A nanoscale hollow structure bioactive glass microsphere and its preparation method

Abstract

This invention discloses a nanoscale hollow structure bioactive glass microsphere and its preparation method, comprising: dissolving γ-polyglutamic acid (PGA) as a template agent in deionized water to prepare a γ-PGA solution of a certain concentration, denoted as solution A; adding tetraethyl orthosilicate, triethyl phosphate, and calcium chloride to anhydrous ethanol to prepare a bioactive glass precursor solution, denoted as solution B; mixing solutions A and B uniformly and adjusting the pH of the reaction system with ammonia; collecting the reaction product by centrifugation after the reaction, and washing it with anhydrous ethanol and deionized water respectively; freeze-drying the washed product and removing the γ-PGA template by sintering to obtain hollow structure bioactive glass. The bioactive glass microspheres prepared by this invention have a uniform structure, a high specific surface area, and a hollow structure. The equipment used in this invention is simple, the raw materials are inexpensive, and mass production can be carried out under relatively mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of bone repair medical materials technology, specifically involving a nanoscale hollow structure bioactive glass microsphere and its preparation method. Background Technology

[0002] Bone defect repair and regeneration have always been key issues in clinical practice. Although bone has a certain self-healing capacity, large segmental bone defects are too severe to regenerate. To induce repair of large segmental bone defects, an increasing number of bioactive implant materials have been used in this research field.

[0003] Bioactive glass (BG) is one of the most promising biomaterials in the field of bone regeneration. Its most prominent feature is that after implantation, BG can form a bone-like hydroxyapatite layer on its surface, forming stable chemical bonds with bone tissue and inducing bone regeneration. Furthermore, studies have found that silicon, calcium, and phosphorus ions released during BG degradation can stimulate osteoblast proliferation and differentiation, promoting bone regeneration. The ability of BG to form hydroxyapatite (HCA) is influenced by many factors, including its composition, structure, particle size, surface microstructure, and surface area. Spherical bioactive glass nanoparticles (BGNs) are attracting increasing attention due to their small size and large specific surface area, resulting in high bioactivity. In addition, BGNs with hollow structures can serve as suitable drug carriers for delivering drugs, growth factors, and genes, thus enabling their better application in the treatment of bone diseases. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing nanoscale hollow bioactive glass microspheres.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing nanoscale hollow bioactive glass microspheres, characterized in that it includes:

[0008] After γ-polyglutamic acid is completely dissolved in deionized water, tetraethyl orthosilicate is added. After complete hydrolysis, the solution is recorded as solution A.

[0009] Anhydrous ethanol was added to deionized water, followed by triethyl phosphate and calcium chloride as a precursor solution for bioactive glass. The solution was stirred until homogeneous and then labeled as solution B.

[0010] The above solution A is slowly added dropwise to solution B, and the pH value of the reaction system is adjusted by ammonia.

[0011] After reacting under magnetic stirring, the reaction product was collected by centrifugation and washed with anhydrous ethanol and deionized water, respectively. The washed product was freeze-dried and then calcined to remove the γ-polyglutamic acid template, thus obtaining hollow bioactive glass.

[0012] As a preferred embodiment of the preparation method described in this invention, the theoretical molar ratio of the components of the nanoscale hollow structure bioactive glass microspheres is 75-90% SiO2, 6-16% CaO, and 4-10% P2O5.

[0013] In a preferred embodiment of the preparation method described in this invention, the concentration of γ-polyglutamic acid in solution A is 5wt%-15wt%, and the molecular weight is 150-200kDa; the mass fraction of tetraethyl orthosilicate is 11wt%-63wt%.

[0014] In a preferred embodiment of the preparation method described in this invention, the molar ratio of triethyl phosphate to calcium chloride in solution B is 1:4 to 1:0.77.

[0015] As a preferred embodiment of the preparation method described in this invention, anhydrous ethanol is added to the deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 4:1 and the volume fraction is 30% to 70%.

[0016] In a preferred embodiment of the preparation method described in this invention, solution A is added to solution B and the pH value of the system is adjusted to 10.5.

