CN113683820B - 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 abundant hydroxyl groups, which is favorable for the formation of hydrogen bonds, and a composite hydrogel layer containing microcrystals is formed in situ in the process of carrying out freeze thawing treatment on the PVA; the microcrystalline regions in the microcrystalline-containing composite hydrogel layer may promote an increase in the density, strength, and thermal stability properties of the composite hydrogel, thereby improving the properties of the composite hydrogel; meanwhile, the swelling behavior of the composite hydrogel can be changed, so that the composite hydrogel layer containing microcrystals and the composite hydrogel layer not containing microcrystals have different swelling behaviors, 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
The intelligent hydrogel driver is an intelligent response device which can reversibly acquire/lose water molecules under the stimulation action so as to change the breeding shape or volume, and has potential application in the fields of bionics, intelligent valves, soft robots, biological medicines and the like. Generally, the method of constructing a gel driver mainly comprises the steps of introducing a bilayer structure, a gradient structure and a pattern structure in the gel, wherein the bilayer structure, the gradient structure and the pattern structure are oriented, so that the gel is induced to generate anisotropic swelling and driving actions. Among the numerous methods, the construction of double-layer structured hydrogels is one of the most common, and three main ways are currently involved in order to achieve intelligent response behavior: firstly, different contents of nano particles (clay, carbon nano tube or silicon dioxide and the like) or cellulose microcrystals are introduced into a two-layer gel structure, and a component has a double-layer structure with different swelling and response sensitivity to realize the construction of a driver: for example, the Liangyin group of subjects (Poly (N-isopropyranylamide) -clay nanocomposite hydrogels with responsive bending property as temperature-controlled mangers.adv. Funct. Mater.2015,25, 2980-2991.) developed a series of Poly (N-isopropylacrylamide) -clay nanocomposite hydrogels as temperature sensitive drives, clay nanocomposites The sheet is introduced into the hydrogel, so that the sheet can be used as a physical cross-linking agent to improve the mechanical strength of the hydrogel, and can be used for adjusting the thermal shrinkage rate of the hydrogel, and the driving behavior of the gel is realized by adjusting and controlling the content of clay in the double-layer structure of the hydrogel. Second, polymer chains with different response behaviors and functions can be used as bilayers to build hydrogel actuators: zhang Lina et al (Bilayer hydrogel actuators with tight interfacial adhesion fully constructed from natural polysacharides. Soft Matter 2017,13,345-354.) developed an intelligent two-layer hydrogel actuator consisting of chitosan and cellulose/carboxymethyl cellulose, the chitosan layer having a different pH responsiveness than the cellulose/carboxymethyl cellulose composite layer, ionization of carboxyl groups in the cellulose/carboxymethyl cellulose layer (pH>3.8 Protonation of the amino groups in the chitosan layer (pH)<3.8 Forcing it to deform under different pH conditions, such as S-shape, spiral shape, tubular shape, bamboo shape, wavy shape and flower shape; huang's group of topics (Polyelectrolyte and Antipolyelectrolyte Effects for Dual Salt-Responsive Interpenetrating Network Hydrogels. Biomacromolecules 2019,20,3524-3534) constructed a salt-responsive interpenetrating network (IPN) hydrogel composed of cationic pTMAEMA layer and amphoteric pSBVI layer in saline solution, the two polymer networks exhibiting opposite swelling behavior due to polyelectrolyte and anti-polyelectrolyte effects, and the prepared hydrogels exhibited a range of reversible regulatory properties including structure, antibacterial properties, and interfacial regeneration. Third, a gel driver of Janus bilayer structure was constructed by varying the crosslink density in the bilayer structure: for example, in Fe 3+ In the presence of PAAC/Clay hydrogel with overlarge crosslinking density, the swelling degree is lower, the modulus is higher, and the PAAC/Clay layer is combined with Fe 3+ -PAAC/class layer combination, a dual layer drive can be built.
With the development of software drivers, more strategies and design ideas are required to build a dual-layer structure.
Disclosure of Invention
The invention aims at providing a double-layer hydrogel material, a preparation method and application thereof, wherein the double-layer hydrogel material comprises a compound hydrogel layer containing microcrystals and a compound hydrogel layer without microcrystals, and the double-layer hydrogel material is constructed by utilizing different swelling behaviors of the compound hydrogel layer containing microcrystals and the compound 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 laminated;
the composite hydrogel in the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogel; and no nanoparticles are included in the polyvinyl alcohol-stimulus responsive polymer composite hydrogel;
The microcrystals in the microcrystal-containing composite hydrogel layer are polyvinyl alcohol microcrystals;
the microcrystal-containing composite hydrogel layer is subjected to freeze thawing treatment.
