Microfluidic chip printing port partial super-hydrophobic modification structure and preparation method thereof

Abstract

The application relates to a microfluidic chip printing port local super-hydrophobic modification structure and a preparation method thereof. The microfluidic chip printing port local super-hydrophobic modification structure comprises a microfluidic chip body, the microfluidic chip body has a micro-channel and a printing port in communication with the micro-channel, the printing port is used for outputting liquid and generating liquid drops; a micro-column array is arranged on the chip surface around the printing port, the micro-column array comprises a plurality of interval-arranged micro-scale protrusions, and a micro-column gap is formed between adjacent micro-scale protrusions; wherein the micro-column array is configured to trap an air layer at the printing port in a printing process, form an air cushion layer between the liquid and the chip surface around the printing port, form a solid-liquid-air composite contact state between the liquid to be printed and the chip surface around the printing port, and inhibit the spreading, liquid hanging, liquid residue and liquid leakage of the liquid to be printed at the printing port.

Description

Technical Field

[0001] This invention relates to the field of microfluidic chip technology, and in particular to a locally superhydrophobic modified structure for the printing port of a microfluidic chip and its preparation method. Background Technology

[0002] Microfluidic chip technology has been widely applied in droplet printing, biosensing, drug screening, and precision medicine. In microfluidic printing, the printhead, as a key component for liquid output and droplet formation, directly affects the droplet formation quality, size consistency, and printing accuracy due to its surface wettability. However, existing microfluidic chip printheads typically use hydrophilic or weakly hydrophobic materials. During printing, the liquid to be printed can easily spread uncontrollably around the printhead, leading to unstable droplet formation and trajectory deviation. After printing, residual liquid can cause leakage and cross-contamination, severely impacting print repeatability and long-term reliability.

[0003] In related technologies, methods such as overall chemical hydrophobic treatment, fluorination modification, or surface coating are often used. However, these methods often require processing the entire microfluidic chip, which is not only complex and costly, but also has poor compatibility with microfabrication processes. They may also alter the surface properties inside the microchannels, affecting the normal transport and driving performance of fluids, and even pose risks such as coating peeling, microchannel blockage, or the introduction of chemical contamination. Furthermore, it is difficult to achieve precise localized superhydrophobic modification in the printing port area, and it is also difficult to maintain the original performance of other functional areas of the microfluidic chip. Summary of the Invention

[0004] This invention provides a locally superhydrophobic modified structure for the printing port of a microfluidic chip and its preparation method, aiming to solve at least one of the technical problems existing in the prior art.

[0005] The technical solution of this invention is a locally superhydrophobic modified structure for the printing port of a microfluidic chip, comprising: A microfluidic chip body, the microfluidic chip body having a microchannel and a printing port communicating with the microchannel, the printing port being used to output liquid and generate droplets; A micropillar array is disposed on the chip surface around the printout, the micropillar array comprising a plurality of spaced microscale protrusions, with micropillar gaps formed between adjacent microscale protrusions; The micropillar array is configured to trap an air layer at the print port during the printing process, forming an air cushion layer between the liquid and the chip surface around the print port, so that the liquid to be printed and the chip surface around the print port form a solid-liquid-gas composite contact state, thereby inhibiting the spread, hanging, residue and leakage of the liquid to be printed at the print port.

[0006] According to some embodiments of the present invention, the microscale protrusion is at least one of a square column, a cylinder, a rectangular column, a prism, a frustum, a cone, or an annular protrusion.

[0007] According to some embodiments of the present invention, the micro-pillar array is a regular square pillar array, the side length of the square pillar is within a first preset range, the height of the square pillar is within a second preset range, and the spacing between adjacent square pillars is within a third preset range.

[0008] According to some embodiments of the present invention, the fill factor of the square column array is a first threshold, and the aspect ratio of the square columns is a second threshold.

[0009] According to some embodiments of the present invention, the micropillar array is disposed on the outer periphery of the printing port and arranged in one or more rings around the printing port, so that the liquid to be printed at the printing port contacts the top of the micropillars first when it leaves the printing port.

