Microfluidic chip, control method thereof, and circulation control system and method thereof

Abstract

The application discloses a micro-fluidic chip and a control method thereof, a circulation control system and a method thereof, relates to the technical field of micro-fluidic technology and a fluid mechanics experiment platform, and comprises a substrate, a top sealing layer arranged on the substrate, a cross micro-fluid channel arranged between the substrate and the top sealing layer to form a stagnation point, and a fluid interface penetrating through the top sealing layer and being communicated with one end of the cross micro-fluid channel away from the stagnation point, wherein the fluid interface comprises oppositely arranged first and second inlets and oppositely arranged first and second outlets; the first and second inlets are used for injecting fluid into the cross micro-fluid channel; and the first and second outlets are used for discharging fluid from the cross micro-fluid channel. A stable or oscillating two-dimensional saddle-shaped stagnation point wall shear stress field is constructed inside the chip, thereby providing a new platform for studying the influence of a complex fluid mechanics environment on cells and other micro-scale objects.

Description

Technical Field

[0001] This invention relates to the field of microfluidics technology and fluid mechanics experimental platform technology, specifically to a microfluidic chip and its control method, and a cyclic control system and its method. Background Technology

[0002] Microfluidics has been widely applied in biomedical research, cell mechanics experiments, and microscale fluid manipulation in recent years. In many biological studies, the wall shear stress exerted by fluids on cells is considered a crucial mechanical stimulus influencing cell morphology, migration behavior, and signaling pathways. For example, in the vascular system, blood flow exerts continuous shear stress on vascular endothelial cells, and this mechanical environment plays a vital role in vascular development, vascular remodeling, and diseases such as atherosclerosis.

[0003] In existing technologies, common microfluidic shear force experimental devices mainly employ linear or parallel-plate microchannel structures, forming a unidirectional shear force field on the channel walls through continuously flowing culture medium. These devices can be used to study the biological responses of cells in a unidirectional laminar flow environment. However, the fluid dynamics conditions in real physiological environments are often much more complex. For example, in areas of vascular bifurcation, stenosis, or dilation, blood flow lines may converge, separate, or recirculate, thus forming complex flow field structures in localized regions.

[0004] Studies have shown that stagnation structures, particularly saddle-shaped topological features, may appear in the blood flow wall shear field near pathological structures such as vascular stenosis. In such flow fields, fluid converges in one direction and diverges in another, thus forming a shear force distribution with topological characteristics in a localized region. Driven by the cardiac cycle, this stagnation point may even oscillate periodically along the vessel wall, thereby forming an oscillating topological shear force field.

[0005] However, in existing microfluidic experimental platforms, most devices can only generate a unidirectional laminar shear force environment, making it difficult to stably construct a stagnation point shear force field with a two-dimensional topology, and also difficult to achieve controllable oscillations of the stagnation point. Therefore, there is still a lack of an in vitro experimental platform capable of stably constructing a two-dimensional saddle-shaped stagnation point shear force field.

[0006] Therefore, it is necessary to develop and design microfluidic chips and their control methods, as well as cyclic control systems and their methods, to construct a stable or oscillating two-dimensional saddle-shaped stagnation point wall shear force field inside the chip, thereby providing a new platform for studying the effects of complex fluid dynamic environments on cells and other microscale objects. This is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the aforementioned issues, this invention provides a microfluidic chip and its control method, as well as a cyclic control system and its method. This system constructs a stable or oscillating two-dimensional saddle-shaped stagnation point wall shear force field within the chip, thereby providing a new platform for studying the impact of complex fluid dynamics environments on cells and other microscale objects.

[0008] To achieve the above objectives, the present invention provides the following solution: A microfluidic chip includes a substrate, a top cap layer disposed on the substrate, a cross microchannel disposed between the substrate and the top cap layer to form a stagnation point, and a fluid interface penetrating the top cap layer and communicating with the end of the cross microchannel away from the stagnation point. The fluid interface includes a first inlet and a second inlet disposed opposite to each other, and a first outlet and a second outlet disposed opposite to each other. The first inlet and the second inlet are used to inject or draw back fluid into the cross microchannel, and the first outlet and the second outlet are used to discharge or recover fluid into the cross microchannel.

[0009] Preferably, the cross microchannel includes an inlet channel and an outlet channel, which are arranged in a cross shape. The two ends of the inlet channel are the first inlet and the second inlet, respectively, and the two ends of the outlet channel are the first outlet and the second outlet, respectively.

[0010] Preferably, the inlet channel and the outlet channel have rectangular cross-sections, and the fluid interface is a cylindrical orifice-shaped interface.

[0011] Preferably, the substrate is a glass substrate, and the top sealing layer is a polydimethylsiloxane sealing layer.

