Conductive nanofiber membrane flexible piezoresistive sensor with biocompatibility and preparation method and application thereof

Abstract

The invention belongs to the field of polymer fibers, and particularly relates to a conductive nanofiber membrane flexible piezoresistive sensor with biocompatibility and a preparation method and application thereof. The preparation method comprises the following steps: carrying out electrostatic spinning on polylactic acid and silk fibroin to obtain a flexible polymer composite fiber membrane; then growing polypyrrole on the flexible polymer composite fiber membrane in situ to obtain a conductive fiber membrane; the flexible fiber membrane substrate and the conductive fiber membrane are compounded together in a layer-by-layer stacked sandwich combination mode, and the periphery of the flexible fiber membrane substrate and the conductive fiber membrane are adhered and fixed through adhesive dripping glue. The flexible piezoresistive sensor prepared by the preparation method disclosed by the invention has the advantages of good biocompatibility, high sensitivity (about 1.088 kPa <-1 >), relatively high response speed and wide detection range (0.5 kPa <-1.6 MPa). The method has a wide application prospect in wearable equipment, flexible electronic skin and man-machine interaction in the future.

Description

Technical Field

[0001] This invention belongs to the field of polymer fibers, specifically relating to a biocompatible conductive nanofiber membrane flexible piezoresistive sensor, its preparation method, and its application. Background Technology

[0002] Mechanical sensors are a crucial component of smart devices, responsible for sensing and identifying various physical properties during device operation. Traditional sensors primarily require stability and durability of the device itself, while also considering commercial interests such as cost-effectiveness. Rigid sensors, including mechanical sensors, displacement sensors, and accelerometers, are mainly used in fields requiring long-term stable operation, such as industrial automation and aerospace. In most cases, rigid sensors can effectively address and meet these requirements. However, with the increasing demand for wearable devices, medical and health monitoring, soft robotics, and the Internet of Things (IoT), rigid sensors have begun to encounter numerous problems. These include limitations imposed by their inherent form and materials, inability to adapt to bending, torsion, and stretching requirements, and the unavoidable motion artifacts that occur in the miniaturization design of wearable bracelets, leading to inaccurate measurements. This hinders their applicability in flexible human-computer interaction and portable wearable smart devices. To address these issues, skin-inspired flexible tactile sensors have emerged.

[0003] Flexible sensors, due to their flexibility, agility, and portability, improve measurement accuracy, making them more suitable for applications requiring delicate tactile feedback, such as health monitoring and responsive interaction in biomimetic robots. In addition to meeting the basic requirements of flexibility and portability, materials used to fabricate flexible pressure sensors also need good biocompatibility to ensure they do not cause discomfort when applied to human skin. Therefore, to address these issues, this invention uses biocompatible biomaterials to fabricate sensors that meet these requirements. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a biocompatible flexible piezoresistive sensor based on a polylactic acid / silk fibroin / polypyrrole composite conductive nanofiber. This method utilizes simple raw materials, is cost-effective, and allows for large-scale fabrication.

[0005] Another objective of this invention is to provide a flexible piezoresistive sensor based on a conductive nanofiber membrane. It exhibits good biocompatibility, is easy to operate, can be used for extended periods, and, while meeting basic health monitoring needs, does not cause discomfort to the human skin.

[0006] Another object of the present invention is to provide an application of the above-mentioned flexible piezoresistive sensor based on conductive nanofiber membrane.

[0007] The objective of this invention is achieved through the following technical solution: The fabrication method of a flexible piezoresistive sensor based on polylactic acid / silk fibroin / polypyrrole composite conductive nanofibers includes the following steps: S1. Preparation of conductive fiber membrane: Polylactic acid (PLA) and silk fibroin (SF) were dissolved in an organic solvent to obtain a spinning solution, which was then spun by electrospinning to obtain a flexible polymer composite fiber membrane; the prepared flexible polymer composite fiber membrane was immersed in an aqueous solution of pyrrole monomer (Py), and then an oxidant solution was added to carry out an in-situ polymerization reaction. After the reaction was completed, a conductive fiber membrane was obtained. S2. Preparation of flexible fiber membrane substrate: Hydrophobic polymer material is dissolved in organic solvent to obtain spinning solution and electrospinned to obtain flexible nanofiber substrate; then, silver paste is coated in the middle of the prepared flexible nanofiber substrate to obtain flexible fiber substrate with electrodes. S3. The obtained flexible fiber membrane substrate is combined with a conductive fiber membrane and then encapsulated.

