CN109503757B

CN109503757B - Preparation of double-network hydrogel, obtained double-network hydrogel and application

Info

Publication number: CN109503757B
Application number: CN201811277536.2A
Authority: CN
Inventors: 隋坤艳; 盛楠楠; 张肖辉; 王丽男; 谭业强; 范汶鑫; 夏延致
Original assignee: Qingdao University
Current assignee: Qingdao University
Priority date: 2018-02-06
Filing date: 2018-10-30
Publication date: 2021-03-30
Anticipated expiration: 2038-10-30
Also published as: CN109503757A

Abstract

The invention discloses a preparation method of double-network ionic hydrogel, the obtained double-network ionic hydrogel and application thereof, wherein the method comprises the following steps: firstly, obtaining a sodium alginate supermolecular fiber network, and then carrying out cross-linking polymerization on the sodium alginate supermolecular fiber network and an acrylamide monomer to obtain the double-network hydrogel, namely the sodium alginate-polyacrylamide double-network hydrogel. The preparation method is simple and easy to realize; the obtained ion-conductive double-network hydrogel has excellent characteristics of strong strength, toughness, softness, elasticity, fatigue resistance and the like, solves the contradiction between the strength and the toughness and between the softness and the elasticity, and has excellent injectability and self-healing capability; the double-network hydrogel can generate effective current at ultralow voltage (0.04V), can realize the induction of ultra-small and ultra-large strain, achieves the ultra-wide strain induction range (0.3-1800%), and can be used for 3d printed ionic skin, tissue organs, wearable equipment, resistance sensors and the like.

Description

Preparation of double-network hydrogel, obtained double-network hydrogel and application

Technical Field

The invention relates to the field of natural polymer materials, in particular to a double-network hydrogel, and particularly relates to a preparation method and application of a sodium alginate-polyacrylamide type ion-conductive double-network hydrogel.

Background

Hydrogel refers to a three-dimensional network polymer structure that can rapidly absorb and retain a large amount of water and is insoluble in water. The hydrogel can keep higher water content through swelling of the polymer, and a special flexible wet structure is formed, and the hydrogel has the property between solid and liquid. The characteristic enables the hydrogel to have wide application, such as the fields of tissue engineering, drug controlled release, biological nanotechnology and the like. However, most conventional synthetic hydrogels are mechanically weak and have insufficient toughness, which prevents their further use.

In order to improve the mechanical properties of hydrogels, researchers have proposed many ideas in recent years, and one of the more successful ideas is the concept of Double network hydrogel (DN). In the prior art, the design idea of the double-network hydrogel is to synthesize a first layer network with a high degree of crosslinking, use the first layer network as a template, and introduce a second layer network with a neutral low degree of crosslinking into the first layer network to form a double-network structure. The first layer network provides a rigid framework for DN hydrogel, keeps the shape of the hydrogel, and the flexible second layer network fills the rigid framework, thereby well playing a role in absorbing stress. Researches show that the strength and toughness of the DN hydrogel are greatly improved while the DN hydrogel keeps high water content. However, the hydrogel obtained by the double-network structure in the prior art still has the defects of poor recovery, poor elasticity, poor functionality, poor manufacturability and the like.

Disclosure of Invention

In order to overcome the problems, the inventor of the present invention has conducted intensive research, and the present invention has been completed by first constructing a sodium alginate supramolecular fiber network by using sodium alginate and monovalent cations, and then compounding the sodium alginate supramolecular fiber network with a polyacrylamide cross-linked network to realize enhancement of hydrogel, thereby obtaining a double-network hydrogel, i.e., a sodium alginate-polyacrylamide double-network ion-conductive hydrogel.

One of the purposes of the invention is to provide a preparation method of a double-network hydrogel, which is embodied in the following aspects:

(1) a method for preparing a double-network hydrogel, wherein the method comprises the following steps:

step 1, constructing a sodium alginate supermolecular fiber network by using monovalent cation salts and sodium alginate;

step 2, adding acrylamide monomers, cross-linking agents, initiators and catalysts into the sodium alginate supermolecular fiber network obtained in the step 1, and stirring and mixing;

and 3, carrying out reaction under heating, illumination or radiation to obtain the double-network hydrogel, namely the sodium alginate-polyacrylamide double-network ion-conductive hydrogel.

(2) The production method according to the above (1), wherein the step 1 includes the substeps of:

step 1-1, adding monovalent cation salt into water, and stirring to obtain a monovalent cation salt solution;

step 1-2, adding sodium alginate into the monovalent cation salt solution obtained in the step 1-1, and stirring to obtain a mixed solution;

and step 1-3, standing the mixed solution obtained in the step 1-2 to form a sodium alginate supramolecular fiber network.

