Erythrocyte Sorting And Directional Trajectory Study Within DLD Microfluidic Chip

The sorting and enrichment of diseased or healthy erythrocytes is an essential step in the diagnosis and research of many blood diseases and requires the use of corresponding bioparticle sorting devices.Among many particle sorting devices,microfluidic sorting chips based on deterministic lateral displacement（DLD）technology have become one of the hot research topics in cell biology,biotechnology and medicine because of their low cost,easy handling,simple device and low damage to biological particles such as cells.In this paper,experimental studies and simulations are carried out to investigate the applicability of deterministic lateral displacement technology to I-shaped pillar DLD arrays of non-spherical cells such as erythrocytes.A complete red blood cell flow experiment scheme was established in this paper,and I-shaped pillar DLD microfluidic chip was designed and manufactured for sorting different deformable red blood cells.In the aspect of chip preparation,polydimethylsiloxane（PDMS）was selected as the chip material,and two finished chips with different distance between arrays were made by soft lithography.According to the specific needs of the experiment,a microfluidic separation experiment platform composed of injection pump,inverted microscope and other instruments was built.Suspension erythrocytes were prepared from fresh whole blood and samples of erythrocytes with different deformability were prepared by leaving erythrocytes for 1,7,and 14 days.The experimental procedure was designed and the treated red blood cell samples were used for the flow experiment in the DLD chip.The flow trajectory of red blood cells observed in the microscope and the enrichment efficiency at the chip outlet were recorded by a high-speed camera to verify the sorting performance of the I-shaped pillar DLD chip.Through the analysis of the experimental results,it is found that the use of I-shaped pillar DLD chip can realize the different deformability of red blood cells in the chip sorting.The enrichment rate of red blood cells with different deformability in the chip was compared,and the enrichment rate of red blood cells with poor deformability in the chip was up to three times that of soft cells.In order to save research costs and establish a more widely applied research method,a two-dimensional numerical model of vesicles with cell membrane structure was established.The influence of changes in membrane thickness,hardness and cytoplasmic viscosity on the deformation of the vesicles model was explored by simulating flow in the simulation chip.Finally,the cell membrane thickness w=0.05μm,cell membrane modulus E₁=6000Pa,cytoplasmic viscosityη=0.045Pa·s were established by screening,and the deformation and flow path of the experimental results were simulated in the numerical flow calculation.Subsequently,the model was simplified to linear elastic solid structure according to the deformation law of red blood cells,and the model was verified according to the experimental results.By comparing the calculation results of two kinds of red blood cell models in flow simulation,two kinds of red blood cell simulation models suitable for different working conditions were finally established.Finally,in order to explore the influencing factors of red blood cell flow trajectory in I-shaped pillar DLD array and explore the optimization method of I-shaped pillar DLD array,three I-shaped pillars were established based on different sizes,and the corresponding arrays were respectively constructed through the design and layout parameters.Solid red cell models were used for flow simulation in these arrays to explore the induction effect of three different pillars on red cell flow trajectories.The changes of the flow trajectory of the erythrocyte model were studied after the array row spacing,cycle and fluid velocity were further changed.This work demonstrates the flow trajectories of erythrocyte models in a series of I-shaped pillar arrays with different design parameters and provides an improved scheme for I-shaped pillar DLD arrays.In conclusion,the study carried out in this paper confirmed the feasibility of using I-shaped pillar DLD chip to sort different deformable red blood cells,and further optimized the two-dimensional red blood cell model,which laid a good foundation for the subsequent research on more extensive red blood cell flow and sorting.