Degradable moisture-responsive polylactic acid sustained-release microspheres, preparation method and application

Abstract

This invention discloses biodegradable, moisture-responsive polylactic acid (PLA) slow-release microspheres, their preparation method, and their applications, belonging to the field of microspheres. Addressing the problems of slow environmental response and uncontrollable release in existing PLA microspheres, this invention provides biodegradable, moisture-responsive PLA slow-release microspheres, prepared using a microfluidic method from an outer aqueous phase, an oil phase, and an inner aqueous phase. The outer aqueous phase is a sulfonated polyvinyl alcohol solution; the oil phase is a PLA-carbon quantum dot mixture; and the inner aqueous phase is a Na₂SO₄·10H₂O solution. In this invention, the outer aqueous phase imparts acid and alkali resistance to the microspheres and stabilizes the dual-emulsion structure; the oil phase constructs a biodegradable framework, where CQDs act as pore-forming agents to create micropores, and real-time detection of salt concentration and reporting of degradation progress are achieved through fluorescence quenching; the inner aqueous phase regulates osmotic pressure, driving moisture-responsive water absorption and release. Through the synergistic design of sulfonated PVA, PLA-CQDs, and Na₂SO₄·10H₂O, combined with the microfluidic method, the problems of slow response and uncontrollable release in existing microspheres are solved, showing broad application prospects in the agricultural field.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable microsphere technology, and more specifically, relates to biodegradable moisture-responsive polylactic acid slow-release microspheres, their preparation method, and their applications. Background Technology

[0002] Currently, low efficiency in the utilization of water resources and agrochemicals is a widespread problem in agricultural production, leading to resource waste and seriously affecting food security and ecological sustainable development. Statistics show that global agricultural water consumption accounts for 70% of total freshwater consumption, but the water resource utilization rate is extremely low. Biodegradable polylactic acid (PLA) slow-release microspheres, as a precise delivery carrier, achieve slow and continuous release by encapsulating active ingredients in a biodegradable polymer matrix. However, PLA's strong hydrophobicity and poor water absorption and swelling capacity make it difficult to flexibly control the release cycle, resulting in a mismatch with crop growth rhythms. Furthermore, the degradation rate of PLA in the natural environment is constrained by conditions such as temperature and humidity, exhibiting a sluggish response, which limits its universality and controllability in field applications.

[0003] For example, Chinese patent application CN202211433698.7, published on January 31, 2023, discloses a method for preparing modified polylactic acid (PLA) microspheres with controllable particle size. The method involves surface amination of the PLA microspheres with ethylenediamine to improve their hydrophilicity. The method first prepares the microspheres using an emulsion solvent evaporation method, where PLA is dissolved in dichloromethane to form a dispersed phase. A polyvinyl alcohol solution of a certain concentration is used as the continuous phase. The dispersed phase is injected into the continuous phase at a constant dropping rate. Through stirring, curing, washing, and freeze-drying, PLA microspheres with controllable particle size are obtained. Then, under certain temperature conditions, the PLA microspheres are ammonolyzed with ethylenediamine / isopropanol to finally obtain aminated modified PLA microspheres. This patent uses an emulsion solvent evaporation method combined with constant-rate dripping and sieving technology to control particle size. It modifies the surface of polylactic acid microspheres with ethylenediamine by ammonolysis, introduces amino groups to enhance hydrophilicity, and significantly improves the dispersibility, sphericity and biocompatibility of the microspheres.

[0004] For example, Chinese patent application number CN202510480820.3, published on July 15, 2025, discloses a polylactic acid microsphere with controllable degradation properties, its preparation method, and its application. The process includes the following steps: S1, dissolving polylactic acid with a molecular weight of 50-200 kDa in an organic solvent to obtain an oil phase, and dissolving a drug in the solvent to obtain an aqueous phase; S2, adding the aqueous phase to the oil phase to form a W / O primary emulsion; S3, adding the W / O primary emulsion to a solution containing a surfactant with a mass-volume concentration of 0.5%-2%, and stirring to form a W / O / W system; S4, evaporating the solvent from the W / O / W system; S5, collecting the microspheres and drying them to obtain the final product. This patent employs a W / O / W dual emulsification method, precisely controlling the microsphere size and degradation rate by adjusting the molecular weight of polylactic acid (50–200 kDa) and the concentration of surfactant (0.5%–2%); dopants (such as chitosan and hydroxyapatite) improve mechanical properties and bioactivity, enhancing the controllability of drug release.

