Liquid metal-hydrogel bioelectrode and preparation method thereof

Abstract

The present application relates to a kind of liquid metal-water gel biological electrode and its preparation method, which can obtain the hydrophilic fiber felt of thickness in the range of hundreds of nanometers to hundreds of microns by electrospinning with hydrophilic polymer as base material, after crosslinking treatment, print liquid metal on crosslinking hydrophilic fiber felt to build conductive network to form liquid metal-hydrophilic polymer composite felt, in-situ rapid gelation can be realized by interface solution to obtain liquid metal-water gel biological electrode, through the mechanism of on-demand gelation, the technical problems of traditional ultrathin water gel electrode in preparation, storage and attachment are solved, the thickness can be effectively thinned and the integrity of conductive network is maintained, the liquid metal-water gel biological electrode obtained combines the dual advantages of ultrathin dry electrode and wet electrode, with excellent conformal adhesion and low interface impedance characteristics.

Description

Technical Field

[0001] This invention relates to the field of bioelectrode technology, specifically to a liquid metal-hydrogel bioelectrode and its preparation method. Background Technology

[0002] Bioelectrodes, as core components of bioelectronic systems, play a crucial role in electrophysiological signal acquisition and electrical stimulation therapy, such as electrocardiography (ECG), electromyography (EMG), electroencephalography (EEG), and charge injection.

[0003] In clinical practice, electrocardiogram (ECG) testing often uses metal ball electrodes, while portable devices commonly use disposable adhesive Ag / AgCl hydrogel electrodes. These electrodes typically consist of four parts: an ion-conductive hydrogel layer, an Ag / AgCl electrode layer, a metal snap connector, and an adhesive substrate. Although the hydrogel layer can achieve ion-electron transduction of biological signals, these electrodes still suffer from drawbacks such as a bulky structure due to the rigid metal snap and external leads, high impedance caused by the non-conformal contact between the excessively thick hydrogel and the skin, long-term use limitations due to hydrogel dehydration, and poor material permeability and Ag... + The skin irritation caused by ion release is a drawback of existing Holter ECG monitors, which, although capable of 48-hour continuous monitoring, are still limited by these limitations, making it difficult to meet the needs of wearable devices and, more importantly, to achieve long-term monitoring in everyday scenarios. Therefore, developing 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 and device stability of bioelectrodes. Conformal contact between the electrode and the surface of biological tissue can eliminate interfacial air gaps, increase the effective contact area, thereby enhancing capacitive coupling and reducing contact impedance. Since the conformal properties of materials are mainly determined by their thickness, flexibility, and adhesion properties, theoretically reducing material thickness and bending stiffness—that is, reducing thickness and Young's modulus—can significantly improve conformality. Based on this, various flexible dry electrodes have been developed by depositing ultrathin metals onto flexible plastics, elastic films, or fiber substrates. These electrodes exhibit excellent conformality and can adhere to the skin surface like electronic tattoos, with their lightweight and tissue-like softness significantly superior to traditional rigid electrodes. However, the contact impedance of dry electrodes is still significantly insufficient. The skin-electrode contact impedance mainly depends on three factors: electrode conductivity, capacitive coupling ability of interfacial ion-electron current, and skin condition. The capacitive coupling ability of interfacial ion-electron current, i.e., the corresponding ion-electron transduction ability, is particularly critical. Charge transport in the physiological environment depends on ion conduction, while the external circuit is dominated by electron conduction. Therefore, dry electrodes that only have electronic conductivity generally exhibit high impedance due to low ion-electron transduction efficiency.

