Interface chelating composite gel material as well as preparation method and application thereof

Abstract

The invention discloses an interface-chelated composite gel material as well as a preparation method and application thereof. According to the material, the problem that effective mechanical connection and conductive connection between the other end of hydrogel and a metal electrode or a rigid circuit are difficult when the hydrogel is used as a bioelectronic contact electrode can be solved; the hydrogel can be used as a chelating binder to realize stable mechanical and electrical bridging on a metal foil or film on a flexible or elastic substrate. And based on the flexible and elastic substrate, the stretchable conductive electrode can be prepared based on the interface chelation. According to the invention, the problem of end-to-end effective and stable conductive connection can be effectively solved. The electrode can be well applied to biological electrodes for electrophysiological signal detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of bioelectrode materials, relates to a composite gel material, and particularly relates to an interfacial chelation composite gel material, a preparation method thereof, and an application in electrophysiological signal transmission. Background Art

[0002] Compared with traditional flexible electrodes, soft hydrogels as bioelectrodes can greatly reduce the contact impedance with the skin / tissue. However, during the data acquisition process, due to the huge modulus difference between the hydrogel and the flexible or rigid circuit board, it is difficult to achieve a stable and reliable electrical connection, resulting in unstable electrophysiological signals, baseline drift, and a low signal-to-noise ratio. Researchers have tried various methods to solve this problem. The literature "Stretchable transistors and functional circuits for human-integrated electronics" (Yahao Dai, Huawei Hu, Maritha Wang, Jie Xu and Sihong Wang, Nature electronics, 4, 2021) lists three general engineering methods to optimize the problem of mechanical property mismatch between rigid elements / semiconductor materials and elastic encapsulation materials in stretchable transistors, namely buckling engineering, stiffness engineering, and intrinsic stretchability engineering. These three performance optimization strategies can effectively improve the stretchability of semiconductor stretchable transistors while maintaining a small resistance change within the stretchable range. However, the above several strategies are not applicable to the gel and flexible electrode / circuit system with end-to-end connection on the plane. The conductive connection between the easily deformable gel and the circuit causes large fluctuations in the baseline during the process of collecting electrical signals, resulting in a poor signal-to-noise ratio. For this end-to-end conductive connection, the viscosity of the hydrogel can also be optimized by molecular structure modification, but a large number of hydroxyl groups will be introduced during the optimization process, and the conductivity will also decrease significantly.

[0003] Based on this, the present invention proposes a hydrogel material that can stably bridge an external electrode or circuit and can stably record electrophysiological signals. Summary of the Invention

[0004] The purpose of the present invention is to provide an interfacial chelation composite gel material, a preparation method thereof, and an application, aiming at the deficiencies of the prior art. This material can overcome the problem that when the hydrogel is used as a contact electrode for bioelectronics, it is difficult to effectively mechanically connect and conductively connect the other end with a metal electrode or a rigid circuit. Under the action of interfacial chelation, this hydrogel can be used as a chelating binder to achieve stable mechanical and electrical bridging on a metal foil or film on a flexible or elastic substrate. It can be well used to stably record electrophysiological signals under common mechanical interference.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A preparation method of an interfacial chelating composite gel material includes the following steps:

[0007] 1) Dissolve polyvinyl alcohol particles in deionized water to obtain an aqueous polyvinyl alcohol solution;

[0008] 2) Mix the aqueous polyvinyl alcohol solution with phytic acid solution and sugar;

[0009] 3) Perform a water bath heating treatment on the mixed solution of the substances in step 2) to promote cross-linking between polymer chains and obtain a partially cross-linked hydrogel solution;

[0010] 4) Take a substrate material, spin-coat the hydrogel solution obtained in step 3) onto the surface of the substrate, and dry and cure it at room temperature; the substrate material is a metal sheet, a flexible material, or an elastic material. When the substrate material is a flexible material or an elastic material, after the hydrogel is dried and cured, a metal thin film or a liquid metal film is formed on the surface of the hydrogel by evaporation coating or brushing; an electrode material capable of stable bridging through interfacial chelation is obtained.

[0011] In the above technical solution, further, the mass concentration of the aqueous polyvinyl alcohol solution is 5% - 15%.

