阅读说明：本技术 一种含有海藻酸钠和聚乳酸的组合物及其制备方法和应用 (Composition containing sodium alginate and polylactic acid as well as preparation method and application thereof ) 是由 陈陆 张志玲 于 2021-10-09 设计创作，主要内容包括：本发明提出了一种含有海藻酸钠和聚乳酸的组合物及其制备方法和应用,属于医疗器械技术领域,包括以下重量百分含量的各组分：1-99％的可吸收聚乳酸材料和1-99％的海藻酸钠凝胶。本发明所提供的技术方案,能够抑制聚乳酸材料在有水环境中的降解速度,进而在临床上提供一种预罐封凝胶注射剂产品,使得在临床使用时,避免医护人员在使用前的复溶操作,可以直接使用,从而降低甚至避免因聚乳酸颗粒聚集而导致的皮下结节等不良反应。(The invention provides a composition containing sodium alginate and polylactic acid, a preparation method and application thereof, belonging to the technical field of medical appliances, and comprising the following components in percentage by weight: 1-99% of absorbable polylactic acid material and 1-99% of sodium alginate gel. The technical scheme provided by the invention can inhibit the degradation speed of the polylactic acid material in an aqueous environment, and further provides a pre-canned gel injection product in clinic, so that the re-dissolving operation of medical workers before use is avoided in clinical use, and the pre-canned gel injection product can be directly used, thereby reducing or even avoiding adverse reactions such as subcutaneous nodules and the like caused by aggregation of polylactic acid particles.)

1. The composition containing sodium alginate and polylactic acid is characterized by comprising the following components in percentage by weight: 1-99% of absorbable polylactic acid material and 1-99% of sodium alginate gel.

2. The composition containing sodium alginate and polylactic acid material according to claim 1, further comprising one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, hyaluronic acid, cross-linked hyaluronic acid, polycaprolactone, polylactic acid-glycolic acid copolymer, polyethylene glycol, polyvinyl alcohol, glycerol, mannitol, and lactose.

3. The composition containing sodium alginate and polylactic acid as claimed in claim 1, which is characterized by comprising the following components in percentage by weight: 1-50% of absorbable polylactic acid material and 50-99% of sodium alginate gel; preferably, 5% -40% of absorbable polylactic acid material and 60% -95% of sodium alginate gel; more preferably, 10% -35% of absorbable polylactic acid material and 65% -90% of sodium alginate gel.

4. The composition containing sodium alginate and polylactic acid as claimed in claim 1, wherein the absorbable polylactic acid material is at least one of dextrorotatory polylactic acid, levorotatory polylactic acid, meso-polylactic acid and racemic polylactic acid.

5. The composition containing sodium alginate and polylactic acid as claimed in any one of claims 1 to 4, wherein the absorbable polylactic acid material is in the form of microparticles or microspheres.

6. The composition containing sodium alginate and polylactic acid as claimed in claim 5, wherein more than 90% of said microspheres have a particle size of 5-200 um; preferably, more than 90% of the microspheres have the particle size of 10-100 um; more preferably, more than 90% of the microspheres have a particle size of between 40 and 60 um.

7. The composition containing sodium alginate and polylactic acid as claimed in any one of claims 1 to 6, wherein the absorbable polylactic acid material is suspended in a gel of sodium alginate.

8. A process for the preparation of a composition comprising sodium alginate and polylactic acid, as claimed in any one of claims 1 to 7, comprising the steps of:

(1) preparing polylactic acid microspheres or polylactic acid particles;

(2) and adding the polylactic acid microspheres or polylactic acid particles into the sodium alginate gel, and uniformly dispersing to obtain the composition containing the sodium alginate and the polylactic acid.

9. The method according to claim 8, wherein the polylactic acid microspheres are prepared by the following steps: dissolving polylactic acid in an organic solvent to prepare a polylactic acid solution; dripping polylactic acid solution into polyvinyl alcohol aqueous solution by adopting a piezoelectric micro-spraying technology, and obtaining polylactic acid microspheres under the stirring condition; and separating the polylactic acid microspheres from the solution, washing, drying and collecting to obtain the polylactic acid microspheres.

