Preparation and application of cellulose-based alkali-responsive sustained-release microspheres

Abstract

The present invention belongs to the technical field of green environmental protection, and specifically relates to a method for preparing cellulose sustained-release drug-loaded microspheres and their application in pesticide carriers. The present invention discloses a method for preparing cellulose-based sustained-release drug-loaded microspheres, comprising the following steps: modifying cellulose through an esterification reaction, introducing a responsive group on the cellulose material, and obtaining modified cellulose; dissolving the pesticide agent and the modified cellulose material in a volatile organic solvent as an oil phase; dissolving a surfactant in water as an aqueous phase; mixing the oil phase and the aqueous phase, and volatilizing the volatile organic solvent from the resulting O / W emulsion under stirring conditions to form cellulose-based drug-loaded microspheres loaded with pesticides. The method of the present invention can achieve a drug loading rate of 61 to 66% for the microspheres, and the microspheres have a sensitive weak alkaline response performance, thereby realizing a responsive controlled release process of the encapsulated drug.

Description

Technical Field

[0001] The present invention belongs to the technical field of green environmental protection, thereby reducing the harmful effects of effective substances on organisms other than harmful organisms, and specifically relates to a preparation method of cellulose sustained-release drug-loaded microspheres and their application in pesticide carriers. Background Art

[0002] To ensure the safety and stability of food production, pesticides play a vital role in agriculture. Pesticides effectively control pests and diseases, saving 20-40% of total crop yield losses annually. Despite their significant effectiveness, traditional pesticides still suffer from drawbacks such as poor light resistance, high toxicity to non-target organisms, and difficulty in accurately delivering their active ingredients to target organisms. These factors lead to low utilization rates during field application, potentially leading to pesticide misuse and serious impacts on food safety and human health. To address this challenge, the development of eco-friendly, cost-effective, and intelligent controlled-release pesticide systems is of great practical significance. This will not only help address my country's current problems with pesticide residues and environmental pollution, but also contribute to ensuring food production safety, food safety, and ecological security, thereby promoting the pesticide industry and achieving sustainable and healthy agricultural development.

[0003] In recent years, by encapsulating pesticides in carrier materials to extend the duration of pesticide effectiveness and even improve the biological activity of pesticides, the purpose of improving the utilization rate of pesticides has been achieved, which has provided new ideas for the development of pesticides. For example, Liang et al. designed a nanoparticle with dual light / pH responsiveness to achieve controlled release of myclobutanil for the long-term prevention and control of rapeseed sclerotinia disease based on the acid production mechanism of rapeseed sclerotinia disease and the defects of low retention and easy off-target when spraying on leaves (ACSNano, 2021, 15 (4): 6987-6997). However, these methods have certain defects, including but not limited to cumbersome preparation processes and difficulty in degradation, which lead to great limitations in the actual industrial production of pesticides. It is of great significance to achieve cost-controllable industrial production of slow-release pesticides by selecting natural degradable materials and developing simple process routes.

[0004] As one of the most widespread and abundant polysaccharides in nature, cellulose boasts a high annual global production volume and is an inexhaustible biomass resource. Cellulose is non-toxic, renewable, biodegradable, and pollution-free, while also being lightweight and strong. These advantages make it a potentially ideal environmentally friendly material for agricultural applications.

[0005] For example, CN116172013 A discloses a slow-release pesticide loaded with carbendazim compounded with modified biochar and cellulose biomass, but the method has high energy consumption for the material modification process and complicated operation steps, which is not conducive to cost control in the industrial synthesis process. The drug loading rate of carbendazim is also low, and the highest can only reach about 36%. CN114766481A discloses a method for stabilizing Pickering emulsion using cellulose nanocrystals and encapsulating pesticides by interfacial polymerization with hexamethylene diisocyanate and ethylenediamine. This method avoids the large-scale use of emulsifiers and can achieve the encapsulation of pesticides at room temperature. However, since cellulose nanocrystals need to be prepared by applying a large amount of strong acid acid hydrolysis and must undergo washing and dialysis steps, the production capacity is limited and therefore will be subject to certain restrictions in the actual production process. It can be seen that the use of cellulose encapsulated drugs to achieve industrial production has certain challenges and practical significance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing weak base responsive cellulose-based drug-loaded microspheres.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing cellulose-based sustained-release microspheres, comprising the following steps:

