1. A method of making an electrically conductive hydrogel, comprising:

in the case of poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) PEDOT: adding a water-soluble sorbitol solution and a water-soluble polyurethane (WPU) solution into the PSS solution to obtain a mixed solution;

adding chitosan quaternary ammonium salt into the mixed solution to obtain a dark blue solution;

adjusting the pH value of the dark blue solution to 10 by using a sodium hydroxide solution, and adding a cross-linking agent to perform chemical cross-linking reaction to obtain a blue solution;

adjusting the pH value of the blue solution by using a hydrochloric acid solution until the pH value is 7 to obtain a conductive hydrogel solution;

and carrying out evaporation treatment on the conductive hydrogel to obtain the conductive hydrogel.

2. The method of claim 1, wherein the crosslinking agent comprises an aldehyde crosslinking agent, a crown ether crosslinking agent, or an epoxy crosslinking agent.

3. The method according to claim 2, wherein the step of adjusting the PH of the deep blue solution to 10 with sodium hydroxide and adding a crosslinking agent to perform a chemical crosslinking reaction comprises:

continuously dropwise adding a sodium hydroxide solution to maintain the pH value of the dark blue solution at 10 in the process of carrying out chemical crosslinking reaction on the aldehyde crosslinking agent, the crown ether crosslinking agent or the epoxy crosslinking agent and the chitosan quaternary ammonium salt in the dark blue solution, reacting at constant temperature for 4 hours, and naturally cooling to room temperature.

4. The method of claim 1, wherein after the step of adjusting the PH of the deep blue solution to 10 with sodium hydroxide solution, the method further comprises:

heating the dark blue solution at pH 10 until the temperature of the dark colored solution reaches 70 ℃.

5. The method of claim 1, wherein after obtaining the conductive hydrogel solution, the method further comprises:

adding glycerol to the conductive hydrogel solution to lower the freezing point of the conductive hydrogel.

6. The method of claim 1, further comprising:

and guiding the conductive hydrogel into an electrode mould to obtain the conductive hydrogel electrode.

Background

At present, the electrode for the brain-computer interface is generally prepared by adopting conductive hydrogel, and the electrode is directly attached to the skin of a human body and plays a role of conducting a medium. The relevant conductive hydrogel exists: firstly, the problem that the hair cannot be penetrated due to being too soft; secondly, the freezing point of the conductive gel is not low enough, and the hydrogel electrode is easy to be seriously damaged and fail due to icing.

Disclosure of Invention

In order to solve at least one of the above technical problems, the present application provides a method for preparing an electrically conductive hydrogel.

The application provides a preparation method of a conductive hydrogel electrode, which comprises the following steps:

adding a water-soluble sorbitol solution and a water-soluble polyurethane (WPU) solution into a poly (3, 4-ethylenedioxythiophene) (poly (styrene sulfonate)) solution to obtain a mixed solution;

adding chitosan quaternary ammonium salt into the mixed solution to obtain a dark blue solution;

adjusting the pH value of the dark blue solution to 10 by using a sodium hydroxide solution, and adding a cross-linking agent to perform chemical cross-linking reaction to obtain a blue solution;

adjusting the pH value of the blue solution by using a hydrochloric acid solution until the pH value is 7 to obtain a conductive hydrogel solution;

and (3) carrying out evaporation treatment on the conductive hydrogel to obtain the conductive hydrogel.

Further, the crosslinking agent is an aldehyde crosslinking agent, a crown ether crosslinking agent or an epoxy crosslinking agent.

Further, the step of adjusting the pH value of the dark blue solution to 10 by using a sodium hydroxide solution and adding a cross-linking agent to perform a chemical cross-linking reaction comprises the following steps:

continuously dropwise adding a sodium hydroxide solution to maintain the pH value of the dark blue solution at 10 in the process of carrying out chemical crosslinking reaction on epoxy chloropropane and chitosan quaternary ammonium salt in the dark blue solution, reacting at constant temperature for 4h, and naturally cooling to room temperature.

Further, after the step of adjusting the PH of the dark blue solution to 10 with a sodium hydroxide solution, the method further comprises:

the dark blue solution, pH 10, was heated until the temperature of the dark colored solution reached 70 ℃.

Further, after obtaining the conductive hydrogel solution, the method further comprises:

glycerol is added to the conductive hydrogel solution to lower the freezing point of the conductive hydrogel.

