Implantable wireless flexible sensing system for monitoring urine content of bladder

Abstract

The invention belongs to the technical field of flexible sensing, and particularly relates to a preparation method of an implantable flexible sensor and a bladder urine content wireless monitoring system based on the sensor and a radio frequency mechanism. Wherein the performance of the sensor is improved by utilizing a microporous structure, n-octane is added into TPU to form a porous dielectric layer through a method of different temperatures and different liquid solubility, and the second dielectric layer is added into TPU by using a core-shell structure of silver nanowires and titanium dioxide, so that the anti-interference performance of the pressure-volume sensor is remarkably improved. In addition, the overall structure of the sensor is designed into a semi-bent snake-shaped structure, and the sensor has good pressure-volume performance, sensitivity, restorability and anti-interference performance. The elastic silicone rubber is used for packaging, so that the biocompatibility and practicability of the material are improved, and unstable factors such as body fluid invasion are eliminated. Meanwhile, a wireless sensing system based on a radio frequency mechanism is designed and manufactured, the urine content of the bladder can be wirelessly known from the outside, and related work such as medical care can be helped.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible sensing, and in particular relates to a preparation method of an implantable flexible sensor and a wireless monitoring system for bladder urine content based on this sensor and radio frequency mechanism. Background Art

[0002] The increasing demand for real-time health monitoring has led to the rapid expansion of the development and use of wearable and implantable sensors. As the "senses" of electronic devices, sensors can convert external signals into digital or analog signals, enabling humans to observe changes in the external environment through ordinary electronic devices. As an important application of flexible sensors, biometric signal acquisition places higher requirements on the diversity, sensitivity, accuracy, stretchability, and biocompatibility of flexible sensors.

[0003] The inventors found that although existing flexible pressure sensors can achieve the acquisition of physiological signals of the bladder, an organ in the body, they still face multiple challenges: on the one hand, their inherent wired connection method limits the convenience of long-term dynamic monitoring and it is difficult to achieve a truly wireless sensing function; on the other hand, the piezocapacitive sensor, as the core component, has significant shortcomings in mechanical adaptability, and its insufficient stretchability and sensitivity severely restrict its stable working ability in complex deformation environments. In addition, existing sensors generally rely on external power supply systems, and the self-powered design scheme has not yet broken through the practical bottleneck in terms of energy density, conversion efficiency, and environmental adaptability. Finally, the limitation of noise interference also needs to be considered, and these problems have greatly restricted their practical applications in wearable and implantable scenarios. Summary of the Invention

[0004] To solve the above problems, the present invention proposes a preparation method of a flexible piezocapacitive sensor and a wireless monitoring system for bladder urine content based on this sensor and radio frequency mechanism. To improve the sensitivity and stretchability of the flexible piezocapacitive sensor, using the improvement effect of microstructures on capacitance performance, a thermoplastic polyurethane elastomer rubber with good stretchability is selected and the first porous dielectric layer is prepared by a hybrid liquid phase separation method. Considering that implantable sensors are easily interfered by the environment and lead to unstable signals, silver nanowires and titanium dioxide and core-shell structures are added to the thermoplastic polyurethane elastomer rubber to increase the dielectric constant of the material and reduce the dielectric loss of the material, ultimately improving the anti-interference ability of the sensor, and the second dielectric layer is fabricated. Stretchable conductive silver paste is screen-printed on both sides of the dielectric layer to form electrodes. Using this flexible pressure sensor, a passive wireless sensing system is designed based on the radio frequency mechanism, enabling wireless monitoring of bladder volume in vitro, which has an auxiliary effect on the medical treatment of bladder diseases.

[0005] To achieve the above object, in a first aspect, the present invention provides a preparation method of a flexible piezocapacitive sensor, adopting the following technical solution:

[0006] A preparation method of a flexible piezocapacitive sensor, which prepares a dielectric layer and arranges conductive electrodes of the piezocapacitive sensor on both sides of the prepared dielectric layer.

[0007] A doped method is used to prepare a thin film to form a dielectric layer, improve the dielectric constant of the thin film, reduce the dielectric loss of the thin film, and improve the anti-interference ability. The dielectric layer is constructed by doping a core-shell structure formed by silver nanowires (AgNWs) and titanium dioxide (TiO2) into thermoplastic polyurethane (TPU) to form an anti-interference thin film (TPU@AgNWs@TiO2 thin film). Further, the preparation of the TPU@AgNWs@TiO2 thin film includes: adding thermoplastic polyurethane elastomer rubber (TPU) to an N,N-dimethylformamide (DMF) solution to form TPU solutions with different concentrations.

