High-strength high-storage-stability temperature-sensitive phase-change reversible hydrogel and preparation method thereof

Abstract

The application discloses a high-strength high-storage-stability temperature-sensitive phase-change reversible hydrogel and a preparation method thereof, and belongs to the technical field of hydrogel preparation. The high-strength high-storage-stability temperature-sensitive phase-change reversible hydrogel is prepared by using poly-N-isopropyl acrylamide as a matrix, gelatin grafted gallic acid as a entanglement agent, polyvinyl alcohol as a deconstruction agent, and deionized water as a solvent, and stirring at low temperature. The hydrogel prepared by the application has high phase-change temperature and storage stability, good mechanical properties, excellent biocompatibility, temperature-sensitive phase-change property and temperature-sensitive phase-change reversibility, is non-toxic, injectable, degradable, and simple in the preparation method, and is mainly used in the medical and cosmetic fields, and has remarkable economic value and social benefits.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogel preparation, and particularly relates to a high-strength high-storage-stability temperature-sensitive phase-change reversible hydrogel and a preparation method thereof. BACKGROUND

[0002] Hydrogels have become excellent drug carrier materials due to their versatility in preparation methods, tunability in components, and biocompatibility, and are widely used in medical and cosmetic fields. However, hydrogels need to have certain mechanical properties when used, so the hydrogels widely used at present are mainly solid-state hydrogels. When patients receive treatment, solid-state hydrogels loaded with biological factors or drugs are injected into the human body through a needle tube. On the one hand, the large viscosity of the solid-state hydrogel will seriously affect the uniformity of the dispersion of the biological factors or drugs in the hydrogel carrier, and on the other hand, the large viscosity of the solid-state hydrogel makes it difficult to be injected into the human body through a generally thin needle tube, and only a thick needle tube can be selected to inject the solid-state hydrogel, which will result in a larger wound surface during the administration process and increase the pain of the patient. Patent CN117467159 A injectable medical temperature-sensitive hydrogel and a preparation method thereof uses N-isopropyl acrylamide as a monomer, azobisdimethylaminoformamide hydrochloride as an initiator, and poly-N-isopropyl acrylamide is prepared by free radical polymerization. After dialysis to remove impurities, the injectable medical temperature-sensitive hydrogel is prepared by mixing with polyvinyl alcohol and gallic acid and low-temperature stirring. Although the above hydrogel has certain mechanical properties, excellent biocompatibility, temperature-sensitive phase change and temperature-sensitive phase change reversibility, the phase change temperature of the above hydrogel is only 12-13℃, and the hydrogel needs to be stored at low temperature, and the storage stability is poor, and the maximum storage modulus of the above hydrogel is only 198-200 Pa, and the strength is relatively low, which seriously affects the wide application of the above hydrogel.

[0003] Patent CN118576748A Preparation method and application of an adhesive and antibacterial wound dressing gel and patent CN118496523A 3D printing hydrogel and preparation method and application thereof also have research reports on grafting gelatin with gallic acid for hydrogel, but these technologies usually use chemical catalytic reaction or photochemical reaction to chemically bond gelatin grafted with gallic acid and other high molecular polymers to form a hydrogel. On the one hand, chemical catalytic reaction or photochemical reaction involves a complex chemical reaction process, resulting in a relatively complex process of forming a hydrogel, and on the other hand, because gelatin grafted with gallic acid and other high molecular polymers form stable covalent bonds through chemical catalytic reaction or photochemical reaction, the formed hydrogel does not have phase change reversibility and has poor degradability. SUMMARY

[0004] The present application provides a high-strength and high-storage-stability temperature-sensitive phase-change reversible hydrogel and a preparation method thereof to solve the problems of low phase-change temperature, poor storage stability and low strength of the currently reported hydrogel.

