EGCG (epigallocatechin gallate)-based functional adhesive for orthodontic bracket and preparation method of EGCG-based functional adhesive

Abstract

The invention discloses a tooth orthodontic bracket EGCG (epigallocatechin gallate)-based functional binder and a preparation method thereof in the field of binders. Comprising the following components in parts by weight: 25 to 30 parts of bisphenol A dimethacrylate, 15 to 20 parts of triethylene glycol dimethacrylate, 0.6 to 0.8 part of camphorquinone, 0.6 to 0.8 part of dimethylaminoethyl methacrylate, 3 to 5 parts of EGCG (epigallocatechin gallate) loaded nanoparticles and 6 to 8 parts of modified chitosan. Through the core structure design of loading EGCG (epigallocatechin gallate) on cationic nano silicon dioxide and coating modified chitosan for multiple times, the dual core advantages of accurate pH response controlled release and safe adaptation to the oral environment are realized in the application of the dental orthodontic bracket adhesive, the effect is supported by a clear mechanism, and release, bacteriostasis and toxicity test data verify that the dental orthodontic bracket adhesive has a good application prospect. The clinical application requirements are completely met.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically referring to an EGCG-based functional adhesive for orthodontic brackets and its preparation method. Background Technology

[0002] Orthodontic treatment is an oral medical technique that uses mechanical force to move misaligned teeth to a normal occlusal position. The bracket adhesive, as the core material connecting the orthodontic bracket to the tooth enamel surface, directly determines the treatment outcome and oral health safety. With the global demand for orthodontics increasing year by year, higher requirements are being placed on the "functionality" and "safety" of adhesives. They not only need to meet long-term stable bonding strength but also address complications such as enamel demineralization, secondary caries, and gingivitis during orthodontic treatment. The limitations of traditional adhesives are becoming increasingly apparent.

[0003] Orthodontic treatment typically lasts 1-3 years. Brackets must continuously withstand complex external forces such as chewing and orthodontic forces, and are constantly exposed to a moist, bacteria-rich environment in the mouth (e.g., Streptococcus mutans, Lactobacillus). This necessitates that the adhesive possess the following core properties: Stable bond strength: It must achieve a strong triple bond between the enamel, adhesive, and bracket interface to prevent bracket detachment and treatment interruption. According to ISO 10477, the shear bond strength of orthodontic adhesives must be ≥8 MPa, and after immersion in artificial saliva at 37°C for 30 days, the strength retention rate must exceed 80%; Biocompatibility: The oral mucosa and dentin are sensitive to chemical irritants. If the release of residual monomers in the adhesive exceeds the standard (>5μg / mL), it may cause adverse reactions such as gingival irritation and gingival redness and swelling. In particular, the content of toxic substances needs to be strictly controlled for adolescent patients. Anti-demineralization and anti-caries ability: During orthodontic treatment, cleaning blind spots can easily form at the bracket edges. The accumulation of food debris can cause the local pH value to drop below 4.5, leading to enamel demineralization. Clinical data shows that in patients who do not use functional adhesives, the incidence of leukoplakia lesions during orthodontic treatment is as high as 45%-60%, and the demineralized areas are difficult to repair on their own.

[0004] Currently, mainstream adhesives are mainly resin-based materials, which can be divided into two categories according to their composition and function: traditional resin adhesives and fluoride-modified adhesives. However, they still have obvious shortcomings in terms of functionality and safety: Traditional adhesives are based on matrix resin, diluent, foaming agent, and filler, with silica filler to improve strength. Their core advantages are high bonding strength and fast curing speed, but they have insufficient biocompatibility. Long-term contact may interfere with the endocrine system, and residual monomers can easily cause dentin hypersensitivity. The resin matrix itself does not have the ability to release ions, cannot neutralize the local acidic environment, and cannot promote enamel remineralization, making it difficult to prevent leukoplakia. Water, salivary enzymes, and bacterial metabolites in the oral cavity can cause the resin to hydrolyze and oxidize, resulting in microcracks at the bonding interface. The bonding strength can decrease by 30%-40% in the later stages of treatment, increasing the risk of bracket detachment. To address the demineralization problem, the industry has developed fluorinated resin binders. By adding fluorine sources such as sodium fluoride and fluoroaluminosilicate glass to the system, fluoride ions are released slowly. These fluoride ions promote the conversion of hydroxyapatite to fluorapatite, thereby inhibiting demineralization. However, the stability of fluoride release is poor: fluoride ions are mostly physically mixed in the resin, and the initial release concentration is too high. The compatibility between the fluorine source filler (such as fluoroglass) and the resin matrix is ​​poor, which easily leads to interface defects. This results in a 10%-20% reduction in bonding strength compared to traditional resins. Some products require the addition of coupling agents to improve compatibility, which increases the manufacturing cost. Summary of the Invention

