CN108586682B

CN108586682B - Hyperbranched polymer and preparation method thereof

Info

Publication number: CN108586682B
Application number: CN201710156154.3A
Authority: CN
Inventors: 王文新; 郭琳茹
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2017-03-16
Filing date: 2017-03-16
Publication date: 2020-10-23
Anticipated expiration: 2037-03-16
Also published as: CN108586682A

Abstract

The invention discloses a hyperbranched polymer and a preparation method thereof, wherein polyethylene glycol diacrylate is used as a monomer for homopolymerization, the polyethylene glycol diacrylate is polymerized by a reverse enhanced atom transfer radical polymerization method, and in the initial stage of reaction, the polymer distribution is gradually widened along with the reaction of single addition products and low polymers of the monomer and an initiator which mainly exist in a polymer system. The constant of Mark-Houwink formula of the hyperbranched polymer is 0.36-0.4. The hyperbranched polymer has compact structure, presents a spherical structure, is easy to degrade and has good biocompatibility.

Description

Hyperbranched polymer and preparation method thereof

Technical Field

The invention belongs to the field of novel biomedical materials, and mainly relates to a hyperbranched polymer and a preparation method thereof.

Background

Wound dressings are the primary means of treating acute and chronic wounds. In recent decades, various special wound dressings have been researched and invented according to different wound conditions. As one of the novel wound dressings, the hydrogel wound dressing is widely used due to the advantages of smooth surface, good biocompatibility, tight combination with uneven wound surfaces, promotion of epithelial cell growth and the like. However, the synthetic hydrogel dressings widely used at present generally have the problems of poor adhesive capacity of wound tissues, mismatching of mechanical properties and wound tissues, high biological toxicity and the like. It has been found that improvements in the performance of synthetic hydrogel wound dressings can be achieved by controlling the composition, structure, degree of polymerization, etc. of the polymers used to synthesize the hydrogel. In controlling polymer structure and properties, polyvinyl monomers are of great interest because of their ready availability and multiple reactive sites. Particularly, the polymer derived from the polyvinyl monomer has a large amount of unreacted ethylene groups, can be further modified to obtain a preset functional group, optimizes biocompatibility, bioadhesive property and the like, and provides possibility for application of the polymer in hydrogel dressings.

However, the polymerization of multiolefin monomers has been a major challenge in the polymer field, and as early as more than 70 years ago, the well-known Flory-Stockmayer theory (F-S theory) predicts that: polymerization of polyvinyl monomers reaches the gel point at very low monomer conversion (< 10%) to form a gel, and this theory has been confirmed by extensive experimentation. However, due to the multiple reaction sites of the polyvinyl monomer, the gel point can be delayed by controlling the polymerization process of the polyvinyl monomer, and even a novel polymer with a complex structure can be obtained. The polymer synthesized by the polyvinyl monomer has a special cyclization structure and high content of vinyl, so that the polymer can be widely applied after being modified. However, there are still few reports on the preparation of hydrogel materials by homopolymerization of polyvinyl monomers.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a hyperbranched polymer and a preparation method thereof, and homopolymerizes polyethylene glycol diacrylate (PEGDA) by a reverse enhanced atom transfer radical polymerization (in situ DE-ATRP) method₇₀₀) Hyperbranched polymer Poly (PEGDA) is synthesized₇₀₀)_HPAnd preparing the aqueous solution into the hydrogel wound dressing. The prepared hydrogel material has higher storage modulus G', stronger tissue adhesion capability, easy degradation and good biocompatibility, and is expected to be used as a novel material for wound dressings, tissue adhesives and bioengineering.

The technical purpose of the invention is realized by the following technical scheme:

the hyperbranched polymer is prepared by homopolymerizing polyethylene glycol diacrylate serving as a monomer, polymerizing the polyethylene glycol diacrylate by using a reverse enhanced atom transfer radical polymerization method, wherein in the initial stage of reaction, a mono-adduct and an oligomer of the monomer and an initiator mainly exist in a polymer system are gradually widened along with the progress of the reaction, the cross-linking reaction of the oligomer with low molecular weight mainly occurs at the moment, and because most of the monomers are exhausted at the moment, the branching reaction among molecules is more likely to occur and the nonlinear growth is carried out, and finally the hyperbranched polymer with high branching degree is obtained.

The number average molecular weight of the polyethylene glycol diacrylate was 700.

The weight average molecular weight of the hyperbranched polymer is 10KDa-40KDa, and the PDI is 1.65-4.13.

The vinyl content of the hyperbranched polymer is 28-35%.

The degree of branching of the hyperbranched polymer is between 66 and 72%.

The constant of Mark-Houwink formula of the hyperbranched polymer is 0.36-0.4.

