Microfluidic device and layered fluid control method

Abstract

The invention discloses a micro-fluidic device and a control method thereof, and the micro-fluidic device comprises a main body which has a length direction and is provided with at least three injection ports and an outlet; the first channel is formed in the main body and comprises a first cavity and a second cavity which are communicated with each other, have different sectional dimensions in the vertical length direction and are respectively communicated with at least one injection port; the at least one second channel is formed in the main body, is positioned on the periphery of the first channel and is communicated with the at least one injection port; the inlet end of the confluence part is simultaneously communicated with the outlet ends of the first channel and the second channel, and the channel wall and the length direction form an inclined angle; the inlet end of the transition neck part is communicated with the outlet end of the confluence part; the inlet end of the extrusion part is communicated with the outlet end of the transition neck part, the cross sectional area of a runner is gradually reduced in the length direction, and the outlet end of the extrusion part is communicated with the outlet. According to the device, through the synergistic effect of an inner-layer multi-cavity size difference structure and a peripheral channel, stable forming and flexible regulation and control of complex internal layering and multi-layer wrapping are achieved.

Description

Technical Field

[0001] This invention relates to the field of microfluidic manufacturing and manipulation, specifically to a microfluidic device and control method for generating multilayer fluids with complex internal structures. Background Technology

[0002] Microfluidics, a technology capable of precisely manipulating fluids within micrometer-scale channels, has demonstrated immense application potential in fields such as 3D printing, drug delivery, fluid lithography, and concentration gradient generation. In particular, the advent of stop-flow lithography has provided a new pathway for the photopolymerization of fluids, distinct from traditional droplet microfluidics. This technology can be used for the large-scale fabrication of micro-hydrogel microspheres with precise morphology and chemical composition, such as amphiphilic hydrogel microspheres for biomarker detection. Compared to droplet microfluidics, functionalized hydrogel microspheres prepared using stop-flow lithography can be directly used for subsequent biochemical analysis, eliminating the cumbersome droplet fragmentation and screening steps and reducing reliance on expensive specialized instruments and skilled operators. This is of great significance for promoting the widespread adoption and commercialization of functionalized microspheres.

[0003] In microfluidics, achieving complex layered fluid structures is a key prerequisite for fabricating multifunctional microspheres and fibers. Currently, the most commonly used technique in this field is coaxial flow microfluidic devices. These devices typically employ a "casing" structure, where one fluid encapsulates another through nested inner and outer channels, thus forming a simple core-shell fluid structure at the outlet.

[0004] However, existing coaxial flow microfluidic technologies have significant limitations, the main problems of which are: (1) Simple inner layer structure: The inner layer channels of existing devices are usually simple circular or rectangular channels, which can only inject a single type of fluid through a single inlet. This makes it impossible to form a finer and more complex multi-level layered structure in the inner layer fluid, which greatly limits the functional complexity of the final products (such as microspheres and fibers).

[0005] (2) Fixed encapsulation pattern: The outer channel can usually only achieve simple concentric circle encapsulation. This single encapsulation pattern is difficult to adapt to advanced application scenarios that require multiple chemical gradients or physical isolation, such as controlled drug release and cell co-culture.

[0006] Therefore, existing coaxial flow microfluidic devices are ill-suited for the fabrication of complex stratified fluids. Summary of the Invention

[0007] To overcome the deficiencies in the prior art, the first objective of this invention is to provide a microfluidic device, and the second objective of this invention is to provide a control method for forming stratified fluids using a microfluidic device.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, a microfluidic device includes: A main body having a length direction, wherein the main body is provided with at least three injection ports and one outlet; A first channel is formed inside the main body. The first channel includes a first cavity and a second cavity that are interconnected. The maximum cross-sectional dimension of the second cavity in the direction perpendicular to the length is greater than the maximum cross-sectional dimension of the first cavity in the direction perpendicular to the length. The first cavity and the second cavity are respectively connected to at least one injection port. At least one second channel is formed inside the body and located on the periphery of the first channel, and the second channel communicates with at least one of the injection ports; The inlet of the confluence section is connected to the outlet of both the first channel and the second channel, and the channel wall of the confluence section forms an inclined angle with the length direction. The transition neck has its inlet end connected to the outlet end of the manifold. The extrusion section has its inlet end connected to the outlet end of the transition neck, and the cross-sectional area of ​​its flow channel gradually decreases along the length direction perpendicular to the length direction. The outlet end of the extrusion section is connected to the outlet.

