One-way flow guiding Janus flexible patch and preparation method and application thereof

Abstract

This invention discloses a unidirectional Janus flexible patch, its preparation method, and its application, belonging to the field of flexible wearable functional materials and body fluid sensing technology. The patch includes a Janus nanofiber membrane and a colorimetric detection area disposed thereon. The Janus nanofiber membrane is composed of a hydrophobic polyurethane nanofiber layer and a hydrophilic silica / polyacrylonitrile composite nanofiber layer. In use, the hydrophobic layer serves as the skin-contact side, and the hydrophilic composite layer serves as the outer liquid-conducting, evaporating, heat-managing, and detection-bearing layer, allowing sweat to be spontaneously transported unidirectionally from the hydrophobic side to the hydrophilic side and inhibiting reverse osmosis. The hydrophilic composite layer enhances sweat absorption, diffusion, and evaporation capabilities, improves light scattering and infrared emission performance, enabling the patch to simultaneously perform sweat excretion, skin dehumidification, evaporative cooling, and passive radiative cooling functions. The detection area is loaded with a colorimetric detection reagent, which can be used to detect Ca in sweat. 2+ Cl ‑ and Na + Visual detection of target objects and smartphone-assisted quantitative analysis.

Description

Technical Field

[0001] This invention relates to the field of flexible wearable functional materials and body fluid sensing technology, specifically to a unidirectional Janus (double-sided heterogeneous) flexible patch based on electrospinning technology, which integrates self-pumping sweat excretion, heat management and multi-target colorimetric detection, as well as its preparation method and application. Background Technology

[0002] The human body produces a large amount of sweat during exercise, in high temperature, or in high humidity environments. Traditional fabrics can only passively absorb sweat, which can easily cause the skin surface to become damp, sticky, and stuffy, affecting wearing comfort. Especially during prolonged exercise or outdoor activities, retained sweat can lead to increased skin humidity and reduced heat dissipation efficiency, and in severe cases, may even cause skin irritation or inflammation.

[0003] Janus membranes, due to their different wettability on both sides, enable directional transport of liquids. Existing Janus membranes are mostly used for sweat wicking, oil-water separation, or basic fluid management; however, most materials have relatively limited functionality, making it difficult to simultaneously achieve rapid sweat evaporation, passive cooling, and physiological indicator detection. Furthermore, existing sweat sensors typically require additional sweat collection structures, microfluidic channels, or external driving devices, resulting in complex structures and insufficient wearing comfort.

[0004] Therefore, there is an urgent need to develop a wearable material and device that integrates unidirectional sweat transport, heat management, and multi-index sweat detection, enabling it to spontaneously collect, transport, react, and detect sweat without the need for external pumping, while improving the heat environment on the skin surface. Summary of the Invention

[0005] The purpose of this invention is to provide a unidirectional liquid transport Janus flexible patch, its preparation method, and its application, addressing the shortcomings of existing technologies. This invention integrates a unidirectional liquid-transmitting Janus nanofiber membrane with a colorimetric detection reagent, enabling the integration of sweat collection, transport, reaction, and detection, thus simplifying the structure of wearable sweat detection devices.

[0006] The specific technical solution for achieving the objective of this invention is as follows:

[0007] A unidirectional Janus flexible patch includes a Janus nanofiber membrane and at least one detection area disposed on the Janus nanofiber membrane; the Janus nanofiber membrane includes a hydrophobic nanofiber layer and a hydrophilic composite nanofiber layer; the hydrophobic nanofiber layer includes polyurethane nanofibers; the hydrophilic composite nanofiber layer includes polyacrylonitrile nanofibers and silica nanoparticles dispersed therein; the hydrophobic nanofiber layer serves as the skin-contact side, and the hydrophilic composite nanofiber layer serves as an outer liquid-conducting layer, a sweat evaporation layer, a thermal management layer, and a detection support layer; the detection area is disposed on one side of the hydrophilic composite nanofiber layer and is loaded with a colorimetric detection reagent for detecting target substances in sweat.

[0008] Furthermore, the hydrophobic nanofiber layer and the hydrophilic composite nanofiber layer constitute an asymmetric wetting structure, which enables the liquid to be transported unidirectionally from the hydrophobic nanofiber layer side to the hydrophilic composite nanofiber layer side, and inhibits the reverse permeation of the liquid from the hydrophilic composite nanofiber layer side to the hydrophobic nanofiber layer side.

[0009] Furthermore, the mass fraction of the silica nanoparticles relative to the polyacrylonitrile precursor solution is 0.5%–10%; preferably 2.5%.

[0010] Furthermore, the detection area includes Ca 2+ Detection area, Cl - Detection area and Na + One or more of the detection regions. When there are multiple detection regions, each detection region is loaded with the same or different colorimetric detection reagents to achieve single target analyte detection or parallel detection of multiple targets analytes.

[0011] Furthermore, the detection area includes Ca 2+ Detection area, Cl - Detection area and Na + One or more of the following in the detection area. The Ca 2+ The detection area is composed of Ca 2+ Colorimetric detection reagent loading formation, wherein the Ca 2+ The colorimetric assay reagent loading solution includes o-cresolphthalein complex ketone and 8-hydroxyquinoline; the Cl - The detection area consists of Cl - Colorimetric detection reagent loading formation, wherein Cl - The colorimetric reagent loading solution includes mercuric thiocyanate and ferric nitrate; the Na + The detection area consists of Na + Colorimetric detection reagent loading formation, wherein the Na + The colorimetric assay reagent loading solution includes β-galactosidase and o-nitrophenyl-β-D-galactopyranoside.

[0012] Furthermore, the Ca 2+ The concentration of o-cresolphthalein complex ketone in the colorimetric assay reagent loading solution was 0.2 mg / mL, and the concentration of 8-hydroxyquinoline was 0.4 mg / mL; the Cl... - The concentration of mercuric thiocyanate in the colorimetric reagent loading solution was 0.5 mM, and the concentration of ferric nitrate was 18.8 mM; the Na... + The concentration of β-galactosidase in the colorimetric assay reagent loading solution was 7.5 mg / mL, and the concentration of o-nitrophenyl-β-D-pyranogalactoside was 3 mM.

[0013] Furthermore, the colorimetric detection reagent is applied to a predetermined detection area on one side of the hydrophilic composite nanofiber layer by micro-spotting, dripping, spraying, or printing, and then fixed in the detection area by drying, vacuum drying, or freeze-drying.

[0014] Furthermore, the color signal of the detection area is captured by an image obtained from a smartphone, camera, scanner, or portable image acquisition device, and the target object Ca is calculated by extracting the RGB values. 2+ Cl - and Na + concentration.

