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

Abstract

The invention relates to preparation and application of a wearable hydrogel sensor for strain and temperature dual-mode monitoring, and the preparation method comprises the following steps: 1, mixing acrylamide, N, N-methylene bisacrylamide, PEDOT: PSS, beta-cyclodextrin and gallic acid; step 2, after mixing, putting the mixture into a mixed solution of glycerol and deionized water, and uniformly stirring at normal temperature to obtain a conductive hydrogel precursor solution; 3, adding ammonium persulfate into the hydrogel precursor solution, and uniformly mixing to obtain a hydrogel precursor solution; step 4, cutting an I-shaped mold and an S-shaped mold, pouring the precursor solution in the step 3 into the mold, and obtaining conductive hydrogel under a heating condition; 5, conductive adhesive tapes or wires are arranged on the left side and the right side of the conductive hydrogel and directly extend to serve as lead wires connected with external equipment, waterproof breathable adhesive tapes are used for packaging, the I-shaped hydrogel serves as a strain sensor, the S-shaped hydrogel serves as a temperature sensor, and an IS wearable sensor is formed. According to the invention, the two modes do not interfere 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 one of the hot topics in the current electronic technology field. As people's demand for health monitoring, sports tracking and convenience in life continues to increase, traditional rigid electronic devices cannot fully meet people's needs. Flexible wearable electronic sensors can provide strong support for these needs.

[0003] At present, researchers have successfully developed flexible sensors with diverse functions, excellent conductivity and good mechanical flexibility 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. These innovative designs not only broaden the application range of flexible sensors, but also significantly improve their stability and durability in actual 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 are not very sensitive, have low linearity, and are mostly single-mode monitoring. For example, in a hydrogel-based thermistor epidermal sensor, cellulose nanocrystals coated with tannic acid inspired by catechol chemistry are used to provide adhesion balance and superior thermal sensitivity, which is used to monitor the epidermal temperature of the human body. The sensor has a thermal sensitivity (TCR = 1.43% / ℃), and its single-mode thermal sensitivity is less than the thermal sensitivity of the temperature mode in this application (TCR = 1.7% / ℃).

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

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a preparation and application of 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 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. It has the characteristics of high strength, high toughness, on-demand peeling, good anti-oxidation 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-ethyldioxythiophene), β-cyclodextrin and gallic acid;

[0011] Step 2: After mixing, place 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 well 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 wire on the left and right sides of the conductive hydrogel and extend it directly to serve as a lead connected to external equipment. 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-temperature dual-mode monitoring.

[0015] In the step 1, the mass fraction of acrylamide is 40-60%, the mass fraction of N,N-methylenebisacrylamide is 0.1%-0.2%; the mass fraction of PEDOT:PSS is 5%-10%; the mass fractions of β-cyclodextrin and gallic acid are both 1%-5%, the mass fraction of ammonium persulfate is 0.5%-0.1%, and the rest are water and glycerol; the above ingredients are added to 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 carry out 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, the three-dimensional network structure is formed by introducing gallic acid into an interpenetrating network, the interpenetrating network is formed by introducing PEDOT:PSS conductive polymer into a copolymer gel network, the copolymer gel network is formed by grafting acrylamide monomers 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 size 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 to 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, and the "I"-shaped hydrogel is used for strain monitoring after measuring the temperature. The linear relationship between the measured electrical value and the temperature is used 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, is suitable for application on the skin surface, and has good stability.

[0027] The "IS" wearable sensor has good conductivity (conductivity>0.025S / m), biocompatibility (hemolysis rate <2.20%), antibacterial property (Staphylococcus aureus inhibition rate>82%, Escherichia coli inhibition rate>90%), water retention (water retention rate>65% after 30 days at room temperature), air permeability (>3000g / m 3 / 12h), adhesion (strong adhesion on a variety of substrates such as glass, plastic, skin, metal, etc.) and on-demand peeling (can be peeled off on demand after being stuck on the skin and cold compressed), 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 deduce 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 deformations at the joints in wearable devices, and avoid mutual interference of signals.

[0030] Beneficial effects of the present invention:

[0031] The temperature sensing principle of the present invention is that the thermosensitive PEDOT:PSS can provide more carriers at high temperature and the increase in temperature can greatly promote the probability and distance of electron jumps, thereby reducing the resistance value. The strain sensing principle is that stretching causes changes in length and cross-sectional area, thereby synergistically increasing the resistance value.

[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, anti-oxidation, UV protection and visualization. The prepared wearable sensor 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-mode 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 It 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 with a temperature difference of 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-mode wearable sensor of the present invention.

[0042] Fig. 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 in conjunction with the accompanying drawings.

[0044] Example 1

[0045] 0.8g PEDOT:PSS was dissolved in a mixed solvent of 4g glycerol and 8g water and mixed at 500r / min on a magnetic stirrer, and then 6g acrylamide monomer, 0.02g N,N-methylenebisacrylamide, 0.1g β-cyclodextrin, and 0.1g gallic acid were added to the mixed light blue liquid in sequence until the liquid became clear and transparent to obtain a hydrogel precursor solution. The hydrogel precursor solution was added to the "IS" mold made by a laser cutting machine and placed in a vacuum drying oven at 60°C for 4h to obtain a conductive hydrogel flexible temperature and strain dual-mode sensor.