[0008] Preferably, in step S1, polylactic acid and silk fibroin are dissolved in an organic solvent at a mass ratio of 10:7.

[0009] More preferably, the polylactic acid has a molecular weight of 120 kda to 180 kda, and the silk fibroin has a molecular weight of 1000 da to 1500 da.

[0010] Preferably, the organic solvent in step S1 includes at least one of hexafluoroisopropanol, trifluoroacetic acid, and dichloromethane, more preferably hexafluoroisopropanol.

[0011] Preferably, the preparation of the spinning solution in step S1 is carried out in the following order: first, add an organic solvent, then add polylactic acid while stirring, heat to 40~90 ℃ and stir, and after the solution is stirred until it becomes clear and transparent, add silk fibroin powder, stir until it becomes clear and transparent, and let it stand for 4~12 h to eliminate bubbles.

[0012] Preferably, the parameters for electrospinning in step S1 include: spinning voltage 9-14 kV, receiving distance 12-20 cm, drum speed 100-2000 rpm, spinning solution supply rate 1 mL / h-4 mL / h, spinning time 4-12 h, spinning ambient temperature 20-60 ℃, and relative humidity 30-60 RH.

[0013] Preferably, the oxidant in the oxidant solution in step S1 includes at least one of ammonium persulfate, ammonium pernitrate, ferric chloride, and ferric nitrate; the mass ratio of oxidant to Py monomer is 8:1 to 1:1, more preferably 2:1; the flexible polymer mixed fiber membrane is placed in the oxidant solution and subjected to in-situ polymerization at -10 ℃ to 10 ℃ for 0.5 h to 24 h, more preferably 1 ℃ to 3 ℃ for 12 h.

[0014] Preferably, in step S1, the flexible polymer composite fiber membrane is immersed in an aqueous solution of pyrrole monomer (Py) and allowed to stand at 0-3°C for 4-12 hours to ensure a suitable polymerization rate for subsequent reactions. An oxidant solution is then added after the standing period.

[0015] Preferably, in step S1, the conductive fiber membrane obtained by in-situ polymerization is further washed multiple times with deionized water, and then dried at 20-60 °C for 1-24 h; preferably, it is dried at room temperature overnight.

[0016] Preferably, the hydrophobic polymer material in step S2 includes at least one of polylactic acid, polycaprolactone, polyglycolic acid, polylactic acid-glycolic acid copolymer, and polyvinyl alcohol.

[0017] Preferably, the organic solvent in step S2 includes at least one of hexafluoroisopropanol, trifluoroacetic acid, dichloromethane, ethyl acetate, and acetone.

[0018] Preferably, the preparation of the spinning solution in step S2 is carried out in the following order: first, add an organic solvent, then add a polymer material while stirring, heat to 40~90 ℃ and stir, and after the solution is stirred until it becomes clear and transparent, let it stand for 4~12 h to eliminate bubbles.

[0019] Preferably, the silver paste mentioned in step S2 is a commercially available conductive silver paste with a coating thickness of 50~100μm.

[0020] Preferably, in step S2, the flexible nanofiber substrate is cut into pieces approximately 1*1.5 cm in size. 2 After shaping the rectangle to the desired area, apply copper tape and coat it with commercial conductive silver paste.

[0021] Preferably, the composite and encapsulation in step S3 refers to combining the prepared flexible fiber membrane substrate and the conductive fiber membrane together in a sandwich assembly method of layer stacking, and fixing them together with an adhesive epoxy resin around the edges; the layer stacking refers to stacking the conductive flexible fiber membrane in 1 to 5 layers; the sandwich assembly method refers to placing one layer of flexible fiber membrane substrate with electrodes on the top and bottom in an orthogonal manner, with the conductive fiber membrane placed vertically in the middle; the adhesive epoxy resin is one of the following materials: polyurethane epoxy resin, UV curable epoxy resin, epoxy resin epoxy resin.

