A three-layer composite nanofiber dressing and a preparation method thereof

Abstract

The application provides a kind of three-layer composite nanofiber dressing and its preparation method.The dressing includes three layers of hydrophilic layer, hydrophobic layer and outer protective layer structure.The hydrophobic layer uses thermoplastic polyurethane and polyacrylonitrile as base material, nanofiber membrane is prepared by electrospinning, and zinc acetate is used as metal source to grow metal organic framework material ZIF-8 on the fiber surface in situ, and load antibacterial drug polyhexamethylene biguanide hydrochloride (PHMB) at the same time;The hydrophilic layer is modified bacterial cellulose, and the protective layer is non-woven material, the interface of bacterial cellulose hydrophilic layer, electrospinning hydrophobic layer and non-woven material layer is combined to form a complete unit by vacuum suction filtration method.The composite dressing has antibacterial, anti-inflammatory, antioxidant and microenvironment regulation functions, can effectively promote the natural transition of wound from inflammation to proliferation, and accelerate the healing process.The preparation process of the application is simple, the cost is low, the obtained multifunctional dressing has good biocompatibility, and has wide application prospect of medical dressing.

Description

Technical Field

[0001] This invention relates to the field of medical functional textiles and drug carrier materials, specifically to a three-layer composite nanofiber dressing and its preparation method, which falls under the category of functional medical dressings. Background Technology

[0002] Chronic wounds are challenging to treat clinically due to their long healing period and susceptibility to recurrent infections. Long-term non-healing wounds are prone to bacterial growth, increasing the risk of local and even systemic infection, which can lead to tissue necrosis in severe cases, impacting patients' quality of life and significantly increasing the medical burden. Current wound dressings mainly include traditional dry dressings and wet dressings. With the development of the theory of moist wound healing, wet dressings, due to their ability to maintain a moderately moist microenvironment in the wound, are beneficial for the removal of necrotic tissue and the formation of new tissue and have been widely used clinically. However, existing wet wound dressings still have certain limitations, such as limited ability to manage wound exudate, easy adhesion to the wound surface, and pain during dressing changes; at the same time, some dressings have only one function and cannot achieve continuous regulation of the wound microenvironment, usually requiring frequent changes, increasing the burden on patients. Therefore, there is an urgent need to develop a functional wound dressing that can effectively absorb wound exudate and regulate the microenvironment of the wound healing process to improve the treatment effect of chronic wounds. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of low drug loading, insufficient exudate absorption, difficulty in maintaining a moist environment, and poor antibacterial persistence in existing moist wound dressings, and to provide a three-layer composite nanofiber dressing based on Zn-MOF drug loading and its preparation method. This dressing can achieve high drug loading, pH-responsive controlled release, unidirectional moisture conduction, and multiple antibacterial and anti-inflammatory effects, effectively improving the microenvironment of chronic wounds and promoting the healing process.

[0004] The first aspect of this invention provides a three-layer composite nanofiber dressing, comprising an inner layer, a middle layer, and an outer layer; wherein the inner layer is a hydrophobic layer that contacts the wound surface; the outer layer is made of a nonwoven material, providing support and protection; the inner layer is a functionalized nanofiber membrane, which is obtained by loading a polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane onto a zeolite imidazole ester framework encapsulated in polyhexamethylene biguanide hydrochloride; the middle layer is located between the inner and outer layers and is obtained by depositing bacterial cellulose homogenate / ZIF-8 / polyhexamethylene biguanide hydrochloride onto the inner layer. The inner layer is hydrophobic, the middle layer is hydrophilic, and the inner and middle layers together construct a unidirectional moisture-wicking structure; the inner layer is constructed by in-situ growing a metal-organic framework material and encapsulating the loaded drug.

[0005] Preferably, the thickness of the inner layer is 0.04 to 0.08 mm; the thickness of the middle layer is 0.5 to 0.7 mm; and the thickness of the outer layer is 0.6 to 1.0 mm.

[0006] Preferably, the average diameter of the inner layer is 0.56 μm.

[0007] A second aspect of the present invention provides a method for preparing the above-mentioned three-layer composite nanofiber dressing, characterized by comprising the following steps:

[0008] Step S1: Polyurethane and polyacrylonitrile are dissolved in N,N-dimethylformyl and tetrahydrofuran as solutes at a predetermined mass ratio. Then, zinc oxide is added as a metal precursor at 10-20 wt% of the solute to obtain a spinning solution. Polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane is prepared by electrospinning.