[0009] This microfluidic device achieves the fabrication of complex fluid structures through the synergy of internal stratification and peripheral encapsulation. Interconnected first and second cavities with different dimensions constitute a fluid behavior control unit: when fluid flows from the smaller first cavity into the larger second cavity, the flow velocity decreases and the flow channel space suddenly expands, causing the fluid to diffuse laterally. Upon encountering other fluids injected into the second cavity, it naturally forms an encapsulation or laminar parallel structure, completing the initial stratification of the inner fluid. At least one second channel located on the periphery of the first channel constitutes the outer fluid transport structure. A single channel provides basic single-layer encapsulation, while multiple channels can achieve multi-layer encapsulation, expanding the structural complexity. The confluence section guides the outer fluid to converge and encapsulate the inner fluid through inclined walls, forming a "pre-stratified fluid." The transition neck eliminates flow disturbances, and the compression section compresses the fluid size through a gradually narrowing channel, ultimately resulting in a complex stratified fluid at the outlet.

[0010] Optionally, the first cavity is connected to at least two of the injection ports. The first cavity connects to multiple injection ports, allowing the simultaneous injection of two identical or different fluids. These two fluids can undergo laminar parallel flow, mutual encapsulation, or mixing reactions within the second cavity, greatly enriching the possible structures and chemical compositions of the inner fluid and providing a basis for creating more complex functional structures.

[0011] Optionally, along the length direction, the first cavity is located upstream of the second cavity. With the first cavity upstream of the second cavity along the length direction, combined with the larger cross-sectional size of the second cavity, a flow channel structure that is narrow at the beginning and wide at the end is formed. When fluid flows from the first cavity (narrow channel) into the second cavity (wide channel), according to the principle of fluid continuity, the flow velocity decreases, the lateral diffusion capacity increases, and the fluid naturally flows around and envelops the fluid injected from the second cavity, forming a stable internal stratification.

[0012] Optionally, the first channel further includes a third cavity, which is connected to the second cavity and located downstream of the second cavity. The maximum cross-sectional dimension of the third cavity in the vertical length direction is smaller than that of the second cavity in the vertical length direction. The third cavity is connected to at least one of the injection ports. The third cavity can compress and reshape the fluid that has undergone preliminary stratification in the second cavity, and inject new fluid components through the connected injection ports to further modify or encapsulate the formed stratified structure, thereby achieving complex stratification of three or more fluids.

[0013] Optionally, there are two second channels, which are concentrically arranged along the periphery of the first channel and each communicates with at least one injection port. By providing two second channels, two concentric fluid sheaths can be formed. The inner and outer sheaths can be injected with fluids of different properties (such as different hydrogel precursors, cell suspensions, or drug solutions), thereby preparing complex microspheres or fibers with three or more functional regions (inner core / middle layer / outer layer), meeting the needs of high-end applications such as sequential drug release and multi-cell co-culture.

[0014] Optionally, both second channels have rectangular cross-sections, and their extension paths along the length direction are parallel to each other, with equal channel widths. The rectangular cross-sections and parallel, equal-width channel structure ensure that the fluids in the inner and outer sheath layers have a uniform velocity distribution and stable flow pattern before confluence, guaranteeing uniform final coating thickness and concentric interfaces, thus avoiding the problem of uneven coating thickness that is easily caused by elliptical or irregular channels.

[0015] Optionally, the inclination angle formed between the channel wall of the confluence and the length direction is 45° to 49°, and the channel walls of the confluence are parallel to each other. This angle range is the optimal choice verified by fluid dynamics simulations and experiments. Within this angle range, the outer fluid can achieve smooth and gradual convergence, with moderate encapsulation pressure on the core fluid, ensuring the integrity of the encapsulation while minimizing interfacial shear stress and preventing mixing of different fluid layers. Parallel channel walls ensure parallel streamlines, further stabilizing the flow pattern.

[0016] Optionally, the minimum channel width of the first channel is not less than 0.8 mm, and the minimum channel width of the second channel and the confluence is not less than 0.6 mm. These lower limits are empirical values ​​set based on the dual considerations of preventing fluid blockage and maintaining laminar flow. Channels that are too narrow are prone to blockage due to particulate impurities or fluid viscosity, and will also significantly increase fluid resistance, easily inducing turbulence and disrupting the stability of the layered interface. These dimensions ensure the reliability of device operation and the quality of fluid shaping.

