A method for preparing a hydrogel based on the synergistic effect of freezing and soaking and the hydrogel

Abstract

The present invention belongs to the technical field of hydrogel materials, and relates to a method for preparing a hydrogel based on the synergistic effect of freezing and soaking and the hydrogel. The method includes stirring and mixing an aqueous sodium alginate solution and a soluble sodium salt to obtain a mixed solution of alginate precursor; dropwise adding a crosslinking agent solution to the mixed solution of alginate precursor and stirring evenly to obtain a pre-gel solution; pouring the pre-gel solution into a mold for curing treatment to generate a cured single-network sodium alginate hydrogel; freezing the cured single-network sodium alginate hydrogel in a low-temperature environment to generate a frozen single-network sodium alginate hydrogel; soaking the frozen single-network sodium alginate hydrogel at room temperature in ultrapure water to generate a target single-network sodium alginate hydrogel based on the synergistic effect of freezing and soaking. Based on the above method, the strength and toughness of the single-network sodium alginate hydrogel are enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogel materials, and particularly relates to a method for preparing a hydrogel based on the synergistic effect of freezing and soaking and the hydrogel. Background Art

[0002] Natural load-bearing materials usually exhibit a combination of conflicting mechanical properties. For example, wood is both light and strong, nacre is hard and elastic, and muscle and tendon are soft and tough. The special properties of these materials have made them widely used in various structural applications. In many fields, as an excellent structural material, hydrogels have been widely used in wearable electronics, artificial scaffolds, soft robots, underwater communication and other fields, and these applications have put forward higher requirements for the mechanical properties of hydrogels.

[0003] However, traditional hydrogels generally have the problems of low strength and easy permanent fracture, which limits their application in actual engineering. For example, alginate single-network hydrogels break when stretched to 1.2 times their original length, and their tensile properties are poor, far from meeting the requirements of high load, impact resistance and large deformation. This phenomenon greatly limits the use of hydrogels in applications with high strength and durability requirements.

[0004] In summary, the hydrogels in the prior art generally have the problems of low strength and easy permanent fracture, which limits their performance in actual applications such as high load, impact resistance and large deformation. Summary of the Invention

[0005] A method for preparing a hydrogel based on the synergistic effect of freezing and soaking and the hydrogel provided by an embodiment of the present invention at least solves the problems of low strength and easy permanent fracture existing in the hydrogel in the related art.

[0006] According to the first aspect of the embodiment of the present invention, a method for preparing a hydrogel based on the synergistic effect of freezing and soaking is provided, including:

[0007] Stir and mix an aqueous sodium alginate solution and a soluble sodium salt to obtain a mixed solution of alginate precursor;

[0008] Dropwise add a crosslinking agent solution to the mixed solution of alginate precursor and stir evenly to obtain a pre-gel solution;

[0009] Pour the pre-gel solution into a mold for curing treatment to generate a cured single-network sodium alginate hydrogel;

[0010] Freeze the cured single-network sodium alginate hydrogel in a low-temperature environment to generate a frozen single-network sodium alginate hydrogel;

[0011] After bringing the frozen single-network alginate hydrogel to room temperature, it is soaked in ultrapure water to generate a target single-network alginate hydrogel based on the synergistic effect of freezing and soaking.

[0012] According to an embodiment of the present invention, it further includes:

[0013] At room temperature, sodium alginate is slowly added to ultrapure water and stirred evenly to form the homogeneous and transparent sodium alginate aqueous solution;

[0014] Wherein, the mass fraction of sodium alginate is 1 wt.% to 4 wt.%, and the stirring time after mixing sodium alginate and the ultrapure water is 8 hours to 24 hours.

[0015] According to an embodiment of the present invention, the stirring time when stirring and mixing the sodium alginate aqueous solution and the soluble sodium salt is 5 minutes to 30 minutes;

[0016] Wherein, the soluble sodium salt is sodium pyrophosphate, sodium citrate, sodium oxalate, sodium carbonate or sodium sulfate, and the mass ratio of the soluble sodium salt to the cross-linking agent in the cross-linking agent solution is 0 wt.% to 40 wt.%.

[0017] According to an embodiment of the present invention, the stirring time when dropwise adding the cross-linking agent solution to the alginate precursor mixed solution and stirring evenly is 5 minutes to 30 minutes;

[0018] Wherein, the cross-linking agent in the cross-linking agent solution is anhydrous calcium sulfate or calcium sulfate dihydrate, and the mass ratio of the cross-linking agent to sodium alginate is 10 wt.% to 95 wt.%.

