A self-healing gel and its preparation method and application

Abstract

The present invention discloses a self-healing gel and its preparation method and application. The present invention uses polyvinyl alcohol (PVA) as a substrate and modifies the substrate by adding phytic acid (PA) and glucose (Glucose). The cured hydrogel of the present invention can form a highly non-covalently cross-linked polymer network due to the presence of a large number of hydrogen bonds in the system. At the same time, due to the strong hydrogen bonding between polyvinyl alcohol, phytic acid and glucose molecules, the hydrogel has good stretchability (1200%) and self-healing properties at room temperature. When the healing time is 2 hours, the strain of this organic hydrogel based on natural materials can be restored to more than 900%, reflecting a strong and fast self-healing performance, so it can be used in flexible electronic devices.

Description

Technical Field

[0001] The invention relates to a hydrogel in the technical field of hydrogels, and in particular to a hydrogel with high biocompatibility and self-healing ability at room temperature, and a preparation method and application thereof. Background Art

[0002] In recent years, high-quality human life has put forward many challenges to flexible electronic devices in terms of wearing comfort, multifunctionality, and biocompatibility. Although most of the wearable electronic devices that have been studied can be flatly attached to curved surfaces or skin surfaces, due to the limitations of common substrates or conductive materials, most flexible devices have poor stretchability and skin affinity. For example, polyimide (PI), polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS) have Young's modulus much larger than that of human skin, so they will affect the comfort and safety of use during long-term use. In order to solve this problem, it is key to develop stretchable materials with similar mechanical strength and strong biocompatibility to human skin. After a lot of research, it was found that hydrogel is a polymer material with low Young's modulus, high water content and good biocompatibility. Therefore, the mechanical flexibility and functional designability of hydrogel are more similar to those of biological organisms, making it increasingly important in the fields of flexible electronic devices, tissue engineering, soft robots, and smart Internet of Things. However, traditional hydrogels with polyvinyl alcohol (PVA) as the main component have poor mechanical properties and need to be improved by chemically modifying them.

[0003] A Chinese patent (CN 107987439 B) proposes a method for modifying polyvinyl alcohol-based hydrogels by compounding lincomycin and succinyl chitosan. The modified hydrogel has better mechanical properties because chitosan molecules contain more amino and hydroxyl groups, have high reactivity, and are easier to chemically modify. In the literature "One-Step Preparation of a Highly Stretchable, Conductive, and Transparent Poly(vinylalcohol)-Phytic Acid Hydrogel for Casual Writing Circuits" (Shuai Zhang, Yihan Zhang, Bo Li, Peng Zhang, Lei Kan, Guojun Wang, Hao Wei, Xinyue Zhang and Ning Ma, ACS Applied Materials and Interfaces, 32441-32448, 2019), polyvinyl alcohol (PVA) and small molecule phytic acid (PA) were used as raw materials to prepare highly elastic and highly conductive hydrogels. The strong hydrogen bonding between polyvinyl alcohol (C-OH) and phytic acid (P-OH) allows the hydrogel to be cured in an ice bath. In addition to a strain of 1100%, this PVA-PA composite hydrogel also has high conductivity and transparency, reaching 1.34 kΩ / cm and 95% respectively. Phytic acid and glucose are two natural polymer materials, both of which have good hydrophilicity and biocompatibility. Phytic acid, also known as inositol hexaphosphate, has abundant phosphate groups and has strong chelating effects with many metals. Phytic acid reacts with polyvinyl alcohol under heating conditions to form a dense network structure with multiple cross-links of ester bonds and hydrogen bonds. Summary of the invention

[0004] In view of the shortcomings of the existing organic hydrogel synthesis technology, the present invention proposes a self-healing gel that does not require the addition of toxic crosslinking agents. The high-density crosslinked organic hydrogel is prepared in a simple physical freeze-thaw method using polyvinyl alcohol (PVA) as a substrate and utilizing the strong covalent bonds and non-covalent bonds between polyvinyl alcohol, phytic acid small molecules and glucose molecules. The hydrogel has good tensile properties and self-healing properties at room temperature.