[0012] The present invention also discloses a microfluidic chip control method, which applies the microfluidic chip described above, characterized in that the first inlet and the second inlet are set as symmetrical flow inputs, and the first outlet and the second outlet flow are set as symmetrical flow splits, so as to form a static stagnation point shear force field at the stagnation point; The first inlet and the second inlet are configured as periodic flow inputs with a phase difference, and the first outlet and the second outlet flow are configured as symmetrical flow splits, so as to form an inlet oscillating stagnation point shear force field at the stagnation point; The first inlet and the second inlet are configured as symmetrical flow inputs, and the first outlet and the second outlet flow are configured as periodic flow splits with a phase difference, so as to form an outlet oscillating stagnation shear force field at the stagnation point.

[0013] The present invention also discloses a circulation control system, including the microfluidic chip described above, characterized in that it further includes a first flow control device connected to the first inlet and the second inlet, a second flow control device or venting device connected to the second outlet, and a control system electrically connected to the first flow control device, the second flow control device and the venting device, wherein the venting device is also connected to the first outlet, and the first flow control device controls the first inlet and the second inlet respectively.

[0014] Preferably, the discharge device includes a peristaltic pump and a storage bottle connected in sequence; When the second outlet is connected to the second flow control device, the liquid storage bottle is connected to the first flow control device and the second flow control device through a valve, and the peristaltic pump is connected to the first outlet; When the second outlet is connected to the venting device, the liquid storage bottle is connected to the first flow control device through a valve, and the peristaltic pump is connected to the first outlet and the second outlet.

[0015] Preferably, both the first flow control device and the second flow control device are injection pumps.

[0016] This invention also discloses a loop control method, which applies the loop control system described above, characterized in that... When the second outlet is connected to the discharge device; The first inlet and the second inlet are set as symmetrical flow inputs by the first flow control device, and the first outlet and the second outlet are set as symmetrical flow diversions by the discharge device, so as to form a static stagnation point shear force field at the stagnation point. The first flow control device sets the first inlet and the second inlet to periodic flow input with a phase difference, and the discharge device sets the first outlet and the second outlet flow to symmetrical flow splitting, so as to form an inlet oscillating stagnation point shear force field at the stagnation point. When the second outlet is connected to the second flow control device; The first inlet and the second inlet are configured as symmetrical flow inputs by the first flow control device, and the first outlet and the second outlet flow are configured as periodic flow splits with a phase difference by the second flow control device and the discharge device, so as to form an outlet oscillating stagnation shear force field at the stagnation point.

[0017] Preferably, the fluid in the venting device is delivered to the first flow control device and the second flow control device to achieve fluid recycling.

[0018] The present invention achieves the following technical effects compared to the prior art: By setting up intersecting microchannels with dual inlets and dual outlets inside the chip, fluids converge in the central region and split in two directions, thus forming a saddle-shaped stagnation point flow field structure in the confluence region. Near this region, the fluid velocity gradient and wall shear force distribution exhibit a typical two-dimensional topological structure. By constructing a stable or oscillating two-dimensional saddle-shaped stagnation point wall shear force field inside the chip, a new platform is provided for studying the effects of complex fluid dynamic environments on cells and other microscale objects. It can be used to study the mechanical response of cells in complex fluid topological environments, such as cell migration, changes in cell population organization structure, and nanoparticle uptake behavior. In addition, this platform can also be used for microfluidic research such as particle transport, droplet manipulation, and material aggregation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Appendix Figure 1 This is a schematic diagram of the planar structure of the microfluidic chip disclosed in this invention; Appendix Figure 2 This is a schematic diagram of the three-dimensional structure of the microfluidic chip disclosed in this invention; Appendix Figure 3 This is a schematic diagram of the structure of the circulation control system disclosed in this invention when the second outlet is connected to the discharge device; Appendix Figure 4 This is a schematic diagram of the structure of the circulation control system disclosed in this invention when the second outlet is connected to the second flow control device; Appendix Figure 5 This is a schematic diagram of the shear force field at a stationary point. Appendix Figure 6 Schematic diagram of the shear force field at the stagnation point of the inlet oscillation; Appendix Figure 7 This is a schematic diagram of the shear force field at the stagnation point of the outlet oscillation (the dashed circle represents the stagnation point region; the dashed ellipse represents the range of possible movement of the stagnation point under oscillation driving conditions; the arrow indicates the direction of stagnation point oscillation).

