CN114948791A

CN114948791A - Cross-linked polysaccharide-based gels and uses thereof

Info

Publication number: CN114948791A
Application number: CN202210571728.4A
Authority: CN
Inventors: 李致; 朱沁; 丛远华; 贾海东
Original assignee: Shanghai Jahwa United Co Ltd
Current assignee: Shanghai Jahwa United Co Ltd
Priority date: 2022-05-24
Filing date: 2022-05-24
Publication date: 2022-08-30

Abstract

The invention provides a cross-linked polysaccharide-based gel, which comprises a natural polysaccharide and an alpha-hydroxy acid, wherein the natural polysaccharide is contained in an amount of 0.1-1 wt%, and the alpha-hydroxy acid is contained in an amount of 0.01-5 wt%, based on the total weight of the gel, wherein the weight ratio of the alpha-hydroxy acid to the natural polysaccharide is 1: 10-10: 1. The invention also discloses application of the gel in a skin external preparation.

Description

Cross-linked polysaccharide-based gels and uses thereof

Technical Field

The invention relates to the field of natural macromolecules and skin external preparations, in particular to a novel method for preparing gel based on natural polysaccharide macromolecules and alpha-hydroxy acid and application of the novel method in the field of cosmetics.

Background

Hydrogels are generally composed of hydrophilic polymers, have a three-dimensional network structure, and are widely used in various fields. According to the source classification of raw materials, the hydrogel can be divided into natural polymer hydrogel and synthetic polymer hydrogel.

The polysaccharide is a natural polymer raw material, generally has the characteristic of forming gel, and is used as a framework of a cross-linked network to construct hydrogel, so that the hydrogel has the advantages of better environmental friendliness, renewability, low or no cytotoxicity and the like. For the cosmetic industry, "green cosmetics" has become an important industry trend, and natural polysaccharide-based hydrogels have also become the first choice of hydrogels in the cosmetic field. Wherein, a natural polysaccharide polymer (such as gellan gum, pectin, algin, etc.) containing uronic acid units has the capability of forming hydrogel, and each uronic acid unit contains a carboxyl group (-COOH). It has been reported in the literature that when Ca is introduced into a solution ²⁺ 、Al ³⁺ Isometal cation, carboxyl anion (-COO) ^– ) And metal cations, to help the polysaccharide macromolecules to form a cross-linked network. However, the literature "polysaccharide hydrogels and their application analysis", asian journal of beauty cosmetics, 2020, 18 (1): 129-35 indicate that the addition of hydrogel crosslinkers may have low toxic or irritating effects on the skin and that safety is of concern. Therefore, it is a challenge to prepare hydrogel without adding crosslinking agent and add functional ingredients.

alpha-Hydroxy Acid (Hydroxy Acid), also called fruit Acid, is a class of aliphatic Hydroxy Acid with hydroxyl group on alpha, and is a common component in cosmetics. Alpha-hydroxy acids are a class of compounds, mainly including Citric Acid (Citric Acid), Lactic Acid (Lactic Acid), Glycolic Acid (Glycolic Acid), Malic Acid (Malic Acid), Tartaric Acid (Tartaric Acid), and the like. Review of patent technology on the application of alpha-hydroxy acids in cosmetics, Shandong chemical, 2020, 49 (14): 70, the compounds are mainly used as exfoliants, moisturizers, antioxidants and the like in cosmetics, and after a cuticle is formed, alpha-hydroxy acid can accelerate the peeling speed of epidermic cells by reducing the adhesiveness of the epidermic cells, so that the effect of improving the skin appearance is achieved.

The citric acid is a natural small molecular organic acid which is rich in source, non-toxic, cheap, biocompatible and biodegradable, has wide application, and can be used as a preservative, a flavoring agent, a chelating agent, a buffering agent and the like in the food and pharmaceutical industries. Meanwhile, citric acid belongs to alpha-hydroxy acid and is a good skin conditioner in the field of skin care products. For example, the document "dual action of alpha-hydroxy acid on skin", molecule, 2018, 23 (4): 863 reports that citric acid can stimulate the synthesis of type I collagen and type II procollagen, improve skin elasticity, and effectively reduce the influence of photodamage; in addition, citric acid may also increase the rate of skin metabolism, which may be associated with induction of keratinocyte apoptosis. It is worth noting that in the literature, the medical application of citric acid, future journal of pharmaceutical science, 2021, 7(1):54, it was mentioned that citric acid has gradually developed into an effective green cross-linking agent in the biomedical field in recent 20 years for the construction of bio-based hydrogels. Therefore, citric acid provides a new idea for preparing hydrogel under the condition of only adding functional components and not adding additional cross-linking agents.

