A conductive bilayer hydrogel based on photocontrolled RAFT polymerization, its preparation method and application

Abstract

This invention provides a method for preparing a conductive bilayer hydrogel based on photocontrolled RAFT polymerization, comprising: S1 adding a photocontrolled RAFT reagent to acrylic acid and subjecting it to phototreatment, followed by adding N,N-methylenebisacrylamide, chitosan, glycerol, and deionized water and mixing thoroughly to obtain an adhesion layer prepolymer solution; S2 adding a photocontrolled RAFT reagent to N,N-dimethylacrylamide and subjecting it to phototreatment, followed by adding N,N-methylenebisacrylamide, polyvinyl alcohol, sodium tetraborate, lithium chloride, and deionized water to obtain a conductive layer prepolymer solution; S3 pouring the adhesion monolayer hydrogel prepolymer solution into a mold and subjecting it to photocuring to obtain a monolayer hydrogel; coating the conductive monolayer hydrogel prepolymer solution onto the monolayer hydrogel and subjecting it to photocuring to obtain a conductive bilayer hydrogel based on photocontrolled RAFT polymerization. This conductive bilayer hydrogel exhibits tunable electrical properties and interlayer conductivity differences, asymmetric adhesion ability, excellent antifreeze ability, and significant moisture retention and environmental stability.

Description

Technical Field

[0001] This invention relates to the technical field of functional polymer materials, and in particular to a conductive bilayer hydrogel based on photocontrolled RAFT polymerization, its preparation method, and its application. Background Technology

[0002] Hydrogels are polymer materials with a three-dimensional network structure. They have good biocompatibility, flexibility, adjustable mechanical properties and excellent adhesion properties. In the field of wearable sensors, they can enable sensors to form a stable, tight and slip-free interface contact with the skin surface, effectively eliminating interface gaps and signal noise, and significantly improving the detection accuracy and response sensitivity of weak physiological signals and small deformations of the human body.

[0003] However, single-component adhesive conductive hydrogels still present some challenges in application. For instance, the current flowing through the hydrogel may damage the skin during use. Although an insulating layer can be placed between the hydrogel sensor and the skin, this leads to mechanical property mismatch and reduced measurement accuracy. Furthermore, due to the high water content within the hydrogel, its tensile strength, adhesion, and conductivity change as the water evaporates, significantly impacting the long-term reliable operation of the hydrogel sensor. Moreover, it is prone to freezing in low-temperature environments, significantly reducing the material's flexibility and deformability, thus limiting the normal use of related electronic devices under low-temperature conditions. CN121293534A discloses a bilayer integrated asymmetric adhesive hydrogel, its preparation method, and its application; however, this bilayer hydrogel lacks antifreeze and moisturizing properties, making it difficult to apply under extreme conditions. CN118955949A discloses a bilayer cellulose fiber hydrogel and its preparation method; however, the connection between the hydrogel layers relies solely on simple mechanical interlocking and weak interaction forces, making separation easy.

[0004] In recent years, photocontrolled reversible addition-fragmentation chain transfer polymerization (RAFT), as an advanced polymerization technology capable of spatiotemporally controlled polymerization, has gradually attracted attention in the preparation of functional hydrogels due to its advantages such as mild polymerization conditions, strong reaction controllability, and the ability to achieve layer-by-layer construction. Utilizing photocontrolled RAFT polymerization technology, continuous growth of polymer chains can be achieved in different time and spatial regions, thereby realizing covalent connections between multilayer structures and providing an effective approach for constructing structurally stable, functionally defined multilayer hydrogels.

[0005] Therefore, there is an urgent need to develop a multifunctional conductive bilayer hydrogel that combines bilayer asymmetric adhesion, freeze resistance, moisture retention, and good mechanical properties to meet the application needs of flexible electronic devices and smart wearable devices. Summary of the Invention

[0006] The purpose of this invention is to address the difficulty in simultaneously achieving asymmetric adhesion, good mechanical properties, freeze resistance, and moisturizing properties in existing wearable sensing hydrogels. This invention provides a conductive bilayer hydrogel based on photocontrolled RAFT polymerization, its preparation method, and its applications. Utilizing the characteristic of photocontrolled RAFT polymerization, which allows polymerization to be "on" and "off" at will with the switching on and off of light, a strong covalent bond connection between the two hydrogel layers and asymmetric adhesion of the bilayer hydrogel are achieved. This conductive bilayer hydrogel exhibits tunable electrical properties and interlayer conductivity differences, excellent freeze resistance, and significant moisturizing and environmental stability.