[0005] In comparison, hydrogels, as excellent ion conductors, exhibit significant low contact impedance advantages when used to construct ion-conducting bioelectrodes, corresponding to wet electrodes or hydrogel electrodes. Furthermore, aqueous hydrogel systems effectively maintain the hydration of the stratum corneum, the epidermis and a major source of skin impedance, further reducing interfacial contact impedance through osmosis. However, traditional hydrogel electrodes, due to their relatively large thickness (greater than 1 mm), suffer from inherent drawbacks such as limited skin adhesion and high bulk resistivity. Therefore, simultaneously optimizing interfacial adhesion and impedance characteristics by reducing hydrogel thickness has become an important research direction. In recent years, several studies have achieved significant improvements in impedance performance by combining hydrogels with thin metal electrodes; for example, the PEDOT:PSS / PAAm hydrogel bioelectrode has achieved a thickness of approximately 150 μm.

[0006] Theoretical predictions indicate that further thinning of the hydrogel layer to below 10 μm could provide an ideal biointerface for ECG, EMG, and EEG detection. However, existing conventional molding methods, such as casting, spin coating, and lamination, face significant technical bottlenecks in preparing sub-10 μm ultrathin hydrogels. Strict control of molding conditions is required, and precise structural control is difficult. Although films approximately 10 μm thick can be prepared by impregnating a hydrogel precursor solution with an elastic polymer framework, significant challenges remain in achieving uniformity and large-scale production. Therefore, developing hydrogel-based bioelectrodes that combine ultrathin thickness, excellent flexibility, high ionic conductivity, low skin impedance, and good comfort remains a pressing technical challenge in this field. Summary of the Invention

[0007] Therefore, it is necessary to provide a liquid metal-hydrogel bioelectrode and its preparation method.

[0008] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a liquid metal-hydrogel bioelectrode, comprising the following steps:

[0009] Hydrophilic fiber felt was obtained by electrospinning using a hydrophilic polymer as the substrate.

[0010] The hydrophilic fiber felt is subjected to crosslinking treatment to obtain crosslinked hydrophilic fiber felt;

[0011] A conductive network is constructed by printing liquid metal onto the cross-linked hydrophilic fiber felt to obtain a liquid metal-hydrophilic polymer composite felt;

[0012] The liquid metal-hydrophilic polymer composite felt is gelled through an interfacial solution to form a liquid metal-hydrogel bioelectrode.

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

[0014] A hydrophilic polymer was added to deionized water and heated while 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. After setting the spinning parameters, electrospinning is performed.

[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 crosslinking treatment of the hydrophilic fiber felt includes: performing physical crosslinking or chemical crosslinking 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 to construct a conductive network on the cross-linked hydrophilic fiber felt, the liquid metal pattern is printed using methods such as stencil printing, screen printing, photolithography, or vapor deposition.

[0020] In one embodiment, the liquid metal loading on the cross-linked hydrophilic fiber mat is controlled to be 0.5 mg / cm³. 2 -15mg / cm 2 .

[0021] In one embodiment, the interface 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 0.1wt%-10wt%.

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

[0024] The beneficial effects of this invention are as follows: The method for preparing a liquid metal-hydrogel bioelectrode provided by this invention involves electrospinning a hydrophilic polymer as a substrate to obtain a hydrophilic fiber mat with a thickness ranging from hundreds of nanometers to hundreds of micrometers. After cross-linking treatment, liquid metal is printed on the cross-linked hydrophilic fiber mat to construct a conductive network, forming a liquid metal-hydrophilic polymer composite mat. In-situ rapid gelation can be achieved through an interfacial solution to obtain a liquid metal-hydrogel bioelectrode. By using the on-demand gelation mechanism, the technical problems of traditional ultrathin hydrogel electrodes in preparation, storage, and attachment are solved. The thickness can be effectively reduced while maintaining the integrity of the conductive network. The resulting liquid metal-hydrogel bioelectrode combines the advantages of both ultrathin dry and wet electrodes, exhibiting excellent conformal adhesion and low interfacial impedance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart illustrating a method for preparing a liquid metal-hydrogel bioelectrode according to an embodiment of the present invention.

[0027] Figure 2 The diagram shows a microscopic view of the hydrophilic fiber mat of the present invention and a graph showing the relationship between the thickness of the hydrophilic fiber mat and the amount of different electrospinning precursor solutions.

