CN109438728B

CN109438728B - Temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect and preparation method thereof

Info

Publication number: CN109438728B
Application number: CN201811269721.7A
Authority: CN
Inventors: 郝京诚; 郭依依
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2018-10-29
Filing date: 2018-10-29
Publication date: 2020-04-21
Anticipated expiration: 2038-10-29
Also published as: CN109438728A

Abstract

The invention relates to a preparation method of a temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect, belonging to the technical field of temperature-sensitive conductive hydrogels. The method comprises the following steps: (1) dissolving monomer vinyl imidazole and N-isopropyl acrylamide in deionized water, adding a cross-linking agent, an initiator and an accelerator, dissolving and uniformly mixing, then carrying out prepolymerization, and obtaining a chemically cross-linked hydrogel precursor after complete reaction; (2) and (2) taking out the hydrogel precursor prepared in the step (1), soaking the hydrogel precursor in a solution containing divalent metal zinc, copper, cobalt and nickel ions for coordination, then soaking the hydrogel precursor in water to remove redundant non-coordinated ions, and achieving swelling balance to obtain the temperature-sensitive conductive hydrogel coordinated by the metal ions. The invention firstly utilizes reversible physical crosslinking between metal ions and specific ligands to realize the regulation and control of the mechanical strength of the gel, and the gel has the temperature sensitivity and the conductivity of quick response.

Description

Temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect and preparation method thereof

Technical Field

The invention belongs to the technical field of high-strength temperature-sensitive conductive hydrogel, and particularly relates to temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect and a preparation method thereof.

Background

Hydrogels, as a class of soft materials, have attracted much attention in many fields such as materials and crude drugs because of their excellent biocompatibility and stimulus responsiveness. The application of hydrogel materials is generally limited by two aspects, on one hand, the strength of the hydrogel material is often low due to the soft characteristic of the hydrogel material; on the other hand, many stimuli-responsive gels have a slower response rate, which limits to some extent the widespread use of water gels. Generally, when a hydrogel absorbs a large amount of water in a network structure, good swelling performance is shown, and meanwhile, the mechanical properties of the hydrogel are greatly weakened. Therefore, it is one of the research hotspots in this field to realize a high-strength hydrogel which has a high strength and a high loading capacity and good mechanical properties, like a gel-like tissue in a living body.

Another design direction for hydrogels is to achieve its fast responsiveness, with thermosensitivity being a very important class of properties in stimuli-responsive materials. Temperature sensitive polymers, a typical class of stimuli responsive polymers, undergo a volume phase transition at a particular temperature, causing a change in their solubility state, which results from a change in the hydration state of the polymer. If a polymer solution exhibits a single phase below a certain temperature and phase separation occurs above that temperature, that temperature is at the lowest point on the phase separation curve on the concentration-temperature phase diagram of the polymer solution, the polymer is said to have the lowest eutectic temperature (LCST). And vice versa, called the maximum eutectic temperature (UCST).

At present, some researches have been made to improve the performance of hydrogel by coordination of metal ions, for example, patent application 201710299845.9 discloses a preparation method of a metal ion coordination natural polymer/polyacrylic acid self-repairing gel, which is prepared by reacting chitosan and polyacrylic acid, and adding metal ions to participate in coordination to prepare hydrogel with good mechanical properties and self-repairing function. The hydroxyethyl cellulose, polyacrylic acid and metal ions directly generate coordination reaction to prepare the green and environment-friendly self-repairing hydrogel with good mechanical property. The method utilizes a simple and environment-friendly method to prepare the double-network hydrogel with various physical effects, and the dynamic reversible physical effects endow the hydrogel with certain mechanical strength and good self-repairing capability. The composite hydrogel prepared by the invention has good mechanical property and excellent self-repairing property at normal temperature.

Patent application 201710448483.5 discloses a method for preparing a metal-coordinated physical hydrogel film, comprising: mixing a monomer I (acrylic acid), a monomer II (acrylamide or N-isopropylacrylamide), potassium persulfate and deionized water, introducing inert gas, standing, adding tetramethylethylenediamine, standing at room temperature to obtain a polymer solution, spin-coating the polymer solution on a substrate to obtain a liquid film layer, soaking the liquid film layer in a metal ion solution to obtain a physical hydrogel film, separating the physical hydrogel film from the substrate, and soaking in deionized water to obtain a metal coordination (metal ions and acrylic acid) physical hydrogel film.

