A method for preparing a capacitive sensing hydrogel

Abstract

The application discloses a preparation method of a capacitive sensing hydrogel, which introduces EGCG as a protective modification layer of MXene nanosheets, enhances the oxidation resistance of MXene, improves the continuous sensing and sensitivity of the MXene hydrogel, introduces 4ARM-PEG-ACLT as a crosslinking agent, utilizes the dynamic covalent bond between APBA and EGCG as a secondary crosslinking point, constructs a double crosslinking point network, effectively improves the mechanical strength and rapid recovery ability of the hydrogel, solves the defects of poor deformation ability and easy oxidation of MXene in the design of a sensor device, and the preparation method is simple and efficient, so that the capacitive sensing hydrogel sensor makes a solid step towards practical application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gel materials, and particularly relates to a preparation method of a capacitive sensing hydrogel. BACKGROUND

[0002] With the rapid development of wearable sensors, there is an increasing demand for multifunctional conductive soft materials, and MXene composite materials have become key materials in the design of next-generation sensor devices. However, existing MXene composite materials have high rigidity, limited stretchability, and poor biocompatibility, which is not conducive to daily wear and use. To solve this problem, researchers integrate MXene nanosheets into hydrogels to construct MXene composite hydrogel materials with softness and biocompatibility. Such materials combine the excellent conductivity of MXene and the softness of hydrogels, providing a new approach for the development of flexible sensors.

[0003] However, there are some challenges in current MXene composite hydrogels. MXene is easily oxidized in an environment rich in water and oxygen, which leads to a decrease in its conductivity and mechanical properties, affecting the long-term stability and durability of the composite hydrogel. Therefore, when designing MXene gels, it is necessary to consider how to overcome the oxidation problem and ensure its stability during long-term use. In addition, when using hydrogels as a sensing substrate, although they benefit from their high water content and thus have high biocompatibility, they also have poor mechanical strength. In summary, MXene composite hydrogels have good prospects as wearable sensor materials, but still need to overcome challenges such as poor deformation ability, instability, and easy oxidation to achieve their widespread application in the field of flexible sensors. SUMMARY

[0004] Technical problems solved:

[0005] The present application provides a preparation method of a capacitive sensing hydrogel, which addresses the technical problems of easy oxidation of traditional MXene in water, poor deformation ability, large relaxation of hydrogels in capacitive pressure sensing, and low mechanical strength of hydrogels.

[0006] Technical solutions:

[0007] To achieve the above-mentioned purpose, the present application is implemented by the following technical solutions:

[0008] A preparation method of a capacitive sensing hydrogel, which uses (-)-epigallocatechin gallate (EGCG) as a protective modification layer for MXene nanosheets, and uses four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization. The dynamic covalent bond between 3-acrylamidophenylboronic acid (APBA) and EGCG is used as a secondary crosslinking point to construct a double crosslinking point network, thereby preparing a capacitive sensing hydrogel.

[0009] Furthermore, the preparation method specifically includes the following steps:

[0010] Step 1: Preparation of MXene aqueous dispersion: Monolayer or few-layer Ti3C2T is synthesized from Ti3AlC2MAX phase material by etching the Al layer with HF. x 5 mg mL was obtained -1 MXene dispersion;

[0011] Step 2, Introduce EGCG to protect MXene: Take 1 mL of the 5 mg EGCG obtained in Step 1. -1 MXene dispersion was prepared and ultrasonically dispersed at 40 kHz for 30-50 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with pH 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 7.0-8.5; finally, the mixture was stirred at 500-1000 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0012] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion under a nitrogen gas flow for 5-30 minutes, then place the sample vial in an ultrasonic bath and ultrasonically disperse it at a frequency of 40 kHz for 5-10 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, ultrasonicate at a frequency of 40 kHz for 20-40 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0013] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0014] Further, the step 1 is specifically taking 40 mL of 9M HCl solution into a polytetrafluoroethylene beaker with a volume of 100 mL, and placing the beaker in an ice water bath, then pouring 2 g of LiF into it and continuously stirring for 30-60 minutes until the LiF is completely dissolved; then, 2 g of Ti3AlC2MAX phase material is poured into the beaker at a speed of 0.5 g per minute to make it fully contact with HCl and LiF, and stirred in a 35°C water bath at a speed of 400 rpm for 24 hours to obtain a suspension; then, the suspension is washed with deionized water, centrifuged at 3500 rpm, and the precipitate is collected and the washing step is repeated until the pH of the supernatant reaches 6, and each time the centrifugation time is 5-10 minutes, and the centrifuge tube is shaken for 5-10 minutes after centrifugation to make the black solid fully dispersed; finally, ultrasonic stripping is performed at a frequency of 40 kHz in an ice water bath environment for 1-2 hours, and then centrifuged at 3500 rpm for 1 hour, and the supernatant is reserved to obtain a few-layer or single-layer Ti3C2T x .

