A temperature-sensitive hydrogel and a preparation method and application thereof

Abstract

The application discloses a temperature-sensitive hydrogel and a preparation method and application thereof, and relates to the technical field of temperature-sensitive hydrogels. The preparation method of the temperature-sensitive hydrogel comprises the following steps: S1, dissolving poly(N-isopropyl acrylamide) in water to prepare a PNIPAM aqueous solution; S2, mixing graphene oxide and water, adding and dissolving polyvinyl alcohol to obtain a GO-PVA solution; and S3, mixing the PNIPAM aqueous solution and the GO-PVA solution, and freeze-forming to obtain the temperature-sensitive hydrogel. The mass ratio of poly(N-isopropyl acrylamide), graphene oxide and polyvinyl alcohol is 1:(0.015-0.040):1; and the polyvinyl alcohol is polyvinyl alcohol 1750+ / -50. The application utilizes hydrogen bonds to make PNIPAM and PVA adhere to the surface of GO, not only makes the internal structure of the formed temperature-sensitive hydrogel more compact, but also makes GO uniformly dispersed and fixed in the interior and surface of the temperature-sensitive hydrogel, thereby improving the sensitivity of a temperature sensor.

Description

Technical Field

[0001] This invention relates to the field of hydrogel sensor technology, and more specifically, to a temperature-sensitive hydrogel, its preparation method, and its application. Background Technology

[0002] One of the essential conditions for maintaining normal human life activities is maintaining a relatively constant body temperature. Excessively high or low body temperature will severely affect various systems, especially the nervous system, and may even endanger health. The central nervous system regulates the body's heat production and dissipation. Many diseases related to the central nervous system can affect or even impair this normal temperature regulation, leading to changes in body temperature. Therefore, checking and observing body temperature changes is helpful for disease diagnosis and assessment. Furthermore, body temperature reflects the body's basal metabolic rate; for every 1°C drop in body temperature, the basal metabolic rate decreases by 6-7%. When the ambient temperature drops, the body increases its basal metabolic rate to generate more heat to maintain body temperature. Therefore, checking and observing body temperature changes helps determine whether the body's basal metabolic rate is normal. Thus, monitoring and tracking changes in body temperature over a long period is of great significance.

[0003] A temperature sensor is a sensor that can sense temperature and convert it into a usable output signal. When combined with flexible wearable devices, it forms a resistive flexible temperature sensor capable of detecting and tracking changes in human body temperature over extended periods. Hydrogel is the core component of this resistive flexible temperature sensor, and sensitivity is one of its key performance parameters. Therefore, developing a temperature-sensitive hydrogel that can improve the sensitivity of resistive flexible temperature sensors would facilitate faster and more accurate detection and long-term tracking of changes in human body temperature, possessing significant economic value. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a thermosensitive hydrogel, its preparation method, and its application.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a thermosensitive hydrogel, the method comprising the following steps:

[0007] S1. Prepare an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) by dissolving it in water for later use;

[0008] S2. Mix graphene oxide (GO) and water, then add and dissolve polyvinyl alcohol (PVA) to obtain a GO-PVA solution;

[0009] S3. Mix PNIPAM aqueous solution and GO-PVA solution, freeze-mold, and the thermosensitive hydrogel is obtained;

[0010] The mass ratio of poly(N-isopropylacrylamide), graphene oxide, and polyvinyl alcohol is 1:(0.015-0.040):1.

[0011] The polyvinyl alcohol is polyvinyl alcohol 1750±50.

