A method for direct writing of micropillar structures using near-field electrospun beaded fibers

Abstract

This invention discloses a method for direct writing micropillar structures using near-field electrospun beaded fibers. In this method, magnetic domain-dependent metal particles are added to the spinning solution to form a uniform beaded structure. The micropillar structure can be prepared in one step by utilizing the electrostatic repulsion and jet attraction between the beads. During the electrostatic jet process, the charge is carried by the beaded fibers, and the liquid droplets carrying the same charge repel each other. After the beaded fibers are deposited on the receiving plate, they are polarized under the action of a high-voltage electric field, carrying a positive charge and attracting liquid droplets carrying the opposite charge from the air jet. Upon contact, the liquid droplets fuse together under the action of surface tension, and then continue to attract the jet deposition to form the micropillar structure. This method solves the problems of high cost, expensive equipment, and complex preparation processes associated with traditional micropillar processing methods. Furthermore, this method can be widely used for various electrojet direct writing materials.

Description

Technical Field

[0001] This invention relates to the field of near-field electrospinning direct writing microstructure technology, and to a method for preparing micropillar structures. Background Technology

[0002] Micropillar arrays have a wide range of applications, with significant potential in electrochemical detection. Compared to planar electrodes, micropillar array electrodes offer advantages such as larger surface area and column height, stronger mass transfer capabilities, and lower detection limits. When used as three-dimensional microelectrodes, they exhibit greater specific capacitance than two-dimensional planar electrodes. Furthermore, depositing nanoparticles on micropillars can directly yield superhydrophobic surfaces. While micropillar structures hold broad application prospects, current micropillar fabrication methods suffer from significant drawbacks. Traditional methods for fabricating micropillar arrays typically include template methods, photolithography, femtosecond laser micromachining, and electrodeposition, which generally suffer from complex processes, expensive equipment, and high costs.

[0003] Near-field electrospinning direct writing technology offers a novel method for fabricating ordered micro / nanostructures. This method operates at room temperature and under normal conditions. By shortening the distance between the receiving plate and the nozzle, ordered nanofibers can be directly written using a single jet between the nozzle and the receiving plate. The geometry and deposition position of individual nanofibers can be precisely controlled. Electrospinning direct writing technology eliminates the need for templates and photolithography, providing a universal top-down technique for fabricating organic or biological nanostructures. Direct writing technology offers advantages such as high efficiency, low cost, and high flexibility, attracting increasing attention in the fabrication of micro / nano systems. Liquid droplets on electrospun fibers are often considered a "byproduct" or defect because their presence significantly reduces the surface area per unit mass. Micropillar array structures were successfully fabricated by utilizing the mutual repulsion between bead strings and the attraction and fusion after deposition. Near-field electrospinning direct writing technology requires no expensive equipment, has simple process conditions, and eliminates the need for complex procedures. Summary of the Invention

[0004] To address the aforementioned problems, this invention discloses a method for near-field electrospinning direct writing of micropillar structures. Based on near-field electrospinning direct writing technology, this invention adds magnetic domain metal particles to the spinning solution to form a uniform beaded structure. The micropillar structure can be prepared in one step by utilizing the electrostatic repulsion between the beads and the self-focusing effect of the jet. In the electrospinning jet, the charge is carried by the beaded fibers. The liquid droplets carrying the same charge repel each other but are attracted by the receiving plate. When the beaded fibers are deposited on the receiving plate, they are polarized under the action of a high-voltage electric field, carrying a positive charge, which attracts liquid droplets carrying the opposite charge from the air jet. The liquid droplets from the air jet preferentially deposit on the polarized liquid droplets, and under the action of surface tension and the attraction of the electric field, they fuse together to form small protrusions. These protrusions continue to attract jet deposition, forming the micropillar structure.

[0005] To achieve the above objectives, the present invention includes the following steps:

[0006] Step 1: Use a magnetic stirrer to fully dissolve the polymer in the solvent to obtain a polymer solution;

[0007] Step 2: Take out the magnetic stirring rotor, add magnetic domain metal particles to the polymer solution, use mechanical stirring blades to evenly disperse the magnetic domain metal particles in the polymer solution, seal with plastic wrap and let stand for 5-10 hours to eliminate air bubbles and obtain spinning solution.