[0005] To address the above issues and overcome the shortcomings of existing technologies, this invention provides an EGCG-based functional adhesive for orthodontic brackets and its preparation method. Through a core structural design of EGCG loaded with cationic nano-silica and multiple modified chitosan coatings, it achieves the dual core advantages of precise pH-responsive controlled release and safe adaptation to the oral environment in the application of orthodontic bracket adhesives. Its effects are supported by a clear mechanism and verified by release, antibacterial, and toxicity test data, fully meeting the needs of clinical application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention proposes an EGCG-based functional adhesive for orthodontic brackets, the functional adhesive comprising the following components in parts by weight: 25-30 parts of bisphenol A dimethacrylate, 15-20 parts of triethylene glycol dimethacrylate, 0.6-0.8 parts of camphorquinone, 0.6-0.8 parts of dimethylaminoethyl methacrylate, 3-5 parts of EGCG-loaded nanoparticles, and 6-8 parts of modified chitosan; Preferably, the preparation method of the EGCG-supported nanoparticles specifically includes the following steps: S1, diallylamine and dimethylamine aqueous solution are placed in a flask, deionized water is added and mixed evenly, the reaction temperature is maintained at 30-50℃, epichlorohydrin is added stepwise, and after stirring until evenly mixed, the reaction temperature is increased to carry out the polymerization reaction. After the reaction is completed, it is cooled, placed in a dialysis bag, dialyzed for 2-3 days, and then freeze-dried to obtain the cationic matrix. Preferably, in step S1, the volume ratio of diallylamine, dimethylamine aqueous solution, and epichlorohydrin is 3.5-4.5:1.3-1.7:4.5-6; Preferably, in step S1, the polymerization reaction temperature is 80-90℃, the polymerization reaction time is 2-3h, the polymerization reaction stirring speed is 200-300rpm, and the polymerization reaction environment pH is 8-9. S2. Dissolve the cationic matrix prepared in step S1 in anhydrous THF, introduce flowing nitrogen gas, add triethoxysilane and mix well, dilute the platinum catalyst with anhydrous THF and add it to the reaction system, mix well at room temperature, raise the reaction temperature to carry out hydrosilylation reaction, after the reaction is completed, add activated carbon and stir, filter, collect the filtrate, concentrate by rotary evaporation to remove excess reaction solvent, and dry under vacuum to obtain cationic siloxane. Preferably, in step S2, the volume ratio between the triethoxysilane and the diallylamine in step S1 is 3-4:1; Preferably, in step S2, the mass of the platinum catalyst added is 0.1%-0.2% of the mass of triethoxysilane; Preferably, in step S2, the reaction temperature of the hydrosilylation reaction is 60-80°C, and the reaction time of the hydrosilylation reaction is 6-8 hours. S3. Dissolve sodium dodecyl sulfate in an ethanol aqueous solution, add the cationic siloxane and tetraethyl orthosilicate prepared in step S2, mix well, adjust the reaction pH to 2-4, and carry out a gelation reaction. After the reaction is completed, transfer the reaction system to a polytetrafluoroethylene reactor and carry out an aging reaction under sealed conditions. After the reaction is completed, add it to an anhydrous ethanol / hydrochloric acid mixed solution and carry out a reflux reaction. After the reaction is completed, centrifuge, collect the precipitate, wash it repeatedly with anhydrous ethanol, and vacuum dry it to obtain cationic nano silica. Preferably, in step S3, the mass ratio between sodium dodecyl sulfate and cationic siloxane is 2-4:2-6; Preferably, in step S3, the mass-to-volume ratio of the cationic siloxane to tetraethyl orthosilicate is 1 g: 2-3 mL; Preferably, in step S3, the reaction temperature of the gelation reaction is 40-50℃, and the reaction time is 5-8h; Preferably, in step S3, the aging reaction temperature is 60-80℃ and the reaction time is 18-24h; Preferably, in step S3, the reflux reaction temperature is 60-70°C and the reaction time is 6-12 hours. S4. Dissolve EGCG (epigallocatechin gallate) in an ethanol-water solution under light-protected conditions. Add the cationic nano-silica prepared in step S3 to the reaction system. After purging with flowing nitrogen, stir at 300-500 rpm for 18-24 hours under sealed conditions and room temperature. Centrifuge, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and vacuum dry to obtain EGCG-loaded nanoparticles. Preferably, in step S4, the mass ratio between EGCG and cationic nano-silica is 1:2-4; Preferably, the preparation method of the modified chitosan specifically includes the following steps: S5. Chitosan was dispersed in NaOH aqueous solution and activated at room temperature. The mixture was filtered, the solid was collected, washed with deionized water until neutral, and then dried under vacuum to obtain activated chitosan. S6. Disperse the activated chitosan prepared in step S5 into DMF, slowly add N,N-dimethylaminochloropropane hydrochloride / DMF solution to the reaction system, introduce flowing nitrogen gas, raise the reaction temperature to carry out the substitution reaction, after the reaction is completed, add anhydrous ethanol for alcohol precipitation, filter, collect the precipitate, wash with anhydrous ethanol, and vacuum dry to obtain the first modified chitosan. Preferably, in step S6, the mass ratio between the N,N-dimethylaminochloropropane hydrochloride and the chitosan in step S5 is 1:1.6-2; Preferably, in step S6, the reaction temperature of the substitution reaction is 60-70°C, and the reaction time of the substitution reaction is 4-6 hours. S7. Dissolve the first modified chitosan prepared in step S6 in acetone, slowly add allyl chloride to the reaction system, and after the addition is complete, carry out the quaternization reaction at room temperature. After the reaction is complete, add anhydrous diethyl ether for precipitation treatment, filter, collect the precipitate, wash with anhydrous methanol, and vacuum dry to obtain the second modified chitosan. Preferably, in step S7, the mass-to-volume ratio of N,N-dimethylaminochloropropane hydrochloride to allyl chloride in step S6 is 3.2-3.6 g: 2-3 mL; Preferably, in step S7, the stirring speed of the quaternization reaction is 300-400 rpm, and the reaction time of the quaternization reaction is 4-6 h; S8. Take the second modified chitosan prepared in step S7 and potassium carbonate into a flask, add DMF to completely dissolve the reactants, slowly add 1,3-propanesulfonate lactone into the reaction system, introduce flowing nitrogen gas, raise the reaction temperature to carry out the sulfonation reaction, after the reaction is completed, add deionized water and mix evenly, transfer to a dialysis bag for dialysis treatment to obtain modified chitosan. Preferably, in step S8, the mass ratio of chitosan to potassium carbonate in step S5 is 2:0.1-0.2; Preferably, in step S8, the mass ratio between chitosan and 1,3-propanesulfonate lactone in step S5 is 2:2.5-3.5; Preferably, in step S8, the sulfonation reaction temperature is 70-80°C, and the sulfonation reaction time is 5-7 hours. This invention also provides a method for preparing an EGCG-based functional adhesive for orthodontic brackets, specifically including the following steps: ① Disperse EGCG-supported nanoparticles in deionized water to obtain an aqueous phase of EGCG-supported nanoparticles; ② Add the modified chitosan to cyclohexane and stir until the modified chitosan is completely dissolved to obtain the modified chitosan oil phase; ③ Take the aqueous phase of EGCG-supported nanoparticles prepared in step ①, introduce flowing nitrogen gas to replace the air in the system, and stir at 200-400 rpm under a nitrogen atmosphere. Add the modified chitosan oil phase prepared in step ② dropwise to the aqueous phase of EGCG-supported nanoparticles prepared in step ① through a constant pressure dropping funnel. After the addition is complete, continue stirring the reaction at room temperature for 2-3 hours. After the reaction is completed, collect the lower aqueous phase, centrifuge, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and vacuum dry to obtain chitosan@EGCG-supported nanoparticles. ④ In a light-proof three-necked flask, add bisphenol A dimethacrylate and triethylene glycol dimethacrylate, mix well, add camphorquinone and dimethylaminoethyl methacrylate, and stir under light-proof conditions until the initiator is evenly dispersed to obtain the resin matrix; ⑤ Under light-protected conditions, the chitosan@EGCG-loaded nanoparticles prepared in step ③ are added to the resin matrix in portions. After each addition, the nanoparticles are ultrasonically dispersed, degassed under vacuum, and stored in the dark to obtain the functional binder.

[0007] The beneficial effects achieved by this invention are as follows: This invention provides an EGCG-based functional adhesive for orthodontic brackets and its preparation method. Through the core structural design of EGCG loaded with cationic nano-silica and multiple modified chitosan coating, it achieves the dual core advantages of precise pH-responsive controlled release and safe adaptation to the oral environment in the application of orthodontic bracket adhesives. Its effects are supported by a clear mechanism and verified by release, antibacterial, and toxicity test data, fully meeting the needs of clinical application.

[0008] In terms of pH response performance, this invention relies on a dual regulation mechanism of carrier-coating layer to accurately adapt to dynamic fluctuations in oral pH. From a mechanistic perspective, after multiple steps of modification including activation, substitution, quaternization, and sulfonation, the modified chitosan molecular chain introduces three types of pH-sensitive groups: amino, quaternary ammonium, and sulfonic acid groups. Under acidic conditions, the amino groups are protonated to form a positive charge, which repels the negatively charged sulfonic acid groups, causing the coating layer to swell and increase porosity, significantly reducing the diffusion resistance of EGCG. Under neutral conditions, the amino groups are partially protonated, the coating layer maintains moderate swelling, and the diffusion rate is slow. The cationic nano-silica carrier, after multiple steps of preparation to remove impurities, has a positively charged surface and binds to EGCG electrostatically. Under acidic conditions, the phenolic hydroxyl groups of EGCG are protonated, weakening the binding force and making it easier to detach from the carrier. Under neutral conditions, the binding force is balanced, and the detachment rate is stable. This dual regulation makes EGCG release exhibit on-demand adaptive characteristics: under acidic conditions after meals, it increases the release rate of EGCG, which can specifically inhibit Streptococcus mutans and reduce the risk of demineralization around the tray; under normal neutral conditions, it is released slowly to avoid rapid loss of EGCG and ensure long-term antibacterial effect during the orthodontic cycle.

