CN110903498B - Preparation method of hydrogel with hierarchical micro-nano structure - Google Patents
Preparation method of hydrogel with hierarchical micro-nano structure Download PDFInfo
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- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
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- C08J2305/04—Alginic acid; Derivatives thereof
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- C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
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- C08J2405/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2401/00 or C08J2403/00
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- C08J2429/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
- C08J2429/02—Homopolymers or copolymers of unsaturated alcohols
- C08J2429/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
Abstract
The invention relates to a preparation method of hydrogel with a hierarchical micro-nano structure. According to the method, firstly, the polyvinyl alcohol/sodium alginate hydrogel is molded in a microfluidic mode, and then the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure on the microstructure is prepared by a limited drying method, so that the material has anisotropy in the structure, and the mechanical strength and toughness of the material can be effectively improved. The maximum breaking strength of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure can reach 4-15 MPa, the elastic modulus can reach 0.3-1.5 MPa, and the breaking energy can reach 4-15 MJ/m3。
Description
Technical Field
The invention belongs to the technical field of preparation of reinforced and toughened composite hydrogel, and particularly relates to a method for preparing hydrogel with a hierarchical micro-nano structure by combining a micro-fluidic forming mode with a limited drying process.
Background
The hydrogel is a hydrophilic three-dimensional network high polymer formed by crosslinking linear high molecular chains by using water as a medium through the actions of covalent bonds, hydrogen bonds and the like, can absorb a large amount of water and has stable physicochemical properties. The hydrogel has the advantages of excellent biocompatibility, excellent elastic performance, high water content, low sliding friction and the like, so that the hydrogel is widely researched in the fields of soft robots, biomedicine, tissue engineering, waste treatment and the like.
Most conventional natural and synthetic hydrogels are inherently mechanically weak, which greatly limits the application of hydrogels in some applications where high mechanical properties are required. The existing reinforcing and toughening strategies mainly comprise nano composite hydrogel, double-network hydrogel, topological hydrogel with slidable cross-linking points and hydrophobic association hydrogel. Although the mechanical properties of the hydrogel are greatly improved compared with the traditional natural and synthetic hydrogels, in the strategies, the tensile strength of the traditional double-network polyvinyl alcohol/sodium alginate hydrogel can only reach 2-3MPa, and the hydrogel cannot meet the requirements in the fields with higher requirements on the mechanical properties, such as a soft robot and the like.
Disclosure of Invention
The invention aims to provide a preparation method of hydrogel with a hierarchical micro-nano structure aiming at the defects in the prior art. According to the method, firstly, the polyvinyl alcohol/sodium alginate hydrogel is molded in a microfluidic mode, and then the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure on the microstructure is prepared by a limited drying method, so that the material has anisotropy in the structure, and the mechanical strength and toughness of the material can be effectively improved. The maximum breaking strength of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure can reach 4-15 MPa, the elastic modulus can reach 0.3-1.5 MPa, and the breaking energy can reach 4-15 MJ/m3。
The technical scheme of the invention is as follows:
a preparation method of hydrogel with a hierarchical micro-nano structure is one of the following two modes:
the method comprises the following steps: the preparation method of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure comprises the following steps:
(1) injecting the polyvinyl alcohol/sodium alginate mixed solution into a container filled with a calcium chloride solution in a micro-fluidic system, and standing for 10-15 hours to obtain fibrous hydrogel with the length of 3-10 cm and the diameter of 0.5-1.5 mm;
wherein, in the mixed solution of polyvinyl alcohol and sodium alginate, the mass fraction of sodium alginate is as follows: 1wt% -4 wt%, and the mass fraction of polyvinyl alcohol is as follows: 1wt% -5 wt%; the injection rate is 3-15 ml/min, and the concentration of the calcium chloride solution is 0.3-1.0M; the diameter of the injection end of the microfluidic system is 0.5-2 mm;
