Multi-level micro-nano structure flexible wearable pressure sensor inspired by skin and preparation method and application thereof

Abstract

The invention discloses a multi-stage micro-nano structure flexible wearable pressure sensor inspired by skin, and a preparation method and application of the multi-stage micro-nano structure flexible wearable pressure sensor. The sensor is composed of a piezoresistive layer, an electrode layer and a packaging layer. The piezoresistive layer takes polydimethylsiloxane (PDMS) as a flexible substrate, a submillimeter-level cylindrical array main structure and a micron-level skin-like spinous secondary microstructure randomly distributed at the top end of the submillimeter-level cylindrical array main structure are constructed through a composite mold, and a nano-level conductive network is formed by adopting an MXene / MWCNT hybrid material through a dispensing process, so that multi-scale stress synergistic response is realized; the electrode layer takes a degradable lignocellulose biological plastic film prepared from bagasse as a base material, and a silver paste interdigital electrode is loaded through a screen printing process; the packaging layer is fully coated with a medical-grade polyurethane (PU) film so as to ensure signal stability. The sensor shows ultrahigh sensitivity, wide detection range and low detection limit through the synergistic effect of the submillimeter-micron-nano multilevel structure, and can be applied to the fields of human motion monitoring, intelligent electronic skin and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible wearable pressure sensors, and in particular to a skin-inspired multi-level micro-nano structure flexible wearable pressure sensor and its preparation method and application. Background Art

[0002] With the rapid development of intelligent technology, high-performance flexible pressure sensors with real-time sensing capabilities, high integration potential, and mechanical flexibility have shown important application values in the fields of personal health monitoring, wearable electronics, artificial intelligence, and soft robotics. As an important member of the flexible electronics family, the new flexible sensor device can accurately and quickly capture the subtle changes in pressure and has a wide range of demands in many fields. According to the sensing principle, flexible pressure sensors are mainly divided into resistive, capacitive, piezoelectric, and self-powered types. Among them, piezoresistive sensors are regarded as one of the most promising candidates in the fields of electronic skin and human-computer interaction due to their advantages such as simple structure, low power consumption, low cost, and easy signal acquisition. However, to promote the development of flexible piezoresistive pressure sensors, several challenges must be addressed. First, it is still crucial to achieve high sensitivity in a wide pressure detection range. Second, the production process of flexible piezoresistive pressure sensors, including material selection, manufacturing, and performance optimization, must be improved to ensure green, cost-effective, and scalable manufacturing, thereby promoting their wide application. Summary of the Invention

[0003] One of the purposes of the present invention is to provide a skin-inspired multi-level micro-nano structure flexible wearable pressure sensor and its preparation method. The multi-level micro-nano structure flexible wearable pressure sensor provided by the present invention has ultra-high sensitivity, and at the same time realizes a wide pressure detection range, an ultra-low detection limit, and excellent cycle stability.

[0004] Another purpose of the present invention is to provide an application of a skin-inspired multi-level micro-nano structure flexible wearable pressure sensor in human motion monitoring. The human motion monitoring includes the monitoring of finger bending, running, and wrist pulse, but is not limited to the above monitoring contents.

