD 24.202 microcomputer-controlled electronic universal testing machine under tensile speeds of 100 mm / min and clamping distances of 2 cm. The elastic modulus was calculated from the slope of the stress-strain curve within the strain range of 5% to 15%, and the toughness was calculated from the area enclosed by the stress-strain curve and the strain axis. The test results are as follows: Figure 3 and Figure 4 As shown.

[0061] To further investigate the effect of the amount of hybrid conductive nanofiller on the mechanical properties of hydrogels, this invention conducted comparative tests on hydrogels containing different masses of MXene-AgNPs. The results showed that when the mass of MXene-AgNPs was 2 mg, the hydrogel exhibited excellent comprehensive mechanical properties, with an elongation at break of 1180%, a tensile strength of 2.12 MPa, and a toughness of 14.34 KJ / m. 3 Its elastic modulus is 0.21 MPa.

[0062] The above results indicate that the dual-network structure based on the polyvinyl alcohol first network and the poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide) second network can preferentially dissipate energy under stress through the reversible breakage of hydrogen bonds in the first network, while the second network maintains structural integrity and provides elastic recovery. The two networks work together to bear the load, enabling the hydrogel to maintain high tensile strength, large elongation at break, and high toughness while introducing conductive fillers. This effectively overcomes the problem that existing conductive hydrogels cannot simultaneously achieve both mechanical and conductive properties.

[0063] Example 6 Conductive hydrogel conductivity test: The conductive hydrogel prepared in Example 2 was cut into 10mm × 10mm × 1mm squares. The top and bottom sides of the hydrogel were connected to conductive copper strips, which were then connected to the working electrode clip and counter electrode clip of a CHI 660E electrochemical workstation, respectively. The resistance of the hydrogel was tested using a linear voltammetry method with a potential window range of -0.5V to 0.5V and a scan rate of 100mV / s. The conductivity of the hydrogel was calculated using the formula R = (ρ × S) / L. The test results are as follows: Figure 5 As shown.

[0064] When the mass of MXene-AgNPs is 2 mg, the conductivity of the hydrogel is 2.1 mS / cm. This result indicates that the silver nanoparticles loaded on the surface of MXene nanosheets form conductive bridges between adjacent nanosheets, while PEDOT:PSS coats and connects the dispersed MXene nanosheets. Together, they construct a three-dimensional continuous conductive network, enabling the hydrogel to achieve high conductivity with a relatively low filler content.

[0065] Example 7 Conductive hydrogel strain sensing performance testing: The conductive hydrogel prepared in Example 2 was fixed on an LD24.202 microcomputer-controlled electronic universal testing machine. The tensile speed was set to 100 mm / min, the clamping distance was 2 cm, and a tensile strain ranging from 0% to 1000% was applied. Both ends of the hydrogel were connected to a CHI660E electrochemical workstation via conductive copper tape, and a voltage of 0.8 V was applied. Current-time measurements were used to record the current changes under different strains. The resistance of the hydrogel under different strains was calculated using R=U / I, and the relative resistance change under different strains was calculated using (R-R0) / R0. Finally, the (R-R0) / R0-strain curve was plotted, and the strain sensitivity coefficient (GF) of the hydrogel was calculated.

[0066] Test results are as follows Figure 6 As shown, the hydrogel has a wide strain detection range of 0% to 1000% and excellent sensitivity, and exhibits three different linear response intervals: the strain sensitivity coefficient is 1.54 in the strain range of 0% to 400%, the strain sensitivity coefficient is 3.53 in the strain range of 400% to 700%, and the strain sensitivity coefficient is 7.35 in the strain range of 700% to 1000%.

[0067] This segmented, incremental sensitivity characteristic stems from the phased structural evolution of the conductive network during the stretching process of the hydrogel: at low strain, the conductive network undergoes only slight deformation, resulting in a gradual change in resistance; at medium strain, the overlaps between MXene nanosheets gradually slip, some conductive pathways break, and the resistance change accelerates; at high strain, the conductive network undergoes significant reconstruction, a large number of conductive pathways break, and the resistance changes drastically. Thus, the hydrogel achieves a sensing response with both high sensitivity and good resolvability over a wide strain range, effectively solving the technical problem of existing conductive hydrogels failing to simultaneously satisfy both sensing sensitivity and a wide strain detection range.