Hyperbranched polymers are compact in structure, exhibiting a spherical structure similar to 5.367 ± 1.2nm in diameter.

The preparation method of the hyperbranched polymer comprises the steps of mixing polyethylene glycol diacrylate, 2-bromo-2-methylpropionate and CuCl₂And N, N, N' -pentamethyldiethylenetriamine in a molar ratio of 80:40: (1-1.2): (1.8-2) uniformly dispersing in butanone, adding L-ascorbic acid with half mole of copper chloride, reacting under the condition of removing oxygen, using reverse enhanced atom transfer radical polymerization method to polymerize polyethylene glycol diacrylate, in the initial stage of reaction, the monomer mainly existed in the polymer system and mono-adduct and oligomer of initiator are gradually widened along with the progress of reaction, at the moment, the cross-linking reaction of low molecular weight oligomer is mainly occurred, and because most of monomer is exhausted, the branching reaction between molecules is more easily occurred and nonlinear growth is more easily occurred, finally the hyperbranched polymer with high branching degree is obtained.

When the hyperbranched polymer is prepared, the reaction temperature is 50-70 ℃, preferably 50-60 ℃; the reaction time is from 0.5 to 4.5 hours, preferably from 1 to 3 hours.

The hydrogel based on the hyperbranched polymer is prepared by using hyperbranched polyethylene glycol diacrylate obtained by a reverse enhanced atom transfer radical polymerization method as a precursor, 2-dimethoxy-phenylacetophenone as an ultraviolet initiator and water as a solvent, and initiating carbon-carbon double bonds in the precursor to crosslink under the irradiation of an ultraviolet lamp.

The mass ratio of the precursor to the photoinitiator is 100: (1-1.2).

The concentration of the precursor is 10-30 wt%, i.e. the mass (mg) of the precursor/volume (μ L) of water.

The irradiation intensity of the ultraviolet lamp is 1-2W/cm²Preferably 1.5 to 1.7W/cm². The irradiation time of the ultraviolet lamp is 10-20 s.

The crosslinking temperature is 20-25 ℃ at room temperature.

The technical scheme of the invention is to polymerize polyethylene glycol diacrylate PEGDA by using a reverse enhanced atom transfer radical polymerization (in situ DE-ATRP) method₇₀₀Hyperbranched polymer Poly (PEGDA) is synthesized₇₀₀)_HPAnd curing the hydrogel material through photocrosslinking. In order to use the hydrogel material in wound dressing, the mechanical property of the hydrogel material is characterized by a rheometer, the tissue adhesion property of the hydrogel material is evaluated by means of Lap-shear, Pull-off and Burst tests and the like, and the biocompatibility of the hydrogel material is further characterized by swelling, degradation and cytotoxicity experiments. The prepared hydrogel material has higher storage modulus G', stronger tissue adhesion capability, easy degradation and good biocompatibility, and is expected to be used as a novel material for wound dressings, tissue adhesives and bioengineering.

Drawings

FIG. 1 is a schematic view of the polymerization principle of ATRP.

FIG. 2 is a schematic diagram of a method of preparing a hyperbranched polymer by a reverse enhanced atom transfer radical polymerization method according to the present invention.

FIG. 3 is a gel permeation chromatography test chart (molecular weight of hyperbranched polymer as a function of time, abscissa GPC retention time) in examples of the present invention.

FIG. 4 is a nuclear magnetic resonance hydrogen spectrum test spectrum of hyperbranched polymers with different molecular weights in the example of the invention.

FIG. 5 is a graph showing the results of the Mark-Houwink equation constant α test for hyperbranched polymers of different molecular weights in examples of the present invention.

Fig. 6 is a graph of laser particle size distribution test (LPSD) results for examples of the present invention, with dimensions on the abscissa and percentages on the ordinate.

FIG. 7 is a graph of rheological measurements of hyperbranched polymers of different molecular weights in examples of the present invention, wherein a is oscillation-time photo-crosslinking and b is oscillation-frequency mode.

FIG. 8 is a graph showing the swelling performance test of hyperbranched hydrogel materials with different molecular weights and a concentration of 30% in examples of the present invention.

FIG. 9 is a graph showing the test results of the degradation performance of hyperbranched hydrogel materials with different molecular weights at a concentration of 30% in the examples of the present invention.

Detailed Description

The technical scheme of the invention is further illustrated by the following specific examples, and the experimental materials and instruments are shown in the following table.

