Photo-thermal antibacterial and pH-responsive hydrogel film as well as preparation and application thereof

Abstract

The invention belongs to the field of high polymer materials, and particularly relates to a photo-thermal antibacterial and pH-responsive hydrogel film as well as preparation and application thereof. The hydrogel film contains polysaccharide, polyphenol and metal ions, the polysaccharide and the polyphenol form a stable gel network through hydrogen bonds and electrostatic interaction, the metal ions are embedded into the gel network through coordination with the polyphenol and form a metal polyphenol network, mechanical and pH response performance is enhanced, the hydrogel film is endowed with a photothermal effect, and the hydrogel film has a good application prospect. The defects of an existing natural polysaccharide-based film in the aspects of mechanical performance, antibacterial ability, photo-thermal conversion efficiency, environmental stability, intelligent monitoring and the like are overcome. The method is suitable for application and development in the fields of food packaging, medical health, intelligent monitoring and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to a photothermal antibacterial and pH-responsive hydrogel membrane and its preparation and application. Background Technology

[0002] With the fast pace of life, meat products are playing an increasingly important role in modern diets due to their convenience and nutritional value. However, these cooked meat products typically undergo heat sterilization during processing, lack the protection of preservatives, and are high in protein and fat. They are highly susceptible to microbial growth and lipid oxidation under refrigeration conditions, leading to increased pH, deterioration in texture, off-flavors, and decreased sensory quality, significantly shortening shelf life and posing potential food safety hazards. Cooked chicken breast, in particular, is highly nutritious, but rapid microbial proliferation and enzymatic degradation cause adverse changes in pH, texture, and sensory quality, shortening its shelf life. Therefore, developing packaging materials that can effectively inhibit bacteria, delay spoilage, and provide visual monitoring of food freshness is of great significance for improving the storage safety and quality of cooked food products.

[0003] In recent years, with the increasing demand for green and biodegradable packaging materials, research on functional films based on natural polymers has gradually become a hot topic. Chitosan (CS) and its derivative carboxymethyl chitosan (CMCS) are widely used in food preservation, medical dressings, and drug-controlled release carriers due to their good biocompatibility, film-forming properties, and natural antibacterial properties. Chitosan and its derivative films are prepared using existing casting methods. First, chitosan or its derivatives are dissolved in acidic aqueous solution, then plasticizers are added to improve flexibility. The film is then cast and dried at room temperature. Crosslinking agents can be added as needed to form a chemical crosslinked structure, resulting in polysaccharide-based films with certain mechanical and antibacterial properties. For example, a multifunctional double-layer active edible film with a hydrophobic ethyl cellulose outer layer and a hydrophilic gelatin / carboxymethyl chitosan inner layer, produced by layer-by-layer casting, exhibits certain antibacterial properties, but such films have high ultraviolet light transmittance. Chitosan swells easily in water, and its physical cross-linking effect is weak, resulting in poor water resistance and decreased wet mechanical properties of the film. Commonly used chemical cross-linking methods require the addition of cross-linking agents such as glutaraldehyde, which brings potential toxicity and biosafety hazards. Pure CMCS films have poor inhibitory effect on Gram-negative bacteria, which limits their application in the food packaging field, especially their direct application in high-humidity food environments.

[0004] Tannic acid (TA) is a polyphenolic natural compound containing multiple phenolic hydroxyl groups. It can form stable complexes with proteins, metal ions, or polysaccharides, exhibiting antibacterial, antioxidant, and metal ion chelating abilities. Polyphenols primarily bind to polysaccharides through weak interactions such as hydrogen bonding and π-π stacking. Due to the lack of effective three-dimensional cross-linking, the resulting structures lack stability and struggle to form durable network structures, limiting the improvement in film mechanical strength and barrier properties, making it difficult to meet high-requirement packaging or antibacterial applications. When modifying natural polysaccharides with tannic acid, tannic acid is first mixed with natural polymers such as chitosan, gelatin, and cellulose. Physical cross-linking is then formed using hydrogen bonds and hydrophobic interactions between polyphenol molecules or between polyphenols and polysaccharides. Some studies introduce metal ions (such as Fe). 3+ Al 3+ To promote further cross-linking of polyphenol molecules, modified films with antioxidant, antibacterial, and UV-blocking functions can be prepared. For example, multifunctional polysaccharide-based hydrogels prepared from quaternized chitin and tannic acid have good antibacterial and antioxidant activity and bioavailability.