[0015] Furthermore, the silica nanoparticles are used to improve the surface roughness, number of hydrophilic sites, liquid absorption and diffusion capacity, and capillary transport capacity of the hydrophilic composite nanofiber layer. The silica nanoparticles are dispersed as a reinforcing component in the polyacrylonitrile nanofibers to improve the mechanical properties of the hydrophilic composite nanofiber layer.

[0016] Furthermore, when the liquid comes into contact with the Janus nanofiber membrane from the hydrophobic nanofiber layer, the liquid can pass through the hydrophobic nanofiber layer under the capillary adsorption of the hydrophilic composite nanofiber layer and be absorbed and diffused by the hydrophilic composite nanofiber layer.

[0017] Furthermore, the Janus nanofiber membrane can achieve anti-gravity liquid transport through the capillary adsorption of the hydrophilic composite nanofiber layer when liquid comes into contact with it from the side of the lower hydrophobic nanofiber layer. The silica nanoparticles and porous nanofiber structure in the hydrophilic composite nanofiber layer enhance sunlight scattering and human infrared radiation emission, enabling the Janus flexible patch to have sweat evaporation cooling and passive radiative cooling functions.

[0018] A method for preparing the above-mentioned unidirectional Janus flexible patch includes the following steps:

[0019] Step 1: Dissolve polyacrylonitrile in N,N-dimethylformamide to obtain a polyacrylonitrile precursor solution; the mass concentration of the solution is 8-15 wt%.

[0020] Step 2: Add silica nanoparticles to the polyacrylonitrile precursor solution and stir until homogeneous to obtain a silica / polyacrylonitrile composite spinning solution; the mass fraction of the silica nanoparticles relative to the polyacrylonitrile precursor solution is 0.5%-10%.

[0021] Step 3: Electrospin the silica / polyacrylonitrile composite spinning solution to obtain a hydrophilic composite nanofiber layer; wherein the electrospinning conditions are: applied voltage 15-25 kV, nozzle-to-receiver distance 10-20 cm, spinning solution feed rate 0.5-2 mL / h, roller receiver rotation speed 100-400 rpm, spinning environment temperature 15-30℃, relative humidity 30-60%, and spinning time 2-4 h;

[0022] Step 4: Dissolve polyurethane in a mixed solvent composed of acetone and N,N-dimethylformamide to obtain a polyurethane spinning solution; the mass concentration of the polyurethane spinning solution is 10-20 wt%, and the mass ratio of acetone to N,N-dimethylformamide is 5:5-10:5.

[0023] Step 5: Electrospin the polyurethane spinning solution onto the surface of the hydrophilic composite nanofiber layer to form a hydrophobic nanofiber layer, thereby obtaining a Janus nanofiber membrane; wherein, the electrospinning conditions are: applied voltage 15-25 kV, nozzle-to-receiver distance 10-20 cm, spinning solution propulsion rate 0.5-2 mL / h, and spinning time 1-2.5 h;

[0024] Step 6: A detection area is set on one side of the hydrophilic composite nanofiber layer of the Janus nanofiber membrane, and a colorimetric detection reagent is loaded in the detection area to obtain a unidirectional flow-directing Janus flexible patch.

[0025] An application of the unidirectional Janus flexible patch in wearable sweat detection, sports health monitoring, skin heat management, passive cooling, electrolyte balance analysis, dehydration status assessment, or individualized health assessment.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] First, the present invention constructs a Janus asymmetric wetting structure composed of a hydrophobic polyurethane layer and a hydrophilic silica / polyacrylonitrile layer, which can realize unidirectional transport of sweat from the hydrophobic side to the hydrophilic side and inhibit reverse permeation.

[0028] Secondly, the patch of the present invention can achieve gravity-resistant self-pumping liquid transport without the need for an external pumping device, which is conducive to the rapid excretion of sweat from the skin surface.

[0029] Third, by introducing silica nanoparticles into the polyacrylonitrile hydrophilic layer, the present invention improves the roughness, hydrophilicity, and mechanical properties of the hydrophilic layer.

[0030] Fourth, the present invention can transport sweat from the skin-contact side to the outer hydrophilic layer and promote sweat diffusion and evaporation, thereby reducing skin humidity and skin surface temperature.

[0031] Fifth, the porous structure of silica nanoparticles and nanofibers in this invention can improve the reflection of sunlight and the emission of mid-infrared rays, thereby achieving passive radiative cooling.

[0032] Sixth, this invention integrates a unidirectional liquid-guiding Janus nanofiber membrane with a colorimetric detection reagent, enabling integrated sweat collection, transport, reaction, and detection, thus simplifying the structure of wearable sweat detection devices.

[0033] Seventh, this invention can be configured with multiple detection areas according to detection needs to detect Ca in sweat. 2+ Na + Cl - Visual detection of multiple indicators and smartphone-assisted quantitative analysis. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the fabrication process, overall structure, and functional applications of the unidirectional Janus flexible patch of the present invention.

[0035] Figure 2 The following are the preparation process of the Janus nanofiber membrane described in this invention, scanning electron microscope images of the hydrophilic composite nanofiber layers with different SiO2 doping amounts, and fiber diameter distribution diagrams.

[0036] Figure 3 These are the mechanical properties and structural characterization diagrams of the SiO2-PAN composite nanofiber layer described in this invention;

[0037] Figure 4 These are test images of the wetting properties and unidirectional liquid transport properties of the Janus nanofiber membrane described in this invention.

[0038] Figure 5 This is a test diagram of the sweat management and skin moisture regulation performance of the Janus nanofiber membrane described in this invention;

[0039] Figure 6 The graph shows the test results of the cooling performance and passive radiative cooling performance of the Janus nanofiber membrane described in this invention.

[0040] Figure 7 This is a colorimetric response standard curve, patch structure, and sample detection verification diagram of the sweat three-index detection patch described in this invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0042] The Janus nanofiber membrane of this invention comprises a hydrophobic nanofiber layer and a hydrophilic composite nanofiber layer. The hydrophobic nanofiber layer is a polyurethane nanofiber layer (PU), and the hydrophilic composite nanofiber layer is a silica / polyacrylonitrile composite nanofiber layer (SiO2-PAN). In the hydrophilic composite nanofiber layer, the mass fraction of silica nanoparticles relative to polyacrylonitrile is 0.5%-10%, most preferably 2.5%. The silica nanoparticles can improve the surface roughness and the number of hydrophilic sites of the hydrophilic composite nanofiber layer, enhancing the liquid absorption, diffusion, and capillary transport capabilities. Simultaneously, it improves the mechanical properties and structural stability of the hydrophilic composite nanofiber layer.

