Liquid metal-hydrogel bioelectrode and preparation method thereof

Abstract

The invention relates to a liquid metal-hydrogel bioelectrode and a preparation method thereof.According to the preparation method, a hydrophilic polymer serves as a base material for electrostatic spinning, a hydrophilic fibrofelt with the thickness ranging from hundreds of nanometers to hundreds of micrometers can be obtained, and after crosslinking treatment, the liquid metal-hydrogel bioelectrode is obtained. Liquid metal is printed on a cross-linked hydrophilic fiber felt to construct a conductive network to form a liquid metal-hydrophilic polymer composite felt, in-situ rapid gelation can be realized through an interface solution to obtain a liquid metal-hydrogel biological electrode, and the liquid metal-hydrogel biological electrode is prepared through an on-demand gelation mechanism. The technical problems of preparation, storage and attachment of a traditional ultrathin hydrogel electrode are solved, the thickness can be effectively reduced, the integrity of a conductive network can be effectively kept, and the obtained liquid metal-hydrogel biological electrode integrates the dual advantages of an ultrathin dry electrode and a wet electrode and has the characteristics of excellent conformal attachment and low interface impedance.

Description

Technical Field

[0001] The present invention relates to the technical field of bioelectrodes, and in particular to a liquid metal-hydrogel bioelectrode and a preparation method thereof. Background Art

[0002] As the core component of bioelectronic systems, bioelectrodes play a key role in electrophysiological signal acquisition and electrical stimulation therapy, such as electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), and charge injection.

[0003] In clinical practice, electrocardiogram (ECG) detection mostly uses metal ball electrodes, while portable devices generally use disposable adhesive Ag / AgCl hydrogel electrodes. Such electrodes are usually composed of four parts: an ion-conductive hydrogel layer, an Ag / AgCl electrode layer, a metal snap connector, and an adhesive base. Although the hydrogel layer can realize ion-electron transduction of biological signals, such electrodes still have the following problems: a bulky structure caused by rigid metal snaps and external lead wires, high impedance caused by non-conformal contact between the hydrogel thickness and the skin, long-term use restrictions caused by hydrogel dehydration, and poor material permeability and Ag / AgCl adhesion. + Existing Holter monitors, while capable of 48 hours of continuous monitoring, are limited by the aforementioned drawbacks of skin irritation caused by ion release. This makes them difficult to meet the demands of wearable devices, let alone achieve the goal of long-term monitoring in everyday scenarios. Therefore, the development of lightweight electrodes with excellent biointerface properties has become a research focus.

[0004] High-quality conformal contact and low impedance are key factors in improving the signal quality of bioelectrodes and the stability of equipment. Conformal contact between electrodes and the surface of biological tissues can eliminate interfacial air gaps, increase the effective contact area, thereby enhancing the capacitive coupling effect and reducing contact impedance. Since the conformal properties of a material are mainly determined by its thickness, flexibility, and adhesion properties, theoretically reducing the thickness and bending stiffness of the material, that is, reducing the thickness and Young's modulus, can significantly improve conformality. Based on this, a variety of flexible dry electrodes have been developed by depositing ultra-thin metals on flexible plastics, elastic films, or fiber substrates. These electrodes exhibit excellent conformality and can be attached to the skin surface like electronic tattoos. Their lightweight and tissue-like softness are significantly better than traditional rigid electrodes. However, the contact impedance of dry electrodes still has obvious shortcomings. The skin-electrode contact impedance mainly depends on three factors: electrode conductivity, capacitive coupling ability of interface ion-electron current, and skin condition. The capacitive coupling ability of interface ion-electron current, that is, the corresponding ion-electron transduction ability, is particularly critical. In the physiological environment, charge transfer depends on ion conduction, while the external circuit is dominated by electron conduction. Therefore, dry electrodes that only have electronic conductivity generally exhibit higher impedance due to low ion-electron transduction efficiency.

[0005] In comparison, hydrogels are high-quality ion conductors, and the ion-conducting bioelectrodes they construct, that is, the corresponding wet electrodes or hydrogel electrodes, have a significant advantage of low contact impedance. In addition, aqueous hydrogels can effectively maintain the hydration state of the skin's stratum corneum, which is the main source of skin impedance, and further reduce the skin interface contact impedance through osmosis. However, traditional hydrogel electrodes have inherent defects such as limited skin conformability and high bulk resistance due to their large thickness, that is, greater than 1 mm. Therefore, it has become an important research direction to simultaneously optimize the interface conformability and impedance characteristics by thinning the thickness of the hydrogel. In recent years, many studies have achieved significant improvements in impedance performance by combining hydrogels with thin metal electrodes. For example, PEDOT:PSS / PAAm hydrogel bioelectrodes have achieved a thickness of approximately 150μm.