[0022] The sensor assembled in step S3 has good sensing performance and biocompatibility, and can be applied to fields such as life and health monitoring, human-computer interaction, electronic skin and smart healthcare.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. This invention uses biocompatible polymer materials combined with electrospinning technology to prepare fiber membranes.

[0024] 2. The conductive nanofibers prepared by this invention have the advantages of high porosity and aspect ratio. Since polypyrrole has excellent electron transport capability, a flexible piezoresistive sensor with excellent sensitivity is prepared.

[0025] 3. The technical solution of this invention has advantages such as simple preparation process, low cost, and the ability to achieve mass production. Simultaneously, the prepared flexible piezoresistive sensor exhibits good biocompatibility and high sensitivity (~1.088 kPa). -1 It features a fast response speed and a wide detection range (0.5 kPa~1.6 MPa). It has broad application prospects in future wearable devices, flexible electronic skin, and human-computer interaction. Attached Figure Description

[0026] Figure 1 The image shown is a scanning electron microscope image of the conductive fiber membrane prepared in Comparative Example 1. The upper right corner is a photograph of the actual product. It can be seen that only a small amount of pyrrole is attached to the fiber surface, and the fiber surface has not undergone obvious changes, proving that the pyrrole has not grown uniformly in situ.

[0027] Figure 2 The image shown is a scanning electron microscope image of the conductive fiber membrane prepared in Comparative Example 2. The upper right corner is a photograph of the actual product. It can be seen that only a small amount of pyrrole is attached to the fiber surface, and the fiber surface has not undergone obvious changes, proving that the pyrrole has not grown uniformly in situ.

[0028] Figure 3 The image shown is a scanning electron microscope image of the conductive fiber membrane prepared in Comparative Example 3. The upper right corner shows a photograph of the actual product. It can be seen that a small amount of pyrrole begins to adhere to the fiber surface, but the fiber membrane is not yet conductive.

[0029] Figure 4 The image shown is a scanning electron microscope (SEM) image of the conductive fiber membrane prepared in Example 1. The upper right corner shows a photograph of the actual product. It can be seen that there are a large number of pyrrole particles on the fiber surface, confirming that the polypyrrole conductive particles have been successfully attached to the fiber, and that the fiber membrane is conductive enough to meet the requirements for sensor fabrication.

[0030] Figure 5 The image shown is a high-magnification scanning electron microscope image of the conductive fiber membrane prepared in Example 4. The fiber surface is noticeably rougher, which confirms that the polypyrrole conductive particles have been successfully attached to the fiber.

[0031] Figure 6 The contact angle data are for the SF / PLA composite nanofiber membranes prepared in Comparative Examples 1-3 and Example 1, where PLA, SP-1, SP-3, SP-5, and SP-7 represent pure PLA membranes and the SF / PLA composite nanofiber membranes prepared in Comparative Examples 1, 2, 3, and 1, respectively. It can be seen that as the proportion of silk fibroin increases, the contact angle gradually decreases, thereby affecting the wettability of the fiber membrane in water and consequently affecting the in-situ growth of pyrrole.

[0032] Figure 7 The figure shows a physical image of the flexible piezoresistive sensor prepared in Example 1. The image illustrates a piezoresistive flexible sensor constructed based on a PLA fiber membrane as a substrate and an SPP fiber membrane as a sensitive layer.

[0033] Figure 8 The figure shows the CV curves of the flexible piezoresistive sensor prepared in Example 1 under different pressures. It can be seen from the figure that the device conforms to the Ohm effect and its resistance continues to decrease as the applied pressure increases.

[0034] Figure 9 The sensitivity of the flexible piezoresistive sensor prepared in Example 1 is shown to be 1.388 kPa within the pressure range of 0-500 kPa. -1 The sensitivity is 0.358 kPa within the pressure range of 100-500 kPa. -1 .