[0008] Further, an additive is prepared and incorporated into the matrix. 0.1 to 0.5 g of tetrabutyl titanate and 1 to 2 g of silver nanowires (AgNW) are added to 5 to 15 ml of an N,N-dimethylformamide solution, and ultrasonic oscillation is carried out for 20 minutes to obtain a core-shell structure of silver nanowires and titanium dioxide (AgNWs@TiO2). Ultrasonic treatment utilizes the cavitation effect of ultrasonic waves to generate a large number of tiny bubbles. When the bubbles burst, a huge amount of energy will be released, which helps to break the possible agglomerates of silver nanowires and make titanium dioxide more evenly dispersed on the silver nanowires, thereby forming a core-shell structure of silver nanowires and titanium dioxide. The formation of the core-shell structure is mainly based on the processes of adsorption, chemical reaction, and self-assembly between substances. To form a core-shell structure of silver nanowires and titanium dioxide, it is necessary for the titanium dioxide precursor to selectively adsorb and deposit on the surface of the silver nanowires and then be converted into titanium dioxide through further reaction and heat treatment.

[0009] Take 0.1 to 0.5 ml of the obtained solution of the core-shell structure of titanium dioxide and silver nanowires and add it to 5 to 15 ml of TPU solutions with different concentrations. Magnetically stir at room temperature for thirty minutes. After stirring evenly, use the spin-coating process to evenly cover the mixed solution on a circular hydrophilic carrier with a certain radius at a rotation speed of 200 - 300 revolutions to form a TPU@AgNWs@TiO2 thin film. Put the TPU@AgNWs@TiO2 thin film into a vacuum drying oven, remove the excess gas therein, and take it out after heating and curing for 40 minutes.

[0010] Further, a porous thin film is prepared by a method of mixed liquid phase separation. Different masses of thermoplastic polyurethane elastomer rubber (TPU) are added to an N,N-dimethylformamide (DMF) solution, and after mixing, magnetic stirring is carried out at 100 °C for 2 to 3 hours until completely dissolved to generate TPU solutions with different concentrations.

[0011] After that, a liquid separation process is carried out. After the solution is completely dissolved, 3 g of n-octane is added, and the mixture is stirred at 140 °C for 30 minutes. Then, while the solution is still not cooled, the mixed solution is evenly coated onto a circular hydrophilic carrier with a certain radius using a spin-coating process at a rotational speed of 200 - 300 revolutions to form a thin film. Then the thin film is placed in deionized water for 20 minutes, taken out and left to dry in a fume hood.

[0012] Furthermore, an anti-interference thin film prepared by a doping method and a porous thin film prepared by a mixed liquid separation method are used as the dielectric layer, and a stretchable conductive silver paste is used as the electrode layer to assemble a parallel plate (sandwich) structure sensor.

[0013] Furthermore, a flexible sensor is prepared. Two dielectric layers are overlapped and combined into one dielectric layer, and then cut into an annular serpentine shape using ultraviolet light. Then, screen printing is used on the upper and lower layers respectively to print the stretchable conductive silver paste onto the dielectric layer. Subsequently, the silver paste is cured at 125 °C to form a stretchable electrode. The electrode is led out using an enameled wire with a diameter of 1 mm.

[0014] Furthermore, for the encapsulation of the sensor, liquid elastic silicone rubber (Ecoflex) is evenly applied to the surface of the sensor and then cured at room temperature for 1 hour to form the encapsulation.

[0015] To achieve the above object, in a second aspect, the present invention also provides a flexible piezocapacitive sensor, adopting the following technical solution:

[0016] A flexible piezocapacitive sensor is obtained by using the preparation method of the flexible piezocapacitive sensor described in the first aspect.

[0017] To achieve the above object, in a third aspect, the present invention also provides a wireless monitoring system for bladder urine volume, adopting the following technical solution:

[0018] A wireless monitoring system for bladder urine volume is based on the radio frequency mechanism and the flexible sensor obtained by the flexible sensor preparation method described in the first aspect. A wireless monitoring system for bladder urine volume includes a flexible sensor, a sensing coil interconnected with the sensor to form an LC resonant circuit, a frequency acquisition circuit, a Bluetooth module, and a host computer.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] In the present invention, a capacitive sensor for wirelessly monitoring the urine volume in the bladder is designed in terms of its structure as a semi-curved serpentine structure, which has excellent piezocapacitive performance, sensitivity, recoverability, and anti-interference performance. Among them, by utilizing the promoting effect of the microstructure on the sensor performance, octane is added to thermoplastic polyurethane elastomer rubber to form a porous dielectric layer through a liquid-phase separation method with different temperatures and different liquid solubilities. The second dielectric layer uses a core-shell structure of silver nanowires and titanium dioxide added to thermoplastic polyurethane elastomer rubber, which improves the overall dielectric constant, reduces the dielectric loss, increases the polarization effect of the dielectric layer, and significantly improves the anti-interference performance of the piezocapacitive sensor. In addition, the adult structure of the sensor is designed, and the sensor is fabricated using ultraviolet lithography into an annular serpentine shape, which improves the stretchability and fatigue resistance of the sensor. Encapsulation with elastic silicone rubber improves the biocompatibility and practicality of the material and eliminates unstable factors such as body fluid intrusion. At the same time, a wireless sensing system based on the radio frequency mechanism is designed and fabricated, which can wirelessly obtain the urine volume in the bladder from outside the body to assist in relevant work such as medical care. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 is the signal acquisition and transmission process of the wireless monitoring system for the urine volume in the bladder based on a flexible sensor.

