Preparation method of core-shell structure polylactic acid microspheres for promoting collagen generation

Abstract

The invention relates to the technical field of medical cosmetology, in particular to a preparation method of core-shell structure polylactic acid microspheres for promoting collagen generation, which comprises the following steps: dissolving polylactic acid and first PEG-PLA in an organic solvent to form an oil phase; adding the oil phase into an emulsifier aqueous solution, and emulsifying to form an oil-in-water primary emulsion; adding the primary emulsion into a compound second PEG-PLA aqueous solution containing different molecular weights, and carrying out a curing reaction; in a solvent volatilization process, a stable and compact hydrophilic shell layer is constructed on the surface of the microsphere by utilizing the embedding effect of a second PEG-PLA hydrophobic segment and space complementation of molecules with different molecular weights. The microsphere has a hydrophobic polylactic acid core and a hydrophilic PEG-PLA shell, and is good in suspension property in an aqueous solution and high in biocompatibility; when being applied in vivo, the collagen can be rapidly degraded through the shell to stimulate early collagen regeneration, long-term physical support is provided by the inner core, and both quick effect and long effect are taken into account.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical cosmetology, in particular to a preparation method of a core-shell structure polylactic acid microsphere for promoting collagen production. BACKGROUND

[0002] Polylactic acid is widely used in the field of medical devices such as surgical sutures, bone nails, and tissue engineering scaffolds due to its good biocompatibility and biodegradability. In the field of medical cosmetology, polylactic acid microspheres have been used as dermal fillers for more than twenty years. The mechanism of action is that lactic acid produced during the in vivo degradation of polylactic acid has a signal molecule function, which can up-regulate the activity of proline hydroxylase and stimulate fibroblasts to secrete collagen, thereby achieving the effect of filling facial depressions, improving wrinkles, and tightening the skin.

[0003] However, the existing polylactic acid microsphere products still have the following technical bottlenecks in clinical application: 1. Delayed onset and back-off phenomenon: The surface of traditional PLA microspheres is hydrophobic, and after being injected into the deep dermis, only the physical occupation of the carrier (such as sodium carboxymethyl cellulose) and the microspheres themselves produces an immediate effect. As the carrier is absorbed within 3-7 days, the filling effect will have a significant back-off period. It usually takes 15 days or even longer for PLA to degrade enough lactic acid to stimulate collagen regeneration, resulting in a long effect window period after injection.

[0004] 2. Inflammation risk: The hydrophobic PLA surface easily causes non-specific protein adsorption, leading to redness, nodules, and other inflammations caused by foreign body reactions at the injection site.

[0005] 3. Poor suspension: PLA microspheres easily aggregate and precipitate in aqueous solvents, leading to needle blockage during injection and uneven distribution in tissues.

[0006] 4. Limitations of single material: Although some products attempt to use polyethylene glycol-polylactic acid (PEG-PLA) copolymer microspheres to improve hydrophilicity, PEG-PLA degrades too quickly to maintain long-term filling support.

[0007] Existing surface modification techniques mostly use physical adsorption methods to modify the microspheres after they are formed, which has the problem of weak shell bonding and easy shedding. Or the preparation process is complex, involving a large amount of toxic solvent residues, which is not suitable for industrial production.

[0008] Therefore, it is an urgent need in the industry to develop a modified polylactic acid microsphere that can quickly stimulate collagen production, maintain long-term support, and have good suspension and biocompatibility. SUMMARY

[0009] In view of the deficiencies of the prior art, the present application provides a preparation method of collagen production promoting core-shell structure polylactic acid microspheres, which introduces polyethylene glycol-polylactic acid block copolymer molecules by a special two-step method, and constructs a stable hydrophilic shell layer by using a compounding strategy of polyethylene glycol-polylactic acid block copolymers with different molecular weights, so as to realize the unity of rapid availability and long-term support.

