Hydrogel for flexible sensing signal detection and preparation method and application thereof

Abstract

The invention discloses a hydrogel for flexible sensing signal detection and a preparation method and application thereof.The preparation method of the hydrogel for flexible sensing signal detection has the advantages of being simple, convenient, efficient, safe, rapid to form, low in price and the like, and meanwhile the prepared hydrogel has high mechanical performance, high conductivity and antibacterial property and can be used for preparing flexible sensing signals. The method can be applied to manufacturing of various hydrogel flexible sensors. Based on molds and processing devices with different shapes, the forming of the high-strength conductive hydrogel is controlled, and the hydrogel can be poured into different structures. The high-strength conductive hydrogel provided by the invention can be used as a flexible strain sensor, is applied to human physiological signal detection or is applied to a biocompatible sensor, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of hydrogel preparation, and particularly relates to a hydrogel for flexible sensing signal detection and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of flexible electronic devices, wearable medical sensors and intelligent bionic systems, functional materials with excellent mechanical properties and stable conductive properties have become a research hotspot. Hydrogel materials are considered as ideal carriers for flexible conductive materials due to their high water content, biocompatibility and adjustable mechanical properties brought by the three-dimensional network structure.

[0003] Traditional hydrogels have the disadvantages of insufficient conductivity, limited flexibility, and inability to withstand large-scale strain, which seriously limits their practical application. SUMMARY

[0004] In order to solve the above problems, the application provides a hydrogel for flexible sensing signal detection and a preparation method and application thereof.

[0005] The preparation method of the hydrogel for flexible sensing signal detection of the application comprises the following steps:

[0006] S1. An ethanol solution is configured;

[0007] S2. A reduced graphene oxide (rGO) suspension is configured;

[0008] S3. The reduced graphene oxide suspension is placed in an ice water bath for stirring, and 1ml of pyrrole (PPy) and 1.535g of iron trichloride hexahydrate (FeCl3·6H2O) are sequentially added during the stirring process for polymerization reaction;

[0009] S4. After the reaction is completed, the solution changes from yellow-green to black, the black solution is centrifuged, and the black solid product after centrifugation is washed and centrifuged for multiple times until the solution after centrifugation becomes colorless, and an undried black solid is obtained;

[0010] S5. The black solid is placed in an oven at 60 DEG C for baking for 12h, and then transferred to a vacuum drying box at 60 DEG C for drying again for 12h, to obtain reduced graphene oxide / poly pyrrole (rGO / PPy) powder;

[0011] S6. Glycerol and water are configured into 9ml of glycerol aqueous solution according to a mass ratio of 1:2, 24mg of prepared reduced graphene oxide / poly pyrrole (rGO / PPy) powder and 5mg of carbon nanotubes (CNT) are added into the glycerol aqueous solution, mixed and then ultrasonically treated for 30min to obtain a mixed solution A;

[0012] S7. 1 g of 1-vinyl-3-butylimidazolium bromide was added to the sonicated mixed solution A, and after thorough mixing, 1.1 g of polyvinyl alcohol (PVA) and 0.12 g of sodium alginate (SA) were added to obtain a mixture B, and the mixture B was heated with stirring at 90 ° C for 2.5 h;

[0013] S8. When the temperature of the mixture B was cooled to 70°C, 0.12 g of chitosan (CS) was added and stirred at high speed for half an hour to obtain a solution C, which was centrifuged to remove bubbles;

[0014] S9. Pour the centrifuged solution C into a custom-made polytetrafluoroethylene mold.

[0015] S10. The mold containing solution C was placed in a refrigerator and frozen for 20 h, then taken out and thawed for 2 h. The semi-finished hydrogel was obtained after repeating the freeze-thaw process twice;

[0016] S11. After the freeze-thawed semi-finished hydrogel is taken out, it is immersed in a 25% CaCl2 solution for 10 minutes, and then taken out to obtain the finished hydrogel.

[0017] The ethanol solution is prepared by mixing deionized water and anhydrous ethanol in a mass ratio of 4:1 to form a 1000 ml solution.

