Double-layer integrated asymmetric viscous hydrogel as well as preparation method and application thereof

Abstract

The invention relates to double-layer integrated asymmetric viscous hydrogel as well as a preparation method and application thereof, and belongs to the technical field of hydrogel. The invention relates to a preparation method of double-layer integrated asymmetric viscous hydrogel, which comprises the following steps: adding natural macromolecular polysaccharide and a polymeric monomer into a salt solution, stirring at room temperature, then adding an initiator and a cross-linking agent, stirring and polymerizing to obtain the double-layer integrated asymmetric viscous hydrogel. Through a one-pot method, a salt component is introduced into a hydrogel system, and the hydrogel has a double-layer structure with asymmetric viscosity under the salting-out action; in addition, the hydrogel is doped with a carbon nanotube with the surface modified by polydopamine and silver nanoparticles, so that the mechanical property and the conductivity of the hydrogel are remarkably improved. The preparation method provided by the invention is simple, is suitable for various hydrogel systems, has good universality and is easy to popularize and apply.

Description

Technical Field

[0001] This invention relates to a bilayer integrated asymmetric viscous hydrogel, its preparation method and application, belonging to the field of hydrogel technology. Background Technology

[0002] Hydrogels are widely used in biosensing, tissue engineering, and medical devices due to their high biocompatibility, tunable mechanical properties, and biomimetic structural characteristics. Despite their ideal nature, challenges remain in practical applications. Self-adhesive hydrogels can cause unwanted adhesion to clothing, environmental contaminants, and non-sensoring areas on the side furthest from the skin. This not only causes discomfort during wear but also easily leads to secondary damage by adhering to skin wounds and affecting the accuracy and integrity of sensing signals. Therefore, the preparation of hydrogels with asymmetric adhesion properties is crucial in many fields.

[0003] Currently, constructing bilayer asymmetric adhesive hydrogels typically requires first preparing a first-layer hydrogel, and then combining a second hydrogel with different adhesion properties onto the first layer to achieve the bilayer asymmetric adhesiveness. Chinese Patent Publication No. CN113769120A discloses a method for preparing a bilayer conductive hydrogel. This method involves bonding a P(HEAA-co-SBAA) / PEDOT:PSS conductive hydrogel based on monomers HEAA and SBAA to a PNIPAM / PEDOT:PSS conductive hydrogel based on monomer N-isopropylacrylamide, thereby obtaining a bilayer conductive hydrogel. Chinese Patent Publication No. CN116985489B discloses a smart-responsive bilayer hydrogel, its preparation method, and its applications. This patent uses acrylamide, octadecyl methacrylate and carboxymethyl chitosan as raw materials to prepare a tough hydrogel layer by utilizing hydrophobic association; then, using modified hyaluronic acid, N-isopropylacrylamide, acrylamide and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) as raw materials, a viscous hydrogel layer is prepared on the tough hydrogel layer by a continuous in-situ polymerization process, and finally a bilayer hydrogel with intelligent response is obtained.

[0004] However, the hydrogels prepared by the above methods have weak interfacial bonding, are prone to peeling, and have complex, time-consuming, and poor interfacial compatibility. In addition, existing methods cannot simultaneously achieve the integration of a "self-supporting non-adhesive layer" and a "highly adhesive porous layer" in a single system, making the devices very prone to failure in dynamic environments (such as skin joint movement and moist tissue surfaces). Summary of the Invention

[0005] To address the aforementioned deficiencies in existing technologies, this invention provides a bilayer integrated asymmetric adhesive hydrogel, its preparation method, and its applications. This invention employs a one-pot method, introducing salt components into the hydrogel system and utilizing salting-out to create an asymmetric bilayer structure. One layer exhibits a non-adhesive, salt-stabilized layer, while the other layer exhibits an adhesive, porous hydrogel structure. Furthermore, by doping the hydrogel with carbon nanotubes surface-modified with polydopamine and silver nanoparticles, a bilayer integrated asymmetric adhesive hydrogel possessing both high mechanical and electrical properties is obtained. Finally, by varying the hydrogel materials and salt types, the versatility of the method described in this invention in preparing bilayer integrated asymmetric adhesive hydrogels is verified.

[0006] The first objective of this invention is to provide a method for preparing a bilayer integrated asymmetric adhesive hydrogel, comprising the following steps: adding natural high molecular weight polysaccharide and polymeric monomer to a salt solution, stirring at room temperature, then adding an initiator and a crosslinking agent, stirring, and polymerizing to obtain a bilayer integrated asymmetric adhesive hydrogel.

