Preparation method and application of soluble paper-based flexible intelligent wearable sensor

Abstract

The invention discloses a preparation method and application of a soluble paper-based flexible intelligent wearable sensor, a soluble paper-based material is selected as a carrier, MXene and silver nanowires are coated on a paper base to construct a conductive layer, then a polyvinyl butyral / ethyl cellulose waterproof layer is scraped and coated, and the soluble paper-based flexible intelligent wearable sensor is obtained. And the paper-based flexible intelligent wearable sensor with excellent conductivity and waterproof performance is successfully prepared. The paper-based material is modified and optimized, so that the conductivity and stability of the paper-based material are improved; according to the invention, the surface modification process of the paper-based material and the compounding method of the conductive functional material are optimized, the sensitivity, response time and mechanical stability of the sensor are greatly improved, and the soluble behavior of the sensor and the degradation characteristics of the sensor in different environments are systematically researched; it is proved that the sensor can effectively monitor human physiological signals, has excellent degradability, and provides a new thought for solving the problem of electronic waste pollution.

Description

Technical Field

[0001] The present invention relates to the field of wearable devices, and in particular to a preparation method of a soluble paper-based flexible intelligent wearable sensor and applications thereof. Background Art

[0002] In the digital age, the Internet of Things and artificial intelligence technologies are developing rapidly. Efficient connectivity of data interaction and decision-making rely heavily on high-quality big data. The fundamental role of sensors in digital transformation is to convert physical characteristics in the real world into digital data. However, traditional sensor technology often has difficulty achieving such large-scale monitoring. As electronic devices develop towards high integration and miniaturization, modern sensors, as a key part of intelligent electronics and machines, are beginning to fully play their role.

[0003] However, their small size and rigidity limit their use in many fields, such as wearable medical devices, interactive robots, and smart packaging. To meet these application demands, flexible sensors have emerged. Flexible smart wearable devices offer enormous potential in areas such as medical health monitoring, motion tracking, and environmental perception. Flexible smart wearable devices are a general term for wearable devices designed and developed for everyday wear. These devices can collect a variety of human data and provide interactive experiences in various aspects, including vision, touch, hearing, and health monitoring. They can also serve as an extension of mobile phone usage, offering functions such as message notifications, music listening, and phone calls. Furthermore, their high level of integration, compact size, and practicality have made them increasingly popular in the consumer market.

[0004] The wearable device market continues to expand, with medical wearables being a key component. According to a Swiss research report, medical wearables have the potential to save 1.3 million lives. This medical device technology is not only crucial to human health, but also holds enormous commercial potential.

[0005] Currently, traditional sensors suffer from numerous shortcomings, including a narrow operating temperature range, an inability to combine high stretchability with high sensitivity, large hysteresis, and poor self-adhesion. Traditional flexible sensors, mostly based on silicon or polymer substrates, have good electrical properties, but their environmental impact due to their non-degradability and poor fit with human skin limit their application in sustainable development and biocompatibility scenarios. Unlike traditional electronics, paper-based electronics utilize cellulose or a blend of materials rather than traditional polymers and metals.

[0006] Research shows that the rapid development of the electronics industry has led to increased demand for electronic products and the rapid replacement of these products. As of 2019, over 50 million tons of e-waste have been generated annually. Most of this e-waste is non-degradable, and significant quantities of hazardous substances are generated during landfill and incineration. The environmental impacts of e-waste have garnered widespread attention worldwide, significantly hindering industrial production and sustainable development.

[0007] In this context, the development of new flexible sensor materials that are highly sensitive, environmentally friendly and degradable has become a key direction of current research.

[0008] Paper-based materials are typically prepared using electrospinning, surface coating, and self-assembly techniques. Due to their widespread availability, relatively low cost, excellent foldability, and natural biodegradability, paper-based materials have garnered significant attention in the field of flexible electronics in recent years. Replacing plastics with renewable and biodegradable biofiber-based materials has become a key research topic.

[0009] Researching and developing biodegradable green materials that can replace plastic products has key practical significance for the clean and sustainable development of China's social economy. Summary of the Invention

[0010] In view of this, the present invention provides a preparation method and application of a soluble paper-based flexible smart wearable sensor.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0012] A method for preparing a soluble paper-based flexible smart wearable sensor comprises the following steps:

[0013] Step 1: Preparation of MXene

[0014] Step 1.1: Slowly add lithium fluoride into a polytetrafluoroethylene beaker containing hydrochloric acid solution and stir magnetically. Then slowly add titanium aluminide powder in multiple portions and continue stirring at a constant temperature.

[0015] Step 1.2: After the reaction is complete, wash the solid product and centrifuge to separate impurities. When the pH value of the supernatant is stable at 6, transfer it to a conical flask.

[0016] Step 1.3: Ultrasonic treatment is performed in an ice-water environment, followed by centrifugation. The precipitate after centrifugation is collected and freeze-dried to obtain the MXene powder required for the experiment.

