Sodium hyaluronate eye drop with low viscosity attenuation degree and preparation method thereof

Abstract

The present application relates to the field of pharmaceutical preparations, and discloses a sodium hyaluronate eye drop with low viscosity attenuation degree and a preparation method thereof.The sodium hyaluronate eye drop is composed of sodium hyaluronate, a tea polyphenol derivative with a steric hindrance structure, an isotonicity regulator composed of sodium chloride and boric acid, a phosphate buffer and water for injection.The phenolic hydroxyl group of the derivative forms a non-covalent hydrogen bond wrapping layer with the uronic acid residue of the sodium hyaluronate, which covers the glycosidic bond site.The preparation method comprises the following steps: dissolving the tea polyphenol derivative in anhydrous ethanol, injecting it into hot water, reducing pressure distillation, low-temperature swelling of the sodium hyaluronate, low-speed dropwise addition, temperature control incubation and low-temperature filtration sterilization.The steric hindrance effect of the wrapping layer blocks the attack of oxidase on the main chain, reduces the glycosidic bond rupture probability, prolongs the molecular weight degradation half-life, maintains the viscosity stability, and increases the firmness of the wrapping layer structure through glycol-boric acid complexation and ion-dipole interaction.

Description

Technical Field

[0001] This invention relates to the field of pharmaceutical preparations, and discloses a sodium hyaluronate eye drop with low viscosity attenuation and its preparation method. Background Technology

[0002] Sodium hyaluronate eye drops are used in ophthalmic treatment to lubricate the ocular surface and delay tear evaporation. Conventional sodium hyaluronate eye drop formulations with low viscosity decay primarily consist of sodium hyaluronate, isotonic adjusters, and buffer salts. In existing formulation processes, to reduce viscosity degradation of sodium hyaluronate during storage, a simple anaerobic filling process or the addition of conventional preservatives to inhibit bacterial growth is typically employed. Anaerobic filling involves introducing inert gas during the filling process to remove oxygen from the container headspace, while preservatives maintain the sterility of the solution by disrupting microbial cell membranes. Both of these conventional methods address external physical isolation or bacterial inhibition, failing to intervene in the structure of the sodium hyaluronate polymer chain itself.

[0003] The aforementioned conventional technical solutions have a core technical problem in practical applications: they cannot suppress the cleavage of sodium hyaluronate glycosidic bonds by residual oxygen in the bottle and reactive oxygen species and oxidases present in the tear fluid after instillation into the conjunctival sac. This leads to irreversible viscosity degradation of the product within its shelf life or during a single use after opening. Since a simple physical anaerobic process cannot completely eliminate trace amounts of dissolved oxygen in the solution, and preservatives do not have the function of blocking chemical bond cleavage, when the eye drops come into contact with the tear fluid on the ocular surface, the polymer backbone is directly exposed in an oxidative and enzymatic microenvironment, causing glycosidic bonds to break, molecular weight to decrease, and consequently, the eye drops to lose their original rheological water-retention properties. Summary of the Invention

[0004] To address the shortcomings of existing sodium hyaluronate eye drops, which cannot inhibit the cleavage of sodium hyaluronate glycosidic bonds by residual oxygen and reactive oxygen species and oxidases in ocular tear fluid, resulting in irreversible viscosity degradation and loss of original rheological water-retaining properties during the product's shelf life and single use, this invention provides a sodium hyaluronate eye drop with low viscosity attenuation and its preparation method.

[0005] To address the aforementioned technical problems, this invention provides a sodium hyaluronate eye drop with low viscosity attenuation. The eye drop comprises the following components by mass / volume percentage: 0.1%-0.3% sodium hyaluronate, 0.001%-0.05% a sterically hindered tea polyphenol derivative, 0.5%-1.0% an isotonic adjuster, an appropriate amount of pH adjuster, and the remainder being water for injection. The phenolic hydroxyl groups of the sterically hindered tea polyphenol derivative interact with the uronic acid residues on the sodium hyaluronate molecular chain to form a non-covalent hydrogen bond coating layer. This non-covalent hydrogen bond coating layer physically covers the glycosidic bond sites of the sodium hyaluronate molecular chain. The sterically hindered tea polyphenol derivative is an esterified derivative formed by introducing an aliphatic acyl substituent at the hydroxyl site of the tea polyphenol core.

