A covalent organic framework-cellulose hydrogel composite dressing and preparation method thereof

Abstract

The present invention relates to the technical field of medical supplies, and discloses a covalent organic framework-cellulose hydrogel composite dressing and a preparation method thereof, wherein the composite dressing includes a covalent organic framework with a porous structure, quercetin loaded in the pores of the covalent organic framework, and a covalent organic framework loaded with quercetin in the pores dispersed in the cellulose hydrogel; the cellulose hydrogel is used to absorb the blood or tissue fluid of the wound, so that the covalent organic framework is gradually decomposed and then slowly releases the quercetin in the pores. The composite dressing is loaded with the natural drug quercetin in the COF of the porous structure, and is dispersed in the cellulose-based hydrogel. After the cellulose hydrogel absorbs the blood / tissue fluid (pH is alkaline) of the wound, the COF will gradually decompose, so that the quercetin can be continuously and slowly released, and the cellulose-based hydrogel can be provided with antibacterial properties and the ability to promote wound healing.

Description

Technical Field

[0001] The invention relates to the technical field of medical supplies, and in particular to a covalent organic framework-cellulose hydrogel composite dressing and a preparation method thereof. Background Art

[0002] The healing process of diabetic wounds involves complex and dynamic biological mechanisms. In wound treatment, traditional cotton gauze dressings are common but have problems such as poor hemostasis, limited healing-promoting performance, and easy excessive absorption of blood. In view of this, it is particularly important to develop new wound dressings with efficient hemostasis, self-healing ability and antibacterial function.

[0003] In recent years, natural hydrogels have attracted much attention from researchers due to their excellent biocompatibility, biodegradability, non-toxicity and biomimicry properties. As a functional polymer material, hydrogels form a three-dimensional hydrophilic network structure through specific cross-linking and can swell in water without dissolving. Based on their sources, hydrogels can be divided into two categories: natural and synthetic.

[0004] As an important raw material for natural hydrogels, cellulose has a rich renewable resource base and has the characteristics of biodegradation, regeneration and recycling, which meets the requirements of environmental protection and sustainable development. Compared with traditional hydrogels, cellulose-based hydrogels show high water content, suitable porosity and good cell compatibility, which can effectively provide the moist environment required by wounds and promote gas exchange and exudate absorption. In addition, it is easy to cut into various shapes, which is convenient for close fitting with the wound site and improves the self-healing effect.

[0005] It is worth noting that the carboxyl groups in the cellulose molecular structure can bind to hemoglobin iron ions, activate coagulation factors, promote the coagulation process, and enhance the adhesion of platelets, thereby improving the hemostatic effect. If the cellulose-based hydrogel is further modified and optimized, its self-healing ability, cell proliferation promotion, antibacterial and injectable properties will be significantly improved, providing a more efficient and reliable treatment option for diabetic wound healing.

[0006] However, it must be pointed out that usually a single cellulose-based hydrogel itself does not have antibacterial activity to prevent wound infection. In order to give it antibacterial properties, antibiotics or metal ions with antibacterial activity (such as silver ions, copper ions) are usually added. However, this long-term dependence on antibiotics will cause a large number of pathogens to develop resistance to them, and the consequences may affect the healing effect of the wound at the least, and may cause serious deterioration of the patient's condition or even life-threatening at the worst. Although the addition of nano antibacterial metal particles (such as silver ions) can significantly enhance the antibacterial spectrum and antibacterial properties, the long-term accumulation of such particles in the human body may also pose health risks.

[0007] Currently, in order to improve the antibacterial properties of diabetic wound dressings, some innovative studies have attempted to incorporate metal organic frameworks (MOFs) into dressings. This strategy uses the porous structure of MOFs to effectively load antibacterial substances such as antibiotics or metal ions in their structures to achieve antibacterial effects.

[0008] As an organic-inorganic hybrid material, MOF forms a crystalline porous material with a periodic network structure through the self-assembly connection of inorganic metal centers and organic ligands. Its unique properties, such as nanoscale pores, strong acid-base catalytic activity, high specific surface area, multiple metal sites and adjustable pore structure, make it a research hotspot in the field of materials science.

[0009] However, it is worth noting that MOF has stability issues in aqueous solution and its structure is prone to collapse. In addition, since the center of the MOF structure contains metal ions, long-term use may cause accumulation of metal ions, and in severe cases may even lead to heavy metal poisoning. Therefore, before further promoting and applying MOF in diabetic wound dressings, these potential problems need to be solved.