[0043] The Janus nanofiber membrane exhibits asymmetric wettability on both sides. When sweat comes into contact with the hydrophobic polyurethane nanofiber layer, the sweat can pass through the hydrophobic layer under the influence of the wetting gradient and capillary adsorption of the hydrophilic composite nanofiber layer, and is absorbed and diffused by the outer hydrophilic layer. When sweat comes into contact with the hydrophilic composite nanofiber layer, the sweat mainly spreads within the hydrophilic layer and is blocked by the hydrophobic polyurethane layer, thereby inhibiting reverse liquid permeation.

[0044] In terms of heat and humidity management, the Janus flexible patch can transfer sweat from the hydrophobic side of the skin to the outer hydrophilic layer, allowing the sweat to diffuse and evaporate within the hydrophilic layer, thereby reducing skin surface humidity and temperature. The silica nanoparticles and porous nanofiber structure also enhance sunlight scattering and human infrared radiation emission, giving the patch both evaporative cooling and passive radiative cooling functions.

[0045] In sweat detection, the detection area is located on one side of the hydrophilic composite nanofiber layer and is loaded with a colorimetric reagent. Sweat is transported unidirectionally from the hydrophobic layer to the hydrophilic layer and enters the detection area, where it reacts with the colorimetric reagent to produce a colorimetric reaction. The detection results can be observed visually or obtained by acquiring a color image and extracting the RGB signal using a smartphone or image acquisition device, and the concentration of the target substance can be calculated based on a preset standard curve.

[0046] Example 1: Preparation and structural control of Janus nanofiber membranes

[0047] This embodiment provides a method for preparing a PU / SiO2-PAN Janus nanofiber membrane. The Janus nanofiber membrane comprises a hydrophobic PU nanofiber layer and a hydrophilic SiO2-PAN composite nanofiber layer, wherein the hydrophobic PU nanofiber layer is used to construct a skin-adhesive barrier and prevent reverse osmosis interface, and the hydrophilic SiO2-PAN composite nanofiber layer is used to construct liquid absorption, diffusion, evaporation and detection functions.

[0048] First, a hydrophilic composite layer spinning solution was prepared. Polyacrylonitrile was dissolved in N,N-dimethylformamide to prepare a PAN precursor solution with a suitable spinning viscosity. The mass concentration of this solution could be controlled within a wide range of 8-15 wt%, and in this specific embodiment, 12 wt% was preferred. Subsequently, SiO2 nanoparticles (SiO2 NPs) were added to the PAN precursor solution. To ensure the hydrophilicity and liquid conductivity of the film after formation, the mass fraction of SiO2 nanoparticles relative to the solution was controlled within an effective range of 0.5%-10%. In this embodiment, SiO2 nanoparticles were added at mass fractions of 1%, 2.5%, 5%, and 7.5%, and the mixture was thoroughly stirred and homogenized to obtain the SiO2-PAN composite spinning solution. In addition, a PAN precursor solution without added SiO2 nanoparticles was used as a control spinning solution (i.e., 0% control) for subsequent comparison.

[0049] The above-mentioned spinning solutions were loaded into syringes, and PAN nanofiber layers or SiO2-PAN composite nanofiber layers were prepared by electrospinning. The electrospinning conditions could be controlled within a suitable film-forming range, for example, an applied voltage of 15-25 kV (preferably 18 kV in this specific embodiment), a nozzle-to-receiver distance of 10-20 cm (15 cm in this embodiment), a spinning solution propulsion rate of 0.5-2 mL / h (1 mL / h in this embodiment), a roller receiver rotation speed of 100-400 rpm (200 rpm in this embodiment), a spinning environment temperature of 15-30 ℃ (20 ℃ in this embodiment), a relative humidity of 30-60% (40% in this embodiment), and a spinning time of 2-4 h (3 h in this embodiment). Subsequently, a hydrophobic PU spinning solution was prepared. Polyurethane was dissolved in a mixed solvent of acetone and N,N-dimethylformamide, wherein the mass ratio of acetone to N,N-dimethylformamide could be adjusted to 5:5 to 10:5 (8:5 in this embodiment) according to the dissolution requirements, to prepare a PU spinning solution with a mass concentration of 10-20 wt% (15 wt% in this embodiment). The PU spinning solution was then directly electrospun onto the surface of the above-mentioned PAN nanofiber layer or SiO2-PAN composite nanofiber layer to form a hydrophobic PU nanofiber layer. The electrospinning conditions of the PU layer were also within the above-mentioned preset conventional film-forming range, for example, the applied voltage was controlled at 15-25 kV (18 kV in this embodiment), the distance from the nozzle to the receiver was 10-20 cm (15 cm in this embodiment), the spinning solution propulsion rate was 0.5-2 mL / h (1 mL / h in this embodiment), and the spinning time was 1-2.5 h (2 h in this embodiment). After spinning, a PU / PAN or PU / SiO2-PAN Janus nanofiber membrane with a hydrophobic / hydrophilic bilayer structure is obtained.

[0050] See Figure 1 Figure a illustrates the fabrication process of the unidirectional Janus flexible patch of this invention. First, silica nanoparticles (SiO2 NPs) are added to the PAN precursor solution to form a hydrophilic composite spinning system. A hydrophilic SiO2-PAN composite nanofiber layer is then prepared via electrospinning. Subsequently, a hydrophobic polymer solution is deposited onto the surface of the hydrophilic layer via electrospinning, forming a bilayer Janus nanofiber membrane structure composed of a hydrophobic layer and a hydrophilic composite layer. Figure b is a schematic diagram of the structure and surface properties of the Janus nanofiber membrane. This membrane consists of a hydrophobic nanofiber layer and a hydrophilic composite nanofiber layer, with inorganic nanoparticles distributed in the hydrophilic layer to improve the composite fiber structure and interfacial properties. The right side of the figure shows the wetting behavior of different surfaces, used to characterize the asymmetric wetting characteristics on both sides of the membrane. Figure c is a schematic diagram of the application functions of the Janus nanofiber membrane. Due to the different wetting properties on both sides of the membrane, liquids can exhibit directional transport behavior under the influence of interfacial wetting differences. Simultaneously, this structure can realize sweat transport, humidity and heat regulation, and sweat detection based on colorimetric response.

