Water-soluble composite air filtration membrane constructed by physical-chemical synergistic crosslinking and preparation method and application thereof

Abstract

The application discloses a kind of physical-chemical synergic crosslinking construction water-soluble composite air filter membrane and preparation method and application thereof, and relates to air filter membrane technical field.The technical scheme is as follows:the filter membrane is biological base water-soluble composite air filter membrane, with gelatin and carboxymethyl chitosan as raw material, with glutaraldehyde as surface crosslinking reinforcing agent, is prepared by physical crosslinking and surface chemical crosslinking synergic process, and the film thickness is 0.3-0.5mm;Preparation method includes: film solution preparation, physical crosslinking construction porous structure and surface chemical crosslinking modification.The application provides a set of efficient, safe and adaptable material platform for the active prevention and control of biological aerosol pollution.

Description

Technical Field

[0001] This invention relates to the field of air filter membrane technology, specifically to a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking, its preparation method, and its application. Background Technology

[0002] Airborne microbial contamination poses a persistent threat to global public health and biosafety. Various pathogens, fungi, and viruses can persist in ambient air for extended periods as microbial aerosols and spread over long distances. Microbial pollutants and their metabolic byproducts also pose significant threats to critical industries such as pharmaceuticals, food processing, and healthcare. Persistent biocontamination can lead to product spoilage, decreased safety, and severe economic losses. Especially in controlled environments such as cleanrooms, biomedical laboratories, and hospital clinics, stringent air quality standards are essential for ensuring human health and research reliability. Therefore, effective monitoring and control of bioaerosol contamination is a core element of risk prevention and control. Gravity sedimentation sampling has been established as the reference standard method for quantitative counting of airborne microorganisms in national health and environmental monitoring regulations. However, this passive sampling mode has several inherent drawbacks, including low collection efficiency, narrow particle size capture range, and poor detection accuracy. To overcome these problems, various active bioaerosol samplers have been developed. Among them, filtration sampling technology has a wide particle size capture range (0.1-100 μm), covering most pathogenic microorganism sizes, and has high and predictable collection efficiency, attracting widespread attention and research. However, existing filter media are generally based on organic polymers and inorganic materials, making it difficult to elute captured microorganisms, resulting in significant sample loss and hindering accurate detection through capture-re-release. In recent years, the emergence of water-soluble filter membranes as a novel sampling medium has provided a new approach to solving these problems. Its core advantage lies in its ability to efficiently release captured microorganisms through a soluble filter membrane matrix and its seamless integration with various downstream microbial detection and analysis methods. However, currently reported water-soluble filter membranes generally rely on single physical cross-linking in their preparation processes. This is particularly true for biomass filter membranes, which require stringent selection and compatibility of biomacromolecule raw materials. Furthermore, the flexibility in controlling the microporous structure of the filter membrane is limited, often resulting in a dilemma where structural stability and solubility are difficult to balance. Therefore, there is an urgent need to develop a novel water-soluble filter membrane that can overcome the limitations of single physical cross-linking and achieve precise multi-dimensional control of its microstructure. Summary of the Invention

[0003] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a water-soluble composite air filter membrane constructed through physical-chemical synergistic crosslinking, its preparation method, and its applications. This method employs a co-crosslinking preparation approach that combines ethanol-induced macromolecular self-assembly physical crosslinking with glutaraldehyde chemical crosslinking. Using renewable gelatin and carboxymethyl chitosan as biomass structural precursors, it achieves independent control of the membrane's external surface densification and internal pore structure. This overcomes the limitations of previous water-soluble filter membranes that relied solely on single physical crosslinking, providing a highly efficient, safe, and adaptable material platform for the proactive control of bioaerosol pollution.

[0004] The technical solution of this invention is as follows: Firstly, a water-soluble composite air filter membrane (GGFM) constructed through physicochemical co-crosslinking is disclosed. This membrane is a bio-based water-soluble composite air filter membrane, prepared using gelatin and carboxymethyl chitosan (CMCS) as raw materials and glutaraldehyde (GA) as a surface crosslinking enhancer through a synergistic process of physical crosslinking and surface chemical crosslinking. The membrane thickness is 0.3-0.5 mm. This physicochemical co-crosslinking mode achieves independent control of the membrane's microstructure in two dimensions: adjusting the amount of GA achieves directional densification of the membrane surface, preventing particle shedding and structural breakage; adjusting the amount of ethanol added to the initial membrane solution effectively controls the porous network structure inside the membrane, endowing it with a water-soluble honeycomb-like hierarchical porous structure, achieving a balance between retention efficiency and permeability. Through the integrated approach of external surface reinforcement and internal pore control, the GGFM membrane simultaneously possesses excellent particle interception efficiency, low airflow resistance, and outstanding water solubility.