[0017] Step 2: Preparation of MXene-anhydrous ethanol conductive solution

[0018] Weigh MXene powder, add anhydrous ethanol, ultrasonicate the mixture, and seal it for storage to obtain a MXene-ethanol conductive solution.

[0019] Step 3: Preparation of silver nanowires

[0020] Step 3.1: Place PVP in an oil bath and stir to dissolve it in ethylene glycol to prepare a PVP-ethylene glycol solution;

[0021] Step 3.2: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to obtain a silver nitrate-ethylene glycol solution, and dissolve sodium chloride in ethylene glycol to obtain a sodium chloride-ethylene glycol solution;

[0022] Step 3.3: Place the PVP-ethylene glycol solution in a reactor, add the sodium chloride-ethylene glycol solution as a morphology modifier, heat, and maintain constant temperature with stirring; slowly add the silver nitrate-ethylene glycol solution dropwise, and continue stirring in an oil bath to react;

[0023] Step 3.4: After the reaction is complete, the product is mixed with ethanol and centrifuged for purification to obtain high-purity silver nanowires.

[0024] Step 4: Prepare PVB / EC waterproof material

[0025] Weigh polyvinyl butyral and ethyl cellulose, add them into anhydrous ethanol to dissolve, stir magnetically to obtain PVB / EC waterproof material, and then store it at room temperature;

[0026] Step 5: Preparation of paper-based flexible smart wearable sensors

[0027] Using a soluble paper-based material as a carrier, MXene and silver nanowires are coated on the paper base to construct a conductive layer, and then a polyvinyl butyral / ethyl cellulose waterproof layer is scraped off to obtain a paper-based flexible smart wearable sensor with excellent conductive and waterproof properties.

[0028] Preferably, in step 1.1, the amount of lithium fluoride added is 1.6 g, 20 mL of 12 mol / L hydrochloric acid solution is pre-placed in the beaker, the magnetic stirring rate is 500 r / min, and the duration is 30 minutes; the amount of titanium carbon aluminide powder added is 1.0 g, and the reaction is stirred at a constant temperature of 50°C for 24 hours.

[0029] Preferably, in step 1.2, the solid product is washed alternately with 1 mol / L hydrochloric acid and deionized water at a centrifugal speed of 4000 r / min.

[0030] Preferably, in step 1.3, the ultrasonic treatment time is 2 hours, the centrifugal speed is 6000 r / min, the centrifugal time is 20 minutes, and the freeze-drying time is 12 hours.

[0031] Preferably, in step 2, the amount of MXene powder added is 50 mg, the amount of anhydrous ethanol added is 10 ml, and the ultrasonic treatment time is 30 to 60 min, finally obtaining a MXene-ethanol conductive solution with a concentration of 5 mg / ml.

[0032] Preferably, in step 3.1, the PVP is a high molecular weight PVP with a molecular weight of 1,600,000, the added amount is 2 g, the oil bath temperature is 170° C., and the added amount of ethylene glycol is 160 mL, to prepare a PVP-ethylene glycol solution with a concentration of 12.5 g / L.

[0033] Preferably, in step 3.2, the amount of silver nitrate added is 2 g, and the amount of ethylene glycol added is 40 mL, to obtain a silver nitrate-ethylene glycol solution with a concentration of 50 g / L; the amount of sodium chloride added is 67.2 mg, and the amount of ethylene glycol added is 160 mL, and the concentration of the sodium chloride-ethylene glycol solution is 0.42 g / L.

[0034] Preferably, in the step 3.3, the amount of PVP-ethylene glycol solution added is 160 mL, the amount of sodium chloride-ethylene glycol solution added is 16 mL, the mixture is heated to 110° C., the amount of silver nitrate-ethylene glycol solution added is 40 mL, the dropwise addition rate is 2 mL per minute, the oil bath temperature is 110° C., and the stirring reaction time is 12 hours.

[0035] Preferably, in step 4, the amount of polyvinyl butyral added is 2.5 g, the amount of ethyl cellulose added is 2 g, the amount of anhydrous ethanol added is 25 g, the temperature of magnetic stirring is 50° C., and the magnetic stirring time is 30 min.

[0036] A method for preparing a soluble paper-based flexible smart wearable sensor is used in sustainable development of smart wearable devices.

[0037] Compared with the prior art, the present invention has achieved the following technical effects:

[0038] (1) The purpose of using soluble paper (not ordinary paper) as the substrate of the intelligent flexible sensor in the present invention is that the soluble paper can be easily dispersed in water. After the sensor is used and loses its usefulness, it can be removed by washing with water without causing pollution or garbage.

