Full-degradable flexible pressure sensor based on luffa sponge structure and preparation method thereof

Abstract

The application provides a full-degradable flexible pressure sensor based on a luffa sponge biological structure and a preparation method.The sensor comprises, from bottom to top, a lower degradable flexible packaging layer, a lower conductive electrode, a luffa sponge structure composite conductive layer, an upper conductive electrode and an upper degradable flexible packaging layer.The application combines the natural luffa sponge flexible three-dimensional skeleton with the degradable conductive material, fully utilizes the multi-stage deformation between different conductive networks, single conductive fiber and the conductive material itself in the luffa sponge structure composite conductive layer, realizes the switching of the force sensing mechanism in different pressure ranges, expands the pressure detection range and keeps good linear response in a wide range.The device structure provided by the application utilizes the topography structure of the natural plant, is simple to manufacture and low in cost, is fully degradable under natural conditions, is environment-friendly, and can have good response to external static and dynamic pressure in a wide range.

Description

Technical Field

[0001] This invention belongs to the field of pressure-sensitive materials, and relates to film formation technology and energy conversion technology, specifically to a wide-range flexible pressure sensor and its preparation method. Background Technology

[0002] Pressure is a crucial parameter among common physical quantities measured by sensors, with significant applications in cargo weighing and identification, building structure stability monitoring, pipeline pressure monitoring, road traffic detection, pulse and blood pressure monitoring, and electronic skin pressure sensing. Pressure sensors are sensitive elements that convert externally sensed pressure signals into electrical signals, playing a vital role in fields such as electronic skin, human-computer interaction, artificial intelligence, and implantable medical devices. Traditional pressure sensors, such as metal strain gauge pressure sensors utilizing the strain effect and semiconductor strain gauge pressure sensors utilizing the piezoresistive effect, have limitations in measurement range and temperature stability. Furthermore, they struggle to meet the growing demands of healthcare applications for biocompatibility, good flexibility, and stable measurement on complex and variable surfaces. Pressure-sensitive materials with low elasticity not only increase wearer discomfort but also fail to conform well to the measurement surface, leading to accuracy loss.

[0003] In recent years, with the rapid development of the Internet of Things (IoT) and the arrival of the 5G era, electronic technology has seen unprecedented development in industries such as manufacturing, medicine, and the military. To meet the diverse needs of flexible pressure sensors in various fields, optimizing the performance of existing flexible pressure sensors and developing sensors based on new principles, structures, and materials have been research hotspots in the field of flexible pressure sensing. Meanwhile, the widespread use of electronic products results in 20-50 million tons of consumer electronics being discarded globally each year. Considering the enormous waste disposal costs and environmental pollution caused by electronic waste, developing biodegradable flexible pressure sensors has become a goal pursued by researchers worldwide.

[0004] Currently used flexible resistive pressure sensors mainly employ composite thin films and porous aerogel sensing structures. These devices suffer from drawbacks such as weak wide-range detection capability, complex fabrication processes, high cost, and non-degradability, hindering their practical application and commercialization. However, by using a solution impregnation method to composite biodegradable conductive materials onto a flexible framework of natural loofah sponge, the multi-level deformation of different conductive networks, individual conductive fibers, and the conductive material itself within the composite conductive layer of the loofah sponge structure is fully utilized. Leveraging the large specific surface area, large deformation capacity, and strong deformation recovery ability of the loofah sponge framework, it can exhibit good response over a wide pressure detection range. This approach offers advantages such as simple fabrication, low cost, wide measurement range, and biodegradability, providing a new direction for the research of flexible pressure sensors.

[0005] Compared with traditional pressure sensors, this sensor makes full use of biological structures in nature and innovatively introduces multi-level micro-nano structures into the conductive layer, thereby significantly improving the pressure detection range and sensitivity of the sensor. At the same time, biodegradable materials are used in the preparation of each component of the device, which is environmentally friendly, non-toxic and harmless. The entire preparation process is simple to operate, low in cost, can be completely degraded in the natural environment, and has good wearability and biocompatibility. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an organic fully biodegradable flexible pressure sensor based on the structure of a loofah sponge and its preparation method.