[0008] 1) Preparation of modified cellulose:

[0009] Modifying cellulose by esterification reaction, introducing responsive groups into the cellulose material to obtain modified cellulose;

[0010] 2) dissolving the pesticide and the modified cellulose material in a volatile organic solvent, and the resulting mixed organic solution is used as the oil phase; dissolving the surfactant in water, and the resulting surfactant aqueous solution is used as the aqueous phase;

[0011] The oil phase and the water phase are mixed and emulsified to prepare an O / W emulsion;

[0012] 3) The O / W emulsion obtained in step 2) is subjected to volatilization of the volatile organic solvent under stirring conditions to form cellulose-based drug-loaded microspheres loaded with pesticides.

[0013] Note: Stir to evaporate the organic solvent, remove the organic solvent, and obtain a modified cellulose nanoparticle suspension.

[0014] As an improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention, step 1) is:

[0015] Add cellulose to an organic solvent, heat and stir at (50±10)°C until the cellulose is completely dissolved, cool to room temperature, first add an organic base and mix evenly, then add acyl chloride (add acyl chloride dropwise), heat to (50±10)°C and react for 3-12 hours, cool to room temperature, pour into water to precipitate, collect by suction, and vacuum dry the solid to obtain modified cellulose;

[0016] The usage ratio of the organic solvent to the cellulose is (15-30) ml:1 g; the mass ratio of the cellulose, the organic base and the acyl chloride is 1:(1-2):(1-2).

[0017] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the cellulose is at least one of microcrystalline cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose;

[0018] The organic solvent is at least one of acetonitrile, tetrahydrofuran, dimethylformamide, dichloromethane, dichloroethane, dimethylformamide, dimethylacetamide and dimethyl sulfoxide;

[0019] The organic base is at least one of triethylamine, N,N-diisopropylethylamine, pyridine, and 4-dimethylaminopyridine;

[0020] The acid chloride is at least one of methyl oxalyl chloride and ethyl oxalyl chloride.

[0021] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the step 2) is:

[0022] The oil phase is added dropwise to the water phase (addition is completed in about 3 to 7 minutes), and after high shear dispersion, cell disruption and emulsification are performed to obtain a homogenized emulsion;

[0023] The mass ratio of the modified cellulose, the pesticide agent and the volatile organic solvent is 1: (0.5-2.5): (10-20);

[0024] In the aqueous phase, the mass concentration of the surfactant is 0.25 to 2.0%;

[0025] The volume ratio of the oil phase to the water phase is 1:(3-5).

[0026] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the volatile organic solvent is at least one of acetonitrile, acetone, dichloromethane, dimethylformamide and dimethylacetamide;

[0027] The surfactant is at least any one (i.e., one or more) of cetyltrimethylammonium bromide, sodium dodecylsulfonate, sodium dodecylbenzenesulfonate, polyvinyl alcohol, styrylphenol formaldehyde resin, polyoxyethylene sorbitan monooleate, polyoxyethylene polyoxypropylene block polyether, alkylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene and silicone.

[0028] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the high-shear emulsion dispersion is processed (emulsification treatment) at 10,000 to 20,000 rpm for 3 to 10 minutes;

[0029] The cell disruption and emulsification were processed under 70% power (emulsification process) for 1 to 5 minutes.

[0030] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the volatilization of the volatile organic solvent in step 3) is carried out at 25-65° C. (preferably room temperature).

[0031] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the loaded pesticide is an insecticide, a fungicide or a herbicide.

[0032] As a further improvement to the preparation method of the cellulose-based sustained-release microspheres of the present invention: the pesticide agents are abamectin, fipronil, chlorpyrifos, indoxacarb, pyraclostrobin, metconazole, difenoconazole, fenpropimorph, prometryn, and quizalofop-Ph-ethyl.

