Preparation of resistance / capacitance dual-responsive mxene-based hydrogel flexible sensor

Abstract

The application discloses a preparation method of a resistance / capacitance dual-response MXene-based hydrogel flexible sensor, and the hydrogel flexible sensor is prepared by combining a microstructure hydrogel prepared from polyacrylamide, gelatin and MXene with an interdigital electrode. The hydrogel flexible sensor can simultaneously detect resistance response signals and capacitance response signals. The detected resistance and capacitance signals are complementary to each other, the single response signal mode of the flexible sensor is widened, the mutual calibration of the same group of data is realized, and the detection precision of the flexible sensor is improved. The MXene-based hydrogel flexible sensor is applied to the detection of human biological signals, for example, carotid artery pulse detection and radial artery pulse detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible sensors, in particular to the preparation of MXene-based hydrogel flexible sensors with resistance / capacitance dual response. BACKGROUND

[0002] Flexible sensors are widely used in soft robots, motion detection and health care due to their portability and elasticity. Current hydrogels as flexible sensor materials have good flexibility, excellent conductivity and mechanical stability. However, the functions of existing flexible sensors are often single. They can all detect resistance, capacitance or piezoelectric signals, but almost all of them exist in a single response signal mode, which not only has low signal sensitivity but also has a single response signal mode, and cannot realize some detection with high precision requirements, such as human pulse signal detection, which greatly hinders the application range of flexible sensors. SUMMARY

[0003] The present application aims to solve the above problems in the prior art and provide the preparation of MXene-based hydrogel flexible sensors with resistance / capacitance dual response for the detection of human biological signals.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] The preparation of MXene-based hydrogel flexible sensors with resistance / capacitance dual response is assembled by the inherent viscosity of the hydrogel between the MXene-based hydrogel with microstructure and the interdigital electrode.

[0006] The preparation of the MXene-based hydrogel with microstructure includes the following steps:

[0007] 1) Acrylamide monomer, N,N'-methylenebisacrylamide, ammonium persulfate and deionized water are stirred to prepare a polyacrylamide (PAM) solution;

[0008] 2) Mix the PAM solution, gelatin solution and MXene solution by volume ratio, and magnetically stir to dissolve to obtain a PGM mixed solution;

[0009] 3) Mix the PGM mixed solution and tetramethyl ethylenediamine and add to the mold, and heat polymerization crosslinking to obtain the MXene-based hydrogel with microstructure.

[0010] In step 1), the stirring time is 20-60 min, the stirring speed is 100-500 rpm, and the stirring temperature is 20-30℃; preferably 30 min, 200 rpm and 25℃.

[0011] In step 1), the mass concentration of the PAM solution is 400-450 mg / mL; preferably 430 mg / mL.

[0012] In step 2), the mass percentage of gelatin in the gelatin solution is 1%-8%, preferably 4%.

[0013] The single or mixed dispersion of one or more of the transition metal carbides or nitrides in the MXene solution is preferably a single-layer or few-layer titanium carbide dispersion, with a mass concentration of 1-20 mg / mL, preferably 13 mg / mL, and a solvent of deionized water.

[0014] In step 2), the volume ratio of the PAM solution: gelatin solution: MXene solution is 10:4:(1-4), preferably 10:4:3.

[0015] In step 2), the stirring time is 10-30 min, the temperature is 20-30℃, and the rotation speed is 100-500 rpm; preferably 25℃, 200 rpm.

[0016] In step 3), the volume of tetramethyl ethylenediamine is 10-100 uL, i.e. the volume ratio of PGM mixed solution to tetramethyl ethylenediamine is 400:(1-10), preferably 400:5; the thermal polymerization crosslinking temperature is 40-90℃, and the crosslinking reaction time is 3-10 min; preferably 80℃, 10 min.

[0017] In step 3), the microstructure of the mold is a cylinder with a diameter of 0.4-2 mm and a height of 0.4-2 mm, and the spacing between the cylinders is 0.4-2 mm; preferably a cylinder with a diameter and height of 0.5 mm, and a spacing of 0.5 mm between the cylinders.