[0019] According to an embodiment of the present invention, after dropwise adding the cross-linking agent solution to the alginate precursor mixed solution and stirring evenly to obtain a pre-gel solution, the method further includes:

[0020] Performing a mixing and defoaming treatment on the pre-gel solution by a mixing defoamer to eliminate the bubbles generated during the stirring process;

[0021] Wherein, the mixing time of the mixing and defoaming treatment is 30 seconds to 60 seconds, the defoaming time of the mixing and defoaming treatment is 30 seconds to 60 seconds, and the number of times of the mixing and defoaming treatment is 1 to 3 cycles.

[0022] According to an embodiment of the present invention, pouring the pre-gel solution into a mold for curing treatment to generate a cured single-network alginate hydrogel includes:

[0023] Pouring the pre-gel solution into the mold and standing for curing at room temperature to eliminate the bubbles generated during the solution transfer process;

[0024] Encapsulate the mold using a glass plate coated with a nano superhydrophobic self-cleaning coating;

[0025] Let the encapsulated mold stand and cure at room temperature to obtain the cured single-network alginate hydrogel.

[0026] According to an embodiment of the present invention, when pouring the pre-gel solution into the mold and letting it stand at room temperature to eliminate the bubbles generated during the solution transfer process, the standing time is 0.5 hour to 1 hour; when letting the encapsulated mold stand and cure at room temperature, the standing and curing time is 12 hours to 48 hours.

[0027] According to an embodiment of the present invention, the freezing treatment of the cured single-network alginate hydrogel at a low temperature to generate a frozen single-network alginate hydrogel includes:

[0028] Place the cured single-network alginate hydrogel in the low-temperature environment for freezing treatment for 12 hours to 72 hours to obtain the frozen single-network alginate hydrogel, wherein the temperature of the low-temperature environment is -10°C to -25°C.

[0029] According to an embodiment of the present invention, the soaking time of the soaking treatment is 12 hours to 72 hours.

[0030] According to a second aspect of the embodiments of the present invention, there is provided a single-network alginate hydrogel, which is prepared according to the hydrogel preparation method based on the freezing-soaking synergistic effect described in the first aspect.

[0031] According to the hydrogel preparation method based on the freezing-soaking synergistic effect provided by the embodiments of the present invention, it can effectively enhance the strength and toughness of the single-network alginate hydrogel. First, the cured single-network alginate hydrogel is subjected to freezing treatment, and then it is directly immersed in ultrapure water after being placed at room temperature. The freezing process not only provides ion channels with microstructures for subsequent soaking toughening, but also prepares polymer chains for the strong hydrophobic aggregation and crystallization caused by subsequent soaking through polymer concentration and close packing. At the same time, the ultrapure water soaking process enables the continued dissolution of the excessive slightly soluble cross-linking agent during the curing process to form a hypertonic salt solution, thereby further increasing the ionic cross-linking density of the hydrogel and achieving the effect of salting-out toughening. The synergistic effect of freezing and soaking introduces an energy dissipation mechanism, significantly enhancing the mechanical properties of the alginate hydrogel, solving the problems of weak mechanical properties and fragility faced by traditional alginate hydrogels in practical applications, providing an innovative method for enhancing and toughening alginate hydrogels, and thus providing a new solution for its practical applications in engineering fields such as high load, impact resistance, and large deformation.

[0032] The details of one or more embodiments of the invention are set forth in the following drawings and description so that other features, objects, and advantages of the invention are more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other embodiments can be obtained based on these drawings without creative work.

[0034] Figure 1 A flow chart of a method for preparing a hydrogel based on freezing-immersion synergy provided in an embodiment of the present invention.

[0035] Figure 2 The present invention provides a flowchart of a pre-gel solution curing method according to an embodiment of the present invention.

[0036] Figure 3 A flow chart of another method for preparing a hydrogel based on freezing-immersion synergy provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] Embodiments of the present embodiment will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present embodiment are shown in the accompanying drawings, it should be understood that the present embodiment can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein, which are instead provided for a more thorough and complete understanding of the present embodiment. It should be understood that the drawings and embodiments of the present embodiment are only for exemplary purposes and are not intended to limit the scope of protection of the present embodiment.

[0038] Hydrogels are widely used in many fields, such as wearable electronic devices, artificial tissue scaffolds, soft robots, and underwater communications, due to their excellent hydration properties and biocompatibility. With the continuous development of related technologies, higher requirements are put forward for the mechanical properties of hydrogels, especially in applications under extreme conditions such as high load, impact resistance, and large deformation. The practical application of traditional hydrogels is limited by their low strength and easy permanent fracture.