[0010] This invention also provides a method for preparing a locally superhydrophobic modified structure for the printing port of a microfluidic chip, used to prepare the locally superhydrophobic modified structure for the printing port of a microfluidic chip as described in the above embodiments, comprising: Preparation of donor substrates with micropillar arrays; The surface of the micropillar array of the donor substrate is bonded to the surface of the printing port area of ​​the target microfluidic chip; A peeling load is applied to the donor substrate in a direction away from the target microfluidic chip to perform directional peeling, causing the micropillar array to break at a predetermined interface or position and remain in the printing port area of ​​the target microfluidic chip, forming a locally superhydrophobic modified structure.

[0011] According to some embodiments of the present invention, the preparation of the donor substrate with the micropillar array includes: A micropillar array template is prepared on a hard substrate by photolithography, and a PDMS donor substrate with a micropillar array is prepared by using a PDMS soft etching process. By adjusting the mass ratio of PDMS main agent to curing agent, the crosslinking density, elastic modulus and fracture behavior of PDMS can be changed, so that the micropillar array breaks at a predetermined interface or predetermined position during the directional peeling process.

[0012] According to some embodiments of the present invention, bonding the surface of the micropillar array of the donor substrate to the surface of the printing port region of the target microfluidic chip includes: The PDMS donor substrate and the target microfluidic chip were placed in a plasma cleaner; Plasma activation treatment is performed on the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip to form high-energy active groups on their surfaces; The micropillar array region is aligned and bonded to the printing port region using thermosetting bonding, so that the PDMS donor substrate is stably bonded to the target microfluidic chip.

[0013] According to some embodiments of the present invention, the process parameters of the plasma activation treatment are as follows: in an oxygen environment, the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip are treated at a preset power level for a first preset time, and the temperature of the thermosetting bonding is controlled at a preset temperature, and the mixture is left to stand at the preset temperature for a second preset time.

[0014] According to some embodiments of the present invention, the mass ratio of the PDMS main agent to the curing agent ranges from 10:1 to 20:1.

[0015] The microfluidic chip printing port local superhydrophobic modification structure and its preparation method provided in this invention have at least one of the following advantages or beneficial effects: By setting a micropillar array on the surface of the microfluidic chip around the printing port, the gaps between the micropillars between the microscale protrusions effectively trap air during the printing process, forming a stable air cushion layer between the liquid and the surface of the microfluidic chip, thereby constructing a solid-liquid-gas composite contact state. This solid-liquid-gas composite contact state significantly increases the apparent contact angle of the liquid to be printed on the surface around the printing port, making the surface exhibit excellent local superhydrophobic properties, effectively suppressing the spreading behavior of the liquid to be printed at the printing port, and preventing the uncontrolled spread of liquid along the surface of the microfluidic chip.

[0016] Meanwhile, the presence of the air cushion layer significantly reduces the actual contact area and adhesion between the liquid to be printed and the surface of the microfluidic chip, fundamentally reducing liquid residue at the edge of the printhead and preventing liquid from remaining around the printhead after printing, thus significantly reducing the risk of leakage. This not only ensures the consistency of droplet size and morphological stability, improving the accuracy and repeatability of microfluidic printing, but also effectively avoids contamination of subsequent printing processes by residual liquid, reducing the possibility of cross-contamination.

[0017] Furthermore, the locally superhydrophobic modified structure does not require complex chemical hydrophobic treatment of the entire microfluidic chip. Targeted functional optimization can be achieved simply by integrating a micropillar array in the area around the printing port. It has good process compatibility, low fabrication cost, and does not affect the fluid transport characteristics inside the microchannel.

[0018] Furthermore, additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the microfluidic chip printing port local superhydrophobic modification structure provided in the embodiment of the present invention; Figure 2 This is a schematic diagram of different array shapes of microscale protrusions provided in the embodiments of the present invention; Figure 3 This is a time-series experimental result diagram of droplet printing residue in the microfluidic chip printing port locally superhydrophobic modified structure provided in the embodiment of the present invention; Figure 4 This is a time-series experimental result of the stability of droplet printing trajectory of the microfluidic chip printing port locally superhydrophobic modified structure provided in the embodiment of the present invention; Figure 5 This is a flowchart illustrating the overall process for preparing a locally superhydrophobic modified structure for a microfluidic chip printing port, as provided in this embodiment of the invention. Figure 6 This is a detailed flowchart of a method for preparing a locally superhydrophobic modified structure for a microfluidic chip printing port, provided in an embodiment of the present invention. Figure 7 This is a schematic diagram of a method for directional transplantation of a locally superhydrophobic modified structure at the microfluidic chip printing port, provided in an embodiment of the present invention. Detailed Implementation

[0020] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with the embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0021] It should be noted that, unless otherwise specified, when a feature is referred to as "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. Furthermore, the descriptions of "upper," "lower," "left," "right," "top," and "bottom" used in this invention are only relative to the relative positional relationships of the various components of the invention in the accompanying drawings.

