An experimental study of the effect of deformability on cell distribution in tubular microchannels

The lateral migration of cells in microchannels is crucial for label-free microfluidic cell sorting. However, the mechanisms by which cell deformability affects migration and distribution remain insufficiently understood. Here, the evolution of distribution patterns and underlying mechanics of cells is investigated with physiologically typical Young's modulus of cells (E = 190–2685 Pa) under wide microfluidic hydrodynamic conditions (Reynolds number Re = 1–336 and cell-to-channel diameter ratio ap/d = 0.068–0.271) in Poiseuille flows of straight microtubes. Cross-sectional distribution analysis reveals four cell focusing patterns: central focusing, Segre–Silberberg annular, double-annular, and inner-annular distributions, whose transitions are jointly governed by Re, E, and ap/d. Morphological analysis suggests that cells with larger deformability are associated with reduced orientational fluctuations and greater orientational stability under flow. The onset of significant deformation is captured by the local capillary number Ca, with Ca ≈ 0.2 associated with the transition to pronounced deformation and the emergence of annular bifurcation. Furthermore, a dimensionless parameter γ based on the Weber number and ap/d is introduced as a phenomenological descriptor of different annular distribution patterns within the present experimental range. This study elucidates how deformability modifies cell focusing in microchannel flows and provides a phenomenological framework for organizing the observed transitions among different focusing patterns in the present system.