A self-adhesive breathable nanofiber membrane with directional water displacement and its application

Abstract

This invention discloses a self-adhesive, breathable nanofiber membrane with directional water repellency and its applications. The membrane is a double-layer nanonetwork fiber membrane composed of a hydrophilic layer and a hydrophobic adhesive layer prepared by electrospinning. Due to the asymmetric wettability of the membrane's two sides and the nanofiber's significant capillary behavior, it achieves flexible self-adhesion, breathability, and directional water repellency, providing a universal substrate for electronic skin. This invention applies the self-adhesive, breathable nanofiber membrane with directional water repellency to a flexible hydration sensor. A flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-interdigitated electrodes is proposed, enabling low-cost, pressure-free, multi-point, accurate, and reliable detection of the water content of the skin's stratum corneum.

Description

Technical Field

[0001] The present invention relates to the fields of micro-nano processing technology, electronic information and medical health, and in particular to a processing method and application of a self-adhesive breathable nanofiber membrane with directional water repellency. Background Art

[0002] With the aging of society and people's concern about personal health in recent years, electronic skin for daily health monitoring applications has achieved rapid development [1] While making progress in acquiring various physiological parameters (such as electrocardiogram signals, electromyography signals, skin temperature, blood pressure, sweat composition, etc.), these electronic skin systems also face a common challenge: how to ensure and improve the reliability of measurement and wearing comfort.

[0003] Transepidermal water loss (TEWL) is the non-sensical evaporation of water from the body through the stratum corneum, including non-sensical sweating when the temperature is below the sweating temperature. This is continuous. The accumulation of water from TEWL and perspiration is one of the main factors affecting the measurement reliability and comfort of electronic skin systems. This accumulation can lead to poor signal quality, even short circuits, and detachment of electronic skin devices from the skin. It can also cause discomfort when worn and induce skin diseases. Furthermore, most electronic skin devices are not self-adhesive and require additional tape to secure them to the skin. The non-breathable nature of the tape can also cause a range of skin problems, including maceration and contact dermatitis.

[0004] Therefore, the research and design of breathable, perspiration-wicking, and self-adhesive electronic skin substrates is an indispensable and important step in the development of electronic skin systems. In order to make electronic skin breathable and alleviate the accumulation of moisture at the skin / electronic skin interface, many researchers have increased the breathability of electronic skin by introducing meshes. Rogers et al. [2] The electrodes were designed on a microporous silicon substrate; Wang et al. [3] prepared substrate-free gold nanonetwork electrodes; Zhou et al. [4] A breathable electrode was prepared on a porous TPU skeleton. Although this design of introducing mesh holes into the electronic skin improves the breathability, it relies on the natural evaporation of water and cannot effectively remove the moisture accumulated on the skin immediately. Inspired by the way that organisms in nature achieve directional liquid transport through asymmetric wettability, Xu et al. [5] proposed a nanofiber electronic skin based on biomimetic gold / thermoplastic polyurethane / cellulose film, but it was not self-adhesive and required additional tape fixation. Yang et al. [6]A nanofiber epidermal electrode with a multilayer film structure of super-hydrophilic polyacrylonitrile / medical adhesive / polyurethane / medical adhesive / silver nanowires has been proposed, achieving targeted water removal. However, this electronic skin suffers from the drawbacks of a multilayer structure and complex manufacturing process. Therefore, further research is needed to develop an electronic skin basement membrane that is breathable, self-adhesive, and capable of targeted water removal with simple manufacturing processes.

[0005] Among all types of electronic skin sensors, the accumulation of water on the skin surface has the most significant impact on the performance of hydration sensors. Hydration sensors evaluate the hydration of human skin, that is, the ability of keratin or its degradation products in the outer layer of the skin to bind water. People have made some explorations in the measurement of the moisture content of the skin stratum corneum. [7] , but the research on flexible and wearable hydration sensors is still immature.

[0006] According to the measurement principle, the hydration measurement methods mainly include direct method and indirect method. The direct method is based on the principle that water can absorb infrared rays, and the water content of the stratum corneum is directly measured through the infrared absorption spectrum. However, the test equipment developed based on this principle is large and expensive, and can usually only be used in hospitals or beauty salons. The indirect method is based on the phenomenon that the electrophysiological characteristics of the skin change with the change of skin water content, and indirectly reflects the water content by measuring its electrophysiological parameters (electrical impedance, conductivity, capacitance). [8] The contact interface between the electrode and the stratum corneum can be represented by an equivalent circuit consisting of a resistor and a capacitor in parallel. The pressure applied by the measuring electrode and the water content of the stratum corneum are the main factors affecting its electrophysiological characteristics. [9] A method for indirectly measuring the water content of the stratum corneum based on the equivalent electrical impedance value is proposed, that is, by using two metal electrode measurement probes to measure the equivalent impedance of the outer layer of the skin stratum corneum in contact, using a square wave signal of a certain frequency, the signal received by the measurement probe is amplified by the circuit amplifier element, and the amplified voltage value is collected by the AD conversion method, and finally the corresponding moisture content is found through the voltage value and the corresponding moisture content comparison table. However, this type of traditional skin impedance measurement uses rigid electrodes, which will cause the skin to deform during instrument measurement, resulting in inaccurate measurement values, and the pressure applied each time is different, making it difficult to ensure consistency of the measurement results, and continuous detection is impossible. The common measurement method on the market is to use Ag / AgCl macro electrodes, including block dry electrodes, gel-adhesive electrodes and electrolyte electrodes. The electrode size is mainly 0.76-10cm 2 However, this method has problems such as difficulty in fitting with the skin or changing the electrical properties of the skin, which can also lead to inaccurate measurement results.

