WO2023024055A1

WO2023024055A1 - Preparation method of polyvinyl alcohol-acrylamide -agarose hydrogelwith high mechanical strength

Info

Publication number: WO2023024055A1
Application number: PCT/CN2021/114907
Authority: WO
Inventors: Wei Zhang; Jinming LI; Heng Li; Chengwei WU
Original assignee: Dalian University Of Technology
Priority date: 2021-08-27
Filing date: 2021-08-27
Publication date: 2023-03-02

Abstract

Provided is a method for preparing polyvinyl alcohol-acrylamide-agarose hydrogel with high mechanical strength. Polyvinyl alcohol and acrylamide are used as matrix materials, and a small amount of agarose is added. The acrylamide molecules form the first network on the application of a chemical cross linking agent. The polyvinyl alcohol molecules physically crosslink with each other in freeze-thawing cycle and form the second network. Agarose can form hydrogen bonds with the molecular chains of polyvinyl alcohol and acrylamide, which further improves the mechanical strength of the hydrogel. Additionally, the introduction of agarose enables the hydrogel to adhere chondrocyte and promote chondrocyte proliferation. The hydrogel prepared by this method has the potential to be applied in articular cartilage replacement.

Description

PREPARATION METHOD OF POLYVINYL ALCOHOL-ACRYLAMIDE -AGAROSE HYDROGELWITH HIGH MECHANICAL STRENGTH

Technical field

The present invention belongs to the field of biological materials, especially to the field of articular cartilage replacement materials, in particular to a preparation method of polyvinyl alcohol-acrylamide-agarose hydrogelwith high mechanical strength.

Background

Hydrogels have the characteristics of high water content, low friction coefficient and good chemical stability, and are expected to be used in articular cartilage replacement materials. However, traditional hydrogels, which are usually composed of a single network of hydrophilic polymers, have poor mechanical properties and are difficult to meet the requirements of high mechanical strength of articular cartilage, which limits the application of hydrogels in the field of replacement materials of articular cartilage. At the same time, as a substitute for articular cartilage, the hydrogel must have good biocompatibility. The addition of a large amount of bioactive components (such as gelatin, collagen, growth factors, etc. ) into hydrogel can effectively improve the biocompatibility of hydrogel materials, but the introduction of these materials usually leads to the significant reduction in the mechanical properties of hydrogel. It is still a challenge to develop hydrogels with excellent mechanical properties and good biocompatibilitysimultaneously.

Previous studies have shown that the double network structure can effectively improve the mechanical properties of hydrogels. Polyvinyl alcohol hydrogel has relatively high mechanical strength, while acrylamide is suitable as the component of covalent cross-linkingnetwork, since the amide groups in its structure can form hydrogen bonding with many functional groups. Therefore, polyvinyl alcohol-acrylamide (PVA-AAm) double network hydrogels have become a hot spot in the field of research and development of hydrogels with high mechanical strength. Although the double network structure can improve the mechanical properties of hydrogels, there is still a gap between the mechanical properties of existing PVA-AAmdouble network hydrogels and articular cartilage. (Journal of Materials Science, 2019, 54, 3368-3382; Journal of Materials Chemistry A, 2020, 8, 6776-6784; Materials Letters, 2018, 207, 53-56) . As a replacement material for articular cartilage, the mechanical properties should meet the following conditions: compression modulus is greater than 0.53 MPa, compression strength is greater than 4MPa, and tensile strength is greater than 0.8 MPa. In addition, the biocompatibility of these PVA-AAm hydrogels is still unclear.

The present invention introduces agarose (AG) into the PVA-AAm hydrogel system, and the function of AG includes two aspects: (1) Agarose can generate strong hydrogen bonds with polyvinyl alcohol and acrylamide molecular chains in hydrogel, enhancing the mechanical properties of hydrogel. (2) Agarose has good biocompatibility, and the introduction of agarose can improve the adhesion ability of hydrogel to cell, promoting the biocompatibility of implanted hydrogel. The hydrogel of the present invention shows excellent mechanical properties in both compression and tension, with a compression modulus of 0.9 MPa and a compression limit of 8.17 MPa, and a Young's modulus of 0.97 MPa and a tensile limit of 2.45 MPa, meeting the performance requirements of the replacement material for articular cartilage. In addition, cell experiments show that the developed hydrogelsdemonstrate good chondrocyte adhesion andpromote cell proliferation. The hydrogel is expected to be used as articular cartilage replacement materials.

