A chitosan porous membrane and its preparation method and application

Abstract

The present application discloses a chitosan porous membrane and its preparation method and application. The present application utilizes the processes of electrospinning, urushiol cross-linking, and swelling to prepare a porous chitosan membrane with a nanoscale pore structure. By introducing oligomeric urushiol, a structure is constructed with chitosan molecules that are easily soluble in a swelling agent solution as the main chain and acid-resistant and hydrophobic polymeric urushiol as the cross-linking bridge. This allows for slow and controllable swelling of chitosan nanofibers, solving the problem of precise and effective control of the pore size and structure of the chitosan membrane. Furthermore, the nanofiber swelling process is utilized to transform the disordered stacked nanofiber precursors formed by electrospinning into a cross-fused continuous network, thereby forming a continuous porous membrane with high strength.

Description

Technical Field

[0001] The present application relates to the field of functional polymer materials, and in particular to a chitosan porous membrane and a preparation method and application thereof. Background Art

[0002] Because chitosan is neither hot-melt nor soluble in most organic solvents, preparing porous chitosan materials that both block foreign matter and provide surface permeability is challenging. While numerous reports have demonstrated the production of nanoscale chitosan porous membranes with varying pore sizes through electrospinning, efficient and precise control of the pore size and structure of chitosan membranes remains difficult simply by adjusting the spinning process or optimizing the formulation. Summary of the Invention

[0003] In view of this, the present application provides a chitosan porous membrane and its preparation method and application, aiming to provide a method with simple operation, obvious effect and controllable process, for preparing a chitosan porous membrane with adjustable thickness and pore structure, so as to better meet the performance requirements of wound dressing materials in terms of safety, antibacterial, breathability, strength, etc.

[0004] The embodiment of the present application is implemented as follows: a method for preparing a chitosan porous membrane of the present application comprises the following steps:

[0005] providing a first solution comprising chitosan, oligomeric urushiol, and a spinning aid;

[0006] Taking the first solution and forming a nanofiber precursor by electrospinning;

[0007] Taking the nanofiber precursor, drying it and forming an urushiol-crosslinked chitosan nanofiber membrane through a cross-linking reaction;

[0008] The urushiol cross-linked chitosan nanofiber membrane is placed in an atmosphere containing a swelling agent to swell at least a portion of the urushiol cross-linked chitosan nanofiber membrane.

[0009] Optionally, in some embodiments, the mass ratio of the chitosan, the oligomeric urushiol and the spinning aid is 1:(0.1-0.5):(0.05-0.2);

[0010] Wherein, the molecular weight of the chitosan is 100,000-300,000, and the degree of deacetylation of the chitosan is 85-95%; and / or,

[0011] The molecular weight of the oligomeric urushiol is 600-3000, and the degree of polymerization of the oligomeric urushiol is 2-10; and / or,

[0012] The molecular weight of the spinning aid is 100,000-200,000.

[0013] Optionally, in some embodiments, the spinning aid is selected from at least one of polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose.

[0014] Optionally, in some embodiments, the first solution further includes a first solvent, and the first solvent is selected from at least one of acetic acid, trifluoroacetic acid, and formic acid; wherein the mass concentration of the first solvent in the first solution is 90-98%.

[0015] Optionally, in some embodiments, in the electrospinning, the spinning voltage is 20-25 kV, the injection rate is 0.5-3.0 mL / h, the collection distance is 6-15 cm, and the humidity is 35±5%.

[0016] Optionally, in some embodiments, in the step of taking the nanofiber precursor, drying and forming the urushiol cross-linked chitosan nanofiber membrane through a cross-linking reaction, the temperature of the drying and cross-linking reaction is 10-50° C., and the time of the drying and cross-linking reaction is 2-8 hours.

[0017] Optionally, in some embodiments, the step of placing the urushiol-crosslinked chitosan nanofiber membrane in an atmosphere containing a swelling agent further comprises:

[0018] providing a second solution comprising the swelling agent;

[0019] heating the second solution to form steam containing the swelling agent;

[0020] The urushiol cross-linked chitosan nanofiber membrane is placed in the steam for fumigation to obtain a chitosan porous membrane.

[0021] Optionally, in some embodiments, the swelling agent is selected from at least one of acetic acid, hydrochloric acid, trifluoroacetic acid, formic acid, lactic acid, citric acid, and ascorbic acid; and / or,

[0022] The mass concentration of the swelling agent in the second solution is 5-30%; and / or,

[0023] The fumigation time is 5-30 minutes.

[0024] Optionally, in some embodiments, the present application further provides a chitosan porous membrane, which is prepared by the above-mentioned method for preparing a chitosan porous membrane.

[0025] Optionally, in some embodiments, the present application also provides an application of a chitosan porous membrane as a medical wound dressing.