[0010] It can be seen that the existing technology still needs to be improved and enhanced. Summary of the invention

[0011] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a covalent organic framework-cellulose hydrogel composite dressing and a preparation method thereof, aiming to solve the problem that cellulose hydrogel does not have antibacterial properties and that MOF contains metal ions and is not suitable as a drug carrier.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] A covalent organic framework-cellulose hydrogel composite dressing comprises a covalent organic framework with a porous structure, quercetin loaded in the pores of the covalent organic framework, and a covalent organic framework loaded with quercetin in the pores dispersed in the cellulose hydrogel; the cellulose hydrogel is used for absorbing blood or tissue fluid of a wound, so that the covalent organic framework is gradually decomposed and the quercetin in the pores is slowly released.

[0014] The covalent organic framework-cellulose hydrogel composite dressing has a mass ratio of the covalent organic framework to quercetin of 1:(1-5); the mass of the covalent organic framework loaded with quercetin in the pores is 4%-30% of the mass of the cellulose hydrogel.

[0015] A method for preparing a covalent organic framework-cellulose hydrogel composite dressing comprises the following steps:

[0016] S1. Synthesis of COF: A monomer containing an amino group and a monomer containing an aldehyde group are added to an organic solvent, and then an acetic acid aqueous solution is added as a catalyst, and the formed solution is transferred to a hydrothermal reactor, and heated for copolymerization to obtain COF;

[0017] S2. dissolving quercetin in a hot organic solvent to obtain a quercetin solution; and ultrasonically dispersing the COF obtained in step S1 into the quercetin solution to load the quercetin into the internal pores of the COF;

[0018] S3. The quercetin-loaded COF is separated from the organic solvent by centrifugal precipitation, and then vacuum dried or naturally dried until the organic solvent is completely volatilized to obtain a quercetin-loaded COF in the pores;

[0019] S4. After dissolving cellulose in hot water, a cellulose solution is obtained; polyvinyl alcohol is added to the cellulose solution and stirred to obtain a cellulose / PVA mixed solution;

[0020] S5. The COF loaded with quercetin in the pores prepared in step S3 is added to the cellulose / PVA mixed solution in step S4 and mixed evenly;

[0021] S6. After removing water from the cellulose / PVA mixed solution in step S5, the covalent organic framework-cellulose hydrogel composite dressing is prepared.

[0022] The preparation method of the covalent organic framework-cellulose hydrogel composite dressing, wherein the monomer containing an amino group is one or more of 4,4'-diaminobiphenyl, 4,4'-methylenedianiline, 1,3,5-tris(4-aminophenyl)benzene, 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine; the monomer containing an aldehyde group is one or more of trimesic acid, 4,4',4"-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde; the molar ratio of the monomer containing an amino group to the monomer containing an aldehyde group is 1:1.

[0023] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the organic solvent in step S1 is one or more of toluene, xylene, o-dichlorobenzene, trimethylbenzene, dioxane, and n-butanol.

[0024] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the reaction temperature of the reactor in step S1 is 80-130° C., and the reaction time is 2-7 days.

[0025] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the concentration of the acetic acid aqueous solution in step S1 is 3 mol / L or 6 mol / L.

[0026] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the organic solvent in step S2 is one of methanol, ethanol, isopropanol, acetone, ethyl acetate, and cyclohexane; and the content of the quercetin solution is 10 to 200 mg / mL.

[0027] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the dissolved cellulose concentration in step S4 is 2-10 g / 100 ml water, and the hot water temperature is 40-65° C.; the concentration of the polyvinyl alcohol is 2-5 g / 100 ml water.

[0028] The method for preparing the covalent organic framework-cellulose hydrogel composite dressing, wherein the operation of step S6 is specifically as follows: freezing the cellulose / PVA mixed solution in step S5 at -20°C for 24 hours, and then thawing it at room temperature for 4 hours, and repeating the above freezing and thawing steps 3 times.

[0029] Beneficial effects:

[0030] The present invention provides a method for preparing a covalent organic framework-cellulose hydrogel composite dressing, by loading the natural drug quercetin in COF and dispersing it in a cellulose-based hydrogel, the cellulose-based hydrogel can be provided with antibacterial properties and the ability to promote wound healing. Moreover, quercetin is loaded in the porous structure of COF, and after the cellulose hydrogel absorbs the blood / tissue fluid (pH is alkaline) of the wound, COF will gradually decompose, so that quercetin can be continuously and slowly released, so that the hydrogel can achieve a sustained and stable antibacterial effect and a wound healing effect on the wound. Moreover, the components used in the preparation process of the cellulose-based composite hydrogel are non-toxic to cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a scanning electron microscope image of the COF prepared in Example 1.

[0032] Figure 2 This is a transmission electron microscope image of the COF prepared in Example 1; the right image is an enlarged image in the red frame of the left image.

[0033] Figure 3 This is the X-ray element distribution energy spectrum of the COF material prepared in Example 1.