[0015] Further, in the step 2, EGCG is used to protect MXene and form a stable MXene@EGCG dispersion liquid, and a hydrogen bond "Ar-OH…OHMXene" between the phenolic hydroxyl group of EGCG and the hydroxyl group on the surface of MXene is formed, wherein "…" represents a hydrogen bond, Ar-OH represents the phenolic hydroxyl group in EGCG, and OH MXene represents the hydroxyl group on the surface of MXene, so that a more stable and effective antioxidant mechanism is achieved, and the continuous sensing of MXene in the hydrogel is facilitated.

[0016] Further, in the step 3, the dynamic covalent bond of APBA and EGCG is introduced as a secondary crosslinking point, which further effectively improves the mechanical bearing capacity, fatigue resistance and recovery speed.

[0017] Original explanation: The preparation method of the present application introduces EGCG as a protective modification layer of MXene nanosheet, so that the MXene forms a stable aqueous dispersion liquid, enhances the antioxidant capacity of MXene, and improves the continuous sensing and sensitivity of the MXene hydrogel. By introducing 4ARM-PEG-ACLT with more excellent spatial extension as a crosslinking agent for Aam polymerization, and using the dynamic covalent bond of APBA and EGCG as a secondary crosslinking point, a double crosslinking point network is constructed, which effectively improves the mechanical strength and rapid recovery ability of the hydrogel. When the compression strain reaches 100%, the sample will not break, and after the stress is removed, it can quickly recover to the initial state. The introduction of few-layer or single-layer MXene makes the hydrogel have better capacitive effect, and the sensitivity and continuous compression resistance are more excellent than other materials. The preparation method proposed in the present application is simple and efficient, which makes the hydrogel capacitive sensor take a solid step towards practical application.

[0018] Beneficial effects:

[0019] The application provides a preparation method of a capacitive sensing hydrogel, which has the following beneficial effects compared with the prior art:

[0020] 1. The method improves the mechanical properties and fatigue resistance of the capacitive sensing hydrogel, which helps to realize the practical application of the capacitive sensing hydrogel;

[0021] 2. Compared with the traditional capacitive sensing hydrogel, the capacitive sensing hydrogel preparation method has high strength, fast recovery and fatigue resistance, which can effectively improve the stability of MXene in water and enhance the continuous sensing of MXene in the hydrogel;

[0022] 3. The application effectively improves the strength of the hydrogel, and when the compression strain reaches 100%, the sample is still not broken, and after the stress is removed, it can quickly recover to the initial state;

[0023] 4. The fatigue resistance is effectively improved, and when the maximum compression strain is set to 80% and continuously tested for 100 times, the sensing effect does not show observable attenuation;

[0024] 5. The preparation method is simple and efficient, which makes the capacitive sensing hydrogel sensor take a solid step towards practical application. After 1 hour of ultrasonic treatment at a frequency of 40 kHz under ice water bath, centrifugation at 3500 rpm for 1 hour, and taking the supernatant to obtain few-layer or single-layer Ti3C2Tx, the MXene obtained by this method has thinner size and better dispersibility, and the flexible material prepared by this method can obtain better capacitive sensing effect, such as higher sensitivity of capacitive sensing. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a network diagram of the capacitive sensing hydrogel of the application, wherein a, b and c are the chemical formulas of 4ARM-PEG-ACLT, APBA and EGCG respectively, and d is a preparation process diagram;

[0026] Figure 2 It is an optical image of the capacitive sensing hydrogel of the application under extreme compression conditions, wherein a is a TEM image of EGCG-protected MXene in water, b is a TEM image of exfoliated single MXene in water, and c is a SEM image of a freeze-dried sample of the hydrogel;

[0027] Figure 3 It is a performance diagram of the capacitive sensing hydrogel of the application under high-pressure mechanical environment, wherein a is a diagram of directly compressing the hydrogel using a sharp blade without causing permanent damage to the hydrogel, and b is a diagram of continuously compressing the gel to a strain of about 80% without causing damage to the gel;

[0028] Figure 4 Figures for characterizing the high-strength mechanical properties of the capacitive sensing hydrogel of the present application, wherein a is a compression strength figure, b is a compression strength cycle figure, c is a residual strain only figure, d is a Young's modulus and toughness figure;

[0029] Figure 5 Figures for characterizing the ultra-sensitive sensing properties of the capacitive sensing hydrogel of the present application, wherein a is a strain capacitive sensing figure, b is a capacitive sensing sensitivity coefficient figure;

[0030] Figure 6 Figures for characterizing the sensing fatigue resistance of the capacitive sensing hydrogel of the present application, wherein a is a low-strain capacitive sensing figure, b is a high-strain capacitive sensing figure, c is a high-strain retention sensing figure, d is a capacitive sensing figure at different compression speeds, e is a 100-time compression sensing figure;

[0031] Figure 7 Figures for characterizing the mechanical and electrical properties of the capacitive sensing hydrogel of the present application after adjusting the concentration of APBA and MXene@EGCG, wherein a is a strain capacitive sensing figure after adjusting the concentration of MXene@EGCG, b is a strain capacitive sensing figure after adjusting the concentration of MXene@EGCG, c is a strain capacitive sensing figure after adjusting the concentration of APBA, d is a strain capacitive sensing figure after adjusting the concentration of APBA. DETAILED DESCRIPTION

[0032] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below. In the following description, specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many different ways than those described herein, and those skilled in the art can make similar improvements without departing from the scope of the present application, so the present application is not limited to the specific implementation disclosed below.

