A stereo bifurcated hybrid based on lelo triangle and application thereof

Abstract

The present application relates to the technical field of microfluidic chip, in particular to a three-dimensional bifurcated mixer based on Luer triangle and application thereof. The three-dimensional bifurcated mixer is a 2.5-dimensional structure, which is bonded by two layers of sheet materials, and a square microchannel is formed between the two layers of materials. The microchannel includes a first inlet pipe, a second inlet pipe, a plurality of mixing units and an outlet pipe. Each mixing unit is a Luer triangle ring, which is composed of two concentric Luer triangles inside and outside. The microchannel width of each mixing unit is the widest at the triangle tip, gradually narrows along the sidewall to the middle, and is the narrowest at the middle of the sidewall. The micro-mixer of the present application can stably operate under the condition of medium-high flow rate with Re number greater than 200, and can still maintain a high uniform mixing effect under the actual industrial synthesis condition of FRR=3, realize the synergistic optimization of mixing efficiency and reaction time, and meet the multiple performance requirements of industrialized preparation of lipid nanoparticles.

Description

Technical Field

[0001] This invention relates to the field of microfluidic chip technology, specifically to a three-dimensional bifurcation mixer based on the Reuleaux triangle and its application. Background Technology

[0002] Microfluidic chips have found increasingly widespread applications in drug delivery systems, biomedicine, drug analysis, and chemical analysis. Microfluidic systems offer numerous advantages, including miniaturization, portability, low reagent consumption, fast response times, and high reaction efficiency. However, due to the low flow rate and the tendency for fluid flow to remain laminar, mixing two fluids in a T-channel can only occur through molecular diffusion, requiring a length of at least a meter to achieve uniform mixing – a concept contrary to the principles of microfluidics. To address the challenge of rapid and uniform mixing of two fluids, microfluidic systems typically employ micromixers. Micromixers are crucial components in microfluidics, MEMS devices, and other similar IVD methods. While many different types of micromixers have been designed, the strong specificity of different nanomaterials in the microfluidics field means that no single micromixer is universally applicable.

[0003] Lipid nanoparticles (LNPs) are currently a key carrier for nucleic acid drug delivery. They are complex nanoparticles, primarily composed of ionizable cationic lipids, PEG lipids, cholesterol, etc. Generally, LNP particle sizes range from 50 to 100 nanometers. The most common commercial mixers used for LNP production are bifurcation mixers, such as the one disclosed in Chinese patent CN108778477B. These bifurcation mixers use Dean's vortex to mix at least two different fluids, utilizing the impedance mismatch between the Dean's vortex and the fluid channels forming the mixer to optimize microfluidic mixing. They can produce nanoparticles with particle sizes from 40 to 120 nm that meet the requirements, but they suffer from the risk of clogging during long-term operation. Furthermore, their structural design operates at medium flow rates, resulting in low throughput, which is insufficient to meet the requirements for industrial scale-up. Although the Dean's vortex design theoretically improves the overall mixing effect by increasing the number of mixing units, the insufficient vortex disturbance intensity and limited structural curvature variation within individual mixing units lead to low mixing efficiency per unit length. Therefore, to achieve the mixing performance required for practical applications, more mixing units need to be stacked, resulting in a significant extension of the mixing path and a marked increase in mixing time. For the synthesis of nanomaterials that are highly sensitive to reaction time (such as lipid nanoparticles, LNPs), this design poses a significant risk of prolonged reaction windows and particle inhomogeneity. Furthermore, the Dean vortex bifurcation mixer has a complex structure with multiple internal bends and radially intersecting paths, which may induce flow "short-circuiting" or bypassing under high flow rate operating conditions, affecting the convection intensity in the main mixing zone.

[0004] Chinese patent CN117959970A discloses a passive superelliptical bifurcation mixer, which uses multiple superelliptical ring mixing units to form a mixing module. The inner and outer wall profiles of each individual superelliptical ring mixing unit are both superelliptical. Based on Dean's vortex bifurcation impact mixing, the superelliptical shape formed between the inner and outer walls is changed by altering the n-value of the superelliptic function, thus constructing various superelliptical mixing units with different structures. Through optimization, the mixing efficiency of this mixer can be improved to some extent compared to the traditional Dean's vortex bifurcation mixer under the same conditions. However, this improvement is not significant, and other factors limiting its mixing efficiency have not been properly addressed; the problem of long mixing time remains. Furthermore, the structural design of this mixer does not consider the industrial requirements of various flow rate ratios, resulting in a lack of universality in material synthesis. Furthermore, in terms of manufacturing implementation, although the variation of structural parameter n has mathematical significance in CAD design, in actual micro-nano manufacturing, especially when using DLP, 2PP or other 3D microlithography methods, the subtle structural differences caused by different n values ​​are difficult to be stably replicated. This places high demands on mold precision and equipment parameter tuning, which is not conducive to process stability and batch replication.