[0033] The present invention uses cheap and readily available cellulose materials and can achieve mass production of modified cellulose materials through esterification modification, thus overcoming the problems of the prior art such as high material cost, complex process and difficulty in scaled-up production.

[0034] The method of the present invention utilizes the hydroxyl groups on a cellulose material for reactive modification under relatively mild reaction conditions, imparting environmentally specific responsiveness to the material. Specifically, the cellulose is first hydrophobically modified through an esterification reaction, converting the cellulose from hydrophilic to hydrophobic, while simultaneously introducing responsive groups. The modified cellulose and a pesticide are then dissolved in an organic solvent to form an oil phase, and a surfactant is dissolved in water to form an aqueous phase. The aqueous and oil phases are then mixed and emulsified to prepare an O / W emulsion. The solvent is then evaporated and removed at a specific temperature, forming pesticide-loaded modified cellulose microspheres.

[0035] Another object of the present invention is to provide the use of the cellulose microspheres as pesticide carriers.

[0036] The technical solution of the present invention is as follows: modified cellulose and pesticides are dissolved in an organic solvent to form an oil phase; a surfactant is dissolved in water to form an aqueous phase; the aqueous phase and the oil phase are mixed and emulsified to prepare an O / W emulsion; and the solvent is volatilized to obtain drug-loaded modified cellulose microspheres.

[0037] The amount of each component used can be, for example, the following parts by mass: 100 parts of water; 0.25 to 2 parts of surfactant; 0.1 to 1 part of cellulose; and 10 to 50 parts of organic solvent.

[0038] Compared with the prior art, the present invention has the following technical advantages:

[0039] The present invention uses cellulose as a raw material, which is cheap and readily available, has a simple preparation process, and mild reaction conditions, and can be used to load fat-soluble pesticides. The drug-loaded cellulose microspheres of the present invention are mainly made of cellulose, a surfactant, and a pesticide, and the pesticide is encapsulated in the microspheres by a solvent volatilization method.

[0040] 2. Commercially available cellulose is used as raw material, and fat-soluble modified cellulose is synthesized through a one-step modification. After the material is mixed with the oil-soluble original drug, a stable emulsion is obtained through shear emulsification. Under stirring and volatilization conditions, micro-nano-scale cellulose microspheres with weak alkaline environmental irritation response characteristics are prepared.

[0041] 3. The photostability of the drug loaded in the prepared cellulose microspheres is improved in the environment, extending the duration of the pesticide. Furthermore, the microspheres can achieve specific responses to the usage environment, thereby controlling the drug release rate.

[0042] 4. The particle size and drug loading capacity of the drug-loaded cellulose microspheres prepared according to the present invention are controllable, and can be targeted and adapted to different usage scenarios. They have considerable application prospects in the field of pesticide formulations, especially in the field of sustained-release formulations.

[0043] 5. The modification reagents used in the present invention (i.e., monomethyl oxalyl chloride and monoethyl oxalyl chloride) are sensitive to alkaline substances, and cellulose can be degraded by cellulase. The release rate of the encapsulated drug can be controlled by the above conditions. Therefore, the drug-loaded cellulose microspheres prepared by the present invention have pH and enzyme response characteristics.

[0044] The present invention provides a method for using cellulose microspheres in the controlled release of pesticides, wherein the cellulose microspheres are solid microspheres with controllable particle size. The pesticides involved in the present invention can be insecticides, fungicides, or herbicides, such as abamectin, fipronil, chlorpyrifos, indoxacarb, pyraclostrobin, metconazole, difenoconazole, fenpropimorph, prometryn, and quizalofop-Ph-ethyl.

[0045] In summary, the present invention has developed a method for producing responsive cellulose-based drug-loaded microspheres with a convenient process flow: a commercially available hydrophilic cellulose material is converted from hydrophilic to lipophilic by modifying the lipophilic groups, and an oil phase for emulsification is prepared by dissolving the drug and the modified material in a small amount of solvent. A stable emulsion is obtained by adding it to an aqueous phase containing a surfactant and performing high-shear emulsification and ultrasonic cell disruption operations. On this basis, drug-loaded microspheres with an average particle size of about 500 nm can be obtained by evaporation of the solvent. The materials required for this process are cheap and easy to obtain, and the operating steps are simple. Through process optimization, the drug loading rate of the microspheres can reach 61-66%, and the microspheres have sensitive weak alkaline response properties, realizing a responsive controlled release process of the encapsulated drug. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0047] Figure 1 The cellulose prepared in Example 1 and the modified cellulose 1 H NMR spectrum.