[0017] Optionally, the extrusion section has a trapezoidal cross-section, with the two opposite channel walls inclined at an angle of 30° to 60° relative to the length direction, and the ratio of the cross-sectional area of ​​the inlet end to the cross-sectional area of ​​the outlet end of the extrusion section is 2:1 to 5:1. The trapezoidal cross-section and the 30° to 60° inclination angle provide a balanced compression process. Too small an inclination angle will result in an excessively long compression process and excessive fluid resistance; too large an inclination angle will produce excessively violent compression, potentially damaging the fine internal layered structure. A compression ratio range of 2:1 to 5:1 is suitable for most hydrogel systems, significantly reducing fluid size while well maintaining its internal structure.

[0018] Secondly, a hierarchical fluid control method for a microfluidic device includes the following steps: Multiple fluids are injected into the first and second channels through the injection port, and the flow rates of the fluids injected into the first and second channels are adjusted independently. The fluid in the first channel forms a layered internal fluid during the flow process, while the fluid in the second channel converges at the confluence and surrounds the internal fluid of the first channel, forming a pre-layered fluid; The pre-stratified fluid is allowed to flow through the extrusion section, where its cross-sectional area is compressed and reduced. The complex stratified fluid with the target cross-sectional shape is output from the outlet and collected.

[0019] Multiple fluids are injected into different functional regions (first channel and second channel) of the device through multiple injection ports, and the flow rates of the fluids injected into the first and second channels can be adjusted independently. Any change in the flow rate ratio directly alters the dynamic behavior of the fluids as they flow through cavities with different dimensions, converge and encapsulate, and compress and shape, ultimately manifesting as differences in the relative thickness, spatial distribution, and overall size of the fluid layers in the outlet fluid cross-section. Therefore, operators can prepare complex layered fluids with specific target cross-sectional shapes for different applications without altering the device's physical structure, simply by adjusting the software-controlled injection pump parameters. This method transforms the complex fluid forming process into stable, repeatable, and standardized operating procedures, supporting the on-demand manufacturing of advanced functional materials.

[0020] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: 1. By setting up interconnected first and second cavities with size differences within the first channel, the larger cross-sectional size of the second cavity causes the flowing fluid to generate a bypass and expansion effect, thereby squeezing and enveloping the fluid injected from the second cavity. This successfully forms a stable layered fluid structure within the first channel, breaking through the limitation that the inner channel of traditional coaxial flow devices can only transport single-phase fluids, and realizing multi-level layering of the inner fluid.

[0021] 2. By setting at least one second channel located on the outer periphery of the first channel, especially two concentric rectangular second channels, and in conjunction with the parallel channel walls inclined at 45° to 49° in the confluence section, the outer fluid from the second channel can smoothly and uniformly converge and wrap around the fluid that has already formed internal stratification, forming a stable pre-stratified fluid with the outer layer wrapping the inner layer. This structure effectively avoids the interface disorder or mixing problems that may occur when multiple fluids converge, ensures the integrity of the complex stratified structure, overcomes the limitations of the single wrapping mode in the prior art, and improves the flexibility and functionality of fluid wrapping.

[0022] 3. The minimum width and wall thickness of each channel ensure that the fluid is not easily blocked during flow and that the microfluidic devices are stable. At the same time, the trapezoidal cross section of the extrusion section and the 30° to 60° inclined wall structure can accurately control the fluid forming size under a compression ratio of 2:1 to 5:1, ensuring that the complex layered structure does not become disordered during compression, and improving the dimensional accuracy and morphological consistency of the final product.

[0023] 4. This invention, by independently adjusting the fluid flow rate at each injection port, can precisely control the relative proportions and spatial distribution of each fluid layer in the final stratified fluid cross-section, achieving flexible and controllable adjustment of complex stratified fluid morphology. This method is simple to operate and highly controllable, providing the possibility for preparing customized microstructures to meet different application requirements.

[0024] 5. The microfluidic device of this invention has a clear structure and smooth integration of its functional modules. It can be designed using conventional software and fabricated using commercial 3D printing technology, making it easy to integrate with existing microfluidic systems due to its low manufacturing threshold. This device provides a novel technological platform for the preparation of microspheres, microfibers, and other products with complex internal structures, and has broad application prospects in biomedical fields such as multiple drug release, tissue engineering, and organoid culture.