Experimental materials

Laboratory apparatus

The invention relates to a reverse enhanced atom transfer radical polymerization (in situ DE-ATRP) method, which is based on the ATRP basis. The polymerization principle of ATRP is shown in FIG. 1, wherein M.is a monomer, MⁿIs a polymeric chain of n units; mⁿt is a reduced transition metal complex; R-X are initiator (halogenated compound); mⁿ⁺¹t isAn oxidized state transition metal complex; R-M, R-MⁿAll are active species, R-M-X, R-MⁿAnd all X are dormant species. In the initiation phase, CuX (X is a halogen atom) and 2, 2' -bipyridine (bpy complex) in low oxidation state grab the halogen atom from R-X to generate a primary free radical R and CuX/bpy high oxidation state complex dormant species. The active species is generated by a primary free radical initiating monomer, which can not only continue to initiate the monomer to realize active free radical polymerization, but also can capture halogen atoms from a CuX/bpy high oxidation state complex to become dormant species. During the polymerization, reversible switching equilibrium between dormant species and living radicals is simultaneously carried out until the polymer reaches a predetermined molecular weight. Since in such reactions, reversible transfer of halogen atoms from the halide to the high oxidation state metal complex and then from the high oxidation state metal complex to the atoms of the radicals is involved, and the reactive species are radicals, such polymerization reactions are referred to as atom transfer radical polymerization. in situ DE-ATRP polymerization is carried out by increasing the deactivation rate in ATRP (reverse enhanced atom transfer radical polymerization, DE-ATRP) through adding divalent copper ion concentration, so that the homopolymerization of polyvinyl monomer is carried out under the kinetic control.

The method for preparing the hyperbranched polymer by using the reverse enhanced atom transfer radical polymerization method is shown in figure 2:

(1) accurately weighing polyethylene glycol diacrylate (PEGDA) in sequence₇₀₀24mmol,16.80g), butanone (43.00mL), CuCl₂A solution (0.3mmol,40.34mg), ethyl 2-bromo-2-methylpropionate (EBRIB,12mmol, 1780.02. mu.L), N, N, N' -pentamethyldiethylenetriamine (PMDETA,0.6mmol, 103.98. mu.L) was charged to a 100mL two-necked round bottom flask. Wherein PEGDA₇₀₀:EBriB:CuCl₂PMDETA ═ 80:40:1: 2. Sealing with cleaned rubber plug and sealing film, and introducing argon for 15min to remove oxygen. Meanwhile, L-Ascorbic Acid (AA) was prepared as an aqueous solution having a concentration of 100mg/mL and used after the completion of oxygen removal.

(2) After deoxygenating for 15min, one of the necks of the round-bottomed flask was opened rapidly and 264.18 μ L (0.15mmol,1/2 × CuCl) of the prepared AA solution was taken₂) Adding into the reaction system, and sealing againSealing, and continuously deoxidizing for about 1 min. After the oxygen removal was completed, the two-necked round bottom flask was placed in an oil bath heater at 50 ℃ and 700r/min, and the reaction was started and timed.

(3) At the same time intervals, argon was introduced and then placed below the liquid level using a 5mL syringe which was purged and the sample was allowed to flow into the syringe by positive pressure. When the sample amount reaches 2mL, the syringe is taken out and then the argon introduction is stopped. The samples taken were placed in 20mL disposable glass vials and labeled. A100. mu.L sample was taken with a pipette and diluted to 1mL with DMF (dimethylformamide) and mixed well. A small alumina column was selected and wetted with DMF, and then the diluted polymer sample was filtered to remove Cu. The sample was observed to change from light blue to clear at this point. The sample was then filtered through a 0.4mm diameter filter head and finally placed in a GPC test vial and the test labeled.

(4) The progress of the reaction was monitored by GPC, and when the molecular weight reached the target molecular weight, the two-necked round-bottomed flask was taken out of the oil bath heater, and the sealed neck was opened to sufficiently contact with air. Adding 5-7 times of diethyl ether in volume of the reaction stock solution into a cleaned 1000mL big beaker, and setting the rotating speed at 600 r/min. Under the condition of high-speed rotation, the reaction stock solution is dropwise added into ether through a separating funnel and the beaker is sealed by tinfoil. After the dropwise addition is finished, stirring is continued for about 30min, and standing is carried out for 5-7h at room temperature. And when the mixed solution is kept stand for layering and the supernatant is clear and transparent, pouring out the supernatant. Adding diethyl ether 3-5 times the volume of the subnatant under high-speed stirring, stirring for about 30min under the condition of sealing with tinfoil, and standing for layering again. After repeating this twice, the polymer of the lower layer gradually increased in viscosity and adhered to the bottom of the beaker.

(5) Selecting a medium-sized alumina column, and sequentially adding a small amount of cotton and sand to flatten the alumina column. Alumina powder about 3/5 alumina column height was then added to produce an alumina filter column. It was wetted with acetone before use. The polymer precipitated and collected at the bottom of the beaker was diluted with a small amount of acetone, dissolved sufficiently and poured along the column wall into an alumina filter column, and the filtered clear polymer solution was collected in a weighed mass of disposable glass bottle.