Preferably, the mass ratio of polyvinyl alcohol to stimulus-responsive polymer in the microcrystal-containing composite hydrogel layer and the microcrystal-free composite hydrogel layer is independently (0 to 3): 3;
and the mass of the polyvinyl alcohol is not 0.
Preferably, the stimulus-responsive polymer in the polyvinyl alcohol-stimulus-responsive polymer composite hydrogel comprises a pH-responsive polymer or a temperature-responsive polymer.
Preferably, the pH-responsive polymer is sodium carboxymethyl cellulose, 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 stimulus-responsive polymer and polyvinyl alcohol;
Pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer 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 crosslinking agent and an initiator, and crosslinking to obtain a pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol;
pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer to obtain the double-layer hydrogel material.
Preferably, when the stimulus responsive polymer is a natural high molecular polymer:
the mass concentration of the 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, a step of;
and the mass of the polyvinyl alcohol is not 0.
Preferably, the number of times of the freeze thawing treatment is 1 to 10.
The invention also provides the application of the double-layer hydrogel material prepared by the technical scheme or the preparation method of the double-layer hydrogel material in the intelligent response field.
The invention also provides the application of the double-layer hydrogel material prepared by the technical scheme or the preparation method of the double-layer hydrogel material 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 laminated; the composite hydrogel in the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogel; and no nanoparticles are included in the polyvinyl alcohol-stimulus responsive polymer composite hydrogel; the microcrystals in the microcrystal-containing composite hydrogel layer are polyvinyl alcohol microcrystals; the microcrystal-containing composite hydrogel layer is subjected to freeze thawing treatment. The polyvinyl alcohol (PVA) in the double-layer hydrogel material is a biologically extremely friendly polymer, a molecular chain contains abundant hydroxyl groups, hydrogen bonds are formed easily, ice crystals formed in situ can squeeze the PVA chain in the process of freeze thawing treatment of the double-layer hydrogel material to form a local high-concentration area, and adjacent molecular weights further form a microcrystalline area through intermolecular/intramolecular hydrogen bond action to form a compound hydrogel layer containing microcrystals; the microcrystalline regions in the microcrystalline-containing composite hydrogel layer may promote an increase in the density, strength, and thermal stability properties of the composite hydrogel, thereby improving the properties of the composite hydrogel; meanwhile, the swelling behavior of the composite hydrogel can be changed, so that the composite hydrogel layer containing microcrystals and the composite hydrogel layer not containing microcrystals have different swelling behaviors, and the double-layer hydrogel material is constructed by utilizing the different swelling behaviors.
Drawings
FIG. 1 is a schematic illustration of the preparation flow of examples 1-9 for preparing a bilayer hydrogel material;
FIG. 2 is an infrared spectrum 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 containing no crystallites prepared in example 1;
FIG. 3 is an XRD pattern 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 containing no crystallites prepared in example 1;
FIG. 4 is a 3D-Raman spectrum of the composite hydrogel layer without crystallites prepared in example 1;
FIG. 5 is a 3D-Raman spectrum of the microcrystal-containing composite hydrogel layer prepared in example 1;
FIG. 6 is a graph showing the tensile-stress strain curves of the bilayer hydrogel material prepared in example 1;
FIG. 7 is a graph showing swelling performance curves of the composite hydrogel layer containing crystallites and the composite hydrogel layer containing no crystallites prepared in example 1;
FIG. 8 is a graph showing the swelling properties of the bilayer hydrogel materials prepared in examples 1 to 4 over time;
fig. 9 is a sensitivity of the bilayer hydrogel material prepared in example 1 under different pH conditions, wherein a is a response curve of the bilayer hydrogel material to different pH, b is a full-scale physical image of the bilayer hydrogel material under the condition of ph=2, and c is an SEM image of the bilayer hydrogel material after swelling under the condition of ph=2;
FIG. 10 is a graph showing the swelling properties of the composite hydrogel layer containing crystallites and the composite hydrogel layer containing no crystallites prepared in example 5;
fig. 11 is a schematic structural diagram and a physical diagram of a double-layer driver with different structures before and after swelling in a hydrochloric acid solution with ph=2;
fig. 12 is a process of capturing an object in an acidic solution with ph=2 by using the bionic robot according to the application example;
FIG. 13 is a plot of the deswelling performance of the microcrystalline containing and microcrystalline free composite hydrogel layers prepared in example 10 as a function of the mass ratio of poly (N-isopropylacrylamide) to PVA;
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 t=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 laminated;
the composite hydrogel in the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogel; and no nanoparticles are included in the polyvinyl alcohol-stimulus responsive polymer composite hydrogel;
The microcrystals in the microcrystal-containing composite hydrogel layer are polyvinyl alcohol microcrystals;
the microcrystal-containing composite hydrogel layer is subjected to freeze thawing treatment.
