CN113045778B - Preparation method of dual-response self-repairing hydrogel - Google Patents
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Abstract
The invention belongs to the technical field of high polymer materials, and relates to a dual-response self-repairing hydrogel and a preparation method thereof. P-nitrobenzaldehyde is reduced to obtain P-aminobenzaldehyde, the P-aminobenzaldehyde is subjected to diazo coupling reaction to prepare 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde), then, 4- ((4-formylphenyl) diazenyl) phenyl methacrylate is prepared through acylation reaction, and the phenyl benzaldehyde and polyethylene glycol methyl ether methacrylate are subjected to free radical copolymerization to prepare the water-soluble gel factor P (Azo-co-EGMA) containing azobenzene and aldehyde group. Copolymerizing N-isopropylacrylamide and methyl acrylate to obtain poly (N-isopropylacrylamide-co-methyl acrylate), and hydrolyzing the poly (N-isopropylacrylamide-co-acrylhydrazide) in hydrazine hydrate to obtain poly (N-isopropylacrylamide-co-acrylhydrazide) serving as a second gel factor. And (3) forming reversible acylhydrazone bonds by the two gel factors through hydrazide groups and aldehyde groups to form the dual-response self-repairing hydrogel through crosslinking.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a dual-response self-repairing hydrogel.
Background
The hydrogel is a three-dimensional network structure formed by hydrophilic macromolecules through physical and chemical actions. Hydrogels contain large amounts of water and are soft in texture similar to biological tissue, and are an ideal class of biomaterials. The hydrogel has very low toxicity, excellent biocompatibility, low tissue rejection and good solubility to water-soluble macromolecules, proteins and gene drugs. And the surface tension is low, the tissue adhesion is good, the permeability to oxygen, nutrition and water-soluble metabolites is good, the elastic modulus is good, and the elasticity similar to that of human tissues is good. These characteristics have led to extensive attention and research on hydrogels as controlled release materials for biomaterials and drugs. The current research focus is mainly to apply the nano-particles to biomedical equipment, soft actuators, bionic systems and other aspects.
The self-repairing material can repair damaged parts and prolong the service life of the damaged parts under the condition of not needing additional substances or energy, and the self-repairing material is developed in a diversified manner all the time for decades. The self-repairing hydrogel has important application in the fields of biomedicine, tissue engineering and the like, and once the hydrogel is damaged under the action of an external force, the service life and the function of the hydrogel can be influenced. The self-repairing applied to the hydrogel is mainly divided into two categories, the first category is the application of supermolecular chemistry, such as hydrogen bond, pi-pi stacking effect and the like, and the defects of poor stability and low strength of the hydrogel are overcome. The second is the use of dynamic covalent chemical bonds such as acylhydrazone bonds, disulfide bonds, and the like. The dynamic covalent chemical bond not only can realize repeated self-repairing, but also has the advantages of higher strength, better stability and the like.
Acylhydrazone bonds, as a representative of reversible covalent bonds, make a significant contribution in the development of controllable polymers, which are obtained by the reaction of aldehydes (ketones) and hydrazides. The acylhydrazone bond is in equilibrium movement towards the hydrolysis direction in an acidic environment, can stably exist under a neutral or alkaline condition, and is reversibly generated and broken in a weakly acidic environment. The hydrogel crosslinked by the acylhydrazone bond has self-repairing performance and pH responsiveness, and the conditions generated by the dynamic exchange reaction of the acylhydrazone bond are also suitable for the environment in a living body. The formation of acylhydrazone bonds is simple, the structure of the product is flexible and changeable, the exchange reaction does not need harsh conditions, the generated external conditions and the external conditions existing in organisms are mild, and the acylhydrazone bond exchange method has potential application in biology and medicine.
[1] Reversible reaction of acylhydrazone bonds.
The azobenzene compound is a compound in which aromatic rings are connected by a nitrogen-nitrogen double bond. Under the action of ultraviolet light or heat, the azobenzene can generate reversible cis-trans isomerization. The carbon distance dimension of azobenzene is trans-form under the irradiation of ultraviolet light
Become cis-form
The dipole moment changes from 0D in trans to 3D in cis. Compared with small organic molecules, the azobenzene polymer has remarkable advantages in the aspects of mechanical property, processability, thermal stability, film forming property and the like. The azobenzene polymer has the advantages of photoinduced cis-trans isomerization performance, excellent mechanical property and processing performance, and great application potential in the fields of molecular switches, liquid crystal materials, optical drive and the like. Meanwhile, the change of dipole moment and molecular size caused by cis-trans hook of the group can cause the swelling capacity of the hydrogel to change.
