CN112442194A

CN112442194A - Preparation method of conductive adhesive hydrogel

Info

Publication number: CN112442194A
Application number: CN201910830968.XA
Authority: CN
Inventors: 但卫华; 陈一宁; 但年华; 王璐
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2019-09-04
Filing date: 2019-09-04
Publication date: 2021-03-05

Abstract

The invention discloses a preparation method of conductive adhesive hydrogel, which comprises the steps of firstly using dopamine modified carbon nano-tubes and grafting the dopamine modified carbon nano-tubes to saccharides containing free carboxyl groups through an amide reaction, then mixing acrylamide, the modified carbon nano-tubes and the modified saccharides to form hydrogel under the action of a cross-linking agent and an initiator. The modified carbon nano tube can be stably dispersed in aqueous solution and forms hydrogen bonds and dynamic supermolecular crosslinking with other substances in hydrogel; the sugar grafted with the dopamine catechol structure can form a hydrogel network, so that the complexity of the hydrogel structure is improved, and the biocompatibility, the adhesion performance and the toughness of the hydrogel are enhanced; the hydrogel has physical and chemical properties such as conductivity, self-adhesion, high toughness, biocompatibility and the like. The method can be used for preparing the conductive hydrogel in the fields of biomedicine, electronic skin, human-computer interface, human activity monitoring, wearable electronic equipment and the like.

Description

Preparation method of conductive adhesive hydrogel

Technical Field

The invention relates to a preparation method of conductive adhesive hydrogel, belonging to the field of materials.

Background

Hydrogels are a class of condensed materials cross-linked by chemical bonds or physical nodes and characterized by the presence of a three-dimensional hydrophilic polymer network at macroscopic distances, thereby immobilizing large amounts of water. Conductive hydrogels are an emerging class of hydrogels that combine a hydrophilic matrix with a conductive filler, such as metal nanoparticles, conductive polymers, or carbon-based materials. Conductive hydrogels have reversible capacity between swelling and debulking and can be designed to perform liquid exchange or volume transition through a controllable response to a wide range of environmental conditions, such as electric or magnetic fields, light, and ionic conductivity. Therefore, the conductive hydrogel has remarkable prospect in a plurality of application fields from renewable energy sources, flexible electronic products and environmental engineering to medical instruments, drug delivery systems and the like.

Electrically conductive hydrogels have been widely used in the fields of electronic skins, human-machine interfaces, biomedical implants, human activity monitors, wearable electronics, and the like. Most flexible conductors are composites of elastomers and metal particles, liquid metals, carbon, ionic liquids, or conductive polymers, and many contain higher filler content, lower strain to failure, poor biocompatibility, lack of mechanical toughness due to poor filler-matrix compatibility. If the adhesive is directly applied to human body, the defects of irritation to human skin, no adhesion to human skin, low ductility and low stability which are not matched with normal activities of human body exist, and the further application of the adhesive is hindered. Electrically conductive hydrogels for biomedical applications, in particular wearable devices, require flexibility and tissue adherence to allow integration with the human body, thus placing better demands on such hydrogels, for example: low irritation, good biocompatibility and stable conductivity. Therefore, conductive hydrogels with good biocompatibility and inherent flexibility have recently become ideal materials for wearable devices or implantable sensors.

Common methods for preparing electrically conductive hydrogels include hydrogel formation from suspensions of electrically conductive fillers, polymerization of electrically conductive monomers in preformed hydrogels, cross-linking of electrically conductive polymers with dopant molecules, supramolecular interaction self-assembly of graphene hydrogels, and the like. Since the conductive filler and the conductive polymer are generally difficult to have good biocompatibility, the biocompatibility, adhesion property, strain property and matching property with human body of the conductive hydrogel are often realized by depending on other substances in the hydrogel. A common solution is to mix conductive polymers with traditional insulating hydrogels to prepare materials that retain the mechanical properties of the latter, some other physicochemical properties and biocompatibility. Unfortunately, such mixing processes often alter the physical properties of the insulating matrix, and the resulting composite hydrogels still have various problems, and therefore, cannot simply be directly compounded with a conductive filler or polymer.

The polyacrylamide hydrogel is generally synthesized from a polyacrylamide monomer, and according to the actual situation of application, the performance of the polyacrylamide hydrogel can be changed by adjusting the synthesis conditions and copolymerizing the polyacrylamide hydrogel with other monomers, or the performance of the polyacrylamide hydrogel can be changed by chemically modifying the synthesized hydrogel. The polyacrylamide has good toughness and elasticity, can be used as a filling material to be placed into a human body, and can also generate synergistic action with other functional materials to prepare high-toughness and high-strength hydrogel which can be applied to the human body; thus, polyacrylamide is suitable as a hydrogel matrix material.

