Antibacterial and breathable medical gauze sheet

Abstract

The application relates to the technical field of medical textile materials, and discloses an antibacterial and breathable medical gauze sheet, which comprises a base material and an antibacterial functional layer loaded on the base material, and the functional layer is formed by chemical reaction of carboxymethyl chitosan, tannic acid, boric acid, citric acid and zinc ions. Through boric acid complexation and citric acid competitive coordination, a double interpenetrating network structure of covalent bonds and coordination bonds is formed inside and outside the gauze fibers. The structure effectively inhibits the oxidative browning of tannic acid and eliminates the difference in the skin-core distribution of the functional components. The obtained gauze sheet is not only high in whiteness and good in breathability, but also has excellent washing fastness and long-acting and broad-spectrum antibacterial performance.

Description

Technical Field

[0001] This invention relates to the field of medical textile materials technology, and in particular to an antibacterial and breathable medical gauze sheet. Background Technology

[0002] Medical gauze, as the most commonly used wound dressing in clinical practice, needs to possess good absorbency, breathability, and biocompatibility. Imparting antibacterial properties to gauze to prevent wound infection has become an industry consensus. Among numerous antibacterial finishing agents, tannic acid, as a natural polyphenol compound, has attracted much attention due to its broad-spectrum antibacterial and hemostatic properties. In particular, the metal-polyphenol network constructed by tannic acid and metal ions (such as zinc ions) can further enhance antibacterial efficacy and promote wound healing, making it a current research hotspot in the field of biomedical materials.

[0003] However, the application of tannic acid metal complexes in the finishing of medical gauze still faces several technical bottlenecks. First, tannic acid molecules are rich in ortho- and tho-dihydroxy structures, which are chemically reactive. During processing or storage, especially under humid or weakly alkaline conditions, they are prone to auto-oxidation to form quinone structures, resulting in severe yellowing or browning of the gauze surface, making it difficult to meet the stringent requirements for whiteness and cleanliness in medical dressings.

[0004] Secondly, the coordination reaction between tannic acid and metal ions (especially zinc ions) is extremely rapid, often forming an insoluble complex precipitate immediately upon contact. This rapid nucleation and accumulation behavior causes the antibacterial agent to mainly deposit on the surface of the gauze fibers, which not only easily clogs the gauze mesh and reduces its breathability and moisture-wicking properties, but also hinders the penetration of functional components into the fiber interior, resulting in a "rich on the outside, poor on the inside" core-sheath distribution structure in the gauze. When the surface coating is removed due to friction or washing, the internal fibers lack effective protective capabilities, leading to insufficient long-term antibacterial effect.

[0005] Furthermore, existing finishing processes mostly rely on physical adsorption or simple coordination deposition, lacking stable chemical bonding. After repeated washing or immersion in tissue fluid, the active ingredients are easily lost, which not only reduces the antibacterial effect, but also poses a potential cytotoxic risk if the concentration of released metal ions is too high. Therefore, how to achieve deep loading and firm bonding of tannic acid metal complexes within the fibers while maintaining good air permeability and whiteness of the gauze is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] The technical problem solved by this invention is to address the existing technical difficulties in tannic acid-based antibacterial finishing technology, such as the easy oxidation and browning of tannic acid leading to a decrease in the whiteness of gauze, the excessively fast reaction rate of metal ions with tannic acid resulting in insufficient surface sealing and inner layer penetration, and the poor wash fastness of physical deposition coatings.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing an antibacterial and breathable medical gauze pad, comprising the following steps:

[0009] S1, Preparation of the first padding working solution: Dissolve carboxymethyl chitosan, tannic acid and boric acid in water and adjust the pH value to alkaline to obtain the first padding working solution;

[0010] S2, Preparation of the second padding working solution: Dissolve citric acid, zinc salt, hypophosphite and penetrant in water and adjust the pH value to acidic to obtain the second padding working solution;

[0011] S3, Pre-complex adsorption: Medical degreased gauze is immersed in the first impregnation working solution, and after pressing, it undergoes intermediate micro-drying treatment to make the gauze reach the set moisture content.

[0012] S4, competitive coordination penetration: The gauze treated in step S3 is immersed in the second padding working solution, and after padding, it is subjected to gradient drying and high-temperature baking.

[0013] S5, Post-processing: Wash the baked gauze with water and dry it to obtain the finished product.

[0014] By employing the above technical solution, this invention utilizes a step-by-step padding and intermediate micro-drying process, combined with boric acid protection and a citric acid competitive coordination mechanism, to achieve high whiteness retention and deep immobilization of tannic acid. The mechanism of action of this invention is as follows:

[0015] (1) Inhibiting oxidative browning of tannic acid by using borate esterification protection mechanism:

[0016] In a weakly alkaline environment, the ortho-dihydroxyl groups in tannic acid molecules are in a highly reactive state and are easily oxidized to a quinone structure, leading to yellowing of the fabric. This invention introduces boric acid into the first padding working solution, utilizing the borate ion [B(OH)4]- to undergo a complexation reaction with the ortho-dihydroxyl groups of tannic acid, generating a borate ester complex. This reaction chemically masks the active oxidation sites of tannic acid, creating steric hindrance and inhibiting the oxidation reaction of phenolic hydroxyl groups by oxygen free radicals. During the subsequent contact with the acidic second padding solution and high-temperature baking process, as the pH value decreases and moisture evaporates, boric acid gradually dissociates, releasing phenolic hydroxyl groups to participate in subsequent metal coordination and cross-linking reactions. This retains antibacterial activity while preventing oxidative browning during processing, thus improving the whiteness of the finished gauze.

[0017] (2) Regulation of permeation depth based on citric acid competitive coordination kinetics:

[0018] Zinc ions react rapidly with tannic acid upon direct contact, resulting in rapid complexation and precipitation. This causes the agent to accumulate on the gauze surface, clogging the pores and hindering internal penetration. This invention addresses this problem by constructing a competitive coordination system between citric acid and zinc, and tannic acid and zinc. In the second padding working solution, the high concentration of citric acid preferentially forms a water-soluble zinc citrate complex with zinc ions, reducing the concentration of free zinc ions in the system. When the working solution penetrates into the gauze fibers adsorbed with tannic acid, a displacement equilibrium exists between the dissociation of zinc citrate and the formation of zinc tannic acid, slowing down the formation rate of insoluble zinc tannic acid precipitate. This delayed reaction kinetic effect provides time for zinc ions to diffuse into the fiber core, ensuring a uniform distribution of the antibacterial component along the gauze thickness, improving the phenomenon of surface adhesion only, and ensuring that the gauze retains its antibacterial capability even after wear.

[0019] (3) The intermediate micro-drying and double network construction improves washability and breathability:

[0020] The intermediate micro-drying treatment in step S3 controls the moisture content of the gauze within a specific range, preventing the loss of the first working solution while reserving capillary adsorption space for the absorption of the second working solution. During the high-temperature baking stage, the system undergoes the following chemical transformations:

[0021] 1) Esterification and amidation crosslinking: Under the catalysis of hypophosphite, the polycarboxyl groups of citric acid undergo dehydration condensation with the hydroxyl groups of cellulose fibers and the amino and hydroxyl groups of chitosan to form a network of covalent ester bonds and amide bonds, which anchor the polymer skeleton to the fiber.