[0018] The reduced graphene oxide suspension is prepared by adding 0.1 g of reduced graphene oxide to a prepared ethanol solution, and then ultrasonicating the mixture of the ethanol solution and the reduced graphene oxide for 30 minutes to form a uniform reduced graphene oxide suspension.

[0019] The yellow-green solution in S4 is a mixed solution of pyrrole monomer, reduced graphene oxide and ferric chloride.

[0020] The stirring at 90° C. in S7 refers to heating at 90° C. in a water bath and stirring.

[0021] The finished hydrogel in S11 is polyvinyl alcohol-sodium alginate-chitosan-reduced graphene oxide / polypyrrole-carbon nanotube hydrogel.

[0022] The shape of the polytetrafluoroethylene mold is a dumbbell-shaped mold, and the model is prepared according to sample type 3 in GB / T528-2009.

[0023] A hydrogel for flexible sensing signal detection prepared according to the method of the present invention comprises the following raw materials: 0.1 g of reduced graphene oxide, 1 ml of pyrrole, 1.535 g of ferric chloride hexahydrate, 5 mg of carbon nanotubes, 1 g of 1-vinyl-3-butylimidazolium bromide, 1.1 g of polyvinyl alcohol, 0.12 g of sodium alginate, and 0.12 g of chitosan.

[0024] The invention discloses an application of a hydrogel for flexible sensing signal detection in a flexible strain sensor or a biocompatible sensor.

[0025] The beneficial effects of the present invention are that the method for preparing a hydrogel for flexible sensing signal detection has the advantages of being simple, convenient, efficient, safe, quick to form, and inexpensive. The prepared hydrogel has high mechanical properties, high electrical conductivity, and antibacterial properties, and can be applied to the production of various hydrogel flexible sensors. Based on molds and processing devices of different shapes, the molding of the high-strength conductive hydrogel can be controlled, and the hydrogel can be cast into different structures. The high-strength conductive hydrogel provided by the present invention can be used as a flexible strain sensor, applied to human physiological signal detection, or applied to biocompatibility sensors, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a high-strength hydrogel finished product prepared by the present invention;

[0027] Figure 2 This is the second high-strength hydrogel product prepared by the present invention.

[0028] Figure 3 This is the microscopic imaging of the high-strength hydrogel prepared in the present invention in SEM.

[0029] Figure 4 The stress-strain curves of the high-strength hydrogel prepared in the present invention were immersed in CaCl2 solution for different immersion times.

[0030] Figure 5 This is the loading-unloading curve of the high-strength hydrogel prepared in the present invention at a strain of 1%-10%.

[0031] Figure 6 This is the loading-unloading curve of the high-strength hydrogel prepared in the present invention at a strain of 100%-500%.

[0032] Figure 7 This is the 900-cycle stretching curve of the high-strength hydrogel prepared in the present invention.

[0033] Figure 8 This is a diagram showing the sensing performance of the prepared high-strength conductive hydrogel sensor.

[0034] Figure 9 Stress-strain curves of hydrogels with different rGO / PPy contents.

[0035] Figure 10 is the electrical conductivity of hydrogels with different rGO / PPy contents.

[0036] Figure 11 The radar chart of the six key indicators of the example of the present invention is shown in FIG.

[0037] Figure 12 The results of antibacterial experiments.

[0038] Figure 13 Cell viability test results of hydrogel materials at different culture durations.

[0039] Figure 14 The biocompatibility test results of hydrogel materials.

[0040] Figure 15 The stability test of the hydrogel sensor under approximately 1000 cycles of stretching at 50% compressive strain.

[0041] Figure 16 The application of this hydrogel sensor in flexible electronic devices. DETAILED DESCRIPTION

[0042] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0043] The method for preparing a hydrogel for flexible sensing signal detection of the present invention comprises the following steps:

[0044] S1. Prepare ethanol solution;

[0045] Prepare 100 ml of a solution by mixing deionized water and anhydrous ethanol in a mass ratio of 4:1.

[0046] S2. preparing a reduced graphene oxide suspension;

[0047] 0.1 g of reduced graphene oxide was added to the prepared ethanol solution, and the mixture of the ethanol solution and the reduced graphene oxide was ultrasonicated for 30 minutes to form a uniform reduced graphene oxide suspension.

