A hydrogel electrochemical strain sensor and its preparation method and application

Abstract

The present invention discloses a hydrogel electrochemical strain sensor and a preparation method and application thereof, belonging to the technical field of ion conductive hydrogels, and provides a hydrogel electrochemical strain sensor, wherein the hydrogel electrochemical strain sensor comprises a PET substrate, a working electrode, a counter electrode, a reference electrode and an ion conductive hydrogel; the working electrode, the counter electrode and the reference electrode are sequentially arranged on the PET substrate; the working electrode, the counter electrode and the reference electrode are covered with the ion conductive hydrogel on top. The present invention utilizes the excellent ion piezoelectric effect and good mechanical properties of the ion conductive hydrogel, and the prepared hydrogel electrochemical strain sensor has the characteristics of low noise, stable signal, high sensitivity and fast response\recovery speed, and shows great application potential in low-force detection fields such as human pulse wave monitoring and artificial larynx.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a hydrogel electrochemical strain sensor and a preparation method and application thereof. Background Art

[0002] Flexible strain sensors are wearable devices that detect the action of force by converting stress or strain into electrical signals. In recent years, such sensors have attracted widespread attention in the fields of electronic skin, artificial larynx, human health monitoring, and human-computer interaction. Recently, hydrogels have become the key materials for flexible strain sensors due to their excellent flexibility, stretchability, strong self-healing properties, and high biocompatibility. The conductive mechanism of hydrogels can be divided into electronic conductivity based on conductive polymers and ionic conductivity based on ionic solutions. The electronic conductivity mechanism is similar to that of traditional strain sensors, but the ionic conductivity mechanism is different. However, the current testing methods for strain sensors based on ion-conductive hydrogels are the same as those for traditional sensors, which may not accurately reflect their true sensing capabilities.

[0003] Recently, electrochemical devices based on organic ion-electron conductors have shown significant potential in a variety of applications. Unlike traditional semiconductor devices, electrical measurements in electrochemical devices require reference electrodes. In electrochemical systems, reference electrodes provide a stable potential reference, thereby ensuring the accuracy and repeatability of electrical measurements. Strain sensors based on ionic hydrogels are also electrochemical devices because their electrical transport mechanism based on ionic conduction is similar to that of electrolytes. This suggests that electrochemical testing methods may be more suitable for such sensors. In addition, electrochemical wearable devices have made significant progress in health monitoring, sports tracking, and in vitro molecular detection. These advances provide new opportunities for the development of hydrogel-based electrochemical wearable strain sensors.

[0004] Due to variations in the degree of cross-linking and water content, hydrogels exhibit a wide range of mechanical properties, including highly tough, impact-resistant materials, and ultra-soft semisolids. Typically, researchers tend to choose hydrogels with superior mechanical properties as strain sensors because these materials are often required to withstand cyclic strain loading. However, softer hydrogels are often overlooked. As the strength of a hydrogel increases, its sensitivity to force generally decreases because less strain is generated under the same force. Therefore, the force detection range required by the sensor is critical in determining the appropriate mechanical properties of the hydrogel. Low-strength hydrogels are suitable for detecting small forces, while high-strength hydrogels are better suited for detecting larger forces. Accurately detecting small forces is particularly important in applications such as pulse monitoring and artificial larynxes, suggesting that low-strength hydrogels may play a more important role in these areas.

[0005] Polyvinyl alcohol (PEG) hydrogel is a soft, nontoxic and biocompatible material. Due to its high cell and tissue adhesion strength, PEG hydrogels show potential applications in fetal membrane healing and ultrafast hemostatic agents. However, PEG hydrogels exhibit low mechanical strength due to their large network pore size, strong water absorption and high swelling, making them suitable for rapid aptamer selection and concentration. In addition, PEG hydrogels are widely used in long-term culture of human small intestine (hSI) organoids due to their dynamic reorganization ability. In addition, PEG-based injectable thermosensitive hydrogels have been widely studied in tumor therapy and drug delivery applications. Although large-pore PEG hydrogels can accommodate conductive ionic solutions to achieve conductivity, strain sensors based on PEG hydrogels have not been reported due to their poor mechanical properties.

