Polylactic acid microspheres, and preparation method and application thereof
Polylactic acid microspheres were prepared by emulsion mesh cutting technology, which solved the problems of uneven particle size distribution and low production efficiency in the existing technology, and achieved high uniformity and controllability, making them suitable for drug carriers, tissue engineering and medical aesthetic fillers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- RESEARCH INSTITUTE OF TRANSVASCULAR IMPLANTATION EQUIPMENT ZHEJIANG MEDICAL SECOND HOSPITAL BINJIANG DISTRICT HANGZHOU
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-05
AI Technical Summary
Existing methods for preparing polylactic acid microspheres suffer from problems such as uneven particle size distribution, insufficient size controllability, and low production efficiency, which limits their application, especially in the field of medical aesthetics and regeneration.
Using emulsion mesh cutting technology, the primary emulsion formed by mixing the oil phase and the water phase under negative pressure or pressure is passed through a mesh to form a highly uniform oil-in-water emulsion system. Subsequently, solvent evaporation and curing are carried out to obtain polylactic acid microspheres with controllable size and high uniformity.
It achieves precise control of microsphere particle size, improves uniformity and production efficiency, is suitable for large-scale production, has low cost, and is applicable to drug carriers, tissue engineering scaffolds, and medical aesthetic filler materials.
Smart Images
Figure CN122145835A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of biomedical materials technology, and relates to a polylactic acid microsphere, its preparation method and application, specifically to an efficient preparation method of polylactic acid microspheres with controllable size and high uniformity, the obtained polylactic acid microspheres and their applications. Background Technology
[0002] Polylactic acid (PLA) and its copolymers (such as PLA-glycolic acid copolymer) are widely used in drug delivery, tissue engineering, and regenerative medicine due to their excellent biocompatibility and biodegradability. In recent years, with the rapid development of medical aesthetic regeneration technologies, PLA microspheres, as an injectable filler, have gradually become an important component of the medical aesthetic field. These microspheres can stimulate collagen production, improve skin texture and appearance, and have broad application prospects.
[0003] However, existing methods for preparing polylactic acid (PLA) microspheres have many limitations, mainly in terms of uneven particle size distribution, insufficient size controllability, and low production efficiency. For example, homogenization emulsification is commonly used to prepare PLA microspheres. Although simple to operate, it is difficult to precisely control the particle size, resulting in a wide distribution and poor reproducibility. Spray drying, while offering the advantage of rapid drying, suffers from poor size controllability during microsphere formation, easily leading to adhesion and agglomeration, affecting uniformity and reliability. Membrane emulsification can form relatively uniform emulsion droplets, but it is prone to clogging membrane tubes, resulting in low production efficiency. Microfluidics technology can prepare highly uniform microspheres, but it suffers from high equipment costs, high process complexity, a high risk of microchannel clogging, and low production efficiency. These limitations significantly restrict the promotion and application of PLA microspheres in biomedicine, especially in the field of medical aesthetics and regeneration, where particle size uniformity and controllability are extremely important.
[0004] Therefore, developing a method for efficiently preparing polylactic acid microspheres with controllable size and high uniformity is of great scientific and applied value to the biomedical field. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide polylactic acid (PLA) microspheres, their preparation method, and applications. Specifically, it provides an efficient method for preparing PLA microspheres with controllable size and high uniformity, as well as the obtained PLA microspheres and their applications, thereby overcoming the deficiencies of existing technologies. This invention utilizes a unique emulsion mesh cutting technology (a schematic diagram of the basic principle of emulsion mesh cutting is shown below). Figure 1 As shown in the figure, precise control of the particle size of polylactic acid microspheres from nanometer to micrometer level has been achieved, which improves the uniformity, size controllability and production efficiency of polylactic acid microspheres.
[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing polylactic acid microspheres, the method comprising the following steps: (1) Dissolve polylactic acid in an organic solvent to obtain an oil phase; (2) Dissolve the surfactant in water to obtain an aqueous phase; (3) Mix the oil phase and the water phase and stir to form an oil-in-water primary emulsion; (4) The oil-in-water emulsion is cut into a grid to form a highly uniform oil-in-water emulsion system, wherein the grid cutting process is carried out under negative pressure or pressure conditions to assist the oil-in-water emulsion in passing through the grid; (5) The solvent in the oil-in-water emulsion system is evaporated to obtain solidified microspheres, and then the solidified microspheres are post-treated to obtain polylactic acid microspheres.
