All-textile microfluidic sweat collection and sensing system and method of making the same

Abstract

The present invention relates to a microfluidic sweat collection and sensing system comprising a bottom layer proximal to the skin of a wearer, a top layer distal to the skin of the wearer; and a separation layer between the bottom and top layers; wherein the separation layer is made of a hot melt material and the top and bottom layers are bonded together with the hot melt separation layer by heat pressing such that a gap is formed between the top and bottom layers; wherein the top and bottom layers are each formed with a water channel and the fabric constituting the bottom and top layers is hydrophilic in the portion corresponding to the water channel and is hydrophobic in the remaining portion.

Description

Technical Field

[0001] This invention relates to the creation of an all-fabric microfluidic system for real-time sweat collection and biomarker monitoring. Background Technology

[0002] Existing microfluidic and sweat sensors suffer from deficiencies in terms of abrasion resistance, breathability, and cost-effectiveness. Specifically, the limitations of existing microfluidic and sweat sensor products include:

[0003] 1. Insufficient collection of fresh sweat makes accurate sensing impossible.

[0004] The real-time sensing performance of sweat sensors in existing wearable systems largely depends on the composition of human sweat. Changes in sweat composition significantly affect the stability and accuracy of the sensor's sweat sensing. After sweating, perspiration primarily relies on evaporation. On one hand, new sweat is secreted onto the skin surface; on the other hand, already secreted sweat continuously evaporates. When the evaporation rate is lower than the perspiration rate, new sweat secreted onto the skin surface mixes with old sweat, which may affect the concentration of biomarkers in the mixed sweat. Therefore, in existing wearable systems, such as fabric sensors, sensor readings provide a rolling average of the distribution of analytes in sweat, rather than precise real-time measurements, posing a challenge to accurately reflecting an individual's health status.

[0005] Existing measurement technologies typically require profuse sweating to ensure adequate contact between the sweat and electrodes. However, accumulated sweat can negatively impact the long-term accuracy and fidelity of the sensor. But people don't always sweat profusely unless under conditions of strenuous exercise or extreme heat. Currently, miniaturized electronic sensors adhering to the skin reduce sweat leakage, but the limited collection area beneath the microfluidic channels doesn't provide sufficient volume for accurate sensing. Therefore, a novel sweat-modulated sensor is needed to rapidly provide enough fresh sweat even under normal human perspiration conditions.

[0006] 2. Poor user experience and comfort.

[0007] Recent advancements in technology, including microfluidic systems, electrochemical sensors, microchips, and wireless transmitters, have provided a crucial foundation for sweat sensing on human skin. However, the discomfort they cause to wearers severely hinders the acceptance and widespread adoption of wearable sensors in industry and the market. Patches made of plastic films and silicone pads adhere to the body, offering poor breathability to the skin, which can lead to skin inflammation, redness, heat, itching, and swelling. Fabric-based microfluidics and sensors offer enhanced tactile properties and breathability, especially in dry conditions, but become saturated and heavy under heavy sweating, with insufficient wicking speed based on passive wicking and evaporation. Furthermore, excessive sweating can cause skin damage and heat stress, and sweat-permeable fabric pores reduce breathability and moisture permeability. Moisture and adhesion on the skin not only affect comfort and restrict movement but also lead to abnormal sweating and reduced sensor accuracy.

[0008] 3. Lack of durability and washability

[0009] There is a great need for wearable sweat sensors that are both durable and washable, but achieving both is difficult. Existing integrated wearable electronic sensors are generally compact, but their long-term performance, including safety when washed with clothing and tensile strength, still needs comprehensive evaluation. Fabric microfluidics and sensors achieve a better balance between handling and mechanical properties, but the stable integration of electrochemical sensing materials on fabric and fiber electrodes still requires further improvement. Summary of the Invention

[0010] This invention addresses the problems of existing technologies by introducing an all-fabric microfluidic system. The system integrates sensing functions, reduces wearer discomfort, and optimizes sweat collection, movement, and dissipation, thereby improving accuracy and wearability. Specifically, this invention provides rapid collection of fresh sweat and accurate sweat sensing, while maintaining high device comfort and durability. The system controls the transport of sweat from the skin to the microfluidic system (normal transport), and then guides it to the sensing area (lateral transport). The system according to the invention can operate in two modes: a fully passive mode and an active-passive combined mode. In the fully passive mode, sweat transport relies on a humidity gradient, guiding sweat movement in a plane through specific geometry (lateral transport). In the active-passive combined mode, normal transport is driven by electroosmotic force, and in-plane movement is guided by geometry (lateral transport). Electrochemical sensing yarns are wrapped in skin-friendly fibers and sewn into the sweat collection area, ensuring that processing performance is not affected. The active layer of the sensing yarns includes glucose oxidase and an ion-selective membrane, which are adequately protected to ensure high durability and washability. An ultralight, detachable wireless signal transmission unit is housed in a small pocket within the fabric sensor. This wearable sweat sensor offers enhanced sensing accuracy, abrasion resistance, and durability. The system can be applied to sports T-shirts, headbands, wristbands, and other clothing. Furthermore, the system is suitable for detecting various biofluids, including wound exudate, blood, tears, and urine, making it applicable to wound dressings, goggles, diapers, and similar applications. Attached Figure Description