Summary

Aiming at the problems of poor mechanical properties and poor biocompatibility of PVA-AAm hydrogel, the present invention provides a preparation method of polyvinyl alcohol-acrylamide-agarose (PVA-AAm-AG) hydrogel. The polyvinyl alcohol and acrylamideare used as the matrix materials. The hydrogel-formation methodcombinesthe chemical crosslinking withphysical freeze-thawing method. The preparation method has the advantages of simple operation, high gelation speed and the resultant hydrogel also demonstrates excellent mechanical strength. Agarose can generate strong hydrogen bonds with the molecular chains of polyvinyl alcohol and acrylamide, which can improve the mechanical properties of hydrogel. Moreover, due to the introduction of natural polysaccharides into the hydrogels, the prepared hydrogels show good biocompatibility and are expected to be usedas articular cartilage replacement materials.

To realize the above purposes, the technical soluion of the present invention is:

A preparation method for PVA-AAm-AG hydrogel with high mechanical strength comprises steps of:

In the first step, polyvinyl alcohol, acrylamide, agarose, chemical crosslinking agentN, N'-methylene bisacrylamide (NNMBA) are added to the deionized water in proportion, heated inwater bath at 90-99℃, and continuously stirred until polyvinyl alcohol is completely dissolved and other substances are uniformly mixed to obtain mixture solution A. In mixture solution A, the mass fraction of polyvinyl alcohol is 10 -20 wt. %, the mass fractionof acrylamide is 10 -20 wt. %, the mass fraction of N, N'-methylene bisacrylamide is 0.1 -0.5 wt. %, and the mass fractionof agarose is 0.5 -5 wt. %.

In the second step, the mixture solution A is kept stirring at room temperature and the temperature is reduced to 20 -50℃. Tetramethyl ethylenediamine (TEMED) is addedto the above mixture solution A, andin ice water bath environment, saturated ammonium persulfate aqueous solution (APS) is addedto obtain mixture solution B. For 100 mL of the mixture solution A, 100 -400μL tetramethylenediamine is added and 3 -6mL saturated ammonium persulfate solutionis added.

In the third step, the mixture solution B is poured into the mold and thefreeze-thawing cycle is performed to obtain the PVA-AAm hydrogel. One freeze-thawingcycle refers to the process where the mixture solution B is frozen once and subsequently thawed out once. The process can berepeated for many times to form PVA-AAm-AG hydrogel. The freezing temperature is -18 --25℃, the freezing time is 12 -20 h, the thawing temperature is 15 -25℃, and the thawing time is 6 -12h. More than two cycles are conducted.

The gelation mechanism of PVA-AAm-AG hydrogel provided by the present invention: The polyvinyl alcohol and acrylamide was mixed and heated until dissolution. The acrylamide forms the first network on the application of achemical crosslinking agent. The polyvinyl alcoholmolecules physically crosslink in with each otherfreeze-thawing cycle and formsthe second network. The two matrixes form an interpenetrating network after gelation, which has advantages over single network hydrogel. Furthermore, the molecular chains of the two matrixes will react with one another to generate covalent bond crosslinking, strengthening the mechanical properties of hydrogel. Agarose is a natural polysaccharide and can form hydrogen bonds with the molecular chains of polyvinyl alcohol and acrylamide. The formation of hydrogen bonding promotes the aggregation of molecular chains in hydrogel, makes the structure more compact and improves the mechanical strength of materials. Through multiple freeze-thawing cycles, the structure of hydrogel was further optimized, and the mechanical properties of hydrogel were greatly improved.

Compared with prior art, the beneficial effects of the present invention are:

The present invention proposes a preparation method for PVA-AAm-AG hydrogel. The mechanical properties of the hydrogel are enhanced and the biocompatibility of the hydrogel is improved by introducing agarose. The method proposed by the present invention is simple in operation and has obvious effect on improving the mechanical properties of PVA-AAm-AG hydrogel. The hydrogel prepared by this method can adhere chondrocyte and promote chondrocyte proliferation, which is beneficial to the application in articular cartilage replacement.