[0021] The components include: 1. Microfluidic chip; 2. First inlet; 3. Second inlet; 4. First outlet; 5. Second outlet; 6. Cross microchannels; 7. Stagnation point; 8. Substrate; 9. Top sealing layer; 10. First injection pump; 11. Second injection pump; 12. First valve; 13. Second valve; 14. Reservoir; 15. Peristaltic pump; 16. Control system; 17. Piping; 18. Control signal line; 19. Dual-channel injection pump; 20. Third injection pump; 21. Third valve; 22. Fourth valve. Detailed Implementation

[0022] 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.

[0023] The purpose of this invention is to provide a microfluidic chip and its control method, and a cyclic control system and its method, which constructs a stable or oscillating two-dimensional saddle-shaped stagnation point wall shear force field inside the chip, thereby providing a new platform for studying the effects of complex fluid dynamics environments on cells and other microscale objects.

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] refer to Figures 1-2The microfluidic chip disclosed in this embodiment of the invention includes at least a substrate 8, a top sealing layer 9 attached to the substrate 8, and intersecting microchannels 6 between the substrate 8 and the top sealing layer 9. The intersection of the intersecting microchannels 6 forms a saddle-shaped stagnation point 7. A fluid interface is connected to the end of the intersecting channel away from the stagnation point 7, and the fluid interface penetrates the top sealing layer 9. The fluid interface includes a first inlet 2 and a second inlet 3 arranged opposite to each other, and a first outlet 4 and a second outlet 5 arranged opposite to each other. The first inlet 2 and the second inlet 3 are used to inject fluid into or draw back fluid into the intersecting microchannels 6, and the first outlet 4 and the second outlet 5 are used to discharge fluid into or recover fluid from the intersecting microchannels 6. The intersecting microchannels 6 form fluid channels within the chip, the stagnation point 7 forms the saddle-shaped stagnation point 7 and its surrounding flow field structure, and the substrate 8 provides the structure. Supporting and serving as a cell culture surface, the top sealing layer 9 forms a sealed flow channel structure. By setting up a dual-inlet, dual-outlet intersecting microchannel 6 inside the chip, the fluid converges in the central region and splits in two directions, thereby forming a saddle-shaped stagnation point flow field structure in the convergence region. Near this region, the fluid velocity gradient and wall shear force distribution exhibit a typical two-dimensional topological structure. A stable or oscillating two-dimensional saddle-shaped stagnation point wall shear force field is constructed inside the microfluidic chip 1, thus providing a new platform for studying the effects of complex fluid dynamic environments on cells and other microscale objects. It can be used to study the mechanical response of cells in complex fluid topological environments, such as cell migration, changes in cell population organization structure, and nanoparticle uptake behavior. In addition, this platform can also be used for microfluidic research such as particle transport, droplet manipulation, and material aggregation.

[0026] It should be noted that stagnation point 7 does not necessarily correspond to an independent chamber, but rather refers to the region near the confluence area where a saddle-shaped stagnation point 7 and its neighboring two-dimensional topological flow field can be formed. In this region, the fluid velocity gradient and wall shear force distribution exhibit a typical saddle-shaped topological structure.

[0027] refer to Figure 1 As an implementation method, the cross-channel 6 includes an inlet channel and an outlet channel, which are arranged in a cross shape. The two ends of the inlet channel are the first inlet 2 and the second inlet 3, respectively, and the two ends of the outlet channel are the first outlet 4 and the second outlet 5, respectively. Through the cross-shaped cross-channel structure, the controllable diversion and merging of fluid in a two-dimensional plane are realized. The symmetrical channel layout simplifies the control logic. Only the flow rate of the inlet or outlet needs to be adjusted to flexibly switch the fluid path, which significantly improves the operational flexibility and integration of the microfluidic chip 1.

[0028] It should be noted that the cross microchannels 6 can be fabricated using conventional PDMS soft lithography, without the need for complex three-dimensional structures or special microstructures, thereby reducing the manufacturing difficulty and improving experimental repeatability.

[0029] refer to Figures 1-2 In one embodiment, the inlet and outlet channels have rectangular cross-sections, and the fluid interface is a cylindrical orifice interface. The rectangular cross-section channel can provide a uniform flow profile, reduce eddies and dead volumes, and facilitate precise control of laminar flow at the micrometer scale. The fluid interface is set as a cylindrical orifice interface to facilitate the connection between the cross microchannel 6 and the external fluid pipeline 17. Preferably, the chip interface can be connected to the external system through a plastic connector and a silicone hose, but the present invention is not limited to this specific connection method.

[0030] It should be noted that the width of the rectangular cross microchannel 6 is approximately 700μm to 900μm, and the height is 110μm to 130μm; the length of a single DC channel from the inlet end to the outlet end is 10mm to 20mm; the diameter of the cylindrical orifice interface is 2mm to 4mm, used to connect to the external fluid pipeline 17; and the overall thickness of the microfluidic chip 1 is 4mm to 6mm.