[0011] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, in which:

[0012] Figure 1a This is a schematic diagram of a cross-section of a microfluidic system in a fully passive mode according to some embodiments of the present invention;

[0013] Figure 1b This is a schematic diagram of a cross-section of a microfluidic system in an active-passive hybrid mode according to some embodiments of the present invention, wherein the circuit schematically represents an electroosmosis device;

[0014] Figure 1c It shows Figure 1b A schematic split perspective view of some embodiments of the electroosmotic flow device shown;

[0015] Figure 2a This is a planar schematic diagram of the bottom layer of a microfluidic system according to some embodiments of the present invention;

[0016] Figure 2b This is a planar schematic diagram of the top layer of a microfluidic system according to some embodiments of the present invention;

[0017] Figure 2c , Figure 2d They are Figure 2a and Figure 2b A schematic diagram showing the water channels located at the bottom and top levels;

[0018] Figure 2e A schematic diagram of a bottom water channel with a wicking assembly is shown according to some embodiments of the present invention;

[0019] Figure 3 a shows a perspective view of the bottom layer cut to form water channels according to some embodiments of the present invention;

[0020] Figure 3 b shows a schematic diagram of the normal and lateral flow of sweat secreted from the skin according to some embodiments of the present invention;

[0021] Figure 4a The results showed that the sweating simulator produced a sweat at a rate of 2 μL / min / cm. 2 A photograph of the sweat flow pattern on the water channels inherent in the microfluidic system structure according to the present invention when the flow rate continuously supplies sweat;

[0022] Figure 4b It is an image of sweat accumulation in the sweat sensing area of ​​an all-textile microfluidic system with wicking components;

[0023] Figure 5 a is a schematic diagram illustrating the operation of an electroosmotic flow device according to some embodiments of the present invention;

[0024] Figure 5 b is a diagram showing the effect of normal sweat transfer after the electroosmotic device is turned off and on according to some embodiments of the present invention;

[0025] Figure 5 c shows a plan view of a large-scale electroosmotic flow apparatus according to some embodiments of the present invention;

[0026] Figure 6 The preparation process of electrochemically inductive yarn according to some embodiments of the present invention is illustrated schematically;

[0027] Figure 7 a is a schematic diagram illustrating the preparation of a protective layer for a sensing yarn according to some embodiments of the present invention;

[0028] Figure 7 b is a design flowchart of a printed circuit board according to some embodiments of the present invention;

[0029] Figure 8 a is a cyclic voltammetry measurement curve using a ferricyanide redox probe;

[0030] Figure 8 b is a bar chart of the active surface area of ​​the two yarn electrodes;

[0031] Figure 8 c represents the impedance spectra of the two yarn electrodes;

[0032] Figure 9a The calibration curve of the K+ sensing electrode is shown;

[0033] Figure 9b The calibration curve of the glucose sensing electrode is shown.

[0034] Figure 10a The anti-interference performance diagram of the K+ yarn electrode is shown;

[0035] Figure 10b The anti-interference performance curve of the glucose yarn electrode is shown.

[0036] Figure 11a The graphs show the stability of the internal and external K+ signal voltage outputs with and without a microfluidic sweat collection system.

[0037] Figure 11b The stability curves of the current signal output of glucose inside and outside the microfluidic system are shown in the case of / without the microfluidic sweat collection system. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] This invention proposes an all-textile microfluidic system comprising a sweat collection component and a sensing component. The sweat collection component operates in two modes: a fully passive mode and a combined active-passive mode (Figure 1). Figure 1a This is a schematic diagram of a partial cross-section of a microfluidic system substrate in fully passive mode according to some embodiments of the present invention. The microfluidic system shown in the figure has a root-branched design with a two-layer structure. The two-layer structure includes a lower layer (i.e., bottom layer) close to the skin and an upper layer (i.e., top layer) away from the skin, as well as a separation layer between the lower and upper layers. Sweat secreted from the skin is first absorbed by the lower layer of the microfluidic system and then diffuses to the upper layer. This transport perpendicular to the microfluidic system or perpendicular to the skin is referred to herein as normal transport. Correspondingly, sweat can also be transported along the microfluidic system or along the skin, which is referred to herein as lateral or transverse transport.

