Self-adhesive hydrogels, methods of making, uses thereof, and electrophysiological sensing electrodes and methods of making

Abstract

The application discloses a self-adhesive hydrogel and a preparation method, application and electrophysiological sensing electrode thereof. The self-adhesive hydrogel is prepared from modified protein source, acrylic monomer, acrylic acid grafted with N-succinimidyl ester, acrylated silk fibroin and water. The preparation method comprises the following steps: providing a modified protein solution; dispersing the modified protein solution, acrylic monomer, acrylic acid grafted with N-succinimidyl ester, photoinitiator, acrylated silk fibroin and water in a mass ratio of (540-660):(270-330):(9-11):(1.8-2.2):1:(78.3-95.7) to obtain a precursor solution of the self-adhesive hydrogel; and performing ultraviolet irradiation treatment on the precursor solution in an inert atmosphere to obtain the self-adhesive hydrogel. The self-adhesive hydrogel prepared by the self-adhesive hydrogel preparation method can maintain conformation and adhesion on a dynamic wet interface.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of biomaterials and sensors, and particularly relates to a self-adhesive hydrogel, a preparation method and use thereof, and an electrophysiological sensing electrode and a preparation method thereof. BACKGROUND

[0002] In the field of sports science, flexible electrophysiological sensing monitoring is crucial for effective guidance of sports training, including but not limited to prevention of muscle injury and reasonable design of exercise intensity. However, actual sports monitoring faces various challenges, including but not limited to secretion of sweat, stretching of the skin, and external scratching, which can seriously interfere with the contact interface between the electrode and the skin. Traditional Ag / AgCl gel electrodes have poor stretchability and adhesion in the wet state due to their inherent properties, resulting in unstable contact interfaces, which can cause signal distortion or even loss.

[0003] To solve the interference caused by dynamic interfaces such as stretching and vibration, researchers have developed a series of electrode materials that are highly conformal to the skin, including but not limited to ultra-thin metal electrodes, carbon electrodes, and gel electrodes. These ultra-thin materials are highly conformal to the skin through physical interactions such as van der Waals forces, and this conformality is the key to flexible electrophysiological sensing with low motion artifacts and high signal-to-noise ratio. However, metal electrodes and carbon electrodes are easily affected by deformation and external scratching during exercise due to their poor stretchability and fragility. In contrast, ultra-thin gel materials have good stretchability and mechanical stability, but their adhesion based on physical forces is weak and can fail when sweat forms at the electrode / skin interface, causing the electrode to easily detach from the skin. Currently, there is no effective solution to this problem. SUMMARY

[0004] The embodiments of the present application provide a self-adhesive hydrogel that can maintain conformality and adhesion on a dynamic wet interface.

[0005] In a first aspect, the present application provides a self-adhesive hydrogel, the raw materials of which include a modified protein source, an acrylic monomer, an acrylic acid grafted with N-succinimidyl ester, an acrylated silk fibroin, and water.

[0006] According to an embodiment of the first aspect of the present application, the mass ratio of the modified protein source, the acrylic monomer, the acrylic acid grafted with N-succinimidyl ester, the acrylated silk fibroin, and water is (87-140):(270-330):(9-11):1:(78.3-95.7).

[0007] According to an embodiment of the first aspect of the present application, the modified protein source is selected from a combination of one or more of modified silk fibroin, modified spider silk protein, and modified gelatin.

[0008] According to an embodiment of the first aspect of the present application, the modified silk fibroin is selected from calcium ion modified silk fibroin, lithium ion modified silk fibroin, zinc ion modified silk fibroin, or a combination thereof.

[0009] According to an embodiment of the first aspect of the present application, the modified spider silk protein is selected from calcium ion modified silk fibroin, lithium ion modified silk fibroin, zinc ion modified silk fibroin, or a combination thereof.

[0010] According to an embodiment of the first aspect of the present application, the modified gelatin is selected from calcium ion modified gelatin, lithium ion modified gelatin, zinc ion modified gelatin, or a combination thereof.

[0011] According to an embodiment of the first aspect, the mass content of calcium ions in the calcium ion modified silk fibroin is 1.16wt%-1.90wt%.

[0012] According to an embodiment of the first aspect, the mass content of lithium ions in the lithium ion modified silk fibroin is 0.528wt%-0.86wt%.

[0013] According to an embodiment of the first aspect, the mass content of zinc ions in the zinc ion modified silk fibroin is 1.54wt%-2.52wt%.

[0014] According to an embodiment of the first aspect, the acrylic monomer is selected from acrylic acid, methacrylic acid, ethyl acrylic acid, propyl acrylic acid, butyl acrylic acid, hydroxymethyl acrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, or a combination thereof.

[0015] According to an embodiment of the first aspect, the interfacial toughness of the self-adhesive hydrogel under dry conditions is 370J·m -2 -450J·m -2 , and the shear strength of the self-adhesive hydrogel under dry conditions is 31kPa-40kPa.

[0016] In a second aspect, the present application provides a preparation method of a self-adhesive hydrogel, comprising: providing a modified protein solution; dispersing the modified protein solution, an acrylic monomer, an acrylic acid grafted with N-succinimidyl ester, a photoinitiator, an acrylated silk fibroin, and water in a mass ratio of (540-660):(270-330):(9-11):(1.8-2.2):1:(78.3-95.7) to obtain a precursor solution of a self-adhesive hydrogel; and performing ultraviolet irradiation treatment on the precursor solution in an inert atmosphere to obtain a self-adhesive hydrogel containing a modified protein-polyacrylic acid double network structure.

[0017] According to an embodiment of the second aspect of the present application, the method for preparing the modified protein solution comprises: modifying a protein source selected from one or more of degummed silk, spider silk, and gelatin in an acid solution using a calcium ion salt containing calcium ions to obtain a calcium ion modified protein solution.

[0018] According to an embodiment of the second aspect of the present application, the calcium ion salt containing calcium ions is selected from one or more of calcium chloride, calcium acetate, and calcium gluconate.

[0019] According to an embodiment of the second aspect of the present application, the method for preparing the modified protein solution comprises: modifying a protein source selected from one or more of degummed silk, spider silk, and gelatin in an acid solution using a lithium ion salt containing lithium ions to obtain a lithium ion modified protein solution.

[0020] According to an embodiment of the second aspect of the present application, the lithium ion salt containing lithium ions is selected from one or more of lithium chloride, lithium bromide, lithium sulfate, lithium acetate, and lithium gluconate.

[0021] According to an embodiment of the second aspect of the present application, the method for preparing the modified protein solution comprises: modifying a protein source selected from one or more of degummed silk, spider silk, and gelatin in an acid solution using a zinc ion salt containing zinc ions to obtain a zinc ion modified protein solution.

[0022] According to an embodiment of the second aspect of the present application, the zinc ion salt containing zinc ions is selected from one or more of zinc chloride, zinc bromide, zinc sulfate, zinc acetate, and zinc gluconate.

[0023] According to an embodiment of the second aspect of the present application, the acid solution is selected from one or more of formic acid, acetic acid, and propionic acid.

[0024] According to an embodiment of the second aspect of the present application, the calcium ion salt is calcium chloride, the acid solution is formic acid, and the mass ratio of calcium chloride, degummed silk, and formic acid is 1:(3-5):(15-25).

[0025] According to an embodiment of the second aspect of the present application, the photoinitiator is selected from lithium phenyl-2,4,6-trimethylbenzoylphosphinate and 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone.

[0026] According to an embodiment of the second aspect of the present application, when the photoinitiator is lithium phenyl(2,4,6-trimethylbenzoyl)phosphate, the wavelength of the ultraviolet light is 365-400 nm; or when the photoinitiator is 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone, the wavelength of the ultraviolet light is 254-400 nm.

[0027] In a third aspect, embodiments of the present application provide a use of the aforementioned self-adhesive hydrogel in the preparation of an electrophysiological sensing electrode.

[0028] In a fourth aspect, the present application provides an electrophysiological sensing electrode, comprising: a first container having a containing cavity with an open side; and the self-adhesive hydrogel as described above disposed in the containing cavity.

[0029] According to an embodiment of the fourth aspect of the present application, the electrophysiological sensing electrode further comprises a connecting structure for disposing the self-adhesive hydrogel in the containing cavity.

[0030] According to an embodiment of the fourth aspect of the present application, the connecting structure comprises an adhesive layer disposed between the inner surface of the containing cavity and the self-adhesive hydrogel.