[0007] The first objective of this invention is to provide a method for preparing a conductive bilayer hydrogel based on photocontrolled RAFT polymerization, the method comprising: S1 Add the light-controlled RAFT reagent to acrylic acid, stir evenly, and then irradiate it. Then add N,N-methylenebisacrylamide, chitosan, glycerol and deionized water and mix evenly to obtain the adhesion layer prepolymer solution. S2 adds the photo-controlled RAFT reagent to N,N-dimethylacrylamide, followed by photo-treatment, and then adds N,N-methylenebisacrylamide, polyvinyl alcohol, sodium tetraborate, lithium chloride and deionized water and mixes them evenly to obtain a conductive layer prepolymer solution. S3 pours the prepolymer solution of the adhesive monolayer hydrogel into a mold and performs photocuring to obtain the adhesive monolayer hydrogel; the prepolymer solution of the conductive monolayer hydrogel is coated on the monolayer hydrogel and then subjected to photocuring to obtain the conductive monolayer hydrogel, thus forming a conductive bilayer hydrogel based on photocontrolled RAFT polymerization.

[0008] Specifically, the light-controlled RAFT reagent is 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate.

[0009] Specifically, in step S1, the mass percentages of the light-controlled RAFT reagent are 0.25-0.35 wt%, the mass percentages of acrylic acid are 27-40 wt%, the mass percentages of N,N-methylenebisacrylamide are 0.25-0.35 wt%, the mass percentages of chitosan are 1.0-1.5 wt%, the mass percentages of glycerol are 10-40 wt%, and the mass percentages of deionized water are 31-60 wt%.

[0010] Specifically, in step S2, the mass percentages of the light-controlled RAFT reagent are 0.23~0.35 wt%, N,N-dimethylacrylamide is 25.0~32.0 wt%, N,N-methylenebisacrylamide is 0.23~0.35 wt%, polyvinyl alcohol is 25~30 wt%, sodium tetraborate is 3~5 wt%, lithium chloride is 4.5~10.0 wt%, and deionized water is 35~42 wt%.

[0011] Specifically, the illumination treatment is performed under a 405 nm light source with an illumination intensity of 60 mW / cm². 2 The time is 3-5 minutes.

[0012] Specifically, the photocuring process in step S3 is performed under a 405 nm light source with a light intensity of 60 mW / cm². 2 The time is 30-40 minutes.

[0013] The second objective of this invention is to provide a conductive bilayer hydrogel based on photocontrolled RAFT polymerization prepared as described above.

[0014] The second and third objective of this invention is to provide an application of the above-described conductive bilayer hydrogel in the manufacture of wearable flexible sensors.

[0015] Compared with the prior art, the beneficial effects of the present invention include: (1) From the perspective of preparation method, this invention addresses the technical bottlenecks of traditional bilayer hydrogels, such as weak interlayer bonding, easy delamination, and difficulty in achieving functional partitioning, by innovatively introducing photocontrolled reversible addition-fragmentation chain transfer polymerization (RAFT) technology. Utilizing the unique advantage of photocontrolled RAFT polymerization, which allows the polymerization reaction to be "started" and "paused" at any time depending on the light exposure, a monolayer hydrogel is first formed by in-situ solidification of the adhesion layer prepolymer solution using a light source. Then, while maintaining the active chain ends, the conductive layer prepolymer solution is directly cast onto the adhesion layer and photo-initiated polymerization is performed again. This allows the polymer chains of the second layer hydrogel to continue chain growth at the network ends of the first layer, thereby forming a stable and continuous covalent chemical bond connection between the two layers, rather than a simple physical superposition. Compared to traditional bilayer hydrogels, the interlayer bonding strength constructed by the method of this invention is significantly improved, effectively avoiding the problem of delamination failure during use. Meanwhile, the entire preparation process does not require high temperature or harsh reaction conditions. Layer-by-layer curing can be achieved simply by visible light irradiation. It is easy to operate, has low energy consumption, is easy to scale up, and can achieve in-situ molding in complex molds. It provides a new and controllable preparation path for multilayer hydrogel materials with clear functional partitions and stable structures.

