CN113683820A - Double-layer hydrogel material and preparation method and application thereof - Google Patents
Double-layer hydrogel material and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of intelligent hydrogel drivers, in particular to a double-layer hydrogel material and a preparation method and application thereof. PVA in the double-layer hydrogel material contains rich hydroxyl, which is beneficial to the formation of hydrogen bonds, and a composite hydrogel layer containing microcrystals is formed in situ in the process of freeze thawing treatment of the PVA; the crystallite regions in the crystallite-containing composite hydrogel layer contribute to the increase in density, strength and thermal stability properties of the composite hydrogel, thereby improving the properties of the composite hydrogel; and meanwhile, the swelling behavior of the composite hydrogel can be changed, so that different swelling behaviors exist between the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals, and the double-layer hydrogel material is constructed by utilizing the different swelling behaviors.
Description
Technical Field
The invention relates to the technical field of intelligent hydrogel drivers, in particular to a double-layer hydrogel material and a preparation method and application thereof.
Background
Intelligent hydrogel driver is a type under stimulationThe intelligent response device capable of reversibly obtaining/losing water molecules so as to change breeding shapes or volumes has potential application in the fields of bionics, intelligent valves, soft robots, biomedicines and the like. Generally, the method for constructing the gel actuator mainly comprises the steps of introducing a double-layer structure, a gradient structure and a pattern structure, namely an oriented structure, into the gel, so as to induce the gel to generate anisotropic swelling and actuating behaviors. Among the numerous methods, the construction of a hydrogel with a bilayer structure is the most common method, and currently, three methods are mainly used for realizing intelligent response behavior: firstly, different contents of nano particles (clay, carbon nano tubes or silicon dioxide, etc.) or cellulose microcrystals are introduced into a two-layer gel structure, and the components have two-layer structures with different swelling and response sensitivities to realize the construction of an actuator: for example, Poly (N-isopropylacrylamide) -clay nanocomposite hydrogels of the group of mythium ananatis (Poly (N-isopropylacrylamide) -clay nanocomposites hydrogel with a reactive binding property as a controlled catalyst, adv. function. mater.2015,25, 2980-doped 2991.) were developed as temperature sensitive actuators, and clay was introduced into the nanosheet hydrogel, which not only served as a physical cross-linker to increase the mechanical strength of the hydrogel, but also to adjust the thermal shrinkage of the hydrogel, and the content of clay in the hydrogel bilayer structure was controlled to achieve the driving behavior of the gel. Second, the hydrogel actuator can be constructed with polymer chains with different response behavior and function as a bilayer: zhang Li Na et al (Bilayer hydrogel actuators with light interface adsorbed from natural polysaccharides, Soft Matter 2017,13, 345) developed an intelligent two-layer hydrogel actuator composed of chitosan and cellulose/carboxymethyl cellulose, the chitosan layer and the cellulose/carboxymethyl cellulose composite layer have different pH responsiveness, and the carboxyl groups in the cellulose/carboxymethyl cellulose layer are ionized (pH value>3.8) and protonation of amino groups in the Chitosan layer (pH)<3.8) causing it to deform under different pH conditions, such as S-shape, spiral shape, tubular shape, bamboo shape, wave shape and flower shape; huang topic group (polyelectrodes and anti-polyelectrodes Effects for Dual Salt-Responseiv)e Interpenetrating networks hydrogels 2019,20,3524-3534) constructs a salt response Interpenetrating Network (IPN) hydrogel composed of a cationic ptmaea layer and an amphoteric pSBVI layer in a salt solution, the two polymer networks show opposite swelling behaviors due to the action of polyelectrolyte and counter-polyelectrolyte, and the prepared hydrogel shows a series of reversible regulation and control characteristics including structure, antibacterial performance and interface regeneration. Third, the gel driver of the Janus bilayer structure was constructed by varying the crosslink density in the bilayer structure: for example, in Fe3+In the presence of the catalyst, the PAAC/Clay hydrogel with excessive crosslinking density has lower swelling degree and higher modulus, and the PAAC/Clay layer is mixed with Fe3+PAAC/Clay layer combination can construct a dual-layer driver.
With the development of software drivers, more strategies and design ideas need to be developed to construct a two-layer structure.
Disclosure of Invention
The invention aims to provide a double-layer hydrogel material, a preparation method and application thereof, wherein the double-layer hydrogel material comprises a composite hydrogel layer containing microcrystals and a composite hydrogel layer without microcrystals, and the double-layer hydrogel material is constructed by utilizing different swelling behaviors of the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a double-layer hydrogel material, which comprises a composite hydrogel layer containing microcrystals and a composite hydrogel layer without microcrystals, which are sequentially stacked;
the composite hydrogel in the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogels; and the polyvinyl alcohol-stimulus responsive polymer composite hydrogel does not comprise nanoparticles;
the microcrystals in the composite hydrogel layer containing microcrystals are polyvinyl alcohol microcrystals;
the composite hydrogel layer containing microcrystals is subjected to freeze-thawing treatment.
Preferably, the mass ratio of the polyvinyl alcohol to the stimulus-responsive polymer in the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals is independently (0-3): 3;
and the mass of the polyvinyl alcohol is not 0.
