Micro-fluidic chip for tightly arranging solid gel microspheres, application of micro-fluidic chip and preparation method of emulsified liquid drops
By adding branch channels to discharge buffer in the microfluidic chip, the gap problem of solid gel microspheres was solved, the microspheres were closely arranged, and the single package rate and cell capture efficiency were improved.
Patent Information
- Application Number
- CN202511153977.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-18
- Publication Date
- 2025-09-30
AI Technical Summary
In existing microfluidic chips, buffer gaps exist between solid gel microspheres, which reduces the single-packaging rate and affects the cell capture efficiency.
By adding branch channels in the microfluidic chip, the buffer gaps between the solid gel microspheres are reduced or eliminated, and the buffer is discharged through the branch channels to achieve close arrangement of the microspheres.
The single packaging rate of solid gel microspheres is improved, the cell capture efficiency is enhanced, and the cell utilization rate is improved.
Smart Images
Figure CN120714720A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of microfluidics, and in particular to a microfluidics chip for closely arranging solid gel microspheres, its application, and a method for preparing emulsified droplets. Background Art
[0002] Selective gene expression is a common phenomenon within different tissues of an individual, as well as between different cells within the same tissue. This selective expression characterizes distinct cellular functions. Single-cell sequencing utilizes solid-state gel microspheres modified with differentially encoded proteins to encapsulate individual cells into independent droplets. The differentially encoded proteins on the microspheres capture the mRNA selectively expressed by the cells. Through reverse transcription, amplification, fragmentation, ligation of sequencing tags, and sequencing, data on the cells' selective expression are ultimately obtained. This is of great significance for studying and analyzing cellular expression heterogeneity.
[0003] Single-cell sequencing requires the use of elastically deformable solid gel microspheres as carriers of differential encoding. These microspheres intersect and fuse with the cell sample within a microfluidic chip. They then flow through the chip's "X" or "T"-shaped channels into a dispersed oil phase, where they are sheared by the oil phase to form monodisperse water-in-oil droplets. Within these independent droplet environments, the solid gel microspheres lyse cells and capture mRNA within them. While cells follow a Poisson distribution when dispersing into droplets, the elastically deformable solid gel microspheres allow for dense packing within the microfluidic chip channels, allowing them to disperse into droplets beyond the Poisson distribution. Therefore, cell utilization is the product of the proportion of droplets encapsulating a single cell multiplied by the proportion of droplets encapsulating only one solid gel microsphere. However, since cells in this case always follow a Poisson distribution, increasing cell utilization requires increasing the proportion of droplets encapsulating a single solid gel microsphere.
[0004] However, under the preparation conditions of existing microfluidic chip designs, there are still gaps filled with buffer between the solid gel microspheres. When this gap is sheared by the oil phase, oil-in-water droplets that do not contain solid gel microspheres will be formed, which will reduce the single-packaging rate of solid gel microspheres when forming monodisperse droplets, thereby reducing the cell capture efficiency.
[0005] Existing single-cell droplet generation systems have not made corresponding improvements to this parameter, so it is an urgent problem to be solved in this field. Summary of the Invention
[0006] In light of this, the present invention provides a microfluidic chip, application, and method for preparing emulsified droplets that enable densely packed solid gel microspheres. By adding branch channels on one or both sides of the original solid gel microsphere phase channel, the present invention reduces or even eliminates buffer gaps between the solid gel microspheres, achieving dense packing of the solid gel microspheres and ultimately increasing the single-packaging rate of the solid gel microspheres.
[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:
[0008] In a first aspect, the present invention provides a microfluidic chip comprising a main channel, a flow channel for a solid gel microsphere phase, a flow channel for a cell phase, a flow channel for an oil phase, an injection port, and a collection port;
[0009] The main channel is connected to the flow channel of the solid gel microsphere phase, the flow channel of the cell phase, and the flow channel of the oil phase respectively;
[0010] The cell phase flow channel is vertically connected to the main channel via a first intersection;
[0011] The flow channel of the oil phase is vertically connected to the main channel via a second intersection;
[0012] The flow channel of the oil phase and the flow channel of the solid gel microsphere phase are arranged on both sides of the flow channel of the cell phase;
[0013] The microfluidic chip further includes a buffer discharge channel.