[0006] The glycosidic bonds in the sodium hyaluronate molecular chain are the core targets for its degradation. They are easily attacked and broken by reactive oxygen species in the system or the ocular microenvironment, and hydrolyzed by glycosidases, leading to a decrease in molecular weight and viscosity. In this scheme, the aliphatic acyl esterified tea polyphenol derivative forms multidentate non-covalent hydrogen bonds with the carboxyl and hydroxyl groups on the uronic acid residues of the sodium hyaluronate molecular chain through the phenolic hydroxyl groups retained on the parent nucleus. This forms a non-covalent hydrogen bond coating layer in situ on the surface of the sodium hyaluronate molecular chain, which can directly and physically shield the vulnerable glycosidic bond sites on the sodium hyaluronate backbone. At the same time, the aliphatic acyl substituents introduced by the derivative can form a significant steric hindrance effect, further blocking the contact between reactive oxygen molecules, oxidases and glycosidic bonds. This blocks the degradation pathway of sodium hyaluronate at the molecular structure level and fundamentally inhibits the viscosity decrease of the eye drops during storage and ocular surface action.

[0007] Furthermore, in the above technical solution, the tea polyphenol derivative with a sterically hindered structure is acetylated epigallocatechin gallate, wherein the hydroxyl hydrogen atom on the galloyl group of the acetylated epigallocatechin gallate is completely replaced by an acetyl group, the phenolic hydroxyl hydrogen atom on the epigallocatechin skeleton is partially replaced by an acetyl group, and the degree of acetyl substitution of the acetylated epigallocatechin gallate is 3 to 5.

[0008] In practice, the galloyl group on the core of epigallocatechin gallate serves as the steric hindrance site. Complete acetylation of the hydroxyl group at this site forms a stable hydrophobic steric hindrance structure at the molecule's end, preventing disassembly of the assembled encapsulation layer in an aqueous system. Meanwhile, partial acetylation of the phenolic hydroxyl group on the epigallocatechin skeleton ensures sufficient phenolic hydroxyl groups for hydrogen bonding while precisely controlling the molecule's spatial conformation. An acetyl substitution degree of 3 to 5 balances the hydrogen bonding ability and steric hindrance effect of the derivative, ensuring both the efficiency of non-covalent hydrogen bond encapsulation layer formation and efficient steric shielding of glycosidic bond sites.

[0009] Furthermore, in the above technical solution, the weight-average molecular weight of the sodium hyaluronate is 800,000 to 1,200,000 Daltons, the molar ratio of uronic acid residues to N-acetylglucosamine residues in the sodium hyaluronate molecular chain is 1:1, and the molar binding ratio of the tea polyphenol derivative to the uronic acid residues in the non-covalent hydrogen bond coating layer is 0.5:1 to 2:1.

[0010] In practice, sodium hyaluronate with a weight-average molecular weight of 800,000 to 1,200,000 Daltons possesses rheological properties suitable for the lubrication and water retention needs of the ocular surface, as well as sufficient and uniformly distributed uronic acid residue binding sites. A 1:1 molar ratio of uronic acid residues to N-acetylglucosamine residues ensures a regular and uniform distribution of binding sites on the sodium hyaluronate molecular chain, preventing local aggregation or coverage gaps in the coating layer. A molar binding ratio of 0.5:1 to 2:1 allows for the formation of a non-covalent hydrogen-bonded coating layer with appropriate continuity on the sodium hyaluronate molecular chain. This avoids insufficient coverage of glycosidic bond sites due to an excessively low binding ratio, while also preventing intermolecular aggregation of derivative molecules caused by an excessively high binding ratio, thus ensuring the uniformity and structural stability of the coating layer.

[0011] Furthermore, in the above technical solution, the isotonic regulator is composed of sodium chloride and boric acid, wherein the mass-volume percentage of sodium chloride is 0.3%-0.6%, the mass-volume percentage of boric acid is 0.2%-0.4%, and the hydroxyl oxygen atom in the boric acid molecule forms a diol-boric acid complex with the free hydroxyl groups in the sodium hyaluronate molecular chain that are not covered by the non-covalent hydrogen bond coating layer.

[0012] In practice, sodium chloride can quickly adjust the osmotic pressure of the eye drop system to the physiologically compatible range of the ocular surface, avoiding ocular irritation caused by osmotic pressure differences. Boric acid molecules can form a stable five-membered ring diol-boric acid complex with the ortho-diol structure (free hydroxyl group) on the sodium hyaluronate molecular chain that is not covered by the hydrogen bond coating layer. This complex can further fix the conformation of the sodium hyaluronate molecular chain, reduce the random coiling of the molecular chain, and fill the weak sites of the molecular chain not covered by the coating layer, further blocking the attack of degradation factors. In addition, the weak buffering capacity of boric acid can help maintain the stability of the system pH value and reduce the adverse effects of environmental fluctuations on the hydrogen bond coating layer structure.

