Piezoelectric polymer and blood pressure monitoring device based on same

Abstract

The invention discloses a piezoelectric polymer and a blood pressure monitoring device based on the piezoelectric polymer, and relates to the technical field of blood pressure monitoring, the piezoelectric polymer comprises polyvinylidene fluoride, polyvinyl alcohol and N, N-dimethylacetamide according to the weight ratio of (61-71): (19-22): (400-500); the blood pressure monitoring device comprises a pressure sensor and a signal processing system, and the pressure sensor is in communication connection with the signal processing system; a sensitive material in the pressure sensor is a piezoelectric polymer; the piezoelectric polymer has higher piezoelectric property and has higher sensitivity to the real-time change state of the blood pressure in the blood pressure monitoring process, the detection result can be more accurate, and the device is suitable for being used in the treatment process of critical patients.

Description

Technical Field

[0001] The present invention relates to the technical field of blood pressure monitoring, and in particular to a piezoelectric polymer and a blood pressure monitoring device based thereon. Background Art

[0002] Non-invasive blood pressure monitoring equipment is a device that can measure the systolic and diastolic blood pressure of the human body without applying pressure to the human body using a cuff or needle. There are many types of non-invasive blood pressure monitoring equipment, such as equipment based on technologies such as pulse wave propagation velocity, pulse wave morphology, and near-infrared light sensors. The advantage of non-invasive blood pressure monitoring equipment is that it can monitor blood pressure in real time or continuously, reduce discomfort and damage to the human body, and improve the accuracy and reliability of measurement. It is suitable for a variety of scenarios, such as ambulances, operating rooms, and general wards.

[0003] The principle and performance of non-invasive blood pressure monitoring equipment depends on the specific technology and design. Generally speaking, non-invasive blood pressure monitoring equipment requires the use of pressure sensors to detect the pulse signal of the human body and calculate the blood pressure through a special algorithm. Pressure sensors are devices that can detect and convert pressure signals. They are widely used in various fields, such as medical, industrial, automotive and consumer electronics. The working principle of pressure sensors is usually to use the piezoelectric effect, piezoresistive effect or capacitive effect of certain sensitive materials to convert pressure changes into measurable electrical signals.

[0004] In the prior art, pressure sensors in blood pressure monitoring devices usually use piezoelectric polymers, piezoresistive polymers and capacitive polymers as sensitive materials; since human blood pressure is constantly changing, blood pressure detection equipment needs to have stable performance to ensure the accuracy of measurement. Using these sensitive materials as pressure sensors, their sensitivity can meet general blood pressure monitoring requirements, but for critically ill patients, blood pressure is an important reference indicator, and its slight changes may become the key to affecting the direction of treatment research. Therefore, the sensitivity of general blood pressure monitoring devices cannot meet the use needs of critically ill patients. Summary of the invention

[0005] The purpose of the present invention is to provide a piezoelectric polymer and a blood pressure monitoring device based thereon to solve the following technical problems:

[0006] How to improve the sensitivity of blood pressure monitoring devices.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present invention discloses a piezoelectric polymer, the components of which include polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide in a weight ratio of (61-71):(19-22):(400-500).

[0009] Preferably, the weight ratio of polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide is (64-68):(45-55):(420-480); more preferably, it is 66:21:450.

[0010] Polyvinylidene fluoride is a piezoelectric material with excellent mechanical properties, thermal stability and chemical stability. The piezoelectric polymer obtained by modifying it has stronger piezoelectric properties.

[0011] Wherein, the preparation method of the polyvinylidene fluoride solution comprises the following steps:

[0012] Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide into a container, and stir at a constant speed for 2-4 hours at 60-80°C to mix them evenly to obtain a mixed solution;

[0013] Step 2: Keep the temperature of the mixed solution constant and let it stand for 4-6 minutes to degas. Then, the polyvinylidene fluoride solution is obtained.

