Flexible pressure sensor simulating human skin microstructure and manufacturing method thereof

Abstract

The invention discloses a flexible pressure sensor simulating a human skin microstructure and a preparation method thereof, the flexible pressure sensor adopts a multi-layer packaging structure, and the flexible pressure sensor comprises an upper flexible protective film, a bionic skin pressure-sensitive layer, a planar electrode and a lower flexible protective film from top to bottom in sequence; wherein the bionic skin pressure-sensitive layer is a conductive composite film, a bionic human skin mastoid structure on the upper surface of the bionic skin pressure-sensitive layer is in an irregular micro-convex form, and a bionic skin fiber network in the film is of a porous structure; the planar electrode is integrated on the surface of the lower-layer protective film. The preparation method comprises the following steps: forming a pressure-sensitive layer with a micro-convex and porous structure in one step by taking abrasive paper as a template and combining an ammonium bicarbonate foaming process; through the bionic composite structure design, stress concentration and buffer compression characteristics are effectively coordinated, so that the sensor has high sensitivity and wide pressure detection range, the preparation process is simple and convenient, the cost is low, and the product has excellent durability and stability.

Description

Technical Field

[0001] This invention belongs to the field of pressure sensor technology, specifically relating to a flexible pressure sensor with a microstructure that mimics human skin and its manufacturing method. Background Technology

[0003] Flexible pressure sensors, as an emerging type of sensing device, possess advantages over traditional rigid sensors, including high flexibility, excellent conductivity, outstanding biocompatibility, and lightweight portability. They can monitor key signals such as pressure intensity, duration, and frequency in real time, demonstrating broad application potential in fields such as medical health monitoring, electronic skin, and smart wearable devices. To improve their performance, microstructures are often designed on the surface of flexible substrates to enhance sensing capabilities. However, traditional microstructures, such as pyramids, microdome structures, or folded structures, perform well under low-pressure conditions but are prone to structural saturation or even collapse under medium or high pressure environments, leading to a decrease in sensing capability and difficulty in maintaining high sensitivity over a wide pressure range.

[0004] In recent years, bio-inspired sensors have attracted widespread attention due to their superior performance. However, most biomimetic sensors still resemble traditional types, often excelling in only one aspect and struggling to balance high sensitivity with a wide detection range. Furthermore, the fabrication processes for these sensors are typically complex and costly, limiting their large-scale application.

[0005] Therefore, there is still an urgent need to further research and develop a flexible pressure sensor that can be fabricated in an efficient and economical way, so that it can maintain high sensitivity over a wide pressure range to meet the growing practical application needs. Summary of the Invention

[0007] The present invention aims to provide a flexible pressure sensor that mimics the microstructure of human skin and its manufacturing method, so as to solve the technical problems in the prior art that the sensor is difficult to achieve a wide pressure detection range while having high sensitivity, and the manufacturing process is complicated and costly.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A flexible pressure sensor with a microstructure mimicking human skin includes an upper flexible protective film, a biomimetic skin pressure-sensitive layer, and a lower flexible protective film arranged sequentially from top to bottom; a planar electrode is deposited on the upper surface of the lower flexible protective film, and the planar electrode contacts the biomimetic skin pressure-sensitive layer and forms an electrical connection; The biomimetic skin pressure-sensitive layer is a conductive polymer composite film with an irregular micro-protrusion structure on its upper surface and a porous structure inside the conductive polymer composite film body.

[0009] Furthermore, both the upper and lower flexible protective films are polydimethylsiloxane films.

[0010] Furthermore, the material of the planar electrode is gold or silver.

[0011] Furthermore, the irregular micro-convex structure is a papillary structure that mimics the dermal layer of human skin.

[0012] Furthermore, the porous structure is a porous fiber network structure that mimics the internal structure of human skin.

