Preparation method of resistance-type strain sensing hydrogel

Abstract

The invention discloses a preparation method of resistance-type strain sensing hydrogel, and belongs to the technical field of gel materials.The preparation method comprises the steps that surface modification is conducted on carboxylated carbon nanotubes through levodopa, so that the CNTs form stable water-phase dispersion liquid; meanwhile, the strong hydrogen bond interaction between the catechol group and the functional group on the surface of the MXene is utilized, so that the DCNT and the MXene are stably combined, the oxidation resistance of the MXene is enhanced, and the mechanical property and the conductivity of the MXene hydrogel are improved; the defects that MXene is easy to oxidize and CNT is poor in dispersity in water are effectively overcome; the preparation method has the advantages of simplicity and convenience in operation and cost controllability, and effectively promotes the conversion process of the flexible electronic device from laboratory research to practical application.

Description

Technical Field

[0001] The present invention belongs to the technical field of gel materials, and particularly relates to a preparation method of a resistive strain sensing hydrogel. Background Art

[0002] The design of flexible sensors is of great significance in modern technology. Because it can detect a variety of complex deformations with high precision, it is widely used in flexible electronics, wearable devices, robots, medical health monitoring, and human-computer interaction and other fields. These sensors have the characteristics of lightweight, flexibility, stretchability, and high sensitivity, and can adapt to irregular surfaces and dynamic environments, significantly improving the comfort and performance of devices. MXene materials show irreplaceable core advantages in the field of flexible sensing: First, its intrinsic metallic conductivity (>6000 S / cm) provides the sensor with extremely low interfacial impedance and a fast charge transport channel, significantly improving the device sensitivity and response speed; Second, the unique hydrophilic surface chemistry endows it with excellent aqueous phase dispersion stability, and a uniform conductive network can be directly constructed in the water-based system, avoiding the dependence on organic solvents of traditional nanomaterials (such as graphene, carbon nanotubes); In addition, the rich surface termination groups (-OH, -O, -F, etc.) make it easy to achieve functional customization through chemical modification or physical composite. For example, cross-linking with polymers enhances mechanical toughness, or loading active components to construct multiple response characteristics, providing an ideal material platform for the development of high-performance flexible sensing systems.

[0003] However, the current MXene-CNT composite sensing hydrogel has some defects. Two-dimensional transition metal carbides (nitrides) (MXene) as a new type of two-dimensional nano-conductive material, MXene has various advantages, such as high metallic conductivity, hydrophilicity, and high specific surface area, but it is extremely easy to oxidize in an air environment, resulting in a decrease in its conductivity and mechanical properties. At the same time, MXene itself has self-stacking defects, and it is easily aggregated during the formation of the hydrogel, which will also deteriorate the conductivity and mechanical properties of the MXene-filled composite hydrogel, affecting the long-term stability and durability of the composite hydrogel. CNT has good conductivity, but the dispersibility and biocompatibility of CNT in water are poor, which will also affect the mechanical properties and sensing ability of the MXene-CNT hydrogel. Therefore, when designing MXene-CNT hydrogels, it is necessary to consider how to overcome problems such as the easy oxidation of MXene and the poor dispersibility of CNT in water to ensure its stable performance during long-term use. In addition, when using a hydrogel as a sensing substrate, although it has high biocompatibility due to its high water content, it will also lead to poor mechanical strength. In summary, MXene-CNT composite hydrogels have good development prospects as wearable sensor materials, but still need to overcome challenges in terms of poor deformation ability, instability, and easy oxidation to achieve their wide application in the field of flexible sensors. Summary of the Invention

[0004] Technical problems to be solved: In view of the problems existing in the prior art that MXene has the defects of easy self-stacking, is easy to oxidize in the aqueous dispersion, has poor long-term stability, and the high energy dissipation characteristics in the application of resistive tensile sensors will cause significant hysteresis phenomena in the material under cyclic loading. At the same time, due to insufficient intrinsic mechanical strength, structural damage is likely to occur. The present application provides a preparation method of a resistive strain sensing hydrogel. This method improves the mechanical properties and sensing ability of the resistive strain sensing hydrogel, which helps to realize the practical application of the resistive strain sensing hydrogel. By using dopamine as the modification layer of CNT, a stable aqueous dispersion of CNT is formed, the hydrogen bond interaction between CNT and the surface functional groups of MXene is improved, and then the mechanical properties and electrical conductivity of the MXene hydrogel are improved. By introducing 4ARM-PEG-ACLT with more excellent spatial ductility as the cross-linking agent for AAm polymerization, the mechanical strength of the hydrogel is effectively improved. When the tensile strain reaches 1400%, the sample will not break, and at the same time, it also has high sensitivity. The introduction of few-layer or single-layer MXene enables the hydrogel to obtain better electrical conductivity and is also more sensitive than other materials. The preparation method proposed by the present invention is simple and efficient, taking a solid step towards the practical application of the hydrogel resistive strain sensor.