[0006] In previous studies, the piezoelectric ion output and mechanical properties of hydrogel-based strain sensors were enhanced by adding SnSe nanosheets to reduce the pore size. However, the increased difference in the diffusion rates of positive and negative ions resulted in a prolonged recovery time, limiting its application in detecting cyclic loading strain at short intervals. In addition, the high mechanical strength of the hydrogel reduced its sensitivity to small forces. In addition, the conventional two-electrode resistance test method showed poor stability. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a hydrogel electrochemical strain sensor and its preparation method and application, which can solve the limitations of traditional sensors in sensitivity, comfort and stability in the field of low-force detection, and obtain a highly sensitive electrochemical strain sensor with excellent microscale stress / strain performance, which shows great application potential in low-force detection fields such as human pulse wave monitoring and artificial larynx.

[0008] To achieve the above object, the present invention provides a hydrogel electrochemical strain sensor, which comprises a PET substrate, a working electrode, a counter electrode, a reference electrode and an ion conductive hydrogel;

[0009] The working electrode, the counter electrode and the reference electrode are sequentially located on the PET substrate; the tops of the working electrode, the counter electrode and the reference electrode are covered with the ion conductive hydrogel.

[0010] Preferably, the thickness of the ion-conductive hydrogel covering the surfaces of the working electrode, the counter electrode and the reference electrode is 0.2-1.5 mm.

[0011] Preferably, the ion conductive hydrogel is prepared from a four-arm PEG acrylate aqueous solution, a SHPEG-SH aqueous solution, an ion buffer and deionized water; the volume ratio of the four-arm PEG acrylate aqueous solution, the SHPEG-SH aqueous solution, the ion buffer and the deionized water is 6:4:5:25~100; the concentration of the four-arm PEG acrylate aqueous solution is 35.5wt%, and the concentration of the SHPEG-SH aqueous solution is 35.5wt%.

[0012] Preferably, the ionic buffer is deionized water as solvent, and HCl, (NH 4 ) 2 SO 4 , KCl and MgSO 4 The ion buffer has a HCl concentration of 20 mM, (NH 4 ) 2 SO 4 The concentration was 10 mM, the concentration of KCl was 50 mM, and the concentration of MgSO 4 The concentration is 2mM.

[0013] The present invention also provides a method for preparing the hydrogel electrochemical strain sensor, comprising the following steps:

[0014] S1, using screen printing technology to form a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode on the working electrode, the counter electrode and the reference electrode on the PET substrate respectively;

[0015] S2, pipetting the conductive nanomaterial aqueous solution onto the carbon working electrode described in S1, and vacuum drying to form a nanomaterial-modified carbon working electrode;

[0016] S3. Cover the top of the carbon working electrode modified with nanomaterials prepared in S2, the carbon counter electrode prepared in S1, and the Ag / AgCl reference electrode prepared in S1 with ion conductive hydrogel, and let it stand for 2 to 5 minutes to obtain a hydrogel electrochemical strain sensor.

[0017] Preferably, the thickness of the PET substrate in S1 is 0.1 mm.

[0018] Preferably, the concentration of the conductive nanomaterial aqueous solution in S2 is 1.5 mg / mL; the ratio of the conductive nanomaterial aqueous solution in S2 to the carbon working electrode is 1-5 μL:1 mm 2 ; The vacuum degree of the vacuum drying in S2 is 10~100Pa, the temperature of the vacuum drying is 55~65℃, and the vacuum drying time is 5~7h.

[0019] The present invention also provides the use of the hydrogel electrochemical strain sensor or the hydrogel electrochemical strain sensor prepared by the preparation method in preparing a low-force monitoring device.

[0020] The present invention also provides the use of the hydrogel electrochemical strain sensor or the hydrogel electrochemical strain sensor prepared by the preparation method in preparing a pulse detection device.

[0021] The present invention also provides the use of the hydrogel electrochemical strain sensor or the hydrogel electrochemical strain sensor prepared by the preparation method in preparing an artificial larynx.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] The present invention provides an electrochemical strain sensor based on hydrogel, and the electrochemical measurement method provides a more stable piezoelectric ion output. The hydrogel used has excellent ion piezoelectric effect and good mechanical properties, and the sensor has the characteristics of low noise, stable signal, high sensitivity and fast response\recovery speed. The piezoelectric ion dynamics were deeply analyzed using diffusion theory. The strain sensor showed excellent performance in detecting microscale stress / strain, and has important application potential in human pulse wave monitoring and artificial laryngeal technology. It also indicates the broad development prospects of flexible sensing technology in the future, and provides a new idea for solving the limitations of traditional sensors in sensitivity, comfort and stability in the field of low-force detection. It shows great application prospects in the future fields of personal health management, remote medical diagnosis and non-invasive detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 The ion conductive hydrogel and the electrochemical strain sensor prepared therefrom of the present invention, wherein a is the structure of the ion conductive hydrogel, the red dots in the figure represent the cross-linking points, b is the FTIR spectrum of the ion conductive hydrogel, c is a schematic diagram of the electrochemical strain sensor prepared by the ion conductive hydrogel, and d is the electrical signals measured at the two and three terminals of the electrochemical strain sensor;