[0009] In step S2, zinc acetate and 2-methylimidazole are dissolved in deionized water at a molar ratio of 1:9 to 3:7 and then mixed to obtain a mixture. Polyhexamethylene biguanide hydrochloride (PHMB) is added to the mixture, and the polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane from step S1 is immersed in the reaction system to react and synthesize the metal-organic framework material ZIF-8. At the same time, PHMB is grown and loaded in situ on the surface of the fiber membrane to obtain a functionalized nanofiber membrane. In this step, the preferred molar ratio of zinc acetate to 2-methylimidazole is 1:9, 2:8, or 3:7.

[0010] Step S3: The composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride is vacuum filtered and then composited onto the surface of the functionalized nanofiber membrane to obtain a bilayer composite fiber membrane.

[0011] Step S4: The bilayer composite fiber membrane obtained in step S3 is composited again onto the outer nonwoven material layer by vacuum filtration, thereby obtaining a three-layer composite nanofiber dressing with a metal-organic framework for drug loading.

[0012] In step S1 above, the solute refers to polyurethane and polyacrylonitrile as solutes, and it is expressed as "10-20% of the solute", which means that the mass of zinc oxide is 10-20% of the mass of polyurethane and polyacrylonitrile.

[0013] In step S1 above, zinc oxide is added to the spinning solution as a precursor for Zn-MOF, and a polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane with good mechanical properties and hydrophobicity is prepared by electrospinning technology. In step S2, a metal-organic framework material (Zn-MOF) is grown in situ on the surface of the nanofiber membrane to achieve drug loading. Step S3 involves the composite of a hydrophilic layer and a hydrophobic layer. A blended bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride slurry is deposited on the surface of the above-mentioned functionalized nanofiber membrane by vacuum filtration. Stable interlayer composite is achieved through tight interfacial assembly, resulting in a bilayer composite dressing with both unidirectional moisture wicking and functionalization.

[0014] Preferably, in step S1, the molecular weight of polyurethane is 80,000-100,000, the molecular weight of polyacrylonitrile is 120,000-150,000, and the predetermined mass ratio of polyurethane to polyacrylonitrile is 2:8, 3:7, or 4:6, respectively; the concentration of the spinning solution is 10%, 15%, or 20%. In this invention, all molecular weights are weight-average molecular weights, and the data are obtained by GPC instrument detection.

[0015] Preferably, in step S2, the concentration of polyhexamethylene biguanide hydrochloride (PHMB) in the system is 0.5-1 mg / mL; the polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane from step S1 is immersed in the reaction system and reacted at 40 °C for 20 h.

[0016] Preferably, step S2 further includes: washing the hydrophobic inner layer of the functionalized nanofiber membrane obtained after the reaction with anhydrous ethanol and deionized water in sequence, and drying it under vacuum conditions.

[0017] Preferably, step S3, the preparation method of the composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride, specifically involves: adding 0.12 g of ZIF-8 nanoparticles loaded with polyhexamethylene biguanide hydrochloride to 10 mL of deionized water, ultrasonically dispersing for 10 min to obtain a ZIF-8@PHMB premixed suspension; subsequently, adding the premixed suspension to 10 g of a bacterial cellulose homogenate with a solid content of 0.8 wt%, and stirring at 300 rpm for 24 h at room temperature to obtain the composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride; the mass ratio of nanoparticles to bacterial cellulose dry weight in the ZIF-8@PHMB premixed suspension is 1.5:1.

[0018] Preferably, both ZIF-8 and ZIF-8 / polyhexamethylene biguanide hydrochloride nanoparticles exhibit a regular dodecahedral structure with a uniform particle size of approximately 300-600 nm.

[0019] Preferably, in step S2, the electrospinning conditions are: voltage 15-18 kV, draw distance 15-18 cm, receiving roller speed 200-250 rpm, feed rate 0.5-0.8 mL / h, temperature 20℃-27℃, and relative humidity below 45%; in step S3, the bacterial cellulose homogenate has a solid content of 0.5 wt% and a filtration pressure of -0.1~-0.08 MPa; in step S4, the filtration pressure is -0.1~-0.08 MPa.

