Composite hydrogel with stable size and rapid temperature-sensitive response and preparation method thereof

Abstract

The invention relates to the technical field of intelligent high polymer materials, in particular to a composite hydrogel with stable size and rapid temperature-sensitive response and a preparation method thereof. The preparation method comprises the following steps: preparing an N-isopropylacrylamide aqueous solution, adding a cross-linking agent into the solution, stirring and dissolving, then introducing N2 to remove dissolved oxygen, heating the solution, then adding an initiator, stirring and reacting, finally centrifuging and washing, and freeze-drying to obtain PNIPAM microgel, preparing the PNIPAM microgel into a microgel solution, then adding acrylamide and the cross-linking agent, and finally preparing the PNIPAM microgel. The molar concentration of acrylamide in the mixed solution is 1.5 mol / L, stirring and dissolving, then adding an initiator and a promoting initiator, and reacting at 5-15 DEG C to prepare the composite hydrogel. The mechanical property of the obtained material can be quickly regulated along with the temperature change, and the size and shape are always stable; the product is pure, the preparation method does not involve complex equipment, raw materials are low in price, and the technological process is simple and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent polymer materials, and in particular to a dimensionally stable and fast temperature-sensitive response composite hydrogel and a preparation method thereof. Background Art

[0002] Hydrogel is a new type of polymer material with a three-dimensional network structure. It can still maintain a certain shape and mechanical properties after absorbing water and swelling. It has good water retention and biocompatibility and is widely used in agriculture, water treatment, food industry, biomedicine and many other fields. Among them, thermosensitive hydrogels have attracted widespread attention because their physical and chemical properties can spontaneously change in response to external temperature changes. They show broad application prospects in tissue engineering, wound management, soft / micro robots, biosensor detection and other aspects.

[0003] Mechanical properties are an important basis for the application of hydrogels, and directly determine the application effects of hydrogels in tissue engineering, biomedicine, and structural components. Usually, under the stimulation of external temperature, the hydrophilicity or dynamic cross-linking structure of the thermosensitive hydrogel changes, causing macroscopic volume swelling / contraction, water absorption / release, and changes in mechanical properties. At present, the volume change and water absorption / release of conventional thermosensitive hydrogels are highly coupled with mechanical properties. While dynamically regulating the mechanical properties of hydrogels, they are inevitably accompanied by significant changes in volume, causing their size structure to become unstable, which seriously limits their use in closed, size-sensitive scenarios such as medical implants and tissue engineering. In addition, the water absorption / release process of the hydrogel is controlled by water diffusion dynamics, and its dominant thermosensitive response process brings about the problem of long equilibrium time. The equilibrium of the water absorption and swelling process often takes several hours, which limits the application effect of the material. Therefore, improving the response speed and dimensional stability of thermosensitive hydrogels during mechanical property changes has become the key to expanding their applications.

[0004] The present invention proposes a method for preparing a composite hydrogel with stable dimensions and thermosensitive variable mechanical properties. A composite hydrogel with stable dimensions and thermosensitive variable mechanical properties is prepared by synthesizing thermosensitive microgels and compounding them with a hydrogel matrix. The thermosensitive microgel undergoes hydrophilic and hydrophobic changes in response to changes in external temperature, and the water absorption / release process occurs between the microgel and the hydrogel matrix. The small size effect of the microgel significantly improves the response equilibrium speed. At the same time, the thermosensitive transition only occurs in the microgels distributed in the matrix, and does not change the overall volume size of the composite gel, thereby significantly improving the dimensional stability of the composite gel. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of response speed and dimensional stability in the process of mechanical property change of thermosensitive hydrogel involved in the above-mentioned background technology, and provide a method for preparing a composite hydrogel with stable dimensions and rapid thermosensitive response. The method prepares a composite hydrogel with stable dimensions and thermosensitive mechanical properties by synthesizing thermosensitive microgels and compounding them with hydrogel matrix, wherein the thermosensitive microgel undergoes hydrophilic and hydrophobic changes in response to changes in external temperature, and the water absorption / release process is carried out between the microgel and the hydrogel matrix, and the response equilibrium speed is significantly improved based on the small size effect of the microgel. At the same time, the thermosensitive transition only occurs in the microgels distributed in the matrix, does not change the overall volume size of the composite gel, and significantly improves the dimensional stability of the composite gel. The material prepared by this method has the advantages of simple preparation, stable dimensions, and rapid change of mechanical properties, and has important practical significance and application value.