[0005] To achieve the above object, the present application adopts the following technical scheme:

[0006] The preparation method of the high-strength and high-storage-stability temperature-sensitive phase-change reversible hydrogel comprises the following steps:

[0007] The preparation method of the high-strength and high-storage-stability temperature-sensitive phase-change reversible hydrogel comprises the following steps:

[0008] (1) 2-10 g of gelatin is added to 100-300 mL of deionized water, and mechanical stirring is carried out at 30-60 °C for 10-30 min to obtain a gelatin solution; then a mixture of gallic acid, 1-ethyl-(3-dimethylaminopropyl) carbonyl diimide and N-hydroxysuccinimide is added to a mixed solution of 100-300 mL of N,N-dimethylformamide and deionized water, and mechanical stirring is carried out at room temperature for 30-60 min to obtain a gallic acid mixed solution; finally, the gallic acid mixed solution is added dropwise to the gelatin solution, and mechanical stirring is carried out at 30-50 °C for 6-18 h; the reaction mixture is subjected to dialysis, filtration and freeze-drying to obtain gelatin grafted gallic acid;

[0009] (2) 3-12 g of poly-N-isopropyl acrylamide is added to 40-100 mL of deionized water, and mechanical stirring is carried out at 10-25 °C for 20-40 min to obtain a poly-N-isopropyl acrylamide solution; then 1-3 g of gelatin grafted gallic acid and 0.4-0.8 g of polyvinyl alcohol are added to 20-100 mL of deionized water, and mechanical stirring is carried out at 60-100 °C for 30-60 min, and then mechanical stirring is carried out at 10-25 °C for 20-40 min to obtain a mixed solution of gelatin grafted gallic acid and polyvinyl alcohol; finally, the mixed solution of gelatin grafted gallic acid and polyvinyl alcohol is added dropwise to the poly-N-isopropyl acrylamide solution, and mechanical stirring is carried out at 10-25 °C for 20-40 min, and then the mixture is placed at 10-15 °C for 10-20 min to obtain the high-strength and high-storage-stability temperature-sensitive phase-change reversible hydrogel.

[0010] Further, the relative molecular mass of the gelatin in step (1) is 10000-100000; the mass ratio of the gelatin and gallic acid is 2:1-4:1; the mass ratio of the 1-ethyl-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide mixture and gallic acid is 1:1-1.5:1; and the molar ratio of the 1-ethyl-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide is 1:2.

[0011] Further, the volume ratio of the N,N-dimethylformamide and deionized water in step (1) is 1:2-1:4.

[0012] Further, the temperature of the dialysis in step (1) is 25-35 ℃, the time is 7-14 d, the molecular weight cut-off is 3500 Da, and the dialysate is deionized water.

[0013] Further, the relative molecular mass of the polyvinyl alcohol in step (2) is 10000-100000.

[0014] A high-strength high-storage-stability temperature-sensitive phase-change reversible hydrogel prepared by the above method, wherein the phase transition temperature of the hydrogel is 32-33 ℃, the storage modulus at 37 ℃ is 542-548 Pa, the complex viscosity at 5 ℃ is 1.62-1.73 Pa·s, the complex viscosity at 37 ℃ is 78.5-79.6 Pa·s, the storage effective period is greater than 365 d, and the weight loss rate is 68.4-71.7 %.

[0015] The present application has the following advantages:

[0016] (1) The present application uses poly-N-isopropyl acrylamide as a base, gelatin grafted gallic acid as a entanglement agent, and polyvinyl alcohol as a deconstruction agent, and the three polymers are uniformly mixed by mechanical stirring. When the temperature is lower than the phase transition temperature, the hydrophilic effect of poly-N-isopropyl acrylamide dominated by amide group is stronger than the hydrophobic effect dominated by isopropyl group, the molecular chain segment is stretched, and it is stably dissolved in deionized water. At the same time, through the hydrogen bond effect between gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide, gelatin grafted gallic acid and polyvinyl alcohol can also be stably dissolved in deionized water, at this time the three polymers form transparent liquid hydrogel, and the gel strength is very low. When the temperature is higher than the phase transition temperature, the hydrophobic effect of poly-N-isopropyl acrylamide dominated by isopropyl group is stronger than the hydrophilic effect dominated by amide group, the molecular chain segment is curled, and at the same time, through the hydrogen bond effect between gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide, gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide form a stable entanglement structure, at this time the three polymers form white solid hydrogel. Because the molecular weight of gallic acid is much lower than that of gelatin, the entanglement effect of gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide is stronger than that of gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide, so when the temperature is higher than the phase transition temperature, the hydrogel prepared by the present application has high strength.