[0051] See Figure 2 Figure 1 shows the preparation process of the Janus nanofiber membrane described in this invention, scanning electron microscope images of hydrophilic composite nanofiber layers with different SiO2 doping amounts, and fiber diameter distribution diagrams. In the figure, a is a schematic diagram of the preparation process, b is a morphology diagram of the hydrophobic PU nanofiber layer, c is a morphology diagram of the PAN nanofiber layer, d to g are morphology diagrams of 1%, 2.5%, 5%, and 7.5% SiO2-PAN composite nanofiber layers, respectively, and h is a fiber diameter distribution diagram.

[0052] like Figure 1 a and Figure 2 As shown in Figure a, this embodiment employs a sequential electrospinning method to first construct a hydrophilic SiO2-PAN composite nanofiber layer, and then construct a hydrophobic PU nanofiber layer on its surface, thereby obtaining a Janus nanofiber membrane with an asymmetric wetting structure. One side of the membrane is a hydrophobic PU layer, and the other side is a hydrophilic SiO2-PAN layer.

[0053] Figure 2 As shown in Figure b, the PU nanofiber layer exhibits a porous network structure, with interconnected pores between the fibers. The surface of the undoped SiO2 PAN nanofibers is relatively smooth, with an average diameter of approximately 427.3 nm. Figure 2 c and Figure 2 (h). As the doping concentration of SiO2 nanoparticles increased from 1% to 7.5%, the surface of the SiO2-PAN composite nanofibers gradually became rougher, and the average diameter increased from approximately 466.2 nm to 536.5 nm. Figure 2(dh), and it can be observed that SiO2 nanoparticles are distributed on the fiber surface or embedded in the fiber structure ( ) Figure 2 (The arrow in dg). The above results show that the introduction of SiO2 nanoparticles can regulate the surface morphology and diameter distribution of PAN nanofibers and increase the micro-nano rough structure of the fiber surface.

[0054] See Figure 3 Figure 1 shows the mechanical properties and structural characterization of the SiO2-PAN composite nanofiber layer described in this invention; wherein, Figure 3 In the figure, 'a' represents the stress-strain curve. Figure 3 In the middle, b is the statistical graph of elastic modulus. Figure 3 In the middle, c represents the tensile strength statistics chart. Figure 3 In the diagram, d represents the X-ray diffraction pattern. Figure 3 In the image, 'e' represents the high-resolution X-ray photoelectron spectrum of Si 2p. Figure 3 f is the Fourier transform infrared spectrum.

[0055] like Figure 3 As shown in Figure ac, the mechanical properties of PAN and SiO2-doped PAN nanofiber films were evaluated. Compared with the original PAN film, the 2.5% SiO2-PAN composite nanofiber layer exhibited superior mechanical properties. Its elastic modulus and tensile strength increased from 30.54 MPa and 2.44 MPa to 146.55 MPa and 5.35 MPa, respectively. However, further increasing the silica content led to a decrease in mechanical properties; both the elastic modulus and tensile strength decreased significantly, reaching the lowest values ​​of 8.52 MPa and 0.75 MPa, respectively, in the 7.5% SiO2-PAN sample.

[0056] The XRD pattern of 2.5% SiO2-PAN showed characteristic diffraction peaks corresponding to both PAN and silica components: a distinct peak at 16.9°, attributed to the (100) crystal plane of PAN; and a broad diffraction band between 22 and 25°, indicating the presence of amorphous silica. Figure 3 (d). XPS results showed that the high-resolution Si 2p spectrum obtained at 102.3 eV confirmed the presence of Si-O-Si chemical bonds. Figure 3 Fourier transform infrared spectroscopy (FTIR) analysis was performed on PU, PAN, SiO2 nanoparticles, 2.5% SiO2-PAN, PU / PAN, and PU / 2.5% SiO2-PAN samples to investigate their chemical composition. Figure 3 (f). The original PAN sample at 2244 cm⁻¹ -1 and 1730 cm -1The peaks at 2938 cm⁻¹ exhibit distinct characteristic absorption peaks, which are attributed to the stretching vibrations of the cyano group and the carbonyl group in the methacrylate comonomer, respectively. -1 The absorption band at 1451 cm⁻¹ is attributed to the CH stretching vibration, while the absorption band at 1451 cm⁻¹ is attributed to the CH stretching vibration. -1 and 1388 cm -1 The absorption peaks at these locations correspond to the CH bending vibration and the -CH3 symmetric bending vibration, respectively. Furthermore, at 3617 cm⁻¹... -1 The absorption peak at 1091 cm⁻¹ is attributed to the OH stretching vibration. When SiO₂ nanoparticles are introduced into PAN fibers, the absorption peak at 1091 cm⁻¹ is... -1 A distinct broad absorption band appears at 798 cm⁻¹, corresponding to the asymmetric stretching vibration of Si-O-Si. Furthermore, at 798 cm⁻¹... -1 and 468 cm -1 New absorption bands appear at the points, attributed to the symmetrical stretching and bending vibrations of Si-O-Si, respectively. Finally, the infrared spectrum of the integrated PU / 2.5%SiO2-PAN bilayer film simultaneously shows the superimposed characteristic peaks of the hydrophobic PU substrate and the hydrophilic SiO2-PAN layer, fully demonstrating the successful construction of the Janus composite structure. Considering the dispersion state of nanoparticles, fiber morphology uniformity, hydrophilic conductivity, and mechanical properties, this embodiment preferably uses a 2.5%SiO2-PAN composite nanofiber layer as the hydrophilic layer of the Janus nanofiber film.

[0057] Example 2: Preparation and structural control of Janus nanofiber membranes

[0058] This embodiment provides a method for preparing a PU / SiO2-PAN Janus nanofiber membrane. The Janus nanofiber membrane comprises a hydrophobic PU nanofiber layer and a hydrophilic SiO2-PAN composite nanofiber layer, wherein the hydrophobic PU nanofiber layer is used to construct a skin-adhesive barrier and prevent reverse osmosis interface, and the hydrophilic SiO2-PAN composite nanofiber layer is used to construct liquid absorption, diffusion, evaporation and detection functions.

[0059] First, a hydrophilic composite layer spinning solution was prepared. Polyacrylonitrile was dissolved in N,N-dimethylformamide to prepare a PAN precursor solution with a suitable spinning viscosity. The mass concentration of this solution could be controlled within a wide range of 8-15 wt%, and in this specific embodiment, 8 wt% was preferred. Subsequently, SiO2 nanoparticles were added to the PAN precursor solution. To ensure the hydrophilicity and liquid conductivity after film formation, the mass fraction of SiO2 nanoparticles relative to the solution was controlled within an effective range of 0.5%-10%. In this embodiment, 0.5% and 10% of SiO2 nanoparticles were specifically added, and the mixture was thoroughly stirred and homogenized to obtain the SiO2-PAN composite spinning solution. In addition, a PAN precursor solution without added SiO2 nanoparticles was used as a control spinning solution (i.e., 0% control) for subsequent comparison.