[0007] In the above technical solution, the salt solution is one or more of the following: sodium chloride (NaCl) aqueous solution, lithium chloride (LiCl) aqueous solution, potassium chloride (KCl) aqueous solution, sodium citrate aqueous solution, or sodium sulfate aqueous solution.

[0008] Preferably, the salt solution is two of the following: sodium chloride aqueous solution, lithium chloride aqueous solution, potassium chloride aqueous solution, sodium citrate aqueous solution, or sodium sulfate aqueous solution.

[0009] More preferably, the mass ratio of salts in the two salt solutions is 0.5 to 2.5.

[0010] In the above technical solution, the natural high molecular weight polysaccharide is one or more of sodium alginate, chitosan, or agarose.

[0011] In the above technical solution, the polymerizing monomer is acrylamide.

[0012] Preferably, the natural high-molecular-weight polysaccharide is sodium alginate.

[0013] Preferably, the sodium alginate is an ultra-low viscosity sodium alginate.

[0014] More preferably, when the natural high molecular weight polysaccharide is sodium alginate, the method of the present invention further includes: immersing the obtained bilayer integrated asymmetric viscous hydrogel in a 0.2~0.3 mol / L calcium chloride (CaCl2) solution for crosslinking for 0.5~1 h.

[0015] In the above technical solution, the initiator is potassium persulfate.

[0016] In the above technical solution, the crosslinking agent is N,N'-methylenebisacrylamide.

[0017] In the above technical solution, the mass-to-volume ratio of salt to water in the salt solution is 0.6~3.2 g : 13 mL.

[0018] In the above technical solution, the mass ratio of salt, natural high molecular weight polysaccharide, monomer small molecule, initiator and crosslinking agent is 0.6~3.2 : 0.9 : 2.0~3.5 : 0.035~0.045 : 0.001~0.003.

[0019] In the above technical solution, the polymerization conditions are polymerization at 55~65℃ for 3.5~4.5 h.

[0020] The strategy proposed in this invention, based on the salting-out-induced formation of a bilayer integrated asymmetric viscous structure, can be widely applied to other hydrogel systems.

[0021] A second objective of this invention is to provide a bilayer integrated asymmetric viscous hydrogel prepared by the above method.

[0022] The third objective of this invention is to provide a bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties. The hydrogel comprises a hydrogel matrix and CNT / PDA-Ag nanoparticles doped in the hydrogel matrix. The hydrogel matrix is ​​a hydrogel prepared by the above method, and the CNT / PDA-Ag nanoparticles are carbon nanotubes with surface-modified polydopamine and silver nanoparticles.

[0023] In the above technical solution, the CNT / PDA-Ag nanoparticles are prepared by the following method: carbon nanotubes are added to a Tris-HCl buffer solution, sonicated, and then dopamine hydrochloride is added. The mixture is stirred for 22-24 h to obtain CNT / PDA nanoparticles; then, the CNT / PDA nanoparticle aqueous dispersion is mixed with a silver ammonia solution, polyvinylpyrrolidone is added, and the mixture is stirred continuously at 75-85°C for 5-6 h, with continuous ultraviolet irradiation for the last 40 min to obtain CNT / PDA-Ag nanoparticles; wherein, The mass-to-volume ratio of the carbon nanotubes, dopamine hydrochloride, and Tris-HCl buffer solution is 0.05~0.10 g : 0.4~1.0 g : 200 mL; The mass-to-volume ratio of polyvinylpyrrolidone, CNT / PDA nanoparticle aqueous dispersion, and silver ammonia solution is 1.5 g : 80~100 mL : 50~60 mL, and the concentration of the CNT / PDA nanoparticle aqueous dispersion is 0.5~1.5 mg / mL.

[0024] Preferably, the Tris-HCl buffer solution is prepared by the following method: 0.62 g of tris(hydroxymethyl)aminoethane (Tris) is dissolved in 450 mL of deionized water, the pH of the solution is adjusted to 8.5 with concentrated hydrochloric acid (HCl), the volume is brought to 500 mL, and the pH of the solution is adjusted to 8.5 again with concentrated hydrochloric acid to obtain a Tris-HCl buffer solution with a concentration of 10 mM and a pH of 8.5 (10 mM, pH=8.5).