[0014] The preparation method of the polyvinylidene fluoride film comprises the following steps:

[0015] Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide into a container, and stir at a constant speed for 2-4 hours at 60-80°C to mix them evenly to obtain a casting solution;

[0016] Step 2: Keep the temperature of the casting solution constant, let it stand for 4-6 minutes to degas, and pour the casting solution onto the glass plate to form a uniform coating with a thickness of 0.8-1.2 mm;

[0017] Step 3: Immerse the glass plate and the coating in deionized water at 25-28°C. After the coating is removed from the glass plate, keep the coating immersed in the deionized water for 45-50 hours to form a film. Take out the film and dry it to obtain a polyvinylidene fluoride film.

[0018] The process of polyvinyl alcohol piezoelectric polymer is, from a microscopic point of view, a process in which polyvinyl alcohol and polyvinylidene fluoride are entangled with each other, forming hydrogen bonds and strong van der Waals forces, and finally obtaining a supramolecular complex.

[0019] By introducing polyvinyl alcohol into polyvinylidene fluoride, the hydrophilicity of polyvinylidene fluoride can be increased, thereby improving its affinity with human skin, thereby reducing pressure on human skin and allergic reactions. Polyvinyl alcohol is a polymer containing hydroxyl groups, which has strong hydrophilicity and polarity. When polyvinyl alcohol is blended or grafted with polyvinylidene fluoride, hydroxyl groups can be introduced into the polyvinylidene fluoride molecular chain, and the hydroxyl groups can form hydrogen bonds with water, thereby increasing the polarity and hydrophilicity of polyvinylidene fluoride. Polyvinyl alcohol piezoelectric polymers can reduce the crystallinity and glass transition temperature of polyvinylidene fluoride, and improve the flexibility and processability of polyvinylidene fluoride. When polyvinyl alcohol piezoelectric polymers are prepared into films or fibers, a porous structure can be formed, which increases the specific surface area of ​​polyvinylidene fluoride and the contact area with water, thereby improving the hydrophilicity of polyvinylidene fluoride. Polyvinyl alcohol piezoelectric polymers can improve the piezoelectric properties and electromechanical coupling characteristics of polyvinylidene fluoride, so that it generates electrical signals when subjected to pressure changes.

[0020] At the same time, N,N-dimethylacetamide is introduced on the basis of polyvinyl alcohol, which can promote the formation of the β phase of the polyvinylidene fluoride film, thereby improving its piezoelectric coefficient and sensitivity; there is a strong hydrogen bond between the N,N-dimethylacetamide molecules and the polyvinylidene fluoride molecules, and it can also form a dipole interaction with the fluorine atoms on the polyvinylidene fluoride molecular chain; these two interactions can stabilize the structure of the β phase and prevent the β phase from transforming to the α phase. The β phase is a polar crystal form of polyvinylidene fluoride, with high piezoelectric properties and electromechanical coupling characteristics; the α phase is the opposite, it is a non-polar crystal form, with low piezoelectric properties and electromechanical coupling characteristics.

[0021] N,N-dimethylacetamide can also reduce the glass transition temperature of polyvinylidene fluoride films, thereby improving their flexibility and wearability. N,N-dimethylacetamide is a polar aprotic solvent that can dissolve polyvinylidene fluoride to form a uniform solution. When the solution solidifies into a film under certain conditions, N,N-dimethylacetamide will remain between the polyvinylidene fluoride molecular chains and act as a plasticizer, reducing the interaction force between the molecular chains, thereby reducing the glass transition temperature of polyvinylidene fluoride. In more depth, N,N-dimethylacetamide is a small molecule. After adding N,N-dimethylacetamide to the polymer system, N,N-dimethylacetamide can separate the chain segments of polyvinylidene fluoride, weakening the interaction force between the polyvinylidene fluoride molecular chains, making it easier to move, thereby increasing the plasticity of polyvinylidene fluoride. N,N-dimethylacetamide molecules are inserted between polyvinylidene fluoride molecular chains, weakening the stress between polyvinylidene fluoride molecular chains, resulting in increased mobility of polyvinylidene fluoride molecular chains and reduced crystallinity of polyvinylidene fluoride molecular chains, thereby increasing the plasticity of polyvinylidene fluoride, which is the main factor against the plasticization of polyvinylidene fluoride, the crystallization and stress of polyvinylidene fluoride molecular chains. The glass transition temperature refers to the transition temperature of polymer materials from the glassy state to the highly elastic state, which reflects the rigidity and flexibility of polymer materials. Lowering the glass transition temperature can improve the flexibility, toughness and processability of polyvinylidene fluoride films, and can also improve their piezoelectric properties and electromechanical coupling characteristics.