[0060] The above-mentioned spinning solutions were loaded into syringes, and PAN nanofiber layers or SiO2-PAN composite nanofiber layers were prepared by electrospinning. The electrospinning conditions could be controlled within a suitable film-forming range, for example, an applied voltage of 15-25 kV (preferably 15 kV in this specific embodiment), a nozzle-to-receiver distance of 10-20 cm (10 cm in this embodiment), a spinning solution propulsion rate of 0.5-2 mL / h (0.5 mL / h in this embodiment), a roller receiver rotation speed of 100-400 rpm (100 rpm in this embodiment), a spinning environment temperature of 15-30 ℃ (15 ℃ in this embodiment), a relative humidity of 30-60% (30% in this embodiment), and a spinning time of 2-4 h (4 h in this embodiment). Subsequently, a hydrophobic PU spinning solution was prepared. Polyurethane was dissolved in a mixed solvent of acetone and N,N-dimethylformamide, wherein the mass ratio of acetone to N,N-dimethylformamide could be adjusted to 5:5 to 10:5 according to the dissolution requirements (5:5 was used in this embodiment), to prepare a PU spinning solution with a mass concentration of 10-20 wt% (20 wt% in this embodiment). The PU spinning solution was then directly electrospun onto the surface of the above-mentioned PAN nanofiber layer or SiO2-PAN composite nanofiber layer to form a hydrophobic PU nanofiber layer. The electrospinning conditions of the PU layer were also within the above-mentioned preset conventional film-forming range, for example, the applied voltage was controlled at 15-25 kV (25 kV in this embodiment), the distance from the nozzle to the receiver was 10-20 cm (20 cm in this embodiment), the spinning solution propulsion rate was 0.5-2 mL / h (2 mL / h in this embodiment), and the spinning time was 1-2.5 h (1 h in this embodiment). After spinning, a PU / PAN or PU / SiO2-PAN Janus nanofiber membrane with a hydrophobic / hydrophilic bilayer structure is obtained.

[0061] The flexible patch prepared in this embodiment was tested and found to have the same physicochemical properties and application effects as in Example 1.

[0062] Example 3: Preparation and structural control of Janus nanofiber membranes

[0063] This embodiment provides a method for preparing a PU / SiO2-PAN Janus nanofiber membrane. The Janus nanofiber membrane comprises a hydrophobic PU nanofiber layer and a hydrophilic SiO2-PAN composite nanofiber layer, wherein the hydrophobic PU nanofiber layer is used to construct a skin-adhesive barrier and prevent reverse osmosis interface, and the hydrophilic SiO2-PAN composite nanofiber layer is used to construct liquid absorption, diffusion, evaporation and detection functions.

[0064] First, a hydrophilic composite layer spinning solution was prepared. Polyacrylonitrile was dissolved in N,N-dimethylformamide to prepare a PAN precursor solution with a suitable spinning viscosity. The mass concentration of this solution could be controlled within a wide range of 8-15 wt%, and in this specific embodiment, 15 wt% was preferred. Subsequently, SiO2 nanoparticles were added to the PAN precursor solution. To ensure the hydrophilicity and liquid conductivity of the film after formation, the mass fraction of SiO2 nanoparticles relative to the solution was controlled within an effective range of 0.5%-10%. In this embodiment, SiO2 nanoparticles with mass fractions of 3%, 6%, and 9% were specifically added and thoroughly mixed to obtain the SiO2-PAN composite spinning solution. In addition, a PAN precursor solution without added SiO2 nanoparticles was used as a control spinning solution (i.e., 0% control) for subsequent comparison.

[0065] The above-mentioned spinning solutions were loaded into syringes, and PAN nanofiber layers or SiO2-PAN composite nanofiber layers were prepared by electrospinning. The electrospinning conditions could be controlled within a suitable film-forming range, for example, an applied voltage of 15-25 kV (preferably 25 kV in this specific embodiment), a nozzle-to-receiver distance of 10-20 cm (20 cm in this embodiment), a spinning solution propulsion rate of 0.5-2 mL / h (2 mL / h in this embodiment), a roller receiver rotation speed of 100-400 rpm (400 rpm in this embodiment), a spinning environment temperature of 15-30 ℃ (30 ℃ in this embodiment), a relative humidity of 30-60% (60% in this embodiment), and a spinning time of 2-4 h (2 h in this embodiment). Subsequently, a hydrophobic PU spinning solution was prepared. Polyurethane was dissolved in a mixed solvent of acetone and N,N-dimethylformamide, wherein the mass ratio of acetone to N,N-dimethylformamide could be adjusted to 5:5 to 10:5 according to the dissolution requirements (10:5 was used in this embodiment), to prepare a PU spinning solution with a mass concentration of 10-20 wt% (10 wt% in this embodiment). The PU spinning solution was then directly electrospun onto the surface of the above-mentioned PAN nanofiber layer or SiO2-PAN composite nanofiber layer to form a hydrophobic PU nanofiber layer. The electrospinning conditions of the PU layer were also within the above-mentioned preset conventional film-forming range, for example, the applied voltage was controlled at 15-25 kV (15 kV in this embodiment), the distance from the nozzle to the receiver was 10-20 cm (10 cm in this embodiment), the spinning solution propulsion rate was 0.5-2 mL / h (0.5 mL / h in this embodiment), and the spinning time was 1-2.5 h (2.5 h in this embodiment). After spinning, a PU / PAN or PU / SiO2-PAN Janus nanofiber membrane with a hydrophobic / hydrophilic bilayer structure is obtained.

[0066] The flexible patch prepared in this embodiment was tested and found to have the same physicochemical properties and application effects as in Example 1.

[0067] Example 4: Unidirectional liquid transport properties of Janus nanofiber membranes

[0068] This embodiment is used to illustrate the asymmetric wetting characteristics, unidirectional liquid transport capability, and anti-gravity self-pumping capability of the PU / SiO2-PAN Janus nanofiber membrane described in this invention.

[0069] Following the method described in Example 1, PU nanofiber membranes, PAN nanofiber membranes, and composite nanofiber membranes of 1% SiO2-PAN, 2.5% SiO2-PAN, 5% SiO2-PAN, and 7.5% SiO2-PAN were prepared, and their water contact angles were tested. During the test, water droplets were dropped onto the surface of each membrane, and the droplet morphology and contact angle changes were recorded at different times.