[0005] Through TA and metal ions (such as Fe) 3+ The formation of metal polyphenol networks (MPNs) can enhance the mechanical strength and stability of materials. Previous studies have utilized tannic acid (TA) and Fe... 3+ Ions self-assemble to form metal polyphenol networks, which are then used in the preparation of photothermal antibacterial hydrogel spheres, nanoparticles, surface coatings, and other materials. The preparation method is as follows: 1) Fe is added dropwise to a solution containing tannic acid. 3+ Solution; 2) Formation of TA-Fe through coordination 3+ 3) Coating, incorporating, or encapsulating the obtained MPN onto a substrate material. Under near-infrared irradiation, utilize TA-Fe... 3+ The photothermal effect of the complex structure generates localized heating, achieving antibacterial or tumor ablation. In recent years, TA-Fe... 3+Self-assembled metal polyphenol networks (MPNs) have become an important research direction in medical dressings, smart sensing, and photothermal therapy due to their tunable optical properties, pH responsiveness, antioxidant properties, antibacterial properties, and biosafety. However, MPNs suffer from defects such as structural brittleness, insufficient flexibility, and susceptibility to cracking during bending and stretching. They are difficult to fabricate into continuous, film-forming natural polymer films. Most existing MPN systems are based on nanoparticles, hydrogels, or coatings, making it difficult to achieve a continuous film structure uniformly dispersed in natural polysaccharides. While MPNs have a strong photothermal effect, their insufficient mechanical stability and flexibility limit their practical application in packaging materials or wearable devices. Furthermore, although polyphenol metal complexes exhibit some pH sensitivity, the pH-changing color effect is not significant in most existing systems, or structural instability prevents reversible color changes, thus hindering their use in applications such as visual monitoring of food spoilage. In addition, existing photothermal antibacterial films often rely on precious metal materials (such as nano-silver and nano-gold), resulting in high costs, heavy ecological burden, and difficulty in degradation.

[0006] Currently based on CMCS and TA-Fe 3+ Research on composite multifunctional films is limited, especially in the field of photothermal antibacterial packaging. There is a lack of polymer film materials that can simultaneously achieve synergistic functions such as "mechanical properties + photothermal antibacterial properties + intelligent color change + barrier properties", making it difficult to meet the comprehensive application needs of food preservation, intelligent monitoring, biodegradability and environmental protection, and biosafety.

[0007] Therefore, developing a biodegradable natural polymer film that combines mechanical stability, antibacterial properties, photothermal effect, and ultraviolet blocking capability is of significant scientific importance and application value. Summary of the Invention

[0008] This invention provides a photothermal antibacterial and pH-responsive hydrogel membrane, its preparation and application, which overcomes the shortcomings of existing natural polysaccharide-based films in terms of mechanical properties, antibacterial ability, photothermal conversion efficiency, environmental stability and intelligent monitoring.

[0009] The technical solution of the present invention is a photothermal antibacterial and pH-responsive hydrogel membrane containing polysaccharides, polyphenols and metal ions. The polysaccharides and polyphenols form a stable gel network through hydrogen bonding and electrostatic interaction. The metal ions are embedded in the gel network through coordination with the polyphenols to form a metal polyphenol network, thereby enhancing the mechanical and photothermal effects.

[0010] The metal ions are selected from Fe. 3+ Zn 2+ Cu 2+ Al 3+ Ca 2+ Any one or any combination thereof.

