Preparation method and application of PVA coated high drug loading microspheres based on electrostatic and coordination action

Abstract

This invention discloses a method for preparing and applying PVA-coated high-pesticide-loading microspheres based on electrostatic and coordination interactions, belonging to the field of novel pesticide preparation technology. The method uses three economical and high-yield negatively charged natural clays—attapulgite, halloysite, and kaolin—as templates, utilizing electrostatic effects to adsorb appropriate amounts of Ca. 2+ By coordinating with the hexapeptide ligand ethylenediaminetetraacetic acid (EDTA), a novel carrier system (i.e., drug-loaded microspheres) was developed through a one-step method that simultaneously loaded the targeted drug molecule avermectin and self-assembled clay, forming micro / nano-scale aggregates. Finally, these aggregates were coated with a polyvinyl alcohol layer to create a new type of carrier system. Beneficial effects: This system exhibits high stability and biocompatibility, and is low-cost and simple to operate. On the other hand, EDTA... 2‑ With Ca 2+ The bridging mechanism is sensitive to low pH levels, which is beneficial for achieving controlled release under specific needs. This provides a practical basis and theoretical reference for achieving precise drug delivery and efficient supply.

Description

Technical Field

[0001] This invention relates to the field of novel pesticide preparation technology, and in particular to a method for preparing and applying PVA-coated microspheres with high pesticide loading based on electrostatic and coordination interactions. Background Technology

[0002] With the increasing global population and growing demand for food, agricultural production faces multifaceted pressures, making the use of traditional pesticides to control and manage crop diseases and pests increasingly important. However, traditional pesticides often suffer from problems such as short-lived efficacy and easy loss of pesticides, often requiring repeated and large-scale application in practice. This not only results in serious waste, but also causes adverse effects on the environment and non-target organisms due to the dispersed pesticides.

[0003] To address the aforementioned issues, controlled-release pesticide technology based on nanocarriers has garnered significant attention in recent years. Its aim is to regulate the release rate and duration of pesticides, achieving more efficient and precise pest and disease control. Utilizing the strong adsorption properties of nanocarriers, pesticides are released slowly in the absence of irritation, significantly enhancing the duration of efficacy and reducing pesticide runoff. Under specific external stimuli, drug molecules on the carrier surface can desorb through physicochemical processes, facilitating on-demand pesticide delivery. Therefore, controlled-release pesticides not only provide long-lasting crop protection and reduce application costs but also minimize pesticide runoff and reduce environmental pollution risks.

[0004] Among numerous nanomaterials, natural clay has become a research hotspot in the pesticide field due to its low cost, abundant sources, high stability, and safety. Its high specific surface area and abundant porous structure endow it with excellent adsorption capacity, enabling it to immobilize pesticide molecules and achieve stable controlled release. However, existing clay-based pesticides only utilize the surface adsorption of clay to immobilize target molecules, resulting in low pesticide loading capacity, which cannot meet the needs of agricultural production and the further development of a resource-saving society. Besides utilizing surface hydrogen bonds and intermolecular forces to adsorb drugs, constructing vesicles, capsules, and other cavity-based formulations to directly "ingest" drug molecules is one of the important ways to increase drug loading. Natural clay itself does not possess large-volume cavities, and relying solely on surface engineering such as chemical modification is insufficient to significantly increase drug loading. Therefore, there is an urgent need to construct novel clay-based carrier systems with high drug loading capacity through physical and chemical processes.

[0005] Electrostatic adsorption and coordination interactions, as key technologies in drug loading and material synthesis, have attracted significant attention in the field of materials science. Electrostatic interactions, through the attraction of charges, allow target molecules with dissimilar charges to firmly bind to the surface or interior of a carrier. Coordination interactions, generally through the specific binding of metal ions to organic ligands, can effectively increase the structural stability of materials and even endow them with unique chemical properties. How to rationally apply these technologies to improve the drug loading and utilization rate of existing clay-based controlled-release pesticides has become an urgent problem to be solved. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to solve the problems of low pesticide loading and low utilization rate of existing clay-based controlled-release pesticides.

