Conductive hydrogel adhesive with temperature phase transition properties for securing epidermal electrodes

Abstract

The present application relates to the technical field of conductive adhesive, in particular to a conductive hydrogel adhesive with temperature phase change characteristics for fixing skin electrode, comprising the following components by weight: structural component 5-20 parts; at least one selected from gelatin, collagen, agar, chitosan, sodium alginate, gellan gum, methyl cellulose and xanthan gum; conductive substance 1-5 parts; water retention component 5-10 parts; water 50-70 parts. The prepared adhesive has excellent adhesive performance and conductivity, low material cost, green environmental protection, simple use method, and can promote the optimized use of most electrodes on the market.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of conductive hydrogel adhesive, in particular to a conductive hydrogel adhesive with temperature phase change characteristics for fixing epidermal electrodes. BACKGROUND

[0002] Adhesive is used to bond two substances at the interface, and the adhesion between two conductive materials requires the adhesive to have adhesion, conductivity and certain mechanical strength. The adhesive in the prior art adheres two materials together through the adhesion and cohesion of the interface, mainly including epoxy resin, polyacrylic acid, polyurethane and the like. The use process mainly relies on high molecular monomers or oligomers for coating, and the materials are polymerized or dried before being bonded.

[0003] A hydrogel adhesive for a battery negative electrode is prepared in CN119242253A. The invention has a chain entanglement foam structure, which can effectively solve the swelling problem of Si-based negative electrode and improve the cycle life and cycle stability of the battery. However, the hydrogel adhesive does not have the ability of temperature phase change, and cannot be used for the adhesion and peeling of skin electrodes.

[0004] A hydrogel adhesive that can be used underwater is prepared in CN114149753A. The hydrogel adhesive provided by the invention includes A liquid and B liquid before curing. The initiator in the A liquid can form an oxidation-reduction initiation system with the reducing agent in the B liquid, initiate in-situ polymerization and crosslinking of water-soluble monomers, and form an interpenetrating network structure with water-soluble polymer chains to achieve fast and strong adhesion. However, the adhesive does not have the ability of temperature phase change and does not have the effect of conductivity; after bonding the electrode, the electrode cannot work.

[0005] Conductive hydrogel adhesive requires good mechanical strength, excellent adhesion, suitable use temperature and suitable conductivity. In the prior art, the electrode is bonded mainly by polymerization of high molecular or in-situ curing of hydrogel. The problem of not being able to simultaneously satisfy the requirements of electrode bonding in terms of conductivity and mechanical properties is common. Moreover, the current adhesive often has toxicity, no temperature phase change and other problems. SUMMARY

[0006] In view of this, the purpose of the present application is to provide a conductive hydrogel adhesive with temperature phase change characteristics for fixing epidermal electrodes. Through the optimization of structural components, the synergistic effect of firm adhesion, excellent conductivity and reversible phase change is achieved, and the stability of the electrode is improved.

[0007] The present application constructs a hydrogel adhesive by introducing various structural components with phase change properties, and the adhesive has high mechanical strength and good adhesion by optimizing the composition of the structural components, and can firmly adhere to the electrode. The simultaneously introduced conductive component has excellent conductivity to ensure the normal use of the electrode.

[0008] Unlike conventional adhesives, the adhesive provided by the present application has temperature phase change, adhesion and conductivity. The adhesive is in a solid state at normal temperature, and will melt into a liquid state when heated to 50 degrees. The liquid adhesive is applied to the interface of the conventional electrode on the skin, and will return to a solid state when cooled to body temperature, and adhere the electrode to the skin. Since the adhesive itself has good conductivity, it does not affect the detection of various signals of the conventional electrode.

[0009] The adhesive provided by the present application is composed of structural components, conductive substances, water and water-retaining components, wherein the structural components are composed of natural polymers (such as proteins and polysaccharides) with reversible phase change properties; the adhesive has reversible temperature phase change function, and the natural polymers (proteins / polysaccharides) with reversible phase change properties such as gelatin, collagen and agar are used as the core to regulate the phase change temperature and adhesion performance through compounding. The conductive substances and components are reasonably matched and proportioned to make the adhesive have optimized water-retaining performance and conductivity. The prepared adhesive has excellent adhesion and conductivity, low material cost, green environmental protection, simple use method, and can promote the optimized use of most electrodes on the market.