[0005] Secondly, a method for preparing the aforementioned physicochemically cross-linked water-soluble composite air filter membrane is disclosed, comprising the following steps: 1) Preparation of membrane solution: Add carboxymethyl chitosan and gelatin to water and mix. Stir at 55-65℃ until completely dissolved. Add ethanol and continue stirring until the solution is clear. Cool to room temperature to obtain membrane solution. 2) Physical cross-linking to construct a porous structure: The membrane solution is transferred into a petri dish, and ethanol is added to induce the precipitation and self-assembly of carboxymethyl chitosan and gelatin biomolecules. A white precipitate with a porous structure is formed at the bottom of the petri dish. The white precipitate gradually increases and cross-links with each other. After standing for 3-5 hours, a continuous physical solid membrane is obtained. 3) Surface chemical crosslinking modification: Glutaraldehyde ethanol solution is added to the petri dish to chemically crosslink the physical solid film. The reaction is continued for 1-2 hours. The supernatant is discarded and the unreacted glutaraldehyde is washed away. 4) Vacuum drying: The modified and washed filter membrane is vacuum dried to obtain the water-soluble composite air filter membrane. The front side of the obtained composite air filter membrane GGFM presents a unique multi-layer honeycomb structure with an interconnected micro-nano porous network, while the back side presents a relatively dense porous structure. The entire membrane contains a continuous interpenetrating three-dimensional micro-nano structure.

[0006] Preferably, in step 1), the mass ratio of carboxymethyl chitosan to gelatin is (0.1-0.4):(0.3-1.0).

[0007] Preferably, in step 1), the mass-to-volume ratio of the total mass of carboxymethyl chitosan and gelatin to the volume of ethanol added is (0.1-0.6) g: 10 mL, which is used to regulate the size of the biomacromolecule aggregates and the internal porous network structure, thereby adjusting the porosity, interception efficiency and airflow resistance of the filter membrane.

[0008] Preferably, the mass concentration of the glutaraldehyde ethanol solution in step 3) is 0.02-0.09%, more preferably 0.05%. Glutaraldehyde achieves selective curing and structural reinforcement of the filter membrane surface by forming a stable Schiff base structure (-C=N-) covalently crosslinking with the primary amine groups on the gelatin and carboxymethyl chitosan chains.

[0009] Preferably, the vacuum drying temperature in step 4) is 25-35℃ and the time is 2-3h.

[0010] Thirdly, the application of the aforementioned filter membrane is disclosed for the filtration, sampling, capture, and quantitative detection of bioaerosols. Specifically, the filter membrane efficiently intercepts and collects airborne microorganisms under airflow. After sampling, its water solubility allows for direct transfer to agar plates. Upon contact with moist agar, the filter membrane rapidly absorbs water and spontaneously disintegrates, achieving complete release of the captured microorganisms. The composite air filter membrane GGFM possesses excellent water solubility. After sampling, the filter membrane can be directly transferred to the surface of an agar plate. Upon contact with moist agar, it rapidly absorbs water and spontaneously disintegrates, achieving non-destructive release and uniform inoculation of captured microorganisms, with a microorganism recovery rate approaching 100%. The airborne microorganisms include Gram-negative and Gram-positive bacteria. The filter membrane achieves a 99.3% retention efficiency for aerosol particles and a 99.7% capture efficiency for airborne microorganisms. The capture amounts of Escherichia coli and Staphylococcus aureus are 2.9 times that of the traditional impaction method and 11.5 times that of the gravity sedimentation method, respectively.

[0011] Preferably, the filter membrane is used in conjunction with the standard plate count method to achieve the maximum transfer limit of captured microorganisms without elution after sampling, and the microorganisms maintain high cell viability. The filter membrane is used in conjunction with a rapid total bacterial count test strip. After sampling, the filter membrane is dissolved in sterile phosphate buffer to form a bacterial suspension, which is then transferred to the test strip for rapid 24-hour incubation and counting. This shortens the detection cycle and improves the timeliness of monitoring. Compared with the traditional agar plate method (48 hours), the detection cycle is not only halved, but the accuracy of quantitative detection is also maintained.

[0012] Preferably, the filter membrane is used in conjunction with live / dead cell fluorescence staining. After sampling, the filter membrane is dissolved to release the captured microorganisms. After staining with fluorescent dye, confocal laser scanning microscopy imaging analysis is performed to assess the activity status, morphological integrity, and community composition of the captured microorganisms.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention proposes a method for preparing a water-soluble composite air filter membrane through synergistic co-crosslinking of physical and chemical processes, achieving precise control over both the densification of the outer surface and the porosity of the internal structure of the membrane. By adjusting the amount of glutaraldehyde (GA), the membrane surface can be selectively enhanced, transforming the loose and uneven aggregate structure into a dense and uniform continuous surface; by adjusting the amount of ethanol added, the internal porous structure can be controlled, transforming it from a fine and compact aggregate morphology into a loose and permeable porous network structure. Through the synergistic co-crosslinking of physical and chemical processes, the membrane achieves an optimal balance between interception efficiency, airflow resistance, and dissolution rate.

