Citric acid modified polyurethane and preparation method thereof

Abstract

The invention provides citric acid modified polyurethane and a preparation method thereof. The preparation method mainly comprises the following steps: (1) modifying citric acid; (2) synthesizing a polyurethane prepolymer; and (3) preparing the citric acid modified polyurethane. According to the invention, the citric acid is successfully introduced into the polyurethane through a chain extension reaction by methyl alkyne triphenyl triisocyanate, so that the prepared polyurethane coating shows weak adhesive force to animal tissues while realizing strong adhesive force to metals.

Description

Technical Field

[0001] The present invention relates to the field of polymer materials, and in particular to a citric acid modified polyurethane and a preparation method thereof. Background Art

[0002] Polyurethane coatings are widely used in the biomedical field due to their excellent processing, mechanical properties, and biosafety. However, their application to medical compression metal devices, such as implants and fistula clamps, presents multiple challenges. The use of these devices typically involves three phases: first, compression-induced tissue swelling and inflammation; second, increased inflammation, leading to wound exudate; and finally, after treatment is complete, when the compression metal is removed, adhesion of the material to the tissue must be prevented to avoid secondary injury.

[0003] Therefore, polyurethane coatings applied to these medical metal surfaces must first demonstrate strong adhesion to the metal; secondly, they must possess anti-inflammatory and antibacterial properties to alleviate tissue inflammation, adequately absorb exudate to prevent excessive absorption that can cause tissue moisture imbalance and coating expansion and displacement; and finally, prevent the coating from adhering to the tissue during removal. However, currently available polyurethane coatings struggle to simultaneously meet these multiple requirements. Summary of the Invention

[0004] In view of the above problems in the prior art, the technical problem to be solved by the present invention is to provide a citric acid modified polyurethane and a preparation method thereof, the purpose of which is to make the polyurethane coating have strong adhesion to metal and weak adhesion to animal tissue.

[0005] The technical solutions of the present invention are as follows: A citric acid modified polyurethane and a preparation method thereof, the preparation method comprising the following steps: (1) Modification of citric acid: Add citric acid and acetone to a 50 mL beaker and stir at 22-28 °C until completely dissolved. Then add methyl acetylene tris-p-phenylene triisocyanate and continue stirring for 3-8 min to obtain methyl acetylene tris-p-phenylene triisocyanate-modified citric acid and excess methyl acetylene tris-p-phenylene triisocyanate. (2) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, add polyol and isophorone diisocyanate, then add N,N-dimethylformamide, and stir at 85-95 °C and 200-300 rpm for 1.5-2.5 h to obtain a polyurethane prepolymer; (3) Preparation of citric acid modified polyurethane: The whole polyurethane prepolymer prepared in step (2) was cooled to 45-55°C, and the whole methyl acetylene triisocyanate-modified citric acid prepared in step (1) and an excess of methyl acetylene triisocyanate were added, and stirred at a speed of 200-300 rpm for 0.5-1.5 h. Acetone and N,N-dimethylformamide were added to adjust the viscosity, and then the temperature was raised to 70-80°C, and the stirring was continued at a speed of 200-300 rpm for 0.5-1.5 h to obtain citric acid modified polyurethane.

[0006] Preferably, in step (1), the mass ratio of citric acid, methyl acetylene triisocyanate and acetone is 1: (19.0-19.5): (10-15).

[0007] Preferably, in step (2), the mass ratio of polyol, N,N-dimethylformamide and isophorone diisocyanate is (7-8): (2.5-3.5):1.

[0008] Preferably, the polyol in step (2) is WT-1024B produced by Asahikawa Chemical (Suzhou) Co., Ltd.

[0009] Preferably, the ratio of the volume (mL) of acetone and the volume (mL) of N,N-dimethylformamide in step (3) to the mass (g) of the polyol in step (2) is (0.7-0.9):(1.4-1.8):1.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. In this invention, citric acid is successfully introduced into polyurethane via a chain extension reaction of methylacetylene tri-p-phenylene triisocyanate. This design stably retains a large number of carboxyl functional groups in the polyurethane coating. The resulting coating achieves strong adhesion to metal (>4.7 N / 25 mm) while exhibiting weak adhesion to animal tissue (<2.0 N / 25 mm).

