CN113143281A

CN113143281A - Screen-printed fibroin-based high-adhesion degradable flexible electrodes and their application in human-computer interface

Info

Publication number: CN113143281A
Application number: CN202010075696.XA
Authority: CN
Inventors: 牛智凯; 杨辉; 张晓盈; 杜晓慧; 李荣金
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2020-01-22
Filing date: 2020-01-22
Publication date: 2021-07-23

Abstract

The invention discloses a silk-screen printing fibroin-based high-adhesion degradable flexible electrode and application thereof in a human-computer interaction interface, and the preparation method comprises the following steps: soaking fibroin in Na₂CO₃Boiling in water solution for removing sericin, taking out, washing with water, and drying to obtain degummed silk; mixing the degummed silk, calcium chloride and formic acid, stirring at 60-80 ℃ for at least 30min to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, volatilizing the formic acid in the solution to obtain a soft silk protein film, and printing nano silver paste on the silk protein film by a screen printing method to obtain the flexible electrode. The silk protein film and the nano silver paste in the flexible electrode obtained by the invention are combined closely, and the adhesive strength is more than 10 times of that of PDMS.

Description

Silk-screen printing fibroin-based high-adhesion degradable flexible electrode and application thereof in human-computer interaction interface

Technical Field

The invention belongs to the technical field of flexible electronics, and particularly relates to a silk-screen printing fibroin-based high-adhesion degradable flexible electrode and application thereof in a human-computer interaction interface.

Background

Stretchable electronics are particularly suitable for wearable and implanted devices for healthcare monitoring. Unlike conventional rigid electronic systems, flexible stretchable electronic devices have mechanical properties similar to those of the soft organs of the human body, including the brain and skin. In skin applications, these devices can achieve compatible contact with any shape and active skin (Young's modulus 0.1-2 MPa, stretchability 30-70%). Therefore, the stretchable skin sensor can reduce the uncomfortable feeling when worn and improve the signal fidelity even during movement. For example, stretchable skin care sensors for pressure, temperature and electrophysiology have been reported. Furthermore, the device is very suitable for obtaining long-term measured biocompatibility, as well as environmentally friendly biodegradability.

Biomaterials are a unique selection of materials that provide this function, including fibroin, cellulose, chitin, and lignin. In particular, fibroin has been demonstrated to have a variety of functions and can be made into desired forms, such as nanofibers, sponges and films with high flexibility, robustness and optical refractive index. These attractive functions have been fully exploited in the fields of photovoltaics and biology. The integration of fibroin into flexible electronic devices has enabled the construction of a variety of devices with the desired functionality. Flexible fibroin has been used for the substrate of transient electrons, sacrificial layers of super-flexible electrons, dielectrics of transistors, active layers of memristors, and the like. In addition, stretchable electronic devices have also been developed. The fibroin film made of silk is soft and has stretchability similar to that of skin. However, how to fabricate nano-silver electrodes on such an adhesive substrate reduces signal noise, and it is still difficult to collect high-fidelity electrophysiological signals as signal inputs for a human-computer interface.

Disclosure of Invention

In order to solve the problem that the nano-silver electrode attached to the skin is used for collecting high-fidelity electrophysiological signals by using an electronic technology, the invention aims to provide a preparation method of a high-adhesion flexible electrode.

Another object of the present invention is to provide a flexible electrode obtained by the above preparation method, which is a highly stretchable electrode array.

The invention also aims to provide application of the flexible electrode in reducing signal noise in acquiring skin surface electromyographic signals.

The purpose of the invention is realized by the following technical scheme.

A preparation method of a high-adhesion flexible electrode comprises the following steps:

1) soaking fibroin in Na₂CO₃Boiling in water solution for removing sericin, taking out, washing with water, and drying to obtain degummed silk;

in the step 1), the Na₂CO₃The concentration of sodium carbonate in the aqueous solution is 5-50 g/L.

In the step 1), the boiling time is 60-120 min.

In the step 1), the drying is carried out for 6-24 hours at 30-60 ℃.

2) Mixing degummed silk, calcium chloride and formic acid, stirring at 60-80 ℃ for at least 30min to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, wherein the ratio of the degummed silk to the calcium chloride is 1: (0.05-0.35);

in the step 2), the ratio of the mass part of the degummed silk to the volume part of formic acid is 1 (3-10), and when the unit of the mass part is g, the unit of the volume part is ml.