[0035] Figure 10 The sensitivity of the flexible piezoresistive sensor prepared in Example 2 is shown to be 0.00617 kPa in the pressure range of 0-500 kPa. -1 The sensitivity is 0.0025 kPa within the pressure range of 100-500 kPa. -1 .

[0036] Figure 11 The sensitivity of the flexible piezoresistive sensor prepared in Example 3 is shown to be 0.343 kPa within the pressure range of 0-500 kPa. -1 The sensitivity is 0.014 kPa within the pressure range of 100-500 kPa. -1 .

[0037] Figure 12 The sensitivity of the flexible piezoresistive sensor prepared in Example 4 is shown to be 0-500 kPa. It can be seen that the highest sensitivity is 0.4 kPa in the pressure range of 0-100 kPa. -1The sensitivity is 0.005 kPa within the pressure range of 100-500 kPa. -1 .

[0038] Figure 13 The sensitivity of the flexible piezoresistive sensor prepared in Example 5 is shown to be 0.888 kPa within the pressure range of 0-500 kPa. -1 The sensitivity is 0.09 kPa within the pressure range of 100-500 kPa. -1 .

[0039] Figure 14 The figure shows the dynamic response (it) curves of the flexible piezoresistive sensor prepared in Example 1 at 2-10 kPa. The sensor can output regular and distinguishable current signals in cyclic tests at different pressure ranges, and the response has good robustness.

[0040] Figure 15 The figure shows the dynamic response (it) curves of the flexible piezoresistive sensor prepared in Example 1 within the pressure range of 200-1000 kPa. The sensor outputs regular and distinguishable current signals during cyclic testing in different pressure ranges, demonstrating good robustness.

[0041] Figure 16 The figure shows the dynamic response (it) curve of the flexible piezoresistive sensor prepared for Comparative Example 4 in the range of 200-1000 kPa. The sensor attenuates the signal at pressures above 400 kPa and cannot distinguish between different pressures within this range.

[0042] Figure 17 The figure shows the dynamic response (it) curve of the flexible piezoresistive sensor prepared for Comparative Example 5 in the range of 2-10 kPa. The sensor has no signal output for pressures below 4 kPa and cannot distinguish between different pressures within this range.

[0043] Figure 18 The experiment verified the air permeability of the PLA fiber membrane used in Example 1 compared with other commonly used substrates. As can be seen from the figure, the PLA fiber membrane has good air permeability, and compared with SF-based hydrogels, the good air permeability and pressure resistance of the fiber membrane make it more suitable for a wider range of human physiological testing scenarios.

[0044] Figure 19 The image shown is a scanning electron microscope image of the fiber membrane prepared in Comparative Example 6. It can be seen that after being placed under the preparation conditions for a period of time, the fiber membrane absorbs water and dissolves, indicating that the fiber is hydrophilic and soluble in water, and cannot be combined with subsequent pyrrole in situ growth experiments.

[0045] Figure 20The image shows a scanning electron microscope (SEM) image of the fiber membrane prepared in Comparative Example 7. It can be seen that the fiber morphology improves with increasing PVA concentration. Furthermore, the fiber morphology improves further when the solution stirring conditions are changed from room temperature to a constant temperature of 80 °C. However, the fibers remain hydrophilic and water-soluble, making it impossible to bind them to subsequent in-situ pyrrole growth experiments. Therefore, anhydrous ethanol was used to adjust the hydrophilicity of the SF / PVA fiber membrane, but due to the presence of PVA, the fiber membrane rapidly crosslinks. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0047] The raw materials used in the examples without a specified preparation process are all commercially available products, with many purchasing channels and reasonable costs.