[0034] Figure 4 This is a graph of the specific surface area (BET) test data of the COF material prepared in Example 1.

[0035] Figure 5 Schematic diagram of cellulose / PVA hydrogel prepared in Example 1 Figure 1 .

[0036] Figure 6 Schematic diagram of cellulose / PVA hydrogel prepared in Example 1 Figure 2 .

[0037] Figure 7 This is a scanning electron micrograph of the cellulose / PVA hydrogel prepared in Example 1.

[0038] Figure 8 Schematic diagram of the release curve of the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1 in PBS buffer at pH 7.4.

[0039] Fig. 9 Schematic diagram of the antibacterial rate of the control group (COF material), cellulose / PVA hydrogel, and the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1 against Escherichia coli.

[0040] Fig.10 Schematic diagram of the cell survival rate of the control group (COF material), cellulose / PVA hydrogel, cellulose / PVA hydrogel / COF (not loaded with quercetin), and the covalent organic framework-cellulose hydrogel composite dressing (1 mg / mL) prepared in Example 1 after incubation with L929 cells for 48 hours.

[0041] Fig.11 This is a schematic diagram of the cell survival rate of the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1 after incubation with L929 cells at different concentrations for 48 hours.

[0042] Fig.12 This is a comparison chart of the healing effects of mouse wounds in the control group (hydrogel prepared in Example 1) and after using the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1. DETAILED DESCRIPTION

[0043] The present invention provides a covalent organic framework-cellulose hydrogel composite dressing and a preparation method thereof. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0044] The invention provides a covalent organic framework-cellulose hydrogel composite dressing, comprising a covalent organic framework with a porous structure, quercetin loaded in the pores of the covalent organic framework, and a covalent organic framework loaded with quercetin in the pores dispersed in the cellulose hydrogel; the cellulose hydrogel is used for absorbing blood or tissue fluid of a wound, so that the covalent organic framework is gradually decomposed and the quercetin in the pores is slowly released.

[0045] Covalent organic framework (COF) is a periodically arranged organic polymer with a certain degree of crystallinity and high porosity. The skeleton of COF is composed entirely of light elements (B, C, N, O, Si, H, etc.) connected by strong covalent bonds, such as BO, CN, BN, BO-Si, -C=N, etc. Covalent organic framework (COF) has unique properties, including metal-free organic framework, predetermined structure and pore geometry, high porosity, large surface area (from Figure 4 As can be seen from the surface area test data of the COF material prepared in Example 1, it is becoming a new porous nanomaterial in drug delivery systems due to its easy surface modification potential and good biocompatibility. COF can be used as a drug carrier to deliver growth factors that promote cell proliferation, anti-inflammatory drugs, antibacterial drugs and other drugs.

[0046] COF, as a crystalline porous material, has the excellent properties of MOF. Its carefully designed molecular building blocks are connected into a preset topological structure through covalent bonds, so that COF materials have better stability and regular pore structure, and have the potential for pre-functionalization and post-modification. In addition, due to the presence of a large number of imino groups in the COF molecular structure, it will be hydrolyzed into structural units under specific conditions (pH values). Therefore, non-toxic building block elements can be modified into the COF structure, so that its COF nanomaterials have the advantage of lower long-term toxicity. More importantly, since COF is formed by covalent bonds, there may be some unbonded functional groups on its matrix. The multifunctional functional groups or bonding defects on the internal channels of COF are suitable for nanocarriers through chemical functionalization or host-guest encapsulation strategies.

[0047] Using COF to load natural antibacterial extracts can not only overcome the drawbacks of antibiotics or metal ions, but also the presence of a large number of imino groups in the COF molecular structure makes it more suitable for modification, thereby loading more natural antibacterial extracts and achieving a long-term sustained release effect. Figure 3 It can be seen from the X-ray element distribution spectrum of the COF material prepared in Example 1 that the COF skeleton is entirely composed of light elements (B, C, N, O, Si, H, etc.) connected by strong covalent bonds, and it itself does not produce toxic substances.

[0048] Quercetin is a heterocyclic polyphenol flavonoid compound that can promote the proliferation of human epidermal stem cells, regulate inflammatory responses, and promote angiogenesis. It can promote skin wound healing and improve the healing quality of the epidermis by promoting the proliferation and migration of fibroblasts.