[0014] In some specific embodiments of the present invention, the buffer discharge channel includes a buffer discharge main channel and a buffer discharge branch channel.
[0015] In some specific embodiments of the present invention, one side of the buffer discharge branch channel is connected to the buffer discharge main channel; the other side of the buffer discharge branch channel is vertically connected to the main channel through a third intersection.
[0016] In some specific embodiments of the present invention, the buffer discharge branch channel is disposed between the flow channel of the solid gel microsphere phase and the flow channel of the cell phase;
[0017] and / or
[0018] The buffer solution discharge branch channel is arranged between the injection ports of the solid gel microsphere phase.
[0019] In some specific embodiments of the present invention, the cross-sectional width of the buffer discharge branch channel is smaller than the diameter of the solid gel microsphere.
[0020] In a second aspect, the present invention also provides the use of the microfluidic chip in preparing emulsion droplets.
[0021] In a third aspect, the present invention also provides applications of the microfluidic chip in trace reagent synthesis, micron material synthesis, trace molecular reaction and analysis, single cell encapsulation, single cell separation, single cell capture, single cell sequencing, and single cell proteomics analysis.
[0022] In a fourth aspect, the present invention also provides a kit comprising the microfluidic chip and acceptable reagents.
[0023] In a fifth aspect, the present invention also provides a device comprising the microfluidic chip.
[0024] In a sixth aspect, the present invention further provides a method for preparing emulsion droplets, based on the microfluidic chip, injecting an oil phase into the flow channel of the oil phase, injecting a solid gel microsphere phase into the flow channel of the solid gel microsphere phase, and injecting a cell phase into the flow channel of the cell phase;
[0025] The solid gel microsphere phase and the cell phase intersect at the first intersection to form a mixed phase;
[0026] The buffer solution in the solid gel microsphere phase is collected into the buffer solution discharge main channel through the buffer solution discharge branch channel;
[0027] The mixed phase and the oil phase meet and shear at the first intersection to form droplets.
[0028] The present invention effectively reduces or even eliminates the buffer gaps between the solid gel microspheres by adding drainage channels on one or both sides of the solid gel microsphere phase, so that the solid gel microspheres are arranged one by one. They are then dispersed by the cell phase and sheared by the oil phase to form oil-in-water droplets that only encapsulate one solid gel microsphere, thereby improving the cell capture efficiency.
[0029] Experiments have shown that the microfluidic chip with branch channels increases the proportion of encapsulated individual gel microspheres by 20% compared to the microfluidic chip without branch channels. Therefore, the microfluidic chip provided by the present invention can improve the utilization rate of cell samples. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.
[0031] Figure 1A microfluidic chip channel design for closely arranging solid gel microspheres is shown; wherein, channel C10 is the flow channel of the solid gel microsphere phase, C12, C13, and C14 are the discharge channels for the solid gel microsphere phase buffer solution, C11 is the connection port between the solid gel microsphere phase flow channel and the solid gel microsphere phase buffer solution discharge channel, and 1-6, 1-7, 1-8, and 1-9 are the flow directions of the solid gel microsphere buffer solution;
[0032] Figure 2 Figure 1 shows the preparation of monodisperse droplets using a single-cell microfluidic system; wherein (A) shows the flow state of each phase of fluid at an early moment in the process of generating a single-encapsulated droplet in the microfluidic chip; (B) shows the flow state of each phase of fluid at a later moment in the process of generating a single-encapsulated droplet in the microfluidic chip;
[0033] Among them, channel C1 is the flow channel of the solid gel microsphere phase, and direction 1-1 is the flow direction of the solid gel microsphere phase in its channel; channel C2 is the flow channel of the cell phase, and direction 1-2 is the flow direction of the cell phase in its channel; channel C3 is the intersection and mixing point of the solid gel microsphere phase and the cell phase; channel C4 is the mixed flow channel of the solid gel microsphere phase and the cell phase, and direction 1-3 is the flow direction of the mixed phase of the solid gel microsphere phase and the cell phase; channel C5 is the flow channel of the oil phase as the continuous phase, and direction 1-4 is the flow direction of the oil phase; channel C6 is the intersection