Patent application 201510778176.4 discloses a method for preparing a chemically crosslinked interpenetrating network hydrogel complexed with metal ions (polyphenol is coordinated with metal ions), which is a kind of multiphase continuous hydrogel formed by interpenetrating and intertwining two networks. The method comprises the steps of controlling the positions and the number of polymer chain connecting points by using an amino-epoxy polymerization reaction, and preparing a first polymerization network structure by using a click chemical reaction; dopamine has excellent characteristics of good cell compatibility, biocompatibility and the like.

The preparation of the hydrogel utilizes the coordination between metal ions and carboxyl and phenolic hydroxyl (i.e. the ligand is an oxygen-containing functional group), which is a common coordination mode in the experiment in the field, and the coordination mode and mechanism are well researched. In addition, at present, the preparation of the high-strength hydrogel usually comprises complex organic synthesis steps, the preparation method is complicated, the prepared high-strength hydrogel lacks a quick and effective response mechanism, and the application field is single. Therefore, it is necessary to research a new temperature-sensitive conductive hydrogel and a preparation method thereof.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide the temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect and the preparation method thereof, the invention firstly utilizes chemical crosslinking to obtain relatively longer molecular chains, and utilizes reversible physical crosslinking between metal ions and imidazole ligands on the basis to realize stress dispersion of the gel and introduce a stimulus response mechanism while keeping the high elasticity of the gel, so that the gel has the temperature sensitivity of quick response; the preparation method is simple, does not damage the material structure, and is an effective way for controlling the crosslinking density and the material strength.

The invention aims to provide a preparation method of a temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect.

The second purpose of the invention is to provide the temperature-sensitive conductive hydrogel with enhanced metal ion coordination effect prepared by the method.

The third purpose of the invention is to provide the application of the temperature-sensitive conductive hydrogel with enhanced coordination of metal ions.

In order to achieve the above purpose, the invention specifically discloses the following technical scheme:

the invention discloses a preparation method of a temperature-sensitive conductive hydrogel coordinated by metal ions, which comprises the following steps:

(1) dissolving monomer vinyl imidazole and N-isopropyl acrylamide in deionized water, adding a cross-linking agent, an initiator and an accelerator, dissolving and uniformly mixing, then carrying out prepolymerization, and obtaining a chemically cross-linked hydrogel precursor after complete reaction;

(2) and (2) taking out the hydrogel precursor prepared in the step (1), soaking the hydrogel precursor in a solution containing any one of divalent metal zinc, copper, cobalt and nickel ions for coordination, then soaking the hydrogel precursor in water to remove redundant non-crosslinked coordinated ions, and achieving swelling balance to obtain the temperature-sensitive conductive hydrogel coordinated by the metal ions.

Preferably, the invention provides a method for purifying N-isopropylacrylamide in step 1), which specifically comprises the following steps: 1) adding N-isopropylacrylamide into toluene, heating to dissolve, adding N-hexane, 2) performing suction filtration, standing the filtrate in an environment at-20 ℃, cooling for 2 hours, performing suction filtration to obtain white crystals, 3) repeating the step 2) for three times, performing vacuum drying at 30 ℃, sealing, and placing in a refrigerator in an environment at 5 ℃ for later use.

Poly (N-isopropylacrylamide) is the most representative of temperature-sensitive polymers, and the lowest eutectic temperature of homopolymers of the poly (N-isopropylacrylamide) is about 32 ℃. The N-isopropyl acrylamide structurally has both hydrophilic amide groups and hydrophobic isopropyl groups, and the structure enables the N-isopropyl acrylamide to undergo reversible expansion-contraction change after polymerization in LCST, macroscopically shows that the hydrogel can realize rapid volume and transparency change in a normal temperature range, thereby completing the design goal of high-strength and rapid response to the hydrogel.

In the step (1), the cross-linking agent is N, N' -methylene bisacrylamide; the initiator is ammonium persulfate; the accelerator is N, N, N ', N' -tetramethyl ethylenediamine.