[0049] In order to solve the problem that cellulose hydrogels do not have antibacterial properties, the present invention uses a synthetic organic framework material (COF) with a porous structure as a drug carrier, and uses the high specific surface area and internal porous structure of COF to load quercetin, which has antibacterial and anti-inflammatory properties and can promote wound healing. Figure 7 It can be seen from the hydrogel prepared in Example 1 that the hydrogel also has a porous structure, which can utilize the porous structure to adsorb blood or tissue fluid). In an alkaline environment, COF will gradually decompose, thereby slowly and continuously releasing quercetin, and the release rate of quercetin can be better controlled. Quercetin is a natural medicine that can play an antibacterial, regulate inflammatory response, and promote angiogenesis. It can promote skin wound healing and improve the healing quality of wounds by promoting the proliferation and migration of fibroblasts. On the other hand, the quercetin molecule contains multiple phenolic hydroxyl groups, which can form hydrogen bonds with the imino groups on COF, thereby increasing the loading amount of the drug.

[0050] In some embodiments, the mass ratio of the covalent organic framework to quercetin is 1: (1-5). As mentioned above, quercetin is a flavonoid compound with biological activities such as antioxidant, anti-inflammatory and wound healing. The pore structure of COF can control the release rate of quercetin. The ideal drug release rate should be able to match the physiological needs in the wound healing process, neither too fast nor too slow. Too fast release may cause quercetin to be exhausted in a short time and unable to continue to play a role; too slow release may affect the therapeutic effect due to insufficient quercetin concentration. The pore structure, pore size and pore shape of COF can accurately adjust the release rate of the drug, thereby achieving precise treatment of the wound healing process. COF can also achieve intelligent drug release by changing environmental factors such as pH value, that is, changing the drug release rate under specific stimulation, such as accelerating the release of quercetin in an alkaline wound environment to enhance its anti-inflammatory and healing effects. Moreover, excessive concentrations of COF or quercetin may cause local irritation or toxicity problems. The above mass ratio can ensure safety and biocompatibility.

[0051] Specifically, the mass of the covalent organic framework loaded with quercetin in the pores is 4% to 30% of the mass of the cellulose hydrogel. COF is a carrier of quercetin, and its pore structure can control the release rate of quercetin. Cellulose hydrogel is used as the matrix of the dressing, which provides a moist environment suitable for the release of quercetin, and its physical properties (such as viscosity, elasticity and porosity) will affect the diffusion rate of quercetin. The appropriate mass ratio can ensure that the release rate of quercetin matches the treatment needs and avoids too fast or too slow release. In addition, the mixing ratio of cellulose hydrogel and COF determines the physical and mechanical properties of the composite dressing. Cellulose hydrogel gives the material flexibility and moisture retention, while COF provides structural stability and porosity. The above ratio can ensure that the composite dressing has good adhesion, ductility and strength, so that it is neither fragile nor too viscous when used, and is easy to operate and use. Moreover, different mass ratios may affect the biocompatibility and safety of the composite dressing. Specifically, too high a COF content may increase the hardness of the composite dressing, causing discomfort or irritation to the skin, while too high a cellulose hydrogel content may affect the stability of the composite dressing. The above ratio helps to maintain good biocompatibility and reduce potential side effects. Furthermore, too high or too low a ratio will affect the structural integrity of COF and the stability of quercetin, and may cause damage to the quercetin or COF structure. Moreover, the moisturizing effect of cellulose hydrogel can also be combined with the drug delivery function of COF to accelerate wound healing. The above ratio can maximize this synergistic effect.

[0052] The present invention also provides a method for preparing a covalent organic framework-cellulose hydrogel composite dressing, comprising the following steps:

[0053] S1. Synthesis of COF: One or more of the monomers containing amino groups, such as 4,4'-diaminobiphenyl (BZD), 4,4'-methylenedianiline (MDA), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine (TTA) and the monomers containing aldehyde groups, such as trimesic acid (TFB), 4,4',4"-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (TTB) ), 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP)) are added to an organic solvent (one or more of toluene, xylene, o-dichlorobenzene, trimethylbenzene, dioxane, n-butanol) in a molar ratio of 1:1, and then an acetic acid aqueous solution with a concentration of 3 mol / L or 6 mol / L is added as a catalyst, and the formed solution is transferred to a hydrothermal reactor (the reaction temperature of the reactor is 80-130°C, and the reaction time is 2-7 days), and heated copolymerization is performed to obtain COF.