[0012] In the thermosensitive hydrogel of this invention, graphene oxide (GO), with a large number of oxygen-containing functional groups such as carboxyl and hydroxyl groups on its surface, has a large number of sites that can be used to form intermolecular hydrogen bonds. It can serve as an intermediate medium, allowing poly(N-isopropylacrylamide) (PNIPAM) and polyvinyl alcohol (PVA) to adhere to the GO surface through intermolecular hydrogen bonds. This increases the interaction force between PNIPAM and PVA, reduces the distance between them, and makes the internal structure of the thermosensitive hydrogel more compact. This enables it to quickly sense and transmit temperature stimuli and react rapidly, thereby improving the sensitivity of the resistive flexible temperature sensor prepared using the thermosensitive hydrogel. At the same time, the intermolecular hydrogen bonds between PNIPAM, PVA, and GO allow GO to be uniformly dispersed and fixed inside and on the surface of the thermosensitive hydrogel, improving the conductivity of the thermosensitive hydrogel and further enhancing the sensitivity of the resistive flexible temperature sensor prepared using the thermosensitive hydrogel.

[0013] When the amount of graphene oxide (GO) is too small, it cannot effectively adhere to PNIPAM and PVA through hydrogen bonds, reducing the interaction force between PNIPAM and PVA and increasing the distance between them. This results in a looser internal structure of the formed thermosensitive hydrogel, hindering its ability to quickly sense and transmit temperature stimuli and respond rapidly, thus negatively impacting the sensitivity of the resistive flexible temperature sensor fabricated using the thermosensitive hydrogel. Conversely, when the amount of graphene oxide (GO) is too large, GO can adhere not only to PNIPAM and PVA through hydrogen bonds but also to other GO molecules, causing GO aggregation. This reduces the utilization rate of intermolecular hydrogen bond sites on the GO surface, weakening the interaction force between PNIPAM and PVA and increasing the distance between them. This further loosens the internal structure of the formed thermosensitive hydrogel and hinders the uniform dispersion and fixation of GO within and on the surface of the hydrogel, ultimately reducing the sensitivity of the resistive flexible temperature sensor fabricated using the thermosensitive hydrogel.

[0014] Through numerous experiments, the inventors discovered that thermosensitive hydrogels formed with polyvinyl alcohol 1750±50 (with a degree of hydrolysis not constant and ≤99%) not only have a more compact internal structure but also better flexibility and are less prone to breakage. In contrast, thermosensitive hydrogels formed with polyvinyl alcohol 1799 (with a degree of hydrolysis of 99%) have a higher viscosity but a looser internal structure, making them more brittle and prone to breakage. Therefore, thermosensitive hydrogels prepared using polyvinyl alcohol 1750±50 are more suitable for fabricating resistive flexible temperature sensors.

[0015] The polyvinyl alcohol 1750±50 used in this invention is commercially available and can be purchased from companies such as Shanghai Yuanye Biotechnology Co., Ltd., Sinopharm Chemical Reagent Co., Ltd., Nanjing Chemical Reagent Co., Ltd., and Shanghai Aichun Biotechnology Co., Ltd.

[0016] In a preferred embodiment of the preparation method of the thermosensitive hydrogel of the present invention, the mass ratio of poly(N-isopropylacrylamide), graphene oxide and polyvinyl alcohol is 1:(0.015-0.036):1. More preferably, the mass ratio of poly(N-isopropylacrylamide), graphene oxide and polyvinyl alcohol is 1:(0.024-0.036):1.

[0017] In a preferred embodiment of the preparation method of the thermosensitive hydrogel of the present invention, the mass-to-volume ratio of poly(N-isopropylacrylamide) to water in step S1 is (0.5-1.5) g: 5 mL. More preferably, the mass-to-volume ratio of poly(N-isopropylacrylamide) to water in step S1 is 1 g: 5 mL.

[0018] In a preferred embodiment of the method for preparing the thermosensitive hydrogel of the present invention, the mass-to-volume ratio of polyvinyl alcohol to water in step S2 is (0.5-1.5) g: 5 mL. More preferably, the mass-to-volume ratio of polyvinyl alcohol to water in step S2 is 1 g: 5 mL.

[0019] In a preferred embodiment of the method for preparing the thermosensitive hydrogel of the present invention, the dissolution in step S1 is carried out at 0-5°C. More preferably, the dissolution in step S1 is carried out at 0°C.

[0020] In a preferred embodiment of the preparation method of the thermosensitive hydrogel of the present invention, the mixing of graphene oxide and water in step S2 is achieved by ultrasound.