[0022] 2) Coordination solidification: The released zinc ions form polydentate coordination bonds with tannic acid, chitosan and citric acid residues.

[0023] The resulting interpenetrating covalent-coordinate network structure improves the bonding strength of the functional coating, making it resistant to repeated washing. Simultaneously, because the precipitation process is chemically regulated, physical blockage of the fiber gaps is avoided, preserving the original breathability and moisture-wicking properties of the gauze.

[0024] Preferably, in step S1, the concentrations of each component in the first padding working solution are as follows: carboxymethyl chitosan 15-25 g / L, tannic acid 8-12 g / L, boric acid 4-6 g / L; and the pH value of the first padding working solution is adjusted to 7.5-8.5.

[0025] By employing the above technical solution, this concentration ratio ensures that carboxymethyl chitosan forms a sufficient film-forming framework, while the molar ratio of tannic acid to boric acid is within the optimal complexation range. If the tannic acid concentration is too high, it will lead to a darker color; if the boric acid concentration is insufficient, it cannot provide adequate antioxidant protection. Maintaining the pH value within the range of 7.5–8.5 is beneficial for the dissolution of carboxymethyl chitosan and falls within the thermodynamically favorable range for the boric acid coordination reaction.

[0026] Preferably, in step S2, the concentrations of each component in the second padding working solution are as follows: citric acid monohydrate 50-70 g / L, zinc acetate dihydrate 25-35 g / L, sodium hypophosphite monohydrate 15-25 g / L, and isomeric tridecyl alcohol polyoxyethylene ether 1-3 g / L; the pH value of the second padding working solution is adjusted to 4.0-5.0.

[0027] By employing the above technical solution, high-concentration citric acid simultaneously acts as a crosslinking agent and a coordination masking agent. A citric acid concentration of 50–70 g / L is sufficient to form a stable buffer system with 25–35 g / L zinc acetate, preventing zinc hydroxide precipitation when zinc ions come into contact with the alkaline gauze interface. Adjusting the pH to 4.0–5.0 meets the activity conditions of the catalyst sodium hypophosphite and promotes the appropriate dissociation of the borate ester complex adsorbed in the first step in subsequent processes, releasing active sites.

[0028] Preferably, the carboxymethyl chitosan is O,N-carboxymethyl chitosan with a degree of substitution of 0.8 to 1.2, a degree of deacetylation ≥90%, and a viscosity of 200 to 500 mPa·s for a 1% aqueous solution at 25°C; the penetrant is selected from isotridecyl alcohol polyoxyethylene ether.

[0029] By adopting the above technical solution, O,N-carboxymethyl chitosan is selected due to its water solubility and amphoteric electrolyte properties, enabling it to remain stable under different pH conditions. The higher degree of deacetylation provides more amino reaction sites, enhancing the amidation crosslinking density with citric acid. A specific viscosity range endows the padding solution with suitable rheological properties, preventing dripping and allowing for effective penetration into the yarn gaps. Isotridecyl alcohol polyoxyethylene ether, as a nonionic surfactant, is used to reduce surface tension, assisting the working solution in wetting and penetrating the waxy layer on the cotton fiber surface.

[0030] Preferably, in step S1, the preparation temperature is 35-45°C, the dissolution and stirring time is 25-45 minutes, and sodium bicarbonate is used to adjust the pH value; in step S2, the preparation temperature is 20-30°C, and sodium hydroxide is used to adjust the pH value.

[0031] By adopting the above technical solution, moderate heating in step S1 is beneficial for the dissolution of high molecular weight chitosan and the formation of tannic acid-boric acid complex; sodium bicarbonate is used as a regulator, resulting in a mild reaction and avoiding local over-alkaliness caused by strong alkali, which could lead to tannic acid oxidation. Room temperature preparation in step S2 prevents the hydrolysis of zinc salt; sodium hydroxide is used to adjust the system to a weakly acidic state, simplifying the operation and preventing the introduction of impurity ions.

[0032] Preferably, in step S3, the impregnation time is 20 to 40 seconds, and the liquid content after rolling is controlled to be 75% to 85%.

[0033] By adopting the above technical solution, the impregnation time and liquid carryover rate ensure the adsorption amount of the first working solution on the surface of the gauze fibers, providing sufficient reaction precursors for subsequent reactions. Too low a liquid carryover rate will result in insufficient effective components, while too high a rate will increase energy consumption during the micro-drying process and easily cause migration.

[0034] Preferably, the intermediate drying process in step S3 uses infrared pre-drying or hot air drying, and the drying temperature is controlled at 60-80℃, so that the moisture content of the gauze when it comes out of the drying room is reduced to 40%-55%.

[0035] By adopting the above technical solution, intermediate micro-drying is a key step to prevent cross-contamination between the two working solutions in the tank and to control the reaction interface. Maintaining a semi-dry state with a moisture content of 40%–55% allows space to be created in the large pores within the fibers, enabling the absorption of the second impregnation solution using capillary pressure difference. Simultaneously, residual moisture on the fiber surface prevents complete film formation of the first component, facilitating the diffusion and penetration of the second component. If the moisture content is too high, the second solution will be diluted and difficult to penetrate the core layer; if the moisture content is too low, the chitosan film layer will become dense, hindering the penetration of zinc ions.

[0036] Preferably, in step S4, the impregnation time is 10-20 seconds, and the liquid content after rolling is controlled at 65%-75%; the specific process of gradient drying and high-temperature baking is as follows: the first stage pre-drying temperature is 80-90℃, and the time is 60-90 seconds; the second stage baking and curing temperature is 150-170℃, and the time is 120-180 seconds.

[0037] By adopting the above technical solution, ion exchange and permeation can be completed in a shorter second-step impregnation time. In the gradient baking process, the low-temperature pre-baking stage slowly removes moisture to avoid rapid vaporization of moisture that could damage the continuity of the membrane layer; the high-temperature baking stage provides sufficient activation energy to promote the esterification reaction of citric acid and cellulose hydroxyl groups and the amidation reaction of chitosan amino groups, thus completing the curing of the covalent crosslinked network.

[0038] Preferably, the washing process in step S5 involves passing the water through two warm water washing tanks at 50-60°C and one cold water washing tank in sequence; the drying temperature is 90-100°C.

[0039] By adopting the above technical solution, warm water washing removes unreacted citric acid, free zinc salts, and boric acid residues, reducing the risk of acid residues in the finished gauze and ensuring the biosafety of medical materials.

[0040] Secondly, the present invention provides an antibacterial and breathable medical gauze sheet, which is prepared by any of the above-described preparation methods.

[0041] By adopting the above technical solution, the gauze pad produced has a uniformly distributed organic-inorganic hybrid antibacterial network inside, which has antibacterial properties and wash fastness, while maintaining whiteness, soft hand feel and breathability, and no obvious surface dust shedding, which meets the requirements of medical dressings.