[0039] At present, a variety of methods have been used to enhance the mechanical properties of hydrogels, such as improving their stretchability and fracture resistance by designing double network hydrogels and composite hydrogels. However, most of these methods have certain limitations, such as complex manufacturing processes, high costs, or difficulty in improving both strength and toughness. Therefore, how to improve the strength and toughness of hydrogels at the same time through simple and efficient methods has become a technical problem that needs to be solved urgently in this field.

[0040] Figure 1 The flowchart of a method for preparing a hydrogel based on freezing-immersion synergy provided by an embodiment of the present invention is as follows. Figure 1 As shown, the method includes the following steps.

[0041] Step S101, stirring and mixing the sodium alginate aqueous solution and the soluble sodium salt to obtain an alginate precursor mixed solution.

[0042] Step S102, adding a crosslinking agent solution dropwise to the alginate precursor mixed solution and stirring evenly to obtain a pre-gel solution.

[0043] Step S103, pouring the pre-gel solution into a mold for curing to generate a cured single-network alginate hydrogel.

[0044] Step S104, freezing the solidified single-network alginate hydrogel in a low-temperature environment to generate a frozen single-network alginate hydrogel.

[0045] Step S105, after the frozen single-network alginate hydrogel is cooled to room temperature, it is immersed in ultrapure water to generate a target single-network alginate hydrogel based on the freezing-immersion synergistic effect.

[0046] First, the sodium alginate aqueous solution and the soluble sodium salt are stirred and mixed to obtain an alginate precursor mixed solution.

[0047] In this embodiment, before stirring and mixing the sodium alginate aqueous solution and the soluble sodium salt, the sodium alginate aqueous solution needs to be prepared first.

[0048] Specifically, when preparing the sodium alginate aqueous solution, sodium alginate can be slowly added to ultrapure water at room temperature and stirred evenly to form a uniform and transparent sodium alginate aqueous solution. That is, sodium alginate is slowly added to ultrapure water and stirred sufficiently until a uniform and transparent sodium alginate aqueous solution is formed.

[0049] Sodium alginate is a natural polysaccharide that can usually be dissolved in water to form a transparent solution. In order to avoid the influence of impurities and pH value on the stability of the sodium alginate aqueous solution, ultrapure water is selected instead of ordinary water source in this embodiment. In the process of preparing the sodium alginate aqueous solution, the purpose of slowly adding sodium alginate is to avoid the formation of undissolved sodium alginate particles, accelerate the dissolution of sodium alginate, ensure the uniformity of the aqueous solution, and facilitate the subsequent curing reaction.

[0050] In practical applications, the mass fraction of sodium alginate can be between 1 wt.% and 4 wt.% to ensure that the solution has good fluidity and uniformity. During the preparation of the sodium alginate aqueous solution, the stirring time should be long enough to ensure that sodium alginate is completely dissolved in ultrapure water to form a homogeneous and transparent sodium alginate aqueous solution. Optionally, the stirring time after mixing sodium alginate and ultrapure water can be 8 hours to 24 hours.

[0051] On the basis of obtaining the sodium alginate aqueous solution, a soluble sodium salt is continuously added for mixing and stirring to obtain a mixed solution of alginate precursor.

[0052] Specifically, the stirring time for mixing and stirring after adding the soluble sodium salt to the sodium alginate aqueous solution can be 5 minutes to 30 minutes. The addition of the soluble sodium salt ensures the formation of a hydrogel network with both high crosslinking density and uniformity in the subsequent crosslinking reaction, thereby enhancing the mechanical strength and toughness of the hydrogel. In practical applications, the soluble sodium salt can be sodium pyrophosphate, sodium citrate, sodium oxalate, sodium carbonate or sodium sulfate. Among them, the mass ratio of the soluble sodium salt to the crosslinking agent in the crosslinking agent solution is 0 wt.% to 40 wt.%. In practical applications, experiments have shown that when the mass ratio of the sodium salt to the crosslinking agent is 10 - 30 wt.%, the uniformity of the hydrogel is most significantly improved.

[0053] Then, a crosslinking agent solution is added dropwise to the mixed solution of alginate precursor and stirred evenly to obtain a pre - gel solution.

