A hyaluronic acid-polylactic acid copolymer crosslinked gel and its preparation method and application

Abstract

The present disclosure relates to a hyaluronic acid-polylactic acid copolymer crosslinked gel and its preparation method and application. The method includes the following steps: S1. Changing the ions of hyaluronic acid through an ion exchange resin, adjusting the pH of the solution to 7.0 with a basic reagent, and freeze-drying to obtain amphiphilic hyaluronic acid; S2. Activating the carboxyl group of polylactic acid using a catalyst to obtain carboxyl-activated polylactic acid; S3. Performing an esterification reaction between the carboxyl-activated polylactic acid and the amphiphilic hyaluronic acid, and obtaining a hyaluronic acid-polylactic acid copolymer after dialysis and freeze-drying; S4. Placing the hyaluronic acid-polylactic acid copolymer in a basic solvent, performing a crosslinking reaction under the action of a crosslinking agent, and swelling with a PBS buffer solution to obtain a hyaluronic acid-polylactic acid copolymer crosslinked gel. By grafting polylactic acid onto the molecular chain of hyaluronic acid, compared with a single hyaluronic acid gel and polylactic acid, the degradation time of the crosslinked gel is prolonged and the hydrophilic property of polylactic acid is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of biomaterials, and particularly relates to a hyaluronic acid-polylactic acid copolymer cross-linked gel, a preparation method thereof, and an application thereof. Background Art

[0002] Facial aging (such as the appearance of wrinkles, dry skin, and pigmentation) is a complex process, which is affected not only by internal conditions, such as the breakage of tissue fibers such as collagen and elastin, the loss of hyaluronic acid and moisture, but also by external environmental factors, such as air environment, living habits, and bacterial diseases.

[0003] Hyaluronic acid (HA), as a natural biopolymer composed of D-glucuronic acid and N-acetyl-D-glucosamine, is widely present in various parts of the human body, such as skin, joints, and blood. It has excellent functions such as maintaining moisture, improving skin elasticity, and signal transduction, and is widely used in skin anti-aging products.

[0004] Filling-type hyaluronic acid is one of the main types of hyaluronic acid products. By injecting hyaluronic acid gel into the dermis of the skin, it can enhance skin elasticity and supplement moisture, thereby achieving the purpose of improving the skin condition. Filling-type hyaluronic acid has a short operation time and remarkable effects, and is the mainstream product in the current medical aesthetic filling field. However, traditional filling-type hyaluronic acid gels still have disadvantages such as weak support performance, fast degradation rate, and short maintenance time.

[0005] Polylactic acid (PLA) is a biodegradable polymer material approved by the US Food and Drug Administration (FDA) for use in the human body and is polymerized from lactic acid. In the human body, polylactic acid is first decomposed into oligomeric lactic acid, and then further decomposed into lactic acid. By participating in human metabolism, it is degraded into carbon dioxide and water and excreted from the body. When polylactic acid is used as an injection material and filled into the dermis of the human body, it can stimulate fibroblasts to produce collagen, thereby improving facial volume and achieving the purpose of regenerative filling. However, polylactic acid has extremely strong hydrophobic properties and is insoluble in water. Direct injection into the human body will cause immune reactions, resulting in adverse phenomena such as swelling and inflammation.

[0006] Many existing technologies combine hyaluronic acid and polylactic acid to obtain anti-aging filling products with better effects.

[0007] CN117085178A discloses a facial filler composition for injection cosmetic plastic surgery and its preparation method. In this method, poly (L-lactic acid) and poly (D-lactic acid) are added to a hyaluronic acid solution respectively, and a gel is formed by self-crosslinking through the physical interaction between poly (L-lactic acid) and poly (D-lactic acid). Although this method prolongs the degradation time of hyaluronic acid, the gel formed by self-crosslinking has poor stability, weak mechanical properties and a fast degradation rate.