Preferably, in step (1), the monomer vinyl imidazole: the mass ratio of the N-isopropyl acrylamide is 1-5: 1-2 percent, the solid content is 20-40 percent, and the chemical crosslinking degree is 0.2-0.4 percent. If the solid content and the chemical crosslinking degree are too low, the hydrogel is soft and is not easy to form, and if the solid content and the chemical crosslinking degree are too high, the hydrogel chain segment is short, so that the hydrogel is large in brittleness and small in elasticity, is fragile and is too low in strength.

Preferably, in step (1), the mole fractions of the initiator and the accelerator are both 0.2 to 3% of the total amount of the monomeric vinylimidazole.

Preferably, in the step (1), the reaction temperature is 20-30 ℃ and the reaction time is 20-28 hours.

Preferably, in the step (2), the divalent metal ions of zinc, copper, cobalt and nickel can be sulfate, nitrate or chloride; more preferably sulfate, the concentration of which is 10 to 90 mol/L.

Preferably, in the step (2), the two soaking times are both 6-12 hours, and the coordination action occurs in the soaking process.

Preferably, in the step (2), the temperature of the two soaking is 20-30 ℃.

Secondly, the invention discloses the temperature-sensitive conductive hydrogel with enhanced metal ion coordination prepared by the method.

Finally, the invention discloses the application of the temperature-sensitive conductive hydrogel coordinated by the metal ions in the fields of materials, biology, medicines and the like.

The invention utilizes the first transition metal ion Zn²⁺、Cu²⁺、Co²⁺、Ni²⁺And the reversible metal ion-imidazole coordination effect between the hydrogel and imidazole adds a layer of reversible physical crosslinking on the basis of hydrogel chemical crosslinking, so that not only can stress dispersion be realized, but also the elasticity of the gel can be enhanced, and the strength of the hydrogel is improved.

Specifically, the method of substantially improving strength mainly includes achieving sufficient stress dispersion while large deformation occurs, and having high elasticity so that the gel can recover the shape before deformation. The mechanism for realizing stress dispersion mainly comprises the following steps: (1) the principle of the double-network gel is that stress dispersion is realized by utilizing the breakage of partial molecular chains; (2) stress dispersion is achieved by using non-covalent crosslinking, such as reversible crosslinking of metal ion coordination, hydrogen bonding, hydrophobic interactions, and the like; the non-covalent interaction is a kind of existence relative to the covalent interaction, the covalent bond is a strong chemical bond formed by utilizing a common electron pair, the bond strength is large, the bond cannot be formed spontaneously, and the bond cannot be reconstructed spontaneously after being fractured. Whereas a non-covalent interaction is a spontaneous, sustained formation/decomposition process that is experienced under specific conditions. Therefore, the coordination bond can be destroyed temporarily after the external force is applied, and the ligand and the central ion can be recovered spontaneously as long as the ligand and the central ion exist after the external force disappears. The method has the advantages that part of stress dispersion is born through the breakage of coordination bonds, the covalent crosslinking network can be replaced to bear stress, the structure of the material is not essentially damaged, the coordination bonds can be spontaneously formed after being broken, the hydrogel can be restored to the original state after being deformed, namely, the integrity of the material is maintained, the hydrogel has higher elasticity and higher strength in a macroscopic view, and (3) the biomacromolecules are used as the material and comprise protein, polysaccharide and the like, and the stress dispersion is realized by utilizing the length of a variable molecular chain segment or the length of a variable crosslinking chain segment.

Methods of maintaining the high elasticity of hydrogels include: (1) an interpenetrating network is constructed by utilizing a longer molecular chain, and compared with a shorter molecular chain, the interpenetrating network is not easy to break or crosslink during deformation; (2) a loose network is firstly constructed by chemical crosslinking, and then the crosslinking density is increased by reversible physical crosslinking, so that the chemical structure of the material can be ensured to be basically unchanged before and after deformation; (3) constructing a plurality of crosslinking points, wherein a plurality of molecular chains between two crosslinking points have different lengths, and after a short chain is damaged, the unbroken long chain can still keep the elasticity of the network; (4) a network structure with a molecular chain with uniform length is constructed, so that uneven stress of long and short chains can be avoided, and unrecoverable inelastic deformation is reduced.

