Visual flexible yarn strain sensor and preparation method and application thereof

Abstract

The application discloses a visual flexible yarn strain sensor and a preparation method and application thereof, and steps are as follows: a TPU and TPE mixed spinning solution is prepared; the TPU and TPE mixed spinning solution is used to prepare a fluorescent flexible fiber base TPU-TPE fiber of the sensor through a wet spinning process; a PDMS liquid bead is dropped on the base and is solidified to prepare a heterogeneous structure to obtain a TTS fluorescent porous fiber; two TTS fibers are twisted through a twisting machine, the liquid beads on the fibers are staggered in the twisting process, and a TTS yarn is obtained; then the yarn is soaked in a dopamine Tris buffer solution, reacts at normal temperature, is cleaned and dried after the reaction is completed, and a TTS@PDA yarn with a surface loaded with polydopamine is obtained; the TTS@PDA yarn loaded with the polydopamine is used to load polypyrrole PPy through an in-situ frozen interface polymerization method, and a TTS@PDA@PPy yarn (a SCFY strain sensor) is obtained. The product prepared by the application has strain visualization, high sensitivity, a wide strain range, an ultralow detection limit and excellent cyclic use, and meets the demand of wearable medical monitoring equipment.

Description

Technical Field

[0001] This invention relates to the field of wearable medical monitoring equipment technology, specifically to a visual flexible yarn strain sensor, its preparation method, and its application. Background Technology

[0002] Epilepsy is a neurological disorder with a persistent tendency to cause seizures. Currently, treatment primarily involves long-term medication. Detailed medical records and seizure history are crucial for diagnosis, serving as essential evidence. However, current real-time monitoring of the physiological state of epilepsy patients is often incomplete, and doctors lack access to detailed patient information. If a seizure is not detected promptly, it can lead to sudden epileptic death (SUDEP). Therefore, real-time monitoring of epilepsy patients is of paramount importance.

[0003] Wearable medical devices have great potential to improve individual health management and prevention. They can monitor physiological signals and joint activity signals in the human body in real time. As one of the key components in wearable electronic devices, strain sensors can convert mechanical signals into detectable resistance signals and have been widely used in health monitoring, electronic skin and intelligent robots.

[0004] Compared to traditional sensor substrates, yarn strain sensors can be directly woven or embroidered onto textiles, exhibiting excellent tensile strength, abrasion resistance, and integrability, showing great promise for applications in flexible electronics. However, the inherent contradiction between high sensitivity and wide sensing range limits their further development as high-performance strain sensors, restricting their application and preventing the simultaneous monitoring of weak human signals (strain ≤1%), such as pulse and heartbeat, and vigorous human movements, such as jumping and running. To develop stretchable yarn strain sensors, various flexible polymers, such as polydimethylsiloxane, silicone rubber, and polyurethane, have been used as stretchable supports, while carbon nanotubes, silver nanowires, and conductive polymers have been used as conductive materials.

[0005] Wearable technology is increasingly being used to monitor neurological disorders such as epilepsy. Flexible, stretchable strain sensors have attracted widespread research interest due to their ability to withstand greater external strain and their significant potential for real-time monitoring of human movement and health. Good stability, high sensitivity, and a wide strain range are crucial for the development of wearable medical monitoring devices. However, developing a stretchable yarn strain sensor that simultaneously possesses high sensitivity and a wide operating range remains a challenge for future wearable sensing technology. Summary of the Invention

[0006] Technical problems solved: To address the technical problems of existing yarn strain sensors, such as the inability to simultaneously achieve high sensitivity and wide sensing range, and the inability to monitor weak signals, this invention proposes a visual flexible yarn strain sensor, its preparation method, and its application. The prepared product has high sensitivity, wide strain range, ultra-low detection limit, and excellent recyclability, meeting the needs of wearable medical monitoring devices.

[0007] Technical solution: A method for fabricating a visual flexible yarn strain sensor, comprising the following steps:

[0008] Step 1: Prepare a mixed spinning solution of thermoplastic polyurethane (TPU) and tetraphenylethylene (TPE);

[0009] Step 2: Prepare porous TPU-TPE fibers. The TPU and TPE mixed spinning solution is used to prepare the fluorescent flexible fiber substrate TPU-TPE fibers of the sensor through a wet spinning process.