[2] Reversible reaction of azobenzene
Hydrogels formed based on acylhydrazone bond crosslinking alone or hydrogels containing only azobenzene groups capable of photoisomerization transformations often achieve only one stimulus response. The research of the hydrogel has the defect of single stimulus response mode, and the practical application of the hydrogel is limited.
Disclosure of Invention
The invention aims to provide a dual-response self-repairing hydrogel and a preparation method thereof. The double-response self-repairing hydrogel with multiple responsiveness is prepared by combining the characteristic of dynamic reversibility of an acylhydrazone bond and the reversible cis-trans isomerization behavior of azobenzene under the excitation of ultraviolet light and visible light and applying the cooperation of two photoresponse structures. Firstly, a monomer containing azobenzene groups and aldehyde groups, 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA), is synthesized by a multi-step reaction method. And secondly, using Azo-CHO-MMA and polyethylene glycol methyl ether methacrylate as monomers, using azobisisobutyronitrile or dibenzoyl peroxide (BPO) as an initiator, and performing conventional free radical copolymerization to prepare the azobenzene and aldehyde group-containing gelator P (Azo-co-EGMA). Then, N-isopropylacrylamide and methyl acrylate are subjected to conventional free radical copolymerization to obtain P (NIPAM-co-MA), and the P (NIPAM-co-MA) is hydrolyzed in hydrazine hydrate to obtain poly (N-isopropylacrylamide-co-acrylhydrazide) serving as a second gelator. And finally, crosslinking the two gel factors in buffers with different pH values through forming dynamic covalent bonds (acylhydrazone bonds) by the hydrazide groups and the aldehyde groups to form the hydrogel.
The invention adopts the following technical scheme:
the chemical structure of the double-response self-repairing hydrogel is shown in the formula [3 ]:
[3] chemical Structure of hydrogel
Wherein m and n are 1 to 5, and the m and n are integers.
The double-response self-repairing hydrogel is formed by crosslinking a polymer P (Azo-co-EGMA) containing azobenzene and aldehyde groups and a polymer P (NIPAM-co-AH) containing hydrazide groups in buffers with different pH values through forming reversible acylhydrazone bonds through the hydrazide groups and the aldehyde groups, and the reaction equation is shown as the formula [4 ]:
[4] equation of hydrogel formation Process
The structural general formula of the azobenzene and aldehyde group-containing polymer P (Azo-co-EGMA) is [5 ]:
[5] chemical structure of P (Azo-co-EGMA)
In the formula [5 ]: m and n are 1 to 5, m and n are integers with the molecular weight of 5000 to 120000, and PDI is 1.3 to 2.5.
The P (Azo-co-EGMA) is obtained by carrying out conventional free radical polymerization by taking 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA) and polyethylene glycol methyl ether methacrylate (EGMA) as monomers, taking Azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) as an initiator, taking Tetrahydrofuran (THF), N-dimethylformamide, acetone, anisole, toluene and other good solvents as solvents, controlling the temperature to be 50-100 ℃, and purifying after the reaction is finished to obtain the P (Azo-co-EGMA), wherein the reaction equation is [6]:
[6] reaction equation of P (Azo-co-EGMA)
The structural general formula of the polymer P (NIPAM-co-AH) containing the hydrazide group [7 ]:
[7] chemical structure of P (NIPAM-co-AH)
Wherein m and n are 1 to 4, and the m and n are integers.
P (NIPAM-co-AH) is prepared by copolymerizing N-isopropylacrylamide and methyl acrylate with conventional radicals to obtain P (NIPAM-co-MA), and hydrolyzing the P (NIPAM-co-MA) in hydrazine hydrate to obtain P (NIPAM-co-AH) with the reaction equation of [8]:
[8] reaction equation of P (NIPAM-co-AH)
The intermediate P (NIPAM-co-MA) is prepared by taking N-isopropylacrylamide and methyl acrylate as monomers, taking Azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) as an initiator, taking Tetrahydrofuran (THF), N-dimethylformamide, acetone, anisole, toluene and other good solvents as solvents, controlling the temperature to be 50-100 ℃, and purifying after the reaction is finished to obtain the P (NIPAM-co-MA). The reaction equation is [9]:
[9] reaction equation of P (NIPAM-co-AH)
In the formula [9]: m and n are 1 (1-4), m and n are integers, the molecular weight is 5000-100000, and PDI is 1.5-2.5.
