CN116110636B - Fully flexible stretchable liquid metal-based bioelectrode and preparation method and application thereof - Google Patents

Abstract

The present invention discloses a fully flexible and stretchable liquid metal-based bioelectrode and a preparation method and application thereof, belonging to the technical field of functional composite materials and their preparation. The present invention solves the technical problems of the existing liquid metal having excessive surface tension, difficult molding, and easy leakage. The present invention first prepares a liquid metal nanoparticle/heat-expandable microsphere ink that can be heat-sintered, prints the ink using a mask printing method to prepare a conductive path, and uses the force of thermal expansion of the heat-expandable microspheres to destroy the oxide layer of the liquid metal nanoparticles to activate the liquid metal to form a conductive path, and finally uses a conductive hydrogel to encapsulate the detection site to obtain a bioelectrode. The obtained bioelectrode can have good conformal contact with the skin, so as to achieve the purpose of long-term and stable collection of various bioelectric signals generated on the skin surface. In addition, the preparation method provided by the present invention also has the advantages of simple operation and easy industrialization.

Description

A fully flexible, stretchable liquid metal-based bioelectrode and its preparation method and application

Technical Field

The invention relates to a fully flexible and stretchable liquid metal-based biological electrode and a preparation method and application thereof, belonging to the technical field of functional composite materials and preparation thereof.

Background technique

The conductive materials of existing commercial bioelectronic devices are rigid, and their Young's modulus is much higher than that of human tissue. The rigidity of materials and devices reduces user comfort. At the same time, the mismatch of Young's modulus leads to incomplete interface contact between rigid devices and soft human skin, which limits the quality of skin surface sensing signals. Compared with traditional bioelectrodes, flexible and stretchable bioelectrodes can conformally contact with soft, curved, and dynamically deformed human tissue to improve the quality of electrical signals. And through this bioelectrode, real-time and continuous monitoring of personal physiological parameters and personal health management can be achieved, which can improve the treatment effect of diseases, reduce medical costs, and improve the quality of life, which is of great significance.

Therefore, it is very necessary to provide a bioelectrode that is simple to prepare, easy to industrialize, and can have good conformal contact with the skin, so as to achieve long-term and stable collection of various bioelectric signals generated on the skin surface.

Summary of the invention

The purpose of the present invention is to provide a method for preparing a fully flexible and stretchable liquid metal-based bioelectrode. Specifically, the liquid metal is made into a nanoparticle state to solve the technical problems of excessive surface tension of liquid metal, difficult molding, and easy leakage. Thermal expansion microspheres are used to destroy the surface oxide layer of the liquid metal nanoparticles. This method is simple to operate and easy to industrialize. The fully flexible and stretchable liquid metal-based bioelectrode prepared by the present invention can have good conformal contact with the skin, thereby achieving the purpose of long-term and stable collection of various bioelectric signals generated on the skin surface.

The technical solution of the present invention:

One of the purposes of the present invention is to provide a method for preparing a fully flexible and stretchable liquid metal-based bioelectrode, the method comprising the following steps:

S1, ink preparation and printing:

Liquid metal, heat-expandable microspheres and solvent are mixed, subjected to ultrasonic treatment to obtain ink, and the ink is printed on a cured Ecoflex elastomer using a mask to obtain a bioelectrode pathway;

S2, package:

The part of the bioelectrode pathway obtained by S1 except the detection site was encapsulated using Ecoflex elastomer;

S3, Encapsulation of detection sites:

Dissolve acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid and gelatin in deionized water and stir, add 2-methoxyethyl acrylate and dimethyl sulfoxide after they are completely dissolved, add α-ketoglutaric acid and methacrylated gelatin after mixing evenly, stir until they are completely dissolved to obtain a conductive hydrogel, drop the conductive hydrogel on the detection site, cross-link and cure it using ultraviolet irradiation, complete the encapsulation of the detection site, and obtain a bioelectrode to be activated;

S4, activate the bioelectrode:

The bioelectrode to be activated obtained by S3 is placed in an oven for heating. The heat-expandable microspheres expand and rupture due to the heat. During this process, the force of the expansion of the microspheres destroys the oxide layer of the liquid metal ink nanoparticles, thereby activating the liquid metal to connect into a conductive path. Deionized water is then dropped on the detection site of the bioelectrode, and the wires are connected to obtain a fully flexible and stretchable liquid metal-based bioelectrode.

It is further defined that the mass ratio of the liquid metal to the heat-expandable microspheres in S1 is (0.5-2):50, and the volume ratio of the liquid metal to the solvent is 1:(1-5).

It is further defined that the liquid metal is a mixture of one or more of gallium, mercury, rubidium, cesium and francium.

It is further defined that the liquid metal consists of 75 wt % Ga and 25 wt % In.

It is further defined that the solvent is one of n-decanol, ethanol, water and acetone.