[0016] (2) From a performance perspective, the bilayer hydrogel prepared by the present invention through the optimized ratio of each component possesses multiple multifunctional properties such as asymmetric adhesion, gradient conductivity, antifreeze properties, and long-lasting moisturizing properties. The hydrogel adopts a bilayer integrated design. The adhesion layer uses polyacrylic acid as the main covalent network, introduces chitosan to provide abundant amino and hydroxyl groups, and glycerol to construct a hydrogen bond network, giving the layer strong adhesion to different substrates, and can be repeatedly adhered more than 10 times without significant performance degradation. The conductive layer uses poly(N,N-dimethylacrylamide) as the main network, and introduces lithium chloride as an ion-conducting medium. The dynamic borate ester bond formed by polyvinyl alcohol and sodium tetraborate gives the layer good flexibility, while the ion hydration of lithium chloride and the hydrogen bond network of glycerol respectively give the conductive layer and the adhesion layer excellent antifreeze properties and long-lasting moisturizing ability (the moisture retention rate of the adhesion layer reaches 59.5% after 84 hours, and the moisture retention rate of the conductive layer reaches 79.2% after 7 days). The polyacrylic acid hydrogel adhesion layer has a large number of carboxyl groups in its molecular chain, which can form hydrogen bonds and electrostatic interactions with the substrate to achieve good adhesion. The adhesion strength between the hydrogel and pigskin can reach 10.2 kPa. After repeated adhesion 10 times, the adhesion strength did not change significantly. The bilayer hydrogel constructed in this invention achieves asymmetric adhesion characteristics, ensuring that when the hydrogel is in contact with the skin, most of the current passes through the conductive layer, with only a very small amount of current passing through the adhesion layer. This effectively protects the skin from electrical damage while achieving high-sensitivity sensing.

[0017] (3) In terms of raw material composition and product structure, glycerol in the adhesion layer can form a stable hydrogen bond network with water molecules, effectively limiting the migration and evaporation rate of water molecules, thereby weakening the orderly arrangement between water molecules and inhibiting the nucleation and growth of ice crystals. Lithium chloride in the conductive layer can establish a strong correlation with water molecules through ion solvation, significantly enhancing the binding ability of water and weakening the ability of water molecules to form an ordered ice crystal structure at low temperatures; glycerol and lithium chloride work together to regulate the low-temperature behavior of hydrogels, providing a basis for stable sensor output. Lithium chloride in the conductive layer, as a strong electrolyte, ionizes into a large number of freely moving lithium ions and chloride ions in the hydrogel, and its ion hydration optimizes the structure of water and ion migration channels, thereby significantly improving the conductivity of the hydrogel.

[0018] (4) From the perspective of application effect, the bilayer asymmetric adhesive multifunctional conductive hydrogel prepared by this invention shows outstanding practical value and promotion prospects in the field of wearable flexible sensors. This bilayer hydrogel can be used as a flexible strain sensing material, and can output stable and repeatable electrical signals under different strain conditions. When it is adhered to the surface of human skin, it can monitor a variety of subtle and large-amplitude human movement behaviors in real time and with good periodicity and repeatability of the signal. Due to the strong adhesion of the adhesive layer, the hydrogel can form a tight and non-slip interface contact with the skin, effectively eliminating interface gaps and signal noise, and significantly improving the detection accuracy of weak physiological signals and small deformations; at the same time, the non-adhesive properties of the conductive layer side avoid the adhesion of foreign objects, dust and microorganisms in the external environment, reducing the risk of infection and cleaning and maintenance costs. In addition, thanks to the excellent anti-freezing properties and long-term moisturizing ability given by glycerol and lithium chloride, the hydrogel can still maintain good flexibility and conductivity stability in low temperature environment, and the performance decay caused by water evaporation during long-term use is effectively suppressed, thus breaking through the bottleneck of poor reliability of traditional hydrogel sensors in extreme environments and long-term service conditions. This invention provides a core material for smart wearable devices, flexible electronic devices, and human-computer interaction interfaces that is safe, comfortable, sensitive, weather-resistant, and easy to integrate. Attached Figure Description

