Polylactic acid microspheres and preparation method and application thereof

Abstract

The present invention belongs to the technical field of biomedical materials, and specifically relates to a polylactic acid microsphere and a preparation method and application thereof. The method comprises the following steps: (1) grafting a hydrophobic compound onto chitosan to obtain modified chitosan; (2) adding a dilute polylactic acid solution or dichloromethane to an aqueous solution of modified chitosan, performing a primary emulsification, and then adding a concentrated polylactic acid solution to perform a secondary emulsification to obtain a mixed solution; (3) removing the solvent from the mixed solution to obtain a mixture; performing a first sieving and a second sieving on the mixture, and washing and drying the sieved mixture to obtain the polylactic acid microsphere. The method has the advantages of high efficiency, simplicity, and low cost, and the prepared polylactic acid microsphere can be used to prepare a sustained-release drug carrier system, medical and aesthetic filling materials, or tissue engineering scaffolds.

Description

Technical Field

[0001] The invention belongs to the technical field of biomedical materials, and specifically relates to polylactic acid microspheres and a preparation method and application thereof. Background Art

[0002] Polylactic acid (PLA), as a biodegradable polymer, has received extensive attention in recent years. This is mainly due to the many advantages of PLA, such as good biocompatibility, renewability and biodegradability under certain conditions, making it an ideal choice for drug controlled release systems, tissue engineering scaffolds, medical materials and other fields. However, how to efficiently prepare PLA microspheres with uniform particle size and both physical and chemical stability is still a hot topic and difficulty in current research.

[0003] Polylactic acid microspheres have outstanding performance in drug release systems due to their biodegradability and excellent mechanical properties. By encapsulating drugs in PLA microspheres, slow release of drugs can be achieved, thereby extending the effective time of drugs in the body, reducing the frequency of administration, and improving patient compliance. At the same time, PLA microspheres are also widely used in medical cosmetic filling materials, which can effectively fill depressions in the skin and improve appearance. In addition, PLA microspheres also show great potential in tissue engineering scaffolds. Its degradable properties allow it to be gradually degraded and absorbed in the body, thereby reducing the risk of secondary surgery.

[0004] At present, the methods for preparing PLA microspheres mainly include solvent evaporation, double emulsion method, spray drying method, etc. Among them, the solvent evaporation method is widely used due to its simple operation and low equipment requirements, but this method has the problems of uneven microsphere particle size and difficulty in completely removing the solvent. The double emulsion method can prepare microspheres with smaller and more uniform particle size by emulsifying the first emulsion again, but the operation is complicated, impurities are easily introduced, and the problem of solvent residue is still prominent. The spray drying method is suitable for large-scale production, but the equipment is expensive, the energy consumption is high, and the particles of the product are easy to aggregate, affecting its dispersion and uniformity. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, one of the objects of the present invention is to provide a method for preparing polylactic acid microspheres to solve the problems of complex preparation process, low yield, high cost, etc. in the prior art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing polylactic acid microspheres, comprising the following steps:

[0008] (1) Grafting a hydrophobic compound onto chitosan to obtain modified chitosan;

[0009] (2) adding a dilute polylactic acid solution or dichloromethane to the aqueous solution of modified chitosan to perform a primary emulsification, and then adding a concentrated polylactic acid solution to perform a secondary emulsification to obtain a mixed solution;

[0010] (3) removing the solvent from the mixed solution to obtain a mixed material; performing a primary screening and a secondary screening on the mixed material, and washing and drying the screened mixed material to obtain the polylactic acid microspheres.

[0011] Furthermore, the hydrophobic compound is at least one of cinnamic acid, ferulic acid and caffeic acid.

[0012] Furthermore, the concentration of the modified chitosan aqueous solution is 1-2 g / L; the concentration of the polylactic acid dilute solution is 50-100 g / L; and the concentration of the polylactic acid concentrated solution is 150-200 g / L.