[0025] Preferably, the silver ammonia solution is prepared by the following method: 0.5 g of silver nitrate (AgNO3) is dissolved in 50 mL of deionized water to form a silver nitrate solution, and 95% ammonia water is added dropwise, causing the solution to change from clear to turbid and then back to clear, thus obtaining the silver ammonia solution.

[0026] Preferably, the CNT / PDA nanoparticle aqueous dispersion is obtained by dispersing CNT / PDA nanoparticles in deionized water and sonicating for 2 hours.

[0027] More preferably, the CNT / PDA-Ag nanoparticles are prepared by the following method: 0.05 g of carbon nanotubes are added to 200 mL of Tris-HCl buffer solution and sonicated for 2 h to obtain a homogeneous solution; 0.4 g of dopamine hydrochloride is added, and the mixture is stirred magnetically for 24 h. The mixture is then centrifuged at 13000 rpm, the precipitate is collected, and the precipitate is washed three times with ethanol and deionized water, respectively, and then freeze-dried to obtain CNT / PDA nanoparticles; the obtained CNT / PDA nanoparticles are then dispersed in 100 mL of deionized water to obtain an aqueous dispersion of CNT / PDA nanoparticles, which is mixed with 50 mL of silver ammonia solution, and 1.5 g of polyvinylpyrrolidone is added. The mixture is stirred continuously at 80 °C for 6 h, and then continuously irradiated with ultraviolet light for the last 40 min to obtain CNT / PDA-Ag nanoparticles.

[0028] In the above technical solution, the hydrogel has a tensile strength of 0.04~0.20 MPa, a breaking force of 2.0~6.0 N, an elongation at break of 844%~1287%, and an electrical conductivity of 0.005~0.01 S / cm.

[0029] The fourth objective of this invention is to provide a method for preparing the above-mentioned bilayer integrated asymmetric adhesive hydrogel with both high mechanical and electrical properties, comprising the following steps: adding natural polymeric polysaccharides and polymeric monomers to a salt solution and stirring at room temperature; then adding CNT-PDA / Ag nanoparticles and stirring at room temperature; finally adding an initiator and a crosslinking agent, stirring, and polymerizing to obtain a bilayer integrated asymmetric adhesive hydrogel with both high mechanical and electrical properties.

[0030] Further, the mass-to-volume ratio of salt to water in the salt solution is 0.6~3.2 g : 13 mL, and the mass ratio of salt, natural high molecular weight polysaccharide, polymeric monomer, initiator, crosslinking agent, and CNT-PDA / Ag nanoparticles is 0.6~3.2 : 0.9 : 2.0~3.5 : 0.035~0.045 : 0.001~0.003 : 0.010~0.015.

[0031] Furthermore, the polymerization conditions are polymerization at 55~65℃ for 3.5~4.5 h.

[0032] The fifth objective of this invention is to provide the application of the above-mentioned bilayer integrated asymmetric adhesive hydrogel or a bilayer integrated asymmetric adhesive hydrogel with both high mechanical and electrical properties in the fabrication of flexible sensors.

[0033] The beneficial effects of this invention are: (1) The method for preparing bilayer asymmetric adhesive hydrogels provided by this invention is simple, and the hydrogel can be integrally formed by a single "one-pot method" without the need for subsequent processing steps. During the forming process, the hydrogel undergoes spontaneous phase separation induced by salting out, thereby forming a bilayer structure with asymmetric adhesion properties. Furthermore, chemical bonding interfaces are formed between the layers through salting out deposition, resulting in no interlayer delamination and a stable structure. In addition, this method has good versatility, is applicable to various hydrogel systems, and is easy to promote and apply.

[0034] (2) The present invention incorporates carbon nanotubes with surface-modified polydopamine and silver nanoparticles into the bilayer asymmetric adhesive hydrogel described in the present invention. This composite strategy not only significantly enhances the mechanical properties of the hydrogel, but also significantly improves its electrical conductivity, enabling the hydrogel to achieve not only bilayer integrated asymmetric adhesiveness, but also to take into account both mechanical and electrical properties, and has a very broad application prospect. Attached Figure Description

[0035] Figure 1 The flowchart shows the preparation and experimental process of a bilayer integrated asymmetric viscous hydrogel loaded with CNT-PDA / Ag nanoparticles.