[0008] CN110964215A discloses a preparation method of a composite gel of injectable poly (L-lactic acid) and crosslinked hyaluronic acid. By adding polylactic acid to a hyaluronic acid solution, a freeze-dried substance is obtained, and a composite gel is prepared by secondary crosslinking. Due to the poor hydrophilicity of polylactic acid, when polylactic acid is directly added to a hyaluronic acid solution in this method, it is difficult to disperse evenly in the aqueous solution and is prone to agglomeration, resulting in needle clogging.

[0009] CN117024770A discloses a preparation method of a mixed gel of modified polylactic acid microspheres and sodium hyaluronate. In this method, polylactic acid microspheres are first modified with nicotinamide, and then the modified polylactic acid microspheres are added to a hyaluronic acid solution and mixed evenly to obtain a gel. This method increases the hydrophilicity of polylactic acid to a certain extent, but injecting nicotinamide into the body will have an irritating effect on the skin, causing phenomena such as redness, swelling, itching, etc., and the degradation rate of the hyaluronic acid solution in the body is relatively fast, without obvious filling and shaping effects. Summary of the Invention

[0010] The purpose of the present disclosure is to provide a skin anti-aging filler with high stability and high biosafety.

[0011] To achieve the above purpose, the present disclosure provides a preparation method of a hyaluronic acid-polylactic acid copolymer crosslinked gel, including the following steps:

[0012] S1. Changing the ions of hyaluronic acid through an ion exchange resin, adjusting the pH of the solution to 7.0 with an alkaline reagent, and freeze-drying to obtain amphiphilic hyaluronic acid with the following structure

[0013] ;

[0014] S2. Activating the carboxyl group of polylactic acid using a catalyst to obtain carboxyl-activated polylactic acid;

[0015] S3. The carboxyl-activated polylactic acid reacts with the amphiphilic hyaluronic acid through an esterification reaction, and after dialysis and freeze-drying, a hyaluronic acid-polylactic acid copolymer including the following structure is obtained

[0016] ;

[0017] S4. Place the hyaluronic acid - polylactic acid copolymer in an alkaline solvent, and carry out a cross - linking reaction under the action of a cross - linker. After swelling with PBS buffer solution, a hyaluronic acid - polylactic acid copolymer cross - linked gel is obtained.

[0018] Preferably, the molecular weight of the polylactic acid is 5,000 - 200,000 Da;

[0019] The polylactic acid is selected from one of poly - L - lactic acid, poly - D - lactic acid, racemic poly - lactic acid or poly - lactic acid modified with polyethylene glycol.

[0020] Preferably, in the reaction system of step S2, the catalyst includes at least one of N-(3 - dimethylaminopropyl) - N'-ethylcarbodiimide, dicyclohexylcarbodiimide, 4 - dimethylaminopyridine and N - hydroxysuccinimide, and the solvent used includes dichloromethane or chloroform.

[0021] More preferably, the catalyst is N - hydroxysuccinimide and N-(3 - dimethylaminopropyl) - N'-ethylcarbodiimide;

[0022] The mass ratio of the polylactic acid, the N - hydroxysuccinimide and N-(3 - dimethylaminopropyl) - N'-ethylcarbodiimide is 1:0.01:0.01 to 1:5:5, the reaction temperature is 25 - 50 °C, and the reaction time is 8 - 48 h.

[0023] Preferably, in the reaction system of step S3, the solvent used includes dimethyl sulfoxide, the mass ratio of the amphiphilic hyaluronic acid to the carboxyl - activated polylactic acid is 1:0.01 to 1:5, the reaction temperature is 40 - 60 °C, the reaction time is 8 - 24 h, and the dialysis time is 2 - 5 days.

[0024] Preferably, in step S1, the molecular weight of the hyaluronic acid is 20,000 - 2,000,000 Da, the ion - exchange resin is a cation - exchange resin, the treatment time is 18 - 36 h, and the alkaline reagent includes tetrabutylammonium hydroxide solution.