[0054] In this embodiment, before preparing the pre - gel solution, it is also necessary to first prepare a crosslinking agent solution. Specifically, the crosslinking agent can be dissolved in an appropriate amount of solvent to prepare a crosslinking agent solution. In practical applications, the mass ratio of the crosslinking agent to sodium alginate can be between 10 wt.% and 95 wt.%. Among them, the crosslinking agent can be anhydrous calcium sulfate or calcium sulfate dihydrate.

[0055] After obtaining the crosslinking agent solution, the crosslinking agent solution can be added dropwise to the mixed solution of alginate precursor and stirred evenly to obtain a pre - gel solution.

[0056] In practical applications, calcium ions in the crosslinking agent can react with carboxyl groups on sodium alginate molecules to form stable ionic bonds, thereby generating a cross - linked network structure of sodium alginate hydrogel. By adding the crosslinking agent solution dropwise, it can ensure that the crosslinking reaction process proceeds evenly and improve the degree of homogenization of the hydrogel.

[0057] After adding a crosslinking agent to the alginate precursor mixed solution, stirring can enable the crosslinking agent to fully react with sodium alginate to form a hydrogel with a crosslinked structure. During this process, it is necessary to set the stirring time and speed to ensure the uniformity of the crosslinking reaction. Optionally, the stirring time can be 5 minutes to 30 minutes to ensure the full reaction of the crosslinking agent with sodium alginate.

[0058] There may be a large number of bubbles in the pre-gel solution without mixing and degassing treatment, and the bubbles will cause uneven distribution inside the hydrogel, affecting the mechanical properties. Especially in high-load and high-strength applications, the presence of bubbles may cause cracks and fractures in the hydrogel. Therefore, after obtaining the pre-gel solution, it is necessary to first perform mixing and degassing treatment on the pre-gel solution. By performing mixing and degassing treatment to eliminate the bubbles generated during the stirring process, the overall structure and properties of the hydrogel can be improved.

[0059] In this embodiment, a mixing and degassing machine can be used to perform mixing and degassing treatment on the pre-gel solution. In practical applications, when using a mixing and degassing machine, the processing parameters (mixing time, degassing time) during the mixing and degassing treatment can be set. Optionally, the mixing time can be set to 30 seconds to 60 seconds, and the degassing time can be set to 30 seconds to 60 seconds. Further optionally, according to the actual processing situation, the pre-gel solution can be subjected to one or more mixing and degassing treatments. Specifically, the pre-gel solution can be subjected to 1 to 3 mixing and degassing cycles using a mixing and degassing machine.

[0060] After the pre-gel solution is subjected to mixing and degassing treatment, the pre-gel solution can be poured into a mold for curing treatment to generate a cured single-network alginate hydrogel.

[0061] Figure 2 It is a flowchart of a method for curing a pre-gel solution provided by an embodiment of the present invention. As Figure 2 shown, the method includes the following steps.

[0062] Step S201, pour the pre-gel solution into a mold and let it stand at room temperature to eliminate the bubbles generated during the stirring process.

[0063] In this embodiment, the pre-gel solution that has been mixed and degassed is poured into a pre-prepared mold and left standing at room temperature to allow the bubbles inside the pre-gel solution to be released and cured. Curing is the process of forming a hydrogel, and at this time, the pre-gel solution begins to change from a liquid state to a solid state. During the standing process, the bubbles in the pre-gel solution will rise to the liquid surface. Removing the bubbles helps to improve the uniformity and mechanical properties of the hydrogel. In practical applications, the standing time is 0.5 hour to 1 hour to ensure that the bubbles are completely eliminated.

[0064] Optionally, the mold can be a container of any shape, and the specific shape can be selected according to the desired hydrogel morphology.

[0065] Step S202, encapsulate the mold using a glass plate coated with a nano superhydrophobic self-cleaning coating.

[0066] In this embodiment, the encapsulation process can avoid water loss during the curing process, maintain the stability of the hydrogel, and ensure that its internal structure is not disturbed during the entire curing process. The use of the nano superhydrophobic coating helps prevent the hydrogel from adhering to the mold surface, enhances the self-cleaning function, and reduces contamination.

[0067] Step S203, leave the encapsulated mold standing at room temperature to obtain a cured single-network alginate hydrogel.

[0068] In this embodiment, the encapsulated mold can be left standing for 12 to 48 hours until the hydrogel is completely cured to form a cured single-network alginate hydrogel.

[0069] Subsequently, the cured single-network alginate hydrogel can be subjected to a freezing process at a low temperature to generate a frozen single-network alginate hydrogel.