[0031] The cross-section of the intersecting microchannel 6 can also be trapezoidal, semi-circular, or other cross-sectional shapes suitable for microfluidic processing. By changing the cross-sectional shape or size ratio of the intersecting microchannel 6, the local fluid velocity distribution and shear force can be adjusted, but a saddle-shaped stagnation flow field can still be formed in the channel intersection area. In addition, the inlet and outlet channels can also adopt a tapered, expanded, or curved structure to change the local flow resistance or velocity distribution without affecting the basic formation principle of the stagnation flow field.

[0032] refer to Figure 1 In one implementation, the substrate 8 is a glass substrate 8, i.e., a standard coverslip is used, and the top sealing layer 9 is a polydimethylsiloxane sealing layer. PDMS (polydimethylsiloxane) is an elastic material commonly used in the manufacture of microfluidic chips. It has good optical transparency and biocompatibility and is suitable for cell culture and microscopic observation.

[0033] It should be noted that the top capping layer 9 of the microfluidic chip 1 can also be made of other common microfluidic materials, such as PMMA (polymethyl methacrylate), COC (cyclic olefin copolymer), glass or other transparent polymer materials. The substrate 8 can also be selected from different materials according to experimental requirements, such as glass substrate 8, quartz substrate 8 or flexible polymer film, so as to adapt to different optical detection or mechanical experimental requirements.

[0034] This invention also discloses a microfluidic chip control method. By applying the microfluidic chip described above and adjusting the flow or pressure boundary conditions of the first inlet 2, the second inlet 3, the first outlet 4, and the second outlet 5, various types of stagnation point shear force fields can be formed in the central intersection region of the chip. The specific modes are as follows: The first inlet 2 and the second inlet 3 are set as symmetrical flow inputs, and the flow of the first outlet 4 and the second outlet 5 is set as symmetrical flow splits, so as to form a static stagnation point shear force field at the stagnation point 7. The first inlet 2 and the second inlet 3 are set to periodic flow input with a phase difference, and the flow of the first outlet 4 and the second outlet 5 is set to symmetrical flow splitting, so as to form an inlet oscillating stagnation point shear force field at the stagnation point 7. By setting the first inlet 2 and the second inlet 3 as symmetrical flow inputs and setting the flow of the first outlet 4 and the second outlet 5 as periodic flow splits with a phase difference, an outlet oscillating stagnation point shear force field is formed at the stagnation point 7. Through the above different combinations of fluid boundary conditions, a variety of two-dimensional shear force field environments with different topological characteristics can be constructed in the same chip structure.

[0035] It should be noted that the symmetrical flow rate mentioned in this embodiment refers to the two fluids having equal flow rates and opposite directions, while the periodic flow rate refers to the two fluids having equal flow rates, opposite directions, and different phase differences. Preferably, the two fluids have a phase difference of 180 degrees.

[0036] It should be noted that the following three typical stagnation point shear field modes can be constructed using different flow control methods: 1. Static shear force field at a stationary point In static stagnation mode, the two inlet channels serve as fluid input channels, and the two outlet channels serve as fluid output channels. When the first inlet 2 and the second inlet 3 continuously inject fluid into the chip at the same flow rate, and the first outlet 4 and the second outlet 5 form a symmetrical flow split, the fluid forms a stable saddle-shaped stagnation flow field in the cross intersection region. Under this condition, the position of the stagnation point 7 remains basically stable. In a typical embodiment, the flow rates of the two inlets can be set to the same constant flow rate, for example: Q1=Q2=145μL / min Under these conditions, a wall shear force on the order of approximately 1 Pa can be generated in the DC channel region, while a stable saddle-shaped stagnation point shear force field is formed in the intersection region.

[0037] 2. Inlet oscillation stationary point shear force field: In the inlet oscillation mode, the two inlet flows maintain the same average flow rate, but exhibit periodic changes in time and a phase difference: For example, you can set: Q1 = Q0 + A·sin(ωt) Q2 = Q0 - A·sin(ωt) in: Q0 represents the average flow rate; A represents the oscillation amplitude; ω is the angular frequency of the oscillation.

[0038] Under these conditions, the location of station 7 will periodically shift along the entrance direction.

[0039] 3. Shear force field at the outlet oscillation station: In the outlet oscillation mode, the two inlet flows remain constant, while the two outlet flows exhibit periodic changes and have a phase difference.

[0040] For example: Q3 = Q0 + A·sin(ωt) Q4 = Q0 - A·sin(ωt) Under these conditions, by adjusting the outlet flow distribution, an asymmetric split is generated in the confluence area, thereby driving the stagnation point 7 to oscillate periodically along the outlet direction.

