Strain hardening hydrogel as well as preparation method and application thereof

Abstract

The invention relates to strain hardening hydrogel as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, preparing a first mixed solution containing sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, a cross-linking agent, an initiator and deionized water; carrying out curing and water soaking balance treatment on the obtained first mixed solution to obtain amphoteric polyelectrolyte hydrogel PA; the obtained amphoteric polyelectrolyte hydrogel PA is soaked in a second mixed solution containing sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, a cross-linking agent, an initiator and deionized water, then curing and water soaking balance treatment are conducted, and the strain hardening hydrogel HE-PA is obtained. The preparation process is simple, the production cycle is short, the process conditions are simple and convenient, the raw materials are easy to obtain, the production cost is low, and the obtained hydrogel not only has the performance of high toughness and low friction, but also has the typical strain-hardening characteristic of biological soft tissue, can be used in the medical field of ionic skin and the like, and has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a strain-hardening hydrogel, a preparation method thereof and an application thereof. Background Art

[0002] Biological soft tissues have mechanical characteristics different from those of ordinary elastomers including hydrogels: the tangent modulus is very low under small stresses, so that large soft strains are easily generated, and with the increase of strain, a significant increase in the tangent modulus will occur. This stress-strain mechanical response of biological soft tissues in which the tangent modulus increases with the increase of strain is also called the "strain hardening" characteristic. Strain hardening can limit the excessive deformation of biological tissues, effectively prevent tissue damage caused by large deformations, and maintain the integrity of tissue structure and biological functionality. This is because biological soft tissues are composed of hard collagen fibers and a fibrous protein network, and elastic recoil can resist large deformations and self-healing functions. Most ordinary elastomer materials including hydrogels are reticular cross-linked structures, showing typical mechanical characteristics of synthetic materials: having a large modulus of elastic deformation under small strains, while under large strains, the cross-linking points will be damaged, showing the "strain softening" phenomenon, that is, the tangent modulus decreases with the increase of strain. This is because the elastic behavior of ordinary elastomers depends on strong chemical / physical cross-linking interactions between molecules. Strain causes an increase in the entropy of the elastomer to generate entropy elasticity, and the damage of cross-linking points under large deformations causes a decrease in entropy elasticity.

[0003] Hydrogels are an ideal biomaterial. The Gong research group [Sun T L, Kurokawa T, Kuroda S, et al. Physical hydrogels composed of polyampholytes demonstrate high toughness and viscoelasticity [J]. Nature Materials, 2013, 12(10): 932-937.] has shown that neutral polyampholytes form tough physical hydrogels by forming ionic bonds with a wide range of strengths above the critical concentration C m above. P(NaSS-co-DAC) is a random copolymer of the positively charged monomer sodium styrene sulfonate (NaSS) and the negatively charged monomer acryloyloxyethyl trimethyl ammonium chloride (DAC), without or with only slight chemical cross-linking. The amphoteric polyelectrolyte gel containing 50% water has good stretchability and toughness: the fracture stress is 0.8 MPa, the fracture strain is 7 times, and the tensile fracture work is 1.27 MJ / m 3Due to the reversible ionic bonds, the P(NaSS-co-DAC) hydrogel also exhibits complete self-healing ability (100%) and high fatigue resistance. However, the monomer dosage reaches the dissolution limit at 2.5 M, and it is impossible to obtain a high-strength and tough hydrogel. The Suo team [Junsoo Kim, Zhigang Suo et al. Fracture, fatigue, and friction of polymers in which entanglements [J]. Science, 2021, 374, 212-216.] reported that conventional hydrogels have a network cross-linked structure, while highly entangled hydrogels have a texture-like topological structure. Conventional hydrogels adjust the strength, toughness, and anti-swelling properties of the hydrogel through the cross-linking point density: highly cross-linked hydrogels have high anti-swelling properties but a significant decrease in toughness, and low cross-linked hydrogels have high toughness but a significant decrease in anti-swelling properties. In this way, there is a contradiction between the strength, toughness, and anti-swelling properties of conventional hydrogels with network cross-linking. The topological structure of the novel hydrogel reported by Suo with highly entangled molecular chains is different from the network cross-linking of conventional hydrogels, and excellent anti-swelling properties and strength and toughness can be obtained simultaneously. However, the difference between the hydrogel for biological tissues and the reported ones is that most of the macromolecules in biological tissues are polyelectrolyte compounds, and the interaction force between the polyelectrolyte molecular chain and water molecules is significantly higher than that of the non-electrolyte hydrophilic macromolecules reported above. The interaction force between the polyelectrolyte molecular chain and water is more than one order of magnitude higher. The polyelectrolyte hydrogel with a common structure will become disentangled after swelling in water. In this way, the polyelectrolyte hydrogel undergoes large swelling in water, destroying the initial highly entangled structure of the molecular chain. There has been no report on how to construct a hydrogel with a highly entangled topological structure of anti-swelling polyelectrolytes, nor a report on a polyelectrolyte hydrogel with the strain hardening characteristics of biological soft tissues.