[0014] 2. This invention uses gelatin and carboxymethyl chitosan as fully bio-based raw materials, providing a feasible green route for developing high-performance, fully degradable, water-soluble filtration membranes. The prepared GGFM filtration membrane exhibits excellent biocompatibility and environmental compatibility. It shows no cytotoxicity against *Escherichia coli* and *Staphylococcus aureus* within a wide concentration range (0-30 mg / mL), and bacterial proliferation is unaffected under co-culture conditions. In humid environments, GGFM rapidly absorbs water, dissolves, and infiltrates the soil matrix, achieving complete biodegradation within 48 hours, resulting in a green and pollution-free process.

[0015] 3. The GGFM filter membrane prepared by this invention exhibits significantly superior capture performance compared to traditional gravity sedimentation and impaction capture methods, and can be seamlessly integrated with various downstream microbial testing and analysis platforms. Specifically, when combined with the standard plate count method, the GGFM filter membrane achieves near 100% recovery of captured microorganisms and completes microbial detection within 48 hours, effectively avoiding colony overlap; when combined with fluorescence staining, it enables visual observation of the morphology and species of captured microorganisms; and when combined with rapid colony test strips, it allows for rapid detection of captured microorganisms within 24 hours. 4. The filter membrane of this invention can achieve a 99.3% retention efficiency for aerosol particles and a 99.7% capture efficiency for airborne microorganisms. The capture capacity for Escherichia coli and Staphylococcus aureus can reach 2.9 times that of the traditional impaction method and 11.5 times that of the gravity sedimentation method, respectively. Attached Figure Description

[0016] Figure 1 A photograph of the GGFM water-soluble composite air filter membrane prepared in Example 1 of this invention.

[0017] Figure 2 Photos of GGFM water-soluble composite air filter membranes of different sizes prepared for Example 2 of the present invention and actual objects cut into different shapes.

[0018] Figure 3 Photographs show the preparation process of a gelatin and carboxymethyl chitosan mixed solution through ethanol-induced phase separation and GA surface crosslinking to form a final film.

[0019] Figure 4 The image shows a SEM image of the GGFM filter membrane prepared in Example 2 of this invention, where (A) is the front side, (B) is the back side, and (C) is the cross-section.

[0020] Figure 5 This is a photograph showing the process of a GGFM filter membrane rapidly absorbing water, swelling, and dissolving after being placed in water.

[0021] Figure 6 This is a three-dimensional structural disintegration SEM image of a GGFM filter membrane after localized water contact.

[0022] Figure 7 This is a photograph of the process after a pure gelatin solution undergoes ethanol-induced phase separation.

[0023] Figure 8 This is a photograph of the process after pure carboxymethyl chitosan solution undergoes ethanol-induced phase separation.

[0024] Figure 9 The photo shows the preparation process of a filter membrane obtained by physical crosslinking of a mixture of gelatin and carboxymethyl chitosan through ethanol-induced phase separation, without chemical crosslinking of the GA surface, and by direct drying.

[0025] Figure 10 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 3.

[0026] Figure 11 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 4.

[0027] Figure 12 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 5.

[0028] Figure 13 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 6.

[0029] Figure 14 This is a comparison diagram of the solubility between the GGFM filter membrane prepared in Example 2 and the filter membrane prepared in Comparative Example 6.

[0030] Figure 15 SEM images of the front and back microstructures of the GGFM filter membrane prepared in Comparative Example 7.

[0031] Figure 16 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 8.

[0032] Figure 17 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 9.

[0033] Figure 18 SEM images of the front and back microstructures of the GGFM filter membrane prepared for Comparative Example 10.

[0034] Figure 19 Comparative photos of the GGFM filter membrane prepared for Comparative Example 10 and filter membranes prepared with other amounts of ethanol addition.

[0035] Figure 20 For the biocompatibility verification of the GGFM filter membrane prepared in Example 2 of the present invention, (A) is the cytotoxicity test under co-incubation, and (B) is the growth curve of the filter membrane and bacteria under co-culture.

[0036] Figure 21 This is a diagram verifying the degradability of the GGFM filter membrane prepared in Example 2 of the present invention in soil.

[0037] Figure 22 The images show the SEM images of the front (A) and back (B) microstructures of the GGFM filter membrane prepared in Example 2 of this invention after front sampling.

[0038] Figure 23 This is a comparison of the colony results of the GGFM filter membrane prepared in Example 2 of the present invention after sampling and culturing from the front and back sides at different aerosol concentrations.

[0039] Figure 24 SEM images of the microstructure of the GGFM filter membrane prepared in Example 2 of this invention after reverse sampling (A) and front (B).

[0040] Figure 25 The images show SEM images of microorganisms captured by the GGFM filter membrane prepared in Example 2 of this invention. (A) shows Escherichia coli, and (B) shows Staphylococcus aureus.

[0041] Figure 26 The images show the live / dead fluorescent staining of microorganisms captured by the GGFM filter membrane prepared in Example 2 of this invention under a laser confocal microscope. (A) is Escherichia coli, and (B) is Staphylococcus aureus.