[0005] The technical solution is as follows: S1. Prepare a piezoresistive layer; First, design and fabricate a hole plate mold, place it on the surface of sandpaper and fix it with tape. Then, mix and stir the PDMS base agent and curing agent with a mass ratio of 10:1 for 20 minutes. After vacuum degassing for 10 minutes, slowly pour it into the mold and cure it in a vacuum drying oven at 85°C for 15 minutes. Peel off to obtain a PDMS film with a composite microstructure, and perform plasma treatment on its surface to enhance adhesion; The Al layer in the Ti3AlC2 MAX-phase precursor was selectively etched by the hydrochloric acid-lithium fluoride (HCl-LiF) chemical etching method to prepare multi-layer MXene. Subsequently, the multi-layer MXene was ultrasonically exfoliated and centrifuged in a nitrogen atmosphere, and the supernatant was collected to obtain a monolayer MXene nanosheet dispersion. At the same time, a MWCNT dispersion was prepared using a carbon nanotube dispersion (TNWDIS). The obtained MXene nanosheet dispersion and MWCNT dispersion were mixed in a certain proportion, magnetically stirred for 30 minutes, and ultrasonically treated for 20 minutes to prepare a uniform MXene / MWCNT hybrid material. Finally, the hybrid material was uniformly drop-coated on the surface of the composite microstructured PDMS membrane and vacuum dried at 40 °C for 1 hour to form a piezoresistive layer with a multi-level micro-nano structure; S2. Prepare the interdigital electrode layer; A deep eutectic solvent (DES) was prepared using choline chloride (ChCl) and oxalic acid (OA) as raw materials. The two were mixed at a molar ratio of 1:1 and stirred at a speed of 120 rpm and a temperature of 80 °C until a uniform transparent solution was formed, and then it was cooled to room temperature for use; The bagasse was washed with hot water multiple times to reduce the sticky tissues and debris adhering to the fiber surface. The washed bagasse was dried, ground, and sieved to obtain bagasse powder with a mesh size of 200. Subsequently, the bagasse powder was mixed with DES at a mass ratio of 1:15 and heated and stirred at 110 °C for 7 hours for reaction. After the reaction was completed, deionized water was added to the brown liquid at a volume ratio of 10:1 and continuously stirred for 2 hours. The obtained suspension was washed with deionized water multiple times and centrifuged to completely remove the DES residue, and finally a uniformly dispersed cellulose-lignin slurry was obtained by ultrasonic treatment. The lignocellulose bioplastic film was obtained by vacuum filtration of the cellulose-lignin slurry. After the film material was completely dried, conductive silver paste was coated on the film surface by screen printing, and the interdigital electrode layer was prepared after curing treatment; S3. Assemble the multi-level micro-nano structure flexible wearable pressure sensor; The wire was bonded to the edge of the interdigital electrode using a thermosetting conductive silver paste, and then the multi-level micro-nano structure piezoresistive layer and the interdigital electrode were placed face to face. The flexible piezoresistive layer, electrode layer, and wire were encapsulated inside with the help of a flexible encapsulation layer (PU film), and finally a multi-level micro-nano structure flexible wearable pressure sensor was obtained.

[0006] Preferably, in the S1, the mesh size of the sandpaper is 360.

[0007] Preferably, in the S1, after removing the micro-structure, the thickness of the composite micro-structured PDMS membrane is 0.1 mm.

[0008] Preferably, in the S1, the height of the sub-millimeter cylinder is 0.1 mm and the diameter is 0.6 mm.

[0009] Preferably, the content of MXene in the prepared MXene / MWCNT hybrid material accounts for 90 wt% of the total content of MXene / MWCNT.

[0010] Preferably, in the step S2, the thickness of the prepared lignocellulose bioplastic film is 0.035 mm.

[0011] A skin-inspired multi-level micro-nano structure flexible wearable pressure sensor is prepared by the above preparation method.

[0012] The advantages of the flexible wearable pressure sensor prepared in the present invention are as follows: (1) The flexible wearable pressure sensor has ultra-high sensitivity and a wide pressure detection range. The design of its multi-level micro-nano structure and the combination of one-dimensional and two-dimensional conductive materials make it excellent in various performances and can stably monitor human physiological signals in real time.

[0013] (2) On the surface of the piezoresistive layer, skin-like micron-scale spiky microstructures are randomly distributed on the top of sub-millimeter-scale cylindrical arrays. Under slight pressure, the micron-scale spiky microstructures can first come into contact with the interdigital electrodes, greatly increasing the conductive paths and sharply decreasing the contact resistance, thereby enabling it to have an ultra-low detection limit and ultra-high sensitivity under ultra-low pressure; under relatively large pressure, the sub-millimeter-scale cylindrical arrays begin to deform and come into contact with the interdigital electrodes, further increasing the conductive paths and decreasing the contact resistance. At the same time, during the force application process, the pressure is evenly transmitted and dispersed between the MXene layers. The contact areas between two-dimensional MXene sheets, between two-dimensional MXene sheets and one-dimensional MWCNT, and between MWCNT and MWCNT will increase, and the bulk resistance of the piezoresistive layer will decrease, which means that the total resistance of the pressure sensor will correspondingly decrease. Therefore, the multi-level micro-nano structure flexible wearable pressure sensor can make full use of this synergistic effect to significantly improve its sensitivity to pressure detection and broaden the pressure detection range.

