Hydrogel as well as preparation method and application thereof

Abstract

The invention relates to hydrogel as well as a preparation method and application thereof, the preparation method comprises the following steps: S1, mixing polyvinyl alcohol, graphene oxide and a solvent to obtain a GO-PVA solution; s2, mixing the GO-PVA solution with a temperature-sensitive high-molecular polymer solution, and performing freeze forming to obtain a hydrogel precursor; s3, the hydrogel precursor is soaked in a sodium salt solution, and the hydrogel is obtained. According to the invention, the hydrogel precursor is soaked in a sodium salt solution with a certain concentration, and the flexible sensor prepared from the obtained hydrogel has the characteristics of temperature response and pH response. In addition, the hydrogel precursor is soaked in a sodium salt solution with a certain concentration, and the temperature sensitivity of the flexible sensor prepared from the obtained hydrogel is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogel sensors, and more specifically, to a hydrogel and a preparation method and application thereof. Background Art

[0002] Body temperature and sweat pH are important indicators of human health. On the one hand, body temperature reflects the metabolic state of the human body. Every time the body temperature drops by 1°C, the basal metabolic rate decreases by 6% to 7%. When the room temperature drops, the human body generates more heat by increasing the basal metabolism to keep the body temperature stable. Therefore, by monitoring body temperature, it is possible to assess whether the body's metabolic function is normal. On the other hand, changes in the pH value (i.e., acidity and alkalinity) of sweat can not only indicate whether the body is dehydrated, but also assist in the diagnosis of skin-related symptoms. Flexible sensors have the characteristics of being able to obtain important biological information (such as body temperature or sweat pH) from the human body, and are currently widely used in the field of flexible wearable electronics.

[0003] In order to meet the needs of multifunctionality, the functions of temperature sensing and pH sensing need to be integrated into flexible wearable electronic devices. However, most resistive sensors currently only have a single temperature sensing function or a single pH sensing function. For example, integrating resistive temperature sensors and resistive pH sensors in flexible wearable electronic devices will complicate the design and production of electronic devices. At present, there are few sensors that have both temperature and pH responses.

[0004] A Chinese patent discloses a thermosensitive hydrogel and its preparation method and application. The thermosensitive hydrogel is prepared by adhering poly(N-isopropylacrylamide) and polyvinyl alcohol (PVA) to the surface of graphene oxide (GO) respectively, and is applied to a resistive flexible temperature sensor. However, the temperature sensor made of the thermosensitive hydrogel does not have the characteristics of pH response. In addition, the temperature sensitivity of the temperature sensor made of the thermosensitive hydrogel needs to be improved.

[0005] Therefore, a hydrogel with both temperature and pH response characteristics is developed to meet its application in sensors with both temperature and pH response characteristics. Summary of the invention

[0006] The primary purpose of the present invention is to overcome the problem that the above-mentioned existing hydrogel-made resistive flexible sensors have only a single temperature or pH response characteristic, and to provide a method for preparing a hydrogel material. The present invention soaks the hydrogel precursor in a sodium salt solution of a certain concentration, so that the obtained hydrogel-made flexible sensor has both temperature and pH response characteristics. In addition, the temperature sensitivity of the obtained hydrogel-made flexible sensor is further improved by soaking the hydrogel precursor in a sodium salt solution of a certain concentration.

[0007] A further object of the present invention is to provide a hydrogel.

[0008] Another object of the present invention is to provide use of the above hydrogel in preparing a flexible sensor.

[0009] Another object of the present invention is to provide a flexible sensor.

[0010] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0011] A method for preparing a hydrogel comprises the following steps:

[0012] S1. mixing polyvinyl alcohol, graphene oxide and a solvent to obtain a GO-PVA solution;

[0013] S2. mixing the GO-PVA solution with a thermosensitive polymer solution, and freezing and molding the mixture to obtain a hydrogel precursor;

[0014] S3. The hydrogel precursor is immersed in a sodium salt solution to obtain the hydrogel;

[0015] In step S2, the mass ratio of polyvinyl alcohol in the GO-PVA solution, graphene oxide in the GO-PVA solution, and the thermosensitive polymer in the thermosensitive polymer solution is 1:(0.015-0.040):(0.8-1.2);

[0016] The lower critical solution temperature of the thermosensitive polymer in the thermosensitive polymer solution is 30 to 50° C.