[0010] Step 3: Prepare TTS fluorescent porous fibers by dropping PDMS liquid droplets onto the substrate and curing them to prepare a heterogeneous structure to obtain TTS fluorescent porous fibers.

[0011] Step 4: Prepare TTS@PDA yarn. The two TTS fibers obtained in Step 3 are twisted using a twisting machine. One end of the fiber is held while the other end rotates around the axis to obtain a yarn with a fixed number of twists. During the twisting process, the liquid droplets on the fiber are arranged alternately to obtain TTS yarn. Then, the TTS yarn is immersed in Tris buffer solution of dopamine and reacted at room temperature. After the reaction is completed, it is washed and dried to obtain TTS@PDA yarn with polydopamine loaded on the surface.

[0012] Step 5: Prepare TTS@PDA@PPy yarn, i.e., a visual flexible yarn strain sensor. TTS@PDA yarn loaded with polydopamine is loaded with PPy through in-situ frozen interfacial polymerization to obtain TTS@PDA@PPy yarn, i.e., a visual flexible yarn strain sensor (named SCFY strain sensor).

[0013] Preferably, the preparation method of the TPU and TPE mixed spinning solution in step one is as follows: TPU and TPE are dissolved in the solvent DMF and dissolved in a shaking water bath at 50°C to obtain the TPU and TPE mixed spinning solution, wherein the ratio of TPU to DMF in the mixed spinning solution is 60g:147.6mL, and the concentration of TPE in the mixed spinning solution is 1-5mg / mL.

[0014] As a preferred embodiment, the wet spinning process in step two is as follows: the spinning solution is injected into a mixed coagulation bath of IPA / water = 0-80wt% at an extrusion speed of 0.1-2mL / min. After the obtained fibers are fully cross-linked in the coagulation bath for 24 hours, porous TPU-TPE fibers are obtained.

[0015] Since DMF diffuses into water more easily than IPA, adding IPA to the coagulation bath can slow down the coagulation rate. Therefore, by controlling the concentration of IPA, uniform and regular pores can be formed inside the fiber.

[0016] As a preferred embodiment, the preparation of a heterogeneous structure by dripping PDMS liquid droplets onto the substrate and curing them in step three is as follows: PDMS liquid droplets are dripped onto the surface of TPU-TPE fibers using a flat-tipped needle, with a distance of 1 cm between the droplets, to construct a heterogeneous liquid droplet structure on the fiber surface. Then, the fiber is placed in a 60°C forced-air oven for curing for 12 hours to obtain TPU-TPE@PDMS fluorescent porous fibers.

[0017] The preparation of heterogeneous structures by adding PDMS droplets and curing them involves designing a heterogeneous structure by adding PDMS droplets to the fiber surface based on the principle of surface stress redistribution. A single-sided droplet structure is formed by the balance between the gravity and surface tension of PDMS, and then cured in an oven.

[0018] Preferably, in step four, the TTS yarn is soaked in a Tris buffer solution containing dopamine, with a yarn-to-tris buffer solution ratio of 0.2g:200mL. The Tris buffer solution containing dopamine is prepared as follows: a 10mM dopamine (DA) solution is dissolved in the Tris buffer solution, and 0.1M HCl solution is added to adjust the pH to 8.5. The reaction is carried out at room temperature for 36 hours to initiate the self-polymerization of DA. After the reaction is completed, the yarn is washed with distilled water and air-dried to obtain TTS@PDA yarn with polydopamine loaded on the surface.

[0019] Preferably, the in-situ frozen interface polymerization method in step five is as follows: The TTS@PDA yarn is placed in a petri dish containing a mixed solution of 0.4M ferric chloride and 0.4M NaSSA, wherein the ratio of TTS@PDA yarn to the mixed solution is 0.1g:10mL, and frozen at -5℃ for 2 hours; subsequently, an equal volume of cyclohexane solution containing different concentrations of pyrrole monomers is poured into the above petri dish, and freezing is continued for 1 hour, wherein the molar ratio of pyrrole monomers to ferric chloride is (0.25~2):1; finally, the petri dish is statically maintained at 5℃ for polymerization for 12 hours; the yarn is removed, washed with distilled water, and the TTS@PDA@PPy yarn, i.e., the visual flexible yarn SCFY strain sensor, is obtained.