[0011] 2. In addition, under the synergistic effect of citric acid and methyl acetylene tri-p-phenylene triisocyanate, the polyurethane coating has a certain exudate absorption performance, and its absorption rate of simulated wound exudate slowly increases with the extension of the exposure time.

[0012] 3. The polyurethane coating prepared by the present invention also has good bactericidal, anti-inflammatory and antioxidant properties.

[0013] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1FT-IR spectra of Examples and Comparative Examples.

[0015] Figure 2 is the surface carboxyl content of the embodiment.

[0016] Figure 3 (a) is the liquid absorption rate of the coating of Example 3; (b) is the effect of coating thickness on the liquid absorption rate of Example 3.

[0017] Figure 4 (a) is a schematic diagram of a 180° peel test of a polyurethane coating; (b) is the adhesion of the example coating to different surfaces; (c) is the residue of the example and comparative example coatings on pig skin; (d) is the residue of the example and comparative example coatings on pork tissue.

[0018] Figure 5 These are pictures showing the bactericidal effects of the examples and comparative examples on Escherichia coli.

[0019] Figure 6 (a) is the DCFH fluorescence imaging picture of the embodiment and comparative example; (b) is the sum of the regional fluorescence intensities of ROS in cells treated with H2O2.

[0020] Figure 7 This is a graph showing the effects of the examples and comparative examples on the concentration of the inflammatory factor IL-6. DETAILED DESCRIPTION

[0021] The present invention is described in detail below by way of examples, which are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. It should be understood that after reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and such equivalent forms also fall within the scope defined by the claims appended hereto.

[0022] Example 1 The preparation method of the citric acid modified polyurethane is as follows: (1) Modification of citric acid: Add 0.67 g of citric acid and 10 g of acetone to a 50 mL beaker and stir at 25 °C until completely dissolved. Then add 12.85 g of methyl acetylene tris-p-phenylene triisocyanate and continue stirring for 5 min to obtain methyl acetylene tris-p-phenylene triisocyanate-modified citric acid and excess methyl acetylene tris-p-phenylene triisocyanate. (2) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, add 25 g of polyol and 3.33 g of isophorone diisocyanate, then add 10 g of N,N-dimethylformamide, and stir at 90 °C and 250 rpm for 2 h to obtain a polyurethane prepolymer; (3) Preparation of citric acid modified polyurethane: The whole polyurethane prepolymer prepared in step (2) was cooled to 50°C, and the whole methyl acetylene triisocyanate-modified citric acid and excess methyl acetylene triisocyanate prepared in step (1) were added, and stirred at a speed of 250 rpm for 1 h. 40 mL of N,N-dimethylformamide and 20 mL of acetone were added to adjust the viscosity. The mixture was then heated to 75°C and stirred at a speed of 250 rpm for 1 h to obtain citric acid modified polyurethane.

[0023] The polyol used was WT-1024B from Asahikawa Chemical (Suzhou) Co., Ltd., isophorone diisocyanate was I742552 from Shanghai MacLean Biochemical Technology Co., Ltd., and methylacetylene tri-p-phenylene triisocyanate was M890168 from Shanghai MacLean Biochemical Technology Co., Ltd.

