Liquid metal-silver-porous flexible substrate patterned circuit for flexible wearable electrocardiogram monitoring and methods
By selectively depositing silver and adsorbing liquid metal on porous styrene-butadiene-styrene block copolymer fiber membranes, the problem of weak adhesion between liquid metal and substrate is solved, realizing a flexible circuit with high conductivity and mechanical stability, suitable for wearable ECG monitoring.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG UNIV
- Filing Date
- 2026-05-09
- Publication Date
- 2026-06-05
AI Technical Summary
Existing flexible circuits exhibit weak adhesion between liquid metal and substrate after patterning, resulting in poor stability and difficulty in achieving high conductivity and fine lines. In particular, laser-induced selective metallization on flexible substrates suffers from problems such as poor heat resistance, low crystallinity, and easy cracking.
A porous styrene-butadiene-styrene block copolymer fiber membrane was used as the substrate. A porous flexible substrate was prepared by electrospinning. Silver was selectively deposited on the substrate by combining stencil printing and electrochemical electroplating techniques. Liquid metal was then adsorbed to form a highly conductive, stretchable, and self-healing liquid metal-silver composite circuit.
It achieves high conductivity, mechanical stability, and deformation adaptability, and can maintain conductivity stability under high tensile strain and multiple cyclic stretching, making it suitable for high-precision ECG and heart rate monitoring in static, dynamic, and motion scenarios.
Smart Images
Figure CN122140257A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic skin materials technology, and specifically relates to a patterned circuit of liquid metal-silver-porous flexible substrate for flexible wearable electrocardiogram monitoring. Background Technology
[0002] Flexible circuits are currently still in a stage of high cost and process optimization. Gallium alloy liquid metal has attracted widespread attention due to its advantages such as high conductivity, safety and non-toxicity, high boiling point, and self-healing ability. However, the adhesion between the patterned liquid metal and the substrate is weak and the stability is poor. Therefore, improving the adhesion between the liquid metal and the substrate is the key to fabricating highly conductive and stable circuits.
[0003] While existing spray coating processes offer flexibility in patterned circuit fabrication, their inherent imprecise deposition nature leads to drawbacks such as insufficient pattern precision, difficulty in controlling film quality, and narrow material compatibility. This makes it challenging to achieve fine circuitry, control electrical performance, and affect signal transmission stability, particularly impacting demanding bioelectrical acquisition circuits. Laser-induced selective metallization (LAM) is another common method for fabricating flexible metal circuits. It uses laser irradiation to induce localized photothermal or photochemical reactions in the metal precursor on the substrate surface, selectively reducing metal sites. Subsequent chemical plating then completes the conductive circuitry. However, this method has significant limitations when working with flexible substrates such as fiber membranes. Lasers are high-energy heat sources, easily causing melting, deformation, and even carbonization of heat-sensitive fiber membrane substrates, limiting substrate applicability. Furthermore, the laser-induced metal layer exhibits low crystallinity, a loose structure, and high internal stress, making it prone to cracking and detachment under tensile conditions, and lacking self-healing properties. Additionally, this technology relies on precision laser equipment, is sensitive to process parameters, and is susceptible to pattern edge roughness and decreased precision due to thermal diffusion, making it difficult to consistently achieve high-precision patterning. Summary of the Invention
[0004] To address the aforementioned issues, this invention provides a patterned circuit based on a liquid metal-silver porous flexible substrate for flexible wearable electrocardiogram monitoring, along with its fabrication method and application.
[0005] Compared to circuits of the same system, the patterned circuits of this invention have stronger adhesion, more stable conductivity, and better tensile strength. The flexible patterned conductive circuit material prepared by the process of porous flexible polymer substrate-silver selective patterned growth-electroplating to enhance silver conductivity-liquid metal adsorption of this invention exhibits excellent conductivity stability under high tensile strain and multiple cyclic stretching.
[0006] The wearable ECG monitoring system based on liquid metal-silver-porous flexible substrate conductive material of the present invention exhibits excellent performance in terms of signal fidelity, deformation adaptability, and dynamic anti-interference, and can realize high-precision ECG and heart rate monitoring in static, dynamic and motion scenarios.
[0007] The technical solution of the present invention is as follows: The substrate of this invention is the aforementioned flexible substrate, specifically a porous styrene-butadiene-styrene block copolymer fiber membrane. After preparing the porous flexible substrate by electrospinning, the substrate is placed in a silver solution to fully adsorb silver ions and then dried. A highly conductive silver microcircuit is constructed by combining selective reduction of the stencil printing area with electrochemical electroplating enhancement. Subsequently, eutectic gallium indium liquid metal is introduced and adsorbed into the silver conductive network to obtain a flexible, breathable, stretchable liquid metal-silver composite patterned circuit with self-healing properties.