[0017] (2) The present application uses gelatin grafted gallic acid as an entanglement agent. Because gelatin grafted gallic acid and poly-N-isopropyl acrylamide have good compatibility, when the temperature is lower than the phase transition temperature, the stability of transparent liquid hydrogel can be greatly improved through the hydrogen bond effect between gelatin grafted gallic acid and poly-N-isopropyl acrylamide. And because the molecular weight of gelatin is much higher than that of gallic acid, when the temperature rises, the hydrogen bond effect between gelatin grafted gallic acid and poly-N-isopropyl acrylamide limits the curling of poly-N-isopropyl acrylamide molecular chain segment, so the hydrogel prepared by the present application has a high phase transition temperature. In addition, because the compatibility of gelatin and poly-N-isopropyl acrylamide is poor, if gelatin is directly mixed with poly-N-isopropyl acrylamide and polyvinyl alcohol, gelatin and poly-N-isopropyl acrylamide will appear stratification phenomenon, so the present application grafts gallic acid to the molecular chain of gelatin, mainly to improve the compatibility of gelatin and poly-N-isopropyl acrylamide.

[0018] (3) The present application uses the hydrogen bond effect between gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide to form white solid hydrogel, so the hydrogel has excellent temperature-sensitive phase transition reversibility. At the same time, because there is no chemical bond effect between gelatin grafted gallic acid, polyvinyl alcohol and poly-N-isopropyl acrylamide, the rapid degradation of gelatin grafted gallic acid in vivo will lead to the rapid decomposition of white solid hydrogel, and the hydrogel has excellent degradability.

[0019] (4) The polyvinyl alcohol in the present application mainly plays a role of deconstructing the coiled molecular chain of poly-N-isopropyl acrylamide. The hydroxyl density of the polyvinyl alcohol molecular chain is high, and with the decrease of temperature, the hydrophobic effect of the polyvinyl alcohol rapidly decreases, and the hydrophilic effect rapidly increases, so the polyvinyl alcohol can well eliminate the effect of the gelatin grafted gallic acid on stably entangling poly-N-isopropyl acrylamide, the molecular chain segment of the poly-N-isopropyl acrylamide can be rapidly converted into an extended structure, and the gelatin grafted gallic acid, the polyvinyl alcohol and the poly-N-isopropyl acrylamide are rapidly converted from a white solid hydrogel into a transparent liquid hydrogel, and the reversible phase transition of the hydrogel is completed.

[0020] (5) The hydrogel prepared by the present application has high phase transition temperature and storage stability, good mechanical properties, excellent biocompatibility, temperature-sensitive phase transition and temperature-sensitive phase transition reversibility, the phase transition temperature is 32-33 ℃, the storage modulus at 37 ℃ is 542-548 Pa, the complex viscosity at 5 ℃ is 1.62-1.73 Pa·s, the complex viscosity at 37 ℃ is 78.5-79.6 Pa·s, the storage effective period is greater than 365 d, the weight loss rate is 68.4-71.7 %, and the hydrogel is non-toxic, injectable and simple to prepare, and is mainly used in the fields of medical treatment and beauty, and has significant economic value and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the gelatin grafted gallic acid and the gelatin prepared in Example 1.

[0022] Figure 2 The infrared absorption spectrum of the poly-N-isopropyl acrylamide prepared in Example 1.

[0023] Figure 3 The morphology diagram of the hydrogel prepared in Example 1 at 18 ℃ (A), when the temperature is raised to 37 ℃ (B), and when the temperature is lowered to 18 ℃ (C) again.

[0024] Figure 4 The morphology diagram of the hydrogel prepared in Example 1 at 18 ℃ (A) and the finished product prepared in Comparative Example 1 at 5 ℃ for 15 d (B).