[0039] (2) The present invention improves the hydrophobicity of the water-soluble paper-based sensor by utilizing a polyvinyl butyral / ethyl cellulose waterproof layer, which is another innovation;

[0040] (3) The present invention constructs a conductive sensing layer by coating MXene and silver nanowires, giving the water-soluble paper-based sensor excellent signal conduction performance;

[0041] (4) This paper proposes an innovative preparation strategy for soluble paper-based flexible sensors. Using carboxymethyl cellulose (CMC) as a raw material and combining it with nanocomposites to construct a highly sensitive sensing unit, this strategy achieves the unification of device sensing performance and environmentally friendly properties. This strategy significantly simplifies the complex preparation process of traditional flexible sensors.

[0042] (5) This invention reveals the synergistic mechanism between paper-based dissolution kinetics and sensing performance. By systematically studying the correlation between the degree of material modification, conductive network density, and hollow structure, it confirms the key role of cellulose porous structure in improving ion permeation efficiency and signal stability. Experiments show that the optimized sensor maintains stable working characteristics under repeated bending conditions, and the residue after dissolution is non-toxic to the environment, providing a theoretical basis for the design of degradable electronic devices.

[0043] (6) The present invention expands the application scenarios of sensors in the fields of medical monitoring and intelligent interaction. The developed sensor can seamlessly fit the curved surface of the human body, achieving long-term and stable collection of physiological signals. Combined with Bluetooth signal transmission, it provides a new technology platform for the development of personalized health management and intelligent rehabilitation systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Diagram of the entire process for preparing dual-functional coatings for soluble paper-based flexible sensors;

[0045] Figure 2 Schematic diagram for calculating the bending radius r

[0046] Figure 3 (a) Paper; (b) CM and (c) CMA surface SEM images; (d) SEM images of paper (e) CM and (f) CMA cross sections; (g) element distribution on the surface of CMAs;

[0047] Figure 4 (a) XPS spectra of paper, CMA, and CMAs; (b) high-resolution spectra of the O 1s peak and (c) high-resolution spectra of the C 1s peak;

[0048] Figure 5 (a) XRD of paper, CMA, and CMAs; (b) FTIR spectra of paper, CM, and CMAs;

[0049] Figure 6 (a) Contact angles of paper, CMA, and CMAs; (b) Images of various droplets on the surface of the CMAs flexible hydrophobic sensor.

[0050] Figure 7 (a) Resistance change of CMAs flexible hydrophobic sensor at a small bending angle; (b) Response time and recovery time of CMAs flexible hydrophobic sensor when bent at 30°.

[0051] Figure 8 (a) Relative resistance changes of CM and CMAs flexible hydrophobic sensors at different bending angles and corresponding GF values; (b) Relative resistance changes of CMAs at a bending angle of 30° at different bending ratios;

[0052] Figure 9 (a) Surface contact angle change of the CMAs flexible hydrophobic sensor immersed in water for 60 min; (b) Mass loss of the CMAs flexible hydrophobic sensor immersed in water for 60 min.

[0053] Figure 10 (a) Degradation of CMAs flexible hydrophobic sensors in soil for 50 days; (b) Degradation of CMAs flexible hydrophobic sensors in water;

[0054] Figure 11 Air permeability testing of CMAs flexible hydrophobic sensors, PU films, and band-aids;

[0055] Figure 12 (a) Illustration of the CMAs flexible wireless wearable sensor for human motion monitoring; (b) Photograph of the Bluetooth signal transmission system; Application of the PMS flexible hydrophobic sensor in detecting bending signals of various body parts, including the pulse (c), index finger (d), and knee (e). DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] The present invention discloses a preparation method and application of a soluble paper-based flexible intelligent wearable sensor

[0058] 1. Experimental instruments and equipment

[0059] The instruments used in the experiment are shown in Table 1.

[0060] Table 1: Experimental instruments

[0061]

[0062] 2. Experimental drugs

[0063] The drugs used in the experiment are shown in Table 2.

[0064] Table 2: Experimental drugs

[0065]

[0066] 3. Experimental Methods

[0067] Preparation of soluble paper-based flexible smart wearable sensors

[0068] Step 1: Preparation of MXene

[0069] Step 1.1: 1.6 g of lithium fluoride was slowly added to a polytetrafluoroethylene beaker containing 20 mL of 12 mol / L hydrochloric acid solution. The beaker was magnetically stirred at 500 rpm for 30 minutes to allow the solvent system to fully pre-activate. Subsequently, 1.0 g of titanium aluminide powder was slowly added in multiple portions. The mixture was stirred at a constant temperature of 50°C for 24 hours to achieve material etching.

[0070] Step 1.2: After the reaction is complete, wash the solid product alternately with 1 mol / L hydrochloric acid and deionized water. Centrifuge at 4000 rpm to separate impurities until the pH value of the supernatant stabilizes at approximately 6. Transfer the washed solid and an appropriate amount of deionized water to a conical flask.

[0071] Step 1.3: Ultrasonic treatment was performed in an ice-water environment for 2 hours to promote the exfoliation of the layers. The precipitate was collected by centrifugation at 6000 rpm for 20 minutes and freeze-dried for 12 hours to obtain the MXene powder required for the experiment.

