MXene-based conductive hydrogel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of flexible conductive materials, and particularly relates to MXene-based conductive hydrogel as well as a preparation method and application thereof. The conductive hydrogel disclosed by the invention is a compound of PVA (Polyvinyl Alcohol), PAM (Polyacrylamide) and MXene; and carrying out thermal initiation reaction in the presence of a cross-linking agent. The conductive hydrogel has excellent flexibility, stretchability, fatigue resistance and self-adhesion, and is wide in sensing response interval, relatively high in sensitivity and high in response recovery speed; the material can be used for preparing a biological sensing electrode or a biological strain sensor, can be used as an implantable or wearable device, and can be used for various scenes such as human body limb movement monitoring, respiratory disease judgment, voice recognition or fatigue driving detection.

Description

Technical Field

[0001] The invention belongs to the technical field of flexible conductive materials, and specifically relates to a conductive hydrogel and a preparation method and application thereof. Background Art

[0002] Conductive hydrogels are widely used in flexible electronics, artificial skin, tissue engineering and other fields. Traditional bioelectronic devices are mostly based on metals or inorganic materials, but these materials differ greatly from biological tissues in mechanical and chemical properties, often leading to poor biocompatibility or local inflammatory reactions. Therefore, conductive hydrogels that can match biological tissues well have gradually become ideal alternative materials, especially for wearable and implantable bioelectronic devices.

[0003] However, existing conductive hydrogels still face many key technical bottlenecks in practical applications and are difficult to meet the requirements of use in complex biological environments.

[0004] First, there is a significant contradiction between the conductivity and mechanical properties of conductive hydrogels. Conductivity is usually achieved by adding conductive polymers or conductive fillers, but these additions can lead to uneven hydrogel structure and decreased mechanical strength, thereby reducing the flexibility and durability of the material. This problem is particularly prominent in wearable devices and bio-implanted devices that require high flexibility and fatigue resistance. How to optimize the mechanical properties of the material while maintaining high conductivity so that it has good durability in a dynamic environment is a difficult problem that needs to be solved urgently.

[0005] In addition, conductive hydrogels need to have high biocompatibility and good tissue adaptability in biological applications. The mechanical properties of hydrogels should match the softness and elasticity of biological tissues to adapt to the dynamic changes of the tissue surface and avoid irritation or damage caused by excessive rigidity of the material. This matching is particularly critical in flexible biosensors and implantable electronic devices, because the long-term use of the equipment requires the material to form a reliable and comfortable contact with the tissue.

[0006] Currently, conductive hydrogels are prepared mainly through two methods: one is a single hydrogel network based on conductive polymers, and the other is a nanocomposite structure formed by incorporating conductive fillers (such as carbon nanotubes, graphene, MXene or metal nanoparticles) into non-conductive hydrogels. However, the former usually exhibits low ductility and durability due to its rigid structure, while the latter, when incorporating a large amount of conductive fillers, will lead to a decrease in the mechanical properties of the hydrogel, such as reduced stretchability and fatigue resistance.

[0007] In summary, how to develop a conductive hydrogel with high conductivity, excellent mechanical properties, long-term stability and biocompatibility to meet the needs of flexible electronic devices, biosensors and tissue engineering is a core problem that needs to be solved urgently in the current technical field.

[0008] Polyvinyl alcohol (PVA) and polyacrylamide (PAM) hydrogels have been widely studied due to their biocompatibility and good mechanical properties. Combining the two with two-dimensional MXene nanomaterials (such as Ti3C2Tx) will significantly improve the conductivity of the hydrogel and enhance the fatigue resistance while maintaining the flexibility and stretchability of the hydrogel. In addition, embedding MXene nanosheets into the PVA / PAM matrix by physical mixing can enhance the structural stability of the hydrogel, making it have great application potential in the fields of sensing, medical devices, etc. There is no report at present. Summary of the Invention

[0009] The purpose of the present invention is to provide a novel MXene-based conductive hydrogel with good mechanical properties, conductivity and biocompatibility, as well as its preparation method and application, to meet the requirements for conductive and flexible materials in bioelectronic devices, wearable devices and tissue engineering.