[0005] The aforementioned patents mainly focus on PLA modification and optimization of preparation processes. Although they have improved the release performance of PLA microspheres to some extent, the current sustained-release systems still suffer from bottlenecks such as slow environmental response and uncontrollable release, making it difficult to promote and apply them on a large scale in the agricultural field. Summary of the Invention

[0006] 1. The problem to be solved To address the issues of slow environmental response and uncontrollable release in existing polylactic acid (PLA) microspheres, this application provides biodegradable, water-responsive, sustained-release PLA microspheres, their preparation method, and their applications. This invention imparts acid and alkali resistance and stabilizes the dual-emulsion structure to the microspheres through an external aqueous phase; an oil phase constructs a biodegradable framework, in which CQDs act as pore-forming agents to create micropores, and real-time detection of salt concentration and reporting of degradation progress are achieved through fluorescence quenching; the internal aqueous phase regulates osmotic pressure, driving water-responsive absorption and release. This is achieved through sulfonated PVA, PLA-CQDs, and Na2SO4. The synergistic design of 10H2O, combined with microfluidics, solves the problems of slow response and uncontrollable slow release in existing technologies, and has broad application prospects in the agricultural field.

[0007] 2. Technical Solution To solve the above problems, the present invention adopts the following technical solution.

[0008] Biodegradable, moisture-responsive polylactic acid (PLA) slow-release microspheres are prepared using a microfluidic method from an external aqueous phase, an oil phase, and an internal aqueous phase. The external aqueous phase is a polyvinyl alcohol solution that has undergone sulfonation; the oil phase is a PLA-carbon quantum dot mixture; and the internal aqueous phase is Na₂SO₄. 10H2O solution.

[0009] Furthermore, the solubility of polyvinyl alcohol after sulfonation is 5wt%~15wt%; the concentration of polylactic acid-carbon quantum dots is 5wt%~10wt%; and the concentration of Na2SO4 is... The concentration of 10H2O is 5wt%~10wt%.

[0010] A method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres as described in any of the above technical solutions includes the following steps: S1: Prepare the external aqueous phase, oil phase, and internal aqueous phase respectively; S2: Inject the external aqueous phase, oil phase and internal aqueous phase into the microfluidic device respectively to obtain stable droplets, and then collect the stabilized emulsion with a centrifuge tube; S3: The collected emulsion is transferred to an open container or fume hood, and after stirring, washing, freezing and drying, biodegradable water-responsive polylactic acid sustained-release microspheres are obtained.

[0011] Furthermore, the preparation of the internal aqueous phase in step S1 includes: preparing Na2SO4 Dissolve 10H2O in deionized water to prepare Na2SO4. 10H2O solution; The preparation of the oil phase includes: dissolving polylactic acid in dichloromethane to form a polylactic acid solution; dispersing carbon quantum dot powder in dichloromethane to form a uniform dispersion; and adding the dispersion dropwise to the polylactic acid solution to obtain a polylactic acid-carbon quantum dot mixture. The preparation of the external aqueous phase includes: dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution; adding sulfosuccinic acid to the polyvinyl alcohol solution, stirring to dissolve and complete the reaction, and obtaining a polyvinyl alcohol solution after sulfonation.

[0012] Furthermore, in the preparation of the external aqueous phase, polyvinyl alcohol is dissolved in deionized water at 85℃~95℃ to obtain a polyvinyl alcohol solution. The polyvinyl alcohol solution is then cooled to 65℃~75℃ before sulfosuccinic acid is added, and the stirring time is 2~6 hours.

[0013] Furthermore, the microfluidic device in step S2 includes three pressure-controlled channels for respectively conveying the inner aqueous phase, the oil phase, and the outer aqueous phase. When the solution enters the channel, the pressure value of the inner aqueous phase channel is controlled to be within 5 mbar of the pressure value of the outer aqueous phase channel; the pressure value of the oil phase channel is greater than the pressure values ​​of the inner and outer aqueous phases, and the pressure value of the oil phase channel is at least one order of magnitude different from the pressure value of the outer aqueous phase channel.

[0014] Furthermore, the pressure value of the inner water phase channel is 70~75 mbar, the pressure value of the outer water phase channel is 75~80 mbar, and the pressure value of the oil phase channel is 190~200 mbar.

[0015] An application of biodegradable moisture-responsive polylactic acid slow-release microspheres as described in any of the above claims, for use in agriculture for crop moisture control.