[0026] Figure 2 is the relationship curve between the piezoelectric ion output current and the inward bending strain;

[0027] Figure 3The performance of electrochemical strain sensors prepared by ion conductive hydrogels with different water contents, where a is the SEM image of ion conductive hydrogel with a water content of 80%, the scale is 20μm, b is the SEM image of ion conductive hydrogel with a water content of 85%, the scale is 20μm, c is the SEM image of ion conductive hydrogel with a water content of 90%, the scale is 20μm, d is the loading and unloading cycle curve of hydrogel under 0-16.7% compressive strain, e is the elastic modulus of ion conductive hydrogel, f is the effect of water content on the residual strain and hysteresis ratio of ion conductive hydrogel, g is the pressure ion current, h is the pressure ion coefficient, and i is the relationship between the decay time and the water content of ion conductive hydrogel;

[0028] Figure 4 The pulse waveforms of the radial artery, ulnar artery, digital artery and carotid artery measured by the electrochemical strain sensor, wherein a is the radial artery position, b is the radial artery pulse waveform, c is the radial artery single pulse wave, d is the ulnar artery position, e is the ulnar artery pulse waveform, f is the ulnar artery single pulse wave, g is the digital artery position, h is the digital artery pulse waveform, i is the digital artery single pulse wave, j is the carotid artery position, k is the carotid artery pulse waveform, and l is the carotid artery single pulse wave;

[0029] Figure 5 The electrochemical strain sensor measures the pulse waveforms under different exercise states, where a is the fat burning exercise pulse, b is the fat burning exercise pulse waveform, c is the fat burning exercise single pulse wave, d is the aerobic exercise pulse, e is the aerobic exercise pulse waveform, f is the aerobic exercise single pulse wave, g is the anaerobic exercise pulse, h is the anaerobic exercise pulse waveform, i is the anaerobic exercise single pulse wave, j is the stop exercise pulse, k is the stop exercise pulse waveform, and l is the stop exercise single pulse wave;

[0030] Figure 6 The electrochemical strain sensor measures the changes in the pulse signal when holding the breath and breathing, where a is the continuous pulse monitoring diagram from 55 to 120 seconds, i.e., breathing for 15 seconds, holding the breath for 30 seconds, and then breathing for 15 seconds; b is the single pulse wave of the breathing state at 59 seconds; c is the single pulse wave of the breathing state at 74 seconds; d is the single pulse wave of the breathing state at 87 seconds; e is the single pulse wave of the breathing state at 98 seconds; f is the single pulse wave of the breathing state at 105 seconds; and g is the single pulse wave of the breathing state at 112 seconds;

[0031] Figure 7 The electrochemical strain sensor is used for an artificial throat, wherein a is the signal of the throat movement detected by the sensor installed on the throat of the user during speech production, b is the piezoelectric current of flat tongue and rolled tongue pronunciation, c is the piezoelectric current of different tones, d is the piezoelectric current of different letters, e is the piezoelectric current of different words, f is the response of different phrases, and g is the change of the response signal corresponding to the change from a word to a sentence;

[0032] Figure 8For speech recognition with the help of machine learning algorithm, where a is the flow chart of the machine learning algorithm, b is the text accuracy as a function of the data set size, c is the confusion matrix of the sentence recognition task, and d is the receiver operating characteristic curve of machine learning recognition based on ultra-sensitive electrochemical strain sensor. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] Example 1

[0039] 55 mg of four-arm PEG acrylate with a molecular weight of 10000 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a four-arm PEG acrylate aqueous solution with a concentration of 35.5 wt%; 55 mg of SHPEG-SH with a molecular weight of 3400 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a SHPEG-SH aqueous solution with a concentration of 35.5 wt%.

[0040] The HCl concentration in the ionic buffer was 20 mM, (NH 4 ) 2 SO 4 The concentration was 10 mM, the concentration of KCl was 50 mM, and the concentration of MgSO 4 The concentration is 2mM.

