Preparation method and application of flexible conductive hydrogel sensor

Abstract

The application discloses a preparation method of a flexible conductive hydrogel sensor and application thereof, and the flexible conductive hydrogel sensor is formed by free radical polymerization of a macromolecular crosslinking agent and monomers in a solution, and then is sequentially soaked in a salt solution and deionized water to form a hydrogel through solvent exchange, wherein the monomers are acrylamide and acrylic acid monomers; the salt solution is at least one of ferric chloride, aluminum chloride, magnesium chloride, calcium chloride and copper chloride; and the macromolecular crosslinking agent is a hyperbranched poly(caprolactone) functionalized with acrylate groups and carboxylic acid groups. The flexible conductive hydrogel sensor prepared by the application has high stretchability, good conductivity and stable detection signal capacity, and good monitoring of different human tissue movements is realized.

Description

Technical Field

[0001] This invention relates to the field of sensor materials technology, specifically to a method for preparing a flexible conductive hydrogel sensor, and also to the application of this flexible conductive hydrogel sensor. Background Technology

[0002] Touch is one of the main functions that helps humans perceive their external environment. In recent years, flexible sensors based on this natural sensing ability have received widespread attention from researchers and have developed rapidly. Compared with traditional rigid sensors, flexible sensors have excellent tensile strength, portability, and hydrophilicity, and have broad application prospects in human-computer interaction technology, medical monitoring, and electronic skin. However, flexible sensors usually have certain drawbacks, such as poor biocompatibility, low sensitivity, high rigidity, and limited monitoring signals.

[0003] Conductive hydrogels have become ideal candidate materials for flexible electronic devices due to their excellent electrical properties, self-healing ability, high stretchability, and biocompatibility. However, currently developed flexible conductive hydrogel sensor materials cannot simultaneously achieve excellent flexibility, good signal detection stability, and the ability to monitor multiple motion signals, making it difficult to realize flexible signal monitoring. Therefore, developing a conductive hydrogel sensor with excellent mechanical properties, good signal detection stability, and the ability to monitor multiple motion signals is key to further expanding the application fields of hydrogels. Summary of the Invention

[0004] To address the limitations of existing conductive hydrogel materials in simultaneously achieving excellent flexibility, good signal stability, and the ability to monitor multiple motion signals, this invention provides a method for preparing a flexible conductive hydrogel sensor. This method offers advantages such as simplicity, rapid application, simple composition, low initiator dosage, ease of industrialization, and wide applicability. Introducing hyperbranched polycaprolactone into the hydrogel effectively improves its mechanical properties. The prepared flexible conductive hydrogel sensor exhibits high stretchability, good conductivity, and stable signal detection capability.

[0005] Another objective of this invention is to provide a method for preparing a flexible conductive hydrogel sensor. The flexible conductive hydrogel sensor prepared by this invention can be used to monitor human motion signals. It can accurately monitor various human motions, has the characteristics of high sensitivity and good stability, and can be perfectly applied to wearable sensing devices.

[0006] To achieve the above objectives, the present invention employs the following technical measures:

[0007] A flexible conductive hydrogel sensor is formed by free radical polymerization of macromolecular crosslinking agents and monomers in solution, followed by solvent exchange through sequential immersion in salt solution and deionized water;

[0008] The monomers are acrylamide and acrylic acid monomers;

[0009] The salt solution is at least one of ferric chloride, aluminum chloride, magnesium chloride, calcium chloride, and copper chloride;

[0010] The macromolecular crosslinking agent is hyperbranched polycaprolactone (APCL) functionalized with acrylate and carboxylic acid groups, and its structural formula is as follows:

[0011]

[0012] In the formula, R1 is

[0013] In the formula, R2 is

[0014] In the formula, R3 is

[0015] A method for fabricating a flexible conductive hydrogel sensor, comprising the following specific steps:

[0016] (1) Dissolve hyperbranched polycaprolactone (APCL) functionalized with acrylate and carboxylic acid groups, acrylamide and acrylic acid in dimethyl sulfoxide, and purge the solution with nitrogen for 30 min to obtain a mixed solution.

