Injectable hydrogel, and preparation method therefor and use thereof

Abstract

The present invention provides an injectable hydrogel, and a preparation method therefor and the use thereof. In the preparation method, energy generated by high-energy rays is used to enable the covalent crosslinking of polymers, so as to form a hydrogel, which is then thinned so that it becomes possible to inject and extrude same by means of a small-diameter syringe needle. The entire hydrogel preparation process is highly safe because no cross-linking agents or organic solvents are added. In addition, the hydrogel prepared by the method described has good physicochemical properties (water-retaining properties, formability, degradation time, storage modulus and solid content) and achieves inter-batch consistency, making it highly suitable for the field of medical cosmetology.

Description

An injectable hydrogel, its preparation method and application Technical Field

[0001] This invention relates to the field of hydrogel preparation technology, and more specifically, to an injectable hydrogel, its preparation method, and its application. Background Technology

[0002] As we age, the human body undergoes morphological changes and physiological decline due to a combination of endogenous and exogenous factors. Tissue fillers can be used to enhance tissues that may have suffered volume loss due to malnutrition, pathological atrophy, or trauma, or in areas such as facial plastic surgery, skin rejuvenation, and body sculpting, including procedures like eyelid surgery, rhinoplasty, lip augmentation, ear and eyebrow surgery, facial contouring, breast augmentation, and buttock augmentation. Injectable tissue fillers can repair and correct soft tissue shapes non-surgically, and have garnered widespread attention.

[0003] The most widely used injectable filler is hyaluronic acid (sodium hyaluronate), which has a significant immediate filling effect. However, due to the presence of hyaluronidase in the human body, exogenous sodium hyaluronate has a short duration of action in the body, making it difficult to achieve long-lasting shaping effects. To improve the clinical efficacy of hyaluronic acid, some products have extended its degradation time through cross-linking methods, such as "Juvederm," "Hypervita," and "Ellansé." These products use different cross-linking agents to connect sodium hyaluronate molecules to form a network structure, thereby improving the stability of hyaluronic acid in the body. Existing cross-linked sodium hyaluronate gel products often use divinyl sulfone (DVS) and 1,4-butanediol diglycidyl ether (BDDE) as cross-linking agents. However, many of these cross-linking agents are toxic or carcinogenic, and since they are encapsulated within the cross-linked sodium hyaluronate gel, they are difficult to remove completely. As hyaluronic acid degrades, residual cross-linking agents enter the body, posing a significant risk. Some recent studies have used safer crosslinking agents. For example, Chinese patent CN 104761734B discloses a method for crosslinking hyaluronic acid with lysine. However, the preparation of this material still uses toxic solvents and small molecules, which still pose potential safety hazards.

[0004] Therefore, there is an urgent need to find a safer and more effective method for preparing injectable hydrogels. The resulting injectable hydrogels can be used to prepare hydrogel tissue fillers, which can meet the needs of facial plastic surgery, skin beauty, and body shaping. Summary of the Invention

[0005] The present invention provides an injectable hydrogel, its preparation method and application. The preparation method utilizes the energy generated by high-energy rays to cause covalent crosslinking of polymers to form a hydrogel, and then through thinning treatment, it can be extruded and injected with a small-diameter syringe needle. The entire hydrogel preparation process does not involve the use of any crosslinking agents and organic solvents, so it has high safety.

[0006] On the one hand, the present invention provides a preparation method of an injectable hydrogel, and the method comprises the following steps: preparing a non-injectable hydrogel by radiation crosslinking; after thinning treatment of the non-injectable hydrogel, preparing a hydrogel that can be extruded or injected through a needle.

[0007] The injection refers to injecting a liquid or gas into a living body through a medical device such as a syringe to break through the physical barrier (such as the skin) of the living body, so as to achieve the purpose of diagnosis, treatment, repair, and prevention of diseases. This method has a quick effect, and the liquid component is not easily damaged. The injectable hydrogel refers to a hydrogel that can be extruded or injected through a needle, and the hydrogel still presents a gel state after extrusion or injection; the non-injectable hydrogel refers to a hydrogel that cannot be extruded or injected through a needle.

[0008] The thinning treatment in the present invention means that the non-injectable hydrogel obtains injectable performance, which can be achieved by partially breaking the covalent bonds inside the hydrogel and reducing the solid content.

[0009] A hydrogel refers to a water-rich polymer network, and its state cannot be described simply by "solid" or "liquid". In fact, a hydrogel has both solid characteristics and liquid characteristics. The state of a hydrogel can be defined by rheological parameters. Among them, the "storage modulus" (G') reflects the "solid" characteristics, and the "loss modulus" (G") reflects the "liquid" characteristics. When G'>G", the hydrogel behaves more like a "solid", and when G">G', the hydrogel behaves more like a "liquid". Injectable hydrogels are divided into two types. One is that the hydrogel behaves more like a "liquid" in any state, and the other is that the hydrogel behaves more like a "solid" in the unloaded state and behaves more like a "liquid" when subjected to shear force (such as through a narrow needle tube), so it can also be injected. The latter injectable hydrogel has the property of "shear thinning". When not subjected to shear force, G'>G" of the hydrogel, showing as a solid. When subjected to shear force, G"<G' of the hydrogel, showing as a fluid, so it can be extruded from the needle tube. After the extrusion is completed, the hydrogel is no longer subjected to shear force, so it returns to the state of G'>G", that is, it behaves more like a solid again.