(3) The production method according to the above (1) or (2), wherein, in step 1-1,

the monovalent cation salt is a water-soluble monovalent cation salt, preferably, the monovalent cation salt is selected from one or more of a water-soluble sodium salt, a water-soluble potassium salt and a water-soluble lithium salt, more preferably, the monovalent cation salt is selected from one or more of sodium chloride, sodium carbonate, sodium iodide, potassium chloride, potassium carbonate and lithium chloride; and/or

The concentration of the monovalent cation salt solution is 0.5-5 wt%, preferably 1-4 wt%, and more preferably 1.5-3.5 wt%.

(4) The production method according to one of the above (1) to (3), wherein,

in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (0.5-2.5): 1, preferably (1-2): 1, more preferably (1.5-2): 1; and/or

In the step 1-2, the weight average molecular weight of the sodium alginate is 10-600 kDa, preferably 100-600 kDa, and more preferably 200-600 kDa.

(5) The production method according to one of the above (1) to (4), wherein in the step 1-3, the mixture is allowed to stand for 1 to 120 hours, preferably for 5 to 60 hours, more preferably for 10 to 20 hours, for example, for 12 hours.

(6) The production method according to one of the above (1) to (5), wherein,

in step 2, the acrylamide-based monomer is selected from acrylamide and/or acrylamide derivatives including N, N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-isopropylacrylamide, N-isobutylacrylamide, N-t-butylacrylamide, N-cyclohexylacrylamide, and the like; and/or

The weight ratio of the acrylamide monomer to the sodium alginate is (6-25):1, preferably (10-20): 1, for example, 15: 1.

(7) The production method according to one of the above (1) to (6), wherein, in step 2,

the cross-linking agent is selected from one or more of N, N ' -methylene bisacrylamide, N ' -diallyl tartaric acid diamide, divinyl benzene, polyethylene glycol diacrylate and polyethylene glycol dimethacrylate, such as N, N ' -methylene bisacrylamide; and/or

The weight ratio of the cross-linking agent to the acrylamide monomer is (0.0003-0.001): 1, preferably (0.0004-0.0008): 1, for example 0.0006: 1; and/or

The initiator is selected from a thermal initiator or a photoinitiator, preferably, the initiator is selected from one or more of ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide and Irgacure 2959; and/or

The weight ratio of the initiator to the acrylamide monomer is (0.0005-0.003): 1, for example, 0.001: 1; and/or

The catalyst is selected from one or more of N, N, N ', N' -tetramethylethylenediamine, sodium sulfite, sodium bisulfite and sodium thiosulfate; and/or

The weight ratio of the catalyst to the acrylamide monomer is (0.001-0.004): 1, such as 0.0025: 1.

(8) The production method according to one of the above (1) to (7), wherein, in step 3,

when heating is employed, the reaction proceeds as follows: reacting at 40-60 ℃ for 0.5-6 h, preferably at 50 ℃ for 2-4 h, such as 3 h; or

When light illumination is used, the reaction proceeds as follows: the reaction is carried out for 0.5 to 2 hours under ultraviolet irradiation, preferably for 1 to 1.5 hours under ultraviolet irradiation of 200 to 400 nm.

It is a further object of the present invention to provide a double-network hydrogel, preferably obtainable by the process according to the first aspect of the invention, wherein,

the elongation at break of the double-network hydrogel is 1500-2500%;

the fracture strength of the double-network hydrogel is 0.4-0.8 MPa;

the fracture toughness of the double-network hydrogel is 3-6 MJ/m 3.

The third objective of the present invention is to provide a double-network hydrogel obtained by the preparation method of the first aspect of the present invention or an application of the double-network hydrogel of the second aspect of the present invention, which is used for ionic skin, wearable devices, and resistive sensors.

Drawings

Figure 1a shows a schematic of the formation of a sodium alginate supramolecular fiber network;

figure 1b shows a schematic diagram of the formation of self-assembly of sodium alginate supramolecular fiber networks;

FIG. 2 shows the tensile mechanical property curves of the products obtained in example 1 and comparative examples 1-2;

FIG. 3 shows tensile mechanical property curves of the products obtained in examples 1-2 and comparative example 3;

FIG. 4 shows the tensile mechanical property curves of the products obtained in examples 1 and 3;

FIG. 5 shows AFM diagram of the intermediate obtained in example 1, sodium alginate supramolecular fiber network;

FIG. 6 shows TEM image of the intermediate obtained in example 1, sodium alginate supramolecular fiber network;

FIG. 7 shows the tension-relaxation cycle curves for 20 cycles of the product obtained in example 5;

FIG. 8 shows the energy dissipated and recovery curves for a gel in 20 consecutive stretch-relaxation cycles of the product obtained in example 5;

FIG. 9a shows the resistance versus change curve of the hydrogel obtained in example 5 under the application of tensile strain;