[0019] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0020] Figure 1 (a) Comparison of the moisturizing properties of adhesive monolayer hydrogels with different glycerol contents prepared in Examples 1-2 and 5-7 of the present invention; Figure 1 (b) is a comparison of the moisturizing properties of conductive monolayer hydrogels with different lithium chloride contents prepared in Examples 1 and 3-4 of the present invention. Figure 2 (a) is a schematic diagram of the experimental model of the conductive bilayer hydrogel prepared in Example 1 of the present invention; Figure 2 (b) is a comparison diagram of the adhesion strength of the conductive bilayer hydrogel prepared in Example 1 of the present invention on different substrates; Figure 2 (c) is a physical image of the conductive bilayer hydrogel prepared in Example 1 of the present invention adhering to different substrates; Figure 3The asymmetric adhesion properties characterization diagram of the conductive bilayer hydrogel prepared in Example 1 of this invention; Figure 4 The conductive monolayer hydrogels prepared in Examples 1 and 3-4 of this invention and the adhesive monolayer hydrogel prepared in Example 5 are compared in terms of their conductivity characteristics. Figure 5 (a) is a schematic diagram of the electrical signal detection of frowning action by the conductive bilayer hydrogel prepared in Example 1 of the present invention in a sensor; Figure 5 (b) is a schematic diagram of the conductive bilayer hydrogel prepared in Example 1 of the present invention being used in a sensor to detect electrical signals of finger bending movements; Figure 5 (c) is a schematic diagram of the electrical signal detection of smiling motion by the conductive bilayer hydrogel prepared in Example 1 of the present invention in a sensor; Figure 5 (d) is a schematic diagram of the conductive bilayer hydrogel prepared in Example 1 of the present invention being used in a sensor to detect electrical signals of wrist flexion movements; Figure 6 (a) Characterization of the antifreeze properties of adhesive monolayer hydrogels with different glycerol contents prepared in Examples 1-2 and 5-7 of the present invention; Figure 6 (b) is a DSC comparison diagram of conductive monolayer hydrogels with different lithium chloride contents prepared in Examples 1 and 3-4 of the present invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention.

[0022] Example 1 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 10 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.2 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 10% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.2 ; and formed Example 1 to prepare a conductive bilayer hydrogel AC based on photocontrolled RAFT polymerization. 0.4 G 10% / DBP 1.1 L 0.2 .

[0023] Example 2 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 20 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.2 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²).2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 20% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel BP. 1.1 L 0.2 Example 2 shows the preparation of a conductive bilayer hydrogel AC based on light-controlled RAFT polymerization. 0.4 G 20% / DBP 1.1 L 0.2 .

[0024] Example 3 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 20 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.3 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 10% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.3 And form the conductive bilayer hydrogel AC based on light-controlled RAFT polymerization prepared in Example 3. 0.4 G 10% / DBP 1.1 L0.3 .

[0025] Example 4 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 20 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.4 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 10% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.4 And form the conductive bilayer hydrogel AC based on light-controlled RAFT polymerization prepared in Example 4. 0.4 G 10% / DBP 1.1 L 0.4 .

[0026] Example 5 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 30 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.3 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 30% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.2 And form the conductive bilayer hydrogel AC based on light-controlled RAFT polymerization prepared in Example 5. 0.4 G 30% / DBP 1.1 L 0.2 .

[0027] Example 6 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 35 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.3 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2(Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 35% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.2 And form the conductive bilayer hydrogel AC based on light-controlled RAFT polymerization prepared in Example 6. 0.4 G 35% / DBP 1.1 L 0.2 .

[0028] Example 7 S1: 0.04 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 4.8 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.04 g of N,N-methylenebisacrylamide, 0.16 g of chitosan, 40 wt% glycerol and 6 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.01 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate was added to 1.1 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (3 min), then add 0.01 g of N,N-methylenebisacrylamide, 1.1 g of polyvinyl alcohol, 0.15 g of sodium tetraborate, 0.3 g of lithium chloride and 1.5 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in monolayer hydrogel AC 0.4 G 40% The conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and then photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 30 min), resulting in conductive monolayer hydrogel DBP. 1.1 L 0.2 And form the conductive bilayer hydrogel AC based on light-controlled RAFT polymerization prepared in Example 7. 0.4 G 40% / DBP 1.1 L 0.2 .

