FIGURE 6.

Parameters of cell rolling under flow. (a) Balance of forces acting on a rolling cell. Shear stress applies a resultant force F_s and a torque T_s to the cell, which are balanced by a tether force F_t on the receptor—ligand bonds at the trailing edge of a tethered cell and by a compressive force F_c at the sphere bottom. Elevating the viscosity by addition of 6% Ficoll increases shear stress by 2.6-fold and increase F_t on the sphere of the same size, as illustrated by the comparative lengths of the thin and thick vectors for F_t on the small sphere on the right. At the same shear stress, F_t is 9-fold greater for a sphere of 3-μm radius then for a sphere of 1-μm radius, as illustrated by the comparative lengths of the thin vectors for F_t on the large and small spheres. The conversion of wall shear stress into F_t is described in Yago et al.¹⁹ (b) Decomposition of a cyclic rolling step. See text for a detailed description. Reproduced from Yago et al.²⁰