[0023] Figure 2 is a conceptual diagram of the flexible sensor

[0024] Figure 3 is the flowchart for preparing the dielectric layer of the flexible piezocapacitive sensor with high anti-interference performance

[0025] Figure 4 is the flowchart for preparing the dielectric layer of the flexible piezocapacitive sensor with high sensitivity

[0026] Figure 5 is the fabrication drawing of the flexible sensor shape

[0027] Figure 6 is the three-dimensional shape schematic diagram of the flexible piezocapacitive sensor

[0028] Figure 7 is the three-dimensional structure schematic diagram of the flexible piezocapacitive sensor

[0029] Figure 8It is a characterization diagram of silver nanowire and titanium dioxide (AgNWs@TiO2) materials. Figure 8(a) is a scanning electron microscope image (SEM) of AgNWs@TiO2 inside the dielectric layer in a flexible piezoresistive sensor; Figure 8 (b) is an energy-dispersive X-ray spectroscopy analysis test (EDS) of titanium element of AgNWs@TiO2 inside the dielectric layer in a flexible piezoresistive sensor; Figure 8 (c) is the EDS of silver element of the silver nanowire and titanium dioxide core-shell structure inside the dielectric layer in a flexible piezoresistive sensor

[0030] Figure 9 It is the surface SEM image of the porous thin film of the dielectric layer in a flexible piezoresistive sensor

[0031] Figure 10 It is a physical diagram of a flexible piezoresistive sensor

[0032] Figure 11 It is a comparison diagram of the capacitance response performance of the serpentine structure sensor at different bending angles of the flexible sensor

[0033] Figure 12 It is a stability test diagram of the flexible sensor under different urine contents

[0034] Figure 13 It is a comparison diagram of the piezoresistive anti-interference performance between different materials. It is concluded by comparison that the core-shell material film containing silver nanowire and titanium dioxide has the optimal anti-interference performance

[0035] Figure 14 It is a diagram of the change in the coil reflection coefficient at different urine contents in the bladder

[0036] Figure 15 It is a diagram of the change in the coil resonance frequency at different urine contents in the bladder

[0037] Figure 16 It is the upper computer interface of the wireless monitoring system for bladder urine content based on a flexible piezoresistive sensor. Specific implementation manners

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0039] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which this application belongs. It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0041] Wireless health monitoring systems have the ability to continuously collect health-related information, covering a wide range of data, including physiological parameters, metabolic status, and physical movement. By recording this data in real time, it is possible to closely track health conditions. To address the current pain points in urinary tract disease management and promote innovation in medical wearable technology, innovations in bladder monitoring are needed. Traditional bladder monitoring relies on invasive catheterization (which carries a high risk of infection) or bulky ultrasound equipment. Existing commercial wearable devices suffer from insufficient accuracy and reliance on wired connections or external power sources, making them unable to meet the needs of dynamic continuous monitoring. Flexible sensors, by integrating anti-interference design and self-powered technology, can stably sense bladder pressure changes in complex surface environments. Their high sensitivity can capture tiny volume fluctuations. Combined with wireless transmission, remote data monitoring is possible, allowing patients to complete high-precision bladder capacity assessments at home. Therefore, there is an urgent need to develop a wireless bladder urine volume monitoring device based on a flexible sensor with strong anti-interference capabilities, high sensitivity, and good stretchability.

[0042] Generally speaking, traditional bladder health monitoring systems are mainly composed of three key components: sensing devices, data transmission devices, and power supply devices. Among them, the sensing device is responsible for sensing real-time biological signals and converting them into electrical pulse signals, which are then wirelessly transmitted to the cloud or mobile phone for subsequent in-depth analysis. Both the sensing process and the data transmission process are now inseparable from the support of power supply. Compared with other ordinary electronic products, implantable sensor devices have special requirements in terms of power supply, and the impact of power supply on the body must also be considered. Therefore, the power supply needs to be placed outside the body and wireless sensing is used to collect bladder data.

[0043] As described in the background art, although the bladder urine volume monitoring device can monitor the bladder urine volume and contribute to clinical medicine, its inherent wired connection method limits the convenience of long-term dynamic monitoring. On the other hand, the current piezocapacitive sensor, as a key sensing unit, has inherent defects in terms of mechanical adaptability: its mechanical response characteristics (such as tensile deformation tolerance and dynamic signal sensitivity) are difficult to meet the stability requirements in complex deformation scenarios. At the same time, the traditional power supply mode relies on external energy supply, and the implanted self-powered technical solution has not yet broken through the technical barriers for industrial application in key indicators such as energy storage density, energy conversion efficiency, and environmental compatibility. In addition, the problem that the sensing system is easily interfered by environmental noise further exacerbates its reliability challenges in flexible wearable devices and in-vivo implanted devices, resulting in limited practical engineering applications.