[0025] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the microfluidic device structure in an embodiment of the present invention; Figure 2 This is a top view of the microfluidic device in an embodiment of the present invention; Figure 3 This is a schematic cross-sectional view of the microfluidic device in an embodiment of the present invention. Figure 1 ; Figure 4 This is a schematic cross-sectional view of the microfluidic device in an embodiment of the present invention. Figure 2 ; Figure 5 This is a schematic cross-sectional view of the microfluidic device in an embodiment of the present invention. Figure 3 ; Figure 6 This is a diagram showing the fluid cross-sectional distribution at the outlet of the microfluidic device under the same flow rate ratio at each injection port in an embodiment of the present invention. Figure 7 This is a diagram showing the fluid cross-sectional distribution at the outlet of the microfluidic device under different flow rate ratios in an embodiment of the present invention.

[0028] The reference numerals in the above figures are as follows: 1. Main body; 2. First channel; 21. First cavity; 22. Second cavity; 23. Third cavity; 3. Second channel; 4. Confluence section; 5. Transition neck; 6. Extrusion section; 7. Outlet; 81. First injection port; 82. Second injection port; 83. Third injection port; 84. Fourth injection port; 85. Fifth injection port. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: See Figure 1 As shown, a microfluidic device includes a body 1, the body 1 having a length direction, and at least three injection ports and one outlet 7 are provided on the body 1; A first channel 2 is formed inside the main body 1. The first channel 2 includes a first cavity 21 and a second cavity 22 that are interconnected. The maximum cross-sectional dimension of the second cavity 22 in the direction perpendicular to the length is greater than the maximum cross-sectional dimension of the first cavity 21 in the direction perpendicular to the length. The first cavity 21 and the second cavity 22 are respectively connected to at least one injection port. At least one second channel 3 is formed inside the body 1 and located on the periphery of the first channel 2, and the second channel 3 communicates with at least one of the injection ports; The inlet end of the confluence section 4 is connected to the outlet 7 ends of both the first channel 2 and the second channel 3. The channel wall of the confluence section 4 forms an inclined angle with the length direction. The transition neck 5 has its inlet end connected to the outlet 7 end of the manifold 4; The extrusion section 6 has its inlet end connected to the outlet end 7 of the transition neck 5, and the cross-sectional area of ​​its flow channel in the direction perpendicular to the length gradually decreases along the length direction. The outlet end 7 of the extrusion section 6 is connected to the outlet 7.

[0031] In one optional embodiment, the main body 1 is a cuboid with its length direction parallel to the fluid flow direction, and has opposing first and second side surfaces along this direction. The main body 1 has multiple injection ports and an outlet 7, wherein the outlet 7 is located at the center of the second side surface and is a rectangular opening. The multiple injection ports are distributed on the remaining side surfaces of the cuboid, including those adjacent to the first and second side surfaces. Each injection port communicates with an internal channel through a cylindrical through-hole perpendicular to the side surface.

[0032] In an optional implementation, see Figure 3As shown, the main body 1 has an integrated first channel 2 inside, which sequentially connects a first cavity 21, a second cavity 22, and a third cavity 23 along the length of the main body 1. The central axes of the three cavities are collinear and parallel to the length of the main body 1. The first cavity 21 and the third cavity 23 are rectangular channels, while the second cavity 22 is circular, and the maximum cross-sectional dimension of the second cavity 22 in the vertical length direction is greater than that of the first cavity 21 and the third cavity 23 in the vertical length direction. The top surface of the main body 1 has four injection ports along its length direction, including two first injection ports 81, one second injection port 82, and one third injection port 83. Each injection port is connected to the corresponding internal cavity through a cylindrical through-hole perpendicular to the top surface. Two first injection ports 81 are symmetrically arranged on both sides of the central axis of the first channel 2 and are connected to the first cavity 21; the second injection port 82 is located on the central axis and is connected to the second cavity 22; the third injection port 83 is located on the central axis and is connected to the third cavity 23.

[0033] In one optional embodiment, there are two second channels 3, namely an outermost channel and a second outermost channel. The two second channels 3 are arranged in a concentric rectangular ring around the outer periphery of the first channel 2, and their extension paths along the length direction are parallel to each other. The cross-sections of both second channels 3 are rectangular, and their flow channel widths are equal, with equal distances between their inner and outer sidewalls. An injection port is provided on the front and rear sides of the main body 1. The injection port on the front side is a fourth injection port 84, which is connected to the second outermost channel through a cylindrical through-hole perpendicular to the front side; the injection port on the rear side is a fifth injection port 85, which is connected to the outermost channel through a cylindrical through-hole perpendicular to the rear side.