[0010] To achieve the above object, the present application is implemented by the following technical scheme: a preparation method of collagen production promoting core-shell structure polylactic acid microspheres, comprising the following steps: Step S1, oil phase preparation Dissolve polylactic acid and first polyethylene glycol-polylactic acid block copolymer in an organic solvent to form a uniform oil phase solution; Step S2, primary emulsion preparation Dissolve an emulsifier in water to prepare an aqueous phase, add the oil phase solution to the aqueous phase, and form an oil-in-water (O / W) type primary emulsion by shearing or ultrasonic action; Step S3, shell layer assembly and solidification Prepare an aqueous solution containing second polyethylene glycol-polylactic acid block copolymer as a solidification outer aqueous phase; add the primary emulsion to the solidification outer aqueous phase for solidification reaction; Step S4, post-treatment Under stirring conditions, volatilize the organic solvent, and after the microspheres are solidified, separate, wash, and dry to obtain the core-shell structure polylactic acid microspheres; The hydrophilic segment of the second polyethylene glycol-polylactic acid block copolymer faces the outside of the microspheres, and the hydrophobic segment is intertwined or embedded with the polylactic acid segment on the surface of the microspheres during the solvent volatilization process, forming a stable core-shell structure.

[0011] Preferably, the second polyethylene glycol-polylactic acid block copolymer in step S3 is compounded from at least two polyethylene glycol-polylactic acid molecules with different molecular weights; The compounding system includes high molecular weight polyethylene glycol-polylactic acid and low molecular weight polyethylene glycol-polylactic acid, wherein the low molecular weight polyethylene glycol-polylactic acid fills the adsorption voids formed by the high molecular weight polyethylene glycol-polylactic acid on the surface of the microspheres, so as to overcome the steric hindrance and improve the shell coverage.

[0012] Preferably, in the second polyethylene glycol-polylactic acid block copolymer, the number average molecular weight of the PEG segment is 200-20000 Da, and the number average molecular weight of the PLA segment is 200-200000 Da; The PEG segment molecular weight of the high molecular weight polyethylene glycol-polylactic acid is ≥5000 Da, and the PEG segment molecular weight of the low molecular weight polyethylene glycol-polylactic acid is ≤2000 Da.

[0013] Preferably, in step S1, the polylactic acid is selected from one or more of poly-L-lactic acid, poly-D-lactic acid or poly-DL-lactic acid; The mass ratio of the polylactic acid to the first polyethylene glycol-polylactic acid block copolymer is (1-1000):1; The organic solvent is dichloromethane, and the mass ratio of the sum of the polylactic acid and the first polyethylene glycol-polylactic acid block copolymer to the organic solvent is 1:(1-1000).

[0014] Preferably, in step S2, the emulsifier is polyvinyl alcohol, and the mass concentration of the polyvinyl alcohol aqueous solution is 0.1%-20%; The volume ratio of the oil phase solution to the water phase is 1:(1-1000).

[0015] Preferably, in step S3, the mass concentration of the second polyethylene glycol-polylactic acid block copolymer in the solidified external water phase is 0.01%-20%; The volume ratio of the primary emulsion to the solidified external water phase is 1:(1-1000).

[0016] Preferably, the solidification reaction process in step S3 comprises: slowly adding the primary emulsion to the solidified external water phase, and maintaining continuous stirring for 2-24 hours to control the solvent evaporation rate, so that the PLA segment of the second polyethylene glycol-polylactic acid block copolymer molecule completes self-assembly anchoring on the surface of the microspheres.

[0017] Preferably, the microspheres have a hydrophobic inner core composed of polylactic acid and a small amount of the first polyethylene glycol-polylactic acid block copolymer, and a hydrophilic outer shell composed of the second polyethylene glycol-polylactic acid block copolymer. The particle size of the microspheres is monodisperse, and the sedimentation time in an aqueous solution is greater than 30 minutes.