Preferably, the stimuli-responsive polymer in the polyvinyl alcohol-stimuli-responsive polymer composite hydrogel comprises a pH-responsive polymer or a temperature-responsive polymer.
Preferably, the pH-responsive polymer is sodium carboxymethylcellulose, chitosan, or poly [ 2- (N, N-dimethylamino) methacrylate ].
Preferably, the temperature responsive polymer is poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ].
The invention also provides a preparation method of the double-layer hydrogel material, which comprises the following steps:
when the stimulus responsive polymer is a natural high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer solution and a first cross-linking agent to obtain a pre-gel solution of a stimulus-responsive polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material;
when the stimulus responsive polymer is a synthetic high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus response polymer monomer, a second cross-linking agent and an initiator, and carrying out cross-linking to obtain a pre-gel solution of a stimulus response polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material.
Preferably, when the stimulus responsive polymer is a natural high molecular polymer:
the mass concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1-30%;
the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is 0.1-10%.
Preferably, when the stimulus responsive polymer is a natural high molecular polymer:
the mass ratio of the polyvinyl alcohol in the polyvinyl alcohol solution to the stimulus-responsive polymer in the stimulus-responsive polymer solution is (0-3): 3;
and the mass of the polyvinyl alcohol is not 0.
Preferably, the number of times of the freeze-thaw treatment is 1 to 10.
The invention also provides an application of the double-layer hydrogel material in the technical scheme or the double-layer hydrogel material prepared by the preparation method in the technical scheme in the intelligent response field.
The invention also provides an application of the double-layer hydrogel material in the technical scheme or the double-layer hydrogel material prepared by the preparation method in the technical scheme in the intelligent response field.
The invention provides a double-layer hydrogel material, which comprises a composite hydrogel layer containing microcrystals and a composite hydrogel layer without microcrystals, which are sequentially stacked; the composite hydrogel in the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogels; and the polyvinyl alcohol-stimulus responsive polymer composite hydrogel does not comprise nanoparticles; the microcrystals in the composite hydrogel layer containing microcrystals are polyvinyl alcohol microcrystals; the composite hydrogel layer containing microcrystals is subjected to freeze-thawing treatment. Polyvinyl alcohol (PVA) in the double-layer hydrogel material is a biological extremely-friendly polymer, a molecular chain contains rich hydroxyl, the formation of a hydrogen bond is facilitated, ice crystals formed in situ can extrude the PVA chain to form a local high-concentration area in the process of carrying out freeze thawing treatment on the PVA chain, and the adjacent molecular weight further forms a microcrystal area through intermolecular/intramolecular hydrogen bond action to form a composite hydrogel layer containing microcrystals; the crystallite regions in the crystallite-containing composite hydrogel layer contribute to the increase in density, strength and thermal stability properties of the composite hydrogel, thereby improving the properties of the composite hydrogel; and meanwhile, the swelling behavior of the composite hydrogel can be changed, so that different swelling behaviors exist between the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals, and the double-layer hydrogel material is constructed by utilizing the different swelling behaviors.
Drawings
FIG. 1 is a schematic view of the preparation process of the two-layer hydrogel material prepared in examples 1-9;
FIG. 2 is an infrared spectrum of the chitosan hydrogel prepared in comparative example 1, the PVA hydrogel prepared in comparative example 2, the composite hydrogel layer containing crystallites prepared in example 1, and the composite hydrogel layer containing no crystallites;
FIG. 3 is XRD patterns of the chitosan hydrogel prepared in comparative example 1, the PVA hydrogel prepared in comparative example 2, and the composite hydrogel layer containing crystallites and the composite hydrogel layer without crystallites prepared in example 1;
FIG. 4 is a 3D-Raman spectrum of a composite hydrogel layer without crystallites prepared in example 1;
FIG. 5 is a 3D-Raman spectrum of a composite hydrogel layer containing crystallites prepared according to example 1;
FIG. 6 is a graph showing the tensile-stress strain curve of the two-layer hydrogel material prepared in example 1;
FIG. 7 is a graph of swelling performance of the composite hydrogel layer containing crystallites and the composite hydrogel layer without crystallites prepared in example 1;
FIG. 8 is a curve showing the swelling behavior of the two-layer hydrogel materials prepared in examples 1 to 4 with time;
fig. 9 is a graph of the sensitivity of the double-layer hydrogel material prepared in example 1 under different pH conditions, wherein a is a response curve of the double-layer hydrogel material under different pH conditions, b is a physical representation of the completeness of the double-layer hydrogel material under the condition of pH 2, and c is an SEM image of the double-layer hydrogel material after swelling under the condition of pH 2;
FIG. 10 is a graph of swelling performance of the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals prepared in example 5;
fig. 11 is a schematic and physical diagram of a bilayer actuator of different configuration before and after swelling in hydrochloric acid solution at pH 2;
fig. 12 is a process of capturing an object in an acidic solution with pH 2 by a bionic manipulator according to an application example;
FIG. 13 is a graph of the deswelling performance versus the mass ratio of poly (N-isopropylacrylamide) to PVA for the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals prepared in example 10;
fig. 14 is a graph showing the bending behavior of the poly (N-isopropylacrylamide)/PVA bilayer gel driver prepared in example 10 in an aqueous solution at 50 ℃.