[0013] A method for manufacturing a flexible pressure sensor that mimics the microstructure of human skin includes the following steps: (1) The sandpaper and glass plate were cleaned with deionized water and then dried. The surface of the sandpaper has an irregular micro-convex structure. (2) The polydimethylsiloxane precursor and curing agent are mixed at a mass ratio of 10:1 and magnetically stirred to obtain a polydimethylsiloxane mixture; then graphene powder, ammonium bicarbonate particles and n-hexane are added to the polydimethylsiloxane mixture and magnetically stirred again to form a uniform pressure-sensitive layer mixture solution. (3) Spin coat the pressure-sensitive layer mixture solution onto the surface of pretreated sandpaper, then heat and cure it. After curing, peel it off from the sandpaper to obtain a conductive polymer composite film with both surface micro-protrusion structure and internal porous structure, which serves as a biomimetic skin pressure-sensitive layer. (4) Mix the polydimethylsiloxane precursor and the curing agent at a mass ratio of 10:1 and stir magnetically. After stirring and mixing, spin coat the mixture onto the prepared glass plate, heat and cure it, and then peel it off to obtain a smooth polydimethylsiloxane film, which serves as the upper flexible protective film and the lower flexible protective film, respectively. (5) On the upper surface of the lower flexible protective film obtained in step (4), a planar electrode is prepared by a patterning process; the patterning process includes: using photopolymerization printing or photolithography to make an electrode mask, and then depositing a metal conductive layer by magnetron sputtering to form a planar electrode structure containing a main conductive electrode, conductive leads and connecting electrodes. (6) The bionic skin pressure-sensitive layer obtained in step (3) is covered on the planar electrode structure and conductive contact is ensured. The micro-convex structure on the surface of the bionic skin pressure-sensitive layer faces upward. Then it is aligned and bonded with the upper flexible protective film and encapsulated to obtain the final flexible pressure sensor.

[0014] Furthermore, in step (3), the spin coating speed is 600 rpm, the heating and curing temperature is 80℃, and the curing time is 2 hours.

[0015] Furthermore, in step (2), based on 27g of polydimethylsiloxane mixture, the amount of graphene powder added is 3-5g, the amount of ammonium bicarbonate particles added is 15-20g, and the amount of n-hexane added is 60 mL.

[0016] Furthermore, in step (5), the metal used to form the planar electrode is gold, silver, or copper, and its deposition thickness is 200 nm.

[0017] Furthermore, in step (1), the sandpaper has a mesh size of 100 to 400.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1) The core innovation of this invention lies in the simultaneous biomimetic design of a surface micro-protrusion structure and an internal porous structure. The irregular micro-protrusion structure on the surface effectively generates a stress concentration effect, inducing significant changes in the conductive path even under low pressure, thereby endowing the sensor with extremely high initial sensitivity. When the pressure increases, these micro-protrusion structures undergo elastic deformation and form graded contact with the contact surface, avoiding the rapid contact saturation of traditional regular structures. At the same time, the internal porous structure provides sufficient compression space for the thin film under high pressure, preventing structural collapse and thus significantly widening the upper limit of the sensor's detection range. This collaborative working mechanism of "micro-protrusion structure dominating sensitivity and porous structure responsible for measurement range" successfully solves the key technical problem of traditional sensors' inability to simultaneously achieve high sensitivity and wide detection range.

[0019] 2) The irregular micro-convex structure highly mimics the dermal papillae of human skin. Its random distribution allows it to adapt more effectively to different surface morphologies when in contact with objects, achieving a stable and continuous pressure signal response. The internal porous structure mimics the fibrous network inside the skin, jointly simulating the sensing mechanism of human skin, making the sensor's response to external pressure closer to that of real skin, exhibiting excellent linearity and stability. 3) The preparation method employed in this invention has significant cost and process advantages. Using commercially available sandpaper as a template to replicate complex biomimetic micro-convex structures, the method is extremely simple and the raw materials are readily available, eliminating reliance on complex photolithography or etching equipment. The size and density of the micro-convex structure can be precisely controlled by simply changing the sandpaper of different mesh sizes. Similarly, the thermal decomposition of ammonium bicarbonate (NH4HCO3) particles is used to create pores; the process is simple, safe, and residue-free. By selecting NH4HCO3 particles of different sizes, the pore size and porosity of the porous structure can be conveniently and precisely controlled, achieving controllable preparation of the key microstructures of the sensor.