In the embodiment of the application, the conductive hydrogel is prepared by using poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) high-molecular conductive liquid as a conductive network, and the conductive hydrogel has electronic and ionic conductivity due to the PEDOT main chain for charge conduction and the PSS for ionic conduction.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the description of the embodiments of the present application will be briefly described below.

Fig. 1 is a schematic flow chart of a method for preparing a conductive hydrogel according to an embodiment of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

It should be noted that although functional blocks are partitioned in a schematic diagram of an apparatus and a logical order is shown in a flowchart, in some cases, the steps shown or described may be performed in a different order than the partitioning of blocks in the apparatus or the order in the flowchart.

To make the objects, technical solutions and advantages of the present application more clear, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

According to an embodiment of the present application, there is provided a method of preparing an electrically conductive hydrogel, as shown in fig. 1, the method including:

step S101, mixing poly (3, 4-ethylenedioxythiophene) and poly (styrenesulfonate) PEDOT: and mixing the PSS solution with sorbitol and the aqueous polyurethane solution to obtain a mixed solution.

Step S102, adding chitosan quaternary ammonium salt into the mixed solution to obtain a dark blue solution;

step S103, adjusting the pH value of the dark blue solution to 10 by using sodium hydroxide, and adding a cross-linking agent to perform chemical cross-linking reaction to obtain a blue solution;

step S104, adjusting the pH value of the blue solution by using a hydrochloric acid solution until the pH value is 7 to obtain a conductive hydrogel solution;

and S105, evaporating the conductive hydrogel to obtain the conductive hydrogel.

In the examples of this application, PEDOT is named poly 3, 4-ethylenedioxythiophene and PSS is named polystyrene sulfonate.

Specifically, the PH of the deep blue solution is generally adjusted with a 5% by mass sodium hydroxide solution until the PH of the deep blue solution is 10.

Specifically, the pH of the blue solution is generally adjusted to pH 7 using a 20% by mass hydrochloric acid solution.

In the embodiment of the application, a poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) macromolecule conductive solution is used as a conductive network to prepare the conductive hydrogel, and the conductive hydrogel has electronic and ionic conductivities due to the PEDOT main chain for charge conduction and the PSS for ionic conduction; meanwhile, the water-soluble WPU can improve the tensile property of PEDOT PSS gel, and sorbitol is mixed into a PEDOT PSS aqueous solution, so that the tensile property of the gel is further improved, and the adhesion of a polymer film on a substrate can be improved. Then, epichlorohydrin is used as a chemical cross-linking agent to synthesize the chemically cross-linked chitosan quaternary ammonium salt with biocompatibility to be used as a three-dimensional network hydrogel framework. In the conductive hydrogel matrix, sulfonic acid groups of negative ions in the PEDOT, PSS and ammonia radical ions of positive ions in the cross-linked chitosan quaternary ammonium salt form ionic bonds, and strong hydrogen bond interaction exists between the PEDOT, PSS and hydroxyl groups of the cross-linked chitosan. PSS and natural polysaccharide's flexibility to the high molecular conducting solution PEDOT that possesses electron and ion conductivity integrates, thereby has improved the stretchability, rigidity, toughness and the electric conductivity of traditional electrically conductive aquogel, makes it can bear various deformation, for example tensile, knot and compression, and then has guaranteed comfortable and good skin electrode contact, and can conveniently prepare and store, be convenient for in-service use simultaneously because wetting effect and bigger area of contact, it has greatly reduced the impedance that electrode and skin contacted.

In some embodiments, the crosslinking agent includes aldehyde crosslinking agents, crown ether crosslinking agents, epoxy crosslinking agents, and the like. In the embodiment of the application, epichlorohydrin is used as a crosslinking agent to synthesize biocompatible chemically crosslinked chitosan quaternary ammonium salt as a three-dimensional network hydrogel skeleton. Further, step S103 includes: continuously dropwise adding a sodium hydroxide solution to maintain the pH value of the dark blue solution at 10 in the process of carrying out chemical crosslinking reaction on an aldehyde crosslinking agent, a crown ether crosslinking agent or an epoxy crosslinking agent and the chitosan quaternary ammonium salt in the dark blue solution, reacting at a constant temperature for 4 hours, and naturally cooling to room temperature. Through the operation of dropwise adding the sodium hydroxide solution, the environment required by the chemical crosslinking reaction is provided, and the efficiency of the chemical crosslinking reaction is improved.