[0014] (3) The conductive coating is composed of MXene and MWCNT. The presence of the one-dimensional conductive material MWCNT improves the stacking problem of the MXene sheet material to a certain extent, and the presence of the two-dimensional conductive material MXene increases the overall conductivity of the coating.

[0015] (4) The raw material bagasse used to prepare the interdigital electrodes in the present invention is a low-value agricultural residue, and the obtained lignocellulose bioplastic film is a completely biomass-based material and can be biodegradable. The whole process is simple to operate and has the advantages of low cost and environmental protection. Description of the Drawings

[0016] Figure 1It is a cross-sectional scanning electron microscope image of the nanoscale conductive coating MXene / MWCNT.

[0017] Figure 2 It is a bending diagram of the interdigital electrode layer.

[0018] Figure 3 It is a schematic structural diagram of the multi-level micro-nano structure flexible wearable pressure sensor.

[0019] Figure 4 It is a comparison diagram of the pressure response sensitivity of the sensors in Example 1 and Example 2.

[0020] Figure 5 It is a finite element analysis diagram of the sensor in Example 1.

[0021] Figure 6 It is a current response diagram of the sensor in Example 1 under a pressure of 1.8 Pa.

[0022] Figure 7 It is a resistance response diagram of the sensor in Example 1 to the human walking signal.

[0023] Figure 8 It is a current response diagram of the sensor in Example 1 to the human wrist pulse signal. Specific embodiments The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Example 1

[0025] This example provides a multi-level micro-nano structure flexible wearable pressure sensor, and the specific steps are as follows: S1. Prepare the piezoresistive layer; Design and fabricate a hole plate mold (the template thickness is 0.1 mm, and the hole diameter is 0.6 mm). Place the fabricated hole plate mold on the surface of a 360-mesh sandpaper and fix it with tape. Then, mix the PDMS base agent and curing agent with a mass ratio of 10:1 and stir for 20 minutes. After vacuum degassing for 10 minutes, slowly pour it into the mold and cure it in a vacuum oven at 85 °C for 15 minutes. Peel off to obtain a PDMS film with a composite microstructure (ignoring the height of the microstructure, the thickness of the PDMS film is 0.1 mm), and perform plasma treatment on its surface to enhance the adhesion; Prepare MXene nanosheet dispersion and MWCNT dispersion. The preparation method of MXene nanosheet dispersion is as follows: HCl and LiF selectively etch the Al layer in the MAX phase precursor Ti3AlC2 to prepare multi-layer MXene. The multi-layer MXene is dispersed in deionized water and ultrasonically exfoliated under an inert gas (nitrogen). The ultrasonically exfoliated MXene solution is centrifuged for 30 minutes, and the supernatant is collected to obtain a monolayer MXene nanosheet dispersion (diluted to a concentration of 8 mg / ml with deionized water). The preparation method of MWCNT dispersion is as follows: 0.2 g of TNWDIS is dissolved in 48.8 g of deionized water at 40 °C. Then, 0.5 g of MWCNT powder is added to the above solution under continuous stirring until the MWCNT powder is completely wetted. The mixture is ultrasonically treated for 2 hours using an ultrasonic cell disruptor. Then, the dispersion is centrifuged at 2000 r / min for 30 minutes in a centrifuge. After centrifugation, the upper liquid is passed through a 300-mesh filter cloth to obtain the final MWCNT dispersion (diluted to a concentration of 8 mg / ml with deionized water); Mix the obtained MXene nanosheet dispersion (concentration: 8 mg / ml) and MWCNT dispersion (concentration: 8 mg / ml) in a mass ratio of 9:1, magnetically stir for 30 minutes, and ultrasonically treat for 20 minutes to prepare a uniform MXene / MWCNT hybrid material. Finally, the nanoscale MXene / MWCNT hybrid material is drop-coated on the composite microstructured PDMS membrane and placed in a vacuum drying oven for drying to finally obtain a piezoresistive layer with a multi-level micro-nano structure on the surface. Figure 1 Shows the distribution of MXene and MWCNT in the conductive coating; S2. Prepare the interdigital electrode layer; Use choline chloride (ChCl) and oxalic acid (OA) as raw materials to prepare a deep eutectic solvent (DES). Mix the two in a molar ratio of 1:1 and stir at a speed of 120 rpm and a temperature of 80 °C until a uniform and transparent solution is formed, and then cool it to room temperature for use; Wash the sugarcane bagasse with hot water multiple times to reduce the sticky tissues and debris adhering to the fiber surface. After drying the washed sugarcane bagasse, grind and sieve it to obtain sugarcane bagasse powder with a mesh size of 200. Subsequently, mix the sugarcane bagasse powder with DES at a mass ratio of 1:15, and heat and stir at 110 °C for 7 hours for reaction. After the reaction is completed, add deionized water to the brown liquid at a volume ratio of 10:1, and continuously stir for 2 hours. The obtained suspension is washed with deionized water multiple times and centrifuged to completely remove the DES residue, and finally, a uniformly dispersed cellulose-lignin slurry is obtained through ultrasonic treatment. The lignocellulose bioplastic film is obtained by vacuum filtration of the cellulose-lignin slurry. After the film material is completely dried (the thickness after drying is 0.035 mm), conductive silver paste is coated on the film surface through a screen printing process, and the interdigital electrode layer is prepared after curing treatment. As Figure 2 shown, the width of the rectangular interdigital fingers of the interdigital electrode is 0.6 mm, and the overall size is 16 mm × 22 mm; S3. Assemble a multi-level micro-nano structure flexible wearable pressure sensor; As Figure 1 shown, first, use thermosetting conductive silver paste to bond the wire to the edge of the interdigital electrode; then, place the multi-level micro-nano structure piezoresistive layer face-to-face with the interdigital electrode, and wrap the flexible piezoresistive layer, electrode layer, and wire inside with the help of a flexible encapsulation layer (PU film) to finally obtain a multi-level micro-nano structure flexible wearable pressure sensor. Example 2