[0020] In summary, the sensor structure provided by this invention features an ingenious design, and its fabrication process eliminates expensive and complex microfabrication techniques, making the entire process efficient, economical, and environmentally friendly. This strategy of achieving high-performance sensing at low cost significantly reduces production costs, laying a solid foundation for the large-scale application and commercialization of flexible pressure sensors in fields such as medical health, electronic skin, and intelligent robotics. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is an overall schematic diagram of a flexible pressure sensor that mimics the microstructure of human skin according to the present invention. Figure 2 This is a cross-sectional view of a flexible pressure sensor that mimics the microstructure of human skin according to the present invention. Figure 3 This is a top view of a planar electrode; Figure 4 This is a scanning electron microscope (SEM) image of the elastic pressure-sensitive layer in Example 1 of the present invention; Figure 5 Sensitivity test of the flexible pressure sensor in Example 1 of the present invention; Figure 6 This is a stability test of the flexible pressure sensor in Example 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention will be further described in detail below with reference to the embodiments.

[0026] like Figures 1-3As shown, this invention discloses a flexible pressure sensor with a microstructure mimicking human skin, comprising, from top to bottom, an upper flexible protective film 1, a biomimetic skin pressure-sensitive layer 2, and a lower flexible protective film 3. Both the upper and lower flexible protective films 1 and 3 are polydimethylsiloxane films. A planar electrode 4 is deposited on the upper surface of the lower flexible protective film 3, which contacts and electrically connects to the biomimetic skin pressure-sensitive layer 2. The planar electrode 4 is made of gold, silver, or other highly conductive materials. As per existing technology, the planar electrode 4 mainly consists of three parts: a main conductive electrode connecting to the biomimetic skin pressure-sensitive layer 2, conductive leads, and a connecting electrode connecting to an external circuit. The connecting electrode is used to connect to external measuring equipment to measure the sensing performance of the flexible pressure sensor of this invention.

[0027] The biomimetic skin pressure-sensitive layer 2 is a conductive polymer composite film with an irregular micro-protrusion structure 5 on its upper surface. The irregular micro-protrusion structure 5 is a papillary structure that mimics the dermal layer of human skin. Furthermore, the conductive polymer composite film body has a porous structure 6 inside, which mimics the porous fiber network structure inside human skin.

[0028] Example 1 This embodiment provides a flexible pressure sensor with a microstructure mimicking human skin. Its overall structure, from top to bottom, includes: an upper flexible protective film 1 with a thickness of 50 μm, a biomimetic skin pressure-sensitive layer 2 with a thickness of 1 mm, a planar electrode 4 with a thickness of 200 nm, and a lower flexible protective film 3 with a thickness of approximately 50 μm. The planar electrode 4 is in contact with the biomimetic skin pressure-sensitive layer 2 and forms an electrical connection.

[0029] The method for fabricating a flexible pressure sensor with a microstructure mimicking human skin, as described in this embodiment, includes the following steps: 1. Template Preparation: Take 100-grit sandpaper and a glass plate with irregular micro-convex structures, rinse with deionized water, and dry in an oven at 80 ℃ for 20 min. Use this sandpaper as a template to impart a three-dimensional micro-convex structure to the surface of the conductive composite film.

[0030] 2. Preparation of pressure-sensitive layer mixing solution: Mix polydimethylsiloxane precursor and curing agent at a ratio of 10:1 (mass ratio), and stir magnetically for 5 min to obtain polydimethylsiloxane mixture; then, based on 27g of polydimethylsiloxane mixture, add 3g of graphene powder, 15g of ammonium bicarbonate granules and 60ml of n-hexane, and stir magnetically again for 10 min to obtain a uniform pressure-sensitive layer mixing solution; The curing agent is a hydrogen-containing silicone oil (e.g., methylhydrosiloxane), which undergoes a hydrosilylation reaction with the vinyl groups (Vi-Si bonds) at the end of the polydimethylsiloxane precursor under heating conditions to achieve cross-linking and curing.

[0031] The n-hexane is used to dilute the polydimethylsiloxane mixture to ensure uniform dispersion of graphene. The boiling point of n-hexane is 69°C, and it can be removed by volatilization under certain heating temperature conditions.

