A sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics

Abstract

This invention belongs to the field of force / magnetic sensors, specifically relating to a sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics. This force / magnetic sensor material comprises a porous bio-crosslinked macromolecular matrix and bidispersed magnetic microparticles dispersed within the porous bio-crosslinked macromolecular matrix. The porous bio-crosslinked macromolecular matrix is ​​formed by bio-crosslinking and freeze-drying of sodium alginate and polyvinyl alcohol. The bidispersed magnetic microparticles include gelatin-coated magnetic microparticles, with multi-walled carbon nanotubes further coated on the surface of the gelatin. This invention uses sodium alginate and polyvinyl alcohol as a bio-matrix to create a porous bio-matrix through bio-crosslinking and freeze-drying, which, combined with bidispersed magnetic microparticles, produces a sensor material with both force and magnetic dual-response characteristics and higher flexibility. This force / magnetic sensor material can adapt to various shapes and curvatures, thus enabling its wide application in various scenarios.

Description

Technical Field

[0001] This invention belongs to the field of force and magnetic sensors, specifically relating to a sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics. Background Technology

[0002] Wearable force / magnetic sensors, possessing both force and magnetic sensing properties, represent an emerging sensor technology that can be applied in sports medicine and sports training to help monitor and improve athletic skills and posture. For example, they can be used to assess athletes' strength and motor techniques, providing real-time feedback and guidance to improve athletic performance and prevent sports injuries. Wearable force / magnetic sensors also hold broad application prospects in healthcare and smart wearables. However, traditional sensor materials have some limitations, such as rigidity, high cost, and slow response speed.

[0003] Our research group previously disclosed a flexible magnetic sensor (application publication number CN115302902A). The main magnetic sensor material of this flexible magnetic sensor is a porous composite sponge material, mainly made of sodium alginate, carboxymethyl chitosan, magnetic microparticles and other materials. The tensile strain limit of this sensor material is 26.9%. Its flexibility and recoverability need to be further improved to better meet the changes in the curvature of human skin and the shape of joints. Summary of the Invention

[0004] The purpose of this invention is to provide a sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics, in order to address the problem that the flexibility and recoverability of existing sensors need to be improved.

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

[0006] A sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics includes a porous biocrosslinked macromolecular matrix and bidispersed magnetic microparticles dispersed in the porous biocrosslinked macromolecular matrix. The porous biocrosslinked macromolecular matrix is ​​formed by biocrosslinking and freeze-drying of sodium alginate and polyvinyl alcohol. The bidispersed magnetic microparticles include gelatin-coated magnetic microparticles, and the surface of the gelatin is further coated with multi-walled carbon nanotubes.

[0007] This invention provides a sodium alginate-polyvinyl alcohol (PVA) force / magnetic sensor material for wearable electronics. Using sodium alginate and PVA as a biomatrix, a porous biomatrix is ​​created through bio-crosslinking and freeze-drying. Combined with bidispersed magnetic microparticles, this produces a sensor material with both force and magnetic responses and greater flexibility. This force / magnetic sensor material can adapt to various shapes and curvatures, thus enabling its wide application in various scenarios and effectively solving the problems of uncomfortable wearing, high cost, and limited functionality in wearable sensors.

[0008] To further improve the flexibility and recoverability of the sensor material and optimize the force sensing characteristics, preferably, the mass ratio of sodium alginate to polyvinyl alcohol is 1:1 to 4.

[0009] To further optimize the magnetic sensing characteristics of the sensor material, preferably, the mass ratio of sodium alginate to bidispersed magnetic microparticles is 1:5-6.

[0010] To further simplify the bio-crosslinking process of the bio-matrix composed of sodium alginate and polyvinyl alcohol, glycerol and calcium chloride are preferably used for the bio-crosslinking, with a mass ratio of sodium alginate, glycerol, and calcium chloride of 1 g: 4-8 mL: 0.2-0.4 g. The above ratio can be increased or decreased proportionally.

[0011] Preferably, the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics is prepared using a method comprising the following steps:

[0012] (1) A composite biosol was prepared using sodium alginate, polyvinyl alcohol and water;

[0013] (2) The composite biosol and bidisperse magnetic microparticles are mixed, then glycerol and calcium chloride solution are added for biocrosslinking, and then freeze-drying is performed.

[0014] Sodium alginate-polyvinyl alcohol force / magnetic sensor materials were prepared using the aforementioned bio-crosslinking and freeze-drying techniques. The material's microstructure remained intact, ensuring excellent response speed and sensitivity. Furthermore, this method is simple to implement, requiring no complex equipment or conditions, thus reducing production costs.