[0025] Preferably, the alkaline reagent includes a 1% sodium hydroxide solution by mass fraction, and the composition of the PBS buffer solution is: sodium chloride, disodium hydrogen phosphate and sodium dihydrogen phosphate monohydrate;

[0026] The mass ratio of the hyaluronic acid - polylactic acid copolymer to the cross - linker is 1:0.01 to 1:0.5, the cross - linking temperature is 25 - 50 °C, the cross - linking time is 12 - 48 h, and the swelling time is 12 - 72 h;

[0027] The cross - linker includes 1,4 - butanediol diglycidyl ether, divinyl sulfone, ethylene glycol diglycidyl ether, 1,6 - hexanediol diglycidyl ether or diethylene glycol diglycidyl ether.

[0028] To achieve the above object, the present disclosure also provides a hyaluronic acid-polylactic acid copolymer crosslinked gel, and the crosslinked gel is obtained according to the preparation method described in any one of the foregoing.

[0029] Preferably, the crosslinked gel includes the following chemical structure:

[0030]

[0031] To achieve the above object, the present disclosure also provides an application of the crosslinked gel described in any one of the foregoing, and the crosslinked gel is applied in the preparation of a facial filler.

[0032] The technical solutions claimed by the present disclosure have achieved the following beneficial effects:

[0033] In the hyaluronic acid-polylactic acid copolymer crosslinked gel of the present disclosure, since polylactic acid is grafted onto the molecular chain of hyaluronic acid, the degradation time of the crosslinked gel is prolonged by extending the molecular chain. Compared with a single hyaluronic acid gel, the hyaluronic acid grafted with polylactic acid has a stronger effect on stimulating the regeneration of human collagen. Moreover, hyaluronic acid belongs to a natural macromolecule and has no immune reaction. Polylactic acid is connected to hyaluronic acid through a covalent bond, reducing the hydrophobic property of polylactic acid, and can be degraded into carbon dioxide and water in the body, with high biosafety. Description of the Drawings

[0034] To more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following will briefly introduce the drawings required for the description of the embodiments.

[0035] Figure 1 Infrared spectrum results of HA, PLLA and HA-g-PLLA.

[0036] Figure 2 Morphology diagram of the crosslinked gel prepared from HA-g-PLLA. Detailed Embodiments

[0037] To make the objectives, technical solutions and beneficial effects in the embodiments of the present disclosure clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present disclosure with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0038] Example 1

[0039] This example provides a preparation method of a hyaluronic acid-polylactic acid copolymer crosslinked gel, including the following steps:

[0040] S1. Preparation of amphiphilic hyaluronic acid: The ions of sodium hyaluronate were changed by using ion exchange resin, and the pH was adjusted to neutral with a basic reagent. After freeze-drying, amphiphilic hyaluronic acid (HA-TBA) was obtained, and its chemical structural formula is as follows:

[0041]

[0042] In this step, the molecular weight of sodium hyaluronate is preferably 20,000 - 2,000,000 Da, the ion exchange resin is a cation exchange resin, the treatment time is 18 - 36 h, and the basic reagent is tetrabutylammonium hydroxide solution.

[0043] S2. Carboxyl activation of polylactic acid: Polylactic acid was dissolved in an organic solvent, and a catalyst was added to activate the carboxyl group. The chemical reaction equation is as follows:

[0044]

[0045] In this step, the polylactic acid is poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), racemic polylactic acid (PDLLA), or polylactic acid modified with polyethylene glycol (PEG), including PLLA-PEG, PDLA-PEG, and PDLLA-PEG modified with polyethylene glycol. The molecular weight of polylactic acid is preferably 5,000 - 200,000 Da, the organic solvent is dichloromethane or chloroform, preferably dichloromethane;

[0046] The catalyst used in this step is N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC), dicyclohexylcarbodiimide (DCC), 4-dimethylaminopyridine (DMAP), or N-hydroxysuccinimide (NHS), preferably N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS). Among them, the mass ratio of polylactic acid, EDC, and NHS is 1:0.01:0.01 to 1:5:5, the reaction temperature is 25 - 50 °C, and the reaction time is 8 - 48 h.