[0005] Currently, the most common approach to synthesizing lipid nanoparticles is to use small-sized, staggered herringbone mixers. However, due to the 3D structure and small size of these mixers, injection molding becomes difficult during the fabrication process. The bottom of this structure often contains depressions and fine features, which can easily lead to lipid deposition during long-term continuous operation, increasing the risk of microchannel blockage and reducing the particle size uniformity and production stability of the product.

[0006] Besides staggered herringbone mixers, coaxial microfluidic mixers are also commonly used. However, to achieve high mixing efficiency, these mixers typically need to operate at high flow rate ratios (FRRs), often exceeding 5. This significantly dilutes the product concentration, placing an additional burden on subsequent concentration steps (such as ultrafiltration and dialysis). The coaxial structure can also lead to turbulence at high flow rates, making it difficult to control the batch-to-batch consistency of LNP particle size and distribution.

[0007] Most existing micromixer designs are based on the default condition of FRR=1, without structural optimization for the FRR=3~4 required for the synthesis of nucleic acid delivery nanoparticles. Therefore, in practical applications where FRR is not equal to 1, their mixing performance often decreases significantly, affecting application versatility and product stability. Furthermore, current mixer designs often use "mixing index" and "pressure drop loss" as performance evaluation criteria, neglecting the crucial parameter of mixing time. However, in the self-assembly of lipid nanoparticles, mixing time directly determines the degree of abrupt change in ethanol concentration and lipid encapsulation kinetics, playing a decisive role in particle size, uniformity, and encapsulation efficiency. Therefore, while maintaining high mixing efficiency, it is essential to shorten the mixing time as much as possible to achieve an ideal nanoparticle synthesis window, resulting in nanoparticles with low polydispersity index and smaller particle size. Summary of the Invention

[0008] To address the above problems, this invention proposes a three-dimensional bifurcation mixer based on the Reuleaux triangle and its application.

[0009] This invention provides a three-dimensional bifurcated mixer based on Reuleaux triangles. The three-dimensional bifurcated mixer is a 2.5-dimensional structure composed of two layers of sheet material bonded together, forming a square microchannel between the two layers. The microchannel includes a first inlet pipe, a second inlet pipe, multiple mixing units, and an outlet pipe. Each mixing unit is a Reuleaux triangle ring, and each Reuleaux triangle ring is composed of two concentric Reuleaux triangles, one inside and one outside. The width of the microchannel in each mixing unit is the widest at the apex of the triangle, gradually narrowing towards the middle along the sidewall, and narrowest at the middle of the sidewall.

[0010] The 2.5D structure is a quasi-three-dimensional structure with three-dimensional features but with a constant structure in the z-axis direction. Specifically, in this invention, it is formed by bonding the upper layer of polydimethylsiloxane and the lower layer of glass plate together using oxygen plasma technology to form a square microchannel as a fluid channel.

[0011] Furthermore, there are four mixing units, all of the same size.

[0012] Furthermore, the microchannel includes a first inlet pipe, a second inlet pipe, a first mixing section, a first mixing unit, a second mixing section, a second mixing unit, a third mixing unit, a third mixing section, a fourth mixing unit, and an outlet pipe; wherein, one of the sharp corners of the first mixing unit is placed vertically relative to the first mixing section, the first and second inlet pipes extend towards each other and converge at the first mixing section, the first mixing section extends toward the first mixing unit and connects to the middle of one side of the first mixing unit; the middle of the upper side of the first mixing unit is vertically connected to the second mixing section, the second mixing section extends horizontally and then vertically downwards to connect to one of the sharp corners of the second mixing unit, the other sharp corner of the second mixing unit on the outside is connected to one of the sharp corners of the third mixing unit, so that the second and third mixing units form an inclined figure-eight shape, the downward angle of the third mixing unit is vertically connected to the third mixing section, the third mixing section extends horizontally and then vertically upwards to connect to the middle of one side of the fourth mixing unit, and one of the sharp corners of the fourth mixing unit is vertically upwards to connect to the outlet pipe.

[0013] Furthermore, the microchannel width at the triangular tip of each mixing unit is 300.93 μm, and the microchannel width in the middle of the sidewall is 219.31 μm.

[0014] Furthermore, the inner radius of the Reuleaux triangle ring is 442 μm, and the outer radius is 733 μm.

[0015] Furthermore, the geometric center distance between the first mixing unit and the second mixing unit is 1300 μm, and the geometric center distance between the third mixing unit and the fourth mixing unit is 1300 μm.

[0016] Furthermore, the height of the three-dimensional bifurcation mixer is 300 μm.

[0017] Furthermore, the microchannel width of the first inlet pipe, the second inlet pipe, the first mixing section, the first mixing unit, the second mixing section, the third mixing section, and the outlet pipe is 300μm.

[0018] Furthermore, the inner and outer Reuleaux triangles of each Reuleaux triangle ring are arranged at the same angle.

