Preparation and application of a wearable hydrogel sensor for strain-temperature dual-mode monitoring

Abstract

A wearable hydrogel sensor for strain-temperature dual-mode monitoring is prepared and applied. Step 1: acrylamide, N,N-methylenebisacrylamide, PEDOT:PSS, β-cyclodextrin, and gallic acid are mixed; Step 2: the mixed solution is placed in a mixed solution of glycerol and deionized water and stirred at room temperature to obtain a conductive hydrogel precursor solution; Step 3: ammonium persulfate is added to the hydrogel precursor solution and mixed to obtain a hydrogel precursor solution; Step 4: "I" and "S" shaped molds are cut, the precursor solution in Step 3 is poured into the molds, and the conductive hydrogel is obtained under heating conditions; Step 5: conductive tape or wires are placed on the left and right sides of the conductive hydrogel and directly extended to serve as leads for connection to external equipment. The sensor is then encapsulated with waterproof and breathable tape. The "I"-shaped hydrogel serves as a strain sensor, and the "S"-shaped hydrogel serves as a temperature sensor, forming an "IS" wearable sensor. The present invention can achieve two modes without interfering with each other.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomaterials and flexible wearable health electronic devices, and specifically relates to the preparation and application of a wearable hydrogel sensor for strain-temperature dual-mode monitoring. Background Art

[0002] The development of flexible, wearable electronic sensors is a hot topic in the current electronic technology field. As people's demands for health monitoring, fitness tracking, and lifestyle convenience continue to increase, traditional rigid electronic devices cannot fully meet these needs. Flexible, wearable electronic sensors can provide strong support for these demands.

[0003] By combining a variety of high-performance conductive materials, such as reduced graphene oxide, silver nanowires, two-dimensional MXene nanosheets, conductive polymers, and carbon nanotubes, with elastomer composite substrates, researchers have successfully developed flexible sensors with diverse functions, excellent electrical conductivity, and good mechanical flexibility. These innovative designs not only broaden the application range of flexible sensors but also significantly improve their stability and durability in practical use.

[0004] Traditional sensors are mostly made of rigid materials such as metal and single-crystal silicon. Although they are highly sensitive, most of these materials have poor adaptability to the human body interface and may cause irritation and damage to the skin interface.

[0005] However, most of the flexible strain and temperature sensors with good biocompatibility currently have low sensitivity and linearity, and most of them are single-mode monitoring. For example, a hydrogel-based thermistor epidermal sensor uses catechol-inspired tannic acid-coated cellulose nanocrystals to provide adhesion balance and excellent thermal sensitivity, which is used to monitor human epidermal temperature. The sensor has a thermal sensitivity (TCR = 1.43% / °C), and its single-mode thermal sensitivity is lower than the thermal sensitivity of the temperature modality in this application (TCR = 1.7% / °C).

[0006] However, for human physiological monitoring, constructing multimodal, stable, and highly sensitive flexible materials remains the key and challenge. Summary of the Invention

[0007] To overcome the shortcomings of the aforementioned prior art, the present invention aims to provide a wearable hydrogel sensor for strain-temperature dual-mode monitoring. By designing "I" and "S"-shaped hydrogel sensors to monitor strain and temperature signals, respectively, the "S"-shaped sensor's strain signal is almost negligible compared to the "I" sensor, ensuring that the two modes do not interfere with each other. The sensor exhibits high strength, high toughness, on-demand peelability, and excellent antioxidant and antibacterial properties.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring comprises the following steps:

[0010] Step 1: Mix acrylamide monomer, N,N-methylenebisacrylamide, PEDOT:PSS (based on poly(3,4-ethylenedioxythiophene), β-cyclodextrin, and gallic acid;

[0011] Step 2: After mixing, place the mixture in a mixed solution of glycerol and deionized water, and stir evenly at room temperature to obtain a conductive hydrogel precursor solution;

[0012] Step 3: adding ammonium persulfate to the hydrogel precursor solution and mixing to obtain a hydrogel precursor solution;

[0013] Step 4: Use a laser cutting machine to cut "I" and "S" shaped molds, pour the precursor solution in step 3 into the mold, and obtain a conductive hydrogel under heating conditions;

[0014] Step 5: Place conductive tape or wires on the left and right sides of the conductive hydrogel and extend them directly to serve as leads connecting to external devices. Use waterproof and breathable tape for encapsulation. The "I"-shaped hydrogel is a strain sensor and the "S"-shaped hydrogel is a temperature sensor, forming an "IS" wearable sensor, that is, a wearable hydrogel sensor for strain and temperature dual-mode monitoring.