(6) All the products collected after filtration were sealed with tinfoil and uniformly punctured with small holes, and then placed in a vacuum drying oven to remove the solvent and obtain a clear pure polymer. Then weighed and the yield calculated.

As can be seen from the Gel Permeation Chromatography (GPC) test results of FIG. 3, the polymer exhibits a plurality of monomodal distributions in the initial stage of the reaction, indicating the monoadducts and oligomers of the monomers and initiator, which are predominantly present in the polymer system. As the reaction proceeds, the polymer distribution becomes progressively broader (PDI from 1.65 to 4.13), where the crosslinking reaction of the low molecular weight oligomers occurs predominantly. Since most of the monomers are exhausted at this time, intermolecular branching reaction is more likely to occur instead of linear growth, and finally the hyperbranched polymer with higher branching degree is obtained. The hyperbranched polymers with the molecular weights of 10kDa,20kDa and 40kDa are named as H1, H2 and H3 respectively in the invention.

TABLE 1 reaction results for hyperbranched polymers of different molecular weights

FIG. 4 shows NMR spectroscopy tests of hyperbranched polymers of different molecular weights, which revealed that the polymers contained a large number of vinyl functional groups and that the vinyl content and the degree of branching could be calculated (ZHao T, Zhang H, ZHou D, et al. waterborne polymers from controlled radial polymerization of PEG diacrylates [ J ]. RSC advances.2015,5(43): 33823) 33830). The vinyl content and the degree of branching in the polymer can be calculated by the formulae (1) and (2).

Wherein a, d and d' respectively represent respective peak values (the size of the peak, i.e., peak area). As can be seen from the results in Table 1, the vinyl content of the hyperbranched polymer decreases with increasing molecular weight (H1: 33.93%, H2: 29.20%, H3: 28.35%), and the degree of branching increases with increasing molecular weight (H1: 66.07%, H2: 70.80%, H3: 71.65%). This is because when the ratio of initiator to monomer is increased, a large number of very short primary chains are formed at the initial stage of the reaction, and the high polymer concentration and low polymer chain diameter promote intermolecular reactions to inhibit the rate of intramolecular cyclization reactions, i.e., the vinyl groups on one polymer chain are more likely to enter the propagation boundaries of other molecular chains, and intermolecular cross-linking occurs to produce hyperbranched polymers having a high degree of branching and a large number of vinyl functional groups.

The conformation of the polymer in the solvent is related to its Mark-Houwink equation constant α. When alpha is less than or equal to 0.5, the polymer presents a compact structure. When alpha is more than or equal to 0.5 and less than or equal to 0.8, the polymer presents a random coil conformation; and the more the polymer coil is stretched, the closer to 0.8 the alpha is; when the polymer is in a rigid wire-ball shape, alpha is more than or equal to 1. The alpha value of the polymer can be determined by a combination of three detectors of GPC (differential refractometry RI, viscosity detector VS and laser light scattering detector LS). From the test results of fig. 5, it can be seen that the mark-houwinal constant α of the hyperbranched polymer is 0.36 to 0.40, which indicates that the polymer structure formed is similar to a sphere. The laser particle size distribution test (LPSD) results of fig. 6 show that the particle size of the hyperbranched polymer is 5.367 ± 1.2 nm. In conclusion, the polymer with high branching degree is synthesized by polymerizing polyethylene glycol diacrylate by adopting the insitu DE-ATRP polymerization method, and the polymer has compact structure and presents a spherical structure similar to the diameter of 5.367 +/-1.2 nm.

By¹H-NMR test results show that the hyperbranched polymer has high content of vinyl functional groups and PEGDA is water-soluble, so that the hyperbranched polymer can be quickly crosslinked into a hydrogel material under ultraviolet lamp irradiation after being mixed with a photoinitiator and is expected to be used as a tissue engineering or biological adhesive. The physical property and the biological property of the hydrogel material can be specifically characterized through rheological property, adhesion property, swelling property, degradation property and biocompatibility tests.

Hyperbranched polymers with different molecular weights are taken as precursors, 2, 2-dimethoxy-acetophenone (Irgacure2959) is taken as an ultraviolet initiator, water is taken as a solvent, and a series of hydrogel materials with different concentrations are prepared by adopting photo-initiated free radical polymerization. The preparation method comprises the following steps: hyperbranched polymers of different molecular weights were formulated as aqueous polymer solutions of different concentrations, according to table 2, placed in disposable glass bottles and dissolved well. Because the solubility of Irgacure2959 in purified water is poor, the Irgacure2959 is dissolved in acetone and is prepared into Irgacure 2959/acetone solution with the mass concentration of 5 percent, a solution with a corresponding volume is taken by a liquid-transferring gun before photo-crosslinking and added into polymer aqueous solution, and the mixture is quickly and uniformly mixed by shaking by a vortex instrument. Placing a proper volume of colorless transparent solution in a corresponding container, placing the container under a UV lamp, and curing the solution into hydrogel under a certain illumination condition.

