Piezoelectric film with biomimetic texture and preparation method and application thereof

Abstract

The application discloses a piezoelectric film with a biomimetic texture and a preparation method and application thereof, and the piezoelectric film is formed by directional stacking and deposition of fibers with a core-shell structure, has a biomimetic morphology of alternating grooves and protrusions similar to the texture of the surface layer of human skin, and the pore size of the piezoelectric film gradually increases along the thickness direction from the attached surface; wherein the fiber with the core-shell structure comprises: a core layer with a porous structure, and the core layer comprises modified molybdenum disulfide and polyester; and a shell layer wrapping the core layer, and the shell layer comprises collagen; the piezoelectric film comprises a sensing unit area and a flexible connection area, and the crosslinking degree of collagen in the sensing unit area is greater than 75%, and the crosslinking degree of collagen in the flexible connection area is 40%-55%. The piezoelectric film has high piezoelectric constant, excellent mechanical properties, air permeability and moisture permeability under the synergistic effect of the material and structure, and has wide application prospects in the fields of electronic skin, health monitoring and the like.

Description

Technical Field

[0001] This invention relates to the fields of flexible piezoelectric materials and wearable sensing technology, specifically to a piezoelectric film with biomimetic texture, its preparation method, and its application. Background Technology

[0002] With the rapid development of wearable health monitoring, flexible sensing, and flexible energy harvesting technologies, increasingly stringent performance requirements have been placed on flexible piezoelectric films, which serve as core functional components. An ideal flexible piezoelectric film not only needs excellent piezoelectric sensing performance but also, under long-term skin-contact use, must achieve a high degree of adaptation to the microstructure of the human skin surface, efficient sweat wicking (moisture permeability) and gas exchange (breathability), as well as coordinated mechanical performance design for different functional areas. Therefore, how to design a piezoelectric film that simultaneously satisfies electrical output stability, mechanical flexibility, and physiological comfort has become a research hotspot in this field.

[0003] However, existing flexible piezoelectric films still face significant bottlenecks in structural design, making it difficult to meet the aforementioned comprehensive requirements. Firstly, regarding surface morphology adaptability, traditional planar structures cannot precisely conform to the microscopic texture of human skin, easily leading to a foreign body sensation, wrinkles, and signal coupling failure. Secondly, in balancing breathability and barrier properties, piezoelectric films with a single pore size design struggle to achieve dual functions: pores that are too small hinder sweat evaporation and gas exchange, resulting in a stuffy and humid environment at the skin-contact interface, potentially causing skin inflammation; pores that are too large fail to effectively block external dust, bacteria, and other contaminants, both affecting sensing stability. Finally, in terms of functional zoning and structural synergy, existing piezoelectric films mostly employ homogeneous structures, failing to provide gradient functions (such as gradient pore sizes) through layered construction, nor designing a mechanically adjustable sensing-flexibility zoning structure to address multi-directional skin deformation and sensing needs. This results in poor piezoelectric response stability under dynamic deformation, and difficulty in synergistically optimizing mechanical flexibility and skin compatibility, failing to meet the comprehensive performance requirements of long-term wearable devices.

[0004] Therefore, there is an urgent need to develop a novel flexible piezoelectric film and its preparation method that takes into account biomimetic skin-friendliness, breathability, and high voltage sensing accuracy. Summary of the Invention

[0005] To address the shortcomings of existing flexible piezoelectric films, such as the difficulty in balancing piezoelectric performance and biocompatibility, poor air and moisture permeability due to the lack of biomimetic structures, the contradiction between mechanical properties and flexibility, and the inability to achieve zoned functional regulation, this invention provides a piezoelectric film with biomimetic texture, its preparation method, and its applications. Through the synergistic effect of material selection and structural design, it can achieve the integration of piezoelectric performance, biocompatibility, and functional zoning. It not only has a high piezoelectric constant but also exhibits excellent mechanical properties, air permeability, and moisture permeability, showing broad application prospects in fields such as electronic skin and health monitoring.

[0006] Specifically, the following technical solutions are provided:

[0007] The first aspect of the present invention provides a piezoelectric film with biomimetic texture, wherein the piezoelectric film is formed by directional stacking and deposition of fibers with core-shell structure and has a three-dimensional porous network structure; the piezoelectric film has a biomimetic morphology of alternating grooves and protrusions that mimics the texture of human skin surface, and the pore size of the piezoelectric film is distributed in a gradient that gradually increases from the attachment surface along the thickness direction;

[0008] The fibers having a core-shell structure include:

[0009] A core layer having a porous structure and comprising modified molybdenum disulfide and polyester; and

[0010] A shell that encloses the core layer, and the shell contains collagen and polyethylene glycol;

[0011] The piezoelectric film includes a sensing unit region and a flexible connection region. The collagen cross-linking degree of the sensing unit region is greater than 75%, and the collagen cross-linking degree of the flexible connection region is 40%-55%.

