Polylactic acid microspheres, injectable agent and method for preparing the same

Abstract

The present disclosure provides a method for preparing polylactic acid microspheres, comprising the following steps. A first solution is provided, the first solution comprising polylactic acid and an organic solvent. A second solution is provided, the second solution comprising polyvinyl alcohol, sodium carboxymethyl cellulose and an aqueous solution. The first solution is added to the second solution while stirring the second solution until the polylactic acid solidifies to form a plurality of polylactic acid microspheres. The polylactic acid microspheres are collected. The present disclosure also provides polylactic acid microspheres. The polylactic acid microspheres are aggregated from polylactic acid. The surface of the polylactic acid microspheres is smooth, and the particle size is between 30 microns and 100 microns. By using a specific ratio of polyvinyl alcohol and sodium carboxymethyl cellulose, polylactic acid microspheres with a concentrated particle size distribution and a smooth surface can be prepared with a yield of 90%. Furthermore, the prepared injection has a shorter rehydration time, better anti-aggregation and needle passability.

Description

[0001] This disclosure is a divisional application, with its parent application having application number 202110023527.6, application date of January 8, 2021, and invention title "Polylactic acid microspheres, injections and preparation methods thereof". Technical Field

[0002] This disclosure relates to polylactic acid microspheres and methods for their preparation, and particularly to methods for preparing polylactic acid microspheres with high yield and better injectable performance. Background Technology

[0003] Currently, the main methods for preparing microspheres from biological macromolecules include: emulsion solvent evaporation method, emulsion solidification method, or desolvation method, etc.

[0004] The emulsion solvent evaporation method involves mixing an aqueous solution containing biomacromolecules with an organic solvent, preparing an emulsion through ultrasonication or vibration, and then removing the organic solvent through rotary evaporation to obtain microspheres. However, this method has low microsphere yields, carries the risk of organic solvent residue, and exhibits poor encapsulation rates for water-soluble drugs and substances.

[0005] Currently, emulsification-curing methods are commonly used, allowing for the preparation of microspheres with varying particle sizes and distributions depending on the emulsification conditions. This method involves adding an aqueous solution containing biomolecules to an organic solvent such as vegetable oil or isooctane containing an appropriate amount of emulsifier. A water-in-oil emulsion is then prepared through stirring, ultrasound, or membrane emulsification. The droplets are then solidified using heating or a crosslinking agent (such as formaldehyde or glutaraldehyde), followed by separation to obtain solid microspheres. However, emulsification-curing methods often result in microspheres with wide particle size distributions and uneven sizes.

[0006] Clinically, injectable formulations containing microspheres are typically freeze-dried into powder form and then reconstituted before use. Administering them to patients without complete reconstitution poses safety risks. When microspheres have a wide particle size distribution and are non-uniform in size, the reconstitution time becomes difficult to assess, and there is a high risk of uneven reconstitution. Furthermore, current manufacturing processes using biomacromolecules for injection often struggle to simultaneously achieve high microsphere yields while maintaining injectable performance characteristics (such as needle penetration).

[0007] Therefore, it is necessary to improve the existing microspheres and their preparation methods to achieve high microsphere yields while simultaneously enhancing the performance of microspheres as injection agents, such as rehydration, needle penetration, and anti-agglomeration properties. Summary of the Invention

[0008] The present invention provides a polylactic acid microsphere, which is formed by the aggregation of polylactic acid. The polylactic acid microsphere has a smooth surface and a particle size between 30 micrometers and 100 micrometers.

[0009] The present invention also provides a method for preparing polylactic acid microspheres, comprising the following steps: providing a first solution comprising polylactic acid (PLA) and an organic solvent; providing a second solution comprising polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (SCMC), and an aqueous solution; adding the first solution to the second solution while stirring the second solution until the polylactic acid solidifies to form a plurality of polylactic acid microspheres; and collecting the polylactic acid microspheres.

[0010] In some embodiments, the weight percentage of the first solution is 100%, and the weight percentage of polylactic acid in the first solution is between 2.5% and 10%.