[0054] The synthesis method of the above COF is called the Schiff base approach, and the above amino group monomer contains at least one primary amine or secondary amine group. The above aldehyde group monomer contains at least one aldehyde group (-CHO). The amino group monomer and the aldehyde group monomer are reacted in a molar ratio of 1:1, mainly based on the following reasons: 1. In the Schiff base reaction, an amino group can react with an aldehyde group to form an imine bond (Schiff base bond). Therefore, in order to ensure that each amino group has a corresponding aldehyde group to react, it is theoretically necessary to feed the amino group and the aldehyde group in a molar ratio of 1:1, so that all reactants can be utilized to the maximum extent and by-products and unreacted raw materials can be reduced. 2. The formation of the covalent organic framework (COF) depends on a regular network structure, and the formation of this structure requires that each node (i.e., monomer) can be connected to other nodes by covalent bonds. The 1:1 molar ratio ensures that each monomer has enough reaction sites to form a complete three-dimensional network structure, rather than a linear or incompletely connected structure. 3. When the molar ratio deviates from 1:1, the excess reactants may cause side reactions, such as termination of polymer chains or excessive cross-linking, which will not only reduce the purity of the product, but also affect the yield and crystallinity of the product. 4. The 1:1 molar ratio helps control the pore structure and size of the final COF material, which is crucial to the performance of the material, such as gas adsorption, catalytic activity, drug delivery efficiency, etc. The precise molar ratio can ensure that the COF has the expected porosity and functionalization to meet the needs of specific applications.

[0055] The above organic solvent is used to dissolve the amino group monomer and the aldehyde group monomer, and the acetic acid aqueous solution is used as a catalyst to promote the formation of Schiff base and accelerate the synthesis of COF. COF synthesis involves Schiff base reaction, in which the amino group-containing monomer and the aldehyde group-containing monomer form an imine bond through dehydration condensation. Acetic acid, as a proton donor, can promote this process, by protonating the amino group, making it easier to react with the aldehyde group, accelerating the formation of Schiff base. Acetic acid, as a weak acid, can provide protons, reduce the activation energy of the reaction, and accelerate the reaction rate. In the Schiff base reaction, the presence of acid can accelerate the dehydration process and promote the formation of imine bonds. During the Schiff base reaction, some unstable intermediates are generated. Acetic acid can help stabilize these intermediates and prevent them from decomposing, thereby improving the yield and selectivity of the reaction. The acetic acid aqueous solution provides the acidic environment required for the reaction, which is necessary for the Schiff base reaction to proceed. In addition, by adjusting the concentration of acetic acid, the pH value of the reaction environment can be fine-tuned, thereby affecting the rate and direction of the reaction. The aqueous acetic acid solution can improve the polarity of the reaction medium, help dissolve the monomer in the organic solvent, ensure uniform mixing of the reactants, and thus increase the reaction rate. During the reaction, acetic acid can help remove by-products such as water, thereby driving the reaction toward the product and increasing the yield.

[0056] The mixed solution is transferred to a hydrothermal reactor, which is a closed container resistant to high pressure and high temperature, and is used to carry out chemical reactions under high temperature and high pressure conditions. Controlling the reaction temperature can regulate the reaction rate, reduce unnecessary side reactions, and improve the selectivity and yield of the target product. The reaction temperature is also compatible with the catalyst and can accelerate the reaction. In addition, by controlling the reaction time, a higher conversion rate can be achieved, overreaction can be avoided, the formation of by-products can be prevented, and the purity of the product can be improved.

[0057] S2. dissolving quercetin in a hot organic solvent to obtain a quercetin solution; and ultrasonically dispersing the COF obtained in step S1 into the quercetin solution, so that the quercetin is loaded into the internal pores of the COF. The solubility of quercetin in water is very low, and its solubility in organic solvents is relatively high, and the solubility of quercetin can be further improved under heating conditions. Ultrasonic dispersion can further improve the solubility of quercetin in organic solvents, accelerate the diffusion rate of quercetin in the pores of COF, and allow enough quercetin to be fully loaded in the pore structure of COF, and ultrasonic dispersion can disperse quercetin more evenly, avoid precipitation or aggregation caused by local supersaturation, and ensure more uniform drug distribution.

[0058] Specifically, the organic solvent is one of methanol, ethanol, isopropanol, acetone, ethyl acetate, and cyclohexane; the content of the quercetin solution is 10 to 200 mg / mL. The solubility of quercetin in organic solvents is limited. Too high a concentration will cause the solution to be unstable, and quercetin may precipitate to form a precipitate, which not only affects the loading efficiency but also may damage the pore structure of COF. Controlling the concentration of the quercetin solution can optimize its loading efficiency in the COF pores. Too low a concentration may not fully utilize the pore capacity of COF, while too high a concentration may result in too much unloaded quercetin in the solution, resulting in waste. Ultrasound can accelerate the diffusion of quercetin in the COF pores, but if the quercetin content is too high, ultrasonic dispersion may not effectively promote its uniform distribution, but may instead result in excessively high local concentrations, affecting the integrity and stability of the COF structure.

[0059] S3. The COF loaded with quercetin is separated from the organic solvent by centrifugal precipitation, and the COF particles loaded with quercetin are separated from the organic solvent by centrifugation. Then vacuum drying or natural drying is performed until the organic solvent is completely volatilized. Vacuum drying can accelerate the evaporation of the organic solvent at low temperature to avoid the decomposition of quercetin or the destruction of the COF structure due to high temperature. Although natural drying is slower, it can achieve the same purpose under mild conditions. Mild drying conditions help to maintain the pore structure and morphology of COF, ensuring the stability and loading efficiency of quercetin in the pores. A COF loaded with quercetin in the pores is obtained.