[0008] Step 3: Inject the spinning solution into the micro-injector. Connect and fix the micro-injector and extension tube to the micro-injection pump. Connect the extension tube and nozzle with a metal Luer connector. Connect the metal Luer connector to the negative terminal of the electrostatic generator. Ground the receiving plate.

[0009] Step 4: Adjust the flow rate of the micro-injection pump, turn on the electrostatic generator switch to apply voltage to the metal Luer connector. The metal Luer connector can evenly transfer the charge to the nozzle. Adjust the working distance between the nozzle and the receiving plate to make the spinning solution flow out of the nozzle evenly and form a stable Taylor cone. The receiving plate moves repeatedly along the preset trajectory. As the applied voltage increases, beaded fibers can be formed on the receiving plate. After the nozzle continuously jets and deposits onto the receiving plate for a period of time, a uniform micro-pillar structure can be formed at the nozzle movement trajectory on the receiving plate.

[0010] In a further improvement, the polymer material in step one is polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), or polyvinylpyrrolidone (PVP), with a mass fraction of 4%-10%.

[0011] In a further improvement, the magnetic domain metal particles in step two include carbonyl iron powder, high-purity iron powder, and iron(III) oxide powder, with a particle size between 0.1-5 μm. The content of the added magnetic domain metal accounts for 8%-30% of the spinning solution. The addition of magnetic domain metal particles can significantly enhance the conductivity of the solution, allowing the aggregated particles to carry more charge. The metal magnetic domain particles can be uniformly dispersed in the liquid droplet structure in the fiber, making the formed bead strings more uniform.

[0012] A further improvement is made to the principle of forming the micropillar structure in step four. This is achieved by increasing the applied electric field, which increases the surface charge of the spinning jet, leading to a stronger stretching effect of the electric field on the jet and increased jet instability. This results in an increase in the number of beads in the obtained fiber. The droplets carry more of the same charge and repel each other. The droplets can maintain a certain distance when deposited on the receiving plate. The negative charge on the droplets dissipates rapidly and is then polarized under the action of the high-voltage electric field. The polarized droplet surface generates a positive charge that attracts droplets carrying negative charges in the air. The air droplets are attracted and deposited on the polarized droplets. Under the action of surface tension and the attraction of the electric field, they merge and rise. Then, the droplets on the receiving plate continue to attract droplets in the fiber to deposit, forming a micropillar structure.

[0013] Further improvements include the following specific parameters in step four: room temperature should be maintained at 30-40℃, applied voltage is 3-4KV, receiving distance is 5-10mm, flow rate is 0.3-1mL / min, and receiving plate moving speed is 30-70mm / s.

[0014] Further improvements include a bead string structure with a droplet diameter of 30-60 μm, a fiber diameter between droplets of 5-20 μm, a droplet spacing of 30-200 μm, a micropillar structure diameter of 70-150 μm, a spacing of 100-300 μm, and a micropillar height of 0.2-2 mm depending on the direct writing time.

[0015] A further improvement is that the receiving plate is not limited by material and can be a glass slide, paper, silicon plate, or aluminum foil. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the electrospun direct-write micropillar structure in this invention;

[0017] Figure 2 This is a schematic diagram of the preparation process of the spinning solution in this invention;

[0018] In the figure: Figure a shows the polymer solution being magnetically stirred; Figure b shows the polymer solution being mechanically stirred after the addition of magnetic domain metal particles; Figure c shows the spinning solution with uniformly dispersed particles obtained after standing.

[0019] Figure 3 This is a schematic diagram illustrating the forming principle of the micropillars in this invention;

[0020] In the diagram: F1 represents the electrostatic repulsion between the liquid droplets, and F2 represents the electrostatic attraction between the liquid droplets;

[0021] Figure 4 This is a schematic diagram of the nozzle's movement trajectory during the printing of a multi-row micropillar structure in Embodiment 1 of the present invention;

[0022] In the figures: Figure a shows a schematic diagram of multiple rows of micropillars with a spacing greater than 2 mm and the motion trajectory of direct writing by the nozzle; Figure b shows a schematic diagram of multiple rows of micropillars with a spacing less than 2 mm and the motion trajectory of direct writing by the nozzle.