[0004] During the research process, the inventors of the present application found a biological soft tissue-like system that can form a structure similar to the strain-hardening of biological soft tissues and has the characteristics of high strength, toughness, and low friction, and can be used in medical research such as ionic skin. Summary of the Invention

[0005] The purpose of the present invention is to provide a hydrogel with a simple process, easy operation, readily available raw materials, low cost, strain hardening, and high surface lubrication, and its preparation method and application.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a strain-hardening hydrogel, comprising the following steps:

[0008] 1) Prepare a first mixed solution, and the first mixed solution contains sodium styrene sulfonate (NaSS), acryloyloxyethyl trimethyl ammonium chloride (DAC), a cross-linking agent, an initiator, and deionized water;

[0009] 2) Subject the first mixed solution obtained in step 1) to a curing treatment to obtain the amphoteric polyelectrolyte hydrogel PA;

[0010] 3) Prepare a second mixed solution, which includes NaSS, DAC, a crosslinking agent, an initiator, and deionized water. Immerse the amphoteric polyelectrolyte hydrogel PA obtained in step 2) in the second mixed solution;

[0011] 4) Subject the amphoteric polyelectrolyte hydrogel after the immersion treatment in step 3) to a curing treatment to obtain the strain-hardening hydrogel HE-PA.

[0012] Further, in the first mixed solution, the molar ratio of NaSS, DAC, the crosslinking agent, and the initiator is 1:(0.8 - 1.3):(0.0018 - 0.0023):(0.0018 - 0.0023).

[0013] Further, in the first mixed solution, the molar ratio of NaSS to DAC is 1:(1 - 1.1), such as 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09.

[0014] Further, in the first mixed solution, the crosslinking agent accounts for 0.1% of the total molar amount of NaSS and DAC.

[0015] Further, in the first mixed solution, the initiator accounts for 0.1% of the total molar amount of NaSS and DAC.

[0016] The role of the initiator is to initiate the copolymerization reaction of monomer NaSS and monomer DAC to form the amphoteric polyelectrolyte hydrogel P(NaSS-co-DAC).

[0017] Further, the total molar concentration of NaSS and DAC monomers in the first mixed solution is 2 - 2.5 mol / L, such as 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L.

[0018] Further, the concentration of NaSS in the first mixed solution is 1 - 1.2 mol / L, such as 1.12 mol / L, 1.14 mol / L, 1.15 mol / L, 1.16 mol / L, 1.18 mol / L.

[0019] Further, the concentration of DAC in the first mixed solution is 1 - 1.2 mol / L, such as 1.12 mol / L, 1.14 mol / L, 1.15 mol / L, 1.16 mol / L, 1.18 mol / L.

[0020] Further, the preparation temperature of the first mixture and the second mixture is 60 - 70°C, and the stirring and dissolving time is 10 - 15 min.

[0021] Further, in the second mixture, the molar ratio of NaSS, DAC, crosslinking agent, and initiator is 1:(0.8 - 1.3):(0.0018 - 0.0023):(0.0018 - 0.0023).

