CN113999476A

CN113999476A - Dual-stimulus-responsive conductive composite hydrogel and preparation method and application thereof

Info

Publication number: CN113999476A
Application number: CN202111571855.6A
Authority: CN
Inventors: 王艳芹; 廖静文; 张雪慧; 郎博; 张思琪; 李晓; 江文静; 陈维毅; 郑强
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2021-12-21
Filing date: 2021-12-21
Publication date: 2022-02-01
Anticipated expiration: 2041-12-21
Also published as: CN113999476B

Abstract

The invention provides a double-stimulation-responsiveness conductive composite hydrogel and a preparation method and application thereof, and relates to the technical field of conductive polymer materials. The composite hydrogel provided by the invention comprises a gel matrix, and a first nanoparticle and a second nanoparticle which are embedded in the gel matrix; the gel matrix is poly-N-isopropylacrylamide, the first nanoparticles are polypyrrole-coated cellulose nanocrystals, and the second nanoparticles are polydopamine-coated cellulose nanocrystals. The composite hydrogel provided by the invention has excellent conductivity, not only retains the temperature sensitivity and the better flexibility of the poly-N-isopropylacrylamide hydrogel, but also endows the hydrogel with good near-infrared light responsiveness, is a double-stimulation-responsiveness (temperature responsiveness and near-infrared light responsiveness) conductive composite hydrogel, and can be used as a flexible switching device to be applied to a biosensor, an intelligent actuator or a biological electronic device.

Description

Dual-stimulus-responsive conductive composite hydrogel and preparation method and application thereof

Technical Field

The invention relates to the technical field of conductive polymer materials, in particular to a double-stimulation-responsiveness conductive composite hydrogel and a preparation method and application thereof.

Background

The conductive material is a material with certain conductive performance, and the conductive materials commonly used in the market at present are generally metal materials and materials containing conductive polymers (polypyrrole and polyaniline) or nanoparticles (carbon nanotubes and graphene) and the like. The traditional conductive materials have poor flexibility and compatibility, and are difficult to have the characteristics of high conductivity, stability and easy processing at the same time, which limits the practical application of the traditional conductive materials in the biomedical field. More importantly, in the process of application exploration, the material application is continuously enriched and deepened, and the conductive substance with single function is difficult to meet the requirements of various application environments.

The hydrogel is a condensed substance which is cross-linked by covalent bonds or non-covalent bonds, contains a large amount of water as a dispersion medium, and has a three-dimensional network structure. The conductive hydrogel combines the electronic conductivity of the conductive material and the excellent compatibility of the hydrogel, has similarity with a soft tissue structure, provides a new choice for bioelectronics, and is a promising candidate material in the field of biomedical engineering. Polypyrrole is a typical conductive polymer, and has attracted much attention due to its controllable nanostructure, good biocompatibility and high conductivity. The poly-N-isopropylacrylamide (PNIPAM) has good temperature sensitivity, when the external temperature condition changes, the internal network of the gel is correspondingly influenced, the hydrophobicity and the hydrophilicity of the gel correspondingly change, and finally the volume of the gel correspondingly changes. The polypyrrole is compounded with temperature-sensitive PNIPAM gel by utilizing the conductivity of the polypyrrole, so that the composite hydrogel with temperature responsiveness and conductivity can be obtained. But polypyrrole particles in the prior art are easy to agglomerate, so that the dispersibility of the polypyrrole particles in PNIPAM gel is influenced, the formation of a conductive path is prevented, and the conductivity of the conductive hydrogel is reduced.

Disclosure of Invention

In view of the above, the present invention aims to provide a dual stimuli-responsive conductive hydrogel, and a preparation method and an application thereof. The double-stimulation-responsiveness conductive composite hydrogel provided by the invention has excellent conductivity, and also has better temperature sensitivity and near-infrared light sensitivity.

In order to achieve the above object, the present invention provides the following technical solutions:

the invention provides a dual-stimulation-responsive conductive composite hydrogel which comprises a gel matrix, and a first nanoparticle and a second nanoparticle which are embedded in the gel matrix; the gel matrix is poly-N-isopropylacrylamide, the first nanoparticles are polypyrrole-coated cellulose nanocrystals, and the second nanoparticles are polydopamine-coated cellulose nanocrystals; the double-stimulation-responsiveness conductive composite hydrogel is a conductive composite hydrogel with temperature responsiveness and near-infrared light responsiveness.

Preferably, the mass of the first nano-particle and the second nano-particle is 0.0125-0.125% and 0.0625-0.1875% of the mass of the gel matrix, respectively.

The invention provides a preparation method of the double-stimulation-responsiveness conductive composite hydrogel, which comprises the following steps:

(1) mixing cellulose nanocrystals, water and a surfactant to obtain a first dispersion; adding pyrrole and ferric chloride into the first dispersion liquid, and carrying out a first polymerization reaction at 0-5 ℃ under an oxygen-free condition to obtain polypyrrole-coated cellulose nanocrystals;

(2) mixing the cellulose nanocrystals with water, and adjusting the pH value to 8-9 to obtain a second dispersion liquid; adding dopamine into the second dispersion liquid to perform a second polymerization reaction to obtain polydopamine-coated cellulose nanocrystals;

(3) mixing the polypyrrole-coated cellulose nanocrystal, the polydopamine-coated cellulose nanocrystal, an N-isopropylacrylamide monomer, a cross-linking agent, water, an initiator and an accelerator, and carrying out free radical polymerization reaction at the temperature of 20-30 ℃ to obtain the double-stimulation-responsive conductive composite hydrogel;

the step (1) and the step (2) have no time sequence limitation.

Preferably, the surfactant in step (1) is polyvinylpyrrolidone, sodium dodecyl sulfate or cetyltrimethylammonium bromide; the mass ratio of the cellulose nanocrystals to the surfactant is (1-3): (0.1-0.3).