[0044] Based on the above problems, in some embodiments, a method for fabricating a flexible sensor is provided, and a flexible sensor fabricated by using the method for fabricating a flexible sensor is provided. The sensor is a flexible piezocapacitive sensor containing two dielectric layers, capable of having strong anti-interference ability and piezocapacitive sensitivity. When receiving changes in the external environment, it can stably and sensitively generate capacitance changes, and a wireless monitoring system for bladder urine volume is built with this, as Figure 1 shown. The changes in bladder urine volume are collected by the sensor and the information is wirelessly transmitted through coil electromagnetic coupling. The change in the sensor signal can be stably sensed outside the body, that is, the change in the size of the bladder can be wirelessly monitored, realizing the wireless monitoring of bladder urine volume outside the body. As Figure 2 shown, it is a conceptual diagram of the flexible sensor. The proposed flexible piezocapacitive sensor includes a dielectric layer for improving sensitivity, a dielectric layer for assisting in improving anti-interference ability, and a structural design of the sensor, designing a flexible and highly stretchable semi-bent snake-like structure, and stretchable electrodes printed on both sides of the dielectric layer.

[0045] To achieve the sensitivity and high anti-interference performance of the flexible piezoresistive sensor, silver nanowires (AgNWs) and titanium dioxide (TiO2) core-shell structures are introduced into the thermoplastic polyurethane (TPU) matrix. AgNWs serve as the conductive network framework, and their high aspect ratio and three-dimensional cross-linked structure can form a stable conductive path, reducing signal fluctuations caused by external electromagnetic interference (EMI) or mechanical vibration. The TiO2 core-shell structure enhances the chemical stability of the material, inhibits the oxidation and agglomeration of AgNWs, and at the same time its porous characteristics can optimize the strain transfer efficiency and reduce the influence of environmental humidity or temperature changes on the dielectric layer performance. During the preparation process, AgNWs are compounded with TPU through the solution impregnation method to form a conductive network, and then the TiO2 shell layer is grown on the surface of AgNWs by the sol-gel method, finally constructing a core-shell reinforced TPU composite material with anti-interference ability. This structure effectively suppresses external noise interference through the synergistic effect of physical shielding (TiO2 shell layer) and electrical optimization (AgNWs network), while maintaining high sensitivity and cyclic stability.

[0046] The sensitivity of a sensor is increased using microstructures. The sensitivity dielectric layer film is a porous TPU film obtained by liquid phase separation. The principle of diffusion, volatilization, solvent replacement, and phase separation of n-octane from a solution of thermoplastic polyurethane (TPU) and N,N-dimethylformamide (DMF) under specific conditions is utilized to form a small hole structure. N-octane is added to the DMF solution of TPU. As a non-polar solvent, n-octane will disperse in DMF (a polar solvent) and have a certain interaction with TPU molecules. Due to the addition of n-octane, the solvent environment of the original TPU / DMF system is changed, causing a change in the solvation state around TPU molecules. At this time, a homogeneous mixed solution is formed, where TPU is dissolved in DMF in a molecular state and n-octane is dispersed therein. The presence of n-octane will, to a certain extent, reduce the solubility of DMF in TPU, creating conditions for subsequent phase separation. Then, treatments at different temperatures are carried out. As the temperature increases, the molecular thermal motion of n-octane and DMF intensifies. The boiling point of n-octane is relatively low (about 130 °C), and when the temperature approaches its boiling point, n-octane begins to volatilize in large quantities. The volatilized n-octane will form tiny bubbles in the solution, and these bubbles may serve as nucleation centers to promote the occurrence of phase separation. At the same time, the increase in temperature will change the solubility of TPU in DMF. Generally speaking, an increase in temperature will increase the solubility of TPU in DMF, but due to the presence and volatilization of n-octane, the solvent environment of the system becomes complex, resulting in an enhanced interaction between TPU molecules and gradually forming aggregates. During the cooling stage, the movement of TPU molecules slows down, further promoting the stability of the phase separation structure. Then, the samples treated with temperature are immersed in water. Water is a non-solvent and has very different properties from DMF and n-octane. Water will rapidly diffuse into the system and undergo a solvent replacement reaction with DMF and n-octane, finally leaving many small holes in the TPU matrix. The microstructures significantly improve the performance of piezocapacitive sensors by optimizing the material deformation characteristics, interface contact efficiency, and energy dissipation mechanism. Specifically, the porous microstructures make the change in dielectric constant and the reduction in electrode spacing more significant under pressure by increasing the effective contact area and the compressibility of the dielectric layer, thereby enhancing the capacitance response sensitivity; at the same time, the microstructure design can regulate the deformation uniformity, avoid local stress concentration, and ensure signal stability. In addition, the microstructures reduce the frictional contact area between the electrodes and the dielectric layer and the energy dissipation of viscoelastic materials. These synergistic effects enable the piezocapacitive sensors with microstructures to have high sensitivity, a wide dynamic range, and fast response characteristics.