[0026] The beneficial effects of this application are:

[0027] The present application utilizes the processes of electrospinning, urushiol cross-linking and swelling with a swelling agent to prepare a porous chitosan membrane with a nanoscale pore structure; by introducing oligomeric urushiol, a body structure is constructed with chitosan molecules that are easily soluble in the swelling agent solution as the main chain and acid-resistant and hydrophobic polymeric urushiol as the cross-linking bridge, thereby achieving slow and controllable swelling of chitosan nanofibers and solving the problem of precise and effective control of the pore size and structure of the chitosan membrane; and utilizing the swelling process of the nanofibers, the disordered stacked nanofiber precursors formed by electrospinning are transformed into a cross-fused continuous network, thereby forming a continuous porous membrane with higher strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 The microscopic morphology of the oligomeric urushiol cross-linked chitosan membrane provided in Comparative Example 1 and Examples 1, 5, 6, and 7 of the present application after fumigation with acetic acid aqueous solution for different times;

[0030] Figure 2 The microscopic morphology of the oligomeric urushiol cross-linked chitosan membrane provided in Comparative Example 2 and Examples 2, 8, 9, and 10 of the present application after fumigation with acetic acid aqueous solution for different times;

[0031] Figure 3 This is the microscopic morphology of the pure chitosan film provided in Comparative Example 3 of the present application after fumigation with acetic acid aqueous solution for 5 minutes;

[0032] Figure 4 This is the microscopic morphology of the oligomeric urushiol cross-linked chitosan membrane provided in Comparative Example 4 of the present application after being fumigated with distilled water for 30 minutes;

[0033] Figure 5 This is the reaction mechanism of oligomeric urushiol and chitosan provided in the examples of this application;

[0034] Figure 6 The fumigated oligomeric urushiol cross-linked chitosan film provided in Example 2 of the present application is stably suspended with a 50g weight;

[0035] Figure 7 This is a comparison of the number of Staphylococcus aureus colonies on a plate before and after adding a chitosan porous membrane, as provided in Example 2 of the present application;

[0036] Figure 8 This is a comparison of the number of E. coli colonies on the plate before and after adding the chitosan porous membrane provided in Example 2 of the present application. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application and are not used to limit the present application. In the present application, unless otherwise specified, the directional words used, such as "upper" and "lower", specifically refer to the directions of the drawings in the accompanying drawings. In addition, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values within the range. For example, description of a range from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, such as 1, 2, 3, 4, 5, and 6. Furthermore, whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range.

[0038] The inventors of this application have discovered that medical wound dressings, which are materials applied to wound surfaces to cover sores, wounds, or other lesions, can inhibit bacteria and prevent wound infection, making them an important medical material in the current treatment of skin wounds. Natural cotton gauze, the earliest widely used wound dressing, despite its advantages of low cost and safety, also suffers from practical drawbacks such as high permeability, which can easily dehydrate the wound surface, adhere to the wound surface, causing secondary mechanical damage during dressing changes, and difficulty in blocking the invasion of foreign particles and bacteria. In recent years, with the rapid development of medical polymer technology, natural polymer materials such as alginate, chitosan, and cellulose derivatives have rapidly replaced simple cotton gauze dressings. Among these, chitosan and its derivatives are the most representative new medical dressing materials. Chitosan is a natural polysaccharide prepared by deacetylation of chitin. Due to the large number of amino and hydroxyl groups in its molecular structure, chitosan is highly reactive and amenable to chemical modification. Furthermore, compared to other synthetic polymers, chitosan and its derivatives offer a range of unique advantages, including good biocompatibility and biodegradability, safety and non-toxicity, strong moisturizing properties, and natural antibacterial properties. Consequently, chitosan-based antibacterial gels, patches, and sprays have found widespread use in the healthcare sector.

[0039] In combination with the actual application environment, the ideal wound dressing should have the following structural and performance characteristics: (1) safe and non-toxic, with good biocompatibility, and not prone to toxic side effects during use; (2) with good antibacterial properties, which can effectively prevent wound infection, and does not contain antibiotics and heavy metal ions, so it is not easy to produce drug resistance or cytotoxicity during use; (3) with a good pore structure, which can effectively block external particles (such as dust) during use, while also achieving good air permeability; (4) with a certain mechanical strength, which is not easy to break during use. Existing chitosan-based antibacterial gels, patches, and sprays can all construct a continuous chitosan film on the wound surface, thereby achieving the purpose of blocking external foreign matter, preventing wound infection, and promoting wound healing. However, this continuous film lacks a clear pore structure, and the wound dressing made of it has poor air permeability, which is not conducive to the absorption of wound exudate and the volatilization of sweat on the body surface. In addition, poor air permeability may also cause anaerobic bacteria to grow in the wound, affecting wound healing. Therefore, finding the optimal balance between the barrier properties to external foreign bodies and the breathability of the skin surface and preparing porous chitosan membranes with adjustable barrier and breathability are effective means to further improve the comprehensive effectiveness of existing chitosan-based wound dressings.