In order to realize stress dispersion and enhance the elasticity of the gel so as to improve the strength of the hydrogel, firstly, relatively long molecular chains are obtained by chemical crosslinking, and reversible physical crosslinking is added on the basis of the relatively long molecular chains to realize the stress dispersion of the gel and maintain the high elasticity of the gel, so that the method not only has the advantages of stress dispersion and gel high elasticity maintenance, but also has simple preparation method, no damage to the material structure and controllable crosslinking density and material strength.

Compared with the prior art, the invention has the beneficial effects that:

(1) the hydrogel with conductivity, adjustable mechanical property and adjustable temperature-sensitive property is prepared by the method.

(2) The invention utilizes a one-step polymerization and soaking method, the reaction condition is mild, and the preparation method is simple.

(3) According to the invention, reversible metal ion-imidazole coordination sites existing between four first transition metal ions and imidazole are used for coordination, so that the mechanical property of the gel is enhanced, the lowest eutectic temperature of the gel is changed, and the design goals of high strength and quick response of the hydrogel are realized.

(4) Compared with the traditional metal coordination mode mentioned in the background technical content, the coordination effect of the imidazole-transition metal ions (namely the ligand is a nitrogen-containing functional group) adopted by the invention belongs to an important coordination effect in organisms, the difference of the coordination capacity between the four first transition metal ions and the imidazole is compared, the mechanical properties of the prepared four hydrogels are enhanced, and the effective control of the crosslinking density and the mechanical properties of the hydrogel is realized, wherein Zn²⁺The mechanical strength of the hydrogel coordinated with imidazole is remarkably improved compared with that of the hydrogel not coordinated with other three metal ions. Because the four first transition metal ions have similar atomic numbers and outer electronic structures, the invention finds that the similar ions can produce obviously different enhancement effects after coordination, and compares and explains the enhancement effects. Meanwhile, the preparation method of the hydrogel provided by the invention is simple, avoids the complex organic synthesis steps in click chemistry, and only needs one-step conventional polymerization and soaking method.

(5) In contrast to the conventional coordination method described in the background section, the present inventors have found that a vinyl imidazole ligand, which can produce a difference in mechanical strength of gels only by changing the kind of metal ions, is used.

(6) The invention utilizes the copolymerization with monomer N-isopropyl acrylamide, and aims to prepare the hydrogel with high strength and rapid temperature responsiveness by utilizing the temperature sensitivity and combining with enhanced mechanical properties, thereby greatly improving the application value of the hydrogel.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

FIG. 1 is an infrared spectrum of the hydrogel prepared in example 1.

FIG. 2 is a graph showing the equilibrium water content of hydrogels with different chemical crosslink densities after coordination of different kinds of metal ions in example 1.

FIG. 3 is a scanning electron microscope image of the hydrogel prepared in example 1.

FIG. 4 is a stress-strain curve of the hydrogel subjected to the compression test after coordination of different metal ions in example 1.

FIG. 5 is a graph showing the change in transparency with temperature at room temperature and at body temperature for the hydrogel prepared in example 1.

FIG. 6a is a photograph showing a change in conductivity with an external force of the hydrogel prepared in example 1.

FIG. 6b shows the change of the electrical conductivity of the hydrogel prepared in example 1 with the change of external force.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As described in the background art, it is one of the research hotspots in this field to realize a high-strength hydrogel with high strength and high loading capacity, which has good mechanical properties, like the gel-like tissue in the living body. Therefore, the present invention provides a temperature-sensitive conductive hydrogel with enhanced metal ion coordination and a preparation method thereof, and the present invention is further described with reference to the accompanying drawings and the detailed description.

In the following examples and drawings, a-B-X% -Y-ZmM represent hydrogels with different ratios, where a-B is the mass ratio of the monomers Vinylimidazole (VIM) and N-isopropylacrylamide (NIPAM), X% represents a certain mole fraction of the crosslinking agent, Y represents the kind of metal ions, and Z mM represents the concentration of the metal ion soaking solution.