[0019] Furthermore, the inner and outer Reuleaux triangles of each Reuleaux triangle ring are arranged at angles such that the difference between the inner and outer angles is 0° to 120°.

[0020] Furthermore, placing obstacles between some of the Reuleaux triangle rings creates additional disturbances to the fluid flow state within the microchannel.

[0021] Furthermore, the obstacle is baffle-shaped or cylindrical.

[0022] The Reuleaux triangle-based three-dimensional bifurcation mixer of the present invention is applied in fluid mixing systems.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The three-dimensional bifurcation mixer of the present invention is a 2.5-dimensional structure. Since there is no structural change in the z-axis direction, the processing of this structure is simpler and it can be easily manufactured using ordinary soft lithography technology.

[0025] 2. The hybrid units of this invention are all Reuleaux triangular rings, each composed of two concentric Reuleaux triangles, one inside the other. The microchannel width of each hybrid unit is widest at the apex of the triangle, gradually narrowing towards the middle along the sidewall, and narrowest at the middle of the sidewall. The variable cross-section design of the hybrid unit, with the microchannel gradually narrowing from the apex to the middle (from a width of 300.93 μm at the apex to 219.31 μm at the middle), creates a convergence-divergence effect, significantly enhancing the expansion eddies and promoting laminar flow disturbance.

[0026] 3. The stereobibition mixer of the present invention can ensure the uniformity and stability of lipid nanoparticles synthesized in different batches. Furthermore, since there are no small structures in the channels, it has the advantages of low pressure drop and no clogging.

[0027] 4. The core mixing section of this invention has an area of ​​only 25 mm², which can be densely integrated onto a 4-inch wafer (7854 mm²), achieving a unit area utilization rate of 0.31%, and supporting industrial-scale production. Compared to superelliptical mixers, it occupies a smaller area.

[0028] 5. This invention, through chaotic convection and variable cross-section design, achieves a mixing time as low as 6.06 ms at Re=800, meeting the rapid self-assembly requirements of LNPs below 50nm (existing superelliptical mixers require 10-20ms). The unique structural design significantly reduces the number of mixing units compared to superelliptical mixers, shortening the mixing length to achieve the same mixing efficiency, thereby reducing mixing time and improving mixing efficiency.

[0029] 6. The microchannels of this invention have no depressions or micropillar structures, which avoids lipid particle deposition, improves long-term operational stability, and reduces the risk of blockage by 90%.

[0030] 7. This invention can change the rotation angle (0°-120°) of the internal Reuleaux triangle during processing according to mixing needs, optimize the non-equilibrium collision path, and ensure mixing uniformity (CV<5%) at high flow rate ratio (3:1), which is suitable for LNP industrial production.

[0031] 8. The three-dimensional bifurcation mixer of this invention is a passive micromixer with high throughput, low pressure drop, and strong adaptability. This mixer can operate stably at medium-to-high flow rates with a Reynolds number greater than 200, and maintains a highly uniform mixing effect even in actual industrial synthesis conditions such as FRR=3. Structurally, it adopts a variable cross-section unobstructed channel design, avoiding minute obstruction structures and significantly reducing the risk of clogging. Simultaneously, it introduces structural control over mixing time to achieve synergistic optimization of mixing efficiency and reaction time, meeting the multiple performance requirements of the industrial preparation of lipid nanoparticles. Attached Figure Description

[0032] Figure 1 Schematic diagram of the three-dimensional bifurcation mixer structure based on Reuleaux triangle in Example 1;

[0033] Figure 2 Example 2: A schematic diagram illustrating the results of obtaining key performance indicators of the mixer using simulation software. Figure 2 a represents the relationship between mixing efficiency and Re; b represents the relationship between pressure drop loss and Re; c represents the calculation of residence time (based on particle tracking and mathematical expectation of the first moment). By introducing the Lagrange particle massless particle tracking method, the actual mixing time of the mixer was calculated.

[0034] Figure 3 Concentration distribution diagram (a) and streamline diagram (b) of different parts of the structure at different Reynolds numbers in Example 2.

[0035] Figure 4 The process of 3D printing a stereoscopic bifurcation mixer in Example 3;

[0036] Figure 5 A physical image of the micro mixer fixture (embedded three-dimensional bifurcated mixer) manufactured in Example 3;

[0037] Figure 6 Comparison of ink tests using a micromixer fixture in Example 3;

[0038] Figure 7 Figure 1 shows the experimental test results of the mixing case at high Reynolds numbers in Example 4;

[0039] Figure 8 Example 5: A schematic diagram showing the change in the rotation angle of the internal Reuleaux triangle;

[0040] Figure 9 Figure 6 shows the experimental results of the verification experiment on improving the mixing effect at low flow velocities by adding a trapezoidal baffle.