FIG. 9b shows the resistance versus change curve of the hydrogel obtained in example 5 when a compressive strain is applied;

FIG. 9c shows the retention curve of the relative change in resistance of the hydrogel obtained in example 5 after 10 load cycles;

FIGS. 10 a-10 d show relative resistance change versus time curves for release of the finger, neck, knee and elbow, respectively;

FIG. 10e shows the relative resistance change in throat versus time for three different individuals speaking the same Chinese word "hello";

FIG. 10f shows the same person saying the same Chinese word "hello, i am good, great family good" records the relative resistance change at throat versus time for three times;

FIG. 10g shows the relative resistance change at wrist pulse versus time for the same person before and after activity;

fig. 10h shows the relative resistance change at the wrist pulse versus time curve for different persons.

Detailed Description

The present invention will be described in further detail below with reference to examples and experimental examples. The features and advantages of the present invention will become more apparent from the description.

The invention provides a preparation method of a double-network hydrogel, which comprises the following steps:

step 1, constructing a sodium alginate supermolecular fiber network by using monovalent cation salts and sodium alginate.

According to a preferred embodiment of the invention, step 1 comprises the following sub-steps:

According to a preferred embodiment of the present invention, in step 1-1, the monovalent cation salt is a water-soluble monovalent cation salt.

In a further preferred embodiment, in step 1-1, the monovalent cation salt is selected from one or more of a water-soluble sodium salt, a water-soluble potassium salt and a water-soluble lithium salt.

In a still further preferred embodiment, in step 1-1, the monovalent cation salt is selected from one or more of sodium chloride, sodium carbonate, sodium iodide, potassium chloride, potassium carbonate, and lithium chloride.

In the present invention, as shown in fig. 1a and fig. 1b, the monovalent cation salt plays a hydrophobic role and an electrostatic shielding role for sodium alginate, so that semi-rigid sodium alginate molecular chains are aggregated together, and finally self-assembled (self-assembled through hydrogen bonds) to form a supramolecular network of nanofibers.

According to a preferred embodiment of the present invention, in the step 1-1, the concentration of the monovalent cation salt solution is 0.5 to 5 wt%.

In a further preferred embodiment, in step 1-1, the concentration of the monovalent cation salt solution is 1 to 4 wt%.

In a further preferred embodiment, in step 1-1, the concentration of the monovalent cation salt solution is 1.5 to 3.5 wt%.

The inventor finds out through a large number of experiments that the concentration of the monovalent cation salt solution is important in the construction of the sodium alginate supramolecular fiber network. If the concentration of the monovalent cation salt solution is too low, the sodium alginate molecular chains cannot be fully self-assembled, and then a supermolecular network cannot be fully formed, so that the strength and toughness of the final double network can be influenced; however, the inventors have also found that the concentration of the monovalent cation salt solution is not too large, and a large number of experimental data indicate that when the concentration is too large, the strength and toughness of the resulting double network are also reduced, and when the salt concentration is too high, salting out is found to occur with phase separation.

According to a preferred embodiment of the invention, in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (0.5-2.5): 1.

In a further preferred embodiment, in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (1-2): 1.

In a further preferred embodiment, in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (1.5-2): 1.

The inventor finds out through a large number of experiments that the use amount ratio of the monovalent cation salt to the sodium alginate determines the performance of the obtained sodium alginate supermolecule fiber network and the final double-network hydrogel.

According to a preferred embodiment of the present invention, in step 1-2, the weight average molecular weight of the sodium alginate is 10 to 600 kDa.

In a further preferred embodiment, in step 1-2, the weight average molecular weight of the sodium alginate is 100-600 kDa.

In a further preferred embodiment, in step 1-2, the sodium alginate has a weight average molecular weight of 200 to 600 kDa.

Wherein, if the molecular weight of the sodium alginate is too small, the nano-fiber network is not favorably formed; the molecular weight is too large, and the sodium alginate is easy to generate macroscopic precipitation phase separation when salt is added.

According to a preferred embodiment of the invention, in the step 1-3, the mixture is kept still for 1-120 h.

In a further preferred embodiment, in the step 1-3, the mixture is allowed to stand for 5 to 60 hours.

In a further preferred embodiment, in step 1-3, the mixture is allowed to stand for 10 to 20 hours, for example 12 hours.

Wherein the standing is to form hydrogen bonds between the molecular chains of the sodium alginate.

And 2, adding acrylamide monomers, cross-linking agents, initiators and catalysts into the sodium alginate supermolecular fiber network obtained in the step 1, and stirring and mixing.

According to a preferred embodiment of the present invention, in step 2, the acrylamide-based monomer is selected from acrylamide and/or acrylamide derivatives.

Among them, the acrylamide derivatives include N, N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-isopropylacrylamide, N-isobutylacrylamide, N-t-butylacrylamide, N-cyclohexylacrylamide, and the like.