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

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

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

[0031] Figure 6 This is a schematic diagram showing the relationship between the crosslinking density and different crosslinking temperatures of the crosslinked hydrophilic fiber felt of the present invention;

[0032] Figure 7 The graph shows the mechanical property test results of the hydrophilic fiber mat, cross-linked hydrophilic fiber mat, and hydrogel obtained by wetting cross-linked hydrophilic fiber mat according to the present invention.

[0033] Figure 8The figure shows the test results of the adhesion properties of the hydrogel obtained by the wetting crosslinking hydrophilic fiber felt of the present invention on the skin surface;

[0034] Figure 9 The graph shows the test results of the moisture permeability of the hydrogel obtained from the wetting crosslinking hydrophilic fiber felt of the present invention.

[0035] Figure 10 The figure shows the in vitro cytotoxicity test results of the hydrogel and liquid metal-hydrogel bioelectrode obtained by wetting crosslinking hydrophilic fiber felt of the present invention;

[0036] Figure 11 This is a schematic diagram showing the 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 The graph shows the contact impedance test results of liquid metal-hydrogel bioelectrodes of different thicknesses according to the present invention.

[0038] Figure 13 The image shows the test results of the liquid metal-hydrogel bioelectrode of the present invention for testing human electrocardiogram data.

[0039] Figure 14 The image shows the test results of the liquid metal-hydrogel bioelectrode of the present invention for testing human electrocardiogram data.

[0040] Figure 15 The image shows the test results of the liquid metal-hydrogel bioelectrode of the present invention for testing electromyographic signals;

[0041] Figure 16 The image shows the electrocardiogram results of rats implanted with the 6-channel liquid metal-hydrogel bioelectrode of this invention. Detailed Implementation

[0042] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

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

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the 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, such as Figure 1 As shown, a method for preparing a liquid metal-hydrogel bioelectrode includes the following steps:

[0046] Step 110: Electrospinning is performed using a hydrophilic polymer as a substrate to obtain a hydrophilic fiber felt.

[0047] In this embodiment, when electrospinning with a hydrophilic polymer as the substrate, the hydrophilic polymer is added to deionized water and heated while stirring to obtain an electrospinning precursor solution. The electrospinning precursor solution is loaded into a syringe and 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 ultrathin hydrophilic fiber mat with nanofiber diameters 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 polyvinyl alcohol as a substrate, based on electrospinning, polyvinyl alcohol fiber mats with thicknesses ranging from hundreds of nanometers to hundreds of micrometers can be obtained by controlling the amount of electrospinning precursor solution. This results in a high-porosity hydrophilic polymer film with rapid water absorption and gel retention capabilities. Based on this, in-situ convenient preparation of ultrathin liquid metal-hydrogel bioelectrodes with high air permeability, low skin impedance, and high conformability can be achieved. This avoids the problems of complex manufacturing processes, harsh storage conditions, and difficult operation of traditional ultrathin hydrogel electrodes, and solves the problems of gaps at the tissue interface, poor conformability, and high skin impedance of traditional hydrogel electrodes.

[0049] Step 120: The hydrophilic fiber felt is cross-linked to obtain cross-linked hydrophilic fiber felt.

