A cross-scale analysis for the determinants of bonding dynamics on the distributions of rolling velocities of cells in microvessels.

The interplay between subcellular adhesion dynamics and cellular-scale deformations under shear flow drives key physiological and pathological processes. While both bond kinetics and fluid-cell interactions have been extensively studied in rolling adhesion, how bond characteristics quantitatively determine cellular velocity distributions remains unclear. In this study, we systematically investigate how force-free bond kinetics and intrinsic mechanical properties govern rolling adhesion dynamics, using macroscopic velocity distributions as a reference. By coupling the immersed boundary method with stochastic adhesion dynamics, we simulate rolling and deforming cells in straight microtubes with receptor-ligand interactions. Our results reveal that velocity distributions transition from log-normal to normal profiles when bond formation probabilities exceed a critical threshold, corresponding to bond saturation on the cell surface. Nonlinear effects of unstressed bond on/off rates on velocity distributions are observed, with distinct saturation thresholds for different bond types. Nonlinear bonds (modeled via the worm-like chain framework) exhibit fewer surface bonds at saturation compared to linear (Hookean) bonds. These cross-scale analyses of bond dynamics provide critical insights into interpreting cellular mechano-phenotypes through rolling behavior.