Polylactic acid microsphere injection and preparation method thereof

Abstract

The invention relates to an injection of polylactic acid microspheres, and the polylactic acid microspheres are of hollow structures with basically non-porous surfaces and have proper density so as to avoid sedimentation in a carrier. The invention also provides a preparation method of the polylactic acid microspheres.

Description

Technical Field

[0001] This invention relates to the field of biomaterials, specifically to an injectable form of polylactic acid microspheres and its applications. Background Technology

[0002] Polylactic acid (PLA) boasts advantages such as renewability, biodegradability, and good biocompatibility. Its microspheres, with their small size and high specific surface area, can stimulate collagen regeneration after subcutaneous implantation, making them a rising star in the medical aesthetics field. Clinically, functional microspheres are often dispersed in an aqueous matrix to create injectable formulations. As a heterogeneous suspension, slowing down the sedimentation of microspheres is a pressing issue. According to sedimentation kinetics, there are three main ways to improve the sedimentation stability of suspensions: reducing particle size, increasing viscosity, and reducing density difference. Reducing particle size is the most effective method, but the function of many particles is related to particle size and density. For example, embolization microspheres need to have a particle size larger than the diameter of the blood vessel at the embolization site; collagen regeneration microspheres, due to their small size (<20μm), are prone to granuloma formation and are often controlled at 25-50μm; the drug release rate of drug-loaded microspheres is closely related to particle size and is also often controlled within a certain range. In the formulation field, the most common method to improve sedimentation stability is to increase matrix viscosity, but high viscosity can lead to problems such as poor needle penetration and high pushing force. Shear-thinned polymer solutions have high viscosity when standing, but the viscosity decreases under injection shear. They are often used as suspension matrices, but often require high concentrations. At low concentrations, their effect on slowing down the sedimentation rate of microspheres is limited.

[0003] Porous microspheres can reduce the particle density of microspheres. Several patents have disclosed gel formulations incorporating polylactic acid porous microspheres, such as patent 202411705096.1, which discloses a double-swirl polylactic acid porous microsphere composite gel medical aesthetic filler material and its preparation method; and patent 202411131452.3, which discloses a porous microsphere composite botulinum toxin gel and its preparation method. However, existing literature indicates that the rough surface structure of the microspheres can increase acute inflammatory responses after implantation. The open pores on the microsphere surface can heal themselves through appropriate methods, resulting in smooth, hollow microspheres. When porous PLGA (polylactic acid-glycolic acid copolymer) microspheres are treated in a solution above their glass transition temperature, the open pores on the surface heal to form low-density microspheres with smooth surfaces (SE Reinhold, KGH Desai, L. Zhang, KF Olsen, SPSchwendeman, Self‐healing microencapsulation of biomacromolecules without organic solvents, Angew. Chem. Int. Ed. 51(43)(2012)10800–10803.). Patent 201110401710.1 discloses a method for preparing biodegradable polymer microcapsules. First, polylactic acid microspheres with open pore surfaces are prepared by double emulsion method. Then, the open pores on the surface are closed by solvent swelling method, infrared light source irradiation method, or heating annealing method to obtain microcapsules. The microspheres prepared by this method do not completely seal the open pores, have irregular shapes, and still have many open pores on the surface. Furthermore, this patented method does not use ethanol to wash the microspheres, and it produces solid drug-loaded microspheres with a density that does not meet the requirements for anti-settling.

[0004] Solid polylactic acid microspheres are prone to sedimentation, as are polylactic acid microspheres with open pore surfaces. Furthermore, the rough surface can easily cause inflammatory reactions after injection. Therefore, it is necessary to prepare polylactic acid microspheres that are not prone to sedimentation and have a smoother surface. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects in the prior art.

[0006] This invention provides an injectable formulation of polylactic acid (PLA) microspheres, comprising PLA microspheres and a matrix. The PLA microspheres have a hollow structure, and in a 500x electron microscope image, the average number of surface pores does not exceed 10, and the tap density after drying does not exceed 0.40 g / cm³. 3 The matrix is ​​a medically acceptable injectable aqueous solution or hydrogel.

