A pH-sensitive asiaticoside drug-loaded micelle, and a preparation method and application thereof

Abstract

The application discloses a pH-sensitive asiaticoside drug-loaded micelle as well as a preparation method and application thereof, and belongs to the technical field of pharmaceutical preparations. The drug-loaded micelle takes mPEG-PLGA-PHis triblock copolymer as a carrier, realizes high drug loading, high encapsulation efficiency and pH 5.5 precise response drug release by limiting the molar ratio of lactic acid and glycolic acid to 70:30-80:20, the specific molecular weight interval of each block and the mass ratio, the micelle particle size is 30-120 nm, the structure is stable in a neutral environment, and the drug is quickly released by depolymerization in an inflammatory micro-acid environment. The preparation adopts a film dispersion-dialysis process, has low organic solvent residue, uniform particle size, good batch repeatability and is suitable for industrial production. The drug-loaded micelle can be made into gel, cream and other external preparations, is used for skin inflammation repair, wound healing, scar lightening and post-medical beauty repair and has good clinical application and industrial value.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical preparation technology, specifically relating to a pH-sensitive asiaticoside drug-loaded micelle and its preparation method, as well as its application in topical preparations for skin inflammation repair, wound healing, scar fading, and post-medical aesthetic repair. Background Technology

[0002] Asiaticoside is a natural active ingredient extracted from Centella asiatica. It possesses significant anti-inflammatory, wound-healing-promoting, scar-inhibiting, and skin-barrier-repairing pharmacological effects, and is widely used in skin repair and post-medical aesthetic care. However, Asiaticoside is a weakly polar lipophilic component with a high apparent oil-water partition coefficient and extremely poor water solubility. It is difficult to disperse evenly in water-based topical matrices, resulting in poor spreadability and formability of the formulation. In its free state, the drug is easily washed away by sebum and sweat, remaining only in the superficial stratum corneum and failing to accumulate in the dermal lesions. Furthermore, lacking carrier protection, it is prone to oxidation and enzymatic degradation, resulting in low effective drug concentrations for use on inflamed and wound tissues, and limited apparent transdermal bioavailability and local efficacy.

[0003] To address the aforementioned issues, existing technologies often employ micellar carriers to encapsulate asiaticoside, utilizing the core-shell structure of micelles to achieve drug solubilization and transdermal enhancement. However, conventional micelles are mostly non-responsive, exhibiting no difference in drug release between normal and inflamed skin microenvironments. This can easily lead to drug leakage in normal skin areas and insufficient effective concentration at the lesion site. Furthermore, they suffer from low encapsulation efficiency and limited drug loading capacity.

[0004] Existing pH-sensitive micelles are mostly prepared using PEG-PLGA binary block copolymers, relying solely on the slow hydrolysis of PLGA ester bonds in an acidic environment to achieve drug release. This approach suffers from drawbacks such as a wide pH response range and low sensitivity, failing to precisely match the slightly acidic environment of skin inflammation / wounds (pH 5.0–6.0). Furthermore, the micelles lack lesion-targeting enrichment capabilities, resulting in poor drug delivery selectivity. mPEG-PLGA lacks a precise pH-triggered structure, leading to uncontrollable drug release; and mPEG-PHis suffers from insufficient hydrophobic cores, resulting in poor drug loading and structural stability. Simultaneously, existing preparation processes suffer from issues such as high levels of residual organic solvents, poor micelle particle size uniformity, and low batch-to-batch repeatability, failing to meet the requirements of industrial-scale production.

[0005] Therefore, developing a asiaticoside drug-loaded micelle with precise response, excellent drug loading and encapsulation performance, and controllable process is a technical problem that urgently needs to be solved in the field of topical skin preparations. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies such as poor water solubility, uneven dispersion, low transdermal enrichment efficiency, poor pH response sensitivity of conventional micelles, and structural performance imbalance of diblock carriers, the present invention aims to provide a pH-sensitive asiaticoside drug-loaded micelle, its preparation method, and its application.

[0007] One objective of this invention is to provide a pH-sensitive asiaticoside drug-loaded micelle that achieves rapid depolymerization and drug release in a stable neutral skin environment and a slightly acidic inflammatory environment, while also possessing the advantages of high drug loading capacity, high encapsulation efficiency, and suitable particle size for transdermal absorption.