10. The method according to claim 9, wherein the organic solvent is at least one of dichloromethane, ethyl acetate, and n-propyl acetate; in the polylactic acid solution, the weight percentage of the polylactic acid is 0.1-30%; the molecular weight of the polylactic acid is 6-100 ten thousand g/mol; the size of the polylactic acid liquid drop sprayed by the piezoelectric micro-spraying technology is 10-300 mu m; the concentration of the polyvinyl alcohol aqueous solution is 1mg/mL-50 mg/mL.

11. The method according to claim 8, wherein the polylactic acid microspheres are prepared by the following steps: dissolving polylactic acid in an organic solvent to prepare a polylactic acid solution; mixing a polylactic acid solution with a polyvinyl alcohol aqueous solution, shearing the mixed solution at a high speed to obtain an emulsion, mixing the emulsion with purified water, magnetically stirring the mixed solution, centrifuging the magnetically stirred emulsion, washing with the purified water, precipitating, and freeze-drying to obtain the polylactic acid microspheres.

12. The method according to claim 11, wherein the polylactic acid has a weight average molecular weight of 40000-150000 g/mol; the organic solvent is at least one of dichloromethane, ethyl acetate and n-propyl acetate; in the polylactic acid solution, the weight percentage of the polylactic acid is 0.1-30%; in the polyvinyl alcohol aqueous solution, the weight percentage of polyvinyl alcohol is 0.1-5%; the shearing rate of the high-speed shearing is 1000-5000r/min, and the time of the high-speed shearing is 1-10 min; the magnetic stirring speed is 500-1000r/min, the magnetic stirring time is 6-24h, the centrifugal rotation speed is 2000-5000r/min, and the centrifugal time is 5-30 min.

13. The method according to claim 8, wherein the polylactic acid particles are prepared by the following method: and (2) keeping the polylactic acid at a low temperature for a period of time, putting the polylactic acid material into a jet mill for jet milling at the temperature environment, and collecting after milling to obtain polylactic acid particles.

14. The method according to claim 13, wherein the polylactic acid has a weight average molecular weight of 40000-150000 g/mol; the low-temperature keeping time is specifically kept for 2-4h in an environment of 0-4 ℃.

15. The injection filler is characterized by comprising the following components in percentage by weight: 5-50% of absorbable polylactic acid material and 50-95% of sodium alginate hydrogel; preferably 20-40% absorbable polylactic acid material, more preferably 30-35% absorbable polylactic acid material.

16. The injectable filling of claim 15, wherein the absorbable polylactic acid material is PLLA microspheres with a diameter distribution of 10-80 um; the microspheres are uniformly distributed in the sodium alginate hydrogel.

17. The injectable filling of claim 15, further comprising a pharmaceutically or cosmetically acceptable carrier and/or a biomedicine acceptable carrier, preferably at least one of carboxymethyl cellulose, polyvinyl pyrrolidone, hydroxypropyl methyl cellulose.

18. Injectable filling according to any of claims 15-17, wherein the injectable filling has a viscosity of about 20000cp to 200000 cp.

Technical Field

The invention relates to the technical field of medical appliances, in particular to the technical field of implantable medical cosmetic medical appliances, and specifically relates to a composition containing sodium alginate and polylactic acid, and a preparation method and application thereof.

Background

The polylactic acid material has good biodegradability, better mechanical strength and processability, good biocompatibility, and the degradation product is CO₂And H₂O, is nontoxic to human bodies, so that the O-containing material is widely applied to tissue engineering, orthopedic repair and fixation materials, drug delivery, surgical sutures and the like. Is a biomedical material approved by the U.S. Food and Drug Administration (FDA).

In recent years, the beauty industry has developed rapidly, and face fillers of injection type have also developed more and more rapidly, and become an indispensable part in beauty medicine. The facial fillers in the market are various, but the development of a cosmetic product with good cosmetic effect, lasting but non-permanent curative effect, small side effect and low adverse reaction incidence rate is still a great challenge. The polylactic acid can stimulate the skin to regenerate collagen through clinical verification. The polylactic acid facial filler in the medical and American industry at present is prepared by preparing polylactic acid into particles or microspheres, and delivering the particles or microspheres to the face under the skin in an injection mode. Polylactic acid can be slowly degraded into lactic acid through hydrolysis in vivo, and the lactic acid is an inherent component in a human body and can be finally degraded into CO₂And H₂And O. In the degradation process, the lactic acid can stimulate the formation of collagen, so that the collagen which is gradually lost along with the aging is supplemented, thereby achieving the purposes of improving the skin quality and filling the slack and the depression of the skin, and the curative effect can last for more than two years. Therefore, unlike conventional face fillers, l-polylactic acid has recently been favored in the beauty industry, and is called a "child-care needle" in the beauty industry.