[0046] The obtained conductive hydrogel flexible temperature and strain dual-mode sensor was prepared into a dumbbell shape using a mold. The two ends of the sensor were clamped with a clamp and a copper wire was clamped. The sensor was subjected to external tension using a universal material testing machine. The resistance change rate and strain range of the strain sensor were recorded while stretching to calculate the sensitivity, and then the linearity was obtained through linear fitting. The temperature sensing coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the temperature of the hydrogel sensor, and recording its resistance change rate and temperature change range, and the linearity was obtained through fitting.

[0047] The present invention is verified by experiments. Figure 1 Shown is a direct view of the conductive hydrogel that makes up the wearable sensor. Figure 2 The above method is shown 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-mode 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 figure has a response time of 0.6s for temperature and a recovery time of 2.48s for strain. It has a fast response time of 0.162s for strain. When monitoring the motion state of the human body, the response to a small range of temperature 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-40°C. Figure 7 It is shown that 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. Fig. 9 This means that when the "I" and "S" shapes in the "IS" shaped sensor combination design are deformed at different angles, the "S" deformation is almost negligible, so the "IS" combination is the optimal design for monitoring sensor strain and temperature. It is suitable for monitoring rehabilitation movements after joint surgery.

[0048] Example 2

[0049] 0.9g PEDOT:PSS was dissolved in a mixed solvent of 4g glycerol and 8g water and mixed at 600r / min on a magnetic stirrer, and then 7g acrylamide monomer, 0.03g N,N-methylenebisacrylamide, 0.1g β-cyclodextrin, and 0.1g gallic acid were added to the mixed light blue liquid in sequence until the liquid became clear and transparent to obtain a hydrogel precursor solution. The hydrogel precursor solution was added to an "IS" mold made by a laser cutting machine and placed in a vacuum drying oven at 60°C for 4h to obtain a conductive hydrogel flexible temperature and strain dual-mode sensor.

[0050] The obtained conductive hydrogel flexible temperature and strain dual-mode sensor was prepared into a dumbbell shape using a mold. The two ends of the sensor were clamped with a clamp and a copper wire was clamped. The sensor was subjected to external tension using a universal material testing machine. The resistance change rate and strain range of the strain sensor were recorded while stretching to calculate the sensitivity, and then the linearity was obtained through linear fitting. The temperature sensing coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the temperature of the hydrogel sensor, and recording its resistance change rate and temperature change range, and the linearity was obtained through fitting.

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

[0052] Example 3

[0053] 0.95g PEDOT:PSS was dissolved in a mixed solvent of 4g glycerol and 8g water and mixed at 600r / min on a magnetic stirrer, and then 7.5g acrylamide monomer, 0.03g N,N-methylenebisacrylamide, 0.15g β-cyclodextrin, and 0.1g gallic acid were added to the mixed light blue liquid in sequence until the liquid became clear and transparent to obtain a hydrogel precursor solution. The hydrogel precursor solution was added to the "IS" mold made by a laser cutting machine and placed in a vacuum drying oven at 60°C for 4h to obtain a conductive hydrogel flexible temperature and strain dual-mode sensor.

[0054] The obtained conductive hydrogel flexible temperature and strain dual-mode sensor was prepared into a dumbbell shape using a mold. The two ends of the sensor were clamped with a clamp and a copper wire was clamped. The sensor was subjected to external tension using a universal material testing machine. The resistance change rate and strain range of the strain sensor were recorded while stretching to calculate the sensitivity, and then the linearity was obtained through linear fitting. The temperature sensing coefficient (TCR) was calculated by attaching the sensor to the wall of a beaker, adding hot water to change the temperature of the hydrogel sensor, and recording its resistance change rate and temperature change range, and the linearity was obtained through fitting.

[0055] The electromechanical properties were also measured, and it was found through comparison that the sensor prepared in Example 1 had more excellent 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 reasonably designed as an intelligent wearable sensor with multi-response (temperature and strain). It can accurately monitor 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 relative to the "I" sensor can be almost ignored, so that the purpose of non-interference between the two modes can be achieved.

Claims

1. A method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring. It is 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 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 well 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 a conductive hydrogel under heating conditions; Step 5: Place conductive tape or wire on the left and right sides of the conductive hydrogel and extend it directly to serve as a lead connected to external equipment. Use waterproof and breathable tape for packaging. 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-temperature dual-mode monitoring.

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

3. A method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 2, It is characterized in that 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.

4. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, It is characterized in that 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.

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

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

7. The method for preparing a wearable hydrogel sensor for strain-temperature dual-mode monitoring according to claim 1, It is characterized in that 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.

8. Application of a wearable hydrogel sensor prepared by the method according to any one of claims 1 to 7, It is characterized in that The wearable hydrogel sensor is applied to rehabilitation training and health monitoring under conditions of large joint deformation.

9. Use of the wearable hydrogel sensor according to claim 8, It is characterized in that The "IS" wearable sensor is attached to the surface of the skin.

10. Use of the wearable hydrogel sensor according to claim 8, It is characterized in that 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, and after measuring the temperature, the "I"-shaped hydrogel is used for strain monitoring. The linear relationship between the measured electrical value and the temperature is used to infer the actual strain, thereby performing strain monitoring.

Images