[0007] In order to solve the above problems, thin film electrodes were proposed.

[10] A skin-conformable, wearable thin-film hydration sensor was studied. This sensor uses PDMS as a substrate and silver nanowires as interdigitated electrodes. It solves the problem that rigid electrodes and Ag / AgCl macroelectrodes are difficult to conform to the skin or will change the electrical properties of the skin, and realizes pressure-free measurement. However, the performance of this sensor was tested on artificial skin, ignoring the continuous deviation of the measurement results caused by transepidermal water loss of the human skin in its natural state. Since transepidermal water loss is uninterrupted, when using a thin-film hydration sensor for measurement, it is necessary to first fit the thin-film sensor tightly to the skin before starting the measurement. Even if the time is short, the impact of transepidermal water loss on the measurement results cannot be ignored. Under the same skin state, if the thin-film hydration sensor is not breathable, the water vapor lost by natural evaporation of the skin due to transepidermal water loss will continue to accumulate in the sensor, causing the skin impedance measured by the sensor to continue to decrease over time, making it difficult to obtain accurate measurement values. Matsukawa et al.

[11] Gold nanonetwork interdigitated electrodes (GNIs) were used to measure skin impedance and monitor skin hydration. They prepared polyvinyl alcohol (PVA) nanonetwork fibers (300-500 nm in diameter) by electrospinning, then deposited gold (70-100 nm in thickness) onto them by vacuum deposition. Leveraging PVA's water solubility, they transferred the electrodes to the skin using a water spray. This nanonetwork electrode exhibits excellent water vapor permeability, enabling measurements of skin impedance without being affected by transepidermal water loss. However, the breathable nanonetwork design of this nanonetwork electrode, which mitigates moisture effects, is passive, making it difficult to quickly create a suitable sensor operating environment in the presence of sweat. Furthermore, the processing is complex and the sensor cannot be reused. Furthermore, the water spray transfer method is not only complex but also affects the electrical properties of the skin, making it difficult to quickly restore the sensor to its original state, thus affecting the measurement results. Furthermore, residual PVA can cause inaccurate impedance measurements. Therefore, it is imperative to develop self-adhesive hydration sensors that are breathable, provide stable and reliable measurement results, and directional water repellency.

[0008] It is worth noting that Shanshan et al.

[10] and Matsukawa et al.

[11] When designing the hydration sensor experiment, only the effect of measurement frequency on measurement depth was considered, that is, when the frequency is lower than 1kHz, the dielectric response mainly comes from the stratum corneum.

[12] , while ignoring the effect of the interdigital electrode size. The thickness of the skin stratum corneum is about 20-40 μm, and Ivanic et al.

[13] The study showed that when the electrode spacing is smaller than the thickness of the skin layer, the working electric field is mainly concentrated in the depth range corresponding to the thickness of the skin layer.

[10] and Matsukawa et al.

[11] The millimeter-scale interdigitated electrodes used, Zhao Zhan

[14] et al. used micrometer-scale interdigitated electrodes to study skin permeability (a key parameter in physiological and biochemical monitoring, such as transdermal drug delivery and noninvasive blood glucose monitoring). Simulations and experiments confirmed that micrometer-scale interdigitated electrodes can more closely concentrate the effective electric field within the stratum corneum. Therefore, micrometer-scale interdigitated electrodes are particularly suitable for studying changes in stratum corneum water content.

[0009] Furthermore, while spectral moisture meters can reveal the overall moisture level of the face, they are bulky and expensive. Lower-priced handheld meters based on impedance measurement suffer from inaccurate measurements and limited single-point measurement capabilities. While multi-channel data acquisition technology is widely used in various testing systems, the limited form factor of handheld impedance-based meters currently available on the market makes it difficult to integrate multiple sensors for multi-point measurement. Compared to single-point measurement, multi-point measurement can reveal the skin hydration level of a larger measurement area at once, unlike single-point measurement instruments that require multiple measurements.

[0010] In summary, further research is needed on the breathability, directional water repellency, self-adhesion and processing technology of electronic skin. The materials, processes and structural dimensions of flexible hydration sensors also need to be further optimized. It is urgently needed to develop a self-adhesive breathable membrane with simple process and directional water repellency and study its application in flexible hydration sensors.

