Glycyrrhetinic acid-based pH-sensitive slow-release hydrogel material and preparation method and application thereof
阅读说明：本技术 甘草酸基pH敏感型缓释水凝胶材料及其制备方法与应用 (Glycyrrhetinic acid-based pH-sensitive slow-release hydrogel material and preparation method and application thereof ) 是由 万芝力 许梦月 杨晓泉 于 2021-06-29 设计创作，主要内容包括：本发明公开了甘草酸基pH敏感型缓释水凝胶材料及其制备方法与应用。该方法先将甘草酸均匀分散在水中,加热搅拌后得到透明的甘草酸溶液；待甘草酸溶液冷却至室温成凝胶态时,再将其加热至液态；然后将甲基纤维素粉末加入甘草酸溶液中加热搅拌,冷却样品,得到甘草酸-甲基纤维素水凝胶。所得复合水凝胶产品表现出良好的机械性能,凝胶状态在25-100℃保持稳定并可适应相应的热处理过程,同时还具有活性物质荷载能力以及高度可控的pH敏感型释放特性。本发明原料安全无毒,低热量,来源丰富,且工艺条件简单温和,可通过操控过程条件进行快速连续化生产应用在食品、医药中的热稳定凝胶型产品,具有工业化和规模化的应用价值。(The invention discloses a glycyrrhizic acid group pH sensitive type slow-release hydrogel material and a preparation method and application thereof. Uniformly dispersing glycyrrhizic acid in water, heating and stirring to obtain a transparent glycyrrhizic acid solution; cooling the glycyrrhizic acid solution to room temperature to gel state, and heating to liquid state; and then adding the methylcellulose powder into the glycyrrhizic acid solution, heating and stirring, and cooling the sample to obtain the glycyrrhizic acid-methylcellulose hydrogel. The obtained composite hydrogel product has good mechanical properties, the gel state is kept stable at 25-100 ℃, the composite hydrogel can adapt to corresponding heat treatment processes, and meanwhile, the composite hydrogel product also has active substance loading capacity and highly controllable pH sensitive release characteristics. The invention has the advantages of safe and nontoxic raw materials, low calorie, rich sources and simple and mild process conditions, can rapidly and continuously produce the thermostable gel products applied to food and medicine by controlling the process conditions, and has industrial and large-scale application value.)
1. A glycyrrhizic acid base pH sensitive type slow release hydrogel material is characterized in that methylcellulose powder is dispersed in melted glycyrrhizic acid aqueous solution, heated and stirred to form glycyrrhizic acid and methylcellulose mixed solution, and the glycyrrhizic acid base pH sensitive type slow release hydrogel material is obtained by low-temperature storage after cooling; the glycyrrhizic acid aqueous solution is obtained by heating and melting glycyrrhizic acid hydrogel, the glycyrrhizic acid hydrogel is obtained by dispersing glycyrrhizic acid powder in water, adjusting pH to 3.0-5.0, heating and stirring, standing and cooling; the storage modulus G' of the glycyrrhizic acid group pH sensitive slow-release hydrogel is 35000Pa, the breaking stress value is 2-100kPa, the Young modulus is 10-400kPa, and the hydrogel state is kept stable at 25-100 ℃.
2. The glycyrrhizic acid based pH sensitive type sustained-release hydrogel material according to claim 1, wherein the glycyrrhizic acid concentration is 1-8 wt% after the glycyrrhizic acid powder is dispersed in water, and the adjustment of pH to 3.0-5.0 is controlled by hydrochloric acid.
3. The glycyrrhizic acid based pH sensitive slow-release hydrogel material according to claim 1, wherein the heating temperature for heating and stirring is 65-95 ℃, and the stirring time is 5-30 min; the cooling temperature of the standing cooling is 10-25 ℃.
4. The glycyrrhizic acid based pH sensitive slow release hydrogel material according to claim 1, wherein the glycyrrhizic acid hydrogel is heated to melt at a temperature of 65-95 ℃.
5. The glycyrrhizic acid based pH sensitive slow-release hydrogel material according to claim 1, wherein the heating temperature for heating and stirring to form the mixed solution of glycyrrhizic acid and methylcellulose is 70-95 ℃, the heating and stirring time is 5-60min, and the stirring speed is 50-500 rpm.
6. The glycyrrhizic acid based pH sensitive slow-release hydrogel material according to claim 1, wherein the cooling temperature for low-temperature storage after cooling is-4-4 ℃, the cooling time is 2-60min, the temperature for low-temperature storage is 0-10 ℃, and the cooling time is 2-24 h.
7. The glycyrrhizic acid-based pH-sensitive slow-release hydrogel material according to claim 1, wherein the concentration of methylcellulose in the mixed solution of glycyrrhizic acid and methylcellulose is 1-4 wt%.
8. The method for preparing a glycyrrhizic acid based pH sensitive type sustained release hydrogel material according to any one of claims 1 to 7, characterized by comprising the following steps:
1) dispersing glycyrrhizic acid powder in water, adjusting pH to 3.0-5.0, heating and stirring, standing and cooling to obtain glycyrrhizic acid hydrogel;
2) heating and melting the glycyrrhizic acid hydrogel to obtain a glycyrrhizic acid aqueous solution;
3) dispersing methylcellulose powder in melted glycyrrhizic acid water solution, heating and stirring to obtain glycyrrhizic acid-methylcellulose mixed solution, and controlling methylcellulose concentration in glycyrrhizic acid and methylcellulose mixed solution to 1-4 wt%; cooling, storing at low temperature to obtain glycyrrhizic acid-methylcellulose hydrogel.