[0017] In a preferred embodiment of the preparation method described in this invention, the magnetic stirring temperature is 40°C and the reaction time is 6 hours.

[0018] In a preferred embodiment of the preparation method described in this invention, the washing with anhydrous ethanol and deionized water is performed 2 to 3 times.

[0019] In a preferred embodiment of the preparation method described in this invention, the washed product is freeze-dried at a temperature of -20°C for 8 hours.

[0020] In a preferred embodiment of the preparation method described in this invention, the washed product is freeze-dried and then calcined at a temperature of 650°C for 10 hours.

[0021] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing nanoscale hollow bioactive glass microspheres.

[0022] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing nanoscale hollow bioactive glass microspheres, and to apply the product obtained by the method in the field of repair medical materials technology.

[0023] Beneficial effects of this invention:

[0024] (1) The bioactive glass microspheres prepared by the present invention have a uniform structure, a high specific surface area, and a hollow structure.

[0025] (2) The microemulsion technology used in this invention can synthesize BGNs with good dispersibility and uniform composition.

[0026] (3) The equipment used in this invention is simple, the raw materials are inexpensive, and it can be mass-produced in a relatively mild environment without any additives, making it green, environmentally friendly and pollution-free. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0028] Figure 1 This is a TEM image of the bioactive glass microspheres prepared in Example 1 of the present invention.

[0029] Figure 2 This is the SEM image of the bioactive glass microspheres prepared in Example 2 of the present invention.

[0030] Figure 3 The N2 adsorption-desorption isotherm (A) and pore size distribution curve (B) of the bioactive glass microspheres prepared in Example 2 of this invention are shown.

[0031] Figure 4 These are the FITR spectra of the bioactive glass microspheres prepared in Examples 1, 4, and 5 of this invention.

[0032] Figure 5 The images show the XRD patterns of bioactive glass microspheres prepared according to Example 1 of this invention, after being immersed in SBF solution for 1, 3, and 5 days.

[0033] Figure 6These are TEM images of the bioactive glass microspheres prepared in Comparative Examples 4-6 of this invention, used to investigate the effect of the volume ratio of anhydrous ethanol / deionized water on sample preparation.

[0034] Figure 7 These are TEM images of the bioactive glass microspheres prepared in Comparative Examples 1-3 of this invention, used to investigate the effect of pH value of the reaction environment on sample preparation.

[0035] Figure 8 These are TEM images of the bioactive glass microspheres prepared in Example 1 and Comparative Examples 9-10 of the present invention. Detailed Implementation

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0037] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0038] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0039] Note: γ-polyglutamic acid (γ-PGA, molecular weight 150-200kDa), TEOS (ethyl orthosilicate), TEP (triethyl phosphate).

[0040] Example 1

[0041] This embodiment illustrates a hydrothermal method for preparing hollow mesoporous bioactive glass microspheres, the steps of which are as follows:

[0042] (1) Using 0.3g of γ-PGA as a template, dissolve it in 20ml of deionized water. After the γ-PGA is completely dissolved, add 2.5g of tetraethyl orthosilicate to prepare solution A.

[0043] (2) Mix 0.55g triethyl phosphate, 0.30g anhydrous calcium chloride and 80mL anhydrous ethanol together to prepare solution B;

[0044] (3) Under stirring, add solution B to solution A at a constant speed, and adjust the pH of the reaction system with a 33% ammonia solution until the initial pH value is 10.5.

[0045] (4) The above solution was placed at 40°C for hydrothermal reaction for 6 hours to allow the system to react fully and form a milky white suspension.

[0046] (5) The above milky white suspension was allowed to stand at room temperature, and then washed by centrifugation with deionized water and anhydrous ethanol to obtain a wet white precipitate. The obtained white precipitate was freeze-dried to obtain a white dry powder.

[0047] (6) The obtained white powder was heat-treated in a high-temperature furnace at 650°C for 10 hours. The molar ratio of its components was 75% SiO2, 15% CaO, and 10% P2O5. Hollow mesoporous bioactive glass microspheres were obtained.