Detailed Description
The invention provides a double-layer hydrogel material, which comprises a composite hydrogel layer containing microcrystals and a composite hydrogel layer without microcrystals, which are sequentially stacked;
the composite hydrogel in the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogels; and the polyvinyl alcohol-stimulus responsive polymer composite hydrogel does not comprise nanoparticles;
the microcrystals in the composite hydrogel layer containing microcrystals are polyvinyl alcohol microcrystals;
the composite hydrogel layer containing microcrystals is subjected to freeze-thawing treatment.
In the invention, the mass ratio of polyvinyl alcohol to stimulus-responsive polymer in the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals is preferably (0-3): 3 independently, and the mass of polyvinyl alcohol is not 0; more preferably (0.5-2): 3, most preferably (1-1.5): 3.
in the present invention, the thickness of the composite hydrogel layer containing microcrystals is preferably 0 to 10mm, more preferably 0.5 to 4mm, and most preferably 1mm, and the thickness of the composite hydrogel layer containing microcrystals is not 0.
In the present invention, the thickness of the composite hydrogel layer containing no microcrystals is preferably 0 to 10mm, more preferably 0.5 to 4mm, and most preferably 1mm, and the thickness of the composite hydrogel layer containing no microcrystals is not 0.
In the present invention, the stimulus-responsive polymer in the polyvinyl alcohol-stimulus-responsive polymer composite hydrogel preferably includes a pH-responsive polymer or a temperature-responsive polymer; the pH-responsive polymer is preferably sodium carboxymethylcellulose, chitosan, or poly [ 2- (N, N-dimethylamino) methacrylate ], more preferably chitosan; the temperature responsive polymer is preferably poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ]. In the present invention, the poly [ 2- (N, N-dimethylamino) methacrylate ] can be used as both a pH responsive polymer and a temperature responsive polymer.
In the invention, the composite hydrogel layer containing microcrystals is obtained by freeze-thawing treatment of the composite hydrogel layer containing no microcrystals; the freeze-thaw treatment is preferably performed for 1 to 10 times, more preferably for 3 to 8 times, and most preferably for 6 to 7 times. Each freeze-thaw treatment preferably includes freezing and thawing performed sequentially.
The invention also provides a preparation method of the double-layer hydrogel material, which comprises the following steps:
when the stimulus responsive polymer is a natural high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer solution and a first cross-linking agent to obtain a pre-gel solution of a stimulus-responsive polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material;
when the stimulus responsive polymer is a synthetic high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus response polymer monomer, a second cross-linking agent and an initiator, and carrying out cross-linking to obtain a pre-gel solution of a stimulus response polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material.
In the present invention, all the starting materials for the preparation are commercially available products known to those skilled in the art unless otherwise specified.
In the present invention, when the stimulus-responsive polymer is a natural high molecular polymer:
the invention mixes polyvinyl alcohol solution, stimulus response polymer solution and cross linker to obtain stimulus response polymer and polyvinyl alcohol pre-gel solution.
In the present invention, the mass concentration of the polyvinyl alcohol solution is preferably 1 to 30%, more preferably 5 to 25%, and most preferably 10 to 20%. In the present invention, the polyvinyl alcohol solution is preferably an aqueous solution of polyvinyl alcohol.
In the invention, the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably 0.1-10%; when the stimulus-responsive polymer is chitosan, the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably 1-6%; when the stimulus-responsive polymer is sodium carboxymethylcellulose, the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably 0.1-10%.
In the present invention, when the stimulus-responsive polymer is chitosan, the stimulus-responsive polymer solution preferably includes chitosan, lithium hydroxide, potassium hydroxide, urea and water; the mass concentration of the chitosan in the stimulus response polymer solution is preferably 1-6%, more preferably 2-5%, and most preferably 3-4%; the mass ratio of the lithium hydroxide, the potassium hydroxide, the urea and the water is preferably 7.88:7:8: 77.12. In the present invention, the lithium hydroxide is preferably lithium hydroxide monohydrate. In the present invention, the lithium hydroxide and potassium hydroxide may break the hydrogen bonds between chitosan molecular chains; urea can reduce the crystallization of strong bases (lithium hydroxide and potassium hydroxide) at low temperatures and is used to disperse stimulus-responsive polymer molecular chains after hydrogen bond disruption.
In the invention, the mass ratio of the polyvinyl alcohol in the polyvinyl alcohol solution to the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably (0-3): 3, and the mass of the polyvinyl alcohol is not 0; more preferably (0.5-2): 3, most preferably (1-1.5): 3.
in the present invention, the first crosslinking agent preferably includes an epoxy group-containing crosslinking agent; the epoxy group-containing crosslinking agent preferably includes a monoepoxy group-containing crosslinking agent and/or a diepoxy group-containing crosslinking agent. The cross-linking agent containing the monoepoxy group is preferably epichlorohydrin; the crosslinking agent containing a diepoxy group is preferably polyethylene glycol diglycidyl ether. When the cross-linking agent is more than two of the above specific choices, the present invention does not have any special limitation on the proportion of the specific substances, and the specific substances can be mixed according to any proportion.