[0013] Furthermore, the polylactic acid dilute solution and the polylactic acid concentrated solution are both prepared by dissolving polylactic acid in an organic solvent, and the organic solvent is dichloromethane.

[0014] Furthermore, the volume ratio of the polylactic acid dilute solution to the modified chitosan aqueous solution is (1:200) to (1:50); the volume ratio of the polylactic acid concentrated solution to the modified chitosan aqueous solution is (1:20) to (1:10).

[0015] Furthermore, the polylactic acid is at least one of poly-L-lactic acid, poly-D-lactic acid and poly-L-lactic acid; and the molecular weight of the polylactic acid is 50,000-500,000.

[0016] Furthermore, the specific operation of step (1) grafting the hydrophobic compound onto chitosan is: adding EDC and NHS to the hydrophobic compound solution to obtain a mixed solution; adding the mixed solution to the chitosan solution for grafting reaction, after the reaction is completed, subjecting the reaction solution to precipitation treatment, filtering and collecting the precipitate to obtain modified chitosan.

[0017] Furthermore, the mass ratio of the hydrophobic compound, EDC and NHS is 1:(1-1.5):(0.2-1); the mass ratio of chitosan to the hydrophobic compound is 1:0.2-0.5.

[0018] Furthermore, the molecular weight of the chitosan is 5000-500000, and the chitosan solution is an acetic acid solution of 0.2wt%-5wt% chitosan.

[0019] Furthermore, the grafting reaction is carried out under the conditions of avoiding light and at room temperature, the grafting reaction time is 24-48 hours, and the post-treatment method of the grafting reaction is an acetone precipitation method.

[0020] Furthermore, the emulsification speeds of the primary emulsification and the secondary emulsification are both 400-800 rpm / min, and the emulsification time is both 3-15 min.

[0021] Furthermore, the size of the filter used in the first screening in step (3) is 300-500 mesh; the size of the filter used in the second screening is 700-1500 mesh. The first screening is mainly to remove larger microspheres, and the second screening is mainly to remove smaller microspheres.

[0022] Furthermore, the method for removing the solvent in the mixed solution in step (3) is heating, the heating temperature is 30 to 45° C., and the heating time is 4 to 12 hours.

[0023] Furthermore, the washing water in step (3) is deionized water; the weight of the water is more than 100 times the weight of the microspheres.

[0024] Furthermore, the mixed material in step (3) needs to be screened for the third time after washing and drying, and the size of the filter screen used for the third screening is 100-500 mesh.

[0025] The second object of the present invention is to provide a polylactic acid microsphere, which has uniform particle size, smooth surface, good biocompatibility and degradability.

[0026] To achieve the above object, the present invention adopts the following technical solutions:

[0027] The polylactic acid microspheres are prepared by the above preparation method.

[0028] The third object of the present invention is to provide the use of the above-mentioned polylactic acid microspheres in the preparation of sustained-release drug carrier systems, medical filling materials or tissue engineering scaffolds.

[0029] To achieve the above object, the present invention adopts the following technical solutions:

[0030] The polylactic acid microspheres are used in the preparation of sustained-release drug carrier systems, medical filling materials and tissue engineering scaffolds.