[0048] Example 1 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: PLA (molecular weight 160 kDa) was dissolved in hexafluoroisopropanol solution and stirred at 40 °C for 8 h to prepare a 10 wv% PLA solution. Then, 7 wv% silk fibroin powder (molecular weight about 1500 da) was added to make the mass ratio of PLA to SF 10:7. The mixture was stirred at 40 °C for 4 h and then allowed to stand for 2 h to remove air bubbles. The precursor solution was then electrospun. The applied voltage was 12 kV, the liquid pushing speed was 1 mL / h, the distance between the spinning needle and the receiving roller was 12 cm, the rotation speed of the receiving roller was 100 rpm, the ambient temperature was 25 °C, and the humidity was 50 RH%. After spinning, the fiber membrane was placed at room temperature for 12 h to remove residual organic solvents, thus obtaining the SF / PLA composite nanofiber membrane.

[0049] (2) Preparation of conductive fiber membrane: Prepare an aqueous solution of 4 g / L pyrrole monomer (Py), stir until the solution is mixed evenly and clear. Cut the SF / PLA composite nanofiber membrane to a suitable size and immerse it in the solution. Let it stand at 1 °C for 1 h. Then add the corresponding mass of ferric chloride (FeCl3) powder to make the final solution concentration 8 g / L, with a mass ratio of 2:1 to Py monomer. After reacting for 12 h, take out the fiber membrane, rinse it repeatedly with deionized water until there are no obvious adhering substances on the surface, and then dry it at room temperature for 12 h to obtain the conductive fiber membrane.

[0050] (3) Preparation of flexible substrate: 160 kDa PLA was dissolved in hexafluoroisopropanol solution and stirred at 40 °C for 12 h to prepare a 12 wt% PLA solution. After standing for 2 h to remove air bubbles, the precursor was obtained and electrospun. The applied voltage was 14 kV, the liquid pushing speed was 1.6 mL / h, the distance between the spinning needle and the receiving roller was 14 cm, the rotation speed of the receiving roller was 100 rpm, the ambient temperature was 25 °C, and the humidity was 50%RH%. After spinning, the fiber membrane was placed at room temperature for 12 h to remove residual organic solvents, thus obtaining a PLA flexible nanofiber membrane.

[0051] Cut the fiber membrane into 2 cm pieces. 2 A square, coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible substrate is prepared by using a rectangle of the same size (area).

[0052] (4) The conductive fiber membrane is orthogonally placed in the flexible substrate, and finally 3M polyurethane epoxy resin is used to encapsulate the flexible substrate to form a flexible piezoresistive sensor.

[0053] The flexible piezoresistive sensor prepared in Example 1 was subjected to sensing performance tests under compression at different pressures, as well as Morse code and recognition applications with different weights. The specific operations are as follows: 1. Using an Instron universal testing machine, apply 5 cycles of different pressures. The pressures are set to 5, 10, 15, 20, and 25 kPa, the compression speed is set to 40 mm / min, and each compression cycle is set to 5 times. 2. Apply the Morse code corresponding to SCUT by adjusting different compression frequencies under a pressure of 10 kPa; 3. Weights of different weights were placed vertically on the sensor in sequence. The copper foil electrode of the SPP sensor was then connected to the electrodes of the electrochemical workstation. The relative current change ΔI / I0 under different pressures was recorded using an It curve. Here, I0 represents the initial current value measured by the electrochemical workstation when the SPP sensor was not under pressure, and ΔI represents the difference between the current value in the current circuit and the original current value after the SPP sensor is subjected to a certain pressure. During the application of pressure, the gaps between the conductive fibers are compressed, increasing the internal conductive pathways formed by polypyrrole, and the resistance gradually decreases. Therefore, the sensor prepared from this conductive fiber membrane can convert the received pressure signal into an electrical signal. Specific test results are as follows... Figure 12 As shown.

[0054] Example 2 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0055] (2) Preparation of conductive fiber membrane: The method for preparing conductive fiber membrane is basically the same as step (2) in Example 1. The difference is that the concentration of pyrrole monomer (Py) aqueous solution is 1 g / L and the concentration of ferric chloride (FeCl3) solution is 2 g / L in this example, while other conditions remain unchanged.

[0056] (3) Preparation of flexible substrate: PLA flexible nanofiber membrane was prepared by the same method as step (3) in Example 1. The fiber membrane was cut into 2 cm pieces. 2 A square, coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible substrate is prepared by using a rectangle of the same size (area).