[0050] In this embodiment, the hydrophilic fiber felt is crosslinked using a physical crosslinking method, specifically by thermal crosslinking followed by annealing at 60°C-150°C for 1 hour. For example, when thermally crosslinking a hydrophilic fiber felt (polyvinyl alcohol fiber felt) using polyvinyl alcohol as a substrate, the crosslinking conditions are controlled at 80°C-120°C for 1 hour. During the thermal crosslinking process, adjacent hydroxyl groups between the polyvinyl alcohol chains dehydrate to form ester groups, transforming the originally water-soluble polyvinyl alcohol nanofibers into a partially soluble state. Upon contact with water, they swell rather than dissolve, resulting in a crosslinked polyvinyl alcohol fiber felt with a suitable crosslinking density and rapid gelation. This also facilitates the subsequent printing of liquid metal onto the surface of the crosslinked polyvinyl alcohol fiber felt to construct a conductive network. The physical crosslinking method for treating polyvinyl alcohol fiber felt is simple and exhibits good biocompatibility. Furthermore, when performing thermal crosslinking on polyvinyl alcohol fiber felt, controlling the crosslinking conditions to anneal at 100°C for 1 hour results in crosslinked polyvinyl alcohol fiber felt that can gel well, avoiding the situation where insufficient crosslinking density leads to dissolution or excessive crosslinking leads to browning and the formation of a wet paper-like structure.

[0051] In this embodiment, the hydrophilic fiber felt is crosslinked using a chemical crosslinking method, i.e., by using a crosslinking agent to crosslink the hydrophilic fiber felt, and the fumigation time of the hydrophilic fiber felt with the crosslinking agent is controlled to be 0.5h-1.5h. For example, when chemically crosslinking a hydrophilic fiber felt (i.e., polyvinyl alcohol fiber felt) obtained with polyvinyl alcohol as the base material, glutaraldehyde is used as the crosslinking agent. By fumigating the polyvinyl alcohol fiber felt with glutaraldehyde vapor for 0.5h, the obtained crosslinked polyvinyl alcohol fiber felt can have a suitable crosslinking density. Another example is using glutaraldehyde to crosslink gelatin fiber felt and bovine serum albumin fiber felt; yet another example is using divalent and trivalent ions to crosslink sodium alginate fiber felt and polyacrylic acid fiber felt.

[0052] Step 130: A conductive network is constructed by printing liquid metal onto the cross-linked hydrophilic fiber felt to obtain a liquid metal-hydrophilic polymer composite felt.

[0053] In this embodiment, liquid metal patterns are printed on cross-linked hydrophilic fiber felt using methods such as stencil printing, screen printing, photolithography, or vapor deposition. For example, a liquid metal conductive network can be constructed using micro-contact printing technology. This involves printing a mask with the desired pattern onto the cross-linked hydrophilic fiber felt using a template. The liquid metal is a eutectic gallium indium alloy or a eutectic gallium indium tin alloy. Both have good room temperature fluidity, extreme flexibility, high conductivity, and biocompatibility, which can well support functional applications. Using a eutectic gallium indium alloy or a eutectic gallium indium tin alloy as a conductive coating on the cross-linked hydrophilic fiber felt allows the liquid metal pattern to adhere tightly to the cross-linked hydrophilic fiber felt, giving the liquid metal conductive network good conductivity.

[0054] In this embodiment, the liquid metal loading on the cross-linked hydrophilic fiber mat is controlled to be 0.5 mg / cm³. 2 -15mg / cm 2 This ensures that the liquid metal conductive network on the cross-linked hydrophilic fiber felt has good conductivity, thus enabling it to better function as a conformal current collector and transmit signals to external instruments with minimal noise. For example, using eutectic gallium indium alloy or eutectic gallium indium tin alloy as a conductive coating on cross-linked polyvinyl alcohol (PVA) fiber felt with polyvinyl alcohol as the substrate to prepare a liquid metal-PVA composite felt, due to the porous structure of the cross-linked PVA fiber felt and the good affinity between the liquid metal and PVA—that is, the affinity between the abundant hydroxyl groups in the PVA molecular chain and the oxide surface of the liquid metal—allows the liquid metal pattern to adhere tightly to the surface of the cross-linked PVA fiber felt. The liquid metal loading on the cross-linked PVA fiber felt is controlled at 0.5 mg / cm³. 2 -15mg / cm 2 Furthermore, the preferred liquid metal loading is 3.6 mg / cm³. 2 .