[0006] Theoretical predictions show that further thinning the hydrogel layer to below 10 μm can provide an ideal biological interface for electrocardiography, electromyography and electroencephalography detection. However, existing conventional molding methods, such as casting, spin coating, lamination, etc., face major technical bottlenecks in the preparation of sub-ten-micron ultra-thin hydrogels. The molding conditions need to be strictly regulated, and it is difficult to achieve precise control of the structure. Although a film with a thickness of about 10 μm can be prepared by impregnating a hydrogel precursor solution with an elastic polymer skeleton, its uniformity and large-scale production still face significant challenges. Therefore, the development of hydrogel-based bioelectrodes with ultra-thin thickness, excellent flexibility, high ionic conductivity, low skin impedance and good comfort remains a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0007] Based on this, it is necessary to provide a liquid metal-hydrogel bioelectrode and a preparation method thereof.

[0008] The present invention solves the above technical problems with the following technical solutions: A method for preparing a liquid metal-hydrogel bioelectrode comprises the following steps:

[0009] Using a hydrophilic polymer as a substrate for electrospinning, a hydrophilic fiber mat is obtained;

[0010] cross-linking the hydrophilic fiber felt to obtain a cross-linked hydrophilic fiber felt;

[0011] Printing liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network to obtain a liquid metal-hydrophilic polymer composite felt;

[0012] The liquid metal-hydrophilic polymer composite felt is gelled by the interface solution to form a liquid metal-hydrogel bioelectrode.

[0013] In one embodiment, the electrospinning using a hydrophilic polymer as a substrate comprises:

[0014] Adding a hydrophilic polymer into deionized water, heating and stirring, to obtain an electrospinning precursor solution;

[0015] The electrospinning precursor solution is loaded into a syringe, which is then connected to a spinning machine, and electrospinning is performed after setting spinning parameters.

[0016] In one embodiment, the hydrophilic polymer is polyvinyl alcohol, polyacrylic acid, polyacrylamide, chitosan, gelatin, hyaluronic acid, sodium alginate, bovine serum albumin or agarose.

[0017] In one embodiment, the cross-linking treatment of the hydrophilic fiber felt includes: performing physical cross-linking or chemical cross-linking treatment on the hydrophilic fiber felt.

[0018] In one embodiment, the liquid metal is a eutectic gallium-indium alloy or a eutectic gallium-indium-tin alloy.

[0019] In one embodiment, when printing liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network, the liquid metal pattern is printed by screen printing, silk screen printing, photolithography or evaporation.

[0020] In one embodiment, the liquid metal loading on the cross-linked hydrophilic fiber felt is controlled to be 0.5 mg / cm 2 -15mg / cm 2 .

[0021] In one embodiment, the interfacial solution is any one or more of a salt solution, a polyol aqueous solution, and an ionic liquid.

[0022] In one embodiment, when the liquid metal-hydrophilic polymer composite felt is gelled to form a liquid metal-hydrogel bioelectrode through the interface solution, the loading concentration of the interface solution is controlled to be 0.1 wt%-10 wt%.

[0023] The present invention also provides a liquid metal-hydrogel bioelectrode, which is prepared by the preparation method of the liquid metal-hydrogel bioelectrode described in any one of the above embodiments.

[0024] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing a liquid metal-hydrogel bioelectrode, which can obtain a hydrophilic fiber felt with a thickness ranging from hundreds of nanometers to hundreds of microns by electrospinning with a hydrophilic polymer as a substrate. After cross-linking treatment, liquid metal is printed on the cross-linked hydrophilic fiber felt to construct a conductive network to form a liquid metal-hydrophilic polymer composite felt. The interfacial solution can achieve in situ rapid gelation to obtain a liquid metal-hydrogel bioelectrode. Through the on-demand gelation mechanism, the technical problems of traditional ultra-thin hydrogel electrodes in preparation, storage and attachment are solved, the thickness can be effectively reduced and the integrity of the conductive network can be maintained. The obtained liquid metal-hydrogel bioelectrode combines the dual advantages of ultra-thin dry electrodes and wet electrodes, and has the characteristics of excellent conformal adhesion and low interface impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 Schematic diagram of a process for preparing a liquid metal-hydrogel bioelectrode according to one embodiment of the present invention;