[0008] Another objective of this invention is to provide a method for preparing the micelles, which employs a thin-film dispersion-dialysis process, making the process more operable, with low organic solvent residue, uniform particle size, and good batch repeatability, making it suitable for large-scale production.

[0009] Another objective of this invention is to provide applications for the drug-loaded micelles, expanding their use in topical preparations for skin inflammation repair, wound healing, scar fading, and post-medical aesthetic repair, optimizing the pH compatibility of topical preparations, and improving the safety and comfort of clinical use.

[0010] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:

[0011] In a first aspect, the present invention provides a pH-sensitive asiaticoside drug-loaded micelle, which is prepared by encapsulating asiaticoside on an amphiphilic pH-sensitive block copolymer; wherein the amphiphilic pH-sensitive block copolymer is a methoxy polyethylene glycol-polylactic acid-glycolic acid-polyhistidine (mPEG-PLGA-PHis) triblock copolymer.

[0012] As one of the preferred technical solutions for the above-mentioned pH-sensitive asiaticoside drug-loaded micelles, wherein the mPEG-PLGA-PHis contains:

[0013] mPEG is methoxy polyethylene glycol with a number average molecular weight of 2000~5000 Da. If mPEG < 2000 Da, the hydrophilic barrier is insufficient, and it is easy to aggregate and adsorb. If mPEG > 5000 Da, the steric hindrance is large, and the transdermal resistance is increased.

[0014] PLGA is a polylactic acid-glycolic acid copolymer with a number-average molecular weight of 8000~30000 Da and a molar percentage of glycolic acid of 20-30%. Preferably, the molar percentage of glycolic acid in PLGA is 25%. When PLGA < 8000 Da, the hydrophobic core volume is insufficient, and the drug loading and encapsulation efficiency decreases significantly. When PLGA > 30000 Da, the difficulty of polymer micelle formation increases, and the particle size uniformity deteriorates.

[0015] PHis is a polyhistidine with a number-average molecular weight of 1000~5000 Da. When PHis < 1000 Da, the density of imidazole groups is low, resulting in insufficient pH response sensitivity. When PHis > 5000 Da, the hydrophilic ratio is too high, making it easy to leak into neutral environments and reducing structural stability.

[0016] As one of the preferred technical solutions for the above-mentioned pH-sensitive asiaticoside drug-loaded micelles, the mass ratio of mPEG:PLGA:PHis is 1:(2~4):(0.3~0.8); the preferred mass ratio of mPEG:PLGA:PHis is 1:3:0.5.

[0017] As one of the preferred technical solutions for the above-mentioned pH-sensitive asiaticoside drug-loaded micelles, the drug-loaded micelles have a asiaticoside loading of 8%~20%, an encapsulation efficiency of ≥75%, a particle size of 30~120nm, a particle size stability of >90% in a pH 7.0~7.4 environment for 72h, and a cumulative release rate of ≥85% in a pH 5.5 environment for 24h.

[0018] Furthermore, the surface of the pH-sensitive asiaticoside drug-loaded micelles may be coupled with collagen aptamers, fibronectin aptamers, or hyaluronic acid. In some specific embodiments of the present invention, the surface grafting rate can reach 3% to 8%.

[0019] In a second aspect, the present invention provides a method for preparing the pH-sensitive asiaticoside drug-loaded micelles, comprising the following specific steps:

[0020] (1) Dissolve mPEG-PLGA-PHis in a mixed solvent of dichloromethane: anhydrous ethanol = 3~5:1 (V / V) and stir magnetically to obtain polymer mother liquor;

[0021] (2) Dissolve asiaticoside in anhydrous ethanol and add it dropwise to the polymer mother liquor. Stir at room temperature in the dark for 1-2 hours to obtain the drug-loaded mixture.

[0022] (3) Thin film dispersion method: The drug-loaded mixture is rotary evaporated at 35~45℃ for 40~60min to remove the solvent until a uniform film is formed. Then, pH 7.4 phosphate buffer is added and ultrasonically hydrated at 100~300W and 20~40kHz for 20~40min to obtain a coarse micelle solution.

[0023] (4) Use a dialysis bag with a molecular weight cutoff of 3500 Da, dialyze at 2~8℃ for 12~24h, change the solution every 4~6h, and filter with a 0.22μm microporous membrane to obtain the solution.

[0024] Furthermore, the method for preparing the micelles also includes a targeted modification step: adding a targeted ligand to the filtered micelle stock solution and stirring at room temperature for 6-8 hours to complete the coupling.