[0017] (2) Dissolve the initiator in dimethyl sulfoxide to prepare an initiator solution;

[0018] (3) Add the initiator solution to the mixed solution and stir until homogeneous to obtain the precursor solution;

[0019] (4) Inject the precursor solution into a glass mold, seal it, and place the glass mold under ultraviolet light to initiate free radical polymerization to form an organic gel;

[0020] (5) The organic gel was sequentially immersed in salt solution and deionized water for solvent exchange to obtain a flexible conductive hydrogel sensor.

[0021] In step (1), the mass percentage concentration of the crosslinking agent in the mixed solution is 2-20%;

[0022] In step (1), the total mass percentage concentration of monomers in the mixed solution is 20-50%, and the molar ratio of acrylamide to acrylic acid is 1:(0.15-0.5).

[0023] In step (2), the initiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone;

[0024] In step (2), the mass ratio of initiator to monomer (acrylamide and acrylic acid) is (0.1-0.5):100;

[0025] In step (2), the mass percentage concentration of the initiator in the initiator solution is 3.4-17.0%;

[0026] In step (4), the illumination conditions are: 1-2 hours of illumination at a distance of 40cm under a 500W high-pressure mercury lamp;

[0027] In step (5), the salt solution is at least one of ferric chloride, aluminum chloride, magnesium chloride, calcium chloride and copper chloride;

[0028] In step (5), the concentration of the salt solution is 0.01-0.5 mol / L;

[0029] In step (5), the organic gel is soaked in salt solution and deionized water for 24 hours.

[0030] In the aforementioned preparation method of the present invention, the hyperbranched polycaprolactone functionalized with acrylate and carboxylic acid groups is prepared by the following method:

[0031] (1) The tert-Butyl-substituted caprolactone, glycidol and diol were weighed into a reaction flask and mixed evenly. The reaction was carried out under a nitrogen atmosphere and stirred at 37°C for 1 h under the catalysis of diphenyl phosphate (DPP) to obtain BPCL.

[0032] (2) BPCL was dissolved in anhydrous tetrahydrofuran, triethylamine (TEA) was added, followed by slow dropwise addition of methacryloyl chloride. The reaction was stirred at room temperature for 12 h. The insoluble triethylamine hydrochloride was removed by filtration. The solvent was removed from the filtrate by rotary evaporation. The resulting oily substance was dissolved in anhydrous dichloromethane, and trifluoroacetic acid (TFA) was added. The reaction was carried out at room temperature for 3 h. The crude product was precipitated three times in a large amount of cold diethyl ether to obtain high-purity APCL.

[0033] The chemical reaction equation is as follows:

[0034]

[0035] In the formula, R1 is

[0036] In the formula, R2 is

[0037] In the formula, R3 is

[0038] In step (1), the diol is any one of 1,4-cyclohexanediol, 1,4-benzenedimethanol, 1,4-butanediol or 1,6-hexanediol;

[0039] In step (1), the molar ratio of tert-butyl-substituted caprolactone to diol is (40-60):1; the molar ratio of glycidol to diol is (1-15):1.

[0040] In step (1), the ratio of the number of moles of diphenyl phosphate to the number of moles of tert-butyl-substituted caprolactone is 1.0-5.0.

[0041] In step (1), the molecular weight of BPCL is approximately 12000-16000 g / mol;

[0042] In step (2), the ratio of the molar amount of triethylamine to the molar amount of BPCL is 1.0-6.0;

[0043] In step (2), the number of moles of methacrylamide chloride is equal to the number of moles of triethylamine;

[0044] In step (2), the ratio of the number of moles of trifluoroacetic acid to the number of moles of BPCL is 100.0-300.0;

[0045] In step (2), the molecular weight of APCL is approximately 8000-13000 g / mol.

[0046] As described above, this invention uses hyperbranched polycaprolactone with good biocompatibility as a crosslinking agent, and acrylamide and acrylic acid as monomers. The raw materials are environmentally friendly and non-toxic, and the preparation process is green, safe, and time-saving. The prepared flexible conductive hydrogel sensor has ultra-high tensile strength, good conductivity, high sensitivity, and high stability, effectively solving the shortcomings of traditional hydrogel sensors such as poor biocompatibility, low sensitivity, and high rigidity.

[0047] Accordingly, the present invention also provides an application of the flexible conductive hydrogel sensor prepared by the aforementioned preparation method in monitoring human motion signals. It can accurately monitor various human motions, has the characteristics of high sensitivity and good stability, and can be perfectly applied to wearable sensing devices.