In a further preferred embodiment, the weight ratio of the acrylamide monomer to the sodium alginate is (6-25): 1.

In a further preferred embodiment, the weight ratio of acrylamide-based monomer to sodium alginate is (10-20): 1, for example 16: 1.

Among them, the inventors found through a lot of experiments that if the amount of the acrylamide-based monomer is too small, the strength of the obtained double-network hydrogel is too low, and if the amount of the acrylamide-based monomer is too large, the toughness is reduced.

According to a preferred embodiment of the present invention, in step 2, the crosslinking agent is selected from one or more of N, N ' -methylenebisacrylamide, N ' -diallyltartramide, divinylbenzene, polyethyleneglycoldiacrylate and polyethyleneglycoldimethacrylate, such as N, N ' -methylenebisacrylamide.

In a further preferred embodiment, the weight ratio of the crosslinking agent to the acrylamide-based monomer is (0.0003 to 0.001): 1.

In a further preferred embodiment, the weight ratio of the crosslinking agent to the acrylamide-based monomer is (0.0004-0.0008): 1, for example 0.0006: 1.

However, the strength of the double-crosslinked network cannot be increased by an excessively small amount of the crosslinking agent, and the inventors have found through extensive experiments that the elongation at break of the double-crosslinked network is affected by an excessively large amount of the crosslinking agent.

According to a preferred embodiment of the invention, in step 2, the initiator is selected from thermal initiators or photoinitiators.

In a further preferred embodiment, in step 2, the initiator is selected from one or more of ammonium persulfate, potassium persulfate, sodium persulfate and benzoyl peroxide.

In a further preferred embodiment, the weight ratio of the initiator to the acrylamide-based monomer is (0.0005-0.003): 1, for example 0.001: 1.

According to a preferred embodiment of the present invention, in step 2, the catalyst is selected from one or more of N, N' -tetramethylethylenediamine, sodium sulfite, sodium bisulfite and sodium thiosulfate.

In a further preferred embodiment, the weight ratio of the catalyst to the acrylamide-based monomer is (0.001-0.004): 1, for example, 0.0025: 1.

And 3, carrying out reaction under heating, illumination or radiation to obtain the sodium alginate-polyacrylamide double-network ionic conductive hydrogel.

Wherein, after the reactants are mixed in the step 2, the crosslinking reaction is needed to be carried out, in the invention, the crosslinking reaction can be carried out by heating, or can be carried out under illumination or radiation, as long as the crosslinking reaction can be generated. Preferably, step 3 is carried out with heating.

According to a preferred embodiment of the invention, in step 3, when heating is used, the reaction proceeds as follows: reacting for 0.5-6 h at 40-60 ℃.

In a further preferred embodiment, in step 3, when heating is employed, the reaction proceeds as follows: reacting at 50 ℃ for 2-4 h, such as 3 h.

According to a preferred embodiment of the invention, in step 3, when light is used, the reaction proceeds as follows: reacting for 0.5-2 hours under the irradiation of ultraviolet rays.

In a further preferred embodiment, in step 3, when illumination is employed, the reaction proceeds as follows: the reaction is carried out for 1 to 1.5 hours under the irradiation of ultraviolet rays with the wavelength of 200 to 400nm, for example, for 1 hour under the irradiation of ultraviolet rays with the wavelength of 365 nm.

According to a preferred embodiment of the invention, in step 3, when irradiation is used, the reaction proceeds as follows: performing radiation reaction (0.5-1.5) h under the condition of Co-gamma ray and the like.

In the invention, experiments prove that the double-network hydrogel has the characteristics of toughness, softness, elasticity and the like, and the characteristics are generated by the synergistic interaction of the sodium alginate supermolecular fiber network and the covalent network of polyacrylamide.

Among them, the inventors have surprisingly found that the double-network hydrogel has very excellent recoverability and has an adhesive ability. When the double-network hydrogel is sheared by a razor blade and the sheared two pieces are put together, the two pieces can be spontaneously bonded under natural environmental conditions without any external stimulus.

In recent years, flexible wearable devices are attracting more attention, the stretchable and transparent properties of the ionic hydrogel are a research hotspot of future flexible wearable devices, however, the ionic conductive hydrogel obtained by the current technology has the defects of poor mechanical properties, low sensitivity, poor processability and the like.

The double-network hydrogel can generate effective current with very low voltage (0.04V), can be used for ionized skin, wearable equipment, resistance sensors and the like, and has the advantages of excellent mechanical property, strong processability and the like.