[0011] In some embodiments, the weight-volume concentration (w / v) of the first solution is 100%, and the weight-volume concentration of polylactic acid in the first solution is between 2.5% and 10%.

[0012] In some embodiments, polylactic acid includes L-polylactic acid, D-polylactic acid, DL-polylactic acid, or combinations thereof.

[0013] In some embodiments of the present invention, the organic solvent comprises dichloromethane, trichloromethane, ethyl acetate, or combinations thereof.

[0014] In some embodiments, the second solution is expressed as 100% by weight, and the weight percentage of polyvinyl alcohol in the second solution is between 0.5% and 2%, while the weight percentage of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%.

[0015] In some embodiments, the weight-volume concentration (w / v) of the second solution is 100%, the weight-volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight-volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%.

[0016] In some embodiments, the step of adding the first solution to the second solution while stirring the second solution involves a volume ratio between the second solution and the first solution that is between 5:1 and 100:1.

[0017] In some embodiments, the step of adding the first solution to the second solution while stirring the second solution is performed at a rate of 5% to 35% of the first solution per minute, with the volume of the first solution being 100%.

[0018] In some embodiments, the step of adding the first solution to the second solution while stirring the second solution is to stir the second solution at a speed between 300 rpm and 1500 rpm.

[0019] In some embodiments, the step of collecting polylactic acid microspheres includes centrifugation or sieving.

[0020] In some embodiments, the step of collecting the polylactic acid microspheres further includes obtaining the polylactic acid microspheres by freeze drying after centrifugation or sieving.

[0021] The present invention also provides polylactic acid microspheres, which are prepared by the following steps: providing a first solution comprising polylactic acid and an organic solvent; providing a second solution comprising polyvinyl alcohol, sodium carboxymethyl cellulose and an aqueous solution; adding the first solution to the second solution while stirring the second solution to form polylactic acid microspheres; and collecting the polylactic acid microspheres.

[0022] In some embodiments, the weight percentage of the first solution is 100%, and the weight percentage of polylactic acid in the first solution is between 2.5% and 10%.

[0023] In some embodiments, the second solution comprises, by weight percentage, 0.5% to 2% polyvinyl alcohol and 0.1% to 2% sodium carboxymethyl cellulose.

[0024] In some embodiments, the weight-volume concentration (w / v) of the first solution is 100%, and the weight-volume concentration of polylactic acid in the first solution is between 2.5% and 10%.

[0025] In some embodiments, the weight-volume concentration (w / v) of the second solution is 100%, and the weight-volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight-volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%.

[0026] In some embodiments, a first solution is added to the second solution while the second solution is stirred, and the volume ratio between the second solution and the first solution is between 5:1 and 100:1.

[0027] In some embodiments, the polylactic acid microspheres are spherical with a smooth surface and a particle size between 30 micrometers and 100 micrometers.

[0028] The present invention further provides an injectable preparation, which is prepared by the following steps: providing a plurality of polylactic acid microspheres; providing a suspension; mixing the polylactic acid microspheres and the suspension to obtain a microsphere suspension; and freeze-drying the microsphere suspension to obtain an injectable preparation.

[0029] In some embodiments, providing polylactic acid microspheres includes the following steps: providing a first solution comprising polylactic acid and an organic solvent; providing a second solution comprising polyvinyl alcohol, sodium carboxymethyl cellulose, and an aqueous solution; adding the first solution to the second solution while stirring the second solution until the polylactic acid solidifies to form polylactic acid microspheres; and collecting the polylactic acid microspheres.

[0030] In some embodiments, the suspension system comprises surfactants, polymeric silicides, sugar alcohols, and dispersants.

[0031] In some embodiments, the surfactant comprises polysorbate 80 (TWEEN 80), the polymeric silicide comprises polydimethylsiloxane, the sugar alcohol comprises mannitol, and the dispersant comprises sodium carboxymethyl cellulose.

[0032] In some implementations, the injection solution is formed 2 to 10 minutes after rehydration.