[0012] Further, the mass concentration of the phytic acid solution is 50%;

[0013] Further, the mass ratio of the aqueous polyvinyl alcohol solution, phytic acid solution, and sugar is 10:5:4; the mixing is carried out by stirring at 60°C and 800 rpm / min for at least 30 min.

[0014] Further, the water bath heating temperature is 80°C and the time is 2 h;

[0015] Further, the sugar is one or more of glucose, fructose, or other saccharide substances containing glucose or fructose;

[0016] Further, when the material is used for bridging: when the substrate material is a metal sheet, lap the cured hydrogel surface on it with the surface of the metal to be connected, press and then let it stand for 24 - 144 h, preferably 60 - 80 h, more preferably 72 h, to enable sufficient interfacial chelation to form a stable conductive connection interface with excellent bonding strength;

[0017] Furthermore, when the material is used for bridging: when the substrate material is a flexible material or an elastic material, the formed flexible electrode materials, or elastic electrode materials, or between the flexible electrode material and the elastic electrode material are overlapped face to face with the metal thin film surface and the liquid metal film surface respectively, and pressed to form a stable conductive connection interface with interfacial chelation.

[0018] The composite gel material of the present invention has an interfacial chelation effect. The hydrogel containing a chelating agent will undergo heterogeneous passivation on the metal surface, generating a nano-island-like interlocking structure on the metal surface, thereby enhancing the physical bonding strength between metals. This interfacial chelation effect is not only applicable to metal sheets but also to metal thin films prepared by methods such as vacuum evaporation or brushing. Since both of these two metal materials are thin films, the rapid interfacial chelation reaction can also enhance the bonding strength between the metal thin films. In addition, it is also applicable to liquid metal films. When the liquid metal is roll-brush printed on the surface of the hydrogel containing a chelating agent, the chelation reaction rapidly forms a relatively thin and hard chelate layer on the surface of the liquid metal. Under repeated roll-brush times, the liquid metal wrapped with the chelate will change from micron particles to nano particles, and finally form a very uniform conductive thin film. When two roll-brush printed liquid metal thin films are pressed and overlapped, the interlocking structure between the nano particles and the interfacial chelation effect between the gel and the liquid metal simultaneously improve the bonding strength of the overlapping interface. And based on flexible and elastic substrates, the solution of the present invention can be prepared into some stretchable conductive electrodes based on the interfacial chelation effect. The solution of the present invention can effectively solve the problem of effective and stable conductive connection from end to end. It can be well applied to electrophysiological signals and bioelectrodes. Especially when a soft conductive hydrogel with an internal chelation structure adheres to the skin / tissue, and the other side is stably conductively connected to the flexible or elastic-flexible overlapping metal electrode realized by interfacial chelation in the present invention, this mechanical gradient design can achieve high signal-to-noise ratio (SNR) electrophysiological signal recording under mechanical perturbation, including electromyogram signals, nerve signals, and cerebral cortex electrical signals. Description of the Drawings

[0019] Figure 1 Schematic diagram of the adhesion strength and conductive performance after interfacial chelation between the hydrogel and copper foil (100μm);

[0020] Figure 2 Schematic diagram of the adhesion strength and conductive performance after interfacial chelation between the hydrogel and other metal sheets;

[0021] Figure 3 Schematic diagram of the adhesion strength and conductive performance after interfacial chelation between the hydrogel and vacuum-evaporated gold films (thicknesses of 20nm, 40nm, 60nm);

[0022] Figure 4Schematic diagram of the adhesion strength and electrical conductivity between flexible liquid metal electrodes (F-F) printed by a roller brush on the surface of a hydrogel;

[0023] Figure 5 Schematic diagram of the elastic-flexible conductive connection interface of internal chelating gel and bidirectional interface chelation for high signal-to-noise ratio myoelectric signals. Detailed implementation manners

[0024] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Example 1

[0026] 1) First, dissolve polyvinyl alcohol particles in deionized water, stir at 80 °C for 12 hours, and the stirring speed is 600 rpm / min to prepare a viscous polyvinyl alcohol aqueous solution.

[0027] 2) Mix the polyvinyl alcohol mixed solution in step 1) with a phytic acid solution with a mass concentration of 50% and honey in a mass ratio of 10:5:4, the temperature is 60 °C, the stirring speed is 800 rpm / min, and the stirring time is 30 min.