[0007] The present invention provides a method for preparing polylactic acid (PLA) microspheres. This method employs emulsion mesh cutting technology, uniformly dividing a primary emulsion droplet formed by mixing an oil phase containing PLA with an aqueous phase containing a surfactant into stable, target-sized droplets. Subsequently, through solvent evaporation, solidification, separation, and washing steps, highly uniform PLA microspheres are finally obtained. This method offers advantages such as simplicity, efficiency, low cost, good reproducibility, high microsphere uniformity, and controllable size, and is suitable for large-scale production. In particular, this method can prepare various uniform PLA microspheres ranging in size from nanometers to micrometers. Due to their uniformity and controllable size, these microspheres show extremely broad application prospects in biomedical fields such as drug carriers, tissue engineering scaffolds, and cosmetic fillers.
[0008] Preferably, the polylactic acid in step (1) includes any one or a combination of at least two of L-polylactic acid, D-polylactic acid, racemic polylactic acid and their copolymers.
[0009] Preferably, the molecular weight of polylactic acid in step (1) is 8~1000kDa, such as 8kDa, 10kDa, 20kDa, 30kDa, 50kDa, 80kDa, 100kDa, 200kDa, 300kDa, 400kDa, 500kDa, 600kDa, 700kDa, 800kDa, 900kDa, 1000kDa, etc.
[0010] Preferably, the organic solvent in step (1) includes any one or a combination of at least two of the following: dichloromethane, dichloroethane, chloroform, ethyl acetate, methyl acetate, acetone, dimethyl sulfoxide, tetrahydrofuran, pentane, and hexafluoroisopropanol.
[0011] Preferably, the mass concentration of polylactic acid in the oil phase in step (1) is 1% to 20%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, etc.
[0012] Preferably, the surfactant in step (2) includes any one or a combination of at least two of polyvinyl alcohol, Tween, sodium dodecyl sulfate, hyaluronic acid, carboxymethyl cellulose, alginate, polylysine, and polyacetylimide.
[0013] Preferably, the mass concentration of the surfactant in the aqueous phase in step (2) is 0.1% to 10%, for example, 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.
[0014] Preferably, step (3) of mixing the oil phase and the aqueous phase specifically includes: adding the oil phase to the aqueous phase.
[0015] Preferably, the addition includes dropwise addition.
[0016] Preferably, in step (3), the volume ratio of the oil phase to the water phase is (0.01~1):1, for example, 0.01:1, 0.02:1, 0.03:1, 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, etc.
[0017] Preferably, the stirring in step (3) is carried out at 0~50℃ (e.g., 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc.), the stirring time is 0.5~5h (e.g., 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, etc.), and the stirring speed is 100~2000rpm, e.g., 100rpm, 200rpm, 300rpm, 500rpm, 800rpm, 1000rpm, 1200rpm, 1300rpm, 1500rpm, 1800rpm, 2000rpm, etc.
[0018] Preferably, the mesh used for mesh cutting in step (4) includes any one or a combination of at least two of the following: polytetrafluoroethylene mesh, glass fiber mesh, ceramic mesh, carbon fiber mesh, titanium mesh, nickel mesh, stainless steel mesh, copper mesh, aluminum mesh, polypropylene mesh, polyethylene mesh, polyvinylidene fluoride mesh, polyvinyl chloride mesh, nylon mesh, polyethylene terephthalate mesh, and rubber mesh.
[0019] Preferably, the grid used for cutting the grid in step (4) consists of several (at least two) small squares, the side length of which is 0.001~1mm, for example 0.001mm, 0.003mm, 0.005mm, 0.008mm, 0.01mm, 0.02mm, 0.05mm, 0.07mm, 0.1mm, 0.2mm, 0.3mm, 0.5mm, 0.6mm, 0.8mm, 1mm, etc.
[0020] Preferably, the negative pressure in step (4) is -0.01 to -2 MPa, such as -0.01 MPa, -0.03 MPa, -0.05 MPa, -0.06 MPa, -0.08 MPa, -0.1 MPa, -0.2 MPa, -0.4 MPa, -0.7 MPa, -0.9 MPa, -1 MPa, -1.2 MPa, -1.4 MPa, -1.5 MPa, -1.6 MPa, -1.8 MPa, -2 MPa, etc.
[0021] Preferably, the pressure applied in step (4) is 0.01~2MPa, for example 0.01MPa, 0.03MPa, 0.05MPa, 0.06MPa, 0.08MPa, 0.1MPa, 0.2MPa, 0.4MPa, 0.7MPa, 0.9MPa, 1MPa, 1.2MPa, 1.4MPa, 1.5MPa, 1.6MPa, 1.8MPa, 2MPa, etc.