[0060] S4. After dissolving cellulose in hot water at a temperature of 40 to 65°C, a cellulose solution is obtained. Cellulose is almost insoluble in water at room temperature, so the solubility of cellulose in water is increased by heating. Polyvinyl alcohol is added to the cellulose solution and stirred thoroughly to obtain a cellulose / PVA mixed solution. Polyvinyl alcohol (PVA) has good solubility in water. When mixed with the cellulose solution, a certain degree of compatibility can be formed between the two, thanks to the hydrophilicity of PVA and the hydroxyl functional groups of cellulose. It should be noted that if the hot water temperature is too high, it will cause thermal degradation of PVA.

[0061] Specifically, the dissolution concentration of the cellulose is 2-10 g / 100 ml water; the concentration of the polyvinyl alcohol is 2-5 g / 100 ml water. The concentrations of cellulose and PVA need to be adjusted according to the properties of the required materials. Too high a concentration will make the solution too viscous and difficult to process; too low a concentration will affect the mechanical strength of the final material.

[0062] S5. Add the COF with quercetin loaded in the pores prepared in step S3 to the cellulose / PVA mixed solution in step S4 and mix well.

[0063] S6. The cellulose / PVA mixed solution in step S5 is placed in a -20°C environment and frozen for 24 hours, and then thawed at room temperature for 4 hours. The above freezing and thawing steps are repeated 3 times to obtain the covalent organic framework-cellulose hydrogel composite dressing. The purpose of removing moisture through a freeze-drying cycle is to increase the water absorption and biocompatibility of the material when making a porous structure, while maintaining the activity of COF and quercetin. When the cellulose / PVA mixed solution is frozen at -20°C, the water will form ice crystals, which will melt during the subsequent thawing process, but because the space occupied by the ice crystals has been removed, a porous structure is left. This porous structure is crucial for hydrogel materials because it increases the specific surface area of ​​the material, improves water absorption and air permeability, and is conducive to wound healing. Repeated freeze-drying cycles can optimize the microstructure of the material and improve its mechanical properties. Appropriate porosity can give the material better elastic recovery ability when subjected to pressure, while maintaining sufficient strength to support its function in the wound healing process. Freeze drying instead of high temperature drying can minimize the thermal degradation of quercetin and COF structure, ensuring their bioactivity and drug release performance in the final product. The above freezing temperature is low enough to completely freeze the water while avoiding irreversible damage to the material structure caused by too low temperature. Repeating the freeze drying cycle three times is sufficient to form a stable porous structure while ensuring that the water in the material is fully removed. Thawing is carried out at room temperature and heating is avoided to reduce the impact on the material structure and active ingredients.

[0064] In order to further illustrate the covalent organic framework-cellulose hydrogel and the preparation method thereof provided by the present invention, the following examples are provided.

[0065] Example 1

[0066] A method for preparing a covalent organic framework-cellulose hydrogel comprises the following steps:

[0067] (1) Synthesis of COF: 0.3 mmol of 4,4'-diaminobiphenyl, 0.2 mmol of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine, 0.2 mmol of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde and 0.3 mmol of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde were dissolved in 10 mL of o-dichlorobenzene solution.

[0068] (2) Add 1.5 mL of 3 mol / L acetic acid aqueous solution as a catalyst to the above solution and stir thoroughly.

[0069] (3) The above solution was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 110° C. for 4 days.

[0070] (4) Wash the unreacted monomers with THF and DMF, and centrifuge and dry to obtain the prepared COF sample. Figure 1 Scanning electron microscope image of COF material, Figure 2 From the transmission electron microscope image of the COF material, it can be seen that the prepared COF has a uniform morphology and is spherical.

[0071] (5) Prepare a 50 mg / mL quercetin ethanol solution.

[0072] (6) 0.05 g of the COF sample prepared in step (4) was ultrasonically dispersed into 5 mL of a 50 mg / mL quercetin ethanol solution, ultrasonicated for 30 minutes, centrifuged and filtered to evaporate the ethanol, thereby obtaining a COF material with quercetin loaded in the pores.

[0073] (7) 0.8 g of cellulose was dissolved in 20 mL of hot water at 50°C, and then 0.4 g of polyvinyl alcohol was added thereto and stirred thoroughly to obtain a hydrogel (eg Figure 5 and Figure 6 As shown, it can be seen that the prepared hydrogel has a certain viscosity, and the hydrogel will not flow when the container is inverted); then 0.05 g of the COF material with quercetin loaded in the pores in step (6) is added to the hydrogel.