[0041] By appropriately selecting flow parameters, wall shear forces close to physiological levels, such as shear forces on the order of about 1 Pa, can be generated in the DC channel region of the chip, thereby simulating the physiological fluid environment in which vascular endothelial cells are located. At the same time, the saddle-shaped stagnation point shear force field formed in the central region of the chip can simulate the complex fluid topology that appears in structures such as vascular stenosis and vascular bifurcation, providing an experimental model for studying complex blood flow environments.

[0042] In one embodiment, cell samples, such as vascular endothelial cells, can be seeded on the glass substrate 8 of the microfluidic chip 1. The cross microchannels 6 can be sterilized before use and modified with an extracellular matrix protein solution (such as fibronectin solution) to promote cell adhesion and spreading. After the cells adhere to the wall of the glass substrate 8, culture medium is injected into the microfluidic chip 1 through the fluid control system 16, and the above-mentioned stationary shear field construction mode is initiated. During this process: The cells in the DC channel region of the chip are mainly stimulated by unidirectional laminar shear force; Cells near the stagnation point 7 region are stimulated by a two-dimensional topological shear force field; Real-time observation under a microscope allows for comparison of cell morphological changes, migration behavior, and nanoparticle uptake behavior under different hydrodynamic environments, thereby studying the impact of complex fluid topology on cell function. In addition, this microfluidic platform can also be used to study microfluidic phenomena such as particle transport, droplet manipulation, localized material aggregation, and concentration gradient formation, thus having broad application potential.

[0043] The present invention also discloses a circulation control system, including the microfluidic chip described above, a first flow control device connected to the first inlet 2 and the second inlet 3, a second flow control device or a venting device connected to the second outlet 5, and a control system 16 electrically connected to the first flow control device, the second flow control device and the venting device. The venting device is also connected to the first outlet 4. The first flow control device controls the flow rate and pressure of the first inlet 2 and the second inlet 3 respectively. The control system 16 is electrically connected to the first flow control device, the second flow control device, and the discharge device via the control signal line 18.

[0044] When the second outlet 5 is connected to the venting device, it is applicable to the static stagnation shear field mode and the inlet oscillating stagnation shear field mode. At this time, the first flow control device controls the flow of the first inlet 2 and the second inlet 3 respectively, and the first outlet 4 and the second outlet 5 maintain the same outlet pressure through the venting device.

[0045] When the second outlet 5 is connected to the second flow control device, it is suitable for the outlet oscillation stagnation point shear force field mode. At this time, the first flow control device controls the flow of the first inlet 2 and the second inlet 3 respectively, and the second flow control device makes the first outlet 4 and the second outlet 5 form a flow difference.

[0046] refer to Figure 1 As a preferred approach, both the first flow control device and the second flow control device are injection pumps.

[0047] It should be noted that the fluid drive method is not limited to injection pumps. For example, pneumatic drive systems, peristaltic pump systems, electroosmotic drive systems, or other microfluidic drive methods can be used. By adjusting the pressure or flow conditions at the inlet and outlet, the required stagnation shear force field can also be constructed.

[0048] refer to Figure 1 In a preferred embodiment, the discharge device includes a peristaltic pump 15 and a storage bottle 14 connected in sequence. When the second outlet 5 is connected to the discharge device, the storage bottle 14 is connected to the first flow control device through a valve, and the peristaltic pump 15 is connected to the first outlet 4 and the second outlet 5. When the second outlet 5 is connected to the second flow control device, the storage bottle 14 is connected to the first flow control device and the second flow control device through a valve, and the peristaltic pump 15 is connected to the first outlet 4. That is, when the second outlet 5 is connected to the discharge device, the first inlet 2 and the second inlet 3 are respectively transported by the first injection pump 10 and the second injection pump 11. A first valve 12 is provided between the first injection pump 10 and the second inlet 3, and a second valve 13 is provided between the second injection pump 11 and the first inlet 2. The storage bottle 14 is connected to the second injection pump 11 through the second valve 13, and the storage bottle 14 is connected to the first injection pump 10 through the first valve 12. The peristaltic pump 15 is connected to the first outlet 4 and the second outlet 5. The first injection pump 10 and the second injection pump 11 provide fluid driving force to the second inlet 3 and the second outlet 5 respectively. The flow field structure of the confluence area can be adjusted by adjusting the output flow rate of the two injection pumps. The first outlet 4 and the second outlet 5 can maintain the same outlet pressure, for example, by being connected to the storage bottle 14 or the waste container respectively, so that the fluid forms a symmetrical flow in the two outlet directions. The storage bottle 14 is used to store culture medium or experimental fluid, and at the same time serves as a buffer storage unit in the circulation system. The peristaltic pump 15 is used to drive the fluid to circulate in the system, thereby maintaining the stability of the fluid volume in the system and realizing the recycling of the fluid.

