Anisotropic and high-conductivity adhesive hydrogel as well as preparation method and application thereof

Abstract

The invention discloses anisotropic and high-conductivity adhesive hydrogel and a preparation method and application thereof.In the preparation process, PEDOT: SCS-SH is introduced into the hydrogel, so that the hydrogel has good conductivity and adhesion, and meanwhile, a covalent organic framework material of a porous structure is added to improve the electron and ion transmission rate, so that the conductivity is improved. The hydrogel is crosslinked with a prefabricated solution prepared from acrylamide monomers, bacterial cellulose, a phytic acid solution and deionized water through hydrogen bonds, and the anisotropic nano composite ion-electron conductive hydrogel is formed by shearing cellulose orientation. The prepared anisotropic high-conductivity adhesive hydrogel has excellent sensing performance and is expected to play an important role in the field of human-computer interaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedical composite materials and relates to conductive adhesive hydrogels, in particular to an anisotropic, highly conductive adhesive hydrogel and a preparation method and application thereof. Background Art

[0002] With the deepening of global aging and the continuous growth of the number of patients with chronic diseases, the demand for flexible sensing materials that can efficiently convert and accurately analyze measurement information (such as physiological signals such as heart rate, brain neuron activity, and tissue deformation) is growing. Cellulose-based ion-conductive hydrogels (ICCHs) exhibit excellent mechanical properties due to their rich hydrogen bond network structure and high aspect ratio nanofiber structure. ICCHs also have low cost, biocompatibility, and a conductivity mechanism similar to that of tissue, which gives them significant advantages in the field of flexible wearable strain sensing materials. However, the disordered network structure and the dependence of the interfacial bonding force on the ICCHs components make it difficult to balance mechanical properties, conductivity, and tissue adhesion, affecting their strain sensing sensitivity, especially the acquisition of weak signals.

[0003] To this end, Roya Sedghi's team prepared a conductive composite hydrogel by doping multi-walled carbon nanotubes (MWCNTs) into hydroxyethyl cellulose-based conductive hydrogels (ICHs). The hydrogel exhibited good adhesion strength to different substrates and a conductivity of 1.22 Scm -1 , the elongation at break is 400%, and its strain sensitivity (GF) is 10.97 in the strain range of 0 to 80% (Chemical Engineering Journal, 2025, 161112). Yingjie Zhao’s team prepared anisotropic conductive hydrogel PTPB by adding polyaniline-encapsulated bacterial cellulose to polyvinyl alcohol. The hydrogel can adhere well and lift an object weighing 500g. Its elongation at break exceeds 300%, and its GF is 1.77 in the strain range of 0 to 100% (Chemical Engineering Journal, 2025, 162702). Tingjie Chen’s team created a polyvinyl alcohol hydrogel modified with plant fibers and carbon nanotubes, which has self-healing and self-adhesive capabilities and a tensile strain of 4200%, with a conductivity of 0.28S cm -1, the GF is 1.27 in the strain range of 0 to 200% (Advanced Composites and Hybrid Materials, 2025, 8, 214). In addition, the patent (CN116655959A) loads the suspension of nanocrystalline cellulose (CNC) prepared by acid hydrolysis with natural polyphenol tannic acid (TA), and adds ammonium alginate (SA) and TA@CNC to polyvinyl alcohol-styrene pyridinium (PVA-SbQ) solution and stirs evenly to form a pre-gel solution, which is then cured by ultraviolet light to form an isotropic hydrogel. Finally, the hydrogel is placed in an electrolyte solution to fix the pre-stretching of the hydrogel to obtain an anisotropic hydrogel with a strength of 44.23 Jm -2 The adhesion energy, elongation at break and electrical conductivity are 513% and 0.53Sm respectively. -1 The patent (CN118271652A) prepares a mixed aqueous solution of carboxymethyl cellulose and sodium lignin sulfonate, adds acrylamide monomers and initiators to thermally initiate polymerization to obtain a composite hydrogel, and then undergoes in-situ polymerization of aniline and iron ion coordination crosslinking to prepare a carboxymethyl cellulose-based conductive hydrogel. The tensile strength and elongation at break of the hydrogel are 78kPa and 195% respectively, and the conductivity is 0.03Sm -1 , with a GF of 5.17 within the strain range of 0-150%. Although various innovative approaches have been able to address the problems of disordered network structures and insufficient adhesion of conductive hydrogels to a certain extent, the development of conductive hydrogels with high-sensitivity strain sensing performance in the low strain range still faces many severe challenges and urgently requires further breakthroughs and innovations.