In the present invention, the mass ratio of the polyvinyl alcohol and the stimulus-responsive polymer in the microcrystal-containing composite hydrogel layer and the microcrystal-free composite hydrogel layer is independently preferably (0 to 3): 3, and the mass of the polyvinyl alcohol is not 0; more preferably (0.5 to 2): 3, most preferably (1 to 1.5): 3.
in the present invention, the thickness of the microcrystal-containing composite hydrogel layer is preferably 0 to 10mm, more preferably 0.5 to 4mm, and most preferably 1mm, and the thickness of the microcrystal-containing composite hydrogel layer is not 0.
In the present invention, the thickness of the microcrystal-free composite hydrogel layer is preferably 0 to 10mm, more preferably 0.5 to 4mm, and most preferably 1mm, and the thickness of the microcrystal-free composite hydrogel layer 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 carboxymethyl cellulose, 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 without microcrystals; the freezing and thawing 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 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 stimulus-responsive polymer and polyvinyl alcohol;
pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer 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 crosslinking agent and an initiator, and crosslinking to obtain a pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol;
pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer to obtain the double-layer hydrogel material.
In the present invention, all the preparation materials are commercially available products well known to those skilled in the art unless specified otherwise.
In the present invention, when the stimulus responsive polymer is a natural high molecular polymer:
the invention mixes the polyvinyl alcohol solution, the stimulus-responsive polymer solution and the cross-linking agent to obtain the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol.
In the present invention, the polyvinyl alcohol solution preferably has a mass concentration of 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 present invention, the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably 0.1 to 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 to 6%; when the stimulus-responsive polymer is sodium carboxymethyl cellulose, the mass concentration of the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably 0.1 to 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 chitosan in the stimulus-responsive polymer solution is preferably 1 to 6%, more preferably 2 to 5%, most preferably 3 to 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 can break hydrogen bonds between chitosan molecular chains; urea can reduce crystallization of strong bases (lithium hydroxide and potassium hydroxide) at low temperature and is used to disperse the stimulus-responsive polymer molecular chains after hydrogen bond destruction.
In the present invention, the mass ratio of the polyvinyl alcohol in the polyvinyl alcohol solution and the stimulus-responsive polymer in the stimulus-responsive polymer solution is preferably (0 to 3): 3, and the mass of the polyvinyl alcohol is not 0; more preferably (0.5 to 2): 3, most preferably (1 to 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 mono-epoxy group-containing crosslinking agent and/or a di-epoxy group-containing crosslinking agent. The crosslinking agent containing the monoepoxy group is preferably epichlorohydrin; the cross-linking agent containing double epoxy groups is preferably polyethylene glycol diglycidyl ether. When the crosslinking agent is two or more of the above specific choices, the present invention does not particularly limit the ratio of the above specific substances, and the above specific substances may be mixed in any ratio.
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 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 pregelatinized solution of the stimulus-responsive polymer and the polyvinyl alcohol is preferably (0 to 2): 1, and the mass of the first crosslinking 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; the stirring conditions are not particularly limited, and may be carried out under conditions 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 process of the dropping is not particularly limited, and may be performed by a process well 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 invention mixes the polyvinyl alcohol solution, the stimulus-responsive polymer monomer, the second crosslinking agent and the initiator 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 pregel 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 to a high temperature. After the solution had cooled, 3g of NIPAM monomer, 0.1g of N, N' -methylenebisacrylamide and 0.006g of Irgacure 2959 photoinitiator were added and dissolved by stirring on a magnetic stirrer for 90min.
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 pregel solution of stimulus-responsive polymer and polyvinyl alcohol described above is preferably: 0.6g of PVA was dissolved in 16.4mL of water and heated to high temperature. After the solution had 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 by stirring on a magnetic stirrer for 90min.
After the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol is obtained, the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol is poured into a mould to be crosslinked, and the prepared composite hydrogel is subjected to freeze thawing treatment to obtain the composite hydrogel layer containing microcrystals.
When the stimulus responsive polymer is a natural high molecular polymer:
the present invention preferably further comprises centrifuging the pre-gel solution of the stimulus-responsive polymer and polyvinyl alcohol before pouring the pre-gel solution of the stimulus-responsive polymer and polyvinyl alcohol into the mold for crosslinking. The conditions for the centrifugation are not particularly limited, and may be any conditions known to those skilled in the art. In a specific embodiment of the invention, the rotation speed of the centrifugation is 5000r/min, and the time is 5min.