[0020] A visual flexible yarn strain sensor was prepared based on the above method.

[0021] Based on the above, a visual flexible yarn strain sensor is used in the fabrication of wearable sensing devices.

[0022] Preferably, the wearable sensing device is a wearable medical monitoring device.

[0023] Preferably, the medical monitoring device is a medical monitoring device for epilepsy patients.

[0024] Beneficial effects: This invention proposes a strategy that combines the heterogeneous structure of solidified liquid droplets with a twisting process, and the resulting visualized flexible yarn strain sensor has excellent resistance and fluorescence response performance.

[0025] This invention utilizes the heterogeneous structure of liquid droplets solidified on the fiber surface and the crack structure of conductive polymers to synergistically improve the sensitivity of the strain sensor. Subsequently, a yarn twisting process involving displaced liquid droplets further enhances the strain sensing range, ultimately resulting in a yarn strain sensor (SCFY strain sensor). Thanks to this dual-structure design, the SCFY strain sensor achieves high sensitivity (GF = 58.9 at strain 143-180%), a wide strain range (0-184%), an ultra-low detection limit (<0.1%), and excellent cycle life (>2000 cycles), meeting the requirements of wearable medical monitoring devices. By simulating the epileptic seizure process, the SCFY strain sensor acquires resistance signals such as pulse, heart rate, facial expression, and joint movement to achieve real-time monitoring of epilepsy patients. Simultaneously, leveraging the fluorescent visualization characteristics of the SCFY strain sensor, a self-made monitoring device enables nighttime monitoring of epilepsy patients.

[0026] Compared with existing technologies, as shown in Table 1 below, the sensor prepared in this invention not only possesses excellent photothermal responsibility but also exhibits visualized fluorescent crack features. In wearable medical monitoring devices, it can monitor not only large strains in the human body such as fingers, arms, and knees, but also minute strains in pulse, heartbeat, and facial expressions. Applying this sensor to comprehensive real-time monitoring of epilepsy patients provides data that not only helps patients and doctors gain a more objective and comprehensive understanding of the individualized characteristics of epileptic seizures but also provides a reliable basis for locating epileptic foci and developing treatment plans.

[0027] Table 1

[0028]

[0029] Note:

[0030] [1]Xinxin, Z.; Hao, G.; Peng, D.; Wei, Z.; Chuntai, L.; Changyu, S.; Kun, D. Hollow-porous fiber-shaped strain sensor with multiple wrinkle-crackmicrostructure for strain visualization and wind monitoring. Nano Energy2023,108,108197.

[0031] [2]Song, Y.;Niu,L.;Ma,P.;Li,X.;Feng,J.;Liu,Z.

[0032] [3] Yanli, W.;Wenjing, Q.;Min, Y.;Zhenhao, T.;Wenjin, G.;Jinkun, S.;Xiang, Z.;Bin, F.;Baigang, A.;Ruimin, S.;Shougen, Y.;Zunfeng, L. High Linearity, Low Hysteresis Ti3C2Tx MXene / AgNW / Liquid Metal Self-Healing Strain Sensor Modulated by Dynamic Disulfide and Hydrogen Bonds. Adv. Fun. Mater. 2023, 33, 2301587. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] in:

[0035] Figure 1 Flowchart of the fabrication process for the SCFY strain sensor.

[0036] Figure 2 Figure 1: Strength test results of TPU-TPE fibers with different TEP concentrations corresponding to Comparative Example 1.

[0037] Figure 3 Characterization diagrams of TPU-TPE fibers prepared with different IPA concentrations in Comparative Example 2. From left to right, each column in the figure represents 0%, 30wt%, 45wt%, 60wt%, and 80wt%, respectively. From top to bottom in each column, the characterization diagrams are 50μm, 5μm, and pore size analysis diagrams.

[0038] Figure 4 The resistance values ​​of the SCFY strain sensor corresponding to different n(Py) / n(FeCl3) ratios in Comparative Example 3.

[0039] Figure 5 Example 1: The temperature change curve of the SCFY strain sensor under near-infrared (NIR) light irradiation over time.