[0016] 3. Beneficial effects (1) The aqueous phase inside the biodegradable water-responsive polylactic acid slow-release microspheres in this invention is Na2SO4. In a 10H2O solution, sodium sulfate decahydrate (Na2SO4·10H2O) acts as the internal aqueous solute. Under high humidity, sodium sulfate transforms into a highly hydrated state, actively absorbing moisture from the environment, causing the polymer network to swell and thus "locking in" free water, slowing down water evaporation. Under low humidity, sodium sulfate transforms into a low-hydrated or anhydrous state, releasing water of crystallization. At the same time, the polymer network shrinks due to water loss, producing a "squeezing" effect and accelerating water expulsion. This reversible water absorption and release process enables dynamic regulation of the internal moisture of the microspheres. In addition, when the microsphere system completely disintegrates, the released sodium sulfate can be used as an inorganic salt nutrient for crop absorption, serving as both a slow-release carrier and a nutrient supplement. The oil phase uses a mixture of polylactic acid (PLA) and carbon quantum dots (CQDs) as the solute. CQDs can stabilize and utilize the tiny water droplets formed on the PLA (PLA) solution surface by water vapor in the air. These droplets serve as "molds," permanently imprinting the microporous structure onto the PLA surface after the solvent and water evaporate, thus achieving controllable fabrication of micropores on the microsphere surface. More importantly, CQDs also function as a powerful fluorescence sensing module: firstly, the fluorescence intensity of CQDs decreases with the degradation of themselves and the PLA matrix, allowing for real-time monitoring of the microsphere degradation process; secondly, CQDs are highly sensitive to environmental chemical signals—such as those from salt ions in the environment (e.g., Na+). + Cl - When the concentration of ions increases, they compress the electric double layer on the surface of CQDs, weakening the electrostatic repulsion and causing CQDs to aggregate. This aggregates then enhances nonradiative energy transfer through π-π stacking and increases surface defects, resulting in a significant decrease in fluorescence intensity (fluorescence quenching). In acidic environments, changes in the surface charge of CQDs may cause aggregation or increased nonradiative recombination, leading to fluorescence quenching or a redshift. In alkaline environments, the surface negative charge increases, electron cloud density changes, and fluorescence is enhanced or blueshifted. In neutral environments, functional groups are in equilibrium, resulting in the strongest or most stable fluorescence intensity. Therefore, CQDs make microspheres a highly sensitive "chemical sensor," capable of reporting changes in internal salt concentration (reflecting the release state) and monitoring local acid-base environments, providing a basis for constructing intelligent feedback-based moisture management materials. The external aqueous phase uses a sulfonated polyvinyl alcohol solution. The sulfonation reaction reduces the reactive hydroxyl groups in the PVA (polyvinyl alcohol) molecule, introduces stable sulfonic acid groups (-SO3H), and enhances intermolecular interactions, thereby significantly improving the chemical stability and structural integrity of PVA in acidic environments. Simultaneously, the sulfonate (-SO3H)... - It has a strong negative charge and can electrostatically repel hydroxide ions (OH-). - It can resist attacks and reduce the solubility of PVA in water through ionic cross-linking, thus making it exhibit excellent tolerance in alkaline environments as well. The whole process involves sulfonated PVA, PLA-CQDs, and Na2SO4. The synergistic design of 10H2O, combined with microfluidics, enables the preparation of a smart slow-release microsphere that is moisture-responsive, acid and alkali resistant, fluorescently sensing, structurally controllable, and can provide nutrients after degradation. This solves the problems of slow response and uncontrollable slow release in existing materials and has broad application prospects in agriculture, horticulture and environmentally responsive materials. (2) The concentration of PLA in the oil phase of this invention directly determines the quality and thickness of the polymer shell formed after the solvent evaporates. The higher the concentration, the more polymer chains per unit volume, and the thicker the shell; the lower the concentration, the thinner the shell. By limiting the concentration of the oil phase, the release rate can be adjusted over a wide range, and the use of harmful crosslinking agents or pore-forming agents can be avoided. The core layer thickness can be precisely controlled by simply changing the concentration of PLA, a biodegradable material, without introducing any additional additives, thus ensuring the biosafety and environmental friendliness of the microspheres. The concentration of sodium sulfate decahydrate in the internal aqueous phase directly determines the initial osmotic pressure of the core. The higher the concentration, the more salt ions per unit volume, and the greater the osmotic pressure. By adjusting the salt concentration, the critical ambient humidity at which the microspheres begin to significantly absorb water and swell can be precisely set, achieving "on-demand response"—not blindly absorbing water when there is abundant rainfall, and rapidly releasing crystal water when drought occurs; at the same time, a suitable concentration can enhance the water absorption driving force, thereby accelerating the response speed. The external aqueous phase acts as a surfactant and a viscosity modifier for the continuous phase, providing appropriate viscosity and interfacial coverage within a suitable concentration range. This stabilizes the dual emulsion droplets (preventing aggregation) and ensures smooth microfluidic operation. More importantly, the sulfonic acid groups (-SO3) - The introduction of PVA gives it acid and alkali resistance, enabling the external aqueous phase within this concentration range to maintain stable emulsification performance under different pH conditions. By adjusting the concentrations of the three phases, the fabrication feasibility, environmental responsiveness, and mechanical stability of the microspheres are ensured, achieving adjustable, sensitive, and stable moisture-responsive sustained release. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments.