[0027] Figure 2 A microscopic diagram of the hydrophilic fiber mat of the present invention and a diagram showing the corresponding relationship between the thickness of the hydrophilic fiber mat and the amount of different electrospinning precursor solutions;

[0028] Figure 3 is a schematic diagram of a printed liquid metal pattern of the present invention;

[0029] Figure 4 Schematic diagram of the liquid metal-hydrogel bioelectrode of the present invention attached to the skin surface;

[0030] Figure 5 Schematic diagram of the liquid metal-hydrogel bioelectrode of the present invention attached to the surface of a rat heart;

[0031] Figure 6 Schematic diagram of the corresponding relationship between the cross-linking density of the cross-linked hydrophilic fiber felt of the present invention and different cross-linking temperatures;

[0032] Figure 7 Graph showing mechanical property test results of the hydrophilic fiber felt, cross-linked hydrophilic fiber felt, and hydrogel obtained by wetting the cross-linked hydrophilic fiber felt of the present invention;

[0033] Figure 8This is a graph showing the test results of the adhesion performance of the hydrogel obtained by wetting and cross-linking the hydrophilic fiber felt of the present invention on the skin surface;

[0034] Figure 9 This is a graph showing the test results of the moisture permeability of the hydrogel obtained by wetting and cross-linking the hydrophilic fiber felt of the present invention;

[0035] Figure 10 Graph showing the results of in vitro cytotoxicity experiments on the hydrogel obtained by wetting and cross-linking the hydrophilic fiber felt and the liquid metal-hydrogel bioelectrode of the present invention;

[0036] Figure 11 Schematic diagram of the corresponding relationship between the ionic conductivity of the liquid metal-hydrogel bioelectrode of the present invention and different sodium chloride solution loading concentrations;

[0037] Figure 12 Graph showing contact impedance test results of liquid metal-hydrogel bioelectrodes of different thicknesses according to the present invention;

[0038] Figure 13 This is a graph showing the test results of the liquid metal-hydrogel bioelectrode of the present invention testing human electrocardiogram data;

[0039] Figure 14 This is a graph showing the test results of the liquid metal-hydrogel bioelectrode of the present invention testing human electrocardiogram data;

[0040] Figure 15 This is a graph showing the test results of the liquid metal-hydrogel bioelectrode of the present invention testing electromyographic signals;

[0041] Figure 16 This is a graph showing the test results of the electrocardiogram of a rat implanted with the 6-channel liquid metal-hydrogel bioelectrode of the present invention. DETAILED DESCRIPTION

[0042] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0043] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0045] In one embodiment, Figure 1 As shown, a method for preparing a liquid metal-hydrogel bioelectrode comprises the following steps:

[0046] In step 110 , electrospinning is performed using a hydrophilic polymer as a substrate to obtain a hydrophilic fiber felt.

[0047] In this embodiment, when electrospinning is performed using a hydrophilic polymer as a substrate, the hydrophilic polymer is added to deionized water and stirred while heating to obtain an electrospinning precursor solution. The electrospinning precursor solution is loaded into a syringe, which is then connected to a spinning machine. After setting the spinning parameters, electrospinning is performed to obtain a hydrophilic polymer ultrafine fiber membrane, that is, an ultra-thin hydrophilic fiber felt with a nanofiber diameter of 100nm-10μm.

[0048] In this embodiment, the hydrophilic polymer is polyvinyl alcohol, polyacrylic acid, polyacrylamide, chitosan, gelatin, hyaluronic acid, sodium alginate, bovine serum albumin, or agarose. For example, PVA (polyvinyl alcohol) has excellent wettability, green processing characteristics, sustainability, and biocompatibility. Using PVA as the substrate, an electrospinning process can be used to obtain PVA fiber mats with thicknesses ranging from hundreds of nanometers to hundreds of microns by regulating the amount of the electrospinning precursor solution. This allows for the production of high-porosity hydrophilic polymer films with rapid water absorption and gel retention capabilities. This enables the in-situ and convenient preparation of ultra-thin liquid metal-hydrogel bioelectrodes with high air permeability, low skin impedance, and high conformability. This circumvents the complex manufacturing process, harsh storage conditions, and difficult operation of conventional ultra-thin hydrogel electrodes, and addresses the gaps between conventional hydrogel electrodes and tissues, poor conformability, and high skin impedance.