[0041] The conductive nanomaterial aqueous solution is a carbon nanotube aqueous solution.

[0042] 3 μL of a 35.5 wt% aqueous solution of four-arm PEG acrylate, 2 μL of a 35.5 wt% aqueous solution of SHPEG-SH, 2.5 μL of an ion buffer and 17.5 μL of deionized water were mixed to obtain an ion conductive hydrogel.

[0043] S1, using screen printing technology to form a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode on a PET substrate with a thickness of 0.1 mm, respectively;

[0044] S2, pipette the 1.5 mg / mL carbon nanotube aqueous solution onto the carbon working electrode (the ratio of carbon nanotube aqueous solution to carbon working electrode is 3 μL:1 mm 2 ), 55Pa, and vacuum dried at 60°C for 6h to form a carbon working electrode modified with nanomaterials;

[0045] S3. The carbon working electrode, carbon counter electrode and Ag / AgCl reference electrode modified with nanomaterials are covered with 1 mm thick ion conductive hydrogel. The hydrogel can be successfully gelled after standing for 3 minutes to obtain a hydrogel electrochemical strain sensor.

[0046] Insert the electrode of the electrochemical strain sensor into the reading device, connect the electrochemical platform, open the chi440c software, select the test condition It, set the run time to 400s, the sensitivity (A / V) to 10 -7 , and bend the sensor to a certain degree when the current is stable, and then perform the next test after the current is stable. The final strength is the average of at least three parallel integration values ​​of three repeated solutions. It can be used if the test conditions are met.

[0047] The pressure ion output is generated by the transfer of cations and anions caused by strain. When the same force is applied, the strain decreases as the strength of the hydrogel increases. Therefore, it is often difficult to detect small forces in high-strength hydrogels. Polyethylene glycol has a large pore structure that allows the ionic solution to remain conductive. 4 The mixed buffer provides ionic conductivity, and the resulting ion-conductive hydrogel structure is prepared as Figure 1 A and Figure 1 As shown in b. In the above ionic compounds, the diameter of the cation is smaller than that of the anion.

[0048] The conduction mechanism of ion-conductive hydrogels is different from that of electronically conductive conductors or semiconductors. Therefore, conventional two-terminal devices are usually unable to obtain stable electrical signals in ion-conductive hydrogels, and it is difficult to detect responses to small forces or strains. Figure 1 As shown in Figure c, the electrochemical strain sensor is constructed on a 0.1 mm thick polyethylene terephthalate (PET) substrate, showing the geometry, with a 1 mm thick ion-conductive hydrogel covering the top of the three electrodes. In order to improve the conductivity, a carbon electrode modified with carbon nanotubes was used to make the working electrode (WE). The counter electrode (CE) and reference electrode (RE) were carbon and Ag / AgCl, respectively. For two-terminal measurements, in the absence of an applied potential, the current swing was in the range of 6.6 nA, and for three-terminal measurements, this value dropped to 0.4 nA (as shown in Figure d). Figure 1 The results show that the three-terminal electrochemical strain sensor device exhibits more stable and accurate electrical signals in the electrochemical system. In addition, within the strain range of 1.67% to 5.00%, the piezoelectric ion current increases linearly with the strain, and its goodness of fit R 2 is 0.997 (e.g. Figure 2 ).

[0049] Example 2

[0050] 55 mg of four-arm PEG acrylate with a molecular weight of 10000 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a four-arm PEG acrylate aqueous solution with a concentration of 35.5 wt%; 55 mg of SHPEG-SH with a molecular weight of 3400 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a SHPEG-SH aqueous solution with a concentration of 35.5 wt%.

[0051] The HCl concentration in the ionic buffer was 20 mM, (NH 4 ) 2 SO 4 The concentration was 10 mM, the concentration of KCl was 50 mM, and the concentration of MgSO 4 The concentration is 2mM.

[0052] The conductive nanomaterial aqueous solution is a carbon nanotube aqueous solution.

[0053] 3 μL of a 35.5 wt% aqueous solution of four-arm PEG acrylate, 2 μL of a 35.5 wt% aqueous solution of SHPEG-SH, 2.5 μL of an ion buffer and 17.5 μL of deionized water were mixed to obtain an ion conductive hydrogel.