[0024] Example 2 The preparation method of the citric acid modified polyurethane is as follows: (1) Modification of citric acid: Add 0.82 g of citric acid and 10 g of acetone to a 50 mL beaker and stir at 22 °C until completely dissolved. Then add 15.61 g of methyl acetylene triisocyanate and continue stirring for 5 min to obtain methyl acetylene triisocyanate-modified citric acid and excess methyl acetylene triisocyanate. (2) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, 25 g of polyol and 3.33 g of isophorone diisocyanate were added, followed by 10 g of N,N-dimethylformamide. The mixture was stirred at 200 rpm at 90 °C for 2 h to obtain a polyurethane prepolymer. (3) Preparation of citric acid modified polyurethane: The whole polyurethane prepolymer prepared in step (2) was cooled to 50°C, and the whole methyl acetylene triisocyanate-modified citric acid and excess methyl acetylene triisocyanate prepared in step (1) were added, and stirred at a speed of 200 rpm for 1 h. 40 mL of N,N-dimethylformamide and 20 mL of acetone were added to adjust the viscosity. The mixture was then heated to 75°C and stirred at a speed of 200 rpm for 1 h to obtain citric acid modified polyurethane.

[0025] The polyol used was WT-1024B from Asahikawa Chemical (Suzhou) Co., Ltd., isophorone diisocyanate was I742552 from Shanghai MacLean Biochemical Technology Co., Ltd., and methylacetylene tri-p-phenylene triisocyanate was M890168 from Shanghai MacLean Biochemical Technology Co., Ltd.

[0026] Example 3 The preparation method of the citric acid modified polyurethane is as follows: (1) Modification of citric acid: Add 0.96 g of citric acid and 10 g of acetone to a 50 mL beaker and stir at 28 °C until completely dissolved. Then add 18.36 g of methyl acetylene tris-p-phenylene triisocyanate and continue stirring for 5 min to obtain methyl acetylene tris-p-phenylene triisocyanate-modified citric acid and excess methyl acetylene tris-p-phenylene triisocyanate. (2) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, 25 g of polyol and 3.33 g of isophorone diisocyanate were added, followed by 10 g of N,N-dimethylformamide. The mixture was stirred at 300 rpm at 90 °C for 2 h to obtain a polyurethane prepolymer. (3) Preparation of citric acid modified polyurethane: The whole polyurethane prepolymer prepared in step (2) was cooled to 50°C, and the whole methyl acetylene triisocyanate-modified citric acid and excess methyl acetylene triisocyanate prepared in step (1) were added, and stirred at 300 rpm for 1 h. 40 mL of N,N-dimethylformamide and 20 mL of acetone were added to adjust the viscosity. The mixture was then heated to 75°C and stirred at 300 rpm for 1 h to obtain citric acid modified polyurethane.

[0027] The polyol used was WT-1024B from Asahikawa Chemical (Suzhou) Co., Ltd., isophorone diisocyanate was I742552 from Shanghai MacLean Biochemical Technology Co., Ltd., and methylacetylene tri-p-phenylene triisocyanate was M890168 from Shanghai MacLean Biochemical Technology Co., Ltd.

[0028] Comparative Example 1 The conventional polyurethane is prepared by replacing the methyl acetylene triisocyanate in Example 1 with an equal molar amount of isophorone diisocyanate. The specific preparation steps are as follows: (1) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, add 25 g of polyol and 5.56 g of isophorone diisocyanate, then add 10 g of N,N-dimethylformamide, and stir at 250 rpm at 90 °C for 2 h to obtain a polyurethane prepolymer; (2) Preparation of ordinary polyurethane: The entire polyurethane prepolymer prepared in step (1) was cooled to 50°C, 0.90 g of chain extender 1,4-butanediol was added, and the mixture was stirred at 250 rpm for 1 h. The mixture was then heated to 75°C and stirred at 250 rpm for 1 h to obtain ordinary polyurethane.

[0029] Experimental methods 1. Infrared spectrum test The chemical structure of the samples was analyzed by Fourier transform infrared spectrometer using KBr pellet method with a scanning range of 4000-400 cm −1 .