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

[0056] In this embodiment, the interface solution is any one or more of salt solutions, polyol aqueous solutions, and ionic liquids. The salt solutions include monovalent, divalent, and trivalent salt solutions, such as sodium salt solutions, potassium salt solutions, silver salt solutions, magnesium salt solutions, calcium salt solutions, zinc salt solutions, copper salt solutions, iron salt solutions, aluminum salt solutions, and nickel salt solutions. The polyol aqueous solutions include glycerol aqueous solutions, ethylene glycol aqueous solutions, sorbitol aqueous solutions, and polyethylene glycol aqueous solutions. The interface solution serves to wet the liquid metal-hydrophilic polymer composite felt. Simultaneously, animal or human tissue fluid and sweat can also be used as the interface solution. When in contact with moist biological tissues, such as moist skin, the abundant hydrophilic groups in the liquid metal-hydrophilic polymer composite felt rapidly absorb the interfacial solution, enabling in-situ rapid gelation to obtain a liquid metal-hydrogel bioelectrode. The formed liquid metal-hydrogel bioelectrode has a two-layer functional structure: an ion-hydrogel layer and a liquid metal layer. The ion-hydrogel layer can conformally adhere to the skin surface, and its ion conductivity allows for the conduction of biological physiological signals through low-impedance ion-electron conversion, ensuring high-fidelity signal acquisition at the skin interface. Meanwhile, the liquid metal layer acts as a conformal current collector, transmitting signals to external instruments with minimal noise.

[0057] In this embodiment, when a liquid metal-hydrophilic polymer composite felt is gelled to form a liquid metal-hydrogel bioelectrode using an interfacial solution, controlling the loading concentration of the interfacial solution to 0.1 wt%-10 wt% better achieves ion conductivity. For example, using sodium chloride solution as the interfacial solution, a liquid metal-polyvinyl alcohol composite felt made with polyvinyl alcohol as the substrate is gelled to form a liquid metal-hydrogel bioelectrode. Using a sodium chloride solution with a loading concentration of 0.9 wt% while ensuring biocompatibility provides good biocompatibility and ion conductivity.

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

[0059] This invention provides a method for preparing a liquid metal-hydrogel bioelectrode. By electrospinning a hydrophilic polymer as a substrate, a hydrophilic fiber mat with a thickness ranging from hundreds of nanometers to hundreds of micrometers can be obtained. After cross-linking treatment, liquid metal is printed onto the cross-linked hydrophilic fiber mat to construct a conductive network, forming a liquid metal-hydrophilic polymer composite mat. In-situ rapid gelation can be achieved through an interfacial solution to obtain the liquid metal-hydrogel bioelectrode. This on-demand gelation mechanism solves the technical problems of traditional ultrathin hydrogel electrodes in preparation, storage, and attachment. It can effectively reduce the thickness while maintaining the integrity of the conductive network. The resulting liquid metal-hydrogel bioelectrode combines the advantages of both ultrathin dry and wet electrodes, exhibiting excellent conformal adhesion and low interfacial impedance.

[0060] This invention also provides a liquid metal-hydrogel bioelectrode, prepared by the method described in any of the above embodiments. This liquid metal-hydrogel bioelectrode is prepared through an on-demand gelation mechanism, combining the advantages of both ultrathin dry and wet electrodes. It features ultrathinness, high conformability, low impedance, high moisture permeability, and long-term biocompatibility. On-demand shaping can be achieved through wetting with an interfacial solution, which not only avoids the storage problems of traditional hydrogel electrodes but also facilitates immediate application. Moreover, it is in the form of an independent fibrous membrane before use, but transforms into a soft hydrogel form when in contact with a moist biological surface, effectively solving the problem of inconvenient operation of traditional ultrathin and fragile hydrogel electrodes. Based on its excellent conformability and low impedance characteristics, it has multifunctionality in various epidermal bioelectronic applications, including electrophysiological signal acquisition such as electrocardiogram and electromyography, as well as neuromuscular electrical stimulation. It also shows stable performance in multi-channel electrocardiogram rhythm recording during the heartbeat of live rats and maintains excellent biocompatibility during long-term implantation.