[0010] The "shear-thinning" property has a theoretical basis in polymer physics. Simply put, ordinary hydrogels (non-injectable hydrogels) contain interconnected polymer networks, restricting polymer movement. In contrast, hydrogels with "shear-thinning" properties (injectable hydrogels) have polymer chains with a certain degree of mobility. When subjected to shear force, the polymer chains can move parallel to the direction of the shear force. That is, when passing through narrow spaces such as needles, the polymer chains can form a consistent orientation, macroscopically manifested as a decrease in viscosity, a decrease in G', and an increase in G”, allowing for injection extrusion. After the shear force disappears, the polymer chains return to their random orientation, macroscopically manifested as an increase in viscosity, an increase in G', and a decrease in G”, maintaining a stable shape. Furthermore, the non-injectable hydrogel needs to be thinned to prepare an injectable hydrogel; the needle is a small-diameter needle with an inner diameter less than 21G.

[0011] Furthermore, the thinning process includes breaking down the non-injectable hydrogel and mixing it with water. The needle is a small-diameter needle, meaning it has an inner diameter smaller than that of a 21G needle. More specifically, the needle specification is 21G to 34G.

[0012] Generally, the larger the number on the needle, the smaller the inner diameter. For example, a 5mL syringe needle is 21G, and a 1mL syringe needle is 25G. Understandably, it is relatively easy to create hydrogels using large-diameter needles, but it is much more difficult to create them using small-diameter needles, because the smaller the needle, the higher the requirements for the hydrogel's flowability, viscosity, and other properties.

[0013] The injectable hydrogel provided by this invention can be smoothly extruded from the needle (25G) of a 1mL syringe, which is related to the hydrogel crosslinking method, thinning treatment method, and composition. Irradiation crosslinking results in more uniform crosslinking of the hydrogel; sodium polyglutamate molecules contain carboxyl groups, therefore hydrogels prepared from it possess certain hydrophilic properties; furthermore, this invention optimized the thinning method, finding that mutual pushing within the mixer is most suitable for thinning irradiated crosslinked sodium polyglutamate hydrogels. In summary, the above factors are key conditions for transforming non-injectable hydrogels into injectable hydrogels.

[0014] Meanwhile, using small-diameter needles for injection has the following advantages:

[0015] 1. The smaller the needle diameter, the less damage to the skin during injection, thus reducing pain and discomfort for the recipient, especially in the field of cosmetic medicine. In this field, reagents are generally injected into areas of delicate skin (such as the face and hands), which are more sensitive to external stimuli, more prone to inflammation, and more likely to leave scars after healing. Furthermore, multiple injection points are often required. Therefore, small needles are frequently used in cosmetic procedures. In addition, using large needles can cause fear and anxiety for the recipient.

[0016] 2. It allows for more accurate control of the injection dosage. The smaller the needle diameter, the smaller the flow rate per unit time under the same external thrust, thus making it easier to control the volume of the injected reagent.

[0017] 3. It can slow down the flow rate of the injected reagent. The smaller the needle diameter, the greater the resistance to the flow of the reagent, and the lower the flow rate. In the field of medical aesthetics, subcutaneous injection of fillers is often required. During injection, the slower the flow rate of the reagent, the more evenly the filler can be distributed. Otherwise, it will lead to unevenness on the surface of the injection area, thus failing to achieve the desired cosmetic effect.

[0018] Furthermore, the non-injectable hydrogel is obtained by crosslinking a polymer aqueous solution through irradiation.

[0019] Crosslinking can be categorized into physical crosslinking and chemical crosslinking. Physical crosslinking involves the interpenetration of polymer molecules through physical processes to form a mixed macromolecular structure without altering the original molecule's chemical structure. Chemical crosslinking, on the other hand, involves the formation of covalent bonds through chemical reactions to create new polymer structures. To initiate these chemical reactions, chemical crosslinking agents are often added, such as peroxide crosslinking agents, silane crosslinking agents, and azo crosslinking agents. However, the products generated by these crosslinking agents can have adverse effects on the human body or the environment to varying degrees.

[0020] Two types of sodium polyglutamate (SO4) sol were prepared using irradiation and chemical agents, respectively. The results showed that the irradiated SO4 hydrogel exhibited higher water retention and light transmittance than the chemically cross-linked version. Higher water retention indicates better moisturizing and water-locking properties, allowing for a longer-lasting filling effect and maintaining elasticity at the injection site when used in aesthetic injections. Higher light transmittance results in a more aesthetically pleasing product with better user acceptance. Furthermore, light transmittance is an indicator of hydrogel uniformity; higher transmittance indicates a more uniform hydrogel, ensuring a more even feel at the injection site. In addition, irradiation does not involve the addition of any cross-linking agents or organic solvents and is a widely accepted sterilization method. In conclusion, irradiation is the preferred method for generating SO4 hydrogels.

[0021] Furthermore, the polymer includes one or more of the following: sodium polyglutamate, sodium hyaluronate, carboxymethyl cellulose, polyethylene oxide, sodium alginate, and sodium carboxymethyl starch.