[0018] Biodegradable, moisture-responsive polylactic acid (PLA) slow-release microspheres are prepared using a microfluidic method from an external aqueous phase, an oil phase, and an internal aqueous phase. The external aqueous phase is a polyvinyl alcohol solution that has undergone sulfonation; the oil phase is a PLA-carbon quantum dot mixture; and the internal aqueous phase is Na₂SO₄. 10H2O solution. Specifically, in this embodiment, each raw material in the three phases plays the following roles: Na2SO4 in the internal aqueous phase 10H2O solution: Na2SO4 In high humidity environments, salts transform into a highly hydrated state and absorb water, causing the polymer network to swell and further "lock in" free water. In low humidity environments, salts transform into a low hydrated or anhydrous state and release water of crystallization. At the same time, the polymer network shrinks due to water loss, generating a "squeezing" effect that accelerates the expulsion of water, achieving dynamic water absorption and slow release. Moreover, the system can provide crops with inorganic salts and other nutrients after disintegration. Oil-phase polylactic acid (PLA)-carbon quantum dot (CQD) mixture: PLA-CDQs are used, with CDQs added to PLA. Their role is to stabilize and utilize the tiny water droplets formed on the PLA solution surface by water vapor in the air, acting as a "mold." After the solvent and water evaporate, the microporous structure is permanently "etched" onto the PLA surface. Carbon quantum dots (CQDs) are not only a structural control tool (providing micropores) but also a powerful multifunctional module. They can "monitor" their own and the composite material's degradation process through the decay of their own fluorescence, and can also "monitor" environmental chemical signals (such as changes in ion concentration) through fluorescence quenching. CQDs can also detect local chemical environments: in acidic environments, changes in surface charge may cause aggregation or increased non-radiative recombination, resulting in fluorescence quenching or a redshift. In acidic or alkaline environments, an increase in surface negative charge leads to changes in electron cloud density, resulting in enhanced fluorescence or a blueshift. In neutral environments, functional groups are in equilibrium, resulting in the strongest or most stable fluorescence intensity. These mechanisms make CQDs a highly sensitive "chemical sensor" that can report internal salt concentration (reflecting the release state) and monitor changes in the local chemical environment in microcapsule systems, providing a basis for constructing intelligent feedback-based moisture management materials; The external aqueous phase of the polyvinyl alcohol solution after sulfonation reaction: The PVA used is sulfonated PVA. Sulfonated PVA significantly improves its chemical and structural stability in acidic environments by reducing active hydroxyl groups, introducing stable sulfonic acid groups, and forming stronger intermolecular interactions; simultaneously, sulfonated PVA, through sulfonate (-SO3) - The strong negative charge of OH groups causes electrostatic repulsion of OH groups. - The attack of ions, and the reduction of solubility through ionic cross-linking, result in superior alkali resistance.

[0019] Meanwhile, these three phases were used to prepare biodegradable moisture-responsive polylactic acid slow-release microspheres via microfluidic methods. By adjusting the concentration of PLA in the oil phase, the thickness of the outer aqueous core layer can be precisely controlled; by adjusting the concentration of solutes such as sodium sulfate in the inner aqueous phase, the osmotic pressure of the core can be increased, enhancing the driving force for water absorption and making the microspheres more sensitive to changes in humidity. This controllable preparation method ensures the consistency of the microsphere structure and the adjustability of its response performance.

[0020] The whole thing passes through Na2SO4 10H2O is used to enhance the water release switch of the microspheres; CQDs in PLA-CQDs promote the formation of microspheres while detecting the local chemical environment; sulfonated PVA enhances the acid and alkali resistance of the microspheres. After the outer layer of the formed microspheres decomposes, Na2SO4 can also be released through the micropores of the oil phase. 10H2O absorbs and releases moisture, achieving a slow-release effect and greatly extending the lifespan of the microspheres.

[0021] Therefore, this embodiment provides a new approach to alleviating agricultural water shortages. This technology can improve water use efficiency, is not limited by geography, and has great application potential. This embodiment combines a "water-triggered" mechanism with a PLA core-shell microsphere system, enabling immediate release during irrigation / rainfall and automatic dormancy during drought, fundamentally solving the "supply-demand mismatch in time and space." Traditional fertilization systems suffer nutrient loss rates as high as 50% (leaching, volatilization, fixation). By releasing a "switch," the microspheres release almost nothing in low-humidity environments and rapidly in high-humidity environments. Furthermore, the molecular weight of PLA can be modified according to different crop growth cycles, matching the slow-release + degradation cycle with the crop's growth cycle. Water-responsive controlled release can reduce this loss rate by at least 30-50 percentage points. Simultaneously, microfluidic methods can produce microspheres with good dispersibility, uniform size, and stability. PLA ultimately decomposes into CO2 and H2O under the action of soil microorganisms, leaving no toxic residues. This embodiment addresses microplastic residues at the source, and the application of PLA microspheres can directly reduce the carbon footprint of agricultural inputs.