[0049] Step 120 : cross-linking the hydrophilic fiber felt to obtain a cross-linked hydrophilic fiber felt.

[0050] In this embodiment, when cross-linking the hydrophilic fiber felt, the hydrophilic fiber felt is treated by physical cross-linking, that is, by thermally cross-linking the hydrophilic fiber felt and controlling the cross-linking conditions to be annealing at 60°C-150°C for 1 hour. For example, when thermally cross-linking a hydrophilic fiber felt obtained using polyvinyl alcohol as a substrate, i.e., a polyvinyl alcohol fiber felt, the cross-linking conditions are controlled to be annealing at 80°C-120°C for 1 hour. During the thermal cross-linking process, adjacent hydroxyl groups between the polyvinyl alcohol chains are dehydrated to form ester groups, causing the originally water-soluble polyvinyl alcohol nanofibers to become partially soluble. When exposed to water, they swell rather than dissolve. This not only ensures that the resulting cross-linked polyvinyl alcohol fiber felt has an appropriate cross-linking density and rapid gelation, but also facilitates the subsequent printing of liquid metal on the surface of the cross-linked polyvinyl alcohol fiber felt to construct a conductive network. The choice of physical cross-linking to treat the polyvinyl alcohol fiber felt is simple and has good biocompatibility. Furthermore, when the polyvinyl alcohol fiber felt is thermally cross-linked, the cross-linking conditions are controlled to be annealing treatment at 100°C for 1 hour. The obtained cross-linked polyvinyl alcohol fiber felt can be well gelled, which can avoid the situation where insufficient cross-linking density causes dissolution or excessive cross-linking causes browning to form a wet paper-like structure.

[0051] In this embodiment, when cross-linking the hydrophilic fiber felt, the hydrophilic fiber felt is treated by chemical cross-linking, that is, the hydrophilic fiber felt is cross-linked using a cross-linking agent, and the fumigation time of the hydrophilic fiber felt with the cross-linking agent is controlled to be 0.5h-1.5h. For example, when chemically cross-linking a hydrophilic fiber felt obtained by using polyvinyl alcohol as a base material, that is, polyvinyl alcohol fiber felt, the cross-linking agent is glutaraldehyde. By fumigating the polyvinyl alcohol fiber felt with glutaraldehyde vapor for 0.5h, the resulting cross-linked polyvinyl alcohol fiber felt can have a suitable cross-linking density. Another example is the use of glutaraldehyde to cross-link gelatin fiber felt and bovine serum albumin fiber felt; and another example is the use of divalent and trivalent ions to cross-link sodium alginate fiber felt and polyacrylic acid fiber felt.

[0052] Step 130 , printing liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network, thereby obtaining a liquid metal-hydrophilic polymer composite felt.

[0053] In this embodiment, a liquid metal pattern is printed on a cross-linked hydrophilic fiber felt by screen printing, silk-screen printing, photolithography, or vapor deposition. For example, a liquid metal conductive network is constructed by micro-contact printing technology, that is, a desired liquid metal pattern can be printed on the cross-linked hydrophilic fiber felt by combining template printing with a mask of the desired pattern. The liquid metal is a eutectic gallium-indium alloy or a eutectic gallium-indium-tin alloy. The good room temperature fluidity, extreme flexibility, high conductivity, and biocompatibility of the two can well support functional applications. The use of eutectic gallium-indium alloy or eutectic gallium-indium-tin alloy as a conductive coating on the cross-linked hydrophilic fiber felt can make the liquid metal pattern tightly adhere to the cross-linked hydrophilic fiber felt, so that the liquid metal conductive network has good conductivity.

[0054] In this embodiment, the liquid metal loading on the cross-linked hydrophilic fiber felt is controlled to 0.5 mg / cm 2 -15mg / cm 2 , which can ensure that the liquid metal conductive network on the cross-linked hydrophilic fiber felt has good conductivity, so that it can better serve as a conformal current collector and transmit signals to external instruments with minimal noise. For example, a liquid metal-polyvinyl alcohol composite felt is prepared by using eutectic gallium-indium alloy or eutectic gallium-indium-tin alloy as a conductive coating on a cross-linked polyvinyl alcohol fiber felt obtained with polyvinyl alcohol as a substrate. Due to the porous structure of the cross-linked polyvinyl alcohol fiber felt and the good affinity between the liquid metal and polyvinyl alcohol, that is, the affinity between the abundant hydroxyl groups in the polyvinyl alcohol molecular chain and the oxidized surface of the liquid metal, the liquid metal pattern can be tightly attached to the surface of the cross-linked polyvinyl alcohol fiber felt. The liquid metal loading on the cross-linked polyvinyl alcohol fiber felt is controlled to be 0.5 mg / cm 2 -15mg / cm 2 , further the preferred liquid metal loading is 3.6 mg / cm 2 .