[0012] To address the challenges of existing flexible piezoelectric films in simultaneously achieving high piezoelectric sensing accuracy, skin-friendliness, breathability, and mechanical properties, this invention provides a piezoelectric film with a biomimetic texture that combines excellent piezoelectric sensing performance, mechanical flexibility, and biocompatibility, as detailed below:

[0013] The biomimetic textured piezoelectric membrane provided by this invention is a three-dimensional porous network constructed from fibers with a core-shell structure, mimicking the texture of human skin. This network exhibits a gradient pore size distribution along the membrane's thickness. The skin-contact side has a small-pore layer to block external microorganisms, the middle layer forms transition channels, and the outer layer has a large-pore layer to accelerate gas exchange and sweat evaporation. This overcomes the contradiction between protection and breathability inherent in traditional single-pore membranes, and also improves the dynamic fit between the membrane and the skin. Compared to traditional single-component or planar membranes, the biomimetic texture and gradient pore size design significantly enhance the piezoelectric response sensitivity of the membrane, providing extremely high signal-to-noise ratio and capture accuracy for weak physiological signals. Furthermore, it maintains stable electrical output under long-term cyclic bending deformation and exhibits excellent fatigue resistance. Furthermore, by introducing piezoelectrically active molybdenum disulfide and a porous sponge-like structure into the fiber core layer, the molybdenum disulfide in the core layer enhances the signal output through the interlayer piezoelectric effect. The porous structure not only significantly reduces the Young's modulus of the membrane material, making it closer to the softness of human skin, but also provides a larger lattice deformation space for the piezoelectric material molybdenum disulfide, greatly enhancing the piezoelectric signal output and thus further improving the response sensitivity of the piezoelectric membrane. At the same time, the collagen in the outer layer of the fiber endows the piezoelectric membrane with excellent cell compatibility, allowing for long-term skin contact without irritation or sensitization. Furthermore, by differentially cross-linking different functional regions of the piezoelectric membrane, the collagen cross-linking degree in the sensing unit region is controlled to be greater than 75%, giving the sensing unit region high modulus and structural stability, ensuring that the piezoelectric signal is not distorted or drifted. Meanwhile, the collagen cross-linking degree in the flexible connection region is controlled within the range of 45%-50%, thus maintaining low modulus and high elongation at break, absorbing stress generated by skin stretching. This design, combining rigidity and flexibility, allows the membrane material to balance mechanical properties and piezoelectric response stability. Through the synergistic effect of the aforementioned biomimetic texture structure design, fiber material selection and structural design, and differential cross-linking, the piezoelectric membrane can accurately capture minute mechanical signals (such as pulse and respiratory vibrations) on the human skin surface without additional complex sensing modules, while ensuring long-term skin-wearing comfort and safety. This perfectly meets the core requirements of wearable health monitoring devices for accurate sensing, long-term skin-wearing, and stable durability.

[0014] Furthermore, the three-dimensional porous network structure is formed by stacking fibers with a core-shell structure, using the fingerprint grooves and porous structure of the stratum corneum on the surface of human skin as biomimetic prototypes; preferably, the width of the grooves is 200-300 μm and the depth is 80-120 μm. This width and depth match the size of the fingerprint grooves on the surface of human skin. If it deviates from this range, it will cause a foreign body sensation or wrinkles when applied to the skin, reducing the fit.

[0015] Furthermore, the protrusion is a semi-cylindrical structure formed by fiber stacking, with a preferred diameter of 150-200 μm.

[0016] Furthermore, the stacking angle of the three-dimensional porous network structure is 45° / 135°, which allows the fibers to form a stable three-dimensional network while maintaining good flexibility. Other angles can easily lead to a loose structure or excessive rigidity.

[0017] Furthermore, the porosity of the piezoelectric film is preferably 65%-80%. When the porosity is less than 65%, the air permeability is insufficient, which can easily lead to stuffiness and sweating when in contact with the skin. When the porosity is greater than 80%, the mechanical strength of the film material will be reduced, affecting the long-term stability.

[0018] Further, the average pore size of the piezoelectric film is 5-25 μm; more preferably, the piezoelectric film includes an attachment layer, an intermediate layer and an outer layer. By changing the coordination between the moving speed of the receiving platform and the fiber deposition density, a gradient pore size distribution along the thickness direction of the film is achieved, so that the average pore size of the attachment layer is 5-10 μm, the average pore size of the intermediate layer is 12-18 μm, and the average pore size of the outer layer is 20-25 μm. The thickness of the attachment layer, the intermediate layer and the outer layer are all about 1 / 3 of the thickness of the piezoelectric film.

[0019] Furthermore, the modified molybdenum disulfide is a molybdenum disulfide nanosheet coated with a modifier. The modifier is selected from one or more of polydopamine, silane coupling agent, polyethylene glycol, and polyvinyl alcohol. The above-mentioned modifier is used to modify the molybdenum disulfide nanosheet, which improves the dispersibility of molybdenum disulfide in organic solvent system, prevents agglomeration, and enhances its interfacial bonding with polyester while ensuring biocompatibility.

[0020] Furthermore, the polyester is polycaprolactone or polylactic acid, more preferably polycaprolactone, which has good spinnability, flexible mechanical properties, and good interfacial compatibility with modified molybdenum disulfide.

[0021] Furthermore, the thickness of the piezoelectric film is 100-200 μm.

[0022] A second aspect of the present invention provides a method for preparing the piezoelectric film with biomimetic texture as described in the first aspect, comprising the following steps:

[0023] S1. Modified molybdenum disulfide is dispersed in a polyester solution to obtain a mixed solution. An aqueous solution of ammonium bicarbonate is added dropwise to the mixed solution and ultrasonically dispersed to obtain a water-in-oil emulsion core spinning solution.