[0011] The polyphenols are selected from any one or any combination of natural phenols such as tannic acid, gallic acid, catechins, gallocatechins, green tea polyphenol mixtures, and cinnamic acid derivatives. The hydroxyl groups in natural phenols can coordinate with metals, providing antioxidant / antibacterial functions and influencing color / optical absorption.

[0012] The polysaccharides are selected from any one or any combination of carboxymethyl chitosan, chitosan (CS), carboxymethyl cellulose (CMC), sodium alginate, gelatin, hyaluronic acid derivatives, starch modifiers, etc. Different polysaccharides provide different film-forming properties, hydrophilicity / hydrophobicity, and biodegradability; polymers containing amino or carboxyl groups are more likely to interact with polyphenol ligands (TA) / metals.

[0013] The mass ratio of the polysaccharide to the polyphenol is 2-5:10, preferably 3:10.

[0014] Furthermore, it also contains a plasticizer selected from glycerin, which accounts for 8-11 wt% of the total mass of polysaccharides and polyphenols, preferably 10 wt%.

[0015] Furthermore, it also contains photothermal components selected from any one or any combination of dopamine, polydopamine (PDA), graphene oxide (GO), carbon nanodots, metal sulfides, and metal nanoparticles (Au, Ag, etc.). These materials possess strong NIR absorption / photothermal conversion capabilities and can synergize with TA-Fe 3+ Improve the rate and efficiency of photothermal heating.

[0016] Furthermore, it contains food-grade pH indicator dyes or dye microcapsules for more pronounced visualization. Natural dyes exhibit more significant color changes with pH, ​​overcoming the limitations of TA-Fe... 3+ The problem is that the human eye has low visibility at pH 4-10.

[0017] Furthermore, it contains natural antibacterial agents selected from any one or any combination of laurylamide derivatives, citrates, eucalyptus oil, tea polyphenol mixtures, and sustained-release silver complexes.

[0018] This invention also provides a method for preparing a photothermal antibacterial and pH-responsive hydrogel membrane, the steps of which include: (1) Mix polysaccharides and polyphenols in an aqueous solution, and then form a membrane to obtain a primary membrane; (2) The primary membrane from step (1) is immersed in an aqueous solution containing metal ions and dried to obtain a photothermal antibacterial and pH-responsive hydrogel membrane.

[0019] In step (1), the mass ratio of polysaccharide to polyphenol in the aqueous solution is 2-5:10, preferably 3:10; the concentration of polysaccharide is 1-3 wt%, preferably 1-2 wt%. The polysaccharide is selected from any one or any combination of polysaccharides such as carboxymethyl chitosan, chitosan (CS), carboxymethyl cellulose (CMC), sodium alginate, gelatin, hyaluronic acid derivatives, and starch modifiers. The polyphenol is selected from any one or any combination of natural phenols such as tannic acid, gallic acid, catechins, gallocatechins, green tea polyphenol mixtures, and cinnamic acid derivatives.

[0020] Step (1) The aqueous solution also contains a plasticizer selected from glycerol, which accounts for 8-11 wt% of the total mass of polysaccharides and polyphenols, preferably 10 wt%.

[0021] Step (1) The aqueous solution also contains photothermal components, selected from any one or any combination of dopamine, polydopamine (PDA), graphene oxide (GO), carbon nanodots, metal sulfides, and metal nanoparticles (Au, Ag, etc.).

[0022] Step (1) The aqueous solution also contains food-grade pH indicator dye or dye microcapsules.

[0023] Step (1) The aqueous solution also contains natural antibacterial substances selected from any one or any combination of lauramide derivatives, citrates, eucalyptus oil, tea polyphenol mixtures, and slow-release silver complexes.