[0033] Example 1:

[0034] A method for preparing a capacitive sensing hydrogel, using (-)-epigallocatechin gallate (EGCG) as a protective modification layer for MXene nanosheets, using four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization; using the dynamic covalent bond between 3-acrylamidophenylboronic acid (APBA) and EGCG as a secondary crosslinking point to construct a double crosslinking point network, thereby preparing a capacitive sensing hydrogel, the preparation method specifically comprising the following steps:

[0035] Step 1, preparing a MXene aqueous dispersion, using Ti3AlC2MAX phase material, etching the Al layer with HF to synthesize single-layer or few-layer Ti3C2T x -1 ​MXene dispersion: 40 mL of 9 M HC1 solution was taken in a Teflon beaker with a volume of 100 mL and the beaker was placed in an ice water bath, then 2 g of LiF was poured in and stirred for 30 minutes until the LiF was completely dissolved; then, 2 g of Ti3AlC2MAX phase material was poured into the beaker at a rate of 0.5 g per minute to make it fully contact with HC1 and LiF, and stirred at 400 rpm for 24 hours in a 35 °C water bath to obtain a suspension; then, the suspension was washed with deionized water, centrifuged at 3500 rpm, the precipitate was collected and the washing step was repeated until the pH of the supernatant reached 6, and during the washing process, each time the centrifugation was 5 minutes, and after centrifugation, the centrifuge tube was shaken for 5 minutes to make the black solid fully dispersed; finally, the black solid was ultrasonically exfoliated at a frequency of 40 kHz for 1-2 hours in an ice water bath environment, and then centrifuged at 3500 rpm for 1 hour, and the supernatant was reserved to obtain a few-layer or single-layer Ti3C2T x ;

[0036] Step 2, introduction of EGCG to protect MXene: 1 mL of 5 mg mL -1 MXene dispersion obtained in step 1 was ultrasonically dispersed at a frequency of 40 kHz for 30 min; then, 1 mg of EGCG powder was added; then, Tris-HCl buffer with a concentration of 10 mM and a pH of 8.5 was added dropwise to the MXene dispersion containing EGCG until the pH value was adjusted to 7.0; finally, it was stirred at a speed of 500 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion;

[0037] Step 3, preparation of pre-Gel solution: 1 mL of MXene@EGCG dispersion obtained in step 2 was moved into a 3 mL sample bottle; first, the MXene@EGCG dispersion was blown under N2 flow for 5-30 minutes, then the sample bottle was placed in an ultrasonic bath to ultrasonically disperse at a frequency of 40 kHz for 5-10 minutes, repeated 3 times; then, 30 mg of APBA, 250 mg of Aam and 20 mg of 4ARM-PEG-ACLT with a molecular weight of 20000 Da were added under an ice water bath; finally, it was ultrasonically dispersed at a frequency of 40 kHz for 20 minutes to make it uniformly dispersed to obtain a pre-Gel solution;

[0038] Step 4, preparation of high-strength, fast-recovery and anti-fatigue capacitive sensing hydrogel: the pre-Gel solution obtained in step 3 was placed in an ice water bath; 40 μL of 10% TEMED aqueous dispersion with a volume concentration of 10% and 20 μL of 110 mg mL -1 of APS aqueous dispersion with a mass concentration of 110 mg mL -1 ; -1APS is added to the pre-gel solution; after sufficient shaking, the obtained pre-gel liquid is added to the mold, and high-strength, fast-recovery and fatigue-resistant capacitive sensing hydrogel is obtained after waiting for 10 minutes at room temperature.

[0039] In step 2, EGCG is used to protect MXene and form a stable MXene@EGCG dispersion. The hydrogen bond between the phenolic hydroxyl group of EGCG and the hydroxyl group on the surface of MXene realizes a more stable and effective antioxidant mechanism, which facilitates the sustained sensing of MXene in the hydrogel. The chemical formula "Ar-OH…OH MXene "… "indicates the formation of a hydrogen bond. Ar-OH represents the phenolic hydroxyl group in EGCG. OH MXene represents the hydroxyl group on the surface of MXene.

[0040] In step 3, 4ARM-PEG-ACLT with more excellent space extension is used instead of Bis as a crosslinking agent to improve its compressibility and mechanical strength. In step 3, the dynamic covalent bond between APBA and EGCG is introduced as a secondary crosslinking point to further effectively improve its mechanical bearing capacity, fatigue resistance and recovery speed, as shown in Figure 1 d, the small graph introduced by the dotted line on the right.