[0034] In an optional embodiment, the minimum channel width of the first channel 2 is not less than 0.8 mm, and the height is typically between 0.8 mm and 1.5 mm to ensure smooth flow of the inner multiphase fluid, prevent clogging, and maintain a stable laminar flow state. The first cavity 21 and the second cavity 22 have a smooth transition at the connection point, with a transition arc radius of not less than 0.2 mm to avoid the generation of flow dead zones and eddies. The channel width of the second channel 3 is not less than 0.6 mm, and the height-to-width ratio is between 1:1 and 1.5:1, preferably 1:1, to ensure uniform fluid velocity distribution in the outer sheath layer.

[0035] In one optional implementation, the wall thickness of all internal channels (including the first channel 2, the second channel 3, the confluence 4, the transition neck 5, and the extrusion section 6) is not less than 0.5 mm. This dimension ensures sufficient mechanical strength for the device during 3D printing, preventing deformation due to printing or fluid pressure, while also providing stable boundary conditions for the fluid, which helps maintain a clear and stable layered interface. The wall thickness of the gap between the two second channels 3 and the gap between the second channel 3 and the first channel 2 is also not less than 0.5 mm to ensure structural strength and prevent crossflow. Each injection port is connected to the corresponding channel through a cylindrical through-hole, the diameter of which is typically 0.8 mm to 1.2 mm, to ensure compatibility with standard injection needles and reduce flow resistance at the connection.

[0036] In an optional embodiment, the manifold 4 has a tapered rectangular channel structure, with its inlet cross-sectional dimensions matching the total flow area of ​​the outlet 7 of the first channel 2 and the second channel 3. The four side walls of the manifold 4 are inclined at an angle of 45° to 49°, preferably 47°, to the length of the device, and the walls remain parallel. This inclined structure allows the sheath fluid flowing in from the outer periphery of the second channel 3 to converge smoothly and symmetrically towards the center, gradually enveloping the internally layered fluid flowing out from the first channel 2, forming a stable "core-sheath" pre-layered structure. The length of the manifold 4 is determined based on fluid dynamics simulations, typically 1.5 to 2 times its inlet width, to ensure sufficient fluid convergence and interface stability.

[0037] In an optional embodiment, the transition neck 5 is a short, straight rectangular channel with an inlet cross-section identical to the outlet 7 cross-section of the confluence section 4, and the outlet 7 cross-section identical to the inlet cross-section of the extrusion section 6. The transition neck 5 is relatively short, typically no more than 1 mm, and its main function is to eliminate any small eddies or flow instabilities that may occur when the fluid converges in the confluence section 4, ensuring that the fluid streamlines tend to be parallel and the flow velocity distribution is uniform before entering the extrusion section 6, thus providing stable inlet conditions for the subsequent compression process.

[0038] In an optional embodiment, the extrusion section 6 is a tapering channel with an isosceles trapezoidal cross-section, and the inclination angle of its two sidewalls relative to the length direction is 30° to 60°, preferably 45°. The ratio of the cross-sectional area of ​​the inlet end to the cross-sectional area of ​​the outlet end of the extrusion section 6 is controlled between 2:1 and 5:1, for example, 4:1, thereby achieving smooth compression of the fluid. The trapezoidal structure helps to prevent instability or mixing of the fluid's internal stratification interface during compression. The length of the extrusion section 6 is determined based on the compression ratio and inclination angle to ensure that the shear rate the fluid withstands is within the material's allowable range, avoiding damage to the internal structure.

[0039] In one optional implementation, the design and fabrication of the microfluidic device of this application follows this process: First, a three-dimensional geometric model of the microfluidic device is constructed using conventional computer-aided design software (such as AutoCAD). The model includes all the aforementioned channels, cavities, confluence sections 4, transition necks 5, extrusion sections 6, and their dimensional parameters. Then, multiphase flow numerical simulation is performed on the model using fluid dynamics simulation software (such as COMSOL Multiphysics). By adjusting parameters such as the flow rate ratio at each injection port, the flow behavior of the fluid within the device and the layered cross-sectional morphology at the outlet 7 are predicted and optimized before fabrication, providing effective guidance for setting actual experimental parameters. Finally, the optimized model is fabricated into a physical device using commercial high-precision 3D printing technology (such as photopolymerization or PolyJet technology). This manufacturing method has a low barrier to entry, is easy to implement, and the fabricated device is easily integrated with existing microfluidic devices such as injection pumps and acquisition systems, and is simple to operate.