[0006] Specifically, the present invention adopts the following technical solutions: A method for preparing a dimensionally stable and fast temperature-sensitive composite hydrogel, the preparation method specifically comprising the following steps: Step (1), preparing a 0.05-0.3 mol / L N-isopropylacrylamide aqueous solution, then adding a crosslinker to the solution and stirring to dissolve, then introducing N2 to remove dissolved oxygen, heating the solution to 70-90°C and then adding an initiator, stirring to react for 6 hours, and finally centrifuging, washing and freeze-drying to obtain PNIPAM microgel; Step (2), taking the PNIPAM microgel prepared in step (1), preparing a microgel solution with a concentration of 1-10 wt%, then adding acrylamide and a crosslinking agent to the microgel solution so that the molar concentration of acrylamide in the mixed solution is 1.5 mol / L, stirring to dissolve, then adding an initiator and a catalytic initiator, and reacting at 5-15°C for 24 hours to prepare a composite hydrogel.

[0007] Preferably, the cross-linking agent in step (1) is N,N'-methylenebisacrylamide, and the added amount is 5-15% of the amount of N-isopropylacrylamide substance.

[0008] Preferably, the initiator in step (1) is potassium persulfate, and the added amount is 0.1-0.5% of the amount of N-isopropylacrylamide substance.

[0009] Preferably, the cross-linking agent in step (2) is N,N'-methylenebisacrylamide, and the added amount is 0.5-1% of the amount of acrylamide substance.

[0010] Preferably, the initiator in step (2) is ammonium persulfate, and the added amount is 0.1-0.3% of the amount of acrylamide substance.

[0011] Preferably, the initiator in step (2) is tetramethylethylenediamine, and the added amount is 0.1-0.3% of the amount of acrylamide substance.

[0012] When the temperature of the PNIPAM microgel prepared by the present invention is raised to above the LCST temperature, the microgel will switch from a soft filler to a hard filler. The composite gel using the PNIPAM microgel as a filler can significantly improve its own mechanical properties after heating.

[0013] During the thermal response process, water molecules are only exchanged between the microgel and the gel matrix, thus avoiding the transmission of external moisture. In addition, due to the small size of the microgel, its response speed is fast, so it can achieve rapid response to temperature changes and dimensional stability.

[0014] Compared with common thermoresponsive hydrogels with low critical solution temperature (LCST), which take minutes or hours to reach equilibrium, this composite hydrogel can achieve thermoresponsiveness in just seconds. In addition, the mass and volume changes of the composite hydrogel before and after temperature response are less than 3%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The prepared material responds quickly to temperature changes, reaches equilibrium within seconds and maintains a stable size and shape; The product is pure, the preparation method does not involve complicated equipment, the raw materials are cheap, and the process is simple and easy; The application prospects are good and it is expected to be used in biomedicine, flexible smart devices, and smart optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the principle of preparing the composite hydrogel of the present invention.

[0017] Figure 2 This is a comparison diagram of the composite hydrogel prepared by the present invention and the PAM hydrogel before and after heating.

[0018] Figure 3 This is a comparison chart of the response speed and size of the composite hydrogel prepared by the present invention and the PNIPAM hydrogel. DETAILED DESCRIPTION

[0019] Representative embodiments will now be further refined. It should be understood that the following description is not intended to limit the embodiments to a preferred embodiment. On the contrary, it is intended to cover alternatives, modifications and equivalents that may be included in the essence and scope of the embodiments defined by the appended claims.

[0020] The present invention provides a method for preparing a dimensionally stable and fast temperature-sensitive composite hydrogel, which specifically comprises the following steps: Step (1), preparing a 0.05-0.3 mol / L aqueous solution of N-isopropylacrylamide, then adding a crosslinker to the solution and stirring to dissolve, then introducing N2 to remove dissolved oxygen, heating the solution to 70-90°C, adding an initiator, stirring to react for 6 hours, finally centrifuging and washing, and freeze-drying to obtain PNIPAM microgel; the crosslinker is N,N'-methylenebisacrylamide, and the added amount is 5-15% of the amount of N-isopropylacrylamide substance; the initiator is potassium persulfate, and the added amount is 0.1-0.5% of the amount of N-isopropylacrylamide substance; Step (2), taking the PNIPAM microgel prepared in step (1), preparing a microgel solution with a concentration of 1-10 wt%, then adding acrylamide and a crosslinking agent to the microgel solution, so that the molar concentration of acrylamide in the mixed solution is 1.5 mol / L, stirring to dissolve, then adding an initiator and a promoter, reacting at 5-15°C for 24 hours, to prepare a composite hydrogel; the crosslinking agent is N,N'-methylenebisacrylamide, and the added amount is 0.5-1% of the amount of acrylamide substance; the initiator is ammonium persulfate, and the added amount is 0.1-0.3% of the amount of acrylamide substance; the promoter is tetramethylethylenediamine, and the added amount is 0.1-0.3% of the amount of acrylamide substance.