[0022] Furthermore, 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. The terminology used in this specification is for the purpose of describing particular embodiments only and not for limiting the invention. The term "and / or" as used herein includes any combination of one or more of the associated listed items.

[0023] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various elements, these elements should not be limited to these terms. These terms are only used to distinguish elements of the same type from one another. For example, without departing from the scope of this disclosure, a first element may also be referred to as a second element, and similarly, a second element may also be referred to as a first element.

[0024] Reference Figures 1 to 7 The present invention further elaborates on the locally superhydrophobic modified structure of the microfluidic chip printing port and its preparation method provided in the embodiments of the present invention.

[0025] Reference Figure 1 As shown, Figure 1 This is a schematic diagram of the microfluidic chip printing port local superhydrophobic modification structure provided in an embodiment of the present invention. The microfluidic chip printing port local superhydrophobic modification structure includes a microfluidic chip body and a micropillar array 6. The microfluidic chip body has a microchannel 1 and a printing port 2 communicating with the microchannel 1. The printing port 2 is used to output liquid and generate droplets 4. The micropillar array 6 is disposed on the microfluidic chip surface 5 around the printing port 2. The micropillar array 6 includes multiple spaced microscale protrusions, and micropillar gaps 7 are formed between adjacent microscale protrusions. Furthermore, the micropillar array 6 is configured to trap an air layer at the printing port 2 during the printing process, forming an air cushion layer 8 between the liquid and the microfluidic chip surface 5 around the printing port 2, so that the liquid to be printed 3 and the microfluidic chip surface 5 around the printing port 2 form a solid-liquid-gas composite contact state, thereby suppressing the spreading, hanging, residue and leakage of the liquid to be printed 3 at the printing port 2.

[0026] The microfluidic chip printing port 2 locally superhydrophobic modified structure provided in this embodiment of the invention utilizes the micropillar array 6 formed on the surface 5 of the microfluidic chip around the printing port 2. The gaps 7 between the micropillars effectively trap air during the printing process, forming a stable air cushion layer 8 between the liquid and the microfluidic chip surface 5, thus constructing a solid-liquid-gas composite contact state. This solid-liquid-gas composite contact state significantly increases the apparent contact angle of the liquid 3 to be printed on the surface around the printing port 2, giving the surface excellent local superhydrophobic properties. This effectively suppresses the spreading behavior of the liquid 3 at the printing port 2, preventing uncontrolled spread of the liquid along the surface 5 of the microfluidic chip.

[0027] Meanwhile, the presence of the air cushion layer 8 significantly reduces the actual contact area and adhesion between the liquid to be printed 3 and the surface 5 of the microfluidic chip, fundamentally reducing liquid residue at the edge of the printing port 2 and preventing liquid from remaining around the printing port 2 after printing, thus significantly reducing the risk of leakage. This not only ensures the size consistency and morphological stability of the generated droplets 4, improving the accuracy and repeatability of microfluidic printing, but also effectively avoids contamination of subsequent printing processes by residual liquid, reducing the possibility of cross-contamination.

[0028] Furthermore, the locally superhydrophobic modified structure does not require complex chemical hydrophobic treatment of the entire microfluidic chip. Targeted functional optimization can be achieved simply by integrating a micropillar array 6 in the area around the printing port 2. It has good process compatibility, low preparation cost, and does not affect the fluid transport characteristics inside the microchannel 1. It has good application prospects in microfluidic droplet 4 printing and bio-microfluidic chip manufacturing.

[0029] Continue to refer to Figure 1 As shown, in a specific embodiment, the locally superhydrophobic modified structure of the microfluidic chip printing port includes a microchannel 1 and a printing port 2 communicating with the microchannel 1. The printing port 2 is used to output the liquid to be printed 3 and generate droplets 4. A micropillar array 6 is disposed on the microfluidic chip surface 5 around the printing port 2. The micropillar array 6 includes multiple spaced microscale protrusions, and micropillar gaps 7 that can trap air are formed between adjacent microscale protrusions. When the liquid to be printed 3 is output from the printing port 2, the micropillar array 6 causes the liquid to be printed 3 to form an air cushion layer 8 with the microfluidic chip surface 5 around the printing port 2, forming a solid-liquid-gas composite contact state, thereby reducing the actual contact area between the liquid and the microfluidic chip surface 5 and inhibiting the spread and residue of liquid around the printing port 2.