Preferably, the dosage ratio of the cellulose nanocrystals to the pyrrole in the step (1) is 1-3 g: 0.0015-0.003 mol; the molar ratio of the pyrrole to the ferric chloride is 1: 2-1: 4; the time of the first polymerization reaction is 4-6 h.

Preferably, the mass ratio of the cellulose nanocrystals to the dopamine in the step (2) is (1-3): (0.5 to 1); the time of the second polymerization reaction is 3-6 h.

Preferably, in the step (3), the mass of the polypyrrole coated cellulose nanocrystal is 0.1-1.0% of the mass of the N-isopropylacrylamide monomer, and the mass of the polydopamine coated cellulose nanocrystal is 0.5-1.5% of the mass of the N-isopropylacrylamide monomer.

Preferably, the crosslinking agent in the step (3) is N, N' -methylene bisacrylamide, and the mass ratio of the crosslinking agent to the N-isopropyl acrylamide monomer is 0.5-3: 100, respectively; the initiator is potassium persulfate, and the mass ratio of the initiator to the N-isopropylacrylamide monomer is 0.5-2: 100, respectively; the accelerator is N, N, N ', N' -tetramethyl ethylenediamine, and the dosage ratio of the accelerator to the N-isopropyl acrylamide monomer is 20-50 mu L: 1g of the total weight of the composition.

Preferably, the time of the free radical polymerization reaction in the step (3) is 20-30 h.

The invention provides application of the dual-stimulus-responsive conductive composite hydrogel in the technical scheme or the dual-stimulus-responsive conductive composite hydrogel prepared by the preparation method in the technical scheme as a flexible switch device in a biosensor, an intelligent actuator or a biological electronic device.

The invention provides a dual-stimulation-responsive conductive composite hydrogel which comprises a gel matrix, and a first nanoparticle and a second nanoparticle which are embedded in the gel matrix; the gel matrix is poly-N-isopropylacrylamide, the first nanoparticles are polypyrrole-coated cellulose nanocrystals, and the second nanoparticles are polydopamine-coated cellulose nanocrystals; the double-stimulation responsive conductive composite hydrogel is a conductive composite hydrogel with temperature sensitivity and near-infrared light responsiveness. The polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are used as doped particles of the poly-N-isopropylacrylamide gel, wherein the cellulose nanocrystal and the polydopamine have good hydrophilicity, have good affinity for a conductive polymer polypyrrole, and can enhance the dispersibility of the polypyrrole in hydrogel; meanwhile, the polydopamine-coated cellulose nanocrystals play a role of a bridge between the gel matrix and the polypyrrole-coated cellulose nanocrystals and between the polypyrrole-coated cellulose nanocrystal particles, so that the dispersibility of the conductive polymer polypyrrole in the hydrogel can be further enhanced, the connectivity of a conductive path is improved, and the hydrogel has excellent conductivity. In addition, the poly-dopamine (polypyrrole also has good photothermal conversion capability) can enhance the absorption of the composite hydrogel to near infrared, and the response speed of the hydrogel to the near infrared is remarkably accelerated. In addition, the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are used as rigid nanoparticles, have a reinforcing effect on the hydrogel, and can improve the mechanical properties of the composite hydrogel. The composite hydrogel provided by the invention has excellent conductivity, not only retains the temperature sensitivity and the better flexibility of the poly-N-isopropylacrylamide hydrogel, but also endows the hydrogel with good near-infrared light responsiveness, is a double-stimulation responsive conductive composite hydrogel, can generate corresponding volume change aiming at temperature and near-infrared light stimulation, and can be used as a flexible switching device to be applied to a biosensor, an intelligent actuator or a biological electronic device.

Further, the content of polypyrrole-coated cellulose nanocrystals and polydopamine-coated cellulose nanocrystals in the double-stimulation-responsive conductive composite hydrogel can be adjusted to regulate and control the conductivity, the photothermal conversion capacity and the mechanical strength of the composite hydrogel.

The invention provides a preparation method of the double-stimulation-responsiveness conductive composite hydrogel, which adopts the technical scheme that the cellulose nanocrystal is used as a template, polypyrrole is coated on the surface of the cellulose nanocrystal, the polypyrrole grows along the direction of the cellulose nanocrystal, and the polypyrrole-coated cellulose nanocrystal nanoparticles with a core-shell structure are prepared; the invention takes the cellulose nanocrystal as a template, and the surface of the cellulose nanocrystal is coated with polydopamine, so that the polydopamine grows along the direction of the cellulose nanocrystal, and the polydopamine-coated cellulose nanocrystal nanoparticles with the core-shell structure are prepared. According to the invention, after two kinds of nanoparticles, namely the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal, are doped, a free radical polymerization method is adopted to form the hydrogel, and the preparation method is simple and easy to operate. The invention adopts the commonly used raw materials of N-isopropyl acrylamide, pyrrole and dopamine, and has the advantages of easily obtained raw materials and lower cost. In addition, the preparation method provided by the invention does not damage the original poly N-isopropyl acrylamide hydrogel structure and the temperature sensitivity thereof.

The results of the examples show that the elastic modulus of the composite hydrogel provided by the invention reaches 29.51kPa, and the mechanical property is good; the conductivity is 1.19S/m, and the conductivity is excellent; after the composite hydrogel is irradiated by near-infrared light, the composite hydrogel gel has obvious volume shrinkage, and after a near-infrared light source is removed, the volume of the composite hydrogel can be recovered in a short time, so that the composite hydrogel has good near-infrared light response performance; when the composite hydrogel is transferred from the environment at 25 ℃ to the environment at 50 ℃, the volume greatly shrinks within a short time, the composite hydrogel is placed again in the environment at 25 ℃ from the environment at 50 ℃, the volume of the gel can be restored to the original state again, and the good thermal responsiveness and the good restorability of the gel are shown.