[0028] 3) Perform a water bath heating treatment on the mixed solution of various substances in step 2) to promote cross-linking between polymer chains. The water bath heating temperature is 80 °C and the heating time is 2 h to obtain a partially cross-linked hydrogel solution.

[0029] 4) Cut several pieces of copper foil with a thickness of 100 μm, spin-coat the gel solution obtained in step 3) onto the surface of the copper foil, and protect the parts without gel with tape. The spin-coating speed is 300 rpm / min for 6 s; 3000 rpm / min for 20 s. Dry and cure at room temperature for later use.

[0030] 5) Lap the 100-μm-thick copper foils obtained in step 4) face to face, the lap width is 1 cm, cut to a length of 1 cm, press the lapped interface at room temperature with a hot press for 5 min, and then place it at room temperature for 72 h to allow the phytic acid in the gel to fully chelate with the copper surface to obtain a copper foil conductive connection interface with a relatively high bonding strength.

[0031] Examples 2 - 6

[0032] After the pressing and lapping step in step 5) of Example 1, adjust the chelating time at room temperature to 24 h, 48 h, 96 h, 120 h, 144 h, corresponding to Examples 2, 3, 4, 5, 6 respectively.

[0033] Combined with the attached Figure 1From the comparison results with Examples 1 - 6, it can be seen that when the chelation time of the phytic acid - containing hydrogel between two 100 - μm - thick copper foils increases from 24 h to 72 h, the bonding strength between the copper foils gradually increases, and the maximum value reaches 1.95 MPa. Additionally, further increasing the chelation time will affect the shape of the interlocking structure on the copper foil surface, thereby reducing the bonding strength again.

[0034] Examples 7 - 11

[0035] Replace the copper foil in steps 4) and 5) of Example 1 with molybdenum (Mo), iron (Fe), nickel (Ni), aluminum (Al), and silver (Ag), corresponding to Examples 7, 8, 9, 10, and 11 respectively.

[0036] Combined with the attached Figure 2 From the comparison results with Examples 1, 7 - 11, it can be seen the universality of the interfacial chelation reaction of this phytic acid - containing hydrogel with different metal materials. At the same time, due to the conductivity of the hydrogel itself, the ultra - thin hydrogel layer will not affect the conductivity between the connected metal materials.

[0037] Example 12

[0038] 1) First, dissolve polyvinyl alcohol particles in deionized water, stir at 80 °C for 12 hours with a stirring speed of 600 rpm / min to prepare a viscous polyvinyl alcohol aqueous solution.

[0039] 2) Mix the polyvinyl alcohol mixed solution in step 1) with a 50% mass - concentration phytic acid solution and honey in a mass ratio of 10:5:4, at a temperature of 60 °C, with a stirring speed of 800 rpm / min and a stirring time of 30 min.

[0040] 3) Perform a water - bath heating treatment on the mixed solution of various substances in step 2) to promote cross - linking between polymer chains. The water - bath heating temperature is 80 °C and the heating time is 2 h to obtain a partially cross - linked hydrogel solution.

[0041] 4) Cut several poly(ethylene terephthalate) films with a side length of 8 cm for standby, spin - coat a polydimethylsiloxane precursor on the films and cure it. Perform oxygen plasma cleaning treatment on the surfaces of the poly(ethylene terephthalate) films and the cured polydimethylsiloxane respectively, and then spin - coat the partially cross - linked hydrogel solution prepared in step 3) on the poly(ethylene terephthalate) films and polydimethylsiloxane, and dry and cure at room temperature. The spin - coating conditions are 300 rpm / min, 6 s; 3000 rpm / min, 20 s.

[0042] 5) Vacuum evaporate a 20-nm-thick gold film on the surface of the cured hydrogel. The sample with gold evaporation on the polyethylene terephthalate film coated with the hydrogel is a flexible gold electrode, and the sample with evaporation on the surface of polydimethylsiloxane coated with the hydrogel is an elastic gold electrode. After depositing the metal film, cut the sheet, and then lap the side with the gold film deposited. The lap area is 1 cm 2 , and use a hot press to press the lapped interface at room temperature for 5 minutes to obtain a gold-plated conductive connection interface with a relatively high bonding strength.

[0043] Examples 13 - 14

[0044] Adjust the thickness of the evaporated gold film in step 5) of Example 12 to 40 nm and 60 nm, corresponding to Examples 13 and 14 respectively.