[0040] Figure 1b This is a schematic diagram of a partial cross-section of a microfluidic system in an active-passive hybrid mode according to some embodiments of the present invention. Figure 1a The difference is that an electroosmotic device (detailed below) is added to the bottom layer (lower layer) of the fully passive microfluidic system to facilitate the transfer of sweat from the skin into the microfluidic system.

[0041] In fully passive mode (see...) Figure 1a The transport of sweat secreted from the skin depends entirely on the humidity gradient; sweat diffuses from areas of high humidity but not from areas of low humidity, including normal transport and lateral (in-plane) transport. In the active-passive combined mode (see...),... Figure 1b An electroosmotic device facilitates the normal transport of sweat. This device is connected to the bottom layer (lower layer) of the microfluidic system, transferring sweat from the skin into the microfluidic fluid. Therefore, the in-face sweat transport mechanism is the same as in the fully passive mode. In the sensing assembly, yarn electrodes are embroidered on the fabric and connected to a thin, flexible PCB for real-time wireless signal transmission.

[0042] Figure 1c It shows Figure 1b The diagram shows a schematic split perspective view of some embodiments of the electroosmotic flow device. Figure 1c As can be seen, the electroosmotic device includes a cathode fabric layer, an anode fabric layer, and a separation layer (also called a second separation layer) located between them. The cathode and anode fabric layers can be electrically connected to the cathode and anode of a power source (not shown), respectively, to generate an electric field between them, thereby promoting the flow of sweat from the anode fabric layer to the cathode fabric layer. Furthermore, Figure 1c Also shown is another separation layer (also referred to as the first separation layer) between the cathode fabric layer and the top layer of the sweat collection and sensing system, on which a pattern is formed by laser cutting away portions of material. This pattern includes sweat collection areas and sensing areas (detailed below). Additionally, Figure 1c The patterned portion of the top layer is also shown, which corresponds to the bottom layer pattern of the cathode. For clarity, the rest of the top layer is not shown. This top layer pattern corresponds to the pattern of the sweat collection area of ​​the first separation layer and is connected to sensing yarns.

[0043] The preparation of the microfluidic system of this invention is described in detail below.

[0044] I. Fully Passive Simulation Microfluidic System

[0045] Fabrication of substrates for fully passive simulated microfluidic systems

[0046] According to some embodiments of the present invention, the fully passive microfluidic system is prepared as follows: Before use, the fabric is washed with distilled water to remove impurities and foreign matter from the fabric surface, and then dried in an oven. The fabric described herein can be a commercially available hydrophilic fabric, such as cotton. Alumina (Al2O3) nanoparticles and titanium butoxide (TT) are dispersed in deionized water at concentrations of 18 g / L and 12 g / L, respectively, to form an Al2O3 hydrosol, which is then ultrasonically treated for 30 minutes. Subsequently, the washed fabric is immersed in the resulting hydrosol at 40°C for a short time (e.g., 15 to 25 minutes, preferably 20 minutes, or any time deemed appropriate by those skilled in the art), and then the fabric is removed. In a preferred embodiment, to ensure removal of nanoparticles adhering to the fabric, the fabric is rinsed twice with deionized water. Finally, the fabric is dried in air at ambient temperature.

[0047] To prepare the mask solution, a mixed solution of polyvinyl alcohol (PVA) and deionized water was prepared at a ratio of 13 g to 100 mL, and then continuously magnetically stirred at 90 °C for 8 hours. Then, a fabric with an alumina-coated surface (fabric-Al2O3) was attached to a screen-printed frame, which had, for example, a tree-like pattern (see example...). Figures 2a to 2e (See the tree branch pattern shown). The prepared PVA solution is evenly distributed onto the fabric, preferably using a doctor blade to ensure uniform application. After removing the screen printing frame, the fabric is allowed to dry at ambient temperature to promote the curing of the PVA layer.

[0048] In some embodiments, for the top microfluidic pattern, the PVA-coated fabric is rapidly placed in an 80°C oven to accelerate curing, thereby minimizing PVA penetration into the fabric. A hydrophobic solution is prepared by adding 4 g of Nuva-N1811 to every 100 mL of distilled water and magnetically stirring for 1 hour. The mask fabric is then immersed in the hydrophobic solution for 10 minutes, removed, and cured in an oven at 150°C for 20 minutes. Subsequently, the treated fabric is washed with boiling water to remove the PVA layer and then dried in an oven at 60°C.