[0061] The present invention will be further described below with reference to specific embodiments.

[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 polyvinyl alcohol fiber felt; thermally crosslinking the polyvinyl alcohol fiber felt to obtain crosslinked polyvinyl alcohol fiber felt; printing liquid metal on the crosslinked 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 with polyvinyl alcohol as the substrate, polyvinyl alcohol is added to deionized water and heated while stirring to obtain an electrospinning precursor solution. This precursor solution is then loaded into a syringe, connected to a spinning machine, and electrospinning is performed after setting the spinning parameters. This yields a polyvinyl alcohol ultrafine fiber membrane, i.e., an ultrathin polyvinyl alcohol fiber mat with nanofiber diameters of 200nm-300nm. During thermal crosslinking of the polyvinyl alcohol fiber mat, the crosslinking conditions are controlled by annealing at 80℃-120℃ for 1 hour. A liquid metal conductive network is constructed using microcontact printing technology. The desired liquid metal pattern is printed on the crosslinked polyvinyl alcohol fiber mat using a template printing mask combined with the desired pattern. The liquid metal is a eutectic gallium-indium alloy. The liquid metal loading on the crosslinked polyvinyl alcohol fiber mat is controlled to 3mg / cm³. 2 -4mg / cm 2 The interface solution is a sodium chloride solution. Using a sodium chloride solution with a loading concentration of 0.5wt%-1.5wt% enables the liquid metal-polyvinyl alcohol composite felt to gel and form a liquid metal-hydrogel bioelectrode.

[0064] In one embodiment, such as Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, based on electrospinning technology, the thickness of polyvinyl alcohol (PVA) fiber mat can be adjusted from hundreds of nanometers to hundreds of micrometers by controlling the amount of electrospinning precursor solution. Combined with a mask for printing the desired pattern using a template, the required liquid metal pattern can be printed on the cross-linked PVA fiber mat, thus constructing a liquid metal conductive network on the mat and obtaining a liquid metal-PVA composite mat, corresponding to LM-PVAmat. This allows for the production of an ultrathin liquid metal-hydrogel bioelectrode with a thickness of 1 μm. When the cross-linked PVA fiber mat with the liquid metal pattern is applied to moist skin, within seconds, the white cross-linked PVA fiber mat transforms into a transparent PVA hydrogel with a light transmittance greater than 85%. At this point, the ultrathin transparent liquid metal-hydrogel bioelectrode, corresponding to the LMHT electrode, can conformally adhere to the skin surface, exhibiting good conformality and adhesion, and can be easily removed by peeling. The peeled LMHT electrode can reproduce human skin texture or fingerprints. Furthermore, the transition process between fiber mat and hydrogel can also be achieved in vivo. When LM-PVAmat is attached to the surface of a beating rat heart, it transforms into an LMHT electrode within 2 minutes. This liquid metal-hydrogel bioelectrode maintains conformal and stable attachment during heartbeat, and due to the mechanical coupling effect of the soft ultrathin structure, it has no negative impact on heartbeat.

[0065] In one embodiment, such as Figure 6 As shown, the prepared liquid metal-hydrogel bioelectrode exhibits excellent performance in terms of flexibility, stretchability, skin conformability, moisture permeability, biocompatibility, and sustainability. When exploring the crosslinking conditions of polyvinyl alcohol (PVA) fiber felt, physical crosslinking was chosen because of its simple process and good biocompatibility. During thermal crosslinking, adjacent hydroxyl groups between PVA molecular chains dehydrate to form ester groups, transforming the originally water-soluble PVA nanofibers into a partially soluble state. Upon contact with water, they swell rather than dissolve. The optimal crosslinking condition is annealing at 100℃ for 1 hour. Lower crosslinking temperatures, i.e., below 80℃, easily lead to insufficient crosslinking density, resulting in easy dissolution of the crosslinked PVA fiber felt upon wetting. Conversely, excessively high temperatures, i.e., above 120℃, induce over-crosslinking, causing browning of the resulting crosslinked PVA fiber felt. Furthermore, crosslinked PVA fiber felt obtained at 150℃ only forms a wet paper-like structure rather than a hydrogel upon contact with water.