[0022] Further, in the second mixture, the molar ratio of NaSS to DAC is 1:(1 - 1.1), such as 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09.

[0023] Further, in the second mixture, the crosslinking agent accounts for 0.1% of the total molar amount of monomers.

[0024] Further, in the second mixture, the initiator accounts for 0.1% of the total molar amount of monomers.

[0025] Further, in the second mixture, the total molar concentration of NaSS and DAC monomers is 1.5 - 2.5 mol / L, such as 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L.

[0026] Further, in the second mixture, the molar concentration of NaSS monomer is 0.7 - 1.3 mol / L, such as 0.73 mol / L, 0.83 mol / L, 0.92 mol / L, 1.02 mol / L, 1.12 mol / L, 1.17 mol / L, 1.23 mol / L, 1.27 mol / L.

[0027] Further, in the second mixture, the molar concentration of DAC monomer is 0.7 - 1.30 mol / L, such as 0.73 mol / L, 0.77 mol / L, 0.87 mol / L, 0.98 mol / L, 1.08 mol / L, 1.18 mol / L, 1.23 mol / L, 1.27 mol / L.

[0028] Further, in steps 2) and 4), the equilibrium time of the cured hydrogel in water is at least 24 h.

[0029] Further, when the cured hydrogel described in steps 2) and 4) is in equilibrium in water, the water soaking amount is more than 20 times the weight of the hydrogel itself.

[0030] Further, when the cured hydrogel described in steps 2) and 4) is in equilibrium in water, the soaking water is replaced at least once.

[0031] Further, in step 3), the soaking treatment time is 3 - 5 h.

[0032] Further, the crosslinking agent is selected from one of N,N'-methylenebisacrylamide (MBAA), N,N'-bisacryloylcystamine (BAC), polyethylene glycol diacrylamide (PEG - Bis - AAm), polyethylene glycol diacrylate (PEGDA), pentaerythritol triacrylate (PETRA), and trimethylolpropane triacrylate (TMPTA).

[0033] Further, the initiator is a photoinitiator or a thermal initiator; the photoinitiator is selected from 2 - ketoglutaric acid (KA) and Irgacure 2959; the thermal initiator is selected from ammonium persulfate (APS), potassium persulfate (KPS), and water - soluble azo initiator (VA - 044).

[0034] Further, when a photoinitiator is used, the curing treatment in steps 2) and 4) is ultraviolet light irradiation treatment; the conditions of light irradiation under an ultraviolet lamp are, for example, the light irradiation time is 10 - 12 h under an ultraviolet lamp with a wavelength of 365 nm and a power of 300 W.

[0035] Further, when a thermal initiator is used, the curing treatment in steps 2) and 4) is heat treatment, for example, the hydrogel is placed in a water bath at 50 - 80 °C for heat treatment.

[0036] The present invention also provides a strain - hardening hydrogel prepared by the above - mentioned method.

[0037] The present invention also provides the application of the above - mentioned strain - hardening hydrogel as a biological soft tissue substitute, such as ion skin, etc.