[0048] Example 2

[0049] This embodiment illustrates a hydrothermal method for preparing hollow mesoporous bioactive glass microspheres, the steps of which are as follows:

[0050] (1) Using 0.3g of γ-PGA as a template, dissolve it in 20ml of deionized water. After the γ-PGA is completely dissolved, add 14.15g of tetraethyl orthosilicate to prepare solution A.

[0051] (2) Mix 0.55g triethyl phosphate, 0.51g anhydrous calcium chloride and 80mL anhydrous ethanol together to prepare solution B;

[0052] (3) Under stirring, add solution B to solution A at a constant speed, and adjust the pH of the reaction system with a 33% ammonia solution to make the initial pH value 10.5.

[0053] (4) The above solution was placed at 40°C for hydrothermal reaction for 6 hours to allow the system to react fully and form a milky white suspension.

[0054] (5) The above milky white suspension was allowed to stand at room temperature, and then washed by centrifugation with deionized water and anhydrous ethanol to obtain a wet white precipitate. The obtained white precipitate was freeze-dried to obtain a white dry powder.

[0055] (6) The obtained white powder was heat-treated in a high-temperature furnace at 650℃ for 10 hours to obtain hollow mesoporous bioactive glass microspheres with a molar ratio of SiO2 90%, CaO 6%, and P2O5 4%. According to... Figure 3 The nitrogen adsorption-desorption curves and pore size distribution curves shown indicate that the prepared BGN exhibits typical mesoporous adsorption curve characteristics. The N2 adsorption-desorption isotherm is a type IV isotherm, and the H3 type hysteresis loop is present. Furthermore, the surface area, pore volume, and surface mesopore diameter of the prepared BGN are revealed to be 19.29 μm. 2 / g,0.08cm 3 / g, and 14.91nm.

[0056] Example 3

[0057] This embodiment illustrates a hydrothermal method for preparing hollow mesoporous bioactive glass microspheres, the steps of which are as follows:

[0058] (1) Using 0.3g of γ-PGA as a template, dissolve it in 20ml of deionized water. After the γ-PGA is completely dissolved, add 12.58g of tetraethyl orthosilicate to prepare solution A.

[0059] (2) Mix 0.55g triethyl phosphate, 1.34g anhydrous calcium chloride and 80mL anhydrous ethanol together to prepare solution B;

[0060] (3) Under stirring, add solution B to solution A at a constant speed, and adjust the pH of the reaction system with a 33% ammonia solution to make the initial pH value 10.5.

[0061] (4) The above solution was placed at 40°C for hydrothermal reaction for 6 hours to allow the system to react fully and form a milky white suspension.

[0062] (5) The above milky white suspension was allowed to stand at room temperature, and then washed by centrifugation with deionized water and anhydrous ethanol to obtain a wet white precipitate. The obtained white precipitate was freeze-dried to obtain a white dry powder.

[0063] (6) The white powder obtained was heat-treated in a high-temperature furnace at 650°C for 10 hours to obtain hollow mesoporous bioactive glass microspheres with a theoretical molar ratio of SiO2 80%, CaO 16%, and P2O5 4%.

[0064] Example 4

[0065] This embodiment illustrates a hydrothermal method for preparing hollow mesoporous bioactive glass microspheres, the steps of which are as follows:

[0066] (1) Using 0.1g γ-PGA as a template, dissolve it in 20ml of deionized water. After the γ-PGA is completely dissolved, add 2.5g TEOS to prepare solution A.

[0067] (2) Mix 0.55g triethyl phosphate, 0.301g anhydrous calcium chloride and 80mL anhydrous ethanol together to prepare solution B;

[0068] (3) Under stirring, add solution B to solution A at a constant speed, and adjust the pH of the reaction system with a 33% ammonia solution to make the initial pH value 10.5.

[0069] (4) The above solution was placed at 40°C for hydrothermal reaction for 6 hours to allow the system to react fully and form a milky white suspension.