[0025] Figure 5 The morphology diagram of the finished product prepared in Comparative Example 2 (A) and Comparative Example 3 (B) at 18 ℃. DETAILED DESCRIPTION

[0026] In order to make the content of the present application more convenient to understand, the technical solutions of the present application will be further described below in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0027] Example 1

[0028] (1) First, 6 g of gelatin with a relative molecular mass of 50000 was added to 200 mL of deionized water, and a gelatin solution was prepared by mechanical stirring at 45 °C for 20 min. Then, 2 g of gallic acid, 2.4 g of a 1-ethyl-(3-dimethylaminopropyl) carbonyl diimide and N-hydroxysuccinimide mixture (molar ratio 1:2) were added to 200 mL of a mixed solution of N,N-dimethylformamide and deionized water with a volume ratio of 1:3, and a gallic acid mixed solution was prepared by mechanical stirring at room temperature for 45 min. Finally, the gallic acid mixed solution was added dropwise to the gelatin solution, and mechanical stirring was carried out at 40 °C for 12 h. After the reaction was completed, the reaction solution was poured into a dialysis bag with a molecular weight cut-off of 3500 Da, and dialysis was carried out in deionized water for 10 d at a dialysis temperature of 30 °C. After dialysis, filtration and freeze-drying were carried out to obtain gelatin grafted gallic acid.

[0029] (2) 7.5 g of poly-N-isopropyl acrylamide was added to 70 mL of deionized water, and a poly-N-isopropyl acrylamide solution was prepared by mechanical stirring at 18 °C for 30 min. Then, 2 g of gelatin grafted gallic acid and 0.6 g of polyvinyl alcohol with a relative molecular mass of 50000 were added to 60 mL of deionized water, and a mixed solution of gelatin grafted gallic acid and polyvinyl alcohol was prepared by mechanical stirring at 80 °C for 45 min and then at 18 °C for 30 min. Finally, the mixed solution of gelatin grafted gallic acid and polyvinyl alcohol was added dropwise to the poly-N-isopropyl acrylamide solution, and mechanical stirring was carried out at 18 °C for 30 min, and then the solution was left to stand at 12 °C for 15 min to obtain a hydrogel.

[0030] Figure 1 The gelatin grafted gallic acid prepared in this example was subjected to nuclear magnetic resonance hydrogen spectrum analysis. Compared with the nuclear magnetic resonance hydrogen spectrum of gelatin, the nuclear magnetic resonance hydrogen spectrum of the gelatin grafted gallic acid showed a new obvious resonance peak of hydrogen on the benzene ring at a chemical shift of 7.09 ppm, which indicated that the gallic acid was successfully bonded to the gelatin molecular chain.

[0031] Figure 2 The infrared absorption spectrum of the poly-N-isopropyl acrylamide prepared in this example is shown in the figure. As shown in the figure, the absorption peaks at 3417 cm -1 and 3274 cm -1 are N-H bond stretching vibration absorption peaks, the absorption peaks at 2976 cm -1 and 2936 cm -1 are C-H bond stretching vibration absorption peaks, and the absorption peaks at 1640 cm -1 and 1547 cm -1The absorption peaks at 1465 cm⁻¹ are the C=O absorption peak of the amide group and the bending vibration absorption peak of NH, respectively. -1 The absorption peak at 1388 cm⁻¹ is the absorption peak of the CH bending vibration. -1 and 1371 cm -1 The absorption peak at the position is formed by the symmetric deformation vibrational coupling split of the dimethyl group on the isopropyl group, which proves that poly-N-isopropylacrylamide has been successfully synthesized.

[0032] Figure 3 The figures show the morphology of the hydrogel prepared in this embodiment at 18 ℃ (A), heated to 37 ℃ (B), and cooled back to 18 ℃ (C). As shown in the figures, the hydrogel is a transparent liquid at 18 ℃, turns into a white solid at 37 ℃, and turns back into a transparent liquid at 18 ℃. This demonstrates that the hydrogel prepared by this invention has excellent temperature-sensitive phase transition reversibility.