The invention has the advantages that:

(1) the preparation method is simple and easy to realize;

(2) the double-network hydrogel prepared by the preparation method has the characteristics of high strength, toughness, softness, elasticity and the like;

(3) the double-network hydrogel prepared by the preparation method has the advantages of rapid self-recovery capability and excellent fatigue resistance;

the double-network hydrogel prepared by the preparation method has injectability and adhesive property;

(4) the double-network hydrogel prepared by the preparation method has high sensitivity, can generate effective current under ultralow voltage (0.04V), realizes an ultra-wide strain sensing range (0.3-1800%), and can be used for ionic skin, wearable equipment, resistance sensors and the like.

Examples

The invention is further described below by means of specific examples. However, these examples are only illustrative and do not limit the scope of the present invention.

Example 1

Respectively weighing 1.75g of sodium chloride and 1g of sodium alginate according to the mass ratio of 1.75:1 for later use;

dissolving the sodium chloride in deionized water to prepare a sodium chloride solution with the mass percentage concentration of 3.6%, dissolving the sodium alginate powder in the sodium chloride solution, and uniformly stirring to obtain a mixed solution with the sodium alginate concentration of 2 wt%;

and standing the mixed solution for 12 hours to form a supramolecular fiber network.

Adding 16g of acrylamide, 0.0096g N, N ' -methylene bisacrylamide, 0.016g of ammonium persulfate and 0.04g N of N, N ', N ' -tetramethyl ethylenediamine into the supermolecular fiber network formed after standing, uniformly stirring, standing for 0.5h at room temperature, and reacting for 3h at 50 ℃ to obtain the sodium alginate-acrylamide double-network hydrogel.

As shown in figures 2-3, the prepared sodium alginate supermolecular fiber network-polyacrylamide double-network hydrogel has the breaking elongation of 1995%, the breaking strength of 0.65MPa and the breaking toughness of 4.77MJ/m³。

Example 2

The procedure of example 1 was repeated except that: the weight ratio of sodium alginate to monomer is changed from 1:16 to 1:20, namely 20g of acrylamide monomer is adopted.

As shown in FIG. 3, the prepared sodium alginate-polyacrylamide double-network hydrogel has the elongation at break of 1515%, the breaking strength of 0.75MPa and the fracture toughness of 4.13MJ/m 3.

Example 3

The procedure of example 1 was repeated except that: the mass ratio of the N, N '-methylene bisacrylamide crosslinking agent to the acrylamide monomer is changed from 0.0006 to 0.0003, namely 0.0048g N, N' -methylene bisacrylamide is adopted.

As shown in FIG. 4, the prepared sodium alginate-polyacrylamide double-network hydrogel has elongation at break of 2135%, breaking strength of 0.38MPa and fracture toughness of 3.6MJ/m³。

Example 4

The procedure of example 1 was repeated except that: the acrylamide monomer is replaced by N, N-diethyl acrylamide monomer, and other conditions are not changed.

The prepared sodium alginate-poly N, N-diethyl acrylamide double-network hydrogel has the elongation at break of 1345 percent, the breaking strength of 0.21MPa and the fracture toughness of 0.89MJ/m³。

Example 5

The procedure of example 1 was repeated, wherein the NaCl concentration was 1.77 wt%, the sodium alginate concentration was 1.5 wt%, the acrylamide concentration was 24 wt%, and the remaining conditions were unchanged.

The elongation at break, strength at break and toughness at break of the resulting product were similar to those of example 1.

Comparative example

Comparative example 1

The procedure of example 1 was repeated except that: during the preparation of the sodium alginate supermolecular fiber network, sodium chloride is not added.

As shown in FIG. 2, the elongation at break of the obtained product was 1687%, the breaking strength was 0.16MPa, and the fracture toughness was 1.09MJ/m³。

Comparative example 2

The procedure of example 1 was repeated except that: the mass ratio of sodium chloride to sodium alginate was 2.92:1, i.e. the final sodium chloride solution concentration was 6 wt%.

As shown in figure 2, the prepared sodium alginate supermolecular fibrous network-polyacrylamide double-network hydrogel has the elongation at break of 895%, the breaking strength of 0.28MPa and the fracture toughness of 1.25MJ/m³。

Comparative example 3

The procedure of example 1 was repeated except that: the weight ratio of sodium alginate to monomer is changed from 1:16 to 1:6, namely 6g of acrylamide monomer is adopted.

As shown in FIG. 3, the prepared sodium alginate-polyacrylamide double-network hydrogel has elongation at break of 1555%, breaking strength of 0.13MPa and fracture toughness of 0.51MJ/m³。

Comparative example 4

The procedure of example 1 was repeated except that: the mass ratio of the N, N' -methylenebisacrylamide crosslinking agent to the acrylamide monomer was 0.0012.

The prepared sodium alginate-polyacrylamide double-network hydrogel has the breaking elongation of 1687 percent, the breaking strength of 0.16MPa and the breaking toughness of 1.09MJ/m³。

Comparative example 5

The procedure of example 1 was repeated except that: the preparation of the crosslinked polyacrylamide was carried out only, i.e. without the addition of sodium chloride and sodium alginate.