Sculptra is the only PLLA poly L-lactic acid cosmetic brand globally approved by the U.S. FDA, manufactured by Sanofi-aventis U.S. company, Senoffy-Anthrate, and marketed in Europe in 1999. Sculptra was FDA approved in 2006 for the treatment of facial lipoatrophy in HIV patients, and in 2009, was FDA approved in the united states for the treatment of mouth folds. SculptraAesthetic is a cosmetic indication product of Sculptra, the main component of which, PLLA polylactic acid, was approved by the FDA at 7 months 2010 for injection filling of the shallow to deep nasolabial folds and other facial wrinkles.

In 2021, 4 months, the national first III class medical apparatus grade "childhood beauty needle" -polylactic acid facial filler "of Changchun Shengbo Ma biomaterial Co., Ltd.

Because polylactic acid is a degradable material, the molecular chain of the polylactic acid contains ester bonds, the polylactic acid is more easily broken into carboxylic acid and alcohol under the action of hydrogen ions in a water environment, and acid generated in degradation may have a catalytic effect on the degradation to form an autocatalytic effect. The degradation rate depends to a large extent on factors such as pH, morphology of the polymer, phase structure, etc. The degradation half-life of the PLLA material in physiological saline is about 20 weeks. Therefore, in order to inhibit the degradation of the product during the shelf life, the polylactic acid injection which is currently approved in the market is in the form of freeze-dried powder injection. Polylactic acid facial filler particles or microspheres in the prior industry are firstly redissolved before clinical use, the redissolution is insufficient or polylactic acid particles or microspheres are bonded, even the injection is uneven, and subcutaneous nodules or red and swollen and other adverse reactions can be caused. In clinical application, the product is subjected to facial injection after being fully redissolved, and the injection part needs to be kneaded open to prevent the aggregation of PLLA microspheres or particles. Even so, the number of adverse reactions such as subcutaneous nodules or red and swollen by injection in a certain proportion still exists in the current clinic.

Disclosure of Invention

The invention aims to provide a composition containing sodium alginate and polylactic acid, a preparation method and application thereof, which can inhibit the degradation speed of a polylactic acid material in an aqueous environment, and further provide a pre-canned gel injection product in clinic, so that the re-dissolving operation of medical workers before use is avoided in clinical use, and the pre-canned gel injection product can be directly used, thereby reducing or even avoiding adverse reactions such as subcutaneous nodules and the like caused by aggregation of polylactic acid particles.

The technical scheme of the invention is realized as follows:

the invention provides a composition containing sodium alginate and polylactic acid, which comprises the following components in percentage by weight: 1-99% of absorbable polylactic acid material and 1-99% of sodium alginate gel.

As a further improvement of the invention, the composition also comprises one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, hyaluronic acid, cross-linked hyaluronic acid, polycaprolactone, polylactic acid-glycolic acid copolymer, polyethylene glycol, polyvinyl alcohol, glycerol, mannitol and lactose.

As a further improvement of the invention, the feed additive comprises the following components in percentage by weight: 1-50% of absorbable polylactic acid material and 50-99% of sodium alginate gel.

As a further improvement of the invention, the feed additive comprises the following components in percentage by weight: 5 to 40 percent of absorbable polylactic acid material and 60 to 95 percent of sodium alginate gel.

As a further improvement of the invention, the feed additive comprises the following components in percentage by weight: 10 to 35 percent of absorbable polylactic acid material and 65 to 90 percent of sodium alginate gel.

As a further improvement of the invention, the absorbable polylactic acid material is at least one of dextrorotatory polylactic acid, levorotatory polylactic acid, meso-polylactic acid and racemic polylactic acid.

As a further improvement of the invention, the absorbable polylactic acid material is in the form of particles or microspheres.

As a further improvement of the invention, the particle size of more than 90 percent of the microspheres is between 5 and 200 um.

