A mechanism is developed to analyze the cross-stream migration of macromolecules under shear flow in micro channels.The macromolecule is modeled with the bead-spring chain model.The chain is stretched by shear force

and hydrodynamic interaction between two adjacent beads induces a symmetry flow field.However

the symmetry of the flow field is broken in the presence of a wall

thus hydrodynamic interactions between the chain and the wall lead to migration away from the wall.Under strong confinement

this hydrodynamic effect is screened.Then dissipative particle dynamics (DPD) approach is used to investigate the migration of macromolecules under pressure driven flow in micro channel to prove the validity of the mechanism.The simulation results show that the chains migrate away from the channel walls at weak confinement

and there is no such a migration at strong confinement.The migration of -DNA macromolecules in the vicinity of a wall is also studied through experiments.The good agreement of the simulation results and the experimental observations with the mechanism predictions verify the validity of the mechanism.The chain concentration can also affect the migration of the chains.The chains migrate away from the channel walls at a lower chain concentration

but at a higher concentration the chain migration away from the wall diminishes

indicating that the screening of chain-wall hydrodynamic interactions will occur for the higher concentration solutions.