Preparation method and application of chitin-based conductive hydrogel

Abstract

The invention relates to the technical field of flexible sensing, in particular to a preparation method and application of chitin-based conductive hydrogel, and the preparation method comprises the following steps: firstly synthesizing acrylamide chitin in an alkali / urea solution, then introducing Al < 3 + > and polylysine, and forming the conductive hydrogel through a rapid physical crosslinking effect. The chitin-based conductive hydrogel disclosed by the invention has the characteristics of self-healing property, adhesiveness, antibacterial property, sensitivity and the like. The strain sensor prepared from the conductive hydrogel has huge potential in the aspect of human health monitoring, and a new design thought is provided for construction of wearable electronic equipment.

Description

Technical Field

[0001] The invention relates to the technical field of flexible sensing, and in particular to a preparation method of a chitosan-based conductive hydrogel and application thereof. Background Art

[0002] With the substantial improvement of economic level, the importance of people's health has become increasingly prominent. However, traditional health monitoring systems often rely on bulky precision instruments, which have limited applicability and usage scenarios. Therefore, there is an urgent need to design intelligent and convenient health monitoring systems to achieve real-time home health tracking. Wearable electronic devices can monitor human health and movement in real time and provide accurate and stable data for subsequent diagnosis and treatment, so they have received widespread attention. The most important component of wearable electronic devices is the sensor, which can convert mechanical deformation such as stretching or bending into electrical signals, such as changes in electrical signals such as resistance, current or capacitance. At present, hydrogels have the advantages of good flexibility, biocompatibility and similarity to biological tissue structure, and have become ideal candidate materials for designing wearable sensors. However, most hydrogels are prepared by chemical cross-linking, which usually leads to reduced toughness and inability to withstand large mechanical strains. At the same time, these chemically cross-linked hydrogels show limited self-healing ability under external forces, which shortens their lifespan and limits their application potential. In addition, traditional strain sensors based on hydrogels often show poor adhesion, which may cause a gap between the sensor and the skin during movement, resulting in weakened electrical signals or inaccurate measurements. Worse still, the moist environment of the hydrogel provides favorable conditions for bacterial growth, making it easy for bacteria to adhere to the moist surface of the hydrogel. This adhesion can lead to corrosion of the conductive layer and subsequently impair the sensing performance of the sensor. Therefore, an ideal hydrogel sensor should integrate as many functions as possible to meet the needs of practical applications. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention provides a preparation method and application of a chitosan-based conductive hydrogel integrating self-healing, adhesion, antibacterial and other multifunctional properties.

[0004] In order to achieve the above purpose, the technical solution adopted in this scheme is: a method for preparing a conductive hydrogel, comprising the following steps: (1) dissolving chitosan in an alkali / urea solution to obtain a transparent chitosan solution; (2) Adding acrylamide to the chitosan solution in step (1) and mechanically stirring. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+A mixed solution of polylysine and conductive hydrogel is obtained through physical cross-linking.

[0005] As a preferred embodiment, the mass concentration of the chitosan solution in step (1) is 1-3 wt%. More preferably, the mass concentration of the chitosan solution in step (1) is 1 wt%. As a preferred embodiment, the molar ratio of acrylamide in step (2) to the N-acetyl-D-glucosamine unit of chitin is 5:1, 10:1, or 15:1. More preferably, the molar ratio of acrylamide in step (2) to the N-acetyl-D-glucosamine unit of chitin is 10:1.

[0006] As a preferred embodiment, the mechanical stirring speed in step (2) is 600 rpm / min, and the reaction temperature is 30°C. More preferably, the method for preparing the conductive hydrogel in step (2) is characterized in that the mechanical stirring speed in step (2) is 600 rpm / min, and the reaction temperature is 30°C.

[0007] As a preferred embodiment, the mass concentration of the acrylamide chitosan solution in step (3) is 1 to 3 wt%. More preferably, the mass concentration of the acrylamide chitosan solution in step (3) is 3 wt%. As a preferred embodiment, the Al in step (3) 3+ The concentration of Al in step (3) is 0.01 to 1 mol / L. 3+ The concentration is 0.04 mol / L.

[0008] As a preferred embodiment, the concentration of polylysine in step (3) is 1-3 mg / mL. More preferably, the concentration of polylysine in step (3) is 2 mg / mL.

[0009] In the process of preparing conductive hydrogel, it is necessary to follow the provided order, first prepare acrylamide chitosan, dissolve acrylamide chitosan, and then add Al 3+ Otherwise, the conductive hydrogel of the present invention cannot be obtained.

[0010] The present invention also provides a conductive hydrogel prepared by the above preparation method.

[0011] The present invention also provides application of the conductive hydrogel in preparing a strain sensor.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The conductive hydrogel provided by the present invention has the advantages of self-healing, adhesion, antibacterial and sensitivity. The strain sensor prepared by using the conductive hydrogel of the present invention can be applied to the fields of health, motion detection and robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0014] Attached Figure 1 The compression modulus test results of the conductive hydrogels prepared in Examples 1, 2, 3, and 4 are shown, where AMC-Al is Example 1, ε-PL1 / AMC-Al is Example 2, ε-PL2 / AMC-Al is Example 3, and ε-PL3 / AMC-Al is Example 4.