As a further improvement of the invention, the particle size of more than 90 percent of the microspheres is between 10 and 100 um.

As a further improvement of the invention, the particle size of more than 90 percent of the microspheres is between 40 and 60 um.

As a further improvement of the invention, the absorbable polylactic acid material is suspended in sodium alginate gel.

The invention further provides a preparation method of the composition containing sodium alginate and polylactic acid, which is characterized by comprising the following steps:

(1) preparing polylactic acid microspheres or polylactic acid particles;

(2) and adding the polylactic acid microspheres or polylactic acid particles into the sodium alginate gel, and uniformly dispersing to obtain the composition containing the sodium alginate and the polylactic acid.

As a further improvement of the invention, the preparation method of the polylactic acid microspheres comprises the following steps: dissolving polylactic acid in an organic solvent to prepare a polylactic acid solution; dripping polylactic acid solution into polyvinyl alcohol aqueous solution by adopting a piezoelectric micro-spraying technology, and obtaining polylactic acid microspheres under the stirring condition; and separating the polylactic acid microspheres from the solution, washing, drying and collecting to obtain the polylactic acid microspheres.

As a further improvement of the invention, the organic solvent is at least one of dichloromethane, ethyl acetate and n-propyl acetate; in the polylactic acid solution, the weight percentage of the polylactic acid is 0.1-30%; the molecular weight of the polylactic acid is 6-100 ten thousand g/mol; the size of the polylactic acid liquid drop sprayed by the piezoelectric micro-spraying technology is 10-300 mu m; the concentration of the polyvinyl alcohol aqueous solution is 1mg/mL-50 mg/mL.

As a further improvement of the invention, the preparation method of the polylactic acid microspheres comprises the following steps: dissolving polylactic acid in an organic solvent to prepare a polylactic acid solution; mixing a polylactic acid solution with a polyvinyl alcohol aqueous solution, shearing the mixed solution at a high speed to obtain an emulsion, mixing the emulsion with purified water, magnetically stirring the mixed solution, centrifuging the magnetically stirred emulsion, washing with the purified water, precipitating, and freeze-drying to obtain the polylactic acid microspheres.

As a further improvement of the invention, the weight average molecular weight of the polylactic acid is 40000-60000 g/mol; the organic solvent is at least one of dichloromethane, ethyl acetate and n-propyl acetate; in the polylactic acid solution, the weight percentage of the polylactic acid is 0.1-30%; in the polyvinyl alcohol aqueous solution, the weight percentage of polyvinyl alcohol is 0.1-5%; the shearing rate of the high-speed shearing is 1000-5000r/min, and the time of the high-speed shearing is 1-10 min; the magnetic stirring speed is 500-1000r/min, the magnetic stirring time is 6-24h, the centrifugal rotation speed is 2000-5000r/min, and the centrifugal time is 5-30 min.

As a further improvement of the invention, the preparation method of the polylactic acid particles comprises the following steps: and (2) keeping the polylactic acid at a low temperature for a period of time, putting the polylactic acid material into a jet mill for jet milling at the temperature environment, and collecting after milling to obtain polylactic acid particles.

As a further improvement of the invention, the weight average molecular weight of the polylactic acid is 40000-60000 g/mol; the low-temperature keeping time is specifically kept for 2-4h in an environment of 0-4 ℃.

The invention further provides an injection filler, which comprises the following components in percentage by weight: 5-50% of absorbable polylactic acid material and 50-95% of sodium alginate hydrogel; preferably 20-40% absorbable polylactic acid material, more preferably 30-35% absorbable polylactic acid material. The product is in the form of a pre-filled syringe, which is injected subcutaneously into the face during use, under the operation of a physician.

As a further improvement of the invention, the absorbable polylactic acid material is PLLA microspheres, and the diameter distribution is 10-80 um; the microspheres are uniformly distributed in the sodium alginate hydrogel.

As a further improvement of the invention, the composition further comprises a pharmaceutically or cosmetically acceptable carrier and/or a biomedicine acceptable carrier, and preferably at least one of carboxymethyl cellulose, polyvinylpyrrolidone and hydroxypropyl methyl cellulose.

As a further improvement of the invention, the viscosity of the injectable filling is between about 20000cp and 200000 cp.