[0008] I. A patterned circuit using a liquid metal-silver-porous flexible substrate for flexible wearable ECG monitoring: The patterned circuit includes a porous flexible substrate, silver disposed on the porous flexible substrate, and liquid metal adsorbed on the silver. The porous flexible substrate is a styrene-butadiene-styrene block copolymer fiber membrane, which realizes a patterned liquid metal-silver circuit on the porous flexible substrate.
[0009] A silver circuit pattern is precisely reproduced and grown on a styrene-butadiene-styrene block copolymer fiber membrane using a stencil printing method, and liquid metal is adsorbed. The precision of this invention is reflected in the clear and sharp edges of the obtained circuit pattern, without obvious jagged edges, burrs, or smudging, and the regular outline of the lines, maintaining a clear and complete shape even at a linewidth of 100 micrometers.
[0010] In this invention, a customized stencil with a perforated pattern is placed flat on a fiber membrane. A reducing paste is applied to the non-perforated area on the left side of the stencil. Then, a doctor blade is used to print the reducing paste onto the fiber membrane at a certain speed. Since the entire fiber membrane has pre-adsorbed silver ions, the silver ions printed onto the reducing paste in the perforated area are reduced to silver. The remaining silver ions and PVP polymers in the paste are removed by subsequent water dissolution. At this point, the conductivity of the silver circuit pattern is generally low. Electroplating with silver significantly improves the conductivity. Finally, liquid metal is adsorbed into the circuit pattern to obtain a highly conductive, stretchable, self-healing patterned sample. This invention provides a method for obtaining high-precision, highly conductive, and stretchable self-healing silver circuit patterns on a flexible fiber membrane substrate.
[0011] The silver is prepared by adsorbing silver ions onto a porous flexible substrate and then combining them through stencil printing reduction, and the liquid metal is adsorbed onto the silver.
[0012] The molecular structure of the styrene-butadiene-styrene block copolymer is: H-[-CH2-CH(C6H5)-]n-[-CH2-CH=CH-CH-]m-[-CH2-CH(C6H5)-]n.
[0013] III. Fabrication method for the above-mentioned patterned circuits applied to liquid metal-silver-porous flexible substrates: S1: Styrene-butadiene-styrene block copolymer (SBS) was dissolved in a halogenated hydrocarbon organic solvent at a mass-volume concentration of 0.2 g / ml to 0.3 g / ml, and then electrospun to obtain a porous styrene-butadiene-styrene block copolymer fiber membrane. S2: The porous styrene-butadiene-styrene block copolymer fiber membrane obtained in step S1 is placed in a silver trifluoroacetate ethanol solution to allow silver ions to be fully adsorbed onto the fiber membrane and cover the entire surface of the porous fiber membrane. Then, it is removed and dried to obtain a silver ion-porous fiber membrane Ag. + -pSBS; S3: The silver ion-porous fiber membrane obtained in step S2 is printed with a reduction paste through a stencil with a customized pattern, so that the Ag adsorbed on the porous styrene-butadiene-styrene block copolymer fiber membrane is reduced. + Silver ions are selectively reduced to Ag at the perforated areas of the stencil, while silver ions in the non-perforated areas are not reduced and remain in their original state, forming a silver ion-silver-porous fiber membrane. The silver ion-silver-porous fiber membrane is then immersed in deionized water for treatment to obtain the silver-porous fiber membrane Ag-pSBS. S4: The silver-porous fiber membrane Ag-pSBS obtained in step S3 is electroplated with silver using an electrochemical workstation to further enhance its conductivity, thereby obtaining a silver-reinforced porous fiber membrane, which is a silver-porous fiber membrane with significantly enhanced silver conductivity. S5: The sample obtained in step S4 is used to adsorb liquid metal LM in dilute hydrochloric acid to obtain a flexible, porous, and breathable liquid metal-silver-porous flexible substrate patterned circuit, namely LM-Ag-pSBS patterned circuit.
[0014] In step S1, the halogenated hydrocarbon organic solvent is 1,2-dichloroethane. The mass-volume concentration of the styrene-butadiene-styrene block copolymer after being dissolved in the organic solvent 1,2-dichloroethane is 0.2~0.3 g / ml. Under a high voltage of 12~13 kV, a feed rate of 6~8 ml / h, and a distance of 15~20 cm between the receiving device and the nozzle, the porous styrene-butadiene-styrene block copolymer fiber membrane is obtained by electrospinning for 10~15 minutes.
[0015] In step S2, the silver trifluoroacetate ethanol solution is prepared by mixing silver trifluoroacetate and ethanol at a mass-volume ratio of 0.1 g: 1 ml to 0.3 g: 1 ml.
[0016] In step S3, the stencil is a template with a custom-designed circuit pattern cutout. The printing speed of the reduction paste through the stencil is 1~3 mm / s. The silver ion-silver-porous fiber membrane is immersed in deionized water to dissolve the polymer PVP in the reduction paste and the Ag in the blank areas. + That is, the original silver ions Ag in the non-perforated areas + Thus, a silver-porous fiber membrane Ag-pSBS was obtained; The reducing slurry is mainly composed of PVP water-soluble polymer with a molecular weight of 220,000 to 270,000 and reducing liquid in a mass-volume ratio of 1g:1 ml to 1g:3 ml. The reducing liquid is mainly composed of hydrazine hydrate and water in a volume ratio of 1:1 to 1:4.