[0024] Collagen, polyethylene glycol, and photosensitizer are dissolved in fluorinated alcohol solvent to obtain shell spinning solution;

[0025] S2. Construct a 3D printing electrospinning system, inject the core layer spinning solution and shell layer spinning solution into the inner and outer tubes of the coaxial nozzle respectively, plan the printing path with the texture of human skin as the biomimetic prototype, adopt the near-field electrospinning direct writing process, control the relative movement of the nozzle and the receiving platform, and deposit the core and shell structure fibers in a directional manner to form an intermediate membrane with a three-dimensional porous network structure.

[0026] S3. The intermediate membrane is subjected to vacuum drying treatment, the solvent in the fiber core layer evaporates and the ammonium bicarbonate decomposes to form a porous structure, and then stepwise ultraviolet light crosslinking treatment is performed to make the collagen crosslinking degree in the sensing unit area greater than 75% and the collagen crosslinking degree in the flexible connection area 40%-55%, thus obtaining the piezoelectric membrane.

[0027] This invention utilizes a coaxial near-field direct writing process with a water-in-oil emulsion to construct a composite structure of a "porous core layer-biocompatible shell," combined with 3D printing of biomimetic textures and differentiated UV crosslinking to achieve the fabrication of a piezoelectric membrane with synergistically optimized multi-performance characteristics. First, an aqueous phase containing ammonium bicarbonate is dispersed in a modified molybdenum disulfide / polyester oil phase to prepare a core layer emulsion, with a collagen solution serving as the shell layer. Subsequently, fibers are oriented and stacked according to a biomimetic skin texture path, and vacuum drying decomposes the ammonium bicarbonate, creating in-situ pores within the core layer. This not only increases air permeability but also effectively reduces the membrane modulus, providing a larger lattice deformation space for the piezoelectric material, forming a three-dimensional gradient porous network intermediate membrane with a porous core layer and a biocompatible shell. Finally, differentiated modification of the collagen is achieved through stepwise UV crosslinking, forming a piezoelectric membrane with both highly sensitive sensing unit regions and highly flexible connection regions. The piezoelectric film prepared by the above method has a skin-like texture and a gradient pore structure, which can not only greatly improve the skin fit, but also meet the dual requirements of blocking impurities and breathability. Moreover, the differentiated cross-linking process keeps the sensing unit area structurally stable and the flexible connection area retains high deformation capability, effectively solving the contradiction between the sensing accuracy and flexible deformation of traditional piezoelectric films.

[0028] Further, in step S1, the modified molybdenum disulfide includes, but is not limited to, polydopamine-modified molybdenum disulfide. The specific preparation method is as follows: disperse few-layer molybdenum disulfide nanosheets in a dopamine Tris-HCl solution with a concentration of 1-3 mg / mL (e.g., 2 mg / mL) and a pH of 8.0-9.0, stir at room temperature for 4-8 h, and after forming a polydopamine coating layer with a thickness of 5-10 nm, centrifuge and dry to obtain the modified molybdenum disulfide. In the preparation of the above-mentioned polydopamine-modified molybdenum disulfide, it is necessary to control the concentration of the dopamine Tris-HCl solution. This concentration is crucial for forming a uniform coating layer. If the concentration is too low, for example, less than 1 mg / mL, the coating will be insufficient and the dispersibility of molybdenum disulfide will not be effectively improved. If the concentration is too high (for example, greater than 3 mg / mL), dopamine agglomeration is likely to occur, affecting the uniformity of the subsequent spinning solution. In addition, the thickness of the coating layer is controlled by controlling the stirring time, preferably 5-10 nm, to ensure the dispersibility of molybdenum disulfide while retaining its piezoelectric properties. If the thickness is less than 5 nm, the coating effect will be insufficient, which is not conducive to the uniform dispersion of molybdenum disulfide in the polyester solution. However, if the thickness is greater than 10 nm, it will hinder the transmission of piezoelectric signals and reduce the overall piezoelectric response.

[0029] Further, in step S1, the polyester solution is obtained by dissolving polyester in a solvent, wherein the polyester is polycaprolactone or polylactic acid, and the solvent is a mixed solvent of dichloromethane and dimethylformamide; more preferably, the polyester is polycaprolactone, and the solvent is a mixed solvent obtained by mixing dichloromethane and dimethylformamide in a volume ratio of 3:1. In this mixed solvent, polycaprolactone can be fully dissolved, and the prepared core spinning solution has suitable viscosity and volatility, effectively avoiding the problems of insufficient polymer dissolution or poor fiber formation during spinning.

[0030] Further, in step S1, the mass percentage of modified molybdenum disulfide in the core spinning solution is preferably 0.5wt%-2wt%, the mass percentage of polyester is preferably 6wt%-10wt%, and the mass percentage of ammonium bicarbonate is preferably 0.5wt%-1wt%. Adding an appropriate amount of modified molybdenum disulfide to the core layer enhances the piezoelectric signal output. Too little addition has no significant effect, while too much addition, such as greater than 2wt%, can lead to molybdenum disulfide aggregation and uneven dispersion, resulting in unstable piezoelectric signal output. Therefore, preferably, the mass percentage of modified molybdenum disulfide in the core spinning solution is controlled within the range of 0.5wt%-2wt%. Additionally, polyester, as a skeleton providing mechanical support, is an essential component in the core spinning solution. Adding too much polyester will reduce the piezoelectric response, while adding too little polyester will result in poor structural stability. Preferably, the mass percentage of modified molybdenum disulfide in the core spinning solution is controlled within the range of 6wt%-10wt%. Furthermore, the introduction of ammonium bicarbonate is a key component for forming a porous sponge-like structure. If the amount added is too small, for example, the concentration is below 0.5 wt%, a connected micro-nano pore network cannot be formed, resulting in a dense core layer and excessively high modulus. However, if the concentration is above 1 wt%, it will lead to excessive pores or even collapse inside the fiber, destroying the integrity of the core layer skeleton and reducing the mechanical properties of the fiber. Therefore, it is preferable to control the mass ratio of ammonium bicarbonate in the core layer spinning solution within the range of 0.5 wt% to 1 wt%.