[0025] In a third aspect, the present invention provides the application of the pH-sensitive asiaticoside drug-loaded micelles.

[0026] Specifically, the pH-sensitive asiaticoside drug-loaded micelles are used to prepare topical preparations for skin inflammation repair, wound healing, scar fading, and post-medical aesthetic repair.

[0027] Furthermore, the topical formulation includes gels, creams, sprays, and films. In some specific embodiments of the present invention, the drug-loaded micelles may be compounded with moisturizing and repairing ingredients such as ceramides, sodium hyaluronate, and panthenol, with an addition amount of 0.5% to 5% of the total mass of the formulation, to prepare the formulation.

[0028] Furthermore, the pH value of the topical preparation is adjusted to 6.0-7.0 to suit the physiological environment of the skin.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. This invention employs a triblock synergistic structure of mPEG-PLGA-PHis. PLGA provides a hydrophobic drug-loading core to improve encapsulation efficiency and drug loading, while mPEG enhances water solubility and structural stability. The imidazole group of PHis rapidly protonates at pH 5.0~6.0 to trigger micelle depolymerization, achieving neutral stability and precise drug release in acidic conditions. This solves the contradiction between uncontrollable drug release and the inability to balance stability and drug loading in conventional biblock carriers.

[0031] 2. The drug-loaded micelles prepared by this invention have a particle size of 30~120nm, which is suitable for transdermal absorption. The drug loading is 8%~20% and the encapsulation efficiency is ≥75%. Synergistic effects are obtained through precise screening of chain segment ratio and molecular weight, which solves the problems of poor water solubility, uneven dispersion and low transdermal enrichment efficiency of traditional asiaticoside preparations.

[0032] 3. The present invention employs a membrane dispersion-dialysis combined process, which results in low organic solvent residue, uniform particle size, and good batch repeatability, meeting the requirements for industrialization and external use safety.

[0033] 4. The drug-loaded micelles provided by this invention can be used to prepare various topical dosage forms, and can be combined with repairing ingredients to achieve synergistic effects of anti-inflammatory repair and barrier moisturizing, making them widely applicable in clinical practice. Detailed Implementation

[0034] The present invention will now be described in detail with reference to embodiments, but these should not be construed as limiting the scope of protection of the present invention. Various improvements and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, which will be apparent to those skilled in the art. Other embodiments derived from this specification will be obvious to those skilled in the art. The specification and embodiments of this invention are merely exemplary.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0036] Unless otherwise specified, the reagents and materials used in the following embodiments of the present invention are all commercially available products.

[0037] The triblock copolymers used in this invention can be prepared using conventional methods in the art. For example, this invention provides a method for synthesizing mPEG-PLGA-PHis triblock copolymers:

[0038] 1. Using mPEG-OH as an initiator, L-lactide and glycolide ring-opening polymerization was initiated under stannous octoate catalysis, and the feed ratio was controlled to obtain mPEG-PLGA with lactic acid:glycolic acid ratio of 70:30~80:20;

[0039] 2. The terminal hydroxyl groups of mPEG-PLGA were activated to carboxyl groups, and then grafted with His-NCA by condensation. The reaction time and monomer amount were controlled to obtain mPEG-PLGA-PHis with a number average molecular weight of 1000~5000 Da.

[0040] Key performance indicator detection and calculation methods:

[0041] 72h particle size stability: The initial average particle size of micelles and the average particle size after 72h in a neutral environment of 7.0~7.4 were detected by DLS dynamic light scattering method. The stability (%) was calculated according to the formula: stability (%) = (72h average particle size of micelles / initial average particle size) × 100%.

[0042] Grafting rate: The grafting rate of targeted modification groups on the micelle surface is calculated using the formula: Grafting rate (%) = (1 − mass of free modification groups / total mass of modification groups fed) × 100%; Nucleic acid aptamer modification groups are detected by UV or HPLC methods at a detection wavelength of 260 nm; Hyaluronic acid is detected by carbazole colorimetric method at a detection wavelength of 525 nm.

[0043] Drug loading, encapsulation efficiency, and cumulative release rate were all calculated using HPLC (high performance liquid chromatography) to detect the content of asiaticoside.

[0044] Example 1: Single-factor screening: LA:GA=75:25 optimal vector

[0045] mPEG 3000Da, PLGA 20000Da, PHis 3000Da, LA:GA=75:25, mass ratio 1:3:0.5.