[0048] S3. The reduced graphene oxide suspension was placed in an ice water bath and stirred, and 1 ml of pyrrole and 1.535 g of ferric chloride hexahydrate were added sequentially during the stirring process to carry out the polymerization reaction;

[0049] S4. After the reaction was completed for 24 h, the solution turned from yellow-green to black, the black solution was centrifuged, and the black solid product was removed after centrifugation and washed and centrifuged repeatedly. After multiple centrifugations, the color of the solution gradually faded from pure black until the solution became colorless, and an undried black solid was obtained;

[0050] During the polymerization process, the solution surface appears yellow-green. This is because the pyrrole monomer is yellow, while the mixed solution of rGO and ferric chloride is black. The pyrrole monomer then oxidizes, gradually transforming from yellow to black, and forms polypyrrole on the redox graphene sheet. The resulting black solid is rGO / Ppy.

[0051] S5. The black solid was baked in an oven at 60°C for 12 h, and then transferred to a vacuum drying oven at 60°C for another 12 h to obtain reduced graphene oxide / polypyrrole (rGO / Ppy) powder;

[0052] S6. Glycerol and water were configured in a mass ratio of 1:2 to prepare 9 ml of glycerol aqueous solution, 24 mg of the prepared reduced graphene oxide / polypyrrole powder and 5 mg of carbon nanotubes were added to the glycerol aqueous solution, and the mixture was ultrasonicated for 30 min to obtain a mixed solution A;

[0053] S7. 1-vinyl-3-butylimidazolium bromide 1 g was added to the mixed solution A after sonication, and then 1.1 g of polyvinyl alcohol and 0.12 g of sodium alginate were added to obtain a mixture B, and the mixture B was heated with stirring at 90 ° C for 2.5 h;

[0054] S8. The heated mixture B was cooled at room temperature. When the temperature of the mixture B was cooled to 70°C, 0.12 g of chitosan was added and stirred at high speed for half an hour to obtain a solution C. The solution C was centrifuged to remove bubbles.

[0055] Solution C is a polyvinyl alcohol-sodium alginate-chitosan-reduced graphene oxide / polypyrrole-carbon nanotube (PVA-SA-CS-rGO / PPy-CNT) solution. Since the liquid is thick, bubbles will be generated during high-speed stirring, which will have an adverse effect on the performance of the material during the curing process. Therefore, centrifugation is required to remove the bubbles.

[0056] S9. Pour the centrifuged solution C into a custom-made polytetrafluoroethylene mold.

[0057] S10. The mold containing solution C was placed in a refrigerator and frozen for 20 h, then taken out and thawed for 2 h. The semi-finished hydrogel was obtained after repeating the freeze-thaw process twice;

[0058] S11. After the freeze-thawed semi-finished hydrogel is removed, it is immersed in a 25% CaCl2 solution for 10 minutes, and then removed to obtain the finished hydrogel. The finished hydrogel is the PVA-SA-CS-rGO / Ppy-CNT hydrogel.

[0059] Reduced graphene oxide / polypyrrole (rGO / PPy) can improve the mechanical properties and electrical conductivity of hydrogel materials. Reduced graphene oxide / polypyrrole (rGO / PPy) is a two-dimensional material whose high surface area ratio significantly improves the conductivity of the hydrogel. Carbon nanotubes (CNTs) are a one-dimensional conductive material that occupies the contact gap between reduced graphene oxide (rGO) and polypyrrole (PPy), effectively reducing the contact resistance. In addition, reduced graphene oxide / polypyrrole (rGO / PPy) strengthens the connection between carbon nanotubes (CNTs). The combined action of these two materials not only greatly improves the conductivity of the hydrogel, but also enhances the integrity of the conductive pathway. The mechanical properties of the material are enhanced by providing cross-linking sites and hydrogen bonds.