[0010] The MXene-based conductive hydrogel provided by the present invention is a composite of PVA, PAM and MXene, and is prepared by a thermal initiation reaction in the presence of a cross-linking agent. The specific preparation steps are as follows:

[0011] S1. Ultrasonically disperse the MXene solution in a nitrogen atmosphere at a low temperature of 0-5°C for 30-40 min to uniformly disperse it;

[0012] S2. Dissolve and mix a certain amount of cross-linking agent N,N'-methylenebisacrylamide, thermal initiator ammonium persulfate and acrylamide monomer to obtain an acrylamide mixed solution;

[0013] S3. Add PVA to the acrylamide mixed solution obtained in S2 and stir well for 30-40 min;

[0014] S4. Add the MXene dispersion to the PVA and acrylamide mixed solution obtained in S3, uniformly disperse it, stir well and mix for 60-90 min, then fill with nitrogen and ultrasonically disperse for 1-2 h;

[0015] S5. Pour the mixed dispersion into a mold and carry out thermal initiation at 60-70°C for 4-6 h to obtain a PVA / PAM / MXene hydrogel.

[0016] Furthermore:

[0017] In S1, the concentration of the MXene solution is 18-20 mg / ml.

[0018] In S2, in the acrylamide thermal initiation dispersion system, the mass fraction of acrylamide is 30-40%, the cross-linking agent is 0.2-0.3 mol% of the molar amount of acrylamide monomer, and the initiator is 0.2-0.3 mol% of the molar amount of acrylamide monomer.

[0019] In S3, the mass fraction of the PVA solution is 10-12%, and the volume ratio of the PVA and acrylamide mixture is 1:1-1:1.2.

[0020] In S4, the mass percentage of MXene is 3.0-4.0 mg / ml; nitrogen needs to be filled into the reaction vessel during ultrasonic treatment, and the temperature is controlled below room temperature.

[0021] In S5, the mold is a sheet-shaped, cylindrical or barbell-shaped mold.

[0022] The conductive hydrogel prepared by the present invention has excellent flexibility, stretchability, fatigue resistance, and self-adhesion. It has a wide sensing response range (5% to 500%), high sensitivity (GF1 = 2.43, GF2 = 5.47), a fast response recovery speed (<250 ms), and excellent bending resistance stability (more than 100 cycles at 5% strain).

[0023] Based on these characteristics, the PVA / PAM / MXene hydrogel of the present invention can have multiple uses. For example, it can be made into a sensing electrode, a strain sensor, etc., and used as an implantable or wearable device for scenarios such as human limb movement monitoring, respiratory disease diagnosis, speech recognition, and fatigue driving detection; for example, fatigue driving can be judged by detecting the blinking frequency, gesture recognition can be performed by detecting the finger bending degree, speech recognition can be performed by detecting the vocal cord vibration, and so on.

[0024] Compared with traditional hydrogel materials, the present invention can effectively improve the sensitivity and stability of the sensor and still maintain good performance under long-term wearing and high-frequency movement conditions. The hydrogel strain sensor can real-time monitor the human body's motion state, respiratory rate, and speech signal, provide accurate data support, and provide reliable technical guarantees for applications such as early diagnosis of respiratory diseases, speech input systems, and fatigue driving detection.

[0025] The technical features and advantages of the present invention are mainly as follows:

[0026] (1) Using MXene nanosheets as the conductive reinforcement phase and combining with the PVA / PAM double network structure to construct a composite conductive hydrogel with conductivity, stretchability, stability, and adhesion. Through the synergistic effect of the biocompatible polymer substrate (PVA / PAM) and MXene, the problems of poor biocompatibility and single function of traditional conductive hydrogels are solved.

[0027] (2) The strain sensor prepared from this hydrogel has a wide strain detection range (0 - 500%), and can be applied to a variety of human motion monitoring scenarios (such as joint bending, micro-expression recognition, etc.). Its self-adhesion can achieve close fitting with the skin, maintain stable output in complex working environments, and provide a new integrated solution for wearable electronics. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the structure of the PVA / PAM / MXene hydrogel strain sensor provided in Example 1.

[0029] Figure 2 It is an effect diagram of the adhesiveness of the PVA / PAM / MXene hydrogel provided in Example 1.

[0030] Figure 3 It is a schematic diagram of the deformation (tensile / torsion) - recovery of the PVA / PAM / MXene hydrogel provided in Example 1. In the figure, M0 - M4.0 refers to the PVA / PAM / MXene hydrogel with MXene content of 0 - 4.0 mg / ml.

[0031] Figure 4 It is the stress - strain curve and toughness histogram of the PVA / PAM / MXene hydrogel provided in Example 1.

[0032] Figure 5 It is the fracture strength - fracture strain diagram of the PVA / PAM / MXene hydrogel provided in Example 1.

[0033] Figure 6 It is the cyclic stability of the PVA / PAM / MXene hydrogel provided in Example 1.

[0034] Figure 7 It is the corresponding resistance change of the PVA / PAM / MXene hydrogel to coughing provided in Example 1.