TABLE 2 batch rates for hydrogel material preparation

The rheological properties of the polymer and the formation of gel by UV-initiated curing can be studied by means of a pressure-controlled plate (d 8mm) AR2000 rheometer. In the study of the photocrosslinking rheological property, the wavelength is 320-390nm, and the light intensity is 100mW/cm²The Omnicure 1000 type ultraviolet lamp. During the test, the uv light can pass through the PMMA base plate so the polymer can be irradiated by uv light until it gels. After the test was photo-crosslinked at room temperature for 20s, the test was performed in a vibration-time mode with a frequency of 5Hz, a strain of 5% and a height of 0.8 mm. And (3) placing the prepared polymer mixed solution on a test bench, carrying out stability test for 1min, and then carrying out ultraviolet crosslinking for 20 s. After completion of the test, the hydrogel material can be further tested for storage modulus G 'and loss modulus G' in a shaking-frequency mode with a frequency of 0.1 to 100 Hz.

In the shock-time test mode, the storage modulus G 'and the loss modulus G' of the aqueous polymer solution did not change significantly within the first 1 min. After UV irradiation, the G 'of the polymer began to increase sharply and much more than G ", and within 10 seconds G' and G" crossed, indicating the formation of a hydrogel material. As can be seen from fig. 7(a), the modulus of the hydrogel material after crosslinking was 3 orders of magnitude higher than that of the uncrosslinked polymer and reached a constant value without change with time. This further indicates that the hyperbranched polymer can be rapidly polymerized within 20s and fully form a hydrogel material. Furthermore, G 'of the hyperbranched polymer decreases with increasing molecular weight (H1:66kPa, H2:58kPa, H3:52kPa), since the vinyl content decreases with increasing molecular weight as the reaction proceeds, resulting in a decrease in the crosslinking density, which is manifested as a decrease in G'.

The hyperbranched polymer has a compact structure and a high vinyl content, so that the hyperbranched polymer has high crosslinking density and shows high G'. The stability of the hydrogel material was further characterized in the shock-frequency test mode. As shown in FIG. 7(b), the modulus of the hyperbranched polymer remains stable at all times in the frequency range (0.01Hz-200Hz) under the test frequency conditions of 0.01Hz to 256 Hz. It is further shown that the hyperbranched polymer is structurally stable as a result of the combination of the polymer structure and the crosslink density.

To characterize the adhesive properties of the hydrogel materials, the characterization of the mechanical adhesive properties was carried out by means of the Lap-shear, Pull-off, Burst test from the transverse adhesion, the longitudinal adhesion and the degree of impact resistance, respectively.

Lap-shear test

The test samples were prepared before the Lap-shear test was performed. The preparation process comprises the following steps:

1) preparing a polymer mixed solution: preparing pure polymers with different structures and different molecular weights into polymer aqueous solutions with different concentrations (10%, 20%, 30%, 50% w/v) respectively; the uv initiator Irgacure2959 was then configured as a 5% strength acetone solution. The polymer and the photoinitiator are uniformly mixed according to the mass ratio of 100: 1.

2) Preparation of adhesion test specimens: the pretreated pigskin was cut into a shape of 40mm in length, 25mm in width and 1mm in thickness, and its fat side was stuck to a glass plate of 75mm in length, 25mm in width and 1mm in thickness using Superglue. Then, 200. mu.L of the polymer mixed solution was applied by a pipette gun and spread evenly on the skin of the pig skin. Then take the sameA glass plate of a size to lightly cover the polymer mixed solution. Under the conditions of preset light intensity and time (intensity: 0.8,1.2, 1.7W/cm)²(ii) a Time: 10s,15s,20s) and the ultraviolet lamp is used for carrying out photo-crosslinking curing at a position 1cm away from the upper glass sheet. After the photocrosslinking, the sample is placed for 2-3min at room temperature and then subjected to the Lap-shear test.

3) Lap-shear test: the prepared test samples are placed on a testing machine in parallel in the vertical direction. The stretching was carried out at a constant speed of 2mm/min until breakage. The adhesion strength is the maximum before breaking and each set of tests is repeated 3 times.