[0011] References

[0012] [1]Yang,Y.,Cui,T.,Li,D.et al.Breathable Electronic Skins for DailyPhysiological Signal Monitoring.Nano-Micro Lett.14,161(2022).

[0013] [2]Tian,L.,Zimmerman,B.,Akhtar,A.et al.Large-area MRI-compatibleepidermal electronic interfaces for prosthetic control and cognitivemonitoring.Nat Biomed Eng 3,194–205(2019).

[0014] [3]Y.Wang,T.Hong,L.Wang,G.Li,N.Bai,C.Li,P.Lu,M.Cai,Z.Wu,N.Lu,B.Yu,J.Zhang,C.F.Guo,Epidermal electrodes with enhanced breathability and highsensing performance,Materials Today Physics,Volume 12,2020,100191,ISSN 2542-5293.

[0015] [4]Weixin Zhou,Shanshan Yao,Hongyu Wang,Qingchuan Du,Yanwen Ma,andYong Zhu,ACS Nano 202014(5),5798-5805

[0016] [5]Xu,Y.T.,Guo,W.,Zhou,S.Q.,Yi,H.K.,Yang,G.Q.,Mei,S.X.,Zhu,K.H.,Wu,H.,Li,Z.,Bioinspired Perspiration-Wicking Electronic Skins for Comfortableand Reliable Multimodal Health Monitoring.Adv.Funct.Mater.2022,32,2200961.

[0017] [6]Yang,X.,Wang,S.,Liu,M.,Li,L.,Zhao,Y.,Wang,Y.,Bai,Y.,Lu,Q.,Xiong,Z.,Feng,S.,Zhang,T.,All-Nanofiber-Based Janus Epidermal Electrode withDirectional Sweat Permeability for Artifact-Free BiopotentialMonitoring.Small 2022,18,2106477.

[0018] [7]Chin,J.,&Tisan,A.(2015,July).Ubiquitous Approach to Body Hydration Testing.In 2015 International Conference on Intelligent Environments(pp.144-147).IEEE.

[0019] [8]Clarys,P.,Clijsen,R.,Taeymans,J.,&Barel,A.O.(2012).Hydration measurements of the stratum corneum:comparison between the capacitance method(digital version of the C orneometer CM )and the impedance method(S kicon-200 ).Skin Research and Technology,18(3),316-323.

[0020] [9]Dong,Yonggui,Zhou,Guolin,&Lv,Wen'er.A Method for Measuring Skin Moisture.CN 1686048 A.

[0021]

[10] Yao,S.,Myers,A.,Malhotra,A.,Lin,F.,Bozkurt,A.,Muth,J.F.,&Zhu,Y.(2017).A wearable hydration sensor with conformal nanowire electrodes.Advanced healthcare materials,6(6),1601159.

[0022]

[11] Matsukawa R,Miyamoto A,Yokota T,et al.Skin impedance measurements with nanomesh electrodes for monitoring skin hydration[J].Advanced Healthcare Materials,2020,9(22):2001322.

[0023]

[12] G,Martinsen,et al.Measuring depth depends on frequency inelectrical skin impedance measurements[J].Skin Research&Technology,1999.

[0024]

[13] Ivanic R, Novotny I, Rehacek V, et al. Thin film non-symmetricmicroelectrode array for impedance monitoring of human skin [J]. ThinSolidFilms, 2003, 433 (1 / 2): 332-336.

[0025]

[14] Zhao Zhan, Lu Fei, Wang Chenshuo, Zhao Rongjian, Du Lidong, Fang Zhen. Skin permeability evaluation method based on impedance detection microsensing technology[J]. Journal of Electronics & Information Technology, 2018, 40(08): 1927-1933. Summary of the Invention

[0026] Based on the above problems in the prior art, the present invention proposes a self-adhesive breathable nanofiber membrane with directional water repellency and its application in a flexible hydration sensor.

[0027] To achieve the purpose, the present invention adopts the following technical solutions:

[0028] The present invention first provides a self-adhesive breathable nanofiber membrane with directional water repellency, which is a double-layer nano-network fiber membrane composed of a hydrophilic layer and a hydrophobic adhesive layer prepared by electrospinning. The structure and process are simple, and it has the properties of flexible self-adhesion, breathability, and directional water repellency, and can be used as a universal substrate for electronic skin. Due to the asymmetric wettability of the two sides of the membrane and the significant capillary phenomenon of the nanofibers, the liquid can be directed by the skin / hydrophobic adhesive layer interface to the hydrophilic layer / air interface against gravity, and the reverse flow of the liquid can be prevented, which enables the skin / hydrophobic adhesive layer interface to remain dry. The self-adhesive breathable nanofiber membrane with directional water repellency of the present invention provides a new solution to the problems of avoiding water accumulation leading to poor signal quality of electronic skin or even short circuit, device shedding from the skin, discomfort when wearing, and skin disease induction, and provides a universal substrate for electronic skin, which can improve the signal quality, wearing comfort and durability of electronic skin, and promote the development of electronic skin in the fields of health monitoring and medical diagnosis.