[0055] Step 140: The liquid metal-hydrophilic polymer composite felt is gelled to form a liquid metal-hydrogel bioelectrode through the interface solution.

[0056] In this embodiment, the interfacial solution is any one or more of a salt solution, a polyol aqueous solution and an ionic liquid. The salt solution includes: a monovalent salt solution, a divalent salt solution and a trivalent salt solution, such as a sodium salt solution, a potassium salt solution, a silver salt solution, a magnesium salt solution, a calcium salt solution, a zinc salt solution, a copper salt solution, an iron salt solution, an iron salt solution, an aluminum salt solution and a nickel salt solution. The polyol aqueous solution includes: a glycerol aqueous solution, an ethylene glycol aqueous solution, a sorbitol aqueous solution and a polyethylene glycol aqueous solution. The interfacial solution plays the role of wetting the liquid metal-hydrophilic polymer composite felt. At the same time, the tissue fluid and sweat of animals or human bodies can also be used as the interfacial solution. When the liquid metal-hydrophilic polymer composite felt When it comes into contact with moist biological tissue, such as moist skin, the abundant hydrophilic groups in the liquid metal-hydrophilic polymer composite felt quickly absorb the interfacial solution, and can achieve rapid in situ gelation to obtain a liquid metal-hydrogel bioelectrode. The formed liquid metal-hydrogel bioelectrode has a two-layer functional structure of an ionic hydrogel layer and a liquid metal layer. It can be conformally attached to the skin surface through the ionic hydrogel layer. The ionic hydrogel layer has ionic conductivity and can transduce biophysiological signals through low-impedance ion-electron conversion, ensuring high-fidelity signal acquisition at the skin interface. The liquid metal layer acts as a conformal current collector, transmitting the signal to external instruments with minimal noise.

[0057] In this embodiment, when a liquid metal-hydrophilic polymer composite felt is gelled using an interfacial solution to form a liquid metal-hydrogel bioelectrode, the loading concentration of the interfacial solution is controlled to be between 0.1wt% and 10wt%, thereby achieving better ion conductivity. For example, using sodium chloride solution as the interfacial solution to gel a liquid metal-polyvinyl alcohol composite felt based on polyvinyl alcohol to form a liquid metal-hydrogel bioelectrode, while ensuring biocompatibility, a sodium chloride solution loading concentration of 0.9wt% exhibits good biocompatibility and ionic conductivity.

[0058] Compared with the prior art, the present invention has at least the following advantages:

[0059] The present invention provides a method for preparing a liquid metal-hydrogel bioelectrode. By electrospinning a hydrophilic polymer as a substrate, a hydrophilic fiber felt with a thickness ranging from hundreds of nanometers to hundreds of microns can be obtained. After cross-linking treatment, liquid metal is printed on the cross-linked hydrophilic fiber felt to construct a conductive network to form a liquid metal-hydrophilic polymer composite felt. In situ rapid gelation can be achieved through the interfacial solution to obtain the liquid metal-hydrogel bioelectrode. The on-demand gelation mechanism solves the technical problems of traditional ultra-thin hydrogel electrodes in preparation, storage and attachment, and can effectively reduce the thickness and maintain the integrity of the conductive network. The obtained liquid metal-hydrogel bioelectrode combines the dual advantages of ultra-thin dry electrodes and wet electrodes, and has the characteristics of excellent conformal adhesion and low interface impedance.

[0060] The present invention also provides a liquid metal-hydrogel bioelectrode, prepared by the preparation method of the liquid metal-hydrogel bioelectrode described in any of the above embodiments. The liquid metal-hydrogel bioelectrode is prepared by an on-demand gelation mechanism, combining the dual advantages of ultra-thin dry electrodes and wet electrodes, with the characteristics of ultra-thinness, high conformality, low impedance, high moisture permeability and long-term biocompatibility. It can be formed on demand by wetting with an interfacial solution, which not only circumvents the storage problems of traditional hydrogel electrodes but also facilitates immediate application. Moreover, before use, it is in the form of a free-standing fiber membrane, and when it contacts a wet biological surface, it transforms into a soft hydrogel form, effectively solving the inconvenient operation problem of traditional ultra-thin and fragile hydrogel electrodes. Due to its excellent conformality and low impedance characteristics, it has multifunctionality in a variety of epidermal bioelectronic applications, including electrophysiological signal acquisition such as electrocardiogram and electromyography, as well as neuromuscular electrical stimulation. It has demonstrated stable performance in multi-channel ECG rhythm recording during cardiac beating in living rats and maintains excellent biocompatibility during long-term implantation.