[0041] In step 4, by controlling the concentration of APS and using a diluted TEMED aqueous dispersion, a non-heating free radical polymerization reaction in the presence of a reducing agent is realized.

[0042] As shown in Figure 1 , a, b, and c in Figure 1 are the chemical formulas of 4ARM-PEG-ACLT, APBA, and EGCG, respectively. AAm, APBA, and 4ARM-PEG-ACLT are added to water and stirred to form a uniform solution. Then, APS (initiator) and TEMED (catalyst) are added to the mixed solution to obtain APBA hydrogel. In order to improve the mechanical properties and sensing performance, MXene is added to the hydrogel as a conductive material. In order to improve the dispersity and stability of MXene, EGCG is added to the MXene dispersion system. After replacing pure water with MXene@EGCG aqueous dispersion, a high-strength, fast-recovery and fatigue-resistant capacitive sensing hydrogel is successfully prepared, and its preparation process is shown in Figure 1 d. When EGCG and APBA come into contact, the boronic acid group of APBA forms a boron ester bond with the o-diphenol structure of EGCG.

[0043] Example 2:

[0044] A method for preparing a capacitive sensing hydrogel utilizes (-)-epigallocatechin gallic acid (EGCG) as a protective modification layer for MXene nanosheets, and four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization. A dual-crosslinking network is constructed using the dynamic covalent bonds of 3-acrylamidophenylboronic acid (APBA) and EGCG as secondary crosslinking points, thereby preparing the capacitive sensing hydrogel. The specific preparation method includes the following steps:

[0045] Step 1: Prepare MXene aqueous dispersion by synthesizing monolayer or few-layer Ti3C2T from Ti3AlC2MAX phase material using HF etching of the Al layer. x 5 mg mL was obtained -1 MXene dispersion: 40 mL of 9M HCl solution was placed in a 100 mL PTFE beaker and placed in an ice-water bath. 2 g of LiF was then added and stirred continuously for 40 minutes until the LiF was completely dissolved. Next, 2 g of Ti3AlC2MAX phase material was added to the beaker at a rate of 0.5 g per minute to ensure sufficient contact with HCl and LiF. The mixture was stirred at 400 rpm for 24 hours in a 35°C water bath to obtain a suspension. The suspension was then washed with deionized water and centrifuged at 3500 rpm. The precipitate was collected, and the washing process was repeated until the pH of the supernatant reached 6. During washing, the centrifuge tube was centrifuged for 6 minutes each time, and then shaken for 6 minutes after centrifugation to ensure thorough dispersion of the black solid. Finally, the mixture was ultrasonically exfoliated at 40 kHz for 1 hour in an ice-water bath, followed by centrifugation at 3500 rpm for 1 hour. The supernatant was retained to obtain a few-layer or monolayer Ti3C2T. x ;

[0046] Step 2, Introduce EGCG to protect MXene: Take 1 mL of the 5 mg EGCG obtained in Step 1. -1 MXene dispersion was prepared and ultrasonically dispersed at 40 kHz for 35 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with pH 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 7.5; finally, the mixture was stirred at 500-1000 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0047] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion with N2 gas for 10 minutes, then place the sample vial in an ultrasonic bath and sonicate at a frequency of 40 kHz for 6 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, sonicate at a frequency of 40 kHz for 25 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0048] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0049] like Figure 2 As shown, Figure 2 Image a shows a TEM image of EGCG-protected MXene in water. The catechol groups on EGCG interact with the surface hydroxyl groups of MXene nanosheets through hydrogen bonds, forming a passivation layer on the MXene surface, which allows it to maintain its complete sheet-like structure in water. Figure 2 Image b is a TEM image of a peeled monolayer of MXene in water; oxidation of the MXene material disrupts its sheet-like structure. Figure 2 As shown in Figure c, the SEM image of the hydrogel freeze-dried sample in this invention shows the porous structure of the sample.

[0050] like Figure 3 As shown, Figure 3 Figure a shows the effect of direct compression with a sharp blade without causing permanent damage to the hydrogel, while figure b shows the effect of continuous compression (up to ~80% strain) without causing damage to the gel. The high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel of this invention can effectively function under high-pressure mechanical environments. This embodiment visually demonstrates the high-strength characteristics of the capacitive sensing hydrogel material of this invention.