[0031] Chitosan, as a natural cationic polysaccharide, has good biocompatibility and biodegradability. Modified chitosan surfactants are prepared by grafting hydrophobic molecules (such as cinnamic acid, ferulic acid and caffeic acid) on the amino groups of chitosan molecules. The interaction between the polar groups on its molecular chain and water and the interaction between the hydrophobic groups and oil give it excellent emulsification ability. Modified chitosan can not only effectively reduce the surface tension of the emulsion and stabilize the oil-water interface, but also make the particle size of PLA microspheres more uniform, and improve its surface smoothness and stability. Secondly, in the preparation process of PLA emulsion, the uniformity and stability of the emulsion are ensured by strictly controlling the ratio of dilute solution and concentrated solution, emulsification speed and emulsification time. Under the conditions of solvent volatilization and mechanical stirring, the PLA microspheres are gradually formed and dried by controlling the heating temperature and time. In the screening process, two screenings are performed through filters with different mesh sizes to remove unqualified microspheres and ensure the uniformity of the particle size of the microspheres. Finally, by washing with a large amount of deionized water and using anhydrous ethanol, the emulsifier residues were removed to the greatest extent possible to ensure the purity of the PLA microspheres.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention provides a method for preparing polylactic acid microspheres. First, a modified chitosan surfactant is used to effectively reduce the surface tension of the emulsion and stabilize the oil-water interface, thereby preparing PLA microspheres with uniform particle size and smooth surface, which significantly improves the quality and uniformity of the microspheres. Secondly, a dilute solution of polylactic acid is used as an emulsifying protective agent to avoid the phenomenon of direct precipitation of a concentrated solution of polylactic acid when it is added to the aqueous phase, which can directly increase the output of a single preparation, and can also reduce the volatilization and emission of solvents, thereby reducing environmental pollution. The present invention avoids the complexity of the traditional double emulsification process by one-time emulsification and optimizing the heating volatilization step, and greatly improves the quality and production efficiency of PLA microspheres while simplifying the process. Therefore, the method of the present invention is efficient, simple, economical, and environmentally friendly, and has great application potential in industry and research.

[0034] (2) The present invention provides polylactic acid microspheres prepared by the above preparation method. The microspheres use modified chitosan surfactants, which not only reduce costs but also have good biocompatibility and degradability, are environmentally friendly and have a wide source.

[0035] (3) The present invention provides the use of the above-mentioned polylactic acid microspheres in the preparation of drug sustained-release systems, medical and cosmetic filling materials, and tissue engineering scaffolds. The method is applicable to various types of polylactic acid, which expands the scope of application and has broad application prospects in the fields of drug sustained-release systems, medical and cosmetic filling materials, or tissue engineering scaffolds. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1Microsphere morphology diagrams of different embodiments and comparative examples;

[0037] Figure 2 This is a graph showing the fluorescent staining results of type I collagen after the product made of polylactic acid microspheres obtained in Example 1 and normal saline were implanted into rats. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further explained below in conjunction with specific embodiments, comparative examples, test examples and drawings.

[0039] In the following examples, comparative examples and test examples, the raw materials and preparation methods used are conventional materials and techniques in the art unless otherwise specified.

[0040] Example 1

[0041] A method for preparing polylactic acid microspheres comprises the following steps:

[0042] (1) Dissolving 20 g of chitosan (molecular weight 500000) in 10 L of 1% acetic acid solution to prepare a chitosan solution; dissolving 10 g of ferulic acid in 10 mL of N,N-dimethylformamide (DMF), then adding 10 g of EDC and 5 g of NHS, and activating at room temperature in the dark for 2 h to obtain a mixed solution; then adding the mixed solution dropwise to the chitosan solution under stirring conditions, and reacting at room temperature in the dark for 24 h; after the reaction is completed, adding the reaction solution dropwise to an acetone solution for precipitation, and filtering the precipitate to obtain a modified chitosan surfactant;

[0043] (2) dissolving 3 g of left-handed polylactic acid (PLLA, molecular weight 80,000) in 60 mL of dichloromethane to prepare a polylactic acid dilute solution, dissolving 240 g of PLLA in 1.2 L of dichloromethane to obtain a polylactic acid concentrated solution, both of which are used as an oil phase for standby; dissolving 12 g of the modified chitosan surfactant described in step (1) in 12 L of deionized water as an aqueous phase; under stirring at 500 rpm, first pouring 60 mL of the polylactic acid dilute solution into the aqueous phase and emulsifying it for 5 min, then pouring 1.2 L of the polylactic acid concentrated solution into the aqueous phase and emulsifying it for 5 min to obtain an emulsified solution;

[0044] (3) heating the emulsified solution in step (2) to 40° C., stirring at 700 rpm for 8 h, evaporating the solvent to obtain microspheres; first removing microspheres with a diameter of more than 50 μm with a 300-mesh filter, and then removing microspheres with a diameter of less than 20 μm with a 700-mesh filter; rinsing with a large amount of deionized water (the mass of the water is 100 times the mass of the microspheres), collecting the microspheres by suction filtration, and then adding anhydrous ethanol to remove excess water; spreading the powder obtained by suction filtration on a stainless steel plate and drying at room temperature; finally sieving the dried microspheres with a 100-mesh filter to obtain polylactic acid microspheres.