The invention provides a concept and a design strategy of 'green crosslinking' of a skin-care hydrogel material. The present invention thus provides a novel process for the preparation of cross-linked polysaccharide-based gels, while expanding the range of possible applications of alpha-hydroxy acids in cosmetics.

Disclosure of Invention

In one aspect, the invention provides a cross-linked polysaccharide-based gel comprising a natural polysaccharide and an alpha-hydroxy acid, wherein the natural polysaccharide is present in an amount of 0.1 to 1 wt% and the alpha-hydroxy acid is present in an amount of 0.01 to 5 wt%, based on the total weight of the gel, and wherein the weight ratio of the alpha-hydroxy acid to the natural polysaccharide is from 1:10 to 10: 1.

In a preferred embodiment, the natural polysaccharide in the gel of the invention is selected from: gellan gum, pectin, algin or combinations thereof. In a preferred embodiment, the α -hydroxy acid in the gel of the invention is selected from the group consisting of: citric acid, lactic acid, glycolic acid, malic acid, tartaric acid, or combinations thereof.

In a preferred embodiment, the natural polysaccharide is present in the gel according to the invention in an amount of 0.1 to 0.8% by weight. In a preferred embodiment, the α -hydroxy acid content of the gel of the invention is from 0.04 to 4% by weight. In a preferred embodiment, the weight ratio of the alpha-hydroxy acid to the natural polysaccharide is from 1:5 to 10: 1.

In a preferred embodiment, the gel of the invention has a hardness of 50 to 5000 g.

In a preferred embodiment, the gel of the invention is a hydrogel.

In another aspect, the present invention also relates to the use of the gel of the present invention in an external preparation for skin. In a preferred embodiment, the external preparation for skin is selected from: face cleaning lotion, cosmetic water, lotion, cream, facial mask and gel.

Drawings

FIG. 1 shows the gel systems of comparative examples 1 to 4 evaluated at room temperature (25 ℃) by the test tube inversion method. As shown in the figure, gellan gum to which no α -hydroxy acid is added is in a solution state and has fluidity.

FIG. 2 shows the gel systems of examples 1 to 10 evaluated at room temperature (25 ℃) by the tube inversion method. As shown in the figure, the gellan gum added with the citric acid forms a solid gel structure and has no fluidity, which indicates that the citric acid has the function of inducing the gellan gum to crosslink to prepare the hydrogel.

Figure 3 shows the spray bottle in the spray test.

Fig. 4 shows the course of the spray experiment according to the invention.

Fig. 5 shows photographs of example 12 and example 13 in the form of monolithic gels for spray testing. As shown in the figure, the spray pump head is taken out, and the defect area caused by use cannot be filled by the gel with hard texture, but the defect area can be filled by the gel with soft texture in time, so that the result of no gap is achieved.

Detailed Description

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. For the purposes of the present invention, the following terms are defined below.

To provide a more concise description, some of the quantitative representations presented herein are not modified by the term "about". It is understood that each quantity given herein is intended to refer to the actual given value, regardless of whether the term "about" is explicitly used, and also to refer to the approximation to such given value that would reasonably be inferred by one of ordinary skill in the art, including approximations due to experimental and/or measurement conditions for such given value.

To provide a more concise description, some quantitative expressions are recited herein as a range from about an X amount to about a Y amount. It should be understood that when a range is recited, the range is not limited to the upper and lower limits recited, but includes the entire range from about the X amount to about the Y amount or any amount therebetween.

The invention provides a gel system based on natural polysaccharides and alpha-hydroxy acids. Alpha-hydroxy acids (e.g., citric acid and L-lactic acid) are capable of inducing molecules of natural polysaccharides (e.g., gellan gum) to form stable physical structures that remain in the gel state at low (4 ℃), normal (25 ℃) and high (40 ℃) temperatures.

Natural polysaccharides

In recent years, the construction of a gel system using natural polysaccharides as basic structural units has attracted much attention. For example, some natural polysaccharides (such as gellan gum, pectin, algin, etc.) contain carboxyl groups, uronic acid groups, etc. in their molecular structure, these groups are easily dissociated in aqueous solution, so that the polysaccharide molecules carry negative charges, resulting in that the polysaccharide molecules cannot aggregate to form a stable three-dimensional network structure due to electrostatic repulsion. Therefore, the electrostatic repulsion in the destructive system is the key to the preparation of such polysaccharide gels.