[0035] Figure 8 It is the response recovery time of the PVA / PAM / MXene hydrogel provided in Example 1.

[0036] Figure 9 It is the corresponding resistance change of the PVA / PAM / MXene hydrogel to finger bending provided in Example 1.

[0037] Figure 10 It is the corresponding resistance change of the PVA / PAM / MXene hydrogel to emitting different letters provided in Example 1.

[0038] Figure 11It is the resistance change corresponding to blinking of the PVA / PAM / MXene hydrogel provided in Example 1.

[0039] Figure 12 It is the resistance change corresponding to stretching of the PVA / PAM / MXene hydrogel provided in Example 1.

[0040] Figures 13 - 14 It is the biocompatibility test of the PVA / PAM / MXene hydrogel provided in Example 1 on L929 cells. Detailed implementation manners

[0041] The present invention will be further introduced below through examples in conjunction with the accompanying drawings.

[0042] Example 1, Preparation of PVA / PAM / MXene conductive hydrogel

[0043] S1. Ultrasonic the MXene solution in a nitrogen atmosphere at 5 °C for 30 min to uniformly disperse it; the concentration of the MXene solution is 18 mg / ml;

[0044] S2. Dissolve and mix a certain amount of crosslinking agent N-N-methylenebisacrylamide, thermal initiator ammonium persulfate and acrylamide monomer to obtain an acrylamide mixture; in the acrylamide thermal initiation dispersion system, the mass fraction of acrylamide is 40%, the crosslinking agent is 0.2 mol% of the molar amount of acrylamide monomer, and the initiator is 0.3 mol% of the molar amount of acrylamide monomer;

[0045] S3. Add PVA to the acrylamide mixture obtained in S2 and stir well for 30 min; the mass fraction of the PVA solution is 10%, and the volume ratio of PVA to the acrylamide mixture is 1:1.

[0046] S4. Add the MXene dispersion to the PVA and acrylamide mixture obtained in S3, uniformly disperse it, stir and mix well for 60 min, then fill with nitrogen and ultrasonically disperse for 1 h; the mass percentage of MXene is 3.0 mg / ml; nitrogen needs to be filled into the reaction vessel during ultrasonic treatment, and the temperature is controlled below room temperature.

[0047] S5. Pour the mixed dispersion into a mold and carry out thermal initiation at 65 °C for 4 h to obtain a PVA / PAM / MXene conductive hydrogel.

[0048] The performance test results of the prepared PVA / PAM / MXene conductive hydrogel are shown in the attached Figures 1 - 8 related figures.

[0049] Example 2, Biocompatibility test of PVA / PAM / MXene conductive hydrogel

[0050] L929 cells (mouse fibroblasts) were cultured using the extract of the hydrogel, and a cell viability test was conducted. See the appendix Figure 13 and 14 , after culturing for a certain period of time, the CCK-8 kit was used to perform live / dead staining on the cells. Compared with the control group, it was observed that the cell morphology in the MXene hydrogel experimental group also presented a normal spindle shape, and the number of cells in the two groups was similar. It was proved that the cell activity of the MXene hydrogel group did not decrease, further proving its cell compatibility.

[0051] When the raw material dosage ratio and process parameter data in Example 1 were changed within the specified range, the prepared PVA / PAM / MXene conductive hydrogel all had the same or similar performance as the appendix Figures 1 - 8 , appendix Figure 13 and 14 . The specific details are not shown one by one.

[0052] Example 3, sensitivity test of the above PVA / PAM / MXene hydrogel as a strain sensor

[0053] The sensitivity of the hydrogel sensor was tested by combining a universal testing machine and an electrochemical workstation. The universal testing machine stretched the sensor and applied different strains, and the electrochemical workstation was connected to both ends of the sensor to output the signal of the resistance change. The sensitivity of the sensor is usually expressed by the gauge factor (GF), and its calculation formula is: GF = (ΔR / R0) / ε. ΔR = R - R0. See the appendix Figure 12 , when a small strain (0 - 50%) was applied to the sensor, GF1 = 2.43 was calculated. When a large strain (100 - 500%) was applied, GF2 = 5.47, showing a high sensitivity.

[0054] Example 4, the above MXene-based composite hydrogel strain sensor is used for early warning of fatigue driving;

[0055] The PVA / PAM / MXene conductive hydrogel of the present invention was cut into the required rectangle, and copper wires were led out from both ends to assemble an MXene-based composite hydrogel strain sensor (see Figure 1 ), to evaluate the performance of the present invention.