[0013] Furthermore, in the above technical solution, the pH adjuster is a phosphate buffer solution composed of disodium hydrogen phosphate and sodium dihydrogen phosphate, and the pH value of the eye drops is adjusted to 6.8-7.2. At this pH value, the phosphate ions in the phosphate buffer solution form an ion-dipole interaction with the free phenolic hydroxyl groups in the tea polyphenol derivative that are not substituted by aliphatic acyl groups.

[0014] In practice, a pH range of 6.8-7.2 perfectly matches the physiological pH of human tears, preventing irritation to the ocular surface during eye drop use. Simultaneously, this pH range allows phosphate ions in the phosphate buffer to be in a suitable dissociated state, forming stable ion-dipole interactions with the unsubstituted free phenolic hydroxyl groups in the tea polyphenol derivatives. This effect anchors the molecular conformation of the tea polyphenol derivatives, preventing intramolecular rotation in the aqueous system that would lead to the disassembly of the hydrogen-bonded coating layer. This significantly improves the structural stability of the coating layer under physiological ionic conditions, prolonging the effective action time of the eye drops on the ocular surface.

[0015] Furthermore, in the above technical solution, the non-covalent hydrogen bond coating layer is discontinuously distributed on the sodium hyaluronate molecular chain. In the 1H NMR spectrum of the eye drops, the characteristic peak of the phenolic hydroxyl proton of the tea polyphenol derivative is shifted to a lower field by 0.3 ppm to 0.8 ppm relative to the characteristic peak of the phenolic hydroxyl proton of the free state of the tea polyphenol derivative, and the hydrogen bond length of the non-covalent hydrogen bond coating layer is 0.18 nm to 0.22 nm.

[0016] In practice, the discontinuously distributed non-covalent hydrogen bond coating layer can effectively cover the glycosidic bond sites while preserving the hydrophilic properties and rheological properties of the sodium hyaluronate molecular chain itself, avoiding the loss of the lubrication and water retention function of sodium hyaluronate caused by continuous coating. The chemical shift of the phenolic hydroxyl hydrogen proton to the low field of 0.3ppm to 0.8ppm and the hydrogen bond length of 0.18-0.22nm confirm the formation of strong hydrogen bond interactions. The strength of hydrogen bonds not only ensures the structural stability of the coating layer under storage and physiological conditions, but also has a certain degree of dynamic reversibility, and will not irreversibly shield the physiological function of the sodium hyaluronate molecular chain.

[0017] To address the aforementioned technical problems, the present invention also provides a method for preparing sodium hyaluronate eye drops with low viscosity attenuation, used to prepare sodium hyaluronate eye drops with low viscosity attenuation as described in any of the above claims. The preparation method includes the following steps: Step S1: Disperse the tea polyphenol derivative with a sterically hindered structure in a portion of water for injection to obtain a first aqueous solution; Step S2: Add sodium hyaluronate to the remaining water for injection, allow it to stand and swell to obtain a second aqueous solution; Step S3: Under light-protected conditions, the first aqueous solution is added dropwise to the second aqueous solution which is being continuously stirred at a constant flow rate. After the addition is complete, stirring and incubation are continued to obtain a mixture. Step S4: Add isotonic regulator and pH regulator to the mixture in sequence, mix well and make up to volume to obtain initial solution; Step S5: Filter and sterilize the initial solution, and then dispense it.

[0018] This preparation method avoids the problem of excessively high local concentrations that occur when the two components are directly mixed by preparing a first aqueous solution of tea polyphenol derivatives and a second aqueous solution of sodium hyaluronate in steps, thus preventing derivative aggregation and uneven hydrogen bonding. The light-protected conditions prevent oxidative degradation of the tea polyphenol derivatives. The constant flow rate dropwise addition and continuous stirring incubation process allow the tea polyphenol derivative molecules and the fully extended sodium hyaluronate molecular chains to fully contact in a mild aqueous environment, orderly assembling to form a uniform non-covalent hydrogen bond coating layer, avoiding local over-density or missing coating layers caused by rapid mixing. The sequential addition of isotonic and pH adjusters prevents drastic fluctuations in osmotic pressure and pH value from damaging the already formed hydrogen bond coating layer structure. The final filtration sterilization and dispensing process ensures the sterility of the formulation while avoiding the damage to non-covalent interactions caused by high-temperature sterilization, ultimately yielding sodium hyaluronate eye drops with excellent viscosity stability and a homogeneous system.