[0015] Preferably, each 0.5g of sodium alginate corresponds to 45-50ml of water, 2-4ml of glycerol, and 10-15ml of a 1-2% CaCl2 solution. This method ensures a stable and uniform bio-crosslinking process, improving the consistency of the materials.

[0016] To further facilitate the dissolution of polyvinyl alcohol and optimize the physical cross-linking effect between biological matrices, the degree of alcoholysis of polyvinyl alcohol is preferably 87% to 95%. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the fabrication process of the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics according to the present invention.

[0018] Figure 2 This is a structural model diagram of the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics according to the present invention;

[0019] Figure 3This is a cross-sectional scanning electron microscope (SEM) image of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 of the present invention.

[0020] Figure 4 The curve showing the change in tensile mechanical properties of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 of this invention.

[0021] Figure 5 This demonstrates the recoverability of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 of the present invention;

[0022] Figure 6 The force-sensitive electrical response of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 of this invention;

[0023] Figure 7 This refers to the magnetosensitive electrical response of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 of the present invention. Detailed Implementation

[0024] This invention relates to a sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics. This material is prepared using sodium alginate and polyvinyl alcohol as macromolecular biomatrixes through bio-crosslinking and freeze-drying techniques. It exhibits high flexibility, adapting to various shapes and curvatures, making it more suitable for wearable devices and better accommodating changes in the curvature of human skin and joint morphology. Furthermore, this material possesses both force and magnetic sensing properties, potentially replacing the need for two sensors simultaneously in certain situations, thus simplifying device structure and improving wearer comfort and portability.

[0025] The schematic diagram of the above-mentioned sodium alginate-polyvinyl alcohol force / magnetic sensor material preparation process is shown below. Figure 1 As shown, the detailed steps are as follows:

[0026] (1) Preparation of composite biosol

[0027] A composite biosol was prepared using sodium alginate, polyvinyl alcohol, and water. Specifically, sodium alginate and polyvinyl alcohol were added separately to deionized water and stirred at a set temperature until the solution was homogeneous and free of particles. The two were then mixed and stirred to form a homogeneous sol solution, thus obtaining the composite biosol.

[0028] In this step, the degree of alcoholysis of polyvinyl alcohol is 87%–95%, and the weight-average molecular weight is 89,000–98,000. The mass ratio of sodium alginate to polyvinyl alcohol ranges from 1:1 to 4. When dissolving sodium alginate, 25–30 ml of water can be used to dissolve 0.5 g of sodium alginate. The dissolution temperature can be set to 55℃–65℃. When dissolving polyvinyl alcohol, 25–30 ml of water can be used to dissolve 2 g of polyvinyl alcohol. The dissolution temperature can be set to 70℃–80℃. The sodium alginate solution and the polyvinyl alcohol solution are mixed evenly at 55℃–65℃ to obtain the composite biosol.

[0029] (2) Biocrosslinking reaction

[0030] After mixing the composite biosol and bidispersed magnetic microparticles, they are further mixed with glycerol and calcium chloride solution until homogeneous, then allowed to stand and complete biocrosslinking. Glycerol increases the sample's flexibility, acting as a plasticizer. Standing is preferably performed at room temperature for 30±5 minutes; this gel-forming process helps eliminate foaming.

[0031] The mass ratio of sodium alginate to bidisperse magnetic microparticles is 1:5-6. In the bio-crosslinking system, each 0.5g of sodium alginate corresponds to 2-4ml of glycerol and 10-15ml of a 1-2% CaCl2 solution.

[0032] In this step, the bidispersed magnetic microparticles are a prior art technique. Their structural characteristics are: the magnetic microparticles are coated with gelatin, and the surface of the gelatin is further coated with multi-walled carbon nanotubes. The magnetic microparticles are composed of micron-sized carbonyl iron powder and nano-sized Fe3O4 powder, exhibiting bidispersive characteristics. The average particle size of the micron-sized carbonyl iron powder is 3–4 μm, and the average particle size of the nano-sized Fe3O4 powder is 20–25 nm. The mass ratio of carbonyl iron powder to Fe3O4 powder is 4:(0.5–1). The magnetic microparticles are coated sequentially with a gelatin aqueous solution and an acidified multi-walled carbon nanotube solution. The mass concentration of the gelatin aqueous solution is 0.1–0.5 g / mL. To balance the interaction forces between the magnetic particles, a stabilizer, sodium chloride, is added to the gelatin aqueous solution, with 0.2–0.4 g of sodium chloride used per 25–30 mL of gelatin aqueous solution.