In the invention, the centrifugation can remove bubbles in the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol, so that the structure and mechanical properties of the gel material are more uniform and stable.
The present invention is not particularly limited to the above-mentioned mold, and a mold well known to those skilled in the art may be used. In a specific embodiment of the invention, the mold is a polytetrafluoroethylene frame plate. In a specific embodiment of the present invention, the specific process of pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into the mold for crosslinking is to pour the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into the polytetrafluoroethylene frame plate after stacking the polytetrafluoroethylene frame plate on the surface of the glass plate.
In the present invention, the crosslinking is preferably performed under a standing condition, the temperature of the standing is preferably 4 to 80 ℃, more preferably 50 ℃; the time for the standing is preferably 0.1 to 12 hours, more preferably 4 hours.
After the completion of the standing, the present invention preferably includes a process of removing alkali. In the present invention, the alkali removal process is preferably to soak the hydrogel obtained after the completion of the standing in water, and to continuously change the water 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 irradiation is preferably 365nm, the power is preferably 85W, and the time is preferably 30s.
In the present invention, the freezing and thawing treatment is preferably performed 1 to 10 times, more preferably 3 to 8 times, and most preferably 6 to 7 times. Each freeze-thawing treatment preferably comprises freezing and thawing; the invention is not limited in any particular way to the freezing and thawing temperature, and the purposes of freezing and thawing can be achieved.
After the composite hydrogel layer containing the microcrystals is obtained, a die is arranged on the upper surface of the composite hydrogel layer containing the microcrystals, the process of the composite hydrogel is repeated, and a composite hydrogel layer without the microcrystals is formed on the surface of the composite hydrogel layer containing the microcrystals, so that the double-layer hydrogel material is obtained.
The invention does not have any special limitation on the specific process of arranging the die on the upper surface of the microcrystal-containing composite hydrogel layer, and the die can be arranged according to actual needs. In a specific embodiment of the present invention, the specific process of disposing the mold on the upper surface of the composite hydrogel layer containing microcrystals is preferably to continuously laminate a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the composite hydrogel layer containing microcrystals.
In the present invention, the process of preparing the composite hydrogel layer without microcrystals is preferably referred to the above process of preparing the composite hydrogel layer with microcrystals except that the freeze thawing treatment is not performed, and the specific preparation process is not described herein.
After the surface of the microcrystal-containing composite hydrogel layer is formed into the microcrystal-free composite hydrogel layer, 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 adopting a process well known to a person skilled in the art.
The invention also provides the application of the double-layer hydrogel material prepared by the technical scheme or the preparation method of the double-layer hydrogel material in the intelligent response field. In the present invention, the intelligent response field is preferably a bionic field, an intelligent valve field, a soft robot field, and a biomedical field, and more preferably a soft robot field. The method of the present invention is not particularly limited, and may be carried out by methods known to those skilled in the art.
The double-layer hydrogel materials, the preparation method and application thereof provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1 (Chitosan: PVA: mass ratio of 3:1, crosslinker content of 2 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 2g (2 mL) of epichlorohydrin are added into 100mL of chitosan solution with the mass concentration of 4% (lithium hydroxide, potassium hydroxide, urea and water in a mass ratio of 7.88:7:8:77.12) in a dropwise manner, and the dropwise addition process is carried out at the temperature of 0 ℃ under the condition of stirring, so as to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 2 (Chitosan: PVA: mass ratio of 3:0.5, crosslinker content of 1.75 mL)
35mL of PVA water solution with the mass concentration of 1.9% and 1.75g (1.75 mL) of epichlorohydrin are added dropwise to 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 the dropwise addition process is carried out under the condition of stirring at 0 ℃ to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 3 (mass ratio of chitosan: PVA: 3:2, crosslinker content 2.5 mL)
35mL of PVA water solution with the mass concentration of 7.3% and 2.5g (2.5 mL) of epichlorohydrin are added dropwise to 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 the dropwise addition process is carried out under the condition of stirring at 0 ℃ to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 4 (Chitosan: PVA: 3:3 by mass, crosslinker content 3 mL)