[0015] In step 1, the mass fraction of acrylamide is 40% to 60%, the mass fraction of N,N-methylenebisacrylamide is 0.1% to 0.2%; the mass fraction of PEDOT:PSS is 5% to 10%; the mass fractions of β-cyclodextrin and gallic acid are both 1% to 5%, the mass fraction of ammonium persulfate is 0.5% to 0.1%, and the remainder is water and glycerol; the above ingredients are added to the glycerol and water.

[0016] The mass ratios are as follows: the ratio of glycerol to water is 1:2 to 1:4, the ratio of glycerol to acrylamide is 2:3 to 2:3.5, the ratio of glycerol to N,N-methylenebisacrylamide is 200:1 to 200:2, the ratio of glycerol to ammonium persulfate is 80:1 to 80:2, the ratio of glycerol to PEDOT:PSS is 5:1 to 5:2, and the ratio of glycerol to β-cyclodextrin and gallic acid is 40:1 to 20:1.

[0017] In the step 2, the stirring is magnetic stirring, the speed of the magnetic stirring is 500 r / min to 800 r / min, and the time of the magnetic stirring is 10 min to 15 min.

[0018] In the step 4, the heating condition is to conduct the polymerization reaction in a vacuum drying oven at 50° C.-80° C. for 1 to 4 hours.

[0019] In step 4, the conductive hydrogel is a three-dimensional network structure, which is composed of gallic acid introduced into an interpenetrating network, which is formed by introducing PEDOT:PSS conductive polymer into a copolymer gel network, which is formed by acrylamide monomers grafted onto a β-cyclodextrin skeleton, and the gallic acid serves as a bond bridge between the hydrogel networks.

[0020] PEDOT:PSS is a conductive polymer network that interpenetrates with the copolymer gel network to form a hydrogel network.

[0021] The three-dimensional network structure has uniform pores with an average pore diameter of 20 to 30 μm.

[0022] The "IS" wearable sensor has a fast response and good linear relationship to temperature and strain in the temperature range of 10-50°C and the large strain range of 0-600%, respectively, meeting the temperature and strain monitoring needs of the human body.

[0023] The wearable hydrogel sensor is applied for rehabilitation training and health monitoring under conditions of large joint deformation.

[0024] The "IS" wearable sensor is attached to the surface of the skin.

[0025] In the "IS" wearable sensor, basic stress-strain data simulation verifies that when the "S"-shaped and "I"-shaped sensors are subjected to the same strain, the "S"-shaped sensor is used for temperature monitoring to avoid strain interference. After measuring the temperature, the "I"-shaped hydrogel is used for strain monitoring. The measured electrical value corresponds to the linear relationship at the temperature to infer the actual strain, thereby performing strain monitoring.

[0026] The "IS" wearable sensor has good electrical conductivity, biocompatibility, antibacterial properties, water retention, breathability, adhesion and on-demand peeling properties. It is suitable for application on the skin surface and has good stability.

[0027] The "IS" wearable sensor has good electrical conductivity (conductivity>0.025S / m), biocompatibility (hemolysis rate <2.20%), antibacterial properties (Staphylococcus aureus inhibition rate>82%, Escherichia coli inhibition rate>90%), water retention (water retention rate>65% after 30 days of storage at room temperature), and air permeability (>3000g / m 3 / 12h), adhesion (strong adhesion on various substrates such as glass, plastic, skin, metal, etc.) and on-demand peeling (can be peeled off on demand after being stuck on the skin for cold compress), etc., making it suitable for application on the skin surface and has good stability.