[0051] Example 3:

[0052] A method for preparing a capacitive sensing hydrogel utilizes (-)-epigallocatechin gallic acid (EGCG) as a protective modification layer for MXene nanosheets, and four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization. A dual-crosslinking network is constructed using the dynamic covalent bonds of 3-acrylamidophenylboronic acid (APBA) and EGCG as secondary crosslinking points, thereby preparing the capacitive sensing hydrogel. The specific preparation method includes the following steps:

[0053] Step 1: Prepare MXene aqueous dispersion by synthesizing monolayer or few-layer Ti3C2T from Ti3AlC2MAX phase material using HF etching of the Al layer. x 5 mg mL was obtained -1 MXene dispersion: 40 mL of 9M HCl solution was placed in a 100 mL PTFE beaker and placed in an ice-water bath. 2 g of LiF was then added and stirred continuously for 30-60 minutes until the LiF was completely dissolved. Next, 2 g of Ti3AlC2MAX phase material was added to the beaker at a rate of 0.5 g per minute to ensure sufficient contact with HCl and LiF. The mixture was stirred at 400 rpm for 24 hours in a 35°C water bath to obtain a suspension. The suspension was then washed with deionized water and centrifuged at 3500 rpm. The precipitate was collected, and the washing process was repeated until the pH of the supernatant reached 6. During washing, the centrifuge tube was centrifuged for 7 minutes each time, and then shaken for 7 minutes after centrifugation to ensure thorough dispersion of the black solid. Finally, the mixture was ultrasonically exfoliated at 40 kHz for 1-2 hours in an ice-water bath, followed by centrifugation at 3500 rpm for 1 hour. The supernatant was retained to obtain a few-layer or monolayer Ti3C2T. x ;

[0054] Step 2, Introduce EGCG to protect MXene: Take 1 mL of the 5 mg EGCG obtained in Step 1. -1 MXene dispersion was prepared and ultrasonically dispersed at 40 kHz for 30-50 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with pH 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 7.0-8.5; finally, the mixture was stirred at 700 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0055] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion with N2 gas for 5-30 minutes, then place the sample vial in an ultrasonic bath and ultrasonically disperse it at a frequency of 40 kHz for 5-10 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, ultrasonicate at a frequency of 40 kHz for 30 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0056] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0057] To verify the strength of the hydrogel material in this invention, mechanical property tests were conducted. Materials without MXene and without EGCG were used as controls, while a group with the optimal concentration was added was used as a comparison. First, a compression test was performed on the samples, compressing them to 100%. Their various properties are as follows: Figure 4 As shown in a and d, the hydrogel material of this invention has a strength exceeding 4.5 MPa. Figure 4 The compressive strength of (a) is 0.52 kPa; Young's modulus is 0.52 kPa. Figure 4 In the middle (d), the toughness reaches 0.406 MJ / m. -3 ( Figure 4 The hydrogel material (d) outperformed the control group in all aspects, quantitatively demonstrating the high strength of the hydrogel material in this invention. Furthermore, the compressive strength of the hydrogel further increased to over 5.4 MPa with the increase of MXene@EGCG content. Figure 4 (a); Young's modulus increased to 0.708 kPa ( Figure 4 (d) Toughness reaches 0.455 MJ / m -3 ( Figure 4 (d). Next, the strain was set to 80%, and the sample was subjected to cyclic compression testing, such as... Figure 4 As shown in Figures b and c, the hydrogel material of this invention exhibits a compressive strength of 202 kPa at 80% strain, with a residual strain of only 1.25%. Figure 4In the middle c). At the same time, the compression strength of the hydrogel can also be further improved to more than 341 MPa with the increase of MXene@EGCG in it Figure 4 In the middle a), the residual strain is reduced to 0.55%. This embodiment shows the high strength mechanical properties and good elastic recovery performance of the capacitive sensing hydrogel in the application through mechanical testing.

[0058] Example 4:

[0059] A preparation method of a capacitive sensing hydrogel, which uses (-)-epigallocatechin gallate EGCG as a protective modification layer of MXene nanosheets, and uses four-arm polyethylene glycol acrylate 4ARM-PEG-ACLT as a crosslinking agent for acrylamide Aam polymerization; uses the dynamic covalent bond between 3-acrylamidophenylboronic acid APBA and EGCG as a secondary crosslinking point to construct a double crosslinking point network, thereby preparing a capacitive sensing hydrogel, and the preparation method specifically comprises the following steps:

[0060] Step 1, preparation of a MXene aqueous dispersion, which is prepared from Ti3AlC2MAX phase material, and uses HF to etch the Al layer to synthesize single-layer or few-layer Ti3C2T x , to obtain 5 mg mL -1 MXene dispersion: take 40 mL of 9M HCl solution in a polytetrafluoroethylene beaker with a volume of 100 mL, and place the beaker in an ice water bath, then pour 2g of LiF into it and continuously stir for 30-60 minutes until the LiF

[0061] is completely dissolved; then, 2g of Ti3AlC2MAX phase material is poured into the beaker at a rate of 0.5g per minute to make it fully contact with HCl and LiF, and is stirred in a 35℃ water bath at a speed of 400 rpm for 24 hours to obtain a suspension; then, the suspension is washed with deionized water, centrifuged at 3500 rpm, and the precipitate is collected and the washing step is repeated until the pH of the supernatant reaches 6, and during the washing process, each time the centrifugation is 8 minutes, and the centrifuge tube is shaken for 8 minutes after centrifugation to make the black solid fully dispersed; finally, ultrasonic stripping is performed at a frequency of 40 kHz for 1 hour in an ice water bath environment, and then centrifuged at 3500 rpm for 1 hour, and the supernatant is reserved to obtain few-layer or single-layer Ti3C2T x ;