(2) then, clamping and fixing two ends of the fibrous hydrogel by using clamps respectively, keeping the hydrogel sample in a straightened state, wherein the pre-stretching amount of the straightened state is 0-100%, and drying for 12-48 h at room temperature;
(3) swelling the dried product in the last step in water for 6-24 h, freezing at-10 to-30 ℃ for 10-15 h, thawing at room temperature for 2-6 h, and repeating the freezing-thawing operation for 2-6 times; finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure;
or, the second method is to prepare the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano spiral structure, and comprises the following steps:
(1) injecting the polyvinyl alcohol/sodium alginate mixed solution into a container filled with a calcium chloride solution in a micro-fluidic system, and standing for 10-15 hours to obtain fibrous hydrogel with the length of 3-10 cm and the diameter of 0.5-1.5 mm;
wherein, in the mixed solution of polyvinyl alcohol and sodium alginate, the mass fraction of sodium alginate is as follows: 1wt% -4 wt%, and the mass fraction of polyvinyl alcohol is as follows: 1wt% -5 wt%; the injection rate is 3-15 ml/min, and the concentration of the calcium chloride solution is 0.3-1.0M; the injection diameter of the microfluidic system is 0.5-2 mm;
(2) molding a hierarchical micro-nano spiral structure: clamping two ends of the fibrous hydrogel by using clamps respectively, fixing one end of the fibrous hydrogel, connecting the clamp at the other end of the fibrous hydrogel with a motor, keeping the fibrous hydrogel in a straightening state, enabling the fibrous hydrogel to rotate at a constant speed by using the motor, rotating the fibrous hydrogel to a set number of turns, and drying the fibrous hydrogel for 12-48 h at room temperature;
setting the number of rotation turns as the initial distance/cm between the two clamps by 10-30 r;
(3) and (3) swelling the dried product in the previous step in water for 6-24 h, freezing and freezing for 10-15 h at-10 to-30 ℃, thawing for 2-6 h at room temperature, and repeating the freezing-thawing operation for 2-6 times to complete the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano spiral structure.
In the second method, the rotating speed of the motor is 10-100 r/min.
The microfluidic system in the first method or the second method comprises an injector and an injection needle which are connected in sequence, or the injector, the injection needle and an injection guide tube which are connected in sequence.
The volume ratio of the step (1) in the first method or the second method is preferably a polyvinyl alcohol/sodium alginate mixed solution: calcium chloride solution ═ 1: 20 to 30.
The invention has the substantive characteristics that:
the inventors consider that ligament tissue similar to animals or humans and soft tissue of organisms such as cartilage belong to hydrogels. The biological tissues have good toughness and are determined by unique microstructures, for example, the hydrostatic skeletal structure of the octopus arm is the result of the synergistic action of anisotropic graded fiber muscles, and can help octopus to grab objects which are multiple times heavier than the octopus; the vine of the winding vine plant such as morning glory has a hierarchical spiral structure, can climb by winding the support by the vine, and also has good toughness. Therefore, the inventor decides to improve the toughness of the hydrogel material by constructing a hierarchical biomimetic structure.
In actual preparation, the inventor realizes the hierarchical bionic structure by a micro-fluidic forming principle and a limited drying step. Wherein, (the definition of microfluidics is a system for processing or operating micro fluid by using a micro pipeline, the invention forms hydrogel by a simple microfluidic system consisting of an injection pump, an injector and a conduit according to the principle of microfluidics, and can also directly inject the hydrogel by the injector); the limited drying (that is, after the sample is swelled and balanced in water and taken out, the sample is clamped at two ends of the clamp for drying) enables the sample to shrink due to dehydration in the drying process, and the two ends are fixed, so that the sample can be stretched by the action of axial force, the directional arrangement of polymer chains can be promoted, and a required microstructure can be formed.
The invention has the advantages of
On one hand, on the basis of the original reinforcing and toughening strategy, the hydrogel generates a hierarchical micro-nano microstructure by changing a process method, namely combining a micro-fluidic forming principle and a limited drying method, so that an energy dissipation mechanism is optimized. The whole process has the advantages of controllability, easy processing, low cost, greenness, no pollution and the like.