[0004] The patent previously filed by our research group (CN118515857A) increases the solubility of PEDOT in aqueous solution by introducing sulfonated chitosan. Subsequently, SCS is functionalized with sulfhydryl groups. The sulfhydryl functionalized groups include lipoic acid, disulfide bonds in N-acetyl-L-cysteine, or other functional groups containing -SH, -CHO, etc., and finally a complex of sulfhydryl-containing sulfonated chitosan and poly (3,4-ethylenedioxythiophene) (PEDOT:SCS-SH) is prepared. This complex increases its water solubility while broadening its application in The scope of application in special demand scenarios, especially for the preparation of hydrogel materials, can simultaneously improve the conductivity and adhesion of the prepared hydrogel materials; the patent previously applied for by this research group (CN117720750A) combines the covalent organic framework channel structure and uniaxial tensile mechanical shearing action, and uses acrylic monomers, cellulose derivatives, and metal salt solutions as raw materials to prepare anisotropic conductive hydrogels, and achieves its one-sided self-adhesion by post-treatment of the asymmetric surface of the hydrogel, and finally obtains a conductive hydrogel with anisotropic mechanical properties and one-sided self-adhesion. This hydrogel has improved mechanical properties and sensitivity in specific directions, and is not affected by pollutants, and has broad application prospects in the field of human-computer interaction. Based on this research and development result, further development of hydrogel materials that are highly sensitive to low strain ranges is of great significance for meeting the sensitivity and comfort requirements of medical monitoring wearable devices and promoting the development of hydrogels in the field of wearable health monitoring. Summary of the Invention

[0005] In order to solve the problem of low sensing sensitivity faced by ion-conductive hydrogels in the field of physiological signal sensing, the present invention provides an anisotropic, highly conductive and adhesive hydrogel, and a preparation method and application thereof. The method prepares a hydrogel with excellent comprehensive performance that combines conductivity, adhesion and mechanical properties and can be used for sensitive and comfortable biological signal acquisition. This invention aims to fabricate anisotropic, highly conductive and adhesive hydrogels by combining a self-synthesized sulfhydryl-containing sulfonated chitosan complex with poly(3,4-ethylenedioxythiophene) (PEDOT:SCS-SH), the regular channel structure of a porous covalent organic framework (COF), and the anisotropic structure of bacterial cellulose (BC). The addition of the porous COF increases the electron and ion transport rates, significantly improving the conductivity of the hydrogel, and its anisotropic conductivity. Its anisotropic network structure imparts sensitive sensing properties in different directions. The -SH groups on the PEDOT:SCS-SH form -SS- groups on the skin surface to enhance surface adhesion. This comprehensive improvement in conductivity, network structure, and adhesion effectively enhances the sensing performance of the prepared hydrogel. The resulting anisotropic, highly conductive and adhesive hydrogel meets the sensitivity and comfort requirements of wearable medical monitoring devices, and is of great significance for the development of hydrogels in the field of flexible wearable health monitoring.

[0006] The present invention adopts the following technical solution to solve the above technical problems, a method for preparing anisotropic, highly conductive and adhesive hydrogel, and its specific preparation process is as follows:

[0007] Step S1, uniformly dispersing a sulfhydryl-containing sulfonated chitosan and a poly(3,4-ethylenedioxythiophene) complex in deionized water to obtain a PEDOT:SCS-SH solution, and uniformly dispersing a porous covalent organic framework material in deionized water to obtain a COF solution;

[0008] Step S2, stirring and mixing acrylamide monomers, bacterial cellulose, phytic acid solution and deionized water to obtain a mixed solution I, and dissolving an initiator ammonium persulfate in deionized water to obtain an ammonium persulfate solution;

[0009] Step S3, adding the PEDOT:SCS-SH solution and COF solution obtained in step S1 to the mixed solution I obtained in step S2 and stirring to fully dissolve, then adding the ammonium persulfate solution obtained in step S2 and stirring to mix uniformly to obtain a mixed solution II;

[0010] Step S4, pouring the mixed solution II obtained in step S3 into a mold, placing it in an oven for gelation, and then applying lipoic acid solution on the bottom of the hydrogel to finally obtain an anisotropic, highly conductive and adhesive hydrogel.

[0011] Furthermore, the covalent organic framework material of the porous structure in step S1 is a non-ionic covalent organic framework NCOF or a zwitterionic covalent organic framework Zwitt-COF.