[0049] In some embodiments, a hot-melt mesh is used as a separator layer to fabricate a bilayer microfluidic pattern. This hot-melt mesh is precisely cut into a grid conforming to a predetermined pattern using laser technology. The predetermined pattern of the hot-melt mesh is consistent with the top layer, such as... Figure 2d As shown, but with a hollow design, the central pattern has been removed (i.e., the...). Figure 2d(As shown in the pattern), leaving the outer frame. Because the mesh has a certain thickness, a gap can be formed between the upper and lower patterns as a sweat collection channel. Use a hot press at 100°C to bond the top (upper) and bottom (lower) fabrics to the heat-fused release layer for 3 minutes. Thus, a gap is formed between the top and bottom patterns, the height of which corresponds to the thickness of the release layer.

[0050] The top and bottom layers of the fully passive microfluidic system are generally hydrophobic, but the patterned portions (see example) are hydrophobic. Figures 2a to 2e The tree branch pattern shown is hydrophilic, which makes it easy for water in the microfluidic system to concentrate in the patterned area.

[0051] Design of the sweat collection zone and sensing zone of a fully passive simulated microfluidic system

[0052] As shown above, the fabric substrates forming the top and bottom layers of the microfluidic system are processed to achieve overall hydrophobicity. Then, locally branched water channels are further formed on the top and bottom layers of the microfluidic system substrate, wherein the local water channels are hydrophilic, while the rest of the top and bottom layers are hydrophobic. Figure 2a This is a planar schematic diagram of a microfluidic system located at the bottom layer according to some embodiments of the present invention, which includes a sweat collection area (marked by a large rectangle) and a sensing area (marked by a small rectangle). Figure 2b This is a planar schematic diagram of a microfluidic system located at the top layer according to some embodiments of the present invention, which only includes the sweat collection area.

[0053] like Figure 2a , 2b As shown, the sweat-collecting area includes branching water channels resembling a tree branch. The characteristic feature is that the terminal branching channels form a wedge shape laterally, while other interconnected channels have a trapezoidal geometry. To create an air gap between the two layers of channels while simultaneously bonding the top and bottom layers, a fabric-based separator (as shown in Figure 1 from the first separating layer) is employed. This fabric-based separator is a heat-fused adhesive mesh on a fabric substrate, which, under heat treatment, has an adhesive function, bonding the top and bottom fabrics together. Because the mesh has a certain thickness, a gap can be formed between the upper and lower patterns as a sweat-collecting channel. This design is characterized by a narrower inlet width, systematically widening towards the outlet (L'1 < L1, L'0 < L0). Furthermore, the locally branching water channels are identical in the bottom and top layers. Figure 2a -e).

[0054] In a dendritic water channel system, two or more channels branching off from a single channel are considered to be the next level of water channels. Although Figures 2a to 2e The illustrated embodiment only shows three levels of water channels. The present invention is not limited to this. In other embodiments, more levels of water channels can be used, or only two levels of water channels can be used as needed.

[0055] In order to collect sweat through terminal branch channels, Figure 2a A capillary valve is positioned between the collection area and the sensing area. To facilitate the transport of sweat from the terminal branch channels to the sensing area, a capillary valve with a divergence angle α is arranged between the bottom collection area and the sensing area. α is in the range of 0-90 degrees. Sensing yarn is arranged on the bottom sensing area, for example, by embroidery to fix the sensing yarn to the sensing area. The sensing yarn is used for real-time monitoring of biomarkers in sweat.

[0056] The microfluidic system according to embodiments of the present invention is typically 16 square centimeters in size. The thickness of the separation layer is in the range of 0.1-1 mm. However, the present invention is not limited thereto.

[0057] In addition, wicking components ( Figure 2e It can be integrated into the area between the collection area and the sensing area for rapid sweat transfer. For example... Figure 2e As shown, the wicking assembly comprises two parts: a cylindrical conveying section and a circular collecting section. The size of the cylindrical conveying component should not exceed the original pattern.

[0058] The process and results of sweat transport in a fully passive microfluidic system

[0059] Initially, sweat is directed from the skin to the deeper layers through a porous humidity gradient that runs vertically through the pattern. Figure 3 This humidity gradient is generated by PVA screen printing and hydrophobic modification, and is controlled by the flowability of the PVA solution at different temperatures. The humidity gradient is established through PVA screen printing and subsequent hydrophobic modification. This gradient is controlled by manipulating the flowability of the PVA solution at different temperatures. High temperatures enhance the flowability of PVA, allowing it to penetrate vertically into the fabric and coat the fiber surface upon curing. The bottom pattern is prepared using PVA at 80°C, while PVA at ambient temperature is applied to the top pattern. Even after hydrophobic treatment, the inherent hydrophilicity of PVA is maintained. Therefore, a vertical humidity gradient is generated, characterized by a gradual decrease in the amount of PVA from the screen-printed side to the opposite side. Subsequently, sweat is absorbed into the interior of the bottom pattern through the inherent capillary action of the porous medium, continuing until absorption saturation is reached. After saturation, the absorbed sweat is expelled onto the bottom surface, forming droplets. These droplets then gradually expand until they reach the top layer. Thirdly, under the action of Laplace pressure from the top and bottom layers, sweat is transported to the sensing area. By incorporating wedge geometry into the terminal branch pattern, in-plane transport (i.e., lateral transport) of sweat is achieved, ultimately leading to sweat accumulation in the sensing area.