[0070] (5) The above milky white suspension was allowed to stand at room temperature, and then washed by centrifugation with deionized water and anhydrous ethanol to obtain a wet white precipitate. The obtained white precipitate was freeze-dried to obtain a white dry powder.

[0071] (6) The obtained white powder was heat-treated in a high-temperature furnace at 650°C for 10 hours. The theoretical molar ratio of its components was 75% SiO2, 15% CaO, and 10% P2O5. Hollow mesoporous bioactive glass microspheres were obtained.

[0072] Example 5

[0073] The mesoporous bioactive glass prepared in this embodiment was immersed in a biomimetic liquid (SBF) to verify the mineralization properties and bioactivity of the material. The steps are as follows:

[0074] (1) Using 0.2g of γ-PGA as a template, dissolve it in 20ml of deionized water. After the γ-PGA is completely dissolved, add 2.5g of TEOS to prepare solution A.

[0075] (2) Mix 0.55g triethyl phosphate, 0.301g anhydrous calcium chloride and 80mL anhydrous ethanol together to prepare solution B;

[0076] (3) Under stirring, add solution B to solution A at a constant speed, and adjust the pH of the reaction system with a 33% ammonia solution to make the initial pH value 10.5.

[0077] (4) The above solution was placed at 40°C for hydrothermal reaction for 6 hours to allow the system to react fully and form a milky white suspension.

[0078] (5) The above milky white suspension was allowed to stand at room temperature, and then washed by centrifugation with deionized water and anhydrous ethanol to obtain a wet white precipitate. The obtained white precipitate was freeze-dried to obtain a white dry powder.

[0079] (6) The obtained white powder was heat-treated in a high-temperature furnace at 650°C for 10 hours. The theoretical molar ratio of its components was 75% SiO2, 15% CaO, and 10% P2O5. Hollow mesoporous bioactive glass microspheres were obtained.

[0080] Characterization test

[0081] The sample prepared in Example 1 was characterized by TEM, such as... Figure 1As shown, the prepared particles are hollow nanospheres with an average diameter of 103.9 ± 19.8 nm and a wall thickness of approximately 19.8 ± 6.9 nm.

[0082] Samples prepared in Examples 1, 4, and 5 were used, with the mass of the γ-PGA template as the controlled variable, and Fourier transform infrared spectroscopy (FITR) was performed to characterize them and verify the bioactive glass microsphere components. According to... Figure 4 As shown, at 456cm -1 801cm -1 and 1068cm -1 Obvious absorption peaks appeared at the locations, corresponding to the bending vibrations of Si-O-Si bonds, the stretching vibrations of Si-O (non-bridging oxygen) bonds, and the stretching vibrations of PO and Si-O-Si bonds, respectively. The results confirm that the main components of the sintered product include SiO2 and P2O5, and that the sintered product does not contain γ-PGA or other impurities.

[0083] 0.1 g of the prepared bioactive glass sample was dispersed in 50 ml of human body fluid (SBF), and X-ray diffraction (XRD) was performed on days 3 and 5. The results are as follows. Figure 5 As shown, according to Figure 5 As can be seen, after 5 days of soaking, two distinct peaks appeared in the XRD pattern of the sample at 2θ = 32° and 46°, which are characteristic peaks of hydroxyapatite (PDF#09-0432). The results confirm that the bioactive glass sample prepared in this invention has good in vitro mineralization ability.

[0084] Comparative Example 1

[0085] Unlike Example 1, the pH of the system was changed to 8.0, while the other experimental settings were the same as in Example 1.

[0086] Comparative Example 2

[0087] Unlike the previous example, the pH of the system was changed to 9.0, while the other experimental settings were the same as in Example 1.

[0088] Comparative Example 3

[0089] Unlike the previous example, the pH of the system was changed to 15.0, while the other experimental settings were the same as in Example 1.

[0090] Comparative Example 4

[0091] The volume ratio of deionized water to anhydrous ethanol was changed. Except that the volume ratio of deionized water to anhydrous ethanol in the test environment was 3:7, the experimental conditions and steps of this comparative example were the same as those in Example 1.