[0046] I. Synthesis method of mPEG-PLGA-PHis triblock:

[0047] (1) Using mPEG-OH as an initiator, L-lactide and glycolide ring-opening polymerization were initiated under the catalysis of stannous octoate, and the molar ratio of feed was controlled to obtain mPEG-PLGA with lactic acid: glycolic acid 75:25;

[0048] (2) The terminal hydroxyl groups of mPEG-PLGA were activated to carboxyl groups, and then condensed and grafted with His-NCA. The reaction time and monomer amount were controlled to obtain mPEG-PLGA-PHis with a number average molecular weight of 3000 Da.

[0049] (3) The molecular weight was determined by GPC method, and the number average molecular weights of mPEG, PLGA and PHis were 3002 Da, 19985 Da and 2997 Da, respectively. The chain segment composition was characterized by ¹H-NMR, and the molar ratio of LA:GA was 75.1:24.9, which was consistent with the design value.

[0050] II. Preparation method of pH-sensitive asiaticoside drug-loaded micelles:

[0051] (1) Dissolve 3.5g of mPEG-PLGA-PHis in 40mL of a mixed solvent of dichloromethane: anhydrous ethanol = 4:1 (V / V) (concentration 87.5mg / mL) and stir magnetically to obtain polymer mother liquor;

[0052] (2) Dissolve 0.5g of asiaticoside in 5mL of anhydrous ethanol (concentration 100mg / mL), add it dropwise to the polymer mother liquor, and stir at room temperature in the dark for 1.5h to obtain the drug-loaded mixture;

[0053] (3) The drug-loaded mixture was rotary evaporated at 40°C for 50 min to remove the solvent until a uniform film was formed. Then, pH 7.4 phosphate buffer was added and ultrasonically hydrated at 200 W / 30 kHz for 30 min to obtain a coarse micelle solution.

[0054] (4) Use a dialysis bag with a molecular weight cutoff of 3500 Da, dialyze at 4℃ for 18 hours, change the solution every 4 to 6 hours, and filter with a 0.22 μm microporous membrane to obtain the solution.

[0055] Micelle performance test results: particle size 65nm (DLS method), drug loading 15.2% (HPLC method), encapsulation efficiency 82.5% (HPLC method), 72h particle size stability 93.2% (=(72h particle size 60.6nm / initial particle size 65nm)×100%), 24h cumulative release rate at pH 5.5 89.6% (HPLC method).

[0056] Example 2: Investigating the effect of different LA:GA molar ratios on micelle properties

[0057] The difference between this embodiment and Example 1 is that, in the triblock synthesis process, the molar ratio of lactic acid to glycolic acid was controlled to obtain mPEG-PLGA of 60:40 and 90:10. All other process parameters and testing methods are the same as in Example 1. Micellar performance data are listed in Table 1.

[0058] As shown in Table 1, the micelles exhibit the best overall performance when the LA:GA molar ratio is 75:25. Excessive GA content reduces both the encapsulation and release of the drug-loaded micelles; conversely, insufficient GA content leads to slow drug release and easy aggregation upon standing. Therefore, a LA:GA molar ratio of 75:25 is the optimal choice for subsequent experiments.

[0059] Table 1. Effect of different LA:GA molar ratios on micelle properties

[0060]

[0061] Example 3: Optimization of PHis molecular weight

[0062] With a fixed LA:GA ratio of 75:25, mPEG 3000 Da, and PLGA 20000 Da, and a mass ratio of 1:3:0.5, during the synthesis of the triblock, the number-average molecular weight of PHIs was controlled to be 1000 Da, 3000 Da, and 6000 Da, respectively. The remaining processes and detection methods were the same as in Example 1. The release rates of micelles with different PHIs molecular weights at pH 5.5 after 24 hours were 78.2%, 89.6%, and 70.1%, respectively. Among them, the micelles prepared with PHIs 6000 Da had a drug leakage rate of 15.3% after 24 hours in a neutral environment, and the structural stability was significantly reduced.

[0063] The results showed that the number-average molecular weight of PHis was in the range of 1000~5000 Da, and the pH response drug release performance was optimal at 3000 Da. Beyond this range, the response sensitivity was insufficient or the stability decreased.