[0029] Example 8 S1: 0.06 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 7 g of acrylic acid, stirred until homogeneous, and then subjected to phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (The time is 5 min), then add 0.06 g of N,N-methylenebisacrylamide, 0.24 g of chitosan, 15 wt% glycerol and 9.64 g of deionized water and mix well to obtain the adhesion layer prepolymer solution; S2: 0.06 g of 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfide was added to 5.6 g of N,N-dimethylacrylamide, followed by phototreatment under a 405 nm light source with an intensity of 60 mW / cm². 2 (The time is 5 min), then add 0.06 g of N,N-methylenebisacrylamide, 5.4 g of polyvinyl alcohol, 0.8 g of sodium tetraborate, 1.2 g of lithium chloride and 7.07 g of deionized water and mix well to obtain a conductive layer prepolymer solution; S3. The prepolymer solution of the adhesion monolayer hydrogel was poured into a mold and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 The irradiation time was 40 min to obtain a monolayer hydrogel; a conductive monolayer hydrogel prepolymer solution was coated onto the monolayer hydrogel and photocured under a 405 nm light source (intensity of 60 mW / cm²). 2 (Irradiation time was 40 min) to obtain a conductive monolayer hydrogel, and to form the conductive bilayer hydrogel based on photocontrolled RAFT polymerization prepared in Example 8.

[0030] Performance testing The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

[0031] (1) Thermal transition properties of hydrogels: The thermal transition behavior of hydrogels was tested using a DSC 204 F1 differential scanning calorimeter. 5-10 mg of sample was placed in the calorimeter, and the heating range was set from -50℃ to 30℃, with a heating rate of 10℃·min. - ¹.

[0032] (2) Moisture retention stability of the hydrogel: The hydrogels in Examples 1 and 3 were placed in a constant temperature and humidity environment (25°C, 55% relative humidity) for static aging. Samples were taken and weighed after 84 hours and 7 days, respectively, to examine the mass retention of the samples over time. The water retention capacity of the hydrogel was characterized by the mass retention rate (or water retention rate), and the calculation formula is as follows: Water retention rate = ; in, w t The mass of the sample is measured after being placed under constant temperature and humidity conditions for time t. 、w 0 represents the initial mass at the start of the test (usually referring to the mass of the hydrogel immediately after preparation / after the surface water has been gently absorbed).

[0033] Figure 1 (a) Comparison of the moisturizing properties of adhesive monolayer hydrogels with different glycerol contents prepared in Examples 1-2 and 5-7 of the present invention; Figure 1 (b) is a comparison of the moisturizing properties of conductive monolayer hydrogels with different lithium chloride contents prepared in Examples 1 and 3-4 of this invention; Figure 1 (a) It can be seen that initially (0 h), the water retention rate of the adhesion layer hydrogel is close to (approximately 100%); after the time is extended to 84 h, as the glycerol content in the adhesion layer hydrogel gradually increases from 10% to 40%, the water retention rate increases from 40.4% to 69.8%. Glycerol can form abundant hydrogen bonds with water molecules, effectively limiting the migration and evaporation rate of water molecules. Figure 1 (b) It can be seen that the water retention rate of the conductive layer hydrogel is close to (about 100%) at the initial time (0 h); after the time is extended to 7 days, as the LiCl content in the conductive layer hydrogel increases from 0.2 g to 0.4 g, the water retention rate increases from 71.1% to 84.7%. Lithium chloride can establish a strong correlation with water molecules through ionic solvation, which significantly enhances its ability to bind water.