[0032] 3. Film formation and curing: The prepared pressure-sensitive layer mixture solution was spin-coated onto the surface of treated 100-grit sandpaper at 600 rpm and then placed on a heating table for curing at 80 ℃ for 2 h.

[0033] 4. Demolding: After curing, peel it off from the sandpaper to obtain a conductive polymer composite film with both surface micro-protrusion structure and internal porous structure, which serves as a biomimetic skin pressure-sensitive layer 2.

[0034] 5. Preparation of flexible protective film: The polydimethylsiloxane precursor and curing agent are mixed at a mass ratio of 10:1 and magnetically stirred for 5 min. The mixture is then spin-coated onto the treated glass plate and cured at 80 ℃ for 2 h before being peeled off to obtain a smooth polydimethylsiloxane film, which serves as the upper flexible protective film 1 and the lower flexible protective film 3.

[0035] 6. Fabrication and device assembly of planar electrode 4: On the upper surface of the lower flexible protective film 3, an electrode mask is prepared by photopolymerization printing or photolithography. A 200 nm thick metal conductive layer (gold or silver) is deposited by magnetron sputtering to form a planar electrode 4 structure including the main conductive electrode, conductive leads and connecting electrodes.

[0036] The biomimetic skin pressure-sensitive layer 2 obtained in step 4 is placed over the planar electrode 4, ensuring good conductive contact with the micro-convex structure facing upwards. The upper flexible protective film 1 is then aligned and bonded to it to complete the overall encapsulation, resulting in the finished flexible pressure sensor.

[0037] Example 2 As an example of the present invention, a flexible pressure sensor with a microstructure mimicking human skin is described. The difference between this example and Example 1 is that the sandpaper mesh size is adjusted to 240 mesh to obtain micro-convex structures of different scales; the ratio of graphene powder, polydimethylsiloxane mixture, ammonium bicarbonate particles and n-hexane in the pressure-sensitive layer mixture is adjusted to 5 g:27 g:15 g:60 mL.

[0038] Example 3 As an example of the present invention, a flexible pressure sensor with a microstructure mimicking human skin is described. The difference between this example and Example 1 is that the sandpaper mesh size is adjusted to 400 mesh, and the ratio of graphene powder, polydimethylsiloxane mixture, ammonium bicarbonate particles and n-hexane in the pressure-sensitive layer mixture is adjusted to 3 g:27 g:20 g:60 mL.

[0039] Performance testing of a flexible pressure sensor with a microstructure mimicking human skin, according to this invention: (1) Morphological characteristics like Figure 4 As shown in the scanning electron microscope (SEM) image of the conductive polymer composite film prepared based on Example 1, its surface exhibits an irregular micro-protrusion structure derived from the sandpaper template, while the internal porous structure is formed by the decomposition and foaming of NH4HCO3 particles during the curing process. The micro-protrusion structure and the porous structure work together to endow the material with excellent pressure-sensitive properties.

[0040] (2) Sensitivity test Figure 5 The sensitivity curves of the flexible pressure sensor based on Example 1 are shown in the pressure range of 0–1000 kPa. The results show that the sensitivity is as high as 321 kPa⁻¹ in the low-pressure range (0.01–1 kPa) and good sensitivity is maintained in the high-pressure range (100–1000 kPa), indicating that the sensor has a wide range and high sensitivity characteristics.

[0041] (3) Stability test like Figure 6 As shown, under 50 kPa pressure and 2.5 Hz frequency conditions, the flexible pressure sensor in Example 1 was subjected to 5000 loading / unloading cycles, and its output signal did not show obvious drift or performance degradation, proving that the device has excellent cycle stability and reliability.

[0042] The above embodiments illustrate the typical fabrication process of the flexible pressure sensor of the present invention and its excellent mechanical and electrical properties. The mesh size of the sandpaper, the proportion of graphene and ammonium bicarbonate particles can be adjusted according to different application requirements, thereby achieving flexible control over the size, porosity and sensing performance of the micro-convex structure.