[0007] To achieve the above-mentioned objectives, the technical solution of this invention is as follows:

[0008] A fully degradable flexible pressure sensor based on a loofah sponge structure includes, from bottom to top, a lower degradable flexible encapsulation layer 5, a lower conductive electrode 4, a loofah sponge structure composite conductive layer 3, an upper conductive electrode 2, and an upper degradable flexible encapsulation layer 1. The loofah sponge structure composite conductive layer 3 uses natural loofah sponge as a flexible skeleton combined with conductive materials and serves as the core pressure-sensitive structure layer of the device. The upper conductive electrode 2 and the lower conductive electrode 4 each lead out a lead wire for receiving measurement signals. The upper degradable flexible encapsulation layer 1 and the lower degradable flexible encapsulation layer 5 are used for encapsulation and fixation of the device.

[0009] The degree of deformation of the flexible skeleton of the loofah sponge is linearly related to the pressure applied to the surface. This also means that the number of conductive paths formed between the conductive material wrapped in the flexible skeleton and the two conductive electrodes is linearly related to the magnitude of the external pressure. The magnitude of the static and dynamic pressure applied by the external environment can be reflected by detecting changes in the electrical parameters output by the sensor.

[0010] As a preferred embodiment, the loofah sponge structure composite conductive layer 3 is obtained by pre-treating natural loofah sponge and then combining it with a conductive material through a solution impregnation method. The flexible skeleton of the loofah sponge is an elastic and deformable porous block that shrinks or rebounds with the applied pressure. The loofah sponge structure composite conductive layer 3 is combined with a conductive material with a piezoresistive effect.

[0011] The upper conductive electrode 2 and the lower conductive electrode 4 are electrodes prepared by screen printing on the surfaces of the upper biodegradable flexible encapsulation layer 1 and the lower biodegradable flexible encapsulation layer 5, respectively.

[0012] As a preferred method, when static or dynamic pressure is applied to the surface of the device, the loofah-like composite conductive layer deforms. With increasing pressure, changes occur between different conductive networks, individual conductive fibers, and the conductive material itself within the loofah-like composite conductive layer 3. The number of conductive pathways between the upper and lower conductive electrodes, the diameter of the conductive pathways, and the resistivity of the conductive material itself change, becoming the primary reasons for the change in device resistance as pressure increases. Initially, under pressure, the interlayer voids in the loofah-like conductive composite layer decrease, and the number of conductive pathways increases. As the pressure increases to a certain range, the void deformation tends to stabilize, and the number of conductive pathways remains almost unchanged. At this point, the change in the diameter of individual conductive fibers under pressure becomes the primary reason for the change in device resistance. With further increases in pressure, the changes in interlayer voids and conductive fiber diameters become insignificant. At this point, the resistivity of the conductive material changes, thus altering the device resistance. A changing current signal is output under an applied operating voltage to detect the pressure signal.

[0013] It outputs a changing current signal when an external working voltage is applied, thereby enabling the detection of pressure signals.

[0014] As a preferred embodiment, the loofah sponge structure composite conductive layer 3 is an elastic deformable porous block based on a flexible skeleton of loofah sponge composite with a conductive material having a piezoresistive effect.

[0015] And / or the flexible skeleton of the loofah sponge is made by repeatedly soaking, drying and compacting natural loofah sponge in deionized water;

[0016] Furthermore / or the loofah sponge structure composite conductive layer 3 is a square with a side length of 0.5-3cm and a thickness of 0.5-1.5cm.

[0017] As a preferred embodiment, the materials of the upper conductive electrode 2 and the lower conductive electrode 4 are selected from graphite, lithium palmitate, or lithium smithsonite.

[0018] As a preferred embodiment, the flexible skeleton in the composite conductive layer 3 of the loofah sponge structure is selected from natural loofah sponge;

[0019] And / or the flexible framework may also include nerve grass or plant fibers;

[0020] And / or the flexible skeleton has a three-dimensional mesh-like network with a diameter of 100-300μm inside.