[0042] Figure 27 The image shows a comparison of the number of microorganisms captured by the GGFM filter membrane prepared in Example 2 of this invention under different aerosol concentrations with traditional sampling methods (gravity sedimentation and impaction methods). (A) shows the sampling under Escherichia coli aerosol, and (B) shows the sampling under Staphylococcus aureus aerosol.

[0043] Figure 28 The graph shows the correspondence between the detection results of the agar plate culture method and the 3M test strip culture method when the GGFM filter membrane prepared in Example 2 of this invention is involved. Figure 29 The image shows a comparison of the colony counts of microorganisms captured by the GGFM filter membrane prepared in Example 2 of this invention at different aerosol concentrations, after detection by the agar plate culture method and the 3M test strip culture method. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0045] Example 1 The method for preparing the water-soluble composite air filter membrane includes the following steps: 1) Preparation of membrane solution: Add 0.1g carboxymethyl chitosan and 0.4g gelatin to 10mL of deionized water and mix. Stir at 60℃ until completely dissolved to form a homogeneous biopolymer solution. Add 10mL of ethanol and continue stirring until the solution is clear. Cool naturally to room temperature to obtain the membrane solution. 2) Physical cross-linking to construct a porous structure: The membrane solution (1 mL) was transferred into a horizontally placed petri dish, and 2.0 mL of ethanol was added to induce the precipitation and self-assembly of carboxymethyl chitosan and gelatin biomacromolecules. A white precipitate with a porous structure was formed at the bottom of the petri dish. The white precipitate gradually increased and cross-linked with each other. After standing for 4 h, a continuous physical solid membrane was obtained. 3) Surface chemical crosslinking modification: 1 mL of 0.05% glutaraldehyde ethanol solution was added to the petri dish. Glutaraldehyde reacted with the amino groups on the gelatin and carboxymethyl chitosan chains to form a stable covalent crosslinking network to chemically crosslink the physical solid film. The reaction was continued for 1.5 h. The supernatant was discarded and the unreacted glutaraldehyde was washed away. 4) Vacuum drying: The modified and washed filter membrane is vacuum dried at 30°C for 2 hours to obtain the water-soluble composite air filter membrane.

[0046] Figure 1 This is a photo of the water-soluble composite air filter membrane GGFM after vacuum drying. The membrane thickness is 0.3mm, and the edges of the filter membrane are clear and regular, presenting a smooth and uniform white appearance.

[0047] Example 2 The method for preparing the water-soluble composite air filter membrane includes the following steps: 1) Preparation of membrane solution: Add 0.2g carboxymethyl chitosan and 0.4g gelatin to 10mL of deionized water and mix. Stir at 60℃ until completely dissolved to form a homogeneous biopolymer solution. Add 10.0mL of ethanol and continue stirring until the solution is clear. Cool naturally to room temperature to obtain the membrane solution. 2) Physical cross-linking to construct a porous structure: The membrane solution (1 mL) was transferred into a horizontally placed petri dish, and 2.0 mL of ethanol was added to induce the precipitation and self-assembly of carboxymethyl chitosan and gelatin biomacromolecules. A white precipitate with a porous structure was formed at the bottom of the petri dish. The white precipitate gradually increased and cross-linked with each other. After standing for 4 h, a continuous physical solid membrane was obtained. 3) Surface chemical crosslinking modification: 1 mL of 0.05% glutaraldehyde ethanol solution was added to the petri dish. Glutaraldehyde reacted with the amino groups on the gelatin and carboxymethyl chitosan chains to form a stable covalent crosslinking network to chemically crosslink the physical solid film. The reaction was continued for 1.5 h. The supernatant was discarded and the unreacted glutaraldehyde was washed away. 4) Vacuum drying: The modified and washed filter membrane is vacuum dried at 30°C for 2 hours to obtain the water-soluble composite air filter membrane.

[0048] Figure 2 This is a photo of the water-soluble composite air filter membrane GGFM after vacuum drying. The membrane thickness is 0.35 mm. Thanks to the stable preparation route of physical-chemical synergistic crosslinking, filter membranes of different sizes can be easily prepared and cut into arbitrary shapes, including triangles, rectangles and rhombuses, according to the needs of different application scenarios. Figure 3 The process of forming a solid membrane through phase separation after mixing carboxymethyl chitosan (CMCS) and gelatin was demonstrated, as well as the changes in the membrane structure in the petri dish after the addition of GA solution. Through physical cross-linking and then chemical surface cross-linking, a complete and stable membrane structure was finally obtained. Figure 4SEM analysis revealed that the GGFM filter membrane exhibits a unique multi-layered honeycomb structure on its front side and a relatively dense porous structure on its back side, stemming from the gravitational effect during the porous structure construction process. Cross-sectional analysis confirmed the existence of a continuously interconnected three-dimensional micro-nano structure network within the membrane, ensuring smooth airflow while providing ample adsorption loading sites for airborne particulate pollutants and microorganisms. Furthermore, the GGFM filter membrane is completely water-soluble; when placed in water, it rapidly absorbs water, swells, and disintegrates into a colorless, clear solution. Figure 5 ).like Figure 6 As shown, the GGFM filter membrane can trigger rapid structural disintegration of the three-dimensional porous network when it comes into local water contact, while the parts that are not in contact with water maintain structural integrity.