[0017] In step S4, the electroplating potential is -0.5 to -0.1V, the plating solution is a silver nitrate aqueous solution with a concentration of 0.02 M to 0.1 M, and the electroplating time is 200s to 600s. In step S5, the concentration of dilute hydrochloric acid is 1 mol / L, and the liquid metal LM is a eutectic gallium-indium alloy EGaIn with a gallium to indium mass ratio of 75.5:24.5.
[0018] The thickness of the liquid metal-silver-porous flexible substrate patterned circuit sample is 200 micrometers to 250 micrometers.
[0019] In practice, the ECG monitoring circuit pattern is designed first, and then a stencil is customized. The patterned circuit is prepared using the stencil according to the above method. Electronic components are then integrated and fabricated on the prepared patterned circuit to obtain a liquid metal-silver-porous flexible substrate patterned circuit device that can be used to detect the complete ECG signal waveform.
[0020] Electronic components are typically resistors, capacitors, inductors, diodes, transistors, etc., but are not limited to these.
[0021] III. Application of the aforementioned liquid metal-silver-porous flexible substrate patterned circuit in flexible wearable electrocardiogram monitoring.
[0022] Electronic components such as capacitors, resistors, inductors, and BMD101 chips are mounted on the patterned circuit sample of the liquid metal-silver-porous flexible substrate. Then, corresponding signal acquisition devices and controllers are connected to construct a wearable ECG monitoring system based on liquid metal-silver-based flexible conductive materials for real-time ECG monitoring.
[0023] The innovation of this invention lies in combining selective metallization technology and electroless plating to achieve precise deposition of regionally selective metallization on a porous flexible substrate of styrene-butadiene-styrene block copolymer fiber membrane. This constructs a three-level conductive structure of "flexible liquid metal - rigid silver network - porous flexible substrate," significantly improving the conductivity, mechanical stability, and deformation adaptability of flexible circuits. Specifically, through chemical reduction selective metallization technology, a stencil printing process is performed on a porous flexible substrate that has adsorbed silver ions using a water-soluble polymer-reducing solution mixture. A chemical reaction reduces active silver metal particles in the printed area. These active silver particles provide excellent contact sites for metal deposition during electroless plating, triggering the deposition of silver ions in the plating solution in the activated areas. This ultimately yields a silver metal layer with high adhesion and high conductivity, providing an ideal template for the subsequent selective adsorption and wetting of liquid metal, enabling the patterning of liquid metal alloys. Furthermore, silver ions in non-reduced areas can be removed and recovered during the water-soluble polymer removal process, offering advantages such as high efficiency, low cost, and time saving. Furthermore, unlike current flexible and breathable electronic devices that mainly focus on the development of electrodes and substrates, this invention realizes a portable electronic device for ECG monitoring composed of a breathable, stretchable, and self-healing liquid metal-silver-flexible substrate circuit that can be three-dimensionally integrated with high-density electronic components. It can not only monitor heart rate but also acquire complete ECG signal waveforms, diagnose complex heart rhythms, and provide high-fidelity ECG signals. This is of great significance for comprehensively understanding human health status, achieving early disease prediction, self-diagnosis, personalized treatment, and improving chronic disease management.
[0024] This invention combines selective metallization technology and chemical plating to achieve precise deposition of regional selective metallization on porous flexible substrate styrene-butadiene-styrene block copolymer fiber membranes, making the operation more convenient and easier to control.
[0025] This invention utilizes a chemical reduction selective metallization technique. A water-soluble polymer PVP-hydrazine hydrate aqueous solution mixture is used for template printing on a styrene-butadiene-styrene block copolymer flexible fiber membrane substrate that has adsorbed silver ions. Through a chemical reaction, active silver nanoparticles are reduced in the printed area. These active silver nanoparticles provide excellent contact sites for metal deposition during electroless plating, triggering the deposition of silver ions in the plating solution in the activated areas. This ultimately yields a highly adhesive and highly conductive metal layer, providing an ideal template for the subsequent selective wetting of liquid metals and enabling the patterning of liquid metal alloys. Furthermore, silver ions in the non-reduced areas can be removed and recovered during the water-soluble polymer removal process, offering advantages such as high efficiency, low cost, and time saving.
[0026] Furthermore, unlike current flexible breathable electronic devices that mainly focus on the development of electrodes and substrates, this invention realizes a portable electronic device composed of breathable, stretchable, and self-healing silver-liquid metal microcircuits, which can be highly integrated with high-density electronic components. It can not only monitor heart rate, but also acquire complete electrocardiogram signal waveforms, diagnose complex heart rhythms, and provide high-fidelity electrocardiogram signals. This is of great significance and practical application value for comprehensively understanding human health status, realizing early disease prediction, self-diagnosis, personalized treatment, and improving chronic disease management.