[0021] As a preferred embodiment, the conductive material of the loofah sponge structure composite conductive layer 3 is a composite material composed of at least one or more different materials, such as carbon ink, reduced graphene oxide, carbon nanotubes, two-dimensional transition metal carbon or nitride.

[0022] As a preferred embodiment, the materials of the upper biodegradable flexible encapsulation layer 1 and the lower biodegradable flexible encapsulation layer 5 are selected from cellulose, lignin, starch, silk protein, collagen, polylactic acid, or polyvinyl alcohol; and / or the encapsulation layers are made from the materials by solution casting.

[0023] As a preferred approach, the device as a whole is completely degraded in the natural environment and the products are bio-friendly, non-toxic and harmless.

[0024] This invention also provides a method for preparing a fully biodegradable flexible pressure sensor based on a loofah sponge structure, comprising the following steps:

[0025] ① Cut a natural loofah sponge along its axis, clean it with ultrasonic cleaner, and dry it at 60°C for 2 hours on a heating table. Repeat this cleaning and drying process to stabilize the resilience of the loofah sponge. Select a regular area of ​​the pre-treated loofah sponge and cut it into a square structure as a flexible skeleton for the composite conductive layer.

[0026] ② Cut the glass substrate into a substrate and sonicate it in glass cleaning solution, deionized water, and anhydrous ethanol in sequence. Then dry it in an oven for later use. Dilute the nanocellulose aqueous solution with deionized water and centrifuge it at 5000 rpm to remove coarse fibers and impurities from the solution. After centrifugation, keep the supernatant and use the casting method to cover the nanocellulose aqueous solution on the glass substrate. Place it in an oven at 40°C for 8 hours to dry. After cooling to room temperature, peel the nanocellulose film off the glass substrate to obtain a 100-300 μm biodegradable flexible encapsulation layer.

[0027] ③ A layer of graphite electrode is printed on the nanocellulose film using screen printing technology, and leads are connected to the electrode surface to serve as a conductive electrode layer.

[0028] ⑤ The cleaned loofah sponge flexible skeleton is immersed in carbon ink solution by solution impregnation. After being taken out and dried, the process is repeated 1-5 times to obtain a pressure-sensitive loofah sponge structure composite conductive layer. Applying pressure will change the resistance value of the composite conductive layer, thereby changing the output current.

[0029] ⑤ Seal and fix the stacked materials from the edge in sequence for encapsulation. From bottom to top, they are: biodegradable flexible encapsulation layer 5, lower conductive electrode 4, loofah sponge structure composite conductive layer 3, upper conductive electrode 2, and upper biodegradable flexible encapsulation layer 1.

[0030] ⑥ Fix the packaged device on the stage of the push-pull force gauge, connect the two probes of the electrical parameter tester to the two lead electrodes respectively, and apply pressure to the device through the circular pressure probe;

[0031] ⑦ As the applied pressure varies, the output electrical signal of the pressure sensor changes. The output current signal of the device is detected by an electrical parameter tester, thereby enabling the detection of external static and dynamic pressure.

[0032] The working principle of this invention is as follows:

[0033] Under pressure, the composite conductive layer 3 of the loofah sponge structure deforms first due to its inherent elastic variability and porous bulk structure. This change in porosity alters the contact between the conductive material attached to the flexible loofah sponge skeleton and the conductive pathways, leading to a change in the device's resistance. As the pressure continues to increase, the porosity of the flexible loofah sponge skeleton saturates, and the number of conductive pathways no longer changes. Meanwhile, individual loofah sponge composite conductive fibers undergo secondary deformation. According to the definition of resistance:

[0034]

[0035] Where ρ is resistivity, L is length, and S is cross-sectional area. Under pressure, the cross-sectional area of ​​a single composite conductive fiber changes, and the resistance of the device changes accordingly.

[0036] As the pressure continues to increase, the composite conductive layer of the loofah sponge structure is fully deformed. The conductive material with piezoresistive effect inside begins to change its own resistance value under the action of pressure, which eventually leads to a change in the resistance value of the device, realizing a pressure detection mechanism with a wide range from low to high.