[0031] According to an embodiment of the fourth aspect of the present application, the adhesive layer is benzophenone for cross-linking the inner surface of the containing cavity and the self-adhesive hydrogel.

[0032] According to an embodiment of the fourth aspect of the present application, the connecting structure comprises a fixing net or a fixing strip disposed at the open side of the containing cavity.

[0033] According to an embodiment of the fourth aspect of the present application, the first container is made of an elastomer material selected from PDMS or Ecoflex.

[0034] In a fifth aspect, the present application provides a preparation method of an electrophysiological sensing electrode, comprising: preparing a precursor solution of a self-adhesive hydrogel according to the preparation method of the self-adhesive hydrogel; providing a first container having a containing cavity; injecting the precursor solution of the self-adhesive hydrogel into the containing cavity; and treating the self-adhesive hydrogel precursor solution with ultraviolet light irradiation under an inert atmosphere to convert the self-adhesive hydrogel precursor solution into the self-adhesive hydrogel, thereby obtaining the electrophysiological sensing electrode.

[0035] According to an embodiment of the fifth aspect of the present application, the providing of the first container having a containing cavity comprises:

[0036] The containing cavity is pretreated with a treatment solution containing benzophenone to obtain the first container with the inner surface of the containing cavity having benzophenone.

[0037] According to an embodiment of the fifth aspect of the present application, the pretreatment of the containing cavity with the treatment solution containing benzophenone comprises: injecting a 5wt%-15wt% benzophenone ethanol solution into the containing cavity for standing, then washing the containing cavity of the first container with methanol and drying with an inert gas.

[0038] According to an embodiment of the fifth aspect of the present application, the 5wt%-15wt% benzophenone ethanol solution is injected into the containing cavity for standing for 1min-4min.

[0039] The self-adhesive hydrogel of the embodiment of the present application is prepared from modified protein source, acrylic monomer, acrylic acid grafted with N-succinimidyl ester and acrylated silk fibroin. The acrylic acid grafted with N-succinimidyl ester, the acrylic monomer and the acrylated silk fibroin form a network structure of polyacrylic acid after polymerization. The polyacrylic acid can form a firm covalent bond with the abundant primary amine groups on the surface of the skin. The modulus of the modified protein with plasticizing property is significantly reduced under sweating conditions, thereby enhancing the mechanical interlocking effect and adhesion of the self-adhesive hydrogel material to the microstructure of the skin surface, so that the self-adhesive hydrogel material can maintain conformal and good adhesion to the skin on a dynamic wet interface. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced. Those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0041] Fig. 1(a) is an infrared spectrum of the self-adhesive hydrogel provided by the embodiment 1 of the present application.

[0042] Fig. 1(b) is a visible absorption spectrum and a physical picture of the self-adhesive hydrogel provided by the embodiment 1.

[0043] Fig. 1(c) is a scanning electron microscope picture of the self-adhesive hydrogel provided by the embodiment 1.

[0044] Fig. 2(a) is a physical picture of the self-adhesive hydrogel provided by the embodiment 1 in the standard 180° adhesion performance characterization test on dry and sweat-wet pigskin.

[0045] Fig. 2(b) is a result picture of the self-adhesive hydrogel provided by the embodiment 1 in the standard 180° adhesion performance characterization test on dry and sweat-wet pigskin.

[0046] Fig. 2(c) is a physical picture of the self-adhesive hydrogel provided by the embodiment 1 in the lap shear test on dry and sweat-wet pigskin.

[0047] Fig. 2(d) is a result picture of the self-adhesive hydrogel provided by the embodiment 1 in the lap shear test on dry and sweat-wet pigskin.

[0048] Fig. 2(e) is a comparison picture of the self-adhesive hydrogel provided by the embodiment 1 in the standard 180° and lap shear tests on dry and sweat-wet pigskin.

[0049] Fig. 3(a) is a state simulation result picture of the self-adhesive hydrogel provided by the embodiment 1 attached to the human finger joint.

[0050] Figure 3(b) is a comparison of the interfacial toughness and shear strength of the self-adhesive hydrogel provided in Example 1 with existing gel materials under dry and wet conditions.

[0051] Figure 4 The results show the conductivity characteristics of the self-adhesive hydrogel prepared in Example 1 before and after artificial sweat treatment.

[0052] Figure 5 This is a schematic flowchart illustrating the preparation method of the electrophysiological sensing electrode prepared in Example 2.

[0053] Figure 6 This is a schematic diagram of the electrophysiological sensing electrode in Example 2.

[0054] Figure 7 for Figure 6 A longitudinal cross-sectional view of the electrophysiological sensing electrode.

[0055] Figure 8 The results show the water loss resistance characteristics of the electrophysiological sensing electrode prepared in Example 2.

[0056] Figure 9(a) shows the interfacial impedance characterization results of the electrophysiological sensing electrode prepared in Example 2 after it was attached to the surface of human skin and the change over time.

[0057] Figure 9(b) shows the interfacial impedance characterization results of the electrophysiological sensing electrode prepared in Example 2 and the commercial Ag / AgCl gel electrode under dry and sweat conditions.

[0058] Figure 10(a) shows the results of ECG signal changes under three conditions: dry, exercise, and sweat, using the ECG physiological sensing electrode prepared in Example 1 and the commercial Ag / AgCl gel electrode.

[0059] Figure 10(b) shows the intensity ratio of the T peak and R peak in electrocardiogram data based on the electrocardiogram data of the electrocardiogram sensor electrode prepared in Example 1 and the commercial Ag / AgCl gel electrode under three conditions: dry, exercise, and sweat.

[0060] Figure 11(a) shows the electromyographic signal test results of the electromyographic sensor electrode prepared in Example 2 and the commercial Ag / AgCl gel electrode under three conditions: dry, exercise, and sweat.

[0061] Figure 11(b) is a comparison of the signal-to-noise ratio of the electromyographic sensing electrode prepared in Example 2 and the commercial Ag / AgCl gel electrode under three conditions: dry, exercise, and sweat.

[0062] Figure 12(a) shows the test results of the electrooculography signals of the electrooculography sensing electrode prepared in Example 3 under different eye movements.

[0063] Figure 12(b) is a contrast plot of peak difference between looking left and looking right for the electro-physiological sensing electrode prepared in Example 3 and a commercial Ag / AgCl gel electrode.

[0064] BRIEF DESCRIPTION OF DRAWINGS 1. First container; 2. Containing cavity; 3. Self-adhesive hydrogel; 4. Polytetrafluoroethylene mold; 5. Cavity; 6. Protrusion; 7. Annular cavity; 8. Metal wire; 9. Electro-physiological sensing electrode. DETAILED DESCRIPTION

[0065] The features and exemplary embodiments of various aspects of the present application will be described in detail below with reference to the drawings. The following detailed description is merely intended to explain the present application, and is not intended to limit the present application. The present application can be implemented without some of the specific details. The following description of the embodiments is merely provided to give a better understanding of the present application by showing examples of the present application.

[0066] It should be noted that the terms such as first and second, etc., are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between such entities or operations. Also, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed or inherent to such a process, method, article or device. Without more limitations, the elements defined by the statement "include" do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0067] In the prior art, for the sweat wet interface, researchers have developed sweat-absorbing and sweat-releasing dry electrodes, including electrodes that use multi-layer nanofiber membranes to achieve directional sweat release. However, compared with wet electrodes, the interface impedance between dry electrodes and the skin is usually large, making it difficult to achieve high signal-to-noise ratio electro-physiological sensing.

[0068] The inventors of the present application found that as a biocompatible natural material, the Young's modulus of silk fibroin decreases to close to the Young's modulus of the skin under the action of water. This water-responsive plasticizing property enables silk fibroin to maintain its shape retention and adhesion to the skin in the case of skin sweating. However, the interface between the electrode made of silk fibroin and the skin also relies on weak physical action, making it difficult to withstand severe motion interference.

[0069] To solve the problems in the prior art, the application provides a self-adhesive hydrogel, a preparation method and use thereof, and an electrophysiological sensing electrode and a preparation method thereof. First, the preparation method of the self-adhesive hydrogel provided in the application is introduced.

[0070] In a first aspect, the preparation method of the self-adhesive hydrogel provided in the application comprises the following steps.