[0057] (4) The conductive fiber membrane is orthogonally placed in the flexible substrate, and finally 3M polyurethane epoxy resin is used to encapsulate the flexible substrate to form a flexible piezoresistive sensor.

[0058] Example 3 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0059] (2) Preparation of conductive fiber membrane: The method for preparing conductive fiber membrane is basically the same as step (2) in Example 1. The difference is that the concentration of pyrrole monomer (Py) aqueous solution is 2 g / L and the concentration of ferric chloride (FeCl3) solution is 4 g / L in this example, while other conditions remain unchanged.

[0060] (3) Preparation of flexible substrate: PLA flexible nanofiber membrane was prepared by the same method as step (3) in Example 1.

[0061] Cut the fiber membrane into 2 cm pieces. 2 A square, coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible substrate is prepared by using a rectangle of the same size (area).

[0062] (4) The conductive fiber membrane is orthogonally placed in the flexible substrate, and finally 3M polyurethane epoxy resin is used to encapsulate the flexible substrate to form a flexible piezoresistive sensor.

[0063] Example 4 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0064] (2) Preparation of conductive fiber membrane: The method for preparing conductive fiber membrane is basically the same as step (2) in Example 1. The difference is that the concentration of pyrrole monomer (Py) aqueous solution is 8 g / L and the concentration of ferric chloride (FeCl3) solution is 16 g / L in this example, while other conditions remain unchanged.

[0065] (3) Preparation of flexible substrate: PLA flexible nanofiber membrane was prepared by the same method as step (3) in Example 1. The fiber membrane was cut into 2 cm pieces. 2 A square, coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible substrate is prepared by using a rectangle of the same size (area).

[0066] (4) The conductive fiber membrane is orthogonally placed in the flexible substrate, and finally 3M polyurethane epoxy resin is used to encapsulate the flexible substrate to form a flexible piezoresistive sensor.

[0067] Example 5 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0068] (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0069] (3) Preparation of flexible substrate: PLA flexible nanofiber membrane was prepared by the same method as step (3) in Example 1. The fiber membrane was cut into 2 cm pieces. 2 A square, coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible substrate is prepared by using a rectangle of the same size (area).

[0070] (4) The conductive fiber membranes were neatly stacked in three layers and placed orthogonally in a flexible substrate. Finally, 3M polyurethane epoxy resin was used to encapsulate the flexible substrate to form a flexible piezoresistive sensor.

[0071] Comparative Example 1 (1) Preparation of silk fibroin / polylactic acid / polypyrrole fiber membrane: SF / PLA composite nanofiber membrane was prepared according to the method of step (1) in Example 1, except that PLA: silk fibroin powder = 10:1 in this comparative example, and other conditions remained unchanged; (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0072] Comparative Example 2 (1) Preparation of silk fibroin / polylactic acid / polypyrrole fiber membrane: SF / PLA composite nanofiber membrane was prepared according to the method of step (1) in Example 1, except that PLA: silk fibroin powder = 10:3 in this comparative example, and other conditions remained unchanged; (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0073] Comparative Example 3 (1) Preparation of silk fibroin / polylactic acid / polypyrrole fiber membrane: SF / PLA composite nanofiber membrane was prepared according to the method of step (1) in Example 1, except that PLA: silk fibroin powder = 10:5 in this comparative example, and other conditions remained unchanged; (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0074] Comparative Example 4 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0075] (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0076] (3) The prepared conductive fiber membrane is orthogonally placed on a substrate coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 The electrodes were directly encapsulated on a rectangular PI tape (the size of which is rectangular). Sensing performance was tested under compression at different pressures. The specific procedure was as follows: five cycles of different pressures were dynamically applied using an Instron universal testing machine, with a compression speed set to 40 mm / min. The results are as follows: Figure 16 As shown.

[0077] Comparative Example 5 (1) Preparation of silk fibroin / polylactic acid / polypyrrole conductive fiber membrane: SF / PLA composite nanofiber membrane was prepared by the same method as step (1) in Example 1.