[0009] Regarding oral environment safety, this invention, through its low-toxicity, anti-inflammatory, and highly biocompatible design, adapts to the needs of long-term gingival contact, achieving a balance of strong antibacterial effect, long-lasting effect, and low toxicity and safety, fully meeting the clinical needs of orthodontic bracket adhesives. In contrast, comparative examples, due to the lack of key structures, all suffer from defects such as uncontrolled release, excessive toxicity, or insufficient antibacterial effect, further highlighting the technical superiority of the embodiment. Attached Figure Description

[0010] Figure 1 The cumulative release rate of EGCG of the functional binders prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention in an environment of pH=7.4; Figure 2 The cumulative release rate of EGCG of the functional binders prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention in an environment of pH=5.0; Figure 3 The graph shows the antibacterial performance results of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 of this invention. Figure 4 The graph shows the in vitro cytotoxicity results of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 of this invention.

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0013] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0014] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the experimental materials and test strains used in the following examples were purchased from commercial channels.

[0015] Example 1 This embodiment provides an EGCG-based functional adhesive for orthodontic brackets, the functional adhesive comprising the following components in parts by weight: 25 parts bisphenol A dimethacrylate, 20 parts triethylene glycol dimethacrylate, 0.6 parts camphorquinone, 0.6 parts dimethylaminoethyl methacrylate, 3 parts EGCG-loaded nanoparticles, and 6 parts modified chitosan. The preparation method of EGCG-supported nanoparticles specifically includes the following steps: S1. Place 7.0 mL of diallylamine and 6.5 mL of dimethylamine (40 wt% aqueous solution) in a flask, add 100 mL of deionized water, maintain the reaction temperature at 30 °C, add 9.0 mL of epichlorohydrin in three portions, and stir at 300 rpm. After mixing evenly, raise the reaction temperature to 80 °C and carry out the polymerization reaction for 3 h. After the reaction is completed, wait for the reaction system to cool to room temperature, transfer it to a dialysis bag, dialyze with deionized water for 2 days, and then freeze dry to obtain the cationic matrix. S2. Dissolve the cationic matrix prepared in step S1 in 100 mL of anhydrous THF, introduce flowing nitrogen into the reaction system, add 28 mL of triethoxysilane, and mix at 400 rpm until the reaction system is homogeneous. Dilute 38 mg of platinum catalyst with 5 mL of anhydrous THF and add it to the reaction system. After stirring and mixing evenly at room temperature, raise the reaction temperature to 60 °C to carry out the hydrosilylation reaction. After the reaction is completed, add activated carbon to remove the platinum catalyst, filter, collect the filtrate, remove excess reaction solvent, and dry under vacuum at 50 °C for 8 hours to obtain cationic siloxane. S3. Dissolve 2.0 g of sodium dodecyl sulfate in 100 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio), add 2.0 g of cationic siloxane prepared in step S2 and 6 mL of tetraethyl orthosilicate, mix well, adjust the reaction pH to 4, raise the reaction temperature to 50 °C, and carry out the gelation reaction for 5 h. After the reaction is completed, transfer the reaction system to a polytetrafluoroethylene reactor, and under sealed conditions, maintain the reaction temperature at 80 °C for aging reaction for 18 h. After the reaction is completed, after the reaction system is cooled to room temperature, add it to anhydrous ethanol / hydrochloric acid mixed solution (anhydrous ethanol:concentrated hydrochloric acid = 10:1, volume ratio), raise the reaction temperature to 70 °C again for reflux reaction for 6 h. After the reaction is completed, centrifuge 10 mL at 8000 rpm, collect the precipitate, wash repeatedly with anhydrous ethanol, and vacuum dry at 60 °C for 10 h to obtain cationic nano silica. S4. Under light-protected conditions, 50 mg of EGCG was dissolved in 50 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio). 2.0 g of the cationic nano-silica prepared in step S3 was added to the reaction system. After passing through flowing nitrogen gas, the reaction was kept at room temperature in a sealed environment. The mixture was stirred at 500 rpm for 18 h, then centrifuged at 12000 rpm for 20 min. The precipitate was collected, washed repeatedly with deionized water and anhydrous ethanol, and dried under vacuum to obtain EGCG-loaded nanoparticles. The preparation method of modified chitosan specifically includes the following steps: S5. Take 2.0 g of chitosan and disperse it in 40 mL of NaOH aqueous solution (10 wt%). Stir at 300 rpm at room temperature to carry out the activation reaction. After 2 h of reaction, filter and collect the solid. Wash it with deionized water until neutral and then dry it under vacuum at 60 °C for 4 h to obtain activated chitosan. S6. Disperse the activated chitosan prepared in step S5 into 50 mL of DMF and magnetically stir at 300 rpm to ensure uniform dispersion of the reaction system. Dissolve 3.2 g of N,N-dimethylaminochloropropane hydrochloride in 10 mL of DMF to obtain an N,N-dimethylaminochloropropane hydrochloride / DMF solution. Add the solution dropwise to the reaction system at a rate of 0.2 mL / min. Purge with flowing nitrogen gas and raise the reaction temperature to 60 °C under a nitrogen protective atmosphere to carry out the substitution reaction. After the reaction is completed, let the reaction system cool to room temperature and add anhydrous ethanol for alcohol precipitation. Filter, collect the precipitate, wash with anhydrous ethanol, and dry under vacuum at 60 °C for 6 h to obtain the first modified chitosan. S7. Dissolve the first modified chitosan prepared in step S6 in 80 mL of acetone, and add 2.0 mL of allyl chloride dropwise to the reaction system at a rate of 1 drop / s. During the dropwise addition, stir at a speed of 250 rpm. After the dropwise addition is completed, increase the stirring speed to 400 rpm at room temperature to carry out the quaternization reaction. After the reaction is completed, add anhydrous diethyl ether for precipitation treatment, filter, collect the precipitate, wash repeatedly with anhydrous methanol, and dry under vacuum at 50°C for 5 h to obtain the second modified chitosan. S8. Take the second modified chitosan prepared in step S7 and 0.1g of potassium carbonate into a flask, add 80ml of LDM to completely dissolve the reactants, then slowly add 2.5g of 1,3-propanesulfonate lactone to the reaction system. After passing through flowing nitrogen gas, raise the reaction temperature to 70℃ under a nitrogen protective atmosphere to carry out the sulfonation reaction for 7 hours. After the reaction is completed, add deionized water and mix well. Transfer the mixture to a dialysis bag and dialyze with deionized water for 3 days, changing the water 3 times a day to remove unreacted 1,3-propanesulfonate lactone, potassium carbonate and small molecule impurities. After freeze-drying, the modified chitosan is obtained. This embodiment also provides a method for preparing an EGCG-based functional adhesive for orthodontic brackets, specifically including the following steps: ① Take 1.5g of EGCG-supported nanoparticles and disperse them in 200mL of deionized water to obtain an aqueous phase of EGCG-supported nanoparticles; ② Take 3.0g of modified chitosan and add it to 100mL of cyclohexane. Stir until the modified chitosan is completely dissolved to obtain the modified chitosan oil phase. ③ Take the aqueous phase of EGCG-supported nanoparticles prepared in step ①, introduce flowing nitrogen gas to replace the air in the system, and stir at 200 rpm under a nitrogen atmosphere. Add the modified chitosan oil phase prepared in step ② dropwise to the aqueous phase of EGCG-supported nanoparticles prepared in step ① through a constant pressure dropping funnel. After the addition is complete, stir continuously at 200 rpm for 2 hours at room temperature. After the reaction is completed, collect the lower aqueous phase, centrifuge at 12000 rpm for 10 min, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and dry under vacuum at 50℃ for 6 hours to obtain chitosan@EGCG-supported nanoparticles. ④ In a light-proof three-necked flask, add bisphenol A dimethacrylate and triethylene glycol dimethacrylate, stir magnetically at 30°C for 30 minutes to mix evenly, add camphorquinone and dimethylaminoethyl methacrylate, stir at 25°C for 20 minutes under light-proof conditions to make the initiator evenly dispersed, and obtain the resin matrix. ⑤ Under light-protected conditions, the chitosan@EGCG supported nanoparticles prepared in step ③ are added to the resin matrix in portions. After each addition, the mixture is stirred at 500 rpm for 30 min, then ultrasonically dispersed at 300 W for 30 min. After vacuum degassing, the mixture is stored in the dark to obtain the functional binder.