On one hand, the maximum breaking strength of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure can reach 4-15 MPa, the elastic modulus can reach 0.3-1.5 MPa, and the breaking energy can reach 4-15 MJ/m3. The traditional polyvinyl alcohol/sodium alginate double-network hydrogel without the micro-nano structure has the maximum breaking strength of only about 2MPa, the elastic modulus of about 0.1MPa and the breaking energy of 3MJ/m3On the left and right, the mechanical strength and toughness of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano structure are obviously improved.
Drawings
Fig. 1 is an SEM image of a polyvinyl alcohol/sodium alginate hydrogel micron-scale layered fiber structure having a hierarchical micro-nano fiber structure in example 1;
fig. 2 is an SEM image of a hierarchical fiber structure with a hierarchical micro-nano fiber structure, polyvinyl alcohol/sodium alginate hydrogel micro-and nano-scale in example 1.
FIG. 3 is an SEM image of the polyvinyl alcohol/sodium alginate hydrogel with the hierarchical micro-nano spiral structure in example 3; wherein, FIG. 3a is a micrometer scale spiral structure diagram; FIG. 3b is a view of a single-section hierarchical spiral structure; FIG. 3c is a partial magnified view of a micro-and nano-scale hierarchical helical structure.
Detailed Description
Example 1
(1) Preparation of polyvinyl alcohol/sodium alginate composite hydrogel with hierarchical micro-nano fiber structure
1. The preparation of the polyvinyl alcohol/sodium alginate mixed solution (the mass fraction of sodium alginate is 2 wt%, and the mass fraction of polyvinyl alcohol is 1 wt%): weighing 0.6g of polyvinyl alcohol powder, adding 58.2ml of water into a beaker, adjusting the temperature of a constant-temperature magnetic stirrer to be 95 ℃, placing the beaker into the stirrer after the temperature is stable, and stirring for 2 hours at regular time to dissolve the polyvinyl alcohol to form a solution. Taking down and cooling to room temperature, weighing a proper amount of 1.2g of sodium alginate powder, putting the sodium alginate powder into the polyvinyl alcohol solution, using a power-increasing electric stirrer to stir for 2 hours at regular time to form a stable polyvinyl alcohol/sodium alginate mixed solution, and standing for standby without bubbles.
2. The hydrogel is formed by adopting the microfluidic principle: an 18G standard syringe needle (inner diameter 0.84mm, outer diameter 1.27mm) was used, the steel needle end was inserted directly into one end of a polyethylene tube with an inner diameter of 1mm, the plastic end of the steel needle was connected to the outlet end of the syringe, the syringe plunger handle was pushed by the syringe pump to push out 1mL of the liquid in the syringe (through the polyethylene tube and out the other end), and a simple microfluidic system was constructed (the polyethylene tube functions to facilitate longer distance injections). At room temperature, the mixed solution is uniformly injected into a culture dish containing 0.5M calcium chloride solution (50ml) through a needle and a polyethylene catheter at a controlled rate of 10ml/min, and then the culture dish is placed for 12 hours for full crosslinking of sodium alginate. Fibrous hydrogel samples were prepared averaging 0.9mm in diameter and 6cm in length.
3. Molding a hierarchical micro-nano fiber structure: and taking out the hydrogel sample, clamping two ends of the hydrogel sample at two ends of a clamp, fixing the two ends of the clamp, keeping the hydrogel sample in a straightening state, pre-stretching by 10 percent, and drying for 24 hours at room temperature. In the process of drying at room temperature, the sample can shrink axially and radially, and because the two ends are fixed, the hydrogel can be acted by axial force, so that the polymer chains are promoted to be aligned.
4. Taking off the dried sample, placing in water for 12h to swell and balance, freezing in a refrigerator at-20 deg.C for 10h, thawing at room temperature for 2h, and repeating the freezing-thawing operation 4 times. And (3) carrying out repeated freeze-thaw cycles to enable the polyvinyl alcohol to be crosslinked.