[0007] Existing detection methods are insufficient to observe the entire surface of the microspheres; therefore, this invention uses the number of surface pores in electron micrographs for characterization. The polylactic acid microspheres of this invention, in 500x electron micrographs, have an average surface pore count of no more than 10, preferably no more than 6, more preferably no more than 2, and most preferably no more than 1. For comparison, porous microspheres are shown in the appendix to this invention. Figure 4 Its average number of surface pores far exceeds 10. For example... Figure 5 As shown, after 15 minutes of curing, most of the surface pores of the microspheres were sealed. A rough count of the porous spheres (observed at ×500 magnification; small, non-porous spheres were solid spheres due to emulsification failure and were not included; roughly 29 spheres with relatively intact pores were counted, with approximately 174 visible open pores) yielded an average surface pore count of 6. Preferably, this invention includes... Figure 2 The microspheres on display have visible depressions on their surface and virtually no surface pores. Even when observed at a magnification of 1000, the average number of surface pores does not exceed one.

[0008] Preferably, the polylactic acid microspheres have a particle size D 50 The value is 10-100μm, more preferably 20-50μm.

[0009] Preferably, the tap density of the polylactic acid microspheres after drying does not exceed 0.37 g / cm³. 3 More preferably 0.26-0.34 g / cm³ 3 The optimal value is 0.265-0.308 g / cm³. 3 .

[0010] The aqueous solution for injection can be a hypotonic, isotonic, or hypertonic solution, including osmotic pressure regulators such as sodium chloride, and optionally nutrients such as amino acids. Since this application aims to solve the problem of microsphere sedimentation, the specific composition of the aqueous solution is not limited, as long as its density is less than 1.05 g / cm³. 3 That's all.

[0011] The hydrogel is formed by adding a matrix to the injectable aqueous solution. The matrix is ​​selected from one or more of carboxymethyl cellulose or its salts, hyaluronic acid or its salts, cross-linked hyaluronic acid or its salts, hydroxypropyl methylcellulose, hydroxyethyl cellulose, and agarose. In the field of medical aesthetics, different types and concentrations of hydrogels can be used depending on the injection site and purpose. The suspension stability of microspheres in hydrogels is better than that in aqueous solutions.

[0012] The chemical composition of the polylactic acid microspheres can be L-polylactic acid, D-polylactic acid, racemic polylactic acid, or a mixture thereof. Different types of lactic acid have basically the same chemical properties and density, which does not affect the technical effect of the invention.

[0013] The polylactic acid microsphere content in the injection is 1-300 mg / mL, 1-200 mg / mL, preferably 1-100 mg, and more preferably 5-50 mg. This value can be adjusted according to the injection site and purpose; for example, a smaller number of microspheres can be used in a hydrating formulation, while a higher microsphere content is required for neck wrinkle injections. Because the microspheres prepared by this invention have good suspension stability and a relatively smooth surface, the preferred microspheres did not exhibit rapid sedimentation even in gels with concentrations as high as 300 mg / mL, and needle passage was smooth.

[0014] Preferably, the matrix of the hydrogel is selected from one or more of carboxymethyl cellulose or its salt, hyaluronic acid or its salt, cross-linked hyaluronic acid or its salt, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and agarose.

[0015] The present invention also provides a method for preparing hollow polylactic acid microspheres, comprising the following steps: (1) adding an inner aqueous phase containing a pore-forming agent to an oil phase containing polylactic acid, and emulsifying to obtain a primary emulsion containing tiny water droplets; (2) adding the primary emulsion to an outer aqueous phase containing an emulsifier, and emulsifying to obtain an emulsion; (3) mixing the emulsion with a C1-C4 alcohol solvent, and aging to close the surface pores; (4) solidifying, separating the solid and liquid, washing the microspheres, and drying to obtain polylactic acid microspheres.