9. Use of the glycyrrhizic acid based pH sensitive slow release hydrogel material of any one of claims 1 to 7 in a method for loading and controlling release of hydrophilic functional factors.
10. The application of the glycyrrhizic acid based pH sensitive type slow release hydrogel material in a method for loading and controlling the release of the hydrophilic functional factor, according to claim 9, is characterized in that the functional factor is the hydrophilic functional factor of vitamin B12, the loading amount of vitamin B12 is 1-50 wt%, and the release rate and the release amount of the functional factor are controlled by pH within the range of pH 2.0-9.0.
Technical Field
The invention relates to a hydrogel, in particular to a thermally stable and hydrophilic functional factor-embedded glycyrrhizic acid-based pH-sensitive slow-release hydrogel material, a preparation method and application thereof; belongs to the fields of food and medicine, such as controlled release of functional active substances, medicine release and the like.
Background
Hydrogels are "soft and wet" materials with a three-dimensional spatial network structure formed by the crosslinking of hydrophilic polymers in a water-rich environment. The hydrogel has high similarity with biological tissues, and the good absorption and release of the hydrogel form ensure the transmission of substances in organisms. The hydrogel has good bionic performance, is wet and has an adjustable network structure, so that the hydrogel has extremely high value in the field of biomedical materials, and if the hydrogel is used as a carrier of a medicament, the medicament can be effectively delivered to a focus to be released, and is slowly and long-term released, so that the medicament effect of the medicament on an affected part is enhanced, and the damage to normal tissues is reduced.
At present, raw materials for active delivery, such as cellulose, polymers and the like, are prepared, due to chemical structures of main chains and polymer branches, the raw materials are endowed with the characteristics of amphiphilicity, environmental stimulus responsiveness and the like, and the polymers can generate abundant self-assembly behaviors, so that the preparation method has important application in the field of biomedicine, particularly in the aspect of controllable drug release. In the preparation of controlled release carriers for bioactive factors for medical use, natural proteins or synthetic polyhydroxy polymers are mostly used at present, but the formation of macromolecules such as proteins or polyisopropylacrylamide hydrogel involves toxic cross-linking agents (e.g. glutaraldehyde) and other complex treatments, cannot be safely applied to food systems, and is also not beneficial to the delivery and controlled release of functional factors { Ankareddi, Brazel C S.Synthesis and catalysis of transformed thermal hydrogels for transformed activated controlled release [ J ]. International Journal of pharmaceutical devices, 2007,336(2): 241-. The application research progress of intelligent high-molecular hydrogel in controlled release of drugs [ J ] contemporary chemical research, 2021(06):3-9 ] of modern chemical research.
In recent years, hydrogel based on small molecule gel has attracted more and more attention due to the advantages of simple and rapid preparation process, easily regulated structure and function, and the like. Due to the hydrophobicity and hydrophilicity of natural Glycyrrhizic Acid (GA), its molecules can self-assemble in water through non-covalent interactions to form semi-flexible nanofibers of uniform thickness (2.5nm), and when the glycyrrhizic acid concentration is increased to 0.3 wt%, a fiber network can be formed to finally form supramolecular hydrogels { Saha A., Adamcik J., Bolisetty S., et al. The hydrogel prepared by utilizing the natural glycyrrhizic acid has the advantages of low-concentration gelling, simple and quick preparation process, strong gelling capability, environmental responsiveness and the like, and shows wide application prospect in the aspects of active load and controlled release in the fields of functional foods, medicines and cosmetics. However, the hydrogel prepared from glycyrrhizic acid alone has the problems of poor thermal stability, weak mechanical strength, too fast environmental response and the like, is difficult to resist the influences of heat treatment, external and biological tissue mechanical damage and the like in the actual processing process, and further influences the structure and functional properties of the hydrogel, so that the hydrogel cannot play an application role in active load and controlled release.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a safe and nontoxic glycyrrhizic acid-based pH-sensitive slow-release hydrogel material which is induced by a natural micromolecule glycyrrhizic acid composite polymer, is thermally stable and can embed hydrophilic functional factors and a preparation method thereof, wherein the obtained hydrogel has good mechanical properties and is kept stable in a gel state at 25-100 ℃.
The invention also aims to provide the application of the glycyrrhizic acid based pH sensitive type slow-release hydrogel material capable of embedding the hydrophilic functional factors in loading and controlling the hydrophilic functional factors such as vitamin B12.
According to the invention, a cellulose polymer is added to be compounded with the micromolecular glycyrrhizic acid gel, so that the hydrogel which can withstand heat treatment and has good mechanical properties is prepared, and finally, the pH-sensitive slow-release hydrogel material embedded with the hydrophilic functional factors is obtained. The cellulose polymer can strengthen hydrogen bonds in the micromolecular hydrogel due to the hydroxyl of the cellulose polymer, and is combined with the micromolecular gel to form composite gel under certain conditions. The preparation method is simple, rapid, safe and efficient.