The prepared polyacrylamide single-network hydrogel has the elongation at break of 1720 percent, the breaking strength of 0.11MPa and the fracture toughness of 0.83MJ/m³。

Comparative example 6

The procedure of example 1 was repeated except that divalent calcium salt was used instead of sodium chloride.

The product had an elongation at break of 1500%, a strength at break of 0.25MPa and no injectability and adhesive capacity.

Examples of the experiments

Experimental example 1 tensile mechanical Property test

(1) In order to analyze the influence of the dosage of different monovalent cation salts, the tensile mechanical property test is carried out on the products obtained in example 1 and comparative examples 1-2, and the results are shown in fig. 2 and table 1.

Table 1:

as can be seen from fig. 2 and table 1, when no monovalent cation salt is added (comparative example 1), the breaking strength of the obtained product is very low, and is only 0.16MPa, which indicates that the presence of the monovalent cation salt enables self-assembly of sodium alginate molecular chains through hydrogen bonds, and the hydrogen bonds can indeed endow the final product with excellent mechanical properties; similarly, if the amount of the monovalent cation salt is too large (comparative example 2), the mechanical properties of the final product, including the elongation at break, the strength at break and the toughness at break, are also reduced. It is stated that the amount of monovalent cation salt is critical.

(2) In order to analyze the influence of different sodium alginate/monomer dosage ratios, tensile mechanical property tests were performed on the products obtained in examples 1-2 and comparative example 3, and the results are shown in fig. 3 and table 2.

Table 2:

as can be seen from FIG. 3 and Table 2, when the amount of the monomer used is too small (comparative example 3), the decrease in the fracture strength and fracture toughness of the resulting product is very significant, indicating that the amount of sodium alginate and the monomer used must be strictly controlled in the preparation of the double-network hydrogel according to the present invention.

(3) In order to analyze the effect of different amounts of cross-linking agent on the products, tensile mechanical property tests were performed on the products obtained in examples 1 and 3 and comparative example 4 (not shown in fig. 4), and the results are shown in fig. 4 and table 3.

Table 3:

as can be seen from fig. 4 and table 3, when the amount of the crosslinking agent to the monomer is relatively small to 0.0003 (example 3), the breaking strength is much reduced but the elongation at break is much improved compared to example 1 (amount ratio of 0.0006); however, if the amount of the crosslinking agent is too large, the elongation at break is seriously decreased and the strength at break and the fracture toughness are also decreased at a ratio to the amount of the monomer of 0.0012 (comparative example 4). It is noted that in the preparation of the double-network hydrogel of the present invention, the amount ratio of the crosslinking agent to the monomer is strictly controlled in order to obtain a product having excellent mechanical properties.

Experimental example 2 AFM test

The result of AFM test on the supramolecular fiber network of sodium alginate, the intermediate obtained in example 1, is shown in FIG. 5. As can be seen from FIG. 5, when monovalent cation is mixed with sodium alginate, supramolecular network structure can be obtained.

Experimental example 3 TEM test

TEM test is performed on the intermediate obtained in example 1, namely the sodium alginate supramolecular fiber network, and the result is shown in FIG. 6, and supramolecular nanofibers with the diameters of 10-50 nm and several microns can be observed in FIG. 6, which shows that after monovalent cations are mixed with sodium alginate, the sodium alginate molecular chains are self-assembled to form supramolecular nanofibers.

Experimental example 5 mechanical Strength test

(1) The reaction was carried out in a special mold according to the procedure of example 1 to obtain 1.5g of a hydrogel sheet, and the mechanical strength thereof was tested on site, and it was found that it was possible to lift a weight of 2kg more than 1300 times the weight thereof;

also, the hydrogel has very high transparency, and can be knotted, stretched, woven, compressed, polished, and the like, and can withstand a high level of deformation.

(2) The reaction was carried out in a special mold according to the procedure of example 1 to obtain a flat cylindrical hydrogel, which was pressed to be compressed by applying a mechanical load, but after removing the mechanical load, the hydrogel rapidly re-formed the original shape without any damage, indicating that the gel had excellent strength, elasticity and shape-recovering properties.

Experimental example 6 elasticity and recovery test

(1) The product from example 5 was subjected to 20 cycles of tension-relaxation cycling at 1000% strain, and the results are shown in figure 7, where it can be seen that the stress-strain curves for the remaining cycles did not show hysteresis and were completely overlapping, possibly due to residual stress remaining in the original hydrogel after a small hysteresis cycle in the first load-unload cycle.