[0033] In some implementations, the injection solution can pass through a 26G needle at a rate of 0.5 to 2 ml per minute.

[0034] As described above, the preparation method disclosed in this invention uses a specific ratio of polyvinyl alcohol and sodium carboxymethyl cellulose to produce polylactic acid microspheres with a concentrated particle size distribution and smooth surface. Furthermore, the polylactic acid microspheres obtained using this method achieve a yield of up to 90%. Compared to commercially available products, the injectable formulation of this disclosure not only has a shorter rehydration time but also exhibits better anti-agglomeration and needle penetration properties, thus improving its clinical applicability. Attached Figure Description

[0035] To make the above and other objects, features, advantages and embodiments of the present invention more apparent and understandable, the accompanying drawings are described below: Figure 1 A flowchart illustrating the preparation of polylactic acid microspheres is provided as an example of one embodiment of this disclosure.

[0036] Figures 2A to 2D An electron microscope image of polylactic acid microspheres is shown as an embodiment of the present disclosure.

[0037] The reference numerals in the attached figures are explained as follows: S1…Step S2…step S3…Steps S4…step Detailed Implementation

[0038] To make the description of this invention more detailed and complete, the embodiments and specific examples of this invention are described in detail below; however, this is not the only form of implementing or applying the specific examples of this invention. The various embodiments disclosed below can be combined or substituted with each other where advantageously possible, and other embodiments can be added to one embodiment without further description or explanation. In the following description, many specific details will be set forth in detail to enable the reader to fully understand the following embodiments. However, embodiments of the invention can be practiced without such specific details.

[0039] In this document, unless otherwise specified in the text, “a” and “the” may refer to one or more. It will be further understood that the terms “comprising,” “including,” “having,” and similar terms as used herein specify the features, regions, integers, steps, operations, elements, and / or components described herein, but do not exclude other features, regions, integers, steps, operations, elements, components, and / or groups thereof.

[0040] Although the methods disclosed herein are described below using a series of operations or steps, the order in which these operations or steps are shown should not be construed as a limitation of the invention. For example, some operations or steps may be performed in a different order and / or simultaneously with other steps. Furthermore, not all operations, steps, and / or features must be performed to achieve embodiments of the invention. Moreover, each operation or step described herein may comprise several sub-steps or actions.

[0041] Please see Figure 1 This disclosure provides a method for preparing polylactic acid microspheres, comprising the following steps: step S1, providing a first solution containing polylactic acid and an organic solvent; step S2, providing a second solution containing polyvinyl alcohol, sodium carboxymethyl cellulose, and an aqueous solution; step S3, adding the first solution to the second solution while stirring the second solution until the polylactic acid solidifies to form a plurality of polylactic acid microspheres; and step S4, collecting the polylactic acid microspheres.

[0042] In some embodiments, polylactic acid comprises L-polylactic acid, D-polylactic acid, DL-polylactic acid, or combinations thereof. In some embodiments, the organic solvent comprises dichloromethane, chloroform, ethyl acetate, or combinations thereof.

[0043] In some embodiments, if the weight percentage of the first solution is 100%, the weight percentage of polylactic acid in the first solution is between 2.5% and 10%, for example 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between the aforementioned adjacent values.

[0044] In some embodiments, the weight-volume concentration (w / v) of the first solution is 100%, and the weight-volume concentration (w / v) of polylactic acid in the first solution is between 2.5% and 10%, for example, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between the aforementioned adjacent values.

[0045] It is important to note that while a higher weight percentage or weight-volume concentration of polylactic acid (PLA) in the first solution generally increases the yield of PLA microspheres, it also increases the risk of PLA microsphere aggregation. Therefore, the weight percentage or weight-volume concentration of PLA in the first solution must be controlled within an appropriate range during the preparation process.

[0046] In some embodiments, if the weight percentage of the second solution is taken as 100%, the weight percentage of polyvinyl alcohol in the second solution is between 0.5% and 2%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value between the aforementioned adjacent values. The weight percentage of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value between the aforementioned adjacent values.