[0016] Preferably, in step (1), the volume ratio of the aqueous phase to the oil phase is 1:4-10, the concentration of polylactic acid in the oil phase is ≤30%, and the emulsification method is homogenization emulsification or membrane emulsification.

[0017] Preferably, the inner aqueous phase and oil phase in step (1) do not contain emulsifiers, and the osmotic pressure of the inner aqueous phase is higher than that of the outer aqueous phase in step (2). As an example, the inner aqueous phase can be a 3%-5% NaCl solution.

[0018] The C1-C4 alcohol solvent is preferably methanol, ethanol, n-propanol, isopropanol, propylene glycol, glycerol, n-butanol, isobutanol, tert-butanol, butanediol, or glycerol. Ethanol is preferred because it is low in cost, low in toxicity, and easy to remove.

[0019] Preferably, the maturation time in step (3) is not less than 15 minutes, more preferably not less than 20 minutes, more preferably not less than 25 minutes, and more preferably not less than 30 minutes. The longer the maturation time, the higher the porosity and the lower the density of the microspheres, which may cause them to float. Therefore, the most preferred time is 30-45 minutes to obtain microspheres that can be stably suspended in aqueous solution.

[0020] The principle of porous microsphere preparation in this invention is as follows: A double emulsion method is used, where the inner aqueous phase is dispersed as droplets in a polymer solution (oil phase) to prepare a W / O emulsion. This emulsion is then added to the outer aqueous phase containing an emulsifier, and after emulsification, a W / O / W emulsion is obtained. The organic solvent in the oil phase is removed to obtain porous microspheres. The stability of the inner aqueous phase droplets is crucial for the preparation of porous microspheres. Adding an emulsifier is an effective method to stabilize the inner aqueous phase droplets, but the emulsifier can be encapsulated inside the microspheres, making it difficult to remove and increasing the toxicity risk of the microspheres. Osmotically active substances such as NaCl are often added to the inner aqueous phase to create an osmotic pressure difference between the inner and outer aqueous phases, driving the permeation of the outer aqueous phase into the inner aqueous phase, thus preparing open-pore microspheres with an internally and externally penetrating pore structure. The evaporation rate of the oil phase solvent directly affects the micropore size. If the evaporation rate is too slow, the oil phase remains in a low-viscosity state for a long time, and the inner aqueous phase droplets may coalesce. Furthermore, osmotic pressure difference can also induce the diffusion (curing) of water molecules from the outer aqueous phase to the inner aqueous phase of the complex emulsion droplets before solidification. Controlling the curing time can yield porous microspheres with different porosities. The diffusion from the outer aqueous phase to the inner aqueous phase generates expansion force within the microsphere pores, driving the migration of uncured polymers from the pore walls. In this invention, the migration of polymers from the pore walls caused by the expansion of the inner aqueous phase is utilized. Rapid curing of the solvent in the oil phase is achieved through the rapid extraction of solvents in poor solvents such as ethanol, thus enabling controllable curing time. Hollow polylactic acid microspheres with essentially non-porous surfaces (×500 electron microscopy image, average surface pore count not exceeding 10) are prepared in a one-step process and then composited into a gel matrix to prepare an implant for intradermal, subcutaneous injection, or tissue filling.

[0021] The technical solution of this invention has the following advantages: 1. The surface of the microspheres is basically non-porous (×500 electron micrograph, average number of pores on the surface does not exceed 10), and it is not easy to cause an acute inflammatory reaction after injection.

[0022] 2. With the same microsphere volume, hollow microspheres require a smaller injection volume and have a better impact on the human body.

[0023] 3. The selected microspheres have a suitable density and are not prone to settling or floating, thus the prepared injection has better physical stability.

[0024] 4. After the microspheres degrade, the exposed surface area of ​​the structure is larger, which is conducive to cell climbing and collagen production.