[0022] In a further embodiment of the present invention: the polyvinyl alcohol is selected from citric acid-polyvinyl alcohol, and the preparation method of the citric acid polyvinyl alcohol is as follows: polyvinyl alcohol and citric acid in a weight ratio of 1: (0.8-1.2) are uniformly mixed and reacted at 60-80°C for 1-3h, with continuous stirring during the reaction, and cooling and crystallization are performed after the reaction is completed to obtain citric acid-polyvinyl alcohol.

[0023] For polyvinyl alcohol used as piezoelectric polymer, using citric acid for branching can optimize some of its properties. Citric acid-branched polyvinyl alcohol, i.e., citric acid-polyvinyl alcohol, is a water-soluble polymer material that can be blended with polyvinylidene fluoride to form a composite film with improved hydrophilicity, anti-fouling and biocompatibility. It should be noted that when using citric acid-branched polyvinyl alcohol piezoelectric polymer, only the dielectric constant of polyvinylidene fluoride can be improved, but its piezoelectric coefficient cannot be improved. This is because citric acid-polyvinyl alcohol is mainly distributed in the amorphous region of polyvinylidene fluoride, rather than the crystalline region, and may even destroy the crystallization of β-phase polyvinylidene fluoride; therefore, the introduction of citric acid-polyvinyl alcohol cannot promote the formation of β-phase of polyvinylidene fluoride, and thus cannot enhance its piezoelectric effect; however, the increase in its dielectric constant can enable it to store more charge under the action of an electric field, improve dielectric strength and breakdown field strength, and have higher stability and reliability.

[0024] In a second aspect, the present invention further discloses a blood pressure monitoring device, including a pressure sensor and a signal processing system, wherein the pressure sensor is communicatively connected to the signal processing system; the pressure sensor includes a pressure-sensitive element and a conductive electrode, wherein the pressure-sensitive element contains the piezoelectric polymer as described above.

[0025] In a further embodiment of the present invention, the pressure-sensitive element is composed of a flexible substrate and a polyvinylidene fluoride film or a polyvinylidene fluoride solution. The preparation methods of the two pressure-sensitive elements are respectively:

[0026] (1) The polyvinylidene fluoride film is uniaxially stretched and then attached to one side of a flexible substrate; both sides of the polyvinylidene fluoride film are respectively connected to conductive electrodes.

[0027] (2) coating the polyvinylidene fluoride solution on a flexible substrate and then performing a heat treatment; and connecting two sides of the flexible substrate to conductive electrodes respectively.

[0028] In a further embodiment of the present invention: the blood pressure monitoring device is configured as a strip structure worn on the wrist, wherein the pressure sensor can adapt to the curvature of the wrist and cover the position of the artery, thereby meeting the blood pressure monitoring conditions.

[0029] Beneficial effects of the present invention:

[0030] (1) The present invention can obtain a piezoelectric polymer by modifying polyvinylidene fluoride with polyvinyl alcohol; the piezoelectric polymer has strong piezoelectric properties and electromechanical coupling characteristics. When applied to a blood pressure monitoring device, it can more sensitively sense blood pressure changes, improve the accuracy of blood pressure monitoring, and reduce the error of blood pressure monitoring.

