Porous polylactic acid microsphere based on microfluidic technology and preparation method and application thereof

Abstract

The invention discloses a porous polylactic acid microsphere based on a microfluidic technology as well as a preparation method and application thereof, and belongs to the field of biomedical materials. The method comprises the following steps: by taking an ammonium bicarbonate aqueous solution as a water phase and a polylactic acid-dichloromethane solution as an oil phase, carrying out ultrasonic emulsification to prepare a water-in-oil primary emulsion; then taking the primary emulsion as a dispersion phase and a polyvinyl alcohol aqueous solution as a continuous phase, and jointly introducing the dispersion phase and the continuous phase into a micro-fluidic chip with a T-shaped channel for shearing to form uniform liquid drops; and solidifying, washing and freeze-drying the liquid drops to obtain the porous polylactic acid microspheres. Wherein the particle size and the pore structure of the microspheres can be accurately controlled by adjusting the two-phase flow velocity, the concentration and the water-oil volume ratio; according to the invention, the micro-fluidic technology is utilized to realize high uniformity of the size of liquid drops, and the prepared microspheres are narrow in particle size distribution, controllable in pores, regular in structure and suitable for the biomedical fields such as medical beauty filling and the like in combination with decomposition and pore forming of ammonium bicarbonate.

Description

A porous polylactic acid microsphere based on microfluidic technology, its preparation method and application Technical Field

[0001] This invention belongs to the field of biomedical material preparation technology, and particularly relates to a porous polylactic acid microsphere based on microfluidic technology, its preparation method and application. Background Technology

[0002] Polylactic acid (PLA) is a biomaterial certified by the U.S. Food and Drug Administration (FDA) as harmless to the human body. It can be metabolized in the body over a long period of time and eventually degraded into carbon dioxide and water. Due to its high safety and good biocompatibility, it is widely used in clinical and filler fields. In recent years, with the rapid development of medical aesthetic fillers, PLA microspheres, as the main component of injectable facial fillers, can stimulate collagen formation, fill skin depressions, enhance cosmetic effects, and maintain long-term cosmetic effects when injected subcutaneously. High-quality PLA microspheres with uniform particle size and regular shape are of great significance for improving cosmetic effects and long-lasting filling effects.

[0003] Polylactic acid microspheres prepared by traditional methods are mostly solid structures, making it difficult to achieve both immediate filling effect and long-term collagen stimulation effect after injection. In recent years, porous polylactic acid microspheres have shown better filling and long-term maintenance effects due to their sponge-like structure, which can promote collagen ingrowth.

[0004] However, traditional methods for preparing porous microspheres (such as emulsification-solvent evaporation and phase separation methods) have problems such as poor process controllability, wide microsphere particle size distribution (PDI is often greater than 0.2), non-uniform pore structure, and poor batch repeatability, making it difficult to meet the stringent quality requirements of medical aesthetic fillers for microspheres. Summary of the Invention

[0005] This invention provides porous polylactic acid microspheres based on microfluidic technology, their preparation method, and applications, aiming to solve the above-mentioned problems.

[0006] The present invention is implemented as follows: a method for preparing porous polylactic acid microspheres based on microfluidic technology, comprising the following steps: (1) preparing an oil phase solution: dissolving polylactic acid in an organic solvent (such as dichloromethane, chloroform, ethyl acetate) to prepare an oil phase solution with a concentration of 0.5-5wt%; (2) preparing an aqueous phase solution: dissolving ammonium bicarbonate in deionized water to prepare an aqueous phase solution with a concentration of 0.1-3wt%; (3) preparing a primary emulsion: adding the aqueous phase solution to the oil phase solution at a volume ratio of 1:10-1:50, and emulsifying under ultrasonic-stirring conditions for 1-5 min (for example, at 200W power, using an intermittent mode of ultrasonic 3s and pause 5s, with stirring conditions of 200rpm) to obtain a water-in-oil primary emulsion; (4) microfluidic shearing. :The colostrum was used as the dispersed phase and the polyvinyl alcohol aqueous solution was used as the continuous phase. They were respectively injected into the T-channel of the microfluidic chip through the injection pump. The dispersed phase flow rate was 1.5-4.5 mL / min and the continuous phase flow rate was 10-20 mL / min. Shearing was performed to form uniform oil-in-water droplets; (5) Curing and washing: The droplets were collected in 0.1-1 wt% polyvinyl alcohol aqueous solution and cured for 2-6 h at 30-40℃ with stirring (200 rpm). Then, they were ultrasonically cleaned with 0.1 M sodium hydroxide solution (100 W, 10 min) and washed with deionized water at least three times; (6) Freeze-drying: The washed microspheres were freeze-dried (pre-frozen at -60℃ for 3 h, then vacuum freeze-dried for 36-48 h) to obtain porous polylactic acid microspheres.