[0028] In the "IS" wearable sensor, basic stress-strain data simulation verifies that when the "S"-shaped and "I"-shaped sensors are subjected to the same strain, the stress on the "S"-shaped sensor is almost negligible. Therefore, the "S"-shaped sensor is used for temperature monitoring to avoid strain interference. After measuring the temperature, the "I"-shaped hydrogel is used for strain monitoring. The linear relationship between the measured electrical value and the temperature can be used to infer the actual strain, thereby performing strain monitoring.

[0029] Through the above characteristics, the present invention can simultaneously monitor temperature and strain sensing data, realize the decoupling of dual-function sensors, respond to the strain and temperature changes of large deformation at the joints of wearable devices, and avoid mutual interference of signals.

[0030] Beneficial effects of the present invention:

[0031] The temperature sensing principle of this invention is that the thermosensitive PEDOT:PSS provides more charge carriers at high temperatures, and the increase in temperature significantly increases the probability and distance of electron transitions, thereby reducing resistance. The strain sensing principle is that stretching causes changes in length and cross-sectional area, which synergistically increase resistance.

[0032] The flexible wearable hydrogel sensor material prepared by the present invention uses polyacrylamide, β-cyclodextrin and gallic acid as raw materials, all of which are substances with excellent biocompatibility.

[0033] The flexible conductive hydrogel prepared by the present invention has excellent properties such as skin adhesion, water retention, swelling, antioxidant, UV protection, and visualization. The wearable sensor prepared by the invention has good strain and temperature responsiveness, high sensitivity, good linearity, and can be decoupled from each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a picture of the PEDOT:PSS / polyacrylamide-β-CD hydrogel of the present invention.

[0035] Figure 2 This is the temperature sensitivity curve of the flexible dual-modal wearable sensor of the present invention.

[0036] Figure 3 This is the strain sensitivity curve of the flexible dual-modal wearable sensor of the present invention.

[0037] Figure 4 It is the temperature response and recovery time of the flexible dual-modal wearable sensor of the present invention.

[0038] Figure 5 is the strain response and recovery time of the flexible dual-modal wearable sensor of the present invention.

[0039] Figure 6 This is the response curve of the flexible dual-modal wearable sensor of the present invention when the temperature difference is 0.5°C within the body temperature range.

[0040] Figure 7 This is the response curve of the flexible dual-modal wearable sensor of the present invention with a strain gradient of 10% in the strain range of 0-100%.

[0041] Figure 8 This is a curve showing the mutual influence between temperature and strain of the flexible dual-modal wearable sensor of the present invention.

[0042] Figure 9 This is the strain effect of different bending angles of the "I" and "S" hydrogel legs in the flexible dual-modal wearable sensor of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below with reference to the accompanying drawings.

[0044] Example 1

[0045] 0.8g of PEDOT:PSS was dissolved in a mixture of 4g of glycerol and 8g of water and mixed thoroughly using a magnetic stirrer at 500 rpm. 6g of acrylamide monomer, 0.02g of N,N-methylenebisacrylamide, 0.1g of β-cyclodextrin, and 0.1g of gallic acid were then added sequentially to the light blue liquid until it became clear and transparent, resulting in a hydrogel precursor solution. This hydrogel precursor solution was then added to an "IS" mold fabricated using a laser cutter and placed in a vacuum drying oven at 60°C for 4 hours to produce a conductive hydrogel flexible temperature and strain dual-modal sensor.

[0046] The resulting conductive hydrogel flexible temperature and strain dual-modal sensor was molded into a dumbbell shape. A fixture was used to clamp the sensor's ends and attach copper wires. A universal material testing machine was used to apply external tension to the sensor. The strain sensor's resistance change rate and strain range were recorded during stretching to calculate sensitivity, and linearity was then determined through linear fitting. The temperature sensitivity coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the hydrogel sensor's temperature, and recording its resistance change rate and temperature range. Linearity was then determined through fitting.