[0010] The technical scheme of the present application is as follows:

[0011] <First aspect>

[0012] A conductive hydrogel adhesive with temperature phase change properties for fixing skin electrodes, comprising the following components by weight:

[0013] Structural components 5-20 parts; at least one selected from gelatin, collagen, agar, chitosan, sodium alginate, gellan gum, methyl cellulose and xanthan gum;

[0014] Conductive substances 1-5 parts;

[0015] Water-retaining components 5-10 parts;

[0016] Water 50-70 parts.

[0017] The water-retaining component is at least one selected from betaine, sodium citrate, glycerol, ethylene glycol, propylene glycol, sodium tripolyphosphate, ikkodoin, sodium pyrrolidone carboxylate, trehalose and nicotinamide.

[0018] The conductive substance is at least one selected from sodium chloride, lithium chloride, potassium nitrate and silver nanoparticles.

[0019] Preferably, the conductive substance and the water-retaining component satisfy one of the following combinations:

[0020] (A) betaine and sodium chloride;

[0021] (B) sodium citrate and potassium nitrate;

[0022] (C) betaine and silver nanoparticles.

[0023] The combination of betaine and sodium chloride can improve the mobility of free ions, the combination of sodium citrate and potassium nitrate can improve the concentration of free ions, and the combination of betaine and silver nanoparticles can build a connected three-dimensional conductive network and form a synergistic conductive path. The above preferred combinations can improve the conductivity of the adhesive and reduce the tightness during the use of the gel.

[0024] Preferably, the structural component is one of the following combinations:

[0025] (a) gelatin and agar, with a complex weight ratio of (1-5):1;

[0026] (b) gelatin and gellan gum, with a complex weight ratio of (2-8):1;

[0027] (c) collagen and xanthan gum, with a complex weight ratio of (2-4):1;

[0028] (d) gelatin and sodium alginate, with a complex weight ratio of (1-3):1.

[0029] <Second aspect>

[0030] A preparation method of the conductive hydrogel adhesive as described above, comprising the following steps:

[0031] (1) adding the water-retaining component and the conductive substance into water, and physically stirring until completely dissolved to obtain a premixed solution;

[0032] (2) adding the structural component to the premixed solution and stirring to form a uniformly dispersed solution;

[0033] (3) heating the dispersed solution to a certain temperature and stirring at constant temperature for 30-60 minutes;

[0034] (4) cooling to room temperature to form a gel.

[0035] In step (3), the heating conditions are as follows:

[0036] When the structural component is gelatin, the temperature is raised to 60-70 degrees. When the structural component is collagen, the temperature is raised to 40-60 degrees. When the structural component is agar, the temperature is raised to 90-100 degrees. When the structural component is sodium alginate, the temperature is raised to 60-80 degrees. When the structural component is gellan gum, the temperature is raised to 80-100 degrees. When the structural component is xanthan gum, the temperature is raised to 80-90 degrees.

[0037] When the structural component is a combination of gelatin and agar, the temperature is raised to 90 degrees for dissolution; when the structural component is a combination of gelatin and gellan gum, the temperature is raised to 80 degrees Celsius for dissolution; when the structural component is a combination of collagen and xanthan gum, the temperature is raised to 80 degrees for dissolution; and when the structural component is a combination of gelatin and sodium alginate, the temperature is raised to 70 degrees Celsius for dissolution. By adjusting the hydrophilic-hydrophobic balance of the structural components and the physical and chemical cross-linking between them, the adhesion and mechanical strength of the adhesive can be enhanced, and the wearing comfort can be improved.

[0038] <Third aspect>

[0039] Application of the conductive hydrogel adhesive as described above in fixing epidermal electrodes.

[0040] The application is to apply the molten adhesive to the electrode-skin interface, and after cooling and solidification, a conductive adhesive layer is formed. It is suitable for metal electrodes, carbon electrodes and gel electrodes.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] (1) By adding specific structural components with reversible phase change properties (such as gelatin, collagen, agar, chitosan, sodium alginate, gellan gum, methyl cellulose, xanthan gum, etc.) to the adhesive formula, and further optimizing the content range of each component, a phase change gel with a melting point of 50-80 degrees and a solidification point of 30-50 degrees is prepared. The adhesive is immersed in the skin surface wrinkles in liquid state, and after waiting for cooling and solidification, an adhesive effect is formed. In this way, common electrodes on the market (including metal electrodes, shaped gel electrodes, carbon electrodes, etc.) can be adhered to the skin surface, and only 5-15 seconds are needed for solidification and firm adhesion. The temperature during use is maintained within the range that the human body can tolerate and is comfortable.