[0070] See Figure 4 Figure 1 shows the test results for the wetting properties and unidirectional liquid transport properties of the Janus nanofiber membrane described in this invention; wherein, Figure 4 In figure a, there is a physical image showing the variation of water contact angle for different nanofiber membranes. Figure 4 In the curve, b represents the change of the water contact angle over time. Figure 4 In diagram c, the transport process occurs when the droplet contacts the hydrophilic side. Figure 4 The diagram in Figure d shows the transport process when a droplet contacts the hydrophobic side. Figure 4 The diagram in 'e' represents the anti-gravity liquid transport process.

[0071] Electrospun polyurethane (PU) films exhibit stable hydrophobicity, with an initial water contact angle (WCA) of 123.81°. Within 10 seconds, the WCA value remained relatively stable, decreasing only slightly to 121.20°. In stark contrast, the original polyacrylonitrile (PAN) film exhibited dynamic wetting behavior: its initial contact angle was 100.16°, rapidly decreasing to 22.26° within 10 seconds. With increasing SiO2 content, the initial WCA value of the composite film gradually decreased from 102.30° to 38.20°, while the wetting time significantly shortened. Figure 4 (a, b)

[0072] Digital photography was used to visualize the dynamic transport process of the liquid. When the hydrophilic layer is facing upwards, the added droplets can spread rapidly on the membrane surface, but are effectively blocked by the underlying hydrophobic layer, making it difficult for them to penetrate further downwards. Figure 4 (c) In the reverse orientation, i.e., with the hydrophobic layer facing upwards, the droplet can rapidly penetrate the hydrophobic layer within 6 seconds and wet the underlying hydrophilic layer, while the upper surface remains dry. Figure 4 (d). To evaluate the membrane's anti-gravity drainage capability, a droplet was introduced from below the membrane with the hydrophobic layer facing downwards. Notably, the droplet was able to spontaneously overcome gravity within 12 s, passing through the membrane from the hydrophobic side to the hydrophilic side, exhibiting a significant "pumping" effect. Figure 4 (e). Therefore, the PU / 2.5%SiO2-PAN membrane can serve as a self-pumping device with anti-gravity drainage capability.

[0073] Therefore, this invention creates a distinct wetting gradient by constructing a Janus bilayer structure consisting of a hydrophobic PU layer and a hydrophilic SiO2-PAN layer. This wetting gradient allows liquid to be transported unidirectionally from the hydrophobic side to the hydrophilic side, while making it difficult for liquid to permeate back from the hydrophilic side to the hydrophobic side, thus achieving a unidirectional liquid guiding function similar to that of a liquid diode.

[0074] Example 5: Sweat Management and Skin Moisture Reduction Properties of Janus Nanofiber Membranes

[0075] This embodiment illustrates the unidirectional perspiration, skin dryness retention, and humidity regulation capabilities of the PU / SiO2-PAN Janus nanofiber membrane described in this invention when it is attached to the skin.

[0076] A PU / 2.5%SiO2-PAN Janus nanofiber membrane was prepared according to the method described in Example 1. The Janus nanofiber membrane comprises a hydrophobic PU nanofiber layer and a hydrophilic SiO2-PAN composite nanofiber layer. The hydrophobic PU layer serves as the skin-contact side, while the hydrophilic SiO2-PAN layer serves as the outer absorbent, diffuser, and evaporator layer. This bilayer structure allows for the directional transport of sweat from the skin-contact hydrophobic side to the outer hydrophilic layer and inhibits the reverse permeation of sweat from the hydrophilic side back to the skin-contact side.

[0077] See Figure 5 Figure 1 shows a test diagram of the sweat management and skin moisture regulation performance of the Janus nanofiber membrane described in this invention; wherein, Figure 5 Figure 'a' is a schematic diagram illustrating the mechanism of Janus nanofiber membranes for humidity and heat management. Figure 5 Figure b is a schematic diagram of the solar spectrum and the infrared radiation band of the human body. Figure 5 Figure c shows the sweat management effect of the Janus nanofiber membrane with the hydrophobic PU layer facing the skin. Figure 5 The diagram in Figure d shows the sweat management of the Janus nanofiber membrane with the hydrophilic SiO2-PAN layer facing the skin. Figure 5 Image e shows the sweat residue after a single layer of SiO2-PAN nanofibers covers the skin. Figure 5 The middle image (f) shows the sweat residue after cotton fabric has been applied to the skin. Figure 5 Figure g shows a physical test image of skin surface humidity after being covered with different materials. Figure 5 The graph in the middle, h, shows the change in relative humidity of the skin surface over time after being covered with different materials.

[0078] With the increasing demands for personal health and wearable comfort, there is an urgent need to develop wearable fabrics that can synergistically integrate efficient sweat wicking and excellent radiant cooling properties. Such materials are particularly important for maintaining the body's thermal comfort, especially in extreme high-temperature outdoor environments. For example... Figure 5As shown in Figure a, an ideal outdoor wearable fabric should simultaneously possess high solar radiation reflectivity, strong human infrared radiation emissivity, and continuous directional sweat pumping capability. From an optical thermodynamic perspective, relevant electromagnetic waves can be divided into different regions from gamma rays to far-infrared radiation based on wavelength. Figure 5 (b) Among them, high solar reflectivity (0.3-2.5 μm) and high human infrared emissivity (7-14 μm) are crucial for minimizing solar thermal gain and promoting heat dissipation, respectively; the synergistic integration of these two optical properties is indispensable for achieving effective daytime passive radiative cooling.

[0079] To evaluate the material's sweat management performance under real-world conditions, artificial sweat was applied to the skin surface to simulate the sweating process. For example... Figure 5 As shown in Figure cf, when the hydrophobic layer of the Janus membrane comes into contact with sweat, it can quickly transport the liquid to the outer hydrophilic layer, thereby keeping the skin surface dry. In contrast, when the Janus membrane is placed in the opposite direction, i.e., when the hydrophilic layer is in contact with the skin, both the monolayer membrane and cotton fabric leave liquid residue at the skin interface. Furthermore, the relative humidity of the skin surface after different sample treatments was measured using a hygrometer. Figure 5 As shown in the data from gh, skin moisture content was 20.6% under cotton fabric coverage and 18.5% under single-layer membrane coverage. In contrast, the Janus membrane group exhibited the lowest skin moisture content, at approximately 17.5%, a value very close to the baseline moisture content of dry skin.