[0048] Figure 2 This is the SEM image of the cellulose drug-loaded microspheres prepared in Example 3.

[0049] Figure 3 This is the curve equation of the cellulose drug-loaded microspheres prepared in Example 3.

[0050] Figure 4 The release curves of the cellulose drug-loaded microspheres prepared in Example 3 under different pH conditions.

[0051] Figure 5 This is the release curve of the drug-loaded cellulose microspheres prepared in Example 3 at different cellulase concentrations.

[0052] Figure 6 This is the photolysis resistance curve of the drug-loaded cellulose microspheres prepared in Example 3. DETAILED DESCRIPTION

[0053] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0054] Example 1

[0055] (1) Preparation of modified cellulose

[0056] Take 2 grams of hydroxypropyl methylcellulose and 60 milliliters of N, N-dimethylformamide and dissolve them at 50 ° C. After the hydroxypropyl methylcellulose is completely dissolved, remove the heat, cool to room temperature, add 2.6 grams (20 mmol) of N, N-diisopropylethylamine, and stir for 10 minutes to mix evenly. Then, add 2.8 grams (20 mmol) of monoethyl oxalyl chloride dropwise over 15 minutes. After the addition is complete, heat to 50 ° C and react for 12 hours. After the reaction is completed, cool to room temperature, pour the solution into water (about 500 ml) to precipitate, filter and collect the solid, and vacuum dry the solid (-0.1 MPa vacuum, 30 ° C to constant weight); obtain modified cellulose.

[0057] (2) Preparation of drug-loaded cellulose microspheres

[0058] 100 mg of the modified cellulose prepared in step (1) above and 50 mg of avermectin were dissolved in 5 ml of dichloromethane as the oil phase. 15 ml of a 1% polyvinyl alcohol solution was taken as the aqueous phase. The oil phase and the aqueous phase were mixed, sheared using a high-shear emulsifier at 10,000 rpm for 5 minutes, and emulsified using ultrasonic cell disruption at 70% power for 1 minute to obtain a stable O / W emulsion.

[0059] (3) The emulsion was evaporated to dichloromethane at 25°C and a stirring speed of 1000 rpm for 8 hours to obtain drug-loaded cellulose microspheres with a drug loading capacity of 37.6% and a drug loading efficiency of 59.7%.

[0060] Note: The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 497.95 nanometers.

[0061] Example 2

[0062] (1) Preparation of modified cellulose

[0063] Take 2 grams of hydroxycellulose and 60 milliliters of N,N-dimethylformamide and dissolve them at 50°C. After dissolution is complete, remove the heat, cool to room temperature, add 2.6 grams (20 mmol) of N,N-diisopropylethylamine, and stir for 10 minutes to mix evenly. Then, add 2.8 grams (20 mmol) of monoethyl oxalyl chloride dropwise over 15 minutes. After the addition is complete, raise the temperature to 50°C and react for 12 hours. After the reaction is completed, cool to room temperature, pour the solution into water to precipitate, filter and collect the solid, and vacuum dry the solid (-0.1 MPa vacuum, 30°C to constant weight) to obtain modified cellulose.

[0064] (2) Preparation of drug-loaded cellulose microspheres

[0065] 100 mg of the modified cellulose prepared in step (1) above and 100 mg of avermectin were dissolved in 5 ml of dichloromethane as the oil phase. 15 ml of a 1% polyvinyl alcohol solution was taken as the aqueous phase. The oil phase and aqueous phase were mixed, sheared using a high-shear emulsifier at 10,000 rpm for 5 minutes, and emulsified using ultrasonic cell disruption at 70% power for 1 minute to obtain a stable O / W emulsion.