[0020] Preferably, the precursor for synthesizing the metal-organic framework ZIF-8 is zinc acetate, and the ligand is 2-methylimidazole; the structure is as follows:

[0021]

[0022] Zinc acetate 2-methylimidazole

[0023] The dressing of this invention comprises a hydrophobic layer made of thermoplastic polyurethane and polyacrylonitrile as substrates, with nanofiber membranes prepared by electrospinning. A metal-organic framework material (ZIF-8) is grown in situ on the fiber surface using zinc acetate as a metal source, and simultaneously loaded with the antibacterial drug polyhexamethylene biguanide hydrochloride. The hydrophilic layer is modified bacterial cellulose, and the protective layer is a nonwoven material. The bacterial cellulose hydrophilic layer, the electrospun hydrophobic layer, and the nonwoven material layer are bonded together at the interface using a vacuum filtration method to form a complete unit. Under acidic conditions, the dressing can trigger the decomposition of ZIF-8 in a pH-responsive manner, releasing Zn²⁺ and the antibacterial drug, achieving synergistic antibacterial action at different stages of wound healing. The bacterial cellulose layer has excellent moisturizing and wicking properties, capable of self-pumping and absorbing wound exudate to maintain wound moisture. The hydrophobic layer provides mechanical support and hydrophobic anti-reverse seepage properties. This composite dressing combines antibacterial, anti-inflammatory, antioxidant, and microenvironment-regulating functions, effectively promoting the natural transition of the wound from the inflammatory phase to the proliferative phase and accelerating the healing process. The preparation process of this invention is simple and low-cost, and the resulting multifunctional dressing has good biocompatibility and broad application prospects in medical dressings.

[0024] Compared with the prior art, the present invention has at least the following significant advantages:

[0025] (1) Excellent drug loading and pH-responsive controlled release performance: ZIF-8 has regular channels and a large specific surface area of ​​1291 m². 2 / g, Figure 5 Adsorption-desorption curves. The porous structure of ZIF-8 is beneficial for drug molecule loading and sustained release. In an acidic environment (pH≈5.5), the metal-organic framework structure gradually decomposes, achieving sustained release of Zn²⁺ and polyhexamethylene biguanide hydrochloride. Figure 9 ).

[0026] (2) Dual-stage synergistic antibacterial mechanism: The dressing releases Zn²⁺ ions in the early stage of inflammation, exerting antibacterial and wound microenvironment-regulating effects; in the later stage of inflammation, polyhexamethylene biguanide hydrochloride (PHMB) is continuously released, and its positively charged molecular structure binds to the negatively charged bacterial membrane, destroying the cell membrane structure and achieving broad-spectrum antibacterial activity. The presence of ZIF-8 enhances the stability and sustained-release performance of polyhexamethylene biguanide hydrochloride. Figure 10 ).

[0027] (3) Interfacial construction of a unidirectional moisture-wicking structure: The bacterial cellulose layer and the electrospun layer are bonded together by vacuum filtration to construct a double-layer heterogeneous structure. The hydrophilic layer of bacterial cellulose maintains high water absorption and wettability, while the inner hydrophobic layer provides support and absorption channels, thereby achieving unidirectional migration and moisture balance of exudate, which avoids wound maceration and maintains a moderately moist healing environment.

[0028] (4) Antioxidant and microenvironment regulation promote wound healing: The continuous release of Zn²⁺ and PHMB can effectively improve the wound microenvironment and promote tissue regeneration and repair. Figure 11 ).

[0029] (5) Excellent biocompatibility and mechanical properties: The bacterial cellulose membrane and the electrospun membrane form a stable structure through interfacial bonding, which has both flexibility and strength, can fit well to the wound surface, reduce dressing pain, and improve patient comfort.

[0030] In summary, this invention, through its structural design of "Zn-MOF functionalized inner layer + bacterial cellulose hydrophilic layer + nonwoven fabric outer layer", achieves a multifunctional integration of drug controlled release, antibacterial and anti-inflammatory properties, and humidity regulation, providing a novel high-performance dressing for chronic wound repair. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the nanofiber composite dressing of the present invention; wherein 1 is the inner layer, 2 is the middle layer, and 3 is the outer layer;

[0032] Figure 2 This is a diagram showing the diameter distribution of electrospun fibers in Embodiment 3 of the present invention;

[0033] Figure 3 In Example 3 of the present invention, Figure a is a transmission electron microscope image of ZIF-8 and Figure b is a transmission electron microscope image of ZIF-8@PHMB nanoparticles;

[0034] Figure 4 This is a scanning electron microscope image of the PT-ZIF-8@PHMB nanofiber membrane in Example 3 of the present invention;

[0035] Figure 5 This is the adsorption-desorption curve of ZIF-8 in Example 3 of the present invention;

[0036] Figure 6 The Fourier transform infrared spectrum of PT-ZIF-8@PHMB in Embodiment 3 of the present invention;