3) Volatilizing formic acid in the solution obtained in the step 2) to obtain a soft silk protein film, and printing nano silver paste on the silk protein film by a screen printing method to obtain the flexible electrode.

In the step 3), the volatilization time is 24-48 hours, and the volatilization temperature is 20-25 ℃.

In the step 3), the mass fraction of the nano silver in the nano silver paste is 60-80%, and the other components are ethanol and isopropanol.

In the step 3), the thickness of the fibroin film is 180-230 μm.

The flexible electrode obtained by the preparation method.

The flexible electrode is applied to reducing signal noise in the process of collecting skin surface electromyographic signals. The invention has the beneficial effects that:

1. the nano silver paste is screen-printed on different substrates (PET, PDMS or SEBS), so that nano silver electrodes with the thickness of about 20 mu m are obtained on the substrates, and then the PDMS nano silver electrodes, the SEBS nano silver electrodes and the PET nano silver electrodes are obtained. The flexible electrode obtained by the invention not only can obtain the conductivity similar to that of PDMS nano silver electrodes, SEBS nano silver electrodes and PET nano silver electrodes manufactured by common flexible substrates (PET) and stretchable substrates (PDMS and SEBS), but also has higher adhesive strength. Compared with the prior art, the tensile substrate (PDMS, SEBS) has very weak adhesion strength with the nano-silver electrode, and is easy to desorb; the silk protein film in the flexible electrode is tightly combined with the nano-silver electrode, and the adhesion strength of the silk protein film is more than 10 times of that of the PDMS nano-silver electrode. 2. The silk protein film of the invention has different adhesion energy under different relative humidity.

3. The flexible electrode collects the electromyographic signals, recognizes the gesture signals, and controls the intelligent trolley to move forwards, leftwards, rightwards, backwards and stop through wireless transmission (Bluetooth).

Drawings

FIG. 1a is a photograph of the solution in step 2) of example 4;

FIG. 1b is a schematic illustration of a screen printing process;

FIG. 1c is a pattern of a nano-silver electrode screen printed on a fibroin film;

FIG. 2 is SEM images of the surfaces (a-d) of the nano-silver electrodes and the cross-sections (e-h) of the substrate and the nano-silver electrode in the products obtained in examples 1-4, wherein a-d are the surface morphologies of the products obtained in examples 1-4, respectively; e-h are the cross sections of the products obtained in examples 1-4, respectively;

FIG. 3a is a gesture (fist making, palm stretching, wrist bending, palm stretching and relaxing) for controlling different states (back, left, right, forward and stop) of the intelligent trolley;

FIG. 3b is the electromyographic signals of different movements of extensor carpi ulnaris (fist making, palm bending inward, palm bending outward and palm stretching);

FIG. 3c is a diagram of a real object of the intelligent trolley;

FIG. 4 is an electric control schematic diagram of an electromyographic signal acquisition and identification control intelligent trolley system.

Detailed Description

The technical scheme of the invention is further explained by combining specific examples.

TABLE 1 apparatus according to the following examples

TABLE 2 medicines and materials according to the following examples

Example 1 (comparative)

The preparation method of the PDMS nano silver electrode comprises the following steps: PDMS was used as the substrate. Two components a and B of PDMS were mixed as 10: 1 (mass ratio) to form a PDMS mixture, and left in vacuum for 30min to remove air bubbles. The PDMS mixture was poured onto a glass plate and cured at 50 ℃ for 1 h. After peeling off, a 200 μm thick PDMS film was obtained. And printing the nano silver paste on the PDMS film once by using a screen printing method to obtain the PDMS nano silver electrode. The surface topography of the PDMS nanosilver electrode is shown in fig. 2a, and the interface SEM between the PDMS and nanosilver electrode is shown in fig. 2 e.