Description of the drawings

Figure 1 shows the preparation flow chart of PVA-AAm-AG hydrogel.

Figure 2 shows the scanning electron microscope morphology of PVA-AAm-AG hydrogel.

Figure. 3 shows the compression modulus diagram of PVA-AAm-AG hydrogel.

Figure 4 showsthe adhesion rate of PVA-AAm-AG hydrogel to chondrocytes.

Figure 5 shows the proliferation rate of chondrocytes inoculated with PVA-AAm-AG hydrogel.

Detailed Description

The specific embodiments of the present invention will be described in detail following the technical implementation scheme and Figure 1, Figure 2 and Figure 3 in the attached drawings.

Figure 1 is the preparation flow chart of PVA-AAm-AG hydrogel, and PVA-AAm-AG hydrogel can be prepared according to the flow chart. Figure 2 is the micro-morphology of the prepared hydrogel. The cross-sectional structure of the hydrogel was observed after slicing and freeze-vacuum drying. Figure 3 is the compression performance diagram of the prepared hydrogel. A cylindrical hydrogel sample (diameter: 15.3mm) was subjected to unconfined uniaxial compression at a strain rate of 30%/min. The thickness of each sample was measured with a vernier caliper before testing. Prior to testing, the top and bottom platforms were lubricated with physiological saline to approximate a pure sliding state. The secant modulus of compression was calculated at the strain of 0.1-0.2. As can be seen from the Figure 3, compared with pure PVA hydrogels and pure acrylamide hydrogels of the same concentration, the compression modulus of PVA-AAm-AG hydrogels prepared by this method is greatly improved, which can meet the mechanical properties required for articular cartilage replacement materials. Figure 4shows the adhesion rate of chondrocytes, where the adhesion of agarose-free hydrogel after 4 h is taken as a normalized standard. The articular chondrocytes of rats were resuspended in culture medium and inoculated on hydrogel. After 4 h of culture, the hydrogel was taken out and the surface was washed. The amount of cell adhered to the hydrogel was detected by CCK-8 method. The hydrogel inoculated with rat chondrocytes was cultured in a carbon dioxide incubator for 7 days. The hydrogel was taken out at different time intervals, and the proliferation of cells in hydrogel was detected by CCK-8 method. It can be seen from the Figure 4 that the ability of hydrogel to adhere cells is greatly increased after adding agarose. Figure 5 is a graph of chondrocyte proliferation rate. The proliferation of chondrocytes co-cultured with agarose-free hydrogel after 1 day was taken as the normalized standard. It can be found that the proliferation rate of chondrocytes in hydrogel is significantly improved after adding agarose.

Embodiment 1

a) 10g PVA, 10 gAAm, 0.5g agarose, and 0.1gN, N'-methylene bisacrylamide were added into 79 mL deionized water. The resulting mixture was heated at 90℃ and stirred until PVA was completely dissolved to obtain the mixture solution A.

b) The mixture solution Awascontinuously stirred at room temperature, and the temperature was lowered to 20℃. 100μL tetramethyl ethylenediamine was added dropwise to the mixture solution A. 3mL saturated solution of ammonium persulfate was added to A in an ice water bath, and the resulting mixture was stirred to obtain mixture solution B.

c) The mixture solution B was poured into the mold and then was frozen at -18℃ for 12 h and thawed at 15℃ for 6 h. The PVA-AAm-AG hydrogel was obtained by two cycles.

Based on the above steps, the PVA-AAm-AG hydrogel was prepared, themorphologyobservation, the mechanical properties and biocompatibility experiments were carried out. The specific steps are as follows:

1) Morphology observation: The prepared hydrogel was frozen with liquid nitrogen, then quenched, and vacuum dried. The morphology of the quenched section was observed by scanning electron microscope.

2) Mechanical property test: The prepared cylindrical hydrogel sample (diameter: 15.3mm) was subjected to unconfined uniaxial compression test, and the strain rate was 30%/min. Before testing, the thickness of each sample was measured with vernier caliper.