and shear dispersion point of the mixed phase of the solid gel microsphere phase and the cell phase and the oil phase, at this position the mixed phase meets the oil phase and is sheared by the oil phase to form oil-in-water droplets; channel C7 is the flow channel where the oil phase shears the mixed phase to form droplets, and direction 1-4 is the flow direction of the oil-in-water emulsion; G1, G2, G3 and G4 are four solid gel microspheres, among which Microsphere G1 is a solid gel microsphere that will enter the mixing flow channel C4 earlier in the solid gel microsphere flow channel C1, and microsphere G2 is a solid gel microsphere that will enter the mixing flow channel C4 later in the solid gel microsphere flow channel. In the process of the oil phase shearing the water phase to form droplets, the solid gel microsphere G1 first enters the intersection of channel C3, and the solid gel microsphere G2 at a distance L1 behind it immediately enters the intersection of channel C3. The length L1 is the distance between microsphere G1 and microsphere G2 when they are in channel C1, and the space between the two microspheres is filled with the buffer solution of the solid gel microsphere phase. The length L2 is the distance between microsphere G1 and microsphere G2 when they are dispersed by the cell phase and flow into channel C4. The space between the two microspheres is filled with a mixture of the solid gel microsphere phase buffer solution and the cell phase. When the solid gel microspheres flow in channel C1 and the distance is 0, the distance between them when they are dispersed by the cell phase and flow into channel C4 in pairs is L3;
[0034] Figure 3Figure 3. Optimized single-cell microfluidic system for preparing monodisperse droplets. (A) shows the flow state at an earlier time during the microfluidic system's generation of monodisperse droplets. (B) shows the flow state at a later time during the microfluidic system's generation of monodisperse droplets.
[0035] Among them, C8 is a "T"-shaped drainage structure, C9 is a drainage channel; G5 is a solid gel microsphere that will flow through the C8 "T"-shaped drainage structure into the mixed flow channel at an earlier time in the solid gel microsphere flow channel, and G6 is a solid gel microsphere that will flow through the C8 "T"-shaped drainage structure into the mixed flow channel at a later time in the solid gel microsphere flow channel; L4 is the distance between the G5 solid gel microsphere and the G6 solid gel microsphere when flowing in the gel microsphere channel, and L5 is the distance between the G5 solid gel microsphere and the G6 solid gel microsphere when flowing in the mixed channel; 1-5 is the flow direction of the drainage channel;
[0036] Figure 4 1 and 2 show the experimental results of Example 3; wherein, (A) shows the experimental results of the microfluidic chip containing a branch channel design; (B) shows the experimental results of the microfluidic chip not containing a branch channel design. DETAILED DESCRIPTION
[0037] The present invention discloses a microfluidic chip, application and preparation method of emulsified droplets that can closely arrange solid gel microspheres. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the desired effect. It should be noted in particular that all similar replacements and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.
[0038] The present invention utilizes the special design of the branch channels on both sides of the main channel of the solid gel microspheres to discharge the buffer solution between the solid gel microspheres to eliminate the gaps between the microspheres, thereby improving the single package rate of droplets formed when the continuous phase is sheared in the microfluidic droplet generation chip. The solution of improving the single package rate of solid gel microspheres achieved by the elastic deformation characteristics itself is an aspect that needs to be protected. However, this solution should not be limited to the field of gel beads, but can also be extended to solid microspheres and similar microspheres with solid-state properties; in addition, this solution should not be limited to the use scenario of gel microspheres paired with cells, but can also be applied to gel microspheres with gel microspheres, bacteria, etc., as well as use scenarios where pairing is not required but only to improve the single package rate.
[0039] In summary, the present invention mainly protects the method of using branch channels to reduce or even eliminate the gaps between solid gel beads. The applicable scenarios should not be limited to the single-cell field, nor should any restrictions be placed on the objects with which they are paired.
[0040] The raw materials and reagents used in the microfluidic chip for closely arranging solid gel microspheres, its application and the preparation method of emulsified droplets provided by the present invention can all be purchased from the market.