[0018] The overall size of the interdigital electrode is a circle with a diameter of 8-24 mm, the electrode width is 0.4-0.6 mm, and the electrode spacing is 0.4-0.6 mm; preferably a circle with a diameter of 18 mm, and the electrode width and spacing are both 0.4 mm.

[0019] The hydrogel flexible sensor prepared as above widens the single response signal mode of the hydrogel flexible sensor, and can have both resistance response signals and capacitance response signals.

[0020] The application of the hydrogel flexible sensor is used to realize high-sensitivity detection of human biological signals, such as carotid artery pulse detection and radial artery pulse detection of the human body.

[0021] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0022] 1. Unlike the common single-function flexible sensor, the application can detect resistance response signals and capacitance response signals at the same time, which widens the single form of the hydrogel sensor on the response signal, and provides a flexible and controllable method for the recognition of human biological signals (such as carotid and radial artery signal detection).

[0023] 2. Compared with the existing flexible sensor, the application has more excellent sensor performance, including high resistance sensitivity (1.113kPa -1 ) and capacitance sensitivity (14.117kPa -1 ), stable cycle capacity (4000 cycles), etc.

[0024] 3. The preparation method of the application is simple, and can be mass-produced, which provides a new idea for the preparation of flexible wearable sensors. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM (scanning electron microscope) front view (magnification 2000 times) of the prepared MXene-based hydrogel.

[0026] Figure 2 FTIR spectrum (Fourier infrared spectrum) of PAM / Gelatin / MXene hydrogel (MXene-based hydrogel).

[0027] Figure 3 Schematic diagram of the MXene-based hydrogel flexible sensor.

[0028] Figure 4 Stress-strain curve of PAM, PAM / Gelatin / MXene (MXene-based hydrogel) under stretching.

[0029] Figure 5 Real-time resistance change rate of the MXene-based hydrogel flexible sensor under different pressures.

[0030] Figure 6 Real-time capacitance change rate of the MXene-based hydrogel flexible sensor under different pressures.

[0031] Figure 7 Resistance sensitivity of the MXene-based hydrogel flexible sensor under different pressures.

[0032] Figure 8 Capacitance sensitivity of the MXene-based hydrogel flexible sensor under different pressures.

[0033] Figure 9 Cycle test of the MXene-based hydrogel flexible sensor under 0.23kPa pressure.

[0034] Figure 10 The MXene-based hydrogel flexible sensor is pasted on the wrist skin to measure the radial artery pulse signal of the human body.

[0035] Figure 11 The MXene-based hydrogel flexible sensor is pasted on the neck skin to measure the carotid artery pulse signal of the human body. DETAILED DESCRIPTION

[0036] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects more clear, specific embodiments will be described in detail below.

[0037] Example 1

[0038] A preparation method of a MXene-based hydrogel with a microstructure:

[0039] (1) 30 g of acrylamide monomer was dissolved in 70 mL of deionized water, 0.1 g of ammonium persulfate and 0.05 g of N,N'-methylenebisacrylamide were added, and the PAM solution was obtained after uniform magnetic stirring (conditions: temperature 25℃, stirring speed 200 rpm, stirring time 30 min).

[0040] (2) A gelatin solution with a mass percentage of 4wt% was prepared.

[0041] (3) The MAX phase raw material (Ti3AlC2) was etched in an HCl / LiF mixed solution, and was subjected to dilute hydrochloric acid, deionized water and anhydrous ethanol ice bath ultrasonic and centrifugation several times to obtain an MXene dispersion (single-layer or few-layer Ti3C2Tx dispersion, concentration 13 mg / mL, solvent deionized water).

[0042] (4) The PAM solution, the gelatin solution and the MXene solution were mixed according to the optimal volume ratio (10:4:3), and the PGM mixed solution was obtained by magnetic stirring and dissolving (magnetic stirring time 10 min, temperature 25℃, stirring speed 200 rpm).