[0033] Magnetic microparticles are coated with gelatin and dispersed in water, then mixed and dispersed with acidified multi-walled carbon nanotubes. A dense network structure is formed on the surface through ultrasonic oscillation and other methods. The acidified multi-walled carbon nanotubes are obtained by treating them with a mixed acid, consisting of nitric acid and sulfuric acid in a molar ratio of 3:1.

[0034] Specifically, 4g of gelatin-coated magnetic microparticles can be dispersed in 40-50ml of water, and then mixed and dispersed with 0.8-1.0g of acidified multi-walled carbon nanotube solution (mass fraction 20wt%-30wt%).

[0035] The detailed preparation method and performance study of the bidisperse magnetic microparticles are described in the article "Fabrication and Magnetorheology of Bidisperse Magnetic Microspheres Coated with Gelatin and Multi-walled Carbon Nanotubes" published by the inventors in the international journal Smart Materials and Structures in December 2018.

[0036] Specifically, the preparation method of the magnetic microparticles in the following embodiments is as follows:

[0037] 1) Weigh out a certain amount of carbonyl iron powder, magnetic Fe3O4 particles, and sodium chloride, mix them, and add them to a gelatin aqueous solution. Then, subject the mixture to ultrasonic vibration to ensure the gelatin evenly coats the carbonyl iron powder and Fe3O4 powder surfaces. Separate the coated magnetic particles using a permanent magnet, wash the particles with deionized water, and then dry them to obtain gelatin-coated magnetic particles. Disperse 4g of the gelatin-coated magnetic particles in 40mL of distilled water.

[0038] The gelatin aqueous solution has a mass-volume concentration of 0.1 g / mL. The mass ratio of carbonyl iron powder, magnetic Fe3O4, and sodium chloride is 4:0.5:0.2; the mass ratio of the carbonyl iron powder to the gelatin in the gelatin aqueous solution is 4:2.5; the average particle size of the carbonyl iron powder is 3.5 μm, and its density is 7.9 g / cm³. 3 The average particle size of the magnetic Fe3O4 is 20 nm.

[0039] 2) At a temperature of 55℃~65℃, multi-walled carbon nanotubes (diameter 7~11nm, length 10μm) were added to a mixed acid (multi-walled carbon nanotubes: mixed acid 0.2g: 3ml) prepared by mixing nitric acid and sulfuric acid in a molar ratio of 3:1. After ultrasonic irradiation for 12h, the solution was washed with water and dispersed to obtain an acidified multi-walled carbon nanotube solution (in which the mass fraction of multi-walled carbon nanotubes was 25%).

[0040] 3) Add 0.8g of acidified multi-walled carbon nanotube solution to the gelatin-coated magnetic microparticle aqueous dispersion in step (1), and treat with ultrasonic vibration for 12 hours to coat the surface of the gelatin-coated magnetic microparticles with multi-walled carbon nanotubes. Then, separate the magnetic microparticles coated with multi-walled carbon nanotubes with a permanent magnet, and wash and dry them with deionized water to obtain the final product.

[0041] (3) Freeze-drying

[0042] Turn on the freeze-drying oven and start the cooling function. Place the settled sample horizontally in the freeze-drying chamber to freeze it at a low temperature. Then, quickly remove the frozen sample from the freeze-drying chamber, place it on the upper drying rack, cover it with the freeze-drying hood, and turn on the vacuum pump to dry it.

[0043] Freezing time should be at least 4 hours, freezing temperature should be -50 to -70℃, and vacuum degree should be below 10Pa during drying.

[0044] (4) Demolding and molding process

[0045] The solid material prepared by freeze-drying is cut, shaped and adjusted to obtain force / magnetic response sensor material.

[0046] The implementation process of the present invention will be described in detail below with reference to specific embodiments.

[0047] I. Specific embodiments of the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics of the present invention are as follows:

[0048] Example 1

[0049] The structural model diagram of the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics in this embodiment is shown below. Figure 2 As shown, it includes a porous bio-crosslinked macromolecular matrix and bidispersed magnetic microparticles dispersed in the porous bio-crosslinked macromolecular matrix. The porous bio-crosslinked macromolecular matrix is ​​formed by bio-crosslinking and freeze-drying of sodium alginate and polyvinyl alcohol.