[0023] Figure 5 This is a physical image of the micropillar structure of Embodiment 1 of the present invention;

[0024] Figure 6 This is a physical image of the beaded fiber of Embodiment 1 of the present invention;

[0025] In the diagram: 1. Microinjector; 2. Extension tube; 3. Metal Luer connector; 4. Nozzle; 5. Taylor cone; 6. Micropillar structure; 7. Receiving plate; 8. Grounding wire; 9. High-voltage electrostatic generator; 10. Negative electrode wire; 11. Micro-injection pump; 12. Magnetic stirrer; 13. Magnetic stirring rotor; 14. Plastic wrap; 15. Mechanical stirring blade; 16. Magnetic domain metal particles; 17. Liquid droplets in beaded fiber. Detailed Implementation

[0026] The following is a detailed description of the implementation examples of the present invention. These implementation examples are carried out based on the technical solution of the present invention, and provide detailed implementation methods and specific operation procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0027] Example 1

[0028] This invention is based on a method for directly writing micropillar structures using near-field electrospinning. This embodiment describes the steps and forming process for directly writing micropillar structures:

[0029] Step 1: Disperse PEO in a mixed solvent of anhydrous ethanol and deionized water, and use a magnetic stirrer 12 to fully dissolve it to obtain a PEO solution, wherein the ratio of anhydrous ethanol to deionized water is 6:4, and the mass fraction of PEO is 8%.

[0030] Step 2: Take out the magnetic rotor 13, add carbonyl iron powder particles 16 with a particle size of 1μm to the PEO solution, the mass of carbonyl iron powder accounts for 10% of the mass fraction of the solution, use mechanical stirring blades 15 to evenly disperse the carbonyl iron powder particles in the PEO solution to form a spinning solution, seal with plastic wrap 14 and let stand for 10 hours to eliminate air bubbles.

[0031] Step 3: Inject the PEO solution containing carbonyl iron powder particles into the micro-injector 1. The micro-injector 1 and the extension tube 2 are connected and fixed to the micro-injection pump 11. The extension tube 2 and the nozzle 4 are connected by a metal Luer connector 3. The negative electrode of the electrostatic generator 9 is connected to the metal Luer connector 3 to transfer the charge to the spinning solution.

[0032] Step 4: Adjust the voltage to 3.5KV, the flow rate of the syringe pump to 0.5μL / min, the distance between the receiving plates to 5mm, and the receiving speed to 50mm / s. The solution forms a stable Taylor cone 6 at the nozzle 4. Under the action of the electric field, the jet can be stably deposited on the receiving plate 7. The receiving plate 7 moves back and forth in a straight line according to the computer-designed route.

[0033] Step 5: The jet forms a beaded structure on the receiving plate. The charge is carried by the liquid droplets 17 in the beaded fibers. The liquid droplets have a larger size than the fibers and carry more charge. The liquid droplets carry the same charge and repel each other. When the beaded fibers are deposited on the receiving plate with intervals, the negative charge on the liquid droplets dissipates rapidly. Then, under the action of the high voltage electric field, they are polarized. The surface of the polarized liquid droplets generates positive charge, which attracts liquid droplets in the air that carry negative charge. The liquid droplets in the air are attracted and deposited on the polarized liquid droplets. Under the action of surface tension and the attraction of the electric field, they merge and rise together. Afterwards, the liquid droplets on the receiving plate continue to attract the liquid droplets in the fibers to deposit, forming a micro-pillar structure.

[0034] Optionally, when near-field electrospun beaded fibers are directly written into a multi-row micropillar structure, the nozzle motion trajectory is as follows: Figure 3 When the spacing between multiple rows of micropillars is greater than 2mm, the nozzle can directly write a single row of micropillars and then move longitudinally to write the next row of micropillars. When the spacing between multiple rows of micropillars is less than 2mm, the nozzle moves longitudinally to a smaller distance. The formed micropillars will attract the nozzle to continue jetting and depositing onto the original micropillars. Multiple rows of micropillars need to grow simultaneously. The nozzle moves cyclically between multiple rows of micropillars and writes multiple rows of micropillars at the same time.