[0068] The response speed of the hydrogel was further tested. The conductive hydrogel prepared in Example 2 was fixed on an LD24.202 microcomputer-controlled electronic universal testing machine. The tensile speed was set to 100 mm / min, the clamping distance was 2 cm, 50% strain was applied and held for 2 s, and then 0% strain was applied. The two ends of the hydrogel were connected to a CHI660E electrochemical workstation through conductive copper tape, and a voltage of 0.8 V was applied. The current change was recorded using a current-time test.

[0069] Test results are as follows Figure 7 As shown, the prepared hydrogel has a response time of 100 ms and a recovery time of 96 ms. These results demonstrate that the rapid energy dissipation and excellent elastic recovery properties of the dual-network matrix endow the hydrogel with rapid sensing response and recovery capabilities, meeting the application requirements for dynamic real-time monitoring such as human motion.

[0070] Example 8 Construction of a conductive hydrogel electrochemical sensor and performance testing of its ascorbic acid detection capabilities: Preparation of ascorbic acid standard solution: Dissolve 4.4 mg of ascorbic acid standard in 5 mL of deionized water to obtain an ascorbic acid solution with a concentration of 5 mM; then add the 5 mM ascorbic acid solution to a phosphate buffer solution with pH=6.5 and dilute to obtain a series of ascorbic acid solutions with concentrations of 0.5~350 μM.

[0071] Construction of the electrochemical sensor: 2 μL of the precursor solution of the conductive hydrogel described in Example 2 was dropped onto the working electrode area of ​​a screen-printed electrode with an electrode area of ​​0.07065 cm². Photopolymerization was initiated by UV laser irradiation for 2 min, thus obtaining the electrochemical sensor based on MXene-AgNPs / PEDOT:PSS / PVA / P(SBMA-co-HEAA) hydrogel. A three-electrode system was constructed using a carbon electrode as the counter electrode and an Ag / AgCl electrode as the reference electrode for electrochemical testing.

[0072] Electrocatalytic activity evaluation: The electrochemical oxidation behavior of ascorbic acid on different electrodes was studied using differential pulse voltammetry (DPV). The DPV potential range was 0.1V–0.9V, the potential increment was 4mV, the pulse amplitude was 50mV, and the sampling width was 0.0167s. The test results are as follows: Figure 8 As shown, compared with PVA / P (SBMA-co-HEAA) hydrogel electrodes and screen-printed electrodes (SPE), ascorbic acid exhibits a higher oxidation peak current and a lower oxidation peak potential in the hydrogel electrochemical sensor of this invention, indicating that the hydrogel of this invention has higher electrocatalytic activity. Furthermore, the oxidation peak current of the hydrogel electrochemical sensor containing MXene and AgNPs of this invention is significantly higher than that of the hydrogel electrode containing only MXene and the hydrogel electrode containing only PEDOT:PSS, indicating that MXene and silver nanoparticles synergistically enhance the electrocatalytic activity of the hydrogel against ascorbic acid, with silver nanoparticles being the main factor controlling the signal intensity.

[0073] The above results show that the hybrid conductive filler of the present invention not only provides excellent electron transport channels, but also introduces abundant electrocatalytic active sites, enabling the hydrogel to have both strain sensing capabilities and excellent electrochemical sensing performance. Thus, multimodal integration of physical sensing and electrochemical sensing is realized on the same material platform, solving the technical problem that existing conductive hydrogels have single functions and are difficult to achieve multimodal sensing integration.