In some embodiments, after step S103, the method further comprises:

the dark blue solution, pH 10, was heated until the temperature of the dark colored solution reached 70 ℃. The chemical crosslinking reaction is carried out in the required alkaline environment through heating treatment, so that the reaction speed can be accelerated, and the reaction efficiency of the crosslinking reaction is improved.

In some embodiments, after obtaining the conductive hydrogel solution through step S104, the method further comprises: the conductive hydrogel solution is added with glycerol to lower the freezing point of the conductive hydrogel, and the water/glycerol binary solvent is utilized to ensure that the strong interaction between the water and the glycerol enables the mixed solvent to have a very low freezing point, thereby endowing the stretchable hydrogel with excellent freezing resistance.

In some embodiments, the method further comprises:

and (3) introducing the conductive hydrogel into an electrode mould to obtain the conductive hydrogel electrode.

Specifically, the conductive hydrogel and the curing agent can be uniformly mixed according to the weight ratio of 10:1, the ice female is cured for 1 hour in a blast oven at 70 ℃, and the PDMS substrate mold with the columnar structure is obtained after demolding; meanwhile, in order to obtain a wettable surface, PDMS with a columnar structure was immersed in a dopamine solution (pH 8.5) for 60min, thereby coating a polydopamine coating layer on the PDMS mold; and then washing the surface of the PDMS substrate modified by the polydopamine by using deionized water, pouring the evaporated stretchable conductive antifreeze hydrogel solution into the mold, and drying in a blast oven at 70 ℃ for 8 hours to finally obtain the deep blue stretchable antifreeze conductive hydrogel-based brain interface electrode with the soft needle-shaped columnar structure.

The present application will be described below by taking the fabrication of an electrode as an example.

First, 10mL of polystyrene sulfonic acid PEDOT: PSS solution, and added to 200mL of deionized water, and polystyrene sulfonic acid PEDOT: the PSS solution was sonicated in an ice bath for 20 minutes to break down large particle aggregates; then, a water-soluble sorbitol solution (8% wt) was measured in a diluted aqueous solution of PEDOT: PSS and magnetically stirred at room temperature for 30min, followed by addition of WPU (10% wt) solution and magnetic stirring at room temperature for 60 min.

Then, 3g of chitosan quaternary ammonium salt is weighed and added into a beaker of the mixed solution of PEDOT, PSS conductive liquid, and the beaker is placed at room temperature for 24 hours to ensure that the chitosan quaternary ammonium salt is uniformly dissolved to obtain dark blue mixed solution; and (2) adjusting the pH value of the chitosan quaternary ammonium salt-PEDOT/PSS mixed solution to be about 10 by using sodium hydroxide with the mass concentration of 5%, stirring for 30min at the water bath temperature of 70 ℃, adding 4mL of epoxy chloropropane, continuously stirring and stirring for 4h at the water bath temperature of 70 ℃, continuously dropwise adding a sodium hydroxide solution with the mass fraction of 5% during the reaction so as to keep the pH value of the system to be 10, and stopping the reaction. And naturally cooling the dark blue cross-linked chitosan quaternary ammonium salt-PEDOT and PSS mixed gel solution to room temperature. And (3) adjusting the pH value of the reaction system to 7 by using a hydrochloric acid solution with the mass concentration of 10%, and simultaneously adding 2mL of glycerol to obtain a deep blue stretchable anti-freezing conductive hydrogel solution. Putting the gel solution of PEDOT, PSS and cross-linked chitosan quaternary ammonium salt mixed gel into a heat-collecting constant-temperature heating magnetic stirrer, and controlling the temperature of the solution to evaporate the solvent for 8 hours at 70 ℃ so as to evaporate the solvent in the solution to 40 mL.

Then, in order to achieve good contact with the hair, a soft needle type conductive hydrogel electrode with a vertical pillar was fabricated by first uniformly mixing a PDMS polymer with a curing agent in a weight ratio of 10:1, curing in a forced air oven at 70 ℃ for 1 hour, and demolding to obtain a PDMS substrate with a columnar structure. To obtain a wettable surface, PDMS with columnar structures was immersed in a dopamine solution (pH 8.5) for 60min, thereby coating a layer of polydopamine coating on the PDMS substrate. And then washing the surface of the PDMS substrate modified by the polydopamine by using deionized water, pouring the evaporated stretchable conductive antifreeze hydrogel solution into the mold, and drying in a blast oven at 70 ℃ for 8 hours to finally obtain the deep blue stretchable antifreeze conductive hydrogel-based brain interface electrode with the soft needle-shaped columnar structure.

While the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.