Example 1

1. Purifying N-isopropyl acrylamide: weighing 5g N-isopropyl acrylamide, adding into 8ml toluene, heating to 50 ℃ for dissolution, adding 25ml n-hexane, filtering, standing the filtrate in an environment of-20 ℃ after suction filtration, carrying out suction filtration after two hours to obtain white crystals, repeating the steps for three times, carrying out vacuum drying on the obtained product at 30 ℃, sealing, and placing in a refrigerator at 5 ℃ for later use.

2. A preparation method of temperature-sensitive conductive hydrogel coordinated by metal ions comprises the following steps:

(1) the N-isopropylacrylamide purified in the example and the vinylimidazole monomer in a mass ratio of 2:5 were dissolved in deionized water to obtain a solid content of 30% and a chemical crosslinking degree of 0.3%. Then adding a cross-linking agent N, N ' -methylene bisacrylamide accounting for 0.3 percent of the total mole fraction of the monomers, adding an initiator ammonium persulfate and an accelerator N, N, N ', N ' -tetramethyl ethylenediamine accounting for 1.0 percent of the total mole fraction of the monomers, dissolving and uniformly mixing, then reacting at 25 ℃ for 24 hours for prepolymerization, and obtaining a chemically cross-linked hydrogel precursor after complete reaction;

(2) taking out the hydrogel precursors prepared in the step (1), dividing the hydrogel precursors into 4 groups, wherein each group corresponds to a metal ion solution, soaking the 4 groups of hydrogel precursors in an aqueous solution containing zinc sulfate, copper sulfate, cobalt sulfate and nickel sulfate (the concentration of the metal ions is 50mM) for 12 hours for coordination (at the temperature of 25 ℃), then soaking in water at the temperature of 25 ℃ for 12 hours to remove redundant non-crosslinked coordinated ions, and achieving swelling balance to obtain 4 groups of temperature-sensitive conductive hydrogels with different metal ion coordination: 2-5-0.3% -Zn²⁺-50mM、2-5-0.3％-Cu²⁺-50mM、2-5-0.3％-Co²⁺-50mM、2-5-0.3％-Ni²⁺-50mM。

In this example and the accompanying drawings, a-B-X% -Y-ZmM represent hydrogels with different ratios, where a-B is the mass ratio of the monomers Vinylimidazole (VIM) and N-isopropylacrylamide (NIPAM), X% represents a certain mole fraction of the crosslinking agent, Y represents the type of metal ions, and Z mM represents the concentration of the metal ion soaking solution.

Comparative example 1

As a comparative example of example 1, the hydrogel precursor prepared in step (2) was taken out and then soaked in deionized water only, and the other conditions of soaking were the same, and obtained as 2-5-0.3% -H₂O。

Example 2

A preparation method of temperature-sensitive conductive hydrogel coordinated by metal ions comprises the following steps:

(1) dissolving the purified N-isopropylacrylamide and the monomer vinylimidazole in the embodiment according to the mass ratio of 1:1 in deionized water, wherein the solid content is 40% and the chemical crosslinking degree is 0.4%, then adding a crosslinking agent N, N ' -methylenebisacrylamide according to 0.2% of the mole fraction of the total amount of the monomers, adding an initiator ammonium persulfate and an accelerator N, N, N ', N ' -tetramethylethylenediamine according to 1.0% of the mole fraction of the total amount of the monomers, dissolving and uniformly mixing, reacting at 30 ℃ for 20 hours, and performing prepolymerization to obtain a chemically crosslinked hydrogel precursor after the reaction is complete;

(2) and (2) taking out the hydrogel precursor prepared in the step (1), soaking in an aqueous solution of 10mM cobalt chloride for 6h for coordination (at the temperature of 30 ℃), then soaking in water at the temperature of 30 ℃ for 6h to remove redundant non-crosslinked coordinated ions, and achieving swelling balance to obtain the temperature-sensitive conductive hydrogel coordinated with metal ions.

