| Microfluidics is a kind of science and technology for precise control and manipulation of fluid through micropipe on micro scale.It has the advantages of high integration,low labor cost,material saving and high control degree,and has been widely used in in vitro diagnosis,clinical medicine and other fields.As one of the most accurate and powerful separation schemes for microfluidics in recent years,inertial focusing technology is a passive manipulation scheme that utilizes microfluidics to migrate through pipelines to specific equilibrium positions in microchannel cross sections and be effectively screened or separated.It has technical advantages such as high efficiency,high controllability and simple structure,showing strong potential in cell counting and screening.On the other hand,early detection,diagnosis and treatment of circulating tumor cells(CTCs)are the most effective preventive measures for circulating cancer.It is of particular importance to screen and control the circulating tumor cells(CTCS).In this paper,aiming at the separation strategy of CTCs cells and blood cells,the inertial focus separation technology was introduced.With the help of COMSOL software platform,the optimal inertial focus separation strategy was explored by studying the separation effect and focus range of CTCs cells caused by technological factors such as channel thickness,channel inclination,and whether there is any sheathing flow.In order to provide a certain theoretical basis and technical support for the early discovery of cancer tumors.Using COMSOL laminar flow and particle tracking module,four kinds of cells including MCF-7 cells,He La cells,WBC cells and RBC cells with different diameters-24 μm,16 μm,12 μm and 8 μm,respectively,were established in this paper.Furthermore,the spiral inertial focusing microchannel model without sheathing fluid was further constructed.The effects of grid density and Reynolds number on cell separation efficiency,fluid trajectory and focusing range were studied.The results showed that: The effect of mesh density on cell separation efficiency is far less than1%,and the increase of fluid Reynolds number reduces the focusing range of the four types of cells.However,the effect of fluid Reynolds number on the focusing effect and separation efficiency of cells in the non-sheathing flow annular inertial focusing channel is small,and the focusing range of particles with larger particle size is closer to the inner side of the channel.In this paper,the spiral inertial focusing microchannel model of single sheath fluid was established.The influence of relevant technological factors on cell focusing range and separation efficiency was studied by changing the fluid Reynolds number,channel inclination,channel average thickness,and Angle of sheath flow introduction in the channel.The results showed that the introduction of sheath flow would cause disturbance to the microchannel fluid,thus changing the trajectory of the movement of particles.When the flow velocity of the fluid was both 0.221 m/s,the focusing range of cells in the spiral channel with the characteristics of single sheath fluid was reduced by 58% compared with that of the non-sheath fluid.Compared with the rectangular channel,the trapezoidal channel causes the center of Dean vortex to shift to the outside of the channel due to the introduction of the sidewall dip Angle,and generates stronger Dean flow on the outside,which further increases the intensity difference between the inner and outer Dean vortices.The resultant force on the cell will make the particles free from the original position and increase the cell capture efficiency to a certain extent.With the increase of trapezoid Angle,the cell separation becomes more obvious.For He La cells,when the Angle of the trapezoidal microchannel was small,they focused on the center of the channel near the inner wall.With the increase of the Angle of the trapezoidal microchannel,He La cells gradually focused on the Dean vortex center outside the channel.With the increase of channel thickness,the focusing center of He La cells shifted from inside to outside.However,when the microchannel thickness exceeded 155 μm,He La cells would gradually move away from the original focusing position and turn to the outwardly focused Dean flow center,which weakened the separation efficiency.Changing the Angle of sheath fluid introduction into the channel can effectively change the channel length required by the particle to reach the equilibrium position and the focusing position range of the particle at the exit.When the Angle of sheath fluid introduction is 90°,the channel length required is the minimum,and the focusing effect of the particle is the best when the Angle of sheath fluid introduction is 120°.In this paper,a single sheath liquid bending inertial focusing channel was established.By designing the same length,section size and curvature radius as the single sheath liquid channel,the focusing range distance and cell collection efficiency of the curved channel under the change of Reynolds number were studied.The results showed that when the Reynolds number increased from 85 to 94,the focus range of red blood cells shrank sharply,and the focus center shifted from the channel center to the outer wall.The focus center of white blood cells also gradually shifted to the center of the channel from the inside of the channel.Under the same conditions,MCF-7 cells with larger particle sizes focused almost within a small range of the inner wall of the channel.By exploring the focusing range of cells,a three-outlet single sheath fluid bending inertial focusing channel was developed.When the Reynolds number of the fluid in the microchannel was 94,He La cells and MCF-7 cells with 100% separation purity and efficiency were obtained by bending the single sheath liquid at three outlets through the inertial focusing channel.In this case,the separation effect was optimal.This design improves the study of isolating and purifying circulating tumor cells and makes some progress for early identification of cancer. |
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