[0047] In some embodiments, the weight-volume concentration (w / v) of the second solution is 100%, and the weight-volume concentration (w / v) of polyvinyl alcohol in the second solution is between 0.5% and 2%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value between the aforementioned adjacent values. The weight-volume concentration (w / v) of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value between the aforementioned adjacent values.

[0048] It is worth mentioning that polyvinyl alcohol and sodium carboxymethyl cellulose must be present in the second solution to achieve the smooth surface of polylactic acid microspheres. The smoother the surface, the less likely it is to aggregate. In addition, the yield of polylactic acid microspheres can be increased, for example, to 90%.

[0049] In some embodiments, the first solution is added to the second solution while the second solution is stirred, and the volume ratio of the second solution to the first solution is between 5:1 and 100:1. In other embodiments, the volume ratio of the second solution to the first solution is between 5:1 and 50:1, for example, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, or any value between the aforementioned adjacent values. It should be noted that when the weight percentage or weight-volume concentration of polylactic acid, polyvinyl alcohol, and sodium carboxymethyl cellulose is fixed at a specific value, the risk of aggregation of polylactic acid microspheres increases as the volume ratio of the second solution to the first solution decreases. Therefore, it is important to control the volume ratio of the second solution to the first solution within an appropriate range during the preparation process.

[0050] In some embodiments, the step of adding the first solution to the second solution while simultaneously stirring the second solution can be flexibly combined with different equipment and parameter settings depending on the target yield, particle size, and particle size distribution of the polylactic acid microspheres. For example, a peristaltic pump (such as Thermo Fisher Scientific Dry-Bags) can be used. TMThe first solution is added to the second solution at a speed of 25 to 50 rpm, and the second solution is stirred with a stirrer (e.g., IKA EURO-ST 60 C S001, Germany) at a speed between 300 rpm and 1500 rpm (e.g., 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, or any value between the aforementioned adjacent values). The main purpose of setting the above parameters is to control the addition of the first solution to the second solution at an appropriate and consistent rate, and to control the stirring speed of the second solution, so as to obtain polylactic acid microspheres with the target particle size and concentrated particle size distribution, and to improve the yield of polylactic acid microspheres. If the first solution is added to the second solution too quickly, the risk of polylactic acid microsphere aggregation will increase, thereby affecting the particle size of polylactic acid microspheres and reducing the yield. The faster the stirring speed of the second solution, the greater the shear force, and the smaller the particle size of the polylactic acid microspheres will be. Specifically, the peristaltic pump mentioned above adds the first solution to the second solution at a speed of 25 rpm to 50 rpm, mainly to control the amount added per unit time. The volume of the first solution is 100%, and it can be added to the second solution at a rate of 5% to 35% per minute, preferably 5% to 15% per minute, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% per minute.

[0051] In some embodiments, the step of collecting polylactic acid (PLA) microspheres includes centrifugation or sieving. Centrifugation involves centrifuging the second solution from which PLA microspheres are generated at an appropriate speed (e.g., 2460 x g), followed by removal of the supernatant to obtain the PLA microspheres. Sieving involves passing the second solution from which PLA microspheres are generated through a sieve of appropriate pore size to separate the PLA microspheres. In one embodiment, the step of collecting PLA microspheres further includes obtaining the PLA microspheres by freeze-drying after centrifugation or sieving. Freeze-drying removes excess moisture and residual organic solvents, increasing storage stability.

[0052] Increasing the content of polyvinyl alcohol and sodium carboxymethyl cellulose increases the viscosity of the second solution, thus reducing the collection rate of polylactic acid microspheres. In some embodiments, an electrolyte (e.g., sodium chloride) may be added to the second solution to reduce its viscosity and improve the collection rate of polylactic acid microspheres.

[0053] It should be emphasized that the polylactic acid microspheres obtained by the aforementioned preparation method are spherical, and their surface is smooth under an electron microscope at 450x to 1500x magnification at 5kV. In some embodiments, the D50 (particle size corresponding to 50% cumulative particle size percentage) of the polylactic acid microspheres is between 30 and 55 micrometers, while the D90 (particle size corresponding to 90% cumulative particle size percentage) is between 60 and 100 micrometers.