35mL of PVA water solution with the mass concentration of 10.3% and 3g (3 mL) of epichlorohydrin are added into 100mL of chitosan solution with the mass concentration of 4% (lithium hydroxide, potassium hydroxide, urea and water in a mass ratio of 7.88:7:8:77.12) in a dropwise manner, and the dropwise addition process is carried out at the temperature of 0 ℃ under the condition of stirring, so as to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 5 (mass ratio of chitosan: PVA: 3:1, crosslinker content 3 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 3g (3 mL) of epichlorohydrin are added into 100mL of chitosan solution with the mass concentration of 4% (lithium hydroxide, potassium hydroxide, urea and water in a mass ratio of 7.88:7:8:77.12) in a dropwise manner, and the dropwise addition process is carried out at the temperature of 0 ℃ under the condition of stirring, so as to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 6 (Chitosan: PVA: mass ratio of 3:1, crosslinker content of 4 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 4g (4 mL) of epichlorohydrin are added into 100mL of chitosan solution with the mass concentration of 4% (lithium hydroxide, potassium hydroxide, urea and water in a mass ratio of 7.88:7:8:77.12) in a dropwise manner, and the dropwise addition process is carried out at the temperature of 0 ℃ under the condition of stirring, so as to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 7 (mass ratio of chitosan: PVA: 3:1, crosslinker content 2.5 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 2.5g (2.5 mL) of epichlorohydrin are added dropwise to 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 the dropwise addition process is carried out under the condition of stirring at 0 ℃ to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 8 (Chitosan: PVA mass ratio of 3:1, crosslinker content of 1 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 1g (1 mL) of epichlorohydrin are added 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) in a dropwise manner, and the dropwise addition process is carried out under the condition of 0 ℃ and stirring, so as to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 9 (Chitosan: PVA: 3:1 by mass, crosslinker content 1.5 mL)
35mL of PVA water solution with the mass concentration of 3.8% and 1.5g (1.5 mL) of epichlorohydrin are added dropwise to 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 the dropwise addition process is carried out under the condition of stirring at 0 ℃ to obtain a pregelatinized solution of chitosan and polyvinyl alcohol;
according to the flow shown in fig. 1, after stacking the polytetrafluoroethylene frame plates on the surface of a glass plate, centrifuging the pregelatinized solution of chitosan and polyvinyl alcohol for 5min at a rotation speed of 5000r/min, pouring the pregelatinized solution into the polytetrafluoroethylene frame plates, standing overnight, soaking in distilled water, and continuously replacing the distilled water until alkali in the distilled water is completely removed in the soaking process to obtain a composite hydrogel layer (with a thickness of 1 mm) containing microcrystals;
the specific process of setting the die on the upper surface of the microcrystal-containing composite hydrogel layer is preferably to continuously laminate and place a layer of polytetrafluoroethylene frame plate on the polytetrafluoroethylene frame plate in the process of preparing the microcrystal-containing composite hydrogel layer, repeat the process of the composite hydrogel, generate a microcrystal-free composite hydrogel layer (with the thickness of 1 mm) on the surface of the microcrystal-containing composite hydrogel layer, and remove the template to obtain the double-layer hydrogel material.
Example 10 (Poly (N-isopropylacrylamide) to PVA mass ratio of 3:1)
0.6g of PVA was dissolved in 16.4mL of water and heated to high temperature. After the solution 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 (365 nm, 85W) under an ice-water bath for 30s. Repeatedly freezing the treated hydrogel (without demoulding) in a 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 subjected to freeze thawing treatment, and treating with ultraviolet light (365 nm, 85W) under ice bath for 3min. 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 immersed in deionized water for 2 days, with water changed every day to remove impurities.
Example 11 (Poly [ 2- (N, N-dimethylamino) methacrylate ] to PVA mass ratio of 3:1)
0.6g of PVA was dissolved in 16.4mL of water and heated to high temperature. 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 on a magnetic stirrer for 90min, then poured into a mold, and treated with ultraviolet light (365 nm, 85W) under an ice-water bath for 30s. Repeatedly freezing the treated hydrogel (without demoulding) in a 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 subjected to freeze thawing treatment, and treating with ultraviolet light (365 nm, 85W) under ice bath for 3min. 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 immersed in deionized water for 2 days, with water changed every day to remove impurities.
Comparative example 1
The preparation process of the chitosan hydrogel comprises the following steps: liOH, KOH, urea, and H 2 O is mixed 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 and stirred for 5min, frozen at-30℃for 6h, and then thawed with stirring at room temperature. Centrifuging and defoaming the completely thawed solution at 6000rpm and 5 ℃ for 10min to obtain clarified solutionTransparent chitosan alkaline solution. Then, adding 4mL of epoxy propane into the chitosan solution, stirring for 0.5h at 0 ℃, and then centrifugally defoaming for 10min at 6000rpm and 0 ℃ to obtain a clear and transparent chitosan pregelatinized solution; pouring the chitosan pregelatinized solution into a mould, and slowly crosslinking at room temperature to obtain the chitosan raw rubber. Subsequently, the chitosan raw rubber is immersed in deionized water for curing until all residual solvents are removed completely, and the high-strength chitosan gel is obtained.