[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a patterned circuit using a liquid metal-silver-porous flexible substrate for flexible wearable ECG monitoring. Through a composite process involving electrospinning a styrene-butadiene-styrene block copolymer porous flexible fiber membrane substrate, selective silver ion reduction, electroplating reinforcement, and liquid metal adsorption, a three-level conductive structure of "flexible liquid metal-rigid silver network-porous flexible substrate" is constructed, significantly improving the circuit's conductivity and mechanical stability. The liquid metal-silver-porous flexible substrate patterned circuit of this invention maintains a 5.44 × 10⁻⁶ linewidth at 100 micrometers. 5 Siemens' high conductivity per meter maintains stable resistance during 20,000 stretching cycles, with a resistance change rate of less than 1.05, which is a significant improvement over existing patterned circuits.
[0028] 2. This invention provides a method for preparing a patterned circuit of liquid metal-silver-porous flexible substrate for flexible wearable electrocardiogram monitoring. The preparation process is simple, the raw materials are readily available, and it has the advantages of high efficiency and low cost. The silver ions in the non-reduced region can be removed and recovered during the process of dissolving the polymer in water.
[0029] 3. The flexible wearable ECG monitoring circuit provided by this invention, based on a liquid metal-silver porous flexible substrate, exhibits excellent durability under harsh conditions such as friction, peeling, torsion, and washing. ECG monitoring experiments further validate its practical application value; the device can acquire ECG signals with high quality, displaying complete and clear waveform characteristics, and maintaining high signal fidelity in both static and dynamic states.
[0030] In summary, the circuit prepared by this invention has excellent conductivity, mechanical stability, and skin adhesion. It can be integrated with high-density electronic components and applied to wearable ECG monitoring to achieve high-fidelity acquisition of heart rate and complete ECG signal waveforms. It can be used for the detection and diagnosis of complex heart rhythms and has important application value in the fields of human health monitoring, early disease warning, and portable medical electronics. Attached Figure Description
[0031] Figure 1This is a flowchart of the preparation process in Example 1 of the present invention; Figure 2 This is a sample image and a partially enlarged image prepared by the preparation process of Example 1 in this invention; Figure 3 The X-ray diffraction patterns of samples obtained at different stages of the preparation process in Example 1 of this invention are shown below. Figure 4 This is a macroscopic digital photograph of the sample prepared in Example 2 of the present invention and a scanning electron microscope image of its circuit area; Figure 5 The volume conductivity of samples with different linewidths prepared in Example 2 of this invention; Figure 6 This refers to the resistance stability of the sample prepared in Example 2 under repeated friction in this invention. Figure 7 The resistance stability of the sample prepared in Example 2 of this invention under multiple peelings; Figure 8 The resistance stability of the sample prepared in Example 2 of this invention under multiple torsion tests; Figure 9 The resistivity stability of the sample prepared in Example 2 of this invention under different water washing times; Figure 10 The resistivity change rate of the sample prepared in Example 2 of this invention after adsorbing liquid metal under 20,000 cyclic stretching cycles; Figure 11 This refers to the liquid metal-silver-porous flexible substrate patterned circuit device for flexible wearable electrocardiogram monitoring prepared in Example 3 of this invention. Figure 12 This invention relates to the testing of electrocardiogram (ECG) signals of a liquid metal-silver-porous flexible substrate patterned circuit device for flexible wearable ECG monitoring prepared in Example 3 under human resting and exercise conditions. Figure 13 This invention relates to the monitoring of the electrocardiogram (ECG) performance of a liquid metal-silver-porous flexible substrate patterned circuit device for flexible wearable ECG monitoring prepared in Example 3, after human rest, 30 seconds of exercise, and 60 seconds of exercise. Figure 14 In this invention, Comparative Example 1 compares the electrocardiogram (ECG) signal test results of a sample silver-porous fiber membrane device with a silver conductive layer only and a sample liquid metal-porous fiber membrane device with a liquid metal conductive layer only, and the liquid metal-silver porous fiber membrane device of this invention. Figure 15In this invention, Comparative Example 2 compares the electrocardiogram (ECG) signal of a sample whose ECG monitoring circuit was replaced with a commercial solid-state circuit board with the ECG signal of the liquid metal-silver-porous fiber membrane device of this invention. Detailed Implementation
[0032] The following describes a preferred embodiment, with reference to the appendix. Figures 1-15 To further illustrate the present invention, the endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values; for numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed herein; the materials, reagents, etc. used in the following embodiments are commercially available unless otherwise specified; the experimental methods in the following embodiments are conventional methods unless otherwise specified.