[0019] Furthermore, in the above technical solution, in step S1, the tea polyphenol derivative with steric hindrance structure is first dissolved in anhydrous ethanol to form a precursor solution. The precursor solution is then injected into a portion of water for injection at a temperature of 40°C to 50°C under stirring conditions of 200 rpm to 400 rpm. Subsequently, the anhydrous ethanol is removed by vacuum distillation, and the solution is cooled to room temperature to obtain the first aqueous solution.

[0020] In practice, tea polyphenol derivatives with aliphatic acyl substituents are hydrophobic and easily form micron-sized aggregates when directly dispersed in water, making it impossible to achieve molecular-level contact with sodium hyaluronate molecular chains. Anhydrous ethanol can effectively dissolve the derivative, forming a uniform molecular-level precursor solution. Injecting this precursor solution into water for injection at 40℃-50℃ under stirring allows the derivative molecules to disperse rapidly and uniformly in the aqueous phase, avoiding the formation of aggregates. Subsequent vacuum distillation can completely remove anhydrous ethanol, avoiding the irritation of the ocular surface by organic solvents, while ensuring that the subsequent hydrogen bond assembly process is not interfered with by organic solvents. Finally, a molecularly dispersed aqueous solution of tea polyphenol derivatives is obtained, laying the foundation for the formation of a uniform coating layer.

[0021] Furthermore, in the above technical solution, in step S2, the temperature for static swelling is 2°C to 8°C, and the time for static swelling is 12 hours to 24 hours; in step S3, the dropping rate of the first aqueous solution is 0.5 ml / min to 2 ml / min, the continuous stirring rate is 100 rpm to 300 rpm, the temperature for continued stirring and incubation is 25°C, and the time for continued stirring and incubation is 2 hours to 4 hours.

[0022] In practice, static swelling at 2℃-8℃ allows the sodium hyaluronate molecular chains to fully expand in a shear-free environment, avoiding premature degradation caused by high-temperature swelling, while ensuring full exposure of all uronic acid residue binding sites on the molecular chains. Low-speed dropping at 0.5-2 mL / min and gentle stirring at 100-300 r / min allow the tea polyphenol derivative molecules to form hydrogen bonds with the expanded sodium hyaluronate molecular chains point-by-point and in an orderly manner, avoiding uneven hydrogen bond formation and molecular chain breakage caused by excessively fast dropping or stirring rates. Incubation at a constant temperature of 25℃ for 2-4 hours allows the hydrogen bond assembly process to reach thermodynamic equilibrium, ensuring the binding rate and uniformity of the non-covalent hydrogen bond coating layer and achieving effective coverage of glycosidic bond sites.

[0023] Furthermore, in the above technical solution, in step S4, after adding the isotonic regulator to the mixture, the pH value of the system is adjusted using a 0.1 mol / L sodium hydroxide solution, and then the pH regulator is added to adjust the pH value of the system to the final set value. In step S5, the filtration sterilization uses a polyethersulfone microporous filter membrane with a pore size of 0.22 micrometers, the operating temperature of the filtration sterilization is 2°C to 8°C, and the pressure difference of the filtration sterilization is 0.1 MPa to 0.15 MPa.

[0024] In practice, after adding the isotonic adjuster, the pH value is first roughly adjusted with sodium hydroxide solution, and then finely adjusted to the final set value with phosphate buffer solution. This avoids drastic fluctuations in the pH value of the system and prevents the disassembly and assembly of the non-covalent hydrogen bond coating layer caused by sudden pH changes. The 0.22-micron polyethersulfone microporous filter membrane can achieve sterile filtration of the formulation. At the same time, the polyethersulfone material has extremely low adsorption of sodium hyaluronate and tea polyphenol derivatives, which can avoid the loss of effective ingredients. The low temperature filtration conditions of 2℃-8℃ can further reduce the damage of sodium hyaluronate molecular chains to the shear force during filtration, while maintaining the structural stability of the hydrogen bond coating layer. The filtration pressure difference of 0.1-0.15MPa can ensure filtration efficiency while avoiding the breakage of sodium hyaluronate molecular chains and the destruction of the coating layer structure caused by high pressure difference, ultimately ensuring the viscosity stability and sterility level of the finished formulation.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces a tea polyphenol derivative with a sterically hindered structure into the formulation, causing its phenolic hydroxyl groups to form a non-covalent hydrogen bond coating layer with the uronic acid residues on the sodium hyaluronate molecular chain, physically covering the glycosidic bond sites and blocking the attack pathways of dissolved oxygen and oxidases on the main chain. Specifically, acetylated epigallocatechin gallate with an acetyl substitution degree between three and five is used. By controlling the molar binding ratio of this derivative to the uronic acid residues, the steric hindrance effect of the coating layer is utilized to reduce the probability of glycosidic bond breakage in the oxidative and enzymatic microenvironment, prolonging the molecular weight degradation half-life of the product during storage and ocular surface application, and maintaining the stability of solution viscosity.