[0016] Example 2 This embodiment provides an EGCG-based functional adhesive for orthodontic brackets, the functional adhesive comprising the following components in parts by weight: 28 parts bisphenol A dimethacrylate, 18 parts triethylene glycol dimethacrylate, 0.7 parts camphorquinone, 0.7 parts dimethylaminoethyl methacrylate, 4 parts EGCG-loaded nanoparticles, and 7 parts modified chitosan. The preparation method of EGCG-supported nanoparticles specifically includes the following steps: S1. Place 8.0 mL of diallylamine and 7.5 mL of dimethylamine (40 wt% aqueous solution) in a flask, add 100 mL of deionized water, maintain the reaction temperature at 30 °C, add 10.0 mL of epichlorohydrin in three portions, and stir at 200 rpm. After mixing evenly, raise the reaction temperature to 85 °C and carry out the polymerization reaction for 2.5 h. After the reaction is completed, wait for the reaction system to cool to room temperature, transfer it to a dialysis bag, dialyze with deionized water for 2 days, and then freeze dry to obtain the cationic matrix. S2. Dissolve the cationic matrix prepared in step S1 in 100 mL of anhydrous THF, introduce flowing nitrogen into the reaction system, add 24 mL of triethoxysilane, and mix at 400 rpm until the reaction system is homogeneous. Dilute 32 mg of platinum catalyst with 5 mL of anhydrous THF and add it to the reaction system. After stirring and mixing evenly at room temperature, raise the reaction temperature to 70 °C to carry out the hydrosilylation reaction. After the reaction is completed, add activated carbon to remove the platinum catalyst, filter, collect the filtrate, remove excess reaction solvent, and dry under vacuum at 50 °C for 8 hours to obtain cationic siloxane. S3. Dissolve 3.0 g of sodium dodecyl sulfate in 100 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio), add 4.0 g of cationic siloxane prepared in step S2 and 8 mL of tetraethyl orthosilicate, mix well, adjust the reaction pH to 3, raise the reaction temperature to 45 °C, and carry out the gelation reaction for 8 h. After the reaction is completed, transfer the reaction system to a polytetrafluoroethylene reactor, and under sealed conditions, maintain the reaction temperature at 70 °C for aging reaction for 21 h. After the reaction is completed, after the reaction system is cooled to room temperature, add it to anhydrous ethanol / hydrochloric acid mixed solution (anhydrous ethanol:concentrated hydrochloric acid = 10:1, volume ratio), raise the reaction temperature to 65 °C again for reflux reaction for 9 h. After the reaction is completed, centrifuge 10 mL at 8000 rpm, collect the precipitate, wash repeatedly with anhydrous ethanol, and vacuum dry at 60 °C for 10 h to obtain cationic nano silica. S4. Under light-protected conditions, 50 mg of EGCG was dissolved in 50 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio). 1.0 g of the cationic nano-silica prepared in step S3 was added to the reaction system. After passing through flowing nitrogen gas, the reaction was kept at room temperature in a sealed environment. The mixture was stirred at 300 rpm for 21 h, then centrifuged at 12000 rpm for 20 min. The precipitate was collected, washed repeatedly with deionized water and anhydrous ethanol, and dried under vacuum to obtain EGCG-loaded nanoparticles. The preparation method of modified chitosan specifically includes the following steps: S5. Take 2.0 g of chitosan and disperse it in 40 mL of NaOH aqueous solution (10 wt%). Stir at 300 rpm at room temperature to carry out the activation reaction. After 2 h of reaction, filter and collect the solid. Wash it with deionized water until neutral and then dry it under vacuum at 60 °C for 4 h to obtain activated chitosan. S6. Disperse the activated chitosan prepared in step S5 into 50 mL of DMF and magnetically stir at 300 rpm to ensure uniform dispersion of the reaction system. Dissolve 3.6 g of N,N-dimethylaminochloropropane hydrochloride in 10 mL of DMF to obtain an N,N-dimethylaminochloropropane hydrochloride / DMF solution. Add the solution dropwise to the reaction system at a rate of 0.2 mL / min. Purge with flowing nitrogen gas and raise the reaction temperature to 65 °C under a nitrogen protective atmosphere to carry out the substitution reaction. After the reaction is completed, let the reaction system cool to room temperature and add anhydrous ethanol for alcohol precipitation. Filter, collect the precipitate, wash with anhydrous ethanol, and dry under vacuum at 60 °C for 6 h to obtain the first modified chitosan. S7. Dissolve the first modified chitosan prepared in step S6 in 80 mL of acetone, and add 2.5 mL of allyl chloride dropwise to the reaction system at a rate of 1 drop / s. During the dropwise addition, stir at a speed of 250 rpm. After the dropwise addition is completed, increase the stirring speed to 350 rpm at room temperature to carry out the quaternization reaction. After the reaction is completed, add anhydrous diethyl ether for precipitation treatment, filter, collect the precipitate, wash repeatedly with anhydrous methanol, and dry under vacuum at 50°C for 5 h to obtain the second modified chitosan. S8. Take the second modified chitosan prepared in step S7 and 0.15 g of potassium carbonate into a flask, add 80 mL of DMF to completely dissolve the reactants, then slowly add 3.0 g of 1,3-propanesulfonate lactone to the reaction system. After passing through flowing nitrogen gas, raise the reaction temperature to 75 °C under a nitrogen protective atmosphere to carry out the sulfonation reaction for 6 h. After the reaction is completed, add deionized water and mix well, then transfer to a dialysis bag and dialyze with deionized water for 3 days, changing the water 3 times a day to remove unreacted 1,3-propanesulfonate lactone, potassium carbonate and small molecule impurities. After freeze-drying, the modified chitosan is obtained. This embodiment also provides a method for preparing an EGCG-based functional adhesive for orthodontic brackets, specifically including the following steps: ① Take 2.0 g of EGCG-supported nanoparticles and disperse them in 200 mL of deionized water to obtain an aqueous phase of EGCG-supported nanoparticles; ② Take 3.5g of modified chitosan and add it to 100mL of cyclohexane. Stir until the modified chitosan is completely dissolved to obtain the modified chitosan oil phase. ③ Take the aqueous phase of EGCG-supported nanoparticles prepared in step ①, introduce flowing nitrogen gas to replace the air in the system, and stir at 200 rpm under a nitrogen atmosphere. Add the modified chitosan oil phase prepared in step ② dropwise to the aqueous phase of EGCG-supported nanoparticles prepared in step ① through a constant pressure dropping funnel. After the addition is complete, stir continuously at 200 rpm for 2 hours at room temperature. After the reaction is completed, collect the lower aqueous phase, centrifuge at 12000 rpm for 10 min, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and dry under vacuum at 50℃ for 6 hours to obtain chitosan@EGCG-supported nanoparticles. ④ In a light-proof three-necked flask, add bisphenol A dimethacrylate and triethylene glycol dimethacrylate, stir magnetically at 35°C for 20 minutes to mix evenly, add camphorquinone and dimethylaminoethyl methacrylate, stir at 25°C for 20 minutes under light-proof conditions to make the initiator evenly dispersed, and obtain the resin matrix. ⑤ Under light-protected conditions, the chitosan@EGCG supported nanoparticles prepared in step ③ are added to the resin matrix in portions. After each addition, the mixture is stirred at 500 rpm for 30 min, then ultrasonically dispersed at 300 W for 30 min. After vacuum degassing, the mixture is stored in the dark to obtain the functional binder.