[0054] S1, using screen printing technology to form a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode on a PET substrate with a thickness of 0.1 mm, respectively;

[0055] S2, pipette the 1.5 mg / mL carbon nanotube aqueous solution onto the carbon working electrode (the ratio of carbon nanotube aqueous solution to carbon working electrode is 1 μL:1 mm 2 ), 10Pa, and vacuum dried at 55°C for 7h to form a carbon working electrode modified with nanomaterials;

[0056] S3. The carbon working electrode, carbon counter electrode and Ag / AgCl reference electrode modified with nanomaterials are covered with 0.5 mm thick ion conductive hydrogel. The hydrogel can be successfully gelled after standing for 2 minutes to obtain a hydrogel electrochemical strain sensor.

[0057] Example 3

[0058] 55 mg of four-arm PEG acrylate with a molecular weight of 10000 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a four-arm PEG acrylate aqueous solution with a concentration of 35.5 wt%; 55 mg of SHPEG-SH with a molecular weight of 3400 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became transparent to obtain a SHPEG-SH aqueous solution with a concentration of 35.5 wt%.

[0059] The HCl concentration in the ionic buffer was 20 mM, (NH 4 ) 2 SO 4 The concentration was 10 mM, the concentration of KCl was 50 mM, and the concentration of MgSO 4 The concentration is 2mM.

[0060] The conductive nanomaterial aqueous solution is a carbon nanotube aqueous solution.

[0061] 3 μL of a 35.5 wt% aqueous solution of four-arm PEG acrylate, 2 μL of a 35.5 wt% aqueous solution of SHPEG-SH, 2.5 μL of an ion buffer and 17.5 μL of deionized water were mixed to obtain an ion conductive hydrogel.

[0062] S1, using screen printing technology to form a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode on a PET substrate with a thickness of 0.1 mm, respectively;

[0063] S2, pipette the 1.5 mg / mL carbon nanotube aqueous solution onto the carbon working electrode (the ratio of carbon nanotube aqueous solution to carbon working electrode is 5 μL:1 mm 2 ), 100Pa, 65℃ vacuum drying for 5h to form a carbon working electrode modified with nanomaterials;

[0064] S3. The carbon working electrode, carbon counter electrode and Ag / AgCl reference electrode modified with nanomaterials are covered with 1.5 mm thick ion conductive hydrogel. The hydrogel can be successfully gelled after standing for 5 minutes to obtain a hydrogel electrochemical strain sensor.

[0065] Experimental Example 1

[0066] 55 mg of four-arm PEG acrylate with a molecular weight of 10000 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became colorless and transparent, to obtain a four-arm PEG acrylate aqueous solution with a concentration of 35.5 wt%; 55 mg of SHPEG-SH with a molecular weight of 3400 was mixed with 100 mg of deionized water, vortexed, and ultrasonicated at room temperature for 1 hour until the solution became colorless and transparent, to obtain a SHPEG-SH aqueous solution with a concentration of 35.5 wt%.

[0067] The conductive nanomaterial aqueous solution is a carbon nanotube aqueous solution.

[0068] (1) The concentration of HCl in the ionic buffer is 20 mM, (NH 4 ) 2 SO 4 The concentration was 10 mM, the concentration of KCl was 50 mM, and the concentration of MgSO 4 The concentration is 2mM.

[0069] (2) Preparation of 80% water content hydrogel: 3 μL of 35.5 wt% four-arm PEG acrylate aqueous solution, 2 μL of 35.5 wt% SHPEG-SH aqueous solution, 2.5 μL of ionic buffer and 17.5 μL of deionized water were mixed.

[0070] Preparation of 85% water content hydrogel: 2.25 μL of 35.5wt% four-arm PEG acrylate aqueous solution, 1.5 μL of 35.5wt% SHPEG-SH aqueous solution, 2.5 μL of ion buffer and 18.75 μL of deionized water were mixed.

[0071] Preparation of 90% water content hydrogel: 1.5 μL of 35.5 wt% four-arm PEG acrylate aqueous solution, 1 μL of 35.5 wt% SHPEG-SH aqueous solution, 2.5 μL of ion buffer and 20 μL of deionized water were mixed.