[0041] Figure 10 A schematic diagram of the added perturbation structure in Example 6, which is a cylindrical obstacle array;

[0042] Figure 11 The diagram shows the baffle structure added in Example 6. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments.

[0044] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, all reagents used in this method are of analytical grade or higher.

[0045] Example 1: A three-dimensional bifurcation mixer based on Reuleaux triangles:

[0046] A three-dimensional bifurcation mixer based on the Reuleaux triangle, wherein the three-dimensional bifurcation mixer is a 2.5-dimensional structure composed of two layers of sheet material bonded together, forming a square microchannel between the two layers of material.

[0047] The 2.5D structure is a quasi-three-dimensional structure with three-dimensional features but with a constant structure in the z-axis direction. Specifically, in this invention, it is formed by bonding the upper layer of polydimethylsiloxane and the lower layer of glass plate together using oxygen plasma technology to form a square microchannel as a fluid channel.

[0048] like Figure 1 As shown, the microchannel includes a first inlet pipe 1, a second inlet pipe 2, multiple mixing units, and an outlet pipe 10. Each mixing unit is a Reuleaux triangular ring, and each Reuleaux triangular ring is composed of two concentric Reuleaux triangles, one inside the other. The width of the microchannel in each mixing unit is widest at the apex of the triangle, gradually narrowing towards the middle along the sidewall, and narrowest at the middle of the sidewall. The fluid channel within the Reuleaux triangular mixing unit has a variable cross-section, with the channel being widest at the apex of the triangle, and the width of the channel gradually narrowing with distance from the apex. This variable cross-section technology conforms to the mechanism of fluid channel narrowing-divergence generating expansion vortices.

[0049] Specifically, the mixing units consist of four identical units. This invention uses only four mixing units to meet the mixing requirements, reducing volume and improving mixing efficiency.

[0050] Specifically, the microchannel includes a first inlet pipe 1, a second inlet pipe 2, a first mixing section 3, a first mixing unit 4, a second mixing section 5, a second mixing unit 6, a third mixing unit 7, a third mixing section 8, a fourth mixing unit 9, and an outlet pipe 10. One of the pointed corners of the first mixing unit 4 is perpendicular to the first mixing section 3. The first inlet pipe 1 and the second inlet pipe 2 extend towards each other and converge at the first mixing section 3. The first mixing section 3 extends towards the first mixing unit 4 and connects to the middle of one side of the first mixing unit 4. The middle of the upper side of the first mixing unit 4 is vertically connected to the second mixing section 5. The second mixing section 5 extends horizontally and then vertically downwards to connect to one of the pointed corners of the second mixing unit 6. Another pointed corner of the second mixing unit 6 on its outer side connects to one of the pointed corners of the third mixing unit 7, forming an inclined figure-eight shape. The downward angle of the third mixing unit 7 is vertically connected to the third mixing section 8. The third mixing section 8 extends horizontally and then vertically upwards to connect to the middle of one side of the fourth mixing unit 9. One of the pointed corners of the fourth mixing unit 9 is vertically connected to the outlet pipe 10.

[0051] Specifically, the microchannel width at the triangular tip of each mixing unit is 300.93 μm, and the microchannel width in the middle of the sidewall is 219.31 μm. The inner radius of the Reuleaux triangle ring is 442 μm, and the outer radius is 733 μm. The geometric center distance between the first mixing unit 4 and the second mixing unit 6 is 1300 μm, and the geometric center distance between the third mixing unit 7 and the fourth mixing unit 9 is 1300 μm. The height of the three-dimensional bifurcated mixer is 300 μm. The microchannel width of the first inlet pipe 1, the second inlet pipe 2, the first mixing section 3, the first mixing unit 4, the second mixing section 5, the third mixing section 8, and the outlet pipe 10 is 300 μm.

[0052] The inner and outer Reuleaux triangles of each Reuleaux triangle ring are arranged at the same angle.

[0053] The area of ​​the core mixing section of the Reuleaux triangle-based 3D bifurcation mixer in this embodiment refers to the area covered by the microchannels between mixing units 1 and 4, occupying 25 mm². The area of ​​a conventional 4-inch wafer is 7854 mm², meaning the 3D bifurcation mixer of this invention occupies only 0.31% of the area, making it extremely convenient for integration with other channels or microfluidic functional devices. Furthermore, when only this mixer is produced, due to its small footprint, multiple molds can be fabricated in parallel, thereby reducing production costs.

[0054] Example 2: Using simulation software to obtain the key indicators of the three-dimensional bifurcation mixer of the present invention:

[0055] To numerically simulate the mixing phenomena and fluid motion inside a micromixer, the fluid is assumed to be Newtonian, incompressible, and the gravitational field is neglected. Based on the governing equations, namely the continuity equation, the Navier-Stokes equations, and the convection-diffusion equations, the following are established:

[0056] ,

[0057] Where V, P, μ, D, and c are the velocity vector, pressure, dynamic viscosity, diffusion coefficient, and mass fraction of the substance, respectively, and ρ is the fluid density. Specific values ​​are shown in Table 1. The working fluids were set as distilled water and distilled water with a concentration of dye. Since the dye concentration in the water was low in the numerical simulation, the fluid properties did not change with concentration and could be considered constant and similar.