5. And finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure.
Example 2
(1) Preparation of polyvinyl alcohol/sodium alginate composite hydrogel with hierarchical micro-nano fiber structure
1. The preparation of the polyvinyl alcohol/sodium alginate mixed solution (the mass fraction of sodium alginate is 2 wt%, and the mass fraction of polyvinyl alcohol is 2 wt%): weighing 1.2g of polyvinyl alcohol powder, adding 57.6ml of water into a beaker, adjusting the temperature of a constant-temperature magnetic stirrer to 95 ℃, placing the beaker into the stirrer after the temperature is stable, and stirring for 2 hours at regular time to dissolve the polyvinyl alcohol to form a solution. Taking down and cooling to room temperature, weighing a proper amount of 1.2g of sodium alginate powder, putting the sodium alginate powder into the polyvinyl alcohol solution, using a power-increasing electric stirrer to stir for 2 hours at regular time to form a stable polyvinyl alcohol/sodium alginate mixed solution, and standing for standby without bubbles.
2. The hydrogel is formed by adopting the microfluidic principle: an 18G standard syringe needle (inner diameter 0.84mm, outer diameter 1.27mm) was used, the steel needle end was inserted directly into one end of a polyethylene tube with an inner diameter of 1mm, the plastic end of the steel needle was connected to the outlet end of the syringe, the syringe plunger handle was pushed by the syringe pump to push out 1mL of the liquid in the syringe (through the polyethylene tube and out the other end), and a simple microfluidic system was constructed (the polyethylene tube functions to facilitate longer distance injections). At room temperature, the mixed solution is uniformly injected into a culture dish containing 0.5M calcium chloride solution (50ml) through a needle and a polyethylene catheter at a controlled rate of 10ml/min, and then the culture dish is placed for 12 hours for full crosslinking of sodium alginate. Fibrous hydrogel samples were prepared averaging 0.9mm in diameter and 6cm in length.
3. Molding a hierarchical micro-nano fiber structure: and taking out the hydrogel sample, clamping two ends of the hydrogel sample at two ends of a clamp, fixing the two ends of the clamp, keeping the hydrogel sample in a straightening state, pre-stretching by 10 percent, and drying for 24 hours at room temperature. In the process of drying at room temperature, the sample can generate axial and radial shrinkage, and the hydrogel can be acted by axial force due to the fixation of two ends, so that the directional arrangement of polymer chains is promoted.
4. Taking off the dried sample, placing in water for 12h to swell and balance, freezing in a refrigerator at-20 deg.C for 10h, thawing at room temperature for 2h, and repeating the freezing-thawing operation 4 times. And (3) carrying out repeated freeze-thaw cycles to enable the polyvinyl alcohol to be crosslinked.
5. And finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure.
Example 3
(2) Preparation of polyvinyl alcohol/sodium alginate composite hydrogel with hierarchical micro-nano spiral structure
1. The preparation of the polyvinyl alcohol/sodium alginate mixed solution (the mass fraction of sodium alginate is 2 wt%, and the mass fraction of polyvinyl alcohol is 2 wt%): weighing 1.2g of polyvinyl alcohol powder, adding 57.6ml of water into a beaker, adjusting the temperature of a constant-temperature magnetic stirrer to 95 ℃, placing the beaker into the stirrer after the temperature is stable, and stirring for 2 hours at regular time to dissolve the polyvinyl alcohol to form a solution. Taking down and cooling to room temperature, weighing a proper amount of 1.2g of sodium alginate powder, putting the sodium alginate powder into the polyvinyl alcohol solution, using a power-increasing electric stirrer to stir for 2 hours at regular time to form a stable polyvinyl alcohol/sodium alginate mixed solution, and standing for standby without bubbles.