[0024] Further, in step (1), the aqueous solution containing polysaccharides and the aqueous solution containing polyphenols are mixed at a volume ratio of 1:1. The concentration of polysaccharides in the aqueous solution containing polysaccharides is 3 wt%, and the concentration of polyphenols in the aqueous solution containing polyphenols is 10 wt%. Further still, the aqueous solution containing polysaccharides also contains a plasticizer, which accounts for 10 wt% of the total mass of the polysaccharides and polyphenols. The polysaccharides are selected from any one or any combination of carboxymethyl chitosan, chitosan (CS), carboxymethyl cellulose (CMC), sodium alginate, gelatin, hyaluronic acid derivatives, starch modifiers, etc., preferably carboxymethyl chitosan. The polyphenols are selected from any one or any combination of natural phenols such as tannic acid, gallic acid, catechins, gallocatechins, green tea polyphenol mixtures, cinnamic acid derivatives, etc., preferably tannic acid. The plasticizer is glycerol.

[0025] Step (1): The film-forming method is selected from any one of the following: mold drying, layer-by-layer assembly, immersion-drying cycle, spraying or coating, in-situ self-assembly, freeze drying-reconstruction, and hot pressing film formation.

[0026] In step (2), the concentration of the precursor for releasing metal ions in the aqueous solution is 0.05-0.3 wt%, preferably 0.1 wt%; the metal ions are selected from Fe. 3+ Zn2+ Cu 2+ Al 3+ Ca 2+ Any one or any combination thereof.

[0027] Step (2), Step (1) The primary membrane is immersed in an aqueous solution containing metal ions 1-3 times, preferably 2 times, and the immersion time is 1-2 minutes each time.

[0028] The photothermal antibacterial and pH-responsive hydrogel membrane provided by the present invention has the following uses: (1) Prepare food packaging products that are degradable, antibacterial, UV resistant and photothermal, and extend the shelf life of food; (2) Prepare photothermal sterilization products for inhibiting bacterial infection and promoting wound healing; (3) Develop visual intelligent products for pH monitoring and biosensing applications; The products include, but are not limited to, films, coatings (directly applied to PE / paper / cardboard), patches, edible packaging films, and composite layers (film + PE). Coatings or patches are easier to industrialize and compatible with existing packaging lines; edible films are suitable for direct contact with food.

[0029] The following products provided by this invention contain a photothermal antibacterial and pH-responsive hydrogel membrane provided by this invention as described above: (1) Food packaging products are degradable, antibacterial, UV resistant and photothermal, which can extend the shelf life of food; (2) Photothermal sterilization products, used to inhibit bacterial infection and promote wound healing; (3) Visualized intelligent products for pH monitoring and biosensing applications; The products include, but are not limited to, films, coatings (directly applied to PE / paper / cardboard), patches, edible packaging films, and composite layers (film + PE). Coatings or patches are easier to industrialize and compatible with existing packaging lines; edible films are suitable for direct contact with food.

[0030] The present invention also provides a photothermal sterilization method, characterized in that the target object is brought into contact with a photothermal antibacterial and pH-responsive hydrogel membrane provided by the present invention, and sterilized by light irradiation.

[0031] The illumination is selected from sunlight, simulated sunlight (white light + NIR), LED NIR (low power long-term irradiation), and pulsed NIR.

[0032] Furthermore, the target material is also in contact with a photocatalyst, undergoing photothermal and photocatalytic sterilization.

