Research On Mechanism And Application Of Elasto-inertial Particle Focusing

It is necessary to focus particles orderly for particles counting,detection and sorting.Viscoelastic flow can focus particles into a single line only by its own viscoelastic properties in a straight channel,without the help of external field or sheath flow.Moreover,a lot of polymer solutions and biological fluid have a certain of viscoelasticity in natural world.Therefore,viscoelastic focusing attracts extensive attention and has been researched widely.This paper designs and manufactures microfluidic devices based on micro-nano manufacturing technology of the mechanical field,then the viscoelastic focusing mechanism of particles is researched in straight and curved channels.At last,the viscoelastic focusing is applied to cell focusing and particle separation.The results above are valuable to the deep research of viscoelastic focusing mechanism under microfluidic environment,they also may benefit to the subsequent particles counting and detection,as well as the design of low-cost portable flow cytometers.Specifically,innovative research findings in this paper are elucidated as follows.(1)The viscoelastic focusing mechanism of particles is researched in straight channels.Firstly,the novel ?-DNA and HA solution are used to investigate the viscoelastic focusing mechanism of particles in straight channels,with fluid speed,aspect ratio,particles diameter and the concentration of solution.Then,the dynamic focusing process of particles along the straight channel is characterized.According to the experimental results,the viscoelastic focusing effect of particles is enhanced with the increasement of HA solution concentration.However,it is opposite in the case of ?-DNA solution.At last,when expansion-contraction cavity arrays are added to the rectangular cross section straight channel,the secondary flow will be generated,and particles with three peaks distribution are focused into a single line again.The sizes of expansion-contraction cavity arrays to particle focusing are also studied in this paper.(2)The viscoelastic focusing mechanism of particles is studied in curved channels.Firstly,the flow rate regulation mechanism of 2%PVP in symmetrical sinusoidal channels is investigated,and the process of particle migration and focusing can be divided into three stages.Then,the differences of particle migration and focusing are compared with viscoelastic fluid and newtonian fluid.What's more,the effects of key parameters to the viscoelastic focusing are investigated using PVP solution,such as the concentration of solution,the particle diameter and the curvature radius of sinusoidal channels.Then,the dynamic focusing process of particles is observed along the sinusoidal channel.According to the experimental results,not only the effects of particles focusing can be highly enhanced,but also the essential length of channels can be reduced with the help of Dean flow.At last,sinusoidal channels,square wave channels,spiral channels and expansion-contraction channels are compared from the strength of secondary flow and the improvement of the focusing effect.(3)The viscoelastic focusing is applied to the cell manipulation and particle separation.The operation targets are changed from rigid spherical polystyrene particles to flexible biological cells,and similar viscoelastic focusing pattern is observed in both straight and curved channels.Particles with different sizes have different lateral migration speed in viscoelastic solution,and particles sorting is achieved based on this phenomenon.A novel type of channel structure is designed and manufactured coupled with two-stage chips,the first-stage chip is to realize the co-focusing of two sizes of particles,the second-stage chip is to separate particles near the walls after a certain distance of migration.At last,the dimension parameters of second-stage chip are optimized,and the separation efficiency of mixed particles reaches more than 96%.