2. An 18G standard syringe needle (inner diameter 0.84mm, outer diameter 1.27mm) was used, the steel needle end was inserted directly into one end of a polyethylene tube with an inner diameter of 1mm, the plastic end of the steel needle was connected to the outlet end of the syringe, the syringe plunger handle was pushed by the syringe pump to push out 1mL of the liquid in the syringe (through the polyethylene tube and out the other end), and a simple microfluidic system was constructed (the polyethylene tube functions to facilitate longer distance injections). At room temperature, the mixed solution is uniformly injected into a culture dish containing 0.5M calcium chloride solution (50ml) through a needle and a polyethylene catheter at a controlled rate of 10ml/min, and then the culture dish is placed for 12 hours for full crosslinking of sodium alginate. Fibrous hydrogel samples were prepared averaging 0.9mm in diameter and 6cm in length.
3. Molding a hierarchical micro-nano spiral structure: and clamping two ends of the hydrogel sample by using a three-jaw chuck, fixing one end of the hydrogel sample, connecting the three-jaw chuck at the other end of the hydrogel sample with a motor, measuring the initial gauge length to be 5cm, and adjusting the rotating speed to be 20r/min for 5 min. After rotating for 100 circles with preset number of turns, fixing the two ends and keeping the hydrogel sample in a straightening state, pre-stretching by 10 percent, and drying for 24 hours at room temperature.
4. Taking off the dried sample, placing in water for 12h to swell and balance, freezing in a refrigerator at-20 deg.C for 10h, thawing at room temperature for 2h, and repeating the freezing-thawing operation 4 times. And (3) carrying out repeated freeze-thaw cycles to enable the polyvinyl alcohol to be crosslinked.
5. And finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano spiral structure.
Comparative example 1
(1) Preparation of control group (without microstructure) polyvinyl alcohol/sodium alginate composite hydrogel
1. The preparation of the polyvinyl alcohol/sodium alginate mixed solution (the mass fraction of sodium alginate is 2 wt%, and the mass fraction of polyvinyl alcohol is 2 wt%): weighing 1.2g of polyvinyl alcohol powder, adding 57.6ml of water into a beaker, adjusting the temperature of a constant-temperature magnetic stirrer to 95 ℃, placing the beaker into the stirrer after the temperature is stable, and stirring for 2 hours at regular time to dissolve the polyvinyl alcohol to form a solution. Taking down and cooling to room temperature, weighing a proper amount of 1.2g of sodium alginate powder, putting the sodium alginate powder into the polyvinyl alcohol solution, using a power-increasing electric stirrer to stir for 2 hours at regular time to form a stable polyvinyl alcohol/sodium alginate mixed solution, and standing for standby without bubbles.
2. The hydrogel is formed by adopting the microfluidic principle: an 18G standard syringe needle (inner diameter 0.84mm, outer diameter 1.27mm) was used, the steel needle end was inserted directly into one end of a polyethylene tube with an inner diameter of 1mm, the plastic end of the steel needle was connected to the outlet end of the syringe, the syringe plunger handle was pushed by the syringe pump to push out 1mL of the liquid in the syringe (through the polyethylene tube and out the other end), and a simple microfluidic system was constructed (the polyethylene tube functions to facilitate longer distance injections). At room temperature, the mixed solution is uniformly injected into a culture dish containing 0.5M calcium chloride solution (50ml) through a needle and a polyethylene catheter at a controlled rate of 10ml/min, and then the culture dish is placed for 12 hours for full crosslinking of sodium alginate. Fibrous hydrogel samples were prepared averaging 0.9mm in diameter and 6cm in length.
3. Taking out the sample, freezing in a refrigerator at-20 deg.C for 10h, thawing at room temperature for 2h, and repeating the freezing-thawing operation 4 times. And (3) carrying out repeated freeze-thaw cycles to enable the polyvinyl alcohol to be crosslinked.