[0038] The present invention designs a cation-anion copolymer molecular chain highly entangled amphoteric polyelectrolyte hydrogel HE-PA, which has composite strong / weak interactions. The polymerization of the first electrolyte monomer units with opposite charges forms a polyampholyte hydrogel PA with a dynamic entanglement / disentanglement network of a low-density phase first weak entanglement domain through the dynamic penetration of positive and negative ion segments. The penetration of the second electrolyte monomer units with opposite charges regulates the segment relaxation of the PA hydrogel at the swelling equilibrium, and the second polymerization reaction further transforms it into a composite structure of a densely coiled high-density phase molecular chain second texture-like highly entangled domain, significantly improving the water swelling resistance and mechanical properties of the product HE-PA hydrogel. By regulating the hydrophobic cross-linking point units (such as -CH3) and hydrogen bond units (such as -COOR / -CO-NH-) in the molecular chain of the HE-PA hydrogel, the hydrogen bond-hydrophobic interaction synergistically acts with the strong electrostatic interaction behavior of the molecular chain. The formation of the hydrophobic microenvironment is beneficial to the stability of ion pairs, while the hydrogen bond effect enhances the flexibility of the molecular chain and promotes the interpenetration of molecular chains. The triple synergistic regulation mechanism of "electrostatic force-hydrogen bond-hydrophobic interaction" of the molecular chain: the hydrogen bond network regulates the segment motion as an "anchor point" between molecules; the hydrophobic micro-region enhances the stability of ion pairs through the restricted space effect. The HE-PA hydrogel with a texture-like highly entangled topological structure is prepared by double polymerization of electrolyte monomer units with opposite charges, obtaining a composite structure of a low-density phase first weak entanglement domain and a high-density phase second texture-like highly entangled domain. In addition, denser molecular chains form a thicker water lubricating layer, and the spring action between molecular chains brings larger intermolecular meshes, making the water lubricating layer richer and the friction coefficient lower. At the same time, the highly entangled topological structure is a combination of two strong / weak entanglement domains. Under external force, the disentanglement of the first weak entanglement domain of the "low-density phase" in the molecular chain forms a low modulus plateau under small stress, and the slip of the highly entangled domain keeps the hydrogel macroscopically intact; under large deformation, the tight interlocking of the second texture-like highly entangled domain of the "high-density phase" undergoes high elastic deformation, forming a high modulus part under large deformation. This texture-like highly entangled topological structure not only endows the hydrogel with excellent mechanical properties, but also makes it exhibit a strain-hardening mechanical response similar to biological tissues, which is also a characteristic not possessed by general amphoteric polyelectrolytes including ordinary hydrogels such as P(DAC-co-NaSS).

[0039] Compared with the prior art, the present invention has the following advantages and significant progress:

[0040] 1) The preparation process of the present invention is simple, with a short production cycle, simple process conditions, easily available raw materials, and low production costs.

[0041] 2) The hydrogel prepared by the present invention not only has the properties of high strength and toughness and low friction, but also has typical strain-hardening characteristics of biological soft tissues, and can be used in medical fields such as ionic skin, with broad application prospects. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of the preparation process of the amphoteric polyelectrolyte HE-PA hydrogel of the present invention, where (1) is the preparation process of the monolayer PA hydrogel and (2) is the preparation process of the bilayer HE-PA hydrogel. Detailed implementation manners

[0043] Example 1

[0044] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution, so that in the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0045] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for irradiation for 10 h, soak the demolded hydrogel in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0046] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 0.73 mol / L, the concentration of DAC is 0.77 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for irradiation for 10 h again, soak the demolded hydrogel in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0047] For the amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example, its tensile properties were tested using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0048] Example 2

[0049] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution, so that in the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0050] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel.

[0051] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 0.83 mol / L, the concentration of DAC is 0.87 mol / L; the percentage of the crosslinking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel.

[0052] For the amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example, use an electronic universal testing machine to test its tensile properties, and measure its friction coefficient on a rotational rheometer; measure its tensile strength through a tensile test at a speed of 100 mm / min.

[0053] Example 3

[0054] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of the monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of the monomers.

[0055] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel.

[0056] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 0.92 mol / L, the concentration of DAC is 0.98 mol / L; the percentage of the crosslinking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel.

[0057] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0058] Example 4

[0059] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0060] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h, soak the demolded hydrogel in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0061] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in a second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.02 mol / L, the concentration of DAC is 1.08 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for 10 h again, soak the demolded hydrogel in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0062] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0063] Example 5

[0064] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0065] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light exposure. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0066] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.12 mol / L, the concentration of DAC is 1.18 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light exposure again. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0067] For the amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example, its tensile properties were tested using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0068] Example 6

[0069] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, stir it in a 65 °C water bath for 15 min under light-shielding conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0070] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light exposure. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0071] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.17 mol / L, the concentration of DAC is 1.23 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light exposure again. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0072] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0073] Example 7

[0074] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0075] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0076] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.00 mol / L, the concentration of DAC is 1.30 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0077] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0078] Example 8

[0079] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0080] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte PA gel;

[0081] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.07 mol / L, the concentration of DAC is 1.23 mol / L; the percentage of the crosslinking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte HE-PA hydrogel;

[0082] For the amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example, its tensile properties are tested using an electronic universal testing machine, and its friction coefficient is measured on a rotational rheometer; its tensile strength is measured through a tensile test at a speed of 100 mm / min.