[0040] Figure 6 Example 1: Physical diagram, mechanism and application of the controllable resistance adjustment device.

[0041] Figure 7 In Application Example 2, (a) the fluorescent crack effect of the SCFY strain sensor under different strains; (bd) the crack distribution of the SCFY strain sensor under 30%, 60% and 90% strains.

[0042] Figure 8 In Application Example 3, (ad) the SCFY strain sensor monitors the human fingers, wrists, arms, and knee joints respectively; (ef) the SCFY strain sensor monitors the pulse and heartbeat respectively; and (g) the SCFY strain sensor is used to recognize lip movements.

[0043] Figure 9 In application example 4, (a) is a schematic diagram of the SCFY strain sensor monitoring device; (b) the SCFY strain sensor monitoring device monitors the knee of the test subject; and (c) the presence or absence of fluorescence can be observed through mobile phone monitoring. Detailed Implementation

[0044] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples and corresponding drawings.

[0045] Unless otherwise specified, the raw materials and instruments used in the examples in this specification are all from commercially available products.

[0046] Example 1

[0047] A method for fabricating a visual flexible yarn strain sensor, see [link to documentation]. Figure 1 The steps are as follows:

[0048] Step 1: Prepare a mixed spinning solution of thermoplastic polyurethane (TPU) and tetraphenylethylene (TPE). Dissolve TPU and TPE in DMF solvent and place the solution in a shaking water bath at 50°C to obtain the mixed spinning solution of TPU and TPE. The mass of TPU is 60g, the volume of DMF is 147.6mL, and the concentration of TPE is 2mg / mL.

[0049] Step 2: Preparation of porous TPU-TPE fibers. The TPU and TPE mixed spinning solution is used to prepare the fluorescent flexible fiber substrate TPU-TPE fibers of the sensor through a wet spinning process. The wet spinning process is as follows: the spinning solution is allowed to stand for 2 hours to remove air bubbles, then added to a syringe. The spinning solution is injected into a mixed coagulation bath of IPA / water = 45% through an injection pump connected to the syringe at an extrusion speed of 0.3 mL / min. The obtained fibers are fully cross-linked in the coagulation bath to obtain porous TPU-TPE fibers.

[0050] Step 3: Preparation of TTS fluorescent porous fibers. PDMS liquid droplets are dropped onto the substrate and cured to prepare a heterogeneous structure to obtain TTS fluorescent porous fibers. Specifically, PDMS liquid droplets are dropped onto the surface of TPU-TPE fibers using a flat-tipped needle, with a distance of 1 cm between the droplets, to construct a heterogeneous liquid droplet structure on the fiber surface. Then, the fibers are placed in a 60℃ forced-air oven for 12 hours to cure, thus obtaining TPU-TPE@PDMS fluorescent porous fibers.

[0051] Step 4: Preparation of TTS@PDA yarn. The two TTS fibers obtained in Step 3 are twisted using a twisting machine. One end of the fiber is held while the other end rotates around the axis, ultimately obtaining a yarn with a fixed number of twists. During the twisting process, the liquid droplets on the fiber are arranged alternately to obtain TTS yarn. Then, 0.3g of the yarn is immersed in 200mL of Tris buffer containing dopamine and reacted at room temperature. After the reaction, it is washed and dried to obtain TTS@PDA yarn with polydopamine surface loading. The Tris buffer containing dopamine is prepared as follows: a 10mM dopamine (DA) solution is dissolved in the Tris buffer, and 0.1M HCl solution is added to adjust the pH to 8.5. The reaction is carried out at room temperature for 36h to initiate the self-polymerization of DA. After the reaction, it is washed with distilled water and air-dried to obtain TTS@PDA yarn with polydopamine surface loading.

[0052] Step 5: Preparation of TTS@PDA@PPy yarn. TTS@PDA yarn loaded with polydopamine is loaded with PPy via in-situ cryo-interfacial polymerization to obtain TTS@PDA@PPy yarn, which is a visual flexible yarn strain sensor (named SCFY strain sensor). The in-situ cryo-interfacial polymerization steps are as follows: 0.1g of TTS@PDA yarn is placed in a petri dish containing a 10mL mixture of 0.4M ferric chloride and 0.4M NaSSA, and frozen at -5℃ for 2h; subsequently, an equal volume of cyclohexane solution containing different pyrrole monomer concentrations (n(Py) / n(FeCl3) = 0.25-2.0) is poured into the above petri dish, and freezing continues for 1h; finally, the petri dish is statically maintained at 5℃ for polymerization for 12h; the yarn is then removed and washed with distilled water to obtain the TTS@PDA@PPy yarn, which is the visual flexible yarn strain sensor.