[0036] Figure 2 The image shows the asymmetric adhesion of the bilayer integrated asymmetric adhesive hydrogel obtained in Example 1, where the left image represents the non-adhesive layer and the right image represents the adhesive layer.

[0037] Figure 3 This is a photograph of the actual product of the bilayer integrated asymmetric viscous hydrogel obtained in Example 2.

[0038] Figure 4 This is a photograph of the actual double-layer integrated asymmetric viscous hydrogel obtained in Example 3.

[0039] Figure 5 This is a photograph of the actual double-layer integrated asymmetric viscous hydrogel obtained in Example 4.

[0040] Figure 6 This is a photograph of the actual double-layer integrated asymmetric viscous hydrogel obtained in Example 5.

[0041] Figure 7 This is a photograph of the actual double-layer integrated asymmetric viscous hydrogel obtained in Example 6.

[0042] Figure 8 The graph shows the comparison of the adhesion performance of the double-layer integrated asymmetric adhesive hydrogel adhesive layer and the non-adhesive layer obtained in Examples 1-6.

[0043] Figure 9 The bilayer integrated asymmetric hydrogel (Na) obtained in Example 1 + / Li + Figure 1 shows the tensile properties of PAMSA hydrogel, where (a) is the stress-strain curve, (b) is the tensile strength, (c) is the breaking force, and (d) is the elongation at break.

[0044] Figure 10 The bilayer integrated asymmetric adhesive hydrogel (Na2O3) obtained in Example 7 possesses both high mechanical and electrical properties. + / Li + The images and SEM images of the PAMSA@CPA hydrogel are shown, where (a) is a bilayer Na + / Li + -A photograph of the actual PAMSA@CPA hydrogel, (b) showing the bilayer Na + / Li + SEM image of PAMSA@CPA hydrogel, (c) is the bilayer Na + / Li + SEM image of the PAMSA@CPA hydrogel adhesion layer, (d) is the bilayer Na + / Li + -SEM image of the non-adhesive layer of PAMSA@CPA hydrogel.

[0045] Figure 11 The bilayer Na obtained in Example 7 + / Li + - An illustration of the asymmetric adhesion of PAMSA@CPA hydrogel, where the left image shows the non-adhesive layer and the right image shows the adhesive layer.

[0046] Figure 12 The bilayer Na obtained in Example 7 + / Li + -Graphic illustration of the mechanical properties of PAMSA@CPA hydrogel.

[0047] Figure 13 To prepare bilayer Na under different NaCl to LiCl mass ratios + / Li + - Figure 1 shows the tensile properties of PAMSA@CPA hydrogel. (a) is the stress-strain curve, (b) is the elongation at break, (c) is the tensile strength, and (d) is the breaking force.

[0048] Figure 14 To determine the bilayer Na+ prepared under different NaCl and LiCl addition amounts at the optimal mass ratio of 1.5. + / Li + - Figure 1 shows the tensile properties of PAMSA@CPA hydrogel. (a) is the stress-strain curve, (b) is the elongation at break, (c) is the tensile strength, and (d) is the breaking force.

[0049] Figure 15 (a) A graph showing the conductivity of hydrogels prepared under different NaCl to LiCl mass ratios; Figure 15 (b) is a graph showing the conductivity of hydrogels prepared under different NaCl and LiCl addition amounts when the optimal mass ratio is 1.5.

[0050] Figure 16 The bilayer Na obtained in Example 7 + / Li + - The resistance change rate of the PAMSA@CPA hydrogel strain sensor under (a) 5%-25%, (b) 20%-100%, (c) 100%-300% strain; sensor durability and stability test under 200 tensile cycles at 100% strain (d). Detailed Implementation

[0051] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0052] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0053] Example 1 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 1.5 g sodium chloride and 1.0 g lithium chloride in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g sodium alginate and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polytetrafluoroethylene mold, then polymerize at 60°C for 4 h, and then crosslink it in a 0.2 mol / L calcium chloride (CaCl2) solution for 1 h to obtain a bilayer integrated asymmetric viscous hydrogel, denoted as Na. + / Li + -PAMSA hydrogel, its asymmetric viscosity is shown in [link to relevant documentation]. Figure 2 .

[0054] Example 2 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 1.5 g sodium chloride and 1.0 g lithium chloride in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g chitosan and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polychlorotetrafluoroethylene mold, and then polymerize at 60°C for 4 h to obtain a bilayer integrated asymmetric viscous hydrogel. See the photograph of the actual product. Figure 3 .