[0092] Comparative Example 5

[0093] The volume ratio of deionized water to anhydrous ethanol was changed. Except that the volume ratio of deionized water to anhydrous ethanol in the test environment was 1:1, the experimental conditions and steps of this comparative example were the same as those in Example 1.

[0094] Comparative Example 6

[0095] The volume ratio of deionized water to anhydrous ethanol was changed. Except that the volume ratio of deionized water to anhydrous ethanol in the test environment was 7:3, the experimental conditions and steps of this comparative example were the same as those in Example 1.

[0096] Comparative Example 7

[0097] (CN 107500553 B) A method for preparing needle-shaped bioactive glass microspheres:

[0098] (1) Add anhydrous ethanol, deionized water and ammonia to a 100ml beaker, place it on a magnetic stirrer, and stir for 30 minutes until a homogeneous and transparent solution A is obtained. The stirring speed is 600rpm.

[0099] (2) Add anhydrous ethanol and tetraethyl orthosilicate to a 100ml beaker in sequence, place it on a magnetic stirrer, and stir for 30 minutes until a homogeneous and transparent solution B is obtained. The stirring speed is 600rpm.

[0100] (3) Quickly add solution A from step (1) to solution B from step (2) to form suspension C. Stir at 1000 rpm for 1 hour.

[0101] (4) After adding calcium nitrate tetrahydrate to the suspension C in step (3) and stirring continuously for 1 hour, sonicate for 20 minutes, let stand and age for 1 day, wash three times with ethanol, freeze dry, and heat treat at 680℃ for 1 hour to obtain needle-shaped bioactive glass microspheres.

[0102] Comparative Example 8

[0103] Add anhydrous ethanol, deionized water and ammonia to a beaker, add γ-polyglutamic acid and place on a magnetic stirrer, stir until a homogeneous and transparent solution A is obtained;

[0104] Add anhydrous ethanol and tetraethyl orthosilicate sequentially to a beaker, place it on a magnetic stirrer, and stir until a homogeneous and transparent solution B is obtained;

[0105] Add solution A quickly to solution B to form suspension C, and stir continuously for 1 hour;

[0106] After adding calcium chloride to suspension C and stirring continuously for 1 hour, the mixture was sonicated, allowed to stand for aging, washed with ethanol, freeze-dried, and then subjected to heat treatment.

[0107] Comparative Example 9

[0108] A mixed solution was prepared by mixing water, ethanol, organic solvent, and surfactant cetyltrimethylammonium bromide (CTAB). Then, tetraethyl orthosilicate, catalyst, triethyl phosphate, and calcium chloride were added sequentially and stirred until homogeneous to obtain a bioactive glass gel solution. The bioactive glass gel solution was centrifuged and washed to obtain a wet gel precipitate. The wet gel precipitate was then dried in an oven to obtain bioactive glass gel powder. The bioactive glass gel powder was then heat-treated in a high-temperature furnace to obtain nano-bioactive glass microspheres.

[0109] Comparative Example 10

[0110] The catalyst was added to deionized water, followed by tetraethyl orthosilicate, triethyl phosphate, and calcium chloride. After hydrolysis, the organic template agent polyacrylic acid (PAA) was added and stirred thoroughly to obtain a sol. The sol was then aged to form a wet gel. The wet gel was washed with anhydrous ethanol. The wet gel was dried to obtain a dry gel, which was then placed in a crucible for heat treatment to obtain the final product.

[0111] Comparative examples 1-3 were characterized by TEM, and the results are as follows: Figure 7 As shown in the figure. The results showed that when the pH of the reaction environment was less than 9.0, the bioactive glass nanospheres exhibited severe aggregation and no obvious hollow structure; when the pH of the reaction environment was 9.0, the bioactive glass nanospheres possessed a hollow structure, and careful observation revealed the formation of a small number of mesopores on the glass surface; when the pH of the reaction environment was 10.5, the nanospheres exhibited the most regular morphology, the best dispersibility, and a distinct hollow structure. Therefore, this invention uses a component with a pH of 10.5 for the preparation of bioactive glass samples.