The carbon nanotube is tubular nanometer level graphite crystal, and is seamless nanometer level tube with single or multiple graphite sheets curled around the central shaft in certain spiral angle, and each layer has C SP₂Hybridization is carried out to form a cylindrical surface with a hexagonal plane. The P electrons of carbon atoms on the carbon nano tube form a large-range delocalized pi bond, and the carbon nano tube has some special electrical properties due to the obvious conjugation effect. The carbon nano tube has unique conductivity, high thermal stability and intrinsic mobility, has a large specific surface area, and the micropores are concentrated in a certain range, thereby meeting the requirements of ideal electrode materials of the super capacitor. Although the carbon nanotube has excellent conductivity, the carbon nanotube has poor dispersibility in aqueous solution and serious aggregation phenomenon, is easy to deposit at the bottom of the solution after losing stirring effect, and can be directly applied to water condensation if the carbon nanotube is directly applied to water condensationIn the case of a glue system, it is difficult to obtain a good effect.

Dopamine is short for 3, 4-dihydroxy phenethylamine, is a derivative of tyrosine rich in mussel mucin, contains catechol functional groups in the structure, and is endowed with unique biological adhesion performance. In recent years, dopamine has been widely used for preparing bioadhesives, which is mainly inspired by the super-strong adhesion of mussels in the sea and is used for biomimetic mussel mucin. Further studies have shown that catechol groups in the dopamine structure are the main reason for imparting superior adhesion. The catechol group is easy to form hydrogen bond with the surface of polar and hydrophilic material to produce adsorption, and after being oxidized, the catechol group can produce covalent crosslinking with many groups and also produce disproportionation reaction to produce coupling. In the presence of alkalinity and oxygen, the catechol group is easily oxidized into a quinone or semiquinone structure, and at the moment, the catechol group can not only perform Michael addition and Schiff base reaction with amino, imino, sulfydryl and other groups, but also perform intramolecular cyclization to form a dehydroindole structure, perform disproportionation reaction to form free radicals and further couple the free radicals into tannin compounds, finally form polymerization crosslinking, and enhance the adhesion and cohesion between the catechol group and a base material.

The natural carbohydrate (polysaccharide and oligosaccharide) and the derivatives thereof are used as a natural high molecular biological material with rich resources and excellent performance, have the characteristics of no toxicity, no smell, no immunogen and the like, have good biocompatibility and biodegradability, and the decomposition products are safe and harmless to the human body, so the natural carbohydrate and the derivatives thereof are widely applied to the field of biological materials. The saccharides and the derivatives thereof have been widely researched and applied in the hydrogel field, and have incomparable advantages. In addition, many sugar molecules also have biological functional activity, and have anti-inflammatory activity and the like. Thus, natural sugars and their derivatives are suitable for use as natural components in the synthesis of hydrogels, and can impart some unique properties to the hydrogels.

In order to prepare the conductive hydrogel with better biocompatibility, certain functionality (such as antibacterial property, hydrophilicity and the like), high toughness, adhesivity and stable conductivity. Firstly, modifying a carbon nano tube by dopamine to obtain a modified carbon nano tube which can be stable in an aqueous solution and has good dispersibility; secondly, combining amino on dopamine with carboxyl in the carboxyl-containing saccharides by amidation reaction to obtain modified saccharides containing catechol structure; then, dispersing the modified carbon nano tube in an acrylamide monomer solution, and adding a certain amount of modified saccharides containing catechol structures; and finally, obtaining the polyacrylamide-modified carbon nanotube-carbohydrate composite conductive hydrogel under mild conditions. The hydrogel is a double-network hydrogel, has conductivity and sensitivity, also has enough adhesive force, and can be directly contacted with and adhered to human skin; secondly, the hydrogel is non-toxic, biocompatible and non-irritating to human skin; third, the hydrogel has good mechanical properties and can be matched to the mechanical behavior of skin tissue.