[0030] In some embodiments of the present invention, the microscale protrusion is at least one of square column, cylinder, rectangular column, prism, frustum, truncated cone or annular protrusion.

[0031] It is understood that the micro-scale protrusions in this invention can be selected from various shapes such as square prisms, cylinders, rectangular prisms, prismatic prisms, frustums, or annular protrusions. Preferably, referring to... Figure 2 As shown, the micro-scale protrusions can be selected from one of the shapes of prisms, cylinders, frustums, and annular protrusions, giving the micro-scale protrusion structure design a high degree of flexibility. Different shapes can adjust the geometry of the micro-pillar gaps and air trapping capacity, thereby optimizing the thickness, stability, and capillary pressure threshold of the air cushion layer to adapt to the liquid requirements of different surface tensions, viscosities, and printing rates. At the same time, the diverse shapes facilitate matching with different micro-machining processes such as photolithography and molding, reducing manufacturing costs and improving structural reliability and adaptability to mass production.

[0032] In some embodiments of the present invention, the micro-pillar array is a regular square pillar array, the side length of the square pillar is within a first preset range, the height of the square pillar is within a second preset range, and the spacing between adjacent square pillars is within a third preset range.

[0033] In one embodiment, the first preset range is 10μm to 50μm, the second preset range is 5μm to 30μm, and the third preset range is 10μm to 100μm. Therefore, when the micropillar array is a regular square pillar array, the side length of the square pillar is 10μm to 50μm, the height of the square pillar is 5μm to 30μm, and the spacing between adjacent square pillars is 10μm to 100μm. This parameter range is optimized and matched to provide sufficient structural rigidity to prevent micropillar deformation or breakage, and to form gaps with a suitable aspect ratio to stably trap the air layer and prevent liquid from seeping into the gaps and damaging the air cushion. At the same time, this size combination ensures that the air cushion layer has sufficient thickness and capillary pressure threshold, effectively suppressing liquid spreading and hanging, and is fully compatible with standard photolithography and etching processes, facilitating high-precision, low-cost mass production.

[0034] In some embodiments of the present invention, the fill factor of the square column array is a first threshold, and the aspect ratio of the square columns is a second threshold.

[0035] In one embodiment, the first threshold is 0.1–0.5, and the second threshold is 0.2–3.0, meaning the fill factor of the square column array is 0.1–0.5, and the aspect ratio h / a of the square columns is 0.2–3.0. This optimized combination of parameters ensures sufficient voids between the microcolumns to stably trap the air layer, forming a continuous air cushion, while maintaining a moderate solid content to provide sufficient structural strength to prevent the microcolumns from collapsing. The suitable aspect ratio ensures that the air cushion layer has sufficient thickness to effectively isolate the liquid, while also preventing excessively tall columns from bending or breaking during processing or use, thus balancing the durability of the superhydrophobic properties with the mechanical reliability of the microstructure.

[0036] In some embodiments of the present invention, the micropillar array is disposed on the outer periphery of the printing port and arranged in one or more rings around the printing port, so that the liquid to be printed at the printing port contacts the top of the micropillars first when it leaves the printing port.

[0037] Understandably, the micropillar array is arranged in one or more rings around the printhead, ensuring that the liquid to be printed contacts the top of the micropillars first, rather than the planar area, when leaving the printhead. This effectively reduces the solid-liquid contact area, lowers adhesion resistance, and promotes rapid droplet detachment. The multi-ring structure forms a tiered air cushion barrier; even if the outer ring is partially damaged, the inner ring can still maintain protection, enhancing superhydrophobic stability and redundancy reliability. Simultaneously, the symmetrical ring arrangement ensures that the droplets experience balanced forces in all directions, resulting in a symmetrical and uniform generation process, improving droplet size consistency and print direction controllability.