Pull-off test

The test samples need to be prepared before the Pull-off test can be performed. The preparation process comprises the following steps:

2) Preparation of adhesion test specimens: the pretreated pigskin was cut into a circular sheet with a diameter of 25mm and a thickness of 1mm, and its fat side was stuck to an aluminum sheet with a diameter of 25mm using Superglue. Then 100. mu.L of the polymer mixed solution was applied by a pipette gun and spread evenly on the skin of the pig skin. A glass plate 75mm in length, 25mm in width and 1mm in thickness was gently overlaid on the polymer mixed solution. Under the conditions of preset light intensity and time (intensity: 1.7W/cm)²(ii) a Time: 20s), and the ultraviolet lamp carries out photocrosslinking curing at a position 1cm away from the upper glass sheet. After photocrosslinking was complete, the same size aluminum sheet was placed on the glass sheet using a Superglue. The sample is placed at room temperature for 2-3min and then subjected to a Pull-off test.

3) Pull-off test: the prepared test samples are placed on a testing machine in parallel in the horizontal direction. The stretching was carried out at a constant speed of 2mm/min until breakage. The adhesion strength is the maximum before breaking and each set of tests is repeated 3 times. Burst test

Test samples were prepared before Burst testing. The preparation process comprises the following steps:

2) Preparation of adhesion test specimens: cutting the pretreated pigskin into a disc shape with the diameter of 30mm and the thickness of 1mm, fixing the fat surface of the pigskin on the surface of a Burst test pump by Superglue, and pricking a small hole on the surface of the pigskin, wherein the position of the small hole is parallel to that of the small hole on the pump, and the size of the small hole is consistent. Opening the faucet, adjusting the flow rate so that the water can be ejected in the form of a water column and recording the initial pressure P at that time₀. The tap was turned off and the water on the surface of the pigskin was removed. Then, 200. mu.L of the polymer mixed solution was applied by a pipette gun and spread evenly on the skin of the pig skin. Under the conditions of preset light intensity and time (intensity: 1.7W/cm)²(ii) a Time: 20s), and the ultraviolet lamp carries out photocrosslinking curing at a position 1cm away from the upper glass sheet, so that the hydrogel is adhered to the pigskin. After the photocrosslinking is finished, the mixture is placed for 2-3min at room temperature and then subjected to Burst test.

3) Burst test: opening the faucet, testing under the condition of preset flow rate until the hydrogel is broken, spraying out the water column, and recording the maximum pressure value P_t. The maximum adhesion strength is P ═ P_t-P₀Each set of tests was repeated 3 times.

As can be seen from the Lap-shear, Pull-off, Burst test results (Table 3), at 1.7W/cm²The adhesive strength of hyperbranched hydrogels with the same molecular weight increased with increasing polymer concentration (10%, 20%, 30%) under 20s photocrosslinking conditions. When the molecular weight is 10kDa, the Lap-shear adhesion strength of the hyperbranched hydrogel with the concentration of 10 percent, 20 percent and 30 percent is respectively 6.61kPa, 10.25kPa and 18.89kPa, and the Pull-off adhesion strength is respectively 3.45kPa, 6.26kPa and 9.88 kPa. The molecular weights K2 and K3 showed the same tendency. This is due to the fact that the higher the concentration of the vinyl group in the polymer solution, the more densely it is crosslinkedThe degree is also higher.

TABLE 31.7W/cm²Adhesion Performance testing of hyperbranched hydrogel Material under 20s crosslinking conditions

When the polymer concentration is the same, the adhesive strength of the hyperbranched hydrogel decreases as the molecular weight of the polymer increases. At a concentration of 30%, the Lap-shear adhesion strengths of the hyperbranched hydrogels with molecular weights of 10kDa,20kDa and 40kDa are respectively 18.89kPa, 15.03kPa and 9.75kPa, the Pull-off adhesion strengths are respectively 5.39kPa, 3.89kPa and 2.97kPa, and the Burst adhesion strengths are respectively 0.395MPa, 0.347MPa and 0.294 MPa. This is due to the branching and intermolecular reactions consuming part of the vinyl groups, reducing the crosslink density, which is the same conclusion as the hydrogel rheology test. In conclusion, the highest Lap-shear strength of the hyperbranched hydrogel can reach 18.89kPa, the Pull-off strength can reach 9.88kPa, and the Burst strength can reach 0.395 MPa. Therefore, the hydrogel has strong adhesive performance and is expected to be used as a wound dressing.

Polymer hydrogels are composed of water and a polymer network structure that can absorb a certain amount of water and swell into a swollen hydrogel. The swelling ratio of the equilibrium state can be regarded as a direct parameter for characterizing the degree of crosslinking of the polymer, and therefore the structural characteristics of the polymer can be characterized by swelling experiments. The swelling ratio varies depending on the degree of crosslinking.

Characterization of swelling Properties

The swelling performance of the hydrogel can be measured by a weighing method. The specific process is as follows:

1) preparation of hydrogel: polymers with different structures and different molecular weights are prepared into polymer solution with the concentration of 30%, and then photoinitiator Irgacure2959 solution with the concentration of 5% is added, wherein the mass ratio is 100: 1. 50. mu.L of the mixture solution was placed on a weighed glass slide at an intensity of 1.7W/cm²And carrying out photocrosslinking curing under the conditions of 20s time and 1cm height. Immediately after photocrosslinking, the hydrogel is weighed and recorded as the initial weight W₀Then, it was placed in 2mL of PBS buffer and shaken at a slow speed in a shaker at 37 ℃.