In some embodiments, the gels of the present invention comprise 0.1 to 1 wt.% of natural polysaccharides. In a preferred embodiment, the gel of the invention comprises 0.1 to 0.8 wt.% of natural polysaccharides. In a particular embodiment, the gel of the invention comprises 0.1, 0.2, 0.4 or 0.8 wt.% of natural polysaccharides.

Alpha-hydroxy acids

alpha-Hydroxy acids (Hydroxy acids), also known as fruit acids, include Citric Acid (Citric Acid), Lactic Acid (Lactic Acid), Glycolic Acid (Glycolic Acid), Malic Acid (Malic Acid), Tartaric Acid (Tartaric Acid), and the like. The alpha-hydroxy acid can be used as exfoliating agent, humectant, antioxidant, etc. in cosmetics, and after the formation of cutin layer, the alpha-hydroxy acid can reduce the adhesion of epidermal cells, thereby accelerating the exfoliation speed of epidermal cells and achieving the effect of improving the skin appearance.

In the biomedical field, alpha-hydroxy acids have gradually developed into an effective green cross-linking agent for constructing bio-based hydrogels. The present invention has surprisingly found that alpha-hydroxy acids provide a new concept for obtaining hydrogels by adding only functional ingredients without adding additional cross-linking agents. The invention unexpectedly discovers that the alpha-hydroxy acid has the function of inducing the gellan gum to crosslink to prepare the hydrogel.

In some embodiments, the gels of the present invention comprise from 0.01 to 5% by weight of an alpha hydroxy acid. In preferred embodiments, the gels of the present invention comprise from 0.01 to 2%, 0.02 to 2%, 0.04 to 1% or 0.1 to 1% by weight of an alpha hydroxy acid.

Composite gel

The present invention relates to a complex gel based on a natural polysaccharide and an alpha-hydroxy acid capable of inducing in situ cross-linking of the natural polysaccharide to form a gel suitable for dermal application.

According to the invention, the gellan gum added with the alpha-hydroxy acid forms a solid gel structure without fluidity, which indicates that the alpha-hydroxy acid has the function of inducing the gellan gum to crosslink to prepare the hydrogel.

Accordingly, the present invention provides a cross-linked polysaccharide based gel comprising a natural polysaccharide and an alpha hydroxy acid, wherein the natural polysaccharide is present in an amount of 0.1 to 1% by weight and the alpha hydroxy acid is present in an amount of 0.01 to 5% by weight, and wherein the weight ratio of the alpha hydroxy acid to the natural polysaccharide is from 1:10 to 10: 1.

In some embodiments, the weight ratio of alpha-hydroxy acid to natural polysaccharide in the gel of the invention is from 1:5 to 5: 1. In some embodiments, the weight ratio of the alpha-hydroxy acid to the natural polysaccharide in the gel of the invention is from 1:2 to 2: 1.

Method for preparing gel

The invention also provides a preparation method of the polysaccharide-based gel containing the alpha-hydroxy acid, which comprises the following steps: (a) dissolving a natural polysaccharide in an aqueous medium to form a solution; (b) adding an alpha-hydroxy acid to the solution of step (a) to form a mixed solution; (c) stopping stirring, cooling, and standing to obtain gel.

In a preferred embodiment, steps (a) - (b) are carried out under heated conditions. In a preferred embodiment, steps (a) - (b) are carried out at 60 ℃ -100 ℃. In a more preferred embodiment, steps (a) - (b) are carried out at 80 ℃ to 100 ℃. In a specific embodiment, steps (a) - (b) are performed at 90 ℃.

In a preferred embodiment, the aqueous medium in step (a) is water.

In a preferred embodiment, step (c) is carried out under cryogenic conditions. In a preferred embodiment, step (c) is allowed to stand at 0 ℃ to 45 ℃. In a more preferred embodiment, step (c) is allowed to stand at 2 ℃ to 30 ℃. In a specific embodiment, the mixed solution is cooled to room temperature (e.g., 25 ℃) in step (c), and then left to stand at 4 ℃.