[0048] The flexible conductive hydrogel sensor prepared by this invention has high stretchability, good conductivity and stable detection signal capability. These advantages greatly broaden the application of hydrogels in the field of sensors.

[0049] Compared with the prior art, the technical solution of the present invention has the following advantages and beneficial effects:

[0050] A. The synthesis scheme of hyperbranched polycaprolactone of this invention is simple, low-cost, and easy to industrialize. The preparation method has the advantages of being simple and fast, having simple components, requiring less initiator, being easy to industrialize, and having a wide range of applications. Introducing hyperbranched polycaprolactone into hydrogels can effectively improve the mechanical properties of hydrogels.

[0051] B. This invention utilizes the hydrophobic properties of hyperbranched polycaprolactone and the fact that its carboxylic acid groups on its side chains can serve as coordination sites to introduce it as a macromolecular crosslinking agent into the polyacrylic acid-acrylamide hydrogel network. Subsequently, a large number of dynamic interactions (hydrophobic association and metal coordination) are formed through solvent exchange to regulate the crosslinking network of the hydrogel, thereby improving the mechanical properties of the hydrogel.

[0052] C. The hydrogel in this invention incorporates metal ions as conductive fillers during its preparation, giving the hydrogel sensor excellent conductivity. The prepared hydrogel exhibits good biocompatibility and is non-cytotoxic, and is expected to be applied in wearable electronic devices, tissue engineering, soft robotics, and other fields.

[0053] D. The hydrogel sensor in this invention can detect resistance changes in real time and accurately, thereby monitoring various movements of human tissues and micro-movements of facial expressions, exhibiting sensitive electrical signal responsiveness and electrical sensing stability. Attached Figure Description

[0054] Figure 1 For APCL in Embodiment 1 of the present invention 1 HNMR spectrum;

[0055] Figure 2 The GPC spectrum of APCL in Embodiment 1 of the present invention;

[0056] Figure 3 This is a graph showing the tensile stress-strain curve of the hydrogel in Example 2 of the present invention;

[0057] Figure 4 This is a graph showing the real-time resistance change of the hydrogel in Example 2 of the present invention when the tensile strain is 1% to 10%.

[0058] Figure 5 This is a graph showing the real-time resistance change of the hydrogel in Example 2 of the present invention when the tensile strain is 50% to 150%.

[0059] Figure 6 This is a graph showing the resistance change caused by the bending motion of a finger when the hydrogel sensor is attached to the finger in Embodiment 2 of the present invention.

[0060] Figure 7This is a graph showing the resistance change caused by wrist flexion when the hydrogel sensor is attached to the wrist in Embodiment 2 of the present invention. Detailed Implementation

[0061] To further illustrate the features and advantages of the present invention, the present invention will be described in detail below with reference to specific embodiments. The following embodiments are only a part of the present invention, and the scope of protection of the present invention is not limited to the following embodiments.

[0062] Example 1: Preparation of hyperbranched polycaprolactone functionalized with acrylate and carboxylic acid groups

[0063] A. Weigh 10.0 g of tert-butyl-substituted caprolactone, 191.3 mg of glycidol, and 89.2 mg of 1,4-benzenedimethanol into a dry reaction flask. Stir thoroughly to dissolve the mixture. Under a nitrogen atmosphere, add 1.3 g of diphenyl phosphate. Then place the reaction flask in a 37°C constant temperature oil bath and continue stirring for 1 h to obtain BPCL (molecular weight approximately 16000 g / mol). In a 100 ml round-bottom flask, add 10.0 g of BPCL and 30 ml of anhydrous tetrahydrofuran in sequence and stir until completely dissolved. Under a nitrogen atmosphere, slowly add 0.37 ml of triethylamine and continue stirring for 30 min. Then add 0.26 ml of methacryloyl chloride to the reaction flask and stir at room temperature for 12 h. Finally, filter the reaction mixture to remove triethylamine hydrochloride. After removing the solvent from the filtrate using a rotary evaporator, dissolve the resulting oily substance in anhydrous dichloromethane and then add trifluoroacetic acid (TFA). React at room temperature for 3 h. The crude product was precipitated three times in a large amount of cold diethyl ether, and finally dried under vacuum at 37°C to obtain high-purity APCL (molecular weight approximately 13000 g / mol).