[0062] Step 2, introduction of EGCG to protect MXene: take 1 mL of 5 mg mL -1MXene dispersion was prepared and ultrasonically dispersed at 40 kHz for 40 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with pH 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 7.5; finally, the mixture was stirred at 800 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0063] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion with N2 gas for 5-30 minutes, then place the sample vial in an ultrasonic bath and sonicate at a frequency of 40 kHz for 8 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, sonicate at a frequency of 40 kHz for 35 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0064] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0065] To verify the stable sensing and ultrasensitive properties of the capacitive sensing hydrogel in this invention, electrical tests were conducted using the relative capacitance change (ΔC / C0) as a function of strain. Controls were performed using MXene-free and EGCG-free hydrogels. Figure 5 As shown in Figure a, the hydrogel material of this invention exhibits a high degree of overlap in its capacitance change curves during loading and unloading at 80% strain. Furthermore, the capacitance change rate is highest at 80% strain, exceeding 400%. Both the curve overlap and the capacitance change rate are significantly higher than the control group, demonstrating the stable sensing characteristics of the hydrogel sensor in this invention. Figure 5 As shown in Figure b, the sensitivity factor (GF) is calculated as GF = (ΔC / C0)(Δh / h0). -1As a criterion for measuring the sensitivity of capacitive sensing hydrogels, the GF value of the hydrogel material in this invention is 3.48 below 60% strain and 10.4 at 60-80% strain, which is much higher than that of the control group, demonstrating that the capacitive sensing hydrogel sensor in this invention has very high sensitivity.

[0066] Example 5:

[0067] A method for preparing a capacitive sensing hydrogel utilizes (-)-epigallocatechin gallic acid (EGCG) as a protective modification layer for MXene nanosheets, and four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization. A dual-crosslinking network is constructed using the dynamic covalent bonds of 3-acrylamidophenylboronic acid (APBA) and EGCG as secondary crosslinking points, thereby preparing the capacitive sensing hydrogel. The specific preparation method includes the following steps:

[0068] Step 1: Prepare MXene aqueous dispersion by synthesizing monolayer or few-layer Ti3C2T from Ti3AlC2MAX phase material using HF etching of the Al layer. x 5 mg mL was obtained -1 MXene dispersion: Place 40 mL of 9M HCl solution into a 100 mL polytetrafluoroethylene beaker and place the beaker in an ice-water bath. Then add 2 g of LiF and stir continuously for 30-60 minutes until the LiF concentration reaches the specified level.

[0069] Completely dissolve the Ti3AlC2MAX phase material; then, add 2g of Ti3AlC2MAX phase material to a beaker at a rate of 0.5g per minute to ensure full contact with HCl and LiF, and stir at 400rpm for 24 hours in a 35℃ water bath to obtain a suspension; next, wash the suspension with deionized water, centrifuge at 3500rpm, collect the precipitate, and repeat the washing steps until the pH of the supernatant reaches 6. During the washing process, centrifuge for 9 minutes each time, and shake the centrifuge tube for 9 minutes after centrifugation to ensure full dispersion of the black solid; finally, sonicate at 40kHz for 2 hours in an ice-water bath, and then centrifuge at 3500rpm for 1 hour, retaining the supernatant to obtain a few-layer or monolayer Ti3C2T x ;

[0070] Step 2, Introduce EGCG to protect MXene: Take 1 mL of the 5 mg EGCG obtained in Step 1. -1MXene dispersion was prepared and ultrasonically dispersed at a frequency of 40 kHz for 30-50 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with a pH of 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 8.0; finally, the mixture was stirred at 900 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0071] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion under a nitrogen gas flow for 25 minutes, then place the sample vial in an ultrasonic bath and sonicate at a frequency of 40 kHz for 9 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, sonicate at a frequency of 40 kHz for 35 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0072] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0073] To verify the sensing characteristics of the capacitive sensing hydrogel in this invention under different strain conditions, a force-electric coupling test was conducted by setting the strain magnitude and rate. Figure 6 In sections a and b, when the strain is increased incrementally at 5% and 20% respectively, up to 20% and 80%, the hydrogel material of this invention can accurately detect the conductivity signal and exhibits good stability. Figure 6 In equation c, the real-time capacitance change of the sensor increases rapidly with increasing compression. When the strain decreases from 80% to 0% in increments of 10%, the sensor's resistance correspondingly recovers to near its original value. Figure 6 In the middle d, when the compression rate gradually increases, it can accurately reflect the deformation rate of the measured object (v = 5-150 mm min). -1 The electrical signal showed no significant fluctuations. All the above test results demonstrate the excellent repeatability of the hydrogel sensor of this invention under different strain conditions. Figure 6In step e, the hydrogel of this invention underwent 100 compression fatigue tests at 60% strain. The ΔC / C0 signal of the hydrogel sensor remained stable during the compression fatigue test, demonstrating the excellent fatigue resistance of the capacitive sensing hydrogel of this invention.