[0005] Technical solution: To achieve the above object, the present application is realized through the following technical solutions:

[0006] A preparation method of a resistive strain sensing hydrogel, the specific steps are as follows:

[0007] The first step is to prepare an MXene aqueous dispersion: Using MAX phase material as the raw material, etching the Al layer of the MAX phase material with HF, and then synthesizing a single-layer or few-layer Ti3C2T x MXene solution, and freeze-drying to obtain MXene powder;

[0008] The second step is to prepare levodopa-modified carbon nanotubes DCNT:

[0009] S1: Take 0.5 - 1 g of CNT and dissolve it in 25 - 50 mL of deionized water to obtain a CNT aqueous dispersion. Then add 0.16 - 0.32 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide EDC and 0.16 - 0.32 mmol of N-hydroxysuccinimide NHS to the CNT aqueous dispersion, and magnetically stir at 1000 rpm under the conditions of 22 - 28 °C and darkness for 3 hours to carry out the reaction to obtain an activated carboxylated CNT aqueous dispersion;

[0010] S2: Dissolve 0.12 - 0.24 mmol of levodopa and 0.12 - 0.24 mmol of L - ascorbic acid in the activated carboxylated CNT aqueous dispersion, and then stabilize the pH of the dispersion at 7.8 by adding sodium bicarbonate NaHCO₃ to obtain the activated carboxylated CNT aqueous dispersion reaction solution;

[0011] S3: Pass nitrogen into the activated carboxylated CNT aqueous dispersion reaction solution with adjusted pH for 10 - 15 minutes to remove dissolved oxygen, and magnetically stir at 1000 rpm under the conditions of 22 - 28 °C and in the dark for 3 hours to continue the reaction, obtaining the reaction product carboxylated CNT aqueous dispersion;

[0012] S4: Transfer the reaction product carboxylated CNT aqueous dispersion into a 3 kDa dialysis bag, and dialyze it with 1 L of deionized water for 6 hours;

[0013] S5: Freeze the dialyzed dispersion in liquid nitrogen for 5 minutes, and then freeze - dry it in a freeze - dryer for 24 hours to obtain the levodopa - modified carbon nanotube DCNT powder. The levodopa - modified carbon nanotube DCNT powder is stored at 4 °C;

[0014] The third step: Mix the MXene powder prepared in the first step and the levodopa - modified carbon nanotube DCNT powder prepared in the second step at 25 °C

[0015] according to the mass ratios of MXene powder 1 g:DCNT powder 5 g, MXene powder 1 g:DCNT powder 10 g, MXene powder 1 g:DCNT powder 15 g, MXene powder 2 g:DCNT powder 5 g, MXene powder 2 g:DCNT powder 10 g, MXene powder 2 g:DCNT powder 15 g, MXene powder 4 g:DCNT powder 5 g, MXene powder 4 g:

[0016] DCNT powder 10 g, MXene powder 4 g:DCNT powder 15 g for weighing respectively;

[0017] The fourth step: Take 5 g - 10 g of acrylamide AAM and 200 - 400 mg of tetra - arm polyethylene glycol acrylate 4ARM - PEG - ACLT and add them into 20 mL of deionized water to obtain the reaction mother liquor A containing 250 - 500 mg·mL -1 of AAM and 10 - 20 mg·mL -1 of the reaction mother liquor A, ultrasonicate for 60 minutes to uniformly disperse the reaction mother liquor A, and then place the reaction mother liquor A in an ice - water bath;

[0018] The fifth step: Take 4 g of ammonium persulfate APS and add it into 10 mL of deionized water to obtain a solution containing 400 mg·mL -1The reaction mother liquor B was ultrasonically treated for 60 minutes to uniformly disperse it, and then the reaction mother liquor B was placed in an ice-water bath;

[0019] Step 6: Dissolve different mass ratios of MXene powder and DCNT powder weighed in the third step in 2 mL of reaction mother liquor A respectively, then add 50 - 100 μL of reaction mother liquor B, and finally add 4 - 8 μL of an aqueous dispersion of N,N,N',N'-tetramethylethylenediamine TEMED with a volume concentration of 5%. After inverting and shaking by hand 10 times, quickly transfer the obtained pre-gelled liquid to a mold and let it stand at room temperature for 30 - 60 minutes to obtain a resistive strain sensing hydrogel with high tensile performance and high sensitivity.

[0020] Furthermore, the specific steps of the first step are as follows:

[0021] Step 1: Place 30 mL of 12 M hydrochloric acid solution in a 100 mL polytetrafluoroethylene beaker, and place the beaker in an ice-water bath; then pour 2 g of LiF into the hydrochloric acid solution at 25 °C and continuously stir for 45 minutes until lithium fluoride LiF is completely dissolved;

[0022] Step 2: Divide 2 g of Ti3AlC2 MAX phase material into 5 equal parts and pour 0.4 g of each part into the beaker to make it fully contact with hydrochloric acid and LiF, and then seal the beaker for 15 minutes;

[0023] Step 3: Transfer the mixed solution to a 35 °C water bath, and stir at a speed of 500 rpm for 24 hours. Centrifuge the obtained black reaction solution at a speed of 4000 rpm, then wash the precipitate with deionized water, and shake the black solid in the solution by hand to fully disperse it;

[0024] Step 4: Repeat the centrifugation, washing, and shaking steps in Step 3 until the pH of the centrifuged supernatant reaches 6;

[0025] Step 5: Under an ice-water bath environment, ultrasonically exfoliate at a frequency of 40 kHz for 1 hour, centrifuge at 6000 rpm for 1 hour, and retain the supernatant to obtain a few-layer or single-layer Ti3C2T x MXene solution;

[0026] Step 6: Freeze the dispersion in liquid nitrogen for 5 minutes, and then place it in a freeze dryer for freeze-drying for 24 hours. Store the obtained MXene powder at 4 °C.

[0027] Further, in S1, 0.5 g of CNT was dissolved in 25 mL of deionized water to obtain a CNT aqueous dispersion. Then, 0.16 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide EDC and 0.16 mmol of N-hydroxysuccinimide NHS were added to the CNT aqueous dispersion. The reaction was carried out under magnetic stirring at 1000 rpm for 3 h at 25 °C and in the dark to obtain an activated carboxylated CNT aqueous dispersion.