The thermally stable and high-strength glycyrrhiza acid-based hydrogel can be prepared by a simple and rapid method through the composite thermotropic high-molecular cellulose gel. The method for preparing the hydrogel by combining different molecular types, gelling types and two gelling agents is rare in research of applying the hydrogel to the fields of controlled release of functional active substances, slow release of medicines and the like. The composite hydrogel has a complex, compact and controllable network structure, has potential application value in the aspect of controllable release of functional factors, and has a plurality of diffusion paths due to the existence of compact and complex meshes, so that the release characteristic of the functional factors is changed, and the slow release of the functional factors is facilitated. Because the release speed of the functional factors is influenced by the network structure of the hydrogel, the three-dimensional reticular porous structure of the hydrogel can be changed by controlling the proportion of the cellulose, so that the diffusion of the medicine and the erosion of the hydrogel framework material are influenced, and the aim of controlling the slow release of the functional factors is achieved jointly through a bidirectional way. The micromolecular glycyrrhizic acid and macromolecule methylcellulose composite hydrogel material has the advantages of good thermal stability, mechanical property, hydrophilic functional factor load and controlled release capability and the like, so that the hydrogel material has good application value in the aspects of active embedding, controlled release and the like.
The invention starts from the angle of molecular structure and the angle of nutrition and health, the hydrogel with solid shape and enough mechanical property is prepared by utilizing the self-assembly and the gelation capability of natural micromolecular glycyrrhizic acid and compounding safe food-grade methylcellulose and controlling simple process conditions, and the gel is kept stable at the gel state of 25-100 ℃. Compared with most of hydrogels prepared by using cellulose and other high molecules at present, the hydrogel prepared by compounding food-grade glycyrrhizic acid has the advantages that: the preparation method is simple, rapid, safe and nontoxic, the prepared hydrogel material has good thermal stability, can adapt to thermal treatment such as thermal sterilization and the like, simultaneously has good mechanical processing performance and a complex and compact space three-dimensional network structure, can embed hydrophilic functional factors, and has highly controllable pH sensitive release characteristics.
Methyl Cellulose (MC) is a semi-synthetic high molecular compound prepared by substituting hydroxyl on a natural cellulose chain by methyl, has thickening, surface activity, film forming property and thermal gelation property (heating to form a gel and melting when cooling), is widely applied to the aspects of food, pharmacy, cosmetics, ceramic processing and the like, but the application of methyl cellulose in the medical aspect is mostly limited to the adhesive property, and the application in the biomedical fields of functional factor embedding and conveying and the like is worthy of being greatly developed.
Glycyrrhizic Acid (GA) is a natural amphiphilic active substance extracted from the root of liquorice, the chemical structure of the GA consists of acid plant saponin consisting of triterpene aglycone (18 beta-glycyrrhetinic acid) and diglucosonic acid, and the GA can be self-assembled in water to form long nano-fibers and finally form supermolecule hydrogel. At present, in the domestic and foreign research in the field, the hydrogel material prepared from the glycyrrhizic acid is improved in the characteristics of mechanical property, environmental responsiveness and the like through chemical modification, and the research reports that the hydrogel material prepared directly from the natural glycyrrhizic acid can keep a stable gel state and good mechanical property at the temperature of 25-100 ℃ and is applied to the fields of functional factor delivery, controlled release and the like are not found. In the pH sensitive slow-release hydrogel prepared from micromolecular glycyrrhizic acid, thermotropic gel methylcellulose is mainly used as a structure reinforcing phase to improve the network structure and the comprehensive performance of the glycyrrhizic acid hydrogel, broadens the application field of the glycyrrhizic acid hydrogel, and is a new attempt for preparing novel hydrogel. The glycyrrhizic acid-cellulose composite reinforced hydrogel slow-release material has a huge application prospect in the fields of food health products, medical treatment, biological materials and the like.
The technical scheme of the invention is as follows:
a glycyrrhizic acid base pH sensitive type slow release hydrogel material is prepared by dispersing methylcellulose powder in melted glycyrrhizic acid aqueous solution, heating and stirring to form glycyrrhizic acid and methylcellulose mixed solution, cooling and storing at low temperature; the glycyrrhizic acid aqueous solution is obtained by heating and melting glycyrrhizic acid hydrogel, the glycyrrhizic acid hydrogel is obtained by dispersing glycyrrhizic acid powder in water, adjusting pH to 3.0-5.0, heating and stirring, standing and cooling; the storage modulus G' of the glycyrrhizic acid group pH sensitive slow-release hydrogel is 35000Pa, the breaking stress value is 2-100kPa, the Young modulus is 10-400kPa, and the hydrogel state is kept stable at 25-100 ℃.
To further achieve the object of the present invention, preferably, the glycyrrhizic acid powder is dispersed in water at a glycyrrhizic acid concentration of 1 to 8 wt%, and the adjustment of the pH to 3.0 to 5.0 is performed by hydrochloric acid.
Preferably, the heating temperature of the heating and stirring is 65-95 ℃, and the stirring time is 5-30 min; the cooling temperature of the standing cooling is 10-25 ℃.
Preferably, the temperature for heating and melting the glycyrrhizic acid hydrogel is 65-95 ℃.
Preferably, the heating temperature for heating and stirring to form the mixed solution of glycyrrhizic acid and methylcellulose is 70-95 ℃, the heating and stirring time is 5-60min, and the stirring speed is 50-500 rpm.