[0042] In summary, the present invention has at least one of the following beneficial technical effects:

[0043] 1. This invention introduces boric acid into the padding working solution, utilizing the specific binding of borate ions with the ortho-dihydroxyl groups in tannic acid molecules to form a stable borate ester complex. This complexation occupies the active oxidation sites of tannic acid, effectively blocking the self-polymerization oxidation pathway that transforms it into a quinone structure under weakly alkaline conditions. This mechanism overcomes the problem of severe yellowing and discoloration of fabrics caused by traditional tannic acid finishing, ensuring that the finished gauze maintains excellent whiteness and appearance quality, meeting the cleanliness requirements of medical dressings.

[0044] 2. To address the issue of the extremely rapid reaction rate between zinc ions and tannic acid, leading to quick precipitation and pore sealing on fabric surfaces, this invention utilizes high-concentration citric acid to preferentially form water-soluble complexes with zinc ions, kinetically delaying the formation of insoluble zinc tannate precipitates. This competitive coordination mechanism avoids explosive nucleation of the solution upon contact with the gauze, ensuring that zinc ions can penetrate into the fiber core in a complexed state along with the working solution. This achieves a uniform distribution of functional components along the thickness of the gauze, guaranteeing reliable protection even after surface wear.

[0045] 3. This invention employs a high-temperature baking process, under the action of a catalyst, to induce esterification and amidation reactions between the polycarboxyl groups of citric acid and the hydroxyl groups of cellulose and the amino groups of chitosan, constructing a robust covalently cross-linked framework; simultaneously, combined with the coordination cross-linking of metal ions, a stable dual-network structure is formed. This chemical anchoring effect significantly improves the bonding strength of the functional coating, enabling the gauze to maintain an extremely high antibacterial rate even after multiple washes, thus overcoming the shortcomings of poor wash resistance in traditional physical adsorption finishing.

[0046] 4. This invention effectively inhibits surface precipitation through competitive coordination, endowing the gauze with strong antibacterial properties without clogging the fabric pores, thus maintaining unobstructed channels between fibers. The finished gauze retains air permeability close to that of raw cotton and excellent liquid absorption rate, enabling rapid drainage of wound exudate. Furthermore, the moderate cross-linking structure enhances the mechanical strength of the fibers without causing significant hardening or compaction, giving the gauze both the softness and comfort required for medical dressings.

[0047] 5. The raw materials used in this invention are all biological or low-toxic substances, and the release of active ingredients is greatly reduced through dual-network anchoring technology. Experiments have shown that the finished gauze has no inhibitory effect on cell proliferation, and the pH of the dissolved substances is stable in the weakly acidic range, which matches the human skin environment, poses no risk of irritation, and meets the safety requirements for medical-grade contact materials. Attached Figure Description

[0048] Figure 1 The figure shows the results of the solution stability and mechanism verification test in Test Example 1 of the present invention; (a) is the absorbance change curve of control group A and experimental group B with the extension of standing time; (b) is a comparison of the turbidity of the system with the drop volume during the process of adding pure zinc acetate solution and zinc citrate complex solution to tannic acid base solution respectively.

[0049] Figure 2 The figure shown is a test result diagram of the chemical crosslinking degree and network construction verification test in Test Example 2 of the present invention. Detailed Implementation

[0050] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods.

[0051] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0052] Carboxymethyl chitosan, CAS number 83512-85-0, is an O,N-carboxymethyl chitosan with a degree of substitution (DS) of 0.8–1.2, a degree of deacetylation ≥90%, a viscosity of 200–500 mPa·s in a 1% aqueous solution at 25°C, and a weight-average molecular weight (Mw) of 100,000–200,000 Daltons.

[0053] Tannic acid, CAS number 1401-55-4, is gallnut tannin, which belongs to hydrolyzable tannins, with a tannin content ≥95%.

[0054] Isotridecyl alcohol polyoxyethylene ether, CAS number 9043-30-5, product model 1305, HLB value approximately 10.5.

[0055] Medical degreased gauze, conforming to the standards of the Pharmacopoeia of the People's Republic of China, is bleached and refined. It is made of 100% cotton fiber, with a warp and weft density of 30×20 threads / inch and a weight of 14g / m². 2 .

[0056] Example 1:

[0057] This embodiment provides a method for preparing an antibacterial and breathable medical gauze pad, including the following steps:

[0058] (1) Preparation of the first padding working solution: Add deionized water to a reactor equipped with a stirrer, heat to 40°C, add 20 g / L of carboxymethyl chitosan and 10 g / L of tannic acid in sequence while stirring, stir for 25 minutes until completely dissolved; then add 5 g / L of boric acid and continue stirring for 10 minutes; finally, slowly add sodium bicarbonate to adjust the pH of the solution to 8.0 to obtain a clear first padding working solution;

[0059] (2) Preparation of the second padding working solution: At room temperature of 25°C, add 60 g / L citric acid monohydrate, 30 g / L zinc acetate dihydrate, 20 g / L sodium hypophosphite monohydrate and 2 g / L isomeric tridecyl alcohol polyoxyethylene ether to deionized water in sequence. Stir until the solid is completely dissolved, and then adjust the pH of the solution to 4.5 with sodium hydroxide to obtain a clear and transparent second padding working solution.

[0060] (3) Pre-complex adsorption: The medical degreased gauze is introduced into the padding tank containing the first padding working solution for immersion for 30 seconds, and then pressed by a padding machine with the pressure controlled at 0.3 MPa, so that the liquid carrying rate of the gauze is 80%;

[0061] (4) Intermediate drying treatment: The wet gauze after step (3) is partially dehydrated by passing it through the infrared pre-drying zone. The drying temperature is controlled at 70°C, so that the moisture content of the gauze when it comes out of the drying room is reduced to 45%.

[0062] (5) Competitive coordination penetration: The semi-dry gauze after step (4) is introduced into a padding tank containing the second padding working liquid for immersion. The immersion time is 15 seconds. Then, it is pressed by a padding machine, and the padding machine pressure is controlled at 0.4 MPa so that the liquid carrying rate of the gauze is 70%.

[0063] (6) Gradient drying and high-temperature baking: The gauze is sent into the tenter frame for two-stage heat treatment. The first stage pre-drying temperature is 85℃ and the time is 80 seconds; the second stage baking curing temperature is 160℃ and the time is 150 seconds.

[0064] (7) Post-processing: The baked gauze is passed through two 60°C warm water washing tanks and one cold water washing tank in sequence, and finally dried with hot air at 95°C and rolled into rolls to obtain the finished product.

[0065] Example 2:

[0066] This embodiment provides a method for preparing an antibacterial and breathable medical gauze pad, including the following steps:

[0067] (1) Preparation of the first padding working solution: Add deionized water to a reactor equipped with a stirrer, heat to 35°C, add 15 g / L of carboxymethyl chitosan and 8 g / L of tannic acid in sequence while stirring, stir for 30 minutes until completely dissolved; then add 4 g / L of boric acid and continue stirring for 15 minutes; finally, slowly add sodium bicarbonate to adjust the pH of the solution to 7.5 to obtain a clear first padding working solution;

[0068] (2) Preparation of the second padding working solution: At room temperature of 20°C, add 50 g / L citric acid monohydrate, 25 g / L zinc acetate dihydrate, 15 g / L sodium hypophosphite monohydrate and 1 g / L isomeric tridecyl alcohol polyoxyethylene ether to deionized water in sequence. Stir until the solid is completely dissolved, and then adjust the pH of the solution to 4.0 with sodium hydroxide to obtain a clear and transparent second padding working solution.