[0021] In a preferred embodiment of the method for preparing the thermosensitive hydrogel of the present invention, the dissolution of polyvinyl alcohol in step S2 is carried out at 90-150°C. More preferably, the dissolution of polyvinyl alcohol in step S2 is carried out at 120°C.

[0022] In a preferred embodiment of the method for preparing the thermosensitive hydrogel of the present invention, the freezing temperature in step S3 is (-25)-(-15)℃, and the time is ≥15h. More preferably, the freezing temperature in step S3 is -20℃, and the time is 24h.

[0023] Secondly, the present invention provides a thermosensitive hydrogel prepared by the above preparation method.

[0024] Thirdly, the present invention provides an application of a thermosensitive hydrogel in a temperature sensor.

[0025] Fourthly, the present invention provides a thermosensitive hydrogel resistive flexible temperature sensor, which is mainly composed of polyethylene terephthalate (PET) film, conductive silver paste and thermosensitive hydrogel.

[0026] Fifthly, the present invention provides a method for fabricating a thermosensitive hydrogel resistive flexible temperature sensor, the method comprising the following steps:

[0027] S1. Divide the polyethylene terephthalate (PET) film into three regions: a first region, a second region, and a third region. Apply conductive silver paste to the first and third regions, while leaving the second region untreated. This yields a semi-finished temperature sensor.

[0028] S2. Place the thermosensitive hydrogel on the surface of the temperature sensor semi-finished product, so that the thermosensitive hydrogel comes into contact with the first, second and third regions of the polyethylene terephthalate (PET) film, thus obtaining the thermosensitive hydrogel resistive flexible temperature sensor.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The thermosensitive hydrogel of this invention enables poly(N-isopropylacrylamide) (PNIPAM) and polyvinyl alcohol (PVA) to adhere to the surface of graphene oxide (GO) via intermolecular hydrogen bonds. On the one hand, this increases the interaction force between PNIPAM and PVA, reduces the distance between them, and makes the internal structure of the thermosensitive hydrogel more compact, enabling it to quickly sense and transmit temperature stimuli and react rapidly, thereby improving the sensitivity of the resistive flexible temperature sensor. On the other hand, it allows GO to be uniformly dispersed and fixed inside and on the surface of the thermosensitive hydrogel, improving the conductivity of the thermosensitive hydrogel, and thus improving the sensitivity of the resistive flexible temperature sensor. Attached Figure Description

[0031] Figure 1 The image shows a semi-finished temperature sensor product from Example 1. In the image, 1 represents the first region of the PET film, 2 represents the second region of the PET film, and 3 represents the third region of the PET film.

[0032] Figure 2 The image shows a physical diagram of the thermosensitive hydrogel resistive flexible temperature sensor of Example 1. In the diagram, 1 represents the first region of the PET film, 2 represents the second region of the PET film, 3 represents the third region of the PET film, and 4 represents the thermosensitive hydrogel.

[0033] Figure 3 This is a picture of the actual product after ultrasonic mixing of graphene and water in Comparative Example 2.

[0034] Figure 4 The image shows the actual thermosensitive hydrogel of Comparative Example 4.

[0035] Figure 5 The graphs show the resistance versus temperature relationship of the thermosensitive hydrogel resistive flexible temperature sensor in Examples 1-4 and Comparative Example 1. Detailed Implementation

[0036] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] The reagents used in the various embodiments and comparative examples of this invention are as follows:

[0038] Polyvinyl alcohol 1750±50 (polyvinyl alcohol 1750±50 type), Shanghai Yuanye Biotechnology Co., Ltd., S30196-500g;

[0039] Polyvinyl alcohol 1799 (polyvinyl alcohol 1799 type), Shanghai Aladdin Biochemical Technology Co., Ltd., P105126-500g;

[0040] Poly(N-isopropylacrylamide) (PNIPAM), Mn approx. 300,000, Shanghai Maclean Biochemical Technology Co., Ltd., P875492;

[0041] N-Isopropylacrylamide, Shanghai Maclean Biochemical Technology Co., Ltd., N811777;

[0042] Graphene oxide (GO), single-layer graphene oxide powder, Nanjing Xianfeng Nanomaterials Technology Co., Ltd., XF002-2;

[0043] Graphene, single-layer graphene powder, Nanjing Xianfeng Nanomaterials Technology Co., Ltd., XF001H;

[0044] Carbon nanotubes, hydroxylated multi-walled carbon nanotubes, Nanjing Xianfeng Nanomaterials Technology Co., Ltd., 100788.