In some embodiments, it is desirable to form a transparent gel. The inventors have found that as the content of natural polysaccharides (e.g. gellan gum) increases (e.g. from 0.1% to 0.8%), the transparency of the composite gel decreases. This is because the entanglement degree of the polysaccharide polymer chains in unit volume is significantly improved, the size of the "linking region" formed by the aggregation of the polymer chains is increased, and light scattering occurs, so that the gel sample shows an opaque appearance. Thus, for applications where it is desired to form a clear gel, it is also desirable to control the amount of natural polysaccharide used.

In some embodiments, the transparency of the complex gel is a function of the alpha hydroxy acid (e.g., citrate)The rising and falling mass ratio of citric acid)/native polysaccharide subsequently remains. The chemical structure of citric acid has three carboxyl groups and one hydroxyl group, which means that it has 3 ionizable hydrogen ions (H) ⁺ ) The hydrogen ions can inhibit the dissociation of carboxyl groups on the side chains of natural polysaccharides (such as gellan gum), and simultaneously can interact with the rest carboxyl anions to shield electrostatic repulsive force and induce the double helix structure of polysaccharide molecular chains to aggregate, and the larger the density and the size of the formed crosslinking region are, the more the apparent transparency of the composite hydrogel is relatively reduced. Therefore, for applications where it is desired to form a clear gel, it is preferable to control the weight ratio of alpha-hydroxy acid/natural polysaccharide.

In some embodiments, it is also desirable to determine the resistance of gels based on natural polysaccharides and alpha-hydroxy acids to damage by external forces. The inventors have found that at a natural polysaccharide (e.g. gellan gum) content of 0.4 wt%, when the citric acid/natural polysaccharide formulation ratio is less than 1:1, the hardness of the resulting composite gel increases with increasing ratio; when the citric acid/natural polysaccharide compounding ratio is more than 1:1, the hardness of the obtained composite gel is reduced; when the citric acid/natural polysaccharide compound ratio is 1:1, the hardness of the composite gel is the maximum. Under the condition that the content of natural polysaccharide (such as gellan gum) is 0.4 wt%, the hardness of the lactic acid-gellan gum composite gel also has a trend of increasing and then decreasing with the increase of the L-lactic acid/gellan gum compound ratio. The mechanical properties of the gel material are related to the formation of a cross-linked network structure thereof. Alpha-hydroxy acids (e.g., citric acid and L-lactic acid) are key components in inducing cross-linking of molecular chains of natural polysaccharides (e.g., gellan gum), and therefore the concentration of alpha-hydroxy acids has a large effect on the hardness of the gel. This is due to the fact that the molecular chain of natural polysaccharides (e.g.gellan gum) bears a negative charge (-COO) ^- ) The molecules tend to repel each other, while the alpha-hydroxy acids (e.g., citric acid and L-lactic acid) release H in water ⁺ The intervention of the cation helps to generate an electrostatic shielding effect to induce molecular chains to approach, and meanwhile, the hydrogen ion can also inhibit the dissociation degree of the carboxyl functional group (-COOH) to reduce the system potential. Thus, as the concentration of hydrogen ions in the system increases, the molecular chains of the natural polysaccharide (e.g., gellan gum) are physically cross-linked to form a tri-structureThe more uniform and dense the network structure, the greater the hardness exhibited by the resulting composite gel. However, excessive hydrogen ions can cause the crosslinking rate to be too fast, so that the orderly aggregation of double helix chains of natural polysaccharide (such as gellan gum) is not facilitated, and an uneven gel network is formed, and the network structure makes the system have weak resistance when being damaged by external force and shows that the mechanical property is reduced macroscopically.

In some embodiments, the higher the concentration of natural polysaccharide (e.g., gellan gum) in the complex gel system, the higher the complex gel strength. The number of polysaccharide polymer chains in unit volume is increased, entanglement among chains is increased, the generated steric hindrance effect is stronger, and a compact gel network is favorably formed. In addition, the molecular chain of the natural polysaccharide (such as gellan gum) contains a large number of hydroxyl groups, which is beneficial for the natural polysaccharide (such as gellan gum) molecules to contact with each other to form hydrogen bond association, so that the system structure is more stable. Thus, the gel macroscopically exhibits less tendency to break its solid character, i.e., greater hardness.

In some embodiments, the gels of the present invention are applied using a spray bottle. In a preferred embodiment, the hardness of the gel of the invention is determined using a texture analyser. For spray applications, in a preferred embodiment, the gels of the present invention have a hardness of 482.2 to 1972.2 g.