[0072] (3) The working electrode, counter electrode and reference electrode on the PET substrate with a thickness of 0.1 mm were respectively formed into a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode by screen printing technology;

[0073] (4) Pipette a 1.5 mg / mL carbon nanotube aqueous solution onto the carbon working electrode (the ratio of carbon nanotube aqueous solution to carbon working electrode is 3 μL:1 mm 2 ), 55Pa, and vacuum dried at 60°C for 6h to form a carbon working electrode modified with nanomaterials;

[0074] (5) The carbon working electrode, carbon counter electrode and Ag / AgCl reference electrode modified with nanomaterials were covered with a 1 mm thick ion conductive hydrogel. The hydrogel was successfully gelled after standing for 3 min, and a hydrogel electrochemical strain sensor was obtained.

[0075] The pressure ion output of hydrogels with different water contents was studied. Scanning electron microscopy (SEM) images (e.g. Figure 3 Middle a, Figure 3 Medium b and Figure 3 (c) shows the porous structure of the hydrogel. The average size of the pores increases with the increase of the water content of the hydrogel, while the porosity decreases. Cyclic loading-unloading compression curves (e.g., Figure 3 (d) The typical cyclic stress-strain behavior of the hydrogel was observed to contain a hysteresis loop (e.g. Figure 3 f), which is due to the porous structure and hydrogen bonding of the hydrogel. As the water content increases, the elastic modulus decreases from 6.6 to 3.3 Pa (e.g. Figure 3 e). Figure 3 As shown in Figure e, the hysteresis ratio decreases sharply with the increase of water content. The hydrogel with a water content of 90% has an ultra-low hysteresis ratio of 2.54%. The low residual strain and low hysteresis ratio indicate that the hydrogel with a water content of 90% has a stable cross-linked structure and strong mechanical properties. The comprehensive mechanical properties show that the polyethylene glycol hydrogel can withstand cyclic loading and unloading under small strain.

[0076] The piezoresistance of hydrogels increases dramatically with increasing water content (e.g. Figure 3 g). The ionic pressure coefficients of the hydrogels with water contents of 80%, 85%, and 90% were calculated to be 316.1, 624.5, and 1970.4 nA / N, respectively (e.g. Figure 3h). It can be seen that the lower the mechanical strength of the hydrogel, the higher its sensitivity to force. In addition, as the water content increases, its decay time gradually shortens (e.g. Figure 3 (i) This is mainly due to the denser hydrogel network hindering the diffusion of ions and reducing the diffusion coefficient of ions. In addition to low strength, the hydrogel with 90% water content has excellent mechanical properties with small residual strain and low hysteresis, which can fully meet the requirements of small strain / stress detection and has high piezoelectric response sensitivity.

[0077] Experimental Example 2

[0078] The human pulse wave carries a large amount of physiological and pathological information. Pulse monitoring is of great significance for disease diagnosis, prevention of cardiovascular and cerebrovascular diseases, and scientific exercise training.

[0079] The electrochemical strain sensor prepared in Example 1 was attached to the wrist, neck, and fingertips to measure the radial artery (such as Figure 4 Middle a, Figure 4 Medium b and Figure 4 c), ulnar artery (such as Figure 4 Middle d, Figure 4 Zhongehe Figure 4 f), finger artery (such as Figure 4 Medium Figure 4 Medium h and Figure 4 i), carotid artery (such as Figure 4 Middle Figure 4 Medium K and Figure 4 The pulse waveform of the middle (l). The single pulse wave measured from these positions shows three characteristic peaks P1~P3. The pulse measurement results show that the electrochemical strain sensor based on piezoelectric ion hydrogel has ultra-high sensitivity and has potential clinical application value.

[0080] The pulse waveform of a person in the above motion state was measured by an electrochemical strain sensor. The results are as follows Figure 5 First, use the sports watch to determine the exercise status, and then measure the pulse waveform. The result is as follows Figure 5 As shown in the figure, before exercise, HR was 64, Ia was 5.0nA, and Esr was 31%. As the intensity of exercise increased, the intensity of the P2 characteristic peak gradually decreased until it disappeared, while the relative peak intensity of P3 gradually increased. Under aerobic and anaerobic exercise conditions, only P1 and P3 peaks (such as Figure 5 Medium f and Figure 5i). The Esr values ​​of fat burning exercise and aerobic exercise are lower than the resting state. As the intensity of exercise increases, the Ia and Esr values ​​increase slowly during aerobic exercise, while the Ia value drops sharply and the Esr value increases sharply when anaerobic exercise is reached. After stopping exercise, HR and Esr gradually decrease, and Ia gradually increases. One hour after stopping exercise, the HR before exercise is 72, Ia is 6.6nA, and Esr is 25%. These data show that proper exercise makes a person's pulse stronger and more stable.