[0033] The embodiments of the present invention are as follows: Example 1 This embodiment provides a patterning fabrication method for a liquid metal-silver-porous flexible substrate circuit, including the following steps: S1: Styrene-butadiene-styrene block copolymer (SBS) is dissolved in the organic solvent 1,2-dichloroethane at a mass-volume concentration of 0.2 g / ml~0.3 g / ml. Electrospinning is then performed for 10~15 minutes under a high voltage of 12~13 kV, a feed rate of 6~8 ml / h, and a distance of 15~20 cm between the receiving device and the nozzle to obtain a porous styrene-butadiene-styrene block copolymer fiber membrane. S2: Place the porous fiber membrane obtained in step S1 into a silver trifluoroacetate and ethanol solution with a concentration of 0.1 g / ml to 0.3 g / ml, so that silver ions are fully adsorbed on the porous fiber membrane, and then take it out and dry to obtain a silver ion-porous fiber membrane. S3: The reducing paste is printed onto the silver ion-porous fiber membrane obtained in step S2 using a stencil at a printing speed of 1~3 mm / s, so that the Ag adsorbed on the porous fiber membrane... + The sample was regioselectively reduced to Ag. The reducing slurry consisted of water-soluble PVP with a molecular weight of 220,000–270,000 and a reducing solution at a mass-to-volume ratio of 1 g:1 ml to 1 g:3 ml. The reducing solution consisted of hydrazine hydrate and water at a volume ratio of 1:1 to 1:4. Subsequently, the sample was immersed in deionized water to dissolve the PVP and Ag from the blank region. + A silver-porous fiber membrane was obtained; S4: The silver-porous fiber membrane sample obtained in step S3 is electroplated using an electrochemical workstation to further enhance its conductivity. The electroplating potential is -0.5 to -0.1 V, the plating solution is 0.02 M to 0.1 M silver nitrate aqueous solution, and the electroplating time is 200 s to 600 s. S5: The sample obtained in step S4 is adsorbed with liquid metal EGaIn (LM) in 1 mol / L dilute hydrochloric acid. The liquid metal is a eutectic gallium-indium alloy with a mass ratio of gallium to indium of 75.5:24.5, resulting in a flexible, porous, and breathable liquid metal-silver-porous flexible substrate patterned circuit sample.
[0034] In this embodiment, the thickness of the liquid metal-silver-porous flexible substrate patterned circuit sample is 200 micrometers to 250 micrometers.
[0035] Figure 1 For the preparation process of Example 1 of the present invention, firstly, a porous flexible fiber membrane styrene-butadiene-styrene block copolymer is prepared by electrospinning technology as a flexible substrate. This porous flexible substrate fiber membrane is immersed in a silver trifluoroacetate ethanol solution to adsorb Ag. + Then, silver ions are selectively reduced by stencil printing, and Ag in the polymer PVP and non-printed areas is removed by water dissolution. + A patterned silver circuit is formed, and then the silver conductive network is enhanced by electroplating. Finally, liquid metal is adsorbed, thus completing the patterned fabrication of the liquid metal-silver-porous flexible substrate circuit.
[0036] Figure 2 The image shown is a sample obtained in Example 1 of this invention and a partial magnified view, demonstrating the precise control of line width and line spacing by the patterned circuit fabrication method of this invention. As can be seen from the magnified view, the line width of the printed circuit is stably controlled at 150 micrometers, and the line spacing reaches 200 micrometers. The overall circuit pattern has clear edges, no broken lines, no short circuits, and no obvious unevenness in thickness, solving the industry pain points of easy ink bleeding and deformation in flexible substrate printing, and providing reliable process support for the fabrication of flexible electronic devices.
[0037] Figure 3X-ray diffraction (XRD) patterns of samples obtained at different stages of the preparation process in Example 1 of this invention were tested. These XRD patterns compared porous fiber membrane samples from three different treatment stages and were matched with standard PDF cards for four phases: Ag, Ga, In4Ag9, and AgIn2. The patterns clearly demonstrate the phase evolution of the samples before, after, and after adsorbing liquid metal: the unplated silver-porous fiber membrane only showed characteristic diffraction peaks of elemental Ag, with no other impurities, indicating a pure phase and providing a stable silver substrate for subsequent electroplating and liquid metal adsorption; the post-plating silver-reinforced porous fiber membrane still only showed characteristic diffraction peaks of elemental Ag, with peak positions completely different from the unplated sample. While the peak intensity remained consistent, the significant increase in peak intensity indicates that the electroplating process only thickened the silver layer without introducing new phases. This successfully constructed a denser silver network structure on the original silver substrate, providing better active sites for subsequent wettation and adsorption of liquid metal. After adsorbing liquid metal, the liquid metal-silver-porous fiber membrane of the sample retained the characteristic peaks of elemental Ag and added diffraction peaks of three new phases. Elemental Ga corresponds to the gallium matrix in the liquid metal, proving that the liquid metal was successfully adsorbed on the silver network. The intermetallic compounds In4Ag9 and AgIn2 are products generated by the interfacial alloying reaction between Ag and indium in the liquid metal, which are key evidence of the strong bond between the liquid metal and the silver network.