[0053] Example 2

[0054] Same as Example 1, except that the TPE concentration in step one is 4 mg / mL; the injection pump extrusion speed in step two is 0.6 mL / min, and the coagulation bath IPA / water ratio is 60 wt%; and the pyrrole concentration n(Py) / n(FeCl3) in step five is 1.0.

[0055] Example 3

[0056] Same as Example 1, except that the TPE concentration in step one is 5 mg / mL; the injection pump extrusion speed in step two is 1.0 mL / min, and the coagulation bath IPA / water ratio is 60 wt%; and the pyrrole concentration n(Py) / n(FeCl3) in step five is 1.0.

[0057] Comparative Example 1

[0058] Similar to Example 2, except that only steps one and two were used to prepare TPU-TPE fibers. The TPE concentrations were 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, and 5 mg / mL, respectively. Strength tests were conducted on the TPU-TPE fibers with five different TPE concentrations. Figure 2 As can be seen, when the TPE content is 4 mg / mL, a maximum stress of 19.83 MPa and a strain of 588.7% are obtained.

[0059] Comparative Example 2

[0060] Similar to Example 2, except that only steps one and two are used to prepare TPU-TPE fibers. The IPA / water ratio in the coagulation bath was 0 wt%, 30 wt%, 45 wt%, 60 wt%, and 80 wt%. Different IPA concentrations resulted in fibers with different pore sizes. Figure 3As can be seen, the fiber pore size is the smallest and most uniform when IPA / water = 60%.

[0061] Comparative Example 3

[0062] Similar to Example 2, except that in step five, the pyrrole concentration n(Py) / n(FeCl3) = 0.25, 0.5, 1.0, 1.5, and 2.0. The resistance values ​​of the TTS@PDA@PPy yarns prepared with different pyrrole concentrations were measured using a multimeter. Figure 4 It can be seen that the yarn resistance is lowest when n(Py) / n(FeCl3)=1.0.

[0063] Application Example 1: Photothermal Conversion Performance and Intelligent Variable Resistance Application of SCFY Strain Sensor

[0064] To further improve the practicality and user experience of wearable medical monitoring devices, this study explores the introduction of Personal Thermal Management (PTM) technology to achieve specific temperature control and health management. Photothermal conversion technology converts light energy into heat energy through reflection or absorption, aligning with green, environmentally friendly, and energy-saving principles. Furthermore, the photothermal conversion performance of the SCFY strain sensor under near-infrared (NIR) irradiation was investigated. Figure 5 As can be seen, after 15 seconds of NIR irradiation, the surface temperature of the SCFY strain sensor, woven into a "JN" letter pattern, rapidly increased from 27.6℃ to 36.6℃, demonstrating excellent photothermal conversion performance. Based on this, by combining photothermal conversion technology with flexible yarn strain sensing technology, it is hoped to construct wearable health monitoring devices with temperature control and physiological activity monitoring functions.

[0065] By utilizing the tensile resistance properties of the SCFY strain sensor, a controllable resistance adjustment device was fabricated. This device intelligently regulates the intensity of LED lighting by controlling the current in the circuit. Specific details are as follows: Figure 6 As shown, when the device is adjusted to different settings (specifically manifested as different tensile deformations of the SCFY strain sensor), the LED light obtains different light intensities of 1476 lux, 260 lux, 74 lux and 28 lux respectively at 6V voltage.