[0031] (2) In the present invention, N,N-dimethylacetamide is introduced into the polyvinylidene fluoride film on the basis of polyvinyl alcohol, which can promote the formation of the β phase of the polyvinylidene fluoride film, improve its piezoelectric coefficient and sensitivity, and obtain the β phase without high-voltage polarization, which makes the process simpler.

[0032] (3) When the solution solidifies into a film under certain conditions, N,N-dimethylacetamide will remain between the polyvinylidene fluoride molecular chains and act as a plasticizer, reducing the interaction force between the molecular chains, thereby lowering the glass transition temperature of polyvinylidene fluoride and improving its flexibility and wearability.

[0033] (4) The present invention uses citric acid to branch the polyvinyl alcohol of the piezoelectric polymer, thereby improving the dielectric constant of the piezoelectric polymer, so that it can store more charges under the action of the electric field, improve the dielectric strength and breakdown field strength, and have higher stability and reliability; at the same time, the branched polyvinyl alcohol can increase the degradation rate of polyvinylidene fluoride due to the introduction of carboxyl groups, making it easier to be decomposed by organisms and the environment, thereby improving the environmental friendliness and sustainability of polyvinylidene fluoride.

[0034] (5) Citric acid-branched polyvinyl alcohol, i.e., citric acid-polyvinyl alcohol, is a water-soluble polymer material that can be blended with polyvinylidene fluoride to form a composite membrane with improved hydrophilicity, anti-fouling and biocompatibility; when used in a blood pressure monitoring device, it can be more suitable for human use. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] Figure 1 It is a schematic diagram of the working principle of the blood pressure monitoring device in the present invention;

[0037] Figure 2 This is a scanning electron micrograph at 8000 times magnification of the polyvinylidene fluoride film obtained in Example 1 of the present invention;

[0038] Figure 3 is the infrared spectrum of the polyvinylidene fluoride film prepared in Example 1 of the present invention;

[0039] Figure 4 is the infrared spectrum of the polyvinylidene fluoride film prepared in Example 4 of the present invention;

[0040] Figure 5 This is a scanning electron micrograph at 8000 times magnification of the polyvinylidene fluoride film prepared in Comparative Example 1 of the present invention;

[0041] Figure 6 It is the infrared spectrum of the polyvinylidene fluoride film prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] A piezoelectric polymer exists in the form of a polyvinylidene fluoride solution and a polyvinylidene fluoride film.

[0044] Wherein, the preparation method of polyvinylidene fluoride solution comprises the following steps:

[0045] Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide in a weight ratio of (61-71): (19-22): (400-500) into a container, and stir at a constant speed for 2-4 hours at 60-80° C. to mix them evenly to obtain a mixed solution;

[0046] Step 2: Keep the temperature of the mixed solution constant and let it stand for 4-6 minutes to degas. Then, the polyvinylidene fluoride solution is obtained.

[0047] The method for preparing the polyvinylidene fluoride film comprises the following steps:

[0048] Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide in a weight ratio of (61-71): (19-22): (400-500) into a container, and stir at a constant speed for 2-4 hours at 60-80° C. to mix them evenly to obtain a casting solution;

[0049] Step 2: Keep the temperature of the casting solution constant, let it stand for 4-6 minutes to degas, and pour the casting solution onto the glass plate to form a uniform coating with a thickness of 0.8-1.2 mm;

[0050] Step 3: Immerse the glass plate and the coating in deionized water at 25-28°C. After the coating is removed from the glass plate, keep the coating immersed in deionized water for 45-50 hours to form a film. After taking out the film, air-dry it at 25-28°C to obtain a polyvinylidene fluoride film.

[0051] See also Figure 1 The present invention also discloses a blood pressure monitoring device based on the above-mentioned piezoelectric polymer, the blood pressure detection device includes a pressure sensor and a signal processing system, the pressure sensor is communicatively connected to the signal processing system; the sensitive material in the pressure sensor is the above-mentioned piezoelectric polymer.