The solvent adopted by hydrolysis is ethanol, and the hydrolysis temperature is 80-100 ℃.
Has the advantages that:
the preparation method is low in toxicity and high in efficiency, the research on the hydrogel is more focused on the regulation and control of single response behavior at present, and the research on the multiple environment response behavior of the anisotropic hydrogel is less. The hydrogel obtained by the invention integrates and coordinates a plurality of response modes in the same hydrogel system, and can endow the material with more application scenes.
Drawings
FIG. 1, nuclear magnetic hydrogen spectrum of 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde (Azo-CHO) (deuterated DMSO as solvent);
FIG. 2, nuclear magnetic hydrogen spectrum (CDCl) of 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA)3Is a solvent);
FIG. 3, Polymer P (Azo-co-EGMA) ([ Azo-CHO-MMA)]:[EGMA]Nuclear magnetic hydrogen spectrum (CDCl) of ═ 1:3)3Is a solvent);
FIG. 4, Polymer P (Azo-co-EGMA) ([ Azo-CHO-MMA)]:[EGMA]＝1:3)(Mn＝6.03×104g/mol, D ═ 1.83) molecular weight differential profile；
FIG. 5, Polymer P (Azo-co-EGMA) ([ Azo-CHO-MMA)]:[EGMA]＝1:3)(Mn＝6.03×104g/mol, D ═ 1.83) uv-visible absorption spectrum of the dilute solution under uv (365nm) irradiation;
FIG. 6 Polymer P (Azo-co-EGMA) after UV (365nm) irradiation
([Azo-CHO-MMA]:[EGMA]＝1:3)(Mn＝6.03×104g/mol, D ═ 1.83) uv-vis absorption spectrum of the dilute solution under blue light (460nm) irradiation;
FIG. 7, Polymer P (NIPAM-co-MA) ([ MA)]:[NIPAM]＝1:4)(Mn＝1.76×104g/mol, D ═ 1.89) nuclear magnetic hydrogen spectrum (CDCl)3Is a solvent);
FIG. 8, Polymer P (NIPAM-co-MA) ([ MA)]:[NIPAM]＝1:4)(Mn＝1.76×104g/mol, D ═ 1.89) molecular weight differential profile
FIG. 9, Polymer P (NIPAM-co-AH) ([ AH ]]:[NIPAM]Nuclear magnetic hydrogen spectrum (D) of 1:4)2O is a solvent);
fig. 10, ir spectra of polymer polymers P (NIPAM-co-MA) ([ MA ]: NIPAM ═ 1:4) and P (NIPAM-co-AH) ([ AH ]: NIPAM ═ 1: 4);
fig. 11, microfluidic performance curves of gelators forming hydrogels at different pH buffers (pH 4.5, 6, 7);
FIG. 12 is a diagram showing the sol-gel transition of a hydrogel under different pH conditions.
Detailed Description
The invention is further illustrated by the following examples:
example 1
Synthesis of 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde (Azo-CHO). The synthesis reaction equation is as follows [9]
[9] Synthesis process of 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde
Reacting NH4Cl (0.13mol, 7.08g) was dissolved in deionized waterTo a three-necked flask (40mL), iron powder (79.46mmol, 4.45g) and NH were added4An aqueous solution of Cl. 4-nitrobenzaldehyde (26.5mmol, 4.00g) was dissolved in 130mL of methanol and charged to a rapidly stirred three-necked flask for nitro reduction. The reaction was carried out at room temperature, and the progress of the reaction was followed. After the reaction is finished, filtering to remove iron powder, carrying out rotary evaporation to remove methanol, carrying out suction filtration, washing with clear water and drying to obtain 4-aminobenzaldehyde, wherein the yield is about 72%.