[0049] The first valve 12 and the second valve 13 can be electromagnetic clamp valves, used to control the connection relationship between different pipelines 17. In the figure, the valve structure uses circular symbols to represent the connection status of pipelines 17. Among them, solid circles represent pipeline nodes that are currently connected, and hollow circles represent pipeline nodes that are not currently connected. When the system is in injection mode, the valve connects the output end of the injection pump to the chip inlet, so that the fluid in the syringe can be injected into the chip channel.

[0050] When the system is in the backflow mode, the valve switches to another state, creating a communication path between the syringe pump and the reservoir 14. This allows the fluid in the reservoir 14 to enter the syringe when the syringe pump performs the backflow operation, enabling fluid circulation or system replenishment.

[0051] When the second outlet 5 is connected to the second flow control device, the first flow control device can be configured as a dual-channel injection pump 19, whose two channels are connected to the first inlet 2 and the second inlet 3 respectively, to provide fluid input with the same flow rate to the two inlets, thereby ensuring that the boundary conditions on the inlet side remain symmetrical. The second outlet 5 is connected to the third injection pump 20, to apply a periodically varying backflow or push flow rate to the second outlet 5. The first outlet 4 is connected to the storage bottle 14 to maintain a constant outlet pressure, thereby serving as a relatively stable outlet boundary. With this configuration, an asymmetrical instantaneous flow distribution can be established between the two outlets, thereby causing the stagnation point 7 to oscillate along the outlet direction. In addition, a third valve 21 is provided between the dual-channel injection pump 19 and the first inlet 2 and the second inlet 3, and a fourth valve 22 is provided between the third injection pump 20 and the second outlet 5. The storage bottle 14 is connected to the third valve 21 and the fourth valve 22 respectively, and the peristaltic pump 15 is connected to the first outlet 4. The working process can be divided into two alternating stages. In the first stage, the dual channels are in an injection state, with the same flow rate of fluid being injected into the first inlet 2 and the second inlet 3 simultaneously, forming a stable input boundary on the chip inlet side. At the same time, the third injection pump 20 is in a retraction state and is connected to the second outlet 5, retracting fluid from the second outlet 5. At this time, the first outlet 4 maintains a constant outlet pressure and does not apply additional active suction. Since the second outlet 5 has active retraction, while the first outlet 4 only relies on the pressure difference to flow out naturally, an instantaneous flow difference is formed between the two outlets, causing the stagnation point 7 in the cross intersection area to deviate from the geometric center and move towards the second outlet 5 side along the outlet direction.

[0052] In the second stage, the control system 16 controls the valves to switch and change the connection between each pump, the reservoir bottle 14, and the chip. The dual-channel injection pump 19 switches from the injection state to the aspiration state, forming a connection with the reservoir bottle 14, thereby drawing fluid back from the reservoir bottle 14 to complete the replenishment of the dual-channel injection pump 19. At the same time, the third injection pump 20 switches from the aspiration state to the injection state, pushing the fluid drawn back in the previous stage back into the system, or providing reverse replenishment to the corresponding outlet branch. Through this alternating process, the overall fluid volume of the system can be kept relatively stable, and long-term unidirectional aspiration can be avoided, which may lead to the exhaustion of the syringe stroke or the imbalance of the liquid volume in the system.

[0053] By coordinating the working sequence of the dual-channel injection pump 19, the third injection pump 20, the third valve 21, the fourth valve 22, and the peristaltic pump 15 through the control system 16, the above two stages can be periodically alternated. As a result, the flow boundary condition at the second outlet 5 can exhibit periodic changes, while the first outlet 4 always maintains a constant pressure boundary. This creates a time-varying flow difference between the two outlets, which will change the local flow field distribution in the cross intersection area, causing the stagnation point 7 to move periodically back and forth along the outlet direction, ultimately forming an outlet oscillating stagnation point shear force field.

[0054] In this system, the main functions of the storage bottle 14 are: firstly, to serve as a storage and buffer unit for the circulating fluid, providing a source of replenishment for the dual-channel syringe pump 19 during the evacuation phase; secondly, to maintain the overall stability of the system's liquid volume, reducing the need for frequent fluid changes; and thirdly, to act as a stable pressure boundary or intermediate liquid exchange container at the outlet side. The peristaltic pump 15 is used to maintain the circulating flow in the branch where the storage bottle 14 is located, preventing the liquid from stagnating during long-term operation and helping to maintain the overall flow balance of the system.