Comparative example 2
Preparation process of PVA sample: 12g of PVA powder was dissolved in 88g of deionized water, which was heated to complete dissolution at 90 ℃; it was then freeze-dried.
Test case
The chitosan hydrogel (denoted as CS) prepared in comparative example 1, the PVA sample prepared in comparative example 2, and the microcrystal-containing composite hydrogel layer (denoted as FH-Gel) and the microcrystal-free composite hydrogel layer (denoted as H-Gel) prepared in example 1 were subjected to infrared spectroscopic test, the test results are shown in FIG. 2, and the absorption band of the PVA hydroxyl group characteristic is 3297cm as can be seen from FIG. 2 -1 Where the CS addition was moved to 3322cm -1 The band is widened, and the absorption band width of H-Gel is larger than that of FH-Gel; PVA at 2923cm -1 The C-H stretching vibration absorption band at the position is weakened due to the addition of CS, and the positions of FH-Gel and H-Gelc are deviated; C-H rocking vibration of PVA (833 cm) -1 ) The absorption band was reduced by CS addition and shifted to 842cm in FH-Gel -1 Where it is moved to 846cm in H-Gel -1 A place; the reason for the small difference between the absorption spectra generated by FH-Gel and H-Gel is that the FH-Gel generates a microcrystalline region after repeated freeze thawing operation;
XRD tests were performed on the chitosan hydrogel (denoted CS) prepared in comparative example 1, the PVA hydrogel (denoted PVA) prepared in comparative example 2, and the microcrystal-containing composite hydrogel layer (denoted FH-Gel) and the microcrystal-free composite hydrogel layer (denoted H-Gel) prepared in example 1, and the test results are shown in FIG. 3, and as can be seen from FIG. 3, the PVA was used in the range of 11.7 °, 19.7 °, 40.9 ° and 44.5 ° in 2θHas obvious crystal peak; the XRD spectrum of CS shows a strong peak at about 20℃in 2. Theta. Due to the presence of a large amount of-OH and-NH in the chitosan structure 2 Groups which can form stronger intermolecular and intramolecular hydrogen bonds, and the chitosan structure has certain regularity, so that the molecules are easy to form a crystallization area. The peaks of chitosan around 20℃in FH-Gel and H-Gel were weakened, representing a strong interaction between chitosan and PVA, and the crystallinity of chitosan was decreased. Thus, both XRD results and FTIR results demonstrate some interactions between chitosan and PVA. In addition, the peak value of FH-Gel at about 20 degrees 2. Theta. Is higher than that of H-Gel, indicating that PVA will form a microcrystalline region after freezing;
The microcrystal-containing composite hydrogel layer (denoted as FH-Gel) prepared in example 1 and the microcrystal-free composite hydrogel layer (denoted as H-Gel) were subjected to 3D-Raman spectroscopy, the results of which are shown in FIGS. 4 and 5, and the proportion of microcrystal regions in the H-Gel and the FH-Gel were evaluated by Multivariate Curve Resolution (MCR), as shown in the inset diagrams in FIGS. 4 and 5, respectively, wherein FIG. 4 is the 3D-Raman spectrum of the H-Gel and FIG. 5 is the 3D-Raman spectrum of the FH-Gel; as can be seen from fig. 4 to 5, the reconstructed raman image shows the tensile strength in blue and red (3000 to 3400cm -1 ). 3234cm in the blue spectrum -1 The apparent intensity of (a) comes from the OH-rich region (microcrystalline region), while the corresponding peak in the red spectrum corresponds to the OH-deficient region (chemical cross-linked domain). The area of the microcrystalline region in FH-Gel was approximately 35.87%;
the double-layer hydrogel material prepared in example 1 is stretched, the test result is shown in fig. 6, and as can be seen from fig. 6, the tensile breaking stress of the double-layer hydrogel material prepared in example 1 reaches 61.53KPa, the tensile breaking strain reaches 216.22%, and the double-layer hydrogel material has good toughness and tensile characteristics;
the swelling performance test is performed on the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals, which are prepared in example 1, wherein the swelling balance is respectively carried out on the composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals in hydrochloric acid aqueous solutions with ph=2 and 7, the test result is shown in fig. 7, wherein an H-Gel curve in fig. 7 corresponds to the composite hydrogel layer without microcrystals (marked as H-Gel), an FH-Gel curve corresponds to the composite hydrogel layer containing microcrystals prepared in example 1, and as can be seen from fig. 7, the larger the ratio of chitosan to PVA is, the larger the difference between the swelling degrees of frozen hydrogels and unfrozen hydrogels is;