[0029] The present invention uses electrospinning technology to process and manufacture a self-adhesive breathable nanofiber membrane with directional water repellency. The main steps of the method are as follows:

[0030] First, a hydrophilic material or a hydrophilic material treated to be hydrophilic (including but not limited to polyacrylonitrile, cellulose acetate and other materials) is deposited on a receiving device by electrospinning, and after hydrolysis, a hydrophilic layer with irregular meshes formed by interlaced stacks of nanofibers is formed. The electrospinning parameters are set according to the properties of the selected material. The diameter of the resulting hydrophilic layer fiber is in the range of 10nm-10μm (preferably 100-900nm), the pore size is in the range of 50nm-20μm (preferably 0.1-5μm), the thickness is in the range of 20-500μm (preferably 50-110μm), and the water contact angle is <5°. The electrospinning parameters for the hydrophilic layer for reference are: needle-collector distance 10-25cm, needle +10-+30kV, collector 0-negative 5kV, injection propulsion speed 0.01-0.05mL / min, temperature 15-50°C, and relative humidity 20-50%.

[0031] Then, the hydrophobic material / medical adhesive mixed solution is spun onto the hydrophilic layer by electrospinning to form a nano-network hydrophobic adhesive layer, thereby obtaining a double-layer nano-network fiber membrane of a hydrophilic layer and a hydrophobic adhesive layer. The medical adhesive includes but is not limited to materials such as acrylic medical pressure-sensitive adhesive and acrylate medical pressure-sensitive adhesive, and the hydrophobic material includes but is not limited to polyurethane, thermoplastic polyurethane, etc. Taking thermoplastic polyurethane and acrylate medical pressure-sensitive adhesive as an example, a 22% by mass solution of thermoplastic polyurethane in N,N-dimethylformamide (DMF) is mixed with acrylate medical pressure-sensitive adhesive in a mass ratio of 1:1 to obtain a hydrophobic material / medical adhesive mixed solution. The mass percentage of the hydrophobic material and the medical adhesive in the mixed solution obtained from other materials should be based on the ability to successfully spin. Electrospinning parameters are set based on the properties of the prepared hydrophobic material / medical adhesive mixed solution, ensuring that the resulting hydrophobic adhesive layer has a fiber diameter within the range of 50 nm-30 μm (preferably 0.7-15 μm), a pore size within the range of 100 nm-50 μm (preferably 0.5-50 μm), a thickness within the range of 20 nm-500 μm (preferably 50-110 μm), and a water contact angle greater than 90°. Reference electrospinning parameters for the hydrophobic material / medical adhesive mixed solution include: needle-collector distance of 10-25 cm, needle voltage of +8-+30 kV, collector voltage of 0--5 kV, injection velocity of 0.005-0.06 mL / min, temperature of 15-50°C, and relative humidity of 20-50%.

[0032] Finally, the membrane is cut into desired shapes using laser cutting technology, which can be used as a universal substrate for electronic skin.

[0033] The hydrophilic layer and hydrophobic adhesive layer design of the self-adhesive, breathable nanofiber membrane with directional water repellency creates asymmetric wettability between the upper and lower layers of the membrane. The nanofiber mesh structure obtained by electrospinning exhibits excellent air permeability, significant capillary action, and a hydrophilic-hydrophobic gradient, which imparts breathability and directional water repellency to the membrane. The introduction of a medical adhesive imparts self-adhesion to the membrane, enabling a close, conformable fit to the skin. The self-adhesive, breathable nanofiber membrane with directional water repellency allows droplets to be driven by the anti-gravity force of the skin, the hydrophobic adhesive layer, and the hydrophilic layer. Droplets are also less likely to flow back into the skin, keeping the electronic skin sensor interface dry. This effectively reduces measurement errors caused by natural moisture evaporation from the skin and sweat accumulation on the sensor, resulting in accurate and reliable measurement results and improved wearing comfort. This prevents device shedding and skin diseases caused by prolonged wear.

[0034] The present invention also provides the use of the self-adhesive, breathable nanofiber membrane with directional water repellency in a flexible hydration sensor. A flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-interdigital electrodes is proposed. The patch comprises a self-adhesive, breathable nanofiber membrane substrate with directional water repellency, an array of micro-interdigital electrodes, and hardware circuitry. While exhibiting flexible self-adhesion, breathability, and directional water repellency, the patch enables low-cost, pressure-free, and reliable multi-point detection of stratum corneum moisture content. This makes regular skin hydration testing a part of daily life, helping prevent and diagnose a range of skin conditions, slowing skin aging and improving skin condition. The patch can also be used in basic dermatological research, as a testing tool for evaluating the efficacy of skincare products, and as a claims support tool. It holds broad untapped market potential and application prospects in the fields of smart wearable flexible electronics, human health monitoring, and skin disease prevention and diagnosis.