[0066] (3) The emulsion was evaporated to dichloromethane at 25°C and a stirring speed of 1000 rpm for 8 hours to obtain drug-loaded cellulose microspheres with a drug loading capacity of 50.8% and a drug loading efficiency of 67.0%.

[0067] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 509.0 nanometers.

[0068] Example 3

[0069] (1) Preparation of modified cellulose

[0070] Take 2 grams of hydroxycellulose and 60 milliliters of N,N-dimethylformamide and dissolve them at 50°C. After dissolution is complete, remove the heat, cool to room temperature, add 2.6 grams (20 mmol) of N,N-diisopropylethylamine, and stir for 10 minutes to mix evenly. Then, add 2.8 grams (20 mmol) of monoethyl oxalyl chloride dropwise over 15 minutes. After the addition is complete, raise the temperature to 50°C and react for 12 hours. After the reaction is completed, cool to room temperature, pour the solution into water to precipitate, filter and collect the solid, and vacuum dry the solid (-0.1 MPa vacuum, 30°C to constant weight) to obtain modified cellulose.

[0071] (2) Preparation of drug-loaded cellulose microspheres

[0072] 100 mg of the modified cellulose prepared in step (1) above and 150 mg of avermectin were dissolved in 5 ml of dichloromethane as the oil phase. 15 ml of a 1% polyvinyl alcohol solution was taken as the aqueous phase. The oil phase and aqueous phase were mixed, sheared using a high-shear emulsifier at 10,000 rpm for 5 minutes, and emulsified using ultrasonic cell disruption at 70% power for 1 minute to obtain a stable O / W emulsion.

[0073] (3) The emulsion was evaporated to dichloromethane at 25°C and a stirring speed of 1000 rpm for 8 hours to obtain drug-loaded cellulose microspheres with a drug loading capacity of 61.3% and a drug loading efficiency of 78.4%.

[0074] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 551.9 nanometers.

[0075] Example 4

[0076] (1) Preparation of modified cellulose

[0077] Take 2 grams of hydroxycellulose and 60 milliliters of N,N-dimethylformamide and dissolve them at 50°C. After dissolution is complete, remove the heat, cool to room temperature, add 2.6 grams (20 mmol) of N,N-diisopropylethylamine, and stir for 10 minutes to mix evenly. Then, add 2.8 grams (20 mmol) of monoethyl oxalyl chloride dropwise over 15 minutes. After the addition is complete, raise the temperature to 50°C and react for 12 hours. After the reaction is completed, cool to room temperature, pour the solution into water to precipitate, filter and collect the solid, and vacuum dry the solid (-0.1 MPa vacuum, 30°C to constant weight) to obtain modified cellulose.

[0078] (2) Preparation of drug-loaded cellulose microspheres

[0079] 100 mg of the modified cellulose prepared in step (1) above and 150 mg of avermectin were dissolved in 5 ml of dichloromethane as the oil phase. 15 ml of a 1% polyvinyl alcohol solution was taken as the aqueous phase. The oil phase and aqueous phase were mixed, sheared using a high-shear emulsifier at 10,000 rpm for 5 minutes, and emulsified using ultrasonic cell disruption at 70% power for 1 minute to obtain a stable O / W emulsion.

[0080] (3) The emulsion was evaporated to dichloromethane at 25°C and a stirring speed of 1000 rpm for 8 hours to obtain drug-loaded cellulose microspheres with a drug loading capacity of 65.3% and a drug loading efficiency of 70.9%.

[0081] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 516.1 nanometers.

[0082] Example 5

[0083] (1) Preparation of modified cellulose

[0084] Take 2 grams of hydroxycellulose and 60 milliliters of N,N-dimethylformamide and dissolve them at 50°C. After dissolution is complete, remove the heat, cool to room temperature, add 2.6 grams (20 mmol) of N,N-diisopropylethylamine, and stir for 10 minutes to mix evenly. Then, add 2.8 grams (20 mmol) of monoethyl oxalyl chloride dropwise over 15 minutes. After the addition is complete, raise the temperature to 50°C and react for 12 hours. After the reaction is completed, cool to room temperature, pour the solution into water to precipitate, filter and collect the solid, and vacuum dry the solid (-0.1 MPa vacuum, 30°C to constant weight) to obtain modified cellulose.