[0071] S1, providing a modified protein solution;

[0072] S2, dispersing the modified protein solution, an acrylic monomer, an acrylic acid grafted with N-succinimidyl ester, a photoinitiator, an acrylated silk fibroin, and water in a mass ratio of (540-660):(270-330):(9-11):(1.8-2.2):1:(78.3-95.7) to obtain a precursor solution of the self-adhesive hydrogel;

[0073] S3, performing ultraviolet irradiation treatment on the precursor solution in an inert atmosphere to obtain the self-adhesive hydrogel.

[0074] The preparation method of the self-adhesive hydrogel provided in the application can form a network structure of polyacrylic acid by grafting the acrylic acid grafted with N-succinimidyl ester, the acrylic monomer, and the acrylated silk fibroin after polymerization. On the one hand, the abundant carboxyl groups in the polyacrylic acid network and the abundant amino groups, hydroxyl groups, and carboxyl groups in the modified protein network can make the two high-molecular networks form effective hydrogen bonding and physical entanglement. For example, the addition of the acrylated silk fibroin can make part of the silk fibroin network be integrated into the polyacrylic acid network in a covalent crosslinking manner, so as to enhance the mechanical properties of the self-adhesive hydrogel containing the modified protein-polyacrylic acid double network structure through physical crosslinking and chemical crosslinking. On the other hand, the addition of the modified protein and the acrylated silk fibroin can enhance the adhesion and shape retention of the self-adhesive hydrogel to the skin in the case of an increase in water content (water-responsive plasticization property), so that the self-adhesive hydrogel can adapt to the modulus and movement of the skin.

[0075] In addition, the acrylic monomer, the acrylic acid grafted with N-succinimidyl ester, the photoinitiator, and the ultraviolet irradiation treatment can promote the morphological transformation of the precursor solution of the self-adhesive hydrogel to a block hydrogel, so that the self-adhesive hydrogel has good tensile properties and mechanical stability.

[0076] In some embodiments of the application, the step of providing the modified protein solution comprises: using a calcium ion salt containing calcium ions to modify a protein source selected from one or more of degummed silk, spider silk, and gelatin in an acid solution to obtain a calcium ion-modified protein solution.

[0077] In the embodiments of the present application, the degummed silk, spider silk and gelatin are respectively modified by calcium ion salt containing calcium ions to obtain calcium ion modified silk fibroin.

[0078] The preparation method of the self-adhesive hydrogel in the embodiments of the present application utilizes the abundant carboxyl groups in the polyacrylic acid network and the abundant amino groups, hydroxyl groups and carboxyl groups in the modified silk fibroin network. The two polymer networks form effective hydrogen bonding and physical entanglement. At the same time, the addition of acrylated silk fibroin enables part of the silk fibroin network to be integrated into the polyacrylic acid network in the form of chemical covalent crosslinking, and the calcium ion modified degummed silk containing calcium ion modified silk fibroin can be dispersed in the polyacrylic acid network to achieve physical crosslinking. The mechanical properties of the self-adhesive hydrogel containing the modified protein-polyacrylic acid double network structure are enhanced by physical crosslinking and chemical crosslinking, so that the modulus and movement of the self-adhesive hydrogel are adapted to the skin. In addition, the acrylic monomer will polymerize under the combined action of the photoinitiator and ultraviolet light irradiation, promoting the morphological transformation of the precursor solution of the self-adhesive hydrogel into a block hydrogel.

[0079] In the embodiments of the present application, calcium ions can destroy the hydrogen bonds in the silk fibroin in the degummed silk, spider silk and gelatin, promote the dissolution of the silk fibroin, and thus enable the silk fibroin to be fully dispersed in the acrylic acid, so that more uniform entanglement is achieved after the polymerization of the acrylic acid, and the self-adhesive hydrogel can better adhere to and conform to the skin. On the other hand, the presence of calcium ions can improve the ionic conductivity of the self-adhesive hydrogel. Therefore, other calcium salts that are easily soluble in water and dissociated or easily soluble in formic acid and suitable for the self-adhesive hydrogel can also be used. Therefore, in some embodiments of the present application, the calcium ion salt containing calcium ions is selected from one or more of calcium chloride, calcium acetate and calcium gluconate.

[0080] In the embodiments of the present application, taking formic acid as an example, the main role of formic acid is to destroy the hydrogen bonds in the silk fibroin in the degummed silk, so that the silk fibroin is dissolved, while the peptide bond is less affected. Weak electrolyte acids with similar properties to formic acid and small acid anions can also be used. In some embodiments, the acid solution is selected from one or more of formic acid, acetic acid and propionic acid.

[0081] In some embodiments, the calcium ion salt is calcium chloride, the acid solution is formic acid, and the mass ratio of calcium chloride, degummed silk and formic acid is 1:(3-5):(15-25). Exemplarily, the mass ratio of calcium chloride, degummed silk and formic acid is 1:3:15, 1:3:16, 1:3:18, 1:3:20, 1:3.5:15, 1:3.6:15, 1:3.8:15, 1:3.5:16, 1:3.5:18, 1:3.5:22, 1:4:15, 1:4.5:15, 1:4:19, 1:4:20, 1:4:24, 1:5:15.

[0082] In some embodiments of the present application, the calcium ion salt, the acid solution and the degummed silk are dispersed by double center mixing, the rotation speed is 2500 r / min-3500 r / min, and the centrifugal time is 5 min-30 min. Alternatively, the rotation speed is 3000 r / min, and the dispersion time is 20 min.

[0083] In the embodiments of the present application, the calcium ion salt, the formic acid and the degummed silk are dispersed to modify the silk fibroin, and a clear and transparent calcium ion silk fibroin formic acid solution is obtained. The formic acid in the calcium ion silk fibroin formic acid solution can be removed by volatilization and is not retained in the self-adhesive hydrogel.

[0084] In some embodiments of the present application, the calcium ion silk fibroin formic acid solution, the acrylic acid, the acrylic acid grafted with N-succinimidyl ester, the photoinitiator, the acrylated silk fibroin and the water can be dispersed by ultrasonic treatment, the power of the ultrasonic treatment is 50 W-1000 W, and the ultrasonic time is 1 min-30 min. Alternatively, the power and the ultrasonic time are 50 W and 1 min, respectively.

[0085] In the embodiments of the present application, the calcium ion silk fibroin formic acid solution, the acrylic acid, the acrylic acid grafted with N-succinimidyl ester, the photoinitiator, the acrylated silk fibroin and the water can be in any ratio between (540-660):(270-330):(9-11):(1.8-2.2):1:(78.3-95.7). For example, the ratio of the above components can also include but is not limited to 540:270:9:1.8:1:78.3, 560:270:9:1.8:1:78.3, 580:270:9:1.8:1:78.3, 600:270:9:1.8:1:78.3, 540:280:9:1.8:1:78.3, 540:290:9:1.8:1:78.3. More preferably, the mass ratio of the calcium ion modified silk fibroin formic acid solution, the acrylic acid, the acrylic acid grafted with N-succinimidyl ester, the photoinitiator, the acrylated silk fibroin and the water is 600:300:10:2:1:87.

[0086] In some embodiments of the present application, the photoinitiator is a photoinitiator capable of initiating polymerization of acrylic acid under the action of ultraviolet light, including but not limited to lithium phenyl-2,4,6-trimethylbenzoylphosphinate, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone. The wavelength of the ultraviolet light is determined by the initiator. Illustratively, in some embodiments of the present application, when lithium phenyl-2,4,6-trimethylbenzoylphosphinate is used as the photoinitiator, the wavelength of the ultraviolet light is 365 nm to 400 nm. When 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone is used as the photoinitiator, the wavelength of the ultraviolet light is 254 nm to 400 nm.

[0087] In some embodiments, the power of the ultraviolet light is 5 W to 40 W, and the irradiation time is 5 min to 40 min. Preferably, the wavelength, power and time of the ultraviolet light irradiation are 365 nm, 10 W and 20 min.

[0088] In some embodiments, the inert atmosphere is formed by a gas selected from nitrogen, argon, neon or a mixture thereof.

[0089] In some embodiments of the present application, the modified protein solution is prepared by using a lithium ion salt containing lithium ions to modify a protein source selected from one or more of degummed silk, spider silk, gelatin in an acid solution to obtain a lithium ion-modified protein solution.

[0090] In some embodiments of the present application, the lithium ion salt containing lithium ions is selected from one or more of lithium chloride, lithium bromide, lithium sulfate, lithium acetate, lithium gluconate.

[0091] In embodiments of the present application, after the degummed silk, spider silk and gelatin are respectively modified using a lithium ion salt containing lithium ions in an acid solution, a lithium ion-modified silk fibroin can be obtained.