The sensitivity test was performed on the bilayer hydrogel materials prepared in examples 1 to 4, in which the bilayer hydrogel was placed in a ph=2 aqueous hydrochloric acid solution, and the test results are shown in fig. 8, and as can be seen from fig. 8, under the same pH condition, during the same time, when chitosan: pva=3:1 (corresponding to example 1), the bending of the bilayer hydrogel is most remarkable, and the time for the bilayer hydrogel to bend to the same angle gradually increases as the ratio becomes larger. This is probably because as the PVA ratio increases, the concentration of CS/PVA hydrogel endoglycans is diluted causing a slow response to pH. And chitosan: the bending at pva=3:0.5 is less than that at 3:1, probably because the hydrogel frozen layer has microcrystalline regions, and the swelling generated by the unfrozen layer cannot offset the swelling generated by the frozen layer, resulting in slow response;
the double-layer hydrogel material prepared in the example 1 is subjected to sensitivity test under different pH conditions, wherein the test process is to place the double-layer hydrogel material in hydrochloric acid aqueous solutions with different pH values; the test results are shown in fig. 9, wherein a is a response curve of the double-layer hydrogel material to different pH, b is a graph of bending degree of the double-layer hydrogel material at different time under the condition of ph=2, c is an SEM graph of the double-layer hydrogel material after swelling under the condition of ph=2 (three graphs are a composite hydrogel morphology without microcrystals, a double-layer hydrogel bonding interface morphology and a composite hydrogel morphology with microcrystals in sequence from left to right); as can be seen from fig. 9 a, the double-layer hydrogel has the most remarkable bending angle at ph=2, and then has no remarkable bending angle at ph=3 at pH 4 or 5 at the same time; when the double-layer hydrogel is bent at the same angle, the time used for the double-layer hydrogel is shortest at the pH=2, and the pH=3 times; as can be seen from fig. 9 b, the longer the time, the greater the degree of completeness; as can be seen from fig. 9 c, after swelling, the composite hydrogel layer containing no crystallites becomes larger because of moisture entering the voids, and the composite hydrogel layer containing crystallites has a more compact structure because of the presence of the microcrystalline regions.
The composite hydrogel layer containing microcrystals and the composite hydrogel layer without microcrystals prepared in example 5 were subjected to swelling performance test, and the test procedure is as follows: the swelling balance of the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals is set in a ph=2 aqueous hydrochloric acid solution, and the test result is shown in fig. 10, wherein the Treated Gel curve in fig. 10 corresponds to the composite hydrogel layer containing microcrystals, the N-Treated Gel curve corresponds to the composite hydrogel layer containing no microcrystals, and the internal Gel curve corresponds to the composite hydrogel layer containing microcrystals, as can be seen from fig. 10, the higher the content of the crosslinking agent, the larger the difference between the swelling degrees of the composite hydrogel layer containing microcrystals and the composite hydrogel layer containing no microcrystals.
The microcrystal-containing PNIPAM/PVA composite hydrogel layer (designated as FH-Gel) and the microcrystal-free composite hydrogel layer (designated as H-Gel) prepared in example 10 are respectively swelled and balanced in water solutions of T=5 ℃ and T=50 ℃, the Gel mass is measured, the deswelling rate of the Gel is calculated, the test result is shown in fig. 13, the swelling property of the composite hydrogel layer has similar change trend along with the change of the proportion of chitosan to PVA, and the deswelling rate of the unfrozen hydrogel when heated is larger than that of the hydrogel layer after freezing treatment.
Application example
With reference to the preparation process of example 5, a double-layer hydrogel material (physical diagram is shown as a 2-e 2 in fig. 11) with a structure shown as a 1-e 1 in fig. 11 is obtained by adjusting the structure of a template, swelling performance test is carried out under the condition that the pH is 2, test results are shown as a 3-e 3 in fig. 11, and as can be seen from fig. 11, a multi-section complete hydrogel can be prepared through geometric design;
the procedure of reference example 5 simulates a biomimetic manipulator (four-arm double-layer hydrogel) capable of grabbing a weight in an "X" cross manner, fixes the biomimetic manipulator to the bottom end of a nail, then dips it into an acidic aqueous solution with ph=2, and hangs over the upper end of a spherical weight, and as the composite hydrogel layer without crystallites is rapidly swelled, the biomimetic manipulator rapidly grabs the weight down completely, lifts and removes it from the medium, and this action is completed within 2 min. Then, the bionic manipulator is placed in an alkaline medium, the original shape of the bionic manipulator can be restored, and the weight is released. It follows that such a manipulator with a rapid response deformation is only able to perform simple mechanical operations in harsh acidic media.