Example 2 (comparative)

The preparation method of the SEBS nano silver electrode comprises the following steps: the substrate used SEBS. 50g of SEBS was dissolved in 100ml of toluene, followed by addition of magnetons and stirring for 1 hour to obtain a SEBS solution, 10ml of the SEBS solution was poured into a glass petri dish, and then evaporated at room temperature for 12 hours in a fume hood, and then peeled off to obtain a 0.1 μm thick SEBS film. And printing once by using a screen printing method, and printing the nano silver paste on the SEBS film to form a nano silver electrode. The surface topography of the SEBS nano-silver electrode is shown in FIG. 2b, and the SEM of the interface between the SEBS and the nano-silver electrode is shown in FIG. 2 f.

Example 3 (comparative)

The preparation method of the PET nano silver electrode comprises the following steps: the substrate was PET. And ultrasonically cleaning PET in deionized water and ethanol for 10 minutes in sequence, and drying by using nitrogen. And printing the water-based nano silver paste on the PET film by using a screen printing method to form a nano silver electrode. The surface topography of the PET nanosilver electrode is shown in FIG. 2c, and the SEM of the interface between the PET and nanosilver electrode is shown in FIG. 2 g.

Example 4

A preparation method of a high-adhesion flexible electrode (silk protein film is used as a substrate) comprises the following steps:

1) soaking fibroin in Na₂CO₃Boiling in water solution for 90min to remove sericin and Na₂CO₃The concentration of sodium carbonate in the aqueous solution was 20 g/L. Taking out, washing with distilled water for 3 times, and drying in oven at 80 deg.C for 12 hr to obtain degummed silk;

2) mixing 3g of degummed silk, 0.15g of calcium chloride and 20ml of formic acid in a beaker, heating and stirring the beaker on a hot table at 80 ℃ for half an hour to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, as shown in figure 1a, wherein the ratio of the degummed silk to the calcium chloride is 1: 0.05.

3) pouring the solution obtained in the step 2) into a culture dish, and naturally volatilizing formic acid in the solution in a fume hood until the formic acid is volatilized, so as to obtain a soft fibroin film, wherein the thickness of the fibroin film is 180-230 mu m, the volatilization time is 12 hours, and the volatilization temperature is 20-25 ℃. As shown in fig. 1b, the nano silver paste is printed on the silk protein film by a screen printing method to form a nano silver electrode, and the nano silver electrode and the silk protein film jointly form a flexible electrode.

The surface topography of the flexible electrode is shown in fig. 2d, and the interface SEM between the fibroin film and the nanosilver electrode is shown in fig. 2 h.

Example 5

2) mixing 3g of degummed silk, 0.45g of calcium chloride and 20ml of formic acid in a beaker, heating and stirring the beaker on a hot table at 80 ℃ for half an hour to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, as shown in figure 1a, wherein the ratio of the degummed silk to the calcium chloride is 1: 0.15.

Example 6

2) mixing 3g of degummed silk, 0.75g of calcium chloride and 20ml of formic acid in a beaker, heating and stirring the beaker on a hot table at 80 ℃ for half an hour to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, as shown in figure 1a, wherein the ratio of the degummed silk to the calcium chloride is 1: 0.25 l.

Example 7

2) mixing 3g of degummed silk, 1.05g of calcium chloride and 20ml of formic acid in a beaker, heating and stirring the beaker on a hot table at 80 ℃ for half an hour to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, as shown in figure 1a, wherein the ratio of the degummed silk to the calcium chloride is 1: 0.35.

In the above embodiments 1 to 7, the (hollow out) pattern of the screen in the screen printing method is the same as that in fig. 1c, so that the pattern of the nano silver electrode is the same as that in fig. 1c, the pattern of the nano silver electrode includes an electrode array of 8 channels, each channel is composed of three circular electrodes, the middle circular electrode is a reference electrode and serves as a zero potential point, and the two circular electrodes at the two sides form a differential input terminal. The introduced reference electrode effectively reduces noise interference and improves common mode rejection capability. The diameter of each circular electrode was 1 cm. The 8 channels were aligned in the transverse direction, the 3 circular electrodes of each channel were aligned in the longitudinal direction, for each channel: and 3 square electrodes are arranged below each channel, each round electrode is connected with one square electrode through a lead belonging to the nano silver electrode, and the 3 round electrodes are connected with the 3 square electrodes.