[0040] Since chitosan is not hot-melt and is insoluble in most organic solvents, it is not easy to prepare porous chitosan materials that have both foreign body barrier and surface breathability functions. The common methods currently used include the following: (1) Freeze-drying method. The chitosan aqueous solution is quickly frozen and iced, and the ice crystals are sublimated by freeze-drying to leave pores inside the chitosan membrane. This method is the simplest process, but because the ice crystal particles are generally coarse, it is mostly used for block chitosan gels with a certain thickness. When used for thinner chitosan membranes, it is easy to produce local large voids and significantly reduce the membrane strength. In addition, it is also difficult to control the size of ice crystals, making it difficult to effectively regulate the pore structure of the chitosan membrane. (2) Powder template method. Inorganic powders such as CaCO3 and SiO2 are used as templates, mixed evenly with chitosan solution, and then cast into a continuous membrane. The template is then dissolved by hydrochloric acid or sodium hydroxide solution to obtain a porous chitosan membrane. Although this method can achieve the regulation of the pore structure of chitosan membrane by controlling the size of inorganic powder, since nano inorganic powder is very easy to agglomerate and the viscosity of chitosan solution is too high to be conducive to powder dispersion, generally only micron-sized pores can be obtained, and the barrier ability to bacteria and fine particles is limited. In addition, long-term acid and alkali soaking to wash off the template powder will lead to rapid degradation of chitosan, which will inevitably reduce its mechanical properties. (3) Polymer phase separation method. Water-soluble polymer materials such as polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) are co-dissolved with chitosan in a specific solvent to form a uniform mixed solution. After casting into a continuous membrane, the water-soluble polymer is extracted with hot water to form a chitosan membrane with a pore structure. This method uses polymer molecules instead of inorganic powder as a template for pores, which can achieve nano-scale pore size; but since there are often interactions such as hydrogen bonds between polymers and chitosan and the polymer molecular weight is polydisperse, the scale control of the phase separation area is extremely random, and it is basically impossible to effectively control the pore size and structure. (4) Electrospinning method. First, chitosan is prepared into a spinning solution of a certain concentration, and chitosan fibers with nanoscale diameters are made using an electrospinning process. A porous chitosan nanofiber membrane is formed by disordered stacking. Although this method can relatively easily obtain a uniformly dispersed nanoscale pore structure, the chitosan membrane obtained by electrospinning generally has poor strength because the fibers are only cross-stacked without interaction. In addition, there are many parameters in the chitosan electrospinning process. Many factors such as the spinning solution concentration, raw material molecular weight, spinning aid type, solvent formula and dosage, electric field strength, ambient temperature and humidity, and spinning rate will have a significant impact on the fiber morphology and diameter of the product, thereby changing the pore size and structure of the membrane. Therefore, although many reports show that people have obtained nanoscale chitosan porous membranes with different pore sizes through electrospinning, it is still difficult to achieve efficient and precise control of the pore size and structure of the chitosan membrane by simply adjusting and optimizing the formula or process during the spinning process.

[0041] Therefore, based on the above problems, this application provides a chitosan porous membrane and its preparation method and application. Detailed descriptions are given below. It should be noted that the description order of the following embodiments does not limit the preferred order of the embodiments.

[0042] The present invention provides a method for preparing a porous chitosan membrane, which comprises the following steps:

[0043] S1: providing a first solution including chitosan, oligomeric urushiol and a spinning aid;

[0044] S2: taking the first solution and forming a nanofiber precursor by electrospinning;

[0045] S3: taking the nanofiber precursor, drying it and forming an urushiol-crosslinked chitosan nanofiber membrane through a cross-linking reaction;

[0046] S4: placing the urushiol cross-linked chitosan nanofiber membrane in an atmosphere containing a swelling agent to swell at least a portion of the urushiol cross-linked chitosan nanofiber membrane.

[0047] The preparation method of the chitosan porous membrane provided in the present application solves the problem of simple and efficient preparation of porous chitosan membrane with nanoscale pore structure by utilizing the technical scheme of electrospinning-urushiol crosslinking-swelling agent; in addition, under the catalytic action of the solvent of the first solution, the catechol groups at both ends of the oligomeric urushiol react with the amino groups of the chitosan molecules to undergo Schiff base reaction, thereby constructing a body structure with chitosan molecules that are easily soluble in the aqueous solution of the swelling agent as the main chain and acid-resistant and hydrophobic polymeric urushiol as the cross-linking bridge. In combination with the action of the swelling agent, the slow and controllable swelling of the chitosan nanofibers is achieved, solving the problem of precise and effective control of the pore size and structure of the chitosan membrane; at the same time, by utilizing the swelling process of the nanofibers, the disordered stacked nanofiber precursors formed by electrospinning are transformed into a cross-fused continuous network, thereby forming a continuous porous membrane with higher strength, solving the problems of poor mechanical strength of the electrospun nanofiber membrane and the problem that other methods such as freeze-drying easily lead to reduced membrane strength.

[0048] In some embodiments, in step S1, the mass ratio of chitosan, oligomeric urushiol, and spinning aid is 1:(0.1-0.5):(0.05-0.2). It is understood that the preferred ranges of chitosan, oligomeric urushiol, and spinning aid include 1:0.3:0.1, 1:0.5:0.08, 1:0.1:0.2, etc.

[0049] Furthermore, in some embodiments, the molecular weight of the chitosan is 100,000-300,000, and the degree of deacetylation of the chitosan is 85-95%. It is understood that the molecular weight of the chitosan is any value between 100,000 and 300,000, or a range between any two values.