[0017] Example 3 This embodiment provides an EGCG-based functional adhesive for orthodontic brackets, the functional adhesive comprising the following components in parts by weight: 30 parts bisphenol A dimethacrylate, 15 parts triethylene glycol dimethacrylate, 0.8 parts camphorquinone, 0.8 parts dimethylaminoethyl methacrylate, 5 parts EGCG-loaded nanoparticles, and 8 parts modified chitosan. The preparation method of EGCG-supported nanoparticles specifically includes the following steps: S1. Place 9.0 mL of diallylamine and 8.5 mL of dimethylamine (40 wt% aqueous solution) in a flask, add 100 mL of deionized water, maintain the reaction temperature at 30 °C, add 12.0 mL of epichlorohydrin in three portions, and stir at 250 rpm. After mixing evenly, raise the reaction temperature to 90 °C and carry out the polymerization reaction for 2 hours. After the reaction is completed, wait for the reaction system to cool to room temperature, transfer it to a dialysis bag, dialyze with deionized water for 2 days, and then freeze-dry to obtain the cationic matrix. S2. Dissolve the cationic matrix prepared in step S1 in 100 mL of anhydrous THF, introduce flowing nitrogen into the reaction system, add 32 mL of triethoxysilane, and mix at 400 rpm until the reaction system is homogeneous. Dilute 24 mg of platinum catalyst with 5 mL of anhydrous THF and add it to the reaction system. After stirring and mixing evenly at room temperature, raise the reaction temperature to 80 °C to carry out the hydrosilylation reaction. After the reaction is completed, add activated carbon to remove the platinum catalyst, filter, collect the filtrate, remove excess reaction solvent, and dry under vacuum at 50 °C for 8 hours to obtain cationic siloxane. S3. Dissolve 4.0 g of sodium dodecyl sulfate in 100 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio), add 6.0 g of cationic siloxane prepared in step S2 and 10 mL of tetraethyl orthosilicate, mix well, adjust the reaction pH to 2, raise the reaction temperature to 40 °C, and carry out the gelation reaction for 7 h. After the reaction is completed, transfer the reaction system to a polytetrafluoroethylene reactor, and under sealed conditions, maintain the reaction temperature at 60 °C for aging reaction for 24 h. After the reaction is completed, after the reaction system is cooled to room temperature, add it to anhydrous ethanol / hydrochloric acid mixed solution (anhydrous ethanol:concentrated hydrochloric acid = 10:1, volume ratio), raise the reaction temperature to 60 °C again for reflux reaction for 12 h. After the reaction is completed, centrifuge 10 mL at 8000 rpm, collect the precipitate, wash repeatedly with anhydrous ethanol, and vacuum dry at 60 °C for 10 h to obtain cationic nano silica. S4. Under light-protected conditions, 50 mg of EGCG was dissolved in 50 mL of ethanol-water solution (ethanol:water = 1:1, volume ratio). 1.5 g of the cationic nano-silica prepared in step S3 was added to the reaction system. After passing through flowing nitrogen gas, the reaction was kept at room temperature in a sealed environment. The mixture was stirred at 400 rpm for 24 h, then centrifuged at 12000 rpm for 20 min. The precipitate was collected, washed repeatedly with deionized water and anhydrous ethanol, and dried under vacuum to obtain EGCG-loaded nanoparticles. The preparation method of modified chitosan specifically includes the following steps: S5. Take 2.0 g of chitosan and disperse it in 40 mL of NaOH aqueous solution (10 wt%). Stir at 300 rpm at room temperature to carry out the activation reaction. After 2 h of reaction, filter and collect the solid. Wash it with deionized water until neutral and then dry it under vacuum at 60 °C for 4 h to obtain activated chitosan. S6. Disperse the activated chitosan prepared in step S5 into 50 mL of DMF and magnetically stir at 300 rpm to ensure uniform dispersion of the reaction system. Dissolve 4.0 g of N,N-dimethylaminochloropropane hydrochloride in 10 mL of DMF to obtain an N,N-dimethylaminochloropropane hydrochloride / DMF solution. Add the solution dropwise to the reaction system at a rate of 0.2 mL / min. Purge with flowing nitrogen gas and raise the reaction temperature to 70 °C under a nitrogen protective atmosphere to carry out the substitution reaction. After the reaction is completed, let the reaction system cool to room temperature and add anhydrous ethanol for alcohol precipitation. Filter, collect the precipitate, wash with anhydrous ethanol, and dry under vacuum at 60 °C for 6 h to obtain the first modified chitosan. S7. Dissolve the first modified chitosan prepared in step S6 in 80 mL of acetone, and add 3.0 mL of allyl chloride dropwise to the reaction system at a rate of 1 drop / s. During the dropwise addition, stir at a speed of 250 rpm. After the dropwise addition is completed, increase the stirring speed to 300 rpm at room temperature to carry out the quaternization reaction. After the reaction is completed, add anhydrous diethyl ether for precipitation treatment, filter, collect the precipitate, wash repeatedly with anhydrous methanol, and dry under vacuum at 50°C for 5 h to obtain the second modified chitosan. S8. Take the second modified chitosan prepared in step S7 and 0.2g of potassium carbonate into a flask, add 80 mL of DMF to completely dissolve the reactants, then slowly add 3.5g of 1,3-propanesulfonate lactone to the reaction system. After passing through flowing nitrogen gas, raise the reaction temperature to 80℃ under a nitrogen protective atmosphere to carry out the sulfonation reaction for 5 hours. After the reaction is completed, add deionized water and mix well. Transfer the mixture to a dialysis bag and dialyze with deionized water for 3 days, changing the water 3 times a day to remove unreacted 1,3-propanesulfonate lactone, potassium carbonate and small molecule impurities. After freeze-drying, the modified chitosan is obtained. This embodiment also provides a method for preparing an EGCG-based functional adhesive for orthodontic brackets, specifically including the following steps: ① Take 2.5g of EGCG-supported nanoparticles and disperse them in 200mL of deionized water to obtain an aqueous phase of EGCG-supported nanoparticles; ② Take 4.0g of modified chitosan and add it to 100mL of cyclohexane. Stir until the modified chitosan is completely dissolved to obtain the modified chitosan oil phase. ③ Take the aqueous phase of EGCG-supported nanoparticles prepared in step ①, introduce flowing nitrogen gas to replace the air in the system, and stir at 200 rpm under a nitrogen atmosphere. Add the modified chitosan oil phase prepared in step ② dropwise to the aqueous phase of EGCG-supported nanoparticles prepared in step ① through a constant pressure dropping funnel. After the addition is complete, stir continuously at 200 rpm for 2 hours at room temperature. After the reaction is completed, collect the lower aqueous phase, centrifuge at 12000 rpm for 10 min, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and dry under vacuum at 50℃ for 6 hours to obtain chitosan@EGCG-supported nanoparticles. ④ In a light-proof three-necked flask, add bisphenol A dimethacrylate and triethylene glycol dimethacrylate, stir magnetically at 40°C for 30 minutes to mix evenly, add camphorquinone and dimethylaminoethyl methacrylate, stir at 25°C for 20 minutes under light-proof conditions to make the initiator evenly dispersed, and obtain the resin matrix. ⑤ Under light-protected conditions, the chitosan@EGCG supported nanoparticles prepared in step ③ are added to the resin matrix in portions. After each addition, the mixture is stirred at 500 rpm for 30 min, then ultrasonically dispersed at 300 W for 30 min. After vacuum degassing, the mixture is stored in the dark to obtain the functional binder.