[0043] (5) 10 mL of the PGM mixed solution and 20 uL of tetramethyl ethylenediamine were mixed and added to the mold (the microstructure size of the mold was a cylinder with a diameter of 0.5 mm and a height of 0.5 mm, and the spacing between the cylinders was 0.5 mm), and the MXene-based hydrogel with a microstructure was obtained by heat polymerization and crosslinking (temperature 80℃, crosslinking reaction time 10 min).

[0044] (6) The characterization test of the MXene-based hydrogel with a microstructure is as follows: 1) After the prepared MXene-based hydrogel is freeze-dried, the internal structure of the MXene-based hydrogel is observed by SEM (scanning electron microscope), as shown inFigure 1 As shown, this is a front view (magnification of 2000x), which shows that it has a porous network structure; 2) After freeze-drying, the functional group information of the prepared MXene-based hydrogel was tested using FTIR (Fourier Transform Infrared Spectroscopy), such as... Figure 2 As shown, the test range is 400–4000 cm. -1 At 3331.91cm -1 A typical absorption peak was observed at 3186.67 cm⁻¹, corresponding to the stretching vibration of -OH, belonging to MXene, polyacrylamide, and gelatin. -1 The broad characteristic peak at 1649.00 cm⁻¹ is related to the tensile vibration of NH₄⁺ in polyacrylamide. -1 The absorption peak at 1599.85 cm⁻¹ corresponds to the carbonyl stretching vibration (amide I). -1 The absorption peak at that point corresponds to the NH bending vibration of the amide group (amide II).

[0045] Example 2

[0046] Fabrication and application of MXene-based hydrogel flexible sensors with resistance / capacitance response signals:

[0047] (1) A microstructured MXene-based hydrogel is combined with interdigitated electrodes (the overall size of the interdigitated electrodes is a circle with a diameter of 18 mm, an electrode width of 0.4 mm, and an electrode spacing of 0.4 mm). The MXene-based hydrogel is then used to assemble a flexible MXene-based hydrogel sensor through its inherent adhesive properties. Figure 3 The diagram shows a schematic of an MXene-based hydrogel flexible sensor.

[0048] (2) The stress-strain curves of PAM hydrogel and PAM / Gelatin / MXene hydrogel (MXene-based hydrogel) under different tensile conditions were tested using a micro tensile tester, such as... Figure 4 As shown, MXene-based hydrogels exhibit superior tensile properties (~1600% strain) compared to pure PAM hydrogels (~600% strain).

[0049] (3) The real-time resistance and capacitance changes of the MXene-based hydrogel flexible sensor under different pressures were tested using a micro-tensile tester and an LCR bridge, such as... Figure 5 and Figure 6 As shown. To evaluate the compressibility of the MXene-based hydrogel flexible sensor, the capacitive pressure sensitivity S was... C Defined as δ(ΔC / C0) / δP, where ΔC is the change in capacitance, C0 is the original capacitance, and δP is the change in applied pressure. Similarly, the resistance pressure sensitivity S RIt is defined as δ(ΔR / R0) / δP, where ΔR is the change in resistance and R0 is the original resistance. According to Figure 5 and 6 The data was used to plot the sensitivity graphs of capacitance and resistance, such as... Figure 7 and Figure 8 As shown, it exhibits excellent resistive sensitivity (1.113 kPa). -1 ), and capacitive sensitivity (14.117 kPa) -1 Furthermore, the cycling performance of the MXene-based hydrogel flexible sensor was tested under a pressure of 0.23 kPa, such as... Figure 9 As shown, the MXene-based hydrogel flexible sensor exhibits excellent cycling performance (4000 cycles).

[0050] (4) Using an LCR bridge to test the measurement of human biosignals (such as) by an MXene-based hydrogel flexible sensor. Figure 10 As shown, it is fitted to the skin of the human neck to measure the carotid artery pulse signal; Figure 11 As shown, the device is fitted to the skin of the human wrist to measure the radial artery pulse signal.