[0038] Example 2 The patterning method is the same as that used in Example 1 for fabricating a liquid metal-silver-porous flexible substrate circuit. The difference is that the influence of different linewidths on the conductivity of the sample was investigated, and the excellent properties of the fabrication method of the present invention, such as high precision, high conductivity, and high tensile stability, were explained in detail.
[0039] Figure 4 The images shown are macroscopic digital photographs and scanning electron microscope (SEM) images of the circuit regions of the sample prepared in Example 2 of this invention. By printing linewidths of 100 micrometers and 1000 micrometers, the high-precision adaptability of this fabrication process to circuits with different linewidths is further demonstrated, meeting the requirements for refined fabrication of flexible circuits. The SEM images show the transition from loose silver particles before electroplating to a dense silver network after electroplating, and then to a liquid metal-silver composite layer after adsorption of liquid metal. This confirms the three-level conductive structure of "flexible liquid metal - rigid silver network - porous flexible substrate," providing structural support for high conductivity and high tensile stability.
[0040] Figure 5 The volumetric conductivity of the samples prepared in Example 2 of this invention varies with different linewidths. The volumetric conductivity increases continuously with increasing linewidth, maintaining 5.44 × 10⁻⁶ at a linewidth of 100 micrometers. 5 Siemens achieves high conductivity per meter, reaching 8.72 × 10⁻⁶ per meter with a linewidth of 1000 micrometers. 5 Siemens verified the high-precision adaptability of the process per meter, with the conductivity consistently maintained at 10.5 The small error bars per meter (over 1 meter) demonstrate the process stability of the fabrication method of this invention, providing electrical support for the high-performance application of flexible circuits.
[0041] Figure 6 , Figure 7 , Figure 8 , Figure 9 The resistance stability of the samples prepared in Example 2 of this invention under four extreme environments—friction, peeling, torsion, and water washing—was verified, demonstrating the mechanical and environmental stability of the patterned circuit prepared by the method of this invention. The results show that after adsorbing liquid metal, the resistance change rate of the sample remained stable at around 1 after 10 cycles of friction, 10 cycles of peeling, 200 cycles of torsion, and 120 minutes of water washing, which is far superior to the unplated sample and the sample without adsorbed liquid metal after plating. This is attributed to the synergistic structure of "flexible liquid metal-rigid silver network." The silver network provides a rigid conductive framework, and the liquid metal achieves metallurgical bonding through interface alloying, combining self-healing effect and flexible adaptability. This completely solves the pain points of traditional flexible circuits, such as easy wear, easy peeling, easy fatigue, and poor water resistance. It proves that the flexible circuit prepared by this invention has excellent mechanical reliability, interface bonding strength, and environmental adaptability, and can meet the long-term use requirements of wearable electronics and other fields.
[0042] Figure 10 The figure shows the resistance change rate of the sample prepared in Example 2 of this invention after adsorbing liquid metal under 20,000 cyclic stretching cycles with a tensile strain of 60%. As can be seen from the figure, the sample after adsorbing liquid metal exhibits excellent electrical and mechanical stability. Furthermore, the resistance remains very stable after 20,000 cyclic stretching cycles. While the overall resistance change rate shows a slight increase, it remains below 1.05. A magnified view shows that the resistance of the circuit exhibits a rapid and reversible periodic change during stretching and release. The resistance increases slightly during stretching and quickly returns to its initial value after release, without significant hysteresis or delay. This is attributed to the synergistic structure of the "flexible liquid metal-rigid silver network." The silver network provides high-strength skeletal support to resist cyclic tensile stress, while the liquid metal, with its fluidity and interfacial metallurgical bonding properties, rapidly repairs microcracks and achieves self-recovery of the conductive path during deformation. These results demonstrate that the flexible circuit prepared in this invention possesses excellent fatigue resistance and reliability, meeting the application requirements of wearable electronics, flexible sensors, and other fields under long-term repeated deformation scenarios.
[0043] Example 3 This embodiment provides a method for fabricating a patterned circuit device on a liquid metal-silver-porous flexible substrate for flexible wearable ECG monitoring. The method is the same as the patterned fabrication method of the liquid metal-silver-porous flexible substrate circuit in Embodiment 1. The difference is that a circuit pattern for ECG monitoring is designed, a corresponding stencil is customized, and finally, a BMD101 chip and electronic components such as capacitors, resistors, and inductors are mounted on the patterned circuit sample for ECG monitoring to obtain a patterned circuit device on a liquid metal-silver-porous flexible substrate for flexible wearable ECG monitoring.
[0044] Figure 11 The liquid metal-silver-porous flexible substrate patterned circuit device for flexible wearable ECG monitoring prepared in Example 3 of the present invention has a size of only about 25×20 mm. It is a miniaturized and integrable flexible circuit, which fully meets the miniaturization and lightweight requirements of wearable devices.