[0069] (3) Pre-complex adsorption: The medical degreased gauze is introduced into the padding tank containing the first padding working solution for immersion for 40 seconds, and then pressed by a padding machine with the pressure controlled at 0.2 MPa, so that the liquid carrying rate of the gauze is 85%;

[0070] (4) Intermediate drying treatment: The wet gauze after step (3) is partially dehydrated by passing it through a hot air drying room. The drying temperature is controlled at 60°C, so that the moisture content of the gauze when it comes out of the drying room is reduced to 40%.

[0071] (5) Competitive coordination penetration: The semi-dry gauze after step (4) is introduced into a padding tank containing the second padding working liquid for immersion. The immersion time is 20 seconds. Then, it is pressed by a padding machine, and the padding machine pressure is controlled at 0.3 MPa so that the liquid carrying rate of the gauze is 75%.

[0072] (6) Gradient drying and high-temperature baking: The gauze is sent into the tenter frame for two-stage heat treatment. The first stage pre-drying temperature is 80℃ and the time is 90 seconds; the second stage baking curing temperature is 150℃ and the time is 180 seconds.

[0073] (7) Post-processing: The baked gauze is passed through two 50°C warm water washing tanks and one cold water washing tank in sequence, and finally dried with hot air at 90°C and rolled into rolls to obtain the finished product.

[0074] Example 3:

[0075] This embodiment provides a method for preparing an antibacterial and breathable medical gauze pad, including the following steps:

[0076] (1) Preparation of the first padding working solution: Add deionized water to a reactor equipped with a stirrer, heat to 45°C, add 25 g / L of carboxymethyl chitosan and 12 g / L of tannic acid in sequence while stirring, stir for 20 minutes until completely dissolved; then add 6 g / L of boric acid and continue stirring for 10 minutes; finally, slowly add sodium bicarbonate to adjust the pH of the solution to 8.5 to obtain a clear first padding working solution;

[0077] (2) Preparation of the second padding working solution: At room temperature of 30°C, add 70 g / L citric acid monohydrate, 35 g / L zinc acetate dihydrate, 25 g / L sodium hypophosphite monohydrate and 3 g / L isotridecyl alcohol polyoxyethylene ether to deionized water in sequence. Stir until the solid is completely dissolved, and then adjust the pH of the solution to 5.0 with sodium hydroxide to obtain a clear and transparent second padding working solution.

[0078] (3) Pre-complex adsorption: Medical degreased gauze is introduced into a padding tank containing the first padding working solution for immersion for 20 seconds, and then pressed by a padding machine with the pressure controlled at 0.4 MPa, so that the liquid carrying rate of the gauze is 75%;

[0079] (4) Intermediate drying treatment: The wet gauze after step (3) is partially dehydrated by passing it through the infrared pre-drying zone. The drying temperature is controlled at 80℃, so that the moisture content of the gauze when it comes out of the drying room is reduced to 50%.

[0080] (5) Competitive coordination penetration: The semi-dry gauze after step (4) is introduced into a padding tank containing the second padding working liquid for immersion. The immersion time is 10 seconds. Then, it is pressed by a padding machine, and the padding machine pressure is controlled at 0.5 MPa so that the liquid carrying rate of the gauze is 65%.

[0081] (6) Gradient drying and high-temperature baking: The gauze is sent into the tenter frame for two-stage heat treatment. The first stage pre-drying temperature is 90℃ and the time is 60 seconds; the second stage baking and curing temperature is 170℃ and the time is 120 seconds.

[0082] (7) Post-processing: The baked gauze is passed through two 60°C warm water washing tanks and one cold water washing tank in sequence, and finally dried with hot air at 100°C and rolled into a roll to obtain the finished product.

[0083] Example 4:

[0084] This embodiment provides a method for preparing an antibacterial and breathable medical gauze sheet. The only difference between this method and Example 1 is that the concentration of citric acid monohydrate in the second impregnation working solution is adjusted to 70 g / L. The remaining raw material ratios and process steps are the same as in Example 1.

[0085] Example 5:

[0086] This embodiment provides a method for preparing antibacterial and breathable medical gauze sheets. The only difference between this embodiment and Embodiment 1 is that in the intermediate micro-drying process of step (4), the moisture content of the gauze is reduced to 55% when it comes out of the drying room. The other raw material ratios and process steps are the same as in Embodiment 1.

[0087] Comparative Example 1:

[0088] The difference between its preparation method and Example 1 is that: in step (1), boric acid was not added to the first impregnation working liquid, and the proportions of other raw materials and process steps were consistent with those in Example 1.

[0089] Comparative Example 2:

[0090] The difference between its preparation method and Example 1 is that the intermediate micro-drying treatment in step (4) is omitted. That is, after the gauze is rolled in step (3), it is directly immersed in the second impregnation working liquid in step (5) in a wet state. The remaining raw material ratio and process steps are consistent with Example 1.

[0091] Comparative Example 3:

[0092] The difference between its preparation method and Example 1 is that: in step (2), citric acid monohydrate was not added to the second padding working solution, but acetic acid was used to adjust the pH value to 4.5, and sodium hypophosphite monohydrate was not added. The remaining raw material ratios and process steps are consistent with Example 1.

[0093] Comparative Example 4:

[0094] The difference between its preparation method and Example 1 is that: in step (6), high-temperature baking and curing at 160°C is not carried out, but only drying at 90°C to constant weight; and the post-treatment water washing process in step (7) is omitted, and after drying, it is directly wound into rolls, while the remaining raw material ratios and process steps are consistent with Example 1.

[0095] Comparative Example 5:

[0096] The preparation method differs from that of Example 1 in that a one-bath process is used. Specifically, all components of the first and second baths in Example 1 are mixed in the same bath solution, citric acid and zinc are added first, and tannic acid is added last. The pH is adjusted to 4.5, and after one impregnation and padding, the product is directly dried and baked.

[0097] Test Example 1:

[0098] The experimental steps are as follows:

[0099] (1) Experiment to verify the antioxidant mechanism:

[0100] A basic tannic acid solution with a concentration of 10 g / L was prepared using deionized water as the solvent. This solution was divided into two groups, designated as control group A and experimental group B. Sodium bicarbonate was added to control group A to adjust the pH to 8.0; in experimental group B, 5 g / L boric acid was first added, stirred to dissolve, and then sodium bicarbonate was added to adjust the pH to 8.0. Both solutions were placed in open beakers and allowed to stand at a constant temperature of 25°C. Samples were taken every 0.5 hours from 0 to 4 hours. The absorbance at 420 nm was measured using a UV-Vis spectrophotometer at each time point to characterize the degree of browning and the oxidation state of the tannic acid.