[0035] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention by those skilled in the art in various equivalent forms fall within the scope defined by the appended claims.

Claims

1. A method for directly writing micropillar structures using near-field electrospun beaded fibers, characterized in that: Includes the following steps: Step 1: Use a magnetic stirrer to fully dissolve the polymer in the solvent to obtain a polymer solution; Step 2: Take out the magnetic stirring rotor, add magnetic domain metal particles to the polymer solution, use mechanical stirring blades to evenly disperse the magnetic domain metal particles in the polymer solution, seal with plastic wrap and let stand for 5-10 hours to eliminate air bubbles and obtain spinning solution. Step 3: Inject the spinning solution into the micro-injector. Connect and fix the micro-injector and extension tube to the micro-injection pump. Connect the extension tube and nozzle with a metal Luer connector. Connect the metal Luer connector to the negative terminal of the electrostatic generator. Ground the receiving plate. Step 4: Adjust the flow rate of the micro-injection pump, turn on the electrostatic generator switch to apply voltage to the metal Luer connector, the metal Luer connector will uniformly transfer the charge to the nozzle, adjust the working distance between the nozzle and the receiving plate to make the spinning solution flow out of the nozzle evenly and form a stable Taylor cone under the action of the high voltage electric field, the receiving plate moves back and forth along the preset trajectory, as the applied voltage increases, beaded fibers can be formed on the receiving plate, after the nozzle continuously jets and deposits onto the receiving plate for a period of time, a uniform micro-pillar structure can be formed at the nozzle movement trajectory on the receiving plate.

2. The method for directly writing micropillar structures using near-field electrospun beaded fibers according to claim 1, characterized in that: The specific process of forming the micropillar structure in step four is as follows: increasing the applied voltage increases the surface charge of the spinning jet, intensifies the stretching effect of the electric field on the jet, and increases the instability of the jet, thereby increasing the number of beads in the obtained fiber. The liquid beads carry more negative charges and repel each other. The liquid beads can maintain a certain distance when deposited on the receiving plate. The negative charges on the liquid beads dissipate rapidly and are then polarized under the action of the high voltage electric field. The positive charge generated on the surface of the polarized liquid beads attracts liquid beads carrying negative charges in the air. The air liquid beads are attracted and deposited on the polarized liquid beads. Under the action of surface tension and the attraction of the electric field, they merge and rise together. Then, the liquid beads on the receiving plate continue to attract liquid beads in the fiber to deposit, forming a micropillar structure.

3. The method for directly writing micropillar structures using near-field electrospun beaded fibers according to claim 1, characterized in that: In step one, the polymers are polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyvinylpyrrolidone (PVP), with a mass fraction of 4%-10%.

4. The method for directly writing micropillar structures using near-field electrospun beaded fibers according to claim 1, characterized in that: In step two, the magnetic domain metal particles include carbonyl iron powder, high-purity iron powder, and iron tetroxide powder, with a particle size of 0.1-5μm. The content of the added magnetic domain metal accounts for 8%-30% of the spinning solution. The metal magnetic domain particles can be evenly dispersed in the liquid droplets, making the formed bead strings more uniform.

5. The method for directly writing micropillar structures using near-field electrospun beaded fibers according to claim 1, characterized in that: The experimental parameters in step four are as follows: the room temperature should be maintained at 30-40℃, the applied voltage is 3-4KV, the receiving distance is 5-10mm, the flow rate is 0.3-1μL / min, and the receiving plate moving speed is 30-70mm / s.

6. The method for directly writing micropillar structures using near-field electrospun beaded fibers according to claim 1, characterized in that: In step four, the diameter of the liquid droplets in the bead string structure is 30-60 μm, the diameter of the fibers between the liquid droplets is 5-20 μm, the spacing between the liquid droplets is 30-200 μm, and the diameter of the formed micropillars is 70-150 μm with a spacing of 100-300 μm.

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