[0038] Reference Figure 3 As shown, Figure 3In the image, region a represents the presence of residue after a droplet falls without a micropillar array, while region b represents the presence of no residue after a droplet falls with a micropillar array (the white dotted line represents the printing port). It can be seen that the air layer and capillary resistance formed by the micropillar array can reduce the adhesion of liquid to the surface around the printing port. Compared with the smooth exit surface without treatment, the micropillar array makes it easier for droplets to detach from the printing port, reducing the accumulation of residual liquid after printing and helping to avoid leakage and contamination during continuous printing.

[0039] Reference Figure 4 As shown, Figure 4 Region a represents droplet generation in the absence of a micropillar array, characterized by instability and trajectory deviation; region b represents droplet generation with a micropillar array, characterized by stable droplet formation and trajectory (the white dashed line represents the printing port). It is evident that the presence of the micropillar array improves droplet generation stability and printing repeatability. Due to reduced liquid residue at the printing port, the boundary conditions during subsequent droplet generation are more stable, significantly improving the consistency of droplet volume, droplet ejection process, and printing position, thus facilitating high-precision microfluidic non-contact printing.

[0040] Reference Figure 5 As shown, Figure 5 This is a general flowchart of the method for preparing a locally superhydrophobic modified structure for a microfluidic chip printing port provided in this embodiment of the invention. The method for preparing a locally superhydrophobic modified structure for a microfluidic chip printing port includes, but is not limited to, steps S100 to S300. Specifically, S100: Fabrication of donor substrates with micropillar arrays; S200: Bond the surface of the micropillar array on the donor substrate to the surface of the printing port area of ​​the target microfluidic chip; S300: Apply a peeling load to the donor substrate along the direction away from the target microfluidic chip to perform directional peeling, causing the micropillar array to break at a predetermined interface or predetermined position and remain in the printing port area of ​​the target microfluidic chip, forming a locally superhydrophobic modified structure.

[0041] First, a donor substrate with a micropillar array is prepared. The micropillar array is then fabricated using a donor substrate transfer method. By bonding the pre-fabricated micropillar array to the printing port area of ​​the target microfluidic chip, a directional peeling load is applied along the opposite direction, causing the micropillar array to fracture controllably at a predetermined interface or position and precisely retain it on the surface of the target chip, thereby forming a locally superhydrophobic modified structure. This method eliminates the need for complex in-situ micro / nano fabrication of the target microfluidic chip, effectively avoiding damage and thermal effects on the microchannel structure, printing port accuracy, and surface properties caused by direct processing techniques such as photolithography and etching, and significantly improving process compatibility and yield.

[0042] Directional peeling is performed by applying a peel load to the donor substrate along a direction away from the target microfluidic chip. By controlling the bonding interface strength and the direction of the peel load, the micropillar array can be controlled to fracture at a preset weak interface or a specific height. This ensures that the micropillars transferred to the printing port area have consistent height, intact morphology, and smooth fracture surfaces, avoiding debris contamination and dimensional deviations caused by traditional cutting or grinding. The directional peeling method also endows the micropillar array with selective transfer capability. During the transfer process, the micropillar array selectively covers only a specific area around the printing port, modifying only a local area of ​​the printing port without affecting the surface properties of other functional areas of the target microfluidic chip or the fluid transport characteristics within the microchannels. This ensures the stability of the fluid-driven performance within the microchannels and achieves true local modification. Furthermore, by controlling the peel load and fracture location, the integrity and consistency of the transferred micropillar array can be guaranteed, ensuring the stability of the superhydrophobic properties.

[0043] In some embodiments of the present invention, step S100, the preparation of the donor substrate with the micropillar array, includes, but is not limited to, steps S110 to S120. Specifically, S110: A micropillar array template is prepared on a hard substrate by photolithography, and a PDMS donor substrate with a micropillar array is prepared by using a PDMS soft etching process. S120: By adjusting the mass ratio of PDMS main agent to curing agent, the crosslinking density, elastic modulus and fracture behavior of PDMS are changed, so that the micropillar array breaks at a predetermined interface or predetermined position during the directional exfoliation process.

[0044] The donor substrate is prepared using photolithography combined with PDMS soft etching technology. This fully leverages the advantages of high precision and good structural consistency of photolithography templates, enabling high-fidelity mass replication of micropillar arrays. Furthermore, PDMS material exhibits good flexibility and low surface energy, facilitating demolding and subsequent bonding and transfer, significantly reducing preparation costs. By adjusting the mass ratio of PDMS main agent to curing agent, its crosslinking density and elastic modulus can be precisely controlled. This allows for continuous adjustment of the crosslinking degree and fracture toughness of PDMS, thereby controlling the fracture behavior of the micropillar array during directional exfoliation. Fracture occurs at predetermined interfaces or locations, significantly improving the success rate and integrity of micropillar array transfer. This ensures that the micropillars transferred to the chip printing port have consistent height and flat cross-sections, avoiding burrs or irregular fractures, and significantly improving the uniformity and reliability of the superhydrophobic structure.