[0037] This invention provides an organic, fully biodegradable flexible pressure sensor based on the structure of a loofah sponge and its preparation method. The flexible pressure sensor has a simple preparation process, is lightweight, has a wide measurement range, low cost, is completely biodegradable, and has good linear response output.

[0038] Compared to traditional pressure sensors, this invention possesses excellent flexibility, enabling it to conform well to the surface of human skin for pressure change detection. Furthermore, this flexible pressure sensor is fully biodegradable, making it environmentally friendly and possessing potential value for bio-implantation. In addition, the device's sensitive structure combines a flexible loofah framework with conductive materials, fully utilizing the multi-level deformation of the loofah framework and the piezoresistive effect of the conductive material itself. This allows for switching of the pressure-sensitive mechanism across different pressure ranges, expanding the pressure detection range and maintaining good linear response over a wide range. The organic, fully biodegradable flexible pressure sensor based on a loofah structure proposed in this invention is simple to fabricate, small in size, lightweight, biocompatible, fully biodegradable, and capable of collecting external pressure from statically and dynamically changing surfaces and converting it into a current output to reflect pressure changes in real time. It has significant application value in fields such as electronic skin, human-computer interaction, artificial intelligence, and implantable medical devices. Attached Figure Description

[0039] Figure 1 This is a three-dimensional structural diagram of the present invention.

[0040] Figure 2 This is a process flow diagram of the fabrication process of an organic fully biodegradable flexible pressure sensor based on the loofah sponge structure according to the present invention.

[0041] Figure 3 This is a schematic diagram showing the change in resistance of the device of the present invention when subjected to external pressure.

[0042] Figure 4 This is a SEM image of the composite conductive layer in the loofah sponge structure of the present invention. (a) shows the overall morphology of the elastic porous block of the composite conductive layer; (b) shows the good adhesion of the conductive carbon ink to the flexible skeleton of the loofah sponge.

[0043] Figure 5 This is a voltage-current curve of the device under different pressure conditions according to the present invention.

[0044] Figure 6 This is a linear fitting graph of the sensitivity of the device of the present invention.

[0045] Figure 7 This is a graph showing the response / recovery time characteristics of the device of the present invention.

[0046] Figure 8 This is the sensor's response curve over time when pressed by a finger, as presented in this invention.

[0047] 1 is the upper biodegradable flexible encapsulation layer; 2 is the upper conductive electrode; 3 is the loofah sponge structure composite conductive layer; 4 is the lower conductive electrode; and 5 is the lower biodegradable flexible encapsulation layer. Detailed Implementation

[0048] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] Example 1

[0050] like Figure 1As shown, this embodiment provides a fully degradable flexible pressure sensor based on a loofah sponge structure. From bottom to top, it includes a lower degradable flexible encapsulation layer 5, a lower conductive electrode 4, a loofah sponge structure composite conductive layer 3, an upper conductive electrode 2, and an upper degradable flexible encapsulation layer 1. The loofah sponge structure composite conductive layer 3 uses natural loofah sponge as a flexible skeleton combined with conductive materials as the core pressure-sensitive structure layer of the device. The upper conductive electrode 2 and the lower conductive electrode 4 each lead out a lead wire to receive measurement signals. The upper degradable flexible encapsulation layer 1 and the lower degradable flexible encapsulation layer 5 are used for encapsulation and fixation of the device.

[0051] The degree of deformation of the flexible skeleton of the loofah sponge is linearly related to the pressure applied to the surface. This also means that the number of conductive paths formed between the conductive material wrapped in the flexible skeleton and the two conductive electrodes is linearly related to the magnitude of the external pressure. The magnitude of the static and dynamic pressure applied by the external environment can be reflected by detecting changes in the electrical parameters output by the sensor.

[0052] In some embodiments, the loofah sponge structure composite conductive layer 3 is obtained by pre-treating natural loofah sponge and then combining it with a conductive material through a solution impregnation method. The flexible skeleton of the loofah sponge is an elastic and deformable porous block that shrinks or rebounds with the applied pressure. The loofah sponge structure composite conductive layer 3 is composited with a conductive material that has a piezoresistive effect.

