A method for preparing a gradient cross-linked hydrogel film

Abstract

The application provides a method for preparing a gradient crosslinking hydrogel film. Polyvinyl alcohol is uniformly dispersed in deionized water, and then a polyvinylpyrrolidone solution dispersed by ultrasonic dispersion and a dissolved sodium carboxymethyl cellulose solution are added, mixed uniformly and ultrasonically defoamed, the mixed and bubble-free solution is poured into a beaker, a certain volume of diluted concentrated sulfuric acid solution is added, stirred uniformly and ultrasonically defoamed, and then the obtained polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose precursor solution is placed on an automatic film coating machine, cast onto a glass plate, dried in a blast drying oven, and a top-and-bottom permeable cylinder is covered on the obtained hydrogel film, and then a prepared ultra-diluted boric acid solution is poured into the cylinder to perform self-osmosis crosslinking. The gradient crosslinking hydrogel film prepared by the method has a crosslinking density from top to bottom, so that the hydrogel film has excellent mechanical properties and good sensing and bionic performance, and realizes stable use of electronic skin for a long time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, and particularly relates to a preparation method of a gradient cross-linked hydrogel film. BACKGROUND

[0002] In recent years, electronic devices with certain flexibility and convenient wearing have become a research hotspot. Flexible electronic technology has attracted widespread attention. Electronic skin is a kind of flexible electronic device that simulates the structure and function of human skin, and has the ability to perceive, transmit and respond to external stimuli. It can be used for bionic skin applications to perceive and simulate the tactile, temperature, humidity and other sensing capabilities of human skin. Electronic skin is usually composed of a flexible substrate, sensors, electronic components and an external protective layer. At present, most of the flexible substrate materials are stretchable materials, including elastic materials, aerogel materials and hydrogel materials. The flexible substrate makes the electronic skin flexible and scalable, and can adapt to various curved surfaces and movements. The external protective layer can protect the electronic device from environmental influences. However, there are still some challenges and problems to be solved. For example, the sensors of the electronic skin need to have high sensitivity and stability to ensure accurate sensing ability. In addition, the electronic skin needs to have good durability and reliability, and can withstand long-term use and environmental changes. The preparation method and cost are also factors to be considered to realize large-scale production and commercial application. In addition, the compatibility with the living body is also an important problem, which needs to ensure the good compatibility of the electronic skin with the human tissue. In order to improve the mechanical properties, sensing performance and bionic effect of the electronic skin, the present application forms a free permeable cross-linked interpenetrating network structure on the hydrogel film, so that it forms a gradient cross-linked structure, so that the upper surface layer of the hydrogel film has high cross-linking density and is hard, has better wear resistance and sliding resistance and good mechanical properties, and the lower surface layer has low cross-linking density and is soft, which improves the adhesion of the composite hydrogel film and better fits the skin. SUMMARY

[0003] The present application aims to solve the problem of unstable mechanical properties of flexible substrates in electronic skin and poor fit with human skin. Electronic skin usually needs to have flexibility and scalability to adapt to the movement and deformation of the skin. However, such flexible substrates may face problems such as mechanical fatigue, environmental factors, and interface stability. Frequent deformation and stretching can cause fatigue of the flexible substrate, thereby reducing its durability. Long-term use and repeated deformation can cause the substrate material to break or be damaged. The flexible substrate may be affected by environmental factors such as humidity, temperature, and chemicals. These factors can cause degradation or damage to the substrate material, thereby affecting the performance and durability of the electronic skin. Electronic skin is usually composed of multiple components such as sensors, electronic elements, and substrate materials. The interface between these components may have stability problems, such as aging or loosening of the adhesive, causing the performance of the electronic skin to decline or fail. The present application uses polyvinyl alcohol and polyvinylpyrrolidone as raw materials, both of which are biocompatible high molecular materials. Under the action of acid catalysis and heating, the -OH of polyvinyl alcohol and the C=O of polyvinylpyrrolidone undergo electronic rearrangement to form C-O-C, forming a covalent crosslinking, and then forming a three-dimensional network structure to form a homogeneous polymer. Carboxymethyl cellulose sodium is added as a reinforcing phase to further improve the mechanical properties of the hydrogel. The crosslinking degree of the hydrogel is not complete, and the hydroxyl groups of polyvinyl alcohol in the polyvinyl alcohol and polyvinylpyrrolidone hydrogel can further react with boric acid to perform a free permeation crosslinking reaction. By controlling the concentration of boric acid solution and the reaction time, a gradient crosslinking is performed to form a structure that is "hard" on the top and "soft" on the bottom, thereby preparing a hydrogel film with good durability, reliability, and bionic sensing performance, allowing it to remain stable under long-term use and various environmental conditions.