[0035] For a flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-interdigitated electrodes, the present invention processes a micro-interdigitated electrode array and a connecting circuit on a self-adhesive, breathable nanofiber membrane substrate that directs water repellency. In addition to using traditional micromachining methods such as photolithography and magnetron sputtering, a direct-write patterning method (including but not limited to laser direct writing technology, atmospheric pressure plasma microjet direct writing technology, inkjet printing technology, screen printing technology, etc.) can also be used, eliminating complex process steps and reducing processing and manufacturing costs and material costs. The flexible, self-adhesive substrate with a micron-level thickness makes the sensor lightweight and portable, capable of conformal contact and close fit with the skin, achieving pressure-free measurement, and effectively solving the problem of inaccurate measurement results caused by the unstable applied pressure of a handheld tester. The micro-interdigitated electrodes can concentrate the effective electric field within the stratum corneum, and the array-type interdigitated electrode distribution can achieve simultaneous measurement of multiple points.

[0036] The material of the interdigitated electrodes is selected according to different processing methods. The magnetron sputtering method can use conductive targets such as gold, aluminum, and copper. The direct writing method can use conductive materials such as graphene, MXene, carbon nanotubes, conductive silver paste, silver nanowires, or materials that generate conductive substances after laser / plasma processing (including but not limited to graphene oxide, molybdenum chloride, etc.). The micro-interdigitated electrodes and connecting circuits are directly engraved on the film substrate in a maskless, direct writing manner. Since complex process conditions and processes such as photoresist, mask, sample pretreatment, vacuum equipment, high-temperature treatment, and clean room processing are not required, the processing cost can be greatly reduced. The micro-interdigitated electrodes are distributed on the substrate in an array form, which can realize multi-point measurement of the water content of the skin's stratum corneum. The width and distance between the micro-interdigitated electrodes are both in the range of 50-300 microns, and the thickness of the interdigitated electrodes is in the range of 0.05-30 microns. The design of the micro-interdigitated electrode enables the effective measurement depth of the electric field to be concentrated within the depth range of the stratum corneum, making the changes in the electrical properties of the stratum corneum the dominant factor affecting the measurement results. Compared with macroelectrodes and millimeter-scale interdigitated electrodes, micron-scale interdigitated electrodes are more suitable for studying changes in the water content of the stratum corneum, that is, detecting skin hydration.

[0037] The hydration sensor patch's hardware circuitry uses the charge-discharge principle to measure the equivalent impedance of the skin's stratum corneum. It includes a microprocessor, control circuitry, waveform conversion circuitry, and a Bluetooth module. Through circuit design and microprocessor programming, it collects and processes data from multiple arrays of hydration sensor units. The data is then transmitted via Bluetooth to a mobile phone or other device for display.

[0038] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0039] (1) The self-adhesive breathable nanofiber membrane with directional water repellency of the present invention is a double-layer nanofiber network structure of a hydrophilic layer and a hydrophobic adhesive layer. Compared with most existing airtight electronic skin substrates, it has good air permeability; compared with existing electronic skins with mesh designs, it has the performance of active directional water repellency; compared with existing two-layer nanofiber membranes, it has self-adhesion; compared with existing multi-layer nanofiber membranes, the double-layer structure is simpler and eliminates complicated processing steps.

[0040] (2) The present invention applies a self-adhesive breathable nanofiber membrane with directional water repellency to a flexible hydration sensor. In response to the problem that spectral measuring instruments are large in size, expensive, and difficult to popularize, the present invention has the advantages of being lightweight, portable, low-cost, and easy to popularize. In response to the problem that handheld rigid electrode measuring instruments may cause skin deformation during measurement, resulting in unstable and inaccurate measurement results, the present invention can achieve pressure-free detection of the water content of the skin stratum corneum, and the measurement results are stable and reliable. In response to the currently studied airtight film hydration sensors, the present invention has the performance of directional water repellency, and can achieve the anti-gravity directional driving of droplets by the skin-hydrophobic adhesive layer-hydrophilic layer, and the droplets are difficult to flow back to the skin, which can keep the contact interface between the sensor patch and the skin dry, and can effectively reduce the measurement error caused by the natural evaporation of skin water and the accumulation of sweat on the sensor, so that the measurement results are accurate and reliable. In response to the problem that the water transfer method of the gold nano-network electrode currently studied will affect the electrical properties of the skin, the present invention can actively rather than passively directionally remove sweat and dehumidify, keep the contact interface between the sensor patch and the skin in a dry state, will not affect the electrical properties of the skin, and the measurement results are accurate and reliable.

[0041] (3) The sensing electrode of the present invention is a plurality of micro-interdigitated electrodes arrayed on a membrane substrate. Compared with the single-point measurement of handheld measuring instruments and thin film electrodes in existing research, the present invention can realize multi-point measurement and can achieve simultaneous multi-point detection of the water content of the skin stratum corneum.