[0052] The pressure sensor includes a flexible substrate and a conductive electrode. A piezoelectric polymer is disposed on the flexible substrate. The piezoelectric polymer can be disposed on the flexible substrate in two ways:

[0053] Method 1: The polyvinylidene fluoride film is uniaxially stretched and then attached to one side of the flexible substrate; both sides of the polyvinylidene fluoride film are connected to conductive electrodes respectively;

[0054] Method 2: coating the polyvinylidene fluoride solution on a flexible substrate and then performing a heat treatment; both sides of the flexible substrate are respectively connected to conductive electrodes.

[0055] The blood pressure monitoring device is configured as a strip structure worn on the wrist, wherein the pressure sensor can adapt to the curvature of the wrist and cover the position of the artery, thereby meeting the blood pressure monitoring conditions.

[0056] Taking method one as an example, first, the polyvinylidene fluoride film is uniaxially stretched to have high crystallinity and piezoelectric properties; then the polyvinylidene fluoride film is pasted on a long flexible substrate, and conductive electrodes are added on both sides of the polyvinylidene fluoride film to form a pressure sensor; the pressure sensor is attached to the wrist and electrically connected to the signal processing system; when the blood vessels are affected by the heartbeat, periodic pressure changes will occur, and these pressure changes will cause the polyvinylidene fluoride film to distort, thereby generating polarization charges proportional to the pressure; the polarization charges are converted into voltage signals through I / V converters, and are processed through signal amplification, filtering, sampling, conversion and other circuits of the signal processing system, and finally, through adaptive calibration algorithms such as the least squares method, a mathematical model between blood pressure and electrical signals is established according to individual information to achieve the calculation and display of blood pressure values.

[0057] Example 1

[0058] 61g of polyvinylidene fluoride, 19g of polyvinyl alcohol and 420g of N,N-dimethylacetamide were added into a container, and stirred at a constant speed for 4h at 60°C to make them evenly mixed to obtain a casting solution; the temperature of the casting solution was kept constant, and the casting solution was allowed to stand for 4min for degassing, and the casting solution was poured onto a glass plate to form a uniform coating with a thickness of 1mm; the glass plate and the coating were immersed in deionized water at 26°C, and after the coating was removed from the glass plate, the coating was still immersed in deionized water for 50h to form a film, and the film was taken out and air-dried at room temperature of 26°C to obtain a polyvinylidene fluoride film, and the film size was cut into 5cm in length and 3cm in width;

[0059] The film was uniaxially stretched to a length of 10 cm using a stretching machine to obtain sample 1; its 8000x scanning electron micrograph is shown in Figure 2 As shown in the infrared spectrum Figure 3 shown.

[0060] Example 2

[0061] 66g of polyvinylidene fluoride, 21g of polyvinyl alcohol and 450g of N,N-dimethylacetamide were added into a container, and stirred at a constant speed for 3h at 70°C to make them evenly mixed to obtain a casting solution; the temperature of the casting solution was kept constant, and the casting solution was allowed to stand for 4min for degassing, and the casting solution was poured onto a glass plate to form a uniform coating with a thickness of 1mm; the glass plate and the coating were immersed in deionized water at 27°C, and after the coating was removed from the glass plate, the coating was still immersed in deionized water for 48h to form a film, and the film was taken out and air-dried at room temperature of 26°C to obtain a polyvinylidene fluoride film, and the film size was cut into 5cm in length and 3cm in width;

[0062] The film was uniaxially stretched to a length of 10 cm using a stretching machine to obtain sample 2.