[0047] The present invention is verified by experiments. Figure 1 Shown is a visual representation of the conductive hydrogel that makes up the wearable sensor. Figure 2 The above method is used to prepare a conductive hydrogel flexible temperature and strain dual-mode sensor which maintains R in the range of 10℃-50℃. 2 =0.981, Figure 3 The conductive hydrogel flexible temperature and strain dual-modal sensor can maintain R in a large strain range of 0-600%.2 = 0.970 linearity, and its sensitivity is 2.0. Figure 4 、 5 The conductive hydrogel flexible temperature and strain dual-mode sensor shown in the paper has a response time of 0.6s to temperature and a recovery time of 2.48s. It has a fast response time of 0.162s to strain. When monitoring human motion, the response to a small temperature range is particularly important. Figure 6 The sensitivity curve of the temperature module in the wearable sensor is shown when the human body temperature changes by 0.5°C within the range of 35°C to 40°C. Figure 7 The sensitivity curve of the wearable sensor strain module shows good sensitivity and response time for every 10% change in the strain range of 0-100%. Figure 8 The middle one is the sensitivity curve in the strain range of 0-200% at different temperatures. It can be seen that different temperatures have almost no effect on the strain. Figure 9 This means that when the "I" and "S" shapes in this "IS"-shaped sensor combination deform at different angles, the "S" deformation is almost negligible. Therefore, the "IS" combination is the optimal design for monitoring sensor strain and temperature. It is suitable for monitoring rehabilitation exercises after joint surgery.

[0048] Example 2

[0049] 0.9g of PEDOT:PSS was dissolved in a mixture of 4g of glycerol and 8g of water and mixed thoroughly using a magnetic stirrer at 600 rpm. 7g of acrylamide monomer, 0.03g of N,N-methylenebisacrylamide, 0.1g of β-cyclodextrin, and 0.1g of gallic acid were then added sequentially to the light blue liquid until it became clear and transparent, resulting in a hydrogel precursor solution. This hydrogel precursor solution was then added to an "IS" mold fabricated using a laser cutter and placed in a vacuum drying oven at 60°C for 4 hours to produce a conductive hydrogel flexible temperature and strain dual-modal sensor.

[0050] The resulting conductive hydrogel flexible temperature and strain dual-modal sensor was molded into a dumbbell shape. A fixture was used to clamp the sensor's ends and attach copper wires. A universal material testing machine was used to apply external tension to the sensor. The strain sensor's resistance change rate and strain range were recorded during stretching to calculate sensitivity, and linearity was then determined through linear fitting. The temperature sensitivity coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the hydrogel sensor's temperature, and recording its resistance change rate and temperature range. Linearity was then determined through fitting.

[0051] The electromechanical properties were also measured, and by comparison, it was found that the sensor prepared in Example 1 had better performance.

[0052] Example 3

[0053] 0.95g of PEDOT:PSS was dissolved in a mixture of 4g of glycerol and 8g of water and mixed thoroughly using a magnetic stirrer at 600 rpm. 7.5g of acrylamide monomer, 0.03g of N,N-methylenebisacrylamide, 0.15g of β-cyclodextrin, and 0.1g of gallic acid were then added sequentially to the light blue liquid until it became clear and transparent, yielding a hydrogel precursor solution. This hydrogel precursor solution was then added to an "IS" mold fabricated using a laser cutter and placed in a vacuum drying oven at 60°C for 4 hours to produce a conductive hydrogel flexible temperature and strain dual-modal sensor.

[0054] The resulting conductive hydrogel flexible temperature and strain dual-modal sensor was molded into a dumbbell shape. A fixture was used to clamp the sensor's ends and attach copper wires. A universal material testing machine was used to apply external tension to the sensor. The strain sensor's resistance change rate and strain range were recorded during stretching to calculate sensitivity, and linearity was then determined through linear fitting. The temperature sensitivity coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the hydrogel sensor's temperature, and recording its resistance change rate and temperature range. Linearity was then determined through fitting.

[0055] The electromechanical properties were also measured, and by comparison, it was found that the sensor prepared in Example 1 had better performance.

[0056] The present invention prepares a multimodal sensor of a fully polymerized biocompatible hydrogel, which has high strength, high toughness, on-demand peeling, good antioxidant and antibacterial properties, increases its wider application range, and has high linearity in a wide range of stretching and temperature. Therefore, the hydrogel is rationally designed as a smart wearable sensor with multi-response (temperature and strain). It accurately monitors large movements (fingers, wrists, knee joints) and small movements (smiles, vocal cords) of the human body and can monitor temperature at the same time. In addition, the wearable hydrogel has high antioxidant and antibacterial properties, so it can also be used for state detection and rehabilitation treatment of wounds after joint surgery. In order to prevent temperature and strain from affecting each other, "I" and "S" shaped hydrogel sensors are designed to monitor strain and temperature signals respectively. The strain signal of the "S" shape is almost negligible relative to the "I" sensor, so that the two modes do not interfere with each other.