4. And finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel of the control group (without microstructure).
The mechanical properties (including stress-strain curves, elastic moduli and fracture energy) of the polyvinyl alcohol/sodium alginate composite hydrogel with the graded micro-nanofibers and the helical structure prepared in examples 1 to 3 and the control group (without microstructure) prepared in comparative example 1 were detected by a microcomputer-controlled electronic universal tester (shenzhen new three systems measuring company, model No. CMT6104), and the test and calculation methods were as follows:
the test was carried out at room temperature and the stretching rate at which the PVA/SA (polyvinyl alcohol/sodium alginate) gel was tested for its tensile properties was 20 mm/min. The original experimental data of the tensile samples are recorded by a computer, the number of each group of samples is 5, and the results are averaged. The elastic modulus, tensile strength, tensile strain and energy at break were calculated according to the following formulas and methods.
1) Calculation of modulus of elasticity
E ═ sigma/epsilon (formula one)
In the formula: e is the modulus of elasticity (MPa); sigma is the stress (MPa) of the material in the elastic deformation stage; ε represents the strain of the sample during the elastic deformation phase.
2) Calculation of tensile Strength
In the formula: sigma1Tensile strength (MPa) of the sample; p is the maximum tensile load (N); b is the width (mm) of the specimen; d is the thickness (mm) of the sample.
3) Calculation of tensile Strain
In the formula: epsilon1Tensile strain (%) of the sample; l0 is the original gauge length (mm) of the specimen; l is the distance (mm) between the upper and lower chucks when the specimen is broken.
4) Calculation of fracture energy
The energy at break W is calculated as the integrated area under the corresponding stress-strain curve of the specimen (MJ/m)3)。
The mechanical properties of the polyvinyl alcohol/sodium alginate hydrogel with the hierarchical micro-nano structure prepared in examples 1 to 3 and the polyvinyl alcohol/sodium alginate composite hydrogel without the microstructure prepared in comparative example 1 were measured, and the measurement results are shown in table 1.
Table 1 mechanical properties of composite hydrogel having a hierarchical micro-nano structure prepared in examples and comparative examples
As can be seen from Table 1, the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nanofiber structure prepared in example 1 has the tensile strength of (11.15 +/-0.79) MPa, the tensile strain of (143.33 +/-4.69)%, the elastic modulus of (0.94 +/-0.08) MPa and the fracture energy of (10.36 +/-0.56) MJ/m3(ii) a The polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure prepared in the embodiment 2 has the tensile strength of (12.86 +/-0.6) MPa, the tensile strain of (161.43 +/-10.49)%, the elastic modulus of (1.05 +/-0.13) MPa and the breaking energy of (13.18 +/-1.16) MJ/m3(ii) a The polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure prepared in the embodiment 1 has the tensile strength of (4.40 +/-0.24) MPa, the tensile strain of (173.05 +/-15.67)%, the elastic modulus of (0.50 +/-0.0026) MPa and the fracture energy of (4.53 +/-0.11) MJ/m3. Compared with the hydrogel without the structure, the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano bionic structure prepared by the method has the advantages that the tensile strength, the elastic modulus and the fracture energy of the material are greatly improved.
Fig. 1 is an SEM image of a polyvinyl alcohol/sodium alginate hydrogel micron-scale layered fiber structure having a hierarchical micro-nano fiber structure in example 1. The hierarchical fiber structure can be seen in fig. 1, with a fiber width at the microscale of 2.36um, where the fiber width at the nanoscale of the hierarchy is 675.68 nm; the part is enlarged to obtain a figure 2, an obvious hierarchical fiber structure can be seen, the width of the fiber with the micron scale is 4.06um, and the width of the fiber with the hierarchical nano scale is 362.32nm, so that the construction of the hierarchical micro-nano fiber structure can be successfully achieved. Fig. 3 is an SEM image of the polyvinyl alcohol/sodium alginate composite hydrogel having the hierarchical micro-nano helical structure in example 3. (a) A distinct helix can be seen, with a width of 239.32 um; when the single-section spiral structure is enlarged, as shown in (b), obvious layering phenomenon can be seen, and the width of the spiral structure at layering is 5.71 um; and (c) the partial part of the graph is continuously enlarged, so that the nanoscale spiral structure still appears in the microscale single-layer spiral structure, and the width of the nanoscale spiral structure is 598.29nm, so that the hierarchical micro-nano spiral structure can be successfully constructed.