[0030] 2. Quantification of carboxyl groups using the toluidine blue method The toluidine blue method is a commonly used method for quantitative analysis of carboxyl groups. This method is based on the pH-dependent adsorption / desorption principle of toluidine blue on negatively charged surfaces. The polyurethane prepared in the example was coated on a 1 cm 2 After the silicon wafer is dried, it is immersed in a 5mM toluidine blue alkaline aqueous solution (0.1mM NaOH) for 2 hours to allow the polyurethane coating to interact with the toluidine blue. After 2 hours, the sample is taken out and rinsed with a 0.1mM NaOH aqueous solution to remove the non-complexed toluidine blue dye on the sample surface. Subsequently, the sample is immersed in 5mL50% acetic acid for 20 minutes to remove the complex toluidine blue from the polymer coating. A toluidine blue standard solution is prepared and a standard curve is measured. The absorbance of the toluidine blue desorbed in the acidic solution is measured at 635nm using a UV-vis spectrophotometer. The recorded spectral data is converted into the carboxyl concentration on the surface of the polyurethane coating in mM / mm 2 .

[0031] 3. Cross-linking degree test Take the sample dried to constant weight and weigh it as M0, put it into Soxhlet extraction apparatus, extract it under reflux in acetone for 12 hours, take it out, dry it at room temperature and weigh it as M1, and calculate the cross-linking degree according to the following formula.

[0032] Crosslinking degree (%) = M1 / M0 4. Swelling test Soak the dried sample in the solvent for 24 hours, weigh it before and after soaking, and calculate the swelling degree according to the following formula.

[0033] Swelling degree (%) = ΔW / W = (W'-W) / W Where W' is the mass of the sample after immersion for 24 h, W is the mass of the sample before immersion, and ΔW is the mass difference between the sample before and after immersion.

[0034] 5. Exudate absorption rate First, a wound exudate simulation solution was prepared, the formula of which was: 0.5844g sodium chloride, 0.3360g sodium bicarbonate, 0.0298g potassium chloride, 0.0278g calcium chloride, 3.3000g bovine albumin, and 100mL pure water. About 1g of the sample dried to constant weight was accurately weighed and then immersed in a wound exudate simulation solution. The samples were taken out after 0.5, 1, 2, 3, and 6 hours, and the water marks visible to the naked eye were erased with weighing paper and weighed. The exudate absorption rate of different thicknesses was represented by Example 3. Samples of Example 3 of different thicknesses were prepared on glass slides, and the exudate absorption rate was subsequently obtained using the same test method.

[0035] 6. Coating adhesion and adhesion residue test Adhesion testing is conducted according to the 180° peel strength test method in GB-T2790-1995. A 25mm wide coating is applied to aluminum foil or pigskin, reinforced with canvas to facilitate peeling. After the coating is dried, the test is performed using a tensile testing machine.

[0036] To determine the residual coating on tissue, we conducted an adhesion residue test. Each sample was stained with methylene blue to more intuitively observe the coating residue. After drying on aluminum foil, the dyed coating was cut and placed on cleaned pigskin and pork tissue. Pressure was applied and an appropriate amount of simulated wound exudate was dripped onto the surface. After 6 hours, the coating residue was observed and photographed.

[0037] 7. Contact sterilization test The antibacterial activity of the coating material was evaluated by contact sterilization experiments using Escherichia coli as a representative. The sample was evenly coated on a sterilized glass slide (2.5 cm × 1.5 cm) and placed in an oven to dry. After drying, it was sterilized by ultraviolet light for 30 minutes. 10 μL of Escherichia coli solution (1.6 × 10 4 cfu / mL), cover with another slide smeared with the same sample, and incubate aseptically in a biological incubator at 37°C for 30 minutes. After incubation, separate the two slides with tweezers and place them in a centrifuge tube. Add 10mL of water to submerge them. Manually shake for a moment, then sonicate for 60 seconds. Then, take 200μL of the supernatant and spread it on a plate for incubation. After 24 hours, observe the number of colonies to evaluate the bactericidal efficacy.