[0074] Example 6:

[0075] A method for preparing a capacitive sensing hydrogel utilizes (-)-epigallocatechin gallic acid (EGCG) as a protective modification layer for MXene nanosheets, and four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization. A dual-crosslinking network is constructed using the dynamic covalent bonds of 3-acrylamidophenylboronic acid (APBA) and EGCG as secondary crosslinking points, thereby preparing the capacitive sensing hydrogel. The specific preparation method includes the following steps:

[0076] Step 1: Prepare MXene aqueous dispersion by synthesizing monolayer or few-layer Ti3C2T from Ti3AlC2MAX phase material using HF etching of the Al layer. x 5 mg mL was obtained -1 MXene dispersion: Place 40 mL of 9M HCl solution into a 100 mL polytetrafluoroethylene beaker and place the beaker in an ice-water bath. Then add 2 g of LiF and stir continuously for 30-60 minutes until the LiF concentration reaches the specified level.

[0077] Completely dissolve the Ti3AlC2MAX phase material; then, add 2g of Ti3AlC2MAX phase material to a beaker at a rate of 0.5g per minute to ensure full contact with HCl and LiF, and stir at 400rpm for 24 hours in a 35℃ water bath to obtain a suspension; next, wash the suspension with deionized water, centrifuge at 3500rpm, collect the precipitate, and repeat the washing steps until the pH of the supernatant reaches 6. During the washing process, centrifuge for 10 minutes each time, and shake the centrifuge tube for 10 minutes after centrifugation to ensure full dispersion of the black solid; finally, sonicate at 40kHz for 2 hours in an ice-water bath, and then centrifuge at 3500rpm for 1 hour, retaining the supernatant to obtain a few-layer or monolayer Ti3C2T x ;

[0078] Step 2, Introduce EGCG to protect MXene: Take 1 mL of the 5 mg EGCG obtained in Step 1. -1MXene dispersion was prepared and ultrasonically dispersed at a frequency of 40 kHz for 30-50 min; then, 1 mg of EGCG powder was added; next, 10 mM Tris-HCl buffer with a pH of 8.5 was added dropwise to the EGCG-containing MXene dispersion until the pH was adjusted to 8.5; finally, the mixture was stirred at 1000 rpm for 12 hours at room temperature and in the dark to obtain a dark green MXene@EGCG dispersion.

[0079] Step 3: Preparation of pre-Gel solution: Transfer 1 mL of the MXene@EGCG dispersion obtained in Step 2 into a 3 mL sample vial; First, purge the MXene@EGCG dispersion under a nitrogen gas flow for 5-30 minutes, then place the sample vial in an ultrasonic bath and ultrasonically disperse it at a frequency of 40 kHz for 10 minutes, repeating 3 times; Then, under an ice-water bath, add 30 mg APBA, 250 mg Aam and 20 mg 4ARM-PEG-ACLT with a molecular weight of 20000 Da; Finally, ultrasonicate at a frequency of 40 kHz for 40 minutes to disperse it evenly, obtaining the pre-Gel solution;

[0080] Step 4: Preparation of high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel: Place the pre-Gel solution obtained in Step 3 in an ice-water bath; take 40 μL mL -1 A 10% (v / v) TEMED aqueous dispersion and 20 μL mL -1 The mass concentration is 110 mg / mL -1 APS is added dropwise to the pre-Gel solution; after thorough shaking, the resulting pre-gel liquid is added dropwise to the mold and left at room temperature for 10 minutes to obtain a high-strength, fast-recovery, and fatigue-resistant capacitive sensing hydrogel.

[0081] To verify the optimal sensing performance of the capacitive sensing hydrogel in this invention, the concentrations of MXene@EGCG and APBA were adjusted. First, the concentration of MXene@EGCG was adjusted to 0, 0.25, 0.5, and 1 mg / mL, respectively. -1 And perform mechanical and force-electric coupling tests. For example... Figure 7 As shown in Figure ab, when the concentration is 0.5 mg / mL -1 At that time, the strength reached 342 kPa, and the relative change rate of capacitance was 416.8%, exhibiting excellent mechanical properties compared to hydrogel samples of other concentrations. Although the change rate of capacitance was relatively low compared to 0.25 mg / mL... -1 The sample concentration was low, but after multiple tests, it was 0.25 mg / mL. -1 Stability will decrease and relaxation will increase. Next, the concentration of APBA was adjusted to 10, 20, 30, and 40 mg / mL.-1 and mechanical and force-electric coupling tests were carried out. As shown in Figure 7 When the concentration was 30 mg mL -1 , the strength reached 342 kPa, and the relative change rate of capacitance was 416.8%, which exhibited excellent mechanical and capacitance sensing performance compared with other hydrogel samples. This embodiment directly shows the optimal concentration for preparing the capacitance sensing hydrogel in the present application.