[0092] In some embodiments of the present application, the modified protein solution is prepared by using a zinc ion salt containing zinc ions to modify a protein source selected from one or more of degummed silk, spider silk, gelatin in an acid solution to obtain a zinc ion-modified protein solution.

[0093] In some embodiments of the present application, the zinc ion salt containing zinc ions is selected from one or more of zinc chloride, zinc bromide, zinc sulfate, zinc acetate, zinc gluconate.

[0094] In embodiments of the present application, after the degummed silk, spider silk and gelatin are respectively modified using a zinc ion salt containing zinc ions in an acid solution, a zinc ion-modified silk fibroin can be obtained.

[0095] In the embodiments of the present application, degummed silk refers to pure fibroin fiber obtained by removing sericin and other impurities in natural silk through chemical or physical treatment methods, and this process retains the main component of silk, i.e., silk fibroin protein.

[0096] In the embodiments of the present application, the calcium ion modified silk fibroin, the lithium ion modified silk fibroin, and the zinc ion modified silk fibroin do not participate in the polymerization of acrylic acid, but can entangle and physically cross-link with the molecular chain segments of the network structure of the polyacrylic acid copolymer, thereby obtaining the modified silk fibroin-polyacrylic acid double network structure self-adhesive hydrogel.

[0097] In the embodiments of the present application, the modified spider silk protein and the modified gelatin can be modified by the same steps as the degummed silk and formic acid and calcium ion salt. The formic acid can be replaced by acetic acid, propionic acid or a combination thereof, and the calcium ion salt can be replaced by lithium ion salt, zinc ion salt or a combination thereof.

[0098] In the second aspect, a self-adhesive hydrogel is provided, and raw materials include a modified protein source, an acrylic monomer, an acrylic acid grafted with N-succinimidyl ester, an acrylated silk fibroin, and water.

[0099] The self-adhesive hydrogel of the embodiments of the present application includes a modified protein source, an acrylic monomer, an acrylic acid grafted with N-succinimidyl ester, and an acrylated silk fibroin. After polymerization, the acrylic acid grafted with N-succinimidyl ester, the acrylic monomer, and the acrylated silk fibroin form a network structure of polyacrylic acid. The polyacrylic acid can form a firm covalent bond with the abundant primary amine groups on the skin surface. The modulus of the modified silk fibroin with plasticizing properties will significantly decrease under sweating conditions, thereby enhancing the mechanical interlocking effect and adhesion of the self-adhesive hydrogel material to the skin microstructure, so that the self-adhesive hydrogel material can maintain conformal and good adhesion to the skin on a dynamic wet interface.

[0100] At the same time, the electrolytes in the sweat generated during the movement of the organism can increase the carriers in the conductive self-adhesive hydrogel, thereby enhancing the ability to conduct the electrical physiological signals. Therefore, the self-adhesive hydrogel of the present application can effectively reduce the interface instability caused by movement and sweat wetting, and improve the signal-to-noise ratio of the conductive electrical physiological signals under the conditions of movement and sweat wetting.

[0101] In some embodiments of the present application, the mass ratio of the modified protein source, the acrylic monomer, the acrylic acid grafted with N-succinimidyl ester, the acrylated silk fibroin, and water is (87-140):(270-330):(9-11):1:(78.3-95.7).

[0102] In some embodiments of the present application, the modified protein source is selected from a combination of one or more of modified silk fibroin, modified spider silk protein, and modified gelatin.

[0103] In embodiments of the present application, the modified protein source is capable of better entanglement and physical cross-linking with the polyacrylic acid of the network structure after polymerization by being selected from a combination of one or more of modified silk fibroin, modified spider silk protein, and modified gelatin. The modified spider silk protein and the modified gelatin can be modified in an acid solution using the same ionic salt as the modified silk fibroin.

[0104] In some embodiments of the present application, the modified silk fibroin is selected from calcium ion modified silk fibroin, lithium ion modified silk fibroin, zinc ion modified silk fibroin, or a combination thereof.

[0105] In some embodiments, the calcium ions in the calcium ion modified silk fibroin, the lithium ions in the lithium ion modified silk fibroin, and the zinc ions in the zinc ion modified silk fibroin not only enhance the anti-water loss performance of the self-adhesive hydrogel, but also enhance the electrical conductivity of the self-adhesive hydrogel, so that the electrophysiological sensing electrode prepared from the self-adhesive hydrogel can more sensitively detect electrical signals.

[0106] In some embodiments, the self-adhesive hydrogel is formed by the synergistic effect of the calcium ion modified silk fibroin and the component containing an acrylic structure, and the strong adhesion to the skin is achieved through covalent bonds and physical interactions. The adhesion and electrical conductivity of the self-adhesive hydrogel are enhanced under sweating conditions, and the self-adhesive hydrogel can maintain stable adhesion and electrical signal conduction on the dynamic sweat-wet skin surface.

[0107] In some embodiments, the mass content of calcium ions in the calcium ion modified silk fibroin is 1.16wt% to 1.90wt%. In some embodiments, the mass content of lithium ions in the lithium ion modified silk fibroin is 0.528wt% to 0.86wt%. In some embodiments, the mass content of zinc ions in the zinc ion modified silk fibroin is 1.54wt% to 2.52wt%.

[0108] In some embodiments of the present application, the acrylic monomer is selected from acrylic acid, methacrylic acid, ethyl acrylic acid, propyl acrylic acid, butyl acrylic acid, hydroxymethyl acrylic acid, hydroxyethyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxybutyl methacrylate, or a combination thereof. These acrylic monomers, due to the presence of exposed carboxyl or hydroxyl groups at one end, can form abundant hydrogen bonds with the skin surface, thereby providing strong physical interactions for interfacial adhesion.

[0109] In some embodiments of the present application, the molecular weight of fibroin in natural silk is 400 kDa, and the molecular weight of fibroin is 200 kDa-300 kDa after calcium ion and formic acid treatment. The interfacial toughness of the self-adhesive hydrogel containing calcium ion modified fibroin under dry conditions is 370 J·m -2 -450 J·m -2 , and the shear strength of the self-adhesive hydrogel under dry conditions is 31 kPa-40 kPa. After treatment with sweat, the interfacial toughness of the self-adhesive hydrogel under sweat-wet conditions can be increased by 15%-30%, and the shear strength can be increased by 10%-20%.

[0110] In embodiments of the present application, since the molecular weight of fibroin in spider silk is as high as 300 kDa-400 kDa, the interfacial toughness of the self-adhesive hydrogel prepared by using calcium ion modified fibroin after calcium ion modification treatment of spider silk is higher than 370 J·m -2 -450 J·m -2 , and the shear strength of the self-adhesive hydrogel under dry conditions is higher than 31 kPa-40 kPa. After treatment with sweat, the interfacial toughness of the self-adhesive hydrogel under sweat-wet conditions can be increased by 20%-50%, and the shear strength can be increased by 15%-30%.

[0111] In embodiments of the present application, the gelatin is edible gelatin, and the molecular weight range is 50 kDa-100 kDa. Alternatively, gelatin derived from pigskin is preferably used.

[0112] In a third aspect, embodiments of the present application provide a use of the above-mentioned self-adhesive hydrogel in the preparation of an electrophysiological sensing electrode. That is, the self-adhesive hydrogel can be used to prepare an electrophysiological sensing electrode, which can at least be applied to the monitoring of electrophysiological signals of electrocardiogram, electromyogram and electrooculogram.

[0113] In a fourth aspect, the present application provides an electrophysiological sensing electrode, comprising: a first container 1 having a one-side-opened containing cavity 2; and the above-mentioned self-adhesive hydrogel 3 arranged in the containing cavity 2.

[0114] As shown in FIGS. Figure 6 and Figure 7 , the self-adhesive hydrogel 3 and the outside first container 1 together constitute an electrophysiological sensing electrode 9, and the self-adhesive hydrogel is responsible for forming firm adhesion with the skin surface, and the first container is responsible for significantly slowing down the evaporation of water in the hydrogel.

[0115] The adhesion mechanism of the self-adhesive hydrogel is mainly composed of chemical bonding, physical interaction and mechanical interlocking effect. Compared with conventional adhesion materials based on hydrogen bonding, electrostatic interaction and other physical interactions, the acrylic acid, acrylic monomer and acrylated silk fibroin grafted with N-succinimidyl ester form a network structure of polyacrylic acid after polymerization. The polyacrylic acid can chemically bond with the abundant primary amine groups on the skin surface, providing stronger bonding force at the interface. In addition, pure physical adhesion is easy to fail under sweating conditions, but chemical bonding can remain stable during sweating, and the modulus of modified silk fibroin with plasticizing properties is reduced by sweat, thereby enhancing the mechanical interlocking effect at the interface and achieving sweat-enhanced adhesion. At the same time, the electrolytes in sweat increase the carriers in the ion-conducting self-adhesive hydrogel, enhancing its ability to conduct electrical signals.