Disclosure of Invention

1. A preparation method of conductive adhesive hydrogel is characterized by comprising the following steps:

(1) preparing the modified carbon nano tube: weighing 1 part by weight of carbon nano tube, adding the carbon nano tube into 1000-10000 parts by weight of Tris-HCl buffer solution with the pH value of 8-9 or citric acid-sodium citrate buffer solution with the pH value of 4-5, and carrying out ultrasonic treatment for 0.4-1 h; then, 0.5-4 parts by weight of dopamine is weighed and added into the carbon nano tube dispersion liquid, and mechanical or magnetic stirring is kept for 12-48 hours; centrifuging the reaction mixture at 5000-8000 rpm for 5-20 min, decanting the supernatant, collecting the lower layer solid, and washing the solid with distilled water; centrifuging under the same condition, repeating for 2-5 times, freeze-drying or drying at 30-70 ℃ on the obtained solid product, and storing for later use;

(2) preparation of catechol group-containing saccharide: weighing 1 part by weight of carboxyl-containing saccharides and dissolving the saccharides in 30-300 parts by weight of 2-morpholine ethanesulfonic acid (MES) buffer solution with the concentration of 10-100 mmol/L, pH of 5.5-6.5; under the protection of nitrogen, adding a certain mass of N-hydroxysuccinimide (NHS) and 1- (3-dimethylaminopropyl) -3-Ethylcarbodiimide (EDC) to ensure that the concentration of EDC is 1-20 mg/ml and the concentration of NHS is 0.5-15 mg/ml, carrying out an activation reaction for 0.5-1.0 h, then adding 0.2-5.0 parts by weight of dopamine, adjusting the pH value of a reaction system to 5.0-6.0 by using hydrochloric acid, and carrying out a stirring reaction for 16-30 h at 20-30 ℃; after the reaction is finished, putting the product into a dialysis bag with the molecular weight cutoff of 300-5000 Da, dialyzing for 4-6 d with distilled water, changing the distilled water for 4-5 times every day, and freeze-drying for later use;

(3) preparation of electrically conductive adhesive hydrogel: weighing 100 parts by weight of acrylamide, dissolving in 250-350 parts by weight of distilled water, weighing 0.1-5 parts by weight of modified carbon nano tube, dispersing in an acrylamide solution, keeping mechanical or magnetic stirring for 0.5-24 hours to uniformly disperse, then weighing 0-5 parts by weight of saccharide containing catechol groups, dissolving, then weighing 1.5-5 parts by weight of ammonium persulfate and 0.08-0.2 part by weight of N, N ' -methylenebisacrylamide, adding into the acrylamide-modified carbon nano tube mixed solution, adding 0-0.01 part by weight of N, N, N ', N ' -tetramethylethylenediamine after dissolving, removing a stirrer after uniformly mixing to form pre-gel, and sealing and storing for 1-5 days at 20-50 ℃ to obtain the hydrogel.

The method for preparing a conductive adhesive hydrogel of claim 1, wherein the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes and carbon nanotube derivatives.

The method for preparing a conductive adhesive hydrogel according to claim 1, wherein the carboxyl group-containing saccharide is a polysaccharide, an oligosaccharide, a polysaccharide derivative or an oligosaccharide derivative having a molecular structure containing a free carboxyl group.

The method of claim 1, wherein the conductive adhesive hydrogel is used in biomedical, electronic skin, human-machine interface, human activity monitoring, wearable electronic device, etc.

The invention has the following advantages:

(1) unlike common hydrogel taking conductive polymer as a conductive substance, the raw materials of the conductive adhesive hydrogel are mostly biological materials, have better biocompatibility and more exact safety, and can be used in the field of biomedicine;

(2) the dopamine modified carbon nanotube improves the hydrophilicity of the carbon nanotube, enables the carbon nanotube to have good dispersibility in aqueous solution, can promote the interaction of the carbon nanotube with polyacrylamide chains and sugar chains, interweaves a highly interconnected network in hydrogel, and can also improve the biocompatibility of the carbon nanotube;

(3) the conductive adhesive hydrogel has excellent and repeatable self-adhesive ability which is not possessed by general hydrogel besides the conductive property, and can be attached on various substrates including organic and inorganic surfaces due to the existence of catechol group and quinone group. Meanwhile, the existence of a sufficient number of free catechol groups in the hydrogel is beneficial to the preparation of the hydrogel with high repeated self-adhesive strength, which is important for meeting the practical application. The hydrogel with biocompatibility and self-adhesiveness can be directly attached to a flexible and dynamic biological surface for signal detection, and can be effectively adhered to the surface of a human body without the action of external adhesion when being used in the fields of human body activity detection, wearable electronic equipment and the like, and the skin of the human body cannot be damaged;