Drawings

FIG. 1 is a scanning electron microscope image of the hydrogel prepared in examples 1 to 4, wherein a) in FIG. 1 is a scanning electron microscope image of the pure PNIPAM hydrogel prepared in example 1; in FIG. 1, b) is a scanning electron microscope image of the CPPY/PNIPAM hydrogel prepared in example 2; in FIG. 1, c) is a scanning electron microscope image of the CPDA/PNIPAM hydrogel prepared in example 3; FIG. 1 d) is the SEM image of the CPPY/CPDA/PNIPAM hydrogel prepared in example 4;

FIG. 2 is a graph showing stress-strain curves and comparative elastic moduli of hydrogels of different compositions prepared in examples 1 to 4, wherein a) is a graph showing a comparison of stress-strain curves and b) is a graph showing a comparison of compressive elastic moduli in FIG. 2;

FIG. 3 is a comparison of the conductivity of hydrogels of different compositions prepared in examples 1-4;

FIG. 4 is a graph showing the temperature and volume changes with time under near infrared irradiation of hydrogels of different compositions prepared in examples 1 to 4, wherein a) is a graph showing the temperature changes, and b) is a graph showing the volume changes in FIG. 4;

FIG. 5 is a graph showing the change of the volume of hydrogel samples of different compositions prepared in examples 1 to 4 with time at 25 ℃ and 50 ℃;

FIG. 6 is a demonstration diagram and a physical diagram of the hydrogel prepared in example 4 applied to a circuit as an electronic switch, wherein a) in FIG. 6 is a demonstration diagram, and b) in FIG. 6 is a physical diagram.

Detailed Description

The invention provides various double-stimulation-responsive conductive composite hydrogels, which comprise a gel matrix and a first nanoparticle and a second nanoparticle embedded in the gel matrix; the gel matrix is poly-N-isopropylacrylamide, the first nanoparticles are polypyrrole-coated cellulose nanocrystals, and the second nanoparticles are polydopamine-coated cellulose nanocrystals. In the invention, the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are core-shell structures and are respectively expressed by CNC @ PPy and CNC @ PDA in the embodiment of the invention; the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are stably embedded in the gel matrix through hydrogen bond acting force. In the present invention, the dual stimuli-responsive conductive composite hydrogel is a conductive composite hydrogel having temperature responsiveness and near-infrared light responsiveness: the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are used as doped particles of the poly-N-isopropylacrylamide gel, wherein the cellulose nanocrystal and the polydopamine have good hydrophilicity, have good affinity for a conductive polymer polypyrrole, and can enhance the dispersibility of the polypyrrole in hydrogel; meanwhile, the polydopamine-coated cellulose nanocrystals play a role of a bridge between the gel matrix and the polypyrrole-coated cellulose nanocrystals and between the polypyrrole-coated cellulose nanocrystal particles, so that the dispersibility of the conductive polymer polypyrrole in the hydrogel can be further enhanced, the connectivity of a conductive path is improved, and the hydrogel has excellent conductivity. In addition, the poly-dopamine (polypyrrole also has good photothermal conversion capability) can enhance the absorption of the composite hydrogel to near infrared, and the response speed of the hydrogel to the near infrared is remarkably accelerated. In addition, the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are used as rigid nanoparticles, have a reinforcing effect on the hydrogel, and can improve the mechanical properties of the composite hydrogel. The composite hydrogel provided by the invention has excellent conductivity, not only retains the temperature sensitivity and the better flexibility of the poly-N-isopropylacrylamide hydrogel, but also endows the hydrogel with good near-infrared light responsiveness, and is a double-stimulation-responsiveness conductive composite hydrogel.

In the invention, the mass of the first nanoparticles is preferably 0.0125-0.125% of the mass of the gel matrix, and more preferably 0.05-0.1%; the mass of the second nanoparticles is preferably 0.0625-0.1875%, and more preferably 0.1-0.15% of the mass of the gel matrix. According to the invention, the electric conductivity, the photo-thermal conversion capability and the mechanical strength of the composite hydrogel can be regulated and controlled by regulating the contents of the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal in the double-stimulation-responsive conductive composite hydrogel.

the step (1) and the step (2) have no time sequence limitation.

Mixing Cellulose Nanocrystalline (CNC), water and a surfactant to obtain a first dispersion liquid; and adding pyrrole and ferric chloride into the first dispersion liquid, and carrying out a first polymerization reaction at 0-5 ℃ under an oxygen-free condition to obtain the polypyrrole-coated cellulose nanocrystal. The source of the cellulose nanocrystals is not particularly required in the invention, and the cellulose nanocrystals can be commercially available or prepared by itself, which is well known to those skilled in the art; when self-prepared, the preparation method is preferably: carrying out hydrolysis reaction on microcrystalline cellulose in a mixed solvent of citric acid and hydrochloric acid; and sequentially centrifuging, cleaning and drying the hydrolysis reaction product to obtain the cellulose nanocrystal. In the invention, the concentration of citric acid in the mixed solvent is preferably 1.8-3.6 mol/L, the concentration of hydrochloric acid is preferably 0.5-0.7 mol/L, and the dosage ratio of the microcrystalline cellulose to the mixed solvent is preferably 1 g: 30-70 mL. In the invention, the temperature of the hydrolysis reaction is preferably 60-90 ℃, and the time is preferably 2-6 h; the hydrolysis reaction is preferably carried out under the condition of stirring, and the stirring speed is preferably 400-800 r/min; the centrifugation and cleaning times are preferably 2-6 times, and the condition that the supernatant is neutral is taken as the standard; the temperature of the drying is preferably 45 ℃. In the invention, the cellulose nanocrystal is prepared by taking the easily available microcrystalline cellulose as a raw material, so that the cost of the cellulose nanocrystal can be reduced.