[0040] The cross-sectional shapes of the first cavity 21, the third cavity 23, and the second channel 3 are chosen to be rectangular or square. Compared with circular, triangular, or other irregular shapes, rectangular cross-section channels are easier to accurately lay out the expected flow paths and relative positions of each layer of fluid during the design phase. Their straight channel walls are also beneficial for maintaining the stability of the flow field during confluence and compression, thus more reliably forming the expected complex layered structure. At the same time, their processing and manufacturing are also simpler.

[0041] This application also discloses a control method for forming a stratified fluid using the above-mentioned microfluidic device, comprising the following steps: S1: Fluid Injection and Flow Rate Regulation Multiple different fluids are injected into the first channel 2 and the second channel 3 through the multiple injection ports. For example, two different inner layer fluids can be injected through the two first injection ports 81 connected to the first cavity 21, an intermediate layer fluid can be injected through the second injection port 82 connected to the second cavity 22, and the innermost encapsulation fluid can be injected through the third injection port 83 connected to the third cavity 23. Simultaneously, two different outer sheath fluids are injected through the two second channels 3 connected to the fourth injection port 84 and the fifth injection port 85 on the front and rear sides, respectively. Each injection port is connected to an independent, software-controlled injection pump to independently adjust the flow rate of each type of fluid injected into the first channel 2 and the second channel 3. The total flow rate is typically controlled within the range of approximately 1.0 mL / min to 2.0 mL / min, for example, 1.5 mL / min, to ensure that the fluid within the device is in a stable laminar flow state. The initial flow rate ratio can be set to 1:1:1:1:1:1 (corresponding to the six injection ports), at which point the flow rate of each injection port is approximately 4.17 μL / min.

[0042] S2: Internal layering and external wrapping forming The multiple fluids injected into the first channel 2 form a stratified internal fluid structure during flow. Specifically, when the two fluids injected from the first cavity 21 flow into the second cavity 22 with a larger cross-section, the flow velocity decreases due to the sudden expansion of the flow channel, resulting in lateral diffusion and mutual bypassing. They encounter the fluid injected from the second cavity 22, naturally forming a stable laminar parallel or enveloping structure. Subsequently, this initially stratified fluid is compressed and shaped as it flows through the third cavity 23 with a narrower cross-section, and can integrate new fluid components injected from the injection port of the third cavity 23, ultimately forming a core fluid with complex internal stratification at the outlet 7 of the first channel 2. At the same time, the outer sheath fluid injected into the two second channels 3 smoothly converges at the confluence 4. Thanks to the inclined parallel wall structure of the confluence 445° to 49° (preferably 47°), the outer fluid can symmetrically and uniformly contract towards the center, completely enveloping the already formed internal fluid flowing out from the first channel 2, forming a stable "core-sheath" structure pre-stratified fluid.

[0043] S3: Flow stabilization The pre-stratified fluid is then passed through a short, straight transition neck 5 (typically ≤1 mm in length). During this process, minor flow disturbances caused by confluence are eliminated, the fluid streamlines become more parallel, and the velocity distribution becomes more uniform, laying a stable flow foundation for the next compression step.

[0044] S4: Compression and Shaping The stabilized, pre-stratified fluid is introduced into the extrusion section 6. The extrusion section 6 is an isosceles trapezoidal tapering channel with a sidewall inclination angle of 30°–60° (preferably 45°), and the ratio of the inlet to outlet cross-sectional area 7 is 2:1–5:1 (e.g., 4:1). Here, the fluid is smoothly compressed, and the cross-sectional area gradually decreases to the target size. The trapezoidal structure and suitable inclination angle effectively maintain the interfacial stability of the internal fluid layers, preventing mixing or instability during compression.

[0045] S5: Output and Collection Finally, a complex stratified fluid with the target cross-sectional shape and size is output from outlet 7 and collected. The fluid cross-sectional morphology at outlet 7 can be observed in real time using a microscope or a high-speed camera system, such as... Figure 4 As shown.