[0033] This invention aims to address the following shortcomings of natural polysaccharide-based hydrogel membranes (which possess good biocompatibility and biodegradability): (1) Insufficient mechanical strength: For example, chitosan and carboxymethyl chitosan films are prone to water absorption and swelling due to weak intermolecular forces, which leads to a decrease in strength and stability and is not suitable for use under high humidity or external force. (2) Unreasonable hydrophilic / hydrophobic balance: Most polysaccharide membranes have high water content and strong solubility, resulting in poor structural stability and limited ability to adhere to food surfaces, which has an adverse effect on antibacterial and preservation performance; (3) Limited antibacterial properties and reliance on external chemical preservatives: Natural polysaccharides themselves have weak antibacterial properties, and single-component modified membranes such as tea polyphenols and metal ions still cannot effectively achieve broad-spectrum killing of Gram-negative and Gram-positive bacteria. (4) Insufficient photothermal conversion capacity: Although existing metal polyphenol materials have a certain photothermal effect, they are limited by insufficient metal coordination and unstable network structure, resulting in limited heating and low sterilization efficiency. (5) Single function and lack of visualization features: Some studies only focus on antibacterial or mechanical properties, but lack pH response color change function that can be used for food spoilage monitoring, which makes it difficult to meet the needs of smart packaging; A photothermal antibacterial and pH-responsive hydrogel membrane was obtained, exhibiting the following technical advantages: (1) A CMCS / TA-Fe metal polyphenol network hydrogel film with high mechanical strength and structural stability was constructed through hydrogen bonds between carboxymethyl chitosan (CMCS) and tannic acid (TA) and TA-Fe 3+ Coordination crosslinking significantly improves the network density, mechanical properties, and swelling resistance of the film; (2) Achieve controllable adjustment of the hydrophilicity, water content and solubility of the film: by controlling Fe 3+ The number of immersion cycles adjusts the number of hydrophilic groups, enabling the film to possess both moderate wettability and high stability, thereby improving its adhesion in humid environments and its usability as a food packaging material. (3) Imparting strong and broad-spectrum antibacterial properties to the film: utilizing the natural antibacterial activity of TA and Fe 3+ -Strengthening the structure of the polyphenol network to achieve control over Escherichia coli (E. coli) E. coli ) and Staphylococcus aureus ( S. aureus Highly effective suppression or killing of ( ); (4) Enhance the photothermal sterilization ability of the film: by improving the TA-Fe 3+ The number of coordination elements enables the material to produce a significant photothermal effect under 808 nm near-infrared irradiation, achieving rapid heating (>100 ℃), thereby achieving physical sterilization without the addition of drugs; (5) Constructing a smart film with antibacterial, photothermal, multiple protective, and pH-responsive properties for food preservation: through TA-Fe 3+ The color change and metal polyphenol network structure enable multiple functions such as ultraviolet shielding, antibacterial properties, and visual color change, thereby improving the safety and intelligence level of food packaging. Attached Figure Description

[0034] Figure 1 A schematic diagram of the CMCS / TA-Fe hydrogel preparation scheme (A) and a schematic diagram of using CMCS / TA-Fe hydrogel to preserve cooked meat (B).

[0035] Figure 2 SEM images of different hydrogels after freeze-drying.

[0036] Figure 3 Images showing the color changes of CMCS / TA-Fe hydrogel films immersed in solutions of different pH values.

[0037] Figure 4 Infrared thermal images of different hydrogel films after 15 min of irradiation with 808 nm near-infrared light. Detailed Implementation

[0038] I. Composition of Thin Film Materials The thin film of the present invention is composed of the following components: Matrix polysaccharide: Carboxymethyl chitosan (CMCS), used to construct flexible film-forming substrates, providing good mechanical properties and biocompatibility.

[0039] Polyphenol crosslinking agent: Tannic acid (TA), as a natural antibacterial agent, provides polyphenol hydroxyl groups and Fe 3+ Coordination imparts antioxidant and UV absorption capabilities to the thin film.

[0040] Metal ions: ferric ions (Fe3+) 3+ By constructing a metal polyphenol network (MPN) through Fe-O coordination, significant photothermal effects are generated, the film is endowed with pH-responsive color-changing ability, and mechanical properties are enhanced.

[0041] Optional component: Glycerin (plasticizer).

[0042] II. Thin Film Preparation Methods 1. Preparation of CMCS film-forming solution (1) Weigh out CMCS and dissolve it in deionized water to a concentration of 3 wt%; (2) Stir until completely dissolved to form a transparent and homogeneous CMCS solution; (3) Add 10 wt% of glycerol as a plasticizer as needed, which accounts for the total mass of CMCS and TA.

[0043] 2. TA introduction and first crosslinking (1) Weigh TA and dissolve it in deionized water to a concentration of 10 wt%; (2) Add TA to the CMCS solution, with a volume ratio of CMCS:TA = 1:1; (3) Stir to make TA uniformly dispersed and form a hydrogen bond system with CMCS; (4) Pour the mixed solution into a mold and dry it to obtain a primary CMCS / TA film.