[0050] The preparation process of the sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics is as follows:

[0051] (1) Preparation of composite biosol: Set the magnetic stirrer temperature to 60℃, weigh 0.5g of sodium alginate solid powder and slowly dissolve it in 25ml of deionized water, stirring for about 30min until the sodium alginate solid is completely dissolved, i.e., the solution is uniform and free of particles. Then weigh 2g of polyvinyl alcohol solid particles and add them to 25ml of deionized water, heat in an 80℃ water bath for about 20min to generate a uniform sol solution. Then pour the polyvinyl alcohol solution into the sodium alginate solution and stir in a 60℃ water bath for 30min.

[0052] (2) Biocrosslinking reaction: Add 3g of bidisperse magnetic microparticles to the composite sol and stir rapidly until the magnetic microparticles are completely dissolved in the composite sol. Add 2ml of glycerol to the composite solution, and then add 10ml of 1% CaCl2 solution to the composite solution and mix well.

[0053] (3) Freeze-drying treatment: Turn on the freeze-drying chamber and start the refrigeration function. After the device has been pre-cooled for 1 hour, place the static sample horizontally in the freeze-drying chamber and freeze the sample at -60℃ for 7 hours. Then, quickly remove the frozen sample from the freeze-drying chamber and place it on the upper drying rack, cover it with a freeze-drying hood, turn on the vacuum pump, and dry for 12 hours.

[0054] (4) Demolding and molding process: The solid material prepared after freeze drying is cut, shaped and adjusted to obtain force / magnetic response sensor material.

[0055] Example 2

[0056] The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics in this embodiment is basically the same as the preparation process in Example 1, except that in step (1), 1g of polyvinyl alcohol is dissolved in 25ml of deionized water.

[0057] Example 3

[0058] The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics in this embodiment is basically the same as the preparation process in Example 1, except that in step (1), 0.5g of polyvinyl alcohol is dissolved in 25ml of deionized water.

[0059] Example 4

[0060] The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics in this embodiment is prepared in basically the same way as in Example 1, except that the amount of glycerol used in step (3) is 4 ml.

[0061] II. Experimental Examples

[0062] Experimental Example 1: SEM Analysis

[0063] Cross-sectional scanning electron microscope (SEM) image of the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1 is shown below. Figure 3 As shown.

[0064] Depend on Figure 3 It can be seen that the porous composite material structure mainly includes a large number of pores, pore wall structure and bidispersed magnetic particles. The pore structure is uniformly distributed, the pore wall thickness is moderate, and the magnetic particles are uniformly dispersed around the skeleton structure.

[0065] Experiment Example 2 Mechanical Property Testing

[0066] The wearable force / magnetic sensor material made of sodium alginate-polyvinyl alcohol prepared in Example 1 was subjected to mechanical property testing, and the results are as follows: Figure 4 As shown.

[0067] Depend on Figure 4 As can be seen, the force / magnetic sensor material prepared in the examples has a high elastic modulus, fractures when the strain exceeds 34.6%, exhibits good ductility, and possesses strong mechanical properties. Compared to the flexible magnetic sensor proposed by our research group (with a tensile strain limit of 26.9% under the same test conditions), its flexibility is further improved.

[0068] Experimental Example 3: Recoverability

[0069] The recoverability test was conducted on the sodium alginate-polyvinyl alcohol wearable force / magnetic sensor material prepared in Example 1, and the results are as follows: Figure 5 As shown.

[0070] Depend on Figure 5 It can be seen that the sample prepared in Example 1 can be squeezed and torn multiple times and fully recover, which demonstrates its good recoverability.

[0071] Example 4: Explanation of Force / Magnetic Dual Response Characteristics

[0072] 4.1 Force-sensitive electrical response characteristics

[0073] The force / magnetic dual-response sensor material prepared in this embodiment of the invention has a porous structure. Under the stimulation of external force, the sensor pores deform, and the distance and contact area between the conductive fillers distributed inside change, thus changing the resistance. When the external force is released, the sensor pore structure returns to its initial state, and the resistance also returns to its initial value. Therefore, changes in tensile force can be sensed by detecting changes in electrical signals, thereby achieving a force-sensitive electrical response.

[0074] In the force-sensitive response experiment, the sample is fixed on a tensile machine, and two wires are led out from the sample to measure its resistance in real time. The change in resistance as the sample is stretched is observed, and the results are as follows: Figure 6 As shown.

[0075] from Figure 6 It can be seen that under the action of lateral tension, the longitudinal pore distance of the sensor material decreases and the lateral pore distance increases. However, since the change in lateral pore distance is more obvious when under tension, as the tension increases, the distance of the conductive filler inside the material increases, the resistance of the sensor material gradually increases, and the relative rate of change of resistance also gradually increases, reflecting the force-sensitive response characteristics.