[0074] Linearity range and detection limit testing: Using a CHI660E electrochemical workstation, the chronoamperometric method was employed. A voltage of 0.38V was applied, and the electrochemical sensor was placed in an ascorbic acid solution with a concentration ranging from 0.5 to 350 μM. Current changes were recorded. The test results are as follows: Figure 9 and Figure 10 As shown, the electrochemical sensor based on the hydrogel of this invention exhibits a detection linear range of 0.5–300 μM for ascorbic acid, with a calculated detection limit of 0.352 μM (S / N = 3). These results demonstrate that the electrochemical sensor of this invention possesses a wide linear range and a low detection limit for ascorbic acid.

[0075] Selectivity testing: Using a CHI660E electrochemical workstation, the chronoamperometric method was employed. A voltage of 0.38V was applied. The electrochemical sensor was placed in a 100μM ascorbic acid solution, and then 50μM uric acid, 170μM glucose, 10μM dopamine, 5mM lactic acid, 10mM urea, 50μM tyrosine, and 40μM tryptophan were added sequentially. Finally, 200μM ascorbic acid was added, and the current changes were recorded. The test results are as follows: Figure 11As shown, the current response did not change significantly when the above-mentioned common interfering substances were added, but the current response changed significantly when ascorbic acid was added, indicating that the electrochemical sensor based on the hydrogel of the present invention has good selectivity and anti-interference ability against ascorbic acid.

[0076] Stability testing: Using a CHI660E electrochemical workstation, the chronoamperometric method was employed. A voltage of 0.38V was applied, and the electrochemical sensor was placed in a 100μM ascorbic acid solution. Ten consecutive measurements were taken, and the current values ​​were recorded. The test results are as follows: Figure 12 As shown, the current values ​​fluctuated little in 10 consecutive measurements, indicating that the electrochemical sensor based on the hydrogel of this invention has good measurement stability.

[0077] Storage stability test: Using a CHI660E electrochemical workstation, the time-amperometry method was employed. A voltage of 0.38V was applied, and the electrochemical sensor was stored at -4℃ for 7 days. The current change over 7 days in 100μM ascorbic acid solution was then measured. The test results are as follows: Figure 13 As shown, the current response remained stable during the 7-day storage period, indicating that the electrochemical sensor based on the hydrogel of this invention has good storage stability.

[0078] Actual sweat sample testing: Using a CHI660E electrochemical workstation, actual sweat samples were tested using a chronoamperometric method. A voltage of 0.38V was applied, and current changes were recorded. The electrochemical sensor was attached to the neck of a subject who had taken 1000mg of vitamin C. The subject then performed running exercises, and the change in ascorbic acid concentration in sweat was measured within 60 minutes after medication administration. The test results are as follows: Figure 14 and Figure 15 As shown, the electrochemical sensor based on the hydrogel of this invention can sensitively detect the dynamic changes in the concentration of ascorbic acid in the sweat of the subject.

[0079] The results indicate that the conductive hydrogel electrochemical sensor of the present invention can be practically applied to the non-invasive, real-time monitoring of ascorbic acid in human sweat, and has good application prospects.

[0080] As can be seen from Examples 1 to 6, the conductive hydrogel provided by the present invention achieves excellent mechanical properties (tensile strength 2.12 MPa, elongation at break 1180%, toughness 14.34 KJ / m) through the synergistic design of a dual-network polymer matrix and hybrid conductive nanofillers. 3It possesses an elastic modulus of 0.21 MPa, high electrical conductivity (2.1 mS / cm), wide-range and highly sensitive strain sensing performance (0%~1000% wide strain detection range, segmented sensitivity coefficient up to 7.35, response time 100 ms, recovery time 96 ms), and excellent electrochemical sensing performance (ascorbic acid detection linear range 0.5~300 μM, detection limit 0.352 μM, with good selectivity, measurement stability, and storage stability). This comprehensively solves the technical problems of existing conductive hydrogels, such as the difficulty in balancing mechanical and electrical conductivity, the easy aggregation and instability of conductive networks, the difficulty in balancing sensing sensitivity and detection range, and the single function.

[0081] The conductive hydrogels prepared in Examples 3-4 can achieve technical effects that are basically equivalent to those in Example 2.