[0015] Attached Figure 2 The conductivity test results of the conductive hydrogel prepared in Examples 1-4 are shown.

[0016] Attached Figure 3 This is a graph showing the rheological test results of the conductive hydrogel prepared in Example 3.

[0017] Attached Figure 4 The results of the adhesion performance of the conductive hydrogel prepared in Example 3 to different substrates (a) and its adhesion strength (b) are shown.

[0018] Attached Figure 5 This is a diagram showing the antibacterial results of the conductive hydrogel prepared in Example 3.

[0019] Attached Figure 6 The sensing performance experimental test results of the hydrogel flexible sensor prepared in Example 3 are shown in Figure 3. (a) is the sensitivity factor (GF) test result of the hydrogel strain sensor, and (b) is the relative resistance change of the hydrogel strain sensor monitoring the bending of a human finger. DETAILED DESCRIPTION

[0020] (1) dissolving chitosan in an alkali / urea solution to obtain a transparent chitosan solution; (2) Adding acrylamide monomer to the chitosan solution in step (1) and mechanically stirring. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of polylysine and conductive hydrogel is obtained through physical cross-linking.

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0022] Example 1 A method for preparing a conductive hydrogel comprises the following steps: (1) Dissolve 1 g of chitosan in an alkali / urea solution to obtain a 1 wt% chitosan transparent solution; (2) Add 3.5 g of acrylamide to the chitosan solution in step (1) and stir mechanically. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of Al and polylysine was stirred to obtain a conductive hydrogel. 3+ The concentration was 0.04 mol / L, and the concentration of poly-lysine was 0 mg / mL.

[0023] Example 2 A method for preparing a conductive hydrogel comprises the following steps: (1) Dissolve 1 g of chitosan in an alkali / urea solution to obtain a 1 wt% chitosan transparent solution; (2) Add 3.5 g of acrylamide to the chitosan solution in step (1) and stir mechanically. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of Al and polylysine was stirred to obtain a conductive hydrogel. 3+ The concentration is 0.04 mol / L, and the concentration of poly-lysine is 1 mg / mL.

[0024] Example 3 A method for preparing a conductive hydrogel comprises the following steps: (1) Dissolve 1 g of chitosan in an alkali / urea solution to obtain a 1 wt% chitosan transparent solution; (2) Add 3.5 g of acrylamide to the chitosan solution in step (1) and stir mechanically. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of Al and polylysine was stirred to obtain a conductive hydrogel. 3+ The concentration is 0.04 mol / L and the concentration of poly-lysine is 2 mg / mL.

[0025] Example 4 A method for preparing a conductive hydrogel comprises the following steps: (1) Dissolve 1 g of chitosan in an alkali / urea solution to obtain a 1 wt% chitosan transparent solution; (2) Add 3.5 g of acrylamide to the chitosan solution in step (1) and stir mechanically. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of Al and polylysine was stirred to obtain a conductive hydrogel. 3+ The concentration is 0.04 mol / L, and the concentration of poly-lysine is 3 mg / mL.

[0026] Note: In “ε-PLx / AMC-Al”: ε-PL stands for polylysine, AMC stands for acrylamide chitosan, Al stands for aluminum ion, and “x” stands for the concentration of polylysine.

[0027] The hydrogel materials prepared in Examples 1-4 were tested for their compression properties on a universal testing machine at a compression rate of 2 mm / min. The test results of Examples 1-4 are shown in the attached figure. Figure 1 As shown in the figure, their compression moduli are 742 Pa, 547 Pa, 967 Pa and 574 Pa, respectively. The results show that the appropriate poly-lysine concentration is beneficial to improve the mechanical properties of the hydrogel and expand its working range.

[0028] The conductivity of the hydrogel materials prepared in Examples 1-4 was measured using a CHI660E electrochemical workstation, and the calculation formula was: σ = L / ( R × S ) (1) in L For hydrogels, S is the cross-sectional area, R is the measured hydrogel resistance.

[0029] The test results are as attached Figure 2 As shown, the conductivity of Examples 1-4 is 5.15, 3.87, 4.53 and 4.50 mS / m, respectively. The conductive hydrogel prepared in Example 3 has the best mechanical properties and conductivity, so the conductive hydrogel prepared in Example 3 is selected for subsequent testing.

[0030] The following is the performance test of the conductive hydrogel prepared in Example 3: (1) Self-healing performance test As attached Figure 3As shown in a, the self-healing performance of Example 3 was evaluated by rheological testing, and a strain amplitude sweep test was performed at 25 °C and a constant frequency of 5 rad / s ( γ = 1~1000%). When the shear strain exceeds 870%, the hydrogel undergoes a sol-gel transition, indicating that there is a reversible bond breakage in the hydrogel network. In the continuous step strain scanning experiment, each strain test interval is 60 s. γ = 50%) and large strains above the maximum critical strain that the hydrogel can withstand ( γ =900%) for 5 times. The results are shown in the attached Figure 3 As shown in b, when 900% strain is applied, G The value of ' immediately dropped. G '' value exceeds G ' value. When the strain recovers to 50%, G ′ value and G The values ​​of '' all recovered quickly to the initial values ​​within a few seconds, proving that the repair behavior of the conductive hydrogel prepared in Example 3 is completely reversible and repeatable.