[0072] Step 2: Preparation of MXene-anhydrous ethanol conductive solution

[0073] Initially, 50 mg of MXene powder was weighed, followed by the addition of 10 ml of anhydrous ethanol. The mixture was then ultrasonicated for 30 to 60 minutes to allow the MXene to be fully exfoliated and evenly dispersed. After the ultrasonication, the mixture was sealed and stored, ultimately obtaining a MXene-ethanol conductive solution with a concentration of 5 mg / ml.

[0074] Step 3: Preparation of silver nanowires

[0075] Step 3.1: First, place 2 g of high molecular weight PVP (1,600,000) in a 170°C oil bath and stir to dissolve it in 160 mL of ethylene glycol to prepare a PVP-ethylene glycol solution with a concentration of 12.5 g / L.

[0076] Step 3.2: In the dark, dissolve 2 g of silver nitrate in 40 mL of ethylene glycol to obtain a 50 g / L silver nitrate-ethylene glycol solution. Also, dissolve 67.2 mg of sodium chloride in 160 mL of ethylene glycol to obtain a 0.42 g / L sodium chloride-ethylene glycol solution.

[0077] Step 3.3: Place 160 mL of PVP-ethylene glycol solution in a reactor, add 16 mL of sodium chloride-ethylene glycol solution as a morphology modifier, and heat to 110°C while stirring. Then, slowly add 40 mL of silver nitrate-ethylene glycol solution dropwise at a rate of 2 mL / min. Continue stirring in a 110°C oil bath for 12 hours.

[0078] Step 3.4: After the reaction is complete, the product is mixed with ethanol and purified by centrifugation to obtain high-purity silver nanowires.

[0079] Step 4: Prepare PVB / EC waterproof material

[0080] First, 2.5 g of polyvinyl butyral (PVB) and 2 g of ethyl cellulose (EC) were weighed and dissolved in 25 g of anhydrous ethanol. The mixture was stirred magnetically at 50°C for 30 minutes to obtain a PVB / EC waterproof material, which was then stored at room temperature.

[0081] Step 5: Preparation of paper-based flexible smart wearable sensors

[0082] Using a soluble paper-based material as a carrier, MXene and silver nanowires are coated on the paper base to construct a conductive layer, and then a polyvinyl butyral / ethyl cellulose waterproof layer is scraped off to obtain a paper-based flexible smart wearable sensor with excellent conductive and waterproof properties.

[0083] Preparation of soluble paper-based flexible smart wearable sensors:

[0084] A conductive network was constructed on the surface of a CMC paper substrate using a dropper coating method. Specifically, 1.5 mL of a 5 mg / mL MXene-ethanol dispersion was evenly applied to both the front and back sides of the paper using a dropper. After each application, the paper was immediately heat-treated in a 95°C vacuum oven for 5 minutes to quickly remove the solvent. Subsequently, 1.5 mL of a silver nanowire solution was applied alternately to the front and back sides of the dried substrate in the same manner to form a MXene / AgNWs composite conductive layer. A PVB / EC waterproof resin was then evenly applied to the conductive paper surface using a doctor blade coating method. The resulting substrate was cured at room temperature, resulting in a soluble, flexible, and highly conductive smart wearable sensor substrate.

[0085] Example 1: Characterization and analysis methods

[0086] 1. Scanning electron microscope (SEM) inspection

[0087] A JSM-IT300LV scanning electron microscope was used to characterize the micromorphology of the soluble paper-based flexible smart wearable sensor. The specific operating steps are as follows: select an appropriate amount of sample, spread it evenly on the surface of the conductive glue, and then use an ion sputtering device to spray gold. Subsequently, scanning electron microscopy observation was carried out under an acceleration voltage of 15kV to obtain a high-resolution micromorphology image of the sample surface.

[0088] 2. Infrared analysis

[0089] The infrared spectra of paper, CMA, and CMAs were measured using a Fourier transform infrared spectrometer. The specific method is as follows: 0.001 g of sample and 0.1 g of potassium bromide were mixed and ground together, and then tableted. The wavelength range of the measurement was 4000 cm -1 Up to 400cm -1 In between, the scanning background is set to air.

[0090] 3. X-ray diffraction (XRD) analysis

[0091] The crystal structure of the sample was analyzed by X-ray diffractometer.

[0092] Under the conditions that the diffraction angle is in the range of 10 to 80° and the scanning rate is 5° / min, the sample sampling and analysis work is carried out, the test current is set to 30mA and the working voltage is set to 40kV.

[0093] 4.X-ray electron spectroscopy (XPS) detection

[0094] The chemical analysis of the sample surface was carried out with the help of an X-ray photoelectron spectrometer. The test conditions were as follows: the vacuum degree was set to 5×10-7 mbar, the fixed transmission energy of the energy analyzer was 50 eV, the surface sampling depth was in the range of 5.0 to 7.0 nm, the scan width was 1000 eV, and the spectral width was 1.00 eV.