[0045] The adjustable mechanism of this invention allows the fracture location to be flexibly adapted to the bonding strength and peel angle of different chip surfaces, improving process tolerance and transfer success rate. Ultimately, the PDMS donor substrate can be completely separated after peeling, with minimal residue, allowing for reuse and further reducing fabrication costs.

[0046] In one embodiment of the present invention, the mass ratio of PDMS main agent to curing agent ranges from 10:1 to 20:1, and preferably, the mass ratio of PDMS main agent to curing agent ranges from 20:1.

[0047] Understandably, to improve the controllability of fracture location during the directional transfer of micropillar arrays, this invention further regulates the mechanical properties of PDMS by adjusting the mass ratio of PDMS main agent to curing agent. Limiting the mass ratio of PDMS main agent to curing agent to the range of 10:1 to 20:1 effectively controls the crosslinking density and elastic modulus of PDMS, enabling it to exhibit suitable flexibility and fracture behavior during directional exfoliation, ensuring that the micropillar array fractures controllably at a predetermined location and is transferred intact. Preferably, at a 20:1 ratio, the PDMS crosslinking density is lower and the elastic modulus is smaller, making it easier for the micropillar array to fracture at the root or predetermined interface, significantly improving the transfer success rate and structural integrity, while reducing the risk of damage to the target chip during the exfoliation process.

[0048] Specifically, when the mass ratio of PDMS main agent to curing agent is adjusted from 10:1 to 20:1, the crosslinking density of PDMS decreases and the elastic modulus declines, making it easier to meet the fracture condition of "soft matrix-brittle interface". During the exfoliation process, the micropillar array is more likely to fracture preferentially near the target interface. Under the mass ratio of 10:1, the micropillars do not fracture or are difficult to fracture at the predetermined interface or location, resulting in a low transfer success rate. Under the mass ratio of 20:1, the micropillars fracture easily at the predetermined interface or location, thereby effectively improving the microstructure transfer efficiency.

[0049] Reference Figure 6 As shown, in some embodiments of the present invention, in step S200, the surface of the micropillar array of the donor substrate is bonded to the surface of the printing port area of ​​the target microfluidic chip, including but not limited to steps S210 to S230. Specifically, S210: Place the PDMS donor substrate and the target microfluidic chip in a plasma cleaner; S220: Plasma activation treatment is performed on the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip to form high-energy active groups on the surface of both. S230: Align and bond the micropillar array region with the printing port region using thermosetting bonding to ensure stable bonding between the PDMS donor substrate and the target microfluidic chip.

[0050] Plasma activation treatment of the bonding regions between the PDMS donor substrate and the target microfluidic chip introduces high-energy active groups onto their surfaces, significantly enhancing surface energy and chemical activity, thereby improving interfacial wettability and bonding affinity. Selective activation and precise alignment of the micropillar array region and the printing port region ensures the positioning accuracy of the micropillar array on the target chip, avoiding contamination of non-target areas. Thermosetting bonding causes the activated surface-active groups to undergo a condensation reaction, forming stable chemical bonds with high bonding strength and durability. Furthermore, it eliminates the need for additional adhesives, preventing clogging of microchannels and impact on printing accuracy. This bonding process is simple to operate, highly controllable, and effectively ensures the reliability and long-term stability of the locally superhydrophobic modified structure.

[0051] In some embodiments of the present invention, the process parameters for plasma activation treatment are as follows: in an oxygen environment, the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip are treated at a preset power level for a first preset time, and the temperature of thermal curing bonding is controlled at a preset temperature, and the mixture is left to stand at the preset temperature for a second preset time.