[0060] like Figure 4a As shown, the sweating simulation system in the skin sweat simulator operates at a rate of 2 μL / min / cm. 2With a continuous supply of sweat at a constant flow rate, images depicting sweat flow patterns within the passively induced microfluidic system structure with all similar tree-like branching were captured without sensing electrodes, and a monolayer was selected as a control sample. Figure 4a The top row shows a photograph of a bilayer microfluidic system according to an embodiment of the present invention. For comparison, Figure 4a The line below is a photograph of a single-layer microfluidic system.

[0061] exist Figure 4a In the photograph above, which depicts the bilayer microfluidic system according to an embodiment of the present invention, it is observed that the microfluidic system is completely saturated with water within 11 minutes, with the liquid advancing towards the sensing region. Subsequently, the water begins to accumulate, forming a hemisphere, reaching its maximum volume at approximately 20 minutes.

[0062] For contrast, in the case of a single-layer bottom layer, see [link / reference]. Figure 4b Several photographs show water being directed to the terminal region of the third-level branch, a process aided by the geometry of the water channel structure. Figure 4b In the three images showing 0, 5, and 10 minutes, droplets are gradually forming in the collection area. During actual testing, it was observed that at 15 minutes, water overflowed the channels instead of continuing to flow directionally towards the sensing area. This phenomenon is attributed to a decrease in Laplace pressure (i.e., capillary force), which results in the area of ​​the tree-branched water channels being larger than the area of ​​the capillary valve, insufficient to push the water towards the sensing area. Approximately 140 microliters of sweat can be collected within 20 minutes, but none of this sweat reaches the sensing area.

[0063] II. Active-Passive Simulation Microfluidic Systems

[0064] Fabrication of active-passive simulated microfluidic systems

[0065] In the combined active and passive modes, the electroosmotic device promotes the normal transport of sweat, while the intrasurface transport mechanism of sweat is the same as in the fully passive mode.

[0066] In some embodiments, the textile-based electroosmotic device is formed by sandwiching a microporous nylon membrane with a carbon fabric using a porous adhesive liner. In other embodiments, the outer surface of the textile-based electroosmotic device is treated primarily with hydrophobic and hydrophilic properties in locally dashed areas. This pattern can also be rectangular, triangular, etc. Based on electroosmosis, sweat can be controllably transported normally, and the illustrated geometry is applied to transport sweat in a plane. Detailed preparation procedures are described below.

[0067] According to some embodiments of the present invention, a scalable screen printing method is applied to manufacture an oversized fabric with a wettable pattern, which can be cut into several small-sized samples for use in an electric-wicking device. First, the carbon fabric is washed with distilled water and dried in an oven. A hydrophilic coating solution is prepared by adding 2g of Hansi WS to 100ml of distilled water, and the fabric is then immersed in the solution and cured in an oven at 180°C for 2 minutes. Here, the hydrophilic fabric can be directly used as the inner layer of the electrode. Next, a mask with a hollow dot pattern is fabricated for screen printing. A mask solution is prepared by adding polyvinyl alcohol (PVA) to water to a concentration of 15% and magnetically stirring at 90°C for 8 hours. The fabric is fixed onto the designed screen mask, and the PVA solution is poured onto the mask. The mask solution is smoothed with a scraper. Afterward, the mask is removed from the fabric, and the fabric is heated, for example, in an oven at 135°C for 10 minutes. Next, a hydrophobic coating solution is prepared. For example, a hydrophobic coating solution is obtained by adding 4g of Novec N1811 to 100ml of distilled water and magnetically stirring for 1 hour. A fabric covered with a PVA mask is immersed in the hydrophobic coating solution and cured in an oven at 150°C for 2 minutes. The coated sample is then immersed in boiling water until all the PVA dissolves and is washed away. Finally, the sample is dried in an oven at 150°C for 3 minutes. In a preferred embodiment, the polyester fabric may undergo a patterned wetting treatment and be attached to the outer carbon fabric, which will give its outer surface the same appearance and feel as the surrounding area.