[0007] Preferably, the microfluidic chip includes an emulsifying chip and a T-shaped shearing chip connected in series, wherein the emulsifying chip channel consists of multiple diamond-shaped structures connected in series, with a channel depth of 50-200 μm and a width of 25-75 μm; the T-shaped chip has a dispersed phase channel and a continuous phase channel with a diameter of 50-200 μm, and a collection channel with a diameter of 150-450 μm.

[0008] Preferably, the polylactic acid is at least one of PLLA, PDLA or PDLLA, with a molecular weight of 50,000 to 100,000 Daltons.

[0009] Preferably, the concentration of the polyvinyl alcohol aqueous solution is 0.1-1 wt%.

[0010] Preferably, the freeze-drying conditions are: pre-freezing to below -60°C, vacuum degree ≤10Pa, and drying time 24-48h.

[0011] Preferably, the ammonium bicarbonate in step (2) is porous ammonium bicarbonate microcrystals, which are prepared by the following method: a saturated solution of ammonium bicarbonate is rapidly mixed with ethanol at a volume ratio of 1:2-5 and ultrasonically treated, then frozen to crystallize at -20°C to -40°C, filtered, and vacuum dried to obtain the product.

[0012] Preferably, the porous ammonium bicarbonate microcrystals are prepared as follows: (1) Under ice-water bath conditions at 0-5°C, ammonium bicarbonate is dissolved in deionized water to prepare a saturated solution (approximately 24g / 100mL, 0°C), and kept at this low temperature for later use to reduce ammonia volatilization at room temperature; (2) Pre-cooled ethanol (analytical grade, 0-5°C) is placed in a beaker, and under magnetic stirring (500-800rpm), 1 volume of the saturated ammonium bicarbonate solution is rapidly poured into 2-5 volumes of cold ethanol in one go within 10-30 seconds; (3) Immediately after mixing, place the mixture in an ultrasonic cleaner for treatment; ultrasonic power 100-200W, frequency 40kHz, treatment time 2-5 minutes, temperature maintained ≤10°C; (4) quickly transfer the ultrasonically treated suspension to a low temperature environment of -20°C to -40°C, let it stand for 2-4 hours for freezing crystallization; (5) in a Buchner funnel pre-cooled to 0-5°C, use filter paper to quickly filter the frozen mixture, and quickly wash the filter cake 1-2 times with an appropriate amount (e.g. 10mL) of pre-cooled anhydrous ethanol to remove residual moisture on the surface.

[0013] (6) Quickly transfer the filter cake to a vacuum dryer; drying temperature 25-35°C, vacuum degree ≤0.1MPa, drying time 4-6 hours.

[0014] The porous microcrystals prefabricated by the above method already have nanoscale pores inside; when decomposed in polylactic acid matrix, the gas release is more gentle and the path is more controllable, inducing the generation of richer and more interconnected secondary nanopores, forming a unique "macropore-mesopore" hierarchical pore structure.