[0026] 2. Based on the aforementioned coating layer, this invention utilizes an isotonic regulator system composed of sodium chloride and boric acid. Boric acid molecules form a diol-boric acid complex with the free hydroxyl groups of sodium hyaluronate. This, combined with the ion-dipole interaction between the phosphate buffer system and the free phenolic hydroxyl groups at specific pH levels, increases the structural robustness of the coating layer in complex ionic environments. In the preparation process, the tea polyphenol derivative is first dissolved in anhydrous ethanol, then injected into hot water, and finally distilled under reduced pressure to remove the solvent, improving the dispersion of the derivative in the aqueous phase. The low-temperature static swelling of sodium hyaluronate and the slow-speed dropwise addition of the first aqueous solution to the second aqueous solution, along with temperature-controlled incubation, ensure the uniform formation of the non-covalent hydrogen bond coating layer. The final low-temperature microporous membrane filtration sterilization process avoids the damage to the coating layer structure caused by high-temperature sterilization, ensuring the overall homogeneity of the final formulation system. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0028] Example 1: Formulation composition (per 1000 mL) Table 1. Formulation composition of Example 1

[0029] Preparation method: Step S1: Weigh 0.2g of acetylated epigallocatechin gallate, add it to 10mL of anhydrous ethanol, and stir until completely dissolved to form a precursor solution; take 300mL of water for injection, heat it to 45℃, and slowly inject the precursor solution at a stirring rate of 300 rpm. After stirring for 30 minutes, remove the anhydrous ethanol by vacuum distillation under a vacuum of 0.08MPa, and cool to room temperature to obtain the first aqueous solution.

[0030] Step S2: Weigh 2.0g of sodium hyaluronate and add it to the remaining 690mL of water for injection. Place the solution in a 4℃ refrigerator and let it swell for 18 hours. Stir gently once every 6 hours for 5 minutes each time to obtain a homogeneous second aqueous solution.

[0031] Step S3: Transfer both the first and second aqueous solutions to a light-protected reaction vessel. Under continuous stirring at 150 rpm, add the first aqueous solution dropwise to the second aqueous solution at a rate of 1.0 mL / min. After the addition is complete, maintain a constant temperature of 25°C and continue stirring and incubating for 3 hours to obtain a mixed solution.

[0032] Step S4: Add 4.0g sodium chloride and 3.0g boric acid to the mixture in sequence, stir until completely dissolved, adjust the pH of the system to 6.5 with 0.1 mol / L sodium hydroxide solution, then add phosphate buffer to finely adjust the pH to 7.0, add water for injection to make up to 1000mL, stir well to obtain the initial solution.

[0033] Step S5: Transfer the initial solution to a low-temperature filtration system and filter it through a polyethersulfone microporous membrane with a pore size of 0.22 micrometers at 5°C and a pressure difference of 0.12 MPa for sterilization. Then, dispense it into 10 mL ophthalmic drop bottles under sterile conditions to obtain the finished product.

[0034] Example 2: The difference from Example 1 is that the mass-volume percentage of sodium hyaluronate is 0.1% (1.0g), the mass-volume percentage of tea polyphenol derivative is 0.001% (0.01g), and the other conditions are the same as in Example 1.

[0035] Example 3: The difference from Example 1 is that the mass-volume percentage of sodium hyaluronate is 0.3% (3.0g), the mass-volume percentage of tea polyphenol derivative is 0.05% (0.5g), and the other conditions are the same as in Example 1.

[0036] Example 4: The difference from Example 1 is that the degree of acetyl substitution of epigallocatechin gallate is 3, the molar ratio of tea polyphenol derivative to uronic acid residue is 0.5:1, and the other conditions are the same as in Example 1.

[0037] Example 5: The difference from Example 1 is that the degree of acetyl substitution of epigallocatechin gallate is 5, the molar ratio of tea polyphenol derivative to uronic acid residue is 2:1, and the other conditions are the same as in Example 1.

[0038] Example 6: The difference from Example 1 is that the mass-volume percentage of sodium chloride in the isotonic conditioner is 0.3% (3.0g), the mass-volume percentage of boric acid is 0.2% (2.0g), and the other conditions are the same as in Example 1.

[0039] Example 7: The difference from Example 1 is that the mass-volume percentage of sodium chloride in the isotonic conditioner is 0.6% (6.0g), the mass-volume percentage of boric acid is 0.4% (4.0g), and the other conditions are the same as in Example 1.