[0005] The technical solution of the present invention is as follows:

[0006] 1. A method for preparing a self-healing gel

[0007] The method comprises the following steps:

[0008] 1) preparing a polyvinyl alcohol solution: dissolving polyvinyl alcohol in deionized water by stirring to obtain a transparent polyvinyl alcohol solution;

[0009] 2) preparing a mixed solution of polyvinyl alcohol, phytic acid and glucose: heating and stirring the polyvinyl alcohol solution, the phytic acid solution and the glucose solution in a mass ratio of 5:5:2 and mixing them uniformly, and standing them to remove bubbles to obtain a transparent mixed solution;

[0010] 3) Preparing a pre-cured hydrogel solution: pre-curing the transparent mixed solution in a water bath at 80° C., a thin film is formed on the surface of the pre-cured solution, and after the thin film is removed, the pre-cured hydrogel solution is obtained;

[0011] 4) Preparation of polyvinyl alcohol-based hydrogel: pouring the pre-cured hydrogel solution into the prepared mold, and then subjecting it to multiple freeze-thaw cycles for curing to obtain a self-healing hydrogel.

[0012] In the step 1), the solid content of the polyvinyl alcohol solution is 10-20%, the dissolution temperature is 80° C., the stirring speed is 900 rpm / min, and the stirring time is 24 hours.

[0013] In the step 2), the mass percentage concentration of the phytic acid solution is 50%.

[0014] In the step 2), the mass percentage concentration of the glucose solution is 20%.

[0015] The stirring temperature in step 2) is 70° C. and the stirring speed is 700 rpm / min.

[0016] In the freezing and thawing cycle in step 4), the freezing temperature is -50°C and the freezing time is 2 hours; the thawing temperature is room temperature, the thawing time is 30 minutes, and the number of freezing and thawing is 3 to 4 times. During the last thawing, the hydrogel is placed at room temperature until the water on the surface of the hydrogel evaporates and becomes sticky.

[0017] 2. A self-healing gel

[0018] 3. Application of a self-healing gel in the preparation of flexible and elastic electronic devices.

[0019] The main mechanism of the present invention includes:

[0020] (1) Taking advantage of the fact that phytic acid is rich in phosphoric acid and hydroxyl groups, it is cross-linked with polyvinyl alcohol, reducing the toxicity of the added cross-linking agent to the human body.

[0021] (ii) utilizing water bath heating conditions to strengthen the strength of the ester bond of polyvinyl alcohol phytate, improve the stability of the organic hydrogel in water, and reduce the probability of hydrolysis of the ester bond in water.

[0022] (iii) Taking advantage of the fact that glucose contains a large number of hydrogen bonds, the self-healing properties of the hydrogel are optimized.

[0023] (iv) In order to further increase the cross-linking network density of the organic hydrogel, the present invention adopts a freezing-thawing cycle curing method repeated three to four times at a temperature of -48°C. The cured organic hydrogel has good elasticity and stretchability while maintaining good conductivity.

[0024] The beneficial effects of the present invention are:

[0025] The hydrogel of the present invention can have a self-healing effect at room temperature or low temperature (-48°C-0°C) after being broken. When the healing time is 2 hours, the elongation at break of the hydrogel can still reach 900%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the infrared spectrum of the hydrogel in Example 1.

[0027] Figure 2 This is the ultraviolet absorption spectrum of the hydrogel in Example 1.

[0028] Figure 3 Schematic diagram of the stretching of the hydrogel in Example 1.

[0029] Figure 4 This is a characterization diagram of the fracture performance of the hydrogel in Example 1.

[0030] Figure 5 This is an optical microscope comparison of the broken part of the hydrogel in Example 1 before and after healing at room temperature.

[0031] Figure 6 This is an optical microscope comparison picture of the hydrogel fracture in Example 2 after healing at room temperature.