[0004] To solve the above technical problems, the polyvinyl alcohol-polyvinylpyrrolidone-carboxymethyl cellulose sodium composite hydrogel in the present application is synthesized by the following steps in mass fraction:

[0005] Step one, weigh polyvinyl alcohol (PVA) in a three-necked flask, add deionized water solution, stir and heat for 2 h.

[0006] Step two, weigh polyvinylpyrrolidone in a beaker, add deionized water solution, and perform ultrasonic dispersion for 5 min.

[0007] Step three, weigh carboxymethyl cellulose sodium in a beaker, add deionized water solution, and stir for 0.5 h.

[0008] Step four, weigh boric acid in a beaker, add deionized water until the boric acid is completely dissolved.

[0009] Step five, the polyvinyl alcohol solution, polyvinylpyrrolidone solution and sodium carboxymethyl cellulose solution are weighed and mixed in a three-necked flask, and stirred for 10 min.

[0010] Step six, the obtained polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose mixed solution is loaded into a beaker, and a transparent and uniform pre-gel solution is obtained after ultrasonic degassing.

[0011] Step seven, deionized water and 98% concentrated sulfuric acid solution are weighed, and the concentrated sulfuric acid solution is slowly added to the water under the guidance of a glass rod.

[0012] Step eight, the obtained transparent and uniform pre-gel solution is added to the diluted sulfuric acid solution.

[0013] Step nine, the pre-gel solution after adding acid is ultrasonically degassed in a beaker to obtain a transparent and uniform solution.

[0014] Step ten, the prepared polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose precursor solution is poured onto a flow coating machine.

[0015] Step eleven, the coated hydrogel film is placed in a blast drying oven for drying treatment until the hydrogel film is completely dried.

[0016] Step twelve, a cylinder with an area smaller than the hydrogel film is placed on the prepared hydrogel film, and a prepared ultra-dilute boric acid solution is poured into the cylinder without flowing out, and the reaction is carried out for 1-3 h.

[0017] Further limitation, the method for preparing a gradient cross-linked hydrogel film is characterized in that in step one, 8-10 parts of polyvinyl alcohol and 90-92 parts of deionized water are added, and the dissolution temperature is 98 ℃ and the stirring rate is 160-170 r / min.

[0018] Further limitation, the method for preparing a gradient cross-linked hydrogel film is characterized in that in step two, 20-30 parts of polyvinylpyrrolidone are dissolved in 70-80 parts of deionized water.

[0019] Further limitation, the method for preparing a gradient cross-linked hydrogel film is characterized in that in step three, 2-10 parts of sodium carboxymethyl cellulose and 90-98 parts of deionized water are added.

[0020] Further limitation, the method for preparing a gradient cross-linked hydrogel film is characterized in that in step four, 1-2 parts of boric acid and 8000-16000 parts of deionized water are added.

[0021] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step five that polyvinyl alcohol is 25-45 parts, polyvinylpyrrolidone is 5-25 parts, sodium carboxymethyl cellulose is 1-5 parts, and stirring rate is 180 r / min.

[0022] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step six that centrifugal rate is 4000 r / min, time is 10 min, and centrifugal treatment is at least three times.

[0023] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step seven that acid solution is 1 part 98 % concentrated sulfuric acid solution and 98 parts deionized water.

[0024] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step eight that mixed solution is 10 parts, and diluted sulfuric acid solution is 1 part.

[0025] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step nine that ultrasonic time is 20 min, and ultrasonic rate is 80 KHz.

[0026] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step ten that hydrogel film thickness is 5-200 μm.

[0027] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step eleven that air blowing drying oven temperature is 88 ℃.

[0028] Further limit, the method for preparing gradient crosslinking hydrogel film is characterized in step twelve that hydrogel film size is 10*10 cm, cylinder diameter is 5 cm, and boric acid solution concentration is 0.00625-0.0125 %.