(2) The energy dissipated and recovery of the gel during 20 consecutive cycles of stretch-relaxation is shown in fig. 8, and it can be seen that the energy dissipated and recovery decreased by 97.5% and 98.3% respectively during the first 5 cycles of high strain loading 1000%. After that, the energy consumption and recovery rate of the remaining cycles remain unchanged, and the gel can completely recover the mechanical properties at room temperature, which indicates that the hydrogel has extremely strong elasticity and recoverability, which are typical behaviors of elastomers.

The fast recovery rate, reliable mechanical property and longer service life of the double-network hydrogel in a high-stress working environment are further proved.

Experimental example 7 compression Property test

Compression tests were performed on the products obtained in example 5, comparative example 1 (without sodium chloride) and comparative example 5 (without sodium chloride and sodium alginate) and found that when compressed to 98% of the original height:

the product obtained in example 5 is elastic, compressible and can recover its original shape after compression;

the product obtained in comparative example 1 can also be compressed but cannot be recovered after compression;

the product obtained in comparative example 5 could not be compressed and the whole product was broken after compression.

The double-network hydrogel disclosed by the invention has very strong and excellent elastic compression performance.

Experimental example 8 measurement of Strain-resistance relative Change Properties

The relative change in resistance of the hydrogel obtained in example 5 when applied with tensile (fig. 9a) and compressive (fig. 9b) strains was detected to obtain a strain-resistance relative change curve showing the resistance dependence of the ion conductor on the applied stress.

As can be seen from fig. 9a, using the double-network hydrogel-linked Light Emitting Diode (LED) obtained in example 5 sandwiched by two copper sheets (electrodes) in the circuit, a change in tensile strength of the double-network hydrogel was observed. It is clearly seen that as the tensile strain increases, the light emitting diode darkens, losing as much as 1800% of the high strain light, further showing its excellent electrical stretchability.

As can be seen from fig. 9b, the light emitting diode becomes brighter as the compressive deformation increases.

Notably, after 10 load cycles, the high resistance relative change of the double-network hydrogel remained consistent with the original properties, indicating excellent high electrical stability at room temperature (as shown in fig. 9 c).

Experimental example 9 evaluation of Ionic skin Properties

In order to evaluate the skin performance of the double-network hydrogel serving as an example in an actual working environment, the double-network hydrogel obtained in example 5 was attached to different parts of a human body, and the relationship between the relative resistance change of various human body movements and time was monitored in real time.

(1) Bending and releasing the fingers, neck, knees and elbows, respectively, and performing the test, with the results shown in fig. 10a to 10 d;

the ionic skin resistance increases to different levels due to the increase in tensile deformation caused by the degree of bending of the fingers, neck, knees and elbows. In particular, it can be seen that the change of resistance is completely synchronized with the movements of fingers, neck, knees and elbows, there is no any hysteresis for many times, the reliability characteristics of fast response, instant recovery and high conductivity are exhibited, and the double-network hydrogel has excellent elasticity; the result shows that the double-network hydrogel can be used as an ion sensor for monitoring large strain and large movement of a human body, and has great application potential in artificial muscle and electronic skin.

(2) The throat was tested: three different people spoken the same Chinese word "hello" three times, the results are shown in FIG. 10 e; the same person said the same Chinese word "hello, i am good, dajia" recorded three times, with the results shown in FIG. 10 f.

The double-network hydrogel can be used as an ionic skin sensor, has higher sensitivity, can detect large deformation of human limb movement, and can measure complex and delicate muscle movement of people during speaking and wrist pulse. The obtained time-dependent resistance change curve shows similar characteristic peaks and valleys when the same person simultaneously speaks the same word for three times, and shows different characteristic peaks and valleys when different persons speak the same word;

to further study its sensitivity and repeatability, the same person recorded three times simultaneously "hello, i am, dajia" this chinese phrase. This curve shows the same characteristic peaks and low reproducibility. Through sensitive and rapid pressure sensing, the double-network hydrogel as an ionized skin provides an interesting and effective method for voice recognition, which is mainly caused by the deformation of muscles around the larynx during the speech process.

(3) Testing the pulse position of the wrist: wrist pulse tests of the same person before and after the activity show that the results are shown in fig. 10 g; wrist pulse tests of different persons, the results are shown in fig. 10 h;

in medical, health and exercise practice, wrist pulse is an important indicator of arterial blood pressure and heart rate, providing a large amount of useful information for non-invasive medical diagnosis;

due to the high strain sensitivity, the double network hydrogel was able to monitor subtle pressure differences before and after human activity (fig. 10 g). FIG. 10g shows the real-time resistance versus time for the ion sensor on the wrist artery, both after relaxation (pre-active) and after rope skipping (post-active). Obviously, the pulse frequency of a person who lays flat is 65 times/minute, the pulse shape is regular and repeatable, the pulse frequency of the person who jumps the rope is 90 times/minute, and the amplitude and the intensity are enhanced and irregular;

the enlarged view of a healthy human wrist pulse (fig. 10h), which can reflect subtle changes in the wrist pulse, clearly shows the shock wave (P-wave), the tidal wave (T-wave), the trough and diastolic wave (D-wave), the ventricular pressure and the heart rate in relation to the systolic and diastolic pressures. The obtained venation curve contains important clinical information, and can be deduced from certain characteristic points through mathematical analysis, so that the obtained venation curve provides guidance for some medical and scientific training.