[0078] (2) Preparation of conductive fiber membrane: The conductive fiber membrane was prepared in the same way as step (2) of Example 1.

[0079] (3) The prepared conductive fiber film is placed orthogonally on a substrate coated with commercial conductive silver paste (approximately 50 μm thick, 1*1.5 cm). 2 A flexible piezoresistive sensor is encapsulated with 3M polyurethane epoxy resin on a PET substrate with electrodes (rectangular in area).

[0080] The sensor performance under compression at different pressures was tested. The specific procedure was as follows: five cycles of different pressures were dynamically applied using an Instron universal testing machine, with the compression speed set to 40 mm / min. The results are as follows: Figure 17 As shown.

[0081] Comparative Example 6 Preparation of silk fibroin / polypyrrolidone (PVP) composite fiber membrane: PVP was dissolved in an ethanol solution and stirred at room temperature for 4 h to prepare a 10 wt% PVP solution. The membrane was then processed using m... PVP :m SF Silk fibroin was added in ratios of 10:3, 10:5, and 10:10, and the mixture was stirred at room temperature for 4 hours. After standing for 2 hours to remove air bubbles, the precursor was obtained and then electrospun. The applied voltage was 10 kV, the liquid pushing speed was 1 mL / h, the distance between the spinning needle and the receiving roller was 12 cm, the rotation speed of the receiving roller was 100 rpm, the ambient temperature was 25 ℃, and the humidity was 50 RH%. After spinning, the fiber membrane was placed at room temperature for 12 hours to remove residual solvent, thus obtaining an SF / PLA composite nanofiber membrane.

[0082] Comparative Example 7 Preparation of silk fibroin / polyvinyl alcohol (PVA) composite fiber membrane: PVA was dissolved in deionized water and stirred at 80℃ for 2-8 h to prepare a 10 wt% PVA solution. The membrane was then processed using m... PVA :m SF Silk fibroin was added in a ratio of 10:5 and 10:10, and the mixture was stirred at 80℃ for 4 h. After standing for 2 h to remove air bubbles, the precursor was obtained and electrospun. The applied voltage was 10 kV, the liquid pushing speed was 1 mL / h, the distance between the spinning needle and the receiving roller was 12 cm, the rotation speed of the receiving roller was 100 rpm, the ambient temperature was 25℃, and the humidity was 50% RH. After spinning, the fiber membrane was placed at room temperature for 12 h to remove residual solvent, thus obtaining an SF / PLA composite nanofiber membrane. The SF / PLA fiber membrane obtained from the precursor prepared by stirring at 80℃ for 12 h was immersed in anhydrous ethanol for 5 minutes for hydrophilic modification.

[0083] Compared to the comparative examples, the core advantage of this invention lies in its systematic solution to the trade-off between biocompatibility, sensitivity, and stability in flexible sensors through a series of precise material and structural designs. Specifically, compared to comparative examples 1-3, which used a low proportion of silk fibroin, this invention employs an optimal SF / PLA ratio of 10:7, significantly improving the hydrophilicity of the fiber membrane. This ensures uniform adsorption and polymerization of pyrrole monomers, forming a continuous and dense conductive layer, overcoming the problems of uneven PPy loading and poor conductivity caused by insufficient hydrophilicity in the comparative examples. Compared to comparative examples 6-7, which used other blended systems, the SF / PLA blended system of this invention can stably exist under different humidity conditions and possesses suitable mechanical strength and flexibility, avoiding motion artifacts during measurement. Structurally, compared to sensors using a rigid PET substrate (Comparative Example 5) or without a fixed substrate (Comparative Example 4), this invention innovatively selects a porous PLA fiber membrane as a flexible substrate, enabling it to effectively transmit stress under low pressure and provide sufficient deformation space under high pressure. This achieves both high sensitivity and a wide detection range, avoiding the shortcomings of the comparative examples where there is no response under low pressure or signal attenuation under high pressure. Ultimately, through the synergistic design of "hydrophilic fiber substrate → uniform conductive layer → porous flexible support," this invention successfully fabricates a flexible piezoresistive sensor with excellent biocompatibility, high sensitivity, and long-term stability, exhibiting significantly superior overall performance compared to the comparative examples.