[0116] In some embodiments of the present application, the electrophysiological sensing electrode further comprises a connecting structure for disposing the self-adhesive hydrogel in the accommodation cavity. The connecting structure is used to dispose the self-adhesive hydrogel in the accommodation cavity of the first container, preventing the self-adhesive hydrogel from coming out of the accommodation cavity.

[0117] In some embodiments, the connecting structure comprises an adhesive layer disposed between the inner surface of the accommodation cavity and the self-adhesive hydrogel. The self-adhesive hydrogel is bonded to the inner surface of the accommodation cavity of the first container through the adhesive layer. In some embodiments, the adhesive layer is benzophenone that crosslinks the inner surface of the accommodation cavity of the first container and the self-adhesive hydrogel. It can be understood that the benzophenone is a layer of structural layer coated between the inner surface of the accommodation cavity and the self-adhesive hydrogel, and its position is clear, so it is not shown in the drawings.

[0118] In some embodiments of the present application, the connecting structure comprises a fixing net or a fixing strip disposed at the opening side of the accommodation cavity. The fixing net or the fixing strip can also be used to dispose the self-adhesive hydrogel crosslinked into a block in the accommodation cavity, and the net-like or strip-like structure does not affect the adhesion of the self-adhesive hydrogel to the skin. Further, the fixing net can be a net-like fiber embedded in the accommodation cavity of the first container and extending into the wall.

[0119] In some embodiments of the present application, the first container is made of an elastomer material selected from polydimethylsiloxane (PDMS) or Ecoflex. Ecoflex is an elastomer material. Optionally, Ecoflex is purchased from Smooth-On Company, model 00-30. PDMS is preferably used as the elastomer material for making the first container.

[0120] In some embodiments, the viscosity of the cured PDMS can be adjusted to have different adhesive properties by adjusting the ratio of the base agent and the curing agent of the PDMS. The curing agent is selected from a compound containing platinum or other metals as a catalyst, also known as "platinum curing agent" or "platinum catalytic curing agent".

[0121] It can be understood that the shape of the first container can be designed as required according to the wearing device or the application scenario. Exemplarily, the shape of the first container made of the elastomer material includes but is not limited to a circular sheet or a square sheet, an oval sheet, a triangular sheet. The thickness of the first container can be 0.2 mm to 10 mm, and the length and the width can both be 5 mm to 50 mm. Alternatively, the shape of the first container is a circular sheet with a thickness of 2 mm and a diameter of 16 mm.

[0122] In some embodiments of the present application, as shown in Figure 5 The metal wire can be arranged between the first container and the self-adhesive hydrogel by being attached to the inner surface of the accommodation cavity, or can be directly embedded in the self-adhesive hydrogel. The metal wire can use copper wire or silver wire. Preferably, copper wire is used. On the one hand, the copper wire has good electrical conductivity, and on the other hand, the copper wire has good oxidation resistance and stability. Moreover, the copper wire is easy to purchase and low in price.

[0123] In a fifth aspect, the present application provides a preparation method of an electrophysiological sensing electrode, comprising: preparing a precursor solution of a self-adhesive hydrogel according to the preparation method of the self-adhesive hydrogel; providing a first container with an accommodation cavity; injecting the precursor solution of the self-adhesive hydrogel into the accommodation cavity; and treating the precursor solution of the self-adhesive hydrogel under an inert atmosphere by ultraviolet irradiation to obtain the electrophysiological sensing electrode.

[0124] In some embodiments, providing the first container with the accommodation cavity comprises: pre-treating the accommodation cavity with a treatment solution containing benzophenone to obtain the first container with the inner surface of the accommodation cavity having benzophenone.

[0125] In some embodiments, the pre-treatment of the accommodation cavity with the treatment solution containing benzophenone comprises: injecting a benzophenone ethanol solution with a concentration of 5 wt% to 15 wt% into the accommodation cavity of the first container, standing for 1 min to 4 min, then washing the accommodation cavity of the first container with methanol and blowing dry with an inert gas. Alternatively, the concentration of the benzophenone ethanol solution is 10 wt%, and the standing time is 2 min.

[0126] In the embodiments of the present application, after the inner surface of the containing cavity of the first container is pretreated with a benzophenone ethanol solution, the self-adhesive hydrogel precursor solution is injected into the containing cavity, ultraviolet irradiation is carried out in an inert atmosphere, benzophenone is used for cross-linking at the interface between the elastomer material of the first container and the self-adhesive hydrogel, and one side of the self-adhesive hydrogel is coated by the elastomer material of the first container, so that the obtained self-adhesive hydrogel-elastomer composite has excellent adhesion and anti-water loss properties. When the self-adhesive hydrogel is used as an electrophysiological sensing electrode, it exhibits high signal-to-noise ratio and strong anti-interference ability to movement and sweat, and is suitable for long-term stable monitoring of physiological signals such as electrocardiogram, electromyogram and electrooculogram.

[0127] The following are specific examples. The purpose is to further illustrate the present application in detail to help those skilled in the art and researchers further understand the present application, and the technical conditions do not constitute any limitation on the present application. The following are the sources of some raw materials, reagents used in the examples or comparative examples: lithium phenyl-2,4,6-trimethylbenzoylphosphinate, CAS No: 85073-19-4; PDMS, model Sylgard 184, purchased from Dow Chemical Company; acrylated silk fibroin, model EFL-SilMA-001, purchased from EFL brand company; acrylic acid grafted with N-succinimidyl ester, CAS No: 38862-24-7, purchased from Meryer company.

[0128] Example 1 Preparation of self-adhesive hydrogel

[0129] 1. Mix calcium chloride, degummed silk and formic acid in a mass ratio of 1:4:20; specifically, weigh 0.25 g of anhydrous calcium chloride and 1 g of silk fibroin, respectively, and add 5 g of formic acid, and perform double-center mixing and dispersion in a FlackTek SpeedMixer at a speed of 3000 r / min and a time of 20 min to obtain a clear and transparent silk fibroin formic acid solution.

[0130] 2. Mix the silk fibroin formic acid solution, acrylic acid, acrylic acid grafted with N-succinimidyl ester, photoinitiator, acrylated silk fibroin and water in a mass ratio of 600:300:10:2:1:87; specifically, mix 6 g of silk fibroin formic acid solution, 3 g of acrylic acid, 0.1 g of acrylic acid grafted with N-succinimidyl ester, 0.02 g of lithium phenyl-2,4,6-trimethylbenzoylphosphinate and 0.01 g of acrylated silk fibroin, and add 0.87 g of water, and then ultrasonic treatment is performed under the conditions of 40 kHz, 50 W and 1 min to obtain a clear and transparent self-adhesive hydrogel precursor solution.

[0131] 3. The precursor solution was injected between two glass slides with a spacing of 500 μm, and placed in a transparent, sealed chamber. High-purity argon gas was introduced into the chamber to create an inert atmosphere. Subsequently, the precursor solution was irradiated with ultraviolet light under the following conditions: 362 nm, 10 W, and 20 min, resulting in a colorless and transparent self-adhesive hydrogel with a silk fibroin-polyacrylic acid dual network structure.

[0132] Material characterization: The structure and properties of the self-adhesive hydrogel prepared in Example 1 were characterized.

[0133] 1. Infrared spectrum, visible absorption spectrum and scanning electron microscope images

[0134] like Figures 1(a)-1(c) Figure 1(a) shows the infrared absorption spectrum, visible light absorption spectrum, physical image, and scanning electron microscope (SEM) image of the self-adhesive hydrogel prepared in Example 1. The infrared spectrum in Figure 1(a) shows that the main infrared peaks of silk fibroin and polyacrylic acid are present in the self-adhesive hydrogel, proving that the two components have successfully combined into a biocomposite material. The visible absorption spectrum in Figure 1(b) shows that the visible light transmittance of the self-adhesive hydrogel is over 86%. The physical image refers to the graph below the transmittance curve. Since the actual product of the prepared self-adhesive hydrogel is a 7cm*5cm transparent rectangular film, when placed on the lower layer of arranged letter strings, the letters in each row can be clearly seen. All of the above demonstrates that the self-adhesive hydrogel has good transmittance in the visible light band and is suitable for preparing invisible wearable devices. Figure 1(c) is a scanning electron microscope image of the self-adhesive hydrogel, which shows the cross-linked network structure of silk fibroin and polyacrylic acid in the prepared self-adhesive hydrogel, demonstrating the structural uniformity of the self-adhesive hydrogel.