[0055] Example 3 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 1.875 g sodium chloride and 1.25 g lithium chloride in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g agarose and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polychlorotetrafluoroethylene mold, and then polymerize at 60°C for 4 hours to obtain a bilayer integrated asymmetric viscous hydrogel. See the photograph of the actual product. Figure 4 .

[0056] Example 4 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 2.5 g of potassium chloride in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g sodium alginate and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polytetrafluoroethylene mold, then polymerize at 60°C for 4 h, and then crosslink in a 0.2 mol / L calcium chloride (CaCl2) solution for 1 h to obtain a bilayer integrated asymmetric viscous hydrogel. See the attached image for a photograph of the actual product. Figure 5 .

[0057] Example 5 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 2.5 g of sodium citrate in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g sodium alginate and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polytetrafluoroethylene mold, then polymerize at 60°C for 4 h, and then crosslink in a 0.2 mol / L calcium chloride (CaCl2) solution for 1 h to obtain a bilayer integrated asymmetric viscous hydrogel. See the attached image for a photograph of the actual product. Figure 6 .

[0058] Example 6 A method for preparing a bilayer integrated asymmetric viscous hydrogel includes the following steps: (1) Dissolve 3.5 g of sodium sulfate in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g sodium alginate and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (4) Pour the mixed solution into a polytetrafluoroethylene mold, then polymerize at 60°C for 4 h, and then crosslink in a 0.2 mol / L calcium chloride (CaCl2) solution for 1 h to obtain a bilayer integrated asymmetric viscous hydrogel. See the attached image for a photograph of the actual product. Figure 7 .

[0059] The comparison results of the adhesion performance of the bilayer integrated asymmetric adhesive hydrogel adhesive layer and the non-adhesive layer obtained in Examples 1-6 are shown in the figure. Figure 8 As can be seen, the hydrogels prepared in all examples exhibit significant asymmetric adhesion characteristics. The adhesive layer has strong adhesion to the substrate and maintains stable bonding during displacement, with a maximum adhesion force of 5-15 kPa; the non-adhesive layer hardly adheres. Among them, the hydrogel prepared in Example 1 shows the most obvious difference in asymmetric adhesion, with good uniformity of adhesion force in the adhesive layer and the best anti-sticking effect in the non-adhesive layer; Examples (2-6) with different combinations of salts (potassium chloride, sodium citrate, sodium sulfate) and natural high molecular weight polysaccharides (chitosan, agarose) can all achieve effective asymmetric adhesion, verifying the versatility of the preparation method.

[0060] The bilayer integrated asymmetric hydrogel (Na) obtained in Example 1 + / Li + The tensile property test results of the PAMSA hydrogel are shown below. Figure 9 It can be seen that the hydrogel has excellent tensile properties, and the stress-strain curve exhibits typical characteristics of a tough material. Figure 9 a). Its tensile strength can reach 0.04 MPa ( Figure 9 b), the breaking force is 0.4 N ( Figure 9 c), the elongation at break reaches 280% ( Figure 9 d) It exhibits good flexibility and fracture resistance. This mechanical property not only meets the deformation requirements when skin is in contact with the skin, but also avoids structural damage caused by stretching in dynamic environments (such as joint movement), making it suitable for wearable applications.

[0061] Example 7 A method for preparing CNT / PDA-Ag nanoparticles includes the following steps: (1) Dissolve 0.62 g of tris(hydroxymethyl)aminoethane (Tris) in 450 mL of deionized water, adjust the pH of the solution to 8.5 with concentrated hydrochloric acid (HCl), bring the volume to 500 mL, and then adjust the pH of the solution to 8.5 with concentrated hydrochloric acid to obtain a Tris-HCl buffer solution (10 mM, pH=8.5). (2) Weigh 0.05 g CNT and add it to 200 mL of Tris-HCl buffer solution (10 mM, pH=8.5). Disperse it under ultrasonic conditions for 2 h to form a homogeneous solution. (3) Add 0.4 g of dopamine hydrochloride (DA) to the above solution and stir magnetically for 24 h. Centrifuge the mixed solution at 13000 rpm to obtain the precipitate product. Then wash it three times with ethanol and deionized water respectively. After freeze drying, CNT / PDA nanoparticles are obtained. (4) The CNT / PDA nanoparticles prepared above were dispersed in 100 mL of deionized water and dispersed under ultrasonic conditions for 2 h to obtain a CNT / PDA nanoparticle dispersion. (5) Dissolve 0.5 g of silver nitrate (AgNO3) in 50 mL of deionized water to form a silver nitrate solution. Add 95% ammonia water dropwise until the solution changes from clear to turbid and then back to clear to obtain a silver ammonia solution. (6) The above CNT / PDA nanoparticle dispersion was mixed with silver ammonia solution, and 1.5 g of polyvinylpyrrolidone (PVP) was added as a stabilizer; the mixture was stirred continuously at 80°C for 6 h, and then continuously irradiated with ultraviolet light for the last 40 min to obtain a mixed solution; (7) The mixed solution was centrifuged at 13,000 rpm, the precipitate was collected, and then washed three times by centrifugation with ethanol and deionized water respectively. After freeze-drying, CNT / PDA-Ag nanoparticles were obtained.