[0081] Study the changes in the pulse signal when a person holds his breath and breathes. Figure 6 As shown in a, it is a continuous pulse waveform of breathing for 15 seconds, holding the breath for 30 seconds, and breathing for 15 seconds. During the breath holding process, the intensity of the P2 characteristic peak is higher than the P3 characteristic peak (such as Figure 6 Middle b, Figure 6 Middle c, Figure 6 Medium D and Figure 6 However, during rebreathing, the intensity of the P2 characteristic peak is lower than that of the P3 characteristic peak (e.g. Figure 6 Medium f and Figure 6 g). HR, Ia, and Esr are calculated every 5 seconds, and the change curves are plotted. The heart rate increases slowly with breath holding and returns to normal after rebreathing. Ia decreases first and then increases during breath holding, and increases sharply after rebreathing. E increases first and then decreases during breath holding, and increases sharply after rebreathing. These results show that piezoelectric ion hydrogel strain sensors can be used for respiratory state detection and have broad application prospects in diving.

[0082] Experimental Example 3

[0083] Intelligent speech recognition combining the acoustic vibration spectrum obtained by the electrochemical strain sensor prepared in Example 1 with machine learning. However, individuals with vocal cord disorders are unable to produce acoustic vibration spectra, which limits its application. In order to avoid the above limitations, it was found that piezoelectric ion dynamics in hydrogels can convert force / strain into precise electrical signals. And piezoelectricity exists in all ion-conductive hydrogels, covering a wide range of mechanical properties. Speech recognition using piezoelectric ion hydrogel dye sensors.

[0084] like Figure 7 As shown in Figure a, a piezoelectric hydrogel strain sensor attached to the user's exogenous throat skin detects throat movement signals. The piezoelectric output current generated by speech is between 15 and 50 nanometers, which is much larger than the current generated by the carotid artery. This result proves that the amplitude of throat movement during speech is between swallowing and pulse. Figure 7 Middle b, Figure 7 Middle c, Figure 7 Middle d, Figure 7 Middle e, Figure 7 Medium f and Figure 7As shown in Figure g, the sensor generates positive and negative current peaks when speaking, which is caused by the dynamic change of ion distribution. This is different from the weak signal change of piezoresistive sensor and will provide more prominent feature information for speech recognition.

[0085] The results show that the movement of the larynx during speech consists of three parts: before phonation, the larynx tightens, driving the sensor to bend outward, generating a positive piezoelectric current; during phonation, the larynx moves slightly inward and outward, generating a piezoelectric current that fluctuates around zero; after phonation, the larynx loosens, driving the sensor to bend outward, generating a negative piezoelectric current. First, it was found that the degree of throat tightening is directly related to the position of the tongue. The piezoelectric output is large when the tongue is flat, indicating a large degree of larynx tightening, while the piezoelectric output is small when the tongue is rolled ( Figure 7 In addition, the piezoelectric current amplitude when the tongue is flat is smaller than that when the tongue is rolled. The piezoelectric current of different tones shows obvious changes during the laryngeal relaxation process ( Figure 7 (c). Figure 7 The d in the figure is the piezoelectric signal waveform of the letters A to G. The ion piezoelectric output signal waveform usually consists of a 45-degree inflection point and a peak for monosyllabic or disyllabic pronunciations, which can be used to recognize most speeches. The waveforms of A and C, as well as the waveforms of train and treat, are very similar (e.g. Figure 7 Medium D and Figure 7 There is no significant difference in the waveforms between words with voiceless consonants and words with voiced consonants. Some words have more inflection points and peaks, such as words containing n or m (e.g. Figure 7 The waveform of a sentence has more inflection points and is therefore easier to identify (e.g. Figure 7 The inflection points in the waveform increase as the number of syllables in the sentence increases (e.g. Figure 7 The above experimental results prove that piezoelectric hydrogel strain sensors have good application prospects in the field of speech recognition.

[0086] For intelligent speech recognition, a random forest-based machine learning workflow is designed to improve the classification accuracy of audio signals, such as Figure 8 As shown. Figure 8 As shown in a, the workflow includes feature extraction, feature scaling and classification. The training parameters of the network are shown in the experimental section. Spectrograms of 6 daily sentences were collected, with 630 samples for each sentence. As the amount of data increases, the average accuracy of recognition increases and the average error decreases. The accuracy rate reaches 87%, which is convenient for patients to use. The final classification accuracy of the optimized algorithm under 630 data can reach 96.3%. On each classification task, its AUC value is close to 1, indicating that the algorithm is effective (such as Figure 8(d) Due to the high stability and reliability of strain sensors, the accuracy of speech recognition has the potential to be further improved through deep learning algorithms.