[0135] 2. Adhesion performance characterization

[0136] Data on the standard 180° adhesion performance of the self-adhesive hydrogel on dry and sweaty pigskin can be measured according to ASTM F2256, and data on the lap shear strength of the self-adhesive hydrogel on dry and sweaty pigskin can be measured according to ASTM F2255. For the dry condition, the self-adhesive hydrogel is adhered to dry pigskin at 25°C and 20% humidity, and the test is conducted after 30 minutes. For the sweat condition, the self-adhesive hydrogel is adhered to dry pigskin at 25°C and 20% humidity, and 0.2 ml of artificial sweat is applied per gram of self-adhesive hydrogel, and the test is conducted after 30 minutes.

[0137] like Figures 2(a)-2(e)Figure 2 shows the photographs and results of the adhesion characterization of the self-adhesive hydrogel prepared in Example 1. Figure 2(a) shows the photographs of the self-adhesive hydrogel performing the standard 180° test on dry and sweat wet pigskin, Figure 2(b) shows the results of the characterization of the self-adhesive hydrogel performing the standard 180° test on dry and sweat wet pigskin, the data in Figure 2(b) indicates that the interfacial toughness of the self-adhesive hydrogel on dry pigskin surface is about 411.66 J·m -2 , while the interfacial toughness on sweat wet pigskin surface increases to 504.64 J·m -2 . Figure 2(c) shows the photographs of the self-adhesive hydrogel performing the lap shear strength test on dry and sweat wet pigskin, Figure 2(d) shows the results of the characterization of the self-adhesive hydrogel performing the lap shear strength test on dry and sweat wet pigskin, the data in Figure 2(d) indicates that the shear strength of the self-adhesive hydrogel on dry pigskin surface is 35.47 kPa, while the shear strength on sweat wet pigskin surface increases to 40.02 kPa. Figure 2(e) shows the performance comparison of the interfacial toughness and shear strength of the self-adhesive hydrogel on dry and sweat wet pigskin, which reflects that the self-adhesive hydrogel can enhance adhesion under sweat conditions.

[0138] Further, in order to visually show the adhesion of the self-adhesive hydrogel under dry, exercise and sweat wet conditions, the colorless transparent self-adhesive hydrogel is colored with blue food dye for visualization. The self-adhesive hydrogel is attached to the human finger joint. As shown in Figure 3(a), under the conditions of dry skin, twisting and sweating, the sweat-enhanced self-adhesive hydrogel shows stable adhesion, firmly and adaptively adheres to the skin surface of the finger, and the peeling process will cause significant deformation of the self-adhesive hydrogel and the tissue.

[0139] Further, the interfacial toughness and shear strength of the self-adhesive hydrogel prepared in Example 1 under dry and sweat wet conditions are compared with the interfacial toughness and shear strength of existing gel materials. Among them, the self-adhesive hydrogel under dry conditions is denoted as BioSP-Dry, the self-adhesive hydrogel under sweat wet conditions is denoted as BioSP-Wet, and the numbers and data sources of the existing gel materials are as follows:

[0140] Gel material numbered [1] see document 1 (document 1 is: Y. Xue, J. Zhang, X. Chen, J. Zhang, G. Chen, K. Zhang, J. Lin, C. Guo, J. Liu, Trigger-Detachable Hydrogel Adhesives for Bioelectronic Interfaces, Adv. Funct. Mater. 31 (47) (2021) 2106446. The document details the ratio of gel materials in the part of Supporting Information: Synthesis of trigger-detachable hydrogel bioadhesives):

[0141] Gel material numbered [2] see document 2 (document 2 is: Z. Lei, W. Zhu, X. Zhang, X. Wang, P. Wu, Bio-Inspired Ionic Skin for Theranostics, Adv. Funct. Mater, Adv. Funct. Mater. 31 (8) (2020) 2008020. The document details the ratio of gel materials in the part of Experimental Section: Preparation of bio-inspired hydrogel);

[0142] Gel material numbered [3] see document 3 (document 3 is: F. M. Carvalho, P. Lopes, M. Carneiro, A. Serra, J. Coelho, A. T. de Almeida, M. Tavakoli, Nondrying, Sticky Hydrogels for the Next Generation of High-Resolution Conformable Bioelectronics, ACS Appl. Electron. Mater. 2 (10) (2020) 3390-3401. The document details the ratio of gel materials in the part of Experimental Section: Hydrogel synthesis);

[0143] Gel material no. [4] see document 4 (document 4 is: H. Yang, S. Ji, I. Chaturvedi, H. Xia, T. Wang, G. Chen, L. Pan, C. Wan, D. Qi, Y.-S. Ong, X. Chen, Adhesive Biocomposite Electrodes on Sweaty Skin for Long-Term Continuous Electrophysiological Monitoring, ACS Mater. Lett. 2(5) (2020) 478-484. This document details the ratio of gel material in the section The fabrication of highly conformal all-polymer electrodes of Supporting Information);

[0144] Gel material no. [5] see document 5 (document 5 is: R. A. Nawrocki, H. Jin, S. Lee, T. Yokota, M. Sekino, T. Someya, Self-Adhesive and Ultra-Conformable, Sub-300 nm Dry Thin-Film Electrodes for Surface Monitoring of Biopotentials, Adv. Funct. Mater. 28(36) (2018) 1803279. This document details the ratio of gel material in the section Fabrication and application of thin film sensors of Experimental Section);

[0145] Gel material no. [6] see document 6 (document 6 is: X. Shi, D. Song, W. Hu, C. Li, W. Zhang, S. Wang, Q. Hu, Y. Wang, X. Wang, Y. Zhang, B. Peng, Z. Wang, N. Liu, A Sweat Absorbing Skin Electrode for Electrophysiology During Exercise, Adv. Funct. Mater. (2024) 2314775. This document details the ratio of gel material in the section Preparation of SAE of Experimental Section).

[0146] As shown in Figure 3(b), the interfacial toughness of the self-adhesive hydrogel (BioSP-Dry) of Example 1 of this application under dry conditions is significantly stronger than that of existing gel materials [1], [2], [3], [4], and [5]. The interfacial toughness of the self-adhesive hydrogel (BioSP-Wet) of Example 1 of this application under sweat-wet conditions is higher than that under dry conditions, and is also significantly stronger than that of existing gel materials [1], [2], [3], [4], and [5]. As shown in Figure 3(b), the shear strength of the self-adhesive hydrogel (BioSP-Dry) of Example 1 of this application under dry conditions is significantly higher than that of existing gel materials [6] (labeled as [6]-Dry and [6]-Wet, respectively) under the same dry and sweat-wet conditions.

[0147] Figure 3(b) shows that the self-adhesive hydrogel material of Example 1 of this application has good interfacial toughness and shear strength, indicating that the self-adhesive hydrogel prepared in Example 1 can enhance adhesion under sweaty conditions.

[0148] 3. Characterization of electrical conductivity

[0149] like Figure 4 The image shows the conductivity characteristics of the self-adhesive hydrogel prepared in Example 1 before and after treatment with artificial sweat. Artificial sweat is a solution prepared artificially and similar in composition and concentration to real sweat, purchased from Shanghai Yuanye Biotechnology Co., Ltd., catalog number R22151. The amount of artificial sweat used was approximately 0.2 mL / g of self-adhesive hydrogel. Figure 4 It can be seen that the self-adhesive hydrogel exhibits good ionic conductivity, which gradually increases with increasing test frequency. At a frequency of 1 MHz, the ionic conductivity is approximately 1.01 S·m. -1 Furthermore, the self-adhesive hydrogel exhibits enhanced ionic conductivity under sweat-treated conditions. Under artificial sweat conditions, the ionic conductivity increases to approximately 1.46 S·m. -1 This is because the electrolytes in artificial sweat provide abundant charge carriers for self-adhesive hydrogels. Therefore, self-adhesive hydrogels can be applied to products that more effectively detect human movement status.

[0150] Example 2: Fabrication of electrophysiological sensing electrodes

[0151] like Figure 5 The diagram shown is a flowchart illustrating the preparation method of the electrophysiological sensing electrode in Example 2.