[0022] In one specific embodiment, the solubility of the sulfonated polyvinyl alcohol is 5wt%~15wt%; the concentration of polylactic acid-carbon quantum dots is 5wt%~10wt%; and the concentration of Na2SO4 is... The concentration of 10H2O is 5wt%~10wt%; the concentration of each substance refers to the mass percentage of the solute.

[0023] The core of this embodiment lies in limiting the concentration of each of the three phases. By controlling the concentration of the solute in each phase, the shapeability, structural stability, moisture response sensitivity, and final release performance of the microspheres are determined. Specifically: For the external aqueous phase, the concentration of sulfonated polyvinyl alcohol (PVA) in the sulfonated PVA solution is controlled at 5 wt% to 15 wt%. This solute plays a dual role as a surfactant and a viscosity modifier for the continuous phase. If its concentration is too low, the solution viscosity will be too low, failing to provide sufficient shear stress and steric hindrance for the oil phase droplets. The double emulsion droplets are prone to coalescence after formation, leading to microsphere adhesion or structural damage. At the same time, if the adsorption layer of PVA molecules at the oil-water interface is too thin, the interfacial film strength will be insufficient, resulting in poor droplet stability. If the concentration is too high, the solution viscosity will be too high, resulting in poor flowability and a significant increase in flow resistance within the microfluidic channel, which may clog the chip or cause droplet generation frequency to run out of control. In addition, an excessively thick PVA adsorption layer will make it difficult to remove residual PVA from the surface of the microspheres during washing, affecting the biocompatibility and release behavior of the final product. Therefore, controlling the concentration within a suitable range provides moderate viscosity and interfacial coverage while ensuring smooth microfluidic operation.

[0024] For the oil phase, the solute polylactic acid (PLA)-carbon quantum dot (CQD) in the PLA-carbon quantum dot mixture is the source of the final microsphere shell framework, and its concentration directly affects the shell thickness, density, and the distribution and function of CQDs. If the PLA content is too low, the shell formed by the oil phase droplets after solvent evaporation will be too thin and brittle, with insufficient mechanical strength, making it prone to breakage during subsequent washing, drying, or application, leading to premature leakage of the core material. At the same time, the CQD concentration will decrease accordingly, weakening the micropore template effect and resulting in insufficient number and depth of surface micropores, affecting the water exchange rate. If the oil phase viscosity is too high, shearing will be difficult when generating droplets in microfluidics, resulting in a wider droplet size distribution and decreased monodispersity. In addition, high PLA concentration will lead to an excessively thick and dense shell, hindering the rapid entry and exit of water and weakening the water response sensitivity. Meanwhile, if the CQD concentration is too high, self-aggregation may occur, leading to fluorescence quenching rather than dispersion and pore formation.

[0025] For the internal aqueous phase, Na2SO4 Na2SO4 solute in 10H2O solution The concentration of 10H₂O directly determines the osmotic pressure of the core and the ability of reversible water of crystallization conversion. If the solute concentration is too low, the resulting osmotic pressure is insufficient. In high-humidity environments, this is insufficient to drive a large number of water molecules into the microspheres, leading to a weak swelling response and poor water retention. In low-humidity environments, the total amount of water of crystallization that can be released is limited, and the shrinkage "squeezing" effect is not significant. Overall, the water response sensitivity decreases. If the concentration is too high, the osmotic pressure is too large. During preparation or storage, water molecules may be prematurely absorbed into the microspheres, causing pre-swelling or even rupture before use. Simultaneously, supersaturated solutions may crystallize and precipitate within the microchannels, clogging the microfluidic chip.

[0026] By adjusting the concentrations of the three phases, the fabrication feasibility, environmental responsiveness, and mechanical stability of the microspheres are ensured, achieving adjustable, sensitive, and stable moisture-responsive sustained release.

[0027] A method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres as described in any of the above embodiments includes the following steps: S1: Prepare the external aqueous phase, oil phase, and internal aqueous phase respectively; S2: The external aqueous phase, oil phase, and internal aqueous phase are injected into the microfluidic device to obtain stable droplets. The stabilized emulsion is then collected using a centrifuge tube. The microfluidic device can be configured to add the internal aqueous phase, oil phase, and external aqueous phase to their respective reservoirs, applying initial high pressures of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to expel air from the tubing. After the tubing is completely filled with liquid, the pressure is adjusted to stabilize and generate biemulsion droplets. During this process, the chip outlet is observed under a microscope to confirm the generation of uniform W1 / O / W2 biemulsion droplets. The characteristic of uniform biemulsion droplets is that one or more small water droplets are encapsulated within an oil droplet. The stabilized emulsion is then collected using a centrifuge tube. S3: The collected emulsion is transferred to an open container or fume hood, and after stirring, washing, freezing and drying, biodegradable water-responsive polylactic acid sustained-release microspheres are obtained.