[0045] Figure 12 This invention presents a patterned circuit device using a liquid metal-silver porous flexible substrate for flexible wearable ECG monitoring, tested in both resting and active states. The resting ECG signal fully displays the P wave, QRS complex, and T wave, with a stable baseline, extremely low noise, and signal amplitude within the normal range for human use, meeting the requirements for high-precision static monitoring. During exercise, the ECG waveform is still fully preserved, accurately capturing physiological changes during movement and effectively suppressing motion artifacts, with only slight baseline fluctuations and excellent anti-interference performance. This wearable ECG monitoring device using a liquid metal-silver porous flexible substrate combines the high precision of static monitoring with the anti-interference capabilities of dynamic monitoring, validating its engineering application feasibility in the field of flexible wearable medical and health monitoring.
[0046] Figure 13 This study investigated the ECG performance of a flexible wearable ECG monitoring device using a liquid metal-silver porous flexible substrate patterned circuit. Tests were conducted after the device was at rest, 30 seconds of exercise, and 60 seconds of exercise. The results showed that the device output a complete P-QRS-T characteristic waveform at rest, with a heart rate of 72 beats / minute, a stable baseline, and extremely low noise, meeting medical-grade static monitoring accuracy. As the exercise load increased, the heart rate synchronously increased to 96 beats / minute (30 s) and 112 beats / minute (60 s), responding in real-time to changes in physiological rhythm. Under all operating conditions, the QRS waveform exhibited regular morphology and complete core features, with no signal distortion. This verified the device's real-time dynamic response, anti-interference stability, and signal integrity under increasing physiological load conditions.
[0047] Comparative Example 1 The only difference between this comparative example and Example 3 is that the conductive layer of the ECG monitoring circuit pattern is replaced with a silver conductive layer or a liquid metal conductive layer. The rest of the preparation process, substrate material, component selection, and welding process are exactly the same as in Example 3. The ECG signal of the prepared circuit device is tested under the same conditions as in the example. Figure 14 To compare the electrocardiogram (ECG) monitoring circuit pattern with a sample silver-porous fiber membrane device (with only a silver conductive layer) and a sample liquid metal conductive layer, ECG signal tests were conducted on the liquid metal-silver porous fiber membrane device of this invention. The tests showed that the liquid metal-silver composite conductive layer device used in this invention outputs a complete P-QRS-T characteristic waveform in the ECG signal, with a regular QRS morphology, stable baseline, and extremely low noise, meeting medical-grade monitoring standards. In contrast, the comparative device using only a liquid metal conductive layer exhibited severe waveform distortion, decreased characteristic waveform recognition, and insufficient signal stability due to uneven circuit resistance caused by the fluidity of the liquid metal. Furthermore, the comparative device using only a silver conductive layer showed continuous attenuation of the QRS amplitude and baseline drift due to microcracks generated under deformation caused by the rigidity of the silver layer, resulting in rapid deterioration of signal quality over time. The results confirm that the liquid metal-silver composite conductive layer of the present invention, through the synergistic effect of the anchoring effect of silver and the high ductility of liquid metal, simultaneously solves the fluidity defects of pure liquid metal and the insufficient flexibility of pure silver layer, achieving a unity of high conductivity, high flexibility and high stability, providing core technical support for flexible wearable ECG monitoring devices, and possessing significant inventiveness and practicality.
[0048] Comparative Example 2 The only difference between this comparative example and Example 3 is that the ECG monitoring circuit is replaced with a commercial solid-state circuit board. Everything else is exactly the same as in Example 3. ECG signal testing is performed on the commercial solid-state circuit board device under the same testing conditions as in Example 3. Figure 15 To test the ECG signals of a sample with an ECG monitoring circuit replaced by a commercial solid-state circuit board, and the liquid metal-silver-porous fiber membrane device of this invention, the tests showed that the output ECG signal of the liquid metal-silver-porous fiber membrane device of this invention fully presents the P-QRS-T characteristic waveform group, with regular QRS morphology, stable baseline, and extremely low noise, and the signal quality meets the medical-grade dynamic monitoring standards. In contrast, commercial solid-state circuit board devices, due to their rigid structure, cannot adapt to the deformation of human skin, resulting in severe distortion of the ECG waveform, significant attenuation of QRS amplitude, T wave submersion by noise, and a significant reduction in signal-to-noise ratio. The results confirm that the flexible circuit design of this invention, through the high ductility of the liquid metal-silver composite conductive layer and the high adhesion of the porous substrate, achieves high-fidelity ECG acquisition in various wearable scenarios, demonstrating significant creativity and practicality compared to existing commercial solutions.
[0049] Therefore, the present invention demonstrates excellent performance in terms of signal fidelity, deformation adaptability, and dynamic anti-interference, enabling high-precision ECG and heart rate monitoring in static, dynamic, and motion scenarios. It provides technical support for the clinical and daily application of wearable medical electronics. The liquid metal-silver-porous flexible substrate preparation method and device provide scientific material design and process reference for the development of high-performance flexible ECG sensors and wearable health monitoring devices.