Example 3

(1) dissolving the purified N-isopropylacrylamide and the monomer vinylimidazole in the embodiment according to the mass ratio of 3:2 in deionized water, wherein the solid content is 20% and the chemical crosslinking degree is 0.2%, then adding a crosslinking agent N, N ' -methylenebisacrylamide according to 2.0% of the mole fraction of the total amount of the monomers, adding an initiator ammonium persulfate and an accelerator N, N, N ', N ' -tetramethylethylenediamine according to 3.0% of the mole fraction of the total amount of the monomers, dissolving and uniformly mixing, reacting at 20 ℃ for 28 hours, and performing prepolymerization to obtain a chemically crosslinked hydrogel precursor after the reaction is complete;

(2) and (2) taking out the hydrogel precursor prepared in the step (1), soaking in 90mM zinc nitrate aqueous solution for 10h for coordination (at the temperature of 20 ℃), then soaking in 20 ℃ water for 10h to remove redundant non-crosslinked coordinated ions, and achieving swelling balance to obtain the temperature-sensitive conductive hydrogel coordinated with metal ions (3-2-2% -Y-90 mM).

And (3) performance testing:

(1) the hydrogels prepared in example 1 and comparative example 1 were tested and their IR spectra are characterized as shown in FIG. 1, wherein 3448cm^-1The corresponding position is the N-H stretching vibration peak of the N-isopropyl acrylamide; 1385cm^-1Where corresponds to-CH on N-isopropylacrylamide₃The bending vibration peak of (1); 1634cm^-1The position corresponds to the C ═ N stretching vibration peak on the imidazole ring. This shows that the present invention successfully produces copolymer hydrogels. When metal ions are coordinated with imidazole rings, the stretching vibration peak of C ═ N moves to 1554cm from low frequency^-1The introduction of metal ions has certain influence on the absorption of C ═ N double bonds, and outer layer electrons of transition metals can participate in weak conjugation, so that the temperature-sensitive conductive hydrogel successfully synthesized and coordinated by double-crosslinked metal ions is proved.

(2) The equilibrium water content of the hydrogels prepared in example 1 and comparative example 1 and coordinated by different metal ions is measured at room temperature, and the specific method is as follows: carefully wiping off the excess water on the surface of the hydrogel sample which is in equilibrium with water absorption by using filter paper, and weighing the weight m on an electronic analytical balance_wetThen dried under vacuum at 50 ℃ for 24 hours, and the dry weight m thereof was measured_dry. Three samples were taken for each proportion of hydrogel and measured, and the average was taken. The equilibrium water content calculation method of the hydrogel comprises the following steps:

equilibrium Water Content (EWC)% (m)_wet－m_dry)/m_wet*100％。

Through tests, the equilibrium water content of the hydrogels obtained in example 1 and comparative example 1 is shown in FIG. 2, the equilibrium water content of the gels after soaking with different metal ions is different, and the equilibrium water content is from high to low, and Ni is shown in the following order²⁺>Co²⁺>Cu²⁺>H₂O>Zn²⁺。

It can be seen that the equilibrium water content of the hydrogel is different after the coordination of different metal ions, and the main reason is that the crosslinking density of the hydrogel is different due to the difference between the coordination modes and the coordination abilities of different metal ions, thereby causing the difference in the equilibrium water content. It is due to the differences in coordination patterns and coordination abilities that the different components of the hydrogel have different mechanical property enhancing effects.

(3) 2-5-0.3% -Zn obtained in example 1²⁺The results of observation of 50mM hydrogel under a scanning electron microscope are shown in FIG. 3, and it can be seen that: the microstructure of the hydrogel is a relatively uniform and compact porous structure, the pore size is smaller than 1 mu m, the pore size and the pore distribution are uniform, the structure is compact, the material structure is uniform, the average dispersion stress is more favorably realized, the mechanical performance is improved, if the pores are not uniform and compact, the structures of different parts of the material are different, the stress dispersion capacity is different, stress concentration can be generated, the stress concentration is positioned, the material is easy to damage), the stress concentration generated at the defect position of the material is avoided, the load capacity caused is reduced, and the material is damaged.