[0085] (2) Preparation of drug-loaded cellulose microspheres

[0086] 100 mg of the modified cellulose prepared in step (1) above and 200 mg of avermectin were dissolved in 5 ml of dichloromethane as the oil phase. 15 ml of a 1% polyvinyl alcohol solution was taken as the aqueous phase. The oil phase and aqueous phase were mixed, sheared using a high-shear emulsifier at 10,000 rpm for 5 minutes, and emulsified using ultrasonic cell disruption at 70% power for 1 minute to obtain a stable O / W emulsion.

[0087] (3) The emulsion was evaporated to dichloromethane at 25°C and a stirring speed of 1000 rpm for 8 hours to obtain drug-loaded cellulose microspheres with a drug loading capacity of 66.8% and a drug loading efficiency of 70.3%.

[0088] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 560.3 nanometers.

[0089] In summary, Example 3 is a preferred embodiment, and the drug loading efficiency is as high as 78.4%.

[0090] Experiment 1

[0091] In order to verify that the cellulose modification was successful, the raw material hydroxypropyl methylcellulose (HPMC) used in Example 3 and the modified cellulose (HPMC-Oxlate) in step 1) were characterized by nuclear magnetic resonance spectroscopy. Figure 1 As shown in the figure, for the raw material hydroxypropyl methylcellulose, there are no obvious peaks at the chemical shift values ​​of 1.27ppm and 4.29ppm. After the material is modified, HPMC-Oxlate shows obvious absorption peaks at 1.27ppm and 4.29ppm, and the chemical shift values ​​of the peaks are consistent with the methylene and methyl groups in ethyl oxalyl chloride. Therefore, the NMR spectrum confirms the successful modification of cellulose.

[0092] Figure 2 This is a scanning electron microscope image of the drug-loaded cellulose microspheres prepared in Example 3. It can be seen that the drug-loaded cellulose microspheres are regular spherical, and the average particle size within the field of view is about 500 nanometers.

[0093] The application performance of drug-loaded cellulose microspheres was determined.

[0094] Experiment 2

[0095] (1) HPLC determination of avermectin content: The analytical column was an Agilent ZORBAX SB-C18 column (4.6×250 mm, 5.0 μm), the mobile phase was V (methanol): V (water) = 90:10; the flow rate was 1.0 mL / min; the detector was an ultraviolet detector, the detection wavelength was 245 nm, the injection volume was 20 μL, the column temperature was 40°C, and the standard curve method was used for quantitative determination. The results are shown in the following table. Figure 3 .

[0096] (2) Accurately weigh 0.02g of drug-loaded cellulose microsphere suspension into a dialysis bag with a molecular weight cutoff of 1000, add 3mL of PBS buffer (pH=5, 7, 9) containing 0.1% Tween 80 into the dialysis bag, then place the dialysis bag into 100mL of PBS buffer (pH=5, 7, 9) containing 0.1% Tween 80, and place the brown glass bottle in a constant temperature shaker at 150rpm and 25℃ for continuous oscillation or stirring; sample 1mL of solution from the outside of the dialysis bag at regular intervals, filter through a 0.45μm organic syringe filter head, and determine the avermectin concentration by HPLC. After each sampling, add 1mL of buffer; use time as the horizontal axis and the cumulative release percentage of avermectin as the vertical axis. Repeat three times and take the average value to draw the release curve of avermectin under different pH conditions. The results are as follows: Figure 4 .

[0097] (3) Accurately measure 0.02g of drug-loaded cellulose microsphere suspension into a dialysis bag with a molecular weight cutoff of 1000, add 3mL of an aqueous solution containing 0.1% Tween 80 and cellulase into the dialysis bag and adjust the enzyme concentration to 0, 6, 12, and 18U / mL respectively, then place the dialysis bag into 100mL of an aqueous solution containing 0.1% Tween 80, place the brown glass bottle in a constant temperature shaker at 150rpm and 25℃ for continuous oscillation or stirring; sample 1mL of solution from the outside of the dialysis bag at regular intervals, filter through a 0.45μm organic syringe filter head, and determine the avermectin concentration by HPLC. After each sampling, add 1mL of an aqueous solution containing 0.1% Tween 80; use time as the horizontal axis and the cumulative release percentage of avermectin as the vertical axis, repeat three times and take the average value to draw the release curve of avermectin under different enzyme concentration conditions. The results are as follows: Figure 5 .