In the present invention, the surfactant is preferably polyvinylpyrrolidone, sodium lauryl sulfate or cetyltrimethylammonium bromide, more preferably polyvinylpyrrolidone; the mass ratio of the cellulose nanocrystals to the surfactant is preferably (1-3): (0.1 to 0.3), more preferably 1: 0.3; the surfactant is used for promoting subsequent polypyrrole to be coated on the surface of the cellulose nanocrystal more uniformly. In the invention, the mixing time of the cellulose nanocrystal, water and the surfactant is preferably 15-30 min; mixing the cellulose nanocrystal, water and a surfactant at room temperature; the method for mixing the cellulose nanocrystal, the water and the surfactant is preferably as follows: mixing the cellulose nanocrystals with water for ultrasonic dispersion, adding a surfactant into the obtained ultrasonic dispersion liquid, and stirring for 15-30 min to fully combine the cellulose nanocrystals with the surfactant to obtain a first dispersion liquid.

In the invention, the dosage ratio of the cellulose nanocrystals to the pyrrole is preferably 1-3 g: 0.0015 to 0.003mol, more preferably 1 g: 0.003 mol; the molar ratio of the pyrrole to the ferric chloride is preferably 1: 2-1: 4, and more preferably 1: 2-1: 3; the ferric chloride is preferably added in the form of ferric chloride solution, and the concentration of the ferric chloride solution is preferably 0.5 mol/L; the ferric chloride acts to oxidize the pyrrole to form polypyrrole. In the invention, the time of the first polymerization reaction is preferably 4-6 h; the specific operation of the first polymerization reaction is preferably: dripping pyrrole into the first dispersion liquid, and then stirring for 30-60 min to fully combine the pyrrole with the cellulose nanocrystal; adding a ferric chloride solution into the obtained mixed solution, and carrying out a first polymerization reaction at the temperature of 0-5 ℃ under the condition of stirring; and nitrogen is continuously introduced in the process of the first polymerization reaction, so that the influence of oxygen on the reaction is avoided. After the first polymerization reaction, the obtained first polymerization reaction product is preferably subjected to repeated centrifugation and washing to obtain polypyrrole-coated cellulose nanocrystals; the invention has no special requirements on the specific mode of centrifugation, and the centrifugation mode which is well known to the technical personnel in the field can be adopted; the rinsing detergent is preferably deionized water; the operation times of centrifugation and washing are preferably 2-6 times, wherein one time of centrifugation and washing is one time of operation.

In the invention, in the process of the first polymerization reaction, the cellulose nanocrystal is used as a template, pyrrole is oxidized into polypyrrole under the action of ferric chloride and is coated on the surface of the cellulose nanocrystal, and the polypyrrole grows along the direction of the cellulose nanocrystal to prepare the polypyrrole-coated cellulose nanocrystal nanoparticles with a core-shell structure.

Mixing cellulose nanocrystals with water, and adjusting the pH value to 8-9 to obtain a second dispersion liquid; and adding dopamine into the second dispersion liquid to perform a second polymerization reaction to obtain the polydopamine-coated cellulose nanocrystal. In the present invention, the method of mixing the cellulose nanocrystals and water is preferably ultrasonic dispersion; the invention has no special requirement on the addition amount of the water, and the cellulose nanocrystals can be fully dispersed. According to the invention, the pH value is preferably adjusted by adding a NaOH solution into a dispersion liquid obtained by mixing cellulose nanocrystals and water, wherein the concentration of the NaOH solution is preferably 0.5-1 mol/L; the solution environment with the pH value of 8-9 can promote dopamine to be oxidized into polydopamine. In the invention, the mass ratio of the cellulose nanocrystals to the dopamine is preferably (1-3): (0.5 to 1), more preferably 1: 0.5. in the invention, the second polymerization reaction is carried out at room temperature, and the time of the second polymerization reaction is preferably 3-6 h, and more preferably 4-5 h; the second polymerization reaction is preferably carried out under stirring. After the second polymerization reaction, the obtained second polymerization reaction product is preferably subjected to repeated centrifugation and washing to obtain polydopamine-coated cellulose nanocrystals; the operation frequency of centrifugation and washing is preferably 2-6 times, wherein one time of centrifugation and washing is one time of operation; the rinsing detergent is preferably deionized water. In the invention, the second polymerization reaction takes the cellulose nanocrystals as a template, and dopamine is oxidized on the surfaces of the cellulose nanocrystals to form polydopamine in a solution environment with the pH value of 8-9, so that the polydopamine-coated cellulose nanocrystal nanoparticles with a core-shell structure are prepared.