(4) To the embodiments1 and the stress-strain curves of comparative example 1, the results are shown in fig. 4, and it can be seen that: after the metal ions are coordinated, reversible coordination crosslinking is added, so that stress dispersion is realized, the compressive strength of the obtained hydrogel is greater than that of gel without coordination crosslinking, and the strength sequence is Zn²⁺>Cu²⁺>Co²⁺≈Ni²⁺>H₂And O. Wherein, 2-5-0.3% -Zn²⁺The strength of the hydrogel with the concentration of 70mM is increased to the maximum, and the compressive strength can reach 4638.17 kPa. This indicates Zn relative to the coordination between other metal ions and imidazole²⁺The coordination crosslinking between the hydrogel and imidazole can greatly enhance the compression strength of the hydrogel, effectively realize stress dispersion, maintain the high elasticity of the gel and realize the purpose of preparing the high-strength hydrogel. The different coordination modes and coordination abilities of different metal ions have differences, so that the crosslinking density of the hydrogel is different, and further the equilibrium water content is different.

(5) 2-5-0.3% -Zn obtained in example 1²⁺The thermo-sensitive response of 50mM hydrogel was tested and the results are shown in FIG. 5, from which it can be seen that: the hydrogel is transparent at room temperature, becomes opaque after being touched by fingers for 1min, and can quickly recover the transparency after being recovered to the room temperature because partial moisture is extruded due to volume shrinkage after the temperature is raised, which indicates that the LCST of the gel is between the room temperature and the body temperature, and the hydrogel has quick response and higher utilization value.

(6) 2-5-0.3% -Zn obtained in example 1²⁺The conductivity response of 50mM hydrogel was tested and the results are shown in FIG. 6, from which it can be seen that: the hydrogel contains anions and cations which can move freely, has higher mechanical strength, can bear certain stretching, and has responsiveness along with the change of external force.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of temperature-sensitive conductive hydrogel coordinated by metal ions is characterized by comprising the following steps: the method comprises the following steps:

(2) taking out the hydrogel precursor prepared in the step (1), soaking the hydrogel precursor in a solution containing any one of divalent metal zinc, copper, cobalt and nickel ions for coordination, then soaking the hydrogel precursor in water to remove redundant non-crosslinked coordinated ions and achieve swelling balance, thus obtaining the temperature-sensitive conductive hydrogel coordinated by metal ions;

in the step (1), the cross-linking agent is N, N' -methylene bisacrylamide; the initiator is ammonium persulfate; the accelerator is N, N, N ', N' -tetramethyl ethylenediamine;

in the step (1), the monomer vinyl imidazole: the mass ratio of the N-isopropyl acrylamide is 1-5: 1-2 percent, the solid content is 20-40 percent, and the chemical crosslinking degree is 0.2-0.4 percent.

2. The method for producing a metal ion-coordinated temperature-sensitive conductive hydrogel according to claim 1, characterized in that: in the step (1), the mole fractions of the initiator and the accelerator are both 0.2-3% of the total amount of the monomer vinyl imidazole.

3. The method for producing a metal ion-coordinated temperature-sensitive conductive hydrogel according to claim 1, characterized in that: in the step (1), the reaction temperature is 20-30 ℃, and the reaction time is 20-28 hours.

4. The method for producing a metal ion-coordinated temperature-sensitive conductive hydrogel according to claim 1, characterized in that: in the step (2), the divalent metal ions of zinc, copper, cobalt and nickel are selected from sulfate, nitrate or chloride.

5. The method for producing a metal ion-coordinated temperature-sensitive conductive hydrogel according to claim 1, characterized in that: in the step 1), the purification method of the N-isopropyl acrylamide comprises the following steps:

1) adding N-isopropyl acrylamide into toluene, heating to dissolve, and then adding N-hexane;

2) standing the filtrate after suction filtration in an environment of-20 ℃, cooling for 2h, and then carrying out suction filtration to obtain white crystals;

3) repeating the step 2) for three times, and sealing and placing the obtained product into a refrigerator at 5 ℃ after vacuum drying at 30 ℃ for later use.

6. The method for producing a metal ion-coordinated temperature-sensitive conductive hydrogel according to claim 1, characterized in that: step by step

In the step (2), the soaking time is 6-12 hours for both times; in the step (2), the temperature of the two soaking processes is 20-30 ℃.

7. A metal ion-coordinated temperature-sensitive conductive hydrogel prepared by the method according to any one of claims 1 to 6.