[0080] Example 6: Evaporative cooling and passive radiative cooling performance of Janus nanofiber membranes

[0081] See Figure 6 Figure 1 shows the test results of the cooling performance and passive radiative cooling performance of the Janus nanofiber membrane described in this invention; wherein, Figure 6 In the image, 'a' represents infrared thermal images under different coverage conditions. Figure 6 In the middle, b is a temperature statistics graph. Figure 6 In the figure, c represents the solar spectral reflectance and mid-infrared emissivity curves of the Janus film. Figure 6 In the middle, d represents the optical and infrared images of the Janus membrane on the skin surface and cotton fabric before and after 10 minutes of direct sunlight exposure.

[0082] To simulate human sweating under high temperatures, a drop of water at 36°C was placed on the volunteer's wrist. Figure 6(ab). After 30 seconds, thermal imaging and statistical analysis revealed that the Janus membrane exhibited superior cooling performance, with an average temperature reduction of 1.6 °C and 1.1 °C compared to cotton fabric and single-layer membrane, respectively. This cooling effect is attributed to the rapid transport and spread of sweat to the outer hydrophilic layer, thereby accelerating evaporation and removing excess heat. SiO2 is a promising radiation cooling material, serving as both an optical scatterer and a mid-infrared emitter, with its intrinsic absorption peak located within the atmospheric window. To evaluate the daytime radiation cooling performance of the Janus membrane, its optical properties were tested ( Figure 6 (c) The film exhibits an average reflectance of 83.1% in the solar spectral range (0.3–2.5 μm) and an average infrared emissivity of 90.3% in the atmospheric window range of 8–13 μm. This performance is likely attributed to the SiO2 nanoparticles immobilized in the fibers and the rough nanofiber surface, which together enhance light scattering and infrared emission.

[0083] To further verify its actual cooling performance, the film was applied to the surface of human skin and tested in direct sunlight in Shanghai, China. Figure 6 As shown in Figure d, infrared thermal imaging results indicate that after 10 minutes of exposure, the outer surface temperature of the Janus membrane was approximately 5 °C lower than that of cotton fabric. These results confirm the excellent daytime radiative cooling capability of the Janus membrane, demonstrating its potential for passive cooling without energy consumption in outdoor applications.

[0084] Example 7: Construction and Validation of a Multi-Indicator Sweat Detection Patch

[0085] The Janus nanofiber membrane comprises a hydrophobic PU layer and a hydrophilic SiO2-PAN layer, wherein the hydrophobic PU layer is used for skin contact, and the hydrophilic SiO2-PAN layer is used for sweat transport, diffusion, and color development reaction.

[0086] In this embodiment, the sweat detection patch has three independent detection areas, each used to detect Ca in sweat. 2+ Cl - and Na + Each detection zone is pre-loaded with the colorimetric detection reagent corresponding to the respective target analyte.

[0087] Among them, Ca 2+ The detection area is composed of Ca 2+ The colorimetric reagent loading solution is formed by processing the Ca... 2+ The colorimetric assay reagent loading solution includes o-cresolphthalein complex ketone and 8-hydroxyquinoline, wherein the concentration of o-cresolphthalein complex ketone is 0.2 mg / mL and the concentration of 8-hydroxyquinoline is 0.4 mg / mL; Cl - The detection area consists of Cl- The colorimetric detection reagent loading solution is formed by processing the Cl. - The colorimetric reagent loading solution includes mercuric thiocyanate and ferric nitrate, wherein the concentration of mercuric thiocyanate is 0.5 mM and the concentration of ferric nitrate is 18.8 mM; Na + The detection area consists of Na + The colorimetric detection reagent loading solution is formed by processing the Na... + The colorimetric assay reagent loading solution includes β-galactosidase and o-nitrophenyl-β-D-galactopyranoside, wherein the concentration of β-galactosidase is 7.5 mg / mL and the concentration of o-nitrophenyl-β-D-galactopyranoside is 3 mM.

[0088] The aforementioned colorimetric reagent loading solutions were applied to predetermined detection areas on one side of the hydrophilic SiO2-PAN composite nanofiber layer of the Janus nanofiber membrane via micro-spotting, and then freeze-dried to fix the corresponding colorimetric reagents within the detection areas, thereby forming stable Ca... 2+ Cl - and Na + Detection area.

[0089] During detection, the sample first contacts the hydrophobic PU side of the patch and is unidirectionally transported from the hydrophobic PU side to the hydrophilic SiO2-PAN side under the asymmetric wetting structure of the Janus nanofiber membrane. Subsequently, the sample enters the corresponding detection area and reacts with the pre-loaded colorimetric reagent, producing a visible color change.

[0090] To establish a quantitative detection method, Ca solutions of different concentrations were prepared. 2+ Cl - and Na + A standard solution is prepared and introduced into the corresponding detection area. After the reaction is complete, a color image of the detection area is acquired using a smartphone or image acquisition device. The red, green, and blue channel values ​​are extracted, and a standard curve is established between the RGB signal and the concentration of the target analyte.

[0091] See Figure 7 This diagram shows the colorimetric response standard curve, patch structure, and sample detection verification diagram of the sweat three-index detection patch described in this invention; wherein, Figure 7 From middle a to Figure 7 c represents Ca 2+ Cl - and Na + Colorimetric response and RGB standard curves of the detection area at different target analyte concentrations. Figure 7 The diagram in Figure d shows the structure of the sweat three-index detection patch. Figure 7 The figure in the middle (e) is a comparison chart of the detection results of the detection patch described in this invention and the commercial reagent kit.

[0092] like Figure 7 As shown in Figure a, Ca 2+ The detection area changes with Ca 2+ The concentration gradually increases in intensity, resulting in a deeper purple response. The R signal corresponds to the Ca... 2+ The concentrations exhibit a regular variation. Figure 7 The middle b shows that Cl - The detection area changes with Cl - As the concentration increases, the color changes from pale yellow to orange-yellow. The B channel value and Cl... - The concentration shows a linear relationship. Figure 7 The middle c shows that Na + The detection area changes with Na + Increasing concentration produces a gradually intensifying yellow response; the selected B channel value is related to Na. + The concentration shows a linear relationship.

[0093] like Figure 7 As shown in Figure d, the sweat detection patch constructed in this embodiment includes a central sweat collection area and three branch detection areas, with the three detection areas corresponding to Ca respectively. 2+ Cl - and Na + Detection. This structure enables the collection, distribution, and colorimetric detection of sweat using the self-pumping action of the Janus nanofiber membrane without the need for an external pumping device.

[0094] Furthermore, the sweat detection patch described in this invention was validated using sweat samples. Sweat samples were added to the detection patch, and the Ca content was calculated using an RGB standard curve. 2+ Cl - and Na + Concentration. Simultaneously, commercial reagent kits were used to test the same sweat samples, and the results of the two tests were compared. For example... Figure 7 As shown in e, for Ca 2+ Cl - and Na + For three detection indicators, the detection results obtained by the sweat detection patch of this invention are close to those of commercial reagent kits, and no significant differences were observed between the two methods. This result demonstrates that the detection patch of this invention can reliably detect multiple electrolyte indicators in sweat.