[0047] S3. Preparation of hyaluronic acid-polylactic acid copolymer: The substances obtained in step S1 and step S2 were blended to prepare a copolymer, which was dialyzed and freeze-dried to obtain a solid copolymer (HA-g-PLA). The reaction process is as follows:

[0048] ╋

[0049] ↓

[0050]

[0051] In this step, the mass ratio of hyaluronic acid to polylactic acid is 1:0.01 to 1:5, the blend solvent used is dimethyl sulfoxide (DMSO), the reaction temperature is 40-60 °C, the catalyst is diethylamine, the time is 8-24 h, and the dialysis time required for the copolymer is 2-5 days.

[0052] S4. Preparation of hyaluronic acid-polylactic acid copolymer crosslinked gel: Dissolve the solid copolymer in step S3 in an alkaline solution, add a crosslinking agent, mix well, and then stand for crosslinking for 12-48 h. After swelling with PBS buffer solution, the hyaluronic acid-polylactic acid copolymer crosslinked gel can be obtained.

[0053] +

[0054] ↓

[0055]

[0056] In this step, the alkaline solution is a 1% sodium hydroxide solution by mass fraction, and the crosslinking agent is one of 1,4-butanediol diglycidyl ether (BDDE), divinyl sulfone, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and diethylene glycol diglycidyl ether, preferably 1,4-butanediol diglycidyl ether;

[0057] In the preferred scheme, the mass ratio of the hyaluronic acid-polylactic acid copolymer to the crosslinking agent is 1:0.01 to 1:0.5, the crosslinking temperature is preferably 25-50 °C, and the reaction time is preferably 18-36 h. Among them, the composition of the PBS buffer solution is: sodium chloride, disodium hydrogen phosphate, and sodium dihydrogen phosphate monohydrate, and the swelling time is 72 h.

[0058] The following further describes the solution in Example 1 in detail in combination with specific application examples.

[0059] Application Example 1

[0060] This application example provides a preparation method of an injectable hyaluronic acid-polylactic acid copolymer crosslinked gel, including the following steps:

[0061] S1. Preparation of amphiphilic hyaluronic acid: Weigh 2 g of sodium hyaluronate with a molecular weight of 1,600,000 Da and prepare a 2% hyaluronic acid solution. Immerse the sodium hyaluronate solution in a cation exchange resin for 24 h, adjust the pH of the HA solution to 7.0 with tetrabutylammonium hydroxide solution, and after lyophilization, obtain an amphiphilic hyaluronic acid solid (HA-TBA);

[0062] S2. Activation of carboxyl groups of polylactic acid: Dissolve 5 g of poly-L-lactic acid with a molecular weight of 10,000 Da, 191.70 mg of EDC, and 115.09 mg of NHS in dichloromethane, react at 25 °C for 24 h, and obtain carboxyl-activated polylactic acid (PLLA-NHS) after vacuum drying;

[0063] S3. Preparation of hyaluronic acid-polylactic acid copolymer: Weigh 600 mg of HA-TBA in S1 and 21.6 mg of PLLA-NHS in S2 and dissolve them in dimethyl sulfoxide, add the catalyst diethylamine, and react at 40 °C for 24 h to obtain a copolymer solution. Dialyze the copolymer solution for 48 h and then freeze-dry it to obtain a freeze-dried sample of hyaluronic acid-polylactic acid copolymer (HA-g-PLLA);

[0064] S4. Preparation of crosslinked gel of hyaluronic acid-polylactic acid copolymer: Weigh 500 mg of HA-g-PLLA in S3 and dissolve it in 9.5 mL of 1% sodium hydroxide solution, add 40 μL of 1,4-butanediol diglycidyl ether (BDDE), crosslink at 25 °C for 24 h, and then add 20 mL of PBS buffer solution to swell for 72 h to obtain a crosslinked gel.