[0084] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a flexible piezoresistive sensor based on a biocompatible conductive fiber membrane, characterized in that, Comprising the following steps: S1. Preparation of conductive fiber membrane: dissolve polylactic acid and silk fibroin in an organic solvent to obtain a spinning solution, and then perform spinning by electrospinning to obtain a flexible high polymer composite fiber membrane; immerse the prepared flexible high polymer composite fiber membrane in a pyrrole monomer aqueous solution, then add an oxidizing agent solution to perform in-situ polymerization reaction, and obtain a conductive fiber membrane after the reaction is completed; S2. Preparation of flexible fiber membrane substrate: dissolve a hydrophobic polymer material in an organic solvent to obtain a spinning solution and perform electrospinning to obtain a flexible nanofiber substrate; then, coat silver paste in the middle of the prepared flexible nanofiber substrate to obtain a flexible fiber substrate with electrodes; S3. Composite and package the prepared flexible fiber membrane substrate and the conductive fiber membrane to prepare the flexible piezoresistive sensor based on the biocompatible conductive fiber membrane.

2. The production method according to claim 1, characterized by, In step S1, polylactic acid and silk fibroin are dissolved in an organic solvent according to a mass ratio of 10:7; In step S1, the molecular weight of the polylactic acid is 120 kda-180 kda, and the molecular weight of the silk fibroin is 1000 da-1500 da.

3. The preparation method according to claim 1, characterized in that, The organic solvent in step S1 includes at least one of hexafluoroisopropanol, trifluoroacetic acid, and dichloromethane.

4. The method of claim 1, wherein, The parameters of electrospinning in step S1 include a spinning voltage of 9-14 kV, a receiving distance of 12-20 cm, a drum rotating speed of 100-2000 rpm, a spinning solution supply speed of 1 mL / h-4 mL / h, a spinning time of 4-12 h, a spinning environment temperature of 20-60 ℃, and a relative humidity of 30-60 RH%.

5. The preparation method according to claim 1, characterized in that, The oxidizing agent in the oxidizing agent solution in step S1 includes at least one of ammonium persulfate, ammonium nitrate, ferric chloride, and ferric nitrate; the mass ratio of the oxidizing agent to the pyrrole monomer is 8:1-1:1; the flexible high polymer mixed fiber membrane is placed in the oxidizing agent solution and reacts at-10 ℃-10 ℃ for 0.5 h-24 h, more preferably at 1 ℃-3 ℃ for 12 h.

6. The method of claim 1, wherein, The hydrophobic polymer material in step S2 includes at least one of polylactic acid, polycaprolactone, polyglycolic acid, polylactic acid-glycolic acid copolymer, and polyvinyl alcohol; The organic solvent in step S2 includes at least one of hexafluoroisopropanol, trifluoroacetic acid, dichloromethane, ethyl acetate, and acetone.

7. The preparation method according to claim 1, characterized in that, The silver paste in step S2 is a commercial conductive silver paste, and the coating thickness is 50-100 μm.

8. The method of claim 1, wherein, In step S3, the composite and package means that the prepared flexible fiber membrane substrate and the conductive fiber membrane are combined together by a sandwich assembly mode of layer-by-layer stacking, and the periphery is fixed by a sticky glue drop; the layer-by-layer stacking means that the conductive flexible fiber membrane is stacked in 1-5 layers; the sandwich assembly mode means that the flexible fiber membrane substrates with electrodes on the upper and lower layers are placed in a perpendicular manner, and the conductive fiber membrane is vertically placed in the middle; the sticky glue drop is one of the following materials: polyurethane glue drop, UV light curing glue drop, and epoxy resin glue drop.

9. A flexible piezoresistive sensor based on a conductive nanofiber membrane, characterized by, It is prepared by the preparation method of any one of claims 1-8.

10. Use of the flexible piezoresistive sensor based on the conductive nanofiber membrane according to claim 9 in the field of life health monitoring, human-computer interaction, electronic skin or intelligent medical treatment.

Images