After the polypyrrole-coated cellulose nanocrystal and the polydopamine-coated cellulose nanocrystal are obtained, the polypyrrole-coated cellulose nanocrystal, the polydopamine-coated cellulose nanocrystal, the N-isopropylacrylamide monomer, the cross-linking agent, the water, the initiator and the accelerator are mixed, and free radical polymerization reaction is carried out at the temperature of 20-30 ℃ to obtain the double-stimulation-responsive conductive composite hydrogel. In the invention, the mass of the polypyrrole-coated cellulose nanocrystal is preferably 0.1-1.0% of that of the N-isopropylacrylamide monomer, and more preferably 0.4-0.8%; the mass of the polydopamine-coated cellulose nanocrystal is preferably 0.5-1.5% of that of the N-isopropylacrylamide monomer, and more preferably 0.8-1.2%. In the invention, the cross-linking agent is preferably N, N' -methylene bisacrylamide, and the mass ratio of the cross-linking agent to the N-isopropyl acrylamide monomer is preferably 0.5-3: 100, more preferably 1 to 2.5: 100, respectively; the initiator is preferably potassium persulfate, and the mass ratio of the initiator to the N-isopropylacrylamide monomer is preferably 0.5-2: 100, more preferably 1 to 2: 100, respectively; the accelerator is preferably N, N, N ', N' -tetramethylethylenediamine, and the dosage ratio of the accelerator to the N-isopropylacrylamide monomer is preferably 20-50 μ L: 1g, more preferably 25 to 35 μ L: 1g of the total weight of the composition. In the invention, the temperature of the free radical polymerization reaction is preferably 20-30 ℃, and the time of the free radical polymerization reaction is preferably 20-30 h, and more preferably 24 h. In the present invention, the specific operation of the radical polymerization reaction is preferably: dissolving the N-isopropyl acrylamide monomer and the cross-linking agent in water to obtain a first mixed solution; adding polypyrrole-coated cellulose nanocrystals and polydopamine-coated cellulose nanocrystals into the first mixed solution, and mixing to obtain a second mixed solution; introducing nitrogen into the second mixed solution for deoxygenation to obtain a deoxygenated second mixed solution; adding an initiator and an accelerator into the deoxygenated second mixed solution, and mixing to obtain a third mixed solution; and placing the third mixed solution into a sealed reaction container, and carrying out free radical polymerization reaction at the temperature of 20-30 ℃. In the present invention, the time for oxygen removal is preferably 10 min. In the process of the free radical polymerization reaction, an accelerator catalyzes an initiator to quickly generate free radicals, monomer N-isopropylacrylamide is continuously polymerized under the initiation of the free radicals to generate chain growth to form a macromolecular chain, a cross-linking agent is used as a cross-linking site to connect a plurality of macromolecules to form a polymer network, and finally the poly-N-isopropylacrylamide hydrogel embedded with polypyrrole-coated cellulose nanocrystals and polydopamine-coated cellulose nanocrystals, namely the double-stimulation-responsive conductive composite hydrogel, is prepared.

The preparation method of the double-stimulation responsive conductive composite hydrogel provided by the invention is simple and easy to operate; the raw materials are easy to obtain, and the cost is low; and the condition is mild, and the structure and the temperature sensitivity of the original poly-N-isopropylacrylamide hydrogel can not be damaged.

The invention provides application of the dual-stimulus-responsive conductive composite hydrogel in the technical scheme or the dual-stimulus-responsive conductive composite hydrogel prepared by the preparation method in the technical scheme as a flexible switch device in a biosensor, an intelligent actuator or a biological electronic device. The embodiment of the invention tests the performance of the conductive composite hydrogel as a flexible switch device, prepares the composite hydrogel into a cylindrical test piece with the diameter of 1cm and the height of 1cm, and connects the obtained cylindrical gel test piece into a circuit containing a red LED lamp through two copper electrode plates; in an initial state, the gel is in a contact state with the copper electrode plate as a conductive medium, the circuit is closed, the LED lamp is lighted, and the gel switch is in an 'on' state; when the gel is placed in an environment of 50 ℃ or the gel is irradiated by a near-infrared laser source, the gel shrinks in volume and loses contact with a copper electrode slice within two minutes, a circuit is opened, an LED lamp is immediately turned off, and a gel switch is in an off state; after the heat source or the near-infrared laser source is removed, the gel is cooled to be restored to the contact state with the copper electrode plate after about one minute, the circuit is closed, the LED lamp is turned on, and the gel switch is in the on state again. The double-stimulus-response conductive composite hydrogel provided by the invention has excellent conductivity, and also has better temperature sensitivity and near-infrared light sensitivity, and as a double-stimulus-response flexible switch device, the double-stimulus-response conductive composite hydrogel can realize remote and local control by carrying out simple and convenient stimulation on the double-stimulus-response flexible switch device, and has wide application prospects in the fields of biosensors, intelligent actuators or bioelectronic devices.

The following examples are provided to illustrate the dual stimuli-responsive conductive hydrogel of the present invention and the preparation method and application thereof in detail, but they should not be construed as limiting the scope of the present invention.

Example 1

Preparation of pure poly-N-isopropylacrylamide hydrogel:

dissolving 1g of N-isopropylacrylamide monomer (NIPAM) and 0.02g of cross-linking agent N, N' -methylenebisacrylamide (BIS) in 10mL of deionized water at room temperature, and continuously stirring to obtain a uniform mixed solution; introducing nitrogen into the solution to remove oxygen for 10 min; then, 0.02g of initiator potassium persulfate (KPS) and 30 mu L of accelerator Tetramethylethylenediamine (TEMED) are added into the solution, the mixture is uniformly stirred, transferred into a cylindrical mold for sealing, and reacted for 24 hours at the temperature of 25 ℃ to obtain pure poly N-isopropylacrylamide hydrogel, namely pure PNIPAM hydrogel.

In fig. 1, a) is a scanning electron microscope image of the pure PNIPAM hydrogel prepared in example 1. As can be seen from a) in fig. 1, the pure PNIPAM hydrogel has an interconnected uniform porous structure, which allows moisture to flow rapidly inside the gel, so that the gel has a faster thermal volume phase transition, and meets the requirements of subsequent experiments.

Example 2

Preparation of poly (N-isopropylacrylamide) hydrogel embedded with polypyrrole-coated cellulose nanocrystals (CNC @ PPy):

(1) preparation of Cellulose Nanocrystals (CNC): at room temperature, taking 6g of microcrystalline cellulose (MCC), dispersing the MCC in 300mL of a mixed solvent of citric acid and hydrochloric acid, wherein the concentration of the citric acid and the concentration of the hydrochloric acid in the mixed solvent are respectively 2.7mol/L and 0.6mol/L, stirring, heating to 80 ℃, and carrying out hydrolysis reaction for 4 hours; and after the reaction is finished, repeatedly cleaning and centrifuging the product until the supernatant is neutral, and finally drying the product in a drying box at the temperature of 45 ℃ to obtain Cellulose Nanocrystal (CNC) powder.