The products obtained in examples 1 to 4 were tested for conductivity and adhesive strength, the conductivity being the reciprocal of the resistivity, the resistivity formula being

Wherein R is resistance, rho is resistivity, l is the length of the nano silver electrode, and S is the cross-sectional area of the nano silver electrode.

Adhesive strength

F is the force for separating the substrate and the nano silver electrode, and S is the stressed area of the substrate and the nano silver electrode.

The results of testing the products obtained in examples 1-4 are shown in Table 3.

TABLE 3

As can be seen from Table 3, the conductivity of the nano-silver electrode on four substrates is 10^-6The difference is not obvious, thereby showing that the adhesiveness of the silk protein film has no influence on the conductivity of the nano silver electrode.

The flexible electrodes obtained in examples 4 to 7 were in different relative positionsThe adhesion energy test is carried out under the humidity by adopting the method mentioned by the J-K-R contact theory^[1-3]And testing the adhesion energy of the flexible electrode. The specific implementation method comprises the following steps: the flexible electrode is adhered to a glass slide by epoxy resin glue (one side of the nano silver electrode of the silk protein film is not contacted with the glass slide), and after the epoxy resin glue is cooled and dried, the adhesive strength of the flexible electrode is tested by an MTS CMT4000 tensile machine: the MTS CMT4000 tensile machine clamps the top end of a hard wood rod through a clamp, the bottom end of the hard wood rod is fixedly installed on the plane of a glass plano-convex mirror with the diameter of 20 mm, the convex surface of the glass plano-convex mirror is aligned with the center of a flexible electrode fixed on a glass slide, the flexible electrode is horizontally arranged, a downward force of 50N is firstly applied to enable the glass plano-convex mirror to be tightly adhered to the flexible electrode, then the direction of the force is changed to be upward, and when a critical value F is reached, a ball body can be suddenly disconnected and contacted. In the whole process, the running speed of the tensile machine is 0.02 mm/s. By the formula

The value of the adhesion energy can be calculated. Wherein F is the tensile force of MTS CMT4000 tensile machine, R is the radius of the glass plano-convex lens, and Ea is the adhesion energy. The test results are shown in Table 4. As can be seen from table 4, the adhesion energy of the fibroin film increases with the increase of the relative humidity, and reaches the maximum when the relative humidity reaches about 50%; however, the relative humidity continues to increase, and the adhesiveness is rather decreased because the relative humidity is too high.

Ca⁺The concentration has a large influence on the adhesion of the fibroin film, and Ca has a large influence⁺The concentration increases and the adhesion energy increases.

TABLE 4

The square electrode in the flexible electrode obtained in example 4 is connected with a signal acquisition circuit by a lead, and the specific connection mode is shown in fig. 4. The method comprises the following steps that 24 square electrodes at the bottom end of a flexible electrode are electrically connected with a signal amplifier, the signal amplifier is electrically connected with a low-pass filter, the low-pass filter is electrically connected with an A/D (analog/digital) converter, the A/D converter is electrically connected with a first controller, the first controller is connected with a second controller of the intelligent trolley in a Bluetooth mode, and the second controller receives signals of the first controller to drive a motor of the intelligent trolley to perform corresponding actions.

The electromyographic signals on the skin surface are physiological electrical signals collected from the surface skin of the muscle, and the collected signals are random superposition of action potentials and noise signals (interference of external environment, inherent noise and motion artifacts) of a motion unit due to the fact that the activity of the muscle is a very complex nonlinear process and belong to non-stationary signals. The electromyographic signals are only in millivolt level, the frequency is 10-500 Hz, the energy is concentrated in 10-300 Hz, the electromyographic signals are firstly amplified through a signal amplifier, the high-frequency noise part is removed through a low-pass filter, and analog signals are converted into digital signals through A/D conversion so as to facilitate signal transmission. When the signals are collected, in order to ensure the integrity of the signals, the collection frequency is at least 1000Hz according to the Nyquist law, and at least 1000 data are collected every second. Training and identifying the collected signals by a CNN cyclic convolution algorithm^[4-6]And the recognized gesture signals are transmitted to a second controller (51 single chip microcomputer) of the intelligent car through Bluetooth as shown in a table 5. The second controller of the intelligent trolley converts the received data into an instruction for controlling the trolley to move, so that the purpose that the flexible electrodes acquire signals and recognize myoelectric signals to control the trolley is achieved.