[0047] A wireless monitoring system for the urine volume in the bladder, comprising a flexible piezocapacitive sensor, a sensing coil interconnected with the sensor to form an LC resonant circuit, a frequency acquisition circuit, a Bluetooth module, and a host computer. The flexible piezocapacitive sensor includes a flexible piezocapacitive sensor dielectric layer with high anti-interference performance, a flexible piezocapacitive sensor dielectric layer with high sensitivity, and a stretchable electrode. The basic principle of the frequency acquisition circuit is coil electromagnetic coupling. The chips used are the LDC1612 inductance-digital conversion chip and the CH583 chip.

[0048] The device of the flexible sensor in the wireless monitoring system for the urine volume in the bladder includes a flexible piezocapacitive sensor dielectric layer with high anti-interference performance and a flexible piezocapacitive sensor dielectric layer with high sensitivity. The fabrication of the flexible piezocapacitive sensor includes the following steps:

[0049] As Figure 3 shown, the preparation process of the flexible piezocapacitive sensor dielectric layer with high anti-interference performance is as follows:

[0050] Take 0.1 g of silver nanowires and add them to 5 mL of N,N-dimethylformamide (DMF) solution. Stir magnetically at room temperature for 4 hours to make the silver nanowires form a homogeneous suspension with DMF.

[0051] Add tetrabutyl titanate as a titanium dioxide precursor to the prepared silver nanowire suspension and stir magnetically at room temperature for 4 hours to mix evenly.

[0052] Add a small amount of deionized water to the mixed solution of tetrabutyl titanate and silver nanowires to initiate the hydrolysis reaction of tetrabutyl titanate to generate titanium dioxide.

[0053] Ultrasonically treat the above solution to fully mix the silver nanowires and titanium dioxide in the DMF solution and avoid local aggregation. Make the titanium dioxide disperse more evenly on the silver nanowires, thereby forming a core-shell structure of silver nanowires and titanium dioxide.

[0054] Take 0.2 g of silver nanowires and the titanium dioxide core-shell structure and add them to a mixed solution of 3 g of TPU and 15 mL of DMF stirred evenly. Stir at room temperature for 4 hours to make the core-shell structure uniformly mixed in the TPU solution, forming a TPU, AgNWs@TiO2 mixed solution.

[0055] Then perform the spin-coating process. First, heat the circular carrier to 135 °C, then drop the mixed solution into the circular carrier, and spin-coat at a rotation speed of 200 rpm for 3 seconds. After the spin-coating is completed, let it stand in a fume hood for 5 minutes to cool.

[0056] Put the circular carrier and TPU@AgNWs@TiO2 into water. After the film is separated from the carrier, put it into a drying oven to dry to obtain the flexible piezocapacitive sensor dielectric layer with high anti-interference performance.

[0057] As Figure 4As shown, the preparation process of the dielectric layer of the highly sensitive flexible piezoresistive sensor is as follows:

[0058] First, add 5 g of TPU to 17 g of DMF and stir magnetically at 90 °C for 3 hours to form a uniformly mixed TPU solution.

[0059] Add 7 g of n-octane to the TPU solution and stir magnetically at 135 °C for 1 hour until uniformly mixed.

[0060] Cover the mixed solution evenly on a suitable carrier through the spin coating process to form a thin film and then perform temperature treatment.

[0061] Place the above thin film and carrier on a 150 °C heating table for 1 minute

[0062] Put it into water, take it out and let it stand still after 30 minutes. Thus, the porous TPU thin film is made.

[0063] Fabrication and encapsulation of the highly anti-interference and highly sensitive implantable flexible piezoresistive sensor:

[0064] Overlay the highly anti-interference and highly sensitive piezoresistive dielectric layers to form a dielectric layer.

[0065] Print the stretchable conductive silver paste in a serpentine line shape on both sides of the dielectric layer through screen printing, and after high-temperature curing, it becomes the electrode of the flexible sensor. A parallel plate structure (sandwich type) flexible piezoresistive sensor is formed.

[0066] As Figure 5 shown, it is made into a semi-curved serpentine line shape by ultraviolet light cutting. Finally, Ecoflex is coated to complete the encapsulation of the sensor. [[ID=3)]] Figure 6 is the three-dimensional shape schematic diagram of the flexible piezoresistive sensor. Figure 7 is the three-dimensional structure schematic diagram of the flexible piezoresistive sensor.