[0098] (4) Prepare 100 mL of drug-loaded cellulose microsphere suspension with a concentration of 1000 ppm using an aqueous solution containing 0.1% Tween 80. Place the prepared suspension under a UV lamp with a wavelength of 254 nm and a power of 6 W, with the UV lamp and the suspension at a distance of 15 cm. Take 0.1 mL of the suspension at regular intervals and dissolve it in 1 mL of acetonitrile. After filtering through a 0.45 μm organic syringe filter, use HPLC to determine the concentration of avermectin. Use time as the horizontal axis and the remaining amount of the active ingredient of avermectin as the vertical axis. Repeat three times and take the average value to draw the anti-photolysis performance curve. The results are as follows: Figure 6 .

[0099] from Figure 4 The microspheres exhibit a significant pH-responsiveness. The drug-loaded cellulose microspheres exhibited a rapid response to weak alkalinity. At 25°C and pH 9, the cumulative release of avermectin reached 96.8% after 48 hours. Release rates were significantly lower at pH 5 and 7, with cumulative releases of 1.5% and 22.2% after 48 hours, respectively.

[0100] from Figure 5 It can be seen that the drug-loaded cellulose microspheres have cellulase-responsive properties. In an environment without cellulase, drug release is slow, with a cumulative release of only 20.1% after 24 hours. In environments with concentrations of 6 U / g, 12 U / g, and 18 U / g, the release rate is significantly higher than in the absence of cellulase, with cumulative releases of 32.7%, 39.3%, and 50.4% after 24 hours, respectively.

[0101] from Figure 6 It can be seen that the content of avermectin is significantly affected by the duration of light exposure, with the active ingredient rapidly decreasing with increasing light exposure time. After 24 hours of light exposure, the active ingredient retention rate was only 0.2%, while the active ingredient retention rate of the drug-loaded cellulose microspheres remained at 23.4% over the same period. This demonstrates that the drug-loaded microspheres can effectively block ultraviolet light and thus prolong the drug's effectiveness.

[0102] Comparative Example 1:

[0103] The concentration of the polyvinyl alcohol solution in Example 3 was changed from 1% to 0.25%, and the amount used remained unchanged, still 15 ml, and this was used as the aqueous phase.

[0104] The rest is the same as Example 3.

[0105] A uniform O / W emulsion could not be obtained, and oil-water separation was observed. Even if the emulsification process was extended to 5 minutes, a uniform O / W emulsion could not be obtained.

[0106] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 1078.2 nanometers.

[0107] Therefore, it can be seen that a polyvinyl alcohol solution with too low a concentration makes emulsification difficult.

[0108] Comparative Example 2:

[0109] The concentration of the polyvinyl alcohol solution in Example 3 was changed from 1% to 2%, while the amount used remained unchanged at 15 ml, and this was used as the aqueous phase.

[0110] The rest is the same as Example 3.

[0111] Too high a concentration of polyvinyl alcohol results in a solution with too high viscosity, which hinders the homogenization process of the emulsion and makes it impossible to obtain a uniform O / W emulsion.

[0112] The particle size distribution of the drug-loaded cellulose microspheres prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 913.8 nanometers.

[0113] Therefore, it can be concluded that an excessively high concentration of polyvinyl alcohol solution leads to a high viscosity of the solution and hinders the homogenization process of the emulsion.

[0114] Comparative Example 3-1: The "N,N-diisopropylethylamine" in Example 3 was replaced with triethylamine, and the amount used remained unchanged; the rest was the same as Example 3.

[0115] The final result is:

[0116] The drug loading capacity was 57.9% and the drug loading efficiency was 76.5%.