[0041] The present invention will be further described below in conjunction with the embodiments:
[0042] Example 1 Structural Description of a Microfluidic Chip Channel Design for Closely Arranging Solid Gel Microspheres
[0043] like Figure 1 This is a design scheme for branch drainage channels for gel microspheres. The white channel C10 is the flow channel for the solid gel microsphere phase, C12, C13, and C14 are the solid gel microsphere phase buffer discharge channels, and C11 is the connection between the solid gel microsphere phase flow channel and the solid gel microsphere phase buffer discharge channel. 1-6, 1-7, 1-8, and 1-9 represent the flow directions of the solid gel microsphere buffer. Solid gel microspheres flow into the microfluidic chip along the main channel C10 in the 1-6 direction. When buffer gaps exist between microspheres, the buffer flows from the intersection of the branch channel and the main channel C11 along the 1-7 direction into the branch channel C12. Multiple branch channels flow along the 1-8 direction through the C13 channel into the C14 channel. The buffer flowing into the C14 channel then flows out of the microfluidic chip in the 1-9 direction. This branch channel array can reduce and eliminate the long gaps between solid gel microspheres, achieving a densely packed solid gel microsphere, thereby increasing the encapsulation rate of individual solid gel microspheres during droplet formation. Among them, the cross-sectional design of the branch channel should not be limited to being the same as the main channel, nor should it be limited to a long rectangle. Other ways of discharging the liquid phase through branch channels with different cross-sectional morphologies and sizes should be included in this patent; at the same time, the white C10 channel and the gray C12-C14 channel can be set to different channel heights during design, C10 is a height that matches the diameter of the solid gel microspheres, and C12-C14 is a height that is smaller than the diameter of the solid gel microspheres, so as to eliminate the problem of leakage from the C12-C14 channel caused by the elasticity of the solid gel.
[0044] Example 2 Principle of the drainage channel in this design
[0045] like Figure 2 For the unimproved microfluidic single-cell droplet production chip design and the process of preparing single-encapsulated droplets for the microfluidic single-cell droplet production chip, the optimal preparation result should be that each droplet encapsulates a solid gel microsphere and a cell.
[0046] Figure 2Neutron image A shows the flow state of each phase of fluid at an early moment in the process of generating a single encapsulated droplet in the microfluidic chip. Figure 2 Neutron image B shows the flow state of each phase of fluid at a later time during the generation of a single encapsulated droplet in the microfluidic chip. Among them, channel C1 is the flow channel of the solid gel microsphere phase, and direction 1-1 is the flow direction of the solid gel microsphere phase in its channel; channel C2 is the flow channel of the cell phase, and direction 1-2 is the flow direction of the cell phase in its channel; channel C3 is the intersection and mixing point of the solid gel microsphere phase and the cell phase; channel C4 is the mixed flow channel of the solid gel microsphere phase and the cell phase, and direction 1-3 is the flow direction of the mixed phase of the solid gel microsphere phase and the cell phase; channel C5 is the flow channel of the oil phase as the continuous phase, and direction 1-4 is the flow direction of the oil phase; channel C6 is the intersection and shear dispersion point of the mixed phase of the solid gel microsphere phase and the cell phase and the oil phase, at this position the mixed phase meets the oil phase and is sheared by the oil phase to form oil-in-water droplets; channel C7 is the flow channel where the oil phase shears the mixed phase to form droplets, and direction 1-4 is the flow direction of the oil-in-water emulsion; G1, G2, G3 and G4 are four solid gel microspheres, among which Microsphere G1 is a solid gel microsphere that will enter the mixing flow channel C4 earlier in the solid gel microsphere flow channel C1, and microsphere G2 is a solid gel microsphere that will enter the mixing flow channel C4 later in the solid gel microsphere flow channel. In the process of the oil phase shearing the water phase to form droplets, the solid gel microsphere G1 first enters the intersection of channel C3, and the solid gel microsphere G2 at a distance L1 behind it immediately enters the intersection of channel C3. The length L1 is the distance between microsphere G1 and microsphere G2 when they are in channel C1, and the space between the two microspheres is filled with the buffer solution of the solid gel microsphere phase. The length L2 is the distance between microsphere G1 and microsphere G2 when they are dispersed by the cell phase and flow into channel C4. The space between the two microspheres is filled with a mixture of the solid gel microsphere phase buffer solution and the cell phase. When the solid gel microspheres flow in channel C1 and the distance is 0, the distance between them when they are dispersed by the cell phase and flow into channel C4 in pairs is L3.