2) Weighing: the swollen hydrogel was periodically removed from the PBS buffer, gently wiped to remove excess surface water and weighed, and recorded as W_t. The hydrogel was then replaced in PBS buffer. The Swelling Ratio (SR) of the hydrogel can be calculated by the formula (3-1):

SR＝(W_t-W₀)/W₀x 100% (formula 3-1)

Four samples of each hydrogel were tested and averaged to give the final swelling ratio SR.

To evaluate the swelling properties of hydrogels under physiological conditions, the prepared hydrogels were soaked in 24-well plates of PBS buffer and placed in a shaker at 37 ℃ for testing. The swelling ratio is calculated by the change in weight of the hydrogel material over time. The swelling test results are shown in fig. 8, where the hyperbranched hydrogel swells faster in the early stage and reaches an equilibrium state at about 15 days. When the molecular weights of the polymers are respectively 10kDa,20kDa and 40kDa, the swelling ratios of the hyperbranched hydrogel at equilibrium are respectively 31.62 percent, 35.22 percent and 37.48 percent. This is due to the dense branched structure of the hyperbranched polymer due to its high degree of branching. Water molecules are difficult to enter the intermolecular space and the molecular chains are expanded, so the swelling ratio is low.

In general, an ideal biomaterial for most tissue engineering applications should have a tunable, relatively stable degradation performance. Under the action of oxidation reaction, radiation, thermal decomposition or hydrolysis, the main chain or side chain of the polymer is broken to cause the degradation of the polymer. Among them, the degradation of the polymer by hydrolysis is considered to be the cleavage of chemical bonds between main chains, oligomers or monomers in the polymer by hydrolysis.

Characterization of degradation Properties

The hydrogel degradation performance can be measured by weighing. The specific process is as follows:

1) preparation of hydrogel: polymers with different structures and different molecular weights are configured into a polymer with the concentration of 30 percentAdding a photoinitiator Irgacure2959 solution with the concentration of 5% into the solution, wherein the mass ratio of the Irgacure2959 solution to the Irgacure 29is 100: 1. 50. mu.L of the mixture solution was placed on a weighed glass slide at an intensity of 1.7W/cm²And carrying out photocrosslinking curing under the conditions of 20s time and 1cm height. After photocrosslinking was complete, it was placed in 2mL of PBS buffer and shaken slowly in a shaker at 37 ℃. One group (4) of hydrogels was taken, freeze-dried, weighed to constant weight, and recorded as initial weight W₀。

2) Weighing: periodically taking out hydrogel from PBS buffer solution, and recording weight W after constant weight of hydrogel is achieved by freeze drying_t. The percentage of residual mass after hydrogel degradation can be calculated by the formula (3-2):

Massloss＝(W₀-W_t)/W_tx 100% (equation 3-2)

Four samples of each hydrogel were tested and averaged to give the final percent residual mass.

Due to the ester functional group in the polymer, degradation occurs due to hydrolysis when soaked in PBS buffer, and the experimental results are shown in fig. 9. The hyperbranched hydrogel shows larger degradation behavior, and the polymer is composed of a plurality of PEG chains with shorter length under the branching reaction, the degradation reaction mainly occurs in the ester group breakage in the shorter side chain, and finally the polymer is degraded into oligomer with smaller molecular weight. When the molecular weight of the polymer is different, the degradation behavior of the polymer is changed. The mass fraction of the polymer remained after the degradation of the polymer was 43.19%, 48.74%, 52.96% when the molecular weights of the polymer were 10kDa,20kDa and 40kDa, respectively. The main reasons for this tendency are that as the molecular weight of the polymer increases, the polymer forms a more dense structure relative to a polymer of lower molecular weight, hydrolysis is relatively reduced, the degradation capacity is reduced and the mass fraction of the remaining polymer is relatively increased. In summary, readily degradable hyperbranched polymers may be suitable for use in wound dressings or tissue adhesives for short-term healing.

To characterize the biocompatibility of hydrogel materials, targeting can be achieved by Fibroblast (Fibroblast) metabolic activityIs prepared by

And (5) testing under the condition. After culturing mouse 3T3 fibroblasts for 24h under standard cell culture conditions, the hydrogel material prepared by photo-crosslinking was placed. After further incubation for 24 hours, the hydrogel material was removed and used

Methods to test for cytotoxicity.