[0040] Example 8: The difference from Example 1 is that the pH value of the eye drops is adjusted to 6.8, while the other conditions are the same as in Example 1.

[0041] Example 9: The difference from Example 1 is that the pH value of the eye drops is adjusted to 7.2, and the other conditions are the same as in Example 1.

[0042] Example 10: The difference from Example 1 is that the temperature of the water for injection in step S1 is 40°C and the stirring rate is 200 rpm; in step S3, the dropping rate of the first aqueous solution is 0.5 mL / min, the stirring rate is 100 rpm, the incubation time is 2 hours, and the other conditions are the same as in Example 1.

[0043] Example 11: The difference from Example 1 is that the temperature of the water for injection in step S1 is 50°C and the stirring rate is 400 rpm; in step S3, the dropping rate of the first aqueous solution is 2.0 mL / min, the stirring rate is 300 rpm, the incubation time is 4 hours, and the other conditions are the same as in Example 1.

[0044] Example 12: The difference from Example 1 is that the static swelling temperature in step S2 is 2°C and the swelling time is 12 hours; the filtration sterilization temperature in step S5 is 2°C and the pressure difference is 0.1 MPa, and the other conditions are the same as in Example 1.

[0045] Comparative Example 1: The difference from Example 1 is that no tea polyphenol derivative with a steric hindrance structure was added to the formulation, and the other conditions were the same as in Example 1.

[0046] Comparative Example 2: Using conventional formulations and processes from the background art: The formulation consisted of 0.2% sodium hyaluronate, 0.7% sodium chloride, an appropriate amount of phosphate buffer, and the remainder being water for injection; the preparation process was to directly add sodium hyaluronate to water for injection to swell at room temperature for 8 hours, add sodium chloride and buffer to adjust the pH to 7.0, sterilize at high temperature (121°C, 20 minutes), and then dispense. The remaining conditions were the same as in Example 1.

[0047] Comparative Example 3: The difference from Example 1 is that the degree of acetyl substitution of epigallocatechin gallate is 6 (outside the range of 3-5), the molar ratio of tea polyphenol derivative to uronic acid residue is 3:1 (outside the range of 0.5:1 to 2:1), and the other conditions are the same as in Example 1.

[0048] Comparative Example 4: The difference from Example 1 is that the anhydrous ethanol dissolution-reduced pressure distillation process was not used in step S1. Instead, the tea polyphenol derivative was directly added to water for injection and stirred and dispersed. The other conditions were the same as in Example 1.

[0049] Test method: Initial viscosity: measured using a rotational viscometer at 25°C and a shear rate of 10 s. -1 The initial viscosity (mPa) of the finished product was measured under the following conditions. s).

[0050] Accelerate storage stability: Store the sample in an environment of 40℃ and 75% RH for 3 months, measure the viscosity after storage, and calculate the viscosity retention rate (viscosity after storage / initial viscosity × 100%).

[0051] Ocular surface simulation stability: The sample was mixed with artificial tears at a 1:1 volume ratio and incubated at 37°C for 2 hours. The viscosity retention rate after incubation was measured (viscosity after incubation / initial viscosity × 100%).

[0052] Molecular weight degradation half-life: The time (in days) required for the molecular weight of a sample to decrease to 50% of its initial value under accelerated storage conditions, determined by gel permeation chromatography (GPC).

[0053] System homogeneity: The coefficient of variation (CV%) of the particle size distribution of the dispersed phase in the sample is measured by a laser particle size analyzer. The smaller the CV%, the better the homogeneity.

[0054] Test results: Table 2 Performance test results of each embodiment and comparative example

[0055] Results analysis: All embodiments showed viscosity retention rates above 85% after 3 months of accelerated storage, above 81% after 2 hours of simulated ocular surface storage, and molecular weight degradation half-life exceeding 198 days. The system homogeneity CV% was below 3.8%, fully verifying the effectiveness and robustness of the technical solution of this invention. Example 1, as the best embodiment, exhibited optimal performance across all indicators. This is because: the optimized ratio of sodium hyaluronate to tea polyphenol derivative, the acetyl substitution degree of 4, and the 1:1 molar binding ratio enabled the non-covalent hydrogen bond coating layer to achieve efficient coverage and spatial shielding of glycosidic bond sites; the reasonable isotonicity regulator composition and pH value (7.0) further enhanced the structural stability of the coating layer through diol-boric acid complexation and ion-dipole interaction; and the optimized preparation process (anhydrous ethanol dispersion, low-temperature swelling, low-speed dropwise incubation, and low-temperature filtration) ensured the uniform formation and structural integrity of the coating layer, thereby achieving optimal viscosity stability and molecular weight retention.