[0037] Figure 7 This is a comparison diagram of the water contact angles of PT and BC (bacterial cellulose membrane) in Example 3 of the present invention;

[0038] Figure 8 This is a diagram showing the simulated exudate unidirectional moisture-wicking performance of the double-layer composite dressing in Example 3 of the present invention;

[0039] Figure 9 This is a graph showing the release curves of PHMB under different pH conditions in Example 3 of the present invention;

[0040] Figure 10 This is a test diagram of the antibacterial performance of the composite dressing against bacteria in Example 3 of the present invention;

[0041] Figure 11 The images shown are of the tissue repair performance of the composite dressing in Example 3 of the present invention, and are images of the wound healing status of the experimental group and the control group on days 0, 3, 7 and 11. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0043] Unless otherwise specified, the raw materials and materials used in the embodiments of the present invention were purchased through general commercial channels.

[0044] The source information of the raw materials, materials, and instruments involved in the following embodiments or comparative examples is as follows:

[0045] Polyurethane (TPU) was produced by Wanhua Chemical Group Co., Ltd. Polyacrylonitrile, N,N-dimethylformyl, tetrahydrofuran, zinc oxide, zinc acetate, 2-methylimidazole, polyhexamethylene biguanide hydrochloride, sodium fluorescein, and anhydrous ethanol were all purchased from Aladdin Reagent Co., Ltd. (China). Bacterial cellulose was obtained by culturing *Acetobacter xylinum* in the laboratory. *Acetobacter xylinum* was purchased from Shanghai Baocang Biotechnology Co., Ltd. The specific preparation method of bacterial cellulose was as follows: *Acetobacter xylinum* was inoculated into a sugar-containing optimal medium, activated and expanded to obtain a seed culture, and then inoculated into the fermentation system at a volume ratio of 5%~15% (v / v), preferably 10% (v / v); static culture at 28~30℃ at the gas-liquid interface for 6 days, naturally generating a bacterial cellulose protofilm; after collection, it was soaked in 3% NaOH at 85℃ for 1.5 h to remove bacteria and impurities, repeatedly washed and neutralized with water until pure, and the bacterial cellulose protofilm was subjected to high-speed shearing to obtain a bacterial cellulose homogenate for later use.

[0046] The molecular weight of polyurethane is 90,000; the molecular weight of polyacrylonitrile is 150,000.

[0047] The concentration of polyhexamethylene biguanide hydrochloride is 1 mg / mL.

[0048] Example 1: Preparation of composite nanofiber dressings based on metal-organic framework drug delivery systems

[0049] Preparation of the inner antibacterial drug-loaded composite nanofiber membrane:

[0050] Thermoplastic polyurethane (molecular weight 90,000) and polyacrylonitrile (molecular weight 150,000) were weighed at a mass ratio of polyurethane / polyacrylonitrile 2:8 and added to a mixed solvent of N,N-dimethylformamide and tetrahydrofuran (volume ratio 1:1). ZnO nanoparticles (as crystal nucleation sites, with a content of 20 wt% in the spinning solution) were added, and the spinning solution concentration was 15%. The mixture was magnetically stirred at 50 °C for 24 h under sealed conditions until a uniform and transparent spinning solution was formed.

[0051] The above spinning solution was injected into an electrospinning apparatus with a voltage set at 18 kV, a flow rate of 0.5 mL / h, a receiving roller draft distance of 15 cm, and a speed of 250 rpm, to obtain a polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane with a thickness of approximately 0.04~0.08 mm. The obtained membrane was dried in a vacuum drying oven at 40℃ for 12 h to remove residual solvent and was then ready for use.

[0052] A molar ratio of zinc acetate to 2-methylimidazole was 1:9. 2.75 g of zinc acetate and 11.08 g of 2-methylimidazole were weighed and dissolved separately in 20 mL of deionized water. After stirring at room temperature for 30 min, the zinc acetate solution was injected into the 2-methylimidazole solution. Simultaneously, polyhexamethylene biguanide hydrochloride was added to the mixed solution at a ratio of 1 mg / mL. This allows the metal-organic framework to adsorb drug molecules into the Zn-MOF channels during synthesis, achieving drug loading. (Note that the metal and ligand should be dissolved separately into homogeneous solutions, and the mixing speed should be greater than 1000 rpm to ensure uniform nucleation rate and uniform MOF size during synthesis). Subsequently, a polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane was immersed in this solution and reacted in a 40℃ water bath for 20 h. ZnO and 2-methylimidazole were used to grow Zn-MOF (ZIF-8) in situ on the fiber surface, resulting in a functionalized hydrophobic inner layer of the nanofiber membrane.