[0032] Figure 7 This is an optical microscope comparison picture of the hydrogel fracture in Example 3 after healing at room temperature. DETAILED DESCRIPTION

[0033] In order to better illustrate the advantages of this synthesis technology, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0034] Example 1

[0035] 1) Prepare a polyvinyl alcohol solution with a solid content of 10% by adding 10 g of polyvinyl alcohol to 90 g of deionized water, stirring and dissolving at 80° C. for 24 h to obtain a uniform and transparent polyvinyl alcohol solution, which is then stored for later use;

[0036] 2) preparing a mixed solution of polyvinyl alcohol, phytic acid and glucose: adding 5 g of a phytic acid solution with a mass percentage concentration of 50% and 2 g of a glucose solution with a mass percentage concentration of 20% to 5 g of a polyvinyl alcohol solution, respectively, and stirring and mixing them uniformly at 70° C. at a stirring speed of 700 rpm / min. The stirred solution contained a large amount of bubbles. After standing to remove bubbles, a transparent mixed solution was obtained;

[0037] 3) Preparing a pre-cured hydrogel viscous liquid: The mixed and defoamed mixture solution is pre-cured in a water bath at 80° C. The pre-cured liquid is light brown and viscous. There is a thin film on the surface of the solution, which is formed by rapid water loss of the surface solution during heating. After the thin film is peeled off with tweezers, a pre-cured hydrogel solution is obtained;

[0038] 4) Preparation of polyvinyl alcohol-based hydrogel: pour the pre-cured hydrogel solution into the prepared mold, and then perform three freeze-thaw cycles to solidify, with the freezing temperature being -50°C and the freezing time being 2 hours; the thawing temperature being room temperature and the thawing time being 30 minutes. During the last thawing, leave it at room temperature for a long time until the water on the surface of the hydrogel evaporates and becomes sticky, thereby obtaining a hydrogel with elasticity and self-healing properties.

[0039] from Figure 1 The infrared spectrum of PPH hydrogel shows that -1 The absorption peak at 2916.65 cm is the stretching vibration peak of the phosphate bond POC. -1 and 3291.96cm -1 The two absorption peaks are the stretching vibration peaks of CH and OH in PPH hydrogel. At the same time, phytic acid can ionize a large number of hydrogen ions in water, so the addition of phytic acid can make the hydrogel have better conductivity. Glucose contains more hydroxyl groups and is easy to undergo esterification reaction with phytic acid. At the same time, it can also form stronger hydrogen bonds and electrostatic effects with polyvinyl alcohol and phytic acid molecules, making the hydrogel have a more stable cross-linking structure and faster self-healing performance.

[0040] The hydrogel (PPH) prepared from three polymer raw materials, polyvinyl alcohol, phytic acid and glucose, has good transparency (see Figure 2 ) and elasticity (see Figure 3 ),from Figure 4 From the fracture performance diagram, we can see that the maximum strain of the gel is 1200%. At this time, the maximum stress of the hydrogel is less than 20Kpa, which means that the number of cross-linked non-covalent bonds inside the hydrogel is far greater than the number of covalent bonds. The advantage of this feature is that the self-healing performance of the hydrogel is improved, hydrogen bonds can be formed in a shorter time, and it can recover to the state before fracture to a greater extent. Figure 5 The optical microscope image of the hydrogel healed half an hour after fracture shows that the fracture has healed well.

[0041] Example 2

[0042] 1) Prepare a polyvinyl alcohol solution with a solid content of 15% by adding 15 g of polyvinyl alcohol into 85 g of deionized water, stirring and dissolving at 80° C. for 24 h to obtain a uniform and transparent polyvinyl alcohol solution, which is stored for later use;

[0043] 2) preparing a mixed solution of polyvinyl alcohol, phytic acid and glucose: adding 5 g of a phytic acid solution with a mass percentage concentration of 50% and 2 g of a glucose solution with a mass percentage concentration of 20% to 5 g of a polyvinyl alcohol solution, respectively, stirring and mixing the mixture at 70° C., standing the mixture to remove bubbles, and obtaining a transparent mixed solution;

[0044] 3) Preparing a pre-cured hydrogel viscous liquid: The mixed and defoamed mixture solution is pre-cured in a water bath at 80° C. The pre-cured liquid is light brown and viscous. There is a thin film on the surface of the solution, which is formed by rapid water loss of the surface solution during heating. After the thin film is peeled off with tweezers, a pre-cured hydrogel solution is obtained;

[0045] 4) Preparation of polyvinyl alcohol-based hydrogel: Pour the pre-cured hydrogel viscous solution into a prepared mold, and then freeze-thaw and solidify it to obtain a hydrogel with elasticity and self-healing properties.