[0054] This disclosure also provides a polylactic acid microsphere prepared by the aforementioned steps, which is composed of polylactic acid aggregates. When observed under an electron microscope at 450x to 1500x magnification at 5kV, these polylactic acid microspheres have a smooth surface, and when cut, the internal structure is a solid and smooth cross-section. The particle size is between 30 micrometers and 100 micrometers, preferably between 30 micrometers and 80 micrometers, and more preferably between 35 micrometers and 80 micrometers.

[0055] This disclosure also provides an injectable preparation prepared by the following steps: providing a plurality of polylactic acid microspheres; providing a suspension; mixing the polylactic acid microspheres and the suspension to obtain a microsphere suspension; and freeze-drying the microsphere suspension to obtain an injectable preparation.

[0056] In some embodiments, polylactic acid (PLA) microspheres are prepared through the aforementioned steps S1 to S4, namely: Step S1, providing a first solution containing PLA and an organic solvent; Step S2, providing a second solution containing polyvinyl alcohol, sodium carboxymethyl cellulose, and an aqueous solution; Step S3, adding the first solution to the second solution while stirring the second solution until the PLA solidifies to form multiple PLA microspheres; and Step S4, collecting the PLA microspheres. Compared to existing PLA microspheres, the PLA microspheres prepared through the aforementioned steps S1 to S4 exhibit reduced rehydration time and better needle penetration when prepared as an injection. It is important to emphasize that the second solution must contain both polyvinyl alcohol and sodium carboxymethyl cellulose to achieve these effects.

[0057] In some embodiments, the suspension system comprises a surfactant, a polymeric silicide, a sugar alcohol, and a dispersant. In some embodiments, the surfactant comprises sodium dodecyl sulfate (SDS), a polysorbate (Tween) series (e.g., TWEEN 80), a Triton series, a nonylphenol (NP) series, or a combination thereof. In some embodiments, the polymeric silicide comprises polydimethylsiloxane. In some embodiments, the sugar alcohol comprises mannitol. In some embodiments, the dispersant comprises sodium carboxymethyl cellulose. In some embodiments, the suspension may comprise mannitol, sodium carboxymethyl cellulose, polysorbate 80, and polydimethylsiloxane. In one embodiment, the weight ratio between sodium carboxymethyl cellulose and polylactic acid microspheres may be between 1:4 and 1:10, the weight ratio between mannitol and polylactic acid microspheres may be between 1:3 and 1:10, the weight ratio between polysorbate 80 and polylactic acid microspheres may be between 1:60 and 1:140, and the weight ratio between polydimethylsiloxane and polylactic acid microspheres may be between 1:80 and 1:180. In some embodiments, when the weight ratio of sodium carboxymethyl cellulose to polylactic acid microspheres is between 1:5.5 and 1:10, the weight ratio of mannitol to polylactic acid microspheres is between 1:4 and 1:6.5, the weight ratio of polysorbate 80 to polylactic acid microspheres is between 1:85 and 1:130, and the weight ratio of polydimethylsiloxane to polylactic acid microspheres is between 1:110 and 1:175, an injectable formulation with a rehydration time of less than 8 minutes and excellent needle penetration can be obtained.

[0058] In some embodiments, the injection is rehydrated for 2 to 10 minutes to form an injection solution that can be passed through a 26G needle (with an inner diameter of about 0.26 mm and an outer diameter of about 0.46 mm) at a rate of 0.5 to 2 ml per minute.

[0059] To further verify the improved properties of the polylactic acid microspheres generated by the various embodiments of this disclosure, the following experiments were conducted. It should be noted that the following examples are provided for illustrative purposes only and are not intended to limit the invention.

[0060] Example 1: Preparation method of polylactic acid microspheres

[0061] Please see Table 1 below for the specific preparation conditions of polylactic acid microspheres.