In a further embodiment, the solvent is n-decanol.

It is further defined that the ultrasonic treatment instrument in S1 is a cell crusher, the power is set to 600-1500 W, and the treatment is carried out in an ice water bath for 60-120 min.

It is further defined that the mass ratio of the part A to the part B of the Ecoflex elastomer in S2 is 1:1.

It is further defined that the curing temperature of the Ecoflex elastomer in S2 is 60°C and the curing time is 4 to 6 minutes.

It is further defined that the mass volume ratio of acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, gelatin, deionized water, 2-methoxyethyl 2-acrylate, dimethyl sulfoxide, α-ketoglutaric acid and methacrylated gelatin in S3 is (0.5-1) g: (2-3) g: (0.5-1) g: (1-3) mL: 0.8 g: (0.5-2.5) mL: 0.01 g: 0.005 g.

It is further defined that the stirring and dissolving time in S3 is 20 minutes.

It is further defined that in S3, 2 μL of the conductive hydrogel precursor solution is taken using a pipette and dropped onto the detection site of the bioelectrode.

It is further defined that the ultraviolet irradiation time is 15 to 30 minutes and the light intensity is 10W.

It is further defined that the heating temperature in S4 is 110-150° C. and the heating time is 1-6 min.

It is further defined that in S4, 2 mL of deionized water is dropped on the detection site of the bioelectrode and allowed to stand for 10 minutes to allow the conductive hydrogel at the detection site to absorb water and regain flexibility and conductivity.

The second purpose of the present invention is to provide an application of a fully flexible, stretchable liquid metal-based bioelectrode obtained by the above-mentioned preparation method, which is specifically used to collect bioelectric signals generated on the skin surface and skin electrical stimulation, or implanted into tissues to realize the collection of electrical signals in the tissues and tissue electrical stimulation.

The present invention first prepares liquid metal nanoparticle/heat-expandable microsphere ink, uses a mask printing method to print the ink to prepare a conductive path, and uses the force of thermal expansion of the heat-expandable microspheres to destroy the oxide layer of the liquid metal nanoparticles to activate the liquid metal to form a conductive path, and finally uses a conductive hydrogel to encapsulate the detection site to obtain a bioelectrode. Compared with the prior art, the present application has the following beneficial effects:

The present invention firstly makes liquid metal with high surface energy into liquid metal nanoparticles to solve the problem that the liquid metal surface tension is too large and the molding is difficult, and then uses thermal expansion microspheres to destroy the surface oxide layer of the liquid metal nanoparticles to reactivate the conductivity of the liquid metal, thereby obtaining a fully flexible and stretchable liquid metal-based bioelectrode. The obtained bioelectrode can have good conformal contact with the skin, and achieve the purpose of long-term and stable collection of various bioelectric signals generated on the skin surface. In addition, the preparation method provided by the present invention also has the advantages of simple operation and easy industrialization.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of preparing a fully flexible, stretchable liquid metal-based bioelectrode according to the present invention;

FIG2 is a comparison picture of the contact angle of the liquid metal-heat-expandable microsphere ink prepared in Example 1 on the elastic substrate and the contact angle of the liquid metal on the elastic substrate;

FIG3 is a scanning electron microscope image of the liquid metal-heat-expandable microsphere ink prepared in Example 1;

FIG4 is a scanning electron microscope image of the liquid metal-heat-expandable microsphere ink prepared in Example 1 after heating;

FIG5 is a current variation curve of the activated bioelectrode prepared in Example 1 during the heating process;

FIG6 is a comparison photo of the detection site of the bioelectrode prepared in Example 1 before encapsulation and after encapsulation and activation;

FIG7 is a graph showing the electrochemical impedance comparison of the bioelectrode prepared in Example 1 before and after encapsulation with hydrogel;

FIG8 is a physical picture of the 16-channel bioelectrode prepared in Example 1;

FIG9 is a resistance change curve of the bioelectrode prepared in Example 1 after cyclic stretching for 1000 times at 100% strain;

FIG. 10 is the electromyographic signal detected by the 16-channel bioelectrode prepared in Example 1.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

The heat-expandable microspheres are low-temperature foaming microspheres of model 031DU40 produced by Aksu.

The cell disruptor was JY96-IIN from Ningbo Xinzhi Biotechnology Co., Ltd.

Embodiment 1:

As shown in FIG1 , this embodiment provides a method for preparing a fully flexible and stretchable liquid metal-based bioelectrode. Specifically, the method comprises the following steps:

Step 1, substrate preparation:

Part A and Part B of Ecoflex elastomer were mixed in equal weight ratios, evenly coated on a glass plate, and placed in an oven at 60°C for 20 minutes to cure, thereby obtaining a substrate.