[0060] 1-Butyl-3-vinylimidazolium bromide can enhance the antibacterial properties of hydrogels. The positive charge of the imidazolium bromide cation is attracted to the negatively charged bacterial cell wall, promoting electrostatic interactions that affect the permeability of the cell wall. This interaction ultimately leads to internal osmotic imbalance, destroying the bacterial cell wall and inhibiting microbial proliferation. At the same time, the hydrophobic alkyl chains present in the ionic liquid can penetrate the outer membrane of the bacteria, destroying its structural integrity and leading to bacterial death. The imidazolium bromide ionic liquid exhibits antibacterial effects, enhancing the long-term usability of the hydrogel sensor.

[0061] Polyvinyl alcohol, chitosan, and sodium alginate serve as the support materials for the double-network hydrogel. The imidazolyl ionic liquid VBIMBR and glycerol / water form a ternary solvent system, enhancing the compatibility of chitosan / polyvinyl alcohol and imparting antibacterial, conductive, and antifreeze properties to the hydrogel. The hydrogel is cross-linked through ionic and hydrogen bonds, imparting exceptional mechanical and conductive properties. This allows the hydrogel sensor to maintain its sensing properties over a wide range.

[0062] The PVA-SA-CS-rGO / PPy-CNT hydrogel exhibits a uniform micron-scale porous structure, which is attributed to the interactions between PVA molecular chains, SA, CS, and glycerol. Firstly, freezing promotes hydrogen-bonded crosslinking of PVA with SA, CS, and glycerol, forming a primary crosslinked network. After cyclic freezing, the PVA-SA-CS-rGO / PPy-CNT hydrogel is immersed in a CaCl2 solution, converting sodium alginate into calcium alginate with an "eggshell" structure, forming a secondary crosslinked network. The porous structure within the hydrogel creates transport channels for ions within the hydrogel, facilitating ion migration. This morphology imparts enhanced electrical conductivity to the PVA-SA-CS-rGO / PPy-CNT hydrogel. Secondly, the three-dimensional interconnected porous structure may play a significant role in its mechanical properties.

[0063] The hydrogel for flexible sensing signal detection prepared by the method of the present invention includes the following raw materials: 0.1g of reduced graphene oxide, 1ml of pyrrole, 1.535g of ferric chloride hexahydrate, 5mg of carbon nanotubes, 1g of 1-vinyl-3-butylimidazolium bromide, 1.1g of polyvinyl alcohol, 0.12g of sodium alginate, and 0.12g of chitosan.

[0064] Application of hydrogels for flexible sensing signal detection in flexible strain sensors or biocompatible sensors.

[0065] Figure 1 and Figure 2 The high-strength hydrogel finished product prepared by the present invention, and the prepared hydrogel sensor is a soft black gel. Figure 1 It is a hydrogel fiber, showing the processability of hydrogel; Figure 2 It is a dumbbell-shaped hydrogel film, showing the flexibility and deformability of the hydrogel.

[0066] like Figure 3 As shown, the hydrogel prepared by the method of the present invention has a porous structure, and the porous structure provides the hydrogel with good mechanical and electrical properties.

[0067] like Figure 4 As shown, the hydrogel prepared by the present invention is a hydrogel fiber soaked in a CaCl2 solution. After soaking for 10 minutes, the tensile strength and tensile length change from 815% and 3.333MPa to 1491% and 1.793MPa. However, as the soaking time increases, part of the glycerol gradually dissolves in the water, the plasticizing effect of glycerol weakens, and the crystal structure of the hydrogel is severely damaged. When the soaking time is increased from 30 minutes to 40 minutes, the swelling of the hydrogel reaches its limit due to the increase in the cross-linking density of sodium alginate, which leads to the tensile length and tensile strength of the PVA-SA-CS-rGO / PPy-CNT hydrogel being improved again. Compared with existing hydrogels, higher stress can withstand sudden large stress in the strain sensor without breaking, and higher strain enables the hydrogel to respond to signals in a wide range, expanding its application scenarios.

[0068] Figure 5 、 Figure 6The loading-unloading curves for the hydrogel film are shown at 1%-10% and 100%-500%, demonstrating that under low-strain tension, the PVA-SA-CS-rGO / PPy-CNT hydrogel exhibits a well-defined hysteresis loop. As the maximum tensile strain increases, the hysteresis loop widens, and the dissipated energy increases. This further demonstrates that the PVA-SA-CS-rGO / PPy-CNT hydrogel can maintain its morphology without breaking even under high stress, providing protection when necessary and extending its use cases and service life.