[0053] The hydrophobic inner layer of the obtained functionalized nanofiber membrane was washed three times with ethanol and deionized water to remove unreacted substances, and then dried in a vacuum oven at 60°C.

[0054] Preparation of the intermediate bacterial cellulose hydrophilic layer:

[0055] Take 10g of bacterial cellulose homogenate (solid content 0.8%), place it in a magnetic stirrer and stir at room temperature at 300rpm. Weigh 0.12g of ZIF-8 powder and 10mg of polyhexamethylene biguanide hydrochloride, add 5–10 mL of deionized water (preferably 10 mL in this example), and sonicate for 10 min to prepare a ZIF-8 premixed suspension (avoid direct sprinkling of bacterial cellulose to prevent clumping). Then inject the bacterial cellulose homogenate and stir at low speed for 24 hours to make it a homogeneous solution, i.e., a composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride.

[0056] Three-layer composite structure:

[0057] The prepared hydrophobic inner layer of the functionalized nanofiber membrane was laid flat on top of the filter membrane. A composite slurry of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride was then uniformly spread on the surface of the hydrophobic inner layer of the functionalized nanofiber membrane. Vacuum filtration was then used to uniformly deposit the hydrophilic layer of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride and tightly bond it to the electrospun membrane, resulting in a bilayer composite fiber membrane. In this step, the purpose of deposition is to remove moisture through filtration.

[0058] The aforementioned bilayer composite fiber membrane is then interfacially bonded to the outer nonwoven layer via vacuum filtration to obtain a metal-organic framework drug-loaded composite nanofiber dressing.

[0059] Example 2:

[0060] Preparation method of inner fiber membrane

[0061] Weigh thermoplastic polyurethane (molecular weight 90,000) and polyacrylonitrile (molecular weight 150,000) at a mass ratio of polyurethane:polyacrylonitrile 3:7, and add them to a mixed solvent of N,N-dimethylformamide and tetrahydrofuran at a volume ratio of 1:1. The spinning solution concentration is 15%. Stir magnetically at 50 °C for 24 h until the solution is uniform and transparent.

[0062] The above spinning solution was injected into an electrospinning apparatus with a voltage set at 18 kV, a flow rate of 0.5 mL / h, a receiving roller draft distance of 15 cm, and a speed of 250 rpm, to obtain a polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane with a thickness of approximately 100–300 μm. The membrane was then placed in a vacuum dryer at 40°C for 12 h to evaporate the organic solvent, and stored for later use.

[0063] Zinc acetate and 2-methylimidazole were weighed at a molar ratio of 2:8 and dissolved separately in 20 mL of deionized water. The solutions were stirred at room temperature for 30 min to obtain a turbid solution. (Note that the metal and ligand should be dissolved separately to form a homogeneous solution. Vigorous stirring during mixing is necessary to ensure a uniform nucleation rate and consistent MOF size during synthesis.) Simultaneously, 1 mg / mL polyhexamethylene biguanide hydrochloride was added to the mixed solution to allow the metal-organic framework to adsorb drug molecules into the Zn-MOF channels during synthesis, achieving drug loading. A polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane was immersed in this solution and reacted in a 40°C water bath for 20 h. ZnO and 2-methylimidazole were then used to grow Zn-MOF (ZIF-8) in situ on the fiber surface, resulting in a functionalized hydrophobic inner layer of the nanofiber membrane.

[0064] The hydrophobic inner layer of the obtained functionalized nanofiber membrane was washed three times with ethanol and deionized water to remove unreacted substances, and then dried in a vacuum oven at 60°C.

[0065] Preparation of the intermediate bacterial cellulose hydrophilic layer:

[0066] Take 10g of bacterial cellulose homogenate (solid content 0.8%), place it in a magnetic stirrer and stir at room temperature at 300rpm. Weigh 0.12g of ZIF-8 powder and 10mg of polyhexamethylene biguanide hydrochloride, add 5–10 mL of deionized water (preferably 10 mL in this example), and sonicate for 10 min to prepare a ZIF-8 premixed suspension (avoid direct sprinkling of bacterial cellulose to prevent clumping). Then inject the bacterial cellulose homogenate and stir at low speed for 24 hours to make it a homogeneous solution of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride.