[0050] Furthermore, in some embodiments, the molecular weight of the oligomeric urushiol is 600-3000, and the degree of polymerization of the oligomeric urushiol is 2-10. It is understood that the molecular weight of the oligomeric urushiol is any value between 600 and 3000 or a range between any two values.

[0051] The preparation method of oligomeric urushiol includes: first, extracting urushiol monomer (molecular weight of about 300) from natural raw lacquer using an organic solvent such as ethanol or acetone; then heating and stirring the extracted urushiol monomer in air for a certain period of time to obtain an urushiol polymer with a certain degree of polymerization. Because the molecular weight of this polymer is not high (generally the number average molecular weight is less than 3000), it is called oligomeric urushiol. The degree of polymerization is generally between 2 and 10. The oligomeric urushiol molecule contains multiple catechol structures, which are conducive to the construction of cross-linking bridges between chitosan molecules, transforming the linear molecular structure of chitosan into a three-dimensional molecular structure.

[0052] In some embodiments, the molecular weight of the spinning aid is 100,000-200,000. It is understood that the molecular weight of the spinning aid is any value from 100,000 to 200,000 or a range between any two values.

[0053] Furthermore, in some embodiments, the spinning aid is selected from at least one of polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose. The main function of the spinning aid is to reduce the hydrogen bonding between chitosan molecules, making it easier to electrospin into nanofibers.

[0054] In some embodiments, in order to achieve the subsequent reaction of chitosan and oligomeric urushiol, the first solution also needs to contain some first solvent that acts as a catalyst, and the first solvent is selected from at least one of acetic acid, trifluoroacetic acid, and formic acid; wherein the mass concentration of the first solvent in the first solution is 90-98%.

[0055] In some embodiments, the first solution can be understood as an electrospinning solution for electrospinning. The specific preparation process of the first solution is: first, an appropriate amount of an aqueous solution of a first solvent with a mass concentration of 90-98%, an appropriate amount of chitosan powder with a deacetylation degree of 85-95% and a molecular weight of 100,000-300,000, and an appropriate amount of polyethylene glycol with a molecular weight of 100,000-200,000 are added to a conical flask, and stirred at room temperature for 6-8 hours to completely dissolve the chitosan and the spinning aid. Subsequently, an appropriate amount of oligomeric urushiol with a degree of polymerization of 2-10 is added and stirring is continued for 2-3 hours to fully mix the oligomeric urushiol and the chitosan solution and initially react to form a uniform electrospinning solution.

[0056] In some embodiments, in step S2, the electrospinning voltage is 20-25 kV, the injection rate is 0.5-3.0 mL / h, the collection distance is 6-15 cm, and the humidity is 35±5%.

[0057] It is understood that the specific process of electrospinning is to draw an appropriate amount of electrospinning solution with a syringe and place it in the propeller of the electrospinning machine for electrospinning. During this process, the preferred control is the spinning voltage of 25kV, the injection rate of 2mL / h, the collection distance of 10cm, the humidity of 35±5%, and the collection medium is release paper. By varying the amount of spinning solution, urushiol-chitosan nanofiber precursors of different thicknesses can be obtained.

[0058] In some embodiments, in step S3, the temperature for the drying and cross-linking reaction is 10-50° C., and the time for the drying and cross-linking reaction is 2-8 hours.

[0059] It can be understood that the purpose of step S3 is to allow the oligomeric urushiol in the nanofiber precursor to react completely with the chitosan molecules to form a complete cross-linked structure. Preferably, after the electrospinning is completed, the nanofiber precursor is peeled off from the release paper and placed in a vacuum oven at 40°C for 6 hours to slowly remove volatile components such as water and the first solvent. In this process, the concentration of the reactants is gradually increased to allow the oligomeric urushiol and chitosan molecules to react completely, and finally a urushiol-cross-linked chitosan nanofiber membrane with a specific thickness is obtained.

[0060] In some embodiments, in step S4, the step of placing the urushiol-crosslinked chitosan nanofiber membrane in an atmosphere containing a swelling agent further comprises:

[0061] providing a second solution comprising a swelling agent;

[0062] heating the second solution to form steam containing the swelling agent;

[0063] The urushiol cross-linked chitosan nanofiber membrane was fumigated in steam to prepare a chitosan porous membrane.

[0064] Furthermore, in some embodiments, the swelling agent is selected from at least one of acetic acid, hydrochloric acid, trifluoroacetic acid, formic acid, lactic acid, citric acid, and ascorbic acid.

[0065] In some embodiments, the swelling agent accounts for 5-30% by mass of the second solution.

[0066] In some embodiments, the fumigation time is 5-30 minutes. Preferably, the fumigation time is any one of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes and 30 minutes, or a range between any two of them.

[0067] It is understood that step S4 specifically comprises the following steps: adding an appropriate amount of 5-30% acetic acid aqueous solution to a sealed container, suspending the cross-linked chitosan nanofiber membrane in the container, and sealing the container. A suitable ambient temperature is then controlled, and the chitosan nanofiber membrane is fumigated using the acetic acid-containing vapor volatilized from the container. The chitosan nanofiber membrane is then fumigated for varying fumigation times to achieve varying degrees of swelling of the chitosan nanofibers. The chitosan membrane is then removed and air-dried to obtain a porous chitosan continuous membrane having a specific pore size and structure.