[0043] (2) By adding specific conductive components and water-retaining agents to the adhesive formula, and providing the preferred combination between the two, such as the combination of betaine and sodium chloride, which can improve the mobility of free ions, the combination of sodium citrate and potassium nitrate, which can improve the concentration of free ions, and the combination of betaine and silver nanoparticles, which can construct a connected three-dimensional conductive network and form a synergistic conductive path. Each of the above combinations can improve the conductivity of the adhesive and reduce the tightness during use of the gel.

[0044] (3) By mutual matching of structural components (such as matching of gelatin and agar; matching of collagen and xanthan gum; matching of gelatin and sodium alginate, etc.), the hydrophilic-hydrophobic balance and the mutual physical and chemical cross-linking of the microstructure of the structural components are promoted, so that the adhesive has stronger adhesion and mechanical strength. The gel prepared by this method can be completely peeled off from the skin and the surface of the commercial electrode after use, and does not stick to the hair and leave residues. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, read in conjunction with the accompanying drawings:

[0046] Figure 1 Photos of the adhesive in Example 1 showing solid and liquid states at different temperatures;

[0047] Figure 2 Case of the adhesive in Example 1 in the use of commercial electromyographic signal electrodes, wherein (a) is a test of a commercial electrode without the aid of the adhesive; (b) is a test with the aid of the adhesive prepared in Example 1;

[0048] Figure 3 Comparison of the adhesive in Example 1 with commercially available adhesives in transcranial stimulation applications; wherein (a) is a commercial conductive paste 3M conductive paste; (b) is the adhesive prepared in Example 1;

[0049] Figure 4 Comparison of the adhesive in Example 1 with commercially available adhesives after use in transcranial stimulation applications; wherein (a) is a commercial conductive paste 3M conductive paste; (b) is the adhesive prepared in Example 1. DETAILED DESCRIPTION

[0050] The present application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of adjustments and improvements can be made. These all belong to the protection scope of the present application.

[0051] Example 1

[0052] An electrically conductive gel adhesive comprising the following components in parts by weight: gelatin 10 parts, agar 5 parts, betaine 23 parts, water 60 parts, sodium chloride 2 parts.

[0053] The preparation method of the electrically conductive gel adhesive comprises the following steps:

[0054] (1) Add betaine and sodium chloride into water, stir for 30 minutes until completely dissolved;

[0055] (2) Add gelatin and agar into the solution obtained in step 1, stir for 5 minutes until uniform;

[0056] (3) The mixture obtained in step 2 is heated at 90 degrees, and a completely dissolved solution is obtained after one hour;

[0057] (4) The solution obtained in step 3 is cooled to room temperature to obtain a gel.

[0058] Figure 1 The photos of the adhesive of the present embodiment showing solid and liquid states at different temperatures; solid at 25°C, liquid at 50°C.

[0059] Figure 2 The case of the adhesive of Example 1 in the use of commercial myoelectric signal electrodes, wherein (a) is the test of commercial electrodes without the aid of adhesive; (b) is the test with the aid of the adhesive prepared in Example 1. The results show that the signal obtained with the aid of the adhesive of Example 1 has better signal strength and higher signal-to-noise ratio than the signal obtained by direct measurement of commercial electrodes. The commercial electrode is a commercially available Ag / AgCl surface electrode with a diameter of 2 mm and a thickness of 1 mm. During the test, first wipe the back of the arm with an alcohol pad, then attach the ground electrode to the back of the hand, the reference electrode and the working electrode to the position of the flexor digitorum superficialis (FDS) of the arm, and use a commercial myoelectric signal acquisition device (device model: HKJ-15C, Hefei Huake Electronic Technology Institute; acquisition range: 0.5-400 Hz; acquisition frequency: 2000 Hz) to collect signals. Ten separate samples were used for collection, and the data were averaged. The signal-to-noise ratio SNR is calculated as follows: SNR (dB) = 20 log (A signal / A noise ), where A signal and A noise represent the amplitudes of the signal and the background, respectively. The values of A signal and A noise can be evaluated by root mean square (RMS) analysis, indicating the fluctuation of the signal over time.