[0065] Application Example 2

[0066] This application example provides a preparation method of an injectable crosslinked gel of hyaluronic acid-polylactic acid copolymer, including the following steps:

[0067] S1. Preparation of amphiphilic hyaluronic acid: Weigh 5 g of sodium hyaluronate with a molecular weight of 1,000,00 Da and dissolve it in water to prepare a 5% hyaluronic acid solution. Immerse the sodium hyaluronate solution in an ion exchange resin for 24 h, adjust the pH to 7.0 with tetrabutylammonium hydroxide solution, and freeze-dry the solution to obtain amphiphilic hyaluronic acid (HA-TBA);

[0068] S2. Activation of carboxyl groups of polylactic acid: Dissolve 5 g of poly-D-lactic acid with a molecular weight of 10,000 Da, 383.40 mg of EDC, and 230.18 mg of NHS in dichloromethane, react at 25 °C for 24 h, and obtain carboxyl-activated poly-D-lactic acid (PDLA-NHS) after vacuum drying;

[0069] S3. Preparation of hyaluronic acid-polylactic acid copolymer: Weigh 600 mg of HA-TBA in S1 and 84 mg of PDLA-NHS in S2 and dissolve them in dimethyl sulfoxide, add the catalyst diethylamine, react at 50 °C for 24 h to obtain a copolymer solution. Dialyze the copolymer solution for 72 h and then freeze-dry it to obtain a hyaluronic acid-polylactic acid copolymer;

[0070] S4. Preparation of hyaluronic acid - polylactic acid copolymer cross - linked gel: Weigh 500 mg of the copolymer in S3 and dissolve it in 9.5 mL of 1% sodium hydroxide solution. Add 80 μL of 1,4 - butanediol diglycidyl ether (BDDE). After cross - linking at 25 °C for 24 h, add 20 mL of PBS buffer for swelling to obtain the cross - linked gel.

[0071] Application Example 3

[0072] This application example provides a preparation method of an injectable hyaluronic acid - polylactic acid copolymer cross - linked gel, including the following steps:

[0073] S1. Preparation of amphiphilic hyaluronic acid: Weigh 5 g of sodium hyaluronate with a molecular weight of 1,600,000 Da and dissolve it in water to prepare a 5% hyaluronic acid solution. Immerse the sodium hyaluronate solution in an ion - exchange resin for 24 h, then adjust the pH to 7.0 with tetrabutylammonium hydroxide solution, and freeze - dry the solution to obtain amphiphilic hyaluronic acid (HA - TBA);

[0074] S2. Activation of the carboxyl group of polylactic acid: Dissolve 5 g of poly - L - lactic acid with a molecular weight of 15,000 Da, 191.70 mg of EDC, and 115.09 mg of NHS in dichloromethane. React at 25 °C for 24 h, and after vacuum drying, obtain carboxyl - activated polylactic acid (PLLA - NHS);

[0075] S3. Preparation of hyaluronic acid - polylactic acid copolymer: Weigh 1200 mg of HA - TBA in S1 and 102 mg of PLLA - NHS in S2 and dissolve them in dimethyl sulfoxide. React at 50 °C for 24 h, dialyze the solution for 72 h, and then freeze - dry to obtain a freeze - dried sample of hyaluronic acid - polylactic acid copolymer (HA - g - PLLA);

[0076] S4. Preparation of hyaluronic acid - polylactic acid copolymer cross - linked gel: Weigh 500 mg of HA - g - PLLA in S3 and dissolve it in 4.5 mL of 1% sodium hydroxide solution. Add 100 μL of 1,4 - butanediol diglycidyl ether (BDDE). After cross - linking at 25 °C for 24 h, add 20 mL of PBS buffer for swelling for 72 h to obtain the cross - linked gel.

[0077] Comparative Example 1

[0078] Weigh 500 mg of sodium hyaluronate with a molecular weight of 1,600,000 Da and dissolve it in 9.5 mL of 1% sodium hydroxide solution. Add 80 μL of 1,4 - butanediol diglycidyl ether (BDDE). After cross - linking at 25 °C for 24 h, add 20 mL of PBS buffer for swelling to obtain the cross - linked gel.