[0007] The present invention solves the above-mentioned technical problems through the following technical means:

[0008] The first aspect of this invention provides a method for preparing PVA-coated drug-loaded microspheres, comprising the following steps: (1) Preparation of self-loaded aggregates: The nano clay material was mixed with calcium chloride, stirred and dried, then mixed with an aqueous solution of disodium ethylenediaminetetraacetate (EDTA-2Na), and then an ethanol solution of pesticide was added. The mixture was stirred and dried to obtain pesticide-loaded clay aggregates. (2) Preparation of controlled-release formulation: Disperse the pesticide-loaded clay aggregates in a polyvinyl alcohol (PVA) aqueous solution and stir evenly to obtain PVA-coated drug-loaded microspheres.

[0009] Preferably, the mass ratio of the nano-clay material, calcium chloride, and disodium ethylenediaminetetraacetate is (0.1-0.3):2:2, and more preferably 0.2:2:2.

[0010] Preferably, the ratio of the amount of nano-clay material to pesticide is (0.1-0.3) g: (5-15) mL, and more preferably 0.2 g: 8 mL.

[0011] Preferably, the concentration of the pesticide is 3-8 mg / mL, more preferably 5 mg / mL.

[0012] Preferably, the ratio of the pesticide-loaded clay aggregate to polyvinyl alcohol is (0.1-0.5) g: (40-60) mL, more preferably 0.2 g: 50 mL.

[0013] Preferably, the concentration of the polyvinyl alcohol is 0.5-3 mg / mL, more preferably 1 mg / mL.

[0014] Preferably, the nano-clay material is any one or more of attapulgite (ATP), halloysite (HNTs), and kaolin (Caly).

[0015] Preferably, the pesticide is any one or more of abamectin (AVM), imidacloprid (IMI), MCPA, and thiamethoxam (THI).

[0016] A second aspect of the present invention provides PVA-coated drug-loaded microspheres prepared by the above-described preparation method.

[0017] A third aspect of the present invention proposes the application of the above-mentioned PVA-coated drug-loaded microspheres as controlled-release pesticides in the field of sustainable green agriculture.

[0018] The beneficial effects of this invention are as follows: 1. This invention combines the electrostatic adsorption of clay with metal ions and the coordination of metal ions with organic matter to construct a bridging network structure of "clay-metal ion-organic ligand-metal ion-clay," achieving self-aggregation of nano-clay. This micro / nano aggregate contains numerous large-pore cavities and a large number of active sites on its inner and outer surfaces, thus simultaneously possessing the ability to physically encapsulate and chemically adsorb pesticide molecules. Furthermore, the bridging network structure is sensitive to weak acids, which is beneficial for constructing pH-responsive controlled-release carrier systems. Therefore, PVA-coated drug-loaded microspheres with high pesticide loading capacity based on electrostatic and coordination interactions have been developed, achieving high pesticide loading and improved pesticide utilization, which aligns with the direction of sustainable development in modern agriculture and provides a feasible path for the sustainable development of global agriculture.

[0019] 2. This invention uses the insecticide abamectin (AVM) as an example as a targeted pesticide, and three natural nano-clays—attapulgite (ATP), halloysite (HNTs), and kaolin—as carriers, based on the relationship between clay and Ca... 2+ Electrostatic adsorption, EDTA 2- With Ca 2+ The coordination of ions in a weakly acidic environment enables the controlled rupture of the outer PVA protective film. This aims to overcome the challenges of low pesticide loading and difficulty in further improving pesticide utilization in existing clay-based controlled-release pesticides, and to develop a pH-responsive intelligent pesticide carrier system. This system can significantly increase pesticide loading, achieve a surge in pesticide release under pH control, and significantly improve the controlled-release performance of AVMs. Furthermore, it is low-cost, simple to operate, and environmentally friendly, making it valuable for practical applications.

[0020] 3. The drug-loaded microspheres of this invention exhibit high stability and biocompatibility, and are low in cost and simple to operate. Furthermore, the clay-based aggregates have large and numerous pores and a large number of active groups on their inner and outer surfaces, thus the carrier system possesses both physical encapsulation and chemical adsorption capabilities, allowing it to accommodate more drug molecules. In addition, EDTA... 2- With Ca 2+ The bridging mechanism is sensitive to low pH, which is beneficial for achieving dissociation of the carrier system at low pH and controlled drug release under specific conditions. This method utilizes electrostatic and coordination effects to endow the carrier system with high drug loading capacity and ease of operation, while also being environmentally friendly and highly stable. It provides a novel method for constructing drug carriers, offering a practical foundation and theoretical reference for achieving precise drug delivery and efficient supply. Attached Figure Description