[0068] See also Figure 5 , which is the preparation principle of this embodiment, wherein the two groups of catechol groups of oligomeric urushiol are oxidized to form a quinone structure, and then undergo a Schiff base reaction with the amino group of chitosan to construct a bulk molecular structure with chitosan molecules that are easily soluble in acetic acid aqueous solution as the main chain and acid-resistant and hydrophobic oligomeric urushiol as the cross-linking bridge. Combined with the electrospinning process, the solid content control of the spinning solution and the fumigation method containing a swelling agent solution, the slow and controllable swelling of the chitosan nanofibers and the micron-level control of the fiber membrane thickness can be achieved, providing a simple and easy method for the preparation of ultra-thin chitosan porous membranes with controllable thickness and pore structure.

[0069] In order to make the above implementation details and operations of this application clearly understood by those skilled in the art, and to demonstrate the significant improvement in performance of a chitosan porous membrane and its preparation method and application in the embodiment of this application, the above technical solution is illustrated by multiple embodiments below.

[0070] Example 1

[0071] 20 mL of 95% aqueous acetic acid, 0.6 g of chitosan powder (90% deacetylation, molecular weight 100,000), and 0.1 g of polyethylene glycol (100,000 molecular weight) were added to a conical flask and stirred at room temperature for 6 hours to completely dissolve the chitosan and polyethylene glycol. Subsequently, 0.18 g of oligomeric urushiol (degree of polymerization 8, average molecular weight 2400) was added and stirred for another 3 hours to allow the oligomeric urushiol and chitosan solution to mix thoroughly and react initially to form a uniform electrospinning solution.

[0072] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 25 kV, the injection rate at 2 mL / h, the collection distance at 10 cm, and the humidity at 35 ± 5%. Release paper was used as the collection medium. After electrospinning, the resulting nanofiber membrane precursor was peeled from the release paper and placed in a 40°C vacuum oven for 6 hours to remove volatile components such as water and acetic acid and complete the cross-linking reaction between the oligomeric urushiol and chitosan molecules. The resulting nanofiber membrane had a thickness of 22 μm and was cross-linked with urushiol.

[0073] A sealed glass container was filled with 50 mL of a 10% acetic acid solution. The urushiol-crosslinked chitosan nanofiber membrane was suspended in the container and sealed. The container was maintained at a temperature of 35°C and the chitosan nanofiber membrane was fumigated with acetic acid vapor for 5 minutes.

[0074] Example 2

[0075] 16 mL of 98% acetic acid solution, 0.5 g of chitosan powder (95% deacetylation, molecular weight 200,000), and 0.08 g of polyvinyl alcohol (200,000 molecular weight) were added to a conical flask and stirred at room temperature for 8 hours to completely dissolve the chitosan and polyvinyl alcohol. Subsequently, 0.15 g of oligomeric urushiol (degree of polymerization 5, average molecular weight 1500) was added and stirred for another 2 hours to allow the oligomeric urushiol and chitosan solution to mix thoroughly and react initially to form a uniform electrospinning solution.

[0076] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 20 kV, the injection rate at 1 mL / h, the collection distance at 15 cm, and the humidity at 35 ± 5%. The collection medium was release paper. After electrospinning, the resulting nanofiber membrane precursor was peeled from the release paper and placed in a 30°C vacuum oven for 8 hours to remove volatile components such as water and acetic acid and complete the cross-linking reaction between the oligomeric urushiol and chitosan molecules. The resulting nanofiber membrane had a thickness of 17 μm and was cross-linked with urushiol.

[0077] A sealed glass container was filled with 50 mL of a 20% acetic acid solution. The urushiol-crosslinked chitosan nanofiber membrane was suspended in the container and sealed. The container was maintained at a temperature of 35°C and the chitosan nanofiber membrane was fumigated with acetic acid vapor for 5 minutes.

[0078] Example 3

[0079] 20 mL of 90% trifluoroacetic acid aqueous solution, 0.6 g of chitosan powder with a deacetylation degree of 85% and a molecular weight of 150,000, and 0.06 g of polyethylene glycol (150,000 molecular weight) were added to a conical flask and stirred at room temperature for 6 hours to completely dissolve the chitosan and polyethylene glycol. Subsequently, 0.3 g of oligomeric urushiol with a degree of polymerization of 10 (average molecular weight of 3000) was added and stirred for another 3 hours to allow the oligomeric urushiol and chitosan solution to fully mix and react to form a uniform electrospinning solution.

[0080] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 25 kV, the injection rate at 0.5 mL / h, the collection distance at 6 cm, and the humidity at 35 ± 5%. Release paper was used as the collection medium. After electrospinning, the resulting nanofiber membrane precursor was peeled from the release paper and placed in a 50°C vacuum oven for 2 hours to remove volatile components such as water and trifluoroacetic acid and complete the crosslinking reaction between the oligomeric urushiol and chitosan molecules. The resulting urushiol-crosslinked chitosan nanofiber membrane had a thickness of 24 μm.