[0082] The above has described the present application by way of example, and it should be noted that any simple modification, change or other equivalent replacement without creative labor by those skilled in the art does not depart from the core of the present application and falls within the protection scope of the present application.

Claims

1. A method of preparing a capacitive sensing hydrogel, characterized by: A capacitive sensing hydrogel is prepared by using (-)-epigallocatechin gallate (EGCG) as a protective modification layer of MXene nanosheets, using four-arm polyethylene glycol acrylate (4ARM-PEG-ACLT) as a crosslinking agent for acrylamide (Aam) polymerization, and using 3-acrylamidophenylboronic acid (APBA) and EGCG as a dynamic covalent bond as a secondary crosslinking point to construct a double crosslinking point network, and the preparation method specifically comprises the following steps: Step 1, Preparation of MXene aqueous dispersion: From Ti3AlC2MAX phase material, using HF to etch Al layer to synthesize single-layer or few-layer Ti3C2T x , 5 mg mL -1 MXene dispersion was obtained; Step 2, introduction of EGCG to protect MXene: take 1 mL of 5 mg mL -1 MXene dispersion obtained in step 1 and ultrasonically disperse at a frequency of 40 kHz for 30-50 min; then, add 1 mg of EGCG powder; then, dropwise add Tris-HCl buffer with a concentration of 10 mM and a pH of 8.5 to the MXene dispersion containing EGCG until the pH value is adjusted to 7.0-8.5; finally, stir at a speed of 500-1000 rpm at room temperature and in the dark for 12 hours to obtain a dark green MXene@EGCG dispersion; Step 3, preparing a pre-Gel solution: 1 mL of the MXene@EGCG dispersion obtained in step 2 is transferred into a 3 mL sample bottle; first, the MXene@EGCG dispersion is blown under N2 flow for 5-30 minutes, and then the sample bottle is placed in an ultrasonic bath for ultrasonic dispersion at a frequency of 40 kHz for 5-10 minutes, repeated for 3 times; then, 30 mg of APBA, 250 mg of Aam and 20 mg of 4ARM-PEG-ACLT with a molecular weight of 20000 Da are added under an ice water bath; finally, ultrasonic dispersion is performed at a frequency of 40 kHz for 20-40 minutes to make it uniformly dispersed, and a pre-Gel solution is obtained; Step 4, preparation of high-strength, fast-recovery and fatigue-resistant capacitive sensing hydrogel: the pre-gel solution obtained in step 3 is placed in an ice water bath; 40 μL mL -1 of 10% volume concentration of TEMED aqueous dispersion and 20 μL mL -1 of 110 mg mL -1 of APS are added dropwise to the pre-gel solution; after shaking well, the obtained pre-gel liquid is added dropwise to the mold, and high-strength, fast-recovery and fatigue-resistant capacitive sensing hydrogel is obtained after waiting for 10 minutes at room temperature.

2. The method of claim 1, wherein: The step 1 is specifically to take 40 mL of 9 M HC1 solution into a polytetrafluoroethylene beaker with a volume of 100 mL, and place the beaker in an ice water bath, then pour 2 g of LiF into it and continue to stir for 30-60 minutes until the LiF is completely dissolved; then, pour 2 g of Ti3AlC2MAX phase material into the beaker at a speed of 0.5 g per minute to make it fully contact with HC1 and LiF, and stir in a 35°C water bath at a speed of 400 rpm for 24 hours to obtain a suspension; then, wash the suspension with deionized water, centrifuge at 3500 rpm, collect the precipitate and repeat the washing step until the pH of the supernatant reaches 6, and during the washing process, centrifuge for 5-10 minutes each time, and shake the centrifuge tube for 5-10 minutes after centrifugation to make the black solid fully dispersed; finally, ultrasonic exfoliation at a frequency of 40 kHz for 1-2 hours in an ice water bath environment, and then centrifuge at 3500 rpm for 1 hour, and retain the supernatant to obtain few-layer or single-layer Ti3C2T x .

3. The method of claim 1, wherein: The step 2 utilizes EGCG to protect MXene and form a stable MXene@EGCG dispersion liquid, which realizes a more stable and effective antioxidant mechanism through the hydrogen bond "Ar-OH…OH MXene" between the phenolic hydroxyl of EGCG and the hydroxyl on the surface of MXene, where "…" represents a hydrogen bond, Ar-OH represents the phenolic hydroxyl in EGCG, and OH MXene represents the hydroxyl on the surface of MXene, which is convenient for the continuous sensing of MXene in hydrogel.

4. The method of claim 1, wherein: The dynamic covalent bond between APBA and EGCG introduced in step 3 as a secondary crosslinking point further effectively improves the mechanical bearing capacity, fatigue resistance and recovery speed.

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