[0015] Preferably, after washing and before freeze-drying in step (5), an in-situ gelation step is also included: the washed wet porous microspheres are immersed in a phosphate buffer containing photosensitive biopolymers and photoinitiators, and after being impregnated under negative pressure (4-10℃, vacuum negative pressure -0.05 to -0.1MPa for 1-3 hours) and photo-initiated (irradiated under 405nm wavelength blue light for 10-30 seconds), the photosensitive biopolymers are cross-linked in situ in the pores of the microspheres; the uncross-linked solution on the surface is quickly rinsed with deionized water and then freeze-dried.

[0016] The photosensitive biopolymer is methacrylamide gelatin or methacrylamide hyaluronic acid, with a content of 0.5%-3wt% in phosphate buffer; the photoinitiator is lithium phenyl-2,4,6-trimethylbenzoylphosphine, with a content of 0.05%-0.2% in phosphate buffer; through the above in-situ gelation steps, the final composite microspheres exhibit a unique "dual-network" structure: the first network is a rigid framework network with macroporous structures composed of polylactic acid bulk, the morphology of which is determined by the microfluidic process and pore-forming agent; the second network is... A flexible filling network composed of photocrosslinked hydrogels, filling the pores of the framework, acts as an elastic filler, effectively buffering external forces and preventing the porous microspheres from breaking brittlely during injection and use. It can serve as a loading library for drugs, growth factors, or cells, enabling controlled sustained release. The hydrophilic gel filling greatly reduces pore collapse during freeze-drying and improves the structural recovery rate after rehydration. This dual network is not a simple physical mixture, but rather is anchored to the inner surface of the rigid framework through negative pressure impregnation and in-situ crosslinking, forming a synergistic composite structure by intermolecular forces and possible physical entanglement.

[0017] Compared with the prior art, the embodiments of this application have the following advantages: precise shearing and size control of emulsion droplets are achieved through microfluidic chips, resulting in microspheres with narrow particle size distribution and regular shape; combined with porous ammonium bicarbonate microcrystals as pore-forming agents, rich and interconnected multi-level pore structures can be induced; by adjusting the water-oil phase ratio and ultrasonic emulsification conditions, the pore structure and density of the microspheres can be controllably adjusted; the process is mild and has good repeatability, and is suitable for various polylactic acid materials such as PLLA, PDLA, and PDLLA, and has the potential for large-scale production. Attached Figure Description

[0018] Figure 1 is a flowchart of a method for preparing porous polylactic acid microspheres based on microfluidic technology provided by the present invention.

[0019] Figure 2 is a scanning electron microscope (SEM) image of the porous polylactic acid microspheres prepared in Example 1 of the present invention.

[0020] Figure 3 is a SEM image of the microspheres prepared in Example 2.

[0021] Figure 4 is a SEM image of the microspheres prepared in Example 3.

[0022] Figure 5 shows the SEM image of the microspheres prepared in Comparative Example 1.

[0023] Figure 6 is a schematic diagram of the structure of the microfluidic emulsification chip used in the embodiment of the present invention.

[0024] Figure 7 is a schematic diagram of the structure of the T-shaped shearing chip used in the embodiment of the present invention. Detailed Implementation

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] Raw material preparation: Preparation of porous ammonium bicarbonate microcrystals (1) Prepare 100 mL of saturated ammonium bicarbonate solution in an ice-water bath (2°C), and measure 300 mL of analytical grade ethanol, which is also pre-cooled to 2°C.

[0028] (2) Under magnetic stirring at 600 rpm, 100 mL of saturated ammonium bicarbonate solution was quickly poured into 300 mL of cold ethanol within 15 seconds; (3) The mixture was immediately placed in an ultrasonic cleaner with temperature controlled by an ice-water bath (power 150 W, frequency 40 kHz) for 3 minutes, and the liquid temperature was kept below 8°C; (4) The suspension was transferred to a container and placed in a -30°C low-temperature freezer for crystallization for 3 hours; (5) The mixture was quickly filtered in a pre-cooled (4°C) Buchner funnel and the filter cake was quickly washed once with 10 mL of cold anhydrous ethanol; (6) The filter cake was placed in a vacuum drying oven and dried at 30°C and -0.095 MPa for 5 hours to obtain a white fluffy powder, which is porous ammonium bicarbonate microcrystals.