[0049] Comparative Example 1 Unlike Example 2, in this comparative example, only gelatin was used as a raw material during the preparation of the membrane solution. After complete dissolution, the porous structure was directly induced by ethanol. The resulting filter membrane structure is as follows: Figure 7 As shown, only dispersed aggregated particles are present inside the petri dish, and they cannot form an integrated filtration membrane structure. This indicates the necessity of the presence of carboxymethyl chitosan (CMCS) in the initial membrane solution preparation process.

[0050] Comparative Example 2 Unlike Example 2, in this comparative example, only carboxymethyl chitosan (CMCS) was used as a raw material during the preparation of the membrane solution. After complete dissolution, it was directly subjected to ethanol-induced porous structure shaping. The resulting filter membrane structure is as follows: Figure 8 As shown, irregular large aggregates formed in the middle of the plate, making it impossible to form a uniform and flat filtration membrane structure. This indicates the necessity of the presence of gelatin in the initial membrane solution preparation process.

[0051] Comparative Example 3 Unlike Example 2, in this comparative example, after the filter membrane is formed inside the petri dish, it is not chemically cross-linked with glutaraldehyde (GA) but directly vacuum dried. The remaining preparation methods and steps are the same as in Example 2. The membrane material prepared under these circumstances is as follows: Figure 9 As shown, although physical cross-linking under ethanol-induced phase separation can form a preliminary filter membrane, the insufficient bonding force between the aggregate particles constituting the filter membrane prevents the formation of a dense and continuous surface layer. This leads to severe particle shedding during subsequent liquid removal. The resulting filter membrane is not only thin (0.28 mm) but also exhibits poor structural stability and is prone to breakage. SEM images show that its surface is a loose aggregate structure filled with irregular pores. Figure 10 ).

[0052] Comparative Example 4 Unlike Example 2, in this comparative example, after the filter membrane was formed inside the petri dish, a low concentration of GA (0.01%) was used to chemically cross-link the surface of the filter membrane. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 11 As shown, the addition of GA effectively improves the structural stability of the filter membrane, making its surface structure denser and more uniform, gradually filling and repairing surface pores, and increasing the membrane thickness to 0.32 mm. GA-induced chemical crosslinking significantly enhances the densification of the filter membrane surface microstructure, resulting in a filtration pressure drop of 110 mbar.

[0053] Comparative Example 5 Unlike Example 2, in this comparative example, after the filter membrane was formed inside the petri dish, a higher concentration of GA (0.1%) was used to chemically cross-link the surface of the filter membrane. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 12 As shown, with the gradual increase of GA concentration, the stability of the filter membrane structure continued to improve, and the structure remained intact after drying, while the membrane thickness also increased to 0.38 mm. GA-induced chemical cross-linking significantly enhanced the densification of the microstructure on the filter membrane surface, slightly reduced air permeability, and resulted in a filtration pressure drop of 120 mbar.

[0054] Comparative Example 6 Unlike Example 2, in this comparative example, after the filter membrane was formed inside the petri dish, a high concentration of GA (0.2%) was used to chemically cross-link the surface of the filter membrane. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 13 As shown, excessive GA-induced chemical cross-linking completely altered the original porous surface microstructure of the filter membrane, revealing a dense villous structure. The introduction of high-concentration GA led to excessive cross-linking of the membrane surface, changing the membrane color from white to light yellow. Simultaneously, the membrane thickness increased to 0.40 mm, air permeability decreased further, and the filtration pressure drop increased to 130 mbar. This excessive surface modification caused the membrane to completely lose its water solubility; it could not dissolve even after immersing in water and prolonged agitation and sonication. Figure 14 Meanwhile, the microstructure on the back of the filter membrane remains almost unchanged compared to before chemical cross-linking. This is mainly due to the protective effect of the substrate, which limits the chemical modification to the surface of the filter membrane, allowing the original porous internal network constructed by gelatin and CMCS to persist.

[0055] Comparative Example 7 Unlike Example 2, in the membrane solution preparation process, after CMCS and gelatin formed a homogeneous biopolymer solution, anhydrous ethanol was not added, and the solution was directly cooled to room temperature to obtain the membrane solution. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 15As shown, the appearance of the filter membrane is not much different from that of the filter membrane obtained in Example 2, but the SEM image shows that the microstructure of the filter membrane surface is significantly different. In particular, the back network structure is particularly dense, and the size of the aggregate particles constituting the filter membrane structure is significantly reduced. At this time, the membrane thickness is only 0.26 mm, the air permeability is poor, and the filtration pressure drop is 280 mbar.