[0018] Preferably, the surface of the microspheres is densely coated by polyethylene glycol-polylactic acid block copolymers with different molecular weights, and has the dual release characteristics of delaying the degradation of the inner core polylactic acid and rapidly releasing the polyethylene glycol-polylactic acid block copolymer to stimulate collagen regeneration.

[0019] Preferably, the core-shell structure polylactic acid microspheres are used in the preparation of a facial filler, a subcutaneous injection or a tissue engineering scaffold material.

[0020] The application provides a preparation method of core-shell structure polylactic acid microspheres for promoting collagen production. 1. The present invention utilizes the PEG-PLA molecules in the outer shell, which have strong hydrophilicity and fast degradation speed, to release lactic acid early in the injection period, rapidly stimulating collagen production and filling the fallback period of traditional PLA microspheres; the high molecular weight PLA in the core degrades more slowly, providing continuous physical support and long-term collagen stimulation for 24-38 months or even longer.

[0021] 2. This invention embeds the hydrophobic segments of PEG-PLA into the surface of the microspheres during the microsphere curing process. Compared to traditional physical adsorption after microsphere formation, this results in a stronger shell binding force and less detachment. The hydrophilic PEG outer layer effectively reduces non-specific protein adsorption, lowering the risk of postoperative redness and nodules.

[0022] 3. This invention uses PEG-PLA with different molecular weights to fill the gaps between macromolecules, making the hydrophilic modification of the microsphere surface more thorough, significantly improving the suspension performance of the microspheres in aqueous solution, facilitating clinical operation and reducing needle clogging. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the core-shell structured polylactic acid microspheres of the present invention; Figure 2 This is a particle size characterization diagram of the core-shell structured polylactic acid microspheres of the present invention; Figure 3 This is an electron microscopy characterization image of the core-shell structured polylactic acid microspheres of the present invention; Figure 4 This is a characterization diagram of the glass transition temperature of the core-shell structured polylactic acid microspheres of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1: like Figures 1-4 As shown, this embodiment of the invention provides a method for preparing core-shell structured polylactic acid microspheres that promote collagen production, comprising the following steps: S1 oil phase preparation: Poly(L-lactic acid) (Mn=100kDa) and polyethylene glycol-polylactic acid block copolymer (PEG2k-PLA 10k) were dissolved in dichloromethane to form a homogeneous oil phase solution. The mass ratio of poly(L-lactic acid) to polyethylene glycol-polylactic acid block copolymer was 10:1, and the mass ratio of total polymer to dichloromethane was 1:10.

[0026] S2 Aqueous Phase Preparation: Dissolve medium-viscosity polyvinyl alcohol in pure water to prepare a 1% polyvinyl alcohol aqueous solution.

[0027] S3 Emulsification: The oil phase solution is poured into the aqueous phase solution at a volume ratio of 1:10, and the mixture is vigorously stirred using a high-shear emulsifier to produce a stable oil-in-water primary emulsion.

[0028] S4 Curing and Assembly: Prepare the curing external aqueous phase, with two different molecular weight polyethylene glycol-polylactic acid block copolymers: one is a high molecular weight polyethylene glycol-polylactic acid block copolymer (PEG 5k-PLA 20k), and the other is a low molecular weight polyethylene glycol-polylactic acid block copolymer (PEG 600-PLA 3k), with a total mass concentration of 1%. Slowly pour the primary emulsion into the curing external aqueous phase at a volume ratio of 1:10.

[0029] S5 Post-processing: Stir overnight at room temperature until dichloromethane completely evaporates and the microspheres solidify. Collect the microspheres by centrifugation, wash them three times with water, and freeze-dry to obtain the finished product.

[0030] Results: The obtained microspheres had high PEG-PLA coverage on their surface, excellent dispersibility in water, and a settling time of approximately 60 minutes.

[0031] Example 2: This invention provides a method for preparing core-shell structured polylactic acid microspheres that promote collagen production, comprising the following steps: Preparation of the S1 oil phase: Poly(D-lactic acid) and the first polyethylene glycol-polylactic acid block copolymer were dissolved in dichloromethane. The mass ratio of poly(D-lactic acid) to the first polyethylene glycol-polylactic acid block copolymer was 5:1; the polymer to solvent ratio was 1:9.