Preferably, the cooling temperature of the low-temperature storage after cooling is-4-4 ℃, the cooling time is 2-60min, the temperature of the low-temperature storage is 0-10 ℃, and the time is 2-24 h.
Preferably, the concentration of the methyl cellulose in the mixed solution of glycyrrhizic acid and methyl cellulose is 1-4 wt%.
The preparation method of the glycyrrhizic acid group pH sensitive type slow-release hydrogel material comprises the following steps:
1) dispersing glycyrrhizic acid powder in water, adjusting pH to 3.0-5.0, heating and stirring, standing and cooling to obtain glycyrrhizic acid hydrogel;
2) heating and melting the glycyrrhizic acid hydrogel to obtain a glycyrrhizic acid aqueous solution;
3) dispersing methylcellulose powder in melted glycyrrhizic acid water solution, heating and stirring to obtain glycyrrhizic acid-methylcellulose mixed solution, and controlling methylcellulose concentration in glycyrrhizic acid and methylcellulose mixed solution to 1-4 wt%; cooling, storing at low temperature to obtain glycyrrhizic acid-methylcellulose hydrogel.
The application of the glycyrrhizic acid-based pH-sensitive slow-release hydrogel material in a method for loading and controlling the hydrophilic functional factors.
Preferably, the functional factor is hydrophilic functional factor vitamin B12, the loading capacity of vitamin B12 is 1-50 wt%, and the release rate and release amount of the functional factor are controlled by pH within the range of pH 2.0-9.0. Wherein, the slow release is realized within 0-48h under the condition of pH2.0-6.0, and the release amount is controllable; the pH value is 7.0-9.0, the condition is that the release is completely released for 0.5-24h and is highly controllable, namely the release sensitivity is higher when the pH value is 7.0-9.0.
The three-dimensional network structure constructed by taking the glycyrrhizic acid composite methylcellulose as the scaffold prepared by the invention ensures that the hydrogel has good thermal stability and mechanical property and high active substance loading capacity. The thermal stability, the mechanical property and the slow release efficiency of the hydrophilic functional factors of the hydrogel material can be controlled by regulating and controlling the concentration of the methyl cellulose.
The principle of the invention is as follows: the key point of the invention is that the self-assembly characteristic and the gelling capability of the natural micromolecule glycyrrhizic acid and the physical crosslinking of the self hydroxyl of the methyl cellulose are utilized skillfully to strengthen the network structure, and the prepared hydrogel can withstand heat treatment so as to prepare the pH sensitive slow-release hydrogel material embedded with the hydrophilic functional factors. Firstly, under the conditions of room temperature and glycyrrhizic acid concentration greater than critical gelling concentration (about 0.3 wt%), glycyrrhizic acid can generate ordered self-assembly through intermolecular non-covalent bond acting force (hydrophobic interaction and hydrogen bond) to form long fiber-shaped microstructures, the microstructures are further assembled into a space three-dimensional network, methyl cellulose molecular chains and glycyrrhizic acid nano fibers are mutually interlaced and wound, and the composite methyl cellulose has a large amount of hydroxyl groups and interacts with glycyrrhizic acid molecules to enhance intermolecular non-covalent bond acting force; at high temperature, the methyl cellulose molecular chain is spiral, intermolecular hydrophobic effect is enhanced, and the molecular chain is gathered, so that a three-dimensional network structure formed by assembling glycyrrhizic acid is enhanced, and finally the thermally stable hydrogel is formed. After the methyl cellulose is compounded, the three-dimensional network structure of the hydrogel is changed, so that the hydrogel has good mechanical property, highly controllable pH sensitive release characteristic and slow release characteristic capable of embedding hydrophilic functional factors.
Compared with the prior art, the invention has the following beneficial effects:
1) the invention skillfully utilizes the self-assembly property and the gelling capacity of the micromolecular glycyrrhizic acid, the network structure of the micromolecular glycyrrhizic acid is enhanced by compounding the methylcellulose, the hydrogel has special rheological property and thermal property different from those of the hydrogel with single components, the gel is stable in a gel state at 25-100 ℃, and the thermal stability and the mechanical property at 25-100 ℃ can be adjusted by adjusting the concentration of the methylcellulose. The composite supermolecule hydrogel has uniform appearance, keeps a transparent state at 25 ℃, and is milky white at 80 ℃.
2) Compared with most of hydrogels prepared by high molecules such as cellulose and the like at present, the hydrogel material prepared by the glycyrrhizic acid has the advantages of simple preparation method, high gelling speed, high loading capacity of active substances and highly controllable pH sensitive release characteristic.
3) The raw materials of the invention are rich in source, do not relate to toxic and harmful reagents (chemical cross-linking agents and the like), and are green and safe; the process conditions are simple and mild, the preparation process is simple, the gel product can be prepared and applied to the fields of hot processed foods, medicines and the like by controlling the process conditions, and the gel product has industrial and large-scale application values.
4) The hydrogel system prepared from two food-grade materials of natural micromolecular glycyrrhizic acid and macromolecular methylcellulose can be gelatinized without adding salt and a cross-linking agent. The natural micro-molecular glycyrrhizic acid has good bioactivity, can fully utilize natural resources to create a new material, can be used for loading hydrophilic functional factors such as vitamin B12 and the like, and can be further applied to the fields of controllable drug release, functional activity delivery and the like.