[0067] Three-layer composite structure:

[0068] The prepared hydrophobic inner layer of the functionalized nanofiber membrane was laid flat on top of the filter membrane. A composite slurry of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride was uniformly spread on the surface of the hydrophobic inner layer of the functionalized nanofiber membrane. The hydrophilic layer of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride was uniformly deposited and tightly bonded to the electrospun membrane by vacuum filtration to obtain a double-layer composite fiber membrane.

[0069] The aforementioned bilayer composite fiber membrane is then interfacially bonded to the outer nonwoven layer via vacuum filtration to obtain a metal-organic framework drug-loaded composite nanofiber dressing.

[0070] Example 3:

[0071] The conditions are the same as in Example 1 or 2, except that the mass ratio of polyurethane to polyacrylonitrile is different. In this example, the mass ratio of polyurethane to polyacrylonitrile is 4:6.

[0072] Example 4: Functional Verification

[0073] The nanofiber membrane in Example 1 was subjected to corresponding tests, and the results are shown in [the table below]. Figure 2-11 .in, Figure 6 Curve b represents the nanofiber membrane of Example 2, and curve c represents the nanofiber membrane of Example 3.

[0074] In this embodiment, the metal-organic framework drug-loaded three-layer composite nanofiber dressing prepared in Example 1 was used as the experimental group sample, and the comparative dressing prepared in Example 2 was used as the control group sample. Unless otherwise specified, Figures 2 to 11 The test results shown are all based on the samples obtained in Example 1.

[0075] Figure 2 This image shows the fiber diameter distribution of the polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane prepared by electrospinning in Example 1. The fiber morphology was observed using a scanning electron microscope, and the diameter of at least 100 fibers was randomly measured using ImageJ software. The average diameter and diameter distribution were then statistically analyzed. The results show that the obtained nanofibers are relatively uniformly distributed, with an average diameter of approximately 0.56 μm, indicating that the electrospinning process of Example 1 can stably prepare uniform nanofiber membranes.

[0076] Figure 3 The images show transmission electron microscopy (TEM) images of the ZIF-8 nanoparticles and ZIF-8@PHMB nanoparticles prepared in Example 1. The observations were performed using a JEM-2100 TEM. Figure 3 a represents ZIF-8 nanoparticles. Figure 3 b represents ZIF-8@PHMB nanoparticles. The results show that ZIF-8 exhibits a regular polyhedral structure with a particle size of approximately 300–600 nm. After loading with PHMB, ZIF-8@PHMB still maintains a relatively complete polyhedral structure, indicating that the introduction of PHMB did not significantly disrupt the ZIF-8 framework structure.

[0077] Figure 4 This is a scanning electron microscope (SEM) image of the PT-ZIF-8@PHMB functionalized nanofiber membrane obtained in Example 1. Observation was performed using a TM3000 scanning electron microscope. The results show that the ZIF-8@PHMB nanoparticles are uniformly attached to the nanofiber surface, indicating that metal-organic framework materials can be grown in situ on the surface of polyacrylonitrile / polyurethane / zinc oxide nanofiber membranes and achieve drug loading.

[0078] Figure 5The nitrogen adsorption-desorption curves for the ZIF-8 nanoparticles in Example 1 are shown. Specific surface area and pore size analyzers were used for testing. The results show that the ZIF-8 nanoparticles exhibit typical microporous material adsorption characteristics, indicating that they have a good pore structure, which is beneficial for the loading and subsequent sustained release of PHMB drug molecules.

[0079] Figure 6 Fourier transform infrared (FTIR) spectra of functionalized nanofiber membranes obtained in Example 1 and at different polyurethane / polyacrylonitrile ratios are shown. The FTIR measurements were performed using a NICOLET iS10 variable-temperature Fourier transform infrared spectrometer. The FTIR curves of the metal-organic framework drug-loaded composite nanofiber dressings are also shown below. Figure 6 The results show that curves a, b, and c are the infrared spectra of ZIF-8@PHMB loaded in spinning solution at a concentration of 15% with different polyurethane / polyacrylonitrile ratios. Curves a, b, and c correspond to polyurethane to polyacrylonitrile mass ratios of 2:8 (Example 1), 3:7 (Example 2), and 4:6 (Example 3), respectively. Curve d is the infrared spectrum of polyhexamethylene biguanide hydrochloride (PHMB), at 2167 cm⁻¹. -1 The peak value for biguanide is 1544 cm⁻¹. -1 The characteristic absorption peak is the stretching vibration peak of NH, at 3279 cm⁻¹. -1 NH2 ＋ The bending vibration peak. 1585 cm -1 The absorption peak at that point is the stretching vibration peak of C=N of 2-methylimidazole, which indicates that the structure of the metal-organic framework synthesized in situ after ZIF-8 encapsulates polyhexamethylene biguanide hydrochloride remains unchanged.