A three-neck flask was charged with HCl (7.50mL), distilled water (22.50mL) and 4-aminobenzaldehyde (24.79mmol, 3.00g) dissolved in a prepared hydrochloric acid solution, and NaNO was added thereto at 0 deg.C2(24.78mmol, 1.71g) of an aqueous solution was dropped into a three-necked flask through a constant pressure titration funnel and reacted for 2 hours to prepare a diazonium salt. After completion of the reaction, the reaction mixture was filtered and charged with phenol (24.79mmol, 2.33g), NaOH (29.75mmol, 1.19g), Na2CO3(49.53mmol，5.25g)，NaHCO3(49.52mmol, 4.16g) in aqueous solution, the coupling reaction was carried out while keeping the pH at 8-9, and the progress of the reaction was followed by TLC. After the reaction is finished, carrying out suction filtration, washing the solid for 3-4 times, and drying to obtain 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde (Azo-CHO). The yield was about 67%, and the purity was 92% by liquid chromatography.
FIG. 1 shows the nuclear magnetic spectrum of 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde (Azo-CHO). In fig. 1, chemical shifts δ of 10.52ppm correspond to the proton peak (a) of the hydroxyl group, δ of 8.07ppm, 7.97ppm, 7.85ppm, and 6.97ppm correspond to the proton peak (b-e) on azobenzene, and δ of 10.08ppm corresponds to the area integral area ratio of the proton peak (f) on the aldehyde group to the peak a-f: 0.80: 2.18: 2.09: 2.10: 2.17: 1.00, which is consistent with the theoretical value. The successful preparation of 4- ((4-hydroxyphenyl) diazenyl) benzaldehyde) was demonstrated.
Example 2
Synthesis of 4- ((4-formylphenyl) diazenyl) phenyl methacrylate, the synthesis reaction equation is as follows [10]
[10] Process for the synthesis of 4- ((4-formylphenyl) diazenyl) phenyl methacrylate
4- ((4-hydroxyphenyl) diazenyl) benzaldehyde) (4.43mmol, 1.02g) was dissolved in THF (20mL) in a three-necked flask and triethylamine (6.83mmol, 0.69g) was added. Methacryloyl chloride (5.00mmol, 5.22g) was taken up in THF at 0 deg.C and added dropwise to a three-necked flask via a constant pressure titration funnel. TLC followed the progress of the reaction. After the reaction was completed, the mixture was filtered. With saturated NaHCO3Washing the solution with alkali for 5 times and water for 5 times, adding anhydrous Na into the filtrate2SO4And (5) drying. Drying and removing Na2SO4. Spin-evaporated and chromatographed (ethyl acetate: petroleum ether ═ 1:10) to give 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA). The yield was about 62% and the purity was 95% by liquid chromatography.
FIG. 2 shows a nuclear magnetic spectrum of 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA). In fig. 2, chemical shift δ of 10.11ppm corresponds to the proton peak (a) of aldehyde group, δ of 8.09 to 7.98ppm, 7.33ppm corresponds to the proton peak (b-e) on azobenzene, δ of 6.40ppm, and 5.82ppm corresponds to the proton peak (g, h) on carbon-carbon double bond of 2.09ppm corresponds to the proton peak of methyl group. a. The area ratio of b-d, e, f, g and h is 1.00: 6.10: 2.09: 3.21: 1.10: 1.11 agrees with the theoretical value. The successful preparation of 4- ((4-formylphenyl) diazenyl) phenyl methacrylate was demonstrated.
Example 3
Synthesis of Polymer P (Azo-co-EGMA), its Synthesis reaction equation [6]
4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA, 0.10g, 0.36mmol), polyethylene glycol methyl ether methacrylate (EGMA, 1.02g, 1.05mmol), initiator azobisisobutyronitrile (AIBN, 0.0023g, 0.014mmol), solvent anisole, were added to a polymerization flask, frozen in liquid nitrogen and evacuated, and finally charged with Ar for copolymerization at 70 ℃.
[ Azo-CHO-MMA ]: EGMA ═ 1: 3. after 72h, the reaction was dissolved in tetrahydrofuran and precipitated 3 times in ether to give copolymer P (Azo-co-EGMA) in about 65% yield.