[0045] Example 2

[0046] A method for preparing polylactic acid microspheres comprises the following steps:

[0047] (1) 100 g of chitosan (molecular weight 50,000) was dissolved in 10 L of 1% acetic acid solution to prepare a chitosan solution; 20 g of cinnamic acid was dissolved in 10 mL of DMF, and then 30 g of EDC and 20 g of NHS were added, and activated at room temperature in the dark for 2 h to obtain a mixed solution; then the mixed solution was added dropwise to the chitosan solution under stirring conditions, and reacted at room temperature in the dark for 36 h; after the reaction was completed, the reaction solution was added dropwise to an acetone solution for precipitation, and the precipitate was filtered to obtain a modified chitosan surfactant;

[0048] (2) 300 g of dextrorotatory polylactic acid was dissolved in 1.2 L of dichloromethane to obtain a polylactic acid concentrated solution, and 60 mL of dichloromethane was taken, both of which were used as the oil phase for standby; 24 g of the modified chitosan surfactant described in step (1) was dissolved in 12 L of deionized water as the aqueous phase; then, 60 mL of dichloromethane was first poured into the aqueous phase under stirring at 450 rpm and emulsified for 15 min, and then 1.2 L of the polylactic acid concentrated solution was poured into the aqueous phase and emulsified for 5 min to obtain an emulsified system;

[0049] (3) heating the emulsified system in step (2) to 40° C., stirring at 500 rpm for 8 h, evaporating the solvent to obtain microspheres; first removing microspheres with a diameter of more than 50 μm with a 300-mesh filter, and then removing microspheres with a diameter of less than 20 μm with a 700-mesh filter; rinsing with a large amount of deionized water (the mass of the water is 120 times the mass of the microspheres), collecting the microspheres by suction filtration, and then adding anhydrous ethanol to remove excess water; spreading the powder obtained by suction filtration on a stainless steel plate and drying at room temperature; finally sieving the dried microspheres with a 100-mesh filter to obtain polylactic acid microspheres.

[0050] Example 3

[0051] A method for preparing polylactic acid microspheres comprises the following steps:

[0052] (1) Dissolve 200 g of chitosan (molecular weight 5000) in 10 L of 1% acetic acid solution to prepare a chitosan solution; dissolve 50 g of caffeic acid in 10 mL of DMF, then add 60 g of EDC and 30 g of NHS, activate at room temperature in the dark for 2 h, and obtain a mixed solution; then add the mixed solution dropwise to the chitosan solution under stirring conditions, and react at room temperature in the dark for 48 h; after the reaction is completed, add the reaction solution dropwise to an acetone solution for precipitation, and filter the precipitate to obtain a modified chitosan surfactant;

[0053] (2) Dissolve 24 g of mixed polylactic acid (molecular weight 100,000) in 240 mL of dichloromethane to prepare a polylactic acid dilute solution, and dissolve 150 g of mixed PLA in 1.0 L of dichloromethane to obtain a polylactic acid concentrated solution, both of which are used as the oil phase for standby; dissolve 18 g of the modified chitosan surfactant described in step (1) in 12 L of deionized water as the aqueous phase; then, under stirring at 700 rpm, first pour 240 mL of the polylactic acid dilute solution into the aqueous phase and emulsify for 5 min, and then pour 1.0 L of the polylactic acid concentrated solution into the aqueous phase and emulsify for 10 min to obtain an emulsified system;