[0070] In this embodiment, the cured single-network alginate hydrogel after curing is placed in a low-temperature environment for freezing treatment. The freezing temperature can be set between -10°C and -25°C, and the freezing time is 12 to 72 hours. This process can form microstructural ion channels inside the gel, and the close packing between polymer chains helps enhance the mechanical properties of the gel.

[0071] The freezing process not only promotes the optimization of the microstructure of the alginate hydrogel, but also causes the polymer chains to further pack and contract through the low-temperature environment, thereby enhancing the mechanical stability of the hydrogel. After freezing, a structure with microscopic channels is formed inside the hydrogel, providing a good foundation for the subsequent soaking enhancement process.

[0072] Finally, the frozen single-network alginate hydrogel is placed at room temperature and then subjected to a soaking treatment in ultrapure water to generate a target single-network alginate hydrogel based on the synergistic effect of freezing and soaking.

[0073] In this embodiment, after the frozen alginate hydrogel is taken out of the low-temperature environment, it is restored to room temperature and placed in ultrapure water for soaking. The soaking time is 12 to 72 hours. During the soaking process, the excessive slightly soluble cross-linking agent continues to dissolve and forms a hypertonic salt solution.

[0074] The purpose of the soaking treatment is to further improve the cross-linking density of the hydrogel through the effects of solvent exchange and ion dissolution. Ultra-pure water can dissolve the unreacted cross-linking agent in the alginate hydrogel during the soaking process, increase the ionic cross-linking density, and enhance the mechanical strength and toughness of the hydrogel. After water molecules enter the hydrogel network structure, they can improve its stability and uniformity at the microscale.

[0075] To facilitate the understanding of the hydrogel preparation method based on the synergistic effect of freezing and soaking provided by the embodiments of the present invention, the following further illustrates the hydrogel preparation method based on the synergistic effect of freezing and soaking provided by the embodiments of the present invention with specific examples.

[0076] Figure 3 It is a flowchart of another hydrogel preparation method based on the synergistic effect of freezing and soaking provided by the embodiments of the present invention. As Figure 3 shown, in this embodiment, sodium pyrophosphate is used as the soluble sodium salt and anhydrous calcium sulfate is used as the cross-linking agent to prepare the target single-network alginate hydrogel as an example.

[0077] Step S301, prepare an aqueous sodium alginate solution.

[0078] In this embodiment, 1.5 g of sodium alginate (chemical purity ≥ 98%) is added to 100 mL of ultra-pure water and stirred at room temperature for about 12 hours to ensure that the sodium alginate is completely dissolved, forming a homogeneous and transparent aqueous sodium alginate solution. The mass fraction of sodium alginate is 1.5 wt.%, and at this concentration, sodium alginate can better form a stable hydrogel network.

[0079] Step S302, prepare a mixed solution of alginate precursor.

[0080] In this embodiment, 0.15 g of sodium pyrophosphate is added to the aqueous sodium alginate solution and stirred for 5 minutes to ensure that the sodium pyrophosphate is completely dissolved and uniformly mixed with the aqueous sodium alginate solution to form a mixed solution of alginate precursor. The addition of sodium pyrophosphate can improve the uniformity of the ionic cross-linking reaction and is expected to simultaneously increase the ionic cross-linking density of the hydrogel.

[0081] Step S303, prepare a cross-linking agent solution.

[0082] In this embodiment, 0.75 g of anhydrous calcium sulfate is dissolved in 20 mL of ultra-pure water to obtain a cross-linking agent solution.

[0083] Step S304, prepare a pre-gel solution.

[0084] In this embodiment, the cross-linking agent solution obtained in the above steps is added dropwise to the alginate precursor mixed solution while stirring. The stirring time is 15 minutes to ensure that the cross-linking agent reacts fully with the sodium alginate aqueous solution, and finally a pre-gel solution is obtained. The mass ratio of the added amount of the cross-linking agent to sodium alginate is 1:2 (i.e., the mass ratio of sodium alginate to anhydrous calcium sulfate is 2:1), and this ratio helps to form a moderately cross-linked gel structure.

[0085] Step S305: Perform a mixing and degassing treatment on the pre-gel solution.

[0086] In this embodiment, in order to remove the bubbles in the pre-gel solution, a mixing and degassing machine is used for the mixing and degassing treatment.

[0087] First, transfer the pre-gel solution to the mixing and degassing machine, perform a rapid mixing treatment for 30 seconds, and then perform a degassing treatment for 1 minute. Repeat this process 2 times to ensure that there are no residual bubbles in the solution.