[0032] S2 aqueous phase preparation: Prepare a 1.5% low-viscosity PVA aqueous solution.

[0033] S3 emulsification: The oil phase and water phase are mixed at a volume ratio of 1:7 and then ultrasonically emulsified.

[0034] S4 Curing and Assembly: Pour the primary emulsion into a container containing pure water.

[0035] S5 post-processing: Same as Example 1.

[0036] Results: The microspheres took approximately 30 minutes to settle in water.

[0037] Example 3: This invention provides a method for preparing core-shell structured polylactic acid microspheres that promote collagen production, comprising the following steps: S1 oil phase preparation: Polyracemic lactic acid was dissolved in dichloromethane at a mass ratio of 1:8. In this embodiment, the first polyethylene glycol-polylactic acid block copolymer was not added to the oil phase, aiming to test the effect of simple external coating.

[0038] S2 Aqueous Phase Preparation: High-viscosity polyvinyl alcohol is dissolved in pure water to prepare a high-viscosity polyvinyl alcohol solution with a concentration of 0.8%.

[0039] S3 Emulsification: The oil phase solution is poured into the aqueous phase solution at a volume ratio of 1:9, and the mixture is vigorously stirred using a high-shear emulsifier to produce a stable oil-in-water primary emulsion.

[0040] S4 Curing and Assembly: Prepare the curing aqueous phase, which contains 2% PEG-PLA mixture. The PEG segment has a molecular weight range of 300-10,000 Da, and the PLA segment has a molecular weight range of 2,000-10,000 Da (broad distribution). Slowly pour the primary emulsion into the curing aqueous phase at a volume ratio of 1:8.

[0041] S5 post-processing: Same as Example 1.

[0042] Results: The microspheres settled in water in about 35 minutes.

[0043] To verify the effectiveness of the present invention, the following comparative tests were conducted: Comparative Example 1: Traditional poly(L-lactic acid) microspheres (using only polyvinyl alcohol as an emulsifier, without adding PEG-PLA to the oil phase or the cured phase).

[0044] Comparative Example 2: Microspheres by physical adsorption method (after preparing poly-L-lactic acid microspheres, they were then immersed in PEG-PLA solution and shaken to adsorb).

[0045] Test method: 1. Suspension test: Disperse the same mass of microspheres in the same volume of pure water, shake well and let stand, and record the time when obvious stratification / sedimentation occurs.

[0046] 2. Morphological observation: SEM was used to observe the sphericity and surface condition of the microspheres.

[0047] The test results are shown in the table below: in conclusion: The data from Example 1 fully demonstrate that the microspheres prepared using an internal blending + external curing with a PEG-PLA-containing curing solution and a blend of different molecular weights exhibit optimal suspension stability. This indicates that a large number of hydrophilic PEG segments were successfully grafted onto the microsphere surface, and the binding is strong. This highly hydrophilic surface can be more quickly wetted by body fluids in vivo, accelerating the hydrolysis of the surface PEG-PLA, thereby rapidly releasing lactic acid signaling molecules and stimulating early collagen production; while the PLA core ensures long-term filling effect.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing core-shell structured polylactic acid microspheres that promote collagen production, characterized in that, Includes the following steps: Step S1: Oil phase preparation Polylactic acid and the first polyethylene glycol-polylactic acid block copolymer were dissolved in an organic solvent to form a homogeneous oil phase solution; Step S2: Preparation of the primary emulsion An aqueous phase is prepared by dissolving an emulsifier in water, and the oil phase solution is added to the aqueous phase. An oil-in-water (O / W) type primary emulsion is formed by shearing or ultrasonic action. Step S3: Shell assembly and curing An aqueous solution containing a second polyethylene glycol-polylactic acid block copolymer is prepared as the curing external aqueous phase; the primary emulsion is added to the curing external aqueous phase to carry out a curing reaction; Step S4, Post-processing The organic solvent was evaporated under stirring conditions. After the microspheres solidified, they were separated, washed, and dried to obtain the core-shell structured polylactic acid microspheres. In this process, the hydrophilic segment of the second polyethylene glycol-polylactic acid block copolymer faces the outside of the microsphere, while the hydrophobic segment becomes entangled or embedded with the polylactic acid chain segments on the surface of the microsphere during solvent evaporation, forming a stable core-shell structure.

2. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 1, characterized in that, The second polyethylene glycol-polylactic acid block copolymer in step S3 is composed of at least two polyethylene glycol-polylactic acid molecules with different molecular weights. The compound system includes high molecular weight polyethylene glycol-polylactic acid and low molecular weight polyethylene glycol-polylactic acid, wherein the low molecular weight polyethylene glycol-polylactic acid fills the adsorption voids formed by the high molecular weight polyethylene glycol-polylactic acid on the surface of the microspheres to overcome steric hindrance and improve the shell coverage.

3. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 2, characterized in that, In the second polyethylene glycol-polylactic acid block copolymer, the number average molecular weight of the PEG segment is 200-20000 Da, and the number average molecular weight of the PLA segment is 200-200000 Da. The high molecular weight polyethylene glycol-polylactic acid has a PEG segment molecular weight ≥ 5000 Da, and the low molecular weight polyethylene glycol-polylactic acid has a PEG segment molecular weight ≤ 2000 Da.

4. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 1, characterized in that, In step S1, the polylactic acid is selected from one or more of poly-L-lactic acid, poly-D-lactic acid, or polyracemic lactic acid; The mass ratio of polylactic acid to the first polyethylene glycol-polylactic acid block copolymer is (1-1000):1; The organic solvent is dichloromethane, and the mass ratio of the sum of the masses of polylactic acid and the first polyethylene glycol-polylactic acid block copolymer to the mass of the organic solvent is 1:(1-1000).

5. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 1, characterized in that, In step S2, the emulsifier is polyvinyl alcohol, and the mass concentration of the polyvinyl alcohol aqueous solution is 0.1%-20%. The volume ratio of the oil phase solution to the aqueous phase is 1:(1-1000).

6. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 1, characterized in that, In step S3, the mass concentration of the second polyethylene glycol-polylactic acid block copolymer in the cured external aqueous phase is 0.01%-20%; The volume ratio of the primary emulsion to the solidified external aqueous phase is 1:(1-1000).

7. The method for preparing core-shell polylactic acid microspheres that promote collagen production according to claim 1, characterized in that, The curing reaction process in step S3 includes: slowly adding the primary emulsion dropwise into the external aqueous phase of curing while maintaining continuous stirring for 2-24 hours to control the solvent evaporation rate, so that the PLA segments of the second polyethylene glycol-polylactic acid block copolymer molecules can complete self-assembly and anchoring on the surface of the microspheres.

8. The core-shell polylactic acid microspheres for promoting collagen production prepared by the method according to any one of claims 1-7, characterized in that, The microspheres have a hydrophobic core composed of polylactic acid and a small amount of a first polyethylene glycol-polylactic acid block copolymer, and a hydrophilic shell composed of a second polyethylene glycol-polylactic acid block copolymer. The microspheres exhibit a monodisperse particle size distribution and a settling time of more than 30 minutes in aqueous solution.

9. The core-shell structured polylactic acid microspheres according to claim 8, characterized in that, The surface of the microspheres is densely coated with polyethylene glycol-polylactic acid block copolymers of different molecular weights, which has the dual release characteristics of delaying the degradation of the core polylactic acid and rapidly releasing the polyethylene glycol-polylactic acid block copolymer to stimulate collagen regeneration.

10. The application of the core-shell structured polylactic acid microspheres according to claim 8 in the preparation of facial fillers, subcutaneous injections, or tissue engineering scaffold materials.

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