[0042] (4) The sensing electrode of the present invention is a micrometer-scale interdigital electrode. The design of the micrometer-scale interdigital electrode can make the effective measurement depth of the electric field concentrated within the depth range of the stratum corneum. Compared with the macroelectrode and the millimeter-scale interdigital electrode, the dominant factor for the change in the electrical properties of the skin measured by the micrometer-scale interdigital electrode comes from the change in the water content of the stratum corneum. The measurement results can more accurately reflect the hydration of the skin.

[0043] (5) The process flow of the present invention is simple. The material cost and processing cost of the double-layer nanofiber membrane obtained by the electrospinning method are relatively low. The micro-interdigitated electrodes make the material consumption of a single sensor less and the material cost lower. The direct-write patterning method of the interdigitated electrodes does not require complex process steps such as photoresist, mask, sample pretreatment, vacuum device, high-temperature treatment and clean room processing, thereby reducing the processing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a scanning electron microscope image of a cross section of a self-adhesive breathable nanofiber membrane with directional water repellency.

[0045] Figure 2 This is a scanning electron microscope image of the hydrophilic layer of the self-adhesive breathable nanofiber membrane with directional water repellency.

[0046] Figure 3This is a scanning electron microscope image of the hydrophobic adhesive layer of the self-adhesive breathable nanofibrous membrane with directional water repellency.

[0047] Figure 4 This is a contact angle test diagram of the hydrophobic adhesive layer of the self-adhesive breathable nanofiber membrane with directional water repellency.

[0048] Figure 5 This is a contact angle test diagram of the hydrophilic layer of the self-adhesive breathable nanofiber membrane with directional water repellency.

[0049] Figure 6 This is the anti-gravity directional water displacement effect diagram of the self-adhesive breathable nanofiber membrane for directional water displacement.

[0050] Figure 7 This is a picture of the effect of a self-adhesive breathable nanofiber membrane with directional water repellency attached to human skin.

[0051] Figure 8 This is a schematic diagram of the appearance of a flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-interdigitated electrodes (only mask-shaped sensor patches are listed as implementation examples, and other styles of sensor patches such as square and wristband shapes are also included but not limited to). In the figure, the numbers: 1 is the self-adhesive, breathable nanofiber membrane substrate with directional water repellency; 2 is the micro-interdigitated electrodes; 3 is the hardware circuit.

[0052] Figure 9 This is a process flow chart for preparing a flexible, self-adhesive, breathable hydration sensing patch based on distributed micro-interdigitated electrodes (only inkjet printing is listed as an implementation case for patterning the interdigitated electrodes; direct-write patterning methods such as screen printing are also included but not limited to).

[0053] Figure 10 This is the hardware circuit block diagram of a flexible, self-adhesive, breathable hydration sensing patch based on distributed micro-interdigitated electrodes. DETAILED DESCRIPTION

[0054] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0055] Example 1

[0056] The self-adhesive, breathable nanofiber membrane with directional water repellency provided in this embodiment is a double-layer nanonetwork fiber membrane composed of a hydrophilic layer and a hydrophobic adhesive layer prepared by electrospinning. Specifically, in this embodiment, the hydrophilic layer is made from polyacrylonitrile via electrospinning followed by incomplete hydrolysis, while the hydrophobic adhesive layer is made by electrospinning a mixed solution of a hydrophobic material / medical adhesive (a 22% by mass solution of thermoplastic polyurethane in DMF mixed with an acrylic medical pressure-sensitive adhesive in a 1:1 mass ratio) onto the hydrophilic layer.

[0057] Figure 1This is a scanning electron microscope image of a cross-section of a self-adhesive, breathable nanofiber membrane that provides directional water repellency. The double-layer nanofiber network structure is clearly visible. The upper layer is a hydrophobic adhesive layer with a thickness of 70-100 microns; the lower layer is a hydrophilic layer with a thickness of 60-90 microns.

[0058] Figure 2 This is a scanning electron microscope image of the hydrophilic layer of a self-adhesive, breathable nanofiber membrane that directional-water repellency. The hydrophilic layer has fiber diameters ranging from 100-700 nm and pore sizes ranging from 0.3-3 microns.

[0059] Figure 3 This is a scanning electron microscope image of the hydrophobic adhesive layer of a self-adhesive, breathable nanofiber membrane with directional water repellency. The upper layer in the image is the hydrophobic adhesive layer, with larger fibers and larger pores. Through the network of hydrophobic adhesive fibers, the hydrophilic layer fibers beneath can be seen. The hydrophobic layer fibers have diameters ranging from 2 to 13 microns, and pore sizes range from 2 to 40 microns.

[0060] Figure 4 This is a contact angle test chart of the hydrophobic adhesive layer of the self-adhesive breathable nanofiber membrane with directional water repellency. The hydrophobic contact angle of the hydrophobic adhesive layer is approximately 100°.