[0031] (2) Adhesion performance test As attached Figure 4 As shown in a, the adhesion properties of the conductive hydrogel of Example 3 were evaluated and its adhesion properties to different substrates were investigated. The conductive hydrogel of Example 3 has significant adhesion to a variety of substrates, including rubber, glass, metal, wood, and skin. Even under bending and twisting conditions, it can maintain tight adhesion to pig skin without any signs of cracking or detachment. The adhesion strengths of the conductive hydrogel of Example 3 to rubber, glass, metal, wood, and skin are 4.90, 3.95, 5.61, and 15.67 kPa, respectively (attached Figure 4 b). These results indicate that the hydrogel can directly adhere to the object being measured, ensuring close contact with the object being measured, thereby facilitating the stable and sensitive transmission of electrical signals.

[0032] (3) Antibacterial performance test The conductive hydrogel prepared in Example 2-3 was tested for its antibacterial properties, and the antibacterial activity of Escherichia coli ( Escherichia coli , E. coli ) as the representative of Gram-negative bacteria, with Staphylococcus aureus ( Staphylococcus aureus , S. aureus ) Gram-positive bacteria representatives, and the bacterial solution treated with PBS was used as the control group, and their antibacterial properties were evaluated by plate coating method.

[0033] The results are attached Figure 5As shown, compared with the conductive hydrogel prepared in Example 2, the conductive hydrogel prepared in Example 3 with the addition of polylysine has a E. coli and S. aureus All showed better antibacterial properties. It can be concluded that the addition of polylysine not only improves the mechanical properties of the hydrogel, but also gives it antibacterial ability, making it more conducive to the application of sensors.

[0034] (4) Strain sensing performance The change in relative resistance of the hydrogel prepared in Example 3 during the stretching process was measured by a CHI660E electrochemical workstation, and then its sensitivity factor (GF) was calculated. The calculation formula is: GF = (Δ R / R 0 ) / ε (2) Where Δ R is the change in hydrogel resistance during stretching, R 0 is the initial resistance of the hydrogel before stretching, Δ R / R 0 is the relative resistance of the hydrogel during stretching, ε is the strain value corresponding to the stretching process of the hydrogel.

[0035] As attached Figure 6 As shown in Figure 1, the GF values ​​of the strain sensor prepared based on the conductive hydrogel of Example 3 in the strain range of 0-20% and 20-100% are 0.734 and 0.228, respectively, proving that it can provide sensitive electrical signal response in a relatively wide strain range. The conductive hydrogel prepared in Example 3 was adhered to the finger joint as a strain sensor material to conduct a verification test on the feasibility of flexible strain sensing (see Figure 1). Figure 6 b). It can be found that as the finger bends back and forth, the strain sensor generates stable and repeatable electrical signal feedback, proving that the conductive hydrogel has good repeatability, stability and sensitivity, and is fully suitable for use as a flexible sensing material.

[0036] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-based conductive hydrogel, characterized in that: The following steps are involved: (1) dissolving chitosan in an alkali / urea solution to obtain a transparent chitosan solution; (2) Adding acrylamide to the chitosan solution in step (1) and mechanically stirring. The resulting mixed solution is dialyzed with deionized water and freeze-dried to obtain acrylamide chitosan; (3) After dissolving the acrylamide chitosan obtained in step (2), add Al 3+ A mixed solution of polylysine and conductive hydrogel is obtained through physical cross-linking.

2. The method for preparing the conductive hydrogel according to claim 1, characterized in that: The concentration of the chitosan solution in step (1) is 1-3 wt%.

3. The method for preparing the conductive hydrogel according to claim 1, characterized in that: In step (2), the molar ratio of acrylamide to the N-acetyl-D-glucosamine unit of chitin is 5:1, 10:1, and 15:

1.

4. The method for preparing the conductive hydrogel according to claim 1, characterized in that: The mechanical stirring speed in step (2) is 600 rpm / min, and the reaction temperature is 15-30 °C.

5. The method for preparing the conductive hydrogel according to claim 1, characterized in that: The deionized water dialysis time in step (2) is at least 5 days.

6. The method for preparing the conductive hydrogel according to claim 1, characterized in that: The mass concentration of the acrylamide chitosan solution described in step (3) is 1-3 wt%.

7. The method for preparing the conductive hydrogel according to claim 1, characterized in that: Al in step (3) 3+ The concentration is 0.01~0.1 mol / L.

8. The method for preparing the conductive hydrogel according to claim 1, characterized in that: The concentration of polylysine in step (3) is 1-3 mg / mL.

9. A conductive hydrogel obtained by the preparation method according to any one of claims 1 to 8.

10. Use of a conductive hydrogel obtained by the preparation method according to any one of claims 1 to 8 in preparing a strain sensor.

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