Numerical Studies Of The Movement,Deformation And Aggregation Of Cells In Stenosed Microchannels

The changes in the mechanical properties of a cell are not only the cause of some diseases,but can also be a biomarker for some disease states.In recent years,microfluidic devices with built-in constrictions have been widely used to measure these changes.The transit time of cells in such devices(defined as the time of the cell to pass through the constriction)to measure cell movement is a crucial factor associated with the mechanical properties.Here,we use smoothed dissipative particle dynamics(SDPD),a particle-based numerical method,to explore the relationship between the transit time and mechanical properties of a cell.Three expressions of the transit time are developed from our simulation data,with respect to the stenosed size of constrictions,the shear modulus and bending modulus of cells,respectively.We show that a convergent constriction(the inlet is wider than the outlet),and a sharp-corner constriction(the constriction outlet is narrow)are better in identifying the di?erences in the transit time of cells.Moreover,the transit time increases and gradually approaches a constant as the shear modulus of cells increases,but increases first and then decreases as the bending modulus increases.These relationships may potentially form a basis for a microfluidic devices to measure cell's mechanical properties.In turn,we investigate this recommended chip design and examine its potential for performance.We develop the simultaneous dependence of the transit time on both the shear and bending moduli of a cell,and then examine the chip sensitivity with respect to the cell mechanical properties while serializing a single constriction along the flow direction.We then study the e?ect of the flow velocity on the transit time,and also test the chip's ability to identify heterogeneous cells with di?erent mechanical properties.The results show that the serialization of chip can greatly increase the chip sensitivity with respect to the mechanical properties of cells;The flow with a higher velocity helps in not only promoting the chip throughput,but also in providing more accurate transit time measurements,because the cell prefers a symmetric deformation under a high velocity;The recommended microfluidic chip is capable of identifying heterogeneous cells,even when only one unhealthy cell is included.Thrombus formation is a complex and multistep process.We concentrated on its two crucial steps,(i)platelets adhered to a vessel wall,named platelet adhesion,and(ii)platelets clumping together and arrested to the adherent platelets,named platelet aggregation.We report the first direct simulation of three modes of platelet adhesion,detachment,rolling adhesion and firm adhesion,as well as the formation,disintegration,arrestment and consolidation of platelet plugs.The results show that the bond dissociation in the detachment mode is mainly attributed to a high probability of rupturing bonds,such that all bonds can be broken completely.In the rolling adhesion,however,it is mainly attributed to the strong traction from shear flow or erythrocytes,causing that the bonds are often ruptured at the trailing edge of a platelet.The erythrocytes play an important role in platelet activities,such as the formation,disintegration,arrestment and consolidation of platelet plugs.They exert an aggregate force on platelets,which behaves as a repulsion at a near distance but an attraction at a far distance between them.This aggregate force can push platelets to aggregate together forming a plug,and bring along a part of the platelet plug causing its disintegration.It also greatly influences the arrestment and consolidation of platelet plugs,together with the adhesive force from the vessel wall.