[0017] The polyvinyl alcohol is polyvinyl alcohol 1750±50;

[0018] The sodium ion concentration in the sodium salt solution is 0.5 to 1.5 mol / L.

[0019] In the present invention, the selected thermosensitive polymer has a lower critical solution temperature of 30 to 50°C, which is close to the physiological temperature range of the human body. The hydrogel made of the thermosensitive polymer in this low critical solution temperature range is suitable for the field of flexible wearable electronics.

[0020] The inventors of the present invention have found in previous studies (CN117720747A) that the sensitivity of the resistive flexible temperature sensor made of thermosensitive hydrogel to temperature response can be improved by adjusting the usage ratio of graphene oxide, PVA and thermosensitive polymer and the specific combination of PVA.

[0021] The inventors of the present invention further discovered that the flexible sensor made of the hydrogel precursor (i.e., the thermosensitive hydrogel of CN117720747A) immersed in a sodium salt solution of a certain concentration has good pH response characteristics. The reason may be that as the pH changes, the -COOH functional group in the graphene oxide is ionized (forming -CO - ) is different, and -COO - with Na + There is a strong attraction between them, and the probability of collision between the two changes, resulting in Na + The movement speed changes, which in turn causes the resistance of the hydrogel to change. For example, as the pH increases, the -COOH functional groups in the graphene oxide gradually ionize to form -COO - The number of -COO increases, - with Na + The probability of collision increases, Na + The movement speed decreases, which in turn leads to an increase in the resistance of the hydrogel, so the hydrogel prepared by the present invention has the characteristic of pH response.

[0022] In addition, the inventors of the present invention have also discovered through research that by immersing the hydrogel precursor in a sodium salt solution of a certain concentration, the temperature sensitivity of the flexible sensor made of the resulting hydrogel is further improved. The principle is as follows: as the temperature changes, the presence of sodium ions causes the resistance of the hydrogel to change more significantly, so the temperature sensitivity of the flexible sensor made of the hydrogel obtained by the present invention is improved.

[0023] The polyvinyl alcohol 1750±50 used in the present invention can be obtained commercially, and can be purchased from Shanghai Yuanye Biotechnology Co., Ltd., Aladdin Reagent (Shanghai) Co., Ltd., Shanghai MacLean Biochemical Technology Co., Ltd., etc.

[0024] Preferably, in step S1, the corresponding oxidation degree of the carboxyl groups in the graphene oxide is 0.05% to 0.25%. The corresponding oxidation degree of the carboxyl groups in the graphene oxide can be measured with reference to the document "Determination of the content of carboxyl functional groups in graphene oxide by infrared spectroscopy - Gong Shuishui".

[0025] Preferably, in step S1, the mixing process is: mixing graphene oxide and a solvent to obtain a dispersion, and then adding polyvinyl alcohol to the dispersion to dissolve it.

[0026] More preferably, the dissolving process is stirring at 90-120° C. for 0.5-1 h.

[0027] Preferably, in step S1, the mass volume ratio of graphene oxide to solvent in the GO-PVA solution is (0.015-0.040) g:5 mL.

[0028] Preferably, in step S1, the mass volume ratio of polyvinyl alcohol to solvent in the GO-PVA solution is (0.9-1.2) g:5 mL.

[0029] Preferably, in step S1, the solvent is water.

[0030] Preferably, in step S2, the number average molecular weight of the temperature-sensitive polymer is 200,000-400,000.

[0031] Preferably, in step S2, the temperature-sensitive high molecular polymer is one or both of poly(N-isopropylacrylamide) and poly(N-vinylcaprolactam).