[0095] 5. Sensing performance detection and sensitivity calculation

[0096] The sensor's sensing performance is tested using a system combining an intelligent precision motion controller and a digital source instrument. The specific operation is as follows: The two ends of the sensor are fixed with conductive copper foil electrodes and connected to the digital source instrument via shielded wires to form a test circuit. This allows real-time monitoring of the sensor's resistance response changes under different motion states. The sensor sensitivity is calculated as follows:

[0097]

[0098] GF=(ΔR / R0) / S

[0099] Where l represents half of the bending distance, r represents the bending radius, θ represents the bending angle; S represents the strain of the sensor when it is bent, h represents the sensor thickness; ΔR represents the change in sensor resistance, and R0 represents the initial resistance. The calculation diagram of the bending radius r is as follows: Figure 2 shown.

[0100] Example 2: Sensor Microstructure

[0101] The surface microstructure of CMA paper-based sensor was characterized by SEM. After the fiber surface was treated with fiber broom, a large number of fine fibers were revealed, forming a rich and diverse microstructure. Figure 3 b It can be observed that after being treated with MXene-ethanol conductive solution, MXene nanosheets are tightly attached to the fiber surface, forming a uniform conductive layer. Figure 3 As shown in c, silver nanowires are evenly distributed on the paper surface, and together with MXene nanosheets, they build a three-dimensional conductive network, giving the material good conductive properties. This proves the uniformity of the conductive MXene and hydrophobic sizing agent coating, which is crucial for the working stability of the sensor.

[82] . Figure 3 d, e, and f are cross-sectional views of paper, CM, and CMA, respectively. It can be clearly seen that the conductive layer composed of MXene and AgNWs is tightly attached to the surface of the paper base. Figure 3 Figure g shows the element distribution on the CMA surface. As shown in the figure, Ag is evenly distributed on the CMA surface. This is primarily due to the silver nanowires coating the surface, which form a uniform covering layer that promotes uniform Ag distribution. A small amount of Ti is also observed in the figure, a phenomenon attributed to the presence of MXene. MXene, as a two-dimensional material, generally contains titanium, which forms some traces of Ti on the CMA surface. These Ti elements work together with AgNWs to improve the sensing performance and stability of the CMA.

[0102] Example 3: Sensor Chemical Structure

[0103] (1) Sensor XPS

[0104] The figure shows the XPS spectra of three samples. In the CMA sample, the presence of Ag elements can be observed at 368.1eV and 573.1eV, which means that silver nanowires are deposited on the surface of CMA. Figure 4As can be seen in the graph, a C-OH bond is present at 534.13 eV. This is likely due to hydrogen bonding between the paper and the MXene. Furthermore, hydrogen bonding between the MXene and the silver nanowires allows them to adhere to the fiber surface, forming a dense conductive layer. Table 3 shows that the Ag content in the CMA sample increased from 0 to 23.32, due to the presence of silver nanowires on the surface. The Ti content increased from 0.26 to 1.16, as MXene was deposited on the fiber surface. Furthermore, the Ti and Ag content decreased in the CMA sample, while the C and O content increased, likely due to the presence of a waterproof layer on the surface of the CMA sample. Table 4 shows that the functional groups in the paper, CMA, and CMA samples are primarily C-C / C=C, CO, C=O, and O-C=O.

[0105] Table 3: Element content of samples (%)

[0106]

[0107] Table 4: Functional group content of samples (%)

[0108]

[0109] (2) Sensor XRD and infrared

[0110] like Figure 5 The XRD diffraction patterns of three samples, paper, CMA, and CMAs, are shown. The paper has a characteristic diffraction peak at 9.8° at a 2θ angle, which corresponds to the crystal plane of cellulose. After MXene and AgNWs treatment, a new diffraction peak appears at 18.2°, which corresponds to the (002) crystal plane of MXene. This indicates that MXene is introduced into the paper-based sensor.

[86] The diffraction peak at 22.7° corresponds to the (200) crystal plane of AgNWs, which means that MXene and AgNWs have been introduced into the flexible paper-based sensor.

[0111] Figure 5 The FTIR spectrum analysis results of different samples are shown. The characteristic absorption peaks of paper-based cellulose can be clearly seen, among which the peak at wave number 2925cm -1 、1710cm -1 and 1098cm -1The peaks at 300 nm correspond to the CH, C=O, and CO stretching vibration peaks, respectively. Observing the spectral changes in the CM samples reveals the following key conclusion: with the addition of the MXene component, the vibration peak intensities of the CH and C=O groups gradually decrease, while the vibration peak intensity of the CO group gradually increases. This pattern of intensity changes clearly demonstrates that in the CMAs composite system, the MXene interacts with the paper cellulose, primarily forming chemical bonds involving carbon and oxygen.