[0021] Embodiment 1: A dimensionally stable and fast temperature-sensitive composite hydrogel, the preparation process of which is as follows: (1) Prepare 0.1 mol / L N-isopropylacrylamide solution, then add a crosslinker to the solution and stir to dissolve. The crosslinker is N,N'-methylenebisacrylamide, and the amount added is 5% of the amount of N-isopropylacrylamide. Then, introduce N2 to remove dissolved oxygen, heat the solution to 70 °C, and add an initiator. The initiator is potassium persulfate, and the amount added is 0.1% of the amount of N-isopropylacrylamide. Stir the reaction at a speed of 300 r / min for 6 hours, and finally centrifuge, wash, and freeze-dry to obtain PNIPAM microgel. (2) The PNIPAM microgel prepared in step (1) is prepared into a microgel solution with a concentration of 10 wt%, and then acrylamide is added to the microgel solution to make the molar concentration of acrylamide in the mixed solution 1.5 mol / L; then a crosslinker is added, the crosslinker is N,N'-methylenebisacrylamide, and the addition amount is 0.5% of the amount of acrylamide substance, and the mixture is stirred and dissolved, and then an initiator and a promoter are added, the initiator is ammonium persulfate, and the addition amount is 0.1% of the amount of acrylamide substance; the promoter is tetramethylethylenediamine, and the addition amount is 0.1% of the amount of acrylamide substance. The reaction is carried out at 5-15 °C for 24 hours to prepare a composite hydrogel.

[0022] Embodiment 2: A dimensionally stable and fast temperature-sensitive composite hydrogel, the preparation process of which is as follows: (1) Prepare a 0.2 mol / L N-isopropylacrylamide solution, then add a crosslinker to the solution and stir to dissolve. The crosslinker is N,N'-methylenebisacrylamide, and the amount added is 15% of the amount of N-isopropylacrylamide. Then, introduce N2 to remove dissolved oxygen, heat the solution to 90 °C, and add an initiator. The initiator is potassium persulfate, and the amount added is 0.5% of the amount of N-isopropylacrylamide. Stir the reaction at a speed of 300 r / min for 6 hours, and finally centrifuge, wash, and freeze-dry to obtain PNIPAM microgel. (2) The PNIPAM microgel prepared in step (1) is prepared into a microgel solution with a concentration of 1 wt%, and then acrylamide is added to the microgel solution to make the molar concentration of acrylamide in the mixed solution 1.5 mol / L; then a crosslinker is added, the crosslinker is N,N'-methylenebisacrylamide, and the added amount is 1% of the amount of acrylamide substance, and stirred to dissolve, and then an initiator and a promoter are added, the initiator is ammonium persulfate, and the added amount is 0.3% of the amount of acrylamide substance; the promoter is tetramethylethylenediamine, and the added amount is 0.3% of the amount of acrylamide substance. The reaction is carried out at 5-15 ° C for 24 hours to prepare a composite hydrogel.

[0023] Comparative Example 1: A polyacrylamide hydrogel, the preparation process is as follows: (1) Prepare a 1.5 mol / L acrylamide solution, then add a crosslinker to the solution and stir to dissolve, the crosslinker is N,N'-methylenebisacrylamide, and the added amount is 0.5% of the amount of acrylamide substance; then add an initiator and a promoter, the initiator is ammonium persulfate, and the added amount is 0.1% of the amount of acrylamide substance; the promoter is tetramethylethylenediamine, and the added amount is 0.1% of the amount of acrylamide substance. The reaction is carried out at room temperature for 24 hours to prepare a polyacrylamide hydrogel.

[0024] Comparative Example 2: A poly N-isopropylacrylamide hydrogel, the preparation process is as follows: (1) Prepare a 1.5 mol / L N-isopropylacrylamide solution, then add a crosslinker to the solution and stir to dissolve, the crosslinker is N,N'-methylenebisacrylamide, and the added amount is 0.5% of the amount of N-isopropylacrylamide; then add an initiator and a promoter, the initiator is ammonium persulfate, and the added amount is 0.1% of the amount of N-isopropylacrylamide; the promoter is tetramethylethylenediamine, and the added amount is 0.1% of the amount of N-isopropylacrylamide. The reaction is carried out at 5-15°C for 24 hours to prepare a poly N-isopropylacrylamide hydrogel.