[0028] Further, in S2, 0.12 mmol of levodopa and 0.12 mmol of L-ascorbic acid were dissolved in the activated carboxylated CNT aqueous dispersion.

[0029] Further, in S3, nitrogen was passed through the activated carboxylated CNT aqueous dispersion reaction solution with adjusted pH for 10 min to remove dissolved oxygen. The reaction was continued under magnetic stirring at 1000 rpm for 3 h at 25 °C and in the dark to obtain a reaction product carboxylated CNT aqueous dispersion.

[0030] Further, in S4, water was changed every 2 hours during the 6-hour dialysis.

[0031] Principle explanation: Levodopa Dopa was used to modify the surface of carbon nanotubes CNT to improve the long-term stability of carbon nanotubes CNT in aqueous solution. At the same time, due to the strong hydrogen bond interaction between the catechol group and the functional groups on the surface of MXene, the Dopa-modified carbon nanotubes DCNT and MXene formed a stable combination, enhancing the antioxidant ability of MXene. Finally, there is a strong hydrogen bond interaction between levodopa and the functional groups of Mxe ne. When the hydrogen bond breaks, more energy will be dissipated, which can enhance the mechanical properties of the material such as stretchability and toughness. Thus, a flexible hydrogel substrate with excellent resistive strain sensing effect was prepared.

[0032] Beneficial effects:

[0033] The present application provides a method for preparing a resistive strain sensing hydrogel. Compared with the prior art, it has the following beneficial effects:

[0034] 1. In the present application, the carboxyl groups on the surface of CNT were activated by using EDC and NHS, and then Dopa was introduced while adding L-ascorbic acid to prevent oxidation. The surface of CNT was modified by Dopa to form stable Dopa-CNT. The prepared modified CNT has good dispersion performance and high sensitivity characteristics, and is suitable for application in resistive sensing hydrogels.

[0035] 2. The levodopa-modified carbon nanotubes DCNT of the present application have the ability to protect MXene from oxidation; through hydrogen bond protection between dopas and the antioxidant ability of dopas, the antioxidant ability of MXene is improved; at the same time, by using DCNT to coat MXene nanosheets, the contact between MXene and water molecules and oxygen molecules in water is effectively isolated, further improving the antioxidant ability;

[0036] 3. The improvement of mechanical and sensing properties by the dual-nanocomposite network of MXene and CNT in the present application; the combination between DCNT and MXene can play the role of introducing new crosslinking points, thereby dissipating energy and enhancing mechanical properties; the relative slip between the two conductive components after being stressed increases the resistance-strain change rate, thereby enhancing the sensing ability;

[0037] 4. The introduction of DCNT in the present application enables the gel to obtain multi-interface high adhesion characteristics; the catechol functional groups in the dopa molecules in DCNT can produce strong hydrogen bonds or coordination bonds and other interactions with multi-interfaces such as metals, plastics, and skin, thereby obtaining adhesion characteristics;

[0038] 5. Compared with traditional resistive strain-sensing hydrogels, the present application has the characteristics of high tensile performance and high sensitivity. By using Dopa-modified CNT, the solubility of CNT in water can be effectively improved, enhancing the sensing ability of the DCNT-MXene hydrogel;

[0039] 6. The present application effectively improves the mechanical strength of the hydrogel, with a tensile fracture strain exceeding 1400%; at the same time, it improves the electrical conductivity of the hydrogel, and the maximum GF reaches 20.15 in the strain range of 900% - 1300%;

[0040] 7. The preparation method of the present application has the advantages of simple operation and remarkable efficiency, effectively promoting the practical process of resistive strain-sensing hydrogels based on hydrogels in the field of engineering applications. Description of the Drawings

[0041] Figure 1 It is the synthesis mechanism diagram of DCNT for the high-tensile performance and high-sensitivity resistive strain-sensing hydrogel of the present application and the synthesis mechanism diagram of preparing DCM hydrogel. Among them, a is the mechanism diagram of synthesizing dopa-modified carbon nanotubes DCNT during the preparation process of the resistive strain-sensing hydrogel, and b is the synthesis mechanism diagram of the resistive strain-sensing hydrogel DCM hydrogel;

[0042] Figure 2 It is the microscopic morphology image of the high-tensile performance and high-sensitivity resistive strain-sensing hydrogel of the present application;

[0043] Figure 3 It is the TEM image of DCNT-MXene modified by Dopa of the present application;

[0044] Figure 4 It is the DCNT water dispersibility test diagram of this application; where a is the initial state of the amino-functionalized CNT (NH2-CNT), carboxyl-functionalized CNT (COOH-CNT), and DCNT dispersion (Dopa-CNT) modified by Dopa, b is the state of the three groups of dispersions after standing for 30 minutes; c is the state of the three groups of dispersions after standing for 24 hours; d is the state of the three groups of dispersions after standing for 7 days; e is the state of the three groups of dispersions after standing for 30 days; f is the state of the three groups of dispersions after standing for 60 days;

[0045] Figure 5 It is the mechanical sensing performance characterization diagram of the highly stretchable and highly sensitive resistive strain sensing hydrogel of this application; where a is the typical mechanical images of DCM, CM, C, and M gels; b is the typical sensing images of DCM, CM, C, and M gels; c is the comparison diagram of the Young's modulus and toughness of DCM, CM, C, and M gels; d is the sensitivity diagram of DCM, CM, C, and M gels;