Drawings
Fig. 1 is an appearance diagram of hydrogel of glycyrrhizic acid compounded with methylcellulose with different concentrations at different temperatures, and an appearance diagram of glycyrrhizic acid alone and methylcellulose sample alone in example 1.
FIG. 2 is a small amplitude dynamic temperature scan of a hydrogel of glycyrrhizic acid complexed with 4 wt% methylcellulose of example 1.
Fig. 3 is a small-amplitude dynamic frequency scan of the hydrogel of glycyrrhizic acid compounded with methylcellulose of different concentrations in example 2.
FIG. 4 is the stress-strain curve of hydrogel of glycyrrhizic acid compounded with methylcellulose of different concentrations in example 3.
FIG. 5 is a graph showing the sustained release profile of the hydrogel loaded with vitamin B12 in NaCl-HCl solution at pH 2.5 in example 4.
FIG. 6 shows NaH at pH 7.5 for hydrogel loaded with vitamin B12 of example 42PO4-slow release profile in NaOH solution.
Detailed Description
For better understanding of the present invention, the present invention will be further described with reference to the following drawings and examples, but the present invention is not limited thereto.
In the following examples, the hydrogel release properties were determined as follows:
1.5g of the hydrogel material was cut and placed in NaCl-HCl solution at pH 2.5 and NaH at pH 7.5, respectively2pO4The release of vitamin B12 was carried out in NaOH solution at 37 ℃ with shaking at constant temperature of 100r/min, 2ml of release solution was aspirated at intervals while the same volume of the slow-release solution was added to keep the volume constant. And (3) taking the corresponding controlled release solution as a blank control, measuring the light absorption value of the release solution at 361nm, and calculating the cumulative release rate of the vitamin B12 in different systems according to the change of the concentration of the vitamin B12 in the release system.
Example 1
Dispersing 4 parts of glycyrrhizic acid powder in deionized water containing hydrochloric acid (pH is approximately equal to 4, and the adjustment and control are carried out by hydrochloric acid), stirring for 10min at 70 ℃, and then cooling at normal temperature to obtain glycyrrhizic acid hydrogel with the concentration of 4 wt%; heating 4 parts of glycyrrhizic acid hydrogel again at 70 deg.C to melt. Respectively and uniformly dispersing 3 parts of methylcellulose powder with different masses in 4 wt% glycyrrhizic acid aqueous solution, heating and stirring the obtained mixed solution at 70 deg.C for 30min to obtain glycyrrhizic acid-methylcellulose mixed solution with methylcellulose final concentration of 0 wt% (directly using 4 wt% glycyrrhizic acid aqueous solution), 1 wt%, 2 wt% and 4 wt%, respectively. And (3) carrying out ice-bath stirring and cooling on the mixed solution, and placing the mixed solution at 4 ℃ for freezing and storing for 6 hours to obtain the composite hydrogel.
Dispersing 1 part of methylcellulose powder into deionized water (pH is approximately equal to 4.5 and is regulated and controlled by hydrochloric acid) by mass fraction, stirring for 40min at 80 ℃, then stirring and cooling in an ice bath, and placing at 4 ℃ for freezing and storing for 6h to obtain 4 wt% of methylcellulose solution.
As can be seen from the preparation method of the embodiment 1, the raw materials and the reagents used in the invention are natural, green and safe, and the processing process is simple and convenient to operate and is convenient for rapid continuous production.
FIG. 1 is an appearance diagram of hydrogel of glycyrrhizic acid compounded with methylcellulose with different concentrations at different temperatures, and an appearance diagram of glycyrrhizic acid alone and methylcellulose sample alone. The formation of glycyrrhizic acid hydrogel is very sensitive to ambient temperature. From fig. 1, it can be seen that neither methylcellulose alone nor glycyrrhizic acid alone can maintain the gel state at 25 ℃ and 100 ℃ at the same time, and all the composite samples at 25 ℃ are transparent gel-like; after heating in water bath at 100 deg.C for 30min, glycyrrhizic acid compounded with 1 wt% methylcellulose sample is melted, and methylcellulose samples with concentration of 2 wt% and 4 wt% are still gelatinous. Therefore, the concentration of the methyl cellulose (more than or equal to 2 wt%) is an important factor for keeping the sample in the gel state at 25-100 ℃.
As a consumer product, a hydrogel with good thermal stability is important to maintain the physicochemical properties and sensory attributes of the product, such as stable appearance, texture, safety in use, and the like. For example, many foods and medicines rely on heat sterilization (e.g., pasteurization) to reduce the effect of microorganisms on the quality of the products, to achieve the effects of prolonging the storage time and improving the safety of the products in use, particularly for products without a fixed container, functional products requiring gel molding in the products and heat treatment for use. However, the preparation of the natural polymer materials (such as konjac glucomannan) in the existing research needs strong alkali, so that the loading of functional active substances and medicines is inconvenient, and the independent glycyrrhizic acid hydrogel can generate gel-sol conversion at 55-60 ℃. Based on this, the change of the thermal stability of the glycyrrhizic acid hydrogel has good application value for expanding the application of the glycyrrhizic acid hydrogel in the fields of food, medicine and the like.