[0055] The present invention also discloses a cyclic control method, which applies the cyclic control system described above, when the second outlet 5 is connected to the discharge device; The first flow control device sets the first inlet 2 and the second inlet 3 to symmetrical flow input, and the discharge device sets the flow of the first outlet 4 and the second outlet 5 to symmetrical flow diversion, so as to form a static stagnation point shear force field at the stagnation point 7. The first inlet 2 and the second inlet 3 are set to periodic flow input with a phase difference by the first flow control device, and the flow of the first outlet 4 and the second outlet 5 is set to symmetrical flow diversion by the venting device, so as to form an inlet oscillation stagnation shear force field at the stagnation point 7. When the second outlet 5 is connected to the second flow control device; The first inlet 2 and the second inlet 3 are set to symmetrical flow input by the first flow control device, and the flow of the first outlet 4 and the second outlet 5 is set to periodic flow split with phase difference by the second flow control device and the discharge device, so as to form an outlet oscillating stagnation shear force field at the stagnation point 7.

[0056] In one implementation, the fluid in the venting device is delivered to a first flow control device and a second flow control device to achieve fluid recycling.

[0057] It should be noted that the circulation control system disclosed in this invention is only a preferred embodiment for realizing different stagnation point shear force field modes of this invention. It is used to illustrate the connection relationship between the functional components in the system and their basic working principle. The technical concept of this invention does not depend on a specific model of injection pump, the number of pump channels, or a specific pipeline connection structure. Its core lies in regulating the flow rate or pressure boundary conditions at the inlet and outlet of the microfluidic chip 1, thereby constructing different types of stagnation point shear force fields in the cross-shaped microchannel region.

[0058] Specifically, in the static stagnation point shear field mode, the core is to make the two inlets form symmetrical fluid input boundaries, and at the same time make the two outlets form symmetrical flow splitting boundaries or equivalent constant pressure boundaries, thereby forming a stable saddle-shaped stagnation point 7 in the cross intersection region. When realizing this mode, two independent injection pumps can be used to control the flow rates of the two inlets respectively, or injection pumps with multiple independent channels, pressure drive devices, or other fluid drive units that can independently adjust the inlet flow rates can be used. This invention is not limited to a specific number or type of fluid drive device. As long as the boundary conditions of the two inlet flow rates being basically equal and the two outlets forming symmetrical discharge can be achieved, a stable stagnation point shear field can be formed.

[0059] In the inlet oscillation stagnation shear field mode, the core is to apply periodic flow boundary conditions with the same average value but a phase difference to the two inlets, while the two outlets maintain symmetrical flow splitting or constant pressure boundaries. Under this condition, the stagnation point 7 in the cross intersection region will oscillate periodically along the inlet direction. To achieve this mode, the flow rates of the two inlets can be adjusted by two independently controlled fluid drive units, or by a multi-channel pump, pressure control module, or other devices that can generate periodic flow rate changes. As long as a periodic flow boundary with a phase difference can be formed at the two inlets, the inlet oscillation stagnation shear field can be achieved.

[0060] In the outlet oscillation stagnation shear field mode, the core principle is to maintain symmetrical input boundaries between the two inlets while establishing asymmetric boundary conditions with time-varying characteristics between the two outlets. For example, one outlet can be subject to an active periodic flow boundary, while the other outlet maintains a constant pressure boundary; or, the two outlets can be subject to periodic flow boundaries with a phase difference. In this way, the instantaneous flow distribution in the confluence region can be altered, thereby driving stagnation point 7 to oscillate periodically along the outlet direction.

[0061] Therefore, the cyclic control system structure is only a preferred embodiment for achieving the above-mentioned boundary condition control. The specific connection method of each pipeline 17 in the system is not limited to a single structure. For example, the second outlet 5 and the third injection pump 20 can be connected by a connector, silicone hose, capillary tube or other connectors suitable for microfluidic systems. The first outlet 4 can also be connected to the storage bottle 14, waste bottle, constant pressure container or other fluid buffer unit. If there are solid lines crossing pipelines 17 in the figure, it only indicates the spatial intersection relationship on the plane shown in the figure, and does not mean that the pipelines 17 are necessarily connected.

[0062] Therefore, regardless of the specific fluid drive device, pump channel configuration, or pipeline 17 connection method used, as long as the following boundary condition control concept can be achieved: (1) Two symmetrical inputs at the inlets and two symmetrical splits at the outlets, thus forming a static shear force field at the stationary point; (2) Periodic flow boundaries with a phase difference are applied to the two inlets, thereby forming an inlet oscillating stagnation point shear force field; (3) An asymmetric flow or pressure boundary with time-varying characteristics is formed on the outlet side, thereby forming an outlet oscillation stagnation point shear force field; All of these should be considered to fall within the technical concept and protection scope of this invention.