[0063] Example 3

[0064] 71g of polyvinylidene fluoride, 22g of polyvinyl alcohol and 500g of N,N-dimethylacetamide were added into a container, and stirred at a constant speed for 2h at 80°C to make them evenly mixed to obtain a casting solution; the temperature of the casting solution was kept constant, and the casting solution was allowed to stand for 4min for degassing, and the casting solution was poured onto a glass plate to form a uniform coating with a thickness of 1mm; the glass plate and the coating were immersed in deionized water at 28°C, and after the coating was removed from the glass plate, the coating was still immersed in deionized water for 45h to form a film, and the film was taken out and air-dried at room temperature of 26°C to obtain a polyvinylidene fluoride film, and the film size was cut into 5cm in length and 3cm in width;

[0065] The film was uniaxially stretched to a length of 10 cm using a stretching machine to obtain sample 3.

[0066] Example 4

[0067] Compared with Example 1, the only difference is that polyvinyl alcohol is citric acid-polyvinyl alcohol. The preparation method of citric acid polyvinyl alcohol is as follows: 20g of polyvinyl alcohol and 20g of citric acid are mixed evenly and reacted at 70°C for 3h, stirring continuously during the reaction process, and cooling and crystallizing after the reaction is completed to obtain citric acid-polyvinyl alcohol.

[0068] The final polyvinylidene fluoride film is sample 4, and its infrared spectrum is as follows: Figure 4 shown.

[0069] Comparative Example 1

[0070] Compared with Example 1, the only difference is that polyvinyl alcohol is not included. The polyvinylidene fluoride film finally obtained is sample 5; its 8000 times scanning electron micrograph is as follows Figure 5 As shown in the infrared spectrum Figure 6 shown.

[0071] Comparative Example 2

[0072] Compared with Example 1, the only difference is that the amount of polyvinyl alcohol used is 18 g. The polyvinylidene fluoride film finally obtained is sample 6.

[0073] Comparative Example 3

[0074] Compared with Example 4, the only difference is that the polyvinyl alcohol is malonic acid-polyvinyl alcohol, and the preparation method of malonic acid-polyvinyl alcohol is: 20g of polyvinyl alcohol and 20g of malonic acid are mixed evenly and reacted at 70°C for 3h, stirring continuously during the reaction process, cooling and crystallizing after the reaction is completed, and malonic acid-polyvinyl alcohol can be obtained. The polyvinylidene fluoride film finally obtained is sample 7.

[0075] Test Example 1

[0076] The piezoelectric properties of the samples of Examples 1-4 and Comparative Examples 1-3 were tested by using a piezoelectric pulse method. The piezoelectric constant and dielectric constant of the samples were finally calculated and the results are listed in Table 1. Table 1 is as follows:

[0077] Table 1

[0078]

[0079] By analyzing the data in Table 1, it can be found that the piezoelectric constant and dielectric constant of the polyvinylidene fluoride films prepared in Examples 1-4 are higher than those in Comparative Examples 1-3. It can be seen that the piezoelectric polymer of the present invention has stronger piezoelectric properties.

[0080] Test Example 2

[0081] First, the blood pressure of the same subject was tested in the same time period and under the same conditions. At the same time, a regular electronic blood pressure meter (OMRON-U11 model) was used as a reference to calculate the relative error of the average value, and the data in Table 2 were obtained.

[0082] Table 2

[0083]

[0084] The film samples of Examples 1-4 and Comparative Examples 1-3 are connected to medical tape, reinforced by hot melt, and voltage test leads are connected at both ends of the film and connected to a voltmeter. A dynamometer is used to calibrate the linear equation of the diaphragm force and voltage. The film sample connected with the tape is wrapped around the subject's upper arm, a stethoscope is placed, and the medical tape is gradually tightened. The Korotkoff sound method is used to read the voltage readings corresponding to the diastolic pressure and systolic pressure and converted to pressure values ​​according to the linear equation, which is the measured blood pressure. The data format is "diastolic pressure / systolic pressure" in mmHg.

[0085] It should be noted that the above implementation method is only used for single measurement comparison; in industrial production, the above calibration process is carried out before leaving the factory, and the continuous monitoring process needs to be completed using automated electronic equipment and signal processing systems. According to the blood pressure test convention, the blood pressure value and the average value are integers, and the standard deviation and relative error are rounded to one decimal place.