[0068] According to some embodiments, the device incorporates a lightweight power supply and control unit. Two electrodes are connected to a power box (containing three miniature button batteries) via fine conductive yarn. A tiny vent valve controls the applied voltage based on different perspiration levels or individual sensations. Here, the perspiration rate is adjusted in three levels (low, medium, and high). Voltage and power consumption are predetermined based on theoretical calculations to achieve appropriate liquid dissipation rates at different levels. A tiny 3D-printed TPU shell is fabricated to house the button batteries and embedded in a hollow strap on the sportswear. Conductive yarn is embedded and sewn inside the strap. A small clip is used to securely fasten the box to the wearer's waistband. The total weight of the power supply and control unit will be less than 20 grams. A passive mode microfluidic system capable of transmitting sweat in a plane is fixed to the aforementioned device via an adhesive liner. This layer is identical to that of a fully passive mode microfluidic system.

[0069] Test of sweat transfer effect of electroosmotic device

[0070] Figure 5A diagram illustrating the electroosmotic effect of induced normal transport is shown. Different perspiration rates based on certain sweat glands were measured and recorded at different voltages. Notably, at 9V, the perspiration transport rate exceeded 100g / h, indicating that increasing the number of sweat glands in the electroosmotic device to 50 could provide sufficient flow rate for the wearer in a state of high perspiration to rapidly transport the perspiration away from the skin. Three conventional coin batteries can provide 14.6 hours of continuous operation for 10 sweat glands and approximately 3 hours for 50 sweat glands. This time is generally sufficient, as the wearer cannot remain in a state of extremely high perspiration for extended periods (e.g., more than 3 hours).

[0071] The dissipation rate can be adjusted according to different applied voltages. It is noteworthy that the rapid dissipation of liquid in droplet form on carbon or polyester fabric surfaces is very noticeable. Figure 5 (b) This indicates that sweat can potentially be transported normally. Simultaneously, large-scale electroosmotic devices have been developed that uniformly deliver sweat by increasing voltage. Figure 5 c).

[0072] III. Electrochemically Induced Yarn

[0073] Preparation of induction yarn

[0074] Figure 6 The preparation process of electrochemically inductive yarn according to some embodiments of the present invention is illustrated schematically. See also Figure 6 Three degummed yarns were twisted into a spiral and then passed through carbon paint to coat the yarn surface; the carbon-painted yarn was then cured at 80°C for 1 hour. This process was repeated three times to obtain conductive yarn, named C-silk. C-silk was used directly as the counter electrode (CE). A reference electrode (RE) was prepared by further coating the dried C-silk with Ag / AgCl ink. The C-silk was immersed in a 0.1% HAuCl4 solution containing 0.5M Na2SO4 for electrodeposition. This process was performed using cyclic voltammetry (CV), with an external platinum counter electrode and an Ag / AgCl reference electrode (RE) scanned for 50 cycles from -1.5 to 1.5 V at a scan rate of 50 mV / s. After the electrodeposition process, the electrode surface was thoroughly rinsed with ultrapure water to remove any residual HAuCl4 solution. The resulting yarn, named C-silk@Au, was used as the working electrode (WE).

[0075] In a preferred embodiment, glucose-sensing fibers are prepared by electrodeposition of polyaniline and platinum nanoparticles as an intermediary to improve the sensitivity of the sensing fibers. Furthermore, glucose oxidase immobilized in a CNT / chitosan composite matrix is ​​coated onto the sensing fibers as an active layer. Ion-sensing fibers are prepared by electrodeposition of PEDOT:PSS as an ion-electron conversion layer and drop-coating of a selective ion carrier as an ion-specific adsorption layer. Since the surface protonation changes of polyaniline at different pH values ​​exhibit large potential changes, polyaniline is preferred as a sensor for obtaining pH-sensing optical fibers. The Na+ selective membrane comprises a mixture of sodium tetraphenylborate (NaTFPB 1.1 mg), high molecular weight polyvinyl chloride (PVC, 66 mg), bis(2-ethylhexyl) sebate (DOS, 130 mg), and sodium X ion carrier (1 mg), wherein 200 mg of this mixture is dissolved in 1320 μL of tetrahydrofuran and stirred for 2 hours to obtain the Na+ selective membrane. Similarly, the K+ selective membrane will be prepared by dissolving sodium tetraphenylborate (NaTPB 1 mg), PVC (65.5 mg), DOS (129 mg), and valinemycin (4 mg) in 400 μL of cyclohexanone. To minimize the potential drift of the ion-selective electrode, PEDOT:PSS was used as the ion-electron transducer, and deposited onto the electrode via current-controlled electrochemical polymerization from a solution containing 0.02 M EDOT and 0.2 M NaPSS using an external Ag / AgCl reference electrode, where M indicates mol / L. Next, ion-selective membranes will be prepared by depositing 8 μL of Na+ selective membrane precursor solution and 8 μL of K+ selective membrane precursor onto the corresponding electrodes.