[0012] Furthermore, in step S1, the mass fraction of the PEDOT:SCS-SH solution is 2 wt% to 8 wt%, and the mass fraction of the COF solution is 0.005 wt% to 0.025 wt%.

[0013] Furthermore, the acrylamide monomer in step S2 is one or more of acrylamide, methacrylamide, N-isopropylacrylamide and N,N-dimethylacrylamide; and the mass fraction of the phytic acid solution is 10 wt% to 20 wt%.

[0014] Furthermore, in step S2, the feed mass ratio of acrylamide monomer, bacterial cellulose, phytic acid solution and deionized water is (1-5):(1-7):(6-12):(3-7), and the mass fraction of ammonium persulfate solution is 1.28wt% to 2.56wt%.

[0015] Furthermore, the shear rate of the stirring process in step S2 is greater than 1000s -1The PEDOT:SCS-SH solution and COF solution in step S3 are added to the mixed solution I and ultrasonically stirred for 20 to 40 minutes, and then the ammonium persulfate solution is added and ultrasonically stirred for 5 to 10 minutes.

[0016] Furthermore, in step S3, the mass ratio of the PEDOT:SCS-SH solution, COF solution, mixed solution I and ammonium persulfate solution is (1-3):(0.001-0.005):(16-20):(0.01-0.05).

[0017] Furthermore, in step S4, the temperature of the oven is 40-45° C., and the gelation time is 2-8 hours.

[0018] Furthermore, the concentration of the lipoic acid solution in step S4 is 0.05-2 mol / L.

[0019] The anisotropic, highly conductive and adhesive hydrogel of the present invention is prepared by the above method.

[0020] The application of the anisotropic, highly conductive adhesion hydrogel described in the present invention in the preparation of flexible wearable biosignal acquisition sensors.

[0021] Compared with the prior art, the present invention has the following beneficial effects and advantages:

[0022] (1) The porous COF used in the present invention has the characteristics of regular structure, low density, large specific surface area, strong monomer modification, and diversified functions. The addition of the porous COF will further accelerate the transmission rate of electrons and ions and improve the conductivity.

[0023] (2) The bacterial cellulose used in the present invention has an anisotropic structure, which promotes the transmission of ions in the channel and improves the sensitivity in a specific direction.

[0024] (3) The PEDOT:SCS-SH independently synthesized by the present invention has both conductive effect and adhesiveness (-SH can form a covalent bond with -SH on the skin surface), promoting the application of hydrogels in human-computer interaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 In order to test the electrical conductivity of polyacrylamide hydrogel and nanocomposite ion-electron conductive hydrogel respectively, the electrical conductivity of the hydrogel and the nanocomposite ion-electron conductive hydrogel were tested.

[0026] Figure 2 By connecting nanocomposite ion-electron conductive hydrogels in different directions to the circuit and observing the changes in the brightness of the bulb, the anisotropy of the hydrogel conductivity was obtained.

[0027] Figure 3To characterize the adhesive properties of nanocomposite ion-electron conductive hydrogels, the adhesion performance on various substrates as well as pig skin and lipoic acid treated hydrogels was tested.

[0028] Figure 4 To detect the signals of nanocomposite ion-electronic conductive hydrogel under different deformations using a universal testing machine and an electrochemical workstation.

[0029] Figure 5 The strain sensitivity (GF) of the nanocomposite ion-electronic conductive hydrogel was obtained by calculating the ratio of the resistance change rate under different strain strengths to the inverse of the strain strength. DETAILED DESCRIPTION

[0030] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0031] Example 1

[0032] Preparation of nanocomposite ion-electron conductive hydrogel:

[0033] Step S1: At room temperature, a sulfhydryl-containing sulfonated chitosan and poly (3,4-ethylenedioxythiophene) complex (PEDOT:SCS-SH, for its preparation process, see patent document CN118515857A) is dispersed in deionized water to prepare a PEDOT:SCS-SH solution with a mass fraction of 5 wt%, and a porous covalent organic framework (NCOF, for its preparation process, see patent document CN117720750A) is dispersed in deionized water to prepare a NCOF solution with a mass fraction of 0.015 wt%.

[0034] Step S2: at room temperature, acrylamide monomer, bacterial cellulose and phytic acid solution (mass fraction 15 wt%) were dispersed in deionized water, wherein the mass ratio of acrylamide monomer, bacterial cellulose, phytic acid solution and deionized water was 4:2:7:3, and stirred (shear rate greater than 1000s -1 ) were mixed uniformly to obtain a mixed solution I, and then the initiator ammonium persulfate was dissolved in deionized water to obtain an ammonium persulfate solution with a mass fraction of 2.5 wt%.