[0086] Each group of samples was tested 5 times, and the test results are shown in Table 3. Table 3 is as follows:

[0087] Table 3

[0088]

[0089]

[0090] By analyzing the data in Tables 2-3, it can be found that the standard deviation and relative error of the electronic sphygmomanometer of Example 1 are the lowest among all the examples and the comparative examples, and are basically consistent with the test results of the mercury sphygmomanometer. In addition, the standard deviation and relative error of the example are smaller than those of the comparative example, so the piezoelectric polymer of the present invention can obtain more accurate blood pressure values.

[0091] The sample obtained in Example 4 has a larger dielectric constant, so its test results are relatively stable, but since the piezoelectric coefficient is not improved, its relative error is slightly greater than that in Example 1; Comparative Example 3 uses malonic acid instead of citric acid, which verifies that it is more appropriate to choose citric acid as the grafting agent; the piezoelectric coefficient and dielectric constant of Comparative Example 3 are significantly lower than those of Example 4. This is because the polyvinyl alcohol grafted with malonic acid has poor compatibility with PVDF. After esterification of malonic acid and polyvinyl alcohol, only one free carboxyl group remains, while after esterification of citric acid and polyvinyl alcohol, two free carboxyl groups and one hydroxyl group remain; the free hydroxyl group can help the citric acid branch to better integrate into the polyvinyl alcohol molecular chain, and more free carboxyl groups provide greater polarity, thereby improving the dielectric constant.

[0092] Test Example 3

[0093] The samples prepared in Example 1, Example 4 and Comparative Example 1 were tested by infrared spectroscopy. Figure 3-5 , and perform data analysis to obtain Table 4, which is as follows:

[0094] Table 4

[0095]

[0096]

[0097] See also Figure 6 In the infrared spectrum of Comparative Example 1, 2974 cm -1 The absorption peaks at 1406 and 1386 cm are the stretching vibrations of -CF2-CH2-methylene. Due to the electronegativity of F, they move to high frequencies. -1 The absorption peak at 1312 cm is the angular vibration of methylene. -1 The absorption peaks at 1250 and 1122 cm are the out-of-plane swing vibrations of methylene. -1The broad absorption peaks at 956, 914, 850 cm-1 are the antisymmetric and symmetric stretching vibrations of CF2. -1 The characteristic absorption peak of PVDF crystalline phase is 850cm -1 The absorption peaks at 652 and 550 cm are the bending vibrations of CCC. -1 The absorption peaks at are the antisymmetric and symmetric angular vibrations of CF2.

[0098] See also Figure 3 In the infrared spectrum of Example 1, 3390 cm -1 The absorption peak at 2934 cm is the stretching vibration of hydroxyl OH. -1 The absorption peak at 1716cm is the stretching vibration of methylene; -1 The absorption peak at 1626cm is the frequency doubling of PVDF vibration. -1 The absorption peak at 1414cm is the in-plane bending vibration of residual water -OH; -1 The absorption peak at is enhanced, which is caused by the in-plane bending vibration of alcohol -COH, and the characteristic absorption peak of -OH in polyvinyl alcohol appears; the peak position repeated in comparative example 1 will not be repeated.

[0099] Please refer to FIG. 4 . In the infrared spectrum of Example 4, at 1720 cm -1 The absorption peak at is the stretching vibration of ester and carboxylic acid C=O, which indicates the introduction of citric acid. The other absorption peaks do not change much.

[0100] Analysis of the data in Table 4 shows that the piezoelectric polymer of Example 1 successfully introduced polyvinyl alcohol molecules between polyvinylidene fluoride molecules; at the same time, carboxyl and ester absorption peaks appeared in Example 4, which also proved that citric acid successfully branched the polyvinyl alcohol and then entered the piezoelectric polymer with the modification treatment.