[0058] Table 1 Selection of fluid property parameters

[0059]

[0060] Numerically, calculations were only performed up to the range where Re is less than 200, because only at low flow velocities is the entire flow field undisturbed, allowing for a steady-state solution. Figure 2a shows two curves illustrating the changes in the mixing index (MI) for the two inlet flow ratios FRR=1 and FRR=3 as Re increases, obtained from calculations. The results indicate that after skipping the ultra-low flow velocity (Re=1), the mixing index increases monotonically with flow velocity. At Re=200, both flow ratios FRR=1 and FRR=3 can achieve a mixing index (i.e., mixing efficiency) of 90%.

[0061] Similarly, pressure drop is a key metric, measuring flow resistance within the mixer. Unlike stacked mixers, our design does not introduce excessive pressure drop. Figure 2 As can be seen in b, when Re=200, the pressure drop is 6kPa, which is only 6% of one atmosphere, and is suitable for the pressure range of most microfluidic pump systems.

[0062] Furthermore, another important but often overlooked point is the residence time of the liquid in the mixer. Only mixers with sufficiently short residence times and good mixing effects are truly valuable for application. Taking the synthesis of lipid nanoparticles (LNPs) as an example, it often requires a timescale of several milliseconds to tens of milliseconds, making the time requirements extremely stringent. Calculating the mixing time of the flow in a micromixer requires using the residence time theory of fluids within the device. This involves modeling a large number of particles, neglecting the inertia of small particles, ensuring they move along streamlines at all times. We calculated the first moment of the mathematical expectation curve of the residence time, rigorously obtaining the mean residence time:

[0063] ,

[0064] in,

[0065] Indicates the average length of stay;

[0066] E(t) represents the residence time distribution function, which is the probability density function of fluid leaving the mixer at a certain time t;

[0067] t represents time;

[0068] Or for discrete data:

[0069] ,

[0070] in,

[0071] This represents the i-th time point;

[0072] This represents the probability density function at time t;

[0073] Represents discrete time intervals;

[0074] This represents the cumulative stay time distribution function;

[0075] This represents the discrete change in the distribution of cumulative dwell time.

[0076] As Re increases, the mixing time will inevitably decrease. For example... Figure 2 According to calculations, the difference between the actual residence time and the apparent residence time (calculated by dividing the total volume of the mixing section by the flow rate) is minimal. This indicates that the design of this structure is free from blockages or short circuits. At Re=200, the residence time of the liquid in the mixer is only 26 ms. There is reason to believe that this time will further decrease as the flow rate increases.

[0077] To further visualize the mixing process, concentration distribution maps of multiple cross sections in the flow field were extracted at different Reynolds numbers, and streamline coloring maps were plotted.

[0078] Figure 3 Figure 'a' shows the concentration distribution across the cross-section at Re=20, 100, and 200. As the flow rate increases, the fluid interface gradually changes from clear stratification to a uniform distribution. Longitudinally, the stratification effect caused by streamline disturbance at the first inlet ring where the two fluids contact gradually intensifies. At a low flow rate of Re=20, the cross-section changes from the straight stratification expected in a T-mixer to a tortuous stratification. As the flow rate increases, the tortuous stratification breaks down, and the two liquids begin to mix, due to the Dean secondary flow effect generated by the bend. Laterally, the concentration color at the outlet cross-section gradually lightens, becoming more whitish at Re=200, indicating excellent mixing performance at high flow rates. Figure 3'b' represents the streamline diagram under the corresponding working condition. When the flow velocity increases from Re=20, the streamlines gradually change from stratification at low flow velocity to instability and mixing at high flow velocity, which means that chaotic convection gradually starts as the flow velocity increases. Figure 3 This demonstrates that the three-dimensional bifurcation mixer of the present invention can achieve continuously enhanced mixing efficiency.

[0079] This embodiment yields the key performance indicators of the present invention: After skipping the diffusion-dominant phase at ultra-low flow rates, the mixing efficiency monotonically increases to over 80% with increasing flow rate, exhibiting excellent performance across different flow rate ratios. For LNP synthesis, the mixing efficiency at FRR=3 can reach 90%, meaning this mixer can easily adapt to LNP synthesis. The pressure drop loss is extremely low, only 5% of atmospheric pressure at Re=200, meaning this mixer does not require additional manufacturing costs for high water pressure compared to other mixers. The residence time calculation reveals another core advantage of this mixer. First, the theoretical residence time is extremely close to the actual residence time, with an error of no more than 7%, indicating that this mixer does not suffer from flow short-circuiting or clogging issues. Furthermore, the residence time rapidly decreases to below 30ms with increasing flow rate, meeting the stringent time requirements for nanoparticle synthesis.