(2) Preparation of polypyrrole-coated cellulose nanocrystals (CNC @ PPy): taking 1g of cellulose nanocrystalline powder, and dispersing the cellulose nanocrystalline powder in 100mL of deionized water by using ultrasound for 40min to obtain uniformly dispersed dispersion liquid; then 0.3g of surfactant polyvinylpyrrolidone (PVP) is added into the mixture and stirred evenly; then 0.003mol of pyrrole is dripped into the solution and stirred for 30 min; and adding 12mL of 0.5mol/L ferric chloride solution into the mixed solution, continuously introducing nitrogen, continuously stirring at the speed of 400r/min at the temperature of 0 ℃ for 4 hours, and repeatedly centrifuging and washing the obtained product after the reaction is finished to finally obtain the polypyrrole-coated cellulose nanocrystal (CNC @ PPy).

(3) Preparation of composite hydrogel: at room temperature, 1g N-isopropyl acrylamide monomer (NIPAM) and 0.02g of cross-linking agent N, N' -methylene Bisacrylamide (BIS) are dissolved in 10mL of deionized water, and are continuously stirred to obtain a uniform mixed solution, and then CNC @ PPy accounting for 0.6% of the mass of the NIPAM monomer is added and uniformly mixed; then introducing nitrogen into the solution to remove oxygen for 10 min; then, 0.02g of initiator potassium persulfate (KPS) and 30. mu.L of accelerator Tetramethylethylenediamine (TEMED) are added, uniformly stirred, transferred into a cylindrical mold for sealing, and reacted for 24 hours at the temperature of 25 ℃ to obtain the poly N-isopropylacrylamide hydrogel embedded with CNC @ PPy, which is named CPPY/PNIPAM hydrogel.

In FIG. 1, b) is the SEM image of the CPPY/PNIPAM hydrogel prepared in example 2. As can be seen from b) in FIG. 1, after the CNC @ PPy conductive nanoparticles are added, a small amount of nanorods can be obviously observed in the pores inside the gel, thus proving the successful addition of the CNC @ PPy, and meanwhile, the connected macroporous structure is still remained inside the gel.

Example 3

Preparation of poly-N-isopropylacrylamide hydrogel embedded with polydopamine-coated cellulose nanocrystals (CNC @ PDA):

(1) preparation of Cellulose Nanocrystals (CNC): at room temperature, 6g of microcrystalline cellulose (MCC) is taken and dispersed in 300mL of mixed solvent of citric acid and hydrochloric acid, the concentration of the citric acid in the mixed solvent is 2.7mol/L, the concentration of the hydrochloric acid in the mixed solvent is 0.6mol/L, the mixture is stirred and heated to 80 ℃, hydrolysis reaction is carried out for 4 hours, after the reaction is finished, the product is repeatedly cleaned and centrifuged until the supernatant is neutral, and finally, the product is dried in a drying box at the temperature of 45 ℃ to obtain Cellulose Nanocrystal (CNC) powder.

(2) Preparation of polydopamine-coated cellulose nanocrystals (CNC @ PDA): dispersing 1g of cellulose nanocrystalline powder in 100mL of deionized water at room temperature by using ultrasound, and adjusting the pH value of the solution to 8.5 by using a NaOH solution; and slowly adding 0.5g of dopamine, continuously stirring for 5 hours, repeatedly washing and centrifugally washing the product after the reaction is finished, and obtaining the polydopamine-coated cellulose nanocrystal (CNC @ PDA).

(3) Preparation of composite hydrogel: at room temperature, 1g N-isopropyl acrylamide monomer (NIPAM) and 0.02g of cross-linking agent N, N' -methylene Bisacrylamide (BIS) are dissolved in 10mL of deionized water, and are continuously stirred to obtain a uniform mixed solution, and then CNC @ PDA accounting for 1.0% of the mass of the NIPAM monomer is added and uniformly mixed; introducing nitrogen into the solution to remove oxygen for 10 min; then, 0.02g of initiator potassium persulfate (KPS) and 30 μ L of accelerator Tetramethylethylenediamine (TEMED) are added, uniformly stirred, transferred into a cylindrical mold for sealing, and reacted for 24 hours at the temperature of 25 ℃ to obtain the poly N-isopropylacrylamide hydrogel embedded with CNC @ PDA, which is named as CPDA/PNIPAM hydrogel.

In FIG. 1, c) is the scanning electron microscope image of the CPDA/PNIPAM hydrogel prepared in example 3. As can be seen from c) in FIG. 1, after the CNC @ PDA nano-particles are added, the existence of a small amount of nano-rods can be obviously observed in the pores inside the gel, thus proving the successful addition of CNC @ PDA, and meanwhile, the connected macroporous structure still remains inside the gel.

Example 4

Preparation of poly-N-isopropylacrylamide hydrogel in which polypyrrole-coated cellulose nanocrystals and polydopamine-coated cellulose nanocrystals (CNC @ PPy and CNC @ PDA) were embedded:

(2) Preparation of polypyrrole-coated cellulose nanocrystals (CNC @ PPy): taking 1g of cellulose nanocrystalline powder, and dispersing the cellulose nanocrystalline powder in 100mL of deionized water by using ultrasound for 40min to obtain uniformly dispersed dispersion liquid; adding 0.3g of surfactant polyvinylpyrrolidone (PVP) into the dispersion liquid and stirring uniformly; then 0.003mol of pyrrole is dripped into the solution and stirred for 30min at the temperature of 0 ℃; then adding 12mL of 0.5mol/L ferric chloride solution, continuously introducing nitrogen, and continuously stirring for 4h at the temperature of 0 ℃ at the speed of 400 r/min; and after the reaction is finished, repeatedly centrifuging and washing the obtained product to obtain the polypyrrole-coated cellulose nanocrystal (CNC @ PPy).