[0082] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A conductive hydrogel, characterized in that, It includes a polymer matrix and a conductive filler dispersed in the polymer matrix, wherein, The polymer matrix is ​​a dual-network polymer matrix, which is composed of a first network and a second network that interpenetrate and crosslink. The first crosslinking network is a network formed by crosslinking polyvinyl alcohol, and the second network is poly(sulfobetaine methacrylate-co-N-hydroxyethylacrylamide). The conductive filler is a hybrid conductive nanofiller, which includes MXene nanosheets loaded with silver nanoparticles and poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) composite.

2. The conductive hydrogel according to claim 1, characterized in that, In the MXene nanosheets loaded with silver nanoparticles, the silver nanoparticles are loaded on the surface of the MXene nanosheets; the average diameter of the silver nanoparticles is 50 nm to 90 nm.

3. The conductive hydrogel according to claim 1, characterized in that, The conductive hydrogel has a tensile strength of 1 MPa to 2.5 MPa, an elongation at break of 800% to 1300%, and a toughness of 5 KJ / m. 3 ~15KJ / m 3 The elastic modulus is 0.1 MPa to 0.3 MPa; the electrical conductivity is 0.6 mS / cm to 3 mS / cm.

4. The conductive hydrogel according to claim 1, characterized in that, The strain sensitivity coefficient of the conductive hydrogel is 1.0~2.0 in the tensile strain range of 0%~100%; 2.0~4.0 in the tensile strain range of 100%~500%; and 4.0~8.0 in the tensile strain range of 500%~1000%.

5. The conductive hydrogel according to claim 1, characterized in that, The conductive hydrogel has a response time of no more than 120ms and a recovery time of no more than 100ms under 50% tensile strain.

6. A method for preparing the conductive hydrogel according to claim 1, characterized in that, Includes the following steps: MXene was dispersed in deionized water to obtain an MXene dispersion; AgNO3 solution was added dropwise to the MXene dispersion under stirring to reduce AgNO3 to silver nanoparticles in situ. After dispersion and freeze-drying, MXene nanosheets loaded with silver nanoparticles were obtained. The MXene nanosheets loaded with silver nanoparticles were dispersed in deionized water and mixed with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composite to obtain a hybrid conductive nanofiller mixture. The hybrid conductive nanofiller mixture was mixed evenly with polyvinyl alcohol, a second network monomer and a photoinitiator, transferred to a mold, and photopolymerized by ultraviolet irradiation to obtain a conductive hydrogel. The second network monomer is a mixture of sulfobetaine methacrylate and N-hydroxyethylacrylamide.

7. The method for preparing the conductive hydrogel according to claim 6, characterized in that, The preparation method of the MXene is as follows: After mixing LiF with HCl solution, Ti3AlC2 was added, and the mixture was reacted at 37℃~39℃ for 46h~50h. The product was washed with deionized water and centrifuged until the pH of the supernatant was 4~6. The precipitate was dispersed in deionized water, sonicated, and centrifuged. The supernatant was collected and freeze-dried to obtain MXene.

8. The method for preparing the conductive hydrogel according to claim 6, characterized in that, When preparing MXene nanosheets loaded with silver nanoparticles, the mass ratio of MXene to AgNO3 is (2~14):(2~5). When preparing hybrid conductive nanofillers, the mass ratio of the MXene nanosheets loaded with silver nanoparticles to the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) composite is (1~4):(0.7~2.8). When preparing the conductive hydrogel, the mass ratio of the hybrid conductive nanofiller, polyvinyl alcohol, methacrylate sulfobetaine, and N-hydroxyethyl acrylamide is (3.1~7.1):(50~150):(264~528):(1280~3200). The photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; The ultraviolet irradiation time is 2 min to 4 min.

9. The application of a conductive hydrogel prepared by the method of preparing a conductive hydrogel according to any one of claims 1 to 5 or according to any one of claims 6 to 8 in the fabrication of a flexible sensor, characterized in that, The flexible sensor includes a strain sensor and an electrochemical sensor.

10. The application according to claim 9, characterized in that, The strain sensor is used for human motion monitoring; the electrochemical sensor is used to detect ascorbic acid in human sweat.

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