[0061] The present invention is further described below with reference to specific examples.

[0062] In one embodiment, a method for preparing a liquid metal-hydrogel bioelectrode includes the following steps: electrospinning polyvinyl alcohol as a substrate to obtain a polyvinyl alcohol fiber felt, thermally cross-linking the polyvinyl alcohol fiber felt to obtain a cross-linked polyvinyl alcohol fiber felt, printing liquid metal on the cross-linked polyvinyl alcohol fiber felt to construct a conductive network to obtain a liquid metal-polyvinyl alcohol composite felt, and gelling the liquid metal-polyvinyl alcohol composite felt through an interfacial solution to form a liquid metal-hydrogel bioelectrode.

[0063] In this embodiment, when electrospinning is performed using polyvinyl alcohol as a substrate, polyvinyl alcohol is added to deionized water and heated while stirring to obtain an electrospinning precursor solution. The electrospinning precursor solution is loaded into a syringe, which is then connected to a spinning machine. After setting the spinning parameters, electrospinning is performed to obtain a polyvinyl alcohol ultrafine fiber membrane, that is, an ultrathin polyvinyl alcohol fiber felt with a nanofiber diameter of 200nm-300nm. When the polyvinyl alcohol fiber felt is thermally cross-linked, the cross-linking conditions are controlled to be annealed at 80℃-120℃ for 1 hour. A liquid metal conductive network is constructed using micro-contact printing technology. The desired liquid metal pattern is printed on the cross-linked polyvinyl alcohol fiber felt by template printing combined with a mask of the desired pattern. The liquid metal is a eutectic gallium-indium alloy. By controlling the liquid metal loading on the cross-linked polyvinyl alcohol fiber felt to be 3mg / cm 2 -4mg / cm 2 The interfacial solution is a sodium chloride solution, and a sodium chloride solution with a loading concentration of 0.5wt%-1.5wt% is used to enable the liquid metal-polyvinyl alcohol composite felt to gel to form a liquid metal-hydrogel bioelectrode.

[0064] In one embodiment, Figure 2 、 Figure 3 、 Figure 4 and Figure 5 As shown, based on the electrospinning process, by controlling the amount of electrospinning precursor solution, the thickness of the polyvinyl alcohol fiber mat can be adjusted in the range of hundreds of nanometers to hundreds of microns. In combination with template printing and a mask with the required pattern, the required liquid metal pattern can be printed on the cross-linked polyvinyl alcohol fiber mat, thereby constructing a liquid metal conductive network on the cross-linked polyvinyl alcohol fiber mat to obtain a liquid metal-polyvinyl alcohol composite mat, which corresponds to LM-PVAmat. In this way, an ultra-thin liquid metal-hydrogel bioelectrode with a thickness of 1 μm can be obtained. When the cross-linked polyvinyl alcohol fiber mat printed with the liquid metal pattern is attached to wet skin, within seconds, the white cross-linked polyvinyl alcohol fiber mat is transformed into a transparent polyvinyl alcohol hydrogel with a transmittance of more than 85%. At this time, the ultra-thin and transparent liquid metal-hydrogel bioelectrode, corresponding to LMHT electrode, can be conformally attached to the skin surface with good conformality and adhesion, and can be easily removed by peeling. The peeled LMHT electrode can reproduce human skin texture or fingerprints. Furthermore, the fiber felt-hydrogel transition process can also be achieved in vivo. When the LM-PVAmat is attached to the surface of a beating rat heart, it transforms into a LMHT electrode within 2 minutes. The liquid metal-hydrogel bioelectrode remains conformally and stably attached during cardiac beating, and due to the mechanical coupling of the soft, ultra-thin structure, it has no negative impact on cardiac pulsation.