[0066] Application Example 2: Fluorescent Crack Characterization of the SCFY Strain Sensor

[0067] like Figure 7 As shown in (a), in its original state, the PPy layer can shield ultraviolet light. However, when stress is applied, the conductive layer on the surface cracks, exposing the TPU / TPE substrate within the fiber, which then emits blue fluorescence under ultraviolet light. By applying different strains, the SCFY strain sensor produces cracks of varying degrees, achieving a visual effect with tunable fluorescence. Furthermore, Figure 7(bd) Crack distribution of the SCFY strain sensor under different tensile strains was observed using an optical microscope. It can be seen that when the strain changes from 30% to 90%, the crack area increases from 1.35% to 13.2%, showing a linear relationship. Therefore, the SCFY strain sensor possesses unique fluorescence strain visualization capabilities, demonstrating excellent prospects for visual sensing applications.

[0068] Application Example 3: Wearable Applications of the SCFY Strain Sensor

[0069] To verify the application prospects of the proposed SCFY strain sensor as a wearable medical device for human joints, the SCFY strain sensor was fitted to the fingers, wrists, arms, and knees of test subjects, and the resistance sensing signal of the SCFY strain sensor was recorded in real time during joint movement. Figure 8 (ad)). Experimental results show that when the test area bends, the SCFY strain sensor exhibits a tensile state. The resistance increases accordingly based on the degree of tension, and returns to its initial value when the test area returns to its initial state. Besides joint monitoring, the SCFY strain sensor can also be applied to lip reading. Lip extraction and decoding can be achieved by attaching external sensors to capture facial muscle movements, helping people with speech impairments achieve barrier-free communication. For example... Figure 8 As shown in (g), when the words "Sensor," "Strain," and "Fiber" were expressed using lip reading, a relative characteristic resistance signal was obtained. To further verify the practical application performance of the SCFY strain sensor in monitoring minute human movements, the pulse and heartbeat of the test subjects were tested. Figure 8 (ef) When the pulse and heartbeat occur, the skin surface expands, causing the SCFY strain sensor, which is in close contact with the skin surface, to experience a minute strain, thus generating a corresponding sensing signal. Real-time monitoring of pulse and heart rate can help people understand their physical condition and detect abnormalities in a timely manner, such as arrhythmia, rapid or slow heartbeat. The above test results demonstrate that the SCFY strain sensor holds promise for applications in wearable health monitoring.

[0070] Application Example 4: The SCFY strain sensor is used for monitoring epilepsy patients.

[0071] For epilepsy patients who frequently experience unpredictable and recurrent seizures, the SCFY strain sensor can serve as a wearable device for epilepsy monitoring. Its monitoring and early warning functions allow for real-time monitoring of the patient, enabling timely preventative measures when abnormal data is detected. For healthcare professionals, the monitoring data provides insights into the overall course of the epilepsy, allowing for the development of personalized treatment plans. Detailed device design is as follows... Figure 9As shown in (a), the device includes an SCFY strain sensor, a wireless camera, and a UV LED. The device is fixed to a patient's knee. During a seizure, the patient's violent convulsions cause the SCFY strain sensor to stretch. An external digital source meter obtains the real-time resistance of the SCFY strain sensor, thus enabling monitoring and diagnosis of epileptic seizures. By mimicking the process of a seizure, Figure 9 (b) Recorded the changes in electrical resistance throughout the entire process, including normal conditions, seizures, and recovery to normal. Simultaneously, from... Figure 9 As shown in (c), under ultraviolet LED illumination, two states can be observed in the wireless camera: no fluorescence and blue fluorescence. When the phone displays blue fluorescence, it indicates that the monitored patient is moving their knee. If the fluorescence is irregular and changes rapidly, it suggests that the patient is likely in the process of developing an illness. Therefore, the above monitoring data can provide a basis for patients' self-diagnosis and for doctors to develop personalized treatment plans.