The main mechanism of hydrolytic degradation is generally considered to be that the polylactic acid molecular chain contains ester bonds, which are easily broken into carboxylic acid and alcohol under the action of hydrogen ions, and the acid generated in the degradation may have catalytic action on the degradation to form an autocatalytic effect. The degradation rate depends to a large extent on factors such as pH, morphology of the polymer, phase structure, etc. Adding a certain amount of NaCl, KCl and NaHCO into distilled water₃，NaH₂PO₄As a result of preparing a weakly alkaline artificial simulated body fluid having a pH of 7.40 and an acid-base buffer solution having a pH of 4.80 and a pH of 10.28, and adding PLLA having a Mn of 29980 into each of the three solutions, it was found that polylactic acids were degraded in all of the three solutions, and that they were degraded to such an extent that the alkaline solution was present>Acidic solution>And (4) neutral solution. The different crystallinity of polylactic acid also results in the difference of degradability. In general, PDLA in the amorphous state is more susceptible to degradation by water than PLLA in the crystalline state. It is reported that there are two stages of degradation of the semicrystalline PLLA, the first stage, diffusion of water molecules into the amorphous regions of polylactic acid, resulting in the subsequent cleavage of ester bonds. As the degradation proceedsThe crystallinity increases when the amorphous region degradation is almost complete. In the second stage, the hydrolysis starts to degrade from the edge of the crystalline region to the center of the crystal. In the process of hydrolyzing in the amorphous area, a low molecular substance with regular structure is generated, the crystallinity is increased, and the further hydrolysis is delayed. This property is used in bone repair and bone internal fixation materials, and the degradation rate of the material is adjusted to meet the requirements of the human body on the material.

Polylactic acid is locally strongly acidic during degradation, because polylactic acid is gradually degraded in vivo, and acid is generated during degradation, causing a decrease in the surrounding local pH. Sodium alginate is a pH sensitive material, and is wrapped around polylactic acid microspheres in a gel form, when the pH value of the polylactic acid is reduced, the molecular chains of the surrounding sodium alginate shrink and wrap around the polylactic acid to form a barrier, so that the degradation of the lactic acid in the sodium alginate material is slowed.

The composition utilizes the property of sodium alginate converting to alginic acid in an acid environment, when polylactic acid microspheres or particles start to degrade on the surface and the pH value is reduced, partial sodium alginate is converted to alginic acid, and the polylactic acid microspheres or particles have the tendency of being coated, so that the polylactic acid particles or partial H of the microspheres⁺The diffusion speed to the surrounding environment is reduced, and the degradation speed of the polylactic acid is further reduced.

In experiments, we surprisingly found that under proper composition proportion and preparation process conditions, the polylactic acid material can be prevented from degrading in an aqueous environment within 3 months. Therefore, a feasible technical scheme is provided for the polylactic acid to exist in the form of hydrogel during the shelf life of the product.

The technical scheme provided by the invention can inhibit the degradation speed of the polylactic acid material in an aqueous environment, and further provides a pre-canned gel injection product in clinic, so that the re-dissolving operation of medical workers before use is avoided in clinical use, and the pre-canned gel injection product can be directly used, thereby reducing or even avoiding adverse reactions such as subcutaneous nodules and the like caused by aggregation of polylactic acid particles.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Sodium alginate, CAS number 9005-38-3, purchased from the group of Qingdao Mingyue seaweed. Polylactic acid is synthesized by itself by a synthesis method commonly used in the field: the main molecular weight ranges of the direct polycondensation method and the lactide ring-opening polymerization method comprise: 3-6 thousands, 6-8 thousands and 8-12 thousands.

The embodiment provides a composition containing sodium alginate and polylactic acid.

The preparation method of the polylactic acid microspheres in the examples 1 and 4 is as follows: dissolving polylactic acid in dichloromethane to prepare 5 wt% polylactic acid solution; dripping 5 wt% polylactic acid solution into 25mg/mL polyvinyl alcohol water solution by adopting a piezoelectric micro-spraying technology, and spraying polylactic acid liquid drops with the particle size of 10-300 mu m under the stirring condition to obtain polylactic acid microspheres; and separating the polylactic acid microspheres from the solution, washing, drying and collecting to obtain the polylactic acid microspheres.