[0065] In one embodiment, Figure 6 As shown in the figure, the prepared liquid metal-hydrogel bioelectrode has excellent performance in flexibility, stretchability, skin conformality, moisture permeability, biocompatibility and sustainability. When exploring the cross-linking conditions of polyvinyl alcohol fiber felt, physical cross-linking was chosen to treat the polyvinyl alcohol fiber felt because of its simple process and good biocompatibility. During the thermal cross-linking process, the adjacent hydroxyl groups between the polyvinyl alcohol molecular chains are dehydrated to form ester groups, so that the originally water-soluble polyvinyl alcohol nanofibers are converted into a partially soluble state, which swells rather than dissolves when exposed to water. The optimal cross-linking condition is annealing at 100°C for 1 hour. A lower cross-linking temperature, i.e., when it is less than 80°C, easily leads to insufficient cross-linking density, and the obtained cross-linked polyvinyl alcohol fiber felt is easy to dissolve when infiltrated; while an excessively high temperature, i.e., when it is greater than 120°C, excessive cross-linking is induced, causing the obtained cross-linked polyvinyl alcohol fiber felt to brown, and the cross-linked polyvinyl alcohol fiber felt obtained by cross-linking at 150°C can only form a wet paper-like structure rather than a hydrogel when exposed to water.

[0066] In one embodiment, Figure 7 As shown in the figure, the mechanical properties of polyvinyl alcohol fiber felt, cross-linked polyvinyl alcohol fiber felt and hydrogel obtained by wetting cross-linked polyvinyl alcohol fiber felt were tested. The tensile strain ε, stress σ and Young's modulus E of the polyvinyl alcohol fiber felt corresponding to As-spun PVA NFs were 94.5%, 9.66 MPa and 193.6 MPa, respectively. The tensile strain of the cross-linked polyvinyl alcohol fiber felt after cross-linking, corresponding to Crosslinked PVA NFs, was reduced to 78.5%, while the stress and modulus were slightly increased to 12.55 MPa and 205 MPa, respectively. After wetting the cross-linked polyvinyl alcohol fiber felt to form a hydrogel, the mechanical properties decreased significantly. The tensile strain, stress and Young's modulus were 45.1%, 1.34 MPa and 470 kPa, respectively. It has good flexibility and soft elasticity. Its low Young's modulus is highly matched with biological tissues such as human skin, which helps to avoid mechanical mismatch.

[0067] In one embodiment, Figure 8 As shown in the figure, the hydrogel obtained by wetting the cross-linked polyvinyl alcohol fiber felt exhibits moderate adhesion on the skin surface. When the cross-linked polyvinyl alcohol fiber felt is attached to wet skin, its porous hydrophilic nanofibers quickly absorb moisture from the skin surface, and the fibers are transformed into soft hydrogels that closely adhere to the skin contours and wrinkles. The polyvinyl alcohol molecules are rich in hydroxyl groups and can form intermolecular interactions with functional groups such as carboxyl and amino groups on the hydrophilic surface of the skin through hydrogen bonds, electrostatic effects and van der Waals forces. After a standard 180° peel test, the interface toughness of the obtained hydrogel with fresh pig skin reached 44 Jm -2The lap shear and tensile tests showed that the hydrogel has high shear adhesion strength and tensile adhesion strength to pig skin, with corresponding values ​​of 18.28kPa and 4.096kPa respectively. The moderate adhesion strength can effectively prevent the liquid metal-hydrogel bioelectrode from falling off or sliding, and will not damage the skin when removed.

[0068] In one embodiment, Figure 9 As shown in Figure 2, the hydrogel obtained by wetting the cross-linked polyvinyl alcohol fiber felt has good moisture permeability. The moisture permeability of the hydrogel obtained from the 20 μm thick cross-linked polyvinyl alcohol fiber felt is 588 g·m under constant environmental conditions of 22°C and 55% RH. -2 ·d -1 As the thickness increases to 140 μm, its moisture permeability decreases to 386 g·m -2 ·d -1 , but significantly higher than the commercial medical tape, which is 148g·m -2 The water vapor permeability of the hydrogel is limited due to the swelling of nanofibers and the retained water filling the pores of the fiber membrane. However, the hydrogel can achieve dynamic water balance by absorbing environmental droplets / vapor and losing water through evaporation. The synergistic effect of water absorption and evaporation gives it a reasonably high water vapor permeability, ensuring wearing comfort.

[0069] In one embodiment, Figure 10 As shown, the biocompatibility test was performed on the hydrogel and liquid metal-hydrogel bioelectrode obtained by wetting the cross-linked polyvinyl alcohol fiber felt, and the in vitro cytotoxicity experiment was carried out using NIH3T3 cells as a model. The obtained hydrogel and liquid metal-hydrogel bioelectrode both had low cytotoxicity. After incubation for 72 hours, the cell survival rate of both was close to 100%, while the positive control group with 20% DMSO showed significant cell death.