[0026] This example provides a single micro-structure flexible wearable pressure sensor. The difference in its preparation method from that of Example 1 is that in S1, when preparing the single micro-structure PDMS film, the sandpaper under the orifice plate is replaced with a smooth glass sheet.

[0027] Perform the following property tests on the flexible wearable pressure sensors prepared in the above examples of the present invention: Figure 4 are the current change curves of the multi-level micro-nano structure flexible wearable pressure sensor in Example 1 and the single micro-structure flexible wearable pressure sensor in Example 2 under different pressures, indicating that under the same pressure change, the change in current of the multi-level micro-nano structure flexible wearable pressure sensor in Example 1 is large and significantly better than that of the single micro-structure flexible wearable pressure sensor in Example 2. It demonstrates the wide pressure detection range and high sensitivity of the multi-level micro-nano structure flexible wearable pressure sensor in Example 1.

[0028] Figure 5Figure 0 shows the deformation of the flexible wearable pressure sensor with multi-level micro-nano structures in Example 1 under different stress states, intuitively demonstrating that at a fine pressure, the micron-scale spiky microstructures can come into contact with the interdigital electrodes first, significantly increasing the conductive path. At a larger pressure, the sub-millimeter-scale cylindrical arrays start to deform and contact the interdigital electrodes, further increasing the conductive path.

[0029] A piece of paper was placed on the flexible wearable pressure sensor with multi-level micro-nano structures in Example 1 for current change testing, and the results are as Figure 6 shown. The detection limit of this sensor is as low as 1.8 Pa, proving that the sensor has an ultra-low detection limit.

[0030] The flexible wearable pressure sensor with multi-level micro-nano structures in Example 1 was used for real-time monitoring of human activities, and the results are as Figure 7 shown. The flexible wearable sensor with multi-level micro-nano structures can adhere to the sole of the foot to detect different human motion states.

[0031] Figure 8 Figure 14 shows the detection of the human wrist pulse by the flexible wearable sensor with multi-level micro-nano structures, proving the ability of this sensor to continuously monitor the subtle vital signs of the human body.