[0056] Comparative Example 8 Unlike Example 2, in the membrane solution preparation process, after CMCS and gelatin formed a homogeneous biopolymer solution, only a small amount of anhydrous ethanol (5 mL) was added, then stirred evenly and cooled to room temperature to obtain the membrane solution. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 16 As shown, the appearance of the filter membrane remained unchanged, but the SEM image showed that the microstructure of the filter membrane changed significantly. The surface pores were significantly enlarged, the density of the back network structure decreased, and the size of the aggregate particles constituting the filter membrane structure was significantly increased. At this time, the membrane thickness increased to 0.34 mm, but the air permeability was significantly improved and the pressure drop decreased to 170 mbar. Comparative Example 9 Unlike Example 2, in the membrane solution preparation process, after CMCS and gelatin formed a homogeneous biopolymer solution, a large amount of anhydrous ethanol (15 mL) was added, then stirred evenly and cooled to room temperature to obtain the membrane solution. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 17 As shown, the appearance of the filter membrane remained unchanged, but the SEM image revealed significant changes in its microstructure. Surface pores enlarged further, particularly on the back side, and the particle packing density decreased markedly. Simultaneously, the size of the aggregated particles constituting the membrane structure coarsened significantly. However, the membrane thickness decreased to 0.32 mm, primarily due to the severe disruption of particle adhesion by ethanol. Even with GA surface cross-linking, particle loss still occurred. At this point, the membrane's permeability significantly improved, and the filtration pressure drop decreased to 90 mbar. Comparative Example 10 Unlike Example 2, in the membrane solution preparation process, after CMCS and gelatin formed a homogeneous biopolymer solution, excess anhydrous ethanol (20 mL) was added, then stirred until homogeneous and cooled to room temperature to obtain the membrane solution. The remaining preparation methods and steps were the same as in Example 2. The microstructure of the membrane material prepared under this condition is as follows: Figure 18As shown, only broken filter membranes were obtained after drying. This is because the addition of excessive ethanol severely damaged the adhesion between particles. Even with the surface cross-linking of GA, a large amount of particles were still lost, and the membrane thickness further decreased to 0.29 mm, with a filtration pressure drop of only 50 mbar. SEM images show that both the front and back sides of the filter membrane are microscopically covered with large-sized pores, and the aggregate particles constituting the filter membrane structure are severely coarsened in size. Figure 19 This demonstrates that the effect of ethanol addition on membrane structure regulation permeates the entire membrane matrix, not just the membrane surface. Adding ethanol to the initial membrane solution can completely alter the packing pattern and size of the membrane matrix, thereby simultaneously changing the internal porous network structure and external morphology.

[0057] Comparative Example 11 Unlike Example 2, in step 1) of this comparative example, ethanol was replaced with an equal volume of glycerol, while the rest of the preparation method was the same as in Example 2. Although glycerol is also soluble in water, it has high viscosity, which slows down the physical cross-linking process of the filter membrane, affects the formation of the filter membrane, and makes it difficult to remove in subsequent washing, interfering with subsequent tests.

[0058] Example 3: Biocompatibility and Environmental Compatibility Assessment After completely dissolving the GGFM prepared in Example 2, membrane solutions of different concentrations (0-30 mg / mL) were prepared and then reacted with Escherichia coli (E. coli). E. coli ) and Staphylococcus aureus ( S. aureus After co-incubation, colony counting is performed. For example... Figure 20 As shown in Figure A, within the test concentration range of 0-30 mg / mL, GGFM did not exhibit significant cytotoxicity against either bacterium. Further co-culturing with the bacteria and monitoring their growth curves showed that the presence of GGFM did not affect normal bacterial proliferation, confirming the excellent microbial compatibility of the filtration membrane. Figure 20 (B) The results showed that the growth curves of the two strains in the GGFM-containing medium were highly consistent with those of the blank control group. In the environmental degradation experiment, GGFM dissolved and infiltrated the soil matrix immediately after absorbing water, and was completely biodegraded within 48 hours with no visible residue, while the commercial mixed cellulose (MCE, purchased from Shanghai Xinya Purification Device Factory) filter membrane maintained its structural integrity without significant changes. Figure 21 ).