FIG. 3 shows the nuclear magnetic spectrum of P (Azo-co-EGMA). In the figure, chemical shift δ of 10.09ppm corresponds to proton peak (a) of aldehyde group, δ of 8.08 to 7.81ppm, 7.30ppm corresponds to proton peak (b-e) on azobenzene, δ of 4.11ppm corresponds to proton peak (f) of methylene group connected to ester group in side chain of polyethylene glycol methyl ether methacrylate, (g) δ of 3.51 to 3.84ppm corresponds to proton peak (h) of the remaining methylene group in side chain of polyethylene glycol methyl ether methacrylate, δ of 3.38ppm corresponds to proton peak (h) of terminal methoxy group of side chain of polyethylene glycol methyl ether methacrylate. The ratio of each peak area obtained by integration is basically consistent with the theoretical value, and the successful preparation of P (Azo-co-EGMA) is proved by nuclear magnetic hydrogen spectrum.
FIG. 4 is a graph showing the molecular weight differential distribution of polymer P (Azo-co-EGMA). The integration gave a polymer number average molecular weight of 60300g/mol and PDI of 1.83. The figure shows a monomodal distribution, from which it can be seen that the polymer prepared is of a single composition.
FIG. 5 shows the UV-visible absorption spectrum of a dilute solution of polymer P (Azo-co-EGMA) under UV irradiation (365nm), wherein the polymer P (Azo-co-EGMA) has an absorption peak at 336nm of the azobenzene pi-pi electron transition (trans structure) and an absorption peak at 450nm of the azobenzene n-pi electron transition (cis structure). When the time of ultraviolet irradiation is increased, the absorption peak of azobenzene polymer P (Azo-co-EGMA) at 336nm is gradually weakened, the absorption peak at 450nm is gradually strengthened, and the azobenzene group is changed from a trans-form configuration to a cis-form configuration. The cis-trans isomeric structure of the azobenzene polymer is balanced within 30s of ultraviolet irradiation.
FIG. 6 is a UV-VISIBLE absorption spectrum of a dilute solution of the polymer P (Azo-co-EGMA) irradiated by UV light (365nm), wherein the absorption peak at 336nm is gradually increased and the absorption peak at 450nm is gradually decreased, indicating that the azobenzene polymer PAzo is gradually returned from the cis configuration to the trans configuration under the irradiation of the blue light.
Example 4
Synthesis of Polymer P (NIPAM-co-MA), its Synthesis reaction equation [9]
N-isopropylacrylamide (NIPAM, 1.14g, 0.01mol), methyl acrylate (MA, 0.22g, 2.50mmol), initiator azobisisobutyronitrile (AIBN, 0.039g, 0.23mmol), solvent absolute ethyl alcohol, were added to a polymerization flask, frozen in liquid nitrogen and evacuated, and finally charged with Ar for copolymerization at 70 ℃.
[ NIPAM ]: 4: 1. after the reaction was completed for 72 hours, the reaction mixture was dissolved in tetrahydrofuran and precipitated in n-hexane 3 times to obtain copolymer P (Azo-co-EGMA) with a yield of about 80%.
Fig. 7 is a nuclear magnetic hydrogen spectrum of polymer P (NIPAM-co-MA), where δ ═ 6.31ppm corresponds to the proton peak of amide group, δ ═ 4.00ppm corresponds to the proton peak of methine in isopropyl group, δ ═ 3.64ppm corresponds to the proton peak of methoxy group, and δ ═ 1.14ppm corresponds to the proton peak of methyl group in isopropyl group. The peak area ratios obtained by integration are basically identical with theoretical values, and the successful synthesis of the polymer P (NIPAM-co-MA) is proved.
FIG. 8 is a molecular weight differential distribution diagram of Polymer P (NIPAM-co-MA). The integration gave a polymer number average molecular weight of 17600g/mol with a PDI of 1.89. The figure shows a monomodal distribution, from which it can be seen that the polymer produced is of a single composition.
Example 5
Synthesis of Polymer P (NIPAM-co-AH), its Synthesis reaction equation [8]
And modifying methoxyl on the repeating unit of the obtained P (NIPAM-co-MA) polymer MA by hydrazine hydrate, and replacing methoxyl groups with hydrazide groups to realize functionalization. Dissolving P (NIPAM-co-MA) (0.5g) in absolute ethyl alcohol, adding excess 80% hydrazine hydrate, refluxing at 90 ℃, reacting for 96h, and dissolving the reaction solution in a proper amount of distilled water after rotary evaporation. Dialyzing with deionized water for 2d, and freeze-drying to obtain polymer P (NIPAM-co-AH).