[0061] Figure 5 This is a contact angle test chart of the hydrophilic layer of a self-adhesive, breathable nanofiber membrane that directional-water repellency. When a water droplet lands on the hydrophilic layer, it spreads out instantly, demonstrating excellent hydrophilicity.

[0062] Figure 6 This image shows the effect of directional water repellency using a self-adhesive, breathable nanofiber membrane. The substrate is suspended on two platforms at equal height, with the hydrophilic layer on top and the hydrophobic adhesive layer on the bottom. Small droplets are continuously added to the bottom side. The droplets are rapidly driven toward the hydrophilic layer by the force of gravity. As the total number of droplets increases, they are completely driven to the hydrophilic layer, preventing them from flowing back into the hydrophobic adhesive layer.

[0063] Figure 7 This image shows the self-adhesive properties of a directional, water-repellent, self-adhesive, breathable nanofiber membrane applied to human skin. With the hydrophobic adhesive layer in contact with the skin, the membrane was applied to the inner forearm. The membrane adhered conformably to the skin. When the membrane was removed, it was observed to slightly lift the skin, demonstrating its self-adhesive properties.

[0064] This embodiment also provides a flexible self-adhesive breathable hydration sensor patch based on distributed micro-interdigital electrodes made from the above-mentioned self-adhesive breathable nanofiber membrane patch with directional water repellency, and its appearance is shown in the figure. Figure 8As shown in (the present embodiment only enumerates the sensor patch of facial mask shape, in addition also includes but not limited to the sensor patch of other styles such as square shape, wristband shape), comprising: the self-adhesive breathable nanofiber membrane substrate 1 of directional water-repelling, micro-interdigitated electrode 2, hardware circuit 3. The self-adhesive breathable nanofiber membrane substrate 1 of directional water-repelling has self-adhesion, can be conformably fitted with the skin, and the structural design of its hydrophilic layer-hydrophobic adhesive layer can directional perspiration and dehumidification, effectively reduce the measurement error brought by the evaporation of natural moisture from the skin and the accumulation of sweat on the sensor. The micro-interdigitated electrode 2 carried on the self-adhesive breathable nanofiber membrane substrate 1 of directional water-repelling is array distributed, and the interdigitated finger width and finger spacing are all within the range of 50-300 microns. The micro-interdigitated electrode 2 of array is connected with the hardware circuit 3 part by circuit routing, and the signal measured by the micro-interdigitated electrode 2 is finally sent and displayed on the mobile phone terminal (also can be tablet computer, computer, smart watch etc.) after being processed by the hardware circuit 3.

[0065] Figure 9 This is a process flow chart of a flexible, self-adhesive, breathable hydration sensing patch based on distributed micro-interdigitated electrodes (the patterning of the interdigitated electrodes is only illustrated by inkjet printing, and also includes but is not limited to direct writing patterning methods such as screen printing). Figure 9-1 As shown, the hydrophilic material or the material that has been treated to be hydrophilic is deposited on the substrate by electrostatic spinning to form a fiber membrane with irregular meshes and staggered stacks of nanofibers. The material used for the hydrophilic layer of this embodiment is polyacrylonitrile material, and the spinning parameters are: needle-collector distance 13 cm, needle +16.1 kV, collector -2.1 kV, injection propulsion speed 0.015 mL / min, temperature 40 ° C, relative humidity 40%. After the polyacrylonitrile nanofiber membrane is obtained by spinning, it is incompletely hydrolyzed (the polyacrylonitrile nanofiber membrane obtained by spinning is placed in a solution composed of 85 mL of anhydrous ethanol, 15 mL of deionized water and 3 g of NaOH, hydrolyzed at 50 ° C for 20 minutes, then washed with deionized water to neutrality, and dried) to obtain a hydrophilic layer. If the spinning material itself has good hydrophilicity, the hydrophilic layer can be directly obtained without hydrolysis. As Figure 9-2As shown, the hydrophobic material / medical adhesive mixed solution is deposited on the hydrophilic layer by electrospinning to form a nano-network hydrophobic adhesive layer, and a directional water-repellent self-adhesive breathable nanofiber membrane with a double-layer nano-network fiber structure of a hydrophilic layer and a hydrophobic adhesive layer is obtained. In this embodiment, thermoplastic polyurethane and acrylate medical pressure-sensitive adhesive are used. A thermoplastic polyurethane DMF solution with a mass percentage of 22% is mixed with an acrylate medical pressure-sensitive adhesive in a mass ratio of 1:1 to obtain a hydrophobic material / medical adhesive mixed solution. The spinning parameters are: needle-collector distance 15 cm, needle +9.1 kV, collector -1.1 kV, injection propulsion speed 0.03 mL / min, temperature 40°C, and relative humidity 40%. As shown in 9-3, the membrane substrate is cut into the desired shape (including but not limited to square, strip, and mask shape) by laser cutting technology to obtain Figure 9-4 .like Figure 9-5 As shown, an array of micro-interdigitated electrodes is drawn on a film substrate by direct writing using inkjet printing. The electrode materials include but are not limited to conductive silver paste, graphene and other conductive inks. The width and spacing of the micro-interdigitated electrodes are both in the range of 50-300 microns, and the thickness of the interdigitated electrodes is in the range of 0.05-30 microns. Finally, the result is as shown in FIG. Figure 9-6 The shown figure shows a flexible, self-adhesive, breathable hydration sensing patch based on distributed micro-interdigitated electrodes.