[0022] Irradiated hydrogels prepared with different polymer components exhibit certain differences in their physicochemical properties after dilution into injectable hydrogels. Compared to irradiated crosslinked carboxymethyl cellulose hydrogels, irradiated crosslinked sodium polyglutamate hydrogels showed 10% less water loss after three days of natural standing. This may be because carboxymethyl cellulose has a polysaccharide structure with sterically hindered sugar ring structures in its molecular chain, resulting in a higher viscosity of its aqueous solution. Consequently, it is difficult to obtain a highly soluble carboxymethyl cellulose aqueous solution, leading to a lower concentration and consequently, a lower carboxyl group content in the final product. Furthermore, during irradiation, sufficient crosslinking cannot occur in the carboxymethyl cellulose aqueous solution. Even carboxymethyl cellulose hydrogels prepared under high irradiation doses cannot be diluted to obtain injectable hydrogels with good shapeability. Compared to sodium hyaluronate hydrogels, sodium polyglutamate hydrogels show better filling and shaping effects. In conclusion, compared to the two hydrogels mentioned above, sodium polyglutamate hydrogels are more suitable for cosmetic filling.

[0023] In addition, by adding some polymer compounds to sodium polyglutamate as the basic raw material, the performance of the gel can be improved to varying degrees, especially the water retention rate. Among them, adding sodium hyaluronate has the best effect.

[0024] Further, the molecular weight of the sodium polyglutamate is 100,000 to 2,000,000; the molecular weight of sodium hyaluronate is 200,000 to 3,000,000; the molecular weight of carboxymethyl cellulose is 5,000 to 1,000,000; the molecular weight of polyethylene oxide is 50,000 to 100,000; the molecular weight of sodium alginate is 5,000 to 100,000; and the molecular weight of sodium carboxymethyl starch is 10,000 to 1,000,000.

[0025] Further, the polymer includes sodium polyglutamate. Preferably, the molecular weight of sodium polyglutamate is 700,000 to 2,000,000;

[0026] Further, the concentration of the sodium polyglutamate aqueous solution is 5%–50%, the concentration of the sodium hyaluronate aqueous solution is 5%–15%, the concentration of the carboxymethyl cellulose aqueous solution is 2%–30%, the concentration of the polyethylene oxide aqueous solution is 5%–30%, the concentration of the sodium alginate aqueous solution is 2%–10%, and the concentration of the sodium carboxymethyl starch aqueous solution is 5%–30%.

[0027] Furthermore, nitrogen gas needs to be introduced into the polymer aqueous solution before irradiation crosslinking to purge the oxygen in the polymer aqueous solution.

[0028] Furthermore, the irradiation crosslinking is performed using electron beam irradiation or cobalt-60 irradiation.

[0029] Further, the irradiation crosslinking dose is 5-200 kGy. Preferably, the irradiation crosslinking dose is 70-130 kGy.

[0030] Furthermore, the method for thinning the non-injectable hydrogel includes one or more of the following:

[0031] The first method: Use a mixing syringe to mix the non-injectable hydrogel and water in a mixer until they are thoroughly mixed.

[0032] The second method involves squeezing the non-injectable hydrogel through a sieve and then mixing it thoroughly in water.

[0033] The third method involves drying the non-injectable hydrogel, grinding it, and then mixing it with water.

[0034] The fourth method involves sterilizing the non-injectable hydrogel with moist heat, followed by stirring and mixing it thoroughly in water.

[0035] In some methods, the first method (internal mixing) is preferred for breaking down non-injectable hydrogels.

[0036] All of the above dilution methods can be used to prepare injectable hydrogels, but the products prepared vary. Among them, the hydrogels diluted with a drug-mixing syringe have the most stable quality between batches. This may be because the method is the simplest, and the process is completed entirely in a sealed syringe without the need for transfer or filling steps, which makes it less prone to loss and easier to control the quality.

[0037] Compared to other thinning methods, injectable hydrogels prepared by the drug-mixed syringe repulsion method have better injectability and moldability, and the storage modulus and solid content of the hydrogels are the most stable.

[0038] Furthermore, the volume ratio of the non-injectable hydrogel to water described in the first, second, or fourth type is 1:0.5 to 1:10.

[0039] Furthermore, the mesh size of the sieve used in the second type of sieving is 50-300 mesh.

[0040] Mesh count corresponds to the aperture of the sieve. A sieve with a mesh size greater than 300 has an aperture size of less than 50 micrometers, making it difficult to squeeze through. A sieve with a mesh size less than 50 does not break down the hydrogel sufficiently, making it impossible for the gel to achieve injection properties.

[0041] Furthermore, the mass ratio of the non-injectable hydrogel to water in the third type is 1:100-1:20.

[0042] On the other hand, the present invention provides an injectable hydrogel, which is prepared by the method described above.

[0043] In another aspect, the present invention provides the use of the injectable hydrogel described above for the preparation of hydrogel tissue fillers.

[0044] In some applications, the hydrogel tissue filler is primarily used in areas such as facial plastic surgery, skin rejuvenation, and body sculpting.

[0045] The process of adjusting parameters is to ensure that the injectable hydrogel exhibits different properties after injection, based on the actual application requirements of the injectable tissue filler. In some applications, such as canthoplasty and wrinkle filling, good fluidity of the filler is required, while in other applications, such as rhinoplasty, forehead augmentation, and jaw augmentation, the filler needs to maintain its shape for a long time after injection.