FIG. 2 is a small amplitude dynamic temperature scan of a hydrogel of 4 wt% methylcellulose and 4 wt% glycyrrhizic acid in a composite system. The dynamic temperature scanning detection method comprises the following steps: analyzing the rheological property of the hydrogel by adopting small variable rheological analysis, placing the hydrogel on a sample table of a rheometer, and testing by selecting a 35mm parallel plate, wherein the gap between the sample table and the parallel plate is 1 mm; the fixed strain is 0.1 percent, the fixed frequency is 1Hz, the scanning temperature range is 25-80 ℃, the interval is 1 ℃/min, the temperature is raised and then reduced, the temperature is balanced for 30min, and the trend of G 'and G' along with the temperature change is recorded. The storage modulus G' value, also called the elastic modulus, can represent the elastic (solid state) properties of the sample being tested; the loss modulus G "value, also called the viscous modulus, can be indicative of the viscous (liquid) nature of the sample. As can be seen from the figure, the composite system hydrogel viscoelasticity is only within a certain temperature range. Hydrogels typically contain large amounts of water, up to 70%, and when the water boils, the intermolecular hydrogen bonding interactions are reduced and the hydrogel network is broken. It can be seen from the figure that the elastic modulus of the gel is always greater than the viscous modulus in the interval of 25-80 deg.c, indicating that the gel does not transform into a liquid state and remains stable in this temperature interval. This shows that the non-covalent bond interaction (hydrogen bond and hydrophobic interaction) between glycyrrhizic acid and methylcellulose molecules is relatively stable in the temperature rise, temperature decrease and balance interval of 25-80 ℃, and a stronger three-dimensional network structure is formed by compounding methylcellulose (more than or equal to 2 wt%) glycyrrhizic acid hydrogel.
Example 2
Dispersing 4 parts of glycyrrhizic acid powder with different masses in deionized water (pH is approximately equal to 5, and is regulated and controlled by hydrochloric acid), stirring for 15min at 85 ℃, and then cooling at normal temperature to obtain glycyrrhizic acid hydrogel; heating the glycyrrhizic acid hydrogel again at 85 deg.C to melt. Respectively and uniformly dispersing 4 parts of methylcellulose powder with different masses in 4 wt% glycyrrhizic acid aqueous solution, heating and stirring the obtained mixed solution at 85 ℃ for 45min to obtain glycyrrhizic acid-methylcellulose mixed solution with methylcellulose final concentrations of 0 wt%, 1 wt%, 2 wt% and 4 wt% respectively. And (3) carrying out ice-bath stirring and cooling on the mixed solution, and carrying out freezing storage at 4 ℃ for 12h to obtain the composite hydrogel.
Dispersing 1 part of methylcellulose powder into deionized water (pH is approximately equal to 5 and is regulated and controlled by hydrochloric acid) by mass fraction, stirring for 60min at 85 ℃, then stirring and cooling in an ice bath, and placing at 4 ℃ for freezing and storing for 12h to obtain 4 wt% of methylcellulose solution.
The processing properties of hydrogel materials in the food, cosmetic or pharmaceutical field are mainly reflected in their mechanical properties, where the rheological properties, i.e. the resistance to small deformations, are reflected by the storage (elastic) modulus G' and the loss (viscous) modulus G "of the product. Generally, the higher G' and G ", the stronger the mechanical properties of the sample. Small amplitude dynamic frequency sweep determination: analyzing the rheological property of the hydrogel by adopting small variable rheological analysis, placing the hydrogel on a sample table of a rheometer, and testing by selecting a 35mm parallel plate, wherein the gap between the sample table and the parallel plate is 1 mm; the strain was fixed at 0.1%, the frequency sweep range was 0.1-100Hz, and the trend of the viscoelastic modulus (G 'and G') with frequency was recorded. Fig. 3 is a small amplitude dynamic frequency scan of a hydrogel compounded with different concentrations of methylcellulose with glycyrrhizic acid. As can be seen from fig. 3, the storage modulus (G') of all composite samples in the linear viscoelastic region is significantly higher than the loss modulus (G ") at 25 ℃, showing relatively low frequency dependence, indicating that the samples are mainly elastically deformed to be in a solid state at 25 ℃. In addition, the mechanical strength of the composite hydrogel increases with increasing methylcellulose concentration, suggesting that the mechanical properties of the hydrogel can be tailored to meet different processing requirements by varying the methylcellulose concentration (1-4 wt%). It is worth noting that 1 wt% -4 wt% of high molecular methyl cellulose is added into the small molecular glycyrrhizic acid gel, the composition (G '>20000Pa) improves the viscoelasticity strength of the small molecular glycyrrhizic acid hydrogel (G' <1000Pa) by 20 times, and greatly improves the mechanical performance of the glycyrrhizic acid hydrogel. The 2,2,6, 6-tetramethylpiperidine-1-oxygen radical (TEMPO) oxidized nanocellulose and nano chitin hydrogel prepared by the acid-gas phase condensation method has a complex preparation process, and the obtained hydrogel can reach G' about 10000Pa { Ma H, Yu J, Liu L, et al, amplified preparation of nano fibrous Polymers and the water drive capacity under differential pH recycling-scientific Polymers,2021 } after acetic acid is added and the obtained hydrogel is gelled for 24 hours. The hydrogel prepared from natural high molecules or polymers (such as sodium alginate and glycyrrhiza polysaccharide) has poor mechanical property and mechanical property, is easy to break during gastric movement or other non-predetermined tissue movement, and can not effectively embed active substances and slow release thereof { Bohui, Zhangjie. preparation and performance characterization of sodium alginate/glycyrrhiza polysaccharide hydrogel [ J ]. novel chemical material 2020, v.48; no.571(04), 153- & 156.