[0064] B. The product was confirmed to be APCL by proton nuclear magnetic resonance spectroscopy. Figure 1 ),Depend on Figure 1 The mid-peak integral area ratio indicates that the acrylate grafting rate of the obtained hyperbranched polycaprolactone functionalized with acrylate and carboxylic acid groups is 70%. Its molecular weight was characterized by GPC. Figure 2 The number-average molecular weight M of APCL is... n =1416, weight-average molecular weight M w =5016, APCL exhibits a monodisperse distribution, with a polymer dispersibility index of 1.35.

[0065] Example 2: A flexible conductive hydrogel sensor and its preparation method

[0066] A. Using hyperbranched polycaprolactone (APCL) from Example 1 as a macromolecular crosslinking agent, a flexible conductive hydrogel sensor was prepared. First, 0.89 g of APCL, 4.27 g of acrylamide, and 0.65 g of acrylic acid were weighed into a reaction flask. 8 ml of dimethyl sulfoxide (DMSO) was added to the flask, and the solution was purged with nitrogen for 30 min. The mixture was then stirred thoroughly to dissolve. A 6.8% (w / w) solution of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone was prepared using DMSO to obtain the initiator solution. 2 ml of the initiator solution was then added to the reaction flask, and the mixture was stirred until homogeneous. After purging with nitrogen for 30 min, the solution was injected into a glass mold, sealed, and irradiated at 40 cm under a 500W high-pressure mercury lamp for 2 h to obtain an organic gel. The organic gel was then sequentially immersed in 200 ml of 0.1 mol / L ferric chloride aqueous solution and 200 ml of deionized water for 24 h each for solvent exchange, ultimately yielding the flexible conductive hydrogel sensor.

[0067] B. The flexible conductive hydrogel sensor prepared in Example 2 was cut into strip-shaped specimens (4 cm long, 0.4 cm wide, and 0.07 cm thick). Tensile tests were performed on the specimens at room temperature using a universal testing machine at a tensile rate of 100 mm / min. The tensile stress-strain curves are shown below. Figure 3 As shown, the hydrogel exhibits excellent mechanical properties (tensile strength of 8.0 MPa, elongation at break of 765%, and toughness of 44.1 MJ / m). 3 It has excellent tensile properties, especially.

[0068] Example 3: Application of a flexible conductive hydrogel sensor

[0069] A. Using a universal testing machine and a resistance meter together to test the resistance change rate of the hydrogel sensor under different tensile strains and different bending movements: The flexible conductive hydrogel sensor from Example 2 was fixed on the universal testing machine, and the two clamps of the resistance meter were used to clamp the two ends of the flexible conductive hydrogel sensor. Tensile strains of 1%, 5%, 10%, 50%, 100%, and 150% were set respectively, and tensile tests were performed on the hydrogel. The hydrogel was cyclically stretched 5 times at each strain (e.g., ...). Figure 4 and Figure 5 As can be visually observed from the figure, the flexible conductive hydrogel sensor can monitor the resistance change signal generated by strain of 1% and 150%, and the signal exhibits good stability during multiple stretching processes. Therefore, the flexible conductive hydrogel in this invention can be used as a strain sensor.

[0070] B. Flexible conductive hydrogel sensors are bonded to different tissue sites in the human body, and a resistance meter is connected to both ends of the hydrogel sensor for precise monitoring of motion signals in different areas. For example... Figure 6As shown, the relative resistance changes exhibit good stability as the finger gradually bends from an extended state (0°C) to 30°, 60°, and 90°, indicating the reliability of monitoring finger flexion movements. Furthermore, the change in relative resistance when the hydrogel strain sensor is attached to the wrist is also shown. Figure 7 It also exhibits good stability. These results demonstrate that flexible conductive hydrogel sensors can accurately monitor various human movements, possessing high sensitivity and good stability, making them ideal for wearable sensing devices.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any transformations or substitutions that can be understood by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention.