[0021] Figure 1This is a comparison chart of the loading amount of AVM by three clay materials (ATP, HNTs, Caly) in Examples 1-3 of the present invention; Figure 2 This is a comparison graph showing the response of different pH conditions to the release of AVM from the drug-loaded microspheres in Example 3 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0024] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0025] Example 1: A method for preparing PVA-coated drug-loaded microspheres includes the following steps: 1) Preparation of self-assembled aggregates: First, 0.2 g of nano-attapulgite (ATP) was mixed with 40 ml of aqueous solution containing 2 g of calcium chloride (CaCl2) to form a homogeneous suspension. This mixture was mechanically stirred at 400 rpm for 12 h, and then vacuum dried. The dried ATP@Ca²⁺ aggregates were then... + The mixture was mixed with 32 ml of an aqueous solution containing 2 g of EDTA-2Na. Then, 8 ml of an ethanolic solution of 5 mg / ml avermectin (AVM) was quickly added to the suspension, and the mixture was mechanically stirred for 12 hours. After vacuum drying, the ATP@Ca²-EDTA-AVM aggregates were finally obtained.

[0026] 2) Preparation of controlled-release formulation: ATP@Ca² loaded with AVM was prepared. + - 0.2 g of EDTA-AVM self-contained aggregate was dispersed in 50 ml of PVA aqueous solution with a concentration of 1 mg / ml and mechanically stirred for 2 h to obtain PVA-coated drug-loaded microspheres.

[0027] Example 2: The difference between this embodiment and Example 1 is that nano-attapulgite (ATP) is replaced with "nano-haloite (HNTs)" to obtain HNTs@Ca² +-EDTA-AVM aggregate, the rest is the same as in Example 1.

[0028] Example 3: The difference between this embodiment and Embodiment 1 is that nano-attapulgite (ATP) is replaced with "nano-white clay (Caly)" to obtain Caly@Ca². + -EDTA-AVM aggregate, the rest is the same as in Example 1.

[0029] The drug loading capacity and controlled release performance of the PVA-coated drug-loaded microspheres prepared in Examples 1-3 were tested. Drug loading test: Prepare a series of standard solutions (e.g., 0, 10, 20, 30, 40, 50 mg / L) using pure pesticides of known concentrations.

[0030] The absorbance of these standard solutions was measured at 245 nm using a UV spectrophotometer. A standard curve was obtained by plotting concentration (x-axis) against absorbance (y-axis). Then, 5 mg of each of the three drug-loaded microspheres was accurately weighed and the sample was placed in 50 mL of ethanol-water (V... 乙醇 V 水 In a 3:1 solution, sonicate for 20 minutes to release the pesticide into the solution. Centrifuge to ensure no suspended particles remain in the solution, and measure the absorbance of the sample solution at 245 nm using a UV spectrophotometer. Calculate the pesticide concentration in the solution based on the absorbance using a standard curve equation.

[0031] like Figure 1 As shown, the three different clay materials ATP, HNTs, and Caly in Examples 1-3 exhibited high drug loading capacity, with loadings of abamectin (AVM) reaching 274 mg / g, 372 mg / g, and 279 mg / g, respectively (i.e., drug loading rates of 27.4%, 37.2%, and 27.9%, respectively). This indicates that these clay materials possess excellent drug loading performance, capable of embedding a large amount of active ingredient per unit weight, thereby improving pesticide application efficiency and persistence.

[0032] pH-controlled controlled-release performance test: Place 5-10 mg of the drug-loaded microspheres prepared in Examples 1-3 into 20 mL of ethanol-water mixture (V). 乙醇 V 水 Kinetic release experiments were conducted in a 3:1 solution at different pH values ​​(5.5, 7.0, and 8.5). At specific time points, 1 mL of the suspension was collected, and 1 mL of an aqueous ethanol solution was added to compensate for volume loss. The supernatant was centrifuged, diluted, and the absorbance was measured using a UV spectrophotometer to calculate the AVM release rate.