[0045] Example 1

[0046] This embodiment provides a thermosensitive hydrogel, the preparation method of which includes the following steps:

[0047] S1. Prepare an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) by dissolving 1 g of poly(N-isopropylacrylamide) in 5 mL of water at 0 °C for later use;

[0048] S2. Mix 24 mg of graphene oxide (GO) and 5 mL of water using ultrasound until the graphene oxide is completely dispersed. Then, under heating conditions of 120 °C, add and dissolve 1 g of polyvinyl alcohol (PVA) to obtain a GO-PVA solution.

[0049] S3. Stir and mix the PNIPAM aqueous solution and GO-PVA solution, pour into a mold, freeze at -20℃ for 24 hours to form, demold, and obtain the thermosensitive hydrogel;

[0050] The mass ratio of poly(N-isopropylacrylamide), graphene oxide, and polyvinyl alcohol is 1:0.024:1.

[0051] The polyvinyl alcohol is polyvinyl alcohol 1750±50.

[0052] A thermosensitive hydrogel resistive flexible temperature sensor is mainly composed of polyethylene terephthalate (PET) film, conductive silver paste and thermosensitive hydrogel.

[0053] A method for fabricating a thermosensitive hydrogel resistive flexible temperature sensor, the method comprising the following steps:

[0054] S1. Divide the polyethylene terephthalate (PET) film into three regions: a first region, a second region, and a third region. Apply conductive silver paste to the first and third regions, leaving the second region untreated. This yields a semi-finished temperature sensor. Figure 1 As shown in the figure, 1 represents the first region of the PET film, 2 represents the second region of the PET film, and 3 represents the third region of the PET film;

[0055] S2. Place the thermosensitive hydrogel on the surface of the temperature sensor semi-finished product, making the thermosensitive hydrogel contact the first, second, and third regions of the polyethylene terephthalate (PET) film, thus obtaining the thermosensitive hydrogel resistive flexible temperature sensor, such as... Figure 2 As shown in the figure, 1-the first region of the PET film, 2-the second region of the PET film, 3-the third region of the PET film, and 4-thermosensitive hydrogel.

[0056] Examples 2-4 and Comparative Example 1

[0057] Examples 2-4 and Comparative Example 1 provide different thermosensitive hydrogels and thermosensitive hydrogel resistive flexible temperature sensors. The difference between them and Example 1 is the amount of graphene oxide (GO) used; otherwise, they are the same as Example 1, as shown in the table below:

[0058] Table 1. Amount of GO in the thermosensitive hydrogels of Examples 1-4 and Comparative Example 1

[0059]

[0060] Comparative Example 2

[0061] This comparative example provides a temperature-sensitive hydrogel, which differs from Example 1 in that it uses graphene instead of graphene oxide (GO), as detailed below:

[0062] S1. Prepare an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) by dissolving 1 g of poly(N-isopropylacrylamide) in 5 mL of water at 0 °C for later use;

[0063] S2. Mix 24 mg of graphene and 5 mL of water using ultrasound, as follows: Figure 3 As shown, it was found that graphene could not be dispersed and subsequent operations could not be carried out. That is, graphene could not be used to replace graphene oxide to prepare thermosensitive hydrogels and thermosensitive hydrogel resistive flexible temperature sensors.

[0064] Comparative Example 3

[0065] This comparative example provides a thermosensitive hydrogel and a thermosensitive hydrogel resistive flexible temperature sensor. The difference between this example and Example 1 is that carbon nanotubes are used instead of graphene oxide (GO), while the rest are the same as Example 1.