(4) the conductive adhesive hydrogel is added with carbohydrate containing free carboxyl, so that more possibilities are provided for other functions of the hydrogel. As is known, natural saccharides are very important biomass materials in nature, have rich sources and good functionality, and can endow hydrogel with certain antibacterial functional characteristics if carboxymethyl chitosan is selected; if hyaluronic acid is selected, the hydrogel can be endowed with more hydrophilic and hygroscopic properties; if oxidized sodium alginate is selected, bioactive macromolecules such as collagen can be introduced into a hydrogel system through further reaction and covalence;

(5) the conditions and the reaction in the whole modification process are mild, have no harsh requirements, are easy to realize, are environment-friendly and are friendly to operators;

(6) in the method, the dopamine modified carbon nano tube is adopted to enable the carbon nano tube to be uniformly dispersed in the hydrogel, the biocompatibility of the dopamine modified carbon nano tube is improved, the polysaccharide grafted with the catechol structure can be self-aggregated and self-crosslinked in the hydrogel to form another set of network system which is distinguished from acrylamide, the complexity of the hydrogel structure is improved, the introduction of the functional sugar and the derivative thereof can increase or improve the functionality and the biocompatibility of the hydrogel, and meanwhile, the catechol and the quinoid structure endow the hydrogel with good adhesive property; the method is simple and feasible, and is a novel method for preparing the conductive adhesive hydrogel with strong feasibility and wide application potential.

Detailed Description

The present invention is described in detail below by way of examples, it should be noted that the examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and those skilled in the art can make modifications and adjustments in the above-mentioned invention.

Example 1

(1) Preparing the modified carbon nano tube: weighing 100g of multi-walled carbon nano-tube, dispersing in 250L of Tris-HCl buffer solution with the pH value of 8.5 under the action of ultrasonic waves, transferring the solution into a reaction kettle after half an hour, weighing 150g of dopamine hydrochloride, starting mechanical stirring, reacting for 18 hours, circularly filtering and washing a reaction product, and drying the modified carbon nano-tube at 40 ℃ for later use;

(2) preparing modified carboxymethyl cellulose: weighing a certain mass of carboxymethyl cellulose (with the carboxylation degree of 65-80%) in a reaction kettle, adding 100L of MES buffer solution with the pH value of 5.5, uniformly stirring at 35 ℃ to completely dissolve the carboxymethyl cellulose, and preparing the CMC solution with the mass fraction of 2.5%. And then adding NHS and EDC with certain mass in sequence, carrying out activation reaction for 20min, then adding dopamine with certain mass, adjusting the pH of the reaction system to about 5.0 by using dilute hydrochloric acid, and carrying out stirring reaction for 24 h. And introducing nitrogen for protection all the time in the whole reaction process. And after the reaction is finished, putting the mixture into a dialysis bag with the molecular weight cutoff of 3000Da, dialyzing the mixture for 3 days by using distilled water, and changing the solution 4-5 times every day. Then freeze-drying the product and storing for later use;

(3) preparation of electrically conductive adhesive hydrogel: weighing 2000 g of acrylamide, dissolving the acrylamide in 6L of distilled water, adding 40g of modified carbon nano tube, stirring for 2 hours, adding 30 g of modified carboxymethyl cellulose, uniformly mixing, adding 40g of ammonium persulfate and 1.2g of N, N ' -methylene bisacrylamide, dissolving, adding 10ml of N, N, N ', N ' -tetramethyl ethylenediamine, uniformly mixing, transferring to a special mold, standing at room temperature for 3d under a sealed condition to form hydrogel, and then cutting into required shapes and sizes according to needs.

Example 2

(1) Preparing the modified carbon nano tube: weighing 1g of single-walled carbon nanotube, dispersing the single-walled carbon nanotube in a citric acid-sodium citrate buffer solution with the 2LpH value of 4.4 under the action of ultrasound, then adding 1.2g of dopamine into the dispersion solution, reacting for 24 hours under stirring, then centrifuging the reaction mixture for 10min under 10000rmp, taking the lower-layer solid, re-dispersing in distilled water, centrifuging again, repeating for three times, and then freezing and drying the reaction product for later use;

(2) preparation of oxidized sodium alginate: weighing 5 g of sodium alginate, adding 30 mL of absolute ethanol, performing magnetic stirring to uniformly disperse the sodium alginate in the ethanol, dissolving 3g of sodium periodate in 30 mL of distilled water in a dark place, then adding the sodium periodate into the sodium alginate ethanol dispersion, performing magnetic stirring reaction for 12 hours in a dark place, and then adding ethylene glycol with the same mole as the sodium periodate to terminate the reaction for 2 hours. After the reaction, the reaction solution was taken out, filled in a dialysis bag with a cut-off molecular weight of 3000Da, and dialyzed with distilled water for 3 days, and the distilled water was changed 5 times a day. Freeze-drying with freeze dryer, and storing;