[0072] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for fabricating a visual flexible yarn strain sensor, characterized in that, The steps are as follows: Step 1: Prepare a mixed spinning solution of thermoplastic polyurethane (TPU) and tetraphenylethylene (TPE); Step 2: Prepare porous TPU-TPE fibers. The TPU and TPE mixed spinning solution is used to prepare the fluorescent flexible fiber substrate TPU-TPE fibers of the sensor through a wet spinning process. Step 3: Prepare TTS fluorescent porous fibers. PDMS liquid droplets are dropped onto the TPU-TPE substrate fibers prepared in Step 2 and cured to prepare a heterogeneous structure to obtain TTS fluorescent porous fibers. Step 4: Prepare TTS@PDA yarn. The two TTS fibers obtained in Step 3 are twisted using a twisting machine. One end of the fiber is held while the other end rotates around the axis to obtain a yarn with a fixed number of twists. During the twisting process, the liquid droplets on the fiber are arranged alternately to obtain TTS yarn. Then, the TTS yarn is immersed in Tris buffer solution of dopamine and reacted at room temperature. After the reaction is completed, it is washed and dried to obtain TTS@PDA yarn with polydopamine loaded on the surface. Step 5: Prepare TTS@PDA@PPy yarn, i.e., a visual flexible yarn strain sensor. TTS@PDA yarn loaded with polydopamine is loaded with PPy through in-situ frozen interfacial polymerization to obtain TTS@PDA@PPy yarn, i.e., a visual flexible yarn strain sensor.

2. The method for preparing a visual flexible yarn strain sensor according to claim 1, characterized in that, The preparation method of the TPU and TPE mixed spinning solution in step one is as follows: TPU and TPE are dissolved in the solvent DMF and placed in a shaking water bath at 50°C to obtain the TPU and TPE mixed spinning solution. The ratio of TPU to DMF solvent in the mixed spinning solution is 60 g: 147.6 mL, and the concentration of TPE in the mixed spinning solution is 1~5 mg / mL.

3. The method for preparing a visual flexible yarn strain sensor according to claim 1, characterized in that, The wet spinning process in step two is as follows: the spinning solution is injected into a mixed coagulation bath of IPA / water = 0~80 wt% at an extrusion speed of 0.1~2.0 mL / min. After the obtained fibers are fully cross-linked in the coagulation bath for 24 h, porous TPU-TPE fibers are obtained.

4. The method for preparing a visual flexible yarn strain sensor according to claim 1, characterized in that, The preparation of a heterogeneous structure by dripping PDMS liquid droplets onto the substrate and curing them in step three is as follows: PDMS liquid droplets are dripped onto the surface of TPU-TPE fibers using a flat-tipped needle with a distance of 1 cm between the droplets to construct a heterogeneous liquid droplet structure on the fiber surface. Then, the fiber is placed in a 60 ℃ forced-air oven for curing for 12 h to obtain TPU-TPE@PDMS, i.e., TTS fluorescent porous fibers.

5. The method for preparing a visual flexible yarn strain sensor according to claim 1, characterized in that, In step four, the TTS yarn is soaked in a Tris buffer solution containing dopamine, with a yarn-to-tris buffer solution ratio of 0.2 g: 200 mL. The Tris buffer solution containing dopamine is prepared as follows: a 10 mM dopamine (DA) solution is dissolved in the Tris buffer solution, and 0.1 M HCl solution is added to adjust the pH to 8.

5. The reaction is carried out at room temperature for 36 h to initiate the self-polymerization of DA. After the reaction is completed, the yarn is washed with distilled water and air-dried to obtain TTS@PDA yarn with polydopamine loaded on the surface.

6. The method for preparing a visual flexible yarn strain sensor according to claim 1, characterized in that, The in-situ frozen interface polymerization method in step five is as follows: TTS@PDA yarn is placed in a petri dish containing a mixed solution of 0.4 M ferric chloride and 0.4 M NaSSA, with a TTS@PDA yarn to mixed solution ratio of 0.1 g: 10 mL. The dish is then frozen at -5 ℃ for 2 h. Subsequently, an equal volume of cyclohexane solution containing different pyrrole monomer concentrations is poured into the petri dish, and freezing continues for 1 h, with a pyrrole monomer to ferric chloride molar ratio of (0.25~2):

1. Finally, the petri dish is statically maintained at 5 ℃ for polymerization for 12 h. The yarn is then removed, washed with distilled water, and the TTS@PDA@PPy yarn, i.e., a visual flexible yarn strain sensor, is obtained.

7. A visual flexible yarn strain sensor prepared based on the method described in claim 1.

8. The application of the visual flexible yarn strain sensor according to claim 7 in the fabrication of wearable sensing devices.

9. The application according to claim 8, characterized in that, The wearable sensing device is a wearable medical monitoring device.

10. The application according to claim 9, characterized in that, The medical monitoring equipment mentioned is for patients with epilepsy.

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