[0080] Example 3: Ink Experiment Verification:

[0081] To verify the mixing performance of Example 2 predicted in Example 1 using numerical calculations, this example uses 3D printing technology to fabricate the male mold of the micromixer from Example 1. After printing, it is cured under 405nm UV light and the surface is modified with fluorosilane for hydrophobicity to facilitate PDMS demolding. Subsequently, PDMS is molded using Dow Corning Sylgard 184 as the raw material, and the PDMS layer is peeled off after curing. Finally, the PDMS layer is bonded to the glass substrate after oxygen plasma activation to form a complete micromixer chip.

[0082] Because the micro-mixer chip needs to operate under extremely high flow rate conditions, the interface between the chip and the external fluid requires additional reinforcement with clamps. Figure 4 The af is the 3D printing micromixer process in this embodiment. Figure 5 This is an enlarged view of the final fabricated three-dimensional bifurcated mixer of the present invention assembled in a specially designed fixture. Fluororubber rings are used to seal the chip inlet and outlet to ensure watertightness. During the experiment, 25-fold diluted magenta ink and deionized water were injected into the two inlets respectively, and the mixing behavior was observed in real time under a microscope to evaluate its consistency with the simulation results.

[0083] To verify the predictive ability of the numerical model for mixing behavior under different flow rate ratios, we examined the mixing experiments and simulation numerical models of the aforementioned 3D-printed micromixer under two operating conditions, FRR=1 and FRR=3, at Re=100. Figure 6 As shown. To facilitate observation of the evolution of the mixing process, the mixer is divided into three representative regions (Section A, B, and C) along the main channel direction, corresponding to the three stages of inlet disturbance, main mixing, and mixing completion, respectively. Figure 6 (g) In each region, the left image is a microscopic image taken from the micromixer experiment (Fig. 6a, c, e), and the right image is a concentration cloud map obtained from the simulation model (Fig. 6b, d, f). It can be seen that the micromixer experiment and the simulation model show good consistency in terms of the morphology of the mixing interface and the concentration distribution trend. Taking Section B as an example, obvious stretching and entanglement of the fluid interface can be observed under both FRR conditions, and the contour of the ink distribution in the experimental image is highly consistent with the high concentration area in the simulation image. At the same time, different FRR conditions also have a significant impact on the mixing behavior. When FRR=3, the increased mainstream velocity makes the interface more sheared, the degree of interface curling is intensified, and the mixing process is accelerated; while FRR=1 shows a more symmetrical and milder mixing mode. This trend is reflected in all three regions, further supporting the applicability and prediction accuracy of the simulation model under different operating parameters.

[0084] Example 4: Verifying the mixing performance of the mixer from Example 1 at high Reynolds numbers:

[0085] To evaluate the operational stability and mixing performance of this mixer under high Reynolds number conditions, we further conducted experimental verification in the Re>200 range. Figure 7 As shown, we compared the mixing index (MI) of the simulation model numerical simulation calculations with the experimental results of the micromixer ink in the low Reynolds number range, and supplemented the experimental data at higher flow rates to evaluate the upper limit of the mixer's performance. Figure 7 Figure a shows the comparison of the mixing index under two operating conditions, FRR=1 and FRR=3, when Re ≤ 200. The simulation results were obtained by numerical calculation from the steady-state model, and the ink experiment results were obtained by analysis of magenta dye microscopic images. At different Reynolds numbers, the MI values ​​obtained from the numerical calculation and the ink experiment maintained a high degree of consistency, both showing a monotonically increasing trend with Re, with a maximum error of 20% and a minimum of 5%, which is within the acceptable range for engineering applications. This indicates that the numerical model used has high predictive accuracy within the calculable range. Based on the above verification, we further conducted high Reynolds number experiments (Re ≈ 300–1000) using the physical device of Example 3, and the corresponding results are as follows: Figure 7As shown in b. Within this range, regardless of whether FRR=1 or FRR=3, the mixer achieved a mixing index of over 90%, and no obvious flow deviation, turbulence, or structural failure was observed, indicating that the design can still stably and efficiently complete the mixing task under high-speed flow conditions.

[0086] The comprehensive analysis results show that after reaching the start-up threshold of Re≈200, the mixer can maintain good mixing performance and adapt to higher flow rate conditions, demonstrating strong robustness.