[0046] Therefore, among all the parameters that need to be adjusted, the irradiation dose is the most critical. The irradiation dose actually alters the degree of cross-linking of the hydrogel. When the irradiation dose is low, the hydrogel's cross-linking degree is insufficient, making it impossible to inject and extrude when the solid content is too high. However, by thinning the hydrogel to make it injectable, the resulting hydrogel is more like a "liquid" in any state, exhibiting good flowability after injection. When the irradiation dose is increased to above 70 kGy, the degree of cross-linking of the hydrogel is neither too high nor too low. Through thinning treatment, "shear-thinning" properties can be obtained, resulting in good moldability after injection. When the irradiation dose is increased to above 200 kGy, the degree of cross-linking of the hydrogel is too high, and no matter how much thinning is applied, it can no longer be extruded through a syringe. At this point, even if the hydrogel is broken into fine particles, it cannot pass through a small-diameter syringe needle.

[0047] The aforementioned thinning process is crucial for the injectability of hydrogels. Thinning is not simply swelling the hydrogel to reduce its solid content. For hydrogels to be extruded through a small-bore syringe needle, reversible chemical bonds or forces within the hydrogel are required. Simple swelling does not disrupt the internal polymeric covalent network, thus failing to achieve injectability. Mechanical breakage or hydrothermal treatment disrupts the internal polymeric covalent network of the hydrogel. The macroscopic hydrogel with this disrupted network then reconnects itself through non-covalent interactions, resulting in a self-healing effect. The newly formed non-covalent bonds are weaker, and their formation and breakage are reversible. This facilitates more uniform orientation of the polymer chains under shear forces, allowing for extrusion through a small-bore syringe needle.

[0048] At specific irradiation doses, adjustments to the initial concentration and dilution ratio work together to achieve an injectable state, but they do not determine the flowability or moldability of the hydrogel after injection. For example, at an irradiation dose of 20K, regardless of adjustments to the initial concentration and dilution ratio, only a hydrogel with good flowability but poor moldability can be obtained. When the initial concentration is high (e.g., 20%), a higher dilution ratio is needed to make it injectable; when the initial concentration is low (e.g., 10%), a lower dilution ratio is needed. The initial concentration needs to be higher than a certain value; otherwise, if the concentration is too low, crosslinking to form a hydrogel after irradiation will not be possible. The upper limit of the initial concentration is controlled by the solubility of the polymer.

[0049] Injectable tissue fillers usually need to have a sufficiently long degradation time to achieve a long-term shaping effect. The degradation time is affected by both the irradiation dose and the molecular weight. Generally speaking, when other conditions remain unchanged, the higher the irradiation dose, the higher the degree of cross-linking, and the higher the molecular weight, the longer the degradation time of the hydrogel.

[0050] The injectable hydrogel, its preparation method, and its application provided by this invention have the following beneficial effects:

[0051] 1. A novel method for preparing injectable hydrogels is provided, which can transform non-injectable hydrogels prepared by crosslinking after irradiation into injectable hydrogels, and the properties of the injectable hydrogels are controllable, and they can be in liquid or solid state after being extruded through a needle.

[0052] 2. It was found that injectable hydrogels prepared by different dilution treatments have different properties. It is preferable to use a mixing syringe to mix them evenly.

[0053] 3. Diluting the hydrogel using a mixing syringe ensures that after irradiation, it can be used directly as the final product without the need for removal, processing, packaging, or sterilization. It is then used in conjunction with a vial of sterile water. This method maximizes the cleanliness of the injectable hydrogel, is extremely simple to operate, time-efficient, energy-saving, and environmentally friendly.

[0054] 4. The hydrogel prepared by the method described above has excellent physicochemical properties (water retention, moldability, degradation time, storage modulus and solid content) and batch stability, making it very suitable for the medical aesthetics field. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1: Principle of irradiation cross-linking of glutamic acid

[0057] Figure 2: The principle of chemical cross-linking of glutamic acid

[0058] Figure 3: Comparison of sodium polyglutamate before and after irradiation; Figure A shows the sodium polyglutamate aqueous solution before irradiation, and Figure B shows the sodium polyglutamate hydrogel after irradiation; the scale bar is 0.5 cm.

[0059] Figure 4: Water retention rate of irradiated cross-linked sodium polyglutamate hydrogel

[0060] Figure 5: Water retention rate of chemically cross-linked sodium glutamate hydrogel

[0061] Figure 6: Transmittance of monosodium glutamate hydrogels obtained by different crosslinking methods

[0062] Figure 7: Water retention rate of irradiated cross-linked carboxymethyl cellulose hydrogel

[0063] Figure 8: Subcutaneous filling in rats after implantation of different hydrogels. Figure A shows the implantation of sodium polyglutamate hydrogel, and Figure B shows the implantation of sodium hyaluronate hydrogel.

[0064] Figure 9: Sodium polyglutamate hydrogel formed under 20 kGy (low) dose irradiation. Figure A shows the state of the hydrogel before injection, and Figure B shows the state of the hydrogel after in vitro injection.

[0065] Figure 10: Sodium polyglutamate hydrogel formed under 100 kGy (higher) dose irradiation. Figure A shows the state of the hydrogel at the time of injection, and Figure B shows the state of the hydrogel after in vitro injection. Detailed Implementation

[0066] The preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. It should be noted that the following embodiments are intended to facilitate understanding of the present invention and are not intended to limit it in any way. Unless otherwise specified, the raw materials and equipment used in the following specific embodiments are all known products and were obtained by purchasing commercially available products.

[0067] The inner diameter of the 18G needle described in this invention is 0.84 mm; the inner diameter of the 21G needle is 0.51 mm; the inner diameter of the 25G needle is 0.25 mm; and the inner diameter of the 34G needle is 0.06 mm.