[0047] When preparing monodisperse single-cell droplets, the solid gel microsphere phase flows into the microfluidic chip from the C1 channel in a 1-1 direction. The gel microspheres have two flow states in the C1 channel: one is a flow state in which the distance between the microspheres is 0, and the other is a flow state in which there is a certain distance L1 between the microspheres. The cell phase flows into the microfluidic chip from the C2 channel in a 1-2 direction. The solid gel microsphere phase and the cell phase intersect at the C3 "T"-shaped channel position, and the densely packed solid gel microspheres are dispersed and mixed by the cell phase. The solid gel microspheres flow into the C4 channel with a certain L2 or L3 spacing and a flow direction of 1-3, as the dispersed phase to form droplets; the continuous phase oil phase flows into the microfluidic chip from the C5 channel in the 1-4 direction, and intersects with the mixed phase of the dispersed phase solid gel microspheres and the cell phase at the C6 "T"-shaped channel position, and disperses the mixed phase into independent droplets. Each effective target droplet should contain a cell and a solid gel microsphere. The differential coding connected to the microsphere will capture the mRNA in the lysed cell for subsequent single-cell reverse transcription, amplification, connection to sequencing adapters and sequencing operations. When a pair of solid gel microspheres flows in the C1 channel and there is no spacing, the pair of microspheres (such as Figure 2 -A) enters the C4 channel and is dispersed by the cell phase and separated by a distance L3, which is filled with the cell phase; when a pair of solid gel microspheres flows in the C1 channel, there is a distance of L1, and the gap is filled with the buffer of the solid gel microsphere phase. Figure 2 -A and 2-B) after entering the C4 channel, they will be dispersed by the cell phase and separated by a distance L2. This distance is filled with cell phase and solid gel microsphere phase buffer. When the solid gel microspheres flow into the C6 "T" shaped channel position with a fixed spacing of L3, they will be stably sheared by the continuous oil phase into droplets, and each droplet only encapsulates one solid gel microsphere. However, when the microspheres already have a gap L1 in the C1 channel, when they flow into the C4 channel, they will be dispersed by the cell phase to a larger spacing L2. When they flow into the C6 "T" shaped channel position, they will be stably sheared by the continuous oil phase into droplets. However, due to the large spacing between microspheres, droplets that do not encapsulate microspheres will be formed, which are non-target droplets in single-cell sequencing. Therefore, stabilizing the spacing between microspheres is a method to improve the microsphere encapsulation rate.
[0048] Example 3: Process of forming single-cell solid gel microspheres after optimization of single-cell microfluidic system
[0049] like Figure 3Figure 1 shows the process of forming single-cell solid gel microspheres in the optimized single-cell microfluidic system. Subfigure A shows the flow state at an early point in the microfluidic system's monodisperse droplet generation process, and subfigure B shows the flow state at a later point in the process. Compared to the unoptimized microfluidic chip design, the C8 "T"-shaped drainage structure and C9 drainage channel were added. In the figure, G5 represents a solid gel microsphere that flows through the C8 "T"-shaped drainage structure earlier in the solid gel microsphere flow channel and enters the mixing flow channel. G6 represents a solid gel microsphere that flows through the C8 "T"-shaped drainage structure later in the solid gel microsphere flow channel and enters the mixing flow channel. L4 represents the distance between G5 and G6 solid gel microspheres when flowing in the gel microsphere channel, and L5 represents the distance between G5 and G6 solid gel microspheres when flowing in the mixing channel. 1-5 represents the flow direction of the drainage channel.