[0060] Figure 3For the adhesion comparison of the adhesive in transcranial stimulation application in Example 1 with commercial conductive paste 3M conductive paste; wherein (a) is commercial conductive paste 3M conductive paste; (b) is the adhesive prepared by Example 1. Among them: in the transcranial electrical stimulation test, the commercial electrode is a matched Ag / AgCl surface ring electrode with a diameter of 2mm and a thickness of 1mm. During the test, first clean the head side position, then paste the ring electrode on the corresponding electric stimulation acupoint position of the head, and use the commercial electromyographic signal acquisition device (device model: Starstim 32, Yingful instrument) for electrical stimulation. The commercial conductive paste 3M conductive paste cannot successfully fix the electrode and needs the assistance of the electrode cap, while the adhesive provided by Example 1 of the application can directly fix the commercial transcranial stimulation electrode.

[0061] Figure 4 For the adhesion comparison of the adhesive in transcranial stimulation application in Example 1 with commercial conductive paste 3M conductive paste. Among them, (a) is commercial conductive paste 3M conductive paste; (b) is the adhesive prepared by Example 1. The specific test process is as follows: first, clean the scalp of the test area (F3 / F4 brain area), including cotton cleaning and alcohol cleaning. The commercial conductive paste 3M conductive paste and the adhesive prepared by the application are respectively adhered to the test area, and the dynamic monitoring is carried out for five hours under the condition of temperature 25±2℃, humidity 50±5%. In this process, simulate head movement (head nodding and shaking frequency 1 time / s, interval 5 minutes, test 2 minutes. Last for 30 minutes) and electromagnetic interference control measures (such as Faraday cage shielding) fall off. According to the electrode displacement>2mm, it is judged as failure. The residual amount is tested by residual area method, and the residual area ratio is analyzed by Image J software after image acquisition. The commercial conductive paste 3M™ conductive paste has a large amount of residual leakage after use, while the adhesive provided by the application can be directly removed without residue.

[0062] Example 2

[0063] A conductive gel adhesive, comprising the following components in parts by weight: gelatin 8 parts, gellan gum 2 parts, sodium citrate 15 parts, water 70 parts, potassium nitrate 5 parts.

[0064] The preparation method of the conductive gel adhesive, comprising the following steps:

[0065] (1) Add sodium citrate and potassium nitrate to water, stir for 1 hour until completely dissolved;

[0066] (2) The solution obtained in step 1 is added with gelatin and gellan gum, and stirred for 20 minutes until uniform;

[0067] (3) The mixture obtained in step 2 is heated at 80 degrees, and a completely dissolved solution is obtained after one hour;

[0068] (4) The solution obtained in step 3 is cooled to room temperature to obtain a gel.

[0069] Example 3

[0070] A conductive gel adhesive comprises the following components in weight parts: collagen 15 parts, xanthan gum 5 parts, glycerol 10 parts, water 65 parts, silver nanoparticles 5 parts.

[0071] A preparation method of a conductive gel fixing agent, comprising the following steps:

[0072] (1) Glycerol and silver nanoparticles are added to water, and stirred for 1 hour until completely dissolved;

[0073] (2) The solution obtained in step 1 is added with collagen and xanthan gum, and stirred for 10 minutes until uniform;

[0074] (3) The mixture obtained in step 2 is heated at 90 degrees, and a completely dissolved solution is obtained after one hour;

[0075] (4) The solution obtained in step 3 is cooled to room temperature to obtain a gel.

[0076] Comparative Example 1

[0077] The difference between this comparative example and Example 1 is that agar is omitted, and the amount of gelatin is adjusted to 15 parts.

[0078] Results: When gelatin is used alone as a gelling agent, the network structure is easily broken after omitting agar, and the mechanical properties and adhesion properties of the hydrogel adhesive are greatly reduced.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that the ratio of gelatin to agar is changed from 10 parts and 5 parts to 2 parts and 2 parts, respectively.