[0076] In some embodiments, the outer shell is made of cotton fibers, which wrap and protect the sensing yarn in a protective layer. Figure 7 The core-spun yarn will be manufactured using a ring spinning machine equipped with additional tension and filament guiding devices. The manufacturing process can be simply described as follows: the prepared sensing yarn is stretched under tension by a tension device and a guide, and its position is adjusted in the middle of the core-spun yarn to form the core. The cotton roving will be fed into the drafting zone of the ring spinning machine, and the finally drafted fibers will emerge from the front roller and be wound onto the sensing yarn to form a protective surface layer. All prepared yarn electrodes are embroidered on the sensing area of ​​the microfluidic system and simultaneously connected to a flexible PCB for wireless signal transmission.

[0077] Induction characteristics of each electrode

[0078] Figure 8 Figure a shows the cyclic voltammetry measurement curves using a ferricyanide redox probe; Figure 8b is a bar chart of the active surface areas of the two yarn electrodes. Here, the electrochemical active surface area of ​​the electrodes was estimated by cyclic voltammetry using a ferricyanide redox probe. The measurements conform to the model derived from the Randles-Sevcik equation, which characterizes the reversible redox pair system.

[0079] i p = (2.69 × 10 5 )n 3 / 2 ACD 1 / 2 v 1 / 2

[0080] Where i p is the peak current obtained by cyclic voltammetry in ferricyanide solution, n is the number of electrons transferred in the redox event, A is the electrochemically active surface area, C is the concentration, D is the diffusion coefficient, and v is the scan rate. For example... Figure 8 As shown in b, after depositing Au particles on the electrode surface, the electrochemically active surface area of ​​the yarn electrode increased from 2.2 mm². 2 Significantly increased to 31.1mm 2 Subsequently, the charge transfer resistance (Rct) was determined using electrochemical impedance spectroscopy. Figure 8 The results shown in c indicate that C-silk@Au has an impedance of approximately 9.2 ohms, significantly lower than the 206.5 ohms of the original C-silk. This significant reduction in Rct highlights the effectiveness of the deposited Au nanoparticles in promoting electron transfer efficiency.

[0081] Figure 9a , 9b Calibration curves for the K+ and glucose sensing electrodes are shown separately. Continuous K+ monitoring employs a potential-selective ion electrode, where the interaction between potassium and its ion carrier leads to the electrode potential ( Figure 9a A thin polyvinyl butyral (PVB) coating was applied to the reference electrode to stabilize the voltage and prevent variations inherent in sweat biofluids. The prepared K+ electrode exhibited a logarithmic linear relationship with the concentration of the target ion, achieving a sensitivity of 45.3 mV per decade. Precise and uninterrupted glucose quantification was achieved using an amperotropic enzyme electrode. This electrode incorporates glucose oxidase immobilized within a chitosan membrane, characterized by high permeability, adhesion, and biocompatibility. The addition of electrodeposited Prussian blue (PB) as an electron transfer redox medium promoted the enzymatic reaction. Figure 9b The corresponding calibration curves for the glucose electrode in the 0-200 μM range are shown. The obtained calibration relationship exhibits good linearity (R² = 0.99) and sensitivity (2.3 nA / μM).

[0082] The selectivity of electrochemical sensors is crucial because various biomarkers present in sweat can interfere with the detection of the target biomarker. To assess this, interfering ions are intentionally incorporated into the target biomarker solution to facilitate the observation of current or potential subsequent changes. Figure 10a As shown in -b, the response to the addition of interfering ions or metabolites is less pronounced compared to the target biomarker, indicating that the prepared electrode has excellent selectivity.

[0083] IV. Integration of the sweat sensor system

[0084] Design and manufacturing

[0085] A sweat sensor will be integrated with signal acquisition and transmission circuitry for wireless, in vivo, real-time sweat analysis. This integrated system comprises various functional parts, including signal transduction, conditioning, processing, and wireless transmission from the sensor to a mobile phone. To validate the concept, a fabric sweat sensor will be located on the upper right side of the back of a sportswear garment or T-shirt (slightly below the right shoulder) for real-time sweat analysis. The sensing chip is detachable and can be quickly connected and inserted into the sensing yarn via a conductive yarn connector. The chip will be placed in a small, sealed shoulder pocket. Ergonomic design will ensure that the sweat collection area is always in contact with the skin of the upper back, where sweating rates are high according to body sweat patterns. Biomarkers in the sweat of human subjects (during physical activity) will be tracked in real time, and the results can be displayed on a smartphone for non-invasive health monitoring.