[0068] Example 1: A method for preparing an injectable hydrogel

[0069] This embodiment provides a method for preparing an injectable hydrogel that can be extruded through a 25G needle. The preparation process is as follows: A 10% solution of sodium polyglutamate with a molecular weight of 2,000,000 is prepared. 1 mL of this solution is filled into a mixing syringe, sealed, and then irradiated with a 100 kGy electron beam to obtain a non-injectable hydrogel. A new 5 mL mixing syringe is filled with 4 mL of water, and the two syringes are pushed back and forth 30 times to mix thoroughly, yielding a hydrogel tissue filler. This filler can be injected through a 25G needle, exhibits good shape retention after extrusion, does not collapse within 24 hours, and has a degradation time greater than 720 hours.

[0070] Example 2: A method for preparing an injectable hydrogel

[0071] This embodiment provides a method for preparing an injectable hydrogel that can be extruded through an extremely fine 34G needle. The specific steps are as follows: A 10% solution of sodium polyglutamate with a molecular weight of 2,000,000 is prepared. 0.2 mL of this solution is filled into a mixing syringe, sealed, and then irradiated with a 100 kGy electron beam to obtain a non-injectable hydrogel. A new 5 mL mixing syringe is filled with 4 mL of water, and the two syringes are pushed back and forth 30 times to mix thoroughly, yielding a hydrogel tissue filler. This filler can be injected and extruded through a 34G needle. After extrusion, it exhibits good moldability, does not collapse within 24 hours, and has a degradation time greater than 720 hours.

[0072] Example 3: Disrupting the covalent bonds within non-injectable hydrogels is a necessary condition for preparing injectable hydrogels.

[0073] The non-injectable hydrogel prepared according to Example 1 was immersed in 5 times its weight of water to fully swell. After the hydrogel mass remained unchanged, it was filled into a syringe to obtain a hydrogel tissue filler. This filler can be extruded through an 18G needle but cannot pass through a 25G needle. It exhibits good shape retention after extrusion, does not collapse within 5 hours, and has a degradation time greater than 720 hours. These results indicate that merely swelling the hydrogel without breaking it does not produce a thinning effect, meaning it cannot be directly used for injection.

[0074] Example 4: The effect of crosslinking method on hydrogel

[0075] Both irradiation and chemical crosslinking agents can crosslink sodium polyglutamate (SO4) aqueous solutions to obtain SO4 hydrogels, but their reaction mechanisms differ. Irradiation crosslinking involves the formation of free radicals, which connect the carboxyl groups and methylene groups in SO4 to form a crosslinked network (Figure 1). Chemical crosslinking, on the other hand, uses small-molecule crosslinking agents to connect the carboxyl groups in SO4 to form a crosslinked network (Figure 2). To investigate the effects of these two crosslinking methods on the hydrogels, this example uses SO4 as a raw material to prepare irradiated crosslinked SO4 hydrogels (Figure 3) and chemically crosslinked SO4 hydrogels. The irradiation crosslinking method is the same as described in Example 1, and the chemical crosslinking steps are described in the reference (doi:10.3390 / polym14245505). The water retention rate (Figures 4-5) and light transmittance (Figure 6) of both hydrogels were measured.

[0076] The methods for determining water retention rate and light transmittance are as follows:

[0077] 1. Determination of water retention capacity: Take a fully swollen hydrogel, weigh it, and record the weight as W1. Then place it in an environment with a temperature of 298K and a humidity of 40%, and weigh it every 12 hours, recording the weight as W2. The water content at each time point is calculated as W2 / W1*100%. The ability of the hydrogel to slow down water loss in the environment is called water retention capacity.

[0078] 2. Measurement of transmittance: Using a stable incandescent lamp as the light source, place the hydrogel to be tested between the light source and the optical power meter, and record the reading T1 of the optical power meter. Remove the material to be tested, leaving only the optical power meter, and the reading of the optical power meter is T2. The transmittance of the material is calculated as T1 / T2*100%.

[0079] As shown in Figures 4 and 5, the water content of both irradiated and chemically cross-linked hydrogels decreased to varying degrees within 1.5 days. The irradiated cross-linked glutamate hydrogel experienced the smallest water loss, less than 40%, which was about 10% less than the chemically cross-linked hydrogel. Within the next 1.5 days, the water content of the irradiated cross-linked sodium polyglutamate hydrogel stabilized, while the chemically cross-linked hydrogel continued to decline slowly. By the third day, the water content of the irradiated cross-linked sodium polyglutamate hydrogel was still as high as 60%, while that of the chemically cross-linked sodium polyglutamate hydrogel was only 40%. This is because the chemical cross-linking method for preparing sodium polyglutamate (SPO) results in the linkages between glutamate molecules occurring primarily on the carboxyl groups, leading to a lower number of free carboxyl groups in the resulting SPO hydrogel. In contrast, irradiated cross-linked SPO hydrogels have more carboxyl groups that do not participate in the cross-linking process, resulting in a higher number of free carboxyl groups. Furthermore, carboxyl groups have excellent hydrophilicity, giving irradiated cross-linked SPO better water retention compared to chemically cross-linked SPO. Higher water retention means better moisturizing and water-locking properties, allowing for longer-lasting filling effects and maintaining elasticity at the injection site when used in cosmetic procedures. This characteristic of irradiated cross-linked SPO hydrogels offers significant advantages in cosmetic filling applications.