[0076] 4.2 Magnetosensitive Electrical Response Characteristics

[0077] The force / magnetic dual-response sensor material prepared in this invention exhibits weak conductivity due to the random distribution of magnetic particles within the matrix and a limited number of effective conductive paths when no external magnetic field is applied. However, when a magnetic field is applied, micron-sized carbonyl iron particles align into a series of chain-like structures along or perpendicular to the magnetic field direction. Nano-sized iron(III) oxide particles fill the pores or ends of these chain-like structures, increasing their density and the number of effective conductive paths, thereby altering the output electrical signal. When the magnetic field is removed, the carbonyl iron particles return to their original positions, restoring their electrical properties and achieving a magnetosensitive electrical response.

[0078] In the magnetic response experiment, the sample is fixed on the magnetic field generator, and then two wires are led out from the sample to measure its resistance in real time. The change in the resistance of the sample as the magnetic field increases is observed, and the results are as follows: Figure 7 As shown.

[0079] from Figure 7 It is known that under the action of an external magnetic field, magnetic particles are arranged in a chain along the direction of the magnetic field. The interface of the conductive layer of the sensor material migrates, the lateral size increases, and the pore distance increases. Therefore, as the magnetic induction intensity increases, the distance between the conductive fillers inside the material increases, the resistance of the sensor material gradually increases, and the relative rate of change of resistance also gradually increases. When the magnetic induction intensity reaches a certain value, it will no longer have a significant impact on the electrical properties of the material, thus exhibiting magnetic response characteristics.

[0080] In summary, the force / magnetic dual-response sensor material of the present invention has the following typical characteristics:

[0081] Firstly, the tensile strain limit of the sensor material reaches 34.6%, exhibiting better flexibility and recoverability. This allows it to better accommodate changes in the curvature of human skin and the shape of joints, providing higher quality and more reliable technical support for the development of wearable electronic devices.

[0082] Secondly, the sensor material possesses both force and magnetic sensing properties, which can replace the need for both types of sensors in certain situations, helping to simplify the device structure and improve the wearer's comfort and portability.

[0083] Thirdly, sodium alginate and gelatin are both natural polymers, which are inexpensive, environmentally friendly, and biodegradable. The preparation method does not require complex equipment or conditions, which can reduce production costs, and the production process is environmentally friendly and suitable for large-scale production.

Claims

1. A sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics, characterized in that, The invention comprises a porous bio-crosslinked macromolecular matrix and bidispersed magnetic microparticles dispersed within the porous bio-crosslinked macromolecular matrix. The porous bio-crosslinked macromolecular matrix is ​​formed by bio-crosslinking and freeze-drying of sodium alginate and polyvinyl alcohol. The bidispersed magnetic microparticles include gelatin-coated magnetic microparticles, the surface of which is further coated with multi-walled carbon nanotubes. The mass ratio of sodium alginate to polyvinyl alcohol is 1:1~4; the mass ratio of sodium alginate to bidispersed magnetic microparticles is 1:5~6. The degree of alcoholysis of polyvinyl alcohol is 87%~95%, and the weight-average molecular weight is 89,000~98,000; The magnetic microparticles are composed of micron-sized carbonyl iron powder and nano-sized Fe3O4 powder. The average particle size of the micron-sized carbonyl iron powder is 3~4μm, and the average particle size of the nano-sized Fe3O4 powder is 20~25nm. The mass ratio of carbonyl iron powder to Fe3O4 powder is 4:(0.5~1). The biocrosslinking was carried out using glycerol and calcium chloride, with the ratio of sodium alginate, glycerol and calcium chloride being 1g:4~8mL:0.2~0.4g.

2. The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics as described in claim 1, characterized in that, The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics is prepared using a method comprising the following steps: (1) A composite biosol was prepared using sodium alginate, polyvinyl alcohol and water; (2) The composite biosol and bidispersed magnetic microparticles are mixed, then glycerol and calcium chloride solution are added for biocrosslinking, and then freeze-drying is performed.

3. The sodium alginate-polyvinyl alcohol force / magnetic sensor material for wearable electronics as described in claim 2, characterized in that, For every 0.5g of sodium alginate, the corresponding amount of water is 45-50ml, the corresponding amount of glycerol is 2-4ml, and the corresponding amount of CaCl2 solution with a mass concentration of 1-2% is 10-15ml.

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