[0034] The adhesion strength of the bilayer hydrogel was tested using a universal testing machine to measure the overlap shear strength: a 20×20×3mm layer was used. 3 The hydrogel is sandwiched between similar substrates (paper, pigskin, glass, steel plate, etc.) to form a stable adhesion interface before mechanical load is applied. The loading is 5 mm·min. -1 The sample was sheared and peeled at a certain rate, and the maximum load-bearing capacity was recorded in real time. Adhesion strength was defined as the peak load at which the sample failed in the initial adhesive region. Figure 2 (a) is a schematic diagram of the experimental model of the conductive bilayer hydrogel prepared in Example 1 of the present invention; Figure 2 (b) is a comparison diagram of the adhesion strength of the conductive bilayer hydrogel prepared in Example 1 of the present invention on different substrates; Figure 2(c) is a physical picture of the conductive double - layer hydrogel prepared in Example 1 of the present invention adhering to different substrates; as can be seen from Figure 2 (a), the adhesion performance of the hydrogel was tested by lap - shear, and wood, glass, rubber, metal, plastic, and pig skin were used respectively. As can be seen from Figure 2 (b), the AC 0.4 G 30% hydrogel prepared in Comparative Example 3 has the highest adhesion strength to wood and the lowest adhesion strength to plastic. Figure 2 (c) shows the actual adhesion states of the hydrogel to wood, glass, rubber, metal, plastic, and paper cups, visually verifying the stable adhesion behavior of the hydrogel on various material substrates.

[0035] Based on the characteristics that photo - controlled RAFT polymerization can make the polymerization "start" and "pause" at any time with the on / off of light, a double - layer hydrogel was prepared. The adhesion strength of the AC 0.4 G 30% hydrogel to the skin is 10.2 kPa, while the adhesion strength of the DBP 1.1 L 0.3 hydrogel is only 0.9 kPa, and the adhesion strength difference is about 10 times, achieving significant asymmetric adhesion. Figure 3 is a characterization diagram of the asymmetric adhesion performance of the conductive double - layer hydrogel prepared in Example 1 of the present invention; as can be seen from Figure 3 it that when the finger contacts the AC 0.4 G 30% side and the finger is lifted, the hydrogel will firmly adhere to the finger and be lifted with the finger; when the finger contacts the DBP 1.1 L 0.3 side and the finger is lifted, the hydrogel cannot adhere to the finger and cannot be lifted with the finger, indicating that the double - layer hydrogel has good asymmetric adhesion.

[0036] Figure 4 is a comparative characterization diagram of the conductivity of the conductive single - layer hydrogels prepared in Examples 1, 3 - 4 of the present invention and the adhesive single - layer hydrogel prepared in Example 5; as can be seen from Figure 4 it that with the increase of the lithium chloride content, the conductivity of the conductive - layer hydrogel gradually increases, indicating that the introduction of LiCl can significantly enhance the conductivity of the conductive - layer hydrogel. The conductivity of the AC 0.4 G 30% hydrogel is significantly lower than that of the conductive - layer hydrogel. This ensures that when the double - layer hydrogel is used for conductive sensing, most of the current passes through the conductive layer, and only a small amount of current passes through the adhesive layer, protecting the skin from current damage. Figure 5 (a) is a schematic diagram of the detection of electrical signals of frowning actions by the conductive double - layer hydrogel prepared in Example 1 of the present invention when applied to a sensor; Figure 5(b) is a schematic diagram of the conductive bilayer hydrogel prepared in Example 1 of the present invention being used in a sensor to detect electrical signals of finger bending movements; Figure 5 (c) is a schematic diagram of the electrical signal detection of smiling motion by the conductive bilayer hydrogel prepared in Example 1 of the present invention in a sensor; Figure 5 (d) is a schematic diagram of the conductive bilayer hydrogel prepared in Example 1 of this invention being used in a sensor to detect electrical signals of wrist flexion movements; Figure 5 It can be seen that AC 0.4 G 30% / DBP 1.1 L 0.3 The hydrogel was used as a sensor and adhered to the skin, exhibiting significant and repeatable changes in electrical signal when performing actions such as frowning, bending fingers, smiling, and bending the wrist.

[0037] Figure 6 (a) is a characterization diagram of the antifreeze properties of the adhesive monolayer hydrogels with different glycerol contents prepared in Examples 1-2 and 5-7 of the present invention; in the prepolymer solution of the adhesive layer, the amount of acrylic acid added is 4.8 g, the amount of chitosan added is 0.16 g, and the mass fraction of glycerol is 10%, 20%, 30%, 35% and 40%, respectively. The present invention introduces glycerol to inhibit the nucleation and growth of ice crystals, which is shown in the DSC as the absorption peak gradually shifting to the low temperature. Figure 6 (b) is a DSC comparison chart of conductive monolayer hydrogels with different lithium chloride contents prepared in Examples 1 and 3-4 of this invention. In the conductive layer prepolymer solution, the amount of N,N-dimethylacrylamide added was 1.1 g, the amount of polyvinyl alcohol solution added was 1.1 g, the amount of sodium tetraborate solution added was 0.15 g, and the amount of lithium chloride added was 0.2, 0.3, and 0.4 g, respectively. The introduction of lithium chloride in this invention, through a strong solvation effect, endows the hydrogel with freeze resistance, which is shown in the DSC as the absorption peak gradually shifting to the low temperature.