[0018] Comparative Example 1 This comparative example provides a functional adhesive and its preparation method. The only difference between this example and Example 1 is that all components do not contain modified chitosan, while the remaining components and their contents are the same as in Example 1.

[0019] Comparative Example 2 This comparative example provides a functional binder and its preparation method. The only difference between this and Example 1 is that the preparation method of the EGCG-loaded nanoparticles does not include steps S1 and S2. In step S3, cationic siloxane is replaced with tetraethyl orthosilicate by mass to obtain nano-silica. After loading treatment in step S4, EGCG-loaded nanoparticles are obtained. These EGCG-loaded nanoparticles do not exhibit electropositivity. The remaining components and their contents are the same as in Example 1.

[0020] Comparative Example 3 This comparative example provides a functional adhesive and its preparation method. The only difference between this example and Example 1 is that, in all components, unmodified commercially available chitosan is used to replace modified chitosan, while the remaining components and their contents are the same as in Example 1.

[0021] Experimental Example 1 This experimental example tests the EGCG sustained-release performance of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3. The functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were cured and processed into 4×4×4mm shapes. 3 Standard samples were prepared, and phosphate buffer solutions with different pH values ​​were used as release media to simulate different oral environments and test the sustained-release effect of EGCG. EGCG standard solutions were prepared, and a standard curve was plotted. Samples were taken at time points (1h, 2h, 4h, 8h, 24h), and the concentration of EGCG was determined by UV-VIS (~273nm). The cumulative release rate (%) was calculated using the following formula: ; Among them, C t V: Drug concentration (µg / mL) measured at time point t, V: Total volume of release medium (mL) s : Volume (mL) of each sample taken, C i : The concentration (µg / mL) measured at the i-th time point previously; Figure 1 The graph shows the cumulative release rate of EGCG of the functional binders prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention in an environment with pH=7.4. Figure 2The graph shows the cumulative release rate of EGCG of the functional binders prepared in Examples 1-3 and Comparative Examples 1-3 of this invention in an environment of pH=5.0. As shown in the figure, the release rate of all examples shows that the acidic environment (pH=5.0) > the neutral environment (pH=7.4). Under acidic conditions, the modified chitosan coating layer undergoes amino protonation, molecular chain swelling, and increased porosity, which reduces the diffusion resistance of EGCG. The electrostatic binding force between cationic nano silica and EGCG is weakened, making it easier for EGCG to detach from the carrier, thus accelerating release through a dual effect. At the same time, the increased content of functional components increases the total amount of EGCG that can be released inside the binder. The thickness of the modified chitosan coating layer is moderately increased, but it does not excessively hinder diffusion. Moreover, more coating layers provide stronger pH-responsive sites, balancing release amount and controllability. Under neutral conditions, the 24-hour release rate is only 38.5%-48.6%, reflecting slow and continuous release characteristics. Under acidic conditions, the 24-hour release rate is 62.8%-75.3%, achieving rapid release on demand and fully adapting to oral pH fluctuation scenarios. In Comparative Example 1, the lack of a modified chitosan coating layer meant that EGCG relied solely on cationic nano-silica for loading, lacking secondary barrier protection. This resulted in a significantly accelerated release rate, weakened pH responsiveness, and an inability to achieve on-demand release. EGCG was prone to rapid loss, leading to poor long-term antibacterial effects. In Comparative Example 2, the nano-silica lacked cationic modification and relied solely on physical adsorption to bind with EGCG. Without the pH synergy of the modified chitosan coating layer, the release rate was extremely low, and pH responsiveness was almost nonexistent. Even in an acidic oral environment, EGCG was difficult to release effectively and could not exert its antibacterial effect. In Comparative Example 3, the unmodified chitosan exhibited poor solubility and low swelling in neutral / acidic environments, resulting in insufficient pH responsiveness. Consequently, the 24-hour release rate difference between acidic and neutral environments was only 12.5%, and the 24-hour cumulative release rate was between that of the examples and Comparative Example 1. However, the release curve fluctuated greatly, failing to achieve a stable release effect.

[0022] Experimental Example 2 The antibacterial properties of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were tested using Streptococcus mutans (ATCC25175). The adhesive was prepared into 5mm diameter discs, placed on agar plates inoculated with bacterial solution, and incubated at 37°C for 24 hours. The diameter of the inhibition zone was then measured.

[0023] Figure 3The graph shows the antibacterial performance results of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 of this invention. As shown in the figure, the content of functional components increases with each example, resulting in an increase in the total amount of EGCG released by the adhesive during the 24-hour culture period. This leads to a higher effective antibacterial concentration diffused into the agar, forming a larger antibacterial zone. The pH responsiveness of modified chitosan accelerates the release of EGCG, ensuring a sustained high EGCG concentration in areas with active bacteria and enhancing the antibacterial effect. Comparative Example 1 shows antibacterial performance far exceeding all examples, seemingly having the best effect. However, it is necessary to consider the principle of the inhibition zone test (24-hour static diffusion) and the actual needs of the oral cavity (long-term dynamic antibacterial). Without the modified chitosan coating layer, EGCG is only supported by cationic nano-silica, resulting in no secondary barrier to release. The total amount of EGCG released within 24 hours is much higher than in the examples. The core of the inhibition zone test is the total amount of EGCG diffused into the agar within 24 hours. Although Comparative Example 1 releases too quickly and lacks long-term effectiveness, its high short-term release allows for a larger diffusion range in the agar, resulting in the largest inhibition zone diameter.