[0112] A closer look at the spectrum of the CMAs composite material containing the water-repellent coating reveals a key phenomenon: the C=O group at 1710 cm -1 The vibration peak intensity at is higher than that of CM. The most reasonable explanation for this intensity increase is that it comes from the applied waterproof coating component, in which ethyl cellulose contains a large number of C=O functional groups. The increase in the C=O peak is consistent with the chemical properties of the coating component, and it also directly and strongly confirms the successful presence of the PVB / EC dual-functional waterproof coating on the surface of the CMAs composite material.

[0113] (3) Sensor waterproof performance

[0114] The waterproof performance depends on the synergistic effect of its surface wettability (contact angle) and pore structure. Figure 6 Figure a shows the contact angle test results of the samples. The contact angle of the untreated original paper-based material is 30.2°. After being modified with MXene and AgNWs, the contact angle of the CMA material increases slightly to 31.6°, indicating that the change in surface wettability is not significant. After being treated with a waterproofing material, the contact angle of the CMA increases to 76.3°, demonstrating that the waterproofing treatment effectively improves the hydrophobicity of the material, giving it good water-repellent properties. The significant increase in contact angle is mainly due to the formation of a hydrophobic layer on the surface of the material by the waterproofing material, which reduces the surface energy.

[0115] Figure 6 b shows the condition of CMAs samples after contact with different liquids, including water, juice, Sprite, alcohol, coffee, milk, honey and oil. It was found that the CMAs samples all showed excellent waterproof performance, reflecting their stability and good anti-penetration properties in a variety of liquid environments.

[0116] Example 4: Sensor Sensing Performance

[0117] (1) Sensor sensing mechanism

[0118] The sensing principle of CMAs flexible sensors essentially relies on the dynamic behavior of the pre-designed serrated crack structure in its conductive layer during bending deformation. In its original, unbending, straight state, the edges of these serrated cracks are in close contact with each other, forming a continuous electron conduction path. When the sensor is bent, as the bending angle increases, the steps of the serrated edges on either side of the crack gradually separate, causing the number of steps in contact to continuously decrease, and the gap distance increases proportionally with the degree of bending. This separation process eventually severs most or even all of the conductive path. Conversely, when the bend is released and the sensor returns to its straight state, the serrated edges on either side of the crack reappear and resume contact and connection, rebuilding the conductive network. The dynamic "disconnection-reconnection" process of the conductive path experienced by the sensor during the bending / recovery cycle is directly reflected in the significant change in its overall resistance. This resistance change serves as the core electrical signal for detecting the magnitude of bending deformation.

[0119] (2) The sensor's minimum detection angle and fastest response-recovery time

[0120] This study systematically tests the resistance change characteristics of CMAs paper-based sensors at small bending angles to comprehensively evaluate the dynamic response performance of the sensors, such as Figure 7 As shown in a, the sensor can accurately detect small bending angle changes as low as 0.5°, showing high sensitivity. Figure 7 As shown in Figure b, the sensor exhibits excellent dynamic response performance: a key observation is that when bending strain is applied, the sensor resistance rapidly reaches a new stable state within just 200 milliseconds. It is also worth noting that after the external force is removed, the resistance quickly recovers to its initial value within 200 milliseconds. This fast and symmetrical response is the core of its excellent dynamic performance, which can be attributed to the combined effect of two key factors: the good flexibility of the paper-based material itself and the efficient charge transport capability of the conductive network composed of MXene / AgNWs.

[0121] (3) Sensor sensing performance

[0122] When evaluating the performance of CMAs, two core parameters are crucial: sensitivity and linearity. Sensitivity reflects the sensor's response to bending deformation, that is, the resistance change caused by a change in each unit angle within a specific bending angle range, such as from 0° to 120°. Figure 8As shown in Figure a, the sensor exhibits a high sensitivity of 177 within this range, demonstrating its considerable sensitivity to bending deformation compared to paper-based sensors. Its resistance curve exhibits excellent linearity, indicating that the sensor's output and input signals maintain a highly predictable linear relationship across the entire measurement range, significantly simplifying subsequent signal calibration and usage.

[0123] The unique performance of this sensor under dynamic bending conditions is worth noting, such as Figure 8 As shown in Figure b, even in a scenario with speed fluctuations, which is common during paper machine operation, when the sensor is bent to a fixed angle of 30°, the peak value of its relative resistance change is stable. Experimental observations show that when the rate of applied bending strain varies within a wide range of 1 mm / s to 10 mm / s, the sensor's resistance response remains basically unchanged, exhibiting typical rate-independent sensing behavior.

[0124] Example 5: Long-term stability of sensors

[0125] To meet the key requirement of long-term wearable applications for durable hydrophobicity, which is mainly to effectively resist sweat penetration and corrosion, this study examined in detail the dynamic changes in the surface contact angle of CMAs flexible sensors after immersion in a simulated sweat environment for 60 minutes to evaluate the stability of their hydrophobic properties. Figure 9 As shown in Figure a, with increasing immersion time in sweat (1 min, 5 min, 10 min, 30 min, 40 min, and 60 min), the contact angle of the sensor shows a downward trend, with specific values ​​of 77.6°, 74.77°, 71.33°, 71.3°, 56.97°, and 54.63°, respectively. One observation is worth noting: the contact angle decreases only slightly during the first 10 minutes of immersion, only about 6.27°, indicating good sweat resistance at this stage. However, after the next 50 minutes, and after 30 minutes, the contact angle shows a significant and accelerated decrease, from 71.3° to 54.63°, a decrease of about 16.67°. This phenomenon clearly indicates that this may be related to the damage of the sizing agent on the sensor surface, resulting in a significant decrease in its hydrophobic properties.