[0028] Specifically, the preparation of the internal aqueous phase in step S1 includes: preparing Na2SO4 Dissolve 10H2O in deionized water to prepare Na2SO4. 10H2O solution; The preparation of the oil phase includes: dissolving polylactic acid in dichloromethane to form a polylactic acid solution; dispersing carbon quantum dot powder in dichloromethane to form a uniform dispersion; and adding the dispersion dropwise to the polylactic acid solution to obtain a polylactic acid-carbon quantum dot mixture. The preparation of the external aqueous phase includes: dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution; adding sulfosuccinic acid to the polyvinyl alcohol solution, stirring to dissolve and complete the reaction, and obtaining a polyvinyl alcohol solution after sulfonation.

[0029] In one specific embodiment, during the preparation of the external aqueous phase, polyvinyl alcohol (PVA) is dissolved in deionized water at 85°C to 95°C to obtain a PVA solution. The PVA solution is then cooled to 65°C to 75°C before adding sulfosuccinic acid, with stirring time ranging from 2 to 6 hours. In this embodiment, PVA is first dissolved in deionized water at 85°C to 95°C. This temperature range ensures that the PVA molecular chains are fully extended and completely dissolved, avoiding uneven solution or gel residue due to incomplete dissolution. The subsequent cooling to 65°C to 75°C before adding sulfosuccinic acid is crucial: excessively high reaction temperatures can easily trigger self-polymerization or oxidation side reactions of the sulfonating agent, and may also cause thermal degradation of the PVA backbone, reducing product performance. A temperature of 65°C to 75°C maintains the good mobility of the PVA molecular chains, ensuring uniform sulfonation, and effectively suppresses side reactions, improving the grafting efficiency of sulfonic acid groups. Stirring for 2-6 hours provides sufficient time for the sulfonation reaction, allowing the sulfonic acid groups to be evenly distributed on the PVA chains, thereby obtaining stable, highly substituted sulfonated PVA. This improves the acid and alkali resistance and interfacial activity of sulfonated PVA, laying the foundation for subsequent microfluidic preparation of high-quality microspheres.

[0030] In one specific embodiment, the microfluidic device in step S2 includes three pressure-controlled channels for respectively conveying an inner aqueous phase, an oil phase, and an outer aqueous phase. When a solution enters the channel, the pressure value of the inner aqueous phase channel is controlled to be within 5 mbar of the pressure value of the outer aqueous phase channel; the pressure value of the oil phase channel is greater than the pressure values ​​of the inner and outer aqueous phases, and the pressure value of the oil phase channel differs from the pressure value of the outer aqueous phase channel by at least one order of magnitude.

[0031] The pressure difference between the inner and outer aqueous phases is controlled within 5 mbar, while the oil phase pressure is significantly higher than that of the inner and outer aqueous phases (by at least one order of magnitude). This cleverly adapts to the physical property that the oil phase viscosity is much greater than that of the aqueous phase. The high oil phase pressure can effectively overcome the flow resistance of the high-viscosity polylactic acid (PLA) solution in the microchannel, driving the oil phase to shear the inner aqueous phase droplets at a sufficiently high flow rate and encapsulate them to form uniform W1 / O / W2 biemulsion droplets. Meanwhile, the similar pressure of the inner and outer aqueous phases avoids the segregation of the inner phase droplets or the backflow of the outer phase caused by excessive pressure difference. As a result, structurally complete biemulsion droplets can be generated stably and repeatedly, providing a high-quality template for the subsequent preparation of sustained-release microspheres with uniform shell thickness and consistent moisture response. At the same time, it avoids channel blockage or emulsion agglomeration caused by pressure mismatch, significantly improving the stability and yield of the preparation process.

[0032] More specifically, the pressure value of the inner water phase channel is 70~75 mbar, the pressure value of the outer water phase channel is 75~80 mbar, and the pressure value of the oil phase channel is 190~200 mbar.

[0033] An application of biodegradable moisture-responsive polylactic acid slow-release microspheres as described in any of the above embodiments, using them in the agricultural field for crop moisture control.

[0034] To further understand the technical solution of this application, the following embodiments and comparative examples are provided: Example 1 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained at 8%. Too low a concentration means significant shrinkage of the internal phase after drying or solidification, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0035] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse 1 mg of the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts of the CQDs dispersion dropwise to the PLA solution.

[0036] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 2 hours to complete the esterification reaction.

[0037] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0038] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using a centrifuge tube.

[0039] Example 2 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0040] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0041] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0042] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0043] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using a centrifuge tube.

[0044] Example 3 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0045] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0046] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 6 hours to complete the esterification reaction.

[0047] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0048] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using a centrifuge tube.

[0049] Comparative Example 1 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained at 8%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0050] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse 1 mg of the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 part of the CQDs dispersion dropwise to the PLA solution.

[0051] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) Add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 2 hours to complete the esterification reaction.