The results of the tests are shown in Table 4, where the cytotoxicity of the hydrogel material varies depending on the molecular weight of the polymer. When the molecular weight of the polymer is changed, the cytotoxicity of the hydrogel material is reduced as the molecular weight of the polymer is increased. For example, the cell survival rates of the hyperbranched hydrogel with the molecular weights of 10kDa,20kDa and 40kDa are 82.6%, 83.9% and 86.9%, respectively. Although the content of vinyl groups in the hyperbranched polymer is higher, a part of the hyperbranched polymer is embedded in a branched structure, so that the hyperbranched hydrogel has lower cytotoxicity.

TABLE 4 cytotoxicity testing of hyperbranched hydrogel materials of different molecular weights at a concentration of 30%

This patent homopolymerizes PEGDA by reverse enhanced atom transfer radical polymerization (in situ DE-ATRP)₇₀₀The monomers give hyperbranched polymers Poly (PEGDA)₇₀₀)_HP. The formation of its hyperbranched structure depends on a kinetically controlled polymerization reaction, the intermolecular reaction is promoted, and the intramolecular cyclization reaction is inhibited. Characterization of the polymer demonstrated that the hyperbranched polymer had an alpha of less than 0.5 and a structure similar to a sphere. The aqueous polymer solution may be cured by ultraviolet light crosslinking to prepare a hydrogel material. The hyperbranched polymer can be rapidly formed by the combined test of ultraviolet light and rheology<20s) and the highly branched structure and the high amount of vinyl groups give it a higher storage modulus G'. Tissue adhesion performance evaluation of the hydrogel material by Lap-shear, Pull-off and Burst tests shows that the hyperbranched hydrogel materialThe glue has a high adhesive strength. In addition, the hyperbranched hydrogel has lower swelling performance and easy degradation performance. The cell toxicity test shows that the hyperbranched hydrogel has better cell compatibility. In conclusion, the hydrogel material prepared from the hyperbranched polymer becomes a potential tissue engineering adhesive due to the high modulus, the stable structure, the excellent adhesion strength, the moderate swelling and degradation performance and the good biocompatibility. Namely the application of the hyperbranched polymer and the hydrogel based on the hyperbranched polymer in the invention as a wound dressing or a tissue adhesive.

Both the hyperbranched polymers and the hydrogels based on hyperbranched polymers according to the invention can be prepared with adjustment of the process parameters described in the present disclosure, exhibiting properties substantially in accordance with the examples. The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims

1. The hyperbranched polymer is characterized in that the polyethyleneglycol diacrylate is used as a monomer for homopolymerization, the polyethyleneglycol diacrylate is polymerized by a reverse enhanced atom transfer radical polymerization method, in the initial stage of reaction, a monomer and a single adduct and oligomer initiated by an initiator mainly exist in a polymer system, the polymer distribution gradually widens along with the reaction, the weight-average molecular weight of the hyperbranched polymer is 10KDa-40KDa, the PDI is 1.65-4.13, the number-average molecular weight of the polyethyleneglycol diacrylate is 700, the vinyl content of the hyperbranched polymer is 28-35%, the branching degree is 66-72%, the Mark-Houwink formula constant of the hyperbranched polymer is 0.36-0.4, the hyperbranched polymer has a compact structure, and the diameter is similar to a spherical structure of 5.367 +/-1.2 nm.

2. The preparation method of the hyperbranched polymer is characterized in that polyethylene glycol diacrylate, 2-bromo-2-ethyl methyl propionate and CuCl₂And N, N, N', N", N' -pentamethyldiethylenetriamine in a molar ratio of 80:40: (1-1.2): (1.8-2) uniformly dispersing in butanone, adding L-ascorbic acid with half mole of copper chloride, reacting under the condition of removing oxygen, polymerizing polyethylene glycol diacrylate by using a reverse enhanced atom transfer radical polymerization method, wherein in the initial stage of the reaction, a monomer and a mono-adduct and an oligomer initiated by an initiator mainly exist in a polymer system, the polymer distribution gradually widens along with the reaction, at the moment, a cross-linking reaction of the oligomer with low molecular weight occurs, and as most of the monomer is exhausted at the moment, a branching reaction and nonlinearity are more likely to occur among molecules, and finally, the hyperbranched polymer with high branching degree is obtained.

3. The method for preparing hyperbranched polymer according to claim 2, wherein the reaction temperature is 50-70 ℃ and the reaction time is 0.5-4.5 hours when the hyperbranched polymer is prepared.

4. The method for preparing a hyperbranched polymer according to claim 2, wherein the reaction temperature is 50 to 60 ℃ when the preparation of the hyperbranched polymer is performed; the reaction time is 1-3 hours.

5. Use of the hyperbranched polymer of claim 1 for the preparation of a wound dressing.

6. Use of the hyperbranched polymer of claim 1 for the preparation of a tissue adhesive.