[0051] Two-dimensional (2D) titanium carbide (Ti3C2Tx) is a two-dimensional transition metal carbide and nitride (MXene). Due to its unique metallic conductivity and abundant hydrophilic groups, it possesses excellent processability and can be well-suited as a two-dimensional conductive filler material in hydrogels. Gelatin is a protein obtained by hydrolyzing animal collagen and is a natural biomolecule containing numerous active functional groups. Polyacrylamide (PAM) is a high-molecular-weight polymer. Due to the large number of amide groups in its molecular chain, it readily forms hydrogen bonds and can easily be cross-linked to obtain various modified products with network structures.

[0052] This invention utilizes a hydrogel with a microstructure, prepared from polyacrylamide, gelatin, and MXene, combined with interdigitated electrodes to create a flexible hydrogel sensor capable of simultaneously detecting both resistance and capacitance response signals. By leveraging the complementary nature of these two response signals, the single response signal mode of the flexible sensor can be broadened, enabling mutual calibration of the same set of data and improving the detection accuracy of the flexible sensor. This invention applies the MXene-based hydrogel flexible sensor to the detection of human biosignals, such as carotid and radial artery pulse detection.

Claims

1. A method for fabricating a flexible MXene-based hydrogel sensor with dual resistance / capacitance response, characterized in that: The hydrogel flexible sensor is assembled by bonding microstructured MXene-based hydrogel and interdigitated electrodes using the inherent adhesive properties of the hydrogel; the assembly includes the following steps: 1) A polyacrylamide (PAM) solution was prepared by stirring acrylamide monomer, N,N'-methylenebisacrylamide, ammonium persulfate and deionized water; 2) Mix PAM solution, gelatin solution and MXene solution by volume ratio, and dissolve them by magnetic stirring to obtain PGM mixed solution; 3) The PGM mixed solution and tetramethylethylenediamine were mixed and added into the mold, and then thermally polymerized and crosslinked to obtain an MXene-based hydrogel with a microstructure; In step 3), the microstructure of the mold is a cylinder with a diameter of 0.4~2mm and a height of 0.4~2mm, and the spacing between the cylinders is 0.4~2mm.

2. The method for fabricating the MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 1, characterized in that: In step 1), the stirring time is 20-60 min, the stirring speed is 100-500 rpm, and the stirring temperature is 20-30℃; the mass concentration of the PAM solution is 400-450 mg / mL.

3. The method for fabricating the MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 1, characterized in that: In step 2), the mass percentage of gelatin in the gelatin solution is 1% to 8%; the MXene solution is a monolayer or few-layer titanium carbide dispersion with a mass concentration of 1 to 20 mg / mL, and the solute is deionized water.

4. The method for fabricating the MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 1, characterized in that: In step 2), the volume ratio of PAM solution: gelatin solution: MXene solution is 10:4:(1~4).

5. The method for fabricating the MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 4, characterized in that: In step 2), the volume ratio of PAM solution: gelatin solution: MXene solution is 10:4:

3.

6. The method for fabricating a resistance / capacitance dual-response MXene-based hydrogel flexible sensor as described in claim 1, characterized in that: In step 2), the stirring time is 10~30 min, the temperature is 20~30℃, and the speed is 100~500 rpm.

7. The method for fabricating a resistance / capacitance dual-response MXene-based hydrogel flexible sensor as described in claim 1, characterized in that: In step 3), the volume ratio of the PGM mixed solution to tetramethylethylenediamine is 400:(1~10); the thermal polymerization crosslinking temperature is 40~90℃, and the crosslinking reaction time is 3~10min.

8. The method for fabricating the MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 7, characterized in that: In step 3), the volume ratio of the PGM mixed solution to tetramethylethylenediamine is 400:

5.

9. The method for fabricating a resistance / capacitance dual-response MXene-based hydrogel flexible sensor as described in claim 1, characterized in that: The overall size of the interdigitated electrode is a circle with a diameter of 8~24mm, an electrode width of 0.4~0.6mm, and an electrode spacing of 0.4~0.6mm.

10. The MXene-based hydrogel flexible sensor with dual resistance / capacitance response as described in claim 1, characterized in that: Used to achieve highly sensitive detection of human biosignals.

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