[0044] 3. Fe 3+ Immersion construction of metal polyphenol networks (MPN) (1) Immerse the CMCS / TA film in FeCl3 solution (0.1 wt%); (2) Soak once, twice, and three times respectively, for 1 minute each time; (3) Rinse and dry to generate three types of films: CMCS / TA-Fe1, CMCS / TA-Fe2, and CMCS / TA-Fe3, such as Figure 2 As shown.

[0045] Among them, CMCS / TA-Fe2 has the best overall performance (photothermal, antibacterial, UV blocking, mechanical strength) and is the preferred implementation scheme.

[0046] III. Key Structural Features of Thin Films Formation of MPN (Metal Polyphenol Network) structure: Phenolic hydroxyl groups in TA react with Fe 3+ A dense three-dimensional network is constructed by forming cross-linking points through single / double / triple coordination.

[0047] pH-responsive color change: White in acidic environments (pH < 3), purple in weakly acidic environments (3 < pH < 6), and reddish-brown in alkaline environments (pH > 7). Figure 3 (This can be used for monitoring food rancidity.)

[0048] Photothermal effect structure basis: MPN strongly absorbs 808 nm near-infrared light, and achieves photothermal sterilization by generating heat.

[0049] IV. Thin Film Properties and Realization Methods 1. Ultraviolet shielding performance High UV blocking efficiency is achieved through strong MPN absorption: 0 transmittance in the 200-350 nm ultraviolet region; and in the 400-800 nm visible light region, with the increase of Fe... 3+ The more times it is soaked, the stronger its ability to block light, but all of them can achieve a transmittance of 70-80%.

[0050] 2. Photothermal antibacterial properties Under 808 nm NIR irradiation: CMCS / TA: no temperature rise; CMCS / TA-Fe1: temperature rises to ~70 ℃; CMCS / TA-Fe2: temperature >100 ℃; CMCS / TA-Fe3: local hot spots >400 ℃ (exceeding the detection limit of the thermal imager), such as Figure 4 As shown.

[0051] Sterilization rate: against Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus It has an antibacterial rate of approximately 100%.

[0052] 3. Enhanced mechanical properties Multi-point coordination crosslinking significantly strengthens thin films: with Fe 3+ With increasing immersion times, the storage modulus (G') of the CMCS / TA-Fe film gradually increased, with G' values ​​of 2465.24, 5688.22, and 23570.80 Pa for CMCS / TA-Fe1, CMCS / TA-Fe2, and CMCS / TA-Fe3, respectively. Compared to other crosslinking systems reported in the literature (such as gelatin-oxidized tannic acid (SC-GT / OTA) hydrogel with G' = 1.9 kPa), the SH-CNC / TA-Al formed by the self-assembly of tannic acid (TA)-induced cellulose nanocrystals (CNC) 3+ (Hydrogel G'=367.7 Pa) The G' value of the CMCS / TA-Fe sample obtained in this study is at a high level, indicating that the network structure has excellent mechanical reinforcement effect.

[0053] The storage modulus (G') of the CMCS / TA-Fe2 thin film of this invention is 5688.22 Pa under the conditions of 1% strain, 10 rad / s frequency, 25 °C temperature, and 180 s scan, which is significantly higher than that without the introduction of Fe. 3+ The coordinated CMCS-TA film (G' = 627.57 Pa) shows an increase of approximately one order of magnitude in G', indicating that the TA-Fe... 3+ Networks can improve the stability of structures.

[0054] 5. Food preservation function In a food preservation test, CMCS / TA-Fe2 film was used to preserve cooked chicken breast refrigerated at 4 ℃. The results showed that the CMCS / TA-Fe2+NIR group significantly extended the shelf life of the chicken samples (no signs of spoilage for 10 days). Compared with the group directly exposed to air and the ordinary preservation film group, it significantly reduced colony formation, pH, and weight loss.