[0117] Comparative Example 3-2: The "N,N-diisopropylethylamine" in Example 3 was replaced with pyridine, and the amount used remained unchanged; the rest was the same as Example 3.

[0118] The final result is:

[0119] The drug loading capacity was 46.1% and the drug loading efficiency was 56.5%.

[0120] Comparative Example 4: The "ethyl oxalyl chloride" in Example 3 was replaced with methyl oxalyl chloride, and the amount used remained unchanged; the rest was the same as Example 3.

[0121] The final result is:

[0122] The drug loading capacity was 21.5% and the drug loading efficiency was 40.0%.

[0123] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing cellulose-based sustained-release microspheres, characterized in that The following steps are involved: 1) Preparation of modified cellulose: Modified cellulose is obtained by introducing responsive groups into cellulose through esterification reaction; The details are as follows: Add cellulose to an organic solvent, heat and stir at (50±10)℃ until the cellulose is completely dissolved, cool to room temperature, add an organic base first, then add an acyl chloride, heat to (50±10)℃ and react for 3-12h to obtain modified cellulose; The ratio of the organic solvent to the cellulose is (15-30) ml: 1 g; the mass ratio of the cellulose, the organic base, and the acyl chloride is 1: (1-2): (1-2); The cellulose is at least one of microcrystalline cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose; The organic solvent is at least one of acetonitrile, tetrahydrofuran, dimethylformamide, dichloromethane, dichloroethane, dimethylformamide, dimethylacetamide and dimethyl sulfoxide; The organic base is triethylamine, N , N - at least one of diisopropylethylamine, pyridine, and 4-dimethylaminopyridine; The acyl chloride is at least one of methyl oxalyl chloride and ethyl oxalyl chloride; 2) dissolving the pesticide and modified cellulose in a volatile organic solvent, and using the resulting mixed organic solution as the oil phase; dissolving the surfactant in water, and using the resulting surfactant aqueous solution as the aqueous phase; the surfactant aqueous solution is a polyvinyl alcohol solution with a mass concentration of 1%; The oil phase and the water phase are mixed and emulsified to prepare an O / W emulsion; 3) The O / W emulsion obtained in step 2) is subjected to volatilization of the volatile organic solvent under stirring conditions to form cellulose-based drug-loaded microspheres loaded with pesticides.

2. The method for preparing cellulose-based sustained-release microspheres according to claim 1, characterized in that: The step 2) is: The oil phase is added dropwise to the water phase, and after high shear dispersion, cell disruption and emulsification are performed to obtain a homogenized emulsion; The mass ratio of the modified cellulose, the pesticide agent and the volatile organic solvent is 1: (0.5-2.5): (10-20); The volume ratio of oil phase to water phase is 1:(3~5).

3. The method for preparing cellulose-based sustained-release microspheres according to claim 2, characterized in that: The volatile organic solvent is at least one of acetonitrile, acetone, dichloromethane, dimethylformamide and dimethylacetamide.

4. The method for preparing cellulose-based sustained-release microspheres according to claim 3, characterized in that: The high shear emulsion dispersion is processed at 10000-20000 rpm for 3-10 minutes; The cell disruption and emulsification is carried out at 70% power for 1 to 5 minutes; The volatilization of the volatile organic solvent in step 3) is performed at 25-65°C.

5. The method for preparing cellulose-based sustained-release microspheres according to any one of claims 1 to 4, characterized in that: The loaded pesticide is an insecticide, a fungicide or a herbicide.

6. The method for preparing cellulose-based sustained-release microspheres according to claim 5, characterized in that: The pesticides used are avermectin, fipronil, chlorpyrifos, indoxacarb, pyraclostrobin, metconazole, difenoconazole, fenpropimorph, promethazine, and quizalofop-p-ethyl.

7. The method for preparing cellulose-based sustained-release microspheres according to claim 5, characterized in that: The pesticides used are avermectin, fipronil, chlorpyrifos, indoxacarb, pyraclostrobin, metconazole, difenoconazole, fenpropimorph, promethazine, and quizalofop-p-ethyl.

8. Use of the cellulose-based sustained-release microspheres prepared by the method of any one of claims 1 to 7 as a pesticide carrier.

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