[0066] Figure 10 It is a hardware circuit block diagram of a flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-finger electrodes. The hardware circuit portion of the present invention includes a microprocessor, a control circuit, a waveform conversion circuit, and a Bluetooth module. The microprocessor is programmed, and the control circuit and the waveform conversion circuit realize the acquisition and processing of the sensing signals of the micro-finger electrodes of the array, and finally the Bluetooth module controlled by the microprocessor transmits the data and displays it on a mobile phone terminal (which can also be a tablet computer, computer, smart watch, etc.). Specifically: the area where each micro-finger electrode is located can be regarded as a hydration sensing unit. The control circuit and the Bluetooth module are electrically connected, and the control circuit is electrically connected to the hydration sensing unit through switch S1 and switch S2 respectively, and the hydration sensing unit is electrically connected to the microprocessor through the waveform conversion circuit. The microprocessor charges and discharges the hydration sensing unit through the control circuit. During the charging and discharging process, the hydration sensing unit collects data on the equivalent impedance of the skin stratum corneum and sends it to the waveform conversion circuit. The waveform conversion circuit converts the received equivalent impedance data of the skin stratum corneum into a waveform signal and sends it to the microprocessor. After receiving the waveform signal, the microprocessor analyzes the waveform signal and sends the analysis result to the mobile phone terminal through the Bluetooth module for the user to view.

[0067] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A self-adhesive breathable nanofiber membrane with directional water displacement, characterized by: The self-adhesive breathable nanofiber membrane with directional water displacement is a double-layer nano-network fiber membrane composed of a hydrophilic layer and a hydrophobic adhesive layer prepared by electrospinning; The hydrophilic layer is made by electrospinning a hydrophilic material or a material treated to be hydrophilic; the hydrophobic adhesive layer is made by electrospinning a mixed solution of a hydrophobic material and a medical adhesive onto the hydrophilic layer, wherein the mixed solution is a mixture of a 22% by mass solution of thermoplastic polyurethane in N,N-dimethylformamide and an acrylate medical pressure-sensitive adhesive in a mass ratio of 1:1; The thickness of the hydrophobic adhesive layer is within the range of 70-100 microns; the thickness of the hydrophilic layer is within the range of 60-90 microns.

2. The self-adhesive breathable nanofiber membrane for directional water displacement according to claim 1, characterized in that: The material used for the hydrophilic layer is polyacrylonitrile or cellulose acetate.

3. The self-adhesive breathable nanofiber membrane for directional water displacement according to claim 1 or 2, characterized in that: The fiber diameter in the hydrophilic layer is in the range of 10 nm-10 μm, the pore size of the hydrophilic layer is in the range of 50 nm-20 μm, and the water contact angle is less than 5°.

4. The self-adhesive breathable nanofiber membrane for directional water displacement according to claim 1 or 2, characterized in that: The fiber diameter in the hydrophobic adhesive layer is in the range of 50 nm-30 μm, the pore size of the hydrophobic adhesive layer is in the range of 100 nm-50 μm, and the water contact angle is greater than 90°.

5. The self-adhesive breathable nanofiber membrane with directional water displacement according to claim 1 or 2, characterized in that: The electrospinning parameters of the hydrophilic layer are: needle-collector distance 10-25 cm, needle +10-+30 kV, collector 0--5 kV, injection advancement speed 0.01-0.05 mL / min, temperature 15-50° C., and relative humidity 20-50%.

6. The self-adhesive breathable nanofiber membrane for directional water displacement according to claim 1 or 2, characterized in that: The electrospinning parameters of the hydrophobic adhesive layer are: needle-collector distance 10-25 cm, needle +8-+30 kV, collector 0--5 kV, injection advancement speed 0.005-0.06 mL / min, temperature 15-50° C., and relative humidity 20-50%.

7. Use of the self-adhesive breathable nanofiber membrane with directional water repellency according to any one of claims 1 to 6 in a flexible hydration sensor.

8. A flexible, self-adhesive, breathable hydration sensor patch based on distributed micro-interdigitated electrodes, characterized by: The hydration sensor patch uses the self-adhesive breathable nanofiber membrane with directional water repellency as claimed in any one of claims 1 to 6 as a substrate, and is provided with micro-interdigitated electrodes distributed in an array on the substrate.

9. The hydration sensor patch according to claim 8, characterized in that: The hydration sensor patch is also provided with a hardware circuit for collecting and processing the sensing signals of the micro-interdigitated electrodes of the array.

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