[0059] Example 4: Evaluation of Bioaerosol Capture Performance In a bioaerosol simulation chamber, bacterial suspensions of different bacteria were atomized to create bioaerosol environments of varying concentrations for capture and detection experiments. Specifically, the water-soluble composite filter membrane GGFM prepared in Example 2 was cut into 25mm diameter circles and installed on an air filter sampler for bioaerosol collection (sampling flow rate 10L / min, sampling time 5min). SEM characterization of the membrane's morphology before and after sampling revealed that the membrane surface became significantly rougher after bioaerosol exposure, with abundant particulate matter uniformly filling the interconnected porous network. Figure 22 A). In contrast, the back side of the non-sampled filter membrane remained clean, and the overall porous structure of the filter membrane remained intact, without problems such as pore collapse or structural damage. This indicates that the membrane matrix structure is stable, can effectively filter air, and confine captured particles to the filter surface. Figure 22 B). Furthermore, although the front and back morphologies of the GGFM filter membrane differ significantly, both sides can be used as sampling surfaces for capturing airborne microorganisms, and the retention efficiency for airborne particulate matter remains consistent. For example... Figure 23 As shown, under different aerosol concentrations, the number of microorganisms captured on the front (+) and back (-) sides of the filter membrane remained consistent within the same sampling time. SEM images show that even after sampling the back side, abundant particulate matter was observed accumulating within the porous network, while the non-sampled front side of the filter membrane remained clean. Figure 24 The above results indicate that the capture and enrichment of bioaerosols by GGFM filters mainly depends on the deep filtration under the porous network structure inside the filter membrane, rather than solely on the porous structure on the surface of the filter membrane. Airborne microorganisms can be effectively captured and trapped when passing through any surface.

[0060] Leveraging the water solubility of the filter membrane, a double-layer membrane stacking strategy can accurately determine the capture efficiency of the filter membrane for airborne microorganisms. When two filter membranes are stacked together, airborne microorganisms not intercepted by the upper membrane will continue to be intercepted by the lower membrane. The microbial capture efficiency of the filter membrane can be calculated by counting the number of microorganisms captured by the upper and lower membranes. After the filter membrane sampling is completed, the upper and lower membranes are simultaneously transferred to petri dishes for dispersed culture. By statistically calculating the number of microbial colonies captured by the two membranes, the average capture efficiency of the GGFM filter membrane for airborne microorganisms is 99.7±0.21% (n=3), while the capture efficiency of the commercial MCE membrane under the same conditions is only 99.5±0.28% (n=3). The difference between the two sets of data is statistically significant (*p<0.05). In addition, the GGFM filter membrane also has the property of "green capture". Morphological observation of the microorganisms captured by the filter membrane under SEM showed that the microorganisms maintained an intact morphological structure, and no membrane damage was found. Figure 25 Live / dead fluorescence staining imaging was performed using laser confocal microscopy, and the results showed that all captured microorganisms exhibited a green fluorescence signal characteristic of live cells. Figure 26 ).

[0061] The water-soluble composite air filter membrane prepared in Example 2 was used to filter, sample, capture, and quantitatively detect bioaerosols. Specifically, this involved: [the process was carried out] through 10... 4 -10 6 Filtration sampling was performed within the bioaerosol concentration range of CFU / mL, and compared with traditional impactor and sedimentation methods. The results showed that the GGFM filter membrane captured significantly more microorganisms than either of these two traditional methods. Figure 27 At high aerosol concentrations, the GGFM filter membrane captures 2.9 times more microorganisms than the impaction method and 11.5 times more than the gravity sedimentation method. Compared to passive gravity sedimentation, the GGFM filter membrane significantly improves the collection efficiency of airborne microorganisms, making it a highly efficient and active sampling method. Compared to the impaction capture method, microorganisms captured by the GGFM filter membrane can be uniformly coated onto petri dishes for colony cultivation, effectively avoiding problems such as colony aggregation and coverage, thus improving detection accuracy. Furthermore, the microorganisms captured by the GGFM filter membrane are compatible with various subsequent microbial detection methods. When the captured microorganisms are released into water to form a bacterial suspension, they can be further transferred to a rapid total colony count test strip for detection. The rapid total colony count test strip was purchased from 3M Company in the United States. Because the test strip is pre-filled with indicators and sufficient nutrients, it only requires 24 hours of incubation to produce a clear colony count. By culturing and detecting bacterial suspensions of a defined concentration and those mixed with GGFM on agar plates and 3M test strips, respectively, the compatibility between GGFM and the test strips can be effectively determined. Figure 28 As shown, there is a highly consistent linear correlation between the colony detection results of the agar plate method and the 3M test strip method involving GGFM filter membranes, and the detection results are consistent for different strains, indicating that the filter membrane and the test strip are effectively compatible and do not interfere with each other. After sampling, the filter membrane and the captured microorganisms were transferred together to PBS for dissolution and dispersion, and then transferred to the test strip for 24 hours of incubation before colony counting. Compared with the traditional agar plate method, the strategy of combining GGFM filter membrane sampling and 3M test strip incubation can accelerate the detection speed, shorten the contamination latency window, and is of great significance for the monitoring, early warning, and timely control of airborne microbial pollution.