[0101] The surfaces of the thin film samples obtained in Example 1 and Comparative Example 1 were observed by scanning electron microscope, and the results were obtained after magnification of 8000 times. Figure 2 , Figure 5 ; Observation and comparison show that, Figure 2 It is a typical polyvinylidene fluoride image, which is dense and flat; Figure 5 Some pores and light-colored fibers are introduced into the membrane. The pores are caused by the different degrees of contraction of the two polymers during the gelation process, which partially separates the two phases and forms a gap between the two phases; the white fibers may be partially separated polyvinyl alcohol phases; the pores and part of the polyvinyl alcohol phase improve the hydrophilicity, water absorption and air permeability of the membrane, making the membrane more biocompatible.

[0102] In the description of the present invention, it should be understood that, in addition, "first" and "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0103] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A piezoelectric polymer, characterized in that: The components include polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide in a weight ratio of (61-71):(19-22):(400-500).

2. The piezoelectric polymer according to claim 1, characterized in that The piezoelectric polymer includes polyvinylidene fluoride solution and polyvinylidene fluoride film.

3. The piezoelectric polymer according to claim 2, characterized in that The preparation method of the polyvinylidene fluoride solution comprises the following steps: Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide into a container, and stir at a constant speed for 2-4 hours at 60-80°C to mix them evenly to obtain a mixed solution; Step 2: Keep the temperature of the mixed solution constant and let it stand for 4-6 minutes to degas to obtain a polyvinylidene fluoride solution.

4. The piezoelectric polymer according to claim 2, characterized in that The preparation method of the polyvinylidene fluoride film comprises the following steps: Step 1: Add polyvinylidene fluoride, polyvinyl alcohol and N,N-dimethylacetamide into a container, and stir at a constant speed for 2-4 hours at 60-80°C to mix them evenly to obtain a casting solution; Step 2: Keep the temperature of the casting solution constant, let it stand for 4-6 minutes to degas, and pour the casting solution onto a glass plate to form a uniform coating with a thickness of 0.8-1.2 mm; Step 3: Immerse the glass plate and the coating in deionized water at 25-28° C. After the coating is removed from the glass plate, keep the coating immersed in the deionized water for 45-50 hours to form a film. Take out the film and dry it to obtain the polyvinylidene fluoride film.

5. The piezoelectric polymer according to claim 4, characterized in that The polyvinyl alcohol is citric acid-polyvinyl alcohol. The preparation method of the citric acid-polyvinyl alcohol is as follows: polyvinyl alcohol and citric acid in a weight ratio of 1: (0.8-1.2) are uniformly mixed and reacted at 60-80° C. for 1-3 hours, stirring continuously during the reaction, and cooling and crystallizing after the reaction to obtain the citric acid-polyvinyl alcohol.

6. A blood pressure monitoring device, comprising a pressure sensor and a signal processing system, wherein the pressure sensor is communicatively connected to the signal processing system; characterized in that: The pressure sensor comprises a pressure-sensitive element and a conductive electrode, wherein the pressure-sensitive element contains the piezoelectric polymer according to any one of claims 1-5.

7. The blood pressure monitoring device according to claim 6, characterized in that: The pressure-sensitive element is composed of a flexible substrate and a polyvinylidene fluoride film or a polyvinylidene fluoride solution.

8. The blood pressure monitoring device according to claim 7, characterized in that: The method for preparing the pressure-sensitive element is as follows: the polyvinylidene fluoride film is uniaxially stretched and then attached to one side of the flexible substrate; and both sides of the polyvinylidene fluoride film are respectively connected to the conductive electrodes.

9. The blood pressure monitoring device according to claim 7, characterized in that: The method for preparing the pressure-sensitive element is as follows: coating the polyvinylidene fluoride solution on the flexible substrate and then performing heat treatment; and connecting the two sides of the flexible substrate to the conductive electrodes respectively.

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