[0035] Step S3: The PEDOT:SCS-SH solution and NCOF solution obtained in step S1 were added to the mixed solution I obtained in step S2 and ultrasonically stirred and mixed for 30 minutes to fully dissolve them. The ammonium persulfate solution obtained in step S2 was then added and ultrasonically stirred and mixed for 8 minutes to obtain a mixed solution II, wherein the mass ratio of the PEDOT:SCS-SH solution, the COF solution, the mixed solution I, and the ammonium persulfate solution was 1:0.001:18:0.02.

[0036] Step S4: Pour the mixed solution II obtained in step S3 into a mold, and then place it in an oven at 45°C for 8 hours to react for gelation. Then, apply 2 mol / L lipoic acid solution to the bottom of the hydrogel (to give it -COOH and -SS- to form hydrogen bonds and covalent bonds with the skin surface), and finally obtain a nanocomposite ion-electronic conductive hydrogel.

[0037] Example 2

[0038] Preparation of nanocomposite ion-electron conductive hydrogel:

[0039] Step S1: At room temperature, a sulfhydryl-containing sulfonated chitosan and poly (3,4-ethylenedioxythiophene) complex (PEDOT:SCS-SH, for its preparation process, see patent document CN118515857A) is dispersed in deionized water to prepare a PEDOT:SCS-SH solution with a mass fraction of 5 wt%, and a porous covalent organic framework (Zwitt-COF, for its preparation process, see patent document CN117720750A) is dispersed in deionized water to prepare a ZCOF solution with a mass fraction of 0.015 wt%.

[0040] Step S2: at room temperature, acrylamide monomer, bacterial cellulose and phytic acid solution (mass fraction 15 wt%) were dispersed in deionized water, wherein the mass ratio of acrylamide monomer, bacterial cellulose, phytic acid solution and deionized water was 4:2:7:3, and stirred (shear rate greater than 1000s -1 ) were mixed uniformly to obtain a mixed solution I, and then the initiator ammonium persulfate was dissolved in deionized water to obtain an ammonium persulfate solution with a mass fraction of 2.5 wt%.

[0041] Step S3: The PEDOT:SCS-SH solution and NCOF solution obtained in step S1 were added to the mixed solution I obtained in step S2 and ultrasonically stirred and mixed for 30 minutes to fully dissolve them. The ammonium persulfate solution obtained in step S2 was then added and ultrasonically stirred and mixed for 8 minutes to obtain a mixed solution II, wherein the mass ratio of the PEDOT:SCS-SH solution, the COF solution, the mixed solution I, and the ammonium persulfate solution was 1:0.001:18:0.02.

[0042] Step S4: Pour the mixed solution II obtained in step S3 into a mold, and then place it in an oven at 45°C for 8 hours to react for gelation. Then, apply 2 mol / L lipoic acid solution to the bottom of the hydrogel (to give it -COOH and -SS- to form hydrogen bonds and covalent bonds with the skin surface), and finally obtain a nanocomposite ion-electronic conductive hydrogel.

[0043] Comparative Example 1

[0044] Preparation of polyacrylamide hydrogel:

[0045] Step S1: at room temperature, add acrylamide monomer into deionized water, and stir to completely dissolve it to obtain an acrylamide solution with a mass fraction of 54 wt%.

[0046] Step S2: dissolving ammonium persulfate in deionized water to obtain a 4 wt% ammonium persulfate solution, and adding the solution to the acrylamide solution obtained in step S1, wherein the mass ratio of the ammonium persulfate solution to the acrylamide solution is 2:27. After stirring, the solution is transferred to a mold and reacted in an oven at 45°C for 8 h to obtain a polyacrylamide hydrogel.

[0047] Figure 1 The conductivity test results of the hydrogels prepared in Example 1 and Comparative Example 1 are shown in the figure. It can be seen from the figure that the conductivity of the polyacrylamide hydrogel prepared in Comparative Example 1 is 0.048Sm -1 The conductivity of the nanocomposite ion-electron hydrogel prepared in Example 1 is 18.87Sm -1 .

[0048] Figure 2 By connecting the nanocomposite ion-electron conductive hydrogel in different orientations to a circuit and observing the changes in the brightness of the light bulb, the researchers observed differences in the brightness of the light bulb. This phenomenon reflects the differences in the conductivity of the hydrogel in different orientations, revealing the anisotropic conductivity of the hydrogel.