Step 2, preparation of liquid metal-thermal expansion microsphere ink:

10mL of liquid metal gallium-indium alloy (EGaIn75wt% Ga and 25wt% In) was mixed with 10mL of n-decanol solvent, and thermally expandable microspheres were added, wherein the mass ratio of the thermally expandable microspheres to the liquid metal was 1:50. The mixed liquid was placed in an ice water bath and ultrasonicated for 100 minutes using a cell disruptor, and the power of the probe ultrasound was set to 1500W to obtain liquid metal-thermal expandable microsphere ink.

The wettability of liquid metal-thermal expandable microsphere ink and liquid metal on the substrate is compared, and the results are shown in Figure 2. As shown in Figure 2, the liquid metal-thermal expandable microsphere ink has better wettability to the substrate and is more conducive to the printing of high-resolution conductive paths.

The obtained liquid metal-heat-expandable microsphere ink was characterized by microscopic morphology, and the result is shown in FIG3 . As can be seen from FIG3 , the heat-expandable microspheres are dispersed in the liquid metal nanoparticles, and the initial diameter is about 6 μm.

Step 3, printing of ink:

The liquid metal-thermal expansion microsphere ink obtained in step 2 is printed on the substrate obtained in step 1 using a mask, and then placed in a 60° C. oven for heat treatment for 10 minutes to dry the solvent to obtain a bioelectrode conductive path.

Step 4, Encapsulation of the bioelectrode conductive pathway:

Mix part A and part B of Ecoflex elastomer in equal mass ratio, evenly apply them to the conductive path of the bioelectrode except the detection site, and then place them in an oven at 60°C for 20 minutes to complete the encapsulation of the conductive path of the bioelectrode.

Step 5, preparation of conductive hydrogel precursor solution:

0.5 g of acrylic acid, 2 g of 2-methoxyethyl 2-acrylate, and 0.5 g of gelatin were dissolved in 1 mL of deionized water, stirred until dissolved, 0.8 g of 2-methoxyethyl 2-acrylate and 0.5 mL of dimethyl sulfoxide were added, and stirred for 20 min. After mixing evenly, 0.01 g of α-ketoglutaric acid and 0.005 g of methacrylated gelatin were added, and stirred for 20 min until completely dissolved to obtain a conductive hydrogel precursor solution.

Step 6, Encapsulation of Bioelectrode Detection Sites:

2 μL of the hydrogel precursor solution obtained in step 5 was pipetted with a pipette and dropped onto the detection site of the bioelectrode. The solution was cross-linked and cured by ultraviolet irradiation at a light intensity of 10 W for 20 min to obtain the bioelectrode to be activated.

Step 7, activating the conductivity of the bioelectrode conductive pathway:

The bioelectrode to be activated obtained in step 6 was placed in an oven at 150°C and heated for 5 minutes. During the heating process, the heat-expandable microspheres expanded and ruptured due to the heat. The force generated by the expansion caused the oxide layer on the surface of the liquid metal nanoparticles to rupture, and the liquid metal droplets merged to form a conductive path. The microstructure of the heated sample was characterized, and the SEM photo after heating is shown in Figure 4. As shown in Figure 4, after heating at 150°C for 5 minutes, the oxide layer on the surface of the liquid metal nanoparticles ruptured, forming a conductive path.

In order to prove that the expansion force of the heat-expandable microspheres during the heating process destroyed the oxide layer of the liquid metal ink particles, thereby activating the conductivity of the bioelectrode, the bioelectrode to be activated obtained in step 6 was placed in an oven at 150°C, and a digital source meter was used to apply a voltage of 2V to the electrode, and the current change during the heating process was recorded. As shown in Figure 5, after heating to 152s, the current increased from 0A to 0.022A, proving that the heating process made the bioelectrode conductive.

Step 8, Activate conductivity of the bioelectrode recording site:

2 mL of deionized water was dropped on the bioelectrode detection site and allowed to stand for 10 minutes. The conductive hydrogel on the detection site regained flexibility and conductivity after fully absorbing water. Then the excess deionized water was gently wiped off. Figure 6 is a comparison photo of the bioelectrode detection site encapsulated hydrogel and activated and unencapsulated hydrogel. Figure 7 is a comparison curve of the electrochemical impedance of the detection site encapsulated and unencapsulated hydrogel. As shown in Figure 7, encapsulation of the detection site reduces the electrochemical impedance of the electrode. At the same time, the fully flexible and stretchable liquid metal-based bioelectrode obtained is shown in Figure 8. As shown in Figure 8, the bioelectrode prepared in this embodiment has high transparency, high flexibility and stretchability.

The performance of the final liquid metal-based bioelectrode was tested:

(1) The obtained liquid metal-based bioelectrode was cyclically stretched 1000 times at 100% strain, and the resistance change during the cyclic stretching process was measured. The test results are shown in Figure 9. As can be seen from Figure 9, the resistance change of the bioelectrode during the cyclic stretching 1000 times at 100% strain is very stable, which proves that the bioelectrode has good electrical stability and fatigue resistance.