[0126] In order to analyze the stability of CMAs in water, we monitored their mass loss after immersion in aqueous solution for different time periods. Figure 9As shown in Figure b, the CMAs experienced mass losses of 9%, 15%, and 20% after immersion in water for 10, 30, and 60 minutes, respectively. The key conclusion drawn from these observations is that, while the mass loss reached 20% after 60 minutes, the rate of loss was relatively manageable during the initial immersion period. This relatively high stability and long-term tolerance in aqueous environments is primarily due to the protective effect of the PVB / EC dual-function waterproof coating applied to the CMAs, which effectively slowed the rate of water erosion.

[0127] Example 6: Sensor Degradability

[0128] Reference Figure 10 As can be seen, this degradation experiment is intended to evaluate the degradation performance of CMAs samples in the natural environment to ensure their environmentally friendly properties after use. The experimental results show that the CMAs samples underwent degradation in the soil. By the 20th day, the sample surface began to loosen. On the 30th and 35th days, the CMAs samples began to gradually decompose, eventually transforming into fine fiber fragments. This performance test shows that CMAs samples degrade relatively quickly in the natural environment, have good biodegradability, can effectively reduce environmental pollution, and have the potential for application in sustainable smart wearable devices.

[0129] The degradability of sensors is a key performance aspect, which is closely related to environmental friendliness and sustainable development. Figure 10 b. The diagram of the degradation changes of CMAs samples in water shows significant changes during immersion. When the CMAs samples were immersed in water and stirred for 30 minutes, the back of the samples began to loosen and fall off. This change indicates that the initial degradation process of the CMAs material has begun and that it can quickly respond to changes in the water environment. After 60 minutes of continuous immersion, the CMAs samples have basically broken down into larger fragments, and the degradation rate has accelerated. This demonstrates that the material has the ability to dissolve in water and has good solubility and hydrolysis. Over time, after 240 minutes, the CMAs samples have broken down into fine fiber fragments and have fully entered the decomposition stage. This stage of the degradation process reflects the material's continuous degradation characteristics, allowing it to completely break down into smaller fragments in a short period of time, reducing its potential impact on the environment.

[0130] This set of diagrams depicting degradation changes demonstrates that CMA samples can be decomposed simply and quickly, without causing significant environmental harm. Compared to traditional electronic materials, CMAs offer the advantage of rapid degradation, avoiding the environmental pollution caused by long-term accumulation. This degradable design effectively reduces the burden on the ecological environment after use, ensuring that no persistent pollutants remain, in line with the concept of sustainable development.

[0131] Example 7: Wearable Sensor

[0132] (1) Sensor wearing comfort

[0133] from Figure 11 It can be seen that this study attached the new CMAs flexible sensor to the skin of the volunteers' forearms for five days, and also compared it with the areas covered by common polyurethane or PU film and standard Band-Aids.

[0134] The experimental results show that after the contact period, the sensor area composed of CMAs, which is the part marked with a red frame in the figure, showed good biocompatibility. The skin in this area did not report any significant discomfort, and no allergic contact reactions or signs of inflammation were observed. This shows that CMAs have advantages in microstructure design, surface properties, and potential natural biomass components, and can coexist with the human epidermis for a long time in a gentle and non-irritating manner. In contrast, the PU film (the control group, i.e., the area covered by the yellow frame) and the Band-Aid (i.e., the area covered by the blue frame) clearly showed a very prominent inflammatory reaction. This difference highlights the limitations of traditional polymer film materials such as PU or composite dressings in long-term skin-applied applications.

[0135] These results fully demonstrate that CMAs flexible sensors have low allergenicity and excellent skin tolerance, as well as being comfortable to wear, showing great potential in the field of wearable flexible electronic devices.

[0136] (2) Sensor signal transmission

[0137] This paper combines CMAs flexible sensors with Bluetooth signal transmission technology to verify the feasibility of the sensor in practical applications and realize wireless detection of human motion. The Bluetooth signal transmission module of the system is composed of a Bluetooth transmitter (BTT) and a microcontroller (MCU). Figure 12As shown in Figure c, the sensor, attached to the volunteer's wrist, monitors pulse changes after exercise, displaying regular and stable sensing signals. The sensor can also effectively track repetitive movements of finger joints, demonstrating high stability. In experiments, the sensor was attached to the volunteer's leg joints to measure signal transmission during flexion and extension. The results demonstrate the excellent sensitivity and sensing capabilities of the CMAs flexible sensor.