[0066] Comparative Example 4

[0067] This comparative example provides a temperature-sensitive hydrogel, which differs from Example 1 in that it uses polyvinyl alcohol 1799 instead of polyvinyl alcohol 1750±50, as detailed below:

[0068] S1. Prepare an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) by dissolving 1 g of poly(N-isopropylacrylamide) in 5 mL of water at 0 °C for later use;

[0069] S2. Mix 24 mg of graphene oxide (GO) and 5 mL of water using ultrasound until the graphene oxide is completely dispersed. Then, under heating conditions of 120 °C, add and dissolve 1 g of polyvinyl alcohol (PVA) to obtain a GO-PVA solution.

[0070] S3. Stir and mix the PNIPAM aqueous solution and GO-PVA solution, pour into a petri dish, freeze at -20℃ for 24 hours to solidify, demold, and obtain the thermosensitive hydrogel;

[0071] The mass ratio of poly(N-isopropylacrylamide), graphene oxide, and polyvinyl alcohol is 1:0.024:1.

[0072] The polyvinyl alcohol is polyvinyl alcohol 1799.

[0073] It is worth noting that during the demolding operation in step S3, the inventors discovered that the thermosensitive hydrogel prepared using polyvinyl alcohol 1799 had a high viscosity and a relatively loose internal structure, making it brittle and prone to breakage. Figure 4 As shown, it crumbles easily when pinched with tweezers and cannot be fully molded. Therefore, it cannot be used to prepare thermosensitive hydrogel resistive flexible temperature sensors.

[0074] Comparative Example 5

[0075] This comparative example provides a temperature-sensitive hydrogel, which differs from Example 1 in that N-isopropylacrylamide is used instead of poly(N-isopropylacrylamide) (PNIPAM), as detailed below:

[0076] S1. Prepare an aqueous solution of N-isopropylacrylamide by dissolving 1 g of N-isopropylacrylamide in 5 mL of water at 0 °C for later use;

[0077] S2. Mix 24 mg of graphene oxide (GO) and 5 mL of water using ultrasound until the graphene oxide is completely dispersed. Then, under heating conditions of 120 °C, add and dissolve 1 g of polyvinyl alcohol (PVA) to obtain a GO-PVA solution.

[0078] S3. Stir and mix N-isopropylacrylamide aqueous solution and GO-PVA solution, pour into a petri dish, freeze at -20℃ for 24 hours to form, demold, and obtain thermosensitive hydrogel;

[0079] The mass ratio of N-isopropylacrylamide, graphene oxide, and polyvinyl alcohol is 1:0.024:1.

[0080] The polyvinyl alcohol is polyvinyl alcohol 1750±50.

[0081] It is worth noting that the inventors discovered during the demolding operation in step S3 that the thermosensitive hydrogel prepared using N-isopropylacrylamide could not solidify and could not be formed. This may be because the molecular weight of N-isopropylacrylamide is too small. In the system of this invention, it cannot form a stable hydrogel with a three-dimensional network structure with polyvinyl alcohol and graphene oxide. Therefore, N-isopropylacrylamide is not suitable for preparing thermosensitive hydrogel resistive flexible temperature sensors.

[0082] Performance testing

[0083] The sensitivity of the thermosensitive hydrogel resistive flexible temperature sensors prepared by the thermosensitive hydrogels in each embodiment and comparative example was tested. The specific test method is as follows:

[0084] The prepared thermosensitive hydrogel resistive flexible temperature sensor was attached to the outer wall of a beaker. Water at different temperatures (range 35-50℃) was then poured into the beaker. The resistance of the thermosensitive hydrogel resistive flexible temperature sensor was measured using a Gwinstek LCR-8200 series digital bridge. The test was repeated three times, and the average value was taken. The sensitivity of the thermosensitive hydrogel resistive flexible temperature sensor was then calculated. The sensitivity S was defined as:

[0085] S=(ΔR / R0) / ΔT

[0086] In the above formula, R0 is the initial resistance, ΔR is the relative change in resistance, and ΔT is the relative change in temperature.