[0022] Preferably, the solvent evaporation in step (5) is carried out at 0~50℃ (e.g., 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, etc.).
[0023] Preferably, the post-processing in step (5) includes separation, cleaning, and drying.
[0024] Preferably, the separation method includes centrifugation or vacuum filtration.
[0025] Preferably, the drying method includes any one or a combination of at least two of freeze drying, vacuum drying, supercritical fluid drying, or oven drying.
[0026] As a preferred embodiment of the present invention, the preparation method includes the following steps: (1) Dissolve polylactic acid in an organic solvent to obtain an oil phase with a mass concentration of 1% to 20%; (2) Dissolve the surfactant in water to obtain an aqueous phase with a mass concentration of 0.1% to 10%; (3) The oil phase is added to the aqueous phase, wherein the volume ratio of the oil phase to the aqueous phase is (0.01~1):1, and the mixture is stirred at 0~50℃ for 0.5~5h at a stirring speed of 100~2000rpm to form an oil-in-water primary emulsion. (4) The oil-in-water emulsion is cut into a grid to form a highly uniform oil-in-water emulsion system, wherein the grid cutting process is carried out under negative pressure or pressure conditions to assist the oil-in-water emulsion in passing through the grid; The grid used for cutting the mesh consists of several small squares, each with a side length of 0.001~1mm; the negative pressure is -0.01~-2MPa, and the applied pressure is 0.01~2MPa. (5) The solvent in the oil-in-water emulsion system is evaporated at 0~50℃ to obtain solidified microspheres. Then the solidified microspheres are separated, cleaned and dried to obtain polylactic acid microspheres.
[0027] In a second aspect, the present invention provides polylactic acid microspheres, which are prepared by the preparation method described in the first aspect.
[0028] Preferably, the polylactic acid microspheres have a particle size of 0.05~500μm, such as 0.05μm, 0.08μm, 0.1μm, 0.5μm, 1μm, 2μm, 5μm, 8μm, 10μm, 30μm, 50μm, 80μm, 100μm, 500μm, etc., and the coefficient of variation of the particle size distribution is less than 10%, such as 9%, 8%, 7%, 6%, 5%, etc.
[0029] In this invention, the test method for the particle size and particle size distribution of the polylactic acid microspheres is as follows: images of polylactic acid microspheres are acquired by optical microscope or scanning electron microscope, and the diameters of no less than 100 polylactic acid microspheres are randomly counted using image analysis software (such as ImageJ, Nano Measurer, etc.). The particle size (Davg) and standard deviation (SD) are calculated. The coefficient of variation (CV) of the particle size distribution is calculated by the following formula: CV (%) = (SD / Davg) × 100%, which is used to standardize the uniformity of the particle size distribution of polylactic acid microspheres.
[0030] Thirdly, the present invention provides the application of polylactic acid microspheres as described in the second aspect in drug carriers, tissue engineering scaffolds, and medical aesthetic filler materials.
[0031] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, which has the following advantages: (1) Controllable microsphere size: This invention employs emulsion mesh cutting technology, which can precisely control the particle size distribution of microspheres. By using specific negative or pressurized control, the efficiency of the water-in-oil primary emulsion passing through the mesh is improved, ensuring the uniform formation of polylactic acid microspheres. In particular, this invention can easily prepare polylactic acid microspheres with particle sizes ranging from nanometers to micrometers (0.05~500μm) by adjusting the side length of the small squares in the mesh.
[0032] (2) High uniformity: The polylactic acid microspheres prepared by the present invention have a uniform particle size distribution, smooth surface, high uniformity, and the coefficient of variation of particle size distribution is less than 10%, which is superior to traditional preparation methods (such as homogenization emulsification method and spray drying method).
[0033] (3) High production efficiency: The production process of the present invention is simple to operate and has high production efficiency, making it suitable for large-scale production and superior to emerging preparation methods (such as membrane emulsification and microfluidics).
[0034] (4) Low cost: The materials and equipment used in this invention are low cost and have the characteristics of low carbon and low energy consumption. The equipment maintenance cost is low and it is easy to promote and apply on a large scale. Attached Figure Description
[0035] Figure 1 This is a schematic diagram illustrating the basic principle of emulsion mesh cutting in this invention.
[0036] Figure 2 These are optical images of the oil-in-water emulsion before and after cutting in Embodiment 1 of the present invention.