[0038] 8. Antioxidant test L-929 cells were seeded in a culture medium containing 10% fetal bovine serum and cultured and passaged at 37°C, 5% CO2, and saturated humidity. The cells were used in the experiment when they were in the logarithmic growth phase. 24 hours before drug treatment, L-929 cells in the logarithmic growth phase were trypsinized, prepared into a cell suspension, and counted. The cell concentration was adjusted to 2×10 5 Cells were seeded into 6-well plates (approximately 4×10 cells per well). 5 ) and cultured in an incubator. A 10 μL sample was placed in a sterile EP tube and sterilized with high-concentration ozone and UV irradiation for 24 hours. Under a sterile environment, 10 mL of complete culture medium containing the sample was added and ultrasonicated for 30 minutes to fully resuspend the sample. 2 mL was added to each well and cultured for 6 hours. After 6 hours of drug addition and incubation, the supernatant was discarded, the tubes were washed once with PBS, and 20 μM H₂O₂ was added to each well for an additional 2 hours. The supernatant was then discarded, the tubes were washed three times with PBS, and the amount of green fluorescence in each well was measured using a ROS probe detection kit.

[0039] The specific detection operation is as follows: dilute the DCFH-DA probe with serum-free culture medium at a ratio of 1:1000 to obtain a 10 μM staining working solution; add 1 mL of staining working solution and incubate at 37°C in the dark for 30 minutes; after incubation, wash twice with serum-free culture medium to wash out the probe that has not entered the cells; add PBS and observe and photograph under a microscope.

[0040] 9. Anti-inflammatory test RAW264.7 cells were inoculated in a medium containing 10% fetal bovine serum and cultured in a 37°C, 5% CO2, and saturated humidity incubator until the cells were in the logarithmic growth phase for use in the experiment. 24 h before drug treatment, RAW264.7 cells in the logarithmic growth phase were trypsinized and prepared into a cell suspension. The cells were counted and the cell concentration was adjusted to 2×10 4 Cells were seeded into 6-well plates (approximately 4×10 cells per well). 4 ) and cultured in an incubator. After 24 hours of cell culture, complete culture medium containing 500 ng / mL lipopolysaccharide (LPS) was added for 4 hours to induce inflammation in the cells. The normal control group was replaced with complete culture medium without LPS. After the induction treatment, the supernatant was discarded and fresh complete culture medium was added. Then, 3 μL of the sterilized, standby material sample was placed into the wells of the culture plate, and the group experiments were performed simultaneously: normal control group, induced inflammation group, and inflammation plus material group (Example, Comparative Example). After 24 hours of culture, the culture medium in the wells was aspirated and centrifuged. The supernatant was collected and stored in a -80°C refrigerator for detection of inflammatory factors, etc.

[0041] Inflammatory factors were detected using a mouse interleukin-6 (IL-6) ELISA kit. This kit utilizes a double-antibody one-step sandwich enzyme-linked immunosorbent assay (ELISA). Samples, standards, and HRP-labeled detection antibodies were sequentially added to microwells pre-coated with IL-6 antibodies. The cells were incubated and thoroughly washed. The color was developed using the substrate TMB. TMB converts to blue under the catalysis of peroxidase and to yellow under the action of acid. The color intensity is positively correlated with the level of IL-6 in the sample. The absorbance (OD value) was measured at a wavelength of 450 nm using a microplate reader, and the sample concentration was calculated.

[0042] The test results are shown in Tables 1 and 2, and the instruction manual is attached. Figures 1 to 7 .

[0043] Figure 1 FT-IR spectra of Examples and Comparative Examples. -1 The characteristic peaks near the NH are attributed to the bending vibration peaks, 1700-1750cm −1 is the stretching vibration of the C=O group, 3350cm −1The absorption peaks near 1600cm correspond to the stretching vibration peaks of OH and NH. The above characteristic peaks prove that polyurethane is successfully synthesized. In addition, in the spectra of Examples 1 to 3, at 1600cm -1 The vibration of the benzene ring skeleton appeared nearby, indicating the successful polymerization of methyl acetylene tris-p-phenylene triisocyanate.