In some embodiments, the gels of the present invention are applied in an adhesive form. In a preferred embodiment, the hardness of the gel of the invention is determined using a texture analyser. For adhesive applications, in a preferred embodiment, the gel of the present invention has a hardness greater than 2044.4 g.

In a preferred embodiment, the gel of the present invention is an aqueous system (e.g., pure water, distilled water, deionized water, etc.). In a preferred embodiment, the gel of the invention is a hydrogel.

The invention will be further illustrated by the following specific examples. It should be noted that the examples are given solely for the purpose of illustration and are not to be construed as limitations on the scope of the invention, as many insubstantial modifications and variations of the invention may be made by those skilled in the art in light of the above teachings. Test methods in which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under conditions recommended by the manufacturer. All percentages and parts are by weight unless otherwise indicated.

Comparative example 1:

adding 0.1g of gellan gum into 99.9g of deionized water, heating to 90 ℃, keeping stirring at the temperature, stopping stirring until the gellan gum is completely dissolved to be a transparent solution, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Comparative example 2:

adding 0.2g of gellan gum into 99.8g of deionized water, heating to 90 ℃, keeping stirring at the temperature, stopping stirring until the gellan gum is completely dissolved to be a transparent solution, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Comparative example 3:

adding 0.4g of gellan gum into 99.6g of deionized water, heating to 90 ℃, keeping stirring at the temperature, stopping stirring until the gellan gum is completely dissolved to be a transparent solution, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Comparative example 4:

adding 0.8g of gellan gum into 99.2g of deionized water, heating to 90 ℃, keeping stirring at the temperature, stopping stirring until the gellan gum is completely dissolved to be a transparent solution, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 1:

adding 0.1g of gellan gum into 98.9g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 1.0g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 2:

adding 0.2g of gellan gum into 98.8g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 1.0g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 3:

adding 0.4g of gellan gum into 99.56g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to obtain a transparent solution, adding 0.04g of citric acid, continuously stirring at 90 ℃ to obtain a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 4:

adding 0.4g of gellan gum into 99.52g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.08g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 5:

adding 0.4g of gellan gum into 99.4g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.2g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 6:

adding 0.4g of gellan gum into 99.2g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.4g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 7:

adding 0.4g of gellan gum into 98.8g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.8g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 8:

adding 0.4g of gellan gum into 98.6g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 1.0g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 9:

adding 0.4g of gellan gum into 95.6g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 4.0g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 10:

adding 0.8g of gellan gum into 98.2g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 1.0g of citric acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 11:

adding 0.4g of gellan gum into 99.56g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.04g L-lactic acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and keeping the temperature for 12 hours to obtain a sample to be detected.

Example 12:

adding 0.4g of gellan gum into 99.52g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.08g L-lactic acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and keeping the temperature for 12 hours to obtain a sample to be detected.

Example 13:

adding 0.4g of gellan gum into 99.4g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 0.2g L-lactic acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and keeping the temperature for 12 hours to obtain a sample to be detected.

Example 14:

adding 0.4g of gellan gum into 98.6g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 1.0g L-lactic acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Example 15:

adding 0.4g of gellan gum into 95.6g of deionized water, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent solution, adding 4.0g L-lactic acid, continuously stirring at 90 ℃ to be a transparent mixed solution, stopping stirring, cooling to room temperature, placing in a refrigerator at 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected.

Test example 1: macroscopic topography

Fig. 1 shows photographs of the samples in comparative example 1 to comparative example 4. As can be seen, when the sample is returned to room temperature (25 ℃), the sealed PET bottle containing the sample is inverted and the gellan gum without the addition of alpha-hydroxy acid is in solution and has fluidity. Namely, when the mass concentration of the gellan gum is less than 0.8%, a stable gel structure cannot be formed, because electrostatic force exists between carboxyl groups with negative charges on a polysaccharide molecular chain, the crosslinking of the double-spiral molecular chain of the polysaccharide molecular chain is hindered, and a three-dimensional network structure cannot be formed.