(3) Preparation of polydopamine-coated cellulose nanocrystals (CNC @ PDA): dispersing 1g of cellulose nanocrystalline powder in 100mL of deionized water at room temperature by using ultrasound, and adjusting the pH value of the solution to 8.5 by using a NaOH solution; and then slowly adding 0.5g of dopamine, continuously stirring for reacting for 5 hours, and repeatedly washing and centrifugally washing the product after the reaction is finished to obtain the polydopamine-coated cellulose nanocrystal (CNC @ PDA).

(4) Preparation of composite hydrogel: at room temperature, 1g N-isopropyl acrylamide monomer (NIPAM) and 0.02g of cross-linking agent N, N' -methylene Bisacrylamide (BIS) are dissolved in 10mL of deionized water and are continuously stirred to obtain a uniform mixed solution; then adding CNC @ PPy accounting for 0.6 percent of the mass of the NIPAM monomer and CNC @ PDA accounting for 1.0 percent of the mass of the NIPAM monomer, and uniformly mixing; after nitrogen is introduced into the solution to remove oxygen for 10min, 0.02g of initiator potassium persulfate (KPS) and 30 mu L of accelerator Tetramethylethylenediamine (TEMED) are added, the mixture is uniformly stirred and then transferred into a cylindrical mold to be sealed, and the mixture reacts for 24h in an environment with the temperature of 25 ℃ to obtain poly N-isopropyl acrylamide hydrogel embedded with CNC @ PPy and CNC @ PDA, namely the double-stimulation responsive conductive composite hydrogel which is named CPPY/CPDA/PNIPAM hydrogel.

Fig. 1 d) is a scanning electron microscope image of the CPPY/CPDA/PNIPAM hydrogel, and a uniform pore structure of the gel and an obvious nanoparticle structure in the pores can be observed from fig. 1 d), which proves the successful synthesis of the CPPY/CPDA/PNIPAM composite hydrogel and the uniform dispersion of the nanoparticles, and meanwhile, the gel still maintains a good pore structure after two types of nanoparticles are added, so that the rapid flow of water is ensured.

The performance of the hydrogels of examples 1-4 was tested as follows:

(I) mechanical Property test

FIG. 2 a) is a graph showing a comparison of stress-strain curves of hydrogels of different compositions prepared in examples 1 to 4, and FIG. 2 b) is a graph showing a comparison of compressive moduli of elasticity of hydrogels of different compositions prepared in examples 1 to 4.

As can be seen from FIG. 2, the modulus of elasticity of the neat PNIPAM hydrogel is only 21.04 kPa. After the nanoparticles are added, due to the reinforcing effect of the rigid nanoparticles, the elastic modulus of the composite hydrogel is improved to a certain extent, and the elastic modulus of the CPPY/PNIPAM hydrogel, the CPDA/PNIPAM hydrogel and the CPPY/CPDA/PNIPAM hydrogel are respectively 25.21kPa, 25.52kPa and 29.51kPa, which shows that the mechanical property of the hydrogel is improved.

(II) conductivity Performance test

The hydrogels with different components prepared in examples 1 to 4 were prepared into cylinders with a diameter of 1cm and a height of 1cm, and the conductivity of the gels with different components was tested by an alternating current impedance method.

The test results are shown in FIG. 3, which is a comparison of the conductivity of hydrogels of different compositions prepared in examples 1-4.

As can be observed from FIG. 3, the conductivity of the pure PNIPAM hydrogel is extremely low, which is 0.11S/m, and the conductivity change is extremely small, which is 0.12S/m after the CNC @ PDA nano-particles are added; after the conductive CNC @ PPy nanoparticles are added, the conductivity of the gel is greatly improved to be 0.67S/m due to the fact that the CNC @ PPy nanoparticles form an electronic conductive path in the gel; when CNC @ PDA and CNC @ PPy are added simultaneously, the CNC @ PDA plays a role in bridging between the gel matrix and the CNC @ PPy and between CNC @ PPy nanoparticles, so that the sedimentation effect of the CNC @ PDA in the gel is weakened, a more communicated conductive path is formed, and the conductivity of the composite hydrogel is further improved to be 1.19S/m.

(III) near infrared light and thermal response performance test experiment

(1) The hydrogels of different compositions prepared in examples 1 to 4 were prepared in the form of discs with a diameter of 1cm and a height of 2 mm. The change of the volume and the temperature of the hydrogel with different components along with the time is tested by irradiating the hydrogel with a near infrared laser with 808 nm.

As shown in FIG. 4, a) in FIG. 4 is the temperature change with time of the hydrogels with different components prepared in examples 1-4 under near infrared light irradiation; in FIG. 4 b) shows the change of the volume of the hydrogels with different compositions prepared in examples 1-4 under near infrared light irradiation with time.

As shown in fig. 4, when the gel was irradiated with near infrared light, the gels of different compositions showed temperature and volume changes, and the temperature change and the volume change of the pure PNIPAM were 3.9 ℃ and 3.3% respectively under the irradiation of near infrared light for 10 minutes due to the poor near infrared light absorption ability of the pure PNIPAM. And due to good near infrared light absorption capacity of Polydopamine (PDA) and polypyrrole (PPy), when CNC @ PDA and CNC @ PPy are added into the gel respectively, the temperature change and the volume change of the CPDA/PNIPAM gel are 15.5 ℃ and 47.7%, and the temperature change and the volume change of the CPPY/PNIPAM gel are 33.3 ℃ and 42.5%. When the CPPY/CPDA/PNIPAM composite hydrogel and the gel matrix are added simultaneously, the temperature of the CPPY/CPDA/PNIPAM composite hydrogel is changed by 49.1 ℃, the volume of the CPPY/CPDA/PNIPAM composite hydrogel is changed by 53.6 percent, the CPPY/CPIPAM composite hydrogel is far higher than that of pure PNIPAM hydrogel and that of CPDA/PNIPAM and CPPY/PNIPAM gel, and the CPPY/PNIPAM composite hydrogel shows good near infrared light response performance.