[0152] 1. First, prepare a device with the following features: Figure 5The structure of the shown polytetrafluoroethylene mold 4 contains a plurality of cavities 5 for forming the first container 1, and a protrusion 6 extending upward from the bottom of the cavity 5 for forming the holding cavity 2, the upper surface of the protrusion 6 forms a plane with the cavities 5 of the polytetrafluoroethylene mold 4, and an annular cavity 7 is formed between the plane and the cavities 5. A copper wire is attached to the structure of the protrusion 6 as a metal wire 8.

[0153] 2. Prepare the elastomer precursor solution, and select PDMS as the elastomer. By adjusting the ratio of the base reagent of PDMS and the platinum-catalyzed curing agent to 29:1, a precursor solution of low-crosslinked PDMS is obtained. Inject the low-crosslinked PDMS precursor solution into the bottom of the cavity 5 structure, and after heat treatment at 60°C for 2 hours, obtain the adhesive PDMS.

[0154] 3. Inject the precursor solution of fully crosslinked PDMS (the ratio of the base reagent of PDMS and the platinum-catalyzed curing agent is 10:1) into the top of the cavity 5 structure, until the liquid surface is flush with the upper surface of the polytetrafluoroethylene mold, and after heat treatment at 60°C for 2 hours, obtain the non-adhesive PDMS. Finally, peel the PDMS from the polytetrafluoroethylene mold, thereby obtaining a circular sheet-shaped PDMS first container with a holding cavity, which has an inner adhesive side and an outer non-adhesive side, a diameter of 16 mm, and a thickness of 2 mm. The adhesive side is the holding cavity 2, and the cured PDMS in the annular cavity 7 occupies the space of the cavity 5 to form the holding cavity 2, and the copper wire is located in the holding cavity.

[0155] 4. Inject a 10wt% benzophenone ethanol solution into the holding cavity of the adhesive side of the PDMS first container, stand for 2 minutes, then wash the first container thoroughly with methanol, dry with inert nitrogen gas, and then inject the self-adhesive hydrogel precursor solution prepared according to the method of Example 1 into the holding cavity of the first container, and perform ultraviolet irradiation in an argon inert atmosphere to obtain a composite material of self-adhesive hydrogel and PDMS polymerized under the action of the photoinitiator lithium phenyl-2,4,6-trimethylbenzoylphosphinate. The conditions for ultraviolet irradiation are 365 nm, 10 W, and 20 min, and the prepared Figure 6 and Figure 7 electrophysiological sensing electrode 9 as shown.

[0156] Material characterization The structure and performance of the electrophysiological sensing electrode prepared in Example 2 are characterized.

[0157] 1. Anti-water loss performance characterization

[0158] As shown in Figure 8The figure shows the characterization results of the anti-water loss performance of the electrophysiological sensing electrode prepared in Example 2. After being placed at room temperature of 25°C and relative humidity of 20% for 48 hours, the electrophysiological sensing electrode based on the self-adhesive hydrogel and PDMS first container had a mass retention rate as high as 97.34%, while the mass retention rate of the self-adhesive hydrogel without the PDMS first container as an encapsulation layer was 49.78%; furthermore, the mass retention rate of the self-adhesive hydrogel without calcium ions was only 38.12%. The above test results demonstrate that the PDMS encapsulation layer and calcium ions jointly enhance the anti-water loss performance and long-term stability of the self-adhesive hydrogel, laying the foundation for the application of electrophysiological sensing electrodes in long-term physiological monitoring.

[0159] 2. Electrode / skin interface impedance characterization

[0160] The test method is as follows: Three electrophysiological sensing electrodes are attached to the inner side of the human forearm at a 2cm interval. From the distal end to the proximal end, they are the reference electrode, working electrode and counter electrode. The AC impedance is measured in the range of 1Hz to 100kHz by an electrochemical workstation (Shanghai Chenhua, CHI760E). The test voltage is 0.005V.

[0161] like Figures 9(a)-9(b) Figure 9(a) shows the interfacial impedance characterization results of the electrophysiological sensing electrode prepared in Example 2 after being attached to the surface of human skin. As the adhesion time increases, the interfacial impedance gradually decreases. This is because the strong adhesion between the self-adhesive hydrogel and the skin, as well as the latent sweat generated during long-term adhesion, enhances the adhesion and conductivity of the self-adhesive hydrogel. Simultaneously, the PDMS encapsulation layer imparts resistance to water loss and long-term stability to the electrophysiological sensing electrode. Figure 9(b) shows the interfacial impedance characterization results of the electrophysiological sensing electrode under dry and sweaty conditions. Under sweaty conditions, the interfacial impedance of the electrophysiological sensing electrode / skin significantly decreases due to the enhanced adhesion and conductivity of the electrode caused by sweat. Conversely, the interfacial impedance of the commercial Ag / AgCl gel electrode increases under sweaty conditions because the commercial Ag / AgCl gel electrode, which has interfacial instability, undergoes debonding.

[0162] The following details the three conditions—dry, exercise, and sweat—as described in Application Examples 1 and 2: Dryness refers to being at 25°C and 20% humidity, with no sweat; exercise refers to jogging (at a pace of approximately 8 min / km) under the same temperature and humidity conditions as dryness, but without significant sweat production; sweat refers to the application of artificial sweat at a rate of 0.2 mL per gram of self-adhesive hydrogel. In Application Examples 1 and 2, the electrophysiological sensing electrodes were adhered to the subject's skin.

[0163] Application Example 1

[0164] 1. Take three electrophysiological sensing electrodes prepared in Example 2, and attach them to the corresponding positions on the inner side of the left forearm (positive electrode) and the inner side of the right forearm (negative electrode) of the subject, respectively, and attach the ground electrode to the lower part of the right arm.

[0165] 2. Paste three commercial Ag / AgCl gel electrodes next to the aforementioned three electrophysiological sensing electrodes.

[0166] 3. Under dry, motion, and sweat conditions, use the commercially available AD8232 module (SICHIRAY Company) to simultaneously record the electrocardiogram signals of the electrophysiological sensing electrodes and the commercial Ag / AgCl gel electrodes.

[0167] The electrocardiogram signal is mainly composed of P, Q, R, S, T, and other peak shapes. Among them, the greater the intensity ratio of the T peak and the R peak measured by the electrophysiological sensing electrode, the higher the sensitivity of the electrophysiological sensing electrode. A large peak intensity ratio indicates that the electrophysiological sensing electrode more sensitively monitors the highest and lowest electrocardiogram signals, i.e., the electrophysiological sensing electrode has high sensitivity. A small peak intensity ratio indicates that the sensitivity of the electrophysiological sensing electrode is small, and some details of the electrocardiogram signal are missed during monitoring.

[0168] The electrocardiogram signal data obtained in this application example is analyzed, as shown in FIG. 10(a), under dry and motion conditions, the electrophysiological sensing electrode and the Ag / AgCl gel electrode exhibit similar sensing performance, but under sweat conditions, the commercial Ag / AgCl gel electrode causes signal distortion due to desorption from the skin; the electrophysiological sensing electrode can maintain good signal quality. Further, FIG. 10(b) is based on the intensity ratio of the T peak and the R peak in the electrocardiogram data under different conditions, as a reference for evaluating the sensitivity of the two sensing electrodes. As can be seen from FIG. 10(b), the electrophysiological sensing electrode containing self-adhesive hydrogel has higher sensitivity than the commercial Ag / AgCl gel electrode under dry, motion, and sweat conditions. Application Example 1 applies the sweat-enhanced adhesion and conductivity of the electrophysiological sensing electrode of the present application.

[0169] Application Example 2

[0170] 1. Take three electrophysiological sensing electrodes prepared in Example 2, and take one electrophysiological sensing electrode as a reference electrode and attach it to the back of the right hand of the subject, and attach the other two electrophysiological sensing electrodes to the two ends of the inner side of the right forearm of the subject.

[0171] 2. Paste three commercial Ag / AgCl gel electrodes next to the aforementioned three electrophysiological sensing electrodes.

[0172] 3. Under dry, motion, and sweat conditions, use the commercially available SEN0240 module (DFROBOT Company) to simultaneously record the electromyogram signals of the electrophysiological sensing electrodes and the commercial Ag / AgCl gel electrodes.