[0083] Example 9

[0084] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively and prepare them into a 10 mL aqueous solution. Stir it in a 65 °C water bath for 15 min under light-shielding conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of the monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of the monomers;

[0085] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte PA gel;

[0086] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.17 mol / L, the concentration of DAC is 1.13 mol / L; the percentage of the crosslinking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte HE-PA hydrogel;

[0087] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0088] Example 10

[0089] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath under light-shielded conditions for 15 min to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0090] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte PA gel;

[0091] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.23 mol / L, the concentration of DAC is 1.07 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain an amphoteric polyelectrolyte HE-PA hydrogel;

[0092] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this example was tested for its tensile properties using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0093] Comparative Example 1

[0094] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution, and stir it in a 65 °C water bath under light-shielded conditions for 15 min to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers;

[0095] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte PA gel;

[0096] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of NaSS in the second mixed solution is 1.23 mol / L; the percentage of the cross-linking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte HE-PA hydrogel;

[0097] For the amphoteric polyelectrolyte HE-PA hydrogel material obtained in this comparative example, use an electronic universal testing machine to test its tensile properties and measure its friction coefficient on a rotational rheometer; measure its tensile strength through a tensile test at a speed of 100 mm / min.

[0098] Comparative Example 2

[0099] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution. Stir it in a 65 °C water bath for 15 min under light-shielding conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of the monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of the monomers;

[0100] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielding conditions, place it under an ultraviolet lamp for 10 h of light irradiation. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte PA gel;

[0101] Step 3): Soak the amphoteric polyelectrolyte PA gel obtained in Step 2) in the second mixed solution for 3 h. The concentration of DAC in the second mixed solution is 1.30 mol / L; the percentage of the cross-linking agent in the total molar amount of the monomers is 0.1%; the percentage of the photoinitiator in the total molar amount of the monomers is 0.1%. Place it under an ultraviolet lamp for 10 h of light irradiation again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water and soak it again for 12 h to obtain the amphoteric polyelectrolyte HE-PA hydrogel;

[0102] The amphoteric polyelectrolyte HE-PA hydrogel material obtained in this comparative example was used to test its tensile properties with an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0103] Comparative Example 3

[0104] Step 1): Weigh AMPS, MBAA, and KA respectively to prepare a 10 mL aqueous solution. Stir it for 10 min under light-shielded conditions, then titrate it to neutral with NaOH solution, and finally add deionized water and stir evenly to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of AMPs is 1.00 mol / L, the molar amount of MBAA accounts for 0.4% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers.

[0105] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for irradiation for 10 h. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water, and soak it again for 12 h to obtain PNaAMPs gel.

[0106] Step 3): Soak the PNaAMPs gel obtained in Step 2) in the second mixed solution for 24 h. The concentration of AAM in the second mixed solution is 2.00 mol / L; the percentage of the cross-linking agent in the total molar amount of monomers is 0.01%; the percentage of the photoinitiator in the total molar amount of monomers is 0.01%. Place it under an ultraviolet lamp for irradiation for 10 h again. After the hydrogel is demolded, soak it in 500 ml of ionized water for 12 h, change the water, and soak it again for 12 h to obtain DN hydrogel.