[0029] In the method described in this invention, the organic solvent can be selected from common solvents that can dissolve polylactic acid, such as dichloromethane, chloroform, and ethyl acetate. The following examples use dichloromethane as an example for detailed description, but should not be construed as limiting the invention.

[0030] Example 1 This embodiment of the invention provides a method for preparing porous polylactic acid microspheres based on microfluidic technology, as shown in Figure 1, including the following steps: (1) Dissolve 0.25g PDLLA in 10mL dichloromethane to obtain an oil phase solution with a concentration of 2.5%, and dissolve 0.15g ammonium bicarbonate in 10mL deionized water to obtain an aqueous phase solution with a concentration of 1.5%; (2) Add 1mL of the aqueous phase solution to 10mL of the oil phase solution, and emulsify the two solutions for 150s under stirring and ultrasonication to obtain a primary emulsion, wherein the stirring speed is 200rpm, the ultrasonic power is 200W, the ultrasonication is 3s, and the pause is 5s; (3) Dissolve 1g of polyvinyl alcohol in 1000mL of deionized water, stir and heat to 80℃ to dissolve, and obtain a polyvinyl alcohol-continuous phase solution with a concentration of 0.1%; (4) Use an injection pump to inject the primary emulsion at a rate of 3mL / min The flow rate of n is input into the microfluidic emulsification chip (as shown in Figure 6), and the chip outlet is connected to the dispersed phase inlet of the T-type chip (as shown in Figure 7); using an injection pump, 0.1% polyvinyl alcohol-continuous phase solution is pumped into the continuous phase inlet of the T-type chip at a flow rate of 15 mL / min; (5) the droplets obtained by chip emulsification shearing are collected in 0.1% polyvinyl alcohol solution at 35°C and 150 rpm under stirring. After the droplets are collected, they are heated and stirred for 3 hours to solidify the droplets; (6) the solidified microspheres are soaked in 0.1M sodium hydroxide solution for 1 minute, then washed three times with deionized water, and freeze-dried at -60°C for 36 hours to obtain porous PDLLA microspheres.

[0031] As shown in Figure 2, the porous PDLLA microspheres prepared in this embodiment have uniform particle size, narrow particle size distribution, and clear porous structure. According to the laser particle size analyzer, the average particle size of the microspheres is 50 μm, the particle size distribution index (PDI) is 0.06, the porosity is 55%±3%, and the average pore size is 2-5 μm, which shows excellent monodispersity and pore controllability.

[0032] Example 2 (1) Dissolve 0.25g PDLLA in 10mL dichloromethane to obtain an oil phase solution with a concentration of 2.5%; dissolve 0.15g ammonium bicarbonate in 10mL deionized water to obtain an aqueous phase solution with a concentration of 1.5%; (2) Add 0.5mL of the aqueous phase solution to 10mL of the oil phase solution, and emulsify the two solutions for 150s under stirring and sonication to obtain a primary emulsion, wherein the stirring speed is 200rpm, the ultrasonic power is 200W, the ultrasonication is 3s, and the pause is 5s; (3) Dissolve 1g of polyvinyl alcohol in 1000mL of deionized water, stir and heat to 80℃ to dissolve, and obtain a polyvinyl alcohol-continuous phase solution with a concentration of 0.1%; (4) Use a syringe pump to inject the primary emulsion at a rate of 3mL / m The flow rate of in is input into the microfluidic emulsification chip (as shown in Figure 6), and the chip outlet is connected to the dispersed phase inlet of the T-type chip (as shown in Figure 7); using an injection pump, 0.1% polyvinyl alcohol-continuous phase solution is pumped into the continuous phase inlet of the T-type chip at a flow rate of 15 mL / min; (5) the droplets obtained by chip emulsification shearing are collected in 0.1% polyvinyl alcohol solution at 35°C and 150 rpm under stirring. After the droplets are collected, they are heated and stirred for 3 hours to solidify the droplets; (6) the solidified microspheres are soaked in 0.1M sodium hydroxide solution for 1 minute, then washed three times with deionized water, and freeze-dried at -60°C for 36 hours to obtain porous PDLLA microspheres.