[0053] The upper conductive electrode 2 and the lower conductive electrode 4 are electrodes prepared by screen printing on the surfaces of the upper biodegradable flexible encapsulation layer 1 and the lower biodegradable flexible encapsulation layer 5, respectively.

[0054] When static or dynamic pressure is applied to the surface of the device, the composite conductive layer of the loofah sponge structure deforms. As the pressure increases, changes occur between different conductive networks, individual conductive fibers, and the conductive material itself in the composite conductive layer 3. The number of conductive paths between the upper and lower conductive electrodes, the diameter of the conductive paths, and the resistivity of the conductive material itself change. These changes become the main reasons for the change in device resistance as the pressure increases. Under the condition of an applied working voltage, a changing current signal is output to detect the pressure signal.

[0055] Preferably, the loofah sponge structure composite conductive layer 3 is an elastic deformable porous block based on a flexible skeleton of loofah sponge composite with a conductive material having a piezoresistive effect;

[0056] Preferably, the flexible skeleton of the loofah sponge is made by repeatedly soaking, drying and compacting natural loofah sponge in deionized water;

[0057] Preferably, the composite conductive layer 3 of the loofah sponge structure is a square with a side length of 0.5-3cm and a thickness of 0.5-1.5cm.

[0058] Preferably, the materials of the upper conductive electrode 2 and the lower conductive electrode 4 are selected from graphite, lithium palmitate, or lithium smithsonite.

[0059] Preferably, the flexible skeleton in the composite conductive layer 3 of the loofah sponge structure is selected from natural loofah sponge;

[0060] Preferably, the flexible framework also includes nerve grass or plant fibers;

[0061] Preferably, the flexible skeleton has a three-dimensional mesh-like network with a diameter of 100-300μm inside.

[0062] Preferably, the conductive material of the loofah sponge structure composite conductive layer 3 is a composite material composed of at least one or more different materials, such as carbon ink, reduced graphene oxide, carbon nanotubes, two-dimensional transition metal carbon or nitride.

[0063] Preferably, the materials of the upper biodegradable flexible encapsulation layer 1 and the lower biodegradable flexible encapsulation layer 5 are selected from cellulose, lignin, starch, silk protein, collagen, polylactic acid, or polyvinyl alcohol; and / or the encapsulation layers are made from the materials by solution casting.

[0064] The device is completely degraded in the natural environment and the products are bio-friendly, non-toxic and harmless.

[0065] Example 2

[0066] like Figure 2 As shown, this embodiment provides a method for fabricating an organic, fully biodegradable flexible pressure sensor based on a loofah sponge structure, comprising the following steps:

[0067] ① Cut a natural loofah sponge along its axis and ultrasonically clean it sequentially with deionized water and anhydrous ethanol. Dry it on a heated platform at 60℃ for 2 hours. Repeat this cleaning and drying process 5 times to stabilize the resilience of the loofah sponge. Select a well-structured area of ​​the pre-treated loofah sponge and cut it into square structures with a side length of 0.5-2cm to serve as the flexible framework for the composite conductive layer.

[0068] ② Cut the glass substrate into 5*5cm pieces and sonicate them sequentially in glass cleaning solution, deionized water, and anhydrous ethanol for 10 minutes each. Then dry them in an oven for later use. Dilute the commercial nanocellulose aqueous solution with deionized water and centrifuge it at 5000 rpm to remove large coarse fibers and impurities. After centrifugation, keep the supernatant and use a casting method to cover the nanocellulose aqueous solution onto the glass substrate. Place it in an oven at 40℃ for 8 hours and cool it to room temperature. Peel the nanocellulose film off the glass substrate to obtain a 100-300μm biodegradable flexible encapsulation layer.

[0069] ③ A graphite electrode with a side length of 0.5-2cm and a thickness of 100-500um is printed on the nanocellulose film using screen printing technology, and leads are connected to the electrode surface to serve as a conductive electrode layer.