[0080] As shown in Figure 6, the transmittance of sodium polyglutamate hydrogel obtained by irradiation crosslinking is 5%–10% higher than that obtained by chemical crosslinking. This is because high-energy electron beams have better penetrating power, simultaneously promoting the generation of free radicals in various regions of the sodium polyglutamate aqueous solution and initiating crosslinking, resulting in a more uniform crosslinking of the hydrogel. In contrast, chemical reactions always begin in areas with higher concentrations of chemical crosslinking agents, resulting in a less uniform hydrogel. Therefore, compared to chemically crosslinked sodium polyglutamate hydrogels, irradiation-crosslinked sodium polyglutamate hydrogels have higher transmittance. Injectable products with high transmittance are more aesthetically pleasing and have higher user acceptance. Furthermore, transmittance is an indicator of the uniformity of the hydrogel; higher transmittance indicates a more uniform hydrogel, thus ensuring a uniform feel at the injection site after injection. In addition, fully crosslinked hydrogels can be obtained after approximately 30 minutes of irradiation, while chemically crosslinked sodium polyglutamate typically requires more than 24 hours.

[0081] In summary, considering water retention, light transmittance, and preparation time, the sodium glutamate hydrogel prepared by irradiation crosslinking is more suitable for use as a tissue filler product.

[0082] Example 5: Effect of cross-linking material on hydrogel properties

[0083] Besides sodium polyglutamate, carboxymethyl cellulose can also be used to prepare hydrogels under irradiation crosslinking conditions. To investigate the effect of the crosslinking target on the hydrogel, this embodiment prepared sodium polyglutamate hydrogels and carboxymethyl cellulose hydrogels using an irradiation method. The specific operation steps were the same as described in Example 1, except that the irradiation target was changed. The water retention rate of the carboxymethyl cellulose hydrogel was measured using the same method as described in Example 4. The specific results are shown in Figure 7.

[0084] As shown in Figure 7, the water retention of the irradiated crosslinked carboxymethyl cellulose hydrogel is between that of the irradiated crosslinked sodium polyglutamate hydrogel and the chemically crosslinked sodium polyglutamate hydrogel. It lost 50% of its water within three days, approximately 10% more than the irradiated crosslinked sodium polyglutamate aqueous solution. This may be because carboxymethyl cellulose has a polysaccharide structure with sterically hindered sugar ring structures in its molecular chain, resulting in a high viscosity of the carboxymethyl cellulose aqueous solution. Consequently, a highly soluble carboxymethyl cellulose aqueous solution cannot be obtained, leading to a lower concentration and consequently, a lower carboxyl group content in the final product. Furthermore, sufficient crosslinking cannot occur in the carboxymethyl cellulose aqueous solution during irradiation. Even carboxymethyl cellulose hydrogels prepared under high irradiation doses cannot be diluted to obtain injectable hydrogels with good moldability.

[0085] Sodium hyaluronate hydrogel is also a commonly used filler in medical aesthetics. To further compare the performance of sodium polyglutamate hydrogel and sodium hyaluronate hydrogel, this example also included a subcutaneous injection experiment in rats. Specifically, 1 mL of sodium polyglutamate hydrogel and 1 mL of hyaluronic acid hydrogel were injected subcutaneously into rats, and the filling effect after injection was observed. The preparation method of the injectable sodium polyglutamate hydrogel was the same as described in Example 1, and the sodium hyaluronate hydrogel was prepared with reference to Chinese Patent CN 104761734B.

[0086] As shown in Figure 8, sodium polyglutamate hydrogel exhibits better filling and shaping effects. In conclusion, compared with the two hydrogels mentioned above, sodium polyglutamate hydrogel is more suitable for cosmetic filling.

[0087] Based on the above results, this example uses sodium polyglutamate as a base and adds other polymers to optimize the properties of the resulting hydrogel. The preparation and measurement methods are the same as those described in Examples 1 and 4. The specific hydrogel composition and properties are shown in Table 1.

[0088] Table 1 Comparison of properties of hydrogels formed by composite polymers

[0089] As shown in Table 1, adding some high molecular weight polymers to sodium polyglutamate can improve the performance of the gel to varying degrees, especially the water retention rate. This may be because the addition of other polymers further enhances the cross-linking degree of the hydrogel network, with sodium hyaluronate showing the best effect.

[0090] Example 6: Effect of irradiation dose on the properties of sodium polyglutamate hydrogel

[0091] This embodiment investigated the effect of irradiation dose on sodium polyglutamate hydrogels. Except for the different electron beam irradiation intensities (20 / 40 / 100 / 150 / 200 kGy), the other operations were as described in Example 1. Subsequently, the flowability and shapeability of the obtained hydrogels (samples 12-16) were observed, and their degradation time was statistically analyzed. The specific results are shown in Table 2.

[0092] Table 2. Effect of different irradiation doses on the properties of sodium polyglutamate hydrogel

[0093] Table 2 shows that with increasing irradiation dose, the injectability and flowability of sodium polyglutamate hydrogels decrease, while their shapeability increases and degradation time prolongs. Figure 9 shows that the hydrogel formed after low-dose (20 kGy) irradiation (sample 6) can pass through the needle of a 25G syringe and forms droplet shapes when extruded (Figure 9A). However, when injected into a culture dish in vitro, it exhibits strong flowability but moderate shapeability (Figure 9B). Conversely, the hydrogel formed after higher-dose (100 kGy) irradiation (sample 8) can also pass through the needle of a 25G syringe, but the hydrogel extruded from the needle forms strips (Figure 10A), and does not exhibit significant flow when injected into a culture dish in vitro (Figure 10B). This may be because higher irradiation doses result in higher cross-linking, leading to a more compact molecular arrangement. Therefore, the hydrogel has stronger self-cohesive force, making it easier to maintain its shape and more difficult to degrade. However, considering parameters such as injectability, flowability, and moldability, the optimal dose range for irradiated sodium polyglutamate hydrogels is 70-130 kGy.