[0037] Figure 3 These are optical microscopic images of the oil-in-water emulsion before and after cutting in Embodiment 1 of the present invention. Detailed Implementation
[0038] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.
[0039] Example 1 This embodiment provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, comprising the following steps: (1) Dissolve polylactic acid (molecular weight 100kDa) in dichloromethane to obtain an oil phase with a mass concentration of 10%; (2) Mix polyvinyl alcohol (degree of hydrolysis is 92.0%) with water and stir at 90℃ and 500rpm for 2h to fully dissolve it in water to obtain an aqueous phase with a mass concentration of 2%; (3) Slowly add 40 mL of oil phase to 400 mL of aqueous phase, stir at 25 °C for 2 h at a stirring speed of 300 rpm to form an oil-in-water primary emulsion; (4) At 25°C, the oil-in-water emulsion was cut through a polytetrafluoroethylene (PTFE) mesh. The side length of the small squares in the mesh was 0.1 mm. The cutting process was carried out under a negative pressure of -0.1 MPa to form a highly uniform oil-in-water emulsion system. The optical images of the oil-in-water emulsion before and after cutting are shown below. Figure 2 As shown in the figure, the emulsion system formed after emulsion cutting is more stable. Optical microscopic images of the oil-in-water emulsion before and after cutting are shown below. Figure 3 As shown in the figure, the emulsion after cutting has good uniformity; (5) The above water-in-oil emulsion system was left to stand at 25°C in the dark for 24 hours. After the solvent evaporated, solidified microspheres were obtained. (6) The solidified microspheres were centrifuged, washed with deionized water five times, and dried by freeze drying to obtain polylactic acid microspheres with a particle size range of 40~60μm and a particle size distribution variation coefficient of 6.2%.
[0040] Example 2 This embodiment provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, comprising the following steps: (1) Racemic polylactic acid (molecular weight 8 kDa) was dissolved in dichloromethane to obtain an oil phase with a mass concentration of 5%; (2) Mix polyvinyl alcohol (degree of hydrolysis is 92.0%) with water and stir at 90℃ and 500rpm for 2h to fully dissolve it in water to obtain an aqueous phase with a mass concentration of 1%; (3) Slowly add 5 mL of oil phase to 100 mL of aqueous phase, stir at 10 °C for 2 h at a stirring speed of 500 rpm to form an oil-in-water primary emulsion; (4) At 10℃, the water-in-oil primary emulsion is cut through a glass fiber mesh. The side length of the small squares in the mesh is 0.05mm. The cutting process is carried out under negative pressure control of -0.05MPa to form a highly uniform water-in-oil emulsion system. (5) The above oil-in-water emulsion system was left to stand at 25°C in the dark for 12 hours. After the solvent evaporated, solidified microspheres were obtained. (6) The solidified microspheres were separated by filtration, washed with deionized water 5 times, and dried by freeze drying to obtain polylactic acid microspheres with a particle size range of 20~40μm and a particle size distribution variation coefficient of 5.6%.
[0041] Example 3 This embodiment provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, comprising the following steps: (1) Dissolve dextrorotatory polylactic acid (molecular weight of 10 kDa) in chloroform to obtain an oil phase with a mass concentration of 5%; (2) Sodium dodecyl sulfate was dissolved in water to obtain an aqueous phase with a mass concentration of 2%; (3) Slowly add 5 mL of oil phase to 100 mL of aqueous phase, stir at 25 °C for 2 h at a stirring speed of 300 rpm to form an oil-in-water primary emulsion; (4) At 10℃, the water-in-oil primary emulsion is cut through a nylon mesh with a side length of 0.1 mm for each small square. The cutting process is carried out under a negative pressure of -0.06 MPa to form a highly uniform water-in-oil emulsion system. (5) The above water-in-oil emulsion system was left to stand at 25°C in the dark for 24 hours. After the solvent evaporated, solidified microspheres were obtained. (6) The solidified microspheres were centrifuged, cleaned, and freeze-dried to obtain polylactic acid microspheres with a particle size range of 30~50μm and a particle size distribution variation coefficient of 6.7%.