[0054] (3) heating the emulsified system in step (2) to 40° C., stirring at 300 rpm for 12 h, evaporating the solvent to obtain microspheres; first removing microspheres with a diameter of more than 30 μm with a 500-mesh filter, and then removing microspheres with a diameter of less than 10 μm with a 1500-mesh filter; rinsing with a large amount of deionized water (the mass of the water is 150 times the mass of the microspheres), collecting the microspheres by suction filtration, and then adding anhydrous ethanol to remove excess water; spreading the powder obtained by suction filtration on a stainless steel plate and drying at room temperature; finally sieving the dried microspheres with a 200-mesh filter to obtain polylactic acid microspheres.

[0055] Comparative Example 1

[0056] This comparative example 1 provides a polylactic acid microsphere, which is different from Example 1 in that the modified chitosan surfactant is replaced by a sodium dodecylbenzene sulfonate surfactant, and the rest is consistent with Example 1.

[0057] Comparative Example 2

[0058] This comparative example 2 provides a polylactic acid microsphere, which is different from Example 1 in that the preparation step of the oil phase in step (2) is: dissolving 243 g of PLLA (molecular weight of 80,000) in 1.26 L of dichloromethane to obtain a polylactic acid solution as the oil phase; that is, this comparative example only sets the polylactic acid solution as the oil phase, and the rest is consistent with Example 1.

[0059] Comparative Example 3

[0060] This comparative example 3 provides a polylactic acid microsphere, which is different from Example 1 in that the preparation step of the oil phase in step (2) is: dissolving 3 g of left-handed polylactic acid (PLLA, molecular weight 80,000) in 60 mL of dichloromethane to prepare a polylactic acid dilute solution as the oil phase; that is, this comparative example only sets the polylactic acid dilute solution as the oil phase, and the rest is consistent with Example 1.

[0061] Comparative Example 4

[0062] Comparative Example 4 provides a polylactic acid microsphere, which differs from Example 1 in that the preparation steps of the oil phase in step (2) are as follows: 3 g of left-handed polylactic acid (PLLA, molecular weight 80,000) is dissolved in 60 mL of dichloromethane to prepare a polylactic acid dilute solution, and 160 g of PLLA is dissolved in 1.20 L of dichloromethane to obtain a polylactic acid concentrated solution as the oil phase; the rest is consistent with Example 1.

[0063] In order to verify whether the method for efficiently preparing polylactic acid microspheres of the present invention achieves the expected effect, the yield, morphology and residual emulsifier content of the microspheres prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were measured.

[0064] Test Example 1

[0065] The microspheres obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were weighed to obtain the amount of microspheres. The microsphere yield and the amount of microspheres that can be produced per liter of aqueous phase were calculated according to the initial charge amount and the volume of the aqueous phase. The results are shown in Table 1. In Table 1, the microsphere yield (%) = the actual amount of microspheres produced / initial charge amount, and the amount of microspheres that can be produced per liter of aqueous phase (g / L) = the actual amount of microspheres produced / volume of the aqueous phase.

[0066] Table 1 shows the microsphere yields and the amount of microspheres produced per liter of aqueous phase in Examples 1 to 3 and Comparative Examples 1 to 4.

[0067] Group Initial feed amount Microsphere amount Microsphere yield / % Microspheres per liter of water phase (g / L) Example 1 243 213 87.65 17.75 Example 2 300 259 86.3 21.58 Example 3 174 152 87.35 12.67 Comparative Example 1 243 200 82.30 16.67 Comparative Example 2 243 0 0 0 Comparative Example 3 3 1 66.7 0.083 Comparative Example 4 163 137 84.05 11.42