[0087] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. An application of a hydrogel electrochemical strain sensor, which is used in the preparation of a low-force monitoring device, a pulse detection device or an artificial larynx, characterized in that: The hydrogel electrochemical strain sensor includes a PET substrate, a working electrode, a counter electrode, a reference electrode and an ion-conductive hydrogel; The working electrode, the counter electrode and the reference electrode are sequentially located on the PET substrate; The working electrode, the counter electrode and the reference electrode are covered with the ion conductive hydrogel on top; The thickness of the ion conductive hydrogel covering the surfaces of the working electrode, the counter electrode and the reference electrode is 0.2 to 1.5 mm; The ion conductive hydrogel is prepared from a four-arm PEG acrylate aqueous solution, a SHPEG-SH aqueous solution, an ion buffer and deionized water; the volume ratio of the four-arm PEG acrylate aqueous solution, the SHPEG-SH aqueous solution, the ion buffer and the deionized water is 6:4:5:25-100; the concentration of the four-arm PEG acrylate aqueous solution is 35.5wt%, and the concentration of the SHPEG-SH aqueous solution is 35.5wt%; The ion buffer is prepared by using deionized water as solvent and adding HCl, (NH4)2SO4, KCl and MgSO4; the HCl concentration in the ion buffer is 20mM, the (NH4)2SO4 concentration is 10mM, the KCl concentration is 50mM, and the MgSO4 concentration is 2mM.

2. A method for preparing a hydrogel electrochemical strain sensor, wherein the hydrogel electrochemical strain sensor comprises a PET substrate, a working electrode, a counter electrode, a reference electrode and an ion conductive hydrogel; The working electrode, the counter electrode and the reference electrode are sequentially located on the PET substrate; the tops of the working electrode, the counter electrode and the reference electrode are covered with the ion conductive hydrogel; The thickness of the ion conductive hydrogel covering the surfaces of the working electrode, the counter electrode and the reference electrode is 0.2 to 1.5 mm; The ion conductive hydrogel is prepared from a four-arm PEG acrylate aqueous solution, a SHPEG-SH aqueous solution, an ion buffer and deionized water; the volume ratio of the four-arm PEG acrylate aqueous solution, the SHPEG-SH aqueous solution, the ion buffer and the deionized water is 6:4:5:25-100; the concentration of the four-arm PEG acrylate aqueous solution is 35.5wt%, and the concentration of the SHPEG-SH aqueous solution is 35.5wt%; The ion buffer is prepared by using deionized water as solvent and adding HCl, (NH4)2SO4, KCl and MgSO4; the ion buffer has a HCl concentration of 20 mM, a (NH4)2SO4 concentration of 10 mM, a KCl concentration of 50 mM, and a MgSO4 concentration of 2 mM, characterized in that: The preparation method comprises the following steps: S1, using screen printing technology to form a carbon working electrode, a carbon counter electrode and an Ag / AgCl reference electrode on the working electrode, the counter electrode and the reference electrode on the PET substrate respectively; S2, pipetting the conductive nanomaterial aqueous solution onto the carbon working electrode described in S1, and vacuum drying to form a nanomaterial-modified carbon working electrode; S3. Cover the top of the carbon working electrode modified with nanomaterials prepared in S2, the carbon counter electrode prepared in S1, and the Ag / AgCl reference electrode prepared in S1 with ion conductive hydrogel, and let it stand for 2 to 5 minutes to obtain a hydrogel electrochemical strain sensor.

3. The preparation method according to claim 2, characterized in that: The thickness of the PET substrate in S1 is 0.1 mm.

4. The preparation method according to claim 2, characterized in that: The concentration of the conductive nanomaterial aqueous solution in S2 is 1.5 mg / mL; the ratio of the conductive nanomaterial aqueous solution in S2 to the carbon working electrode is 1~5 μL:1 mm 2 ; The vacuum degree of the vacuum drying in S2 is 10~100Pa, the temperature of the vacuum drying is 55~65℃, and the vacuum drying time is 5~7h.

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