The preparation methods of the polylactic acid microspheres in the examples 7 to 18, 20 and 22 to 28 are as follows: dissolving polylactic acid in dichloromethane to prepare 5 wt% polylactic acid solution; mixing a 5 wt% polylactic acid solution and a 3 wt% polyvinyl alcohol aqueous solution, carrying out high-speed shearing on the mixed solution, wherein the shearing rate is 5000r/min, the high-speed shearing time is 10min, obtaining an emulsion, mixing the emulsion with purified water, carrying out magnetic stirring on the mixed solution, 700r/min, and 18h for magnetic stirring, centrifuging the emulsion after magnetic stirring, wherein the centrifugal rotating speed is 3000r/min, and the centrifugal time is 20min, then washing with the purified water, precipitating, and carrying out freeze drying to obtain the needed polylactic acid microspheres.

The polylactic acid fine particles of examples 2 to 3, 5 to 6, 19 and 21 were prepared as follows: and (2) keeping the polylactic acid in an environment of 4 ℃ for 3h, putting the polylactic acid material into a jet mill for jet milling in the environment of the temperature, and collecting after milling to obtain polylactic acid particles.

The preparation method of the composition containing sodium alginate and polylactic acid comprises the following steps:

(1) preparing polylactic acid microspheres or polylactic acid particles;

(2) adding the polylactic acid microspheres or polylactic acid particles into sodium alginate gel, stirring for 1h at 300r/min, and simultaneously adopting 1000W ultrasound to uniformly disperse the particles or microspheres, thereby obtaining the composition containing the sodium alginate and the polylactic acid.

The parameters of the specific examples are as follows in table 1:

TABLE 1

Note that: racemic means that the amounts of the levorotatory and dextrorotatory polylactic acid substances are equal; CMC is sodium carboxymethyl cellulose; PVP is polyvinylpyrrolidone; HPMC is hydroxypropyl methylcellulose, and has a molecular weight of weight average molecular weight in g/mol.

The compositions prepared in examples 1-24 and containing sodium alginate and polylactic acid were respectively placed in an environment of 25 + -2 deg.C, and the degradation results of polylactic acid within 3 months were examined, as shown in Table 2.

Molecular weight loss calculation method: (original molecular weight-measured molecular weight)/original molecular weight × 100%;

the mass loss calculation method comprises the following steps: (original mass-measured mass)/original mass × 100%.

TABLE 2

From examples 1 to 6, it is understood that when the molecular weight is small (the molecular weight is 3 to 6 ten thousand g/mol), the molecular weight is degraded after 2 months, and thus, the small polylactic acid molecule is inferior in crystallinity and easily causes molecular degradation. Therefore, from the viewpoint of cost reduction and good degradation resistance, polylactic acid having a molecular weight of 6 to 8 kg/mol is selected for use.

From examples 1 and 4, examples 18 and 19, and examples 20 and 21, it can be seen that, regardless of whether the gel material is sodium alginate or CMC, the polylactic acid particles prepared as microparticles have a better effect of resisting degradation than microspheres, and the polylactic acid microparticles are more difficult to degrade than the polylactic acid microspheres.

From examples 4 and 7, it is understood that the degradation of the polylactic acid microspheres can be reduced by increasing the content of the polylactic acid microspheres, and it is understood that the high concentration of polylactic acid is beneficial to forming crystals, thereby reducing the degradation of the polylactic acid.

From examples 8-16, it can be seen that no matter whether levorotatory, dextrorotatory or racemic polylactic acid microspheres are added, when the molecular weight is more than 6 ten thousand g/mol, the prepared polylactic acid composition has no degradation within 3 months.

From examples 17 to 28, it can be seen that when the gel material employs CMC, PVP, and HPMC, the prepared composition degrades the polylactic acid to different degrees within 3 months, and thus the sodium alginate gel material has an obvious effect on the degradation resistance of the polylactic acid. Polylactic acid is locally strongly acidic during degradation, because polylactic acid is gradually degraded in vivo, and acid is generated during degradation, causing a decrease in the surrounding local pH. Sodium alginate is a pH sensitive material, and is wrapped around polylactic acid microspheres in a gel form, when the pH value of the polylactic acid is reduced, the molecular chains of the surrounding sodium alginate shrink and wrap around the polylactic acid to form a barrier, so that the degradation of the lactic acid in the sodium alginate material is slowed.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.