[0033] Figure 4 (A) is a morphology diagram of the hydrogel prepared in this embodiment after standing at 18 °C for 365 days. As shown in the figure, the hydrogel remains a transparent liquid after standing at 18 °C for 365 days, without any layering or precipitation, which indicates that the hydrogel prepared by this invention has excellent storage stability.

[0034] Example 2

[0035] (1) 2 g of gelatin with a relative molecular mass of 10000 was added to 100 mL of deionized water and mechanically stirred at 30 °C for 30 min to obtain a gelatin solution. Then, 1 g of gallic acid, 1 g of a mixture of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide (molar ratio of 1:2) was added to 100 mL of a mixture of N,N-dimethylformamide and deionized water with a volume ratio of 1:2 and mechanically stirred at room temperature for 30 min to obtain a gallic acid solution. Finally, the gallic acid solution was added dropwise to the gelatin solution and mechanically stirred at 30 °C for 18 h. After the reaction was completed, the reaction solution was poured into a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed with deionized water for 14 days at a dialysis temperature of 25 °C. After dialysis, the gelatin-grafted gallic acid was obtained by filtration and freeze-drying.

[0036] (2) 3 g of poly-N-isopropyl acrylamide was added into 40 mL of deionized water, and mechanically stirred at 10 °C for 40 min to prepare a poly-N-isopropyl acrylamide solution; 1 g of gelatin grafted gallic acid and 0.4 g of polyvinyl alcohol with a relative molecular mass of 10000 were added into 20 mL of deionized water, and mechanically stirred at 60 °C for 60 min, and then mechanically stirred at 10 °C for 40 min to prepare a mixed solution of gelatin grafted gallic acid and polyvinyl alcohol, and finally the mixed solution of gelatin grafted gallic acid and polyvinyl alcohol was added dropwise into the poly-N-isopropyl acrylamide solution, and mechanically stirred at 10 °C for 40 min, and then left to stand at 10 °C for 10 min to prepare a hydrogel.

[0037] Example 3

[0038] (1) 10 g of gelatin with a relative molecular mass of 100000 was added into 300 mL of deionized water, and mechanically stirred at 60 °C for 10 min to prepare a gelatin solution, and then 2.5 g of gallic acid, 3.75 g of a mixture of 1-ethyl-(3-dimethylaminopropyl) carbonyldiimide and N-hydroxysuccinimide (molar ratio of 1:2) were added into 300 mL of a mixed solution of N,N-dimethylformamide and deionized water with a volume ratio of 1:4, and mechanically stirred at room temperature for 60 min to prepare a gallic acid mixed solution, and finally the gallic acid mixed solution was added dropwise into the gelatin solution, and mechanically stirred at 50 °C for 6 h, and after the reaction was completed, the reaction liquid was poured into a dialysis bag with a molecular weight cut-off of 3500 Da, and dialyzed against deionized water for 7 d, and the dialysis temperature was 35 °C. After dialysis, filtration, and freeze-drying, gelatin grafted gallic acid was prepared.

[0039] (2) 3 g of poly-N-isopropyl acrylamide was added into 40 mL of deionized water, and mechanically stirred at 10 °C for 40 min to prepare a poly-N-isopropyl acrylamide solution; 1 g of gelatin grafted gallic acid and 0.4 g of polyvinyl alcohol with a relative molecular mass of 10000 were added into 20 mL of deionized water, and mechanically stirred at 60 °C for 60 min, and then mechanically stirred at 10 °C for 40 min to prepare a mixed solution of gelatin grafted gallic acid and polyvinyl alcohol, and finally the mixed solution of gelatin grafted gallic acid and polyvinyl alcohol was added dropwise into the poly-N-isopropyl acrylamide solution, and mechanically stirred at 10 °C for 40 min, and then left to stand at 10 °C for 10 min to prepare a hydrogel.