3) Biocompatibility test: The articular chondrocytes of rats were resuspended in culture medium and inoculated with hydrogel. After 4 h of culture, the hydrogel was taken out and the surface was washed. The cell content adhered to the hydrogel surface was detected by CCK-8 method. The hydrogel inoculated with rat chondrocytes was cultured in a carbon dioxide incubator for 7 days. The hydrogel was taken out at different time intervals, and the proliferation of cells in hydrogel was detected by CCK-8 method.

Embodiment 2

a) 20g PVA, 20 g AAm, 5g agarose, and 0.5g N, N'-methylene bisacrylamide were added into 55 mL deionized water. The resulting mixture was heated at 99℃and stirred until PVA was completely dissolved to obtain the mixture solution A.

b) The mixture solution Awascontinuously stirred at room temperature, and the temperature was lowered to50℃. 200μL tetramethyl ethylenediamine was added dropwise to the mixture solution A. 6mL saturated solution of ammonium persulfate was added to A in an ice water bath, and the resulting mixture was stirred to obtain mixture solution B.

c) The mixture solution B was poured into the mold and then was frozen at -25℃ for 20 h and thawed at 25℃ for 12 h. The PVA-AAm-AG hydrogel was obtained by two cycles.

Based on the PVA-AAm-AG hydrogel prepared by the above steps, morphology observation, mechanical properties and biocompatibility experiments were performed on it, as shown in Example 1.

Embodiment3

a) 15g PVA, 15gAAm, 2.5g agarose, and 0.25gN, N'-methylene bisacrylamide were added into 67 mL deionized water. The resulting mixture was heated at 95℃ and stirred until PVA was completely dissolved to obtain the mixture solution A.

b) The mixture solution Awascontinuously stirred at room temperature, and the temperature was lowered to35℃. 450μL tetramethyl ethylenediamine was added dropwise to the mixture solution A. 4.5mL saturated solution of ammonium persulfate was added to A in an ice water bath, and the resulting mixture was stirred to obtain mixture solution B.

c) The mixture solution B was poured into the mold and then was frozen at -22℃ for 16 h and thawed at 20℃ for 9 h. The PVA-AAm-AG hydrogel was obtained by two cycles.

The above embodiment only expresses the embodiment of the present invention, but cannot therefore be understood as the limitation of the scope of the patent for the invention. It should be pointed out that for technical personnel in this field, on the premise of not breaking away from the idea of the invention, several deformation and improvement can also be made, which belong to the protection scope of the invention.

Claims

A method for preparing polyvinyl alcohol-acrylamide -agarose hydrogel with high mechanical strength, comprisingsteps of:

first step, addingpolyvinyl alcohol, acrylamide, agarose, chemical cross linking agent N, N'-methylene bisacrylamide to deionized water in proportion, heating in water bath at 90-99℃, and continuously stirring until polyvinyl alcohol is completely dissolved and other substances are uniformly mixed to obtain mixture solution A; in mixture solution A, mass fraction of polyvinyl alcohol is 10 -20 wt. %, mass fraction of acrylamide is 10 -20 wt. %, mass fraction of N, N'-methylene bisacrylamide is 0.1 -0.5 wt. %, and mass fraction of agarose is 0.5 -5 wt. %;

second step, keeping the mixture solution A stirring at room temperature and reducing the temperature to 20 -50℃; adding tetramethyl ethylenediamine to the above mixture solution A, and in ice water bath environment, adding saturated ammonium persulfate aqueous solution to obtain mixture solution B; for 100 mL of the mixturesolution A, adding 100 -400μL tetramethylenediamine and adding 3 -6mL saturated ammonium persulfate solution;

third step, pouring the mixture solution B into mold and performing freeze-thawing cycle to obtain the polyvinyl alcohol-acrylamide -agarose (PVA-AAm-AG) hydrogel.
The method for preparing polyvinyl alcohol-acrylamide -agarose hydrogel with high mechanical strengthaccording to claim 1, wherein the freeze-thawing cycle refers to aprocess where the mixture solution B is frozen once and subsequently thawed out once; the process is repeated for many times to form PVA-AAm-AG hydrogel; freezing temperature is -18 --25℃, freezing time is 12 -20 h, thawing temperature is 15 -25℃, and thawing time is 6 -12h; more than two cycles are conducted.