[0066] In one embodiment, such as Figure 7 As shown, the mechanical properties of hydrogels obtained from polyvinyl alcohol fiber mat, cross-linked polyvinyl alcohol fiber mat, and wetted cross-linked polyvinyl alcohol fiber mat were tested. The tensile strain ε, stress σ, and Young's modulus E of the polyvinyl alcohol fiber mat (corresponding to As-spun PVANFs) were 94.5%, 9.66 MPa, and 193.6 MPa, respectively. The tensile strain of the cross-linked polyvinyl alcohol fiber mat (corresponding to Crosslinked PVANFs) decreased to 78.5%, while the stress and modulus increased slightly to 12.55 MPa and 205 MPa, respectively. The mechanical properties of the wetted cross-linked polyvinyl alcohol fiber mat decreased significantly after forming a hydrogel, with tensile strain, stress, and Young's modulus of 45.1%, 1.34 MPa, and 470 kPa, respectively. It has good flexibility and soft elasticity, and its low Young's modulus is highly compatible with biological tissues such as human skin, which helps to avoid mechanical mismatch.

[0067] In one embodiment, such as Figure 8 As shown, the hydrogel obtained by wetting cross-linked polyvinyl alcohol (PVA) fiber mat exhibits moderate adhesion to the skin surface. When the PVA fiber mat is applied to moist skin, its porous hydrophilic nanofibers quickly absorb moisture from the skin surface, transforming the fibers into a soft hydrogel that closely adheres to the skin contours and folds. The PVA molecules are rich in hydroxyl groups, which can form intermolecular interactions with the carboxyl and amino functional groups on the hydrophilic surface of the skin through hydrogen bonds, electrostatic interactions, and van der Waals forces. After a standard 180° peel test, the resulting hydrogel showed an interfacial toughness of 44 Jm with fresh pigskin. -2Overlap shear and tensile tests showed that the hydrogel exhibited high shear and tensile adhesion strengths to pigskin, with corresponding values ​​of 18.28 kPa and 4.096 kPa, respectively. This moderate adhesion strength effectively prevented the liquid metal-hydrogel bioelectrode from detaching or slipping, and it did not damage the skin during removal.

[0068] In one embodiment, such as Figure 9 As shown, the hydrogel obtained by wetting cross-linked polyvinyl alcohol fiber mat exhibits good moisture permeability. The hydrogel obtained from a 20 μm thick cross-linked polyvinyl alcohol fiber mat has a moisture permeability of 588 g·m⁻² 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·m³. -2 ·d -1 However, it is significantly higher than the 148 g·m² of commercial medical tape, i.e., 40 μm TPU. -2 The d-1 moisture permeability is limited by the gas permeability of the hydrogel due to the swelling of nanofibers and the retention of water filling the pores of the fiber membrane. However, the hydrogel can achieve dynamic water balance by absorbing environmental droplets / vapor and evaporating water from the environment. Through the synergistic effect of water absorption and evaporation, it is endowed with reasonable high moisture permeability, ensuring wearing comfort.

[0069] In one embodiment, such as Figure 10 As shown, the biocompatibility of hydrogels and liquid metal-hydrogel bioelectrodes obtained by wetting and crosslinking polyvinyl alcohol fiber felt was tested. In vitro cytotoxicity experiments were conducted using NIH3T3 cells as a model. Both the obtained hydrogels and liquid metal-hydrogel bioelectrodes showed 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, such as Figure 11 As shown, a liquid metal-hydrogel bioelectrode was prepared by impregnating 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 0.9 wt%, which has good biocompatibility and ionic conductivity.