[0038] The adhesive and conductive hydrogels, with their excellent antifreeze properties, hold promise for expanding their applications in low-temperature environments. Glycerol in the adhesive layer hydrogel forms a stable hydrogen bond network with water molecules, thereby weakening the ordered arrangement of water molecules and inhibiting ice crystal nucleation and growth. Lithium chloride in the conductive layer hydrogel exhibits a strong solvation effect with water molecules, reducing their ability to form ordered ice crystal structures at low temperatures. This invention utilizes the characteristic of light-controlled RAFT polymerization, which allows polymerization to be "on" and "paused" at will depending on the on / off state of light, to achieve strong covalent bond connections between the two hydrogel layers and asymmetric adhesion of the bilayer hydrogel. This conductive bilayer hydrogel possesses tunable electrical properties and interlayer conductivity differences, excellent antifreeze ability, and significant moisture retention and environmental stability.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a conductive bilayer hydrogel based on photocontrolled RAFT polymerization, characterized in that, The preparation method includes: S1 Add the light-controlled RAFT reagent to acrylic acid, stir evenly, and then irradiate it. Then add N,N-methylenebisacrylamide, chitosan, glycerol and deionized water and mix evenly to obtain the adhesion layer prepolymer solution. S2 adds the photo-controlled RAFT reagent to N,N-dimethylacrylamide, followed by photo-treatment, and then adds N,N-methylenebisacrylamide, polyvinyl alcohol, sodium tetraborate, lithium chloride and deionized water and mixes them evenly to obtain a conductive layer prepolymer solution. S3 pours the prepolymer solution of the adhesive monolayer hydrogel into a mold and performs photocuring to obtain the adhesive monolayer hydrogel; the prepolymer solution of the conductive monolayer hydrogel is coated on the monolayer hydrogel and then subjected to photocuring to obtain the conductive monolayer hydrogel, thus forming a conductive bilayer hydrogel based on photocontrolled RAFT polymerization.

2. The method according to claim 1, characterized in that, The light-controlled RAFT reagent is 2-cyanobutyl-2-yl-3-methyl-1H-indazole-1-carbonyl disulfate.

3. The method according to claim 1, characterized in that, The light-controlled RAFT reagent in step S1 has the following mass percentages: 0.25-0.35 wt%, acrylic acid has the following mass percentages: 27-40 wt%, N,N-methylenebisacrylamide has the following mass percentages: 0.25-0.35 wt%, chitosan has the following mass percentages: 1.0-1.5 wt%, glycerol has the following mass percentages: 10-40 wt%, and deionized water has the following mass percentages: 31-60 wt%.

4. The method according to claim 1, characterized in that, The light-controlled RAFT reagent in step S2 comprises 0.23-0.35 wt%, N,N-dimethylacrylamide 25.0-32.0 wt%, N,N-methylenebisacrylamide 0.23-0.35 wt%, polyvinyl alcohol 25-30 wt%, sodium tetraborate 3-5 wt%, lithium chloride 4.5-10.0 wt%, and deionized water 35-42 wt%.

5. The method according to claim 1, characterized in that, The illumination treatment was performed under a 405 nm light source with an illumination intensity of 60 mW / cm². 2 The time is 3-5 minutes.

6. The method according to claim 1, characterized in that, The photocuring process described in step S3 is performed under a 405 nm light source with a light intensity of 60 mW / cm². 2 The time is 30-40 minutes.

7. A conductive bilayer hydrogel based on photocontrolled RAFT polymerization prepared by the method as described in claims 1-6.

8. The application of the conductive bilayer hydrogel as described in claim 7 in the manufacture of wearable flexible sensors.

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