[0101] (2) Experimental verification of competitive coordination mechanism:

[0102] A 5 g / L tannic acid solution was prepared as the base solution, and the pH was adjusted to 4.5 to simulate the surface environment of the gauze. Two additional drop solutions were prepared: Drop solution C was a 30 g / L zinc acetate dihydrate aqueous solution (simulating a non-competitive coordination system); Drop solution D was a mixed solution containing 30 g / L zinc acetate dihydrate and 60 g / L citric acid monohydrate, and the pH was adjusted to 4.5 (simulating the second padding working solution system of this invention). Under magnetic stirring, drop solutions C and D were slowly added dropwise to two equal portions of the tannic acid base solution at a rate of 1 mL / min. The turbidity change of the mixed system (unit: NTU) was monitored in real time using a turbidimeter, and the turbidity evolution process caused by the increase of the drop volume was recorded until the drop volume reached 20 mL.

[0103] The experimental results are shown in Table 1.

[0104] Table 1. Test data on antioxidant stability and zinc ion coordination kinetics of the tannic acid system:

[0105]

[0106] According to Table 1 and Figure 1 The data analysis leads to the following conclusions:

[0107] First, regarding the boric acid-mediated transient protection mechanism, in a weakly alkaline environment at pH 8.0, the absorbance of control group A showed a near-linear rapid increase over time, reaching a high of 1.876 after 4 hours. The solution appeared dark brown to the naked eye, indicating that tannic acid underwent a severe oxidative self-polymerization reaction, generating quinone structures and high molecular weight polymers. In contrast, the absorbance of experimental group B, which introduced boric acid, remained at an extremely low level (0.108) throughout the 4-hour test period, with only a slight increase. This data confirms that borate ions can specifically bind to the ortho-diphenolic hydroxyl groups in tannic acid molecules, forming stable borate ester complexes. This complexation effectively occupies the active oxidation sites of tannic acid, blocking the transformation pathway of phenolic hydroxyl groups to quinones, thereby endowing the working solution with excellent antioxidant stability and color retention, providing a chemical basis for maintaining the whiteness of the gauze in the first padding process.

[0108] Secondly, regarding the citric acid-driven competitive coordination mechanism, in the turbidity titration test, the added solution C (pure zinc ions) caused the system turbidity to rise sharply to 45.3 NTU in the initial stage (2 mL), and reached 1320.5 NTU at 20 mL, indicating that the coordination reaction between zinc ions and tannic acid was extremely rapid, instantly generating a large amount of insoluble zinc tannate precipitate. This rapid precipitation can lead to pore blockage on the gauze surface in actual processes, hindering the penetration of antibacterial agents into the fiber. Conversely, the added solution D (citric acid-zinc system) showed a turbidity of only 15.7 NTU when the added volume reached 10 mL, exhibiting a significant "induction period" characteristic. Even at the 20 mL endpoint, the turbidity was only 112.1 NTU, less than one-tenth of the control group. This indicates that the high concentration of citric acid in the solution preferentially forms a water-soluble [Zn-Citrate] complex with zinc ions. The formation of this complex significantly reduces the activity of free zinc ions, thus kinetically delaying the formation of the more thermodynamically stable zinc tannate precipitate.

[0109] This competitive coordination mechanism ensures that zinc ions can penetrate deep into the gauze fibers in a complexed state along with the working fluid, avoiding the surface sealing effect and providing a kinetic control means to achieve homogenized crosslinking from the inside out and maintain air permeability.

[0110] Test Example 2:

[0111] The experimental steps are as follows:

[0112] (1) Gel fraction test:

[0113] Five samples of finished gauze prepared in Example 1 and Comparative Example 4 were selected and cut into 5cm × 5cm samples. They were dried in an oven at 105℃ to constant weight, and the initial mass W0 was recorded. The samples were placed in a Soxhlet extractor, and a 2% acetic acid aqueous solution was used as the solvent (this solvent can dissolve uncrosslinked chitosan, tannic acid and free zinc citrate complex, but cannot destroy the covalent ester crosslinking network).

[0114] Extraction was performed by heating and reflux for 24 hours. After extraction, the sample was removed and repeatedly washed with deionized water to remove residual solvent. It was then dried again in an oven at 105℃ until constant weight, and the extracted mass W1 was recorded. The gel fraction was calculated according to the formula Gel%=(W1 / W0)×100%, and the average value of 5 tests was taken.

[0115] (2) Determination of free carboxyl group content:

[0116] Two g each of the finished gauze prepared in Example 1 and Comparative Example 4 were taken and shredded into fiber powder. The carboxyl content on the fiber surface was determined using the methylene blue adsorption method. The sample was accurately weighed and placed in a stoppered conical flask, and 25 mL of a 0.2 mmol / L methylene blue solution and 25 mL of phosphate buffer (pH 8.0) were added. The flask was shaken at 25°C for 8 hours to reach adsorption equilibrium. The supernatant was centrifuged, and the concentration of the remaining methylene blue in the supernatant was measured at 664 nm using a UV spectrophotometer. Based on the change in methylene blue concentration before and after adsorption, the number of millimoles of methylene blue adsorbed per unit mass of fiber was calculated, which is the carboxyl content of the fiber (mmol / kg). Untreated raw cotton gauze was used as a blank control.

[0117] The experimental results are shown in Table 2.

[0118] Table 2. Test data on gel fraction and free carboxyl group content of gauze samples:

[0119]

[0120] According to Table 2 and Figure 2 The data analysis leads to the following conclusions:

[0121] First, regarding the high-temperature induced covalent network construction, the gel fraction in Example 1 reached as high as 98.66%, even slightly higher than the original cotton blank (97.7%). This indicates that after high-temperature baking at 160°C, the loaded layer (containing citric acid, chitosan, and zinc tannate) on the gauze surface had formed a highly cross-linked network structure. This structure exhibited extremely high stability under the harsh conditions of acidic solvent reflux, with almost no dissociation or loss. In contrast, the gel fraction in Comparative Example 4 was only 87.14%, with a mass loss rate close to 13%. This suggests that under drying conditions of only 90°C, the intermolecular forces within the system were mainly hydrogen bonds and physical adsorption, failing to reach the activation energy threshold required for esterification, thus preventing the formation of covalent bonds. Under solvent attack, the uncross-linked citric acid, chitosan, and some zinc tannate complexes easily desorbed and detached from the fiber surface. This difference confirms that high-temperature baking is a key step in constructing the covalent framework, which permanently anchors the functional layer to the fiber surface.

[0122] Secondly, regarding the chemical evidence for functional group transformation, the test results of free carboxyl group content further confirm the occurrence of esterification. The free carboxyl group content in Comparative Example 4 was as high as 46.86 mmol / kg, significantly higher than the original cotton blank (12.4 mmol / kg). This is because a large amount of polycarboxylic acids (citric acid) and carboxymethyl chitosan were introduced into the system, but due to the lack of high-temperature baking, most of these introduced carboxyl groups remained in a free, unreacted state. In Example 1, the free carboxyl group content significantly decreased to 28.5 mmol / kg. This decrease (approximately 39% less than Comparative Example 4) directly reflects that, under high temperature and sodium hypophosphite catalysis, a large number of citric acid carboxyl groups participated in the esterification / amidation reaction with cellulose hydroxyl groups and chitosan amino / hydroxyl groups. The consumed carboxyl groups were converted into ester or amide bonds, becoming crosslinking points connecting polymer chain segments. In summary, the increase in gel fraction and the decrease in free carboxyl group content show a clear negative correlation, proving that the present invention successfully constructed a stable dual-network interpenetrating structure through high-temperature baking.