[0088] Step S306: Prepare a cured single-network sodium alginate hydrogel.

[0089] In this embodiment, pour the pre-gel solution into a national standard type 2 dumbbell-shaped mold, and let it stand at room temperature for 0.5 hour to further remove bubbles. Subsequently, use a glass plate coated with a nano-superhydrophobic self-cleaning coating to encapsulate the mold, and continue to let it stand and cure at room temperature for 24 hours until the pre-gel solution is completely cured to form a cured single-network sodium alginate hydrogel.

[0090] Step S307: Prepare a frozen single-network sodium alginate hydrogel.

[0091] In this embodiment, take out the cured single-network sodium alginate hydrogel from the dumbbell-shaped mold and place it in a low-temperature environment for freezing treatment. The freezing temperature is set at -15°C, and the freezing time is 48 hours. During this process, the water inside the sodium alginate hydrogel will crystallize to form microstructural ion channels, and the close packing between polymer chains increases the mechanical stability of the hydrogel.

[0092] Step S308: Perform an ultra-pure water immersion treatment on the frozen single-network sodium alginate hydrogel.

[0093] In this embodiment, take out the frozen single-network sodium alginate hydrogel from the low-temperature environment and immediately immerse it in ultra-pure water. The immersion time is set at 24 hours. During this process, the excessive slightly soluble cross-linking agent will continue to dissolve to form a hypertonic salt solution, and the cross-linking density of the sodium alginate hydrogel is further increased, enhancing the mechanical properties and toughness of the hydrogel.

[0094] Step S309: Obtain the target single-network sodium alginate hydrogel.

[0095] In this embodiment, after the freeze-type single-network alginate hydrogel is soaked in ultrapure water, the crosslinking density in the alginate hydrogel is greatly increased, and the mechanical strength and toughness of the hydrogel are significantly enhanced. The finally obtained target single-network alginate hydrogel can be applied to engineering fields such as high load, impact resistance, and large deformation.

[0096] Through the above implementation steps, the method of the embodiment of the present invention effectively improves the mechanical properties of the alginate hydrogel. The microstructural ion channels introduced by the freezing treatment and the ionic crosslinking effect in the subsequent soaking treatment significantly enhance the strength and toughness of the hydrogel, solving the problems of insufficient mechanical properties and easy fracture of traditional alginate hydrogels. By removing the bubbles in the solution through the defoaming treatment, the uniformity and stability of the hydrogel are effectively improved, enabling the hydrogel to exhibit better performance in high-load and high-strength applications.

[0097] The single-network alginate hydrogel prepared by this method has excellent mechanical properties and is particularly suitable for engineering applications with high requirements for the strength, toughness, and durability of the hydrogel, such as wearable electronic devices, artificial scaffolds, soft robots, hydraulic support devices, and underwater communication systems.

[0098] In order to compare the effects of different treatment methods on the maximum tensile strength of the single-network alginate hydrogel and verify the significant toughening effect of the freeze-soaking synergistic treatment on the mechanical properties of the hydrogel. The embodiment of the present invention verifies its improvement effect on the hydrogel properties by setting a control group and multiple experimental groups. Among them, the cured single-network alginate hydrogel is used as the control group in the comparison group, while the experimental groups study its improvement effect on the hydrogel properties through different treatment methods (freezing treatment, soaking treatment, and freeze-soaking synergistic treatment).

[0099] Example 1: Control group (untreated cured single-network alginate hydrogel)

[0100] The hydrogel used in the control group is a cured single-network alginate hydrogel, and the specific preparation process is as follows:

[0101] 1. Preparation of the pre-gel solution:

[0102] (1) 3 g of sodium alginate is slowly added to 89.16 g of ultrapure water and mechanically stirred at room temperature until completely dissolved to form a uniform and transparent sodium alginate aqueous solution.

[0103] (2) 0.46 g of sodium pyrophosphate is added to the sodium alginate aqueous solution and stirred for 10 minutes until the sodium pyrophosphate is completely dissolved to form a uniform alginate precursor mixed solution (sodium alginate-sodium pyrophosphate mixed aqueous solution).

[0104] (3) Continuously add 7.44 g of calcium sulfate dihydrate solution (2.44 g of calcium sulfate dihydrate dissolved in 5 g of ultrapure water) drop by drop, and stir for 10 minutes to obtain a pre-gel solution.

[0105] 2. Mixing and degassing treatment of the pre-gel solution: Use a mixing and degassing machine to perform mixing and degassing treatment on the pre-gel solution. The mixing time is 30 seconds, the degassing time is 30 seconds, and the mixing and degassing cycle treatment is carried out 1 time.