Example 3
Dispersing 4 parts of glycyrrhizic acid powder with different masses in deionized water (pH is approximately equal to 3.5, and hydrochloric acid is used for regulation and control), stirring at 80 ℃ for 10min, and then cooling at normal temperature to obtain glycyrrhizic acid hydrogel; heating the glycyrrhizic acid hydrogel again at 80 deg.C to melt. Respectively and uniformly dispersing 4 parts of methylcellulose powder with different masses in 4 wt% glycyrrhizic acid aqueous solution, heating and stirring the obtained mixed solution at 80 ℃ for 60min to obtain glycyrrhizic acid-methylcellulose mixed solution with methylcellulose final concentrations of 0 wt%, 1 wt%, 2 wt% and 4 wt% respectively. And (3) carrying out ice-bath stirring and cooling on the mixed solution, and placing the mixed solution at 4 ℃ for freezing and storing for 24h to obtain the composite hydrogel.
Dispersing 1 part of methylcellulose powder into deionized water (pH is approximately equal to 3.5 and is regulated and controlled by hydrochloric acid) by mass fraction, stirring for 70min at 80 ℃, then stirring and cooling in an ice bath, and placing at 4 ℃ for freezing and storing for 24h to obtain 4 wt% of methylcellulose solution.
Example 3 hydrogel stress-strain curves for glycyrrhizic acid alone and glycyrrhizic acid composite methylcellulose concentrations of 1 wt%, 2 wt%, and 4 wt%, respectively. The breaking stress value corresponds to the highest point of the curve and represents the capacity of resisting plastic deformation of the material; young's modulus is the slope of the initial linear region of the curve and may represent the rigidity of the gel. By changing the concentration of the methyl cellulose, the network structure of the hydrogel is controlled, and the resistance to plastic deformation and damage and the rigidity of the gel are further controlled, so that the mechanical properties of the hydrogel are changed. As can be seen from fig. 4, as the concentration of methylcellulose increases, the fracture strain value, the fracture stress value, the young modulus, and the like of the hydrogel increase, which indicates that the network structure of the glycyrrhizic acid hydrogel becomes more compact and complex by compounding methylcellulose, and the compact network structure affects the swelling rate and the erosion rate of the hydrogel in the solution, thereby controlling the diffusion of the functional factors and affecting the total amount and the rate of the release of the functional factors. A universal material testing machine is adopted to carry out compression test on the hydrogel material, the hydrogel is cut into a cylinder with the diameter of 14.36mm and the height of 10mm, a probe with the diameter of 25mm is selected, the speed before and after the test is 1mm/s, the test speed is 0.2mm/s, the compression degree of the hydrogel is 50 percent, the trigger force is 0.1g, the trend of the recorded force changing along with the relative displacement is further converted into a stress-strain curve. As seen from the stress-strain curve of the hydrogel of glycyrrhizic acid compounded with methylcellulose of different concentrations in fig. 4, as the methylcellulose increases, the resistance of the hydrogel material to plastic deformation and damage increases, indicating that the strength of the hydrogel is continuously enhanced. Due to the difference of microstructures, the breaking stress value of the glycyrrhizic acid hydrogel alone is only about 2.8kPa, and even if 1 wt% of methylcellulose is compounded, the breaking stress value of the hydrogel is increased to about 16kPa, and the Young modulus is 105 kPa. And when the concentration of the compounded methyl cellulose is 4 wt%, the fracture stress value and the Young modulus are respectively about 60kPa and 250kPa, and the mechanical property is greatly improved. By changing the methylcellulose concentration, the microstructure of the hydrogel is changed, and the physical properties of the hydrogel are further changed. The gel prepared from acidification-induced soy protein has a gel fracture stress value of only about 14kPa and a young's modulus of only about 26kPa at high protein content (10%) { zuki persica. production of micro-granulated soy protein [ D ]. south china university. The glycyrrhizic acid and the methylcellulose are combined to form a space three-dimensional network structure with good mechanical property, so that the hydrogel with the space three-dimensional network and good mechanics (strong rigidity and strong deformation resistance) is prepared.
Example 4
Dispersing 4 parts of glycyrrhizic acid powder with different masses in deionized water (pH is approximately equal to 4.5, and hydrochloric acid is used for regulation and control), stirring at 65 ℃ for 15min, and then cooling at normal temperature to obtain glycyrrhizic acid hydrogel; heating the glycyrrhizic acid hydrogel again at 90 deg.C to melt. Respectively and uniformly dispersing 4 parts of methylcellulose powder with different masses in 4 wt% glycyrrhizic acid aqueous solution, heating and stirring the obtained mixed solution at 90 ℃ for 30min to obtain glycyrrhizic acid-methylcellulose mixed solution with methylcellulose final concentrations of 0 wt%, 1 wt%, 2 wt% and 4 wt% respectively. And (3) carrying out ice-bath stirring and cooling on the mixed solution, and placing the mixed solution at 4 ℃ for freezing and storing for 6 hours to obtain the composite hydrogel.