[0050] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.
Claims
1. A patterned circuit using a liquid metal-silver-porous flexible substrate for flexible wearable electrocardiogram monitoring, characterized in that, The patterned circuit includes a porous flexible substrate, silver disposed on the porous flexible substrate, and liquid metal adsorbed on the silver. The porous flexible substrate is a styrene-butadiene-styrene block copolymer.
2. The liquid metal-silver-porous flexible substrate patterned circuit for flexible wearable ECG monitoring according to claim 1, characterized in that, The silver is prepared by adsorbing silver ions onto a porous flexible substrate and then combining them through stencil printing reduction, and the liquid metal is adsorbed onto the silver.
3. A method for fabricating a patterned circuit on a liquid metal-silver-porous flexible substrate as described in claim 1 or 2, characterized in that, The method includes the following steps: S1: Styrene-butadiene-styrene block copolymer (SBS) is dissolved in a halogenated hydrocarbon organic solvent and electrospinned to obtain a porous styrene-butadiene-styrene block copolymer fiber membrane. S2: Place the porous styrene-butadiene-styrene block copolymer fiber membrane obtained in step S1 into a silver trifluoroacetate ethanol solution to allow silver ions to be fully adsorbed onto the fiber membrane. Remove and dry to obtain a silver ion-porous fiber membrane Ag. + -pSBS; S3: The silver ion-porous fiber membrane obtained in step S2 is printed with a reducing paste using a stencil, so that the Ag adsorbed on the fiber membrane... + It is selectively reduced to Ag to form a silver ion-silver-porous fiber membrane. The silver ion-silver-porous fiber membrane is then immersed in deionized water to obtain the silver-porous fiber membrane Ag-pSBS. S4: The silver-porous fiber membrane Ag-pSBS obtained in step S3 is electroplated with silver using an electrochemical workstation to obtain a silver-reinforced porous fiber membrane. S5: The sample obtained in step S4 is used to adsorb liquid metal LM in dilute hydrochloric acid to obtain a flexible, porous, and breathable liquid metal-silver-porous flexible substrate patterned circuit.
4. The method for fabricating a patterned circuit on a liquid metal-silver-porous flexible substrate according to claim 3, characterized in that, In step S1, the halogenated hydrocarbon organic solvent is 1,2-dichloroethane. The mass-volume concentration of the styrene-butadiene-styrene block copolymer after being dissolved in the organic solvent 1,2-dichloroethane is 0.2~0.3 g / ml. Under a high voltage of 12~13 kV, a feed rate of 6~8 ml / h, and a distance of 15~20 cm between the receiving device and the nozzle, a porous styrene-butadiene-styrene block copolymer fiber membrane is obtained by electrospinning.
5. The method for fabricating a patterned circuit on a liquid metal-silver-porous flexible substrate according to claim 3, characterized in that, In step S2, the silver trifluoroacetate ethanol solution is prepared by mixing silver trifluoroacetate and ethanol at a mass-volume ratio of 0.1 g: 1 ml to 0.3 g: 1 ml.
6. The method for fabricating a patterned circuit on a liquid metal-silver-porous flexible substrate according to claim 3, characterized in that, In step S3, the stencil is a template with a custom-designed circuit pattern cutout. The printing speed of the reduction paste through the stencil is 1~3 mm / s. The silver ion-silver-porous fiber membrane is immersed in deionized water to dissolve the polymer PVP and Ag in the reduction paste. + Thus, a silver-porous fiber membrane Ag-pSBS was obtained; The reducing slurry is mainly composed of PVP water-soluble polymer with a molecular weight of 220,000 to 270,000 and reducing liquid in a mass-volume ratio of 1 g: 1 ml to 1 g: 3 ml. The reducing liquid is mainly composed of hydrazine hydrate and water in a volume ratio of 1:1 to 1:
4.
7. The method for fabricating a patterned circuit on a liquid metal-silver-porous flexible substrate according to claim 3, characterized in that, In step S4, the electroplating potential is -0.5 to -0.1V, the plating solution is a silver nitrate aqueous solution with a concentration of 0.02 M to 0.1 M, and the electroplating time is 200s to 600s. In step S5, the concentration of dilute hydrochloric acid is 1 mol / L, and the liquid metal LM is a eutectic gallium-indium alloy.
8. A patterned circuit device using a liquid metal-silver-porous flexible substrate for flexible wearable electrocardiogram monitoring, characterized in that, The liquid metal-silver-porous flexible substrate patterned circuit device is made from the liquid metal-silver-porous flexible substrate patterned circuit as described in claim 1 or 2, or from the liquid metal-silver-porous flexible substrate patterned circuit prepared by the preparation method described in claims 3-7.
9. An application of the liquid metal-silver-porous flexible substrate patterned circuit of claim 8 for flexible wearable electrocardiogram monitoring, characterized in that, Application in flexible wearable electrocardiogram monitoring.