[0032] More preferably, the temperature-sensitive high molecular polymer is poly(N-isopropylacrylamide).

[0033] Preferably, in step S2, the mass volume ratio of the thermosensitive polymer to the solvent in the thermosensitive polymer solution is (0.9-1.2) g:5 mL.

[0034] Preferably, in step S2, the preparation process of the thermosensitive polymer solution is: the thermosensitive polymer and the solvent are mixed and placed at -5 to 2°C for 24 to 36 hours.

[0035] More preferably, the solvent is water.

[0036] Preferably, in step S2, the freezing molding temperature is -20 to -30°C.

[0037] Preferably, in step S2, the freezing molding time is 24 to 36 hours.

[0038] Preferably, in step S2, the lower critical solution temperature of the thermosensitive polymer in the thermosensitive polymer solution is 30-40°C.

[0039] Preferably, in step S3, the sodium ion concentration in the sodium salt solution is 0.8-1.5 mol / L. When the sodium ion concentration in the sodium salt solution is within this range, the temperature sensitivity of the prepared flexible sensor is better.

[0040] Preferably, in step S3, the sodium salt is an inorganic sodium salt.

[0041] More preferably, the inorganic sodium salt is at least one of sodium chloride, sodium sulfate or sodium carbonate.

[0042] More preferably, the inorganic sodium salt is sodium chloride.

[0043] The soaking time in step S3 can be controlled according to actual conditions, as long as the soaking time is to the extent that the sodium ion content in the hydrogel no longer changes.

[0044] Preferably, in step S3, the soaking time is 12 to 36 hours.

[0045] Preferably, in step S3, the soaking is performed at 15-30°C.

[0046] A hydrogel is prepared by the above preparation method.

[0047] The present invention also protects the use of the hydrogel in preparing flexible sensors.

[0048] Preferably, the flexible sensor is a flexible sensor with temperature response and pH response.

[0049] Preferably, the flexible sensor is a resistive flexible sensor.

[0050] A flexible sensor comprises the above hydrogel.

[0051] Preferably, the flexible sensor further comprises a flexible substrate and a metal electrode electrically connected to the hydrogel.

[0052] The method for preparing the above-mentioned flexible sensor comprises the following steps: two metal electrodes are respectively arranged at two ends above the flexible substrate, and the above-mentioned hydrogel is placed above the two metal electrodes and in contact with the two metal electrodes to obtain the above-mentioned flexible sensor.

[0053] Preferably, the metal electrode is made by coating conductive paste on both ends above the flexible substrate.

[0054] More preferably, the conductive paste is at least one of conductive gold paste, conductive silver paste or conductive copper paste.

[0055] Preferably, the material of the flexible substrate is one or both of polyethylene terephthalate and polyimide.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] The present invention soaks the hydrogel precursor in a sodium salt solution of a certain concentration, and the obtained hydrogel-made flexible sensor has both temperature and pH response characteristics. In addition, soaking the hydrogel precursor in a sodium salt solution of a certain concentration further improves the temperature sensitivity of the obtained hydrogel-made flexible sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the structure of the flexible sensor.

[0059] Figure 2 The graphs are of the changes in relative resistance of the flexible sensors made from the hydrogels of Examples 1 to 3 as a function of temperature.

[0060] Figure 3 This is a graph showing the change in relative resistance of the flexible sensor made from the comparative hydrogel of Comparative Example 1 as a function of temperature.

[0061] Figure 4 The graph shows the change of relative resistance of the flexible sensor made of the hydrogel of Example 1 and the comparative hydrogel of Comparative Example 1 as a function of pH value. DETAILED DESCRIPTION

[0062] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features. In the present invention, it is related to a numerical interval (i.e., a numerical range). Unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only points to the integers in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed herein should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows broadly including numerical interval types such as percentage intervals, ratio intervals, and ratio intervals.