[0024] Experiment Example 4 The functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to cytotoxicity tests using the CCK-8 assay to evaluate the toxicity of the materials to oral mucosal cells. The adhesives from Examples 1-3 and Comparative Examples 1-3 were cured according to standard processes, processed into discs with a diameter of 5 mm and a thickness of 1 mm, sterilized, and prepared as samples. The sterilized samples were immersed in DMEM medium containing 10% fetal bovine serum at a ratio of 1 g to 10 mL of culture medium, and allowed to stand at 37°C and 5% CO2 for 24 h to prepare a 100% concentration extract. This extract was then diluted with fresh culture medium to prepare 50%, 25%, and 10% concentrations for later use.

[0025] The experimental cells were human gingival fibroblasts (HGF-1). After being cultured to the logarithmic growth phase, the HGF-1 cells were inoculated at a rate of 1×10⁻⁶ cells / year. 4 Cells were seeded at a density of 100 μL / well in 96-well plates, with 100 μL of culture medium added to each well. After 24 h of incubation to allow cell adhesion, the old culture medium was discarded. 100 μL of different concentrations of extraction buffer (10%, 25%, 50%, and 100%) were added to each well, with three replicates for each concentration. A negative control (fresh DMEM medium) and a positive control (medium containing 0.1% Triton X-100) were also included. Cells were incubated for another 24 h. 20 μL of MTT solution (5 mg / mL) was added to each well, and the plates were incubated in the dark for 4 h. The liquid in the wells was then discarded. 150 μL of LDMSO was added to each well to dissolve formazan crystals, and the plates were shaken for 10 min to ensure complete dissolution. The absorbance (OD) of each well was measured at 490 nm using a microplate reader. The data were recorded, and the cell viability (%) was calculated using the following formula: ; Among them, OD n OD0 represents the OD value of the experimental group, and OD0 represents the OD value of the control group. - The OD value is for the negative control group. Figure 4 The figures show the in vitro cytotoxicity results of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 of this invention. As shown in the figures, the cell viability of all examples remained at a high level at 10%-100% extract concentration, and only decreased slowly with increasing concentration. Comparative Example 1 lacked the modified chitosan coating layer, and the unreacted monomers in the resin group were more easily released into the extract. These acrylate monomers are cytotoxic to HGF-1, leading to a sharp drop in viability. Comparative Example 2 omitted the S1-S2 steps and directly prepared nano-silica from tetraethyl orthosilicate. The surface charge of the unmodified nano-silica was disordered, which easily combined with the negative charge on the cell surface to "aggregate and encapsulate the cells," resulting in the inability of cells to proliferate. In Comparative Example 3, the unmodified chitosan had poor solubility in DMEM medium (easily forming white particles). These particles physically stimulated HGF-1. At the same time, the amino groups of the unmodified chitosan were easily protonated in the culture medium, causing the local pH to drop to 5.0-5.5. The acidic environment inhibited cell proliferation.

[0026] Experimental Example 5 In vivo toxicity tests were conducted on the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 in rats. SPF-grade SD rats, half male and half female, weighing 180-220g (n=36, 6 rats per group, including 3 males and 3 females), were selected. After acclimatization for 3 days, the experiment began. The ambient temperature was 23±2℃, humidity 50±10%, and a 12-hour light-dark cycle was maintained. The functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 were cured and processed into 2×2×1mm samples, which were then implanted subcutaneously into the backs of rats. Six rats were treated in each group. Observations were conducted at 1, 7, 14, and 28 days post-implantation to observe for redness, swelling, exudation, necrosis, and ulceration at the implantation site. At each time point, a corresponding number of rats were sacrificed (1 rat per group at 1, 7, and 14 days; the remaining 3 rats per group were sacrificed at 28 days). Subcutaneous tissue was removed from the implantation site, and the diameter of the inflamed area was measured. Local toxicity was evaluated according to ISO 10993-6 standard. Non-toxic: The diameter of the inflamed area is <2mm, with only a small number of lymphocytes infiltrating, and no fibrosis or necrosis; Mild toxicity: Inflammatory area diameter 2-4 mm, moderate amount of inflammatory cell infiltration, mild fibrosis, no necrosis; Moderate toxicity: The inflamed area is 4-6 mm in diameter, with extensive infiltration of inflammatory cells, obvious fibrosis, and mild local necrosis; Severe toxicity: Inflammatory area diameter > 6 mm, severe inflammatory cell infiltration, severe fibrosis, and large-area necrosis; The table below shows the local toxicity evaluation of the functional adhesives prepared in Examples 1-3 and Comparative Examples 1-3 of this invention: ; As shown in the table, the local reactions in all embodiments showed a trend of initial mild irritation followed by rapid resolution. The core reason is that the components synergistically reduce local irritation. The modified chitosan coating layer has a buffering effect. The modified chitosan slowly degrades in the subcutaneous tissue, and the released amino and sulfonic acid groups can buffer acidic substances that may be released from the resin matrix, avoiding sudden changes in local pH that could irritate the tissue. At the same time, its degradation products are small molecule polysaccharides that can be metabolized by the tissue without leaving any foreign matter. EGCG is slowly released through pH response, which can inhibit local inflammatory factors and accelerate the resolution of inflammation. In Comparative Example 1, the lack of a modified chitosan coating layer allowed unreacted monomers such as bisphenol A dimethacrylate and triethylene glycol dimethacrylate in the resin matrix to be continuously released into the subcutaneous tissue. These acrylate monomers can damage tissue cell membranes and induce neutrophil aggregation. In Comparative Example 2, the uneven surface charge of the unmodified nano-silica made it prone to agglomeration into micron-sized particles, stimulating the tissue to produce a foreign body reaction, leading to severe fibrosis and local necrosis. Impurities were continuously released, and the particles could not be metabolized by the tissue, maintaining moderate toxicity even after 28 days, completely failing to meet the local safety requirements for oral medical devices. In Comparative Example 3, unmodified chitosan had poor solubility in subcutaneous tissue and easily formed insoluble particles. These particles physically scratched the local tissue, hindered tissue repair, and caused mild inflammation. At the same time, the protonation of the amino groups in unmodified chitosan led to mild local acidification, prolonging the inflammation resolution time.

[0027] 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.

[0028] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A functional adhesive based on EGCG for orthodontic brackets, characterized in that: The functional adhesive comprises the following components in parts by weight: 25-30 parts of bisphenol A dimethacrylate, 15-20 parts of triethylene glycol dimethacrylate, 0.6-0.8 parts of camphorquinone, 0.6-0.8 parts of dimethylaminoethyl methacrylate, 3-5 parts of EGCG-supported nanoparticles, and 6-8 parts of modified chitosan.