In the present invention, the epoxy group in the first crosslinking agent may be ring-opened under alkaline conditions and undergo nucleophilic ring-opening addition reaction with the amino group and the hydroxyl group in the polyvinyl alcohol and the stimulus-responsive polymer.
In the present invention, the ratio of the mass of the first crosslinking agent to the total mass of the stimulus-responsive polymer and the polyvinyl alcohol in the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol is preferably (0 to 2): 1, and the mass of the first cross-linking agent is not 0; more preferably (0.3 to 1.6): 1, most preferably (0.8 to 1.2): 1.
in the present invention, the temperature of the mixing is preferably 0 ℃. The mixing is preferably carried out under stirring; in the present invention, the stirring conditions are not particularly limited, and may be those well known to those skilled in the art.
In the present invention, the mixing is preferably performed by simultaneously dropping the polyvinyl alcohol solution and the first crosslinking agent into the stimulus-responsive polymer solution; the dropping process is not particularly limited, and may be carried out by a process known to those skilled in the art.
In the invention, when the stimulus-responsive polymer in the stimulus-responsive polymer solution is a synthetic high molecular polymer, the polyvinyl alcohol solution, the stimulus-responsive polymer monomer, the second cross-linking agent and the initiator are mixed to obtain the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol.
In a specific embodiment of the present invention, when the stimulus-responsive polymer is poly (N-isopropylacrylamide), the specific process for preparing the pre-gel solution of the stimulus-responsive polymer and polyvinyl alcohol described above is preferably: 0.6g of PVA was dissolved in 16.4ml of water and heated at high temperature to dissolve. After the solution was cooled, 3g of NIPAM monomer, 0.1g of N, N' -methylenebisacrylamide and 0.006g of Irgacure 2959 photoinitiator were added and dissolved for 90min with stirring on a magnetic stirrer.
In a specific embodiment of the present invention, when the stimulus-responsive polymer is poly [ 2- (N, N-dimethylamino) methacrylate ], the specific process for preparing the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol described above is preferably: 0.6g of PVA was dissolved in 16.4mL of water and heated at high temperature to dissolve. After the solution was cooled, 3g of 2- (N, N-dimethylamino) methacrylate monomer, 0.1g of N, N' -methylenebisacrylamide and 0.006g of Irgacure 2959 photoinitiator were added and dissolved for 90min with stirring on a magnetic stirrer.
After the pre-gel solution of the stimulus response polymer and the polyvinyl alcohol is obtained, the pre-gel solution of the stimulus response polymer and the polyvinyl alcohol is poured into a mould for crosslinking, and the prepared composite hydrogel is subjected to freeze-thaw treatment to obtain the composite hydrogel layer containing microcrystals.
When the stimulus responsive polymer is a natural high molecular polymer:
the method of the present invention preferably further comprises centrifuging the pre-gel solution of stimulus responsive polymer and polyvinyl alcohol before pouring the pre-gel solution of stimulus responsive polymer and polyvinyl alcohol into a mold for crosslinking. The conditions for the centrifugation in the present invention are not particularly limited, and the centrifugation may be carried out by using conditions known to those skilled in the art. In a specific embodiment of the present invention, the rotation speed of the centrifugation is specifically 5000r/min, and the time is specifically 5 min.
In the invention, the centrifugation can remove air bubbles in the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol, so that the structure and the mechanical property of the gel material are more uniform and stable.
The mold of the present invention is not particularly limited, and a mold known to those skilled in the art may be used. In a specific embodiment of the invention, the mold is a teflon border plate. In a specific embodiment of the present invention, the pre-gel solution of the stimuli-responsive polymer and polyvinyl alcohol is poured into a mold for crosslinking by stacking the polytetrafluoroethylene bezel sheet on the surface of the glass sheet and then pouring the pre-gel solution of the stimuli-responsive polymer and polyvinyl alcohol into the polytetrafluoroethylene bezel sheet.
In the invention, the crosslinking is preferably carried out under a standing condition, and the standing temperature is preferably 4-80 ℃, and more preferably 50 ℃; the standing time is preferably 0.1-12 h, and more preferably 4 h.
After the completion of the standing, the present invention preferably includes a process of removing the alkali. In the present invention, the alkali removing process is preferably to soak the hydrogel obtained after the standing is completed in water, and the water is continuously replaced during the soaking process until the alkali in the hydrogel is completely removed.
When the stimulus-responsive polymer is a synthetic high-molecular polymer, and the high-molecular polymer is poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ]:
in the present invention, the crosslinking is preferably performed under the conditions of ice-water bath and ultraviolet irradiation; the wavelength of the ultraviolet light irradiation is preferably 365nm, the power is preferably 85W, and the time is preferably 30 s.
In the present invention, the freeze-thaw treatment is preferably performed 1 to 10 times, more preferably 3 to 8 times, and most preferably 6 to 7 times. Each freeze-thaw treatment preferably includes freezing and thawing; the invention does not have any special limitation on the freezing and thawing temperature, and can achieve the purpose of freezing and thawing.