TABLE 5

Gesture	Relax the body	Fist making	Stretching palm	Bent wrist	Wrist extension
						Signal (16 system)	0x00	0x01	0x02	0x03	0x04
Trolley movement	Stop	Retreat	Forward	To the left	To the right

When in use, the fibroin film shown in figure 1c is attached to the human forearm, and the nano-silver electrode is outside and not in contact with the forearm. Fig. 3a is a gesture for controlling different states of the intelligent trolley, wherein corresponding myoelectric signals of different movements of extensor carpi ulnaris are different, so that different movements are recognized, and the purpose of controlling the trolley is achieved, the fist is clenched to enable the trolley to move backwards, the palm is stretched to enable the trolley to move forwards, the wrist is stretched (bent outwards) to enable the trolley to move leftwards, the wrist is bent (bent inwards) to enable the trolley to move rightwards, and the trolley is relaxed to enable the trolley to stop, and fig. 3b is a myoelectric signal of different movements of extensor carpi ulnaris; as can be seen from the figure, the electromyographic signals are extremely noisy and have almost no clutter noise. Fig. 3c is a real object diagram of the intelligent trolley.

Literature

1.Greenwood,J.A.J.P.M.Physical,and E.Sciences,Adhesion of elastic spheres.453(1961):p.1277-1297.

2.V.M.,et al.,On the influence of molecular forces on the deformation of an elastic sphere and its sticking to a rigid plane.

3.Maugis,D.and M.Barquins,Fracture mechanics and the adherence of viscoelastic bodies.1980.11(14):p.1989.

4. Liu Jingzhao, Chi Heng, Wu Jiang Lin, et al. gesture signal recognition algorithm [ J ] information technology and network security based on continuous wave Doppler radar, 2019,38(03):34-38.

5. Mode recognition of gesture action surface myoelectric signals based on BP neural network [ J ] biomedical engineering research, 2009(1):6-10.

6. An optimized gesture feature recognition classification method [ C ] based on surface electromyographic signals, the twelfth shenyang scientific academic society, 2015.

The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims

1. a preparation method of a highly adhesive flexible electrode, is characterized in that, comprises the following steps:

1) immersing fibroin in Na ₂ CO ₃ aqueous solution and boiling for removing sericin, taking out, rinsing with water and drying to obtain degummed silk;

2) Mix the degummed silk, calcium chloride and formic acid, and stir at 60-80° C. for at least 30 minutes to completely dissolve the degummed silk and remove air bubbles to obtain a transparent solution, wherein, in parts by mass, the degummed silk and The ratio of calcium chloride is 1:(0.05～0.35);

3) volatilize the formic acid in the solution obtained in step 2) to obtain a soft silk fibroin film, and print the nano-silver paste on the silk fibroin film by a screen printing method to obtain a flexible electrode.

2. preparation method according to claim 1, is characterized in that, in described step 2) in, the mass fraction of described degummed silk and the volume fraction ratio of formic acid are 1:(3～10), when all When the unit of the mass fraction is g, the unit of the volume fraction is ml.

The preparation method according to claim 2, characterized in that, in the step 3), the volatilization time is 24-48 hours, and the volatilization temperature is room temperature 20-25°C.

4 . The preparation method according to claim 3 , wherein, in the step 3), the mass fraction of the nano-silver in the nano-silver paste is 60-80%. 5 .

5 . The preparation method according to claim 4 , wherein in the step 3), the thickness of the fibroin film is 180-230 μm. 6 .

6 . The preparation method according to claim 5 , wherein in the step 1), the concentration of sodium carbonate in the Na ₂ CO ₃ aqueous solution is 5-50 g/L. 7 .

7 . The preparation method according to claim 6 , wherein, in the step 1), the boiling time is 60-120 min. 8 .

8 . The preparation method according to claim 7 , wherein, in the step 1), the drying is maintained at 30-60° C. for 6-24 hours. 9 .

9 . The flexible electrode obtained by the preparation method according to any one of claims 1 to 8 .

10. The application of the flexible electrode according to claim 9 in reducing signal noise in collecting electromyographic signals on the skin surface.