2. The EGCG-based functional adhesive for orthodontic brackets according to claim 1, characterized in that: The preparation method of the EGCG-supported nanoparticles specifically includes the following steps: S1, diallylamine and dimethylamine aqueous solution are placed in a flask, deionized water is added and mixed evenly, the reaction temperature is maintained at 30-50℃, epichlorohydrin is added stepwise, and after stirring until evenly mixed, the reaction temperature is increased to carry out the polymerization reaction. After the reaction is completed, the mixture is cooled, placed in a dialysis bag, dialyzed for 2-3 days, and then freeze-dried to obtain the cationic matrix. S2. Dissolve the cationic matrix prepared in step S1 in anhydrous THF, introduce flowing nitrogen gas, add triethoxysilane and mix well, dilute the platinum catalyst with anhydrous THF and add it to the reaction system, mix well at room temperature, raise the reaction temperature to carry out hydrosilylation reaction, after the reaction is completed, add activated carbon and stir, filter, collect the filtrate, concentrate by rotary evaporation to remove excess reaction solvent, and dry under vacuum to obtain cationic siloxane. S3. Dissolve sodium dodecyl sulfate in an ethanol aqueous solution, add the cationic siloxane and tetraethyl orthosilicate prepared in step S2, mix well, adjust the reaction pH to 2-4, and carry out a gelation reaction. After the reaction is completed, transfer the reaction system to a polytetrafluoroethylene reactor and carry out an aging reaction under sealed conditions. After the reaction is completed, add it to an anhydrous ethanol / hydrochloric acid mixed solution and carry out a reflux reaction. After the reaction is completed, centrifuge, collect the precipitate, wash it repeatedly with anhydrous ethanol, and vacuum dry it to obtain cationic nano silica. S4. Dissolve EGCG in an ethanol-water solution under light-protected conditions. Add the cationic nano-silica prepared in step S3 to the reaction system. After introducing flowing nitrogen gas, stir at 300-500 rpm for 18-24 hours under sealed conditions and room temperature. Centrifuge, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and vacuum dry to obtain EGCG-loaded nanoparticles.

3. The EGCG-based functional adhesive for orthodontic brackets according to claim 2, characterized in that: The preparation method of the modified chitosan specifically includes the following steps: S5. Chitosan was dispersed in NaOH aqueous solution and activated at room temperature. The mixture was filtered, the solid was collected, washed with deionized water until neutral, and then dried under vacuum to obtain activated chitosan. S6. Disperse the activated chitosan prepared in step S5 into DMF, slowly add N,N-dimethylaminochloropropane hydrochloride / DMF solution to the reaction system, introduce flowing nitrogen gas, raise the reaction temperature to carry out the substitution reaction, after the reaction is completed, add anhydrous ethanol for alcohol precipitation, filter, collect the precipitate, wash with anhydrous ethanol, and vacuum dry to obtain the first modified chitosan. S7. Dissolve the first modified chitosan prepared in step S6 in acetone, slowly add allyl chloride to the reaction system, and after the addition is complete, carry out the quaternization reaction at room temperature. After the reaction is complete, add anhydrous diethyl ether for precipitation treatment, filter, collect the precipitate, wash with anhydrous methanol, and vacuum dry to obtain the second modified chitosan. S8. Take the second modified chitosan prepared in step S7 and potassium carbonate into a flask, add DMF to completely dissolve the reactants, slowly add 1,3-propanesulfonate lactone into the reaction system, introduce flowing nitrogen gas, raise the reaction temperature to carry out the sulfonation reaction, after the reaction is completed, add deionized water and mix evenly, transfer to a dialysis bag for dialysis treatment to obtain modified chitosan.

4. The EGCG-based functional adhesive for orthodontic brackets according to claim 3, characterized in that: In step S1, the volume ratio of diallylamine, dimethylamine aqueous solution and epichlorohydrin is 3.5-4.5:1.3-1.7:4.5-6; in step S1, the polymerization reaction temperature is 80-90℃, the polymerization reaction time is 2-3h, the polymerization reaction stirring speed is 200-300rpm, and the polymerization reaction environment pH is 8-9.

5. The EGCG-based functional adhesive for orthodontic brackets according to claim 4, characterized in that: In step S2, the volume ratio between the triethoxysilane and the diallylamine in step S1 is 3-4:1; in step S2, the added mass of the platinum catalyst is 0.1%-0.2% of the mass of the triethoxysilane; in step S2, the reaction temperature of the hydrosilylation reaction is 60-80℃, and the reaction time of the hydrosilylation reaction is 6-8h.

6. The EGCG-based functional adhesive for orthodontic brackets according to claim 5, characterized in that: In step S3, the mass ratio of sodium dodecyl sulfate to cationic siloxane is 2-4:2-6; in step S3, the mass-to-volume ratio of cationic siloxane to tetraethyl orthosilicate is 1g:2-3mL; in step S3, the gelation reaction temperature is 40-50℃ and the reaction time is 5-8h; in step S3, the aging reaction temperature is 60-80℃ and the reaction time is 18-24h; in step S3, the reflux reaction temperature is 60-70℃ and the reaction time is 6-12h.

7. The EGCG-based functional adhesive for orthodontic brackets according to claim 6, characterized in that: In step S4, the mass ratio between EGCG and cationic nano-silica is 1:2-4.

8. The EGCG-based functional adhesive for orthodontic brackets according to claim 7, characterized in that: In step S6, the mass ratio between N,N-dimethylaminochloropropane hydrochloride and chitosan in step S5 is 1:1.6-2; in step S6, the reaction temperature of the substitution reaction is 60-70℃, and the reaction time of the substitution reaction is 4-6h. In step S7, the mass-to-volume ratio of N,N-dimethylaminochloropropane hydrochloride to allyl chloride in step S6 is 3.2-3.6 g: 2-3 mL; in step S7, the stirring speed of the quaternization reaction is 300-400 rpm, and the reaction time of the quaternization reaction is 4-6 h.

9. The EGCG-based functional adhesive for orthodontic brackets according to claim 8, characterized in that: In step S8, the mass ratio of chitosan to potassium carbonate in step S5 is 2:0.1-0.2; in step S8, the mass ratio of chitosan to 1,3-propanesulfonate lactone in step S5 is 2:2.5-3.5; in step S8, the sulfonation reaction temperature is 70-80℃, and the sulfonation reaction time is 5-7h.

10. A method for preparing an EGCG-based functional adhesive for orthodontic brackets according to any one of claims 1-9, characterized in that: Specifically, the following steps are included: ① Disperse EGCG-supported nanoparticles in deionized water to obtain an aqueous phase of EGCG-supported nanoparticles; ② Add the modified chitosan to cyclohexane and stir until the modified chitosan is completely dissolved to obtain the modified chitosan oil phase; ③ Take the aqueous phase of EGCG-supported nanoparticles prepared in step ①, introduce flowing nitrogen gas to replace the air in the system, and stir at 200-400 rpm under a nitrogen atmosphere. Add the modified chitosan oil phase prepared in step ② dropwise to the aqueous phase of EGCG-supported nanoparticles prepared in step ① through a constant pressure dropping funnel. After the addition is complete, continue stirring the reaction at room temperature for 2-3 hours. After the reaction is complete, collect the lower aqueous phase, centrifuge, collect the precipitate, wash repeatedly with deionized water and anhydrous ethanol, and vacuum dry to obtain chitosan@EGCG-supported nanoparticles. ④ In a light-proof three-necked flask, add bisphenol A dimethacrylate and triethylene glycol dimethacrylate, mix well, add camphorquinone and dimethylaminoethyl methacrylate, and stir under light-proof conditions until the initiator is evenly dispersed to obtain the resin matrix; ⑤ Under light-protected conditions, the chitosan@EGCG loaded nanoparticles prepared in step ③ are added to the resin matrix in portions. After each addition, the nanoparticles are ultrasonically dispersed, degassed under vacuum, and stored in the dark to obtain the functional binder.

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