[0062] First, the dispersed phase (first solution) and the continuous phase (second solution) are prepared. The dispersed phase is obtained by adding polylactic acid (PLA) to dichloromethane (DCM), and the continuous phase is obtained by mixing polyvinyl alcohol (PVA) and sodium carboxymethyl cellulose (SCMC) with water.

[0063] Next, the dispersed phase was pumped using a peristaltic pump (Thermo Fisher Scientific Dry-Bags). TM The Simple Peristaltic Pump Starter Pack (USA) was added to the continuous phase and mixed using a stirrer (IKA EURO-ST 60 CS001, Germany) at a speed of revolutions per minute (rpm). Although four different stirring conditions were used in this embodiment, divided into groups A and D (as shown in Table 1 below) for the preparation of polylactic acid microspheres, those skilled in the art can flexibly adjust the parameters according to the properties of different equipment.

[0064] During the stirring process, dichloromethane, being an organic solvent, evaporates, causing polylactic acid (PLA) to solidify into PLA microspheres. Finally, the mixture is centrifuged at 2460 x g for ten minutes, and the PLA microspheres are collected. The PLA microspheres are then freeze-dried to remove excess moisture and residual organic solvents and for easy storage.

[0065] Table 1. Preparation conditions of polylactic acid microspheres

[0066] Example 2: Preparation method of injection

[0067] Next, the polylactic acid microspheres obtained under four different preparation conditions (AD) in Example 1 were prepared into injections according to formulation a in Table 2 below. Furthermore, to simultaneously test the differences between the different injection formulations, polylactic acid microspheres from group C in Table 1 were selected and then prepared into injections according to formulations b and c in Table 2 below, respectively. The specific preparation process is described below.

[0068] First, 300 mL of an aqueous solution containing polysorbate 80 (TWEEN 80), dimethicone, D-mannitol, and sodium carboxymethyl cellulose (SCMC) was added to the freeze-dried polylactic acid microspheres and mixed thoroughly to form a microsphere suspension. Next, the microsphere suspension was freeze-dried to obtain the injection. Freeze-drying removes moisture, allowing for rehydration before use, thus increasing storage stability.

[0069] Table 2. Injection Formulation Table

[0070] Example 3: Characteristics of Polylactic Acid Microspheres and Injection

[0071] To further understand the characteristics of the polylactic acid microspheres and injections obtained by the preparation methods of Examples 1 and 2, the appearance of the polylactic acid microspheres was first observed using an electron microscope at a voltage of 5 kV and a field of view of 450 to 1500x. The results are consistent with... Figures 2A to 2D Similarly, at magnifications of 470x, 900x, 950x, and 1300x, the surface of polylactic acid microspheres appears smooth, and when the microspheres are cut open, the internal structure is a solid, smooth cross-section.

[0072] Next, the yield and particle size of the polylactic acid microspheres prepared in the AD group of Example 1 were calculated, and the differences in rehydration time, anti-agglomeration properties after rehydration, and needle penetration properties of the injection prepared in Example 2 compared with those of commercially available products 1 and 2 are shown in Table 3 below: Table 3. Comparison of injectable drugs with commercially available products 1 and 2

[0073] In this table, "-" indicates not tested, "x" in the injection rate field indicates failure, "+" indicates poor needle insertion, and "++" indicates smooth needle insertion.

[0074] The yield of polylactic acid (PLA) microspheres was calculated as a percentage of the weight of the PLA microspheres after freeze-drying, with the amount of PLA added during preparation (i.e., the weight of PLA added to the dispersed phase in Example 1) as 100%. The results are shown in Table 3 (Yield of PLA Microspheres).

[0075] The particle size analysis of polylactic acid microspheres was performed using a laser particle size analyzer (Beckman Coulter LS 200, USA) at room temperature. The results are shown in Table 3 (particle size).

[0076] The rehydration time was calculated by adding 5 ml of distilled water (ddH2O) to each of the injections prepared in Example 2 and commercially available products 1 and 2, and then calculating the time required for complete rehydration. The results are shown in Table 3 (Rehydration Time).