[0081] A sealed glass container was filled with 50 mL of 5% hydrochloric acid solution. The urushiol-crosslinked chitosan nanofiber membrane was suspended in the container and sealed. The container was maintained at a temperature of 30°C and the chitosan nanofiber membrane was fumigated with acetic acid vapor for 5 minutes.

[0082] Example 4

[0083] 20 mL of 95% formic acid solution, 0.6 g of chitosan powder (molecular weight, 85% deacetylation, 150,000), and 0.12 g of polyvinylpyrrolidone (molecular weight, 150,000) were added to a conical flask and stirred at room temperature for 6 hours to completely dissolve the chitosan and polyethylene glycol. Subsequently, 0.1 g of oligomeric urushiol (molecular weight, 600) with a degree of polymerization of 2 was added and stirred for another 3 hours to allow the oligomeric urushiol and chitosan solution to mix thoroughly and react initially to form a uniform electrospinning solution.

[0084] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 25 kV, the injection rate at 2 mL / h, the collection distance at 10 cm, and the humidity at 35 ± 5%. Release paper was used as the collection medium. After electrospinning, the resulting nanofiber membrane precursor was peeled from the release paper and placed in a 40°C vacuum oven for 6 hours to remove volatile components such as water and formic acid and complete the cross-linking reaction between the oligomeric urushiol and chitosan molecules. The resulting urushiol-crosslinked chitosan nanofiber membrane had a thickness of 20 μm.

[0085] A sealed glass container was filled with 50 mL of a 10% citric acid solution. The urushiol-crosslinked chitosan nanofiber membrane was suspended in the container and sealed. The container was then kept at a temperature of 40°C and the chitosan nanofiber membrane was fumigated with the citric acid vapor emitted from the container for 30 minutes.

[0086] Example 5

[0087] The specific implementation is the same as that of Example 1, except that the fumigation time is 10 minutes.

[0088] Example 6

[0089] The specific implementation is the same as that of Example 1, except that the fumigation time is 20 minutes.

[0090] Example 7

[0091] The specific implementation is the same as that of Example 1, except that the fumigation time is 30 minutes.

[0092] Example 8

[0093] The specific implementation is the same as that of Example 2, except that the fumigation time is 10 minutes.

[0094] Example 9

[0095] The specific implementation is the same as that of Example 2, except that the fumigation time is 20 minutes.

[0096] Example 10

[0097] The specific implementation is the same as that of Example 2, except that the fumigation time is 30 minutes.

[0098] Comparative Example 1

[0099] The specific implementation is the same as Example 1, except that no fumigation is performed (fumigation for 0 min).

[0100] In Examples 1, 5, 6 and 7, the chitosan nanofibers were fumigated for 5, 10, 20 and 30 minutes to achieve different swelling degrees. The chitosan membrane was taken out and air-dried to obtain a porous chitosan continuous membrane with a thickness of 22 μm. The microscopic morphology of the nanoscale porous chitosan continuous membrane obtained in Comparative Example 1 and Examples 1, 5, 6 and 7 is shown in FIG. Figure 1 Scanning electron micrographs of the membrane show that by controlling the fumigation time from 0 to 30 minutes, a porous chitosan continuous membrane with gradually decreasing pore size and number can be obtained. Simultaneously, the pore edges change from a random overlapping structure to a cross-linked structure. The membrane's pore size and structure change in a controlled manner over time, gradually transitioning from a stacked fiber structure to a continuous membrane.

[0101] Comparative Example 2

[0102] The specific implementation is the same as Example 2, except that no fumigation is performed (fumigation for 0 min).

[0103] In Examples 2, 8, 9 and 10, the chitosan nanofibers were fumigated for 5, 10, 20 and 30 minutes to achieve different swelling degrees. The chitosan membranes were taken out and air-dried to obtain finished porous chitosan membranes with a thickness of 17 μm. The microscopic morphology of the nanoscale porous chitosan continuous membranes obtained in Comparative Example 2 and Examples 2, 8, 9 and 10 is shown in FIG. Figure 2 As shown in the scanning electron micrograph of the acetic acid solution, the time required to achieve a similar fumigation effect as in Example 1 is also reduced in a higher concentration of acetic acid. By controlling the fumigation time from 0 to 30 minutes, a porous chitosan continuous membrane with gradually decreasing pore size and number can be obtained. Simultaneously, the pore edges also change from a disordered overlapping fiber structure to a cross-fused structure. The membrane's pore size and structure change in a controlled manner over time, gradually transforming from a stacked fiber structure to a continuous membrane.

[0104] Comparative Example 3

[0105] Take 20 mL of 95% acetic acid aqueous solution, 0.6 g of chitosan powder with a deacetylation degree of 90% and a molecular weight of 100,000, and 0.1 g of polyethylene glycol with a molecular weight of 100,000 and add them into a conical flask. Stir at room temperature for 6 hours to completely dissolve the chitosan and polyethylene glycol to prepare the electrospinning solution.