[0033] As shown in Figure 3, this embodiment prepared porous PDLLA microspheres by adjusting the volume ratio of the aqueous phase and the oil phase in the primary emulsion. The number and size of the pores were reduced compared to Example 1. The microspheres were tested and found to have an average particle size of 52 μm, a particle size distribution index (PDI) of 0.07, a porosity of 35% ± 3%, and an average pore size of 1-3 μm. This indicates that the porosity of the microspheres can be adjusted by adjusting this ratio.

[0034] Example 3 (1) Dissolve 0.2g PLLA in 10mL dichloromethane to obtain a 2% oil phase solution, and dissolve 0.15g ammonium bicarbonate in 10mL deionized water to obtain a 1.5% aqueous phase solution; (2) Add 0.25mL of the aqueous phase solution to 10mL of the oil phase solution, and emulsify the two solutions for 150s under stirring and sonication to obtain a primary emulsion, wherein the stirring speed is 200rpm, the ultrasonic power is 200W, the ultrasonication is 3s, and the pause is 5s; (3) Dissolve 1g of polyvinyl alcohol in 1000mL of deionized water, stir and heat to 80℃ to dissolve, and obtain a 0.1% polyvinyl alcohol-continuous phase solution; (4) Use a syringe pump to inject the primary emulsion at 3mL / min The flow rate of n is input into the microfluidic emulsification chip (as shown in Figure 6), and the chip outlet is connected to the dispersed phase inlet of the T-type chip (as shown in Figure 7); using an injection pump, 0.1% polyvinyl alcohol-continuous phase solution is pumped into the continuous phase inlet of the T-type chip at a flow rate of 15 mL / min; (5) the droplets obtained by chip emulsification shearing are collected in 0.1% polyvinyl alcohol solution at 35°C and 150 rpm under stirring. After the droplets are collected, they are heated and stirred for 3 hours to solidify the droplets; (6) the solidified microspheres are soaked in 0.1M sodium hydroxide solution for 1 minute, then washed three times with deionized water, and freeze-dried at -60°C for 36 hours to obtain porous PLLA microspheres.

[0035] As shown in Figure 4, in this embodiment, the material was replaced with PLLA to prepare porous PLLA microspheres. The microspheres were tested and found to have an average particle size of 51 μm, a particle size distribution (PDI) of 0.08, a porosity of 25% ± 3%, and an average pore size of 0.8-2 μm. This indicates that the method is applicable to various polylactic acid materials such as PLLA, PDLA, and PDLLA.

[0036] Comparative Example 1 (1) 0.25g PDLLA was dissolved in 10mL dichloromethane to obtain an oil phase solution with a concentration of 2.5%, and 0.15g ammonium bicarbonate was dissolved in 10mL deionized water to obtain an aqueous phase solution with a concentration of 1.5%; (2) 1mL of the aqueous phase solution was added to 10mL of the oil phase solution, and the two solutions were emulsified for 150s under stirring and sonication to obtain a primary emulsion. The stirring speed was 200rpm, the ultrasonic power was 200W, the ultrasonication lasted for 3s, and the pause was 5s; (3) 1g of polyvinyl alcohol was dissolved in 1000mL of deionized water, and the solution was dissolved by stirring and heating to 80℃ to obtain (4) The primary emulsion was directly dripped into a beaker containing 0.1% polyvinyl alcohol solution using a syringe pump at a flow rate of 3 mL / min through a regular flat-mouth needle (with an inner diameter of about 0.5 mm). The solution was collected under stirring at 35°C and 150 rpm. After the droplets were collected, the solution was heated and stirred for 3 hours to solidify the droplets. (5) The solidified microspheres were soaked in 0.1 M sodium hydroxide solution for 1 minute, then washed three times with deionized water, and freeze-dried at -60°C for 36 hours to obtain porous PDLLA microspheres.