[0031] Furthermore, in step S1, the aqueous ammonium bicarbonate is uniformly dispersed in the mixed solution (oil phase) by ultrasonic dispersion to form a stable water-in-oil emulsion. Preferably, the ultrasonic power is 200-400 W and the time is 10-20 min.

[0032] Further, in step S1, the collagen content in the shell spinning solution is preferably 2wt%-6wt%, and the polyethylene glycol content is preferably 0.4wt%-1wt%. Adding an appropriate amount of polyethylene glycol to the collagen solution optimizes the film-forming properties of the collagen.

[0033] More preferably, in step S1, the mass ratio of the photosensitizer to collagen is (0.005-0.015):1, and the photosensitizer is riboflavin. This invention uses riboflavin as a photoinitiator to induce chemical cross-linking between collagen molecules under ultraviolet light irradiation. Furthermore, riboflavin possesses excellent biocompatibility, effectively avoiding the cytotoxic residues of traditional chemical cross-linking agents (such as glutaraldehyde).

[0034] Furthermore, in step S1, the fluorinated alcohol solvent is hexafluoroisopropanol and / or trifluoroethanol, used to dissolve collagen without affecting the structural stability of the protein molecules or the subsequent photocrosslinking reaction.

[0035] Further, in step S2, the parameters of the near-field electrospinning direct writing process are as follows: spinning voltage is 1-5 kV, receiving distance is 0.5-2 cm, core layer advance rate is 0.6-1.0 mL / h, shell layer advance rate is 0.4-0.7 mL / h, receiving platform moving speed is 10-50 mm / s, and spinning temperature is 20-30 ℃; preferably, the printing attachment layer receiving platform moving speed is < the printing intermediate layer receiving platform moving speed < the printing outer layer receiving platform moving speed, for example, the printing attachment layer receiving platform moving speed is 10-20 mm / s, the printing intermediate layer receiving platform moving speed is 20-35 mm / s, and the printing outer layer receiving platform moving speed is 35-50 mm / s.

[0036] Furthermore, in step S2, the intermediate membrane has a biomimetic surface morphology of alternating grooves and protrusions that mimics the texture of human skin, and the pore size of the intermediate membrane is distributed in a gradient manner along the thickness direction.

[0037] Furthermore, in step S3, the vacuum drying process is carried out at a temperature of 35-50 ℃ for 4-8 h, for example, drying at 40 ℃ for 6 h, so that the solvent in the core layer can be fully volatilized and the ammonium bicarbonate can be fully decomposed to generate gas, leaving dense and uniform micropores inside the fiber to form a porous core layer structure.

[0038] Further, in step S3, the stepwise ultraviolet crosslinking treatment specifically involves: first, subjecting the vacuum-dried intermediate membrane to a maskless primary light irradiation treatment; then, covering it with a mask and subjecting the unmasked sensing unit area to a secondary light irradiation treatment, resulting in a collagen crosslinking degree greater than 75% in the sensing unit area and a collagen crosslinking degree of 40%-55% in the flexible connection area, thereby obtaining the piezoelectric membrane. Preferably, in the primary light irradiation step: the wavelength is 365 nm (ultraviolet light at this wavelength has the highest crosslinking efficiency for collagen, and the photon energy is moderate, preventing protein peptide bond breakage or excessive degradation, thus ensuring the biocompatibility and piezoelectric performance of the membrane material), the power is 8-10 W, the irradiation distance is 13-15 cm, and the irradiation time is 3-5 min; in the secondary light irradiation step: the wavelength is 365 nm, the power is 10-15 W, the irradiation distance is 10-12 cm, and the irradiation time is 14-18 min.

[0039] This invention utilizes a stepwise ultraviolet irradiation process to regulate the differentiated cross-linking degree of collagen. Specifically, low-power full-film pre-cross-linking is first performed to establish the baseline performance of the flexible connection region. Then, a mask is used to perform high-power directional enhanced cross-linking on the sensing unit region, thereby improving the structural stability of the sensing unit region and preserving the high deformation capability of the flexible connection region, further optimizing the synergistic adaptation between the sensing accuracy and flexibility of the piezoelectric film.

[0040] Furthermore, the mask is made of flexible polyimide (PI) with a light-blocking rate of ≥98%. This material has excellent adhesion and can closely adhere to the 3D printed textured surface, preventing edge blurring caused by ultraviolet light diffraction.

[0041] Furthermore, the mask plate is formed by laser etching to form a pattern of through holes in the sensing unit area and light-shielding strips in the flexible connection area. Preferably, the thickness of the mask plate is 50-80 μm, the side length of the through holes in the mask plate corresponding to the sensing unit area is 0.8-2 mm, and the width of the light-shielding strips in the mask plate corresponding to the flexible connection area is 200-500 μm.

[0042] Furthermore, in step S3, the stepwise ultraviolet irradiation process is carried out under conditions of 40%-50% humidity. If the humidity is too high (e.g., greater than 50%), the membrane surface will absorb moisture, affecting the uniformity of the crosslinking reaction. If the humidity is too low (e.g., less than 40%), the collagen fibers will lose too much water and become brittle during the irradiation process, reducing the mechanical properties of the membrane.