Claims

1. A flexible conductive hydrogel sensor, characterized in that, A hydrogel is formed by free radical polymerization of macromolecular crosslinking agents and monomers in solution, followed by solvent exchange through sequential immersion in salt solution and deionized water, wherein: The monomers are acrylamide and acrylic acid monomers; The salt solution is at least one of ferric chloride, aluminum chloride, magnesium chloride, calcium chloride, and copper chloride; The macromolecular crosslinking agent is hyperbranched polycaprolactone functionalized with acrylate and carboxylic acid groups, and its structural formula is as follows: In the formula, R1 is , , or In R1, the *-marked connection site connects to the CC on the right. The marked connection point and the left side connect; In the formula, R2 is or In R2, the *-marked connection sites are connected to CC. The marked connection sites are connected to C=O; In the formula, R3 is or In R3, the *-marked connection sites are connected to CC; The hyperbranched polycaprolactone functionalized with acrylate and carboxylic acid groups was prepared by the following method: (1) The tert-butyl-substituted caprolactone, glycidol and diol were weighed into a reaction flask and mixed evenly. The reaction was carried out under a nitrogen atmosphere and catalyzed by diphenyl phosphate at 37°C. o C. Stir for 1 h to obtain BPCL; (2) Dissolve BPCL in anhydrous tetrahydrofuran, add triethylamine, and then slowly add methacrylamide chloride. Stir the reaction at room temperature for 12 h, filter to remove insoluble triethylamine hydrochloride, remove the solvent from the filtrate by rotary evaporator, dissolve the resulting oily substance in anhydrous dichloromethane, add trifluoroacetic acid, and react at room temperature for 3 h. Precipitate the crude product three times in a large amount of cold diethyl ether to obtain high-purity APCL.

2. The method for preparing the flexible conductive hydrogel sensor as described in claim 1, characterized in that, The specific steps include: (1) Hyperbranched polycaprolactone, acrylamide and acrylic acid functionalized with acrylate and carboxylic acid groups were dissolved in dimethyl sulfoxide and the solution was purged with nitrogen for 30 min to obtain a mixed solution. (2) Dissolve the initiator in dimethyl sulfoxide to prepare an initiator solution; (3) Add the initiator solution to the mixed solution and stir until homogeneous to obtain the precursor solution; (4) Inject the precursor solution into a glass mold, seal it, and then place the glass mold under ultraviolet light to initiate free radical polymerization to form an organic gel; (5) The organic gel was successively immersed in salt solution and deionized water for solvent exchange to obtain a flexible conductive hydrogel sensor; In step (1), the mass percentage concentration of the crosslinking agent in the mixed solution is 2-20%; The total mass percentage concentration of monomers in the mixed solution is 20-50%; The molar ratio of acrylamide to acrylic acid is 1:(0.15-0.5).

3. The method for preparing the flexible conductive hydrogel sensor as described in claim 2, characterized in that, In step (2), the initiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; The mass ratio of initiator to monomer is (0.1-0.5):100; The mass percentage concentration of the initiator in the initiator solution is 3.4-17.0%.

4. The method for preparing the flexible conductive hydrogel sensor as described in claim 2, characterized in that, In step (4), the illumination conditions are: 1-2 hours of illumination at a distance of 40cm under a 500W high-pressure mercury lamp.

5. The method for preparing the flexible conductive hydrogel sensor as described in claim 2, characterized in that, In step (5), the salt solution is at least one of ferric chloride, aluminum chloride, magnesium chloride, calcium chloride and copper chloride; The concentration of the salt solution is 0.01-0.5 mol / L; The organic gel was soaked in both salt solution and deionized water for 24 h.

6. The method for preparing the flexible conductive hydrogel sensor as described in claim 1, characterized in that, In step (1), the diol is any one of 1,4-cyclohexanediol, 1,4-benzenedimethanol, 1,4-butanediol or 1,6-hexanediol; The molar ratio of tert-butyl-substituted caprolactone to diol is (40-60): 1; The molar ratio of glycidol to diol is (1-15): 1; The molar ratio of diphenyl phosphate to tert-butyl-substituted caprolactone is 1.0-5.0; The molecular weight of BPCL is 12000-16000 g / mol.

7. The method for preparing the flexible conductive hydrogel sensor as described in claim 6, characterized in that, In step (2), the ratio of the molar amount of triethylamine to the molar amount of BPCL is 1.0-6.0; The number of moles of methacrylamide chloride is equal to the number of moles of triethylamine; The molar ratio of trifluoroacetic acid to BPCL is 100.0-300.0; The molecular weight of APCL is approximately 8000-13000 g / mol.

8. The application of a flexible conductive hydrogel sensor prepared by the method described in any one of claims 2-7 in monitoring human motion signals.

Images