[0080] In the contact angle test ( Figure 7 The instrument, model Kino SL200KS (Kino Industrial Instruments Co., Ltd., USA), as shown in the figure, has a contact angle of 35.2° for the middle layer of bacterial cellulose hydrophilic layer and 103.047° for the inner layer hydrophobic layer, forming a hydrophilic / hydrophobic gradient. This exhibits excellent unidirectional moisture wicking performance.

[0081] In a simulated wound exudate management performance test, deionized water containing 0.5% sodium fluorescein was drawn using a syringe. A propellant pump was then used to inject the sodium fluorescein aqueous solution above and below the dressing, respectively. The unidirectional moisture-wicking and self-pumping performance of the dressing was tested. To observe the unidirectional moisture-wicking performance of the wound dressing in a 0.5% sodium fluorescein-labeled DI solution, a camera (D5300, Nikon) was used under a blue LED (λ=465) to observe the dynamic self-pumping effect of the hydrophobic and hydrophilic layers of the dressing. Figure 8As shown in Figures a, b, and c, the hydrophilic / hydrophobic distribution direction of the obtained bilayer composite dressing is set so that the hydrophobic layer faces the wound, and droplets are pumped from the hydrophobic layer into the hydrophilic layer; Figures d, e, and f simulate droplet absorption from the hydrophilic layer to the hydrophobic layer; it can be observed that the bacterial cellulose layer, as the hydrophilic layer, can quickly absorb exudate and maintain wound moisture; the functionalized nanofiber membrane inner layer, as the hydrophobic layer, prevents liquid backflow, and achieves a unidirectional moisture-wicking effect through the capillary effect between the two layers. Figure 8 Furthermore, this composite dressing can achieve a water absorption rate exceeding 800% of its own weight.

[0082] Experimental results on the pH-responsive drug release properties of this dressing ( Figure 9 The study showed that within 120 hours, the cumulative release of polyhexamethylene biguanide hydrochloride was only 20% at pH 7.4, while at pH 5.4, the ZIF-8 nanoparticle framework collapsed, leading to the release of Zn. 2+ Simultaneously, it releases polyhexamethylene biguanide hydrochloride, with a cumulative release of 75%. The synergistic effect of Zn²⁺ and polyhexamethylene biguanide hydrochloride achieves long-lasting sustained release and antibacterial properties, promoting wound healing.

[0083] Figure 10 The results show the antibacterial performance of the composite dressing obtained in Example 1. *Escherichia coli* and *Staphylococcus aureus* were used as test bacteria, and the antibacterial performance was evaluated using the plate count method or antimicrobial inhibition test. The experimental group was the metal-organic framework drug-loaded three-layer composite nanofiber dressing obtained in Example 1, and the control group was the comparative dressing obtained in Example 2. The results showed that the dressing obtained in Example 1 exhibited significant inhibitory effects on both *Escherichia coli* and *Staphylococcus aureus*, with inhibition rates exceeding 99%, indicating that the synergistic effect of ZIF-8 and PHMB endowed the dressing with excellent antibacterial properties.

[0084] Figure 11 The results show the tissue repair performance of the composite dressing obtained in Example 1. The experimental group consisted of the drug-loaded three-layer composite nanofiber dressing with a metal-organic framework obtained in Example 1, while the control group consisted of the comparative dressing obtained in Example 2. Wound healing was recorded on days 0, 3, 7, and 11. The results showed that, compared with the control group, the experimental group had a faster wound closure speed and a more significant reduction in wound area, indicating that the composite dressing obtained in Example 1 can effectively promote wound repair.

[0085] The results of this embodiment show that the prepared metal-organic framework drug-loaded composite nanofiber dressing has drug loading, pH-responsive release, antibacterial, and unidirectional moisture-wicking capabilities.

[0086] The applicant declares that the above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A three-layer composite nanofiber dressing, characterized in that, It includes an inner layer, a middle layer, and an outer layer; among which, The inner layer is a hydrophobic layer that comes into contact with the wound surface; The outer layer is made of non-woven material and provides a supporting and protective layer. The inner layer is a functionalized nanofiber membrane, which is obtained by loading a polyacrylonitrile / polyurethane / zinc oxide nanofiber membrane with a zeolite imidazole ester framework-encapsulated polyhexamethylene biguanide hydrochloride (PHMB). The intermediate layer, located between the inner and outer layers, is formed by depositing bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride onto the inner layer.