[0043] The third aspect of this invention provides an application of the piezoelectric film with biomimetic texture described in the first aspect or the piezoelectric film with biomimetic texture prepared by the preparation method described in the second aspect in a wearable health monitoring device.

[0044] The beneficial effects of this invention are:

[0045] 1. This invention provides a piezoelectric membrane with a biomimetic texture, which is formed by oriented stacking of composite fibers, with modified molybdenum disulfide / polyester as the porous core layer and collagen / polyethylene glycol as the shell layer, based on the biomimetic texture of human skin surface. Through the synergistic effect of the aforementioned fiber components and the porous core structure, the Young's modulus of the piezoelectric membrane is significantly reduced, making it closer to the softness of human skin, and the piezoelectric signal output is effectively enhanced. It also solves the problems of excessive rigidity, poor skin-feel, and insufficient sensitivity caused by limited deformation in traditional dense piezoelectric membranes. Furthermore, its biomimetic texture design significantly increases the contact area and friction between the piezoelectric membrane and the skin, thereby improving dynamic adhesion stability and achieving a perfect balance between high-sensitivity sensing and flexible skin-feel. In addition, the piezoelectric membrane has a gradient pore size structure along its thickness direction, with smaller inner pores and larger outer pores. The inner layer's micro-mesh pores effectively block external dust particles and, through the tortuous path of the fiber layer, prevent the direct invasion of microorganisms. The outer layer's larger pores accelerate sweat evaporation and gas exchange, effectively solving the problem of "sweating" in wearable devices. Furthermore, by controlling the degree of collagen cross-linking in different regions of the piezoelectric membrane, functional zoning of the sensing unit area and the flexible connection area is achieved. This results in the sensing unit area possessing high modulus and high structural stability, ensuring undistorted and drift-free piezoelectric signal transmission. Meanwhile, the flexible connection area maintains low modulus and high elongation at break, absorbing stress generated by skin stretching. This design, combining rigidity and flexibility, allows the piezoelectric membrane to maintain the stability and accuracy of its sensing function even under significant human body movements, significantly outperforming traditional uniformly cross-linked membrane materials. Through the synergistic effect of the aforementioned materials and structure, the biomimetic textured piezoelectric membrane combines excellent properties such as high piezoelectric sensing accuracy, skin-friendliness, and breathability.

[0046] 2. This invention also provides a method for preparing the above-mentioned piezoelectric membrane with biomimetic texture. On the one hand, by combining water-in-oil emulsion method with coaxial spinning, a composite fiber with modified molybdenum disulfide / polycaprolactone as a porous core layer and collagen / polyethylene glycol as a biological shell layer is constructed, achieving a synergistic improvement in piezoelectric sensitivity and biomechanical adaptability. On the other hand, by combining 3D printing of biomimetic texture and near-field electrospinning direct writing technology, the refined construction of biomimetic texture and gradient breathable network is achieved, significantly improving the skin-fit, breathability, moisture permeability and adhesion stability of the membrane material. Finally, by adopting a differentiated process of stepwise ultraviolet light crosslinking, first pre-crosslinking the whole and then enhancing the local mask, a piezoelectric membrane with a high modulus and high structural stability sensing unit area and a low modulus and high elongation at break flexible connection area is prepared, so that the piezoelectric membrane can maintain the stability and accuracy of sensing function under large human body movements, effectively overcoming the inherent contradiction between the sensing accuracy and flexible deformation of existing piezoelectric membranes.

[0047] 3. The preparation method provided by this invention employs a highly automated, integrated molding process, offering significant advantages for industrial production. Through fully mechanized directional stacking deposition control, it not only achieves precise construction of complex microstructures such as biomimetic textures, gradient pore sizes, and core-shell structures, but also completes the functional partitioning of the sensing and flexible regions on the same membrane material using region-selective crosslinking technology. The entire process is automated by programmed equipment, avoiding errors and uncertainties caused by manual operation and ensuring structural consistency and performance stability between batches of products. This excellent reproducibility, combined with a continuous process flow, allows this preparation method to overcome the limitations of traditional multi-layer physical stacking or manual post-processing, meeting the needs of large-scale, standardized production and providing a reliable technical path for the industrial application of flexible piezoelectric films in the fields of electronic skin and health monitoring. Attached Figure Description

[0048] Figure 1 A flowchart illustrating the preparation process of the piezoelectric film provided by this invention;

[0049] Figure 2 This is a schematic diagram of the structure of a fiber with a core-shell structure provided by the present invention;

[0050] Figure 3 A schematic diagram of the surface texture of human skin;

[0051] Figure 4 A schematic diagram of the gradient aperture structure of the piezoelectric film cross-section provided by the present invention;

[0052] Figure 5 A schematic diagram of the functional partitions of the piezoelectric film provided by the present invention;

[0053] Figure 6 This is a schematic diagram of the coaxial electrospinning device used in this invention;

[0054] In the figure, 101 is the porous core layer, 102 is the shell layer, 201 is the attachment side, 202 is the middle region, 203 is the outer side, 301 is the ultraviolet lamp, 302 is the mask plate, 303 is the sensing unit area, 304 is the flexible connection area, 401 is the core layer spinning solution, 402 is the shell layer spinning solution, 403 is the spinneret, 404 is the receiving platform, and 405 is the high voltage power supply. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0057] In this invention, unless otherwise specified, all equipment and raw materials are available from the market or commonly used in the industry. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0058] The materials and equipment used in the following embodiments are shown in Tables 1 and 2:

[0059] Table 1 Materials and Reagents

[0060]

[0061] Table 2 Equipment

[0062]

[0063] Example 1: This example relates to the preparation of a piezoelectric film with a biomimetic texture, as detailed below:

[0064] (1) The few-layer molybdenum disulfide nanosheets were dispersed in a dopamine Tris-HCl solution with a concentration of 2 mg / mL and pH=8.5. The mixture was stirred at 400 rpm for 6 h at room temperature to form a polydopamine coating layer with a thickness of 8 nm. After centrifugation at 8000 rpm for 15 min, the modified molybdenum disulfide was obtained by vacuum drying at 60 ℃ for 12 h.