FIG. 2 shows photographs of samples in examples 1 to 10. As can be seen from the figure, when the sample is returned to room temperature (25 ℃), the sealed PET bottle containing the sample is inverted, and the gellan gum added with citric acid forms a solid gel structure without fluidity, which indicates that the citric acid has the function of inducing the gellan gum to crosslink to prepare the hydrogel. Furthermore, as can be seen from example 1 to example 2, example 8 and example 10 in fig. 2, as the concentration of gellan gum is increased from 0.1% to 0.8%, the transparency of the composite gel is reduced, because the entanglement degree of the polysaccharide polymer chains per unit volume is significantly increased and the size of the "bonding region" formed by the aggregation of the polymer chains increasesLarge, light scattering occurs, causing the gellan gum-citric acid sample to exhibit an opaque appearance. As can be seen from example 3 to example 9 in fig. 2, at a gellan gum mass fraction of 0.4%, the transparency of the composite gel decreases with increasing citric acid/gellan gum mass ratio and then remains unchanged. The chemical structure of citric acid has three carboxyl groups and one hydroxyl group, which means that it has 3 ionizable hydrogen ions (H) ⁺ ) The hydrogen ions can inhibit the dissociation of carboxyl groups on the side chains of the gellan gum, and can interact with other carboxyl anions to shield electrostatic repulsive force and induce the double-helix structure of polysaccharide molecular chains to aggregate, and the larger the density and the size of a formed crosslinking area are, the lower the apparent transparency of the composite hydrogel is.

Test example 2: characterization of mechanical Properties

And (3) when the sample is recovered to the room temperature (25 ℃), measuring the hardness of the gel by using a texture analyzer (model number is TA.XTplus), and selecting a clamp as P/25P. The operation mode is as follows: the prepressing rate, the testing rate and the recovery rate are all 1.00 mm/s; the test mode is Distance, and the Distance is set to be 8 mm; the trigger value is 1 g. Each set of experiments was repeated 4 times with the results being the average. Table 1 shows gel hardness of the samples in examples 1 to 15.

Alpha-hydroxy acids are key components for inducing the crosslinking of gellan gum molecular chains, and therefore the concentration of alpha-hydroxy acids has a large influence on the hardness of the gel. From the gel hardness test results of the samples in the examples 3 to 9 in the table 1, it can be seen that under the condition that the mass fraction of the gellan gum is 0.4%, when the citric acid/gellan gum compound ratio is less than 1:1, the hardness of the citric acid-gellan gum compound gel is increased along with the increase of the hardness; when the compounding ratio of the citric acid to the gellan gum is more than 1:1, the hardness of the citric acid-gellan gum composite gel is reduced; when the citric acid/gellan gum compound ratio is 1:1, the hardness of the composite gel is the largest and is 2862.8 g. From the gel hardness test results of the samples in the examples 11 to 15 in table 1, it can be seen that under the condition that the mass fraction of the gellan gum is 0.4%, the hardness of the lactic acid-gellan gum composite gel also shows a trend of increasing first and then decreasing as the L-lactic acid/gellan gum compound ratio increases. Mechanical property of gel material and itsThe formation of the crosslinked network structure is relevant. The molecular chain of gellan gum has negative charge (-COO) ^- ) Therefore, polysaccharide molecules tend to repel each other, and the alpha-hydroxy acid releases H in water ⁺ The intervention of cations is helpful for generating electrostatic shielding effect and inducing molecular chains to approach; meanwhile, the hydrogen ions can inhibit the dissociation degree of the carboxyl functional group (-COOH), so that the system potential is reduced. Therefore, with the increase of the hydrogen ion concentration in the system, the more uniform and compact the three-dimensional network structure formed by the physical crosslinking of the gellan gum molecular chains, the greater the hardness represented by the alpha-hydroxy acid-gellan gum composite gel. However, excessive hydrogen ions can cause the crosslinking rate to be too fast, which is not beneficial to the orderly aggregation of the gellan gum double-spiral chains, and an uneven gel network is formed, and the network structure makes the system have weak resistance when being damaged by external force, and macroscopically shows that the mechanical property of the system is reduced.

The basic structural units constituting the gel are polysaccharide molecular chains, and therefore, the concentration of gellan gum is also one of the important factors affecting the hardness of the gel. As can be seen from the gel hardness test results of the samples in table 1 in examples 1 to 2, 8 and 10, the higher the gellan gum concentration is, the higher the composite gel strength is in the citric acid-gellan gum system. The number of polysaccharide polymer chains in unit volume is increased, entanglement among chains is increased, the generated steric hindrance effect is stronger, and a compact gel network is favorably formed. Meanwhile, the molecular chain of the gellan gum contains a large amount of hydroxyl groups, which is beneficial to the contact of the gellan gum molecules with each other to form hydrogen bond association, so that the system structure is more stable. Thus, the gel macroscopically exhibits less tendency to break its solid character, i.e., greater hardness.