The invention has been described in detail with reference to the preferred embodiments and illustrative examples. It should be noted, however, that these specific embodiments are only illustrative of the present invention and do not limit the scope of the present invention in any way. Various modifications, equivalent substitutions and alterations can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of the present invention, and these are within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims

1. A method for preparing a double-network hydrogel, which is characterized by comprising the following steps:

step 3, carrying out reaction under heating, illumination or radiation to obtain the double-network hydrogel, namely the sodium alginate-polyacrylamide double-network ion conductive hydrogel;

the univalent cation salt is a water-soluble univalent cation salt, the concentration of the univalent cation salt solution is 0.5-5 wt%, the weight ratio of the univalent cation salt to the sodium alginate is (0.5-2.5): 1, the weight ratio of the acrylamide monomer to the sodium alginate is (6-25):1, and the weight ratio of the crosslinking agent to the acrylamide monomer is (0.0003-0.001): 1.

2. The method for preparing according to claim 1, wherein step 1 comprises the substeps of:

3. The production method according to claim 2, wherein, in step 1-1,

the monovalent cation salt is selected from one or more of water-soluble sodium salt, water-soluble potassium salt and water-soluble lithium salt; and/or

The concentration of the monovalent cation salt solution is 1-4 wt%.

4. The production method according to claim 3, wherein, in step 1-1,

the monovalent cation salt is selected from one or more of sodium chloride, sodium carbonate, sodium iodide, potassium chloride, potassium carbonate and lithium chloride; and/or

The concentration of the monovalent cation salt solution is 1.5-3.5 wt%.

5. The production method according to claim 2,

in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (1-2): 1; and/or

In the step 1-2, the weight average molecular weight of the sodium alginate is 10-600 kDa.

6. The production method according to claim 5,

in the step 1-1 and the step 1-2, the weight ratio of the monovalent cation salt to the sodium alginate is (1.5-2): 1; and/or

In the step 1-2, the weight average molecular weight of the sodium alginate is 100-600 kDa.

7. The method according to claim 2, wherein the mixture is allowed to stand for 1 to 120 hours in the step 1 to 3.

8. The production method according to claim 1,

in step 2, the acrylamide-based monomer is selected from acrylamide and/or acrylamide derivatives including N, N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-isopropylacrylamide, N-isobutylacrylamide, N-tert-butylacrylamide, and N-cyclohexylacrylamide; and/or

The weight ratio of the acrylamide monomer to the sodium alginate is (10-20): 1.

9. The production method according to claim 1, wherein, in step 2,

the cross-linking agent is selected from one or more of N, N '-methylene bisacrylamide, N' -diallyl tartaric acid diamide, divinylbenzene, polyethylene glycol diacrylate and/or polyethylene glycol dimethacrylate; and/or

The weight ratio of the cross-linking agent to the acrylamide monomer is (0.0004-0.0008): 1; and/or

The initiator is selected from a thermal initiator or a photoinitiator; and/or

The weight ratio of the initiator to the acrylamide monomer is (0.0005-0.003): 1; and/or

The weight ratio of the catalyst to the acrylamide monomer is (0.001-0.004): 1.

10. The preparation method according to claim 9, wherein the initiator is one or more selected from the group consisting of ammonium persulfate, potassium persulfate, sodium persulfate, benzoyl peroxide and Irgacure 2959.

11. The production method according to one of claims 1 to 10, characterized in that, in step 3,

when heating is employed, the reaction proceeds as follows: reacting for 0.5-6 h at 40-60 ℃; or

When light illumination is used, the reaction proceeds as follows: reacting for 0.5-2 h under the irradiation of ultraviolet rays.

12. The production method according to claim 11, wherein, in step 3,

when heating is employed, the reaction proceeds as follows: reacting for 2-4 h at 50 ℃; or

When light illumination is used, the reaction proceeds as follows: reacting for 1-1.5 h under the irradiation of ultraviolet rays with the wavelength of 200-400 nm.

13. A double-network hydrogel obtained by the production method according to any one of claims 1 to 12,

the elongation at break of the double-network hydrogel is 1500-2500%;

the fracture strength of the double-network hydrogel is 0.4-0.8 MPa;

the fracture toughness of the double-network hydrogel is 3-6 MJ/m³。

14. Use of the double-network hydrogel obtained by the preparation method according to one of claims 1 to 12 or the double-network hydrogel according to claim 13 for ionic skin, wearable devices, resistive sensors.