Claims

1. A preparation method of a skin-inspired multi-level micro-nano structure flexible wearable pressure sensor, characterized in that Including the following steps: S1. Prepare a piezoresistive layer; First, design and fabricate a hole plate mold, place it on the surface of sandpaper and fix it with tape. Then, mix the PDMS base agent and curing agent with a mass ratio of 10:1 and stir for 20 minutes. After vacuum degassing for 10 minutes, slowly pour it into the mold, cure it in a vacuum drying oven at 85 °C for 15 minutes, peel off to obtain a PDMS film with a composite microstructure, and perform plasma treatment on its surface to enhance adhesion; Adopt the hydrochloric acid-lithium fluoride (HCl-LiF) chemical etching method to selectively etch the Al layer in the Ti3AlC2 MAX phase precursor to prepare multi-layer MXene. Then, perform ultrasonic exfoliation and centrifugation on the multi-layer MXene in a nitrogen atmosphere, and collect the supernatant to obtain a monolayer MXene nanosheet dispersion. At the same time, prepare a MWCNT dispersion using a carbon nanotube dispersion (TNWDIS). Mix the obtained MXene nanosheet dispersion and MWCNT dispersion in a certain proportion, stir magnetically for 30 minutes, and perform ultrasonic treatment for 20 minutes to prepare a uniform MXene / MWCNT hybrid material. Finally, uniformly drop-coat the hybrid material on the surface of the composite microstructure PDMS film, and dry it in a vacuum at 40 °C for 1 hour to form a piezoresistive layer with a multi-level micro-nano structure; S2. Prepare an interdigital electrode layer; Use choline chloride (ChCl) and oxalic acid (OA) as raw materials to prepare a deep eutectic solvent (DES). Mix the two in a molar ratio of 1:1, stir at a speed of 120 rpm and a temperature of 80 °C until a uniform and transparent solution is formed, and then cool it to room temperature for use; Wash the bagasse with hot water multiple times to reduce the sticky tissues and debris adhering to the fiber surface. Dry the washed bagasse, grind it and sieve it to obtain bagasse powder with a mesh size of 200. Then, mix the bagasse powder and DES in a mass ratio of 1:15, and heat and stir at 110 °C for 7 hours for reaction. After the reaction is completed, add deionized water to the brown liquid in a volume ratio of 10:1, and continuously stir for 2 hours. The obtained suspension is washed with deionized water multiple times and centrifuged to completely remove the DES residue, and finally a uniformly dispersed cellulose-lignin slurry is obtained through ultrasonic treatment. The lignocellulose bioplastic film is obtained by vacuum filtration of the cellulose-lignin slurry. After the film material is completely dried, conductive silver paste is coated on the film surface through a screen printing process, and the interdigital electrode layer is obtained after curing treatment; S3. Assemble a multi-level micro-nano structure flexible wearable pressure sensor; Use thermosetting conductive silver paste to bond the wire to the edge of the interdigital electrode, and then place the multi-level micro-nano structure piezoresistive layer and the interdigital electrode face to face. With the help of a flexible encapsulation layer (PU film), the flexible piezoresistive layer, electrode layer and wire are encapsulated inside, and finally a multi-level micro-nano structure flexible wearable pressure sensor is obtained.

2. The preparation method according to claim 1, wherein In the above S1, the mesh size of the sandpaper is any one of 280 mesh, 320 mesh, 360 mesh, 400 mesh, 500 mesh, 600 mesh or 800 mesh.

3. The preparation method according to claim 1, characterized in that, In the above S1, after removing the microstructure of the composite microstructure PDMS film, the thickness range is 0.1 mm to 0.25 mm.

4. The preparation method according to claim 1, wherein In the S1, the composite microstructure is that micron-scale spiny microstructures are irregularly distributed at the top of sub-millimeter-scale cylindrical arrays; the height range of the sub-millimeter-scale cylinders is 0.1 mm to 0.15 mm, and the cylinder diameter range is 0.4 mm to 0.6 mm.

5. The preparation method according to claim 1, wherein In the S1, the content of MXene in the prepared MXene / MWCNT hybrid material accounts for 70 wt% to 90 wt% of the total content of MXene / MWCNT.

6. The preparation method according to claim 1, wherein, In the S2, the preparation method of the screen printing plate with an interdigital electrode pattern is as follows: design the shape of the interdigital electrode in Adobe Illustrator software, each rectangular interdigital finger is 0.6 mm wide, and the overall size is 16 mm × 22 mm.

7. The preparation method according to claim 1, characterized in that, In the S2, the thickness range of the prepared lignocellulose bioplastic film is 0.035 mm to 0.07 mm.

8. A skin-inspired multi-level micro-nano structured flexible wearable pressure sensor prepared by the preparation method according to any one of claims 1 to 7.

9. Application of a skin-inspired multi-level micro-nano structured flexible wearable pressure sensor according to claim 8 in human motion monitoring for non-disease diagnosis and treatment purposes.

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