[0123] Test Example 3:

[0124] The experimental steps are as follows:

[0125] (1) Whiteness test:

[0126] According to GB / T 8424.2-2001 "Instrumental Evaluation Method for Relative Whiteness in Color Fastness Testing of Textiles", a WSB-2 whiteness meter was used to test each group of gauze samples. Before testing, the instrument was calibrated using a standard black and white board. The sample was folded into four layers to ensure opacity, and five points were randomly selected at different locations on the sample surface for measurement. The CIE whiteness value (W_CIE) was recorded, and the average value was taken as the final whiteness data for that sample.

[0127] (2) Fracture strength test:

[0128] According to GB / T 3923.1-2013 "Textiles - Tensile Properties of Fabrics - Part 1: Determination of Breaking Strength and Elongation at Break (Strip Method)", the tests were conducted on an electronic fabric tensile tester. Each group of yarns was cut into strips with warp and weft dimensions of 50mm × 250mm. The spacing was set to 200mm, the tensile speed to 100mm / min, and the pretension to 2N. Five warp and five weft samples were tested for each group of samples, and the breaking strength (N) was recorded and the average value calculated.

[0129] (3) Flexibility (bending stiffness) test:

[0130] According to GB / T 18318.1-2009 "Determination of bending properties of textiles - Part 1: Inclined plane method", a fully automatic fabric stiffness tester was used for testing. The sample was cut into strips of 25mm × 200mm and placed on an inclined plane with an angle of 41.5°. The length of the sample extending out when it touched the inclined plane was measured (bending length). The bending stiffness was calculated, with units of mN·cm. The smaller the bending stiffness value, the softer the fabric. Each group of samples was tested 5 times on both sides, and the average value was taken.

[0131] The experimental results are shown in Table 3.

[0132] Table 3. Test data on whiteness and physical and mechanical properties of each group of gauze samples:

[0133]

[0134] Based on the data analysis in Table 3, the following conclusions can be drawn:

[0135] First, regarding the antioxidant and color-protecting efficacy of boric acid, the CIE whiteness values ​​of Examples 1-5 remained between 76.8 and 79.2, showing a smaller decrease compared to the untreated cotton blank (82.4), and the gauze appeared a clean, off-white color. This indicates that the introduction of boric acid in the first padding bath successfully inhibited the oxidative browning of tannic acid under alkaline conditions. In contrast, the whiteness value of Comparative Example 1 plummeted to 45.6, and the gauze appeared a severe dark brown. This huge data contrast (whiteness difference exceeding 30) directly confirms the crucial role of the formation of boric acid ester complexes in blocking the formation of tannic acid chromophores. Without this protective mechanism, the oxidation products of tannic acid would not only severely affect the appearance acceptability of medical dressings but also consume their effective polyphenol active sites.

[0136] Secondly, regarding the impact of the crosslinking process on mechanical properties and hand feel, the warp breaking strength of Example 1 was 268.4 N, with a retention rate of approximately 94% compared to the uncrosslinked cotton blank (285.6 N). Although the process involved an acidic environment with pH 4.0–5.0 and high-temperature baking at 160°C, which typically causes hydrolysis of cellulose glycosides and a decrease in polymerization degree, the data shows that this strength loss was within a controllable range. This is mainly due to the mild acid release characteristics of citric acid as a buffer and the physical reinforcement effect of the crosslinking network on the fiber structure. The strengths of Comparative Example 3 (without citric acid / crosslinking) and Comparative Example 4 (without baking) were slightly higher (281.2 N and 283.5 N, respectively), close to that of the uncrosslinked cotton, indicating that the slight decrease in strength did indeed stem from the increased fiber rigidity and trace acid damage caused by the crosslinking reaction. However, the strength levels of the examples fully meet the standards for use in medical gauze. In terms of feel, the bending stiffness of Example 1 (2.12 mN·cm) is slightly higher than that of the original cotton (1.85 mN·cm), indicating that the introduction of the cross-linked network slightly increases the stiffness of the gauze, but does not cause obvious hardening or clumping, and still maintains good fit. Comparative Example 2, due to the omission of the intermediate drying layer, resulted in uneven drug absorption and localized excessive cross-linking, causing the bending stiffness to rise to 2.45 mN·cm, and the feel to become significantly harder. In summary, this invention achieves a balance between mechanical properties and feel while ensuring excellent appearance.

[0137] Test Example 4:

[0138] The experimental steps are as follows:

[0139] (1) Antibacterial performance test (shaking flask method):

[0140] The test was conducted according to GB / T 20944.3-2008 "Evaluation of antimicrobial properties of textiles - Part 3: Shaking method". Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8099) were selected as test bacteria. Each group of gauze samples was cut into 0.5cm × 0.5cm pieces, and 0.75g was weighed and placed in an Erlenmeyer flask. 70mL of phosphate buffer and 5mL of 1×10⁻⁶ pH buffer were added. 5 CFU / mL bacterial suspension was incubated at 24℃ and 150 rpm for 18 hours with shaking. Samples were then diluted and inoculated onto agar plates, incubated at 37℃ for 24 hours, and viable colonies were counted. The inhibition rate was calculated based on the difference in colony count between the control and sample samples.

[0141] (2) Wash fastness test:

[0142] According to GB / T 8629-2017 "Home Washing and Drying Procedures for Textile Testing", the gauze samples were cyclically washed using the 4N procedure (washing in warm water at 40℃). After 20 and 50 washes, the samples were removed, dried, and their antibacterial rate was retested using the shaking flask method described above to evaluate the adhesion of the antibacterial coating.

[0143] (3) Evaluation of penetration uniformity (stripping method):

[0144] To verify the uniformity of functional component distribution along the thickness of the gauze, the core layer was exposed using a tape peeling method. 3M Scotch transparent tape was tightly adhered to both sides of the gauze, pressed firmly, and then quickly peeled off. This process was repeated five times until approximately 30%–40% of the surface fiber layer was removed, exposing the inner core fibers. The treated "core layer sample" was then subjected to the aforementioned antibacterial test, and the data were compared with those of the unpeeled "surface sample" (initial 0 wash). If the data were similar, it indicated uniform penetration; if the core layer data was significantly lower than the surface layer data, it indicated the presence of a core-sheath effect.

[0145] The experimental results are shown in Tables 4 and 5.