Claims

1. A method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring, characterized in that: The following steps are involved: Step 1: Mix acrylamide monomer, N,N-methylenebisacrylamide, PEDOT:PSS, β-cyclodextrin, and gallic acid; Step 2: After mixing, place the mixture in a mixed solution of glycerol and deionized water, and stir evenly at room temperature to obtain a conductive hydrogel precursor solution; Step 3: adding ammonium persulfate to the hydrogel precursor solution and mixing to obtain a hydrogel precursor solution; Step 4: Use a laser cutting machine to cut "I" and "S" shaped molds, pour the precursor solution in step 3 into the mold, and obtain the conductive hydrogel under heating conditions; Step 5: Place conductive tape or wires on the left and right sides of the conductive hydrogel and extend them directly to serve as leads connecting to external devices. Use waterproof and breathable tape to encapsulate them. The "I"-shaped hydrogel serves as a strain sensor, and the "S"-shaped hydrogel serves as a temperature sensor, forming an "IS" wearable sensor, that is, a wearable hydrogel sensor for strain and temperature dual-mode monitoring. The mass ratios are as follows: the ratio of glycerol to water is 1:2~1:4, the ratio of glycerol to acrylamide is 2:3~2:3.5, the ratio of glycerol to N,N-methylenebisacrylamide is 200:1~200:2, the ratio of glycerol to ammonium persulfate is 80:1~80:2, the ratio of glycerol to PEDOT:PSS is 5:1~5:2, and the ratio of glycerol to β-cyclodextrin and gallic acid is 40:1~20:

1.

2. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, characterized in that: In step 1, the mass fraction of acrylamide is 40% to 60%, the mass fraction of N,N-methylenebisacrylamide is 0.1% to 0.2%; the mass fraction of PEDOT:PSS is 5% to 10%; the mass fractions of β-cyclodextrin and gallic acid are both 1% to 5%, the mass fraction of ammonium persulfate is 0.5% to 0.1%, and the rest are water and glycerol.

3. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, characterized in that: In step 2, the stirring is magnetic stirring, the speed of the magnetic stirring is 500 r / min to 800 r / min, and the time of the magnetic stirring is 10 min to 15 min.

4. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, characterized in that: In step 4, the heating condition is to conduct the polymerization reaction in a vacuum drying oven at 50° C.-80° C. for 1 to 4 hours.

5. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, characterized in that: In step 4, the conductive hydrogel is a three-dimensional network structure, which is composed of gallic acid introduced into an interpenetrating network, which is formed by introducing PEDOT:PSS conductive polymer into a copolymer gel network, which is formed by acrylamide monomers grafted onto a β-cyclodextrin skeleton, and the gallic acid serves as a bond bridge between the hydrogel networks.

6. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, characterized in that: The "IS" wearable sensor has a fast response and linear relationship to temperature and strain within the temperature range of 10-50°C and the large strain range of 0-600%, respectively, meeting the temperature and strain monitoring needs of the human body.

7. Application of a wearable hydrogel sensor prepared according to any one of claims 1 to 6, characterized in that: The wearable hydrogel sensor is used for rehabilitation training and health monitoring under conditions of large joint deformation for non-diagnostic and therapeutic purposes.

8. The use of the wearable hydrogel sensor according to claim 7, characterized in that: The "IS" wearable sensor is attached to the surface of the skin.

9. The use of the wearable hydrogel sensor according to claim 7, characterized in that: In the "IS" wearable sensor, stress-strain data simulation verifies that when the "S"-shaped and "I"-shaped sensors are subjected to the same strain, the "S"-shaped sensor is used for temperature monitoring to avoid strain interference. After measuring the temperature, the "I"-shaped hydrogel is used for strain monitoring. The measured electrical value corresponds to the linear relationship at the temperature to infer the actual strain, thereby performing strain monitoring.

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