FIG. 9 is a nuclear magnetic hydrogen spectrum of P (NIPAM-co-AH). In the figure, the chemical shift δ of 1.16ppm corresponds to the proton peak (d) of the methyl group in the pendant group on the NIPAM repeat unit, and δ of 3.90ppm corresponds to the proton peak of the methine group in the pendant group on the NIPAM repeat unit. At the same time, the proton peak of delta-3.20-3.60 ppm methoxyl group disappears. The methoxy on the repeating unit MA of P (NIPAM-co-MA) is successfully modified by hydrazine hydrate, and the polymer P (NIPAM-co-AH) is successfully prepared.
FIG. 10 shows the IR spectra of polymer P (NIPAM-co-MA) and P (NIPAM-co-AH) at 1750cm-1Process MAThe characteristic absorption of the above ester carbonyl (- (C ═ O) -O-CH3) disappeared, further indicating that the methoxy group on repeat unit MA was successfully modified by hydrazine hydrate.
Example 6
Formation of hydrogel, Synthesis reaction equation [4]
First, Na with different pH values is prepared2HPO4/NaH2PO4And (3) buffering the solution, adding polymer P (Azo-co-EGMA) and polymer P (NIPAM-co-AH) into the buffer according to the molar ratio of the aldehyde group to the hydrazide group of 1:1, wherein the solid content is 15%, and standing to form the hydrogel. The thermodynamic equilibrium constant of acylhydrazone bonds increases with increasing pH, the rate of acylhydrazone bond formation decreases with increasing pH in the kinetic aspect, and with increasing pH, the rate of acylhydrazone bond formation increases and the rate of hydrolysis decreases. In a weakly acidic environment (pH is 6), the reaction rate and the equilibrium constant are both large, so that the dynamic equilibrium of the acylhydrazone bond is maintained, the maximum proportion of the acylhydrazone bond is maintained, and the self-repairing performance of the hydrogel is facilitated. The process of forming hydrogel under the conditions of pH 4.5, pH 6 and pH 7 of the two gel factors respectively forms hydrogel after about 1 hour in the buffer with pH 4.5, and forms hydrogel after about 8 hours in the buffer with pH 6. On the other hand, in the pH 7 buffer, no hydrogel was formed after 48 hours, and it is considered that in this system, no hydrogel could be formed in the pH 7 buffer. This is because although the thermodynamic constant is large under the condition of pH 7, the kinetic rate constant is very low, and a certain proportion of acylhydrazone bonds cannot be formed, so that the gelator is crosslinked to form a hydrogel. Under the condition that the pH value is 4.5, the rate constant is large, so that a certain proportion of acylhydrazone bonds can be generated quickly to enable the gel factor to be crosslinked to form the hydrogel.
Fig. 11 is a micro-rheological performance curve of hydrogels formed at different pH after stabilization (when pH is 7, it is characterized after 48h has passed without gel formation), fig. 11a is a MSD curve of hydrogels formed at different pH, and it is found from the figure that the MSD curve shows plateau regions at pH 4.5 and 6, which indicates that brownian motion of particles in the sample is limited, the sol becomes gel, and the MSD curve shows no plateau regions and a high slope under pH 7, which indicates that no gel can be formed due to too small number of acylhydrazone bonds under pH 7. Compared with the hydrogel which is stably cured under the condition of pH 4.5, the MSD curve is the lowest and the plateau region is the lowest under the condition of pH 6 because the reaction rate and the equilibrium constant are larger under the condition of pH 6, so that the dynamic equilibrium of the acylhydrazone bonds is maintained, the maximum proportion of the acylhydrazone bonds is maintained. FIG. 11b is a graph of complex viscosity as a function of frequency for hydrogels stabilized by aging at different pH. It can be seen that all three have shear thinning phenomena and gel viscosity is maximal when aged at pH 6. Fig. 11c is a graph of the change of the elastic modulus of the hydrogel after being cured and stabilized under different pH conditions along with the frequency, the elastic modulus represents the solid-like behavior of the material, and since the number of crosslinking points is large and the network structure is dense under the condition that the pH is 6, the higher the strength of the hydrogel is, the higher or lower the pH is, the number of crosslinking points of the acylhydrazone bond is affected, and thus the elastic modulus of the hydrogel is affected. Fig. 11d is a graph showing the change of viscous modulus with frequency of the hydrogel after being cured and stabilized under different pH conditions, and since the number of crosslinking points is large under the pH 6 condition, the network structure is dense, and the grid size is small, the heat loss due to material deformation and friction is large, and thus the viscous modulus of the hydrogel formed under the pH 6 condition is also maximum.