[0052] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0053] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using centrifuge tubes. The collected emulsion was transferred to an open container or fume hood, and after stirring, washing, freezing, and drying, biodegradable water-responsive polylactic acid sustained-release microspheres were obtained.

[0054] Comparative Example 2 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 35% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0055] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0056] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0057] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0058] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using a centrifuge tube.

[0059] Comparative Example 3 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 1% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0060] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0061] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0062] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure to stabilize the formation of double emulsion droplets: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar Core principle: Oil phase viscosity > External phase viscosity → Oil phase pressure must be significantly higher than that of the internal and external phases.

[0063] Microscopic observation of the chip outlet confirmed the formation of uniform W1 / O / W2 biemulsion droplets. Characteristic: One or more small water droplets are encapsulated within each oil droplet. The stabilized emulsion was then collected using a centrifuge tube.

[0064] Comparative Example 4 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0065] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0066] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0067] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure: Internal phase (W1): 75 mbar; oil phase (O): 60 mbar; external phase (W2): 80 mbar The microspheres were observed under a microscope, and then the emulsion was collected using centrifuge tubes.

[0068] Comparative Example 5 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0069] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0070] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0071] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure: Internal phase (W1): 75 mbar; oil phase (O): 200 mbar; external phase (W2): 5 mbar The microspheres were observed under a microscope, and then the emulsion was collected using centrifuge tubes.

[0072] Comparative Example 6 Preparation of a three-phase solution: Internal aqueous phase (W1): Na2SO4 Dissolve 10H2O in deionized water to prepare 8% Na2SO4. 10H₂O solution. In Na₂SO₄ In the preparation of a three-phase microemulsion with 10H2O as the inner layer, Na2SO4 The concentration of 10H₂O should be maintained between 5% and 10%. Too low a concentration means significant shrinkage of the internal phase after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, are more likely to spread or partially dissolve into the intermediate oil phase, leading to uneven shell thickness and even pores. Too high a concentration causes the oil phase to precipitate on the inner wall of the channels due to salting-out, clogging the microchannels.

[0073] Oil phase (O): Dissolve 1.0 part PLA in 9.0 parts DCM by ultrasonication; pre-disperse the required CQDs powder in 1 mL of DCM (dichloromethane) to form a uniform dispersion; add 0.01 parts CQDs dispersion dropwise to the PLA solution.

[0074] External aqueous phase (W2): The specific method for PVA sulfonation is as follows: a) Dissolve PVA in deionized water at 90℃ to prepare a 10 wt% solution; b) After cooling to 70°C, add sulfosuccinic acid (SSA) and stir to dissolve; c) Stir the reaction for 4 hours to complete the esterification reaction.

[0075] Microfluidic preparation of microspheres: Add the internal aqueous phase (W1), oil phase (O), and external aqueous phase (W2) to the corresponding storage tanks respectively, and apply initial high pressure of 190 mbar for the internal phase, 280 mbar for the middle phase, and 500 mbar for the external phase to purge air from the pipeline. After the pipeline is completely filled with liquid, adjust the pressure: Internal phase (W1): 5 mbar; oil phase (O): 200 mbar; external phase (W2): 80 mbar The microspheres were observed under a microscope, and then the emulsion was collected using centrifuge tubes.

[0076] The experimental results are shown in Table 1 below: Table 1. Test Results

[0077] Note: The acidic environment in this experiment has a pH of 4, and the alkaline environment has a pH of 9, to simulate an accelerated degradation experiment.