[0067] Characterization of the materials and microstructures of the piezoresistive sensor is as Figure 8 shown, which is the material characterization diagram of silver nanowires and titanium dioxide (AgNWs@TiO2). 8(a) is the scanning electron microscope image (SEM) of AgNWs@TiO2 inside the dielectric layer of the flexible piezoresistive sensor; Figure 8 (b) is the energy-dispersive X-ray spectroscopy analysis test (EDS) of titanium element of AgNWs@TiO2 inside the dielectric layer of the flexible piezoresistive sensor; Figure 8 (c) is the energy-dispersive X-ray spectroscopy analysis test (EDS) of silver element of the core-shell structure of silver nanowires and titanium dioxide inside the dielectric layer of the flexible piezoresistive sensor, which can clearly show the core-shell structure of silver nanowires and titanium dioxide. As Figure 9 shown, it is the surface SEM of the porous thin film dielectric layer in the flexible piezoresistive sensor. AndFigure 10 Physical diagram of the flexible piezocapacitive sensor shown

[0068] The serpentine structure of the sensor was also designed, as Figure 11 shown, comparative tests were carried out on serpentine structures with different bending degrees, proving that the semi-bent serpentine structure has the optimal piezocapacitive sensing performance and tensile performance

[0069] The stability of the sensor was tested, as Figure 12 shown, it can maintain the stability of the read capacitance indication under different urine contents

[0070] As Figure 13 shown, the anti-interference of different materials was compared, and it can be proved that the flexible sensor has excellent anti-interference

[0071] In some embodiments, a preparation method of an implantable flexible piezocapacitive sensor with high sensitivity and high anti-interference includes the following steps

[0072] Take 0.2 grams of silver nanowires and add them to 5 milliliters of N, N-dimethylformamide (DMF) solution. After magnetic stirring at room temperature for 4 hours, the silver nanowires can form a homogeneous suspension with DMF. Add tetrabutyl titanate as a titanium dioxide precursor to the prepared silver nanowire suspension and stir magnetically at room temperature for 4 hours to mix evenly. Add a small amount of deionized water to the mixed solution of tetrabutyl titanate and silver nanowires to initiate the hydrolysis reaction of tetrabutyl titanate to generate titanium dioxide. Ultrasonically treat the above solution for 10 minutes. Take 0.2 grams of silver nanowires and the titanium dioxide core-shell structure and add them to a mixed solution of 3 g of TPU and 15 milliliters of DMF stirred evenly, and stir at room temperature for 4 hours to uniformly mix the core-shell structure in the TPU solution to form a TPU, AgNWs@TiO2 mixed solution. Then perform the spin-coating process. First, heat the circular carrier to 135 degrees Celsius, then drop the mixed solution into the circular carrier, and spin-coat at a speed of 200 revolutions per minute for 3 seconds. After the spin-coating is completed, let it stand in a fume hood for 5 minutes to cool. Put the circular carrier and TPU@AgNWs@TiO2 into water. After the straight film is separated from the carrier, put it into a drying oven to dry

[0073] 5 g of TPU was added to 17 g of DMF, and magnetically stirred at 90 °C for 3 hours to form a uniformly mixed TPU solution. 6 g of n-octane was added to the TPU solution, and magnetically stirred at 135 °C for 1 hour until uniformly mixed. The mixed solution was uniformly coated onto a suitably sized carrier by spin coating to form a film and then subjected to temperature treatment. The above-mentioned film and carrier were placed on a 150 °C heating stage for 1 minute and then immersed in water. After 30 minutes, they were taken out and left to stand, and thus the porous TPU film was completed. Fabrication and encapsulation of a highly anti-interference and highly sensitive implantable flexible piezocapacitive sensor: The highly anti-interference and highly sensitive piezocapacitive dielectric layers were overlapped to form a dielectric layer. Stretchable conductive silver paste was screen-printed in a serpentine shape on both sides of the dielectric layer and cured at high temperature to become the electrodes of the flexible sensor. A parallel-plate structure flexible piezocapacitive sensor was formed. Then it was fabricated into a semi-curved serpentine shape by ultraviolet light cutting. Finally, it was coated with Ecoflex for encapsulation.

[0074] In some embodiments, a method for preparing a highly sensitive and highly anti-interference implantable flexible piezocapacitive sensor includes the following steps:

[0075] 0.3 g of silver nanowires was added to 5 mL of N,N-dimethylformamide (DMF) solution, and magnetically stirred at room temperature for 4 hours to enable the silver nanowires to form a uniformly suspended solution with DMF. Tetrabutyl titanate was added as a titanium dioxide precursor to the prepared silver nanowire suspension, and magnetically stirred at room temperature for 4 hours to mix evenly. A small amount of deionized water was added to the mixed solution of tetrabutyl titanate and silver nanowires to initiate the hydrolysis reaction of tetrabutyl titanate to generate titanium dioxide. The above solution was ultrasonically treated for 10 minutes. 0.2 g of silver nanowire and titanium dioxide core-shell structure was added to a mixed solution of 3 g of TPU and 15 mL of DMF stirred evenly, and stirred at room temperature for 4 hours to uniformly mix the core-shell structure in the TPU solution to form a TPU, AgNWs@TiO2 mixed solution. Then spin coating was carried out. First, the circular carrier was heated to 135 °C, and then the mixed solution was dropped into the circular carrier and spin-coated at a speed of 200 revolutions per minute for 3 seconds. After spin coating, it was left to stand in a fume hood for 5 minutes to cool. The circular carrier and TPU@AgNWs@TiO2 were placed in water, and after the film was separated from the carrier, it was put into a drying oven to dry.