2. The three-layer composite nanofiber dressing according to claim 1, characterized in that, The thickness of the inner layer is 0.04~0.08 mm; the thickness of the middle layer is 0.5~0.7 mm; and the thickness of the outer layer is 0.6~1.0 mm.

3. The three-layer composite nanofiber dressing according to claim 1, characterized in that, The average diameter of the inner layer is 0.56 μm.

4. The method for preparing the three-layer composite nanofiber dressing according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1: Polyurethane and polyacrylonitrile are dissolved in N,N-dimethylformyl and tetrahydrofuran as solutes at a predetermined mass ratio, and then zinc oxide is added as a metal precursor at 10~20 wt% of the solute to obtain the spinning solution. Polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membranes were prepared by electrospinning. Step S2: Zinc acetate and 2-methylimidazole are dissolved in deionized water at a molar ratio of 1:9 to 3:7 and then mixed to obtain a mixture. Polyhexamethylene biguanide hydrochloride (PHMB) is added to the mixture. The polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane described in step S1 is then immersed in the reaction system to react and synthesize the metal-organic framework material ZIF-8. At the same time, polyhexamethylene biguanide hydrochloride is grown and loaded in situ on the surface of the fiber membrane to obtain a functionalized nanofiber membrane. Step S3: The composite slurry of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride is vacuum filtered and then composited onto the surface of the functionalized nanofiber membrane to obtain a bilayer composite fiber membrane. Step S4: The bilayer composite fiber membrane obtained in step S3 is composited again onto the outer nonwoven material layer by vacuum filtration, thereby obtaining a three-layer composite nanofiber dressing with a metal-organic framework for drug loading.

5. The method for preparing the three-layer composite nanofiber dressing according to claim 4, characterized in that, In step S1, the molecular weight of the polyurethane is 80,000 to 100,000, the molecular weight of the polyacrylonitrile is 12,000 to 150,000, and the predetermined mass ratio of the polyurethane to the polyacrylonitrile is 2:8, 3:7, or 4:6, respectively; the concentration of the spinning solution is 10%, 15%, or 20%.

6. The method for preparing the three-layer composite nanofiber dressing as described in claim 4, characterized in that, In step S2, the amount of polyhexamethylene biguanide hydrochloride (PHMB) added to the mixture is 1 mg / ml; the polyacrylonitrile / polyurethane / zinc oxide composite nanofiber membrane described in step S1 is immersed in the reaction system and reacted at 40 °C for 20 h.

7. The method for preparing the three-layer composite nanofiber dressing as described in claim 6, characterized in that, Step S2 further includes: the hydrophobic inner layer of the functionalized nanofiber membrane obtained after the reaction is washed sequentially with anhydrous ethanol and deionized water, and then dried under vacuum conditions.

8. The method for preparing the three-layer composite nanofiber dressing as described in claim 4, characterized in that, Step S3, the specific method for preparing the composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride is as follows: 0.12 g of ZIF-8 nanoparticles loaded with polyhexamethylene biguanide hydrochloride were added to 10 mL of deionized water and ultrasonically dispersed for 10 min to obtain a ZIF-8@PHMB premixed suspension. Subsequently, the premixed suspension was added to 10 g of a bacterial cellulose homogenate with a solid content of 0.8 wt%, and stirred at 300 rpm for 24 h at room temperature to obtain a composite homogenate of bacterial cellulose / ZIF-8 / polyhexamethylene biguanide hydrochloride. The mass ratio of nanoparticles to bacterial cellulose dry weight in the ZIF-8@PHMB premixed suspension was 1.5:

1.

9. The method for preparing the three-layer composite nanofiber dressing according to claim 8, characterized in that, Both the ZIF-8 and ZIF-8 / polyhexamethylene biguanide hydrochloride nanoparticles exhibit a regular dodecahedral structure with a uniform particle size of 300-600 nm.

10. The method for preparing the three-layer composite nanofiber dressing according to claim 4, characterized in that, In step S1, the electrospinning conditions are: voltage 15-18 kV, draft distance 15-18 cm, receiving roller speed 200-250 rpm, feed rate 0.5-0.8 mL / h, temperature 20℃-27℃, and relative humidity below 45%. In step S3, the solid content of the bacterial cellulose homogenate is 0.5 wt%, and the filtration pressure is -0.1 to -0.08 MPa; in step S4, the filtration pressure is -0.1 to -0.08 MPa.

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