[0068] As can be seen from Table 1, the method of the present invention has a higher yield than the traditional method; compared with comparative example 4, the amount of microspheres that can be obtained per liter of water phase in Example 1 under the same conditions is increased by 55.43%, and the efficiency is significantly improved. Compared with comparative example 1, Example 1 uses a modified chitosan surfactant instead of a sodium dodecylbenzene sulfonate surfactant, so that the microsphere yield and the amount of microspheres per liter of water phase are improved, indicating that the modified chitosan surfactant can effectively replace the traditional emulsifier to prepare microspheres, and the effect is better; compared with Example 1, comparative example 2 omits the protection of a dilute polylactic acid solution and directly adds a concentrated polylactic acid solution. The microsphere yield and the amount of microspheres per liter of water phase are 0, indicating that after losing the protection of a dilute polylactic acid solution or dichloromethane, polylactic acid microspheres cannot be prepared. This may be due to the excessive concentration of polylactic acid. When the oil phase and the water phase are in contact, polylactic acid is rapidly precipitated, resulting in the inability to emulsify; comparative example 3 omits the addition of a concentrated solution. Although the microsphere yield is 66.7%, the amount of microspheres per liter of water phase is much lower than that of Examples 1 to 3. In Comparative Example 4, the concentration of the polylactic acid concentrated solution was adjusted to 13.3%, and the microsphere yield was 84.05%, but the amount of microspheres per liter of aqueous phase was much lower than that of Examples 1-3.

[0069] Test Example 2

[0070] The content of N in the microspheres of Examples 1 to 3 and Comparative Examples 2 to 4 was determined by the Kjeldahl method, and then the residual amount of the emulsifier was calculated according to formula (1); 0.1 g of the microspheres prepared in Comparative Example 1 was added with 10 mL of concentrated nitric acid for digestion, and then the volume was made up to 10 mL with deionized water, and the content of Na therein was determined by ICP-MS, and the residual amount of the emulsifier in the microspheres was calculated according to formula (2). The results are shown in Table 2.

[0071] Emulsifier residue (mg / g) = (N content / percentage of N in emulsifier) ​​× 100% Formula (1)

[0072] Emulsifier residue (mg / g) = (Na content / percentage of Na in emulsifier) ​​× 100% Formula (2)

[0073] Table 2 shows the residual amount of emulsifier in the microspheres of Examples 1 to 3 and Comparative Examples 1 to 4

[0074] Group Emulsifier residue mg / g Example 1 0.005 Example 2 0.003 Example 3 0.006 Comparative Example 1 0.114 Comparative Example 2 0.009 Comparative Example 3 0.007 Comparative Example 4 0.010

[0075] It can be seen from Table 2 that the residual emulsifier of the microspheres prepared by Examples 1-3 of the present invention is significantly reduced, which is more advantageous for the subsequent application of the microspheres. Comparative Example 1 uses an existing surfactant, and the residual emulsifier is as high as 0.114, which is much higher than Examples 1 to 3, indicating that the use of modified polylactic acid surfactants to prepare polylactic acid microspheres can significantly reduce the residual emulsifier. Comparative Examples 2 to 4 adjusted the concentration and addition form of the oil phase, that is, all used modified chitosan surfactants as the aqueous phase to prepare microspheres. Compared with Examples 1 to 3, there was no significant difference in the residual emulsifier.

[0076] Test Example 3

[0077] The microspheres prepared in Examples 1 to 3, Comparative Examples 1, 3 and 4 were dispersed in water and then dropped onto a glass sheet. The morphology of the microspheres was observed under a microscope and photographed. The results are as follows: Figure 1 As shown, Figures A, B, C, D, E, and F correspond to Examples 1 to 3, Comparative Example 1, Comparative Example 3, and Comparative Example 4, respectively.

[0078] from Figure 1 It can be seen that the microspheres prepared in Examples 1 to 3 of the present invention have a more uniform morphology and a narrower particle size distribution, while the microspheres prepared by the traditional method (Comparative Example 1) have a wider particle size distribution.