[0094] Example 7: Effect of Sodium Polyglutamate Molecular Weight on Sodium Polyglutamate Hydrogel

[0095] In this embodiment, a 10% solution of sodium polyglutamate with a molecular weight of 700,000 was prepared. 25g of this solution was filled into a mixing syringe, sealed, and then irradiated with a 100kGy electron beam. Another 5mL mixing syringe was filled with 4mL of water, and the two syringes were mixed thoroughly by pushing them together to obtain a hydrogel tissue filler. This filler can be extruded through a 25G syringe needle, exhibiting good moldability after extrusion, not collapsing within 24 hours, and degrading in less than 240 hours. Based on the above findings, the optimal molecular weight range for sodium polyglutamate used in preparing hydrogels is 700,000–2,000,000.

[0096] Example 8: Extrusion, sieving, and thinning

[0097] A 10% solution of sodium polyglutamate with a molecular weight of 2,000,000 was prepared, transferred to a 15 cm diameter petri dish, sealed, and then irradiated with an 80 kGy electron beam. The cross-linked hydrogel was then sieved through a 300-mesh sieve. 10 g of the sieved hydrogel was added to 50 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded through a 25 G syringe needle, exhibits good moldability after extrusion, does not collapse within 24 hours, and has a degradation time greater than 720 hours.

[0098] Example 9: Extrusion, sieving, and thinning

[0099] A 10% solution of sodium polyglutamate with a molecular weight of 700,000 was prepared, transferred to a 15 cm diameter petri dish, sealed, and then irradiated with a 40 kGy electron beam. The cross-linked hydrogel was then sieved through a 300-mesh sieve. 10 g of the sieved hydrogel was added to 50 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded through a 25 G syringe needle, exhibits good flowability, and has a degradation time of less than 120 hours.

[0100] Example 10: Extrusion, sieving, and thinning

[0101] A 10% solution of sodium polyglutamate with a molecular weight of 100,000 was prepared, transferred to a 15 cm diameter culture dish, sealed, and then irradiated with a 40 kGy electron beam. The cross-linked hydrogel was then sieved through a 300-mesh sieve. 2 g of the sieved hydrogel was added to 50 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded through a 25 G syringe needle, exhibits excellent flowability after extrusion, and has a degradation time of less than 240 hours.

[0102] Example 11: Drying and then grinding to thin out

[0103] A 10% solution of sodium polyglutamate with a molecular weight of 2,000,000 was prepared, transferred to a 15 cm diameter petri dish, sealed, and then irradiated with an 80 kGy electron beam. The cross-linked hydrogel was dried in a 65°C oven for 48 hours and then ground. 2 g of the ground hydrogel was added to 40 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded through a 25 G syringe needle, exhibits good shape retention after extrusion, does not collapse within 5 hours, and has a degradation time greater than 720 hours.

[0104] Example 12: Drying and then grinding to thin out

[0105] A 10% solution of sodium polyglutamate with a molecular weight of 100,000 was prepared, transferred to a 15 cm diameter culture dish, sealed, and then irradiated with an 80 kGy electron beam. The cross-linked hydrogel was lyophilized and then ground. 2 g of the ground hydrogel was added to 80 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded and injected through a 25 G syringe needle. It exhibits good shape retention after extrusion, does not collapse within 24 hours, and has a degradation time greater than 720 hours.

[0106] Example 13: Thinning by wet heat treatment

[0107] A 10% solution of sodium polyglutamate with a molecular weight of 100,000 was prepared, transferred to a 15 cm diameter petri dish, sealed, and then irradiated with an 80 kGy electron beam. The cross-linked hydrogel was then sterilized by moist heat at 121 °C for 8 minutes. 5 g of the moist-heat treated hydrogel was then added to 50 mL of water and magnetically stirred. After thorough mixing, the mixture was filled into syringes to obtain a hydrogel tissue filler. This filler can be extruded and injected through a 25 G syringe needle, exhibiting good moldability after extrusion and a degradation time greater than 720 hours.

[0108] Example 14: Comparison of thinning methods

[0109] To ensure successful injection of the hydrogel into the skin, a certain shear force needs to be applied to the prepared hydrogel to make it more fluid; this process is called thinning. Thinning methods include drug-injector thinning, sieve-extrusion thinning, drying-grinding thinning, and moist-heat thinning. This example compares the storage modulus and solid content of injectable hydrogels prepared by different thinning methods. The methods for determining the storage modulus and solid content are as follows, and the specific results are shown in Tables 3 and 4.

[0110] 1. Storage Modulus Testing Method

[0111] Take the fully swollen hydrogel and test it in an Anton Paar MCR 302 rheometer using dynamic time scanning. Set the strain to 1% and the frequency to 10 rad / s. Each test lasts for 60 seconds.

[0112] 2. Solid content detection method

[0113] Take the fully swollen hydrogel, weigh it, and record the weight as W1. Then freeze-dry the hydrogel, weigh it, and record the weight as W2. The solid content can be calculated as W2 / W1*100%.