[0044] Figure 2 The surface carboxyl content of the examples was determined by the toluidine blue method. Assuming that the reaction between toluidine blue and the surface carboxyl groups of the material is completed in a 1:1 molar ratio, the concentration of toluidine blue can be converted into the surface carboxyl concentration of the coating. As can be seen from the figure, the surface carboxyl concentrations of Examples 1, 2, and 3 are 0.0008, 0.0012, and 0.0019 mM / cm, respectively. 2 , indicating that the scheme of introducing citric acid into polyurethane designed by the present invention stably retains a large number of carboxyl functional groups in the polyurethane coating, providing a basis for the multifunctionality of the coating in the medical field.

[0045] Table 1 shows the crosslinking degree test results for the examples and comparative examples. Comparative Example 1 completely dissolved after refluxing in acetone, indicating the absence of a three-dimensional network crosslinking structure and a crosslinking degree of 0. The crosslinking degrees of Examples 1, 2, and 3 were 43.29%, 46.78%, and 50.87%, respectively. This is due to the formation of network crosslinks by the addition of methyl acetylene tris-p-phenylene triisocyanate, and increasing its dosage increases the crosslinking density of the polyurethane. Therefore, the polyurethane coatings prepared by the present invention have a certain crosslinking density.

[0046] Table 1 Crosslinking degree of Examples and Comparative Examples Table 2 shows the swelling test results for Examples 1-3 in water. Comparative Example 1 failed to maintain surface stability in water, so its swelling was not tested. Examples 1-3 exhibited very low swelling in water, at 2.04%, 5.75%, and 4.49%, respectively. This is because the crosslinking structure created by methylacetylene tris-p-phenylene triisocyanate prevents water from diffusing into the membrane block. Therefore, the polyurethane coatings prepared by the present invention exhibit excellent water resistance, making them suitable for the human physiological environment.

[0047] Table 2 Swelling degree of Examples 1 to 3 in water Figure 3 (a) is the test results of the liquid absorption rate of Examples 1 to 3, and (b) is the test results of the effect of coating thickness on the liquid absorption rate in Example 3. Figure 3(a) It can be seen that the absorption rate of simulated wound exudate in Examples 1 to 3 increases slowly with the increase of exposure time. This is because the carboxyl group of citric acid is conducive to the absorption of simulated wound exudate, while the cross-linking structure caused by methyl acetylene tris-p-phenylene triisocyanate prevents the simulated wound exudate from diffusing into the coating. The synergistic effect of the two gives the coating a certain exudate absorption capacity, which helps to avoid tissue moisture imbalance and coating expansion displacement caused by excessive absorption. In addition, Figure 3 (b) As can be seen, the amount of simulated wound exudate absorbed by Example 3 is positively correlated with coating thickness. Therefore, the polyurethane coating prepared by the present invention can achieve any desired exudate absorption rate by varying its thickness, which facilitates its adaptation to the exudate control needs of wounds with varying exudate volumes.

[0048] Figure 4 (a) is a schematic diagram of the 180° peeling test of the polyurethane coating, and (b) is the adhesion of Examples 1 to 3 to different surfaces. Figure 4 (b) As can be seen, the adhesion forces of Examples 1, 2, and 3 to aluminum foil were 4.7, 8.1, and 13.3 N / 25 mm, respectively, significantly higher than their adhesion to pigskin (the adhesion forces of Examples 1-3 to pigskin were all less than 2.0 N / 25 mm). The strong adhesion between the polyurethane coatings in the examples and the aluminum foil is hypothesized to be due to the interaction between the negatively charged carboxyl groups in the polyurethane coating and the positively charged metal, as well as the possible formation of chemical bonds with oxides on the metal surface, thereby enhancing the adhesion between the polyurethane coating and the aluminum foil.

[0049] In addition, from Figure 4 (c) and Figure 4 The staining adhesion test (d) clearly shows that Comparative Example 1 leaves residues on the surface of pigskin and pork, while Examples 1 to 3 do not contaminate the surface of pigskin and pork, indicating that the polyurethane coating prepared by the present invention exhibits strong adhesion to metals and low adhesion to animal tissues.