[0029] The composite hydrogel film prepared by the application is prepared by using polyvinyl alcohol, polyvinylpyrrolidone and sodium carboxymethyl cellulose as raw materials, and forming a three-dimensional crosslinked network through ketalization reaction under the conditions of acid catalysis and heating. Then the upper surface of the composite hydrogel film is contacted with a boric acid solution to perform self-permeation crosslinking, so as to form a gradient crosslinking density, form an upper "hard" and lower "soft" structure, improve the mechanical properties of the hydrogel film, and also improve the adhesion to the skin. The gradient crosslinking polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose composite hydrogel film has a wide application prospect in bionic skin, and can integrate sensor elements to realize the sensing ability of bionic skin to external stimulation. By adjusting the concentration of the boric acid solution and the reaction time, the crosslinking density is controlled to form a gradient crosslinking structure, so as to realize the flexibility and stretchability, simulate the flexibility and deformability of human skin, adapt to different curved shapes, and bear various forms of stretching and pressure, so that the gradient crosslinking polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose composite hydrogel film has a wide application prospect in the field of bionic skin and biosensors, and provides a new possibility for the development of related technologies.

[0030] Compared with the prior art, the application has the following technical results:

[0031] The gradient crosslinking technology adopted by the application enables the polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose hydrogel composite film to control the gradient crosslinking density by controlling the concentration of the boric acid solution and the reaction time, form an upper "hard" and lower "soft" structure, and make the crosslinking density of the upper surface layer of the composite hydrogel film large, so that the structure of the hydrogel is more compact and stable, the mechanical properties are improved, and the macro "hard" is exhibited. At the same time, the increase of the crosslinking density changes the pore structure and pore size distribution of the hydrogel, makes the pore structure more compact and uniform, reduces the pore size, reduces the permeability of the composite hydrogel film to liquid and gas, reduces the volatilization of the solvent, and has a certain water retention performance. The crosslinking density of the lower surface layer of the composite hydrogel film is small, the network structure is relatively loose, the elastic modulus is low, and it is relatively soft, which exhibits macro "soft" and can form a good fit with the skin. The gradient crosslinking structure enables the composite hydrogel film to have good longitudinal compression and transverse stretching performance, can simulate the softness and deformability of human skin, adapt to different curved shapes, and has good stability and adaptability.

[0032] The polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose hydrogel film of the application can simulate the sensing ability of human skin, and the thickness of the composite hydrogel film is micron level, can capture small deformation, can convert small deformation into electrical signals, realize rapid response and stable transmission of signals.

[0033] The polyvinyl alcohol-polyvinyl pyrrolidone-sodium carboxymethyl cellulose hydrogel film of the present application is prepared from biocompatible materials and does not cause allergic reactions or other adverse effects in the human body. It can simulate the flexibility, stretchability, biocompatibility and transmission ability of human skin and has excellent bionic performance.

[0034] ACCOMPANYING DRAWINGS AND DESCRIPTION

[0035] Figure 1 Polyvinyl alcohol-polyvinyl pyrrolidone cross-linking schematic diagram;

[0036] Figure 2 Polyvinyl alcohol-boric acid cross-linking schematic diagram;

[0037] Figure 3 Preparation process schematic diagram of gradient cross-linking composite hydrogel film;

[0038] Figure 4 Scanning electron microscope micrograph of the gradient cross-linking composite hydrogel film, the left graph is the upper surface layer of the composite hydrogel film with a magnification of x200, and the right graph is the lower surface layer of the composite hydrogel film with a magnification of x200;

[0039] Figure 5 Schematic diagram of the macroscopic physical object of the gradient cross-linking composite hydrogel;

[0040] Provide at least one specific implementation method

[0041] Example 1

[0042] The embodiment of the present application provides a method for preparing a gradient cross-linking hydrogel film, which specifically comprises the following steps:

[0043] Step one, weigh 8-10 g of polyvinyl alcohol into a three-necked flask, add 90-92 g of deionized water, stir and heat to 98 DEG C, and keep the temperature until the polyvinyl alcohol is completely dissolved.

[0044] Step two, weigh 20-30 g of polyvinyl pyrrolidone into a beaker, add 70-80 g of deionized water, and ultrasonically disperse for 5 min.

[0045] Step three, weigh 2-10 g of sodium carboxymethyl cellulose into a beaker, add 90-98 g of deionized water, and stir for 0.5 h.

[0046] Step four, weigh 0.01-0.02 g of boric acid into a beaker, add 80-160 g of deionized water, and stir until the boric acid is completely dissolved.

[0047] Step five, mix 25-45 g of polyvinyl alcohol solution, 5-25 g of polyvinyl pyrrolidone solution and 1-5 g of sodium carboxymethyl cellulose solution in a three-necked flask, stir and mix for 10 min.

[0048] Step six, the obtained polyvinyl alcohol-polyvinyl pyrrolidone-sodium carboxymethyl cellulose mixed solution was loaded into a beaker and ultrasonicated for 20 min to obtain a transparent and uniform pre-gel solution.