[0046] Figure 6 The optical performance diagram of the hydrogel surface healing shows that when the mass concentration of the polyvinyl alcohol solution increases to 15%, the healing effect of the hydrogel is still very good.

[0047] Example 3

[0048] 1) Prepare a polyvinyl alcohol solution with a solid content of 20% by adding 20 g of polyvinyl alcohol to 80 g of deionized water, stirring and dissolving at 80° C. for 24 h, and storing for later use;

[0049] 2) preparing a mixed solution of polyvinyl alcohol, phytic acid and glucose: adding 5 g of a phytic acid solution with a mass percentage concentration of 50% and 2 g of a glucose solution with a mass percentage concentration of 20% to 5 g of a polyvinyl alcohol solution, respectively, stirring and mixing the mixture at 70° C., standing the mixture to remove bubbles, and obtaining a transparent mixed solution;

[0050] 3) Preparing a pre-cured hydrogel viscous liquid: The mixed and defoamed mixture solution is pre-cured in a water bath at 80° C. The pre-cured liquid is light brown and viscous. There is a thin film on the surface of the solution, which is formed by rapid water loss of the surface solution during heating. After the thin film is peeled off with tweezers, a pre-cured hydrogel solution is obtained;

[0051] 4) Preparation of polyvinyl alcohol-based hydrogel: Pour the pre-cured hydrogel viscous solution into a prepared mold, and then freeze-thaw and solidify it to obtain a hydrogel with elasticity and self-healing properties.

[0052] Figure 7 The optical performance diagram of the hydrogel surface healing shows that when the mass concentration of the polyvinyl alcohol solution increases to 20%, the healing effect of the hydrogel is still very good.

[0053] The above examples illustrate that by changing the solid content of polyvinyl alcohol (10% to 20%), the prepared hydrogels all have good elasticity and self-healing properties.

Claims

1. A method for preparing a self-healing gel, characterized in that: The following steps are involved: 1) Prepare polyvinyl alcohol solution: Dissolve polyvinyl alcohol in deionized water by stirring to obtain a transparent polyvinyl alcohol solution; 2) preparing a mixed solution of polyvinyl alcohol, phytic acid and glucose: heating and stirring the polyvinyl alcohol solution, phytic acid solution and glucose solution in a mass ratio of 5:5:2 and mixing them uniformly, standing them to remove bubbles, and obtaining a transparent mixed solution; 3) Preparing a pre-cured hydrogel solution: pre-curing the transparent mixed solution in a water bath at 80°C. A thin film is formed on the surface of the pre-cured solution. After the thin film is removed, the pre-cured hydrogel solution is obtained. 4) Preparation of polyvinyl alcohol-based hydrogel: pouring the pre-cured hydrogel solution into the prepared mold, and then performing multiple freeze-thaw cycles to cure it to obtain a self-healing hydrogel; In the step 2), the mass percentage concentration of the glucose solution is 20%.

2. The method for preparing a self-healing gel according to claim 1, characterized in that: In the step 1), the solid content of the polyvinyl alcohol solution is 10%-20%, the dissolution temperature is 80°C, the stirring speed is 900 rpm / min, and the stirring time is 24 h.

3. The method for preparing a self-healing gel according to claim 1, characterized in that: In the step 2), the mass percentage concentration of the phytic acid solution is 50%.

4. The method for preparing a self-healing gel according to claim 1, characterized in that: The stirring temperature in step 2) is 70° C. and the stirring speed is 700 rpm / min.

5. The method for preparing a self-healing gel according to claim 1, characterized in that: In the freezing and thawing cycle in step 4), the freezing temperature is -50°C, the freezing time is 2 h; the thawing temperature is room temperature, the thawing time is 30 min, and the number of freezing and thawing is 3 to 4 times. During the last thawing, the hydrogel is placed at room temperature until the water on the surface of the hydrogel evaporates and becomes sticky.

6. A self-healing gel, characterized in that: The self-healing gel is prepared according to the preparation method according to any one of claims 1-5.

7. Use of the self-healing gel according to claim 6 in preparing flexible electronic devices.

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