[0046] Figure 6 It is the force mechanical sensing performance characterization diagram of the highly stretchable and highly sensitive resistive strain sensing hydrogel of this application after adjusting the concentrations of MXene and DCNT; where a is the mechanical property diagram of DCM gels at different DCNT concentrations; b is the mechanical property diagram of DCM gels at different MXene concentrations; c is the sensing ability diagram of DCM gels at different DCNT concentrations; d is the sensing ability diagram of DCM gels at different MXene concentrations; e is the comparison diagram of the Young's modulus of gels at different concentrations; f is the comparison diagram of the toughness of gels at different concentrations; g is the comparison diagram of the sensitivity of gels at different concentrations;

[0047] Figure 7 It is the adhesion property characterization diagram of the highly stretchable and highly sensitive resistive strain sensing hydrogel of this application; where a is the adhesion diagram of the gel to different media; b is the mechanical adhesion test diagram of the gel to different media; c is the comparison diagram of the adhesion strength of the gel to different media;

[0048] Figure 8 It is the sensor application characterization diagram of the highly stretchable and highly sensitive resistive strain sensing hydrogel of this application; where a is the diagram of monitoring finger bending; b is the diagram of monitoring wrist bending; c is the diagram of monitoring elbow bending; d is the diagram of monitoring throat. Detailed implementation manners

[0049] The present invention will be further described below in conjunction with the accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the disclosed content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0050] A preparation method of a resistive strain sensing hydrogel is as follows:

[0051] In the first step, prepare an MXene aqueous dispersion. Using MAX phase material as the raw material, etch the Al layer of the MAX phase material with HF to synthesize a single-layer or few-layer Ti3C2T x MXene solution, and obtain MXene powder by freeze-drying. The specific steps are as follows:

[0052] Step 1: Place 30 mL of 12 M hydrochloric acid solution in a 100 mL polytetrafluoroethylene beaker, and place the beaker in an ice-water bath; then pour 2 g of LiF into the hydrochloric acid solution at 25 °C and stir continuously for 45 minutes until lithium fluoride LiF is completely dissolved;

[0053] Step 2: Divide 2 g of Ti3AlC2 MAX phase material into 5 equal parts and pour 0.4 g of each part into the beaker to make it fully contact with hydrochloric acid and LiF, and then seal the beaker for 15 minutes;

[0054] Step 3: Transfer the mixed solution into a 35 °C water bath, and stir at a speed of 500 rpm for 24 hours. Centrifuge the obtained black reaction solution at a speed of 4000 rpm, wash the precipitate with deionized water, and shake the solution by hand to fully disperse the black solid in the solution;

[0055] Step 4: Repeat the centrifugation, washing, and shaking steps in Step 3 until the pH of the centrifuged supernatant reaches 6;

[0056] Step 5: Under an ice-water bath environment, ultrasonically exfoliate at a frequency of 40 kHz for 1 hour, centrifuge at 6000 rpm for 1 hour, and retain the supernatant to obtain a few-layer or single-layer Ti3C2T x MXene solution;

[0057] Step 6: Place the dispersion in liquid nitrogen and freeze it for 5 minutes, then put it into a freeze-dryer and freeze-dry it for 24 hours. Store the obtained MXene powder at 4 °C;

[0058] In the second step, prepare levodopa-modified carbon nanotubes DCNT:

[0059] S1: Take 0.5 - 1 g of CNT and dissolve it in 25 - 50 mL of deionized water to obtain a CNT aqueous dispersion. Then, add 0.16 - 0.32 mmol of 1 - ethyl - (3 - dimethylaminopropyl) carbodiimide EDC and 0.16 - 0.32 mmol of N - hydroxysuccinimide NHS to the CNT aqueous dispersion. Under the conditions of 22 - 28 °C and in the dark, stir magnetically at 1000 rpm for 3 hours to make the reaction proceed, and obtain an activated carboxylated CNT aqueous dispersion;

[0060] S2: Dissolve 0.12 - 0.24 mmol of levodopa and 0.12 - 0.24 mmol of L - ascorbic acid in the activated carboxylated CNT aqueous dispersion, and then stabilize the pH of the dispersion at 7.8 by adding sodium bicarbonate NaHCO3 to obtain an activated carboxylated CNT aqueous dispersion reaction solution;

[0061] S3: Pass nitrogen into the activated carboxylated CNT aqueous dispersion reaction solution with the pH adjusted for 10 - 15 minutes to remove dissolved oxygen. Under the conditions of 22 - 28 °C and in the dark, stir magnetically at 1000 rpm to make the reaction continue for 3 hours to obtain a reaction product carboxylated CNT aqueous dispersion;

[0062] S4: Transfer the reaction product carboxylated CNT aqueous dispersion into a 3 kDa dialysis bag, and use 1 L of deionized water for dialysis for 6 hours, changing the water every 2 hours;

[0063] S5: Freeze the dialyzed dispersion in liquid nitrogen for 5 minutes, and then place it in a freeze - dryer for freeze - drying for 24 hours to obtain levodopa - modified carbon nanotube DCNT powder. The levodopa - modified carbon nanotube DCNT powder is stored at 4 °C;

[0064] The third step: Weigh the MXene powder prepared in the first step and the levodopa - modified carbon nanotube DCNT powder prepared in the second step at 25 °C

[0065] respectively according to the mass ratios of MXene powder 1 g:DCNT powder 5 g, MXene powder 1 g:DCNT powder 10 g, MXene powder 1 g:DCNT powder 15 g, MXene powder 2 g:DCNT powder 5 g, MXene powder 2 g:DCNT powder 10 g, MXene powder 2 g:DCNT powder 15 g, MXene powder 4 g:DCNT powder 5 g, MXene powder 4 g:

[0066] DCNT powder 10 g, MXene powder 4 g:DCNT powder 15 g;

[0067] Step 4: Take 5 g - 10 g of acrylamide AAM and 200 - 400 mg of tetra-arm polyethylene glycol acrylate 4ARM-PEG-ACLT and add them to 20 mL of deionized water to obtain a reaction mother liquor A containing 250 - 500 mg·mL -1 of AAM and 10 - 20 mg·mL -1 of the reaction mother liquor A,

[0068] Ultrasonicate for 60 minutes to uniformly disperse the reaction mother liquor A, and then place the reaction mother liquor A in an ice-water bath;

[0069] Step 5: Take 4 g of ammonium persulfate APS and add it to 10 mL of deionized water to obtain a reaction mother liquor B containing 400 mg·mL -1 of the reaction mother liquor B, ultrasonicate for 60 minutes to uniformly disperse the reaction mother liquor B, and then place the reaction mother liquor B in an ice-water bath;

[0070] Step 6: Dissolve the MXene powder and DCNT powder with different mass ratios weighed in the third step in 2 mL of the reaction mother liquor A respectively, then add 50 - 100 μL of the reaction mother liquor B, and finally add 4 - 8 μL of an aqueous dispersion of N,N,N',N'-tetramethylethylenediamine TEMED with a volume concentration of 5%. After inverting and shaking 10 times by hand, quickly transfer the obtained pre-gelled liquid to a mold and let it stand at room temperature for 30 - 60 minutes to obtain a resistive strain sensing hydrogel with high tensile performance and high sensitivity.

[0071] Example 1, A preparation method of a resistive strain sensing hydrogel is as follows:

[0072] Step 1, Prepare an aqueous dispersion of MXene. Using MAX phase material as the raw material, etch the Al layer of the MAX phase material with HF to synthesize a single-layer or few-layer Ti3C2T x MXene solution, and obtain MXene powder by freeze-drying. The specific steps are as follows:

[0073] Step 1: Place 30 mL of 12 M hydrochloric acid solution in a 100 mL polytetrafluoroethylene beaker, and place the beaker in an ice-water bath; then pour 2 g of LiF into the hydrochloric acid solution at 25 °C and continuously stir for 45 minutes until lithium fluoride LiF is completely dissolved;

[0074] Step 2: Divide 2 g of Ti3AlC2 MAX phase material into 5 equal parts and pour 0.4 g of each part into the beaker to make it fully contact with hydrochloric acid and LiF, and then seal the beaker for 15 minutes;

[0075] Step 3: Transfer the mixed solution into a 35°C water bath and stir it at a speed of 500 rpm for 24 hours. Centrifuge the resulting black reaction solution at a speed of 4000 rpm, then wash the precipitate with deionized water, and manually shake to fully disperse the black solid in the solution;

[0076] Step 4: Repeat the centrifugation, washing, and shaking steps in Step 3 until the pH of the centrifuged supernatant reaches 6;

[0077] Step 5: Under an ice-water bath environment, ultrasonically exfoliate at a frequency of 40 kHz for 1 hour, centrifuge at 6000 rpm for 1 hour, and retain the supernatant to obtain a few-layer or single-layer Ti3C2T x MXene solution;

[0078] Step 6: Freeze the dispersion liquid in liquid nitrogen for 5 minutes, then put it into a freeze dryer for freeze-drying for 24 hours, and store the obtained MXene powder at 4°C;

[0079] Second step, prepare levodopa-modified carbon nanotubes DCNT:

[0080] S1: Take 0.5 g of CNT and dissolve it in 25 mL of deionized water to obtain a CNT aqueous dispersion. Then add 0.16 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide EDC and 0.16 mmol of N-hydroxysuccinimide NHS to the CNT aqueous dispersion, and magnetically stir at 1000 rpm at 25°C and in the dark for 3 h to obtain an activated carboxylated CNT aqueous dispersion;

[0081] S2: Dissolve 0.12 mmol of levodopa and 0.12 mmol of L-ascorbic acid in the activated carboxylated CNT aqueous dispersion, and then stabilize the pH of the dispersion at 7.8 by adding sodium bicarbonate NaHCO3 to obtain an activated carboxylated CNT aqueous dispersion reaction solution;

[0082] S3: Bubble nitrogen into the activated carboxylated CNT aqueous dispersion reaction solution with adjusted pH for 10 min to remove dissolved oxygen, and magnetically stir at 1000 rpm at 25°C

[0083] and in the dark for 3 hours to continue the reaction, and prepare a reaction product carboxylated CNT aqueous dispersion;

[0084] S4: Transfer the reaction product carboxylated CNT aqueous dispersion into a 3 kDa dialysis bag, use 1 L of deionized water for dialysis, dialyze for 6 hours, and change the water every 2 hours;

[0085] S5: Freeze the dialyzed dispersion liquid in liquid nitrogen for 5 minutes, then put it into a freeze dryer for freeze-drying for 24 hours to obtain levodopa-modified carbon nanotube DCNT powder, and store the levodopa-modified carbon nanotube DCNT powder at 4°C;

[0086] Step 3: Weigh the MXene powder prepared in the first step and the levodopa-modified carbon nanotube DCNT powder prepared in the second step at 25°C

[0087] according to the mass ratios of MXene powder 1g:DCNT powder 5g, MXene powder 1g:DCNT powder 10g, MXene powder 1g:DCNT powder 15g, MXene powder 2g:DCNT powder 5g, MXene powder 2g:DCNT powder 10g, MXene powder 2g:DCNT powder 15g, MXene powder 4g:DCNT powder 5g, MXene powder 4g:

[0088] DCNT powder 10g, MXene powder 4g:DCNT powder 15g respectively;

[0089] Step 4: Take 5g - 10g of acrylamide AAM and 200 - 400mg of tetra-arm polyethylene glycol acrylate 4ARM-PEG-ACLT and add them to 20mL of deionized water to obtain a reaction mother liquor A containing 250 - 500mg·mL -1 of AAM and 10 - 20mg·mL -1 of the reaction mother liquor A,

[0090] ultrasonic for 60 minutes to evenly disperse the reaction mother liquor A, and then place the reaction mother liquor A in an ice-water bath;

[0091] Step 5: Take 4g of ammonium persulfate APS and add it to 10mL of deionized water to obtain a reaction mother liquor B containing 400mg·mL -1 of the reaction mother liquor B, ultrasonic for 60 minutes to evenly disperse the reaction mother liquor B, and then place the reaction mother liquor B in an ice-water bath;

[0092] Step 6: Dissolve the MXene powder and DCNT powder with different mass ratios weighed in the third step in 2mL of the reaction mother liquor A respectively, then add 50 - 100μL of the reaction mother liquor B, and finally add 4 - 8μL of a 5% volume concentration of N,N,N',N'-tetramethylethylenediamine TEMED aqueous dispersion liquid. After inverting and shaking 10 times by hand, quickly transfer the obtained pre-gelled liquid to a mold and let it stand at room temperature for 30 - 60 minutes to obtain a resistive strain sensing hydrogel with high tensile performance and high sensitivity.

[0093] As Figure 1 shown, Figure 1Among them, a and b are respectively the mechanism diagrams of synthesizing Dopa-modified CNT and preparing DCM hydrogel. By using the activation reaction of NHS and EDC, the amino group of Dopa is coupled with the carboxyl group on the surface of carboxylated CNT to obtain DCNT. Then, AAm, DCNT, MXene, and 4ARM-PEG-ACLT are added to deionized water and stirred evenly. Finally, APS (initiator) and TEMED (catalyst) are added to the mixed solution, and the DCM hydrogel is obtained through free radical polymerization reaction.

[0094] As Figure 2 shown, it is the TEM image of DCNT modified by Dopa. It can be seen from the TEM that DCNT binds to the surface of MXene, and there are a large number of N elements on the surface of DCNT modified by Dopa, which proves that Dopa is successfully modified on the surface of CNT.

[0095] As Figure 3 shown, it is the TEM image of DCNT-MXene modified by Dopa. There are a large number of N elements on the surface of DCNT-MXene modified by Dopa, which proves the successful synthesis of DCNT-MXene.

[0096] Example 2: Long-term stable dispersion test of DCNT in aqueous phase.

[0097] To prove the excellent performance of DCNT aqueous dispersion in the present invention, a dispersion test was carried out on this material, using amino-functionalized CNT and carboxylated CNT as the control groups. The concentration of CNT added to the experimental group and the control groups was both 10 mg mL -1 , and the CNT was added to a sample bottle containing 1 mL of deionized water and ultrasonically oscillated until it was evenly dispersed. As Figure 4 shown in a, the three groups of solutions were in a uniformly dispersed state at the initial state. As Figure 4 shown in b, when the standing time of the aqueous dispersion reached 30 minutes, both amino-functionalized CNT and carboxylated CNT showed precipitation, while DCNT modified by Dopa was fully dispersed in water. As Figure 4 shown in c, when the solution was left standing for 24 hours, both amino-functionalized CNT and carboxylated CNT were completely precipitated, while DCNT modified by Dopa was still fully dispersed in water. As Figure 4 shown in d-f, d is the dispersion state diagram of amino-functionalized CNT, carboxylated CNT, and DCNT modified by Dopa after standing for 7 days; e is the dispersion state diagram of amino-functionalized CNT, carboxylated CNT, and DCNT modified by Dopa after standing for 30 days; f is the dispersion state diagram of amino-functionalized CNT, carboxylated CNT, and DCNT modified by Dopa after standing for 60 days. After standing for two months, DCNT still remained stable and had good aqueous dispersion performance.

[0098] Example 3: Testing the mechanical properties and sensing ability of a resistive strain-sensing hydrogel with high tensile performance and high sensitivity.

[0099] To verify the mechanical properties and sensing ability of the resistive strain-sensing hydrogel in the present invention, pure MXene hydrogel (M hydrogel), unmodified CNT hydrogel (C hydrogel), and unmodified CNT-MXene hydrogel (CM hydrogel) were used as control groups, and the modified DCNT-MXene hydrogel (DCM hydrogel) was used as the experimental group. As Figure 5 shown in a-b therein, where a is the comparison diagram of the mechanical properties of DCM, CM, C, and M hydrogels, and b is the comparison diagram of the sensing ability of DCM, CM, C, and M hydrogels. In the present invention, the mechanical properties of the DCM hydrogel are significantly improved. The DCM hydrogel exhibits a high fracture strain of up to 1287%, which is significantly improved compared to 550.2% of the CM hydrogel. The DCM hydrogel has a high Young's modulus of 76.4 kPa, which is significantly improved compared to 50.4 kPa of the CM hydrogel. At the same time, the fracture energy of the DCM hydrogel is 1.59 MJ / m 3 , far exceeding 0.638 MJ / m of the CM hydrogel 3 . By comparing the sensing sensitivities of the DCM hydrogel and other control group hydrogels, it can be seen that the sensing coefficient (Gauge factor) of the DCM hydrogel, i.e., GF = (ΔR / R0)(ΔL / L0) -1 is as high as 20.15 in the strain range of 900% - 1300%, with a sensing ability far stronger than that of the control group hydrogels. By comparing the mechanical properties and sensing abilities of the DCM hydrogel and the control group gels, it can be found that the mechanical properties and sensing abilities of the modified DCM gel are much higher than those of the control group, demonstrating that the resistive strain-sensing hydrogel sensor in the present invention has very high mechanical properties and sensing.