[0106] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 25 kV, the injection rate at 2 mL / h, the collection distance at 10 cm, and the humidity at 35 ± 5%. Release paper was used as the collection medium. After electrospinning, the resulting nanofiber membrane precursor was peeled from the release paper and placed in a 40°C vacuum oven for 6 hours to remove volatile components such as water and acetic acid and complete the cross-linking reaction, ultimately yielding a pure chitosan nanofiber membrane with a thickness of 18 μm.

[0107] Add 50 mL of 10% acetic acid aqueous solution to a sealed glass container, place the pure chitosan nanofiber membrane in the air in the container, and seal the container. Control the container environment temperature to 35°C, and use the acetic acid vapor volatilized in the container to fumigate the chitosan nanofiber membrane. After 5 minutes of fumigation, take out the chitosan membrane and air dry it to observe its microscopic morphology. Figure 3 As shown in the scanning electron microscope image, the chitosan nanofiber membrane is extremely unstable due to the lack of a hydrophilic chitosan backbone cross-linked with hydrophobic oligomeric urushiol. It completely loses its pore structure in a very short time, making it difficult to effectively control its pore size and pore structure.

[0108] Comparative Example 4

[0109] 20 mL of 95% aqueous acetic acid, 0.6 g of chitosan powder (90% deacetylation, molecular weight 100,000), and 0.1 g of polyethylene glycol (100,000 molecular weight) were added to a conical flask and stirred at room temperature for 6 hours to completely dissolve the chitosan and polyethylene glycol. Subsequently, 0.18 g of oligomeric urushiol (degree of polymerization 8, molecular weight 2400) was added and stirred for another 3 hours to allow the oligomeric urushiol and chitosan solution to mix thoroughly and react initially to form a uniform electrospinning solution.

[0110] An appropriate amount of electrospinning solution was drawn up with a syringe and placed in the electrospinning machine's propeller for electrospinning. The spinning voltage was maintained at 25 kV, the injection rate at 2 mL / h, the collection distance at 10 cm, and the humidity at 35 ± 5%. Release paper was used as the collection medium. After electrospinning, the nanofiber membrane was peeled from the release paper and placed in a 40°C vacuum oven for 6 hours to remove volatile components such as water and acetic acid and to complete the crosslinking reaction between the oligomeric urushiol and chitosan molecules. The resulting membrane was a 22 μm thick urushiol-crosslinked chitosan nanofiber membrane.

[0111] Add 50 mL of distilled water to a sealed glass container, place the chitosan nanofiber membrane cross-linked with urushiol in the air, and seal the container. Control the container's ambient temperature to 60°C, and use the volatilized water vapor in the container to fumigate the chitosan nanofiber membrane. After 30 minutes of fumigation, take out the chitosan membrane and air-dry it to observe its microscopic morphology. Figure 4 As shown in the scanning electron microscope image, the nanofiber membrane retains its intact nanofiber morphology after distilled water fumigation, indicating that the introduction of hydrophobic oligomeric urushiol as a crosslink within the linear chitosan molecular structure enhances the nanofiber's water resistance and stability. Without the addition of an appropriate amount of acetic acid, the nanofiber membrane cannot swell, making it difficult to effectively control its pore size and pore structure.

[0112] In order to evaluate the mechanical properties of the prepared oligomeric urushiol cross-linked porous chitosan membrane, the specific test process is as follows: first, the oligomeric urushiol cross-linked chitosan membrane obtained after fumigation for 30 minutes in Example 2 is placed in a 60°C oven to dry to remove the swelling agent and residual moisture; secondly, the dried chitosan membrane is cut into a rectangular test membrane with a length of 3 cm and a width of 1.5 cm; finally, the two ends of the test membrane are clamped with an iron clamp, a 50g weight is hung under one end of the iron clamp, and the other end is slowly lifted to examine the tensile strength of the test membrane. Figure 6 The porous chitosan continuous membrane obtained in Example 2 was used to hang a 50g weight. The results showed that the porous chitosan continuous membrane with a width of 1.5cm and a thickness of only 17um can stably withstand a tensile force of more than 50g, and the corresponding tensile strength can reach 2MPa.

[0113] In order to evaluate the antibacterial effect of oligomeric urushiol cross-linked porous chitosan membrane, the antibacterial effect of the membrane was tested using Staphylococcus aureus and Escherichia coli as the objects, and the plate colony counting method was used to test the antibacterial effect of the membrane. The specific test process is as follows: First, the chitosan porous membrane prepared in Example 1 was uniformly taken and sterilized under ultraviolet light for 30 minutes. Then, 5 mL of LB culture medium was taken with a pipette, and the chitosan porous membrane sample was added, and Staphylococcus aureus or Escherichia coli was inoculated. After the inoculation was completed, it was placed in a constant temperature shaker at 37°C and 230r / min for 24 hours. Subsequently, the bacterial culture solution was diluted to the required concentration, and 100 μL of the diluted bacterial culture solution was evenly spread on the culture medium. After the sample bacterial culture solution was dry, the culture dish cover was covered and inverted in a constant temperature box at 37°C for 16 hours. Finally, the culture dish was taken out, the bacterial growth was observed, the bacterial colony was counted, and the antibacterial effect was evaluated by comparing with the blank sample without chitosan porous membrane. The results are as follows Figure 7 and Figure 8 As shown, Figure 7 Using Staphylococcus aureus, Figure 7 (a) represents the sample without adding oligomeric urushiol cross-linked porous chitosan membrane, Figure 7 (b) shows the sample with oligomeric urushiol cross-linked porous chitosan membrane added; Figure 8 Using Escherichia coli, Figure 8 (a) represents the sample without adding oligomeric urushiol cross-linked porous chitosan membrane, Figure 8 (b) shows a sample containing a cross-linked porous chitosan membrane containing oligomeric urushiol. Test results show that the cross-linked porous chitosan membrane exhibits significant antibacterial activity against both Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). At doses of 2 mg / mL and 3 mg / mL, respectively, the membrane completely inhibited the growth of both bacteria in the culture medium. This high antibacterial performance demonstrates the suitability of the chitosan membrane in this example for use as a wound dressing.