[0050] Figure 5 The following table shows the bactericidal test results for the Examples and Comparative Examples against Escherichia coli. As can be seen from the figure, Comparative Example 1 exhibits significantly higher colony counts and a weaker bactericidal effect, while Examples 1-3 exhibit significantly lower colony counts, demonstrating a superior bactericidal effect. This is because Examples 1-3 successfully introduced citric acid into the polyurethane material, retaining carboxyl groups on the polyurethane coating surface, exerting a moderate antibacterial effect. Therefore, the polyurethane coatings prepared by the present invention exhibit superior bactericidal efficacy.

[0051] Figure 6(a) shows DCFH fluorescence images of the Examples and Comparative Examples, and (b) shows the summed regional fluorescence intensity of ROS in cells treated with H₂O₂. Among all groups, cells from Comparative Example 1 exhibited the highest DCFH fluorescence signal intensity, indicating weak antioxidant capacity. The presence of citric acid enhanced the antioxidant activity in Examples 1-3, resulting in significantly lower DCFH fluorescence signal intensities compared to Comparative Example 1. Therefore, the polyurethane coatings prepared according to the present invention exhibit excellent antioxidant properties.

[0052] In the anti-inflammatory test, the IL-6 concentration of the normal control group was 54.00 pg / mL, and the IL-6 concentration of the inflammation-induced group was 58.50 pg / mL, indicating that lipopolysaccharide can indeed induce cells to release the inflammatory factor IL-6. Figure 7 As shown, the results show that compared with the inflammation-induced group, Comparative Example 1 and Examples 1-3 all had some anti-inflammatory effects. Furthermore, Examples 1-3 had a greater anti-inflammatory effect than Comparative Example 1, with Example 3 showing a low IL-6 concentration of only 41.95 pg / mL. This is due to the presence of citric acid in Examples 1-3, which has anti-inflammatory properties. Therefore, the polyurethane coatings prepared according to the present invention have some anti-inflammatory effects.

[0053] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements, or modifications based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all included in the scope of protection of the present invention.

Claims

1. A citric acid modified polyurethane and a preparation method thereof, characterized in that: The preparation method comprises the following steps: (1) Modification of citric acid: Add citric acid and acetone to a 50 mL beaker and stir at 22-28 °C until completely dissolved. Then add methyl acetylene tris-p-phenylene triisocyanate and continue stirring for 3-8 min to obtain methyl acetylene tris-p-phenylene triisocyanate-modified citric acid and excess methyl acetylene tris-p-phenylene triisocyanate. (2) Synthesis of polyurethane prepolymer: In a 250 mL three-necked flask equipped with an overhead stirrer, add polyol and isophorone diisocyanate, then add N,N-dimethylformamide, and stir at 85-95 °C and 200-300 rpm for 1.5-2.5 h to obtain a polyurethane prepolymer; (3) Preparation of citric acid modified polyurethane: The whole polyurethane prepolymer prepared in step (2) was cooled to 45-55°C, and the whole methyl acetylene triisocyanate-modified citric acid prepared in step (1) and an excess of methyl acetylene triisocyanate were added, and stirred at a speed of 200-300 rpm for 0.5-1.5 h. Acetone and N,N-dimethylformamide were added to adjust the viscosity, and then the temperature was raised to 70-80°C, and the stirring was continued at a speed of 200-300 rpm for 0.5-1.5 h to obtain citric acid modified polyurethane.

2. The preparation method according to claim 1, characterized in that In step (1), the mass ratio of citric acid, methyl acetylene triisocyanate and acetone is 1: (19.0-19.5): (10-15).

3. The preparation method according to claim 1, characterized in that In step (2), the mass ratio of polyol, N,N-dimethylformamide and isophorone diisocyanate is (7-8): (2.5-3.5):

1.

4. The preparation method according to claim 1, characterized in that The polyol in step (2) is WT-1024B produced by Asahikawa Chemical (Suzhou) Co., Ltd.

5. The preparation method according to claim 1, characterized in that The ratio of the volume (mL) of acetone and the volume (mL) of N,N-dimethylformamide in step (3) to the mass (g) of the polyol in step (2) is (0.7-0.9):(1.4-1.8):1.

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