[0076] 5 g of TPU was added to 17 g of DMF and magnetically stirred at 90 °C for 3 hours to form a uniformly mixed TPU solution. 5 g of n-octane was added to the TPU solution and magnetically stirred at 135 °C for 1 hour until uniformly mixed. The mixed solution was uniformly coated onto a suitable carrier by a spin coating process to form a film and then subjected to temperature treatment. The above-mentioned film and carrier were placed on a 150 °C heating stage for 1 minute and then put into water, and taken out and left to stand after 30 minutes. Thus, the porous TPU film was fabricated. Fabrication and encapsulation of a highly anti-interference and highly sensitive implantable flexible piezocapacitive sensor: The piezocapacitive dielectric layers with high anti-interference and high sensitivity were overlapped to form a dielectric layer. Stretchable conductive silver paste was printed in a serpentine shape on both sides of the dielectric layer by screen printing and became the electrodes of the flexible sensor after high-temperature curing. A parallel-plate structure flexible piezocapacitive sensor was formed. Then it was fabricated into a semi-curved serpentine shape by ultraviolet cutting. Finally, it was coated with Ecoflex for encapsulation.

[0077] In some of the following embodiments, a wireless monitoring system for the urine volume in the bladder based on the above-mentioned flexible piezocapacitive sensor is provided. The wireless monitoring system for the urine volume in the bladder consists of an LC resonance circuit formed by interconnecting the flexible sensor in the body and an inductor coil, a resonance frequency acquisition circuit outside the body, and an upper computer.

[0078] Due to the increase in the urine volume in the bladder, the volume of the bladder changes, and the flexible sensor will generate a response based on this change, and the resonance frequency of the LC resonance circuit where it is located will change. This change can be collected by the external frequency acquisition device. The implementation principle is based on the basic characteristics of the LC resonance circuit. The LC resonance circuit consists of an inductor (L) and a capacitor (C). When the inductor and the capacitor are interconnected to form a resonance circuit, resonance can occur at a specific frequency. This resonance frequency is calculated by the following formula:

[0079]

[0080] where f is the resonance frequency, L is the inductance value, and C is the capacitance value. In the wireless monitoring device for the urine volume in the bladder, the capacitance value of the flexible sensor will change with the size of the bladder. When the system parameters deviate, it will cause the deviation phenomenon of the characteristic frequency of the resonance circuit; based on the principle of electromagnetic induction, by measuring the dynamic change of the mutual inductance coupling strength between the two coils, a highly sensitive detection of the resonance frequency detuning amount can be realized, that is, the change in the size of the bladder can be judged.

[0081] The flexible sensor exhibits a voltage response characteristic that is positively correlated with the change in bladder volume. That is, as the bladder filling state changes, its output voltage value shows a linear increasing trend. This sensor and the inductance coil also implanted in the body form a coupling system. The change in its voltage causes a change in the reactance parameter of the inductance coil, which in turn leads to a shift in the resonance frequency of the system. Since the sensor-coil coupling system forms an electromagnetic coupling network with the external coil, this shift in the resonance frequency will be transmitted to the external coil through the electromagnetic field coupling effect, manifested as a shift in the characteristic frequency point in the system impedance spectrum. This phenomenon can be quantitatively characterized by monitoring the S11 parameter (i.e., the return loss parameter) in the S parameters. The external monitoring circuit uses vector network analysis technology to collect the change in the S11 parameter in real time and transmits the digital spectrum data to the host computer processing platform through the Bluetooth wireless transmission module, enabling accurate reconstruction of the bladder volume parameter.

[0082] As Figure 14 and Figure 15 shown, the wireless monitoring system for bladder urine content was tested, and accurate data can be read under the condition of bladder urine content from 0 to 120 milliliters.

[0083] The external frequency acquisition circuit integrates a spiral inductance coil on the top layer of the flexible printed circuit board (FPCB) to capture the radio frequency signal transmitted by the fiber sensing coil. Both ends of the receiving coil are connected to the LDC1612 DNTT type inductance-digital conversion chip to complete the accurate analog-to-digital conversion of the analog signal. Subsequently, the digital signal is transmitted to the microcontroller unit (MCU) through the I 2 C bus protocol for data processing. Finally, the data is wirelessly transmitted to the host computer system using the Bluetooth low energy (BLE) module embedded in the MCU to achieve real-time monitoring and visualization.