[0114] This embodiment utilizes oligomeric urushiol cross-linked chitosan molecules to create a bulk molecular structure with chitosan molecules, which are easily soluble in a swelling agent aqueous solution, as the backbone, and acid-resistant and hydrophobic oligomeric urushiol as the cross-linking bridge. The process involves first preparing nanofiber membranes of varying thicknesses through electrospinning of spinning solutions with varying solid contents. The fibers are then swollen by fumigation with an aqueous swelling agent solution, enabling precise control of the chitosan membrane's thickness and pore structure, effectively balancing the membrane's barrier and air permeability properties. Simultaneously, the originally randomly stacked nanofibers are transformed into a cross-fused, continuous system, enhancing the membrane's mechanical strength.

[0115] In terms of performance, this method can effectively control the thickness and pore structure of the chitosan membrane, thereby achieving precise control and performance balance of the membrane's barrier and air permeability. Secondly, this method can transform the originally disordered stack of chitosan nanofibers obtained by electrospinning into a cross-fused continuous membrane, effectively improving the mechanical strength of the chitosan porous membrane. Finally, the oligomeric urushiol-cross-linked chitosan porous membrane prepared by this method has excellent antibacterial effects against both Gram-positive and Gram-negative bacteria. These three points have effectively solved the problems existing in the practical application of existing chitosan-based wound dressings.

[0116] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0117] The products and preparation methods provided in the examples of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, according to the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A method for preparing a chitosan porous membrane, characterized in that: The following steps are involved: providing a first solution comprising chitosan, oligomeric urushiol, and a spinning aid; Taking the first solution and forming a nanofiber precursor by electrospinning; Taking the nanofiber precursor, drying it and forming an urushiol-crosslinked chitosan nanofiber membrane through a cross-linking reaction; placing the urushiol cross-linked chitosan nanofiber membrane in an atmosphere containing a swelling agent to swell at least a portion of the urushiol cross-linked chitosan nanofiber membrane; The mass ratio of the chitosan, the oligomeric urushiol and the spinning aid is 1:(0.1-0.5):(0.05-0.2); The molecular weight of the chitosan is 100,000-300,000, and the degree of deacetylation of the chitosan is 85-95%; the molecular weight of the oligomeric urushiol is 600-3,000, and the degree of polymerization of the oligomeric urushiol is 2-10; the molecular weight of the spinning aid is 100,000-200,000; The spinning aid is selected from at least one of polyethylene glycol, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone, and carboxymethyl cellulose; The first solution further includes a first solvent, which is selected from at least one of acetic acid, trifluoroacetic acid, and formic acid; the mass concentration of the first solvent in the first solution is 90-98%.

2. The method for preparing a chitosan porous membrane according to claim 1, wherein In the electrospinning, the spinning voltage is 20-25 kV, the ejection rate is 0.5-2.0 mL / h, the collection distance is 6-15 cm, and the humidity is 35±5%.

3. The method for preparing a chitosan porous membrane according to claim 1, wherein In the step of taking the nanofiber precursor, drying it and forming an urushiol cross-linked chitosan nanofiber membrane through a cross-linking reaction, the temperature of the drying and cross-linking reaction is 10-50° C., and the time of the drying and cross-linking reaction is 2-8 hours.

4. The method for preparing a chitosan porous membrane according to claim 1, wherein The step of placing the urushiol cross-linked chitosan nanofiber membrane in an atmosphere containing a swelling agent further comprises: providing a second solution comprising the swelling agent; heating the second solution to form steam containing the swelling agent; The urushiol cross-linked chitosan nanofiber membrane is placed in the steam for fumigation to obtain a chitosan porous membrane.

5. The method for preparing a chitosan porous membrane according to claim 4, wherein: The swelling agent is selected from at least one of acetic acid, hydrochloric acid, trifluoroacetic acid, formic acid, lactic acid, citric acid, and ascorbic acid; and / or, The mass concentration of the swelling agent in the second solution is 5-30%; and / or, The fumigation time is 5-30 minutes.

6. A chitosan porous membrane, characterized in that: The chitosan porous membrane is prepared by the preparation method of the chitosan porous membrane according to any one of claims 1 to 5.

7. Use of the chitosan porous membrane according to claim 6 as a medical wound dressing.

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