[0040] Comparative Example 1

[0041] A solution of poly N-isopropyl acrylamide was prepared by adding 7.5 g of poly N-isopropyl acrylamide into 70 mL of deionized water and mechanically stirring at 18 °C for 30 min. A mixed solution of gelatin and polyvinyl alcohol was prepared by adding 2 g of gelatin with a relative molecular mass of 50000 and 0.6 g of polyvinyl alcohol with a relative molecular mass of 50000 into 60 mL of deionized water, mechanically stirring at 80 °C for 45 min, and then standing at -15 °C for 30 min. Finally, the mixed solution of gelatin and polyvinyl alcohol was added dropwise into the solution of poly N-isopropyl acrylamide, mechanically stirring at 18 °C for 30 min, and then standing at 12 °C for 15 min to obtain the finished product.

[0042] This comparative example was prepared by using gallic acid instead of gelatin to graft gallic acid to obtain the finished product hydrogel. Because the molecular weight of gallic acid is significantly lower than that of gelatin, gallic acid can only be stably dispersed in the hydrogel system by hydrogen bonding with polyvinyl alcohol at a lower temperature. Therefore, the stirring temperature and standing temperature of gallic acid in this comparative example were reduced below the relevant temperatures of Example 1, and the finished product hydrogel with a phase transition temperature of 12.8 °C was obtained. Figure 4 (B) is a morphology diagram of the finished product prepared in this comparative example when standing at 5 °C for 15 d. The results show that it has obvious precipitation when standing at 5 °C for 15 d, which indicates that the finished product prepared in this comparative example has poor storage stability. If the finished product prepared in this comparative example is stored at 18 °C, because 18 °C is higher than the phase transition temperature (12.8 °C) of the finished product prepared in this comparative example, the finished product prepared in this comparative example will be converted into a white solid hydrogel within 1 min, i.e., the finished product prepared in this comparative example is not suitable for storage at 18 °C.

[0043] Comparative Example 2

[0044] A solution of poly N-isopropyl acrylamide was prepared by adding 7.5 g of poly N-isopropyl acrylamide into 70 mL of deionized water and mechanically stirring at 18 °C for 30 min. A mixed solution of gelatin and polyvinyl alcohol was prepared by adding 2 g of gelatin with a relative molecular mass of 50000 and 0.6 g of polyvinyl alcohol with a relative molecular mass of 50000 into 60 mL of deionized water, mechanically stirring at 80 °C for 45 min, and then mechanically stirring at 18 °C for 30 min. Finally, the mixed solution of gelatin and polyvinyl alcohol was added dropwise into the solution of poly N-isopropyl acrylamide, mechanically stirring at 18 °C for 30 min, and then standing at 12 °C for 15 min to obtain the finished product.

[0045] Figure 5 (A) is a morphology diagram of the finished product prepared in this comparative example at 18 °C. The results show that it has obvious delamination at 18 °C, which indicates that the compatibility of gelatin and poly N-isopropyl acrylamide is poor.

[0046] Comparative Example 3

[0047] A poly N-isopropyl acrylamide solution was prepared by adding 7.5 g of poly N-isopropyl acrylamide into 70 mL of deionized water and mechanically stirring for 30 min at 18 °C. A gelatin, gallic acid and polyvinyl alcohol mixed solution was prepared by adding 1.5 g of gelatin with a relative molecular mass of 50000, 0.5 g of gallic acid and 0.6 g of polyvinyl alcohol with a relative molecular mass of 50000 into 60 mL of deionized water, mechanically stirring for 45 min at 80 °C and then mechanically stirring for 30 min at 18 °C. The gelatin, gallic acid and polyvinyl alcohol mixed solution was added dropwise into the poly N-isopropyl acrylamide solution, mechanically stirred for 30 min at 18 °C and then left to stand for 15 min at 12 °C to obtain the finished product.

[0048] Figure 5 (B) is a morphology diagram of the finished product prepared in this comparative example at 18 °C. The results show that it has obvious delamination at 18 °C, which indicates that the compatibility of gelatin and poly N-isopropyl acrylamide is still poor because gelatin and gallic acid are simply added without chemical bonding of gelatin and gallic acid.