[0069] Figure 7 The figure shows the 900-cycle stretching curve. After the first cycle, the hydrogel's hysteresis circles decrease significantly, then remain nearly overlapping for the next 900 cycles, exhibiting similar dissipated energy. This indicates that the PVA-SA-CS-rGO / PPy-CNT hydrogel exhibits excellent fatigue resistance due to its multiple non-covalent crosslinks. Compared to similar hydrogel sensors, the PVA-SA-CS-rGO / PPy-CNT hydrogel maintains excellent levels of dissipated energy after cycles and cycle number. This suggests that in everyday use, when using the PVA-SA-CS-rGO / PPy-CNT hydrogel as a flexible sensor, the sensor will have a longer lifespan and better stability.

[0070] Figure 8 The figure shows that when the human body lowers its head, the hydrogel sensor emits a stable signal change, which shows that the hydrogel sensor has excellent sensitivity.

[0071] Figure 9 、 Figure 10 Figure 2 shows the stress-strain curves and electrical conductivity of hydrogels with varying rGO / PPy content. While increasing the rGO / PPy content improves the mechanical and tensile properties of the hydrogels, an excessive amount of rGO / PPy hinders crosslinking. While the response time and electrical conductivity are improved, the maximum tensile stress and strain both increase and then decrease.

[0072] Figure 11Shown are radar charts of the hydrogel of the present invention across six key metrics. To demonstrate the advantages of the PVA-SA-CS-rGO / PPy-CNT hydrogel, we comprehensively evaluated its superior mechanical properties and electrical conductivity across six key metrics: maximum stress, maximum strain, conductivity, gauge factor (GF), minimum detectable strain, and antibacterial effect. Our results demonstrate that this hydrogel exhibits strong mechanical properties and electrical conductivity. The various cross-linking mechanisms not only impart excellent mechanical properties to the PVA-SA-CS-rGO / PPy-CNT hydrogel, but also highlight its potential as a flexible sensor, demonstrating conductivity up to 8.4 S / m and the ability to detect strains as low as 0.5%.

[0073] Figure 12 The results of the antibacterial experiment are shown. The three columns of colony groups in the figure, from left to right, are the control group, the group without 1-vinyl-3-butylimidazolium bromide, and the PVA-SA-CS-rGO / PPy-CNT hydrogel group. The PVA-SA-CS-rGO / PPy-CNT hydrogel group exhibited some antibacterial activity against Escherichia coli and Staphylococcus aureus. However, the sample without 1-vinyl-3-butylimidazolium bromide showed little antibacterial activity against E. coli and limited effectiveness against Staphylococcus aureus, failing to completely inhibit the growth of the latter, as evidenced by the lack of a completely transparent zone of inhibition. The diameter of the zone of inhibition, used as a measure to further characterize the antibacterial properties of the hydrogel, was 6.5 mm for the PVA-SA-CS-rGO / PPy-CNT hydrogel against E. coli and 7.0 mm for Staphylococcus aureus. Compared with most hydrogels, a humid environment is very likely to cause bacterial growth and infection. PVA-SA-CS-rGO / PPy-CNT hydrogel effectively prevents this situation. While ensuring its use as a flexible sensor, it also increases its use effect that is different from other hydrogels.

[0074] Figure 13 、 14 The results of the hydrogel material cytocompatibility test are shown in Figure 3. Three groups of cytocompatibility experiments were conducted for 48 hours, 72 hours, and 96 hours, respectively, indicating that the hydrogel has good biocompatibility.

[0075] Figure 15 The figure shows the stability test of the hydrogel sensor under approximately 1000 cycles of stretching at 50% strain. The sensor maintained a stable response after 1000 cycles of continuous stretching at 50% strain, demonstrating its excellent stability and fatigue resistance. Good lifespan, stability, and fatigue resistance are the most desirable characteristics of hydrogel sensors today, demonstrating the potential and promise of the PVA-SA-CS-rGO / PPy-CNT hydrogel as a flexible sensor.