[0065] Mix 30 mL of dichloromethane with 10 mL of dimethylformamide (volume ratio 3:1), then add 0.55 g of modified molybdenum disulfide, 4.40 g of polycaprolactone, and 0.40 g of ammonium bicarbonate. First, dissolve the mixture using magnetic stirring, then ultrasonically disperse it at 300 W for 15 min to ensure uniform dispersion of the ammonium bicarbonate aqueous phase, resulting in a stable water-in-oil emulsion core spinning solution. The concentration of modified molybdenum disulfide is 1 wt%, the concentration of polycaprolactone is 8 wt%, and the concentration of ammonium bicarbonate is 0.7 wt%.

[0066] Take 50 mL of hexafluoroisopropanol, add 2.5 g of collagen (3 wt%), 0.5 g of polyethylene glycol (0.6 wt%), and 0.025 g of riboflavin, and stir at room temperature for 4 h until completely dissolved to obtain a shell spinning solution containing a photoinitiator, wherein the concentration of collagen is 3 wt% and the concentration of polyethylene glycol is 0.6 wt%.

[0067] (2) A 3D printing-near-field electrospinning direct writing system was constructed. The core layer spinning solution was injected into the inner tube of the coaxial nozzle (0.25 mm in diameter), and the shell layer spinning solution was injected into the outer tube (0.55 mm in diameter). The printing path was set as a biomimetic fingerprint groove (45° / 135° staggered stacking), and the process parameters were: voltage 2.5 kV, receiving distance 2 cm, core layer propulsion rate 0.8 mL / h, shell layer propulsion rate 0.5 mL / h, and temperature 25 ℃. Taking advantage of the high volatility of hexafluoroisopropanol, the shell layer solvent evaporated rapidly after the coaxial jet was ejected, avoiding dissolution and damage to the polycaprolactone core layer and maintaining the integrity of the core-shell interface. During the printing process, the speed of the receiving platform is set in layers: 10 mm / s when printing the skin layer, 25 mm / s when printing the intermediate layer, and 40 mm / s when printing the outer layer, thus forming a gradient structure with dense inner layers and sparse outer layers, resulting in a 3D intermediate film with a groove width of 250 μm and a depth of 100 μm.

[0068] (3) The 3D intermediate film was vacuum dried at 40 °C for 6 h. During this process, the tiny droplets in the core layer evaporated and the ammonium bicarbonate decomposed to produce gas, creating pores in situ inside the core layer and forming a porous core layer structure. The final measured average pore size was 8 μm on the skin-adhering side, 15 μm on the intermediate layer, and 22 μm on the outer side, with an overall porosity of 72%.

[0069] A stepwise UV crosslinking process was employed. The first step involved pre-crosslinking the entire film without a mask, irradiating the entire film material with low power (9 W, 14 cm distance, 5 min) to establish the basic properties of the flexible connection region. The second step involved localized enhanced crosslinking, covering the sensor unit area with a 60 μm thick flexible polyimide mask with 99% light-blocking capability (1.5 mm square through-holes for the sensor unit area and 300 μm light-blocking strips for the flexible connection area). The sensor unit area was then subjected to high-power directional irradiation (12 W, 11 cm distance, 16 min). The ambient humidity was controlled at 45%, resulting in a 150 μm thick piezoelectric film.

[0070] Example 2: This example relates to the preparation of a piezoelectric film with biomimetic texture. The only difference from Example 1 is that the concentration of modified molybdenum disulfide in the core spinning solution prepared in step (1) is 2 wt%. All other operations are the same, and the corresponding piezoelectric film is prepared.

[0071] Example 3: This example relates to the preparation of a piezoelectric film with biomimetic texture. The only difference from Example 1 is that the collagen concentration in the shell spinning solution prepared in step (1) is 4 wt%, and the rest of the operation is the same, and the corresponding piezoelectric film is prepared.

[0072] Comparative Example 1: This comparative example relates to the preparation of a piezoelectric film with biomimetic texture. The only difference from Example 1 is that no modified molybdenum disulfide was added to the core spinning solution prepared in step (1). All other operations were the same, and the corresponding piezoelectric film was prepared.

[0073] Comparative Example 2: This comparative example relates to the preparation of a piezoelectric film with biomimetic texture. The only difference from Example 1 is that ammonium bicarbonate was not added to the core spinning solution prepared in step (1). All other operations were the same, and the corresponding piezoelectric film was prepared.

[0074] Comparative Example 3: This comparative example relates to the preparation of a piezoelectric film. The only difference from Example 1 is that in step (2), the traditional far-field electrospinning process (voltage 20 kV, distance 15 cm, receiving roller speed 200 rpm) is used instead of the 3D printing-near-field electrospinning direct writing process to collect randomly arranged fiber felts without biomimetic texture structure.