[0049] Comparative Example 4

[0050] (1) A gelatin solution was prepared by adding 6 g of gelatin with a relative molecular mass of 50000 into 200 mL of deionized water and mechanically stirring for 20 min at 45 °C. A gallic acid mixed solution was prepared by adding 2 g of gallic acid, 2.4 g of a mixture of 1-ethyl-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (molar ratio of 1:2) into 200 mL of a mixed solution of N,N-dimethylformamide and deionized water with a volume ratio of 1:3, and mechanically stirring for 45 min at room temperature. The gallic acid mixed solution was added dropwise into the gelatin solution, and mechanically stirred for 12 h at 40 °C. After the reaction was completed, the reaction solution was poured into a dialysis bag with a molecular weight cut-off of 3500 Da, and dialyzed against deionized water for 14 d at a dialysis temperature of 25 °C. After dialysis, filtration and freeze-drying were performed to obtain gelatin grafted gallic acid.

[0051] (2) 7.5 g of poly-N-isopropylacrylamide was added into 70 mL of deionized water, and mechanically stirred at 18 °C for 30 min to prepare a poly-N-isopropylacrylamide solution. 2 g of gelatin grafted gallic acid was added into 60 mL of deionized water, and mechanically stirred at 80 °C for 45 min, and then mechanically stirred at 18 °C for 30 min to prepare a gelatin grafted gallic acid solution. Finally, the gelatin grafted gallic acid solution was added dropwise into the poly-N-isopropylacrylamide solution, and mechanically stirred at 18 °C for 30 min, and then left at 12 °C for 15 min to prepare the finished product.

[0052] The hydrogels prepared in the three groups of examples and the four groups of comparative examples were measured by a rotational rheometer for storage modulus, loss modulus and complex viscosity during temperature rising. When the storage modulus of the hydrogel is greater than the loss modulus with the increase of the test temperature, a phase transition occurs, and the temperature at this time is defined as the phase transition temperature. The white solid hydrogel was left at 18 °C for 1 h, and when the white solid hydrogel was reconverted into a transparent liquid hydrogel, it was determined that the hydrogel had phase transition reversibility. The transparent liquid hydrogel prepared in the examples was left at 18 °C until the transparent liquid hydrogel became turbid, and the standing time was used to characterize the storage shelf life of the hydrogel prepared in the examples. The transparent liquid hydrogel prepared in the comparative examples was left at 5 °C until the transparent liquid hydrogel became turbid, and the standing time was used to characterize the storage shelf life of the hydrogel prepared in the comparative examples. The freeze-dried hydrogel was immersed in a PBS buffer with a pH of 7.4, and oscillated at 37 °C for 15 d. After taking out, it was repeatedly washed with deionized water, and then freeze-dried, weighed, and the degradability of the hydrogel was characterized according to the weight loss rate of the freeze-dried hydrogel. The weight loss rate was calculated according to the following formula:

[0053] Weight loss rate (%) = [(W0-W15) / W0] x 100 %

[0054] Wherein, W0 and W15 are the weights of the freeze-dried hydrogel before and after degradation, respectively.

[0055] The performance test results are shown in Table 1.

[0056] Table 1 Performance test results

[0057]

[0058] The product prepared by using gallic acid instead of gelatin to graft gallic acid in Comparative Example 1 has the temperature-sensitive phase transition reversibility, but has low phase transition temperature, low gel strength and poor storage stability. Comparative Example 2 and Comparative Example 3 show that no matter whether gelatin or gelatin and gallic acid not chemically bonded are added, as long as gelatin and gallic acid are not chemically bonded, the hydrogel prepared will have obvious delamination. Comparative Example 4 does not add polyvinyl alcohol, although the hydrogel will change from transparent liquid to white solid when the temperature is higher than the phase transition temperature, but when the temperature is lowered to below the phase transition temperature again, the white solid hydrogel cannot change to transparent liquid hydrogel, which shows that the hydrogel prepared in Comparative Example 4 does not have the temperature-sensitive phase transition reversibility. Because the phase transition temperature of the hydrogel prepared in Comparative Example 1 is only 12.8℃, the transparent liquid hydrogel prepared in Comparative Example 1 and Comparative Example 4 is placed at 5℃ until the transparent liquid hydrogel becomes turbid, and the storage effective period of the hydrogel prepared in the comparative examples is characterized by the standing time. In theory, the lower the storage temperature, the better the storage stability of the temperature-sensitive phase transition reversible hydrogel, so the test results in Table 1 can prove that the hydrogel prepared in the examples has more excellent storage stability.