[0064] Example 4: Triblock mass ratio optimization

[0065] With the optimal segment molecular weights (mPEG 3000 Da, PLGA 20000 Da, PHis 3000 Da) and LA:GA = 75:25 fixed, only the mass ratio of mPEG:PLGA:PHis was adjusted. The remaining processes and testing methods were the same as in Example 1. The effect of mass ratio on micelle performance was investigated: The micelles prepared with a mass ratio of 1:1.5:0.2 had an encapsulation efficiency of 65.4%, insufficient hydrophobic core volume, and decreased drug loading capacity. When the mass ratio was 1:4.5:1.0, the micelle structure was loose, the drug leakage rate reached 18.7% in a neutral environment after 24 hours, the particle size distribution PDI > 0.3, and the uniformity deteriorated.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the carrier is an mPEG-PLGA binary block copolymer, while the other processes and testing methods are the same as in Example 1.

[0068] The prepared drug-loaded micelles exhibited the following properties: drug loading of 12.7%, encapsulation efficiency of 70.2%, particle size stability of 88.3% over 72 hours, and release rate of 52.3% over 24 hours at pH 5.5. It is evident that the micelles in this comparative example lack precise pH response and rely solely on the slow release of the drug through the hydrolysis of PLGA ester bonds, which is insufficient to meet the rapid drug release requirements of the slightly acidic environment in inflammation.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the carrier is an mPEG-PHis binary block copolymer, while the other processes and testing methods are the same as in Example 1.

[0071] The prepared drug-loaded micelles exhibited the following properties: drug loading of 7.4%, encapsulation efficiency of 58.7%, particle size stability of 75.6% over 72 hours, drug leakage rate of 22.5% over 24 hours in a neutral environment, and release rate of 81.2% over 24 hours at pH 5.5. It is evident that the micelles in this comparative example lack sufficient hydrophobic cores, exhibit poor drug loading and structural stability, and fail to meet the performance requirements of topical formulations.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that mPEG is 1000Da, PLGA is 40000Da, and PHis is 6000Da; the rest are the same as in Example 1.

[0074] The properties of the drug-loaded micelles prepared were as follows: particle size 150~220nm, particle size distribution PDI=0.45, poor uniformity; encapsulation efficiency 69.4%, particle size stability 78.5% after 72h; in vitro transdermal test showed that the drug enrichment in the dermis decreased by 45.2% compared with Example 1, and transdermal absorption and stability decreased significantly.

[0075] Example 5: Collagen Aptamer Modification

[0076] Based on the micelles of Example 1, collagen aptamers (5'-GCGGATGGTGGGTGGGTGGTTGGGTGGAGGGGTGGC-3', Shanghai Sangon Biotech) were added to the filtered micelle stock solution at an amount of 2% of the carrier polymer mass. The mixture was stirred at room temperature for 6 hours. The grafting rate was calculated as 3.1% (UV method, 260nm) using the formula: Grafting rate (%) = (1 − mass of free ligand / total mass of feed) × 100%. In vitro transdermal absorption assays showed that the retention of the modified micelles in the dermal layer of the skin was increased by 12.3% compared to the unmodified micelles, indicating a significant improvement in targeted enrichment ability.

[0077] Example 6 Hyaluronic Acid Modification

[0078] Based on the micelles of Example 1, hyaluronic acid (molecular weight 10,000~30,000 Da, pharmaceutical grade, Bloomage Biotech) was added to the filtered micelle stock solution at an amount of 4% of the carrier polymer mass. The mixture was stirred at room temperature for 8 hours, resulting in a grafting rate of 7.8% (carbazole colorimetric method, 525 nm). The topical formulation prepared with this modified micelle showed a 30% improvement in skin spreadability and a 25% reduction in transdermal water loss compared to the unmodified micelle formulation, significantly improving skin feel and moisturizing effects.

[0079] Example 7 Preparation of gelling agent

[0080] Example 1: 100 mL of micelle stock solution was swollen with 1.5 g of carbomer 940, and the pH was adjusted to 6.5 with triethanolamine. Sodium hyaluronate (1% of the total mass of the preparation) and panthenol (0.5%) were added, and the mixture was stirred thoroughly to obtain a repair gel. This gel has good spreadability, is non-sticky, has a pH suitable for the skin's physiological environment, and causes no skin irritation. It is suitable for repairing superficial wounds after cosmetic procedures.

[0081] Example 8 Preparation of Cream

[0082] Oil phase: 15g petrolatum, 10g liquid paraffin, 5g stearic acid, melted at 70℃; Aqueous phase: 50mL micelle stock solution from Example 1, 5g glycerin, 0.1g methylparaben, melted at 70℃; The aqueous phase was slowly added to the oil phase, stirred, and cooled to room temperature. The pH was adjusted to 6.8 with triethanolamine to obtain a scar-fading cream. This cream has a fine texture, good skin adhesion, and a pH suitable for the skin, making it suitable for fading hypertrophic scars and post-traumatic scars.