(3) preparing oxidized sodium alginate containing catechol groups: dissolving 5.0 g sodium alginate oxide in MES buffer solution with pH of 5.5, adding 2.91g NHS and 4.84g EDC, activating for reaction for 30 min at normal temperature under N₂Under protection, adding 2g of dopamine, stirring for reacting for 24 hours, dialyzing for 5 days by using a dialysis bag with the molecular weight cutoff of 3000Da, changing water 4-5 times per day, and freeze-drying to obtain oxidized sodium alginate grafted with dopamine;

(4) preparation of electrically conductive adhesive hydrogel: dissolving collagen in 0.1mol/L acetic acid to prepare 10mL collagen solution with mass concentration of 1 mg/mL, and adjusting the pH of the collagen solution to 7.4 by using NaOH. And adding 0.02g of oxidized sodium alginate grafted with dopamine into the collagen solution, stirring and reacting for 4 hours at 4 ℃, weighing 3g of acrylamide, adding the acrylamide into the solution, weighing 0.06g of ammonium persulfate and 0.004 g of N, N' -methylene bisacrylamide after dissolving, uniformly mixing, removing the stirrer, transferring the mixture into a mold, and keeping the temperature at 37 ℃ for 6 hours to form hydrogel.

Example 3

(1) Preparing the modified carbon nano tube: 1000L of Tris-HCl buffer solution with the pH value of 8.5 is added into a reaction kettle containing an ultrasonic device by a pump, the mixture is stirred, 1Kg of multi-walled carbon nano-tube is weighed and added into the reaction kettle, and the mixture is stirred for 30 minutes. Weighing 0.5Kg of dopamine hydrochloride, adding the dopamine hydrochloride into a reaction kettle, continuously reacting for 18h, centrifuging the reactant on a centrifuge at the speed of 6000rpm, washing the obtained precipitate with 100Kg of ultrapure water, centrifuging at the speed of 8000rpm, washing the obtained precipitate with 50Kg of ultrapure water, centrifuging at the speed of 8000rpm, freeze-drying the precipitate, and storing for later use.

(2) Preparing modified carboxymethyl cellulose: weighing 2.5Kg of carboxymethyl cellulose (the carboxylation degree is 65-80%) in a reaction kettle with nitrogen as protective gas, adding 97.5 Kg of MES buffer solution with the concentration of 20mmol/L, pH of 5.5, stirring uniformly at 35 ℃ to completely dissolve the carboxymethyl cellulose, and preparing the CMC solution with the mass fraction of 2.5%. Then 1.5Kg of NHS and 2.5Kg of EDC are added in turn to carry out activation reaction for 20min, then 2Kg of dopamine is added, the pH value of the reaction system is adjusted to about 5.0 by hydrochloric acid, and the reaction is stirred for 24 h. And introducing nitrogen for protection all the time in the whole reaction process. And after the reaction is finished, filling the reaction solution into a dialysis bag with the molecular weight cutoff of 3000Da, dialyzing in distilled water for 3 days, and changing the solution 4-5 times every day. Then freeze-drying the product and storing for later use;

(3) preparation of electrically conductive adhesive hydrogel: weighing 2Kg of acrylamide, dissolving the acrylamide in 6L of distilled water, adding 40g of modified carbon nano tube, stirring for 2h, adding 30 g of modified carboxymethyl cellulose, uniformly mixing, adding 40g of ammonium persulfate and 1.2g of N, N ' -methylene bisacrylamide, dissolving, adding 10ml of N, N, N ', N ' -tetramethyl ethylenediamine, uniformly mixing, transferring to a tetrafluoroethylene mold, standing at room temperature for 3d under a sealed condition to form hydrogel, and cutting into required shapes and sizes as required.

Claims

2. The method for preparing a conductive adhesive hydrogel of claim 1, wherein the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes and carbon nanotube derivatives.

3. The method for preparing a conductive adhesive hydrogel according to claim 1, wherein the carboxyl group-containing saccharide is a polysaccharide, an oligosaccharide, a polysaccharide derivative or an oligosaccharide derivative having a molecular structure containing a free carboxyl group.

4. The method of claim 1, wherein the conductive adhesive hydrogel is used in biomedical, electronic skin, human-machine interface, human activity monitoring, wearable electronic device, etc.