[0042] Example 4 This embodiment provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, comprising the following steps: (1) Dissolve L-polylactic acid (molecular weight of 10 kDa) in dichloromethane to obtain an oil phase with a mass concentration of 5%; (2) Dissolve Tween in water to obtain an aqueous phase with a mass concentration of 2%; (3) Slowly add 10 mL of oil phase to 100 mL of aqueous phase, stir at 5°C for 2 h at a stirring speed of 500 rpm to form an oil-in-water primary emulsion; (4) At 5°C, the water-in-oil primary emulsion is cut through a polytetrafluoroethylene mesh. The side length of the small squares in the mesh is 0.05 mm. The cutting process is carried out under pressure control of 0.08 MPa to form a highly uniform water-in-oil emulsion system. (5) The above oil-in-water emulsion system was left to stand at 25°C in the dark for 12 hours. After the solvent evaporated, solidified microspheres were obtained. (6) The solidified microspheres were separated by filtration, washed with deionized water 5 times, and dried by freeze drying to obtain polylactic acid microspheres with a particle size range of 20~40μm and a particle size distribution variation coefficient of 7.1%.
[0043] Example 5 This embodiment provides a highly efficient method for preparing polylactic acid microspheres with controllable size and high uniformity, comprising the following steps: (1) Dissolve L-polylactic acid (molecular weight 20 kDa) in dichloromethane to obtain an oil phase with a mass concentration of 5%; (2) Mix polyvinyl alcohol (degree of hydrolysis is 88.0%) with water and stir at 90℃ and 600rpm for 2h to fully dissolve it in water to obtain an aqueous phase with a mass concentration of 2%; (3) Slowly add 10 mL of oil phase to 200 mL of aqueous phase, stir at 5 °C for 2 h at a stirring speed of 1000 rpm to form an oil-in-water primary emulsion; (4) At 5°C, the water-in-oil primary emulsion was cut through a stainless steel mesh. The side length of the small squares in the mesh was 0.008 mm. The cutting process was carried out under pressure control of 0.2 MPa to form a highly uniform water-in-oil emulsion system. (5) The above oil-in-water emulsion system was left to stand at 5°C in the dark for 24 hours. After the solvent evaporated, solidified microspheres were obtained. (6) The solidified microspheres were centrifuged, washed with deionized water five times, and dried by freeze drying to obtain polylactic acid microspheres with a particle size range of 0.5~1.0μm and a particle size distribution variation coefficient of 7.8%.
[0044] Example 6 The only difference between this embodiment and embodiment 1 is that the side length of the small squares in the grid in step (4) is 0.5mm.
[0045] The polylactic acid microspheres prepared in this embodiment have a particle size range of 200~300μm and a coefficient of variation of particle size distribution of 8.5%.
[0046] Example 7 The only difference between this embodiment and embodiment 1 is that in step (3), the volume of both the oil phase and the water phase is 40 mL.
[0047] The polylactic acid microspheres prepared in this embodiment have a particle size range of 40~60μm and a coefficient of variation of 7.1% for particle size distribution.
[0048] Comparative Example 1 The only difference between this comparative example and Example 1 is that the cutting process was carried out at 0 MPa.
[0049] In this comparative example, the water-in-oil primary emulsion could not be effectively cut through the polytetrafluoroethylene mesh, and the resulting polylactic acid microspheres had a particle size range of 100~600μm and a coefficient of variation of 35.1% for particle size distribution.
[0050] Comparative Example 2 The only difference between this comparative example and Example 1 is that step (4) is different, as follows: (4) At 25°C, the water-in-oil primary emulsion was passed through a needle filter with a polytetrafluoroethylene filter membrane. The pore size of the filter membrane was 1 micrometer. The cutting process was carried out under positive pressure control of 0.1 MPa.
[0051] The polylactic acid microspheres prepared in this comparative example have a particle size range of 300~600μm and a coefficient of variation of 18.0% for particle size distribution.
[0052] Comparative Example 3 The only difference between this comparative example and Example 1 is that the cutting process was carried out under pressure control of 3 MPa.
[0053] The polylactic acid microspheres prepared in this comparative example have a particle size range of 10~60μm and a coefficient of variation of particle size distribution of 21.5%.
[0054] As can be seen from the above embodiments and comparative examples, compared with the comparative examples, the polylactic acid microspheres obtained by the preparation method provided by the present invention have high uniformity, controllable size, and high production efficiency.
[0055] The applicant declares that the present invention illustrates the polylactic acid microspheres, their preparation method, and applications through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
Claims
1. A method for preparing polylactic acid microspheres, characterized in that, The preparation method includes the following steps: (1) Dissolve polylactic acid in an organic solvent to obtain an oil phase; (2) Dissolve the surfactant in water to obtain an aqueous phase; (3) Mix the oil phase and the water phase and stir to form an oil-in-water primary emulsion; (4) The oil-in-water emulsion is cut into a grid to form a uniform oil-in-water emulsion system, wherein the grid cutting process is carried out under negative pressure or pressure conditions; (5) The solvent in the oil-in-water emulsion system is evaporated to obtain solidified microspheres, and then the solidified microspheres are post-treated to obtain polylactic acid microspheres.