[0056] The fatigue state of a driver is detected by monitoring the blinking frequency. This sensor can accurately capture minute strain changes in the eye, and by analyzing the fluctuations in the blinking frequency, it can judge the driver's alertness in real time. The flexible design of the hydrogel enables the sensor to fit comfortably on the skin, avoiding discomfort to the driver while ensuring stability and accuracy during long-term use. By continuously monitoring the blinking frequency, when abnormal fluctuations occur, the system will issue a warning in a timely manner to help prevent fatigue driving accidents. As attached Figure 11 , when the eyelid blinks, the resistance of the hydrogel sensor changes, and a peak can be obtained in the resistance change curve. When the eyelid blinks slower, correspondingly, the frequency of the peak appearance also becomes lower. Therefore, we can determine whether the driver is fatigued by the signal output by the hydrogel sensor.

[0057] Example 5: The MXene-based composite hydrogel strain sensor is used to detect the degree of finger bending for gesture recognition.

[0058] When the sensor detects the finger bending angle, the resistance change of the sensor is positively correlated with the bending angle, and obvious and stable resistance changes are shown at 30°, 60°, and 90° bending. See attached Figure 9 , and the corresponding ΔR / R0 changes from 0 to 1.9%, 3.4%, and 4.7%. This change indicates that the sensor has high sensitivity to finger bending, can accurately capture minute gesture changes, and can achieve efficient response and accurate recognition in the gesture recognition system. It can be seen that this strain sensor can accurately sense the finger bending movement, provide the data required by the gesture recognition system through real-time monitoring of the finger bending angle, and can be widely applied in fields such as intelligent control and virtual reality.

[0059] Example 6: The MXene-based composite hydrogel strain sensor is used to detect vocal cord vibration.

[0060] Specifically, it mainly tests the vocal cord vibration signals of coughing and pronouncing different letters. See attached Figure 10 , when a person pronounces the letters "M" and "X", the sensor causes the resistance change of the sensor through the strain brought by the vocal cord vibration, and the resistance changes brought by pronouncing the same letter show repeatable and highly similar peaks, proving that we can judge the pronounced letter by the characteristics of the resistance change curve. The resistance changes during the pronunciation of different letters also show obviously different peaks, proving that it can accurately capture the vocal cord vibration signal.

Claims

1. A preparation method of MXene-based conductive hydrogel, characterized in that, The specific steps are as follows: S1. Ultrasonic the MXene solution for 30 - 40 min in a nitrogen atmosphere at a low temperature of 0 - 5°C to uniformly disperse it; S2. Fully dissolve and mix the crosslinking agent N,N'-methylenebisacrylamide, the thermal initiator ammonium persulfate, and the acrylamide monomer to obtain an acrylamide mixed solution; S3. Add PVA to the acrylamide mixed solution obtained in S2 and stir well for 30 - 40 min; S4. Add the MXene dispersion to the PVA and acrylamide mixed solution obtained in S3, uniformly disperse it, stir and mix well for 60 - 90 min, then fill with nitrogen and ultrasonically disperse for 1 - 2 h; S5. Pour the mixed dispersion into a mold and carry out thermal initiation at 60 - 70°C for 4 - 6 h to obtain a MXene-based conductive hydrogel, denoted as PVA / PAM / MXene hydrogel.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of the MXene solution is 18 - 20 mg / ml.

3. The preparation method according to claim 1, wherein, In step S2, the mass fraction of acrylamide in the acrylamide mixed solution is 30 - 40%, the crosslinking agent N,N'-methylenebisacrylamide is 0.2 - 0.3 mol% of the molar amount of the acrylamide monomer, and the initiator ammonium persulfate is 0.2 - 0.3 mol% of the molar amount of the acrylamide monomer.

4. The preparation method according to claim 1, characterized in that, In step S3, the mass fraction of the PVA solution is 10 - 12%, and the volume ratio of PVA to the acrylamide mixed solution is 1:1 - 1:1.

2.

5. The preparation method according to claim 1, characterized in that, In step S4, the mass percentage of MXene is 3.0 - 4.0 mg / ml; nitrogen is filled into the reaction vessel during ultrasonic treatment, and it is carried out below room temperature.

6. The preparation method according to claim 1, wherein, In step S5, the mold is sheet-shaped, cylindrical or barbell-shaped.

7. A MXene-based conductive hydrogel obtained by the preparation method according to any one of claims 1 - 6.

8. Use of the MXene-based conductive hydrogel according to claim 7 in the preparation of a biosensing electrode or a bio-strain sensor.

9. The use according to claim 8, wherein the biosensing electrode or the bio-strain sensor is used as an implantable or wearable device for human limb movement monitoring, respiratory disease judgment, voice recognition or fatigue driving detection scenarios.

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