[0043] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0044] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A flexible pressure sensor that mimics the microstructure of human skin, characterized in that: It includes an upper flexible protective film, a biomimetic skin pressure-sensitive layer, and a lower flexible protective film arranged sequentially from top to bottom; a planar electrode is deposited on the upper surface of the lower flexible protective film, and the planar electrode contacts the biomimetic skin pressure-sensitive layer and forms an electrical connection; The biomimetic skin pressure-sensitive layer is a conductive polymer composite film with an irregular micro-protrusion structure on its upper surface and a porous structure inside the conductive polymer composite film body.

2. The flexible pressure sensor with a microstructure mimicking human skin according to claim 1, characterized in that: Both the upper and lower flexible protective films are polydimethylsiloxane films.

3. The flexible pressure sensor with a microstructure mimicking human skin according to claim 1, characterized in that: The planar electrode is made of gold or silver.

4. The flexible pressure sensor with a microstructure mimicking human skin according to claim 1, characterized in that: The irregular micro-convex structure is a papillary structure that mimics the dermal layer of human skin.

5. A flexible pressure sensor with a microstructure mimicking human skin according to claim 1, characterized in that: The porous structure is a porous fiber network structure that mimics the internal structure of human skin.

6. A method for manufacturing a flexible pressure sensor that mimics the microstructure of human skin, characterized in that, The steps include: (1) cleaning the sandpaper and glass plate with deionized water and drying them, the sandpaper having an irregular micro-convex structure on its surface; (2) The polydimethylsiloxane precursor and curing agent are mixed at a mass ratio of 10:1 and magnetically stirred to obtain a polydimethylsiloxane mixture; then graphene powder, ammonium bicarbonate particles and n-hexane are added to the polydimethylsiloxane mixture and magnetically stirred again to form a uniform pressure-sensitive layer mixture solution. (3) Spin coat the pressure-sensitive layer mixture solution onto the surface of pretreated sandpaper, then heat and cure it. After curing, peel it off from the sandpaper to obtain a conductive polymer composite film with both surface micro-protrusion structure and internal porous structure, which serves as a biomimetic skin pressure-sensitive layer. (4) Mix the polydimethylsiloxane precursor and the curing agent at a mass ratio of 10:1 and stir magnetically. After stirring and mixing, spin coat the mixture onto the prepared glass plate, heat and cure it, and then peel it off to obtain a smooth polydimethylsiloxane film, which serves as the upper flexible protective film and the lower flexible protective film, respectively. (5) On the upper surface of the lower flexible protective film obtained in step (4), a planar electrode is prepared by a patterning process; The patterning process includes: fabricating an electrode mask using photopolymerization printing or photolithography, and then depositing a metal conductive layer using magnetron sputtering to form a planar electrode structure containing a main conductive electrode, conductive leads and connecting electrodes. (6) The bionic skin pressure-sensitive layer obtained in step (3) is covered on the planar electrode structure and conductive contact is ensured. The micro-convex structure on the surface of the bionic skin pressure-sensitive layer faces upward. Then it is aligned and bonded with the upper flexible protective film and encapsulated to obtain the final flexible pressure sensor.

7. The method for manufacturing a flexible pressure sensor with a microstructure mimicking human skin according to claim 6, characterized in that, In step (3), the spin coating speed is 600 rpm, the heating and curing temperature is 80℃, and the curing time is 2 hours.

8. A method for manufacturing a flexible pressure sensor with a microstructure mimicking human skin according to claim 6, characterized in that, In step (2), based on 27g of polydimethylsiloxane mixture, the amount of graphene powder added is 3-5g, the amount of ammonium bicarbonate particles added is 15-20g, and the amount of n-hexane added is 60 mL.

9. A method for manufacturing a flexible pressure sensor with a microstructure mimicking human skin according to claim 6, characterized in that, The metal used to form the planar electrode in step (5) is gold, silver or copper, and its deposition thickness is 200 nm.

10. A method for manufacturing a flexible pressure sensor with a microstructure mimicking human skin according to claim 6, characterized in that, The sandpaper used in step (1) has a mesh size of 100 to 400.

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