[0037] As shown in Figure 5, the porous microspheres prepared in this comparative example have uneven surface pore distribution, incomplete microsphere morphology, and low hardness.

[0038] Example 4 (1) Dissolve 0.25g PDLLA in 10mL dichloromethane to obtain an oil phase solution with a concentration of 2.5%, and dissolve 0.15g ammonium bicarbonate in 10mL deionized water to obtain an aqueous phase solution with a concentration of 1.5%; (2) Add 1mL of aqueous phase solution to 10mL of oil phase solution, and emulsify the two solutions for 150s under stirring and sonication to obtain a primary emulsion, wherein the stirring speed is 200rpm, the ultrasonic power is 200W, the ultrasonication is 3s, and the pause is 5s; (3) Dissolve 1g of polyvinyl alcohol in 1000mL of deionized water, stir and heat to 80℃ to dissolve, and obtain a polyvinyl alcohol-continuous phase solution with a concentration of 0.1%; (4) Use a syringe pump to input the primary emulsion into a microfluidic emulsification chip (as shown in Figure 6) at a flow rate of 3mL / min, and connect the chip outlet to a T-shaped core. (5) The droplets obtained by chip emulsification shearing are collected in 0.1% polyvinyl alcohol solution at 35℃ and 150rpm stirring. After the droplets are collected, they are heated and stirred for 3h to solidify the droplets. (6) The solidified microspheres are soaked in 0.1M sodium hydroxide solution for 1min and then washed three times with deionized water to obtain a wet porous polylactic acid microsphere substrate. (7) Methacrylamide gelatin (GelMA, purity ≥95%) and photoinitiator (phenyl-2,4,6-trimethylbenzoyl lithium phosphine, LAP) are dissolved in phosphate buffer (PBS, pH 10). In step 7.4), an impregnation solution containing 2 wt% methacrylamide gelatin and 0.1 wt% phenyl-2,4,6-trimethylbenzoyl lithium phosphinate was prepared and stored at 4°C in the dark for later use; (8) the wet porous polylactic acid microspheres were immersed in a sufficient amount of impregnation solution; the entire system was placed in a vacuum desiccator and maintained at -0.08 MPa negative pressure and 4°C for 2 hours to ensure that the impregnation solution fully penetrated into all the pores inside the microspheres; (9) the microspheres were sieved out with a sieve and placed under a 405 nm wavelength blue light source (light intensity 10 mW / cm²). 2 Irradiate for 20 seconds to induce in-situ crosslinking of the methacrylamide gelatin that has penetrated into the pores, forming a stable hydrogel network; (10) Rinse the microspheres three times with deionized water to remove the uncrosslinked solution on the surface; then freeze-dry the microspheres to finally obtain composite porous polylactic acid microspheres with a double network structure inside.

[0039] The average particle size was 50 μm and the particle size distribution index (PDI) was 0.06. Since the flexible gel network only filled some of the fine pores of the polylactic acid skeleton and did not block the macropores, and the pore collapse during the freeze-drying process was reduced by the gel support, the pore structure was more intact. The porosity was measured to be 52% ± 3% (by mercury porosimetry) and the average pore size was 2-4 μm. The composite microspheres with a dual network structure prepared in this example showed the following effects compared with the microspheres with only a single polylactic acid network in Example 1: (1) Mechanical properties Performance: Its compressive modulus (measured using a microsphere compressor according to GB / T14486-2014 standard) is about 150% higher than that of Example 1, indicating that the internal flexible gel network effectively shares and buffers external forces; (2) Structural stability: After the same freeze-drying-rehydration cycle, its volume recovery rate (calculated by measuring the volume of microspheres before freeze-drying and after rehydration by the water displacement method) is about 40% higher than that of Example 1, indicating that the hydrophilic gel network significantly reduces pore collapse; (3) Functional characteristics: When used as a model drug (such as BSA) carrier, it exhibits a sustained-release effect of more than 28 days in PBS buffer (pH 7.4, 37℃ constant temperature) (the cumulative release amount is measured by ultraviolet spectrophotometry), which is better than the sustained-release effect of microspheres in Example 1, indicating that the gel network forms an effective drug reservoir and diffusion barrier; The above data jointly confirm the successful construction of the internal dual network structure and the comprehensive performance improvement it brings.