[0025] 5. The method provided in this application allows for convenient control of the surface smoothness and density of the prepared microspheres by controlling the ripening time. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 Example 6: Particle size and distribution curves of microspheres prepared; Figure 2 Example 10: SEM image of hollow microspheres prepared; Figure 3 Example 10: SEM image of the cross-section of the prepared hollow microspheres; Figure 4 Example 6: SEM images of hollow microspheres prepared; Figure 5 Example 7: SEM images of hollow microspheres prepared; Figure 6 SEM image of solid microspheres prepared in Comparative Example 1; Figure 7 Sedimentation / suspension properties of different particle densities in water (the microspheres in each test tube in the figure are from left to right: Comparative Example 1, Examples 6, 7, 10, 16, and 17). Figure 8 Settling / suspension properties of different particle densities in water over 10 minutes (the microspheres in each test tube in the figure are from left to right: Examples 11-15); Figure 9 Example 18: Preparation of extrusion force curves after reconstitution of the injection; Figure 10 Comparative Example 2: Extrusion force curve of the reconstituted injection; Figure 11 The filling effect after implantation in Example 18 and Comparative Example 2. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0029] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0030] The test method in the following examples: (1) Microsphere size and particle size distribution Weigh 0.3 g of microspheres and disperse them in 10 mL of an aqueous solution containing 1.0 wt% polyvinyl alcohol. Use a particle size analyzer under ultrasonic conditions to test the particle size and particle size distribution of the microspheres.

[0031] (2) Morphological observation After gold was sprayed onto the surface of PLLA microspheres, conductive adhesive was attached to the test stage, and the morphology, particle size and uniformity of the microspheres were observed by scanning electron microscopy.

[0032] (3) Tap density Weigh an appropriate amount of microspheres and add them to a 10mL graduated cylinder. Tap the mixture until the volume no longer changes. Record the volume of the microspheres and calculate the tapped density.

[0033] (4) True density Weigh 20g of L-polylactic acid raw material, add it to the mold, heat to 180℃, and press under 1MPa pressure for 5 minutes to form a 50×50mm shape. 2 After the polylactic acid (PLA) cube is cooled to room temperature, the weight of the PLA cube, m1, is weighed. The thickness of the cube is measured with a micrometer, and the true density of L-PLA is calculated based on the mass and volume of the cube.

[0034] (5) Calculation method for density and internal porosity of hollow polylactic acid microspheres ① Microsphere internal porosity: φ 内 =1-ρ v / ρ sv ② Particle density of microspheres: ρ p =(1-φ 内 )×ρ t Where, φ 内 ρ is the ratio of the internal pore volume of the microsphere to the total volume of the microsphere. v ρ is the tap density of the hollow microspheres. sv The tap density of solid microspheres (measured by Comparative Example 1, ρ) sv (0.69 g / mL); ρ t The true density of polylactic acid (L-lactic acid) is 1.249 g / cm³. 3 ).

[0035] Note: Solid and hollow microspheres with similar particle size and particle size distribution have similar volume and external porosity. In the absence of precise measurement, this application makes approximate calculations.

[0036] (6) Animal implantation experiments: Sample preparation: Add 5 mL of physiological saline to the vial of the lyophilized sample prepared in Example 18 and Comparative Example 2, reconstitute, and then draw 1 mL into a syringe for later use.

[0037] Implantation Experiment: Healthy rabbits (approximately 2.5 kg) with their backs shaved were used. The reconstituted gels from Example 18 and Comparative Example 2 were injected subcutaneously and intradermally at two sites using a 27G thin-walled needle, with 0.2 mL injected at each site. The rabbits were then housed individually without dietary restrictions. Redness and swelling at the injection sites and the condition of the wheals were observed daily.

[0038] (7) Solution preparation in the examples Oil phase preparation: Weigh 17g of polylactic acid (Mw: 100kDa), dissolve it in 100mL of dichloromethane, and prepare the oil phase solution.

[0039] Preparation of internal aqueous phase solution: Weigh 30g of sodium chloride and dissolve it in 1000mL of water for injection.

[0040] Preparation of external aqueous phase solution: Weigh 10g of polyvinyl alcohol, dissolve it in 1000mL of water for injection at 50℃, filter while hot, and let stand at room temperature for later use.