After the composite hydrogel layer containing the microcrystals is obtained, a mold is arranged on the upper surface of the composite hydrogel layer containing the microcrystals, the process of the composite hydrogel is repeated, and the composite hydrogel layer without the microcrystals is generated on the surface of the composite hydrogel layer containing the microcrystals, so that the double-layer hydrogel material is obtained.
The invention has no special limitation on the specific process of arranging the mould on the upper surface of the microcrystal-containing composite hydrogel layer, and the mould is arranged according to the actual requirement. In a specific embodiment of the present invention, the specific process of disposing a mold on the upper surface of the composite hydrogel layer containing microcrystals is preferably to stack a polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the above-mentioned process of preparing the composite hydrogel layer containing microcrystals.
In the present invention, the process for preparing the composite hydrogel layer containing no microcrystals preferably refers to the process for preparing the composite hydrogel layer containing microcrystals described above, except that the freeze-thaw treatment is not performed, and the specific preparation process is not described herein again.
After the composite hydrogel layer without the microcrystals is formed on the surface of the composite hydrogel layer with the microcrystals, the method also preferably comprises a template removing process, and the template removing process is not limited in any way and can be performed by a process well known to those skilled in the art.
The invention also provides an application of the double-layer hydrogel material in the technical scheme or the double-layer hydrogel material prepared by the preparation method in the technical scheme in the intelligent response field. In the invention, the intelligent response field is preferably the fields of bionics, intelligent valves, soft robots and biomedicines, and more preferably the field of soft robots. The method of the present invention is not particularly limited, and the method may be performed by a method known to those skilled in the art.
The following examples are provided to illustrate the present invention in detail, but should not be construed as limiting the scope of the present invention.
Example 1 (chitosan: PVA mass ratio of 3:1, crosslinking agent content of 2mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 2g (2mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 2 (weight ratio of chitosan to PVA of 3:0.5, crosslinking agent content of 1.75mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 1.9% and 1.75g (1.75mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 3 (chitosan: PVA mass ratio of 3:2, crosslinking agent content of 2.5mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 7.3% and 2.5g (2.5mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 4 (chitosan: PVA mass ratio of 3:3, crosslinker content of 3mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 10.3% and 3g (3mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 5 (chitosan: PVA mass ratio of 3:1, crosslinker content of 3mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 3g (3mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 6 (chitosan: PVA mass ratio of 3:1, crosslinker content of 4mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 4g (4mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 7 (chitosan: PVA mass ratio of 3:1, crosslinking agent content of 2.5mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 2.5g (2.5mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 8 (chitosan: PVA mass ratio of 3:1, crosslinker content of 1mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 1g (1mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 9 (weight ratio of chitosan to PVA 3:1, crosslinking agent content 1.5mL)
Dripping 35mL of PVA aqueous solution with the mass concentration of 3.8% and 1.5g (1.5mL) of epichlorohydrin into 100mL of chitosan solution with the mass concentration of 4% (the mass ratio of lithium hydroxide, potassium hydroxide, urea and water is 7.88:7:8:77.12), and carrying out the dripping process at 0 ℃ under the condition of stirring to obtain a pre-gel solution of chitosan and polyvinyl alcohol;
stacking the polytetrafluoroethylene frame plate on the surface of a glass plate according to the flow shown in the figure 1, centrifuging the pre-gel solution of chitosan and polyvinyl alcohol for 5min at the rotating speed of 5000r/min, pouring the solution into the polytetrafluoroethylene frame plate, standing overnight, soaking in distilled water, and continuously replacing the distilled water in the soaking process until alkali in the solution is completely removed to obtain a composite hydrogel layer (the thickness is 1mm) containing microcrystals;
the specific process of arranging the mold on the upper surface of the composite hydrogel layer containing the microcrystals is preferably to continuously stack a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing the microcrystals, repeat the process of the composite hydrogel, generate a composite hydrogel layer (with the thickness of 1mm) without microcrystals on the surface of the composite hydrogel layer containing the microcrystals, remove the template, and obtain the double-layer hydrogel material.
Example 10 (Poly (N-isopropylacrylamide) to PVA mass ratio 3:1)
0.6g of PVA was dissolved in 16.4mL of water and heated at high temperature to dissolve. After the solution was cooled, 3g of NIPAM monomer, 0.1g of N, N' -methylenebisacrylamide and 0.006g of Irgacure 2959 photoinitiator were added, stirred and dissolved for 90min on a magnetic stirrer, poured into a mold, and treated with ultraviolet light (365nm,85W) in an ice-water bath for 30 s. Freezing the treated hydrogel (without demoulding) in refrigerator for 4 times, thawing for the last time, adding a layer of mould on the original mould to form a double-layer mould, pouring the solution on the hydrogel after freeze thawing, and treating with ultraviolet light (365nm,85W) in ice bath for 3 min. After the treatment was completed, the bilayer hydrogel was peeled off from the mold, the bilayer hydrogel sheet was rinsed with deionized water, and then soaked in deionized water for 2 days with water change every day to remove impurities.