[0052] Understandably, the plasma cleaner has three power settings: low, medium, and high. The preset power setting is the high power mode, corresponding to an output power of 29.6W. The first preset time is 20s to 60s, and the preset temperature is 60℃ to 80℃. The second preset time is 0.5h to 2h. The PDMS donor substrate and the target microfluidic chip are placed in an oxygen environment. The plasma cleaner is controlled to process the micropillar array area on the PDMS donor substrate and the printing port area of ​​the target microfluidic chip at an output power of 29.6W for 20s to 60s. The temperature for thermosetting bonding is controlled at 60℃ to 80℃. After that, the PDMS donor substrate and the target microfluidic chip are left to stand for 0.5h to 2h.

[0053] By limiting plasma activation treatment to a short duration of 20-60 seconds in an oxygen-environment plasma cleaner at 29.6W output power, abundant oxygen-containing active groups can be rapidly introduced into the PDMS donor substrate and the target microfluidic chip surface, significantly improving surface activation efficiency. Simultaneously, it effectively avoids excessive etching or thermal damage to the micropillar array structure caused by prolonged plasma treatment, ensuring the integrity of the micropillar morphology. Controlling the thermosetting bonding temperature at 60℃-80℃ and allowing it to stand for 0.5-2 hours provides suitable thermodynamic conditions for the condensation reaction between surface active groups, promoting the formation of stable and robust chemical bonds, while avoiding thermal stress damage to the chip material from excessively high temperatures. This process parameter combination is reasonable, with a wide window, high bonding strength, good interface stability, strong operational controllability, and excellent repeatability, effectively ensuring the reliable transfer and long-term service performance of the locally superhydrophobic modified structure.

[0054] In one embodiment, refer to Figure 7 As shown, the methods for directional transfer of superhydrophobic structures include: Fabrication of a PDMS donor substrate with a micropillar array: A template with a micropillar array is prepared by photolithography and soft etching processes. The PDMS donor substrate is fabricated using a PDMS molding process. The micropillar array on the PDMS donor substrate is used for subsequent transfer to the printing port area of ​​the target microfluidic chip.

[0055] Bonding the PDMS donor substrate and the target chip printout port: The PDMS donor substrate with micropillar array and the target microfluidic chip were placed in a plasma cleaner chamber that had been wiped clean with alcohol. After closing the chamber door, the vacuum pump was turned on to evacuate the air from the chamber until the pressure stabilized. Then, oxygen was introduced, and the plasma cleaner was set to an output power of 29.6W for 40 seconds to form high-energy active groups on both surfaces. After the plasma treatment, the micropillar array area on the PDMS donor substrate was aligned with the printout port area of ​​the target microfluidic chip, so that the micropillar array covered or surrounded the printout port exit position, and carefully bonded together. The substrate was then placed in a 65°C constant temperature oven for at least 1 hour to cure and bond, allowing a stable bond to form between the PDMS donor substrate and the target microfluidic chip.

[0056] Targeted peeling and microstructure transfer: After cooling to room temperature, the target microfluidic chip is fixed, and a peeling load is applied to the PDMS donor substrate in a direction perpendicular to the surface of the target microfluidic chip. The PDMS donor substrate is slowly peeled off from one side of the target microfluidic chip, causing the micropillar array to break at a predetermined interface or predetermined position, thereby selectively retaining the micropillar array structure in the printing port area of ​​the target microfluidic chip.

[0057] Obtaining a localized superhydrophobic printing port: After peeling, a localized micropillar array structure is formed around the printing port of the target microfluidic chip, while other areas of the target microfluidic chip basically maintain their original surface state, thereby achieving localized superhydrophobic modification of the printing port area.

[0058] The fabrication method provided by this invention achieves precise local construction of micropillar arrays in the printing port area of ​​a microfluidic chip through a complete process of template replication, plasma bonding, and directional exfoliation and transfer. The combination of photolithography and PDMS soft etching enables high-fidelity replication of the micropillar structure, resulting in low-cost, mass-producible donor substrates. Oxygen plasma activation and 65°C thermal curing bonding form strong covalent bonds, ensuring sufficient interfacial bonding strength to withstand the exfoliation load while avoiding the introduction of impurities or contamination of microchannels. During directional exfoliation, the micropillars are controllably fractured at a preset height, selectively remaining around the printing port. After transfer, the pillars have consistent height and intact morphology, while other areas of the microfluidic chip retain their original surface state, without affecting fluid driving performance. The resulting localized superhydrophobic structure stably traps air layers, effectively suppressing droplet spreading, liquid hanging, and leakage, significantly improving printing accuracy and stability.