[0106] 3. Curing treatment:

[0107] (1) Pour the degassed pre-gel solution into an acrylic mold and let it stand at room temperature for 1 hour to remove air bubbles.

[0108] (2) Seal the mold with a glass plate coated with a nano superhydrophobic self-cleaning coating, and let it stand at room temperature for curing for 24 hours to obtain a cured single-network alginate hydrogel, then demold and set aside.

[0109] The cured single-network alginate hydrogel sample is directly used for uniaxial tensile testing. The testing environment is 23 ± 2 °C and the humidity is 30 ± 3%. The test results show that the maximum tensile strength of the untreated cured single-network alginate hydrogel is only 16.28 ± 2.44 kPa

[0110] Example 2: Experimental group 1 (only freezing treatment)

[0111] The cured single-network alginate hydrogel used in experimental group 1 is exactly the same as that prepared in Example 1, but a freezing treatment is carried out on the treated hydrogel after curing. The specific steps are as follows:

[0112] Freezing treatment: Put the cured single-network alginate hydrogel into a constant temperature refrigerator at -20 °C and freeze it for 48 hours.

[0113] Testing: After the freezing treatment is completed, perform uniaxial tensile testing on the hydrogel sample. The test results show that the maximum tensile strength after freezing treatment is 35.73 ± 2.70 kPa, which is significantly increased compared with the control group.

[0114] Example 3: Experimental group 2 (only immersion treatment)

[0115] The cured single-network alginate hydrogel used in experimental group 2 is exactly the same as that prepared in Example 1, but its treatment method is only immersion treatment. The specific steps are as follows:

[0116] Immersion treatment: Put the cured single-network alginate hydrogel sample into ultrapure water for immersion treatment for 48 hours.

[0117] Test: The hydrogel samples after immersion treatment were subjected to uniaxial tensile testing. The test results showed that the maximum tensile strength was 56.47 ± 2.24 kPa, which was further improved compared to the control group.

[0118] Example 4: Experimental group 3 (freezing-immersion combined treatment)

[0119] The solidified single-network alginate hydrogel used in experimental group 3 was prepared in exactly the same process as in Example 1, and was first subjected to freezing treatment and then immersion treatment. The specific steps are as follows:

[0120] Freezing treatment: The solidified single-network alginate hydrogel was placed in a constant temperature refrigerator at -20 °C and frozen for 48 hours to obtain a frozen single-network alginate hydrogel.

[0121] Immersion treatment: The frozen single-network alginate hydrogel was taken out, placed at room temperature, and immersed in ultrapure water for 48 hours.

[0122] Test: The hydrogel samples after freezing-immersion combined treatment were subjected to uniaxial tensile testing. The results showed that the maximum tensile strength was 186.11 ± 8.97 kPa, and there was a significant increase in the maximum tensile strength compared to the control group, experimental group 1, and experimental group 2.

[0123] The uniaxial tensile test data are shown in Table 1 below. It can be clearly seen the influence of different treatment methods on the maximum tensile strength of the hydrogel:

[0124] Table 1 Uniaxial tensile test data

[0125]

[0126] As shown in Table 1, both freezing treatment and immersion treatment can improve the tensile strength of the hydrogel to a certain extent, but the freezing-immersion combined treatment (experimental group 3) shows the most significant effect, with the maximum tensile strength increasing by an order of magnitude to 186.11 ± 8.97 kPa. This indicates that the freezing-immersion combined effect has an extremely excellent toughening effect.

[0127] From the results of this comparative experiment, it can be seen that the freezing-immersion combined treatment can significantly improve the tensile strength of alginate hydrogels. Compared with the individual freezing treatment or immersion treatment, the combined effect of freezing and immersion can better optimize the structure of the hydrogel and enhance its mechanical properties.

[0128] The above are only the preferred embodiments of the present invention. Of course, those skilled in the art can make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and its equivalent technologies, they should be considered as within the protection scope of the present invention.

[0129] It should be noted that the term "including" and its variants used in the embodiments of the present invention are open-ended, that is, "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The modifications of "one" and "a plurality" mentioned in the embodiments of the present invention are illustrative rather than restrictive. Those skilled in the art should understand that unless clearly specified otherwise in the context, it should be understood as "one or more".

[0130] In the method embodiments provided by the embodiments of the present invention, the various steps recorded can be executed in different orders and / or executed in parallel. In addition, the method embodiments may include additional steps and / or omit the steps shown. The protection scope of the present invention is not limited in this regard.