TABLE 1

Test example 3: stability survey

After the sample is returned to room temperature (25 ℃), the sample is placed in three stable thermostats of 4 ℃, normal temperature and 40 ℃, and is inspected for one month to see whether the material body has morphological change, if the material body is still gelatinous, the material body is indicated as O, and if the material body is still gelatinous, the material body is indicated as delta.

The results of the stability tests of the samples in comparative examples 1 to 4 and examples 1 to 15 are shown in table 2. As can be seen from the table, the samples of comparative examples 1 to 4 failed to form gels, and the samples of examples 1 to 15 maintained solid characteristics under low temperature (4 ℃), normal temperature (25 ℃) and high temperature (40 ℃), indicating that gellan gum-alpha-hydroxy acid complex gels formed stable crosslinked structures.

Test example 4: spray test

The spray effect of the prepared gel component was determined by the following method:

the spray bottle used in the experiment was a pump head (Venus model, pump output 130 μ L/time) provided by sieger's constant delivery pump (no tin) ltd, as shown in fig. 3, and was used for spray testing. When the sample returns to room temperature (25 ℃), the sample is cut into pieces with the volume less than 1cm multiplied by 1cm, the pieces are poured into a 100mL transparent bottle, and the spraying pump head is screwed tightly to complete the filling process. As shown in FIG. 4, a black plate was vertically placed, and the distance between the nozzle outlet of the spray bottle and the paper plate was set to 15 cm. The tester applies the same force to press the pump head of the spray bottle for 1 time, and then horizontally places the black plate, draws a circle and calculates the area occupied by the material body. Calculated by the formula S ═ pi × a × b, where S (cm) ² ) Is the spray area; a (cm) is the length of the major semi-axis of the ellipse; and b (cm) is the length of the minor semi-axis of the ellipse. The larger the spray area, the better the spray effect. In this experiment, the spray area for the gel was greater than 20cm ² And less than 20cm ² The spraying effect of (a) was evaluated as good and poor, respectively. Each set of experiments was repeated 3 times, and the experimental results are mean values. In addition, whether the phenomenon of liquid dropping exists in the sprayed material body is further examined, a tester applies the same force to continuously press the pump head of the spray bottle for 5 times, and then whether the liquid flows downwards on the vertical black plate is observed.

The results of the evaluation of the spraying effect of the samples in comparative example 1 to comparative example 4 and example 1 to example 15 are shown in table 2. Among these, the samples of examples 5-8, 10 and 14 (hardness greater than 1972.2g) had poor spray performance, which is mainly related to the gel structure of gellan gum-alpha-hydroxy acid complex gels. Analysis shows that as the crosslinking density of polysaccharide polymer chains increases, the formed net structure is more compact and uniform, the hardness of polysaccharide gel increases, the polysaccharide gel is not easily sheared by external force, and the atomization effect of liquid sprayed from a nozzle is not good, so that slight accumulation of deposits in the nozzle is the main reason for smaller spray area and larger atomized particles. The gel composition according to the present invention (hardness greater than 482.2g) has the advantage of not easily flowing after spraying, compared to the samples of comparative examples 1 to 4, since the spray-formed particles remain in a gel state without flowing. Therefore, the technology solves the problem that the spray mask is easy to flow after being sprayed to the face, which brings inconvenience to users, and is beneficial to the gel composition to stay on the skin to play a role.

In addition, the present invention further compares the effect of the morphology and texture of the gel samples in spray applications. Specifically, in the preparation process of the sample, the transparent mixed solution containing the alpha-hydroxy acid and the gellan gum is poured into a spray bottle at 90 ℃, the spray pump head is screwed to complete the filling process, and the transparent mixed solution is used for spray testing after the transparent mixed solution forms a complete gel block. The tester continuously pressed the pump head of the spray bottle 20 times with the same force and observed whether the spray breaking occurred during the pressing process. Compared with the sample in example 13, the samples in example 2, example 4, example 9, example 12 and example 15 (hardness less than 1347.2g) are filled by the above process and are subjected to the spray test without causing the phenomenon of blowout interruption, which is related to the softness of the gel. As shown in fig. 5, the soft gel block can be refilled in time during the pumping process, so that after the material at the suction pipe opening is sucked, the suction pipe can further extract the surrounding material, and the situation that the material cannot be ejected after the pump head is pressed cannot occur. The process optimizes the step of filling after cutting the composite gel into fragments, and is more beneficial to actual production.