[0063] Some of the reagents selected in the embodiments and comparative examples of the present invention are described as follows:

[0064] Polyvinyl alcohol 1750±50: Shanghai Yuanye Biotechnology Co., Ltd., S30196-500g;

[0065] Graphene oxide: Nanjing Nano-Xianfeng Technology Co., Ltd., model: XF002-2, single-layer graphene oxide powder;

[0066] Poly(N-isopropylacrylamide): Shanghai MacLean Biochemical Technology Co., Ltd., number average molecular weight ~300,000.

[0067] Example 1

[0068] This embodiment provides a method for preparing a hydrogel, comprising the following steps:

[0069] 1) 5 mL of deionized water and 36 mg of graphene oxide were mixed and ultrasonicated for 0.5 h to obtain a dispersion; 1 g of polyvinyl alcohol was added to the dispersion and stirred at 120° C. for 0.5 h to dissolve to obtain a GO-PVA solution;

[0070] 2) Mix 5 mL of deionized water and 1 g of poly(N-isopropylacrylamide) and place at 0°C for 24 hours to obtain a poly(N-isopropylacrylamide) solution;

[0071] 3) mixing the GO-PVA solution of step 1) and the poly(N-isopropylacrylamide) solution of step 2) uniformly at room temperature, pouring into a culture dish, and freezing at -20°C for 24 hours to form a hydrogel precursor;

[0072] 4) Soaking the hydrogel precursor of step 3) in a 1 mol / L NaCl solution, and taking it out from the NaCl solution to obtain a hydrogel; wherein the soaking temperature is 25° C., and the soaking time is 24 h.

[0073] Example 2

[0074] This embodiment provides a method for preparing a hydrogel. The difference from Embodiment 1 is that the concentration of the NaCl solution in step 4) is 0.5 mol / L.

[0075] Example 3

[0076] This embodiment provides a method for preparing a hydrogel. The difference from Embodiment 1 is that the concentration of the NaCl solution in step 4) is 1.5 mol / L.

[0077] Example 4

[0078] This embodiment provides a method for preparing a hydrogel. The difference from Embodiment 1 is that the 1 mol / L NaCl solution in step 4) is replaced by a 0.5 mol / L sodium sulfate solution.

[0079] Example 5

[0080] This embodiment provides a method for preparing a hydrogel. The difference from Embodiment 1 is that the amount of graphene oxide used in step 1) is 24 mg; the amount of poly(N-isopropylacrylamide) used in step 2) is 0.8 g.

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing a comparative hydrogel, which is different from Example 1 in that the treatment in step 4) is not performed. That is, the comparative hydrogel in this comparative example is the hydrogel precursor obtained in step 3) of Example 1.

[0083] Comparative Example 2

[0084] This comparative example provides a method for preparing a comparative hydrogel, which is different from Example 1 in that the concentration of the NaCl solution in step 4) is 2 mol / L.

[0085] Performance and testing

[0086] The hydrogels of the embodiments and the comparative hydrogels of Comparative Example 1 were used to prepare flexible sensors. The preparation method of the flexible sensor includes the following steps:

[0087] Conductive silver paste is coated on both ends of the polyethylene terephthalate flexible substrate to obtain two silver electrodes. Then, the hydrogel is placed on the two silver electrodes and in contact with the two silver electrodes to obtain a flexible sensor. Figure 1 As shown in the figure, 1 is a polyethylene terephthalate flexible substrate, 2 and 3 are two silver electrodes, and 4 is a hydrogel.

[0088] 1. Temperature test

[0089] Connect the two silver electrodes of the flexible sensor to the positive and negative interfaces of the digital bridge, contact the hydrogel with heating ceramic sheets at different temperatures, test the resistance of the flexible sensor at different temperatures, and calculate the temperature sensitivity. The formula is as follows:

[0090] S = (ΔR / R0) / ΔT;

[0091] Among them, S is the sensitivity, R0 is the initial resistance, ΔR is the relative change of resistance, and ΔT is the relative change of temperature.