[0056] Examples 2-9 achieved good results by adjusting the proportion of core components, the degree of substitution of derivatives, the ratio of excipients, and the pH value, demonstrating that the formulation range of the present invention has a wide range of applicability. Examples 10-12 showed no significant decrease in various performance indicators by changing the preparation process parameters (temperature, stirring rate, dropping rate, etc.), confirming the universality and robustness of the preparation method of the present invention. Those skilled in the art can flexibly adjust the parameters within the scope defined in the claims without affecting the technical effect.

[0057] Comparative Example 1, lacking the addition of tea polyphenol derivatives with steric hindrance structures, was unable to form a non-covalent hydrogen bond coating layer. The glycosidic bonds of the sodium hyaluronate molecular chain were directly exposed to the environment, resulting in a viscosity retention rate of only 42.6% after 3 months of accelerated storage, a simulated viscosity retention rate of only 35.8% on the ocular surface, and a molecular weight degradation half-life of only 68 days, significantly lower than the Example Group. This fully demonstrates that the tea polyphenol derivative is the core component for achieving the technical effects of this invention, and the hydrogen bond coating layer it forms can effectively block degradation pathways.

[0058] Comparative Example 2 uses conventional formulations and processes from existing technologies, without adding tea polyphenol derivatives and employing high-temperature sterilization. The high temperature causes partial breakage of the sodium hyaluronate molecular chain, and there is a lack of protection for glycosidic bonds. Its accelerated storage viscosity retention rate is only 51.3%, the ocular surface simulated viscosity retention rate is 40.2%, and the system homogeneity CV% reaches 5.7%, which is far worse than Example 1. This confirms that the technical solution of the present invention has a breakthrough improvement compared with the prior art, and solves the technical pain point that traditional processes cannot inhibit the breakage of glycosidic bonds.

[0059] Comparative Example 3 has a tea polyphenol derivative with an acetyl substitution degree (6) and a molar binding ratio (3:1) that exceed the range defined in the claims. The excessively high substitution degree leads to an insufficient number of phenolic hydroxyl groups in the derivative, resulting in a decrease in hydrogen bonding ability. The excessively high binding ratio causes intermolecular aggregation of the derivative, resulting in uneven coating and easy disassembly. Therefore, its viscosity retention rate and molecular weight degradation half-life are significantly lower than those of the Example Group. This shows that the parameter range defined in the claims is the key to achieving excellent results. If the range is exceeded, the expected technical effect cannot be achieved.

[0060] Comparative Example 4, due to the absence of anhydrous ethanol dissolution-reduced pressure distillation process, resulted in the direct dispersion of tea polyphenol derivatives in water, forming aggregates that could not achieve molecular-level contact with sodium hyaluronate molecular chains. This led to uneven formation of the hydrogen bond coating layer, with the system uniformity CV% reaching as high as 8.9%. Viscosity retention and molecular weight stability also decreased significantly. This demonstrates that the special preparation process of this invention is a necessary condition for ensuring the uniformity and structural stability of the coating layer. Omitting this step would result in a significant reduction in the technical effect.

[0061] In summary, this invention achieves high viscosity stability of sodium hyaluronate eye drops during storage and ocular surface application by introducing a tea polyphenol derivative with a steric hindrance structure to form a non-covalent hydrogen bond coating layer, combined with an optimized excipient system and preparation process. Its technical effect is significantly superior to the prior art and comparative examples that deviate from the technical solution of this invention. Moreover, this effect is achieved through the synergistic effect of various technical features, possessing outstanding substantive characteristics and significant progress, and meeting the inventiveness requirements of patent law.

Claims

1. A sodium hyaluronate eye drop with low viscosity attenuation, characterized in that, The eye drops consist of the following components by weight / volume percentage: Sodium hyaluronate 0.1%-0.3%, sterically hindered tea polyphenol derivatives 0.001%-0.05%, isotonicity regulator 0.5%-1.0%, pH regulator as needed, and the remainder is water for injection; The phenolic hydroxyl group of the sterically hindered tea polyphenol derivative and the uronic acid residues on the sodium hyaluronate molecular chain form a non-covalent hydrogen bond coating layer through intermolecular interactions. The non-covalent hydrogen bond coating layer physically covers the glycosidic bond sites of the sodium hyaluronate molecular chain. The sterically hindered tea polyphenol derivative is an esterified derivative formed by introducing an aliphatic acyl substituent at the hydroxyl site of the tea polyphenol core. The sterically hindered tea polyphenol derivative is acetylated epigallocatechin gallate, wherein the hydroxyl hydrogen atom on the galloyl group of the acetylated epigallocatechin gallate is completely replaced by an acetyl group, and the phenolic hydroxyl hydrogen atom on the epigallocatechin skeleton is partially replaced by an acetyl group, and the degree of acetyl substitution of the acetylated epigallocatechin gallate is 3 to 5. The isotonic regulator is composed of sodium chloride and boric acid, wherein the mass-volume percentage of sodium chloride is 0.3%-0.6% and the mass-volume percentage of boric acid is 0.2%-0.4%. The hydroxyl oxygen atom in the boric acid molecule forms a diol-boric acid complex with the free hydroxyl group in the sodium hyaluronate molecular chain that is not covered by the non-covalent hydrogen bond coating layer. The pH adjuster is a phosphate buffer solution composed of disodium hydrogen phosphate and sodium dihydrogen phosphate. The pH value of the eye drops is adjusted to 6.8-7.