[0083] This invention addresses the core issues of poor dispersion, insufficient enrichment, and uncontrollable drug release in topical formulations of Centella asiatica extract by precisely screening the segment ratio and molecular weight of the mPEG-PLGA-PHis triblock copolymer, combined with well-defined process parameters and performance testing methods. The carrier structure exhibits excellent pH-responsive synergistic effects, and the preparation process, after parameter refinement, is more operable and suitable for large-scale production. It can be formulated into various topical dosage forms such as gels and creams, and the pH of the formulation is optimized to the physiological range of the skin. When combined with moisturizing and repairing ingredients, it achieves synergistic anti-inflammatory repair and skin barrier protection effects, demonstrating significant industrial applicability and clinical application value.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pH-sensitive asiaticoside drug-loaded micelle, characterized in that, It was prepared by encapsulating asiaticoside on an amphiphilic pH-sensitive block copolymer; the amphiphilic pH-sensitive block copolymer is an mPEG-PLGA-PHis triblock copolymer.

2. The pH-sensitive asiaticoside drug-loaded micelles according to claim 1, characterized in that, In the mPEG-PLGA-PHis triblock copolymer, the number average molecular weight of mPEG is 2000~5000 Da, the number average molecular weight of PLGA is 8000~30000 Da, the molar ratio of lactic acid to glycolic acid is 70%-80%:20-30%, the number average molecular weight of PHis is 1000~5000 Da, and the mass ratio of mPEG, PLGA and PHis is 1:(2~4):(0.3~0.8).

3. The pH-sensitive asiaticoside drug-loaded micelles according to claim 1, characterized in that, The drug-loaded micelles contain 8% to 20% asiaticoside and have a particle size of 30 to 120 nm.

4. The pH-sensitive asiaticoside drug-loaded micelles according to claim 1, characterized in that, The drug-loaded micelles are surface-coupled with collagen aptamers, fibronectin aptamers, or hyaluronic acid.

5. The method for preparing pH-sensitive asiaticoside drug-loaded micelles according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Dissolve mPEG-PLGA-PHis in an organic solvent to obtain polymer mother liquor; dissolve asiaticoside in anhydrous ethanol to obtain asiaticoside anhydrous ethanol solution; (2) Add the anhydrous ethanol solution of asiaticoside dropwise to the polymer mother liquor and stir at room temperature in the dark for 1-2 hours to obtain the drug-loaded mixture; (3) The drug-loaded mixture was rotary evaporated to remove the solvent until a uniform film was formed. Then, pH 7.4 phosphate buffer was added and ultrasonically hydrated to obtain a coarse micelle solution. (4) The crude micelle solution is obtained by dialysis and filtration through a microporous membrane.

6. The method for preparing pH-sensitive asiaticoside drug-loaded micelles according to claim 5, characterized in that, In step (1), the mass-volume concentration of the polymer mother liquor is 80~90 mg / mL; the mass-volume concentration of the anhydrous ethanol solution of asiaticoside is 100 mg / mL.

7. The method for preparing pH-sensitive asiaticoside drug-loaded micelles according to claim 5, characterized in that, The rotary evaporation temperature in step (3) is 35~45℃; the ultrasonic hydration conditions are ultrasonic hydration with a power of 100~300W and a frequency of 20~40kHz for 20~40min.

8. The method for preparing pH-sensitive asiaticoside drug-loaded micelles according to claim 5, characterized in that, The dialysis in step (4) is performed by using a dialysis bag with a molecular weight cutoff of 3500 Da, dialysis at 2~8℃ for 12~24 hours, and changing the solution every 4~6 hours.

9. The method for preparing pH-sensitive asiaticoside drug-loaded micelles according to claim 5, characterized in that, The preparation method of the micelles also includes a targeted modification step: adding a targeted ligand to the filtered micelle stock solution and stirring at room temperature for 6-8 hours to complete the coupling.

10. The use of the pH-sensitive asiaticoside drug-loaded micelles according to any one of claims 1-4 in the preparation of topical skin formulations, characterized in that, The topical skin preparation is used for skin inflammation repair, wound healing, scar fading, or post-medical aesthetic repair.

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