[0049] Figure 3 The purpose of this study was to characterize the adhesion properties of nanocomposite ion-electron conductive hydrogels by testing their adhesion properties on various substrates as well as pig skin and lipoic acid treated hydrogels. Figure 3 A and Figure 3 It can be seen from Figure b that the hydrogel can adhere well to a variety of matrices and pig skin surfaces. Figure 3 Zhongb and Figure 3 Figure c shows that the adhesion of the hydrogel treated with lipoic acid on pig skin was significantly enhanced.

[0050] Figure 4This is the result of signal detection of nanocomposite ion-electronic conductive hydrogel under different deformations using a universal testing machine and an electrochemical workstation. The figure shows that the hydrogel exhibits excellent detection stability under various strain conditions, especially in the low strain range, and its detection results show higher stability and reliability.

[0051] Figure 5 The strain sensitivity (GF) of the nanocomposite ion-electronic conductive hydrogel is obtained by calculating the ratio of the resistance change rate under different strain strengths to the inverse of the strain strength. It can be seen from the figure that the prepared hydrogel exhibits a significantly high GF value in the low strain range, proving that it has excellent high-sensitivity strain sensing performance in the low strain range.

[0052] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing anisotropic, highly conductive and adhesive hydrogel, characterized in that The specific preparation process is: Step S1, uniformly dispersing a sulfhydryl-containing sulfonated chitosan and a poly(3,4-ethylenedioxythiophene) complex in deionized water to obtain a PEDOT:SCS-SH solution, and uniformly dispersing a porous covalent organic framework material in deionized water to obtain a COF solution; Step S2, stirring and mixing acrylamide monomers, bacterial cellulose, phytic acid solution and deionized water to obtain a mixed solution I, and dissolving an initiator ammonium persulfate in deionized water to obtain an ammonium persulfate solution; Step S3, adding the PEDOT:SCS-SH solution and COF solution obtained in step S1 to the mixed solution I obtained in step S2 and stirring to fully dissolve, then adding the ammonium persulfate solution obtained in step S2 and stirring to mix uniformly to obtain a mixed solution II; Step S4, pouring the mixed solution II obtained in step S3 into a mold, placing it in an oven for gelation, and then applying lipoic acid solution on the bottom of the hydrogel to finally obtain an anisotropic, highly conductive and adhesive hydrogel.

2. The method for preparing an anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: The covalent organic framework material of the porous structure in step S1 is a non-ionic covalent organic framework NCOF or a zwitterionic covalent organic framework Zwitt-COF.

3. The method for preparing an anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: The mass fraction of the PEDOT:SCS-SH solution in step S1 is 2 wt % to 8 wt %, and the mass fraction of the COF solution is 0.005 wt % to 0.025 wt %.

4. The method for preparing an anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: In step S2, the acrylamide monomer is one or more of acrylamide, methacrylamide, N-isopropylacrylamide and N,N-dimethylacrylamide; and the mass fraction of the phytic acid solution is 10 wt% to 20 wt%.

5. The method for preparing anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: In step S2, the feeding mass ratio of acrylamide monomer, bacterial cellulose, phytic acid solution and deionized water is (1-5):(1-7):(6-12):(3-7), and the mass fraction of ammonium persulfate solution is 1.28wt% to 2.56wt%.

6. The method for preparing an anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: The shear rate of the stirring process in step S2 is greater than 1000s -1 The PEDOT:SCS-SH solution and COF solution in step S3 are added to the mixed solution I and ultrasonically stirred for 20 to 40 minutes, and then the ammonium persulfate solution is added and ultrasonically stirred for 5 to 10 minutes.

7. The method for preparing anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: The mass ratio of the PEDOT:SCS-SH solution, COF solution, mixed solution I and ammonium persulfate solution in step S3 is (1-3):(0.001-0.005):(16-20):(0.01-0.05).

8. The method for preparing anisotropic, highly conductive and adhesive hydrogel according to claim 1, wherein: In step S4, the temperature of the oven is 40-45° C., the gelation time is 2-8 hours, and the concentration of the lipoic acid solution is 0.05-2 mol / L.

9. An anisotropic, highly conductive and adhesive hydrogel, characterized in that The method is prepared by any one of claims 1 to 8.

10. Use of the anisotropic, highly conductive and adhesive hydrogel according to claim 9 in preparing a flexible wearable biosignal acquisition sensor.

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