[0146] Table 4. Wash resistance and permeability data of gauze samples against Staphylococcus aureus:

[0147]

[0148] Table 5. Wash resistance and penetration performance data of gauze samples against Escherichia coli (E. coli):

[0149]

[0150] Based on the data analysis in Tables 4 and 5, the following conclusions can be drawn:

[0151] First, regarding the effect of dual-network anchoring on broad-spectrum antibacterial wash resistance, Example 1 maintained an inhibition rate of 96.5% against Staphylococcus aureus (Gram-positive bacteria) and 95.8% against Escherichia coli (Gram-negative bacteria) after 50 standard water washes. This indicates that the constructed covalent framework and coordination nodes possess excellent structural stability, simultaneously resisting water dissociation and mechanical friction, ensuring that the antibacterial components are not lost. In contrast, Comparative Example 3 (without chemical crosslinking) and Comparative Example 4 (without high-temperature baking) showed inhibition rates against both bacteria dropping below 70% after 20 water washes, and further decreasing to below 30% after 50 water washes. This confirms that the functional layer cannot withstand the shear forces of repeated washing if relying solely on physical adsorption.

[0152] Secondly, regarding the contribution of the competitive coordination mechanism to eliminating the core-sheath effect and improving overall efficacy, permeability test data show that Example 1 exhibits extremely low permeability differences against both bacterial species (1.1% for S. aureus and 1.4% for E. coli), with the core fiber demonstrating the same excellent bactericidal ability as the surface layer. In stark contrast, Comparative Example 3, lacking the competitive coordination effect of citric acid, shows a rapid precipitation reaction between zinc ions and tannic acid on the gauze surface, resulting in surface sealing and preventing the drug solution from penetrating inward. Therefore, its core layer antibacterial rate is only about 50%–60%, with a permeability difference rate exceeding 40%, demonstrating severe uneven distribution of the core-sheath.

[0153] It is worth noting that although Comparative Example 4 achieved good core layer penetration (core layer antibacterial rate of 93.5%) thanks to the competitive coordination of citric acid, its washability was extremely poor due to the lack of covalent cross-linking caused by high-temperature baking, which proves that penetration and curing are both indispensable.

[0154] Similarly, Comparative Example 5, using the one-bath method, showed a core layer inhibition rate of only 48.6% against *E. coli*, with a penetration difference rate as high as 50.9%. Due to the relatively strong drug resistance of *E. coli*, the insufficient drug concentration in the core layer directly led to antibacterial failure. This severe core-skin effect not only reduced the overall antibacterial efficiency, but also resulted in complete loss of protective capability once the gauze surface was worn away. This invention, through a stepwise competitive coordination strategy, achieves homogeneous distribution of the antibacterial agent, ensuring stable and reliable protective performance against multiple pathogens throughout the product's entire life cycle.

[0155] Test Example 5:

[0156] The experimental steps are as follows:

[0157] (1) Air permeability test:

[0158] According to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics", a fully automatic digital air permeability meter was used for testing. Each group of gauze samples was conditioned for 24 hours under standard atmospheric conditions (temperature 20±2℃, relative humidity 65±4%). A 20cm section was selected... 2 The test area was set with a pressure drop of 100 Pa. The sample was held flat on the test head, the instrument was started, and the airflow passed vertically through the fabric. The air permeability (mm / s) after stabilization was recorded. Each group of samples was randomly tested 10 times at different locations, and all data were recorded to examine local uniformity.

[0159] (2) Liquid absorption rate (water droplet settling time) test:

[0160] According to AATCC 79 standard and GB / T 21655.1-2008 "Evaluation of the moisture absorption and quick-drying properties of textiles - Part 1: Single-item combination test method", the hydrophilic liquid absorption capacity of the gauze surface was tested. The sample was laid flat on a suspended embroidery frame, maintaining a uniform surface tension. Using a microburette, a drop of 0.05 mL of distilled water was dropped at a height of 10 mm above the sample surface. The time (s) required from the moment the water droplet touched the sample surface until the specular reflection of the water droplet completely disappeared (i.e., the water droplet completely penetrated into the fabric) was recorded using a stopwatch. Ten points were tested for each group of samples.

[0161] The experimental results are shown in Table 6.

[0162] Table 6. Original data record of air permeability and liquid absorption rate test of gauze samples:

[0163]

[0164] Based on the data analysis in Table 6, the following conclusions can be drawn:

[0165] First, regarding the effectiveness of the competitive coordination mechanism in solving the surface pore sealing problem, the air permeability test results show that the average air permeability of Example 1 was 790.2 mm / s, only a slight decrease of about 7.4% compared to the original cotton blank (853.6 mm / s), indicating that the pore channels between its fibers remained unobstructed. Conversely, the air permeability of Comparative Example 3 (without citric acid) dropped sharply to 461.6 mm / s, and the data dispersion was extremely large (standard deviation of about 42.3), indicating that in the absence of competitive coordination with citric acid, zinc ions and tannic acid underwent a rapid and disordered precipitation reaction on the gauze surface, and the resulting coarse particles randomly blocked the fabric pores. The situation was even more serious in Comparative Example 5 (one-bath method), with an air permeability of only 323.9 mm / s, less than 40% of that of the original cotton. This is because the one-bath method causes the reaction liquid to undergo explosive nucleation upon contact with the fabric, forming a dense hard shell on the gauze surface, which severely hinders air circulation. The data from Example 1 demonstrate that the formation of the citrate-zinc complex effectively inhibits rapid surface deposition, enabling the functional components to fill the interior of the fiber rather than cover the surface.

[0166] Secondly, regarding the regulation of hydrophilic liquid absorption properties by the cross-linking network, in the liquid absorption rate test, the water droplet settling time of Example 1 was 1.37 s, demonstrating excellent instantaneous liquid absorption capacity. This is attributed to two factors: firstly, the surface was not sealed, allowing the capillary effect to be preserved; secondly, the citric acid and chitosan introduced into the cross-linking network contain a large number of hydrophilic carboxyl and hydroxyl / amino groups, maintaining the wettability of the fiber surface. In contrast, the liquid absorption time of Comparative Example 5 was prolonged to 13.83 s, showing a significant tendency to repel water. This is because the dense zinc tannate complex layer on the surface is highly hydrophobic and physically blocks the channels for water to penetrate into the fiber interior. For medical dressings, rapid drainage of wound exudate is crucial to prevent maceration, and the test results of Example 1 confirm that this preparation process imparts antibacterial function to the gauze without sacrificing its core liquid management performance.

[0167] Test Example 6:

[0168] The experimental steps are as follows:

[0169] (1) Cytotoxicity test (MTT method):

[0170] The tests were conducted according to GB / T 16886.5-2017 "Biological Evaluation of Medical Devices Part 5: In Vitro Cytotoxicity Tests". Mouse fibroblasts (L929) were selected as test cells and cultured in DMEM complete medium (containing 10% fetal bovine serum and 1% penicillin-streptomycin solution) at 37°C in a 5% CO2 incubator. The gauze sample from Example 1 was cut into 1cm × 1cm fragments, autoclaved, and then DMEM medium was added at a ratio of 0.2g / mL. The mixture was extracted in a 37°C shaker for 24 hours to obtain the extract. A blank control group (DMEM medium only) and a positive control group (DMEM medium containing 0.1% phenol) were set up. L929 cells in the logarithmic growth phase were cultured at a density of 1 × 10⁶ cells per well. 4 Cells were seeded at a density of [number] cells / well in 96-well plates. After 24 hours of incubation, the original culture medium was aspirated, and 100 μL of blank control solution, positive control solution, and sample extract solution were added to each well, with 6 replicates per group. After 48 hours of further incubation, 20 μL of 5 mg / mL MTT solution was added to each well. After incubation for 4 hours, the supernatant was aspirated, and 150 μL of dimethyl sulfoxide (DMSO) was added to each well to dissolve formazan crystals. The absorbance (OD value) of each well was measured at 490 nm using a microplate reader, and the relative cell proliferation rate (RGR) was calculated using the formula: RGR = (OD value / (OD value)). 试样 / OD 空白 )×100%.