(2) In order to verify the applicability of the liquid metal-based bioelectrode obtained in this embodiment, the bioelectrode was applied to the surface of human skin to collect electromyographic signals. The results are shown in FIG10 . As can be seen from FIG10 , the 16-channel bioelectrode successfully collected electromyographic signals of the human skin surface during the process of clenching and relaxing the fist.

Embodiment 2:

The difference between this embodiment and embodiment 1 is that the ultrasonic treatment power in step 2 is 600 W, the ultrasonic treatment time in the ice water bath is 120 min, and the rest of the operation process is the same as that in embodiment 1.

Example 3: This example is different from Example 1 in that in step 5, the mass volume ratio of acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, gelatin, deionized water, 2-methoxyethyl 2-propenoate, dimethyl sulfoxide, α-ketoglutaric acid and methacrylated gelatin is 1g:3g:1g:3mL:0.8g:2.5mL:0.01g:0.005g, and the rest of the operation process is the same as that in Example 1.

Although the present invention has been disclosed as above in the form of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims (10)

1. A method for preparing a liquid metal-based bioelectrode, characterized in that it comprises the following steps: S1, ink preparation and printing: The liquid metal, the heat-expandable microspheres and the solvent are mixed, and the mixture is ultrasonically treated in an ice-water bath to obtain ink, and the ink is printed on the cured Ecoflex elastomer using a mask to obtain a bioelectrode pathway; S2, package: The part of the bioelectrode pathway obtained by S1 except the detection site was encapsulated using Ecoflex elastomer; S3, Encapsulation of detection sites: Dissolve acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid and gelatin in deionized water and stir, add 2-methoxyethyl acrylate and dimethyl sulfoxide after they are completely dissolved, add α-ketoglutaric acid and methacrylated gelatin after mixing evenly, stir until they are completely dissolved to obtain a conductive hydrogel, drop the conductive hydrogel on the detection site, cross-link and cure by ultraviolet irradiation, complete the encapsulation of the detection site, and obtain a bioelectrode to be activated; S4, activate the bioelectrode: The bioelectrode to be activated obtained in S3 is placed in an oven for heating, and the heat-expandable microspheres expand and rupture due to the heat. Deionized water is dropped on the detection site of the bioelectrode, and the wires are connected to obtain a fully flexible and stretchable liquid metal-based bioelectrode. 2. The method for preparing a liquid metal-based bioelectrode according to claim 1 is characterized in that the mass ratio of liquid metal to heat-expandable microspheres in S1 is (0.1-2):50, and the volume ratio of liquid metal to solvent is 1:(1-5). 3. The method for preparing a liquid metal-based bioelectrode according to claim 1 or 2, characterized in that the liquid metal is a mixture of one or more of gallium, mercury, rubidium, cesium, and francium; and the solvent is a mixture of one or more of n-decanol, ethanol, water, and acetone. 4. The method for preparing a liquid metal-based bioelectrode according to claim 1 is characterized in that the ultrasonic treatment instrument in S1 is a cell crusher, the power is set to 600-1500W, and the treatment is carried out in an ice water bath for 60-120 minutes. 5. The method for preparing a liquid metal-based bioelectrode according to claim 1 is characterized in that the mass volume ratio of acrylic acid, 2-acrylamido-2-methyl-1-propane sulfonic acid, gelatin, deionized water, 2-methoxyethyl 2-acrylate, dimethyl sulfoxide, α-ketoglutaric acid and methacrylated gelatin in S3 is (0.5-1) g: (2-3) g: (0.5-1) g: (1-3) mL: 0.8 g: (0.5-2.5) mL: 0.01 g: 0.005 g. 6. The method for preparing a liquid metal-based bioelectrode according to claim 1, characterized in that the ultraviolet irradiation time is 15 to 30 minutes and the light intensity is 10W. 7. The method for preparing a liquid metal-based bioelectrode according to claim 1, characterized in that the heating temperature in S4 is 110-150°C and the time is 1-6 minutes. 8. The method for preparing a liquid metal-based bioelectrode according to claim 1, characterized in that in S4, 2 mL of deionized water is dropped on the detection site of the bioelectrode and allowed to stand for 10 minutes to allow the conductive hydrogel at the detection site to absorb water and regain flexibility and conductivity. 9. A fully flexible and stretchable liquid metal-based bioelectrode obtained by the preparation method of the liquid metal-based bioelectrode according to claim 1. 10. An application of the liquid metal-based bioelectrode according to claim 1, characterized in that it is used to collect bioelectric signals generated on the skin surface and to electrically stimulate the skin, or to be implanted inside tissues to collect electrical signals inside the tissues and to electrically stimulate the tissues.