[0040] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0041] It should be understood that the disclosed apparatus can be implemented in other ways, as illustrated in the embodiments provided in this application. For example, the apparatus embodiments described above are merely illustrative; the division of units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or communication connections shown or discussed may be through some interfaces; the indirect coupling or communication connections between devices or units may be telecommunications or other forms.

[0042] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0043] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A method for preparing porous polylactic acid microspheres based on microfluidic technology, characterized in that, The process includes the following steps: (1) dissolving polylactic acid in an organic solvent to prepare an oil phase solution; (2) dissolving ammonium bicarbonate in water to prepare an aqueous phase solution; (3) adding the aqueous phase solution to the oil phase solution and emulsifying by ultrasonic stirring to form a water-in-oil pre-emulsion; (4) using the pre-emulsion as the dispersed phase and the polyvinyl alcohol aqueous solution as the continuous phase, passing it through a microfluidic chip for shearing to form uniform droplets; (5) solidifying, washing, and freeze-drying the droplets to obtain porous polylactic acid microspheres.

2. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 1, characterized in that, In step (4), the microfluidic chip includes an emulsification chip and a T-shaped shearing chip.

3. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 2, characterized in that, The emulsification chip has multiple series-connected diamond-shaped channels with a structural depth of 50-200µm and a series channel width of 25-75µm; the T-shaped shearing chip includes a dispersed phase channel, a continuous phase channel, and a collection channel; wherein the diameter of the dispersed phase channel is 50-200µm, the diameter of the continuous phase channel is 50-200µm, and the diameter of the collection channel is 150-450µm.

4. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 3, characterized in that, The concentration of ammonium bicarbonate is 0.1-3 wt%; the concentration of polylactic acid solution is 0.5-5 wt%; and the concentration of polyvinyl alcohol aqueous solution is 0.1-1 wt%.

5. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 1, characterized in that, The volume ratio of the aqueous phase to the oil phase is 1:10-1:50; the ultrasonic emulsification time is 1-5 min; in the microfluidic shearing, the flow rate of the dispersed phase is 1.5-4.5 mL / min, and the flow rate of the continuous phase is 10-20 mL / min.

6. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 1, characterized in that, In step (5), the curing is carried out in a 0.1-1wt% polyvinyl alcohol aqueous solution at 30-40℃ for 2-6 hours with stirring; the washing includes ultrasonic cleaning with 0.1 M NaOH solution, followed by washing with deionized water at least three times.

7. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 1, characterized in that, The ammonium bicarbonate mentioned in step (2) is a porous ammonium bicarbonate microcrystal, which is prepared by the following method: a saturated solution of ammonium bicarbonate is rapidly mixed with ethanol at a volume ratio of 1:2-5 and ultrasonically treated, then frozen to crystallize at -20℃ to -40℃, filtered and vacuum dried to obtain the product.

8. The method for preparing porous polylactic acid microspheres based on microfluidic technology as described in claim 1, characterized in that, After washing and before freeze-drying in step (5), an in-situ gelation step is also included: the washed wet porous microspheres are immersed in a phosphate buffer containing photosensitive biopolymers and photoinitiators, and after negative pressure impregnation and light initiation, the photosensitive biopolymers undergo in-situ cross-linking in the pores of the microspheres.

9. A porous polylactic acid microsphere, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The application of the porous polylactic acid microspheres as described in claim 9 in the preparation of biomedical materials.

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