[0059] Therefore, from the test results of the examples and comparative examples, it can be seen that the hydrogel with high phase transition temperature and storage stability, good mechanical properties, excellent biocompatibility, temperature-sensitive phase transition and temperature-sensitive phase transition reversibility can be prepared by using poly-N-isopropyl acrylamide as the matrix, gelatin grafted gallic acid as the entanglement agent, polyvinyl alcohol as the deconstruction agent and deionized water as the solvent by low-temperature stirring.

[0060] The above only describes the examples of the present application, and any changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a high-strength, high-storage-stability, temperature-sensitive, phase-change reversible hydrogel, characterized in that: Using poly(N-isopropylacrylamide) as the matrix, gelatin-grafted gallic acid as the entanglement agent, polyvinyl alcohol as the destructive agent, and deionized water as the solvent, a high-strength, high-storage-stability, temperature-sensitive, phase-change reversible hydrogel was prepared by low-temperature stirring. The hydrogel has a phase change temperature of 32-33 °C, a storage modulus of 542-548 Pa at 37 °C, a composite viscosity of 1.62-1.73 Pa·s at 5 °C, a composite viscosity of 78.5-79.6 Pa·s at 37 °C, a shelf life of more than 365 days, and a weight loss rate of 68.4-71.7%. The phase change is reversible because it transforms from a liquid hydrogel to a solid hydrogel above the phase change temperature and from a solid hydrogel to a liquid hydrogel below the phase change temperature.

2. The preparation method according to claim 1, characterized in that: Includes the following steps: (1) Add 2~10 g of gelatin to 100~300 mL of deionized water and stir mechanically at 30~60 °C for 10~30 min to obtain a gelatin solution. Then add a mixture of gallic acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to a mixed solution of N,N-dimethylformamide and deionized water and stir mechanically at room temperature for 30~60 min to obtain a gallic acid mixed solution. Finally, add the gallic acid mixed solution dropwise to the gelatin solution and stir mechanically at 30~50 °C for 6~18 h. The reaction mixture is dialyzed, filtered and freeze-dried to obtain gelatin-grafted gallic acid. (2) Add 3~12 g of poly(N-isopropylacrylamide) to 40~100 mL of deionized water and mechanically stir at 10~25 °C for 20~40 min to obtain a poly(N-isopropylacrylamide) solution. Then add 1~3 g of gelatin-grafted gallic acid and 0.4~0.8 g of polyvinyl alcohol to 20~100 mL of deionized water and mechanically stir at 60~100 °C for 30~60 min, and then mechanically stir at 10~25 °C for 20~40 min to obtain a mixed solution of gelatin-grafted gallic acid and polyvinyl alcohol. Finally, add the mixed solution of gelatin-grafted gallic acid and polyvinyl alcohol dropwise to the poly(N-isopropylacrylamide) solution, mechanically stir at 10~25 °C for 20~40 min, and then let stand at 10~15 °C for 10~20 min to obtain the high-strength, high-storage-stability, temperature-sensitive phase change reversible hydrogel.

3. The preparation method according to claim 2, characterized in that: The relative molecular mass of the gelatin in step (1) is 10,000 to 100,000; the mass ratio of the gelatin to gallic acid is 2:1 to 4:1; the mass ratio of the mixture of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to gallic acid is 1:1 to 1.5:1; and the molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide is 1:

2.

4. The preparation method according to claim 2, characterized in that: The volume ratio of N,N-dimethylformamide to deionized water in step (1) is 1:2 to 1:

4.

5. The preparation method according to claim 2, characterized in that: The dialysis temperature in step (1) is 25~35 ℃, the time is 7~14 days, the molecular weight cutoff is 3500 Da, and the dialysate is deionized water.

6. The preparation method according to claim 2, characterized in that: The relative molecular mass of the polyvinyl alcohol in step (2) is 10,000 to 100,000.

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