[0077] The anti-coagulation test method is as follows. First, the injection prepared from group AD of Example 1, commercially available product 1, and commercially available product 2 were rehydrated with 5 ml of redistilled water to prepare injection solutions. After centrifugation at 48 x g for 30 seconds using an electric centrifuge, 1 ml of the injection solution at the same site was taken and freeze-dried. Next, the polylactic acid content in the injection solutions of commercially available products 1 and 2 was used as the denominator to calculate the ratio of polylactic acid in the injection solution prepared from group AD of Example 1 to that in the injection solutions of commercially available products 1 and 2. The larger the ratio, the better the anti-coagulation property of the injection.

[0078] In this document, "needle permeability" refers to the ability of the injectable solution to pass through the syringe and needle without sticking to the syringe wall or clogging the needle. The test method is as follows: 5 ml of redistilled water was added to each of the freeze-dried injectable solution of this disclosure, commercially available product 1, and commercially available product 2. Then, 1 ml of each solution was taken and injected through a 26G needle to test the needle permeability at different flow rates.

[0079] The results show that the preparation method in Example 1 can achieve a polylactic acid (PLA) microsphere yield of over 90%, with the obtained PLA microspheres having a D50 between 30 and 55 micrometers and a D90 between 60 and 100 micrometers. Furthermore, the injectable obtained in Example 2 has a shorter rehydration time compared to commercially available products 1 and 2, i.e., a faster rehydration speed, and the anti-agglomeration properties of the injectable obtained in Example 2 are superior to those of commercially available products 1 and 2. After rehydration to an injectable solution, the injectable obtained in Example 2 exhibits comparable needle penetration at an injection rate of 0.5 ml / min to commercially available products 1 and 2; however, at faster injection rates (1 ml / min and 2 ml / min), it demonstrates better needle penetration compared to commercially available products 1 and 2.

[0080] This disclosure describes the preparation of polylactic acid (PLA) microspheres with a concentrated particle size distribution and smooth surface by using a specific ratio of polyvinyl alcohol and sodium carboxymethyl cellulose in a continuous phase. Furthermore, the yield of PLA microspheres obtained using this method can reach 90%. Compared to commercially available products, the injectable formulation of this disclosure not only has a shorter rehydration time but also exhibits better anti-agglomeration and needle penetration properties, thus improving its clinical applicability.

[0081] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing polylactic acid microspheres, characterized in that, Includes the following steps: A first solution is provided, the first solution comprising polylactic acid and an organic solvent; A second solution is provided, which is composed of polyvinyl alcohol, sodium carboxymethyl cellulose and an aqueous solution, wherein the weight-volume concentration of the second solution is 100%, the weight-volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight-volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%. The first solution is added to the second solution while the second solution is stirred until the polylactic acid solidifies to form multiple polylactic acid microspheres; as well as Collect the plurality of polylactic acid microspheres.

2. The method of claim 1, wherein the weight percentage of the first solution is 100%, and the weight percentage of polylactic acid in the first solution is between 2.5% and 10%.

3. The method according to claim 1, wherein the weight-volume concentration of the first solution is 100%, and the weight-volume concentration of polylactic acid in the first solution is between 2.5% and 10%.

4. The method according to claim 1, wherein the organic solvent comprises dichloromethane, trichloromethane, ethyl acetate, or a combination thereof.

5. The method according to claim 1, wherein the step of adding the first solution to the second solution while stirring the second solution, wherein the volume ratio between the second solution and the first solution is between 5:1 and 100:

1.

6. The method according to claim 1, wherein the step of adding the first solution to the second solution while stirring the second solution is wherein the first solution is added to the second solution at a rate of 5% to 35% of the first solution per minute, with the volume of the first solution being 100%.

7. The method according to claim 1, wherein the step of adding the first solution to the second solution while stirring the second solution is to stir the second solution at a speed between 300 rpm and 1500 rpm.

8. The method of claim 1, wherein the step of collecting the plurality of polylactic acid microspheres comprises centrifugation or sieving.

9. The method of claim 8, wherein the step of collecting the plurality of polylactic acid microspheres further comprises obtaining the plurality of polylactic acid microspheres by freeze drying after centrifugation or sieving.