Example 7
Adding 30 mu L of concentrated HCl into the hydrogel to change the pH value, heating at 60 ℃, converting the hydrogel into sol due to acylhydrazone bond breakage, and adding a neutralizing amount of triethylamine into the sol to convert the sol into the original gel. Reversible functions are realized.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that the technical solutions described in the foregoing embodiments may be modified, or some technical features may be substituted equally. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A double-response self-repairing hydrogel is characterized in that the chemical structure of the double-response self-repairing hydrogel is shown in a formula [3 ]:
wherein m and n are 1 to 5, and the m and n are integers.
2. A preparation method of a dual-response self-repairing hydrogel is characterized by comprising the following steps: forming reversible acylhydrazone bonds by using a polymer P (Azo-co-EGMA) containing azobenzene and aldehyde groups and a polymer P (NIPAM-co-AH) containing hydrazide groups in a buffer solution through the hydrazide groups and the aldehyde groups so as to form the dual-response self-repairing hydrogel through crosslinking;
p (Azo-co-EGMA) structural formula [5]
In the formula [5], m is n ═ 1 (1-5), m and n are integers, the molecular weight is 5000-120000, and PDI is 1.3-2.5;
p (NIPAM-co-AH) structural formula [7]
Wherein m and n are 1 to 4, and the m and n are integers.
3. The preparation method of the dual-response self-repairing hydrogel according to claim 2, wherein the P (Azo-co-EGMA) is prepared by a free radical copolymerization method, and the preparation method comprises the following specific steps:
(1) 4-nitrobenzaldehyde is subjected to nitro reduction to obtain 4-aminobenzaldehyde;
(2)4- ((4-hydroxyphenyl) diazenyl) benzaldehyde is prepared from 4-aminobenzaldehyde through diazo coupling reaction;
(3) preparing 4- ((4-formylphenyl) diazenyl) phenyl methacrylate from the product obtained in the step (2) through acyl chlorination reaction;
(4) copolymerizing 4- ((4-formylphenyl) diazenyl) phenyl methacrylate and polyethylene glycol methyl ether methacrylate to obtain P (Azo-co-EGMA).
4. The preparation method of the dual-response self-repairing hydrogel as claimed in claim 3, wherein in the step (4), 4- ((4-formylphenyl) diazenyl) phenyl methacrylate (Azo-CHO-MMA) and polyethylene glycol methyl ether methacrylate (EGMA) are used as monomers, Azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) is used as an initiator, and P (Azo-co-EGMA) is obtained by purification after the reaction in a solvent is finished.
5. The preparation method of the dual-response self-repairing hydrogel according to claim 4, wherein the solvent is Tetrahydrofuran (THF), N-dimethylformamide, acetone, anisole or toluene, and the reaction temperature is 50-100 ℃.
6. The preparation method of the dual-response self-repairing hydrogel according to claim 2, wherein P (NIPAM-co-AH) is prepared by a free radical copolymerization method, N-isopropylacrylamide (NIPAM) and Methyl Acrylate (MA) are used as monomers, Azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO) is used as an initiator, and P (NIPAM-co-MA) is obtained by purification after the reaction in a solvent is finished; then, the intermediate P (NIPAM-co-MA) is hydrolyzed under the condition of excessive hydrazine hydrate to prepare P (NIPAM-co-AH).
7. The preparation method of the dual-response self-repairing hydrogel according to claim 6, wherein the solvent is Tetrahydrofuran (THF), N-dimethylformamide, acetone, anisole or toluene, the reaction temperature is 50-100 ℃, the hydrolysis solvent is ethanol, and the hydrolysis temperature is 80-100 ℃.
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