[0050] When solid gel microspheres with a spacing of L4 flow in the channel, G5 first passes through the C8 "T"-shaped drainage structure. Since the C9 drainage channel is smaller than the solid gel microspheres in size, the gel microspheres will not enter the C9 channel. However, the buffer solution between the solid gel microspheres G5 and G6 will flow into the C9 channel through the C8 structure under the action of pressure, and be discharged from the solid gel microsphere phase channel in the direction of 1-5, reducing or even eliminating the buffer solution between the solid gel microspheres to achieve the effect of dense packing of solid gel microspheres, as shown in sub-Figure B, where the spacing between the solid gel microspheres G5 and G6 is reduced to 0; when the solid gel microspheres flow to the mixing channel, the two are dispersed by the cell phase to a spacing of L5, filled with cell phase buffer, and finally sheared by the continuous oil phase to form droplets, which can increase the proportion of single gel microspheres by 10% compared with the design without branch channels.
[0051] Example 4
[0052] Table 1 shows the statistical results of "water-in-oil" droplet preparation using a microfluidic chip with a branch channel design and a microfluidic chip without a branch channel design for the same batch of solid gel microspheres, demonstrating the effectiveness of the optimized chip in preparing droplets containing a single solid gel microsphere. During the preparation process, when the aqueous phase is sheared by the continuous oil phase, droplets containing no gel microspheres, a single gel microsphere, and multiple gel microspheres are formed. Droplets containing only a single solid gel microsphere are the desired droplets. Experiments have shown that the design with a branch channel can increase the proportion of droplets containing a single solid gel microsphere by 20%.
[0053] Table 1 Experimental comparison results
[0054]
[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A microfluidic chip, characterized in that: It includes a main channel, a flow channel for the solid gel microsphere phase, a flow channel for the cell phase, a flow channel for the oil phase, an injection port and a collection port; The main channel is connected to the flow channel of the solid gel microsphere phase, the flow channel of the cell phase, and the flow channel of the oil phase respectively; The cell phase flow channel is vertically connected to the main channel via a first intersection; The flow channel of the oil phase is vertically connected to the main channel via a second intersection; The flow channel of the oil phase and the flow channel of the solid gel microsphere phase are arranged on both sides of the flow channel of the cell phase; The microfluidic chip further includes a buffer discharge channel.
2. The microfluidic chip according to claim 1, wherein The buffer discharge channel includes a buffer discharge main channel and a buffer discharge branch channel.
3. The microfluidic chip according to claim 2, wherein: One side of the buffer discharge branch channel is connected to the buffer discharge main channel; the other side of the buffer discharge branch channel is vertically connected to the main channel through a third intersection.
4. The microfluidic chip according to claim 3, wherein The buffer discharge branch channel is arranged between the flow channel of the solid gel microsphere phase and the flow channel of the cell phase; and / or The buffer solution discharge branch channel is arranged between the injection ports of the solid gel microsphere phase.
5. The microfluidic chip according to claim 4, characterized in that: The cross-sectional width of the buffer solution discharge branch channel is smaller than the diameter of the solid gel microspheres.
6. Use of the microfluidic chip according to any one of claims 1 to 5 in preparing emulsion droplets.
7. Application of the microfluidic chip according to any one of claims 1 to 5 in trace reagent synthesis, micron material synthesis, trace molecular reaction and analysis, single cell encapsulation, single cell separation, single cell capture, single cell sequencing and single cell proteomics analysis.
8. A kit, characterized in that The method comprises the microfluidic chip according to any one of claims 1 to 5 and an acceptable reagent.
9. The device, characterized in that The microfluidic chip comprises the microfluidic chip according to any one of claims 1 to 5.
10. A method for preparing emulsion droplets, characterized in that: Based on the microfluidic chip according to any one of claims 1 to 5, an oil phase is injected into the flow channel of the oil phase, a solid gel microsphere phase is injected into the flow channel of the solid gel microsphere phase, and a cell phase is injected into the flow channel of the cell phase; The solid gel microsphere phase and the cell phase intersect at the first intersection to form a mixed phase; The buffer solution in the solid gel microsphere phase is collected into the buffer solution discharge main channel through the buffer solution discharge branch channel; The mixed phase and the oil phase meet and shear at the first intersection to form droplets.