[0075] Comparative Example 4: This comparative example relates to the preparation of a piezoelectric film with biomimetic texture. The only difference from Example 1 is that: instead of using stepwise differentiated crosslinking, the entire film material is directly subjected to uniform high-intensity irradiation parameters (12 W power, 11 cm distance, irradiation for 29 min) to make the entire film material be in a high degree of crosslinking, thus obtaining a corresponding piezoelectric film without functional partitions.

[0076] Performance testing: The piezoelectric films prepared in Examples 1-3 and Comparative Examples 1-4 were tested for piezoelectric properties, mechanical properties, air permeability, moisture permeability, and biocompatibility. The specific test methods are as follows:

[0077] (1) Piezoelectric constant (d 33 (Refer to GB / T 3389.2-1999 "Test Methods for Performance of Piezoelectric Ceramic Materials" - Longitudinal Piezoelectric Strain Constant d) 33 The static test standard is used for determination.

[0078] (2) Elongation at break: Determined in accordance with GB / T 24218.3-2010 Textiles - Test methods for nonwoven fabrics - Part 3: Determination of elongation at break (strip method)

[0079] (3) Air permeability: Determined according to GB / T 5453-2025 "Determination of air permeability of textile fabrics".

[0080] (4) Moisture permeability: Determined according to GB / T 12704.1-2009 "Textiles - Test Methods for Moisture Permeability of Fabrics - Part 1: Moisture Absorption Method".

[0081] (5) Relative cell proliferation rate (biocompatibility): Determined according to GB / T 16886.5-2017 "Biological evaluation of medical devices - Part 5: In vitro cytotoxicity test".

[0082] The test results are shown in Table 3 below:

[0083] Table 3 Sample performance test data

[0084]

[0085] As shown in the table above, the piezoelectric films with biomimetic textures prepared in Examples 1-3 not only have high piezoelectric constants, but also high elongation at break, high air permeability, excellent moisture permeability, and biocompatibility, meeting the various requirements of wearable health monitoring devices for accurate sensing, long-term skin contact, and stable durability.

[0086] As shown in Example 1 and Comparative Example 1, the piezoelectric constant of the piezoelectric membrane prepared without modified molybdenum disulfide in the fiber core layer (Comparative Example 1) is significantly reduced to only 8.2 pC / N, far lower than that of the piezoelectric membrane prepared in Example 1. This indicates that modified molybdenum disulfide is a necessary component for achieving the piezoelectric response of the piezoelectric membrane. Furthermore, the piezoelectric membrane constructed from solid core layer fibers prepared in Comparative Example 2 without the addition of ammonium bicarbonate to the core layer spinning solution exhibits varying degrees of decrease in piezoelectric properties, mechanical properties, and air and moisture permeability. This is because the dense core layer results in excessively high fiber modulus, limiting the piezoelectric lattice deformation of the internal molybdenum disulfide; and the lack of micro-nano pore channels within the fiber hinders gas permeation within the fiber, significantly reducing air and moisture permeability. Therefore, the sponge-like porous core layer constructed in this invention not only reduces modulus and improves sensitivity but also serves as an auxiliary gas exchange microchannel, further optimizing the air and moisture permeability of the membrane material.

[0087] Furthermore, as demonstrated in Example 1 and Comparative Examples 3 and 4, the biomimetic three-dimensional porous network structure constructed in this invention plays a crucial role in air and moisture permeability, and the functional partitions formed through differentiated cross-linking can significantly improve the flexibility of the piezoelectric membrane. The piezoelectric membrane lacking biomimetic texture and gradient structure (Comparative Example 3), due to the disordered and tightly packed fibers and the absence of macroscopic flow channels, has an air permeability reduced to 110 mm / s and a moisture permeability of 2600 g / (m²). 2 • 24 h), which seriously affects the wearing comfort; while compared with the piezoelectric film without functional partitions (Comparative Example 4), the elongation at break of the piezoelectric film prepared in Example 1 is significantly improved, from 45% to 165%, and the piezoelectric constant is not reduced. It can be seen that by performing functional partitioning on the piezoelectric film through differential crosslinking, the flexibility of the piezoelectric film can be effectively enhanced while ensuring excellent piezoelectric performance, and the problem of high rigidity and easy brittleness of fully crosslinked piezoelectric materials can be solved.

[0088] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A piezoelectric film with a biomimetic texture, characterized in that, The piezoelectric film is formed by the directional stacking and deposition of fibers with a core-shell structure, and has a three-dimensional porous network structure. The piezoelectric film has a biomimetic morphology of alternating grooves and protrusions that mimics the texture of human skin, and the pore size of the piezoelectric film is distributed in a gradient that gradually increases from the attachment surface along the thickness direction. The fibers having a core-shell structure include: A core layer having a porous structure, and the core layer comprising modified molybdenum disulfide and polyester; and A shell that encloses the core layer, and the shell contains collagen and polyethylene glycol; The piezoelectric film includes a sensing unit region and a flexible connection region. The collagen cross-linking degree of the sensing unit region is greater than 75%, and the collagen cross-linking degree of the flexible connection region is 40%-55%.

2. The piezoelectric film with biomimetic texture according to claim 1, characterized in that, The three-dimensional porous network structure is formed by stacking fibers with a core-shell structure, using the fingerprint grooves and porous structure of the stratum corneum of human skin as biomimetic prototypes. And / or, the porosity of the piezoelectric film is 65%-80%, and the average pore size is 5-25 μm.