Dispersing 1 part of methylcellulose powder into deionized water containing hydrochloric acid (pH is approximately equal to 4.5 and is regulated and controlled by hydrochloric acid) by mass fraction, stirring for 45min at 90 ℃, then stirring and cooling in an ice bath, and placing at 4 ℃ for freezing and storing for 6h to obtain 4 wt% of methylcellulose solution.
Vitamin B12, also called cobalamin, is the only vitamin containing metal elements, is red crystal powder, vitamin B12 is an indispensable micronutrient for organism growth, and higher animals and plants cannot produce vitamin B12. Vitamin B12 participates in the production of bone marrow red blood cells, can prevent pernicious anemia and damage to cerebral nerves, and promotes skin regeneration, so the vitamin B12 is widely applied in the fields of medicines, cosmetics and functional foods.
FIG. 5 is a graph showing the sustained release profile of the hydrogel loaded with vitamin B12 in NaCl-HCl solution at pH 2.5 in example 4. As can be seen from figure 5, the release amount of vitamin B12 can reach about 80% after 36h of release, and the release process is slow and uniform without sudden release. And the release rate of the soybean 11S protein-LBG blended cold-induced gel after embedding the riboflavin is 5-35%, and the release time is 400min { Zhujiahua, Yang dao. the research on the performance of the soybean 11S protein-locust bean gum cold-induced blended gel for controlling the release of the riboflavin [ J ]. modern food technology, 2012,28(11):1429-1433 })
FIG. 6 shows vitamin B12-loaded water of example 4NaH at pH 7.5 for the gel2PO4-slow release profile in NaOH solution. After the methylcellulose is compounded, a stronger fibrous network structure is formed, as can be seen from fig. 6, the cumulative release amount of all samples for 8h reaches more than 90%, compared with the single glycyrrhizic acid hydrogel, the composite 4 wt% methylcellulose hydrogel can prolong the slow release time from 1.5h to 8h, and the slow release speed of the functional factor can be regulated and controlled by controlling the proportion of the cellulose. Combining FIGS. 5 and 6, it can be seen that the composite methylcellulose hydrogel was NaH at pH 7.52PO4The NaOH solution has higher release speed and stronger sensitivity. The composite methyl cellulose can influence the network structure of the hydrogel and simultaneously influence the diffusion of the vitamin B12 and the erosion effect of the hydrogel framework material, thereby achieving the purpose of controlling the slow release of the functional factors through dual-way high-efficiency and quick-acting. In the functional factor release system, if the time and the concentration of the release of the functional factors can be maintained and controlled, the generation of bacterial drug resistance can be reduced, in addition, different pH values are provided at different tissue parts of a human body, if the slow release material has sensitivity to the pH value, the targeted release can be realized, the benefit is improved, and therefore, the adjustable release and the pH response of the functional substances are of great significance. The slow release system of functional factor prepared from cellulose or polymer (such as chitosan) has small drug loading amount and is easy to produce drug burst release, and the release of the functional factor can not be effectively controlled [ D, synthesis, characterization and in vitro application evaluation of chitosan-based derivatives [ D]West ampere building science and technology university, 2008. The gelatin pH sensitive controlled-release hydrogel enhanced by the cellulose microcrystals is more sensitive under the condition that the pH is 2, and the accumulative release amount of vitamin B2 is only about 70% after 70 hours; release amounts of less than 15% { Boughriba, s., Souissi, n., Nasri, r., Nasri, m.,&li, S. (2021). pH sensitive composite hydrogels based on gels and microorganisms with cellular microorganisms In depth graphics and microorganisms for controlled release of vitamins B2.materials viscosity Communications,27,10233 }. In the invention, the release rate of the vitamin B12 is controlled by controlling the concentration of the methylcellulose, the release behavior of the functional factors is highly controllable,high release rate, pH responsiveness and the like.
The invention utilizes the self-assembly characteristic and the gelling capacity of glycyrrhizic acid to prepare the hydrogel by compounding methyl cellulose, improves the gel strength and endows the hydrogel with new thermal stability. The release speed and release rate (80.77-97.88%) of the functional factor in a specific environment are controlled by changing the concentration of the methyl cellulose and the pH of the functional factor release solution, and the method has the advantages of high utilization rate of active substances, environment response release, controllable release time and the like. The invention prepares the hydrogel with 25-100 ℃ thermal stability by combining the glycyrrhizic acid and the methylcellulose, the hydrogel is convenient to produce, natural and safe, has good space three-dimensional network structure, mechanical property and anti-deformation property, can embed hydrophilic functional factors, and has good active substance loading capacity and highly controllable pH sensitive release characteristic.
As can be seen from the preparation method of the embodiment, the embodiment does not relate to any toxic and harmful raw materials and reagents, and the dosage of each reagent conforms to the GB 2760-; and the heat-stable high-strength gel can be formed without using salts, no toxic and harmful byproducts are generated, no large-scale equipment is used in the processing process, and the continuous production is facilitated.
It should be noted that those skilled in the art to which the invention pertains will appreciate that alternative or obvious modifications of the embodiments described herein may be made without departing from the spirit of the invention, and such modifications are to be considered as falling within the scope of the invention.