[0062] This invention establishes a synergistic physical-chemical co-crosslinking strategy for the preparation of water-soluble biomass air filter membranes by combining physical crosslinking under ethanol-induced phase separation with surface chemical crosslinking under glutaraldehyde. First, using renewable gelatin and carboxymethyl chitosan as raw materials, a honeycomb-like hierarchical porous network is constructed inside the water-soluble filter membrane through ethanol-induced phase separation. Then, using glutaraldehyde as a chemical crosslinking agent, a covalently crosslinked network is directionally constructed on the membrane surface through a Schiff base reaction, thereby reinforcing and encapsulating the surface porous network and stabilizing the filter membrane structure. This physical-chemical co-crosslinking preparation strategy enables multi-dimensional control of the filter membrane structure. By controlling the amount of GA, the degree of curing on the filter membrane surface can be effectively controlled; by controlling the amount of ethanol added to the membrane solution, the porous crosslinked network inside the filter membrane can be deeply controlled. The combined effect of these two strategies achieves synergistic optimization of external surface reinforcement and internal pore network. The prepared GGFM filter membrane possesses high capture efficiency, low airflow resistance, excellent biocompatibility, complete water solubility, and environmental degradability. Furthermore, it can be seamlessly integrated with various downstream detection platforms, including standard plate methods, rapid test strips, and fluorescent staining methods, demonstrating superior performance in bioaerosol capture. In summary, this invention not only provides a novel water-soluble air filter membrane and its preparation and control method, but also offers a matching continuous sampling-detection process. This is of great significance for constructing high-performance bioaerosol monitoring systems for public health and indoor environmental safety applications.

[0063] Although the present invention has been described in detail by way of preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A water-soluble composite air filter membrane constructed by physicochemical synergistic crosslinking, characterized in that, The filter membrane is a bio-based water-soluble composite air filter membrane, made from gelatin and carboxymethyl chitosan as raw materials, and glutaraldehyde as a surface crosslinking enhancer. It is prepared through a synergistic process of physical crosslinking and surface chemical crosslinking, and the membrane thickness is 0.3-0.5 mm.

2. The method for preparing a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking as described in claim 1, characterized in that, Includes the following steps: 1) Preparation of membrane solution: Add carboxymethyl chitosan and gelatin to water and mix. Stir at 55-65℃ until completely dissolved. Add ethanol and continue stirring until the solution is clear. Cool to room temperature to obtain membrane solution. 2) Physical cross-linking to construct a porous structure: The membrane solution is transferred into a petri dish, and ethanol is added to induce the precipitation and self-assembly of carboxymethyl chitosan and gelatin biomolecules. A white precipitate with a porous structure is formed at the bottom of the petri dish. The white precipitate gradually increases and cross-links with each other. After standing for 3-5 hours, a continuous physical solid membrane is obtained. 3) Surface chemical crosslinking modification: Glutaraldehyde ethanol solution is added to the petri dish to chemically crosslink the physical solid film. The reaction is continued for 1-2 hours. The supernatant is discarded and the unreacted glutaraldehyde is washed away. 4) Vacuum drying: The modified and washed filter membrane is vacuum dried to obtain the water-soluble composite air filter membrane.

3. The method for preparing a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking as described in claim 2, characterized in that, In step 1), the mass ratio of carboxymethyl chitosan to gelatin is (0.1-0.4):(0.3-1.0).

4. The method for preparing a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking as described in claim 2, characterized in that, In step 1), the mass-to-volume ratio of the total mass of carboxymethyl chitosan and gelatin to the volume of ethanol added is (0.1-0.6) g: 10 mL.

5. The method for preparing a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking as described in claim 2, characterized in that, In step 3), the mass concentration of the glutaraldehyde ethanol solution is 0.02-0.09%, preferably 0.05%.

6. The method for preparing a water-soluble composite air filter membrane constructed by physical-chemical synergistic crosslinking as described in claim 2, characterized in that, In step 4), the vacuum drying temperature is 25-35℃ and the time is 2-3 hours.

7. The application of the filter membrane as described in claim 1, characterized in that, Used for filtering, sampling, capturing, and quantitatively detecting bioaerosols, specifically: the filter membrane efficiently intercepts and collects airborne microorganisms under the action of airflow, and after sampling, it is directly transferred to an agar plate using its water solubility. After the filter membrane comes into contact with the moist agar, it quickly absorbs water and spontaneously disintegrates, thereby achieving the complete release of the captured microorganisms.

8. The application of the filter membrane as described in claim 7, characterized in that, When used in conjunction with the standard plate count method, the filter membrane can achieve the maximum transfer limit of captured microorganisms without elution after sampling, and all microorganisms maintain high cell viability. When used in conjunction with a rapid total colony count test strip, the filter membrane is dissolved in sterile phosphate buffer to form a bacterial suspension after sampling, and then transferred to the test strip for rapid 24-hour culture and counting, which shortens the detection cycle and improves the timeliness of monitoring.

9. The application of the filter membrane as described in claim 7, characterized in that, The filter membrane is used in conjunction with live / dead cell fluorescence staining. After sampling, the filter membrane is dissolved to release the captured microorganisms. After staining with fluorescent dye, confocal laser scanning microscopy imaging analysis is performed to assess the activity status, morphological integrity, and community composition of the captured microorganisms.

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