[0087] Table 2. Sensitivity test results for each embodiment and comparative example.

[0088]

[0089]

[0090] Figure 5 The graphs show the resistance versus temperature relationship of the thermosensitive hydrogel resistive flexible temperature sensor in Examples 1-4 and Comparative Example 1.

[0091] From Table 1 and Figure 5 It is evident that the thermosensitive hydrogel resistive flexible temperature sensor prepared by the present invention has high sensitivity.

[0092] Specifically, comparing Examples 1-4 and Comparative Example 1 reveals that in the thermosensitive hydrogel of this invention, when the amount of graphene oxide (GO) is too small, it cannot effectively adhere PNIPAM and PVA through hydrogen bonds, reducing the interaction force between PNIPAM and PVA and increasing the distance between them. This results in a looser internal structure of the thermosensitive hydrogel, hindering its ability to quickly sense and transmit temperature stimuli and react rapidly, thus negatively impacting the sensitivity of the resistive flexible temperature sensor prepared using the thermosensitive hydrogel. Conversely, when the amount of graphene oxide (GO) is excessive, GO can adhere not only to PNIPAM and PVA through hydrogen bonds but also to other GO molecules, causing GO aggregation. This reduces the utilization rate of intermolecular hydrogen bond sites on the GO surface, leading to a weaker interaction force between PNIPAM and PVA and a larger distance between them. This further loosens the internal structure of the thermosensitive hydrogel and hinders the uniform dispersion and fixation of GO within and on the surface of the hydrogel, thereby reducing the sensitivity of the resistive flexible temperature sensor prepared using the thermosensitive hydrogel.

[0093] By comparing Example 1 and Comparative Example 3, it can be seen that, compared with the tubular structure of carbon nanotubes, the planar structure of graphene oxide provides a better adhesion between PNIPAM and PVA, and can better reduce the distance between PNIPAM and PVA, making the internal structure of the formed thermosensitive hydrogel more compact, which can more quickly sense and transmit temperature stimuli and react rapidly, thereby improving the sensitivity of the resistive flexible temperature sensor prepared by the thermosensitive hydrogel.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a thermosensitive hydrogel, characterized in that, The preparation method includes the following steps: S1. Prepare an aqueous solution of PNIPAM by dissolving poly(N-isopropylacrylamide) in water for later use; S2. Mix graphene oxide and water, then add and dissolve polyvinyl alcohol to obtain a GO-PVA solution; S3. Mix PNIPAM aqueous solution and GO-PVA solution, freeze-mold, and the thermosensitive hydrogel is obtained; The mass ratio of poly(N-isopropylacrylamide), graphene oxide, and polyvinyl alcohol is 1:(0.015-0.040):

1. The polyvinyl alcohol is polyvinyl alcohol 1750±50.

2. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The mass ratio of poly(N-isopropylacrylamide), graphene oxide and polyvinyl alcohol is 1:(0.015-0.036):

1.

3. The method for preparing the thermosensitive hydrogel as described in claim 2, characterized in that, The mass ratio of poly(N-isopropylacrylamide), graphene oxide and polyvinyl alcohol is 1:(0.024-0.036):

1.

4. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The mass-to-volume ratio of poly(N-isopropylacrylamide) and water in step S1 is (0.5-1.5) g: 5 mL.

5. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The mass-to-volume ratio of polyvinyl alcohol and water in step S2 is (0.5-1.5) g: 5 mL.

6. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The dissolution described in step S1 is carried out at 0-5°C.

7. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The dissolution of polyvinyl alcohol in step S2 is carried out at 90-150°C.

8. The method for preparing the thermosensitive hydrogel as described in claim 1, characterized in that, The freezing temperature in step S3 is (-25)-(-15)℃.

9. A thermosensitive hydrogel prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the thermosensitive hydrogel of claim 9 in a temperature sensor.

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