[0033] Taking Example 3 as an example (e.g.) Figure 2 (As shown) Analysis will be performed: Under pH=7 conditions, Caly@Ca 2+ The release of EDTA-AVM after 24 hours was only 25-30%, indicating that the external PVA-based protective film can effectively prevent the rapid release of AVM under normal conditions, which is beneficial to prolonging the duration of AVM's effectiveness. Under pH 8.5 conditions, Caly@Ca 2+ -EDTA-AVM release was 40-45% over 24 h. On the other hand, after applying a weak acid at pH 5.5, the AVM release rate reached nearly 85-90% within 24 h, significantly exceeding that at pH 7 and pH 8.5 for Caly@Ca. 2+ - Pesticide release values ​​from EDTA-AVM nanoparticles. The above results indicate that weak acids, as a stimulant, can trigger the release of pesticides from Caly@Ca. 2+ The rapid diffusion of AVM in EDTA-AVM nanoparticles shows great promise for applications in sustainable green agriculture. The controlled-release performance of Examples 1 and 2 is similar to that of Example 3.

[0034] The results showed that the cumulative release rates of AVM within 24 h were 85-90%, 25-30%, and 40-45% at different pH values ​​(5.5, 7.0, and 8.5), respectively. The release amount increased significantly under acidic conditions compared to neutral and alkaline conditions. The reason for this is that under weakly acidic conditions, the H+ in the solution... + Concentration increases. H + It has a strong coordinating ability and can bind to the carboxyl group in the EDTA molecule. Furthermore, H... + With Ca² + Competition occurs between them, H + It will gradually replace Ca² + The binding site with EDTA. This substitution weakens Ca²⁺. + Coordination bond with EDTA.

[0035] Comparative Example 1: The paper [Jiangtao Dong, Wang Chen, Dunzhong Qin, Yuxia Chen, Jun Li, ChenWang, Yeqing Yu, Jianguo Feng, Xuezhong Du. Cyclodextrin polymer-valved MoS2-embedded mesoporous silica nanopesticides toward hierarchical targets via multidimensional stimuli of biological and natural environments, Journal of Hazardous Materials, Volume 419, 2021, 126404, ISSN 0304-3894] proposes constructing nanopesticides based on cyclodextrin polymer (CDP)-valved molybdenum disulfide (MoS2)-embedded porous silica (MSN) through multidimensional stimulation simulating biological and natural environments. MoS2@MSN nanoparticles (with a core-shell structure) serve as the nanocarrier for the pesticide. The pesticide loading is only 23 mg / g, far lower than the 274-372 mg / g loading of the materials in Examples 1-3 of this invention.

[0036] Comparative Example 2: [Zhongxuan Hu, Changlong Shu, Meijing Wang, Tingze Yang, Hongling Pei, Teng Wang, Siyu Sun, Fang Zhang. Eco-friendly pH-responsive iron-dopedinsect larval frass extract as a hexaconazole nano-delivery system for controlling fungal disease and promoting crop growth, Chemical Engineering Journal, Volume 494, 2024, 153025, ISSN 1385-8947] This paper describes the development of a pH-responsive, biodegradable dual-pesticide fertilizer using an extract of naturally occurring Protaetia brevitarsis larval frass (PBLF). The extract utilizes iron ions (Fe... 3+The material is integrated into the PBLF as a metal node, and the triazole fungicide hexazole (Hex) is encapsulated in the Fe-PBLF, with a drug loading rate of 22.93%. This is significantly lower than the drug loading rates of 27.4-37.2% in the materials of Examples 1-3 of this invention.

[0037] Comparative Example 3: [Zhiyuan Zhou, Gaohua Hu, Gang Tang, Yulu Liu, Xiaohong Zhang, Yuqi Huang, Guangyao Yan, Jianhua Xiao, Weiyao Yan, Yongsong Cao, Fabrication of dual responsive microcapsules based on starch with enhanced foliar adhesion and photostability for improving control efficacy and reducing environmental risks, Chemical Engineering Journal, Volume 494, 2024, 153290, ISSN 1385-8947] constructed pH and enzyme-responsive pesticide microcapsules (AVE@CPS-Fe-TA) by encapsulating carboxylated porous starch (CPS) loaded with avermectin (AVE) in a tannic acid-iron complex (Fe-TA). The loading rate of AVE@PS increased with starch hydrolysis time over 1–4 hours. When the hydrolysis time reached 5 h, the loading rate of AVE@PS began to decrease with further hydrolysis time. Therefore, the optimal conditions for starch enzymatic hydrolysis are 4 hours, with a maximum drug loading rate of only 8%-10%, which is far lower than the drug loading rates of 27.4-37.2% in Examples 1-3 of this invention.