3. A piezoelectric film with a biomimetic texture according to claim 1 or 2, characterized in that, The stacking angle is 45° / 135°, with alternating stacking. And / or, the width of the trench is 200-300 μm and the depth is 80-120 μm; And / or, the protrusion is a semi-cylindrical structure formed by fiber stacking, with a diameter of 150-200 μm; And / or, the piezoelectric film includes an attachment layer, an intermediate layer and an outer layer, wherein the average pore size of the attachment layer is 5-10 μm, the average pore size of the intermediate layer is 12-18 μm, and the average pore size of the outer layer is 20-25 μm.

4. The piezoelectric film with biomimetic texture according to claim 1, characterized in that, The modified molybdenum disulfide is a molybdenum disulfide nanosheet coated with a modifier, wherein the modifier is selected from one or more of polydopamine, silane coupling agent, polyethylene glycol, and polyvinyl alcohol. And / or, the polyester is polycaprolactone or polylactic acid.

5. A method for preparing a piezoelectric film with biomimetic texture, characterized in that, Includes the following steps: S1. Modified molybdenum disulfide is dispersed in a polyester solution to obtain a mixed solution. An aqueous solution of ammonium bicarbonate is added dropwise to the mixed solution and ultrasonically dispersed to obtain a water-in-oil emulsion core spinning solution. Collagen, polyethylene glycol, and photosensitizer are dissolved in fluorinated alcohol solvent to obtain shell spinning solution; S2. Construct a 3D printing electrospinning system, inject the core layer spinning solution and shell layer spinning solution into the inner and outer tubes of the coaxial nozzle respectively, plan the printing path with the texture of human skin as the biomimetic prototype, adopt the near-field electrospinning direct writing process, control the relative movement of the nozzle and the receiving platform, and deposit the core and shell structure fibers in a directional manner to form an intermediate membrane with a three-dimensional porous network structure. S3. The intermediate membrane is subjected to vacuum drying treatment, the solvent in the fiber core layer evaporates and the ammonium bicarbonate decomposes to form a porous structure, and then stepwise ultraviolet light crosslinking treatment is performed to make the collagen crosslinking degree in the sensing unit area greater than 75% and the collagen crosslinking degree in the flexible connection area 40%-55%, thus obtaining the piezoelectric membrane.

6. The preparation method according to claim 5, characterized in that, In step S1, the modified molybdenum disulfide is prepared as follows: few-layer molybdenum disulfide nanosheets are dispersed in a dopamine Tris-HCl solution with a concentration of 1-3 mg / mL and a pH of 8.0-9.0, stirred at room temperature for 4-8 h, and after forming a polydopamine coating layer with a thickness of 5-10 nm, the mixture is centrifuged and dried to obtain the modified molybdenum disulfide. And / or, the polyester solution is obtained by dissolving polyester in a solvent, wherein the polyester is polycaprolactone or polylactic acid, and the solvent is a mixture of dichloromethane and dimethylformamide; And / or, the modified molybdenum disulfide in the core spinning solution has a mass percentage of 0.5wt%-2wt%, the polyester has a mass percentage of 6wt%-10wt%, and the ammonium bicarbonate has a mass percentage of 0.5wt%-1wt%. And / or, the collagen content in the shell spinning solution is 2wt%-6wt%, and the polyethylene glycol content is 0.4wt%-1wt%. And / or, the mass ratio of the photosensitizer to collagen is (0.005-0.015):1, and the photosensitizer is riboflavin; And / or, the fluorinated alcohol solvent is hexafluoroisopropanol and / or trifluoroethanol.

7. The preparation method according to claim 5, characterized in that, In step S2, the parameters of the near-field electrospinning direct writing process are as follows: spinning voltage is 1-5 kV, receiving distance is 0.5-2 cm, core layer advance rate is 0.6-1.0 mL / h, shell layer advance rate is 0.4-0.7 mL / h, receiving platform moving speed is 10-50 mm / s, and spinning temperature is 20-30 ℃. The intermediate membrane has a biomimetic surface morphology with alternating grooves and protrusions that mimic the texture of human skin, and the pore size of the intermediate membrane is distributed in a gradient manner along the thickness direction.

8. The preparation method according to claim 5, characterized in that, In step S3, the vacuum drying process is carried out at a temperature of 35-50 °C for 4-8 h. And / or, the stepwise ultraviolet crosslinking process specifically involves: first, subjecting the vacuum-dried intermediate film to a maskless first light irradiation treatment, then covering it with a mask and subjecting the unmasked sensing unit area to a second light irradiation treatment, so that the collagen crosslinking degree in the sensing unit area is greater than 75%, and the collagen crosslinking degree in the flexible connection area is 40%-55%, thereby obtaining the piezoelectric film.

9. The preparation method according to claim 8, characterized in that, In step S3, the first light irradiation process has the following characteristics: wavelength of 365 nm, power of 8-10 W, irradiation distance of 13-15 cm, and irradiation time of 3-5 min. And / or, in the secondary light irradiation step: the wavelength is 365 nm, the power is 10-15 W, the irradiation distance is 10-12 cm, and the irradiation time is 14-18 min.

10. The application of a piezoelectric film with biomimetic texture as described in any one of claims 1-4, or a piezoelectric film with biomimetic texture prepared by the preparation method as described in any one of claims 5-9, in a wearable health monitoring device.

Images