An optical-manipulation technique for cells in physiological flows.

We have developed a technique to manipulate human red blood cells (RBCs) in hydrodynamic flows. This method applies optical tweezers to trap and move microbead-attached RBCs in a liquid medium at various speeds, while it significantly minimizes laser heating and photon-induced stress for normal operation with laser-trapped cells. Computational fluid dynamics is applied to simulate flow-induced shear stress over the cell membrane and to correlate quantitatively the forces with the cell deformations. RBCs can be manipulated under physiological conditions by this approach, which may open an avenue to design principles for the next generation of cell sorting and delivery.