[0038] Example 4: (The difference between this example and Example 1 is that the process parameters are slightly different.) A method for preparing PVA-coated drug-loaded microspheres includes the following steps: 1) Preparation of self-assembled aggregates: First, 0.1 g of nano-attapulgite (ATP) was mixed with 40 ml of aqueous solution containing 2 g of calcium chloride (CaCl2) to form a homogeneous suspension. This mixture was mechanically stirred at 400 rpm for 12 h, and then vacuum dried. The dried ATP@Ca²⁺ aggregates were then... +Mix with 32 ml of an aqueous solution containing 2 g of EDTA-2Na. Then, quickly add 5 ml of an 8 mg / ml imidacloprid (IMI) ethanol solution to the suspension, continue mechanical stirring for 12 hours, and vacuum dry again to finally obtain ATP@Ca²-EDTA-IMI aggregates.

[0039] 2) Preparation of controlled-release formulation: ATP@Ca² loaded with IMI was prepared. + - 0.5 g of EDTA-IMI self-contained aggregate sample was dispersed in 60 ml of PVA aqueous solution with a concentration of 0.5 mg / ml and mechanically stirred continuously for 2 h to obtain PVA-coated drug-loaded microspheres.

[0040] Example 5: (The difference between this example and Example 1 is that the process parameters are slightly different.) A method for preparing PVA-coated drug-loaded microspheres includes the following steps: 3) Preparation of self-assembled aggregates: First, 0.3 g of nano-attapulgite (ATP) was mixed with 40 ml of aqueous solution containing 2 g of calcium chloride (CaCl2) to form a homogeneous suspension. This mixture was mechanically stirred at 400 rpm for 12 h, and then vacuum dried. The dried ATP@Ca²⁺ aggregates were then... + Mix with 32 ml of an aqueous solution containing 2 g of EDTA-2Na. Then, quickly add 15 ml of a 3 mg / ml thiamethoxam (THI) ethanol solution to the suspension, continue mechanical stirring for 12 hours, and then vacuum dry again to finally obtain ATP@Ca²-EDTA-THI aggregates.

[0041] 4) Preparation of controlled-release formulation: ATP@Ca²⁺ loaded with THI is used to prepare the controlled-release formulation. + 0.1 g of EDTA-THI self-contained aggregate was dispersed in 40 ml of PVA aqueous solution with a concentration of 3 mg / ml and mechanically stirred continuously for 2 h to obtain PVA-coated drug-loaded microspheres.

[0042] The drug-loaded microspheres prepared in Examples 4 and 5 have similar properties to those in Example 1.

[0043] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing PVA-coated drug-loaded microspheres, characterized in that, Includes the following steps: (1) Preparation of self-loaded aggregates: The nano-clay material was mixed with calcium chloride, stirred, dried, and then mixed with an aqueous solution of disodium ethylenediaminetetraacetate. An ethanol solution of pesticide was added, stirred, and dried to obtain a clay aggregate loaded with pesticide; the pesticide was abamectin. (2) Preparation of controlled-release formulation: Disperse the pesticide-loaded clay aggregate in a polyvinyl alcohol aqueous solution and stir evenly to obtain PVA-coated drug-loaded microspheres; The ratio of the amount of pesticide-loaded clay aggregate to polyvinyl alcohol is (0.1-0.5) g: (40-60) mL.

2. The production method according to claim 1, characterized by, The mass ratio of the nano-clay material, calcium chloride, and disodium ethylenediaminetetraacetate is (0.1-0.3):2:

2.

3. The preparation method according to claim 1, characterized in that, The ratio of the amount of nano-clay material to pesticide is (0.1-0.3) g : (5-15) mL.

4. The production method according to claim 1, characterized by, The concentration of the pesticide is 3-8 mg / mL.

5. The preparation method according to claim 1, characterized in that, The ratio of the pesticide-loaded clay aggregate to polyvinyl alcohol is 0.2 g: 50 mL.

6. The method of claim 1, wherein, The concentration of the polyvinyl alcohol is 0.5-3 mg / mL.

7. The preparation method according to claim 1, characterized in that, The nano-clay material is any one or more of attapulgite, halloysite, and kaolin.

8. The production method according to claim 7, characterized by, The nano-clay material is attapulgite.

9. PVA-coated drug-loaded microspheres prepared by the preparation method according to any one of claims 1-8.

10. The application of the PVA-coated drug-loaded microspheres as described in claim 9 as controlled-release pesticides in the field of sustainable green agriculture.

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