Example 11 (poly [ 2- (N, N-dimethylamino) methacrylate ] to PVA mass ratio 3:1)
0.6g of PVA was dissolved in 16.4mL of water and heated at high temperature to dissolve. After the solution was cooled, 3g of 2- (N, N-dimethylamino) methacrylate monomer, 0.1g of N, N' -methylenebisacrylamide and 0.006g of Irgacure 2959 photoinitiator were added, stirred and dissolved for 90min on a magnetic stirrer, poured into a mold, and treated with ultraviolet light (365nm,85W) in an ice-water bath for 30 s. Freezing the treated hydrogel (without demoulding) in refrigerator for 5 times, thawing for the last time, adding a layer of mould on the original mould to form a double-layer mould, pouring the solution on the hydrogel after freeze thawing, and treating with ultraviolet light (365nm,85W) in ice bath for 3 min. After the treatment was completed, the bilayer hydrogel was peeled off from the mold, the bilayer hydrogel sheet was rinsed with deionized water, and then soaked in deionized water for 2 days with water change every day to remove impurities.
Comparative example 1
The preparation process of the chitosan hydrogel comprises the following steps: LiOH, KOH, urea and H2And mixing the O according to the mass ratio of 7.88:7:8:77.12 to obtain the alkaline solvent. 4g of chitosan powder was dispersed in 100g of the alkaline solvent, stirred for 5min, frozen at-30 ℃ for 6h, and then thawed with stirring at room temperature. And centrifuging and defoaming the completely unfrozen solution at 6000rpm and 5 ℃ for 10min to obtain a clear and transparent chitosan alkaline solution. Then, adding 4mL of propylene oxide with an epoxy rate into the chitosan solution, stirring for 0.5h at 0 ℃, and then performing centrifugal deaeration for 10min at 6000rpm and 0 ℃ to obtain clear and transparent chitosan pregel liquid; pouring the chitosan pre-gel liquid into a mould, and placing the mould at room temperature for slow crosslinking to obtain the chitosan raw rubber. Subsequently, the chitosan "raw gel" is "cured" by immersion in deionized water until all residual solvent is removed to obtain a high strength chitosan gel.
Comparative example 2
Preparation of PVA samples: 12g of PVA powder was dissolved in 88g of deionized water and heated at 90 ℃ to complete dissolution; it was then freeze dried.
Test example
The chitosan hydrogel prepared in comparative example 1 (denoted as CS), the PVA sample prepared in comparative example 2, and the composite hydrogel layer containing microcrystals prepared in example 1 (denoted as FH-Gel) and the composite hydrogel layer containing no microcrystals ((CS))Recorded as H-Gel), the test result is shown in figure 2, and the PVA hydroxyl characteristic absorption band is 3297cm-1Here, the CS is added to move to 3322cm-1The band is widened, and the absorption band width of H-Gel is larger than that of FH-Gel; PVA at 2923cm-1The C-H stretching vibration absorption band is weakened due to the addition of CS, and shifts at FH-Gel and H-Gelc; C-H oscillatory vibration (833 cm) of PVA-1) The absorption band, which is attenuated by the addition of CS, moves to 842cm in FH-Gel-1In H-Gel to 846cm-1At least one of (1) and (b); the reason for the small difference of the absorption spectrograms generated by the FH-Gel and the H-Gel is that a microcrystalline region is generated after the FH-Gel is subjected to repeated freeze thawing operation;
XRD tests were carried out on the chitosan hydrogel (denoted as CS) prepared in comparative example 1, the PVA hydrogel (denoted as PVA) prepared in comparative example 2, the composite hydrogel layer containing microcrystals (denoted as FH-Gel) prepared in example 1 and the composite hydrogel layer containing no microcrystals (denoted as H-Gel), and the results are shown in FIG. 3, from which it can be seen that the PVA has distinct crystal peaks at 2 theta of 11.7 DEG, 19.7 DEG, 40.9 DEG and 44.5 DEG; the XRD spectrum of CS shows a strong peak at about 20 degrees 2 theta due to the presence of a large amount of-OH and-NH groups in the chitosan structure2The groups can form stronger intermolecular and intramolecular hydrogen bonds, and the chitosan structure has certain regularity, so that the molecules can easily form a crystalline region. The peak values of chitosan around 20 ° in FH-Gel and H-Gel became weaker, representing a strong interaction between chitosan and PVA, and chitosan crystallinity decreased. Thus, both the XRD results and the FTIR results demonstrate that some interaction between chitosan and PVA occurs. In addition, the peak value of FH-Gel at about 20 degrees 2 theta is higher than that of H-Gel, indicating that PVA forms a microcrystalline region after being frozen;
the composite hydrogel layer containing microcrystals prepared in example 1 (denoted as FH-Gel) and the composite hydrogel layer without microcrystals (denoted as H-Gel) were subjected to 3D-raman spectroscopy, and the test results are shown in fig. 4 and 5, and the ratio of the region of microcrystals in H-Gel and FH-Gel was evaluated by Multivariate Curve Resolution (MCR), as shown in the inset diagrams of fig. 4 and 5, in turn, where fig. 4 is the depicted diagramA 3D-Raman spectrum of H-Gel, FIG. 5 is a 3D-Raman spectrum of FH-Gel; as can be seen from FIGS. 4 to 5, the reconstructed Raman images showed tensile strengths in blue and red (3000 to 3400 cm)-1). 3234cm in the blue Spectrum-1The apparent intensity of (a) is from OH-rich regions (crystallite regions), while the corresponding peak in the red spectrum corresponds to regions lacking OH (chemically cross-linked domains). The microcrystalline region in FH-Gel was approximately 35.87% in area;