From the above, PVA can form a microcrystalline region which can effectively absorb energy and bear larger deformation after freeze thawing, so that the swelling degree of the prepared composite hydrogel layer containing the microcrystalline region is smaller than that of the composite hydrogel layer without the microcrystalline region, and the composite hydrogel layer shows rapid and reversible deformation behavior under the induction of pH, and has stable cyclic reversibility and excellent mechanical properties. Meanwhile, a plurality of columns of complex 3D structural hydrogels, such as annular, S-shaped, multisection, spiral or flower-shaped hydrogels, can be constructed by utilizing the deformation behavior driven by the double-layer hydrogels, and the deformation can be completed within 3-6 min. In addition, an intelligent hydrogel driver is constructed by combining geometric design, namely, double-layer hydrogel materials of a bionic manipulator capable of grabbing and lifting a weight are simulated in an X-shaped cross mode. Therefore, the construction of introducing the microcrystalline region into the double-layer hydrogel is feasible, and the self-deformation hydrogel based on the natural polymer has wide application prospect in the field of soft robots.
The PNIPAM/PVA hydrogel strip of the double-layer structure prepared in example 10 was subjected to a deformation test in an aqueous solution of 50 c, as shown in fig. 14, which was capable of rapidly undergoing bending deformation within 20 s. Therefore, the double-layer hydrogel with the rapid response deformation has wider application prospect in the field of ultrasensitive gel drivers.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (6)
1. The double-layer hydrogel material is characterized by comprising 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 microcrystals and the composite hydrogel layer without microcrystals are both polyvinyl alcohol-stimulus response polymer composite hydrogel; and no nanoparticles are included in the polyvinyl alcohol-stimulus responsive polymer composite hydrogel;
the microcrystals in the microcrystal-containing composite hydrogel layer are polyvinyl alcohol microcrystals;
the compound hydrogel layer containing the microcrystals is prepared by freeze thawing treatment;
The stimulus-responsive polymer in the microcrystal-containing composite hydrogel layer and the microcrystal-free composite hydrogel layer are the same;
the stimulus-responsive polymer in the polyvinyl alcohol-stimulus-responsive polymer composite hydrogel comprises a pH-responsive polymer or a temperature-responsive polymer;
the pH response polymer is sodium carboxymethyl cellulose, chitosan or poly [ 2- (N, N-dimethylamino) methacrylate ];
the temperature responsive polymer is poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ].
2. The bilayer hydrogel material of claim 1, wherein the mass ratio of polyvinyl alcohol to stimulus-responsive polymer in the microcrystal-containing composite hydrogel layer to the microcrystal-free composite hydrogel layer is independently (0-3): 3;
and the mass of the polyvinyl alcohol is not 0.
3. The method for preparing the double-layer hydrogel material according to claim 1 or 2, comprising the following steps:
when the stimulus-responsive polymer is sodium carboxymethyl cellulose or chitosan:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer solution and a first cross-linking agent to obtain a pre-gel solution of stimulus-responsive polymer and polyvinyl alcohol;
Pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer to obtain the double-layer hydrogel material;
when the stimulus responsive polymer is poly (N-isopropylacrylamide) or poly [ 2- (N, N-dimethylamino) methacrylate ]:
mixing a polyvinyl alcohol solution, a stimulus-responsive polymer monomer, a second crosslinking agent and an initiator to obtain a pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol;
pouring the pre-gel solution of the stimulus-responsive polymer and the polyvinyl alcohol into a mould for crosslinking, and performing freeze thawing treatment on the prepared composite hydrogel to obtain a composite hydrogel layer containing microcrystals;
and arranging a die on the upper surface of the microcrystal-containing composite hydrogel layer, repeating the preparation process of the composite hydrogel, and generating a microcrystal-free composite hydrogel layer on the surface of the microcrystal-containing composite hydrogel layer to obtain the double-layer hydrogel material.
4. A method of preparation as claimed in claim 3 wherein when the stimulus responsive polymer is sodium carboxymethyl cellulose or chitosan:
the mass concentration of the 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%.
5. The method according to claim 3, wherein the number of freeze thawing treatments is 1 to 10.
6. The bilayer hydrogel material according to claim 1 or 2 or the bilayer hydrogel material prepared by the preparation method according to any one of claims 3 to 5, and the application thereof in the field of intelligent response.
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