[0086] The sensing chip will primarily consist of an ultra-low-power mixed-signal microcontroller (Aducm355 SoC device), an FT232 USB interface IC, and a small Bluetooth Low Energy module (RN4871 BLE module). As the core of the system, the microcontroller will be programmed on-board via an in-circuit serial programming interface. The system will also include an analog signal conditioning path terminated by a unity-gain quadrupole low-pass filter. This filter will be used to process the current in the glucose channel and the voltages at the sodium and potassium channel terminals. Active filters will be used to fine-tune the gain in the signal conditioning path. These low-pass filters will connect to the microcontroller's analog-to-digital converter stage, converting the filtered analog signals into their respective digital formats. By utilizing the microcontroller's built-in 10-bit analog-to-digital converter block and its computational and serial communication capabilities, the signal (converted by the sensor module of this invention and conditioned by the analog circuitry of this invention) will be relayed to a Bluetooth transceiver, and the sensing signal will then be displayed in real-time on a mobile device. Figure 10b ).

[0087] performance

[0088] To further verify the signal stability within the microfluidic system, a 40 mM K+ solution was applied to the yarn electrodes integrated inside and outside the all-textile microfluidic system. It was observed that when collecting sweat using microfluidics according to the present invention, the output signal remained stable within the microfluidic system, while it fluctuated when there was no output signal. Figure 11a In contrast, the glucose sensing electrode also obtained similar results without performing microfluidic sweat collection according to the present invention. Figure 11b These findings demonstrate that the microfluidic system of the present invention can not only effectively collect sweat but also maintain signal stability, thereby improving monitoring accuracy.

[0089] Although the present invention has been described through specific embodiments, those skilled in the art will understand that various changes and equivalent substitutions can be made to the invention without departing from its scope. Furthermore, various modifications can be made to the invention for specific situations or materials without departing from its scope. Therefore, the present invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A microfluidic sweat collection and sensing system, comprising: Close to the deeper layers of the wearer's skin, Keep away from the top layer of the wearer's skin; and The separation layer located between the bottom layer and the top layer; The separation layer is made of a hot-melt material, and the top and bottom layers are bonded together with the hot-melt separation layer by hot pressing, thereby forming a gap between the top and bottom layers. Water channels are formed in the top and bottom layers respectively.

2. The microfluidic sweat collection and sensing system as described in claim 1, wherein, The bottom water channel includes a collection area and a sensing area; and the top water channel includes a collection area.

3. The microfluidic sweat collection and sensing system as described in claim 2, wherein, The water channels in the bottom and top collection areas include multi-level branching water channels resembling tree branches, wherein the outer water channel branches have a wedge shape with the tip pointing outwards, and the water channel branches connected to them have a trapezoidal shape, the trapezoid being narrower at the inflow end of the water flow and wider at the outflow end of the water flow.

4. The microfluidic sweat collection and sensing system as described in claim 3, wherein, A capillary valve with a divergence angle α is arranged between the collection area and the sensing area of ​​the bottom layer to facilitate the transport of sweat from the collection area to the sensing area, wherein α is in the range of 0-90 degrees.

5. The microfluidic sweat collection and sensing system according to any one of claims 2-4, wherein, Sensing yarns are arranged on the bottom sensing area to monitor biomarkers in sweat in real time.

6. The microfluidic sweat collection and sensing system as described in any one of claims 2-4, further comprising a wicking assembly integrated into the region between the collection area and the sensing area to facilitate sweat transfer, wherein, The wicking assembly includes a cylindrical transport section and a circular collection section.

7. The microfluidic sweat collection and sensing system as described in claim 1, wherein, The thickness of the separation layer is in the range of 0.1-1 mm, and the area of ​​the microfluidic sweat collection and sensing system is 16 cm². 2 .

8. The microfluidic sweat collection and sensing system of claim 1 further includes an electroosmotic device fixed to the sublayer for promoting normal transport of sweat.

9. The microfluidic sweat collection and sensing system as described in claim 8, wherein, The electroosmotic device is formed by sandwiching a microporous nylon membrane with a carbon fabric using a porous adhesive liner.

10. The microfluidic sweat collection and sensing system as described in claim 5, wherein, The sensing yarn is wrapped with skin-friendly fibers.

11. The microfluidic sweat collection and sensing system as described in claim 5, wherein, The active layer of the sensing yarn includes glucose oxidase and an ion-selective membrane.

12. The microfluidic sweat collection and sensing system as described in claim 1, wherein, The fabrics constituting the bottom and top layers are hydrophilic in the portion corresponding to the water channel and hydrophobic in the remainder.

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