[0070] ⑤ The cleaned loofah sponge flexible skeleton is immersed in a carbon ink solution with a particle size of about 50-70nm by solution impregnation. After being taken out and dried, the process is repeated 1-5 times to obtain a pressure-sensitive loofah sponge structure composite conductive layer. Applying pressure will change the resistance value of the composite conductive layer, thereby changing the output current.

[0071] ⑤ Seal and fix the stacked materials from the edges in sequence for encapsulation. From bottom to top, they are: biodegradable flexible encapsulation layer 5, lower conductive electrode 4, loofah sponge structure composite conductive layer 3, upper conductive electrode 2, and upper biodegradable flexible encapsulation layer 1.

[0072] ⑥ Fix the packaged device on the stage of the push-pull force gauge, connect the two probes of the electrical parameter tester to the two lead electrodes respectively, and apply pressure to the device through the circular pressure probe;

[0073] ⑦ As the applied pressure varies, the output electrical signal of the pressure sensor changes. The output current signal of the device is detected by an electrical parameter tester, thereby enabling the detection of external static and dynamic pressure.

[0074] The above is a detailed description of the fabrication of a wide-range biodegradable flexible pressure sensor based on a loofah sponge structure proposed in this invention. The flexible pressure sensor measures 2cm*2cm*0.5cm. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of the technical solution.

[0075] The principle of this wide-range biodegradable flexible pressure sensor based on the loofah sponge structure is as follows: Figure 3 As shown. Under pressure, the porous block structure of the loofah sponge composite conductive layer 3 deforms first due to its elastic variability. The change in porosity alters the contact between the conductive material attached to the flexible loofah sponge skeleton and the conductive path, resulting in a change in the device's resistance. As the pressure increases, the porosity of the flexible loofah sponge skeleton saturates, and the number of conductive paths no longer changes. However, individual loofah sponge composite conductive fibers undergo secondary deformation. Under pressure, the cross-sectional area of ​​each fiber changes, causing a change in the device's resistance. With continued pressure increase, the loofah sponge composite conductive layer deforms completely. The conductive material with piezoresistive effect inside begins to change its resistance under pressure, ultimately leading to a change in the device's resistance.

[0076] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A fully biodegradable flexible pressure sensor based on a loofah sponge structure, characterized in that: From bottom to top, the structure includes a lower biodegradable flexible encapsulation layer (5), a lower conductive electrode (4), a loofah sponge structure composite conductive layer (3), an upper conductive electrode (2), and an upper biodegradable flexible encapsulation layer (1). The loofah sponge structure composite conductive layer (3) uses natural loofah sponge as a flexible skeleton combined with conductive materials and is used as the core pressure-sensitive structure layer of the device. The upper conductive electrode (2) and the lower conductive electrode (4) each have a lead wire for receiving measurement signals. The upper biodegradable flexible encapsulation layer (1) and the lower biodegradable flexible encapsulation layer (5) are used for encapsulation and fixation of the device. The degree of deformation of the flexible skeleton of the loofah sponge is linearly related to the magnitude of the pressure applied to the surface. Similarly, the number of conductive paths formed between the conductive material wrapped around the flexible skeleton and the two conductive electrodes is also linearly related to the magnitude of the external pressure. The magnitude of the static and dynamic pressure applied by the external environment can be reflected by detecting changes in the electrical parameters output by the sensor. The preparation method includes the following steps: ① Cut a natural loofah sponge along its axis, clean it with ultrasonic cleaner, and dry it at 60°C for 2 hours on a heating table. Repeat this cleaning and drying process to stabilize the resilience of the loofah sponge. Select a regular area of ​​the pre-treated loofah sponge and cut it into a square structure as a flexible skeleton for the composite conductive layer. ② Cut the glass substrate into a substrate and sonicate it in glass cleaning solution, deionized water, and anhydrous ethanol in sequence. Then dry it in an oven for later use. Dilute the nanocellulose aqueous solution with deionized water and centrifuge it at 5000 rpm to remove coarse fibers and impurities from the solution. After centrifugation, keep the supernatant and use the casting method to cover the nanocellulose aqueous solution on the glass substrate. Place it in an oven at 40°C for 8 hours to dry. After cooling to room temperature, peel the nanocellulose film off the glass substrate to obtain a 100-300 μm biodegradable flexible encapsulation layer. ③ A layer of graphite electrode is printed on the nanocellulose film using screen printing technology, and leads are connected to the electrode surface to serve as a conductive electrode layer. ④ The clean loofah sponge flexible skeleton is immersed in carbon ink solution by solution impregnation. After being taken out and dried, the process is repeated 1-5 times to obtain a pressure-sensitive loofah sponge structure composite conductive layer. Applying pressure will change the resistance value of the composite conductive layer, thereby changing the output current. ⑤ Seal and fix the stacked materials from the edge in sequence for encapsulation. From bottom to top, they are: biodegradable flexible encapsulation layer (5), lower conductive electrode (4), loofah sponge structure composite conductive layer (3), upper conductive electrode (2), and upper biodegradable flexible encapsulation layer (1). ⑥ Fix the packaged device on the stage of the push-pull force gauge, connect the two probes of the electrical parameter tester to the two lead electrodes respectively, and apply pressure to the device through the circular pressure probe; ⑦ As the applied pressure varies, the output electrical signal of the pressure sensor changes. The output current signal of the device is detected by an electrical parameter tester, thereby enabling the detection of external static and dynamic pressure.