[0063] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A microfluidic chip, characterized in that, The device includes a substrate (8), a top seal (9) disposed on the substrate (8), a cross microchannel (6) disposed between the substrate (8) and the top seal (9) to form a stagnation point (7), and a fluid interface that penetrates the top seal (9) and communicates with the end of the cross microchannel (6) away from the stagnation point (7). The fluid interface includes a first inlet (2) and a second inlet (3) disposed opposite to each other, and a first outlet (4) and a second outlet (5) disposed opposite to each other. The first inlet (2) and the second inlet (3) are used to inject or draw back fluid into the cross microchannel (6), and the first outlet (4) and the second outlet (5) are used to discharge or recover fluid into the cross microchannel (6).

2. The microfluidic chip according to claim 1, characterized in that, The cross microchannel (6) includes an inlet channel and an outlet channel, which are arranged in a cross shape. The two ends of the inlet channel are the first inlet (2) and the second inlet (3), respectively, and the two ends of the outlet channel are the first outlet (4) and the second outlet (5), respectively.

3. The microfluidic chip according to claim 2, characterized in that, The inlet channel and the outlet channel have rectangular cross-sections, and the fluid interface is a cylindrical orifice-shaped interface.

4. The microfluidic chip according to claim 1, characterized in that, The substrate (8) is a glass substrate (8), and the top sealing layer (9) is a polydimethylsiloxane sealing layer.

5. A microfluidic chip control method, using the microfluidic chip as described in any one of claims 1-4, characterized in that, The first inlet (2) and the second inlet (3) are set as symmetrical flow inputs, and the first outlet (4) and the second outlet (5) are set as symmetrical flow splits, so as to form a static stagnation shear force field at the stagnation point (7); The first inlet (2) and the second inlet (3) are set to periodic flow input with phase difference, and the first outlet (4) and the second outlet (5) are set to symmetrical flow splitting, so as to form an inlet oscillating stagnation shear force field at the stagnation point (7); The first inlet (2) and the second inlet (3) are set as symmetrical flow inputs, and the flow of the first outlet (4) and the second outlet (5) is set as periodic flow splits with a phase difference, so as to form an outlet oscillating stagnation shear field at the stagnation point (7).

6. A circulation control system, comprising the microfluidic chip as described in any one of claims 1-4, characterized in that, It also includes a first flow control device connected to the first inlet (2) and the second inlet (3), a second flow control device or a discharge device connected to the second outlet (5), and a control system (16) electrically connected to the first flow control device, the second flow control device and the discharge device. The discharge device is also connected to the first outlet (4). The first flow control device controls the first inlet (2) and the second inlet (3) respectively.

7. The cyclic control system according to claim 6, characterized in that, The discharge device includes a peristaltic pump (15) and a liquid storage bottle (14) connected in sequence. When the second outlet (5) is connected to the second flow control device, the liquid storage bottle (14) is connected to the first flow control device and the second flow control device through a valve, and the peristaltic pump (15) is connected to the first outlet (4); When the second outlet (5) is connected to the venting device, the liquid storage bottle (14) is connected to the first flow control device through a valve, and the peristaltic pump (15) is connected to the first outlet (4) and the second outlet (5).

8. The cyclic control system according to claim 6, characterized in that, Both the first flow control device and the second flow control device are syringe pumps.

9. A cyclic control method, employing the cyclic control system as described in any one of claims 6-8, characterized in that, When the second outlet (5) is connected to the venting device; The first inlet (2) and the second inlet (3) are set as symmetrical flow inputs by the first flow control device, and the flow of the first outlet (4) and the second outlet (5) is set as symmetrical flow diversion by the discharge device, so as to form a static stagnation shear force field at the stagnation point (7); The first inlet (2) and the second inlet (3) are set to periodic flow input with phase difference by the first flow control device, and the flow of the first outlet (4) and the second outlet (5) is set to symmetrical flow split by the discharge device, so as to form an inlet oscillation stagnation shear force field at the stagnation point (7); When the second outlet (5) is connected to the second flow control device; The first inlet (2) and the second inlet (3) are set as symmetrical flow inputs by the first flow control device, and the flow of the first outlet (4) and the second outlet (5) is set as periodic flow split with phase difference by the second flow control device and the discharge device, so as to form an outlet oscillation stagnation shear force field at the stagnation point (7).

10. The cyclic control method according to claim 9, characterized in that, The fluid in the venting device is delivered to the first flow control device and the second flow control device to achieve fluid recycling.

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