[0074] (8) The hydrogel is placed in a -20°C environment and frozen for 24 hours, and then thawed at room temperature for 4 hours; after the above steps are repeated 3 times, freeze-dried to remove moisture to obtain the desired covalent organic framework-cellulose hydrogel composite dressing.

[0075] from Figure 8 It can be seen that the release curve of the COF material with quercetin loaded in the pores prepared in Example 1 in PBS buffer at pH 7.4 shows that the COF material with quercetin loaded in the pores can slowly release the quercetin in the COF material between 0 and 100 hours, and the sustained slow release of quercetin can be achieved.

[0076] See also Fig. 9 , Fig. 9 Schematic diagram of the antibacterial rate of the control group (COF material), cellulose / PVA hydrogel, and the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1 against Escherichia coli. Fig. 9 It can be seen that neither the COF material nor the hydrogel alone has an antibacterial effect, while the hydrogel loaded with quercetin using the COF material can achieve an antibacterial rate of approximately 100%.

[0077] See also Fig.10 , Fig.10 It is a schematic diagram of the cell survival rate of the control group (COF material), cellulose / PVA hydrogel, cellulose / PVA hydrogel / COF (not loaded with quercetin), and the covalent organic framework-cellulose hydrogel composite dressing (1 mg / mL) prepared in Example 1 after incubation with L929 cells for 48 hours. It can be seen that the covalent organic framework-cellulose hydrogel composite dressing prepared by the present invention does not have an adverse effect on the cell survival rate.

[0078] See also Fig.11 , Fig.11 This is a schematic diagram of the cell survival rate of the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1 after incubation with L929 cells at different concentrations for 48 hours. It can be seen that the cell survival rate gradually increases with the increase in the concentration of the hydrogel extract.

[0079] See also Fig.12 , Fig.12 The figure is a comparison of the healing effects of the wounds of mice in the control group (hydrogel prepared in Example 1) and after using the covalent organic framework-cellulose hydrogel composite dressing prepared in Example 1. It can be seen from the figure that after 7 days of treatment, the healing effect of the wounds of mice is better than that of the control group.

[0080] Example 2

[0081] A method for preparing a covalent organic framework-cellulose hydrogel comprises the following steps:

[0082] (1) Synthesis of COF: 0.3 mmol of 4,4'-diaminobiphenyl, 0.2 mmol of 1,3,5-tris(4-aminophenyl)benzene, 0.3 mmol of trimesaldehyde and 0.2 mmol of 2,5-dimethoxybenzene-1,4-dicarbaldehyde (DMTP) were dissolved in 10 mL of xylene solution.

[0083] (2) Add 1.5 mL of 6 mol / L acetic acid aqueous solution as a catalyst to the above solution and stir thoroughly.

[0084] (3) The above solution was transferred to a polytetrafluoroethylene-lined hydrothermal autoclave and reacted at 90° C. for 6 days.

[0085] (4) The unreacted monomers were washed with THF and DMF and centrifuged to dry to obtain the prepared COF sample.

[0086] (5) Prepare a 50 mg / mL quercetin acetone solution.

[0087] (6) 0.05 g of the COF sample prepared in step (4) was ultrasonically dispersed into 1 mL of a 50 mg / mL quercetin acetone solution, ultrasonicated for 30 minutes, centrifuged and filtered to evaporate the ethanol, thereby obtaining a COF material with quercetin loaded in the pores.

[0088] (7) 0.8 g of cellulose was dissolved in 20 mL of hot water at 40° C., and then 0.4 g of polyvinyl alcohol was added thereto. After sufficient stirring, a hydrogel was obtained. Then, 0.05 g of the COF material with quercetin loaded in the pores in step (6) was added to the hydrogel.

[0089] (8) The hydrogel is placed in a -20°C environment and frozen for 24 hours, and then thawed at room temperature for 4 hours; after the above steps are repeated 3 times, freeze-dried to remove moisture to obtain the desired covalent organic framework-cellulose hydrogel composite dressing.

[0090] Example 3

[0091] A method for preparing a covalent organic framework-cellulose hydrogel comprises the following steps:

[0092] (1) Synthesis of COF: 0.3 mmol of 4,4'-methylenedianiline, 0.2 mmol of 1,3,5-tris(4-aminophenyl)benzene, 0.3 mmol of 4,4',4"-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (TTB) and 0.2 mmol of trimesic acid were dissolved in 10 mL of n-butanol solution.

[0093] (2) Add 1.5 mL of 3 mol / L acetic acid aqueous solution as a catalyst to the above solution and stir thoroughly.

[0094] (3) The above solution was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and reacted at 130° C. for 2 days.