The invention is not the best known technology.
Claims (4)
1. A preparation method of hydrogel with a hierarchical micro-nano structure is characterized by comprising one of the following two modes:
the method comprises the following steps: the preparation method of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure comprises the following steps:
(1) injecting the polyvinyl alcohol/sodium alginate mixed solution into a container filled with a calcium chloride solution in a micro-fluidic system, and standing for 10-15 hours to obtain fibrous hydrogel with the length of 3-10 cm and the diameter of 0.5-1.5 mm;
wherein, in the mixed solution of polyvinyl alcohol and sodium alginate, the mass fraction of sodium alginate is as follows: 1wt% -4 wt%, and the mass fraction of polyvinyl alcohol is as follows: 1wt% -5 wt%; the injection rate is 3-15 ml/min, and the concentration of the calcium chloride solution is 0.3-1.0M; the diameter of the injection end of the microfluidic system is 0.5-2 mm;
(2) then, clamping and fixing two ends of the fibrous hydrogel by using clamps respectively, keeping the hydrogel sample in a straightened state, wherein the pre-stretching amount of the straightened state is 10-100%, and drying for 12-48 h at room temperature;
(3) swelling the dried product in the last step in water for 6-24 h, freezing at-10 to-30 ℃ for 10-15 h, thawing at room temperature for 2-6 h, and repeating the freezing-thawing operation for 2-6 times; finishing the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano fiber structure;
or, the second method is to prepare the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano spiral structure, and comprises the following steps:
(1) injecting the polyvinyl alcohol/sodium alginate mixed solution into a container filled with a calcium chloride solution in a micro-fluidic system, and standing for 10-15 hours to obtain fibrous hydrogel with the length of 3-10 cm and the diameter of 0.5-1.5 mm;
wherein, in the mixed solution of polyvinyl alcohol and sodium alginate, the mass fraction of sodium alginate is as follows: 1wt% -4 wt%, and the mass fraction of polyvinyl alcohol is as follows: 1wt% -5 wt%; the injection rate is 3-15 ml/min, and the concentration of the calcium chloride solution is 0.3-1.0M; the injection diameter of the microfluidic system is 0.5-2 mm;
(2) molding a hierarchical micro-nano spiral structure: clamping two ends of the fibrous hydrogel by using clamps respectively, fixing one end of the fibrous hydrogel, connecting the clamp at the other end of the fibrous hydrogel with a motor, keeping the fibrous hydrogel in a straightening state, enabling the fibrous hydrogel to rotate at a constant speed by using the motor, rotating the fibrous hydrogel to a set number of turns, and drying the fibrous hydrogel for 12-48 h at room temperature;
wherein the set number of rotation turns = the initial distance/cm x 10-30 r between the two clamps;
(3) and (3) swelling the dried product in the previous step in water for 6-24 h, freezing at-10 to-30 ℃ for 10-15 h, thawing at room temperature for 2-6 h, and repeating the freezing-thawing operation for 2-6 times to complete the preparation of the polyvinyl alcohol/sodium alginate composite hydrogel with the hierarchical micro-nano spiral structure.
2. The method for preparing hydrogel with a hierarchical micro-nano structure according to claim 1, wherein in the second method, the rotating speed of the motor is 10-100 r/min.
3. The method according to claim 1, wherein the microfluidic system comprises a syringe and an injection needle connected in sequence.
4. The method for preparing hydrogel with hierarchical micro-nano structure according to claim 1, wherein the volume ratio of the step (1) in the first method or the second method is polyvinyl alcohol/sodium alginate mixed solution: calcium chloride solution = 1: 20 to 30.
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