[0079] Comparative Example 2

[0080] Weigh 500 mg of sodium hyaluronate with a molecular weight of 300,000 Da and dissolve it in 9.5 mL of 1% sodium hydroxide solution. Add 40 μL of 1,4-butanediol diglycidyl ether (BDDE), and crosslink at 25 °C for 24 h. Then add 20 mL of PBS buffer solution for swelling to obtain a crosslinked gel.

[0081] Performance comparison

[0082] Use a Fourier transform infrared spectrometer to perform infrared scanning on HA, PLLA, and HA-g-PLLA in Example 1 in the wavelength range of 4000 - 400 cm -1 Please refer to the range. The results show that the copolymer (HA-g-PLLA) exhibits characteristic peaks of hyaluronic acid (HA) at 3389 cm Figure 1 (-OH), 1610 cm -1 (-COOH), 1378 cm -1 (-CH2), 1150 cm -1 (-CH2), 1150 cm -1 (C-O-C), 1078 cm- 1 (-C=O), etc. And compared with pure HA, the copolymer (HA-g-PLLA) forms new characteristic peaks at 1756 cm -1 , 1456 cm -1 . This is mainly due to the presence of the ester bond (C=O) and methyl group (-CH3) of PLLA, thus confirming that PLLA has successfully modified HA. Figure 2 The morphology of the crosslinked gel prepared from this copolymer (HA-g-PLLA) is shown, indicating that this copolymer has the ability to form a gel.

[0083] Use a rheometer to perform rheological measurements on the crosslinked gels in Examples 1 - 3 and Comparative Examples 1 - 2. The results are shown in Table 1. When the amplitude frequency is 10 Hz, the crosslinked gels have a certain filling and plasticizing effect, and the rheological properties of Examples 1 to 3 are higher than those of the comparative examples.

[0084] Table 1 Rheological properties of Examples 1 - 3 and Comparative Examples 1 - 2

[0085] Elastic modulus / Pa Viscous modulus / Pa Example 1 33.94 6.34 Example 2 47.93 5.96 Example 3 56.46 9.24 Comparative Example 1 32.35 7.23 Comparative Example 2 10.35 4.52

[0086] Use hyaluronidase to perform in vitro degradation on the crosslinked gels of Examples 1 - 3 and Comparative Examples 1 - 2. The degradation rates are shown in Table 2. The degradation rates of Examples 1 - 3 are all lower than those of Comparative Examples 1 - 2, indicating that the polylactic acid group increases the chain length of the hyaluronic acid molecular chain, achieving the purpose of delaying the degradation of the material.

[0087] Table 2 Degradation rates of crosslinked gels of Examples 1 - 3 and Comparative Examples 1 - 2

[0088] 2 days 4 days 6 days Example 1 21.30% 40.30% 63.57% Example 2 15.60% 30.79% 47.19% Example 3 12.02% 21.19% 35.58% Comparative Example 1 19.40% 41.21% 60.17% Comparative Example 2 25.24% 51.24% 72.61%

[0089] The above performance test results show that, compared with the simple hyaluronic acid cross-linked gel, the hyaluronic acid cross-linked gel grafted with polylactic acid in the present disclosure has enhanced mechanical properties and a slower degradation rate, and can enhance the shaping effect and shaping time when used as a skin anti-aging filler.

[0090] In the present disclosure, hyaluronic acid is first converted into amphiphilic HA-TBA using an ion exchange resin, and the carboxyl group of polylactic acid is catalyzed by amidation reaction to obtain PLA-NHS. The activated polylactic acid (PLA-NHS) and hyaluronic acid (HA-TBA) are graft copolymerized through an esterification reaction to form a copolymer (HA-g-PLA), and then this copolymer and a cross-linking agent are prepared into a gel under certain conditions. The gel greatly improves the disadvantages of poor mechanical properties and short retention time in the skin of hyaluronic acid through the covalent interaction between polylactic acid and hyaluronic acid. At the same time, grafting polylactic acid onto hyaluronic acid increases the hydrophilicity of polylactic acid and can reduce the immune rejection reaction. The cross-linked gel prepared by this method can achieve the effects of moisturizing, filling, and shaping, and can stimulate the regeneration of collagen cells in the skin, reduce the generation of wrinkles, and restore skin elasticity.