[0081] Results: The viscosity is insufficient to effectively spread at the interface, and the mechanical properties and adhesion properties of the hydrogel adhesive are greatly reduced.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 1 is that betaine is replaced by a water-absorbing resin (model: Sumitomo SA60N). Due to the competition for water between the water-retaining agent and the structural components, and the inability to combine with the structural components at the microscopic level, the water-retaining property of the hydrogel adhesive is greatly reduced.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 2 is that potassium nitrate is replaced by calcium nitrate. Due to the stronger interaction between calcium ions and the structural components and the decrease in ion mobility, the conductivity of the hydrogel adhesive decreases.

[0086] Comparative Example 5

[0087] The difference between this comparative example and Example 3 is that silver nanoparticles are replaced by graphene. Due to the poor microdispersibility between graphene and the structural components, the conductivity of the hydrogel adhesive decreases.

[0088] Application performance detection:

[0089] The hydrogels prepared in each example and comparative example were subjected to performance tests.

[0090] Test method:

[0091] (1) Tensile test: A universal testing machine (KJ-1065A, Guangdong Kejian) was used to perform uniaxial tensile testing on the hydrogel adhesive samples. Before testing, the hydrogel samples were cut into dumbbell shapes (4 x 50 mm) using a cutting knife. The testing temperature was room temperature, and the tensile rate was 100 mm / min. The tensile strength, i.e., the stress at the breaking point, was obtained from the tensile stress-strain curve.

[0092] (2) Adhesion test: The standard 90-degree peeling method was used to test the adhesion. The adhesion of the hydrogel adhesive was tested. Before testing, the adhesive was pasted on the skin, and a cloth was used as a back plate to fix the adhesive. The adhesion area was a rectangle with a size of 2 cm x 10 cm. The adhesive was stretched for tensile testing at a tensile rate of 50 mm / min. The force required to break the adhesion was measured and calculated using the formula: adhesion σ = 2F / W, where σ is the adhesion toughness, F is the force required to break the adhesion, and W is the pasting width (2 cm, i.e., the dimension perpendicular to the peeling direction).

[0093] (3) Water retention rate test: The hydrogel samples were treated in a forced air drying oven for 30 days to constant weight. The sample mass before and after treatment was measured and the water content was calculated, Water content (%) = (original sample mass - treated sample mass) / original sample mass x 100.

[0094] (4) Conductivity test: The standard conductivity test method was used for testing. Before testing, the hydrogel adhesive was cut into a disc with a diameter of 1 cm and a thickness of 2 mm, and impedance test was performed by an electrochemical workstation (CHI600E). The conductivity was calculated by impedance, and the calculation formula was P=R*S / L, wherein P was the conductivity, R was the impedance, S was the area of the disc, and L was the thickness of the disc.

[0095] Table 1

[0096]

[0097] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application.

Claims

1. An electrically conductive hydrogel adhesive having a temperature phase transition property for fixing an epidermal electrode, characterized by, The composition comprises the following components by weight: Structural component 5-20 parts; Conductive substance potassium nitrate 5 parts; Water retention component sodium citrate 15 parts; Water 50-70 parts; The structural component is one of the following compound combinations: (a) gelatin and agar, compound weight ratio 1-5:1; (b) gelatin and gellan gum, compound weight ratio 2-8:1; (c) collagen and xanthan gum, compound weight ratio 2-4:

1.

2. A method for preparing the conductive hydrogel adhesive according to claim 1, characterized by, The method comprises the following steps: (1) adding the water retention component and the conductive substance into water, stirring until completely dissolved to obtain a premixed solution; (2) adding the structural component into the premixed solution, stirring to form a uniformly dispersed solution; (3) heating the dispersed solution to a certain temperature and stirring at constant temperature; (4) cooling to room temperature to form a gel.

3. The method of claim 2, wherein the conductive hydrogel adhesive is prepared by mixing the conductive polymer solution and the crosslinking agent solution. In step (3), the heating temperature is 50-90℃, and the stirring time is 30-60 minutes.

4. Use of the conductive hydrogel adhesive of claim 1 in the preparation of a fixed epidermal electrode adhesive.

5. Use according to claim 4, characterized in that, The molten conductive hydrogel adhesive is coated on the electrode-skin interface, and after cooling and solidification, a conductive adhesive layer is formed.

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