[0107] The DN hydrogel material obtained in this comparative example was used to test its tensile properties with an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0108] Comparative Example 4

[0109] Step 1): Weigh NaSS, DAC, MBAA, and KA respectively to prepare a 10 mL aqueous solution. Stir it in a 65 °C water bath for 15 min under light-shielded conditions to obtain a uniform first mixed solution. In the obtained first mixed solution, the concentration of NaSS is 1.12 mol / L, the concentration of DAC is 1.18 mol / L, the molar amount of MBAA accounts for 0.1% of the total molar amount of monomers, and the molar amount of KA accounts for 0.1% of the total molar amount of monomers.

[0110] Step 2): Inject the first mixed solution obtained in Step 1) into a glass mold under light-shielded conditions, place it under an ultraviolet lamp for 10 h of light exposure. After the hydrogel is demolded, soak it in 500 ml of ionic water for 12 h, and soak it again for 12 h after changing the water to obtain the amphoteric polyelectrolyte PA gel.

[0111] For the amphoteric polyelectrolyte PA hydrogel material obtained in this comparative example, its tensile properties were tested using an electronic universal testing machine, and its friction coefficient was measured on a rotational rheometer; its tensile strength was measured through a tensile test at a speed of 100 mm / min.

[0112] The mechanical properties of the amphoteric polyelectrolyte HE-PA hydrogels obtained in the above examples and comparative examples are shown in Table 1 below:

[0113] Table 1: Mechanical properties of the amphoteric polyelectrolyte HE-PA hydrogel

[0114]

[0115]

[0116] It can be seen from the data in Table 1 that:

[0117] Examples 1-6 are amphoteric polyelectrolyte HE-PA hydrogel materials prepared by changing the total monomer molar concentration under the condition that the percentage of the DAC mass fraction and the NaSS mass fraction in the soaking monomer solution is the same. Examples 7-10 are amphoteric polyelectrolyte HE-PA hydrogel materials prepared by changing the percentage of the DAC mass fraction and the NaSS mass fraction under the condition that the total monomer molar concentration of the soaking monomer solution is the same. Comparative examples 1 and 2 are amphoteric polyelectrolyte HE-PA hydrogel materials prepared without DAC and NaSS respectively. Comparative example 3 is a double-network DN hydrogel, and comparative example 4 is an amphoteric polyelectrolyte PA hydrogel.

[0118] It can be seen from Examples 1-6 that for the amphoteric polyelectrolyte HE-PA hydrogel material, as the molar concentration of the soaking monomer solution gradually increases, the breaking strength increases from 1.13 MPa to 2.31 MPa, while the elongation at break gradually decreases from 973.13% to 593.65%, and the strain hardening index is basically above 10, which conforms to the strain-hardening modulus ratio of biological soft tissues, and at the same time has an extremely low friction coefficient in the order of 10 -2 For Example 6, due to the too high concentration of the soaking monomer solution, its internal structure is too dense, resulting in a doubling of the modulus in the low-strain region, so that its strain hardening index decreases to 11.48, but it also has the strain-hardening modulus ratio of biological soft tissues, and an extremely low friction coefficient in the order of 10 -2The friction coefficient of the order of magnitude. When the monomer dosage exceeds 2.5M, it reaches the upper limit of dissolution, and a stable soaking monomer solution cannot be obtained.

[0119] As can be seen from Examples 7 to 10, with the change of the mass fractions of DAC and NaSS in the soaking solution, the strength is maintained at about 0.4 MPa, while the elongation at break also decreases from 761.31% to 621.36%, the strain hardening index is maintained at about 5, and the friction coefficient is in the order of magnitude of 10 -1 order of magnitude.

[0120] As can be seen from Comparative Examples 1 and 2, when there is only a single cationic and anionic monomer in the soaking solution, both the strength and the elongation at break decrease significantly. The moduli in the low-strain region and the high-strain region remain basically unchanged, and at the same time, there is a relatively high friction coefficient, which does not conform to the characteristics of strain hardening. Comparative Example 3 is a double-network DN hydrogel with sacrificial bonds. During the stretching process, due to the destruction of the first network, the yield point is generated, resulting in softening in the high-strain region, thus resulting in no strain hardening phenomenon. Therefore, it does not have the strain-hardening characteristics of biological soft tissues, and at the same time, the friction coefficient is also relatively large, and it does not have high-strength and tough mechanical properties. Comparative Example 4 is an amphoteric polyelectrolyte PA hydrogel. Due to its internal structure not being dense enough, the strain hardening index is not prominent. At the same time, the friction coefficient and the strength and toughness do not achieve good effects, so it does not have the characteristics of biological soft tissues.