[0041] Preparation of hollow microspheres in Examples 1-5—Homogeneous emulsification Weigh 30g of the internal aqueous phase and add it to the oil phase. Homogenize at 12500rpm for 2min to obtain a W / O type primary emulsion. Pour the primary emulsion into a 500mL three-necked flask containing the external aqueous phase, fill with the external aqueous phase, and homogenize at 8000rpm for 10min to obtain a W / O / W type double emulsion. Add the double emulsion to 500mL of ethanol and stir at 100rpm for 5min (Example 1), 15min (Example 2), 30min (Example 3), 60min (Example 4), and 120min (Example 5). Then, allow the supernatant to settle and remove it. Wash the microspheres at the bottom with water and dry them to obtain microspheres.

[0042] Example 6-17 Preparation of hollow microspheres—membrane emulsification The preparation of the colostrum was the same as in Examples 1-5. The colostrum was poured into 500 mL of external aqueous phase and emulsified through a 50 μm pore size SPG membrane tube at a membrane pressure of 0.07 MPa, to obtain a W / O / W type double emulsion. The double emulsion was added to 500 mL of ethanol and stirred at 100 rpm for 5 min (Example 6), 15 min (Example 7), 20 min (Example 8), 25 min (Example 9), 30 min (Example 10), 35 min (Example 11), 40 min (Example 12), 45 min (Example 13), 50 min (Example 14), 55 min (Example 15), 60 min (Example 16), and 120 min (Example 17). The supernatant was then removed by sedimentation, and the microspheres at the bottom were washed with water and dried to obtain microspheres.

[0043] Examples 18-23 (Gel Implants) 300 mg of the microspheres prepared in Example 10 were dispersed under mechanical stirring in 10 mL of a 2% sodium carboxymethyl cellulose gel (0.1% aqueous solution with a rotational viscosity of 8000-12000 mPas, Example 18), sodium hyaluronate (molecular weight of 1000 kDa, Example 19), or micro-crosslinked sodium hyaluronate (Example 20, prepared according to Example 1 of CN200810009194.6). The gel was then bottled in vials (5 mL / vial) and freeze-dried under vacuum to prepare a lyophilized implant. Alternatively, the above microsphere composite gel was sterilized by irradiation and aseptically filled into pre-filled syringes (1 mL / syringe) to prepare implants (Examples 21-23).

[0044] Comparative Example 1 (Solid Microspheres) Polylactic acid solid microspheres: The prepared oil phase solution was added to 500 mL of external aqueous phase. The mixture was passed through a 50 µm pore size SPG membrane tube under a membrane pressure of 0.07 MPa for emulsification, and the process was repeated 5 times. The oil phase solvent was then evaporated overnight at 40 °C and 100 rpm stirring rate. Finally, the supernatant was removed by sedimentation, and the microspheres at the bottom were washed with water and dried to obtain solid microspheres.

[0045] Comparative Example 2 (lyophilized implant containing solid microspheres) Weigh 300 mg of the solid microspheres prepared in Comparative Example 1, disperse them in 10 mL of 2% sodium carboxymethyl cellulose under mechanical stirring, bottle them in vials (5 mL / bottle), and freeze-dry them under vacuum to prepare a lyophilized implant.

[0046] Table 1 Formulation methods and ingredients

[0047] Results and Discussion The properties of the microspheres in the examples and comparative examples are shown in Table 2.

[0048] Table 2 Properties of microspheres in Examples and Comparative Examples

[0049] Both homogenization and membrane emulsification can be used to prepare the microspheres of this application.

[0050] Microspheres prepared by membrane emulsification have a smaller span and a more uniform particle size. The particle size distribution of the product in Example 6 is shown below. Figure 1 As shown, the particle size of the microspheres conforms to a normal distribution, D 50 =29.61µm, span is 0.838.