[0055] In summary, the thin film prepared by this invention has the following advantages: (1) The mechanical properties are significantly improved and the structural stability is enhanced.

[0056] This invention utilizes CMCS-TA hydrogen bonds with TA-Fe 3+ The coordination-based dual crosslinking mechanism enables the film to form a denser three-dimensional network structure, which significantly improves its mechanical properties and increases the energy storage modulus (G') by about 10 times.

[0057] (2) The hydrophilicity and solubility can be adjusted to meet the needs of multiple application scenarios.

[0058] This invention achieves higher surface hydrophilicity (contact angle less than 50°) by adjusting the ratio of CMCS to TA.

[0059] This invention adjusts Fe 3+ The number of soaking cycles allows for controlled adjustment of the film's water content and solubility: moderate hydrophilicity enhances the film's adhesion and moisture retention to food surfaces; reduced water content improves the film's water resistance and reduces structural disintegration; and it meets the requirements of various food, medical dressing, and tissue engineering applications for membrane materials that are "wettable yet not easily dissolved." This controllable characteristic is something that traditional polysaccharide films generally cannot achieve.

[0060] (3) The UV shielding capability is significantly improved, extending the shelf life of food.

[0061] The metal polyphenol network introduced in this invention can effectively absorb and block 200-400 nm ultraviolet light, reducing the ultraviolet transmittance to below 40%. The UV blocking capability of the CMCS / TA-Fe film varies with the Fe content. 3+ Enhanced coordination improves transparency; it maintains high transmittance of visible light (transmittance exceeding 70% in the 400-800 nm visible light region) while avoiding problems such as lipid oxidation, discoloration, and vitamin degradation in food caused by ultraviolet radiation. It achieves an optimal balance of "transparency + UV protection," significantly superior to conventional polysaccharide membranes.

[0062] (4) Strong photothermal effect and rapid temperature rise, achieving efficient physical sterilization.

[0063] One of the greatest innovations of this invention is the significantly enhanced photothermal conversion performance: CMCS / TA-Fe2 at 1.5 W / cm 2 Under 808 nm NIR irradiation, the temperature can rise to >100 °C within 15 minutes; the local hot spots of CMCS / TA-Fe3 can further reach high temperatures (>410 °C) beyond the detection range of the infrared spectrometer. Compared with the disclosed TA-Fe photothermal materials (which typically heat up to <60-80 °C), this invention significantly improves photothermal efficiency and achieves a stronger drug-free bactericidal effect.

[0064] (5) Significantly improved broad-spectrum antibacterial properties (dual mode of chemical antibacterial + photothermal sterilization).

[0065] The antibacterial function of this invention comes from: the natural antibacterial effect of TA—damaging the cell wall and reducing bacterial membrane potential and ATP levels; and the instantaneous bactericidal effect induced by photothermal high temperature—rapidly destroying cell proteins and membrane structures under NIR.

[0066] Therefore, the film of the present invention is effective without the addition of drugs. E. coli and S. aureus Both can achieve a 100% antibacterial rate, which is superior to traditional natural antibacterial films.

[0067] (6) It has pH-responsive color-changing properties and can be used for smart food packaging.

[0068] TA-Fe 3+ The metal polyphenol network has reversible pH responsiveness, and the film of this invention can change color with pH changes during the food spoilage process; thus enabling real-time and visual monitoring of food spoilage such as meat and aquatic products.

[0069] It combines preservation and intelligent monitoring functions, thus broadening the application scenarios of the material.

[0070] (7) High safety, natural and sustainable material source.

[0071] The materials used in this invention are all derived from natural renewable resources (CMCS, TA), Fe 3+ It is a common edible metal ion, and is non-toxic, environmentally safe, biodegradable, highly safe for food contact, and in line with the development trend of green packaging materials.

[0072] (8) The preparation method is simple, the conditions are mild, and it can be scaled up.

[0073] The preparation strategy of this invention does not rely on special instruments; it only requires mixing solutions to form films and Fe. 3+ A network can be formed simply by soaking, the process is controllable and easy to scale up, making it suitable for industrial production and commercial applications.