[0087] As can be seen from Examples 1-4, compared with existing micromixers, the Reuleaux triangle-based three-dimensional bifurcation mixer of the present invention requires only four mixing units to achieve a mixing efficiency greater than 96%. This structure not only significantly reduces the number of mixing units but also reduces pressure drop loss. Existing micromixers introduce more than 10 repeating mixing units in their structural design to improve mixing efficiency, which essentially relies on the interface growth and enhanced disturbance caused by structural stacking. However, this method inevitably results in greater pressure drop loss and increased channel space, which is detrimental to system integration and high-throughput fluid applications. In contrast, the three-dimensional bifurcation mixer proposed in this invention, with only 4 mixing units, achieves a mixing efficiency of over 90% under Re>200 conditions through the efficient combined effect of spatial folding and bifurcation disturbance, and can still maintain a mixing efficiency of >96% in the high Re number range (Re≈1000). This performance has been jointly confirmed by Example 1 (simulation results) and Example 4 (microscopic verification) (see Example 1). Figure 2 and Figure 7 ).

[0088] Meanwhile, existing studies on the formation mechanism of lipid nanoparticles (LNPs) indicate that a crucial variable affecting the monodispersity of lipid nanoparticles is the fluid residence time distribution within the mixer, i.e., the average time the fluid actually spends flowing within the device. Although the total flow rate for generating LNPs of the target particle size varies depending on the synthesis formulation and the heterogeneity of the synthesis flow rate ratio using existing micromixers, the fluid residence time in the mixing section remains consistently between a few milliseconds and tens of milliseconds. For example, studies have shown that commonly used herringbone mixers can generate nanoparticles with a diameter of approximately 60 nm with a mixing time of 28 ms when preparing LNPs. Calculations reveal that the stereotactic bifurcation mixer of this invention achieves a mixing time of 88.5 ms at Re=50, enabling the preparation of large lipid nanoparticles at a high mixing time; and a mixing time of 6.06 ms at Re=800, enabling the preparation of small lipid nanoparticles at an extremely low mixing time. Furthermore, with further increases in flow rate, it meets the requirement for generating LNPs with the smallest particle size. Therefore, this mixer can prepare LNPs with a fairly wide particle size range to meet the needs of scientific research and industrial production.

[0089] Example 5: Optimizing the unbalanced collision path by changing the rotation angle of the internal Reuleaux triangle:

[0090] As another embodiment of the present invention, the rotation angle (0°-120°) of the Reuleaux triangle inside the three-dimensional bifurcated mixer of the present invention can be changed during processing, such as... Figure 8 As shown, the unbalanced collision path is optimized.

[0091] Example 6: Improving the mixing effect at low flow velocities by adding turbulence structures:

[0092] The mixer of the present invention can improve the mixing effect at low flow rates by adding a turbulence structure.

[0093] We made minor structural adjustments to the Reuleaux triangle structure in Example 1. Specifically, trapezoidal baffles were introduced in the central region of each connecting section to enhance fluid turbulence, such as... Figure 9 As shown in a, the modified structure maintains the same overall channel topology as the original design, only adding a flow-disrupting element in the collar connection section to achieve enhanced mixing under low-speed flow. Figure 9 b specifies the geometry of the spoiler. The spoiler structure employs a trapezoidal cross-section design, with a short side length of 50 μm, a long side length of 100 μm, and an included angle of 141°. Its length direction is aligned with the mainstream direction. Its mechanism of action is as follows: Figure 9 As shown in c: In the original structure, the connecting section is a straight channel, which only generates limited interface disturbances; while in the improved structure, when the fluid passes through the geometric change region of the baffle, a back step flow and micro vortices appear, which effectively break the laminar flow structure and enhance mixing. Figure 9 The figure shows a comparison of the mixing efficiency of the improved structure and the original structure under different flow rate ratios (FRR=1 and FRR=3). The results show that the mixing efficiency is improved to varying degrees at all Reynolds numbers after the introduction of the spoiler, especially under the condition of FRR=3, the improvement can reach about 20%. It is worth noting that the improved structure reduces the "start-up Reynolds number" of the original design from about Re=200 to Re=100, realizing the effective start-up of low-speed mixing. Figure 9 e represents the pressure drop comparison between the two structures at different Reynolds numbers. Although the introduction of the baffle will lead to a certain increase in pressure drop, at Re=200, the pressure drop of the improved structure (about 14000 Pa) is higher than that of the original structure (about 4000 Pa), but it is still within the acceptable range of the microfluidic system and has engineering applicability. Figure 9f represents the simulated streamline diagrams of the mixing section before and after the improvement. It is clearly observed from the figure that after introducing the turbulence structure, the fluid streamlines exhibit folding, interlacing, and microvortices, resulting in a more complex overall flow pattern and forming shear and disturbance zones conducive to mixing, thus validating the design intent. This structural improvement strategy achieves a significant improvement in mixing performance without altering the overall channel design, making it particularly suitable for microfluidic applications with higher mixing efficiency requirements under low Reynolds number conditions.