[0049] Step seven, 98 g of deionized water and 1 g of 98% concentrated sulfuric acid solution were weighed, and the concentrated sulfuric acid solution was slowly added into the water under the guidance of a glass rod.

[0050] Step eight, 10 g of polyvinyl alcohol-polyvinyl pyrrolidone-sodium carboxymethyl cellulose mixed solution was taken in a beaker, and 1 g of diluted concentrated sulfuric acid solution was added.

[0051] Step nine, the mixed solution obtained in step eight was ultrasonicated for 20 min to remove bubbles, and a transparent and uniform solution was obtained.

[0052] Step ten, the prepared polyvinyl alcohol-polyvinyl pyrrolidone-sodium carboxymethyl cellulose precursor solution was poured onto a casting film coater, and the thickness of the composite hydrogel film was set to 5-200 μm.

[0053] Step eleven, the coated hydrogel film was placed in a drying oven with a temperature setting of 88 ℃ for drying treatment until the hydrogel film was completely dried.

[0054] Step twelve, the prepared hydrogel film was cut into a square of 10×10 cm, covered with a cylinder with a diameter of 5 cm and a through hole, and poured into the prepared ultra-diluted boric acid solution without letting it flow out, and reacted for 1-3 h.

Claims

1. A method for preparing gradient crosslinked hydrogel films, characterized in that, The method includes the following steps: Step 1: Weigh polyvinyl alcohol (PVA) into a three-necked flask, add deionized water solution, stir and heat for 2 hours; Step 2: Weigh polyvinylpyrrolidone into a beaker, add deionized water solution, and ultrasonically disperse for 5 min; Step 3: Weigh sodium carboxymethyl cellulose into a beaker, add deionized water solution, and stir for 0.5 h; Step 4: Weigh boric acid into a beaker, add deionized water, and continue until the boric acid is completely dissolved. Step 5: Weigh out polyvinyl alcohol solution, polyvinylpyrrolidone solution and sodium carboxymethyl cellulose solution and mix them in a three-necked flask, stirring for 10 min; Step 6: The obtained polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose mixed solution is placed into a beaker, and after ultrasonic degassing, a transparent and uniform pregel solution is obtained. Step 7: Weigh out deionized water and 98% concentrated sulfuric acid solution, and slowly add the concentrated sulfuric acid solution to the water under the guidance of a glass rod; Step 8: Add the obtained transparent and uniform pregel solution to the diluted sulfuric acid solution; Step 9: Place the pre-gelled solution with added acid in a beaker and defoam it by sonication to obtain a transparent and homogeneous solution; Step 10: Pour the prepared polyvinyl alcohol-polyvinylpyrrolidone-sodium carboxymethyl cellulose precursor solution onto the casting coating machine; Step 11: Place the coated hydrogel film in a drying oven for drying until the hydrogel film is completely dry. Step 12: Cover the prepared hydrogel film with a cylinder that is smaller in area than the hydrogel film and is open at both ends. Pour in the prepared ultra-dilute boric acid solution and prevent it from flowing out. React for 1 hour. In step 12, the concentration of the boric acid solution is 0.00625~0.0125%.

2. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, In step one, add 8-10 parts of polyvinyl alcohol and 90-92 parts of deionized water, dissolve at 98℃, and stir at 160-170 r / min.

3. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, In step two, 20-30 parts of polyvinylpyrrolidone are dissolved in 70-80 parts of deionized water.

4. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, In step three, 2-10 parts of sodium carboxymethyl cellulose and 90-98 parts of deionized water are used.

5. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The step described involves 1-2 parts of tetraboric acid and 8000-16000 parts of deionized water.

6. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, In step five, 25-45 parts of polyvinyl alcohol, 5-25 parts of polyvinylpyrrolidone, and 1-5 parts of sodium carboxymethyl cellulose are mixed at a stirring rate of 180 r / min.

7. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, In step six, the centrifugation rate is 4000 r / min, the time is 10 min, and the centrifugation process is repeated at least three times.

8. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The acidic solution in step seven consists of 1 part 98% concentrated sulfuric acid solution and 98 parts deionized water.

9. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The mixture in step eight consists of 10 parts, and the diluted sulfuric acid solution consists of 1 part.

10. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The ultrasound time in step nine is 20 minutes, and the ultrasound frequency is 80 kHz.

11. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The thickness of the hydrogel film in step ten is 5~200μm.

12. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The temperature of the drying oven in step eleven is 88 ℃.

13. The method for preparing a gradient crosslinked hydrogel film according to claim 1, characterized in that, The hydrogel film in step twelve has a size of 10×10 cm and a cylinder diameter of 5 cm.

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