[0062] A method for preparing a bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties includes the following steps: (1) Dissolve 1.5 g sodium chloride and 1.0 g lithium chloride in 13 mL of deionized water to obtain a salt solution; (2) Add 0.9 g sodium alginate and 2.475 g acrylamide to the above salt solution and stir continuously at room temperature until a homogeneous solution is formed; (3) Disperse 0.015 g of CNT-PDA / Ag nanoparticles in the solution and stir at room temperature for 10 min; (4) Add 0.0375 g potassium persulfate (KPS) and 0.001 g N,N'-methylenebisacrylamide (MBA) to the system and stir for 1 min to obtain a mixed solution; (5) Pour the mixed solution into a polytetrafluoroethylene mold, then polymerize at 60°C for 4 h, and then crosslink it in a 0.2 mol / L calcium chloride (CaCl2) solution for 1 h to obtain a bilayer Na + / Li + -PAMSA@CPA hydrogel.

[0063] Example 7 yielded a bilayer integrated asymmetric adhesive hydrogel (Na₂O₃) possessing both high mechanical and electrical properties. + / Li + See the actual product photos and SEM images of the PAMSA@CPA hydrogel. Figure 10 It can be seen that the hydrogel exhibits obvious stratification, and there are significant differences in microstructure between the adhesive layer and the non-adhesive layer. Figure 10 b). In the magnified view, salt crystals can be observed precipitating in the non-adhesive layer of the bilayer hydrogel. Figure 10 c), the adhesion layer has a classic hydrogel porous structure ( Figure 10 d), the difference in microstructure between the two endows the bilayer hydrogel with asymmetric viscosity.

[0064] The bilayer Na obtained in Example 7 + / Li + -See the demonstration of the asymmetric viscosity of PAMSA@CPA hydrogel. Figure 11 It can be seen that when the hydrogel is placed on an arc-shaped surface without the application of external force, the non-adhesive layer of the hydrogel cannot completely adhere to the arc-shaped surface, and there are gaps on both sides, proving that it does not have adhesive ability; while the adhesive layer of the hydrogel can completely adhere to the arc-shaped surface, proving that it has adhesive ability.

[0065] This invention demonstrates the mechanical properties of the hydrogel obtained in Example 7 more intuitively through experiments such as loading, bending, torsion, and tension. The results are shown in [Figure 7]. Figure 12 It can be seen that: double Na + / Li + -PAMSA@CPA hydrogel can lift a 500g weight, withstand significant bending and twisting, and when stretched from 5cm to 30cm, the hydrogel edges show no cracking. These experiments demonstrate that the bilayer Na + / Li + -PAMSA@CPA hydrogel has excellent mechanical strength and toughness.

[0066] Bilayer Na₂O obtained under different NaCl to LiCl mass ratios + / Li + The preparation method of -PAMSA@CPA hydrogel is the same as in Example 7, except that the mass ratio of NaCl to LiCl is different, and the resulting hydrogel is denoted as NaCl. + / Li + The tensile properties test results of X-PAMSA@CPA hydrogel are shown in [the table below]. Figure 13 It can be seen that when the mass ratio of NaCl to LiCl increases from 0.5 to 2.0, the bilayer NaCl... + / Li +The elongation at break of the X-PAMSA@CPA hydrogel increased from 1168% to 1287%, at which point the hydrogel exhibited its optimal elongation at break. As the NaCl / LiCl mass ratio continued to increase, the elongation at break began to decrease. When the NaCl / LiCl mass ratio increased from 0.5 to 1.0, the tensile strength increased from 0.0739 MPa to 0.0848 MPa, and the breaking force increased from 4.02 N to 4.26 N, at which point the hydrogel's tensile strength and breaking force reached their optimal values. With further increases in the NaCl / LiCl mass ratio, the bilayer Na... + / Li + The tensile strength and breaking strength of X-PAMSA@CPA hydrogels both showed a decreasing trend. Based on the above trends in the mechanical properties of hydrogels, bilayer Na... + / Li + 1.5-PAMSA@CPA hydrogel has the best mechanical properties, therefore the optimal mass ratio of NaCl to LiCl is 1.5.