[0051] The maturation time after the formation of the double emulsion has a significant impact on the morphology of the microsphere surface, such as... Figure 2 , 4As shown in Figure -5, the microspheres prepared by aging for 5 min are porous microspheres with a large number of open pores on their surface. Figure 4 The curing time has been extended to 15 minutes. Figure 5 The number of open pores on the surface is reduced, averaging less than 10, and numerous self-healing traces of open pores can be observed on the surface of the microspheres; after aging for 30 minutes (see...), the number of open pores on the surface is reduced, averaging less than 10, and numerous self-healing traces of open pores can be observed on the surface of the microspheres. Figure 2 Only slight self-healing traces were observed in a high-magnification SEM of ×1000, and the average number of open pores of the observed microspheres did not exceed 1.

[0052] After liquid nitrogen embrittlement, the microspheres of Example 10 showed a porous structure with pore sizes less than 10 µm in the fracture surface. Figure 3 ).

[0053] The tap density of microspheres prepared with different curing times was measured, and the particle density of the microspheres was calculated. The experimental results are shown in Table 2. It can be seen that the tap density of the microspheres decreases rapidly with the extension of curing time. This further demonstrates the importance of curing time control in the preparation of porous microspheres. In the traditional solvent evaporation method, the curing time is too long, and the internal and external aqueous phases are in a long-term permeation process driven by osmotic pressure difference, which leads to the gradual increase of the volume of the aqueous phase inside the microsphere, the enlargement of the internal pores, and the collapse of the porous structure. In this invention, the polymer migration properties of the pore walls caused by the osmotic pressure expansion of the internal aqueous phase are utilized. Rapid curing of the solvent in the oil phase is achieved by rapidly extracting it with undesirable solvents such as ethanol, thus realizing the controllability of the curing time. Polylactic acid microspheres with essentially non-porous surfaces, porous interiors, and adjustable density are prepared in one step.

[0054] Polylactic acid microspheres with different particle densities exhibit different sedimentation / suspension properties in water, such as Figure 7 As shown (the microspheres in each test tube in the figure are from left to right: Comparative Example 1, Examples 6, 7, 10, 16, and 17), the solid microspheres of Comparative Example 1 and the porous microspheres of Example 6 sank rapidly in water; the results for the microspheres in Examples 16 and 17 were exactly the opposite, with a small portion of the microspheres sinking and the majority floating, and the more microspheres floated as the particle density decreased. The reason for the microspheres floating instead of sinking is that the curing time during the microsphere preparation process was too long, resulting in too many or too large air cells inside the microspheres, or the formation of a completely hollow spherical structure. The essentially non-porous structure on the surface makes it difficult for external water to enter the interior of the microspheres. In addition, the low density of the microspheres means that only a small portion floats on the water surface and is in contact with the water, which further hinders water penetration into the interior of the microspheres. Therefore, in order for the microspheres to remain suspended in the formulation for a long time, the density of the microspheres should be strictly controlled.

[0055] To further investigate the relationship between curing time, microsphere density, and suspension performance, supplementary tests were conducted in Examples 11-15, see [link to relevant documentation]. Figure 8The microspheres in Examples 14 and 15 floated, exhibiting poor suspension stability. Therefore, the preferred microspheres should have a tap density of 0.265-0.308 g / cm³ after drying. 3 .

[0056] The sedimentation stability of the lyophilized hollow microsphere formulation of Example 18 and the lyophilized solid microsphere formulation of Comparative Example 2 after reconstitution was further tested. Slight sedimentation and transparency began to appear in the upper layer of the gel containing solid microspheres after 46 min; after extending the time to 1.5 h, microsphere sedimentation was clearly observed; after extending the time further to 6 h, approximately 1 / 3 of the sample had settled; while the gel containing hollow microspheres maintained a homogeneous state even after 6 h. This characteristic of stable suspension over a long period is more beneficial for clinical use.

[0057] Gels containing both solid and hollow microspheres exhibit good needle-passing properties. For example... Figure 9 As shown, the sample in Example 18 did not experience needle blockage during injection due to the increased number of microspheres, and compared to the sample in Comparative Example 2 (e.g. Figure 10 (As shown) it exhibits a more uniform pushing force.