[0173] Signal-to-noise ratio and sensitivity are two interrelated but relatively independent parameters, both of which are used to evaluate the performance of an electrophysiological sensing electrode. The relationship between the two can be understood as follows: positive correlation: generally, if a sensing electrode has high sensitivity, it can detect smaller signal changes, and if these signal changes can be distinguished above the noise level, the signal-to-noise ratio of the sensing electrode will also be higher. Therefore, to some extent, sensitivity and signal-to-noise ratio are positively correlated. Non-linear relationship: however, the signal-to-noise ratio is not always directly proportional to the sensitivity. The signal-to-noise ratio of a sensing electrode is also affected by the noise level. If a sensing electrode can detect small signal changes (high sensitivity), but its own noise level is also high, the signal-to-noise ratio may not improve.

[0174] The analysis of the electromyographic signal data obtained in this application example is shown in Figure 11(a). Under dry conditions, the electrophysiological sensing electrode and the Ag / AgCl gel electrode exhibit similar sensing performance; but under exercise conditions, the noise collected by the electrophysiological sensing electrode (i.e. the signal changes that can be collected) is smaller than that of the commercial Ag / AgCl gel electrode. Under sweat conditions, the amplitude collected by the electrophysiological sensing electrode is greater than that of the commercial Ag / AgCl gel electrode. Further, Figure 11(b) shows the signal-to-noise ratio of the two sensing electrodes under different conditions. From the size of the signal-to-noise ratio, it can be concluded that the signal-to-noise ratio of the self-adhesive hydrogel electrode under dry, exercise and sweat conditions is significantly better than that of the commercial Ag / AgCl gel electrode. Application Example 2 applies the sweat-enhanced adhesion and conductivity of the electrophysiological sensing electrode of the present application.

[0175] Application Example 3

[0176] 1. Take 3 electrophysiological sensing electrodes prepared in Example 2, take 1 electrophysiological sensing electrode as a reference electrode and paste it behind the left ear of the subject, and paste the other 2 electrophysiological sensing electrodes on the outer side of the left eye (positive electrode) and the outer side of the right eye (negative electrode) of the subject.

[0177] 2. Paste 3 commercial Ag / AgCl gel electrodes next to the aforementioned 3 electrophysiological sensing electrodes.

[0178] 3. Use a commercially available AD8232 module (SICHIRAY Company) to simultaneously record the electrooculogram of the self-adhesive hydrogel electrode and the commercial Ag / AgCl gel electrode.

[0179] The electro-oculogram data obtained by the application example is analyzed, as shown in FIG. 12(a), the electrophysiological sensing electrode can accurately collect the electro-oculogram generated by different eye movement behaviors, revealing its great potential for application in human-computer interaction. Further, FIG. 12(b) is the difference between the peak values in the electro-oculogram data under the condition of different eyeball rotation directions, as a reference for evaluating the sensitivity of the two sensing electrodes. Thus, the difference between the peak values generated by the electrophysiological sensing electrode under the condition of different eyeball rotation directions is slightly greater than that of the commercial Ag / AgCl gel electrode. The large peak difference indicates that the electrophysiological sensing electrode containing self-adhesive hydrogel more sensitively monitors the highest or lowest electro-oculogram, i.e. the electrophysiological sensing electrode has high sensitivity. The small peak difference indicates that the electrode misses part of the electro-oculogram during the monitoring process, i.e. the electrode has low sensitivity. Application Example 3 demonstrates the advantages of the electrophysiological sensing electrode of the application over the commercial Ag / AgCl gel electrode.

[0180] The above is only a specific embodiment of the present application, and those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process described above can refer to the corresponding process in the foregoing method embodiment, which will not be described here. It should be understood that the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application.

Claims

1. A self-adhesive hydrogel, characterized in that, The raw materials include modified protein source, acrylic monomer, acrylic acid grafted with N-succinimide ester, acrylated silk fibroin and water, wherein the modified protein source is calcium ion modified silk fibroin.

2. The self-adhesive hydrogel according to claim 1, characterized in that, The mass ratio of the modified protein source, acrylic monomer, acrylic acid grafted with N-succinimide ester, acrylated silk fibroin and water is (87-140):(270-330):(9-11):1:(78.3-95.7).

3. The self-adhesive hydrogel according to claim 1 or 2, characterized in that, The acrylic monomer is selected from acrylic acid, methacrylic acid, ethylacrylic acid, propylacrylic acid, butylacrylic acid, hydroxymethylacrylic acid, or combinations thereof.

4. The self-adhesive hydrogel according to claim 1, characterized in that, The calcium ions account for 1.16 wt% to 1.90 wt% of the mass of the calcium ion-modified silk fibroin.

5. A method for preparing a self-adhesive hydrogel as described in any one of claims 1-4, characterized in that, include: Provide modified protein solutions; The modified protein solution, acrylic monomer, acrylic acid grafted with N-succinimide ester, photoinitiator, acrylated silk fibroin and water were dispersed in a mass ratio of (540~660):(270~330):(9~11):(1.8~2.2):1:(78.3~95.7) to obtain the precursor solution of the self-adhesive hydrogel. The precursor solution of the self-adhesive hydrogel was subjected to ultraviolet light irradiation in an inert atmosphere to obtain the self-adhesive hydrogel.

6. The preparation method according to claim 5, characterized in that, The provision of the modified protein solution includes: modifying degummed silk with a calcium ion salt containing calcium ions in an acidic solution to obtain a calcium ion modified protein solution.

7. The preparation method according to claim 6, characterized in that, The calcium ion salt containing calcium ions is selected from one or more of calcium chloride, calcium acetate, and calcium gluconate; and / or, The acid solution is selected from one or more of formic acid, acetic acid, and propionic acid.

8. The preparation method according to claim 7, characterized in that, The calcium ion salt is calcium chloride, the acid solution is formic acid, and the mass ratio of calcium chloride, degummed silk and formic acid is 1:(3~5):(15~25).

9. The preparation method according to claim 5, characterized in that, The photoinitiator is selected from lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone; wherein, when lithium phenyl-2,4,6-trimethylbenzoylphosphinic acid is used as the photoinitiator, the wavelength of ultraviolet light is 365nm~400nm; when 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone is used as the photoinitiator, the wavelength of ultraviolet light is 254nm~400nm.

10. Use of a self-adhesive hydrogel as described in any one of claims 1-4 in the preparation of electrophysiological sensing electrodes.

11. An electrophysiological sensing electrode, characterized in that, include: The first container has a receiving cavity with an opening on one side; The self-adhesive hydrogel as described in any one of claims 1-4 is disposed within the receiving cavity.

12. The electrophysiological sensing electrode according to claim 11, characterized in that, The first container is made of an elastomer material selected from PDMS or Ecoflex; and / or The electrophysiological sensing electrode also includes a connection structure for disposing the self-adhesive hydrogel within the receiving cavity.

13. The electrophysiological sensing electrode according to claim 12, characterized in that, The connection structure includes an adhesive layer disposed between the inner surface of the receiving cavity and the self-adhesive hydrogel; or... The connecting structure includes a fixing mesh or fixing strip disposed on the opening side of the receiving cavity.

14. The electrophysiological sensing electrode according to claim 13, characterized in that, The adhesive layer is benzophenone that crosslinks the inner surface of the first container cavity with the self-adhesive hydrogel.

15. A method for preparing an electrophysiological sensing electrode, characterized in that, include: The method for preparing a self-adhesive hydrogel according to any one of claims 5-9 prepares a precursor solution for the self-adhesive hydrogel; Provide a first container with a receiving cavity; The precursor solution of the self-adhesive hydrogel is injected into the receiving cavity, and the precursor solution is subjected to ultraviolet light irradiation under an inert atmosphere to transform the precursor solution of the self-adhesive hydrogel into a self-adhesive hydrogel, thereby obtaining an electrophysiological sensing electrode.

16. The method for preparing the electrophysiological sensing electrode according to claim 15, characterized in that, The provision of the first container having a receiving cavity includes: The cavity is pretreated with a benzophenone-containing treatment solution to obtain a first container with benzophenone on the inner surface of the cavity.

17. The method for preparing the electrophysiological sensing electrode according to claim 16, characterized in that, The pretreatment of the receiving cavity using a treatment solution containing benzophenone includes: A 5wt% to 15wt% benzophenone ethanol solution was injected into the cavity and allowed to stand. The cavity was then thoroughly cleaned with methanol and dried with inert gas.

18. The method for preparing the electrophysiological sensing electrode according to claim 15, characterized in that, Also includes: The self-adhesive hydrogel is placed inside the receiving cavity using a fixing net or fixing strip.

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