[0067] When the optimal mass ratio of NaCl to LiCl is 1.5, the resulting bilayer NaCl under different LiCl addition conditions... + / Li + The preparation method of -PAMSA@CPA hydrogel is the same as in Example 7, except that the mass of LiCl added is different, and the resulting hydrogel is denoted as Na. + / Li + The tensile properties test results of Y-PAMSA@CPA hydrogel are shown in [the table below]. Figure 14 It can be seen that when the amount of LiCl added increases from 0.250 g to 0.750 g, the bilayer Na... + / Li + The elongation at break of the Y-PAMSA@CPA hydrogel decreased from 12.18% to 10.15%, the tensile strength decreased from 0.126 MPa to 0.049 MPa, and the breaking force decreased from 5.76 N to 2.43 N. With further increases in LiCl dosage, when the addition amounts of NaCl and LiCl were 1.500 g and 1.000 g respectively, the bilayer NaCl... + / Li +The mechanical properties of the Y-PAMSA@CPA hydrogel began to improve, with an elongation at break of 1202%, a tensile strength of 0.067 MPa, and a breaking force of 3.55 N. When the addition amounts of NaCl and LiCl reached 1.875 g and 1.250 g, respectively, the mechanical properties of the hydrogel rapidly decreased. This was due to excessive salting-out caused by the high concentration of inorganic salts, which disrupted the internal cross-linking network of the hydrogel, leading to a decline in mechanical properties. At this point, the elongation at break was 844%, the tensile strength was 0.045 MPa, and the breaking force was 2.48 N. The hydrogel exhibited optimal mechanical properties when the addition amounts of NaCl and LiCl were 0.375 g and 0.250 g, respectively. However, due to the low inorganic salt content, the salting-out effect was not significant, and the hydrogel did not exhibit the bilayer and asymmetrical viscous characteristics.

[0068] Na + / Li + X-PAMSA@CPA hydrogel and Na + / Li + The conductivity test results of Y-PAMSA@CPA hydrogel are shown in [the table below]. Figure 15 It can be seen that when the mass ratio of NaCl to LiCl increases from 0.5 to 2.5, the conductivity of the hydrogel increases from 0.00501 S / cm to 0.00860 S / cm (Figure a). When the amounts of NaCl and LiCl added increase from 0.375 g and 0.250 g to 1.875 g and 1.250 g, respectively, the conductivity of the hydrogel increases from 0.0078 S / cm to 0.0100 S / cm (Figure b). In summary, the bilayer NaCl... + / Li + The conductivity of the PAMSA@CPA hydrogel shows a continuous increasing trend with the increase of inorganic salt content. However, considering the influence of inorganic salt on the mechanical properties of the hydrogel, the optimal addition amount is 1.500 g NaCl / 13 mL H2O and 1.000 g LiCl / 13 mL H2O (σ=0.0094 S / cm).

[0069] The bilayer Na obtained in Example 7 + / Li + Application of PAMSA@CPA hydrogel in the fabrication of flexible sensors: This invention uses a universal testing machine to control the continuous stretching and recovery of the hydrogel under different strain levels (5%-25%, 20%-100%, 100%-300%). The results are shown in […]. Figure 16 It can be seen that the hydrogel strain sensor can clearly respond to small-amplitude (5%~25%) strains, but the resistance change rate signal generally shows a gradually increasing trend (a); when it is a bilayer Na... + / Li+ When the PAMSA@CPA hydrogel strain sensor senses a wide range of strains (20%-100% and 100%-300%), the resistance change rate signal of the bilayer Na+ / Li+-PAMSA@CPA hydrogel strain sensor does not show a significant overall increasing trend, and it can clearly distinguish strains of different amplitudes (b and c). The above experiments demonstrate that the bilayer Na+ / Li+-PAMSA@CPA hydrogel strain sensor... + / Li + - The PAMSA@CPA hydrogel strain sensor has excellent sensing sensitivity.