[0095] Therefore, this invention, by integrating a self-pumping Janus nanofiber membrane with a colorimetric detection reagent, enables the construction of a sweat multi-index detection patch that requires no external pumping, is easy to operate, and is suitable for wearable applications. This patch can detect Ca in sweat. 2+ Cl - and Na +Visual detection of electrolytes is possible, and semi-quantitative or quantitative detection can be achieved through smartphone-assisted analysis.

[0096] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A unidirectional Janus flexible patch, characterized in that, The device includes a Janus nanofiber membrane and at least one detection area disposed on the Janus nanofiber membrane. The Janus nanofiber membrane comprises a hydrophobic nanofiber layer and a hydrophilic composite nanofiber layer. The hydrophobic nanofiber layer comprises polyurethane nanofibers. The hydrophilic composite nanofiber layer comprises polyacrylonitrile nanofibers and silica nanoparticles dispersed therein. The hydrophobic nanofiber layer serves as the skin-contact side, and the hydrophilic composite nanofiber layer serves as an outer liquid-conducting layer, a sweat evaporation layer, a thermal management layer, and a detection carrier layer. The detection area is disposed on one side of the hydrophilic composite nanofiber layer and is loaded with a colorimetric detection reagent for detecting target substances in sweat.

2. The unidirectional Janus flexible patch according to claim 1, characterized in that, The hydrophobic nanofiber layer and the hydrophilic composite nanofiber layer constitute an asymmetric wetting structure, which enables liquid to be transported unidirectionally from the hydrophobic nanofiber layer side to the hydrophilic composite nanofiber layer side, and inhibits the reverse permeation of liquid from the hydrophilic composite nanofiber layer side to the hydrophobic nanofiber layer side.

3. The unidirectional Janus flexible patch according to claim 1, characterized in that, The silica nanoparticles have a mass fraction of 0.5%–10% relative to the polyacrylonitrile precursor solution.

4. The unidirectional Janus flexible patch according to claim 1, characterized in that, The detection region includes Ca 2+ The detection region, Cl - The detection region and Na + One or more of the detection regions; when the detection regions are multiple, each detection region respectively loads the same or different colorimetric detection reagent for realizing single target detection or multi-target parallel detection.

5. The unidirectional Janus flexible patch according to claim 4, characterized in that, The Ca 2+ The detection area is composed of Ca 2+ Colorimetric detection reagent loading formation, wherein the Ca 2+ The colorimetric assay reagent loading solution includes o-cresolphthalein complex ketone and 8-hydroxyquinoline; the Cl - The detection area consists of Cl - Colorimetric detection reagent loading formation, wherein Cl - The colorimetric reagent loading solution includes mercuric thiocyanate and ferric nitrate; the Na + The detection area consists of Na + Colorimetric detection reagent loading formation, wherein the Na + The colorimetric assay reagent loading solution includes β-galactosidase and o-nitrophenyl-β-D-galactopyranoside.

6. The unidirectional Janus flexible patch according to claim 5, characterized in that, The Ca 2+ The concentration of o-cresolphthalein complex ketone in the colorimetric assay reagent loading solution was 0.2 mg / mL, and the concentration of 8-hydroxyquinoline was 0.4 mg / mL; the Cl... - The concentration of mercuric thiocyanate in the colorimetric reagent loading solution was 0.5 mM, and the concentration of ferric nitrate was 18.8 mM; the Na... + The concentration of β-galactosidase in the colorimetric assay reagent loading solution was 7.5 mg / mL, and the concentration of o-nitrophenyl-β-D-pyranogalactoside was 3 mM.

7. The unidirectional Janus flexible patch according to claim 1, characterized in that, The colorimetric reagent is applied to a predetermined detection area on one side of the hydrophilic composite nanofiber layer by micro-spotting, dripping, spraying, or printing, and then fixed in the detection area by drying, vacuum drying, or freeze-drying.

8. The unidirectional Janus flexible patch according to claim 1, characterized in that, The color signal of the detection area is captured by an image obtained from a smartphone, camera, scanner, or portable image acquisition device, and the target analyte Ca is calculated by extracting the RGB values. 2+ Cl - and Na + concentration.

9. A method for preparing the unidirectional Janus flexible patch according to claim 1, characterized in that, Includes the following steps: Step 1: Dissolve polyacrylonitrile in N,N-dimethylformamide to obtain a polyacrylonitrile precursor solution; the mass concentration of the solution is 8-15 wt%. Step 2: Add silica nanoparticles to the polyacrylonitrile precursor solution and stir until homogeneous to obtain a silica / polyacrylonitrile composite spinning solution; the mass fraction of the silica nanoparticles relative to the polyacrylonitrile precursor solution is 0.5%-10%. Step 3: Electrospin the silica / polyacrylonitrile composite spinning solution to obtain a hydrophilic composite nanofiber layer; wherein the electrospinning conditions are: applied voltage 15-25 kV, nozzle-to-receiver distance 10-20 cm, spinning solution feed rate 0.5-2 mL / h, roller receiver rotation speed 100-400 rpm, spinning environment temperature 15-30℃, relative humidity 30-60%, and spinning time 2-4 h; Step 4: Dissolve polyurethane in a mixed solvent composed of acetone and N,N-dimethylformamide to obtain a polyurethane spinning solution; the mass concentration of the polyurethane spinning solution is 10-20 wt%, and the mass ratio of acetone to N,N-dimethylformamide is 5:5-10:

5. Step 5: Electrospin the polyurethane spinning solution onto the surface of the hydrophilic composite nanofiber layer to form a hydrophobic nanofiber layer, thereby obtaining a Janus nanofiber membrane; wherein, the electrospinning conditions are: applied voltage 15-25 kV, nozzle-to-receiver distance 10-20 cm, spinning solution propulsion rate 0.5-2 mL / h, and spinning time 1-2.5 h; Step 6: A detection area is set on one side of the hydrophilic composite nanofiber layer of the Janus nanofiber membrane, and a colorimetric detection reagent is loaded in the detection area to obtain a unidirectional flow-directing Janus flexible patch.

10. An application of the unidirectional Janus flexible patch as described in claim 1, characterized in that, Applications include wearable sweat detection, sports and health monitoring, skin heat management, passive cooling, electrolyte balance analysis, dehydration status assessment, and individualized health assessment.

Images