[0112] Comparative examples 4–6 were characterized by TEM, and the results are as follows: Figure 6 As shown, the results revealed that as the deionized water content gradually increased, the morphological regularity of the bioactive glass microspheres gradually decreased, and the dispersibility between microspheres gradually deteriorated. Furthermore, when the volume ratio of deionized water to anhydrous ethanol was greater than 1, the hollow structure of the microspheres disappeared, and severe aggregation occurred. Therefore, this invention uses a deionized water to anhydrous ethanol volume ratio of 1:4 for the preparation of bioactive glass samples. Compared to Comparative Example 7, the first BG obtained in this invention is a spherical nanoparticle; the second BG has a hollow structure. γ-Polyglutamic acid (PGA) in this invention acts as an organic template agent; without PGA, ordinary BG particles are obtained. Polyacrylic acid (PAA) has similar properties, and commonly used surfactants such as small CTAB were selected as a control to highlight the effect of PGA.

[0113] Comparative examples 8-10 were characterized by TEM, and the results are as follows: Figure 8As shown, the results revealed that when the same mass fraction of the surfactant cetyltrimethylammonium bromide (CTAB) was used, the product prepared was a solid bioactive glass nanosphere; when polyacrylic acid (PAA), which has a similar structure and contains a large number of carboxyl functional groups, was used as a template agent, bioactive glass nanospheres with a hollow structure could be obtained, but the dispersibility was poor and the aggregation was severe; when polyglutamic acid (γ-PGA) was selected as a template agent, nanospheres with better dispersibility and uniform size could be obtained.

[0114] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing nanoscale hollow bioactive glass microspheres, characterized in that: include, After γ-polyglutamic acid is completely dissolved in deionized water, tetraethyl orthosilicate is added. After the tetraethyl orthosilicate is completely hydrolyzed, it is recorded as solution A. Anhydrous ethanol was added to deionized water, followed by triethyl phosphate and calcium chloride as a precursor solution for bioactive glass. The solution was stirred until homogeneous and then labeled as solution B. The solution A above is slowly added dropwise to solution B, and the pH value of the reaction system is adjusted by ammonia water; After reacting under magnetic stirring, the reaction product was collected by centrifugation and washed with anhydrous ethanol and deionized water, respectively. The washed product was freeze-dried and then calcined to remove the γ-polyglutamic acid template and other impurities, resulting in nanoscale hollow bioactive glass microspheres. The concentration of γ-polyglutamic acid in solution A is 5wt%~15wt%, and the molecular weight is 150~200 kDa; the mass fraction of tetraethyl orthosilicate is 11wt%~63wt%. The molar ratio of triethyl phosphate to calcium chloride in solution B is 1:4 to 1:0.77; Anhydrous ethanol is added to the deionized water, wherein the volume ratio of anhydrous ethanol to deionized water is 4:1, and the volume fraction is 30%~70%. Under magnetic stirring, solution A was slowly added dropwise to solution B, and the pH of the system was adjusted to 10.

5.

2. The preparation method according to claim 1, characterized in that: The nanoscale hollow structure bioactive glass microspheres have the following molar fractions: SiO2: 75-90%, CaO: 6-16%, and P2O5: 4-10%.

3. The preparation method according to claim 1, characterized in that: The magnetic stirring temperature is 40℃ and the reaction time is 6h.

4. The preparation method according to claim 1, characterized in that: The washing process involves 2 to 3 times with anhydrous ethanol and deionized water.

5. The preparation method according to claim 1, characterized in that: The washed product is freeze-dried, wherein the freezing temperature is -20°C and the time is 8 hours.

6. The preparation method according to claim 5, characterized in that: The washed product is freeze-dried and then calcined to remove the γ-polyglutamic acid template and other impurities, wherein the calcination temperature is 650℃ and the time is 10h.

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