2. The fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The composite conductive layer (3) of the loofah sponge structure is obtained by pre-treating natural loofah sponge and then combining it with conductive materials through solution impregnation. The flexible skeleton of the loofah sponge is an elastic and deformable porous block that shrinks or rebounds with the applied pressure. The composite conductive layer (3) of the loofah sponge structure is combined with a conductive material with piezoresistive effect. The upper conductive electrode (2) and the lower conductive electrode (4) are electrodes prepared by screen printing on the surfaces of the upper biodegradable flexible encapsulation layer (1) and the lower biodegradable flexible encapsulation layer (5), respectively.

3. The fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: When static or dynamic pressure is applied to the surface of the device, the composite conductive layer of the loofah sponge structure deforms. As the pressure increases, the different conductive networks, individual conductive fibers and the conductive material itself in the composite conductive layer (3) of the loofah sponge structure will change. The number of conductive paths between the upper and lower conductive electrodes, the diameter of the conductive paths and the resistivity of the conductive material itself will change. As the pressure increases, these will become the main reasons for the change in the resistance of the device. Under the condition of an external working voltage, the device outputs a changing current signal to realize the detection of the pressure signal.

4. The fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The loofah sponge structure composite conductive layer (3) is an elastic deformable porous block based on a flexible skeleton of loofah sponge and a conductive material with piezoresistive effect; And / or the flexible skeleton of the loofah sponge is made by repeatedly soaking, drying and compacting natural loofah sponge in deionized water; And / or the loofah sponge structure composite conductive layer (3) is a square with a side length of 0.5-3cm and a thickness of 0.5-1.5cm.

5. A fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The materials of the upper conductive electrode (2) and the lower conductive electrode (4) are selected from graphite, lithium palmitate, or lithium smithsonite.

6. The fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The flexible skeleton in the composite conductive layer (3) of the loofah sponge structure is selected from natural loofah sponge; And / or the flexible framework may also include nerve grass or plant fibers; And / or the flexible skeleton has a three-dimensional mesh-like network with a diameter of 100-300μm inside.

7. A fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The conductive material of the loofah sponge structure composite conductive layer (3) is a composite material composed of at least one or more different materials, such as carbon ink, reduced graphene oxide, carbon nanotubes, two-dimensional transition metal carbon or nitride.

8. A fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The materials of the upper biodegradable flexible encapsulation layer (1) and the lower biodegradable flexible encapsulation layer (5) are selected from cellulose or lignin or starch or silk protein or collagen or polylactic acid or polyvinyl alcohol; and / or the encapsulation layer is made of the materials by solution casting.

9. A fully biodegradable flexible pressure sensor based on a loofah sponge structure according to claim 1, characterized in that: The device is completely degraded in the natural environment and the products are bio-friendly, non-toxic and harmless.

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