[0121] In Examples 7 to 10, due to the change of the soaking cationic and anionic concentrations, the cationic and anionic ions do not reach electrical neutrality in the solution and cannot exist stably, which makes the internal structure of the gel unstable. Therefore, the strain hardening characteristics, toughness and friction performance decrease. In Examples 1 to 6, with the increase of the total monomer concentration in the soaking solution, more molecular chains enter the first network, thus forming a denser entanglement structure, so as to achieve high strength, toughness and low friction, and have typical strain hardening characteristics, thus meeting the requirements of synthetic material biological soft tissues and opening up broader thinking for ion skin and medical applications.

[0122] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a strain-hardening hydrogel, characterized in that, It includes the following steps: 1) Prepare a first mixed solution, which contains sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, a crosslinking agent, an initiator, and deionized water; 2) Subject the first mixed solution obtained in step 1) to a curing treatment, and place the cured hydrogel in water for equilibration to obtain an amphoteric polyelectrolyte hydrogel PA; 3) Prepare a second mixed solution, which includes sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, a crosslinking agent, an initiator, and deionized water, and soak the amphoteric polyelectrolyte hydrogel PA obtained in step 2) in the second mixed solution; 4) Subject the amphoteric polyelectrolyte hydrogel after the soaking treatment in step 3) to a curing treatment, and place the cured hydrogel in water for equilibration to obtain the strain-hardening hydrogel HE-PA.

2. The method according to claim 1, wherein In the first mixed solution, the molar ratio of sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, the crosslinking agent, and the initiator is 1:(0.8 - 1.3):(0.0018 - 0.0023):(0.0018 - 0.0023); in the first mixed solution, the total molar concentration of sodium p-styrenesulfonate and acryloyloxyethyl trimethyl ammonium chloride monomers is 2 - 2.5 mol / L.

3. The method according to claim 1, characterized in that In the second mixed solution, the molar ratio of sodium p-styrenesulfonate, acryloyloxyethyl trimethyl ammonium chloride, the crosslinking agent, and the initiator is 1:(0.8 - 1.3):(0.0018 - 0.0023):(0.0018 - 0.0023); in the second mixed solution, the total molar concentration of sodium p-styrenesulfonate and acryloyloxyethyl trimethyl ammonium chloride monomers is 1.5 - 2.5 mol / L.

4. The method according to claim 1, wherein In steps 2) and 4), the equilibration time of the cured hydrogel in water is at least 24 h.

5. The method according to claim 1, characterized in that In step 3), the soaking treatment time is 3 - 5 h.

6. The method according to claim 1, characterized in that The crosslinking agent is selected from one of N,N'-methylenebisacrylamide, N,N'-bisacryloylcystamine, polyethylene glycol bisacrylamide, polyethylene glycol diacrylate, pentaerythritol triacrylate, and trimethylolpropane triacrylate.

7. The method according to claim 1, wherein The initiator is a photoinitiator or a thermal initiator; the photoinitiator is selected from one of 2-ketoglutaric acid and Irgacure 2959; the thermal initiator is selected from one of ammonium persulfate, potassium persulfate, and water-soluble azo initiators.

8. The method according to claim 7, wherein When a photoinitiator is used, the curing treatment in steps 2) and 4) is ultraviolet light irradiation treatment; when a thermal initiator is used, the curing treatment in steps 2) and 4) is heat treatment.

9. A strain-hardening hydrogel, characterized in that, Prepared by the method according to any one of claims 1 - 8.

10. The application of the strain-hardening hydrogel according to claim 9, characterized in that, As a biological soft tissue substitute.

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