10. A polylactic acid microsphere, characterized in that, It is prepared by the following steps: A first solution is provided, the first solution comprising polylactic acid and an organic solvent; A second solution is provided, which is composed of polyvinyl alcohol, sodium carboxymethyl cellulose and an aqueous solution, wherein the weight-volume concentration of the second solution is 100%, the weight-volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight-volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%. The first solution is added to the second solution while the second solution is stirred until multiple polylactic acid microspheres are formed; as well as Collect the plurality of polylactic acid microspheres.

11. The polylactic acid microspheres according to claim 10, wherein the weight percentage of the first solution is 100%, and the weight percentage of the plurality of polylactic acids in the first solution is between 2.5% and 10%.

12. The polylactic acid microspheres according to claim 10, wherein the weight-volume concentration of the first solution is 100%, and the weight-volume concentration of the plurality of polylactic acids in the first solution is between 2.5% and 10%.

13. The polylactic acid microspheres according to claim 10, wherein the first solution is added to the second solution while the second solution is stirred, and the volume ratio between the second solution and the first solution is between 5:1 and 100:

1.

14. The polylactic acid microspheres according to claim 10, wherein the polylactic acid microspheres are spherical and have a smooth surface, and the particle size is between 30 micrometers and 100 micrometers.

15. An injectable preparation, characterized in that, The injection is prepared through the following steps: Providing multiple polylactic acid microspheres includes the following steps: A first solution is provided, the first solution comprising polylactic acid and an organic solvent; A second solution is provided, which is composed of polyvinyl alcohol, sodium carboxymethyl cellulose and an aqueous solution, wherein the weight volume concentration of the second solution is 100%, the weight volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%. The first solution is added to the second solution while the second solution is stirred until the polylactic acid solidifies to form multiple polylactic acid microspheres; as well as Collect the plurality of polylactic acid microspheres; Provide a suspension; The plurality of polylactic acid microspheres and the suspension are mixed to obtain a microsphere suspension; as well as The microsphere suspension was freeze-dried to obtain the injection.

16. The injectable formulation according to claim 15, wherein the suspension comprises a surfactant, a polymeric silicide, a sugar alcohol, and a dispersant.

17. The injectable formulation of claim 16, wherein the surfactant comprises polysorbate 80, the polymeric silicide comprises polydimethylsiloxane, the sugar alcohol comprises mannitol, and the dispersant comprises sodium carboxymethyl cellulose.

18. The injectable formulation according to claim 17, wherein the weight ratio of sodium carboxymethyl cellulose to the plurality of polylactic acid microspheres is between 1:4 and 1:10, the weight ratio of mannitol to the plurality of polylactic acid microspheres is between 1:3 and 1:10, the weight ratio of polysorbate 80 to the plurality of polylactic acid microspheres is between 1:60 and 1:140, and the weight ratio of polydimethylsiloxane to the plurality of polylactic acid microspheres is between 1:80 and 1:

180.

19. The injectable formulation according to claim 15, wherein an injectable solution is formed after rehydration for 2 to 10 minutes.

20. The injectable solution according to claim 19, wherein the injectable solution is capable of passing through a 26G needle at a rate of 0.5 to 2 ml per minute.

21. A method for preparing polylactic acid microspheres, characterized in that, Includes the following steps: A first solution is provided, the first solution comprising polylactic acid and an organic solvent; A second solution is provided, comprising polyvinyl alcohol, sodium carboxymethyl cellulose, an electrolyte, and an aqueous solution, wherein the weight-volume concentration of the second solution is 100%, the weight-volume concentration of polyvinyl alcohol in the second solution is between 0.5% and 2%, and the weight-volume concentration of sodium carboxymethyl cellulose in the second solution is between 0.1% and 2%. The first solution is added to the second solution while the second solution is stirred until the polylactic acid solidifies to form multiple polylactic acid microspheres; as well as Collect the plurality of polylactic acid microspheres.

22. The method of claim 21, wherein the electrolyte is sodium chloride.

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