2. The preparation method according to claim 1, characterized in that, The polylactic acid in step (1) includes any one or a combination of at least two of L-polylactic acid, D-polylactic acid, racemic polylactic acid and their copolymers; Preferably, the molecular weight of the polylactic acid in step (1) is 8~1000kDa; Preferably, the organic solvent in step (1) includes any one or a combination of at least two of the following: dichloromethane, dichloroethane, chloroform, ethyl acetate, methyl acetate, acetone, dimethyl sulfoxide, tetrahydrofuran, pentane, and hexafluoroisopropanol; Preferably, the mass concentration of polylactic acid in the oil phase in step (1) is 1% to 20%.
3. The preparation method according to claim 1 or 2, characterized in that, The surfactant in step (2) includes any one or a combination of at least two of the following: polyvinyl alcohol, Tween, sodium dodecyl sulfate, hyaluronic acid, carboxymethyl cellulose, alginate, polylysine, and polyacetylimide. Preferably, the mass concentration of the surfactant in the aqueous phase in step (2) is 0.1% to 10%.
4. The preparation method according to any one of claims 1-3, characterized in that, Step (3) of mixing the oil phase and the aqueous phase specifically includes: adding the oil phase to the aqueous phase; Preferably, the addition includes dropwise addition; Preferably, in step (3), the volume ratio of the oil phase to the water phase is (0.01~1):1; Preferably, the stirring in step (3) is carried out at 0~50℃, the stirring time is 0.5~5h, and the stirring speed is 100~2000rpm.
5. The preparation method according to any one of claims 1-4, characterized in that, The mesh used for mesh cutting in step (4) includes any one or a combination of at least two of the following: polytetrafluoroethylene mesh, glass fiber mesh, ceramic mesh, carbon fiber mesh, titanium mesh, nickel mesh, stainless steel mesh, copper mesh, aluminum mesh, polypropylene mesh, polyethylene mesh, polyvinylidene fluoride mesh, polyvinyl chloride mesh, nylon mesh, polyethylene terephthalate mesh, and rubber mesh. Preferably, the mesh used for mesh cutting in step (4) consists of several small squares, and the side length of the small squares is 0.001~1mm.
6. The preparation method according to any one of claims 1-5, characterized in that, The negative pressure mentioned in step (4) is -0.01 to -2 MPa; Preferably, the pressure applied in step (4) is 0.01~2MPa.
7. The preparation method according to any one of claims 1-6, characterized in that, The solvent evaporation in step (5) is carried out at 0~50℃; Preferably, the post-processing in step (5) includes separation, cleaning, and drying; Preferably, the separation method includes centrifugation or vacuum filtration; Preferably, the drying method includes any one or a combination of at least two of freeze drying, vacuum drying, supercritical fluid drying, or oven drying.
8. A preparation method according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Dissolve polylactic acid in an organic solvent to obtain an oil phase with a mass concentration of 1% to 20%; (2) Dissolve the surfactant in water to obtain an aqueous phase with a mass concentration of 0.1% to 10%; (3) The oil phase is added to the aqueous phase, wherein the volume ratio of the oil phase to the aqueous phase is (0.01~1):1, and the mixture is stirred at 0~50℃ for 0.5~5h at a stirring speed of 100~2000rpm to form an oil-in-water primary emulsion. (4) The oil-in-water emulsion is cut into a grid to form a uniform oil-in-water emulsion system, wherein the grid cutting process is carried out under negative pressure or pressure conditions; The grid used for cutting the mesh consists of several small squares, each with a side length of 0.001~1mm; the negative pressure is -0.01~-2MPa, and the applied pressure is 0.01~2MPa. (5) The solvent in the oil-in-water emulsion system is evaporated at 0~50℃ to obtain solidified microspheres. Then the solidified microspheres are separated, cleaned and dried to obtain polylactic acid microspheres.
9. A polylactic acid microsphere, characterized in that, The polylactic acid microspheres were prepared using the preparation method described in any one of claims 1-8; Preferably, the polylactic acid microspheres have a particle size of 0.05~500μm and a particle size distribution coefficient of variation of less than 10%.
10. The application of polylactic acid microspheres as described in claim 9 in drug carriers, tissue engineering scaffolds, and medical aesthetic filler materials.