Study On Deformation Characteristics Of Red Blood Cells In Special-shaped Sorting Micropillar Array Under Unsteady Shear Flow

The sorting and detection technology of red blood cells has broad application prospects in medical fields such as early diagnosis of blood circulatory diseases,clinical treatment and research and development of anti-disease drugs.The traditional sorting and detection methods require the help of large-scale equipment,which is complicated in operation,cumbersome,and has a long sorting cycle,making it difficult to achieve rapid clinical sorting and detection.The deterministic lateral displacement（Deterministic Lateral Displacement,DLD）technology has the advantages of low cost,robustness and durability,and can provide high-throughput,high-resolution rapid separation of particles.However,the research on the sorting and motion deformation characteristics of non-spherical deformable biological particles such as red blood cells in a deterministic lateral displacement chip is not sufficient,which limits the application of this technology in practical sorting and detection.Therefore,this paper takes DLD as a research platform to study the movement and deformation characteristics of red blood cells in it.Firstly,based on the basic theory of deterministic lateral displacement,the influence of the microfluidic chip’s structural period,lateral gap,micro-column geometry,and initial flow field conditions on its critical radius was analyzed;The pull method constructs a fluid-structure interaction model to simulate the motion of rigid particles（leukocytes,platelets）in an"I"-shaped array.The interaction between the particle and the fluid under the two-way coupling and the influence on the particle’s trajectory are analyzed,which provides a basis for the later study of the motion and deformation of hyperelastic red blood cells in the flow field.Secondly,a three-dimensional red blood cell model was constructed based on the finite element method,and the influence of the difference of the material model of red blood cells on its mechanical properties under static tension was analyzed,and the Yeoh material model that was in good agreement with the experimental results was finally selected.In the follow-up research,while taking into account the mechanical properties of red blood cells,in order to solve the problem of grid distortion caused by large spatial deformation,the red blood cell model was simplified.And analyzed the influence of its thickness（vertical in-plane direction）d_t on the mechanical properties,the results show that when the thickness is d_t=3.91μm,the deformation degree is basically consistent with the experimental results,this research provides a basis for the research on the deformation characteristics of red blood cells in shear flow Model.On this basis,a fluid-structure interaction model of red blood cells moving in microtubules is constructed,and the effects of the diameter of the circular tube,the initial conditions of the flow field,the diameter of red blood cells and the shear modulus on its movement and deformation under the action of shear flow are analyzed..The deformation index （DI^S） of the three-dimensional and two-dimensional models of red blood cells was extracted for comparison.The results showed that the deformation index of the two-dimensional model of DI^S≤0.3could accurately describe the mechanical properties of red blood cells under the action of shear flow.Reliable erythrocyte stress-strain properties are provided for the study of subsequent erythrocyte movement in the micropillar array.Finally,an"I"-shaped micropillar array that can effectively induce the rolling motion of non-spherical deformable biological cells is designed,and the movement trajectory and deformation degree of red blood cells in the array are analyzed.The research results show that when the offset distance of the"I"-shaped micro-column isΔλ≤1.5μm,the red blood cells move in a"displacement"mode;when it isΔλ≥2μm,the red blood cells move in a"zigzag"mode under the action of the flow field.To further change the elastic characteristics of red blood cells,it was found that when the shear modulus of red blood cells wasμ₀≤5.3μN/m,their motion deformation in the micro-pillar array was large,and the continuous and stable rolling could not be maintained,indicating that the red blood cells were effectively divided in the"I"-shaped array.The selection should be based on reducing the degree of deformation,that is,the effective radius of red blood cells should be greater than the critical radius during the movement.The research results can be used to optimize the structure design of cell sorting chips with higher separation performance,and provide a basis for the improvement of red blood cell sorting throughput and precision.