Claims

1. A method for preparing a bilayer integrated asymmetric viscous hydrogel, characterized in that: Natural high-molecular-weight polysaccharides and polymeric monomers were added to a salt solution and stirred at room temperature. Then, an initiator and a crosslinking agent were added, stirred, and polymerized to obtain a bilayer integrated asymmetric viscous hydrogel.

2. The preparation method according to claim 1, characterized in that: The salt solution is one or more of sodium chloride aqueous solution, lithium chloride aqueous solution, potassium chloride aqueous solution, sodium citrate aqueous solution, or sodium sulfate aqueous solution; the natural high molecular weight polysaccharide is one or more of sodium alginate, chitosan, or agarose; the polymer monomer is acrylamide; the initiator is potassium persulfate; and the crosslinking agent is N,N'-methylenebisacrylamide.

3. The preparation method according to claim 1, characterized in that: The salt solution has a salt to water mass-volume ratio of 0.6~3.2 g : 13 mL, and the salt, natural high molecular weight polysaccharide, polymeric monomer, initiator and crosslinking agent mass ratio is 0.6~3.2 : 0.9 : 2.0~3.5 : 0.035~0.045 : 0.001~0.

003.

4. The preparation method according to claim 1, characterized in that: The polymerization conditions are as follows: polymerization at 55~65℃ for 3.5~4.5 h.

5. The bilayer integrated asymmetric viscous hydrogel prepared by the method according to any one of claims 1 to 5.

6. A bilayer integrated asymmetric viscous hydrogel possessing both high mechanical and electrical properties, characterized in that: The hydrogel comprises a hydrogel matrix and CNT / PDA-Ag nanoparticles doped in the hydrogel matrix, wherein the hydrogel matrix is ​​a hydrogel prepared by the method of any one of claims 1 to 4 or a hydrogel according to claim 5, and the CNT / PDA-Ag nanoparticles are carbon nanotubes with surface-modified polydopamine and silver nanoparticles.

7. The bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties according to claim 6, characterized in that: The CNT / PDA-Ag nanoparticles were prepared by the following method: carbon nanotubes were added to Tris-HCl buffer solution, sonicated, and then dopamine hydrochloride was added. The mixture was stirred for 22-24 h to obtain CNT / PDA nanoparticles. Then, the CNT / PDA nanoparticle aqueous dispersion was mixed with silver ammonia solution, polyvinylpyrrolidone was added, and the mixture was stirred continuously at 75-85℃ for 5-6 h, followed by continuous ultraviolet irradiation for the last 40 min to obtain CNT / PDA-Ag nanoparticles; wherein, The mass-to-volume ratio of the carbon nanotubes, dopamine hydrochloride, and Tris-HCl buffer solution is 0.05~0.10 g: 0.4~1.0 g: 200 mL; The mass-to-volume ratio of polyvinylpyrrolidone, CNT / PDA nanoparticle aqueous dispersion, and silver ammonia solution is 1.5 g : 80~100 mL : 50~60 mL, and the concentration of the CNT / PDA nanoparticle aqueous dispersion is 0.5~1.5 mg / mL.

8. The bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties according to claim 6, characterized in that: The hydrogel has a tensile strength of 0.04~0.20 MPa, a breaking force of 2.0~6.0 N, an elongation at break of 844%~1287%, and an electrical conductivity of 0.005~0.01 S / cm.

9. The method for preparing the bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties as described in any one of claims 6 to 8, characterized in that: Natural high-molecular-weight polysaccharides and polymeric monomers were added to a salt solution and stirred at room temperature. Then, CNT-PDA / Ag nanoparticles were added and stirred at room temperature. Finally, an initiator and a crosslinking agent were added, stirred, and polymerized to obtain a bilayer integrated asymmetric viscous hydrogel with both high mechanical and electrical properties.

10. The preparation method according to claim 9, characterized in that: The salt solution has a salt to water mass-volume ratio of 0.6~3.2 g : 13 mL, and the salt, natural high molecular weight polysaccharide, polymeric monomer, initiator, crosslinking agent, and CNT-PDA / Ag nanoparticles have a mass ratio of 0.6~3.2 : 0.9 : 2.0~3.5 : 0.035~0.045 : 0.001~0.003 : 0.010~0.015.

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