[0100] Example 4: Testing the mechanical properties and sensing ability of a resistive strain-sensing hydrogel with high tensile performance and high sensitivity after adjusting the concentrations of DCNT and MXene.

[0101] To verify the optimal mechanical and sensing properties of the resistive strain-sensing hydrogel in the present invention, the concentrations of DCNT and MXene were optimized and regulated respectively. First, mechanical and force-electric coupling performance tests were carried out for the DCNT concentration (5, 10, 15 mg·mL -1 ). As Figure 6 shown in a and Figure 6 c therein, when the DCNT concentration is 10 mg·mL -1When the concentration is [specific value], the tensile strength of the hydrogel reaches 227.4 kPa, and the relative change rate of resistance is as high as 15929.5%. Based on the calculation formula of the gauge factor (GF): GF = (ΔR / R0)(ΔL / L0) -1 , the maximum GF value of the hydrogel at this concentration reaches 20.15, which is significantly better than that of samples at other concentrations, indicating its excellent mechanical and sensing properties. Subsequently, the MXene concentration (1, 2, 4 mg·mL -1 ) was further optimized and the same tests were carried out. As shown in Figure 6 b and Figure 6 d, when the MXene concentration is 1 mg·mL -1 , the hydrogel exhibits the best mechanical strength and electrical sensing characteristics. Therefore, in this example, by systematically regulating the component concentration, the optimal ratio of DCNT (10 mg·mL -1 ) and MXene (1 mg·mL -1 ) was determined, providing a key parameter basis for the preparation of high-performance resistive strain-sensing hydrogels.

[0102] Example 5: Adhesion performance test of resistive strain-sensing hydrogel with high tensile performance and high sensitivity.

[0103] To verify the adhesion performance of the resistive sensing hydrogel in the present invention, adhesion tests were carried out on iron sheets, pigskins, copper sheets, plastics, and glasses respectively. As shown in Figure 7 , by sandwiching the gel between two layers of substrates for 30 minutes to allow the gel to fully adhere to the substrates, the test results show that the maximum adhesion strengths of the DCM hydrogel to iron sheets, pigskins, copper sheets, plastics, and glasses reach 51.93, 43.78, 32.1, 28.8, and 26.86 kPa respectively, which proves the excellent adhesion ability of the hydrogel.

[0104] Example 6: Application test of resistive strain-sensing hydrogel with high tensile performance and high sensitivity.

[0105] To verify the application test of the resistive strain-sensing hydrogel in the present invention, it was used as a skin wearable device for accurately and real-time monitoring of subtle human activity signals. As shown in Figure 8 , this strain sensor can be used to monitor various human activities. As shown in Figure 8 a, by adhering the gel to the knuckle, when the finger bends, it can be seen that as the finger bending angle increases, the resistance change rate also increases simultaneously, and each bending angle has a corresponding resistance change rate. Therefore, finger activities can be monitored by observing the resistance change rate. As shown in Figure 8 b, by adhering the gel to the wrist, when the wrist bends, the resistance also changes periodically, and the resistance change rate reaches 45%. As shown in Figure 8In c, by adhering the gel to the elbow, when the hand is bent at 90°, the corresponding resistance change rate also varies periodically, and the resistance change rate reaches 70%. As Figure 8 shown in d, by adhering the gel to the throat, when swallowing movements are performed, the corresponding resistance change rate reaches 10%. Therefore, this strain sensor has the potential to monitor human physiological signals and body movements, which provides important information for the control of robot systems.