[0079] Test Example 4

[0080] The PLLA microspheres obtained in Example 1 were compounded with sodium carboxymethyl cellulose and mannitol. The specific process was as follows: 150 mg of the polylactic acid microspheres obtained in Example 1, 45 mg of sodium carboxymethyl cellulose, and 145 mg of mannitol were weighed; compounded to obtain the product, freeze-dried, and then irradiated for sterilization at a dose of 15 kgy; then injected into the back of rats (from Huaxing Experimental Animal Farm, Huiji District, Zhengzhou City), with a single-point injection volume of 0.2 mL, and the control group was saline. The tissues of the injection site 6 months after surgery were taken from the rats, and immunohistochemical staining was performed to evaluate the collagen production content of the rats at the injection site 6 months after surgery. The results are as follows Figure 2 shown.

[0081] from Figure 2 It can be seen that compared with the saline group, after the product made of the polylactic acid microspheres obtained in Example 1 was implanted into rats, the area stained with fluorescence increased, indicating that the product made of the polylactic acid microspheres obtained in Example 1 can effectively induce the regeneration of type I collagen (Col-I) in vivo.

[0082] The above are only preferred embodiments of the present invention, and are not limited to the above examples. For those skilled in the art, various changes and variations are possible under the principle of the present invention. Any modifications and improvements made should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing polylactic acid microspheres, characterized in that: The specific steps include: (1) Grafting a hydrophobic compound onto chitosan to obtain modified chitosan; (2) adding a dilute polylactic acid solution or dichloromethane to the aqueous solution of modified chitosan to perform a primary emulsification, and then adding a concentrated polylactic acid solution to perform a secondary emulsification to obtain a mixed solution; (3) removing the solvent from the mixed liquid to obtain a mixed material; performing a first screening and a second screening on the mixed material, and washing and drying the screened mixed material to obtain the polylactic acid microspheres; The hydrophobic compound is at least one of cinnamic acid, ferulic acid and caffeic acid; The concentration of the modified chitosan aqueous solution is 1-2 g / L; the concentration of the polylactic acid dilute solution is 50-100 g / L; the concentration of the polylactic acid concentrated solution is 150-200 g / L; The polylactic acid dilute solution and the polylactic acid concentrated solution are both prepared by dissolving polylactic acid in an organic solvent, and the organic solvent is dichloromethane.

2. The method for preparing polylactic acid microspheres according to claim 1, characterized in that: The volume ratio of the polylactic acid dilute solution to the modified chitosan aqueous solution is (1:200) to (1:50); the volume ratio of the polylactic acid concentrated solution to the modified chitosan aqueous solution is (1:20) to (1:10).

3. The method for preparing polylactic acid microspheres according to claim 1, characterized in that: The polylactic acid is at least one of poly-L-lactic acid, poly-D-lactic acid and poly-L-lactic acid; the molecular weight of the polylactic acid is 50,000-500,000.

4. The method for preparing polylactic acid microspheres according to claim 1, characterized in that: The specific operation of step (1) grafting the hydrophobic compound onto chitosan is as follows: adding EDC and NHS to the hydrophobic compound solution to obtain a mixed solution; adding the mixed solution to the chitosan solution for grafting reaction; after the reaction is completed, subjecting the reaction solution to precipitation treatment, filtering and collecting the precipitate to obtain modified chitosan.

5. The method for preparing polylactic acid microspheres according to claim 4, characterized in that: The mass ratio of the hydrophobic compound, EDC and NHS is 1:(1-1.5):(0.2-1); the mass ratio of chitosan to the hydrophobic compound is 1:(0.2-0.5).

6. The method for preparing polylactic acid microspheres according to any one of claims 1 to 5, characterized in that: The size of the filter used in the first screening in step (3) is 300-500 mesh; the size of the filter used in the second screening is 700-1500 mesh.

7. Polylactic acid microspheres prepared by the method according to any one of claims 1 to 5.

8. Use of the polylactic acid microspheres as claimed in claim 7 in the preparation of sustained-release drug carrier systems, medical filling materials or tissue engineering scaffolds.

Images