[0025] The hydrogel products prepared in the above examples were subjected to performance tests.

[0026] Mainly for mechanical properties and temperature response speed test, the specific test process is as follows: (1) The mechanical properties of the nanocomposite hydrogel were characterized using an Instron-68TM-30 electronic universal material testing machine. Before the test, the hydrogel sample was cut into a dumbbell shape, where the test area size was 4 mm × 20 mm (width × length). The sample thickness was measured before stretching. Uniaxial tensile tests were performed at 25 ℃ and 45 ℃ at a speed of 20 mm / min, and the data were obtained and the stress-strain curve of the composite hydrogel was plotted. The tensile modulus was determined by the slope of the stress-strain curve in the linear strain range of 0~30%; all mechanical property data are the average of valid data measured from at least 3 specimens.

[0027] 2) The composite gel was cut into small cubes of 10×10×2 mm in size, and then completely immersed in 60 °C hot water. The timing started immediately and ended when the gel became completely opaque. The time required for the gel transparency to change represented its response speed. At the same time, the volume change of the gel before and after the response was measured and recorded. The test results are shown in Table 1 below.

[0028] Microgel addition amount Tensile modulus (kPa) Equilibrium time (s) Volume change rate (%) (wt%) 25 ℃ 45 ℃ Example 1 1 17.2 18.9 1.6 -1.3 Example 2 10 31.2 42.3 3.5 -2.7 Comparative Example 1 0 14.8 14.6 -- -- Comparative Example 2 0 -- -- 200 -41.2

[0029] The table above gives the test result data.

[0030] The volume change rate (R) in Table 1 is calculated by the following formula.

[0031] .

[0032] Where V1 is the volume of the gel after temperature response, and V0 is the original volume of the gel.

[0033] As can be seen from Table 1, the PAM composite hydrogel materials prepared in the present invention all exhibit rapid temperature response and excellent dimensional stability.

[0034] It is obvious to those skilled in the art that certain modifications, combinations and variations can be made based on the above teachings.

[0035] It is obvious to those skilled in the art that the above embodiments are not intended to be exhaustive or limit the embodiments to the specific precise forms disclosed. It is obvious to those skilled in the art that certain modifications, combinations and variations can be made based on the above teachings.

Claims

1. A method for preparing a dimensionally stable and fast temperature-sensitive composite hydrogel, characterized in that: The preparation method specifically comprises the following steps: Step (1), prepare 0.05-0.3 mol / L N-isopropylacrylamide water solution, then add a crosslinker to the solution and stir to dissolve, then introduce N2 to remove dissolved oxygen, heat the solution to 70-90 °C, add an initiator, stir to react for 6 hours, finally centrifuge, wash and freeze-dry to obtain PNIPAM microgel; Step (2), taking the PNIPAM microgel prepared in step (1), preparing a microgel solution with a concentration of 1-10 wt%, then adding acrylamide and a crosslinking agent to the microgel solution so that the molar concentration of acrylamide in the mixed solution is 1.5 mol / L, stirring to dissolve, then adding an initiator and a catalytic initiator, and reacting at 5-15°C for 24 hours to prepare a composite hydrogel.

2. The preparation method according to claim 1, characterized in that: The cross-linking agent in step (1) is N,N'-methylenebisacrylamide, and the added amount is 5-15% of the amount of N-isopropylacrylamide substance.

3. The preparation method according to claim 1 or 2, characterized in that: The initiator in step (1) is potassium persulfate, and the added amount is 0.1-0.5% of the amount of N-isopropylacrylamide substance.

4. The method according to claim 1, characterized in that: The cross-linking agent in step (2) is N,N'-methylenebisacrylamide, and the added amount is 0.5-1% of the amount of acrylamide substance.

5. The preparation method according to claim 1, characterized in that: The initiator in step (2) is ammonium persulfate, and the added amount is 0.1-0.3% of the amount of acrylamide substance.

6. The preparation method according to claim 1 or 4, characterized in that: The initiator in step (2) is tetramethylethylenediamine, and the added amount is 0.1-0.3% of the amount of acrylamide substance.

7. A dimensionally stable and fast temperature-sensitive composite hydrogel, characterized in that: The method is prepared by any one of claims 1 to 6.

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