[0070] In one embodiment, Figure 11 As shown, a liquid metal-hydrogel bioelectrode was prepared by infiltrating a liquid metal-polyvinyl alcohol composite felt with sodium chloride solution as the interface solution. Under the premise of ensuring biocompatibility, the optimal sodium chloride solution loading concentration was 0.9wt%, which had good biocompatibility and ionic conductivity.

[0071] In one embodiment, Figure 12 As shown in the figure, the contact impedance of liquid metal-hydrogel bioelectrodes of different thicknesses was tested. When the thickness decreased, the contact impedance decreased significantly, and this trend was more obvious in the low-frequency region of 0.1-10 Hz. After pre-treating the skin with alcohol cotton pads, the impedance was further reduced. The LMHT-1 electrode with a thickness of about 1 μm showed an impedance of 1.2 kΩ and 8.16 kΩ at frequencies of 1 kHz and 0.1 Hz, respectively.

[0072] In one embodiment, Figure 13 、 Figure 14 、 Figure 15 and Figure 16 As shown, the liquid metal-hydrogel bioelectrode exhibits good ionic conductivity and skin impedance, and is suitable for measuring human physiological signals. When the liquid metal-hydrogel bioelectrode is used to measure human ECG data, the liquid metal-hydrogel bioelectrode can stably measure ECG signals for 3 days and has a better signal-to-noise ratio and accuracy than commercial gel electrodes. Furthermore, the liquid metal-hydrogel bioelectrode is used to measure myoelectric signals. It can well sense myoelectric signals and shows better signal quality and signal-to-noise ratio than commercial gel electrodes. Furthermore, the implantable 6-channel liquid metal-hydrogel bioelectrode is used to implant and measure the electrocardiogram of rats. The liquid metal-hydrogel bioelectrode shows good stability in multi-channel ECG rhythm recording during the beating of the living rat heart and maintains excellent biocompatibility during long-term implantation.

[0073] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The above-described embodiments merely represent several embodiments of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for preparing a liquid metal-hydrogel bioelectrode, characterized in that: The following steps are involved: Using a hydrophilic polymer as a substrate for electrospinning, a hydrophilic fiber mat is obtained; cross-linking the hydrophilic fiber felt to obtain a cross-linked hydrophilic fiber felt; Printing liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network to obtain a liquid metal-hydrophilic polymer composite felt; The liquid metal-hydrophilic polymer composite felt is gelled by the interface solution to form a liquid metal-hydrogel bioelectrode.

2. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 1, characterized in that: When the hydrophilic polymer is used as a substrate for electrospinning, the method comprises: Adding a hydrophilic polymer into deionized water, heating and stirring, to obtain an electrospinning precursor solution; The electrospinning precursor solution is loaded into a syringe, which is then connected to a spinning machine, and electrospinning is performed after setting spinning parameters.

3. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 2, characterized in that: The hydrophilic polymer is polyvinyl alcohol, polyacrylic acid, polyacrylamide, chitosan, gelatin, hyaluronic acid, sodium alginate, bovine serum albumin or agarose.

4. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 1, characterized in that: The cross-linking treatment of the hydrophilic fiber felt includes: performing physical cross-linking or chemical cross-linking treatment on the hydrophilic fiber felt.

5. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 1, characterized in that: The liquid metal is a eutectic gallium-indium alloy or a eutectic gallium-indium-tin alloy.

6. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 5, characterized in that: When printing liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network, the liquid metal pattern is printed by screen printing, silk screen printing, photolithography or evaporation.

7. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 6, characterized in that: The liquid metal loading on the cross-linked hydrophilic fiber felt is controlled to be 0.5 mg / cm 2 -15mg / cm 2 .

8. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 1, characterized in that: The interfacial solution is any one or more of a salt solution, a polyol aqueous solution and an ionic liquid.

9. The method for preparing the liquid metal-hydrogel bioelectrode according to claim 8, characterized in that: When the liquid metal-hydrophilic polymer composite felt is gelled to form a liquid metal-hydrogel bioelectrode through the interface solution, the loading concentration of the interface solution is controlled to be 0.1 wt %-10 wt %.

10. A liquid metal-hydrogel bioelectrode, characterized in that: The liquid metal-hydrogel bioelectrode is prepared by the preparation method of any one of claims 1 to 9.

Images