[0045] Combined with the Figure 3 comparison results in Examples 12, 13, and 14, it can be seen that the gold films evaporated on the surface of the hydrogel on the flexible substrate (F) or the elastic substrate (E) can be lap jointed in any form. The lap joint between the flexible gold electrodes is F - F, the lap joint between the elastic gold electrodes is E - E, and the lap joint between the flexible gold electrode and the elastic gold electrode is F - E. Figure 3 The statistical results in the right figure show that the gold electrodes with F - F and E - E lap joints both have relatively high bonding strengths and are not affected by the thickness of the evaporated gold film.

[0046] Example 15

[0047] 1) First, dissolve polyvinyl alcohol particles in deionized water, stir at 80 °C for 12 hours at a stirring speed of 600 rpm / min to prepare a viscous polyvinyl alcohol aqueous solution.

[0048] 2) Mix the polyvinyl alcohol mixed solution in step 1) with a 50% mass concentration phytic acid solution and honey in a mass ratio of 10:5:4 at a temperature of 60 °C, a stirring speed of 800 rpm / min, and a stirring time of 30 min.

[0049] 3) Perform a water bath heating treatment on the mixed solution of multiple substances in step 2) to promote cross-linking between polymer chains. The water bath heating temperature is 80 °C and the heating time is 2 h to obtain a partially cross-linked hydrogel solution.

[0050] Cut several pieces of polyethylene terephthalate films with a side length of 8 cm for standby, and spin-coat the polydimethylsiloxane precursor on some of the films and cure it. Oxygen plasma cleaning treatment is carried out on the surfaces of the polyethylene terephthalate films and the cured polydimethylsiloxane respectively, and then the prepared partially cross-linked hydrogel solution is spin-coated on the polyethylene terephthalate films and polydimethylsiloxane, and dried and cured at room temperature. The spin-coating conditions are 300 rpm / min, 6 s; 3000 rpm / min, 20 s.

[0051] 4) For the interfacial chelation of the hydrogel and the liquid metal, first mix 2% by mass of copper nanoparticles with the liquid metal in a high-speed mixer, and then evenly roll-coat the liquid metal mixture on the surface of the dried gel film in step 3) with a roller brush, and roll the brush multiple times until the conductivity meets the requirements. The sample with the liquid metal rolled on the polyethylene terephthalate film coated with the hydrogel is a flexible liquid metal electrode, and the sample with the liquid metal rolled on the surface of the polydimethylsiloxane coated with the hydrogel is an elastic liquid metal electrode.

[0052] 5) Overlap the two conductive sheets after the liquid metal is rolled 50 times in step 4) face to face: Cut the sheets, and then overlap the sides with the liquid metal. The overlap area is 1 cm 2 , and press the overlapped interface at room temperature for 5 min with a hot press to make the chelation interface between the liquid metal mixture and the gel more stable.

[0053] Examples 16 - 18

[0054] Adjust the number of times the liquid metal is rolled in step 5) of Example 15 to 1 time, 10 times, and 100 times, corresponding to Examples 16, 17, and 18 respectively.

[0055] Combined Figure 4 , Figure 5 With the comparison results of Examples 15, 16, 17, and 18, it can be seen that as the number of rolling times increases from 1 time to 50 times, the interfacial bonding strength of the obtained overlapped liquid metal electrodes will decrease, but the resistance of the connection interface will decrease significantly, approaching the conductivity of the liquid metal itself. However, when the number of rolling times reaches 100 times, the resistance will increase again, which is due to the oxidation of the liquid metal on the surface under multiple frictions. Therefore, rolling the liquid metal 50 times on the surface of the hydrogel on a flexible or elastic substrate can obtain a flexible conductive connection interface and an elastic conductive connection interface with a relatively large bonding strength.