[0046] In an optional implementation, the morphology of the final stratified fluid can be flexibly controlled by adjusting the flow rate ratio at each injection port. Any change in the flow rate ratio directly affects the stratification behavior of the fluid within the dimensionally different cavities, the encapsulation thickness at the confluence 4, and the final dimensions at the extrusion section 6. For example, increasing the flow rate of an inner layer fluid increases its proportion in the final cross-section; increasing the flow rate of the outer sheath fluid thickens the encapsulation layer. See also Figure 5As shown, when the flow rate ratio of the first injection port 81, the second injection port 82, the third injection port 83, the fourth injection port 84, the fifth injection port 85 and the sixth injection port is set to 1:1:4:1:1:1, the fluid cross-sectional shape is obtained.

[0047] Operators can prepare complex layered fluids with specific layer thicknesses, spatial distributions, and overall dimensions for different applications by simply adjusting the parameters of the injection pump through software, without altering the physical structure of the device. Numerical simulation software (such as COMSOL Multiphysics) can be used to simulate the results at the outlet section 7 under different flow rate ratios before the experiment, providing effective guidance for the selection of experimental parameters. This method transforms the preparation process of complex layered fluids into a stable, controllable, and repeatable standardized operation, providing a powerful tool for the on-demand fabrication of advanced functional materials such as multifunctional microspheres and microfibers.

[0048] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A microfluidic device, characterized in that, The application relates to a device for generating a complex stratified flow, comprising: a main body having a length direction, at least three injection ports and an outlet being arranged on the main body; a first channel formed in the main body, the first channel comprising a first cavity and a second cavity which are in communication with each other, the maximum cross-sectional dimension of the second cavity in the vertical direction of the length direction being greater than that of the first cavity, the first cavity and the second cavity being in communication with at least one of the injection ports respectively; at least one second channel formed in the main body and located at the outer periphery of the first channel, the second channel being in communication with at least one of the injection ports; a converging section, the inlet end of which is in communication with the outlet ends of the first channel and the second channel, the channel wall of the converging section forming an inclined angle with the length direction; a transition neck, the inlet end of which is in communication with the outlet end of the converging section; a compression section, the inlet end of which is in communication with the outlet end of the transition neck, the cross-sectional area of the flow passage of the compression section gradually decreasing along the length direction, and the outlet end of the compression section being in communication with the outlet.

2. The microfluidic device of claim 1, wherein, The first cavity is in communication with at least two of the injection ports.

3. The microfluidic device of claim 1 or 2, wherein, The first cavity is located upstream of the second cavity along the length direction.

4. The microfluidic device of claim 3, wherein, The first channel further comprises a third cavity, the third cavity being in communication with the second cavity and located downstream of the second cavity, the maximum cross-sectional dimension of the third cavity in the vertical direction of the length direction being smaller than that of the second cavity, and the third cavity being in communication with at least one of the injection ports.

5. The microfluidic device of claim 1 or 4, wherein, The number of the second channels is two, the two second channels being arranged concentrically along the outer periphery of the first channel and in communication with at least one of the injection ports respectively.

6. The microfluidic device of claim 5, wherein, The cross sections of the two second channels are rectangular, and the extension paths of the two second channels along the length direction are parallel to each other, and the flow passage widths of the two second channels are equal.

7. The microfluidic device of claim 1, wherein, The inclined angle between the channel wall of the converging section and the length direction is 45-49 degrees, and the channel walls of the converging section are parallel to each other.

8. The microfluidic device of claim 1, wherein, The minimum channel width of the first channel is not less than 0.8 mm, and the minimum channel widths of the second channels and the converging section are not less than 0.6 mm.

9. The microfluidic device of claim 1, wherein, The cross section of the compression section is trapezoidal, the inclined angle between the opposite channel walls of the compression section and the length direction is 30-60 degrees, and the ratio of the cross-sectional area of the inlet end of the compression section to that of the outlet end is 2:1-5:

1.

10. A method of layered fluid control based on the microfluidic device of any one of claims 1-9, wherein, The application further relates to a method for generating a complex stratified flow, comprising the following steps: injecting multiple fluids into the first channel and the second channel through the injection ports, and independently adjusting the flow rates of the fluids injected into the first channel and the second channel; making the fluids in the first channel form stratified internal fluids in the flow process, and making the fluids in the second channel converge at the converging section and wrap outside the internal fluids of the first channel to form pre-stratified fluids; making the pre-stratified fluids flow through the compression section, and the cross-sectional area of the pre-stratified fluids being compressed and reduced; outputting and collecting the complex stratified fluids with a target cross-sectional shape from the outlet.

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