(2) The hydrogels of different compositions prepared in examples 1 to 4 were prepared in a cylindrical shape with a diameter of 1cm and a height of 1 cm. The gels of the different compositions were tested for temperature change over time by placing the gels in an environment of 25 c and 50 c, respectively.

As shown in FIG. 5, FIG. 5 shows the change of the volume of the hydrogel samples of different compositions prepared in examples 1 to 4 with time at 25 ℃ and 50 ℃.

As shown in fig. 5, when the gels of different compositions are transferred from the environment of 25 ℃ to the environment of 50 ℃, a large volume contraction occurs in a short time; when the gel is placed in an environment of 25 ℃ again from an environment of 50 ℃, the volume of the gel can be restored to the original state again, the good thermal response condition and the recoverability of the gel are shown, and the thermal response performance of the composite hydrogel is not influenced by the addition of CNC @ PPY and CNC @ PDA.

(IV) experiments of gel as Dual temperature and near Infrared light response switch

The CPPY/CPDA/PNIPAM composite hydrogel prepared in example 4 was prepared into a cylindrical test piece having a diameter of 1cm and a height of 1 cm. And connecting the gel into a circuit containing a red LED lamp through two copper electrode plates.

The response of the gel as a switch when a thermal or near-infrared light source is used as a stimulus is as follows:

in the initial state, the gel is in a contact state with the copper electrode plate as a conductive medium, the circuit is closed, the LED lamp is lighted, and the gel switch is in an 'on' state.

When the gel is placed in an environment of 50 ℃ or the gel is irradiated by a near-infrared laser source, the gel shrinks in volume and loses contact with a copper electrode slice within two minutes, a circuit is opened, an LED lamp is immediately turned off, and a gel switch is in an off state.

After the heat source or the near-infrared laser source is removed, the gel is cooled to be restored to the contact state with the copper electrode plate after about one minute, the circuit is closed, the LED lamp is turned on, and the gel switch is in the on state again.

Fig. 6 a) is a diagram illustrating the sample prepared in example 4 applied to an electric circuit as an electronic switch, and fig. 6 b) is a diagram illustrating the sample prepared in example 4 applied to an electric circuit as an electronic switch, showing the actual state of the gel as a switch.

The above embodiments show that the double-stimulus-response conductive composite hydrogel provided by the invention has excellent conductivity, and simultaneously has good temperature sensitivity and near infrared light sensitivity, and can be used as a double-stimulus-response flexible switch device.

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

1. A dual stimuli-responsive conductive composite hydrogel comprising a gel matrix and first and second nanoparticles embedded in the gel matrix; the gel matrix is poly-N-isopropylacrylamide, the first nanoparticles are polypyrrole-coated cellulose nanocrystals, and the second nanoparticles are polydopamine-coated cellulose nanocrystals; the double-stimulation-responsiveness conductive composite hydrogel is a conductive composite hydrogel with temperature responsiveness and near-infrared light responsiveness.

2. The dual stimuli-responsive conductive composite hydrogel according to claim 1, wherein the mass of the first and second nanoparticles is 0.0125 to 0.125% and 0.0625 to 0.1875% of the mass of the gel matrix, respectively.

3. The method for preparing the dual stimuli-responsive conductive composite hydrogel according to claim 1 or 2, comprising the steps of:

the step (1) and the step (2) have no time sequence limitation.

4. The method according to claim 3, wherein the surfactant in step (1) is polyvinylpyrrolidone, sodium lauryl sulfate or cetyltrimethylammonium bromide; the mass ratio of the cellulose nanocrystals to the surfactant is (1-3): (0.1-0.3).

5. The preparation method according to claim 3 or 4, wherein the dosage ratio of the cellulose nanocrystals to the pyrrole in the step (1) is 1-3 g: 0.0015-0.003 mol; the molar ratio of the pyrrole to the ferric chloride is 1: 2-1: 4; the time of the first polymerization reaction is 4-6 h.

6. The preparation method according to claim 3, wherein the mass ratio of the cellulose nanocrystals to the dopamine in the step (2) is (1-3): (0.5 to 1); the time of the second polymerization reaction is 3-6 h.

7. The method according to claim 3, wherein in the step (3), the mass of the polypyrrole coated cellulose nanocrystal is 0.1-1.0% of the mass of the N-isopropylacrylamide monomer, and the mass of the polydopamine coated cellulose nanocrystal is 0.5-1.5% of the mass of the N-isopropylacrylamide monomer.

8. The preparation method according to claim 3 or 7, wherein the crosslinking agent in the step (3) is N, N' -methylenebisacrylamide, and the mass ratio of the crosslinking agent to the N-isopropylacrylamide monomer is 0.5-3: 100, respectively; the initiator is potassium persulfate, and the mass ratio of the initiator to the N-isopropylacrylamide monomer is 0.5-2: 100, respectively; the accelerator is N, N, N ', N' -tetramethyl ethylenediamine, and the dosage ratio of the accelerator to the N-isopropyl acrylamide monomer is 20-50 mu L: 1g of the total weight of the composition.

9. The preparation method according to claim 3, wherein the time of the radical polymerization reaction in the step (3) is 20-30 h.

10. Use of the dual stimuli-responsive conductive hydrogel according to any one of claims 1 to 2 or the dual stimuli-responsive conductive hydrogel prepared by the preparation method according to any one of claims 3 to 9 as a flexible switch device in a biosensor, an intelligent actuator or a bioelectronic device.