[0058] After reconstitution of lyophilized samples of hollow and solid microspheres, the samples were implanted subcutaneously into rabbits. Two injection sites were made, one intradermal and one subcutaneous, with 0.2 mL of gel sample injected at each site. Figure 11 As shown, the injection sites are: top left (2 sites), subcutaneous injection for Example 18 sample; top right (2 sites), intradermal injection for Example 18 sample; bottom left (2 sites), subcutaneous injection for Comparative Example 2 sample; bottom right (2 sites), intradermal injection for Comparative Example 2 sample. Compared to immediately after injection, the wheals in both groups gradually decreased in size, but the wheals from hollow microspheres were clearer and more prominent than those from solid microspheres. By day 15, the wheals from solid microspheres were no longer visible, while the wheals from hollow microspheres remained clearly visible. This indicates that the injectable formulation containing hollow microspheres exhibits better long-lasting filling ability.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An injectable formulation of polylactic acid microspheres, characterized in that, The injectable formulation comprises polylactic acid microspheres and a matrix. The polylactic acid microspheres have a hollow structure, and in a 500x electron microscope image, the average number of surface pores does not exceed 10, and the tap density after drying does not exceed 0.40 g / cm³. 3 The matrix is ​​a medically acceptable injectable aqueous solution or hydrogel.

2. The injectable preparation according to claim 1, characterized in that, The injection contains 1-300 mg / mL of polylactic acid microspheres. In a 500x electron microscope image, the average number of pores on the surface of the polylactic acid microspheres does not exceed 6, and the particle size D... 50 It is 10-100μm.

3. The injectable preparation according to claim 2, characterized in that, The injection contains 1-200 mg / mL of polylactic acid microspheres. In a 500x electron microscope image, the average number of pores on the surface of the polylactic acid microspheres does not exceed 2, and the particle size D... 50 The micrometer size is 20-50 μm, and the tap density after drying is 0.26-0.34 g / cm³. 3 .

4. The injectable preparation according to claim 1, characterized in that, The injection contains 1-100 mg / mL of polylactic acid microspheres. The polylactic acid microspheres, in a 500x electron microscope image, have an average surface pore count of no more than one, and a tap density of 0.265-0.308 g / cm³ after drying. 3 The polylactic acid microspheres are composed of L-polylactic acid, D-polylactic acid, racemic polylactic acid, or a mixture thereof.

5. The injectable preparation according to claim 1, characterized in that, The polylactic acid microsphere content in the injection is 5-50 mg / mL, and the matrix of the hydrogel is selected from one or more of carboxymethyl cellulose or its salt, hyaluronic acid or its salt, cross-linked hyaluronic acid or its salt, hydroxypropyl methylcellulose, hydroxyethyl cellulose, and agarose.

6. A method for preparing hollow polylactic acid microspheres, comprising the following steps: (1) Add the inner aqueous phase containing pore-forming agent to the oil phase containing polylactic acid, and emulsify to obtain a primary emulsion containing tiny water droplets; (2) Add the primary emulsion to the outer aqueous phase containing emulsifier, and emulsify to obtain an emulsion; (3) Mix the emulsion with a C1-C4 alcohol solvent, and mature to close the surface pores; (4) After curing, solid-liquid separation, washing, and drying, polylactic acid microspheres are obtained.

7. The method according to claim 6, characterized in that, In step (1), the volume ratio of the aqueous phase to the oil phase is 1:4-10, and the concentration of polylactic acid in the oil phase is ≤30%; the emulsification method is homogenization emulsification or membrane emulsification.

8. The method according to claim 6, characterized in that, The inner aqueous phase and oil phase in step (1) do not contain emulsifiers, and the osmotic pressure of the inner aqueous phase is higher than that of the outer aqueous phase in step (2).

9. The method according to claim 6, characterized in that, The maturation time in step (3) shall be no less than 15 minutes.

10. The method according to claim 9, characterized in that, The maturation time in step (3) is 30-45 minutes.

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