[0094] There are several ways to incorporate a perturbation structure, such as Figure 10 An array of cylindrical obstacles is added within the straight channel between the Reuleaux rings to provide additional perturbation to the flow state. As the flow velocity increases, an adverse pressure gradient is generated along the cylindrical surface, lifting and separating the boundary layer to form a pair of counter-rotating vortices. These vortices combine with the original Dean vortex to produce stronger chaotic convection. Figure 11 This involves adding baffles within the straight channels between the Reuleaux rings to provide additional disturbance to the flow. The sharp edges of the baffles have a significant impact on fluid flow, resulting in large local head losses and strong eddy currents. Applying this specialized structure, originally designed for reservoir discharge, to a mixer can promote mixing at correspondingly high flow velocities. Similarly, combining it with the original Dean vortex produces an even stronger mixing effect.

[0095] It will be apparent to those skilled in the art 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 in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0096] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A three-dimensional bifurcation mixer based on the Reuleaux triangle, characterized in that, The three-dimensional bifurcated mixer is a 2.5-dimensional structure, which is made of two layers of sheet material bonded together, forming a square microchannel between the two layers of material. The microchannel includes a first inlet pipe (1), a second inlet pipe (2), multiple mixing units and an outlet pipe (10). Each mixing unit is a Reuleaux triangle ring, and each Reuleaux triangle ring is composed of two concentric Reuleaux triangles. The width of the microchannel of each mixing unit is the widest at the tip of the triangle, gradually narrowing along the side wall towards the middle, and the narrowest at the middle of the side wall.

2. The Reuleaux triangle-based 3D bifurcation mixer according to claim 1, characterized in that, The mixing unit consists of four identical units.

3. The Reuleaux triangle-based three-dimensional bifurcation mixer according to claim 1 or 2, characterized in that, The microchannel includes a first inlet pipe (1), a second inlet pipe (2), a first mixing section (3), a first mixing unit (4), a second mixing section (5), a second mixing unit (6), a third mixing unit (7), a third mixing section (8), a fourth mixing unit (9), and an outlet pipe (10); wherein, one of the sharp corners of the first mixing unit (4) is placed perpendicular to the first mixing section (3), the first inlet pipe (1) and the second inlet pipe (2) extend towards each other and merge into the first mixing section (3), the first mixing section (3) extends toward the first mixing unit (4) and connects to the middle of one side of the first mixing unit (4); the upper side of the first mixing unit (4) The middle of the side is vertically connected to the second mixing section (5). The second mixing section (5) extends horizontally and then vertically connects to a sharp corner of the second mixing unit (6). The other sharp corner of the second mixing unit (6) on the outside is connected to a sharp corner of the third mixing unit (7), so that the second mixing unit (6) and the third mixing unit (7) form an inclined figure-eight shape. The downward angle of the third mixing unit (7) is vertically connected to the third mixing section (8). The third mixing section (8) extends horizontally and then vertically connects to the middle of one side of the fourth mixing unit (9). A sharp corner of the fourth mixing unit (9) is vertically connected to the outlet pipe (10).

4. The Reuleaux triangle-based 3D bifurcation mixer according to claim 2, characterized in that, The microchannel width at the triangular tip of each mixing unit is 300.93 μm, and the microchannel width in the middle of the sidewall is 219.31 μm.

5. The Reuleaux triangle-based 3D bifurcation mixer according to claim 2, characterized in that, The inner radius of the Reuleaux triangle ring is 442 μm, and the outer radius is 733 μm.

6. The Reuleaux triangle-based 3D bifurcation mixer according to claim 3, characterized in that, The geometric center distance between the first mixing unit (4) and the second mixing unit (6) is 1300 μm, and the geometric center distance between the third mixing unit (7) and the fourth mixing unit (9) is 1300 μm.

7. The Reuleaux triangle-based 3D bifurcation mixer according to claim 6, characterized in that, The height of the three-dimensional bifurcation mixer is 300 μm.

8. The Reuleaux triangle-based 3D bifurcation mixer according to claim 7, characterized in that, The microchannel width of the first inlet pipe (1), the second inlet pipe (2), the first mixing section (3), the first mixing unit (4), the second mixing section (5), the third mixing section (8), and the outlet pipe (10) is 300μm.

9. The Reuleaux triangle-based 3D bifurcation mixer according to claim 1, characterized in that, The inner and outer Reuleaux triangles of each Reuleaux triangle ring are arranged at the same angle.

10. The Reuleaux triangle-based 3D bifurcation mixer according to claim 1, characterized in that, The inner and outer Reuleaux triangles of each Reuleaux triangle ring are rotated at angles, with the difference between the inner and outer angles being 0°-120°.

11. The Reuleaux triangle-based 3D bifurcation mixer according to claim 1, characterized in that, Setting up barriers between some of the Reuleaux triangle rings creates additional disturbances to the fluid flow state within the microchannel.

12. The Reuleaux triangle-based 3D bifurcation mixer according to claim 11, characterized in that, The obstacle is baffle-shaped or cylindrical.

13. The application of the Reuleaux triangle-based three-dimensional bifurcation mixer of claim 1 in a fluid mixing system.

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