[0078] Results analysis and explanation: In Comparative Example 1, because sulfosuccinic acid (SSA) was added directly without cooling, the reaction temperature was too high, leading to PVA decomposition. This resulted in the disappearance of the interfacial barrier, and without the protection of PVA, adjacent oil phase droplets would contact and merge. A large number of small droplets merged into large droplets, causing the final product to no longer be monodisperse microporous particles, but rather large polymer masses with non-uniform size and irregular shape. The fluorescence intensity was the highest. The polymer / solvent mixture encapsulated inside may escape prematurely, preventing the target material from forming the desired microporous structure. Due to Na2SO4... 10H₂O has strong hygroscopic properties, thus increasing water absorption. However, without the protection of acid and alkali sulfonated PVA, its resistance to acidic and alkaline environments decreases. In a short time, it relies on Na₂SO₄... 10H2O absorbs and releases water by resisting acids and alkalis, but this ability is lost over time. In Example 1, due to the short reaction time, the sulfonation of PVA was incomplete, resulting in weak acid and alkali resistance. In Example 3, due to the excessively long reaction time, the sulfonic acid groups (-SO3H) reacted with the hydroxyl groups (-OH) on the PVA molecular chain to form ester bonds (-SO3-), creating a covalent cross-linked network. The higher the degree of cross-linking, the denser the three-dimensional network. Cross-linking restricts the movement and extension of molecular chains, inhibiting water absorption and swelling. In Comparative Example 2, due to the innermost layer of Na2SO4... Excessive concentration of Na₂SO₄ can cause the pressure from the inside out to rupture the intermediate oil layer or the solidified outer shell, resulting in the formation of irregular spherical shapes. At high concentrations of 10H₂O, the ability to absorb and release water was significantly enhanced in the later stages of the experiment. Furthermore, in Comparative Example 2, high concentrations of Na₂SO₄... 10H2O can block some of the pores, thus reducing the fluorescence detection intensity. In Comparative Example 3, due to Na2SO4... When the 10H2O concentration is too low, the internal phase shrinks significantly after drying or curing, resulting in insufficient support for the microsphere shell. This causes the microspheres to collapse inwards during drying, forming concave spheres. Low-concentration solutions, under the influence of surface tension within the emulsion droplets, spread more easily or partially dissolve into the intermediate oil phase, leading to higher fluorescence intensity. In Comparative Example 4, the irregularity of the spherical structure may cause a decrease in fluorescence intensity. In Comparative Example 5, the excessively high internal pressure causes the internal aqueous phase to overflow, resulting in strong initial water absorption. In Comparative Example 6, the excessively low internal aqueous phase pressure results in only a very small amount of material being encapsulated, limiting the effectiveness of the absorbent material and manifesting as low water absorption and release rates. Furthermore, excessively low internal pressure can cause oil phase backflow, leading to a decrease in fluorescence intensity. Example 2 demonstrates the best performance in terms of fluorescence intensity, acid and alkali resistance, and sustained release.

[0079] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. Biodegradable moisture-responsive polylactic acid sustained-release microspheres, prepared by a microfluidic method from an external aqueous phase, an oil phase, and an internal aqueous phase, characterized in that: The external aqueous phase is a polyvinyl alcohol solution that has undergone sulfonation; the oil phase is a polylactic acid-carbon quantum dot mixture; and the internal aqueous phase is Na2SO4. 10H2O solution.

2. The method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres according to claim 1, characterized in that: The solubility of polyvinyl alcohol after sulfonation is 5wt%~15wt%; the concentration of polylactic acid-carbon quantum dots is 5wt%~10wt%; Na2SO4 The concentration of 10H2O is 5wt%~10wt%.

3. A method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres as described in any one of claims 1-2, characterized in that: Includes the following steps: S1: Prepare the external aqueous phase, oil phase, and internal aqueous phase respectively; S2: Inject the external aqueous phase, oil phase and internal aqueous phase into the microfluidic device respectively to obtain stable droplets, and then collect the stabilized emulsion with a centrifuge tube; S3: The collected emulsion is transferred to an open container or fume hood, and after stirring, washing, freezing and drying, biodegradable water-responsive polylactic acid sustained-release microspheres are obtained.

4. The method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres according to claim 3, characterized in that: The preparation of the internal aqueous phase in step S1 includes: preparing Na2SO4 Dissolve 10H2O in deionized water to prepare Na2SO4. 10H2O solution; The preparation of the oil phase includes: dissolving polylactic acid in dichloromethane to form a polylactic acid solution; dispersing carbon quantum dot powder in dichloromethane to form a uniform dispersion; and adding the dispersion dropwise to the polylactic acid solution to obtain a polylactic acid-carbon quantum dot mixture. The preparation of the external aqueous phase includes: dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol solution; adding sulfosuccinic acid to the polyvinyl alcohol solution, stirring to dissolve and complete the reaction, and obtaining a polyvinyl alcohol solution after sulfonation.

5. The method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres according to claim 4, characterized in that: In the preparation of the external aqueous phase, polyvinyl alcohol is dissolved in deionized water at 85℃~95℃ to obtain a polyvinyl alcohol solution. The polyvinyl alcohol solution is then cooled to 65℃~75℃ before sulfosuccinic acid is added, and the stirring time is 2~6 hours.

6. The method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres according to claim 3, characterized in that: The microfluidic device in step S2 includes three pressure-controlled channels for conveying an inner aqueous phase, an oil phase, and an outer aqueous phase, respectively. When a solution enters the channel, the pressure value of the inner aqueous phase channel is controlled to be within 5 mbar of the pressure value of the outer aqueous phase channel; the pressure value of the oil phase channel is greater than the pressure values ​​of the inner and outer aqueous phases, and the pressure value of the oil phase channel differs from the pressure value of the outer aqueous phase channel by at least one order of magnitude.

7. The method for preparing biodegradable moisture-responsive polylactic acid sustained-release microspheres according to claim 6, characterized in that: The pressure value of the inner water phase channel is 70~75 mbar, the pressure value of the outer water phase channel is 75~80 mbar, and the pressure value of the oil phase channel is 190~200 mbar.

8. An application of the biodegradable moisture-responsive polylactic acid sustained-release microspheres as described in any one of claims 1-2, characterized in that: It is used in agriculture for crop moisture control.

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