[0091] The above-described embodiments and application examples are only exemplary descriptions of the present disclosure, and do not limit the scope of the present disclosure. Without departing from the design spirit of the present disclosure, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present disclosure shall fall within the protection scope determined by the present disclosure.

Claims

1. A method for preparing a hyaluronic acid-polylactic acid copolymer cross-linked gel, characterized in that, It includes the following steps: S1. Change the ions of hyaluronic acid through an ion exchange resin, adjust the pH of the solution to 7.0 with an alkaline reagent, and freeze-dry to obtain an amphiphilic hyaluronic acid with the following structural formula ； S2. Activate the carboxyl group of polylactic acid using a catalyst to obtain carboxyl-activated polylactic acid; S3. The carboxyl-activated polylactic acid and the amphiphilic hyaluronic acid undergo an esterification reaction, and after dialysis and freeze-drying, a hyaluronic acid-polylactic acid copolymer including the following structural formula is obtained ； S4. Place the hyaluronic acid-polylactic acid copolymer in an alkaline solvent, and make the hyaluronic acid-polylactic acid copolymers undergo a cross-linking reaction under the action of a cross-linking agent. After swelling with a PBS buffer solution, a hyaluronic acid-polylactic acid copolymer cross-linked gel with the following structural formula is obtained 。 2. The preparation method according to claim 1, characterized in that, The molecular weight of the polylactic acid is 5,000~200,000 Da; The polylactic acid is selected from one of poly-L-lactic acid, poly-D-lactic acid, racemic polylactic acid, or poly(ethylene glycol)-modified polylactic acid.

3. The preparation method according to claim 1 or 2, characterized in that, In the reaction system of step S2, the catalyst includes at least one of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide, dicyclohexylcarbodiimide, 4-dimethylaminopyridine, and N-hydroxysuccinimide, and the solvents used include dichloromethane or chloroform.

4. The preparation method according to claim 3, characterized in that, The catalyst is N-hydroxysuccinimide and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide; The mass ratio of the polylactic acid, the N-hydroxysuccinimide, and the N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide is 1:0.01:0.01 to 1:5:5, the reaction temperature is 25~50 °C, and the reaction time is 8~48 h.

5. The preparation method according to claim 1 or 2, characterized in that, In the reaction system of step S3, the solvent used includes dimethyl sulfoxide. The mass ratio of the amphiphilic hyaluronic acid to the carboxyl-activated polylactic acid is 1:0.01 to 1:5, the reaction temperature is 40~60 °C, the reaction time is 8~24 h, and the dialysis time is 2~5 days.

6. The preparation method according to claim 1, wherein, In step S1, the molecular weight of the hyaluronic acid is 20,000~2,000,000 Da, the ion exchange resin is a cation exchange resin, the treatment time is 18~36 h, and the alkaline reagent includes tetrabutylammonium hydroxide solution.

7. The preparation method according to claim 1 or 2, characterized in that In step S4, the alkaline reagent includes a 1% sodium hydroxide solution by mass fraction, and the composition of the PBS buffer solution is: sodium chloride, disodium hydrogen phosphate, and sodium dihydrogen phosphate monohydrate; The mass ratio of the hyaluronic acid-polylactic acid copolymer to the cross-linking agent is 1:0.01 to 1:0.5, the cross-linking temperature is 25~50 °C, the cross-linking time is 12~48 h, and the swelling time is 12-72 h; The cross-linking agent includes 1,4-butanediol diglycidyl ether, divinyl sulfone, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, or diethylene glycol diglycidyl ether.

8. A hyaluronic acid-polylactic acid copolymer crosslinked gel, characterized in that, The cross-linked gel is obtained according to the preparation method described in any one of claims 1 to 7.

9. Use of the crosslinked gel according to claim 8, characterized in that, The cross-linked gel is applied in the preparation of a facial filler.

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