2. At this pH value, the phosphate ions in the phosphate buffer solution form an ion-dipole interaction with the free phenolic hydroxyl groups in the tea polyphenol derivative that are not substituted by aliphatic acyl groups.

2. The sodium hyaluronate eye drops with low viscosity attenuation according to claim 1, characterized in that, The sodium hyaluronate has a weight-average molecular weight of 800,000 to 1,200,000 Daltons, the molar ratio of uronic acid residues to N-acetylglucosamine residues in the sodium hyaluronate molecular chain is 1:1, and the molar ratio of the tea polyphenol derivative to the uronic acid residues in the non-covalent hydrogen bond coating layer is 0.5:1 to 2:

1.

3. The sodium hyaluronate eye drops with low viscosity attenuation according to claim 1, characterized in that, The non-covalent hydrogen bond coating layer is discontinuously distributed on the sodium hyaluronate molecular chain. In the 1H NMR spectrum of the eye drops, the characteristic peak of the phenolic hydroxyl proton of the tea polyphenol derivative is shifted to a lower field by 0.3 ppm to 0.8 ppm relative to the characteristic peak of the phenolic hydroxyl proton of the free state of the tea polyphenol derivative. The hydrogen bond length of the non-covalent hydrogen bond coating layer is 0.18 nm to 0.22 nm.

4. A method for preparing sodium hyaluronate eye drops with low viscosity attenuation, used to prepare the eye drops according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: Step S1: Disperse the tea polyphenol derivative with a sterically hindered structure in a portion of water for injection to obtain a first aqueous solution; Step S2: Add sodium hyaluronate to the remaining water for injection, allow it to stand and swell to obtain a second aqueous solution; Step S3: Under light-protected conditions, the first aqueous solution is added dropwise to the second aqueous solution which is being continuously stirred at a constant flow rate. After the addition is complete, stirring and incubation are continued to obtain a mixture. Step S4: Add isotonic regulator and pH regulator to the mixture in sequence, mix well and make up to volume to obtain initial solution; Step S5: Filter and sterilize the initial solution, and then dispense it.

5. The method for preparing sodium hyaluronate eye drops with low viscosity attenuation according to claim 4, characterized in that, In step S1, the tea polyphenol derivative with steric hindrance structure is first dissolved in anhydrous ethanol to form a precursor solution. The precursor solution is then injected into a portion of water for injection at a temperature of 40°C to 50°C under stirring conditions of 200 rpm to 400 rpm. Subsequently, the anhydrous ethanol is removed by vacuum distillation, and the solution is cooled to room temperature to obtain the first aqueous solution.

6. The method for preparing sodium hyaluronate eye drops with low viscosity attenuation according to claim 5, characterized in that, In step S2, the temperature for static swelling is 2°C to 8°C, and the time for static swelling is 12 hours to 24 hours. In step S3, the dropping rate of the first aqueous solution is 0.5 mL / min to 2 mL / min, the continuous stirring rate is 100 rpm to 300 rpm, the temperature for continued stirring and incubation is 25°C, and the duration of continued stirring and incubation is 2 hours to 4 hours.

7. The method for preparing sodium hyaluronate eye drops with low viscosity attenuation according to claim 4, characterized in that, In step S4, after adding the isotonic adjuster to the mixture, the pH value of the system is adjusted using a 0.1 mol / L sodium hydroxide solution, and then the pH adjuster is added to adjust the pH value of the system to the final set value. In step S5, the filtration sterilization uses a polyethersulfone microporous filter membrane with a pore size of 0.22 micrometers, the operating temperature of the filtration sterilization is 2°C to 8°C, and the pressure difference of the filtration sterilization is 0.1 MPa to 0.15 MPa.

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