the double-layer hydrogel material prepared in example 1 is stretched, and the test result is shown in fig. 6, and as can be seen from fig. 6, the double-layer hydrogel material prepared in example 1 has a tensile breaking stress of 61.53KPa, a tensile breaking strain of 216.22%, and has good toughness and tensile properties;
the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals, which are prepared in example 1, are subjected to a swelling performance test, the test process is that the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals are respectively placed in hydrochloric acid aqueous solutions with the pH values of 2 and 7 to be swelled and balanced, and the test result is shown in fig. 7, wherein an H-Gel curve in fig. 7 corresponds to the composite hydrogel layer containing no microcrystals (denoted as H-Gel), and an FH-Gel curve corresponds to the composite hydrogel layer containing microcrystals, which is prepared in example 1, and it can be seen from fig. 7 that the larger the ratio of chitosan to PVA is, the larger the difference between the swelling degrees of the frozen hydrogel and the unfrozen hydrogel is;
the double-layer hydrogel materials prepared in examples 1 to 4 were subjected to sensitivity testing, in which the double-layer hydrogel was placed in an aqueous hydrochloric acid solution with pH 2, and the test results are shown in fig. 8, and as can be seen from fig. 8, under the same pH conditions and at the same time, when the chitosan: the bending of the bilayer hydrogel was most pronounced when PVA was 3:1 (corresponding to example 1), and the time for the bilayer hydrogel to bend to the same angle gradually increased as the ratio increased. This is probably because as the PVA ratio increases, the concentration of chitosan within the CS/PVA hydrogel is diluted resulting in a slower response to pH. And the ratio of chitosan: the bending of PVA is less than that of PVA at 3:0.5, probably because the hydrogel frozen layer has microcrystalline areas, and the swelling of the unfrozen layer cannot offset the swelling of the frozen layer, so that the response is slow;
carrying out sensitivity test on the double-layer hydrogel material prepared in the embodiment 1 under the condition of different pH values, wherein the test process is to place the double-layer hydrogel in hydrochloric acid aqueous solutions with different pH values; the test result is shown in fig. 9, where a is a response curve of the double-layer hydrogel material to different phs, b is a physical graph of the double-layer hydrogel material at different bending degrees at different times under the condition that the pH is 2, and c is an SEM graph of the double-layer hydrogel material after swelling under the condition that the pH is 2 (the three graphs are, in order from left to right, a morphology of a composite hydrogel without crystallites, a morphology of a bonding interface of the double-layer hydrogel, and a morphology of a composite hydrogel with crystallites); as can be seen from a in fig. 9, the bending angle of the bilayer hydrogel is most pronounced at pH 2 and, secondly, at pH 3, the bending angle is not pronounced at pH 4 or 5 at the same time; when the double-layer hydrogel is bent at the same angle, the double-layer hydrogel takes the shortest time when the pH value is 2, and the pH value is 3 times; as can be seen from b in fig. 9, the longer the time, the greater the completeness; as can be seen from c in FIG. 9, after swelling of the double-layer hydrogel material, the composite hydrogel layer without crystallites becomes larger due to the moisture entering the voids, and the composite hydrogel layer with crystallites has a more compact structure due to the existence of crystallite regions.
The composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals, which were prepared in example 5, were subjected to a swelling performance test, which was carried out: the composite hydrogel layer containing microcrystals and the composite hydrogel layer not containing microcrystals are placed in a hydrochloric acid aqueous solution with the pH value of 2 for swelling balance, and the test result is shown in fig. 10, wherein a Treated Gel curve in fig. 10 corresponds to the composite hydrogel layer containing microcrystals, an N-Treated Gel curve corresponds to the composite hydrogel layer not containing microcrystals, and an inter Gel curve corresponds to the composite hydrogel layer containing microcrystals, and it can be known from fig. 10 that the higher the content of the cross-linking agent is, the larger the difference between the swelling degrees of the composite hydrogel layer containing microcrystals and the composite hydrogel layer not containing microcrystals is.
The PNIPAM/PVA composite hydrogel layer containing microcrystals (denoted as FH-Gel) and the composite hydrogel layer containing no microcrystals (denoted as H-Gel) prepared in example 10 were respectively subjected to swelling equilibrium in aqueous solutions at T ═ 5 ℃ and T ═ 50 ℃, the Gel mass was measured, the deswelling rate of the Gel was calculated, and the test results are shown in fig. 13, in which the swelling properties of the composite hydrogel layers all showed similar trends with the change in the ratio of chitosan to PVA, and the deswelling rate of the unfrozen hydrogel when heated was greater than that of the hydrogel layer after freezing treatment.