Claims

1. A photothermal antibacterial and pH-responsive hydrogel membrane, characterized in that, It contains polysaccharides, polyphenols and metal ions. The polysaccharides and polyphenols form a gel network through hydrogen bonding and electrostatic interaction. The metal ions are embedded in the gel network through coordination with the polyphenols and form a metal polyphenol network.

2. The photothermal antibacterial and pH-responsive hydrogel membrane according to claim 1, characterized in that, The mass ratio of the polysaccharide to the polyphenol is 2-5:

10. The polysaccharide is selected from any one or any combination of carboxymethyl chitosan, chitosan, carboxymethyl cellulose, sodium alginate, gelatin, hyaluronic acid derivatives, and starch-modified products. The polyphenol is selected from any one or any combination of tannic acid, gallic acid, catechin, gallocatechin, green tea polyphenol mixtures, and cinnamic acid derivatives. The metal ion is selected from Fe. 3+ Zn 2+ Cu 2+ Al 3+ Ca 2+ Any one or any combination thereof.

3. The photothermal antibacterial and pH-responsive hydrogel membrane according to claim 1, characterized in that, It also contains any one or any combination of plasticizers, photothermal components, food-grade pH indicator dyes or dye microcapsules, and natural antibacterial agents.

4. A method for preparing a photothermal antibacterial and pH-responsive hydrogel membrane, characterized in that the steps include... include: (1) Mix polysaccharides and polyphenols in an aqueous solution, and then form a membrane to obtain a primary membrane; (2) The primary membrane from step (1) is immersed in an aqueous solution containing metal ions and dried to obtain a photothermal antibacterial and pH-responsive hydrogel membrane.

5. The preparation method according to claim 5, characterized in that, Step (1): The mass ratio of polysaccharide to polyphenol in the aqueous solution is 2-5:10, the concentration of polysaccharide is 1-3 wt%, and the polysaccharide is selected from any one or any combination of carboxymethyl chitosan, chitosan, carboxymethyl cellulose, sodium alginate, gelatin, hyaluronic acid derivatives, and starch modifiers. The polyphenol is selected from any one or any combination of tannic acid, gallic acid, catechin, gallocatechin, green tea polyphenol mixture, and cinnamic acid.

6. The preparation method according to claim 5, characterized in that, Step (1) The aqueous solution also contains any one or any combination of plasticizer, photothermal component, food-grade pH indicator dye or dye microcapsule, and natural antibacterial agent.

7. The preparation method according to claim 5, characterized in that, In step (2), the primary membrane in step (1) is immersed in an aqueous solution containing metal ions 1-3 times, with each immersion lasting 1-2 minutes; the concentration of the precursor for releasing metal ions in the aqueous solution is 0.05-0.3 wt%, and the metal ions are selected from Fe. 3+ Zn 2+ Cu 2+ Al 3+ Ca 2+ Any one or any combination thereof.

8. A photothermal antibacterial and pH-responsive hydrogel membrane according to any one of claims 1-3, or a photothermal antibacterial and pH-responsive hydrogel membrane prepared by the preparation method according to any one of claims 4-7, has at least one of the following uses: (1) Preparation of food packaging products; (2) Preparation of photothermal sterilization products; (3) Develop visualized intelligent products.

9. At least one of the following products contains a photothermal antibacterial and pH-responsive hydrogel membrane according to any one of claims 1-3 or a photothermal antibacterial and pH-responsive hydrogel membrane prepared by the preparation method according to any one of claims 4-7: (1) Products for food packaging; (2) Products for photothermal sterilization; (3) Visualized intelligent products.

10. A photothermal sterilization method, characterized in that, The target object is brought into contact with a photothermal antibacterial and pH-responsive hydrogel membrane according to any one of claims 1-3 or a photothermal antibacterial and pH-responsive hydrogel membrane prepared by the preparation method according to any one of claims 4-7, and sterilized by light irradiation.

Images