[0056] Example 19

[0057] When a soft conductive hydrogel with an internal chelation structure adheres to the skin / tissue and is stably conductively connected to a metal electrode with flexible or elastic-flexible lap joint achieved through interfacial chelation on the other side, this mechanical gradient design can achieve electrophysiological signal recording with a high signal-to-noise ratio (SNR) under small mechanical perturbations, including electromyogram signals, nerve signals, and electrocorticogram signals. The soft conductive hydrogel with the internal chelation structure is a hydrogel system containing metal ions and a chelating agent, where the chelating agent is phytic acid. Chelation occurs between the metal ions and phytic acid inside the hydrogel to form a chelation structure, thereby reducing the elastic modulus of the hydrogel, and its elastic modulus can be as low as below 300 Pa. Its preparation method includes the following:

[0058] 1) Add metal particles (usually with a mass concentration of 5% - 15%) to an aqueous solution of polyvinyl alcohol and disperse them ultrasonically. The metal particles are one or more of gold nanoparticles or nanowires, silver nanoparticles or nanowires, copper nanoparticles or nanowires, gallium oxide micro- or nanoparticles, and liquid metal EGaIn (usually with a mass concentration of 0.5% - 2% in the solution);

[0059] 2) Mix the solution obtained in 1) with a phytic acid solution and honey in a ratio (usually a mass ratio of 10:5:4) and stir at about 60 °C;

[0060] 3) Subject the solution obtained in 2) to a water bath heating treatment (about 80 °C) to promote the formation of crosslinking and chelation. Control the heating time through the reaction phenomenon. When the solution gradually becomes transparent from turbid and then turns orange-yellow, stable chelates are formed between the metal and the phytic acid small molecules in the gel, and stop the water bath heating;

[0061] 4) Subject the gel solution obtained in 3) after water bath heating with partial crosslinking and stable chelation to a freeze-thaw treatment (-40 °C for 2 h, thaw at room temperature for 30 min, cycle 3 - 4 times) to fully crosslink and solidify, obtaining a metal gel composite system with a reduced elastic modulus based on internal chelation.

[0062] Figure 5 The test results of the bimodal chelation system as an electromyogram test electrode are shown. Using the soft gel after internal chelation as the electromyogram test electrode, and using the elastic and flexible liquid metal electrodes of the present invention as the connection electrodes at the internal chelation gel end and the circuit end respectively after lap joint as the electromyogram test electrodes, high signal-to-noise ratio electromyogram signals can be measured when the skin is flat (Normal), when it deforms (deformed), and even under some weak mechanical perturbations (Vibratile).

[0063] The embodiments described above are only some of the better solutions of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical field can also make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing an interfacial chelating composite gel material, characterized in that: These include: 1) dissolving polyvinyl alcohol particles in deionized water to obtain a polyvinyl alcohol aqueous solution; 2) mixing the polyvinyl alcohol aqueous solution, the phytic acid solution and the sugar; 3) heating the mixed solution of the multiple substances in step 2) in a water bath to promote cross-linking between polymer chains to obtain a partially cross-linked hydrogel solution; 4) taking a substrate material, spin-coating the hydrogel solution obtained in step 3) onto the surface of the substrate, and drying and curing at room temperature; The substrate material is a metal sheet, a flexible material, or an elastic material. When the substrate material is a flexible material or an elastic material, after the hydrogel is dried and solidified, a metal film or a liquid metal film is formed on the surface of the hydrogel by evaporation or painting; thus obtaining an electrode material that can be stably bridged through interface chelation.

2. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: The mass concentration of the polyvinyl alcohol aqueous solution is 5% to 15%.

3. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: The mass concentration of the phytic acid solution is 50%.

4. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: The mass ratio of the polyvinyl alcohol aqueous solution, the phytic acid solution and the sugar is 10:5:

4.

5. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: The water bath heating temperature is 80° C. and the heating time is 2 h.

6. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: The sugar is one or more of glucose and fructose.

7. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: When the material is used for bridging: when the base material is a metal sheet, the cured hydrogel surface thereon is overlapped with the metal surface to be connected, and after pressing, it is left to stand for 24 to 144 hours to allow sufficient interface chelation to form a stable conductive connection interface with excellent bonding strength.

8. The method for preparing the interfacial chelating composite gel material according to claim 1, characterized in that: When the material is used for bridging: when the base material is a flexible material or an elastic material, the formed flexible electrode materials, or the elastic electrode materials, or the flexible electrode material and the elastic electrode material are overlapped and pressed with the metal film surface and the liquid metal film surface facing each other to form a stable conductive connection interface with interface chelation.

9. An interfacial chelating composite gel material, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. The use of the interfacial chelating composite gel material according to claim 9, characterized in that: Used for electrophysiological signal transmission or recording.

Images