[0071] In one embodiment, such as Figure 12 As shown, 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 0.1-10Hz. After pretreatment of the skin with alcohol swabs, the impedance decreased further. The LMHT-1 electrode with a thickness of about 1μm showed an impedance of 1.2kΩ and 8.16kΩ at 1kHz and 0.1Hz, respectively.

[0072] In one embodiment, such as Figure 13 , Figure 14 , Figure 15 and Figure 16 As shown, the liquid metal-hydrogel bioelectrode exhibits good ionic conductivity and skin impedance, making it suitable for measuring human physiological signals. When used to measure human electrocardiogram (ECG) data, the liquid metal-hydrogel bioelectrode can stably measure ECG signals for 3 days, with better signal-to-noise ratio and accuracy compared to commercial gel electrodes. Furthermore, when used to measure electromyographic (EMG) signals, the liquid metal-hydrogel bioelectrode can effectively sense EMG signals, exhibiting better signal quality and signal-to-noise ratio compared to commercial gel electrodes. Even further, when an implantable 6-channel liquid metal-hydrogel bioelectrode is implanted to measure rat ECGs, the liquid metal-hydrogel bioelectrode demonstrates excellent stability in multi-channel ECG rhythm recording during live rat heartbeats and maintains excellent biocompatibility during long-term implantation.

[0073] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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 embodiments described above are merely illustrative of several implementations of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a liquid metal-hydrogel bioelectrode, characterized in that, The method comprises the following steps: electrospinning with a hydrophilic polymer as a base material to obtain a hydrophilic fiber felt; cross-linking treatment is performed on the hydrophilic fiber felt to obtain a cross-linked hydrophilic fiber felt; printing a liquid metal on the cross-linked hydrophilic fiber felt to construct a conductive network, thereby obtaining a liquid metal-hydrophilic polymer composite felt; gelation of the liquid metal-hydrophilic polymer composite felt by an interface solution to form a liquid metal-hydrogel bioelectrode.

2. The method of claim 1, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: When the electrospinning with a hydrophilic polymer as a base material is performed, the following steps are included: adding a hydrophilic polymer into deionized water, and stirring while heating to obtain an electrospinning precursor solution; loading the electrospinning precursor solution into a syringe, and then connecting the syringe to a spinning machine, and performing electrospinning after setting the spinning parameters.

3. The method of claim 2, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: The hydrophilic polymer is polyvinyl alcohol, polyacrylic acid, polyacrylamide, chitosan, gelatin, hyaluronic acid, sodium alginate, bovine serum albumin, or agarose.

4. The method of claim 1, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: When the cross-linking treatment is performed on the hydrophilic fiber felt, the following steps are included: performing physical cross-linking or chemical cross-linking treatment on the hydrophilic fiber felt.

5. The method of claim 1, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: The liquid metal is a eutectic gallium-indium alloy or a eutectic gallium-indium-tin alloy.

6. The method of claim 5, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: When the liquid metal is printed on the cross-linked hydrophilic fiber felt to construct a conductive network, the liquid metal pattern is printed by using a screen printing, silk screen printing, photolithography, or evaporation method.

7. The method of claim 6, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: The liquid metal loading on the crosslinked hydrophilic fiber mat is controlled to be 0.5 mg / cm 2 - 15 mg / cm 2 .

8. The method of claim 1, wherein the liquid metal-hydrogel bioelectrode is prepared by the steps of: The interface solution is any one or more of a salt solution, a polyhydric alcohol aqueous solution, and an ionic liquid.

9. The method of claim 8, wherein the liquid metal-hydrogel bioelectrode is prepared by, When the liquid metal-hydrophilic polymer composite felt is gelated by the interface solution to form a liquid metal-hydrogel bioelectrode, the loading concentration of the interface solution is controlled to be 0.1wt%-10wt%.

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

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