[0059] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this disclosure, as long as they achieve the same technical effects, should be included within the scope of protection of this disclosure and fall under the protection scope of the present invention. Within the protection scope of the present invention, the technical solutions and / or implementation methods can have various modifications and variations.

Claims

1. A locally superhydrophobic modified structure for the printing port of a microfluidic chip, characterized in that, include: A microfluidic chip body, the microfluidic chip body having a microchannel and a printing port communicating with the microchannel, the printing port being used to output liquid and generate droplets; A micropillar array is disposed on the chip surface around the printout. The micropillar array includes multiple spaced microscale protrusions, with micropillar gaps formed between adjacent microscale protrusions. The microscale protrusions are at least one of square pillars, cylinders, rectangular pillars, prisms, frustums, truncated cones, or annular protrusions. The micropillar array is configured to trap an air layer at the print port during the printing process, forming an air cushion layer between the liquid and the chip surface around the print port. This creates a solid-liquid-gas composite contact state between the liquid to be printed and the chip surface around the print port, thereby inhibiting the spread, hanging, residue, and leakage of the liquid to be printed at the print port. Furthermore, the micropillar array is arranged in one or more rings around the print port so that the liquid to be printed at the print port contacts the top of the micropillars first when it leaves the print port.

2. The microfluidic chip printing port locally superhydrophobic modified structure according to claim 1, characterized in that, The micro-pillar array is a regular square pillar array. The side length of the square pillar is within a first preset range, the height of the square pillar is within a second preset range, and the spacing between adjacent square pillars is within a third preset range.

3. The locally superhydrophobic modified structure for the microfluidic chip printing port according to claim 2, characterized in that, The fill factor of the square column array is a first threshold, and the aspect ratio of the square columns is a second threshold.

4. The microfluidic chip printing port locally superhydrophobic modified structure according to claim 1, characterized in that, The micropillar array is disposed on the outer periphery of the printing port and arranged in one or more rings around the printing port, so that the liquid to be printed at the printing port first contacts the top of the micropillars when it leaves the printing port.

5. A method for preparing a locally superhydrophobic modified structure for a microfluidic chip printing port, used to prepare the locally superhydrophobic modified structure for a microfluidic chip printing port as described in any one of claims 1 to 4, characterized in that, include: Preparation of donor substrates with micropillar arrays; The surface of the micropillar array of the donor substrate is bonded to the surface of the printing port area of ​​the target microfluidic chip; A peeling load is applied to the donor substrate in a direction away from the target microfluidic chip to perform directional peeling, causing the micropillar array to break at a predetermined interface or position and remain in the printing port area of ​​the target microfluidic chip, forming a locally superhydrophobic modified structure.

6. The method for preparing the locally superhydrophobic modified structure of the microfluidic chip printing port according to claim 5, characterized in that, The preparation of the donor substrate with the micropillar array includes: A micropillar array template is prepared on a hard substrate by photolithography, and a PDMS donor substrate with a micropillar array is prepared by using a PDMS soft etching process. By adjusting the mass ratio of PDMS main agent to curing agent, the crosslinking density, elastic modulus and fracture behavior of PDMS can be changed, so that the micropillar array breaks at a predetermined interface or predetermined position during the directional peeling process.

7. The method for preparing the locally superhydrophobic modified structure of the microfluidic chip printing port according to claim 6, characterized in that, The bonding of the surface of the micropillar array of the donor substrate to the surface of the printing port area of ​​the target microfluidic chip includes: The PDMS donor substrate and the target microfluidic chip were placed in a plasma cleaner; Plasma activation treatment is performed on the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip to form high-energy active groups on their surfaces; The micropillar array region is aligned and bonded to the printing port region using thermosetting bonding, so that the PDMS donor substrate is stably bonded to the target microfluidic chip.

8. The method for preparing the locally superhydrophobic modified structure of the microfluidic chip printing port according to claim 7, characterized in that, The process parameters for plasma activation treatment are as follows: in an oxygen environment, the micropillar array region on the PDMS donor substrate and the printing port region of the target microfluidic chip are treated at a preset power level for a first preset time, and the temperature of the thermosetting bonding is controlled at a preset temperature, and the mixture is left to stand at the preset temperature for a second preset time.

9. The method for preparing the locally superhydrophobic modified structure of the microfluidic chip printing port according to claim 6, characterized in that, The mass ratio of the PDMS main agent to the curing agent ranges from 10:1 to 20:1.

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