[0095] (4) The unreacted monomers were washed with THF and DMF and centrifuged to dry to obtain the prepared COF sample.

[0096] (5) Prepare a 50 mg / mL quercetin cyclohexane solution.

[0097] (6) 0.05 g of the COF sample prepared in step (4) was ultrasonically dispersed into 3 mL of a 50 mg / mL quercetin cyclohexane solution, ultrasonicated for 30 minutes, centrifuged and filtered to evaporate the ethanol, thereby obtaining a COF material with quercetin loaded in the pores.

[0098] (7) 0.8 g of cellulose was dissolved in 20 mL of hot water at 60° C., and then 0.4 g of polyvinyl alcohol was added thereto. After sufficient stirring, a hydrogel was obtained. Then, 0.05 g of the COF material with quercetin loaded in the pores in step (6) was added to the hydrogel.

[0099] (8) The hydrogel is placed in a -20°C environment and frozen for 24 hours, and then thawed at room temperature for 4 hours; after the above steps are repeated 3 times, freeze-dried to remove moisture to obtain the desired covalent organic framework-cellulose hydrogel composite dressing.

[0100] In summary, the present invention synthesizes a series of novel COF materials formed by copolymerization of different monomers, and uses it as a drug carrier. By loading the natural drug quercetin in COF and dispersing it in a cellulose-based hydrogel, the cellulose-based hydrogel can be provided with antibacterial properties and the ability to promote wound healing. Moreover, quercetin is loaded in the porous structure of COF, and after the cellulose hydrogel absorbs the blood / tissue fluid (pH is alkaline) of the wound, COF will gradually decompose, thereby being able to continuously and slowly release quercetin, so that the hydrogel can achieve a sustained and stable antibacterial effect and the effect of promoting wound healing on the wound. Moreover, the components used in the preparation process of the cellulose-based composite hydrogel are non-toxic to cells.

[0101] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the present invention.

Claims

1. A method for preparing a covalent organic framework-cellulose hydrogel composite dressing, characterized in that: The steps include: S1. Synthesis of COF: A monomer containing an amino group and a monomer containing an aldehyde group are added to an organic solvent, and then an acetic acid aqueous solution is added as a catalyst, and the formed solution is transferred to a hydrothermal reactor, and heated for copolymerization to obtain COF; S2. dissolving quercetin in a hot organic solvent to obtain a quercetin solution; and ultrasonically dispersing the COF prepared in step S1 into the quercetin solution, so that the quercetin is loaded into the internal pores of the COF; S3. The quercetin-loaded COF is separated from the organic solvent by centrifugal precipitation, and then vacuum dried or naturally dried until the organic solvent is completely volatilized to obtain a quercetin-loaded COF in the pores; S4. After dissolving cellulose in hot water, a cellulose solution is obtained; polyvinyl alcohol is added to the cellulose solution and stirred to obtain a cellulose / PVA mixed solution; S5. The COF loaded with quercetin in the pores prepared in step S3 is added to the cellulose / PVA mixed solution in step S4 and mixed evenly; S6. removing water from the cellulose / PVA mixed solution in step S5 to obtain a covalent organic framework-cellulose hydrogel composite dressing; The monomer containing amino groups is one or more of 4,4'-diaminobiphenyl, 4,4'-methylenedianiline, 1,3,5-tris(4-aminophenyl)benzene, 4,4',4"-(1,3,5-triazine-2,4,6-triyl)triphenylamine; the monomer containing aldehyde groups is one or more of trimesic acid, 4,4',4"-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde; the molar ratio of the monomer containing amino groups to the monomer containing aldehyde groups is 1:

1.

2. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: The organic solvent in step S1 is one or more of toluene, xylene, o-dichlorobenzene, trimethylbenzene, dioxane, and n-butanol.

3. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: The reaction temperature of the reactor in step S1 is 80-130° C., and the reaction time is 2-7 days.

4. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: The concentration of the acetic acid aqueous solution in step S1 is 3 mol / L or 6 mol / L.

5. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: The organic solvent in step S2 is one of methanol, ethanol, isopropanol, acetone, ethyl acetate and cyclohexane; the content of the quercetin solution is 10-200 mg / mL.

6. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: In step S4, the dissolved cellulose concentration is 2-10 g / 100 ml water, and the hot water temperature is 40-65° C.; the concentration of the polyvinyl alcohol is 2-5 g / 100 ml water.

7. The method for preparing the covalent organic framework-cellulose hydrogel composite dressing according to claim 1, characterized in that: The operation of step S6 is specifically as follows: freezing the cellulose / PVA mixed solution in step S5 at -20°C for 24 hours, and then thawing it at room temperature for 4 hours, and repeating the freezing and thawing steps three times.

Images