Application example
Referring to the preparation process of example 5, a double-layer hydrogel material (shown in a matter of a2 to e2 in fig. 11) with the structure shown in a1 to e1 in fig. 11 was obtained by adjusting the structure of the template, and a swelling performance test was performed under the condition of pH 2, and the test results are shown in a3 to e3 in fig. 11, as can be seen from fig. 11, a multi-node complete hydrogel can be prepared by geometric design;
referring to the preparation process of example 5, a bionic manipulator (four-arm double-layer hydrogel) capable of grasping a weight was simulated in an "X" crossing manner, fixed to the bottom end of a nail, and then immersed in an acidic aqueous solution having a pH of 2 and suspended over the upper end of a spherical weight, and the bionic manipulator completely grasped the weight rapidly downward due to rapid swelling of the composite hydrogel layer containing no microcrystals as shown in fig. 12, lifted and removed from the medium, which was completed within 2 min. And then, placing the bionic manipulator in an alkaline medium, and recovering the original shape of the bionic manipulator to release the heavy object. It follows that such a robot with a rapid response deformation can only perform simple mechanical work in a harsh acidic medium.
From the above, after being subjected to freeze thawing, PVA can form a microcrystalline region which can effectively absorb energy and bear large deformation, so that the swelling degree of the prepared composite hydrogel layer containing the microcrystalline region is smaller than that of the composite hydrogel layer not containing the microcrystalline region, and the composite hydrogel layer can show a rapid and reversible deformation behavior under pH induction, and has stable cycle reversibility and excellent mechanical properties. Meanwhile, a series of complicated 3D structural hydrogels, such as annular, S-shaped, multi-section, spiral or flower type hydrogels, can be constructed by using the deformation behavior driven by the double-layer hydrogel, and can be deformed within 3-6 min. In addition, an intelligent hydrogel driver is constructed by combining with a geometric design, namely a double-layer hydrogel material simulating a bionic manipulator capable of grabbing heavy objects in an X-shaped cross mode. Therefore, the construction of introducing the microcrystalline region into the double-layer hydrogel is feasible, and the self-deforming hydrogel based on the natural macromolecules has wide application prospect in the field of soft robots.
The double-layer PNIPAM/PVA hydrogel strip prepared in example 10 was subjected to a deformation test in a 50 ℃ aqueous solution, as shown in FIG. 14, and was able to rapidly undergo bending deformation within 20 seconds. Therefore, the double-layer hydrogel with rapid response deformation has wider application prospect in the field of ultra-sensitive gel drivers.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A double-layer hydrogel material is characterized by comprising a composite hydrogel layer containing microcrystals and a composite hydrogel layer without microcrystals which are sequentially laminated;
the composite hydrogel in the composite hydrogel layer containing the microcrystals and the composite hydrogel layer without the microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogels; and the polyvinyl alcohol-stimulus responsive polymer composite hydrogel does not comprise nanoparticles;
the microcrystals in the composite hydrogel layer containing microcrystals are polyvinyl alcohol microcrystals;
the composite hydrogel layer containing microcrystals is subjected to freeze-thawing treatment.
2. The bilayer hydrogel material of claim 1, wherein the mass ratio of polyvinyl alcohol to stimulus responsive polymer in the composite hydrogel layer with crystallites and the composite hydrogel layer without crystallites is independently (0-3: 3;
and the mass of the polyvinyl alcohol is not 0.
3. The bilayer hydrogel material of claim 1, wherein the stimuli-responsive polymer in the polyvinyl alcohol-stimuli-responsive polymer composite hydrogel comprises a pH-responsive polymer or a temperature-responsive polymer.
4. The bilayer hydrogel material of claim 3, wherein the pH responsive polymer is sodium carboxymethylcellulose, chitosan, or poly [ 2- (N, N-dimethylamino) methacrylate ].
5. The bilayer hydrogel material of claim 3 or 4, wherein the temperature responsive polymer is poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ].
6. The method for preparing the double-layer hydrogel material according to any one of claims 1 to 5, comprising the following steps:
when the stimulus responsive polymer is a natural high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer solution and a first cross-linking agent to obtain a pre-gel solution of a stimulus-responsive polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material;
when the stimulus responsive polymer is a synthetic high molecular polymer:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer monomer, a second cross-linking agent and an initiator to obtain a pre-gel solution of a stimulus-responsive polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus response polymer and polyvinyl alcohol into a mould for crosslinking, and performing freeze-thaw treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a mould on the upper surface of the composite hydrogel layer containing the microcrystals, repeating the preparation process of the composite hydrogel, and generating the composite hydrogel layer without the microcrystals on the surface of the composite hydrogel layer containing the microcrystals to obtain the double-layer hydrogel material.
7. The method according to claim 6, wherein when the stimulus-responsive polymer is a natural high molecular polymer:
the mass concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1-30%;
the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is 0.1-10%.
8. The production method according to claim 6 or 7, wherein when the stimulus-responsive polymer is a natural high molecular polymer:
the mass ratio of the polyvinyl alcohol in the polyvinyl alcohol solution to the stimulus-responsive polymer in the stimulus-responsive polymer solution is (0-3): 3;
and the mass of the polyvinyl alcohol is not 0.
9. The method according to claim 6, wherein the number of times of the freeze-thaw treatment is 1 to 10 times.
10. Use of the double-layer hydrogel material according to any one of claims 1 to 5 or the double-layer hydrogel material prepared by the preparation method according to any one of claims 6 to 9 in the field of intelligent response.
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