TABLE 2

The gel composition can be used alone or can be used as a raw material component to be added into a finished product formula.

Application examples 1 to 5: spray mask

TABLE 3

Table 3 shows cosmetic compositions comprising example 4, example 9 and example 15. Adding gellan gum into deionized water according to the dosage shown in phase A in the table 3, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent clear solution, adding alpha-hydroxy acid, continuously stirring at 90 ℃ to be a transparent mixed solution, cooling to 45 ℃, sequentially adding raw materials according to the dosage shown in phase B in the table 3, continuously stirring at 45 ℃ to be a transparent mixed solution, cooling to room temperature, placing in a refrigerator at 4 ℃, and keeping the temperature for 12 hours to obtain a sample to be detected. Wherein panthenol can be replaced by other water soluble active substances, including nicotinamide, dipotassium glycyrrhizinate, madecassoside, tetrahydro-methyl pyrimidine carboxylic acid, anhydrous betaine, sodium hyaluronate, ascorbyl glucoside, allantoin, etc. After the gel is returned to room temperature (25 ℃), it is cut into pieces having a volume of less than 1cm × 1cm × 1cm, poured into a 100mL transparent bottle, and the pump head is screwed tightly to complete the filling process. The gel body in the spray bottle is sucked into the pump head cavity by a continuous pressing mode, and then is sprayed out at a high speed through the micropores of the pump head to atomize the product, the size of the micro-droplets is 10-60 mu m, the micro-droplets can be uniformly covered on the surface of the skin, and the gel body has good adhesion performance and is not easy to drip.

Application examples 6 to 8: 3D facial mask

TABLE 4

Table 4 shows cosmetic compositions comprising example 7, example 10 and example 14. Adding gellan gum into deionized water according to the dosage shown in phase A in the table 4, heating to 90 ℃, keeping stirring at the temperature until the gellan gum is completely dissolved to be a transparent clear solution, adding alpha-hydroxy acid, continuously stirring at 90 ℃ to be a transparent mixed solution, cooling to 45 ℃, sequentially adding raw materials according to the dosage shown in phase B in the table 4, continuously stirring at 45 ℃ to be a transparent mixed solution, pouring into a mold with a certain shape, cooling to room temperature, placing in a refrigerator with 4 ℃, and preserving heat for 12 hours to obtain a sample to be detected. Wherein the madecassoside can be replaced by other water-soluble active substances, including panthenol, nicotinamide, dipotassium glycyrrhizinate, madecassoside, tetrahydro-methyl-pyrimidine-carboxylic acid, anhydrous betaine, sodium hyaluronate, ascorbyl glucoside, acetyl hexapeptide-8, etc. The gel mask is obtained by injection molding, has a thickness of 2-3 cm, and can be directly attached to skin surface.

Claims

1. A cross-linked polysaccharide-based gel comprising a natural polysaccharide and an alpha hydroxy acid, wherein the natural polysaccharide is present in an amount of 0.1 to 1 wt% and the alpha hydroxy acid is present in an amount of 0.01 to 5 wt%, based on the total weight of the gel, and wherein the weight ratio of the alpha hydroxy acid to the natural polysaccharide is from 1:10 to 10: 1.

2. The gel of claim 1, wherein the natural polysaccharide is selected from the group consisting of: gellan gum, pectin, algin or combinations thereof.

3. The gel of claim 1, wherein the α -hydroxy acid is selected from the group consisting of: citric acid, lactic acid, glycolic acid, malic acid, tartaric acid, or combinations thereof.

4. A gel according to any one of claims 1 to 3 wherein the natural polysaccharide is present in an amount of from 0.1 to 0.8% by weight.

5. A gel according to any one of claims 1 to 3, wherein the α -hydroxy acid is present in an amount of from 0.04 to 4% by weight.

6. The gel of any one of claims 1-3, wherein the weight ratio of said alpha-hydroxy acid to said natural polysaccharide is from 1:5 to 10: 1.

7. The gel of any one of claims 1-3, wherein the gel has a hardness of 50-5000 g.

8. The gel of any one of claims 1-3, wherein the gel is a hydrogel.

9. Use of the gel according to any one of claims 1 to 8 in an external preparation for skin.

10. The use of claim 9, wherein the external skin agent is selected from the group consisting of: face cleaning lotion, cosmetic water, lotion, cream, facial mask and gel.