Claims

1. A preparation method of a resistive strain sensing hydrogel, characterized in that, The specific steps are as follows: Step 1, prepare an aqueous MXene dispersion: Using a MAX phase material as a raw material, etch the Al layer of the MAX phase material with HF, and then synthesize a single-layer or few-layer Ti3C2T x MXene solution, and obtain MXene powder by freeze-drying; Step 2: Prepare levodopa-modified carbon nanotubes DCNT: S1: Take 0.5 - 1 g of CNT and dissolve it in 25 - 50 mL of deionized water to obtain a CNT aqueous dispersion. Then add 0.16 - 0.32 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide EDC and 0.16 - 0.32 mmol of N-hydroxysuccinimide NHS to the CNT aqueous dispersion, and stir magnetically at 1000 rpm under the conditions of 22 - 28 °C and light avoidance for 3 hours to make the reaction proceed, obtaining an activated carboxylated CNT aqueous dispersion; S2: Dissolve 0.12 - 0.24 mmol of levodopa and 0.12 - 0.24 mmol of L-ascorbic acid in the activated carboxylated CNT aqueous dispersion, and then stabilize the pH of the dispersion at 7.8 by adding sodium bicarbonate NaHCO3 to obtain an activated carboxylated CNT aqueous dispersion reaction solution; S3: Pass nitrogen into the activated carboxylated CNT aqueous dispersion reaction solution with adjusted pH for 10 - 15 minutes to remove dissolved oxygen, and stir magnetically at 1000 rpm under the conditions of 22 - 28 °C and light avoidance to make the reaction continue for 3 hours, obtaining a reaction product carboxylated CNT aqueous dispersion; S4: Transfer the reaction product carboxylated CNT aqueous dispersion into a 3 kDa dialysis bag, and use 1 L of deionized water for dialysis for 6 hours; S5: Freeze the dialyzed dispersion in liquid nitrogen for 5 minutes, and then place it in a freeze dryer for freeze-drying for 24 hours to obtain levodopa-modified carbon nanotubes DCNT powder, and store the levodopa-modified carbon nanotubes DCNT powder at 4 °C; Step 3: Weigh the MXene powder prepared in Step 1 and the levodopa-modified carbon nanotubes DCNT powder prepared in Step 2 at 25 °C according to the mass ratios of 1 g of MXene powder : 5 g of DCNT powder, 1 g of MXene powder : 10 g of DCNT powder, 1 g of MXene powder : 15 g of DCNT powder, 2 g of MXene powder : 5 g of DCNT powder, 2 g of MXene powder : 10 g of DCNT powder, 2 g of MXene powder : 15 g of DCNT powder, 4 g of MXene powder : 5 g of DCNT powder, 4 g of MXene powder : 10 g of DCNT powder, 4 g of MXene powder : 15 g of DCNT powder respectively; Step 4: Take 5 g - 10 g of acrylamide AAM and 200 - 400 mg of tetra-armed polyethylene glycol acrylate 4ARM-PEG-ACLT and add them to 20 mL of deionized water to obtain reaction mother liquor A containing 250 - 500 mg·mL -1 of AAM and 10 - 20 mg·mL -1 of reaction mother liquor A, ultrasonicate for 60 minutes to evenly disperse reaction mother liquor A, and then place reaction mother liquor A in an ice-water bath; Step 5: Add 4 g of ammonium persulfate (APS) to 10 mL of deionized water to obtain reaction mother liquor B containing 400 mg·mL -1 . Ultrasonicate for 60 minutes to uniformly disperse reaction mother liquor B, and then place reaction mother liquor B in an ice-water bath; Step 6: Dissolve the MXene powder and DCNT powder with different mass ratios weighed in Step 3 in 2 mL of reaction mother liquor A respectively, then add 50 - 100 μL of reaction mother liquor B, and finally add 4 - 8 μL of an aqueous dispersion of N,N,N',N'-tetramethylethylenediamine TEMED with a volume concentration of 5%. After inverting and shaking by hand 10 times, quickly transfer the obtained pre-gelled liquid to a mold and let it stand at room temperature for 30 - 60 minutes to obtain a resistive strain sensing hydrogel with high tensile performance and high sensitivity.

2. The preparation method of the resistive strain sensing hydrogel according to claim 1, characterized in that The specific steps of Step 1 are as follows: Step 1: Take 30 mL of 12 M hydrochloric acid solution and place it in a 100 mL polytetrafluoroethylene beaker, and place the beaker in an ice-water bath; then pour 2 g of LiF into the hydrochloric acid solution at 25 °C and continuously stir for 45 minutes until lithium fluoride LiF is completely dissolved; Step 2: Divide 2 g of Ti3AlC2 MAX phase material into 5 equal parts, with each part being 0.4 g, and pour it into the beaker to make it fully contact with hydrochloric acid and LiF, and then seal the beaker for 15 minutes; Step 3: Transfer the mixed solution into a 35 °C water bath, and at the same time stir at a speed of 500 rpm for 24 hours. Centrifuge the obtained black reaction solution at a speed of 4000 rpm, and then wash the precipitate with deionized water, and manually shake to fully disperse the black solid in the solution; Step 4: Repeat the centrifugation, washing, and shaking steps in Step 3 until the pH of the centrifuged supernatant reaches 6; Step 5: Under an ice-water bath environment, ultrasonically exfoliate for 1 hour at a frequency of 40 kHz, centrifuge at 6000 rpm for 1 hour, retain the supernatant, and obtain few-layer or single-layer Ti3C2T x MXene solution; Step 6: Place the dispersion in liquid nitrogen and freeze it for 5 minutes, and then put it into a freeze dryer for freeze-drying for 24 hours. The obtained MXene powder is stored at 4 °C.

3. The preparation method of the resistive strain sensing hydrogel according to claim 1, characterized in that: In S1, 0.5 g of CNT is dissolved in 25 mL of deionized water to obtain a CNT aqueous dispersion. Then, 0.16 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide EDC and 0.16 mmol of N-hydroxysuccinimide NHS are added to the CNT aqueous dispersion, and the reaction is carried out at 25 °C and in the dark with magnetic stirring at 1000 rpm for 3 h to obtain an activated carboxylated CNT aqueous dispersion.

4. The preparation method of the resistive strain sensing hydrogel according to claim 1, characterized in that: In S2, 0.12 mmol of levodopa and 0.12 mmol of L-ascorbic acid are dissolved in the activated carboxylated CNT aqueous dispersion.

5. The preparation method of the resistive strain sensing hydrogel according to claim 1, wherein: In S3, nitrogen is introduced into the activated carboxylated CNT aqueous dispersion reaction solution with adjusted pH for 10 min to remove dissolved oxygen, and the reaction is continued at 25 °C and in the dark with magnetic stirring at 1000 rpm for 3 hours to obtain a reaction product carboxylated CNT aqueous dispersion.

6. The preparation method of the resistive strain sensing hydrogel according to claim 1, characterized in that: In S4, change the water every 2 hours during dialysis for 6 hours.

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