[0076] Figure 16 The figure shows the application of hydrogel sensors in flexible electronic devices, wherein the material of the writing pen is the conductive hydrogel material proposed in this patent, indicating that the hydrogel sensor can be used as a capacitive pen for writing and drawing on a tablet computer, indicating that the hydrogel of the present invention has good application prospects.

[0077] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for preparing a hydrogel for flexible sensing signal detection, characterized in that: The following steps are involved: S1. Prepare ethanol solution; S2. preparing a reduced graphene oxide suspension; S3. The reduced graphene oxide suspension was placed in an ice water bath and stirred, and 1 ml of pyrrole and 1.535 g of ferric chloride hexahydrate were added sequentially during the stirring process to carry out the polymerization reaction; S4. After the reaction, the solution turned from yellow-green to black, the black solution was centrifuged, and the black solid product was removed after centrifugation and washed and centrifuged several times until the solution became colorless after centrifugation, and an undried black solid was obtained; S5. The black solid was placed in an oven at 60 ° C for 12 h, and then transferred to a vacuum drying oven at 60 ° C and dried again for 12 h to obtain reduced graphene oxide / polypyrrole powder; S6. Glycerol and water were configured in a mass ratio of 1:2 to prepare 9 ml of glycerol aqueous solution, 24 mg of the prepared reduced graphene oxide / polypyrrole powder and 5 mg of carbon nanotubes were added to the glycerol aqueous solution, and the mixture was ultrasonicated for 30 min to obtain a mixed solution A; S7. 1-vinyl-3-butylimidazolium bromide 1 g was added to the mixed solution A after sonication, and then 1.1 g of polyvinyl alcohol and 0.12 g of sodium alginate were added to obtain a mixture B, and the mixture B was heated with stirring at 90 ° C for 2.5 h; S8. When the temperature of the mixture B was cooled to 70°C, 0.12 g of chitosan was added and stirred at high speed for half an hour to obtain a solution C, which was centrifuged to remove bubbles; S9. Pour the centrifuged solution C into a custom-made polytetrafluoroethylene mold. S10. The mold containing solution C was placed in a refrigerator and frozen for 20 h, then taken out and thawed for 2 h. The semi-finished hydrogel was obtained after repeating the freeze-thaw process twice; S11. After the freeze-thawed semi-finished hydrogel is taken out, it is immersed in a 25% CaCl2 solution for 10 minutes, and then taken out to obtain the finished hydrogel.

2. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, wherein: The ethanol solution is prepared by mixing deionized water and anhydrous ethanol in a mass ratio of 4:1 to form a 1000 ml solution.

3. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, wherein: The reduced graphene oxide suspension is prepared by adding 0.1 g of reduced graphene oxide to a prepared ethanol solution, and then ultrasonicating the mixture of the ethanol solution and the reduced graphene oxide for 30 minutes to form a uniform reduced graphene oxide suspension.

4. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, wherein: The yellow-green solution in S4 is a mixed solution of pyrrole monomer, reduced graphene oxide and ferric chloride.

5. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, characterized in that: The stirring at 90° C. in S7 refers to heating at 90° C. in a water bath and stirring.

6. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, characterized in that: The finished hydrogel in S11 is polyvinyl alcohol-sodium alginate-chitosan-reduced graphene oxide / polypyrrole-carbon nanotube hydrogel.

7. The method for preparing a hydrogel for flexible sensing signal detection according to claim 1, characterized in that: The shape of the polytetrafluoroethylene mold is a dumbbell-shaped mold.

8. A hydrogel for flexible sensing signal detection prepared according to the method according to any one of claims 1 to 7, characterized in that: The method comprises the following raw materials: 0.1 g of reduced graphene oxide, 1 ml of pyrrole, 1.535 g of ferric chloride hexahydrate, 5 mg of carbon nanotubes, 1 g of 1-vinyl-3-butylimidazolium bromide, 1.1 g of polyvinyl alcohol, 0.12 g of sodium alginate, and 0.12 g of chitosan.

9. Use of the hydrogel for flexible sensing signal detection according to claim 8 in a flexible strain sensor or a biocompatible sensor.

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