[0092] 2. pH test

[0093] The two silver electrodes of the flexible sensor were connected to the positive and negative interfaces of the digital bridge, and 100 μL of buffer solutions with different pH values ​​were dropped on the hydrogel to test the resistance of the flexible sensor at different pH values.

[0094] Figure 2 The graphs showing the change of relative resistance of the flexible sensor made of the hydrogels of Examples 1 to 3 with temperature; Figure 3 The relative resistance of the flexible sensor made of the hydrogel of Comparative Example 1 varies with temperature. Figure 2 It can be seen that the sensitivities of the flexible sensors of Examples 1 to 3 are 2.23%℃- 1 , 1.27%℃- 1 and 1.49%℃- 1 . And from Figure 3 It can be seen that the sensitivity of the flexible sensor of comparative example 1 is 0.96%℃- 1The temperature sensitivity of the flexible sensors made of the hydrogels of Examples 4 and 5 is similar to that of Example 1. As shown above, the preparation method of the present invention can improve the sensitivity of the flexible sensors made of hydrogels to temperature response by soaking in a sodium salt solution.

[0095] Figure 4 The relative resistance of the flexible sensor made of the hydrogel of Example 1 and Comparative Example 1 varies with pH value. Figure 4 It can be seen that with the increase of pH value, the resistance change rate of the flexible sensor prepared in Example 1 increases significantly. However, the resistance change rate of the flexible sensor prepared by the comparative hydrogel of Comparative Example 1 has almost no significant change. The pH test results of the flexible sensors prepared in other examples are similar to those in Example 1, which shows that the flexible sensor prepared by the hydrogel of the present invention has the characteristic of pH response.

[0096] In step 4) of Comparative Example 2, the sodium ion concentration in the sodium salt solution is too high. Since sodium ions have strong hydration ability, excessively high sodium ion concentration will destroy the interaction between poly(N-isopropylacrylamide) and polyvinyl alcohol in the hydrogel and water molecules, destroying the internal structure of the hydrogel, resulting in the inability to improve the temperature response sensitivity of the hydrogel.

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a hydrogel, characterized in that: The following steps are involved: S1. mixing polyvinyl alcohol, graphene oxide and a solvent to obtain a GO-PVA solution; S2. mixing the GO-PVA solution with a thermosensitive polymer solution, and freezing and molding the mixture to obtain a hydrogel precursor; S3. The hydrogel precursor is immersed in a sodium salt solution to obtain the hydrogel; In step S2, the mass ratio of polyvinyl alcohol in the GO-PVA solution, graphene oxide in the GO-PVA solution, and the thermosensitive polymer in the thermosensitive polymer solution is 1:(0.015-0.040):(0.8-1.2); The lower critical solution temperature of the thermosensitive polymer in the thermosensitive polymer solution is 30 to 50° C. The polyvinyl alcohol is polyvinyl alcohol 1750±50; The sodium ion concentration in the sodium salt solution is 0.5 to 1.5 mol / L.

2. The preparation method according to claim 1, characterized in that: In step S1, the mass volume ratio of graphene oxide to solvent in the GO-PVA solution is (0.015-0.040) g:5 mL.

3. The preparation method according to claim 1, characterized in that: In step S2, the temperature-sensitive high molecular polymer is one or both of poly(N-isopropylacrylamide) and poly(N-vinylcaprolactam).

4. The preparation method according to claim 1, characterized in that: In step S3, the sodium salt is an inorganic sodium salt.

5. The preparation method according to claim 1, characterized in that: In step S3, the soaking time is 12 to 36 hours.

6. A hydrogel, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the hydrogel according to claim 6 in preparing a flexible sensor.

8. The use according to claim 7, characterized in that The flexible sensor is a flexible sensor with temperature response and pH response.

9. A flexible sensor, characterized in that: Comprising the hydrogel according to claim 6.

10. The flexible sensor according to claim 9, characterized in that: The flexible sensor further includes a flexible substrate and a metal electrode electrically connected to the hydrogel.

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