[0084] In terms of the integration of the frequency acquisition circuit, the present invention provides a small and convenient data acquisition circuit board with a size of 2cm * 6cm. This circuit board integrates the capacitance signal acquisition, the controller circuit, and the Bluetooth wireless data transmission. This system uses a spiral inductance coil integrated on the flexible circuit board (FPC) as the radio frequency signal receiving front end, and uses the LDC1612 inductance-digital conversion chip to achieve impedance spectrum analysis. Its output signal is transmitted to the main control unit (optional CH583, STM32H743, ESP32-C6, or FPGA, etc.) through the I 2 C / SPI bus. After completing the digital signal processing, wireless transmission is achieved through the integrated BLE 5.3 module (such as nRF52840).

[0085] As Figure 16 shown, Figure 16The display interface of the represented terminal host computer can be transmitted to the host computer for display through the frequency acquisition circuit via Bluetooth. The host computer is built using Qt, and the process includes: environment configuration, project creation (select the QMainWindow or QWidget base class, configure the.pro file to add QT += serialport to support serial communication), interface design (drag and drop controls such as QSerialPort and QPushButton through Qt Designer, set the layout and object naming), and function implementation.

[0086] In summary, the flexible piezocapacitive sensor prepared in the embodiment has good piezocapacitive performance, anti-interference ability, and excellent mechanical properties. The wireless bladder urine volume monitoring system prepared based on the flexible piezocapacitive sensor and radio frequency mechanism has the ability to wirelessly collect and transmit bladder size parameters and detect the urine volume in the bladder, solving the infection risk of traditional catheterization. Its multi-parameter fusion monitoring - (pressure / volume / electromagnetic signal) provides early warning for bladder dysfunction and promotes the development of implantable medical devices towards ultra-thin flexibility and closed-loop treatment.

[0087] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a flexible sensor, characterized in that, To prepare a flexible piezocapacitive sensor with a semi-bent serpentine structure, the following steps are included: Fabricate a highly anti-interference dielectric layer by doping. Incorporate the core-shell structure of silver nanowires and titanium dioxide with different masses into the TPU solution, and generate a thin film through the spin-coating process. Fabricate a highly sensitive dielectric layer by the method of hybrid liquid phase separation to produce a porous thin film. Overlap the two thin films and set electrode layers on both sides.

2. The method for preparing a flexible sensor according to claim 1, wherein, Prepare the highly anti-interference dielectric layer, including: Add 0.1 g to 0.3 g of silver nanowires into 5 mL of DMF solution, and magnetically stir to make the silver nanowires form a homogeneous suspension with DMF; Add tetrabutyl titanate and a small amount of deionized water to the suspension and magnetically stir until evenly mixed. Ultrasonically treat the above solution to fully mix the silver nanowires and titanium dioxide in the DMF solution; Add 0.2 g of the silver nanowire and titanium dioxide core-shell structure to the mixed solution of 3 g of TPU and 15 mL of DMF and stir evenly, and stir at room temperature for 4 hours to uniformly mix the core-shell structure in the TPU solution to form a TPU, AgNWs@TiO2 mixed solution; Then perform the spin-coating process. First, heat the circular carrier to 135 °C, then drop the mixed solution into the circular carrier, and spin-coat for 3 seconds at a rotation speed of 200 rpm. After the spin-coating is completed, let it stand in the fume hood for 5 minutes to cool; Place the circular carrier and TPU@AgNWs@TiO2 in water. After the film is separated from the carrier, put it into the drying oven to dry to obtain the highly anti-interference dielectric layer.

3. The method for preparing a flexible sensor according to claim 1, wherein, Prepare the highly sensitive dielectric layer, including: First, add 5 g of TPU to 17 g of DMF, and magnetically stir at 90 °C for 3 hours to form a uniformly mixed TPU solution; Add 7 g of n-octane to the TPU solution, and magnetically stir at 135 °C for 1 hour until evenly mixed; Uniformly cover the mixed solution on a carrier with a suitable area through the spin-coating process to form a thin film and then perform temperature treatment; Place the above thin film and carrier on a 150 °C heating table for 1 minute and then put it into water. Take it out and let it stand after 30 minutes. Thus, the porous TPU thin film is fabricated.

4. The method for preparing a flexible sensor according to claim 1, wherein Set the sensor electrodes, including: Use the screen printing process to print conductive silver paste with a semi-bent serpentine structure on both sides of the dielectric layer.

5. The method for preparing a flexible sensor according to claim 1, characterized in that, Package the flexible piezocapacitive sensor, including: Use ultraviolet light to cut the thin film into a semi-bent serpentine structure, then use enameled wire to lead out the electrodes, and finally evenly apply liquid Ecoflex on the sensor. After curing at room temperature for 2 hours, the packaging of the sensor is completed.

6. The method for preparing a flexible sensor according to claim 1, characterized in that Use the porous TPU and TPU@AgNWs@TiO2 thin films as the dielectric layer, and the stretchable conductive silver paste as the electrode layer to assemble a sandwich-structured sensor.

7. Sensor, characterized in that, Prepared by using the flexible sensor preparation method described in any one of claims 1-6.

8. A bladder urine volume monitoring system, characterized in that, A flexible sensor, a data acquisition circuit, and a host computer; the flexible sensor uses the sensor described in claim 7.

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