[0131] The term "embodiment" in this specification means that the specific features, structures or characteristics described in combination with the embodiment may be included in at least one embodiment of the present invention. The phrase appears in various positions in the specification does not necessarily mean the same embodiment, nor does it mean being independent or alternative to other embodiments and mutually exclusive. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments are cross-referred to. In particular, for the device, equipment, and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiments.

[0132] The above-described embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of patent protection. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for preparing a hydrogel based on the synergistic effect of freezing and soaking, characterized in that, Comprising: The sodium alginate aqueous solution and the soluble sodium salt are stirred and mixed to obtain an alginate precursor mixed solution, and the mass fraction of sodium alginate in the sodium alginate aqueous solution is 1 wt. % to 4 wt. %, the soluble sodium salt is sodium pyrophosphate, and the mass ratio of the soluble sodium salt to the crosslinking agent in the crosslinking agent solution is 20 wt. %; The crosslinking agent solution is added dropwise to the alginate precursor mixed solution and stirred evenly to obtain a pre-gel solution. The crosslinking agent in the crosslinking agent solution is anhydrous calcium sulfate or calcium sulfate dihydrate, and the mass ratio of the crosslinking agent to the sodium alginate is 10 wt. % to 95 wt. %; Pour the pre-gel solution into a mold for curing treatment to generate a cured single-network alginate hydrogel; Freeze the cured single-network alginate hydrogel in a low-temperature environment to generate a frozen single-network alginate hydrogel, wherein the temperature of the low-temperature environment is -10°C to -25°C, and the freezing treatment time is 12 hours to 72 hours; After the frozen single-network alginate hydrogel is placed at room temperature, soak it in ultrapure water to generate a target single-network alginate hydrogel based on the synergistic effect of freezing and soaking.

2. The method according to claim 1, characterized in that, Also comprising: At room temperature, slowly add sodium alginate to ultrapure water and stir evenly to form the homogeneous and transparent sodium alginate aqueous solution; Among them, the stirring time after mixing sodium alginate and ultrapure water is 8 hours to 24 hours.

3. The method according to claim 1, wherein The stirring time when stirring and mixing the sodium alginate aqueous solution and the soluble sodium salt is 5 minutes to 30 minutes; Among them, the soluble sodium salt also includes sodium citrate or sodium sulfate.

4. The method according to claim 1, wherein The stirring time when adding the cross-linking agent solution dropwise to the alginate precursor mixed solution and stirring evenly is 5 minutes to 30 minutes.

5. The method according to claim 1, characterized in that, After adding the cross-linking agent solution dropwise to the alginate precursor mixed solution and stirring evenly to obtain the pre-gel solution, the method further comprises: Perform mixing and defoaming treatment on the pre-gel solution by a mixing defoamer to eliminate the bubbles generated during the stirring process; Among them, the mixing time of the mixing defoaming treatment is 30 seconds to 60 seconds, the defoaming time of the mixing defoaming treatment is 30 seconds to 60 seconds, and the number of cycles of the mixing defoaming treatment is 1 to 3 times.

6. The method according to claim 1, wherein The step of pouring the pre-gel solution into a mold for curing treatment to generate a cured single-network alginate hydrogel includes: Pour the pre-gel solution into the mold and let it stand at room temperature to eliminate the bubbles generated during the solution transfer process; Seal the mold with a glass plate coated with a nano-superhydrophobic self-cleaning coating; Let the sealed mold stand and cure at room temperature to obtain the cured single-network alginate hydrogel.

7. The method according to claim 6, wherein When pouring the pre-gel solution into the mold and letting it stand at room temperature to eliminate the bubbles generated during the solution transfer process, the standing time is 0.5 hour to 1 hour; when letting the sealed mold stand and cure at room temperature, the standing and curing time is 12 hours to 48 hours.

8. The method according to claim 1, wherein The step of freezing the cured single-network alginate hydrogel in a low-temperature environment to generate a frozen single-network alginate hydrogel includes: Place the cured single-network alginate hydrogel in the low-temperature environment for freezing treatment for 12 hours to 72 hours to obtain the frozen single-network alginate hydrogel.

9. The method according to claim 1, characterized in that The soaking time of the soaking treatment is 12 hours to 72 hours.

10. A single-network alginate hydrogel, which is prepared by the hydrogel preparation method based on the synergistic effect of freezing and soaking according to any one of claims 1 to 9.

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