[0114] Table 3 Comparison of storage modulus of injectable hydrogels prepared by different thinning methods

[0115] Table 4. Comparison of solid content of injectable hydrogels prepared by different thinning methods

[0116] As shown in Tables 3 and 4, the CV values ​​of storage modulus and solid content of the injectable hydrogel prepared by the drug-mixed syringe dilution method are significantly lower than those of hydrogels prepared by other dilution methods, indicating that the former has more stable quality between batches. This may be because this method has the simplest steps, is completed entirely within a sealed syringe, and does not require transfer or filling steps, thus reducing the risk of loss and facilitating quality control.

[0117] Irradiation not only provides energy for cross-linking polymers but is also a widely recognized sterilization method. Therefore, hydrogels cross-linked by irradiation meet sterility standards. Diluting the hydrogel using a drug-mixing syringe ensures that after irradiation, it requires no further processing, packaging, or sterilization; it can be used directly as the final product, requiring only a tube of sterile water for application. This method maximizes the cleanliness of the injectable hydrogel and is the simplest, most time-efficient, energy-saving, and environmentally friendly approach. Conversely, while hydrogels diluted through sieving, extrusion, drying, grinding, and moist heat treatment can also be used for injection, the numerous steps involved result in less stable physical and chemical properties compared to those obtained through drug-mixing syringe dilution.

[0118] In conclusion, the drug-mixing syringe dilution method is most suitable for diluting sodium polyglutamate hydrogels.

[0119] While the present invention has been disclosed above, it is not limited thereto. Its applications in medicine can be expanded accordingly. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing an injectable hydrogel, characterized in that, The method includes the following steps: preparing a non-injectable hydrogel by irradiation crosslinking; and preparing a hydrogel that can be extruded or injected through a needle after thinning the non-injectable hydrogel.

2. The preparation method according to claim 1, characterized in that, The thinning process involves breaking down the non-injectable hydrogel and mixing it with water.

3. The preparation method according to claim 2, characterized in that, The needle is a small-diameter needle, which is a needle with an inner diameter smaller than that of a 21G needle.

4. The preparation method according to claim 3, characterized in that, The non-injectable hydrogel was obtained by crosslinking a polymer aqueous solution through irradiation.

5. The preparation method according to claim 4, characterized in that, The polymer includes one or more of the following: sodium polyglutamate, sodium hyaluronate, carboxymethyl cellulose, polyethylene oxide, sodium alginate, and sodium carboxymethyl starch.

6. The preparation method according to claim 5, characterized in that, The molecular weight of the sodium polyglutamate is 100,000 to 2,000,000; the molecular weight of sodium hyaluronate is 200,000 to 3,000,000; the molecular weight of carboxymethyl cellulose is 5,000 to 1,000,000; the molecular weight of polyethylene oxide is 50,000 to 1,000,000; the molecular weight of sodium alginate is 5,000 to 100,000; and the molecular weight of sodium carboxymethyl starch is 10,000 to 1,000,000.

7. The preparation method according to claim 6, characterized in that, The polymer includes sodium polyglutamate.

8. The preparation method according to claim 7, characterized in that, The sodium polyglutamate has a molecular weight of 700,000 to 2,000,000.

9. The preparation method according to claim 6, characterized in that, The concentrations of the sodium polyglutamate aqueous solution are 5%–50%, the sodium hyaluronate aqueous solution are 5%–15%, the carboxymethyl cellulose aqueous solution is 2%–30%, the polyethylene oxide aqueous solution is 5%–30%, the sodium alginate aqueous solution is 2%–10%, and the sodium carboxymethyl starch aqueous solution is 5%–30%.

10. The preparation method according to claim 9, characterized in that, Before irradiation crosslinking, nitrogen gas needs to be introduced into the polymer aqueous solution to purge the oxygen in the polymer aqueous solution.

11. The preparation method according to claim 2, characterized in that, The irradiation crosslinking is performed using electron beam irradiation or cobalt-60 irradiation.

12. The preparation method according to claim 11, characterized in that, The dose for irradiation crosslinking is 5-200 kGy.

13. The preparation method according to claim 12, characterized in that, The irradiation crosslinking dose is 70-130 kGy.

14. The preparation method according to claim 2, characterized in that, The method for thinning non-injectable hydrogels includes one or more of the following: The first method: Use a mixing syringe to mix the non-injectable hydrogel and water in a mixer until they are thoroughly mixed. The second method involves squeezing the non-injectable hydrogel through a sieve and then mixing it thoroughly in water. The third method involves drying the non-injectable hydrogel, grinding it, and then mixing it with water. The fourth method involves sterilizing the non-injectable hydrogel with moist heat, followed by stirring and mixing it thoroughly in water.

15. The preparation method according to claim 14, characterized in that, The volume ratio of the non-injectable hydrogel to water described in the first, second, or fourth types is 1:0.5 to 1:

10.

16. The preparation method according to claim 15, characterized in that, The second type of sieve has a mesh size of 50-300 mesh.

17. The preparation method according to claim 16, characterized in that, The third type of non-injectable hydrogel has a mass ratio of 1:100 to 1:20 with water.

18. The preparation method according to claim 14, characterized in that, The method for thinning the non-injectable hydrogel is the first one.

19. An injectable hydrogel, characterized in that, Prepared using the method described in any one of claims 1 to 18.

20. Use of the injectable hydrogel of claim 19 for the preparation of hydrogel tissue fillers.

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