[0138] The above description is merely a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a soluble paper-based flexible smart wearable sensor, characterized in that: The following steps are involved: Step 1: Preparation of MXene Step 1.1: Slowly add lithium fluoride into a polytetrafluoroethylene beaker containing hydrochloric acid solution and stir magnetically. Then slowly add titanium aluminide powder in multiple portions and continue stirring at a constant temperature. Step 1.2: After the reaction is complete, wash the solid product and centrifuge to separate impurities. When the pH value of the supernatant is stable at 6, transfer it to a conical flask. Step 1.3: Ultrasonic treatment is performed in an ice-water environment, followed by centrifugation. The precipitate after centrifugation is collected and freeze-dried to obtain the MXene powder required for the experiment. Step 2: Preparation of MXene-anhydrous ethanol conductive solution Weigh MXene powder, add anhydrous ethanol, ultrasonicate the mixture, and seal it for storage to obtain a MXene-ethanol conductive solution. Step 3: Preparation of silver nanowires Step 3.1: Place PVP in an oil bath and stir to dissolve it in ethylene glycol to prepare a PVP-ethylene glycol solution; Step 3.2: Under light-shielding conditions, dissolve silver nitrate in ethylene glycol to obtain a silver nitrate-ethylene glycol solution, and dissolve sodium chloride in ethylene glycol to obtain a sodium chloride-ethylene glycol solution; Step 3.3: Place the PVP-ethylene glycol solution in a reactor, add the sodium chloride-ethylene glycol solution as a morphology modifier, heat, and maintain constant temperature with stirring; slowly add the silver nitrate-ethylene glycol solution dropwise, and continue stirring in an oil bath to react; Step 3.4: After the reaction is complete, the product is mixed with ethanol and centrifuged for purification to obtain high-purity silver nanowires. Step 4: Prepare PVB / EC waterproof material Weigh polyvinyl butyral and ethyl cellulose, add them into anhydrous ethanol to dissolve, stir magnetically to obtain PVB / EC waterproof material, and then store it at room temperature; Step 5: Preparation of paper-based flexible smart wearable sensors Using a soluble paper-based material as a carrier, MXene and silver nanowires are coated on the paper base to construct a conductive layer, and then a polyvinyl butyral / ethyl cellulose waterproof layer is scraped off to obtain a paper-based flexible smart wearable sensor with excellent conductive and waterproof properties.

2. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In step 1.1, the amount of lithium fluoride added is 1.6 g, 20 mL of 12 mol / L hydrochloric acid solution is pre-placed in the beaker, and the magnetic stirring rate is 500 r / min for 30 minutes; the amount of titanium carbon aluminide powder added is 1.0 g, and the reaction is stirred at a constant temperature of 50°C for 24 hours.

3. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In the step 1.2, the solid product is washed alternately with 1 mol / L hydrochloric acid and deionized water at a centrifugal speed of 4000 r / min.

4. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In the step 1.3, the ultrasonic treatment time is 2 hours, the centrifugal speed is 6000 r / min, the centrifugal time is 20 minutes, and the freeze-drying time is 12 hours.

5. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In step 2, the amount of MXene powder added is 50 mg, the amount of anhydrous ethanol added is 10 ml, and the ultrasonic treatment time is 30 to 60 minutes, and finally a MXene-ethanol conductive solution with a concentration of 5 mg / ml is obtained.

6. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In step 3.1, the PVP is a high molecular weight PVP with a molecular weight of 1,600,000, the added amount is 2 g, the oil bath temperature is 170° C., and the added amount of ethylene glycol is 160 mL, to prepare a PVP-ethylene glycol solution with a concentration of 12.5 g / L.

7. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In the step 3.2, the amount of silver nitrate added is 2 g, and the amount of ethylene glycol added is 40 mL, to obtain a silver nitrate-ethylene glycol solution with a concentration of 50 g / L; the amount of sodium chloride added is 67.2 mg, and the amount of ethylene glycol added is 160 mL, and the concentration of the sodium chloride-ethylene glycol solution is 0.42 g / L.

8. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In the step 3.3, the amount of PVP-ethylene glycol solution added is 160 mL, the amount of sodium chloride-ethylene glycol solution added is 16 mL, the mixture is heated to 110° C., the amount of silver nitrate-ethylene glycol solution added is 40 mL, the dropwise addition rate is 2 mL per minute, the oil bath temperature is 110° C., and the stirring reaction time is 12 hours.

9. The method for preparing a soluble paper-based flexible smart wearable sensor according to claim 1, wherein: In the step 4, the amount of polyvinyl butyral added is 2.5 g, the amount of ethyl cellulose added is 2 g, the amount of anhydrous ethanol added is 25 g, the temperature of magnetic stirring is 50° C., and the magnetic stirring time is 30 min.

10. Application of the preparation method of a soluble paper-based flexible smart wearable sensor according to claims 1-9 in sustainable smart wearable devices.

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