[0171] (2) pH test of the leachate:

[0172] Artificial sweat (pH 5.5) was prepared according to the method of simulating sweat immersion in GB / T 10004-2008 "Dry Lamination and Extrusion Lamination of Plastic Composite Films and Bags for Packaging". The formula was: 0.5 g / L L-histidine hydrochloride monohydrate, 5 g / L sodium chloride, 2.2 g / L sodium dihydrogen phosphate dihydrate, and 5 g / L anhydrous sodium sulfate. The pH was adjusted to 5.5 ± 0.1 with sodium hydroxide solution. The gauze sample from Example 1 was cut into 5 cm × 5 cm pieces, washed with deionized water and dried. 1 g of the sample was weighed and placed in a 100 mL Erlenmeyer flask, and 50 mL of artificial sweat was added. The sample was immersed in the solution for 24 hours at 100 r / min in a constant temperature shaker at 37 °C. After immersion, the sample was removed, and the pH value of the leaching solution was immediately measured using a calibrated pH meter. A blank control group (artificial sweat only) was also set up. Each group was tested three times.

[0173] The experimental results are shown in Tables 7 and 8.

[0174] Table 7. Cytotoxicity test data of gauze sample from Example 1:

[0175]

[0176] Table 8. pH test data of the gauze sample leachate from Example 1:

[0177]

[0178] Based on the data analysis in Tables 7 and 8, the following conclusions can be drawn:

[0179] First, regarding cell compatibility and residue safety, the relative growth rate (RGR) of the gauze extract in Example 1 against L929 cells was 97.8%, far exceeding the threshold (≥80%) for grade 0 (non-toxic) in the cytotoxicity rating, and showing no significant difference in cell proliferation activity compared to the blank control group. This indicates that substances such as boric acid and zinc ions introduced during the preparation process, through the anchoring effect of the dual network structure, hardly dissolved or released, and the residual amount remained within the cell-safe tolerance range. The RGR of the positive control group was only 15.1%, exhibiting severe toxicity, further verifying the reliability of the experimental system. Medical dressings come into direct contact with human wounds, and cytotoxicity is a core indicator for assessing their safety. The test results of Example 1 confirm that the gauze prepared by this process has excellent cell compatibility and will not damage normal tissue cells.

[0180] Secondly, regarding the pH value of the leachate and the risk of skin irritation, after the gauze sample of Example 1 was soaked in artificial sweat for 24 hours, the average pH value of the leachate was 5.60, which was only 0.11 units higher than the pH value of the blank artificial sweat (5.49), still within the slightly acidic range. The normal pH value of the skin surface is 4.5-6.5, and a slightly acidic environment helps maintain the skin's barrier function and microbial balance. If the pH value of the leachate deviates from this range, it may lead to skin irritation or allergic reactions. The minimal change in the pH value of the leachate in Example 1 indicates, on the one hand, the high stability of the functional components on the gauze surface, with almost no hydrolysis or dissociation; on the other hand, it also shows that no strongly acidic or alkaline substances were introduced during the preparation process, avoiding potential risks of skin irritation.

[0181] In summary, the gauze sample from Example 1 demonstrated excellent biocompatibility and safety in both cytotoxicity and pH tests of the dissolution solution, meeting the clinical application requirements for medical dressings. This is attributed to the dual-network structure constructed in this invention, which achieves long-term anchoring of antibacterial functional components while effectively controlling the release of residues, ensuring the safety and reliability of the product.

[0182] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an antibacterial and breathable medical gauze pad, characterized in that, Includes the following steps: S1, Preparation of the first padding working solution: Dissolve carboxymethyl chitosan, tannic acid and boric acid in water and adjust the pH value to alkaline to obtain the first padding working solution; S2, Preparation of the second padding working solution: Dissolve citric acid, zinc salt, hypophosphite and penetrant in water and adjust the pH value to acidic to obtain the second padding working solution; S3, Pre-complex adsorption: Medical degreased gauze is immersed in the first padding working solution, pressed, and then subjected to intermediate micro-drying treatment to bring the gauze to the set moisture content; the intermediate micro-drying treatment adopts infrared pre-drying or hot air drying, and the drying temperature is controlled at 60-80℃, so that the moisture content of the gauze when it comes out of the drying room is reduced to 40%-55%; S4, Competitive coordination penetration: The gauze treated in step 3 is immersed in the second padding working solution, and after padding, it is subjected to gradient drying and high-temperature baking; the specific process of gradient drying and high-temperature baking is as follows: the first stage pre-drying temperature is 80-90℃, and the time is 60-90 seconds; the second stage baking and curing temperature is 150-170℃, and the time is 120-180 seconds; S5, Post-processing: Wash the baked gauze with water and dry it to obtain the finished product.

2. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, In step S1, the concentrations of each component in the first impregnation working fluid are as follows: carboxymethyl chitosan 15-25 g / L, tannic acid 8-12 g / L, and boric acid 4-6 g / L. The pH value of the first impregnation working fluid is adjusted to 7.5-8.

5.

3. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, In step S2, the concentrations of each component in the second padding working solution are as follows: citric acid monohydrate 50-70 g / L, zinc acetate dihydrate 25-35 g / L, sodium hypophosphite monohydrate 15-25 g / L, and isomeric tridecyl alcohol polyoxyethylene ether 1-3 g / L. The pH value of the second impregnation working solution is adjusted to 4.0-5.

0.

4. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, The carboxymethyl chitosan is O,N-carboxymethyl chitosan with a degree of substitution of 0.8 to 1.2, a degree of deacetylation ≥90%, and a viscosity of 200 to 500 mPa·s in a 1% aqueous solution at 25°C; the penetrant is selected from isotridecyl alcohol polyoxyethylene ether.

5. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, In step S1, the preparation temperature is 35–45℃, the dissolution and stirring time is 25–45 minutes, and sodium bicarbonate is used to adjust the pH value; in step S2, the preparation temperature is 20–30℃, and sodium hydroxide is used to adjust the pH value.

6. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, In step S3, the impregnation time is 20 to 40 seconds, and the liquid content after rolling is controlled to be 75% to 85%.

7. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, In step S4, the immersion time is 10 to 20 seconds, and the liquid content after rolling is controlled at 65% to 75%.

8. The method for preparing the antibacterial and breathable medical gauze sheet according to claim 1, characterized in that, The washing process in step S5 involves passing the water through two warm water washing tanks at 50-60°C and one cold water washing tank in sequence; the drying temperature is 90-100°C.

9. An antibacterial and breathable medical gauze pad, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

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