Red Blood Cell Deformability in Microfluidic Constrictions Under Flow and Wall Contact.

Microfluidic devices are widely used for cell manipulation, but the effects of physical contact between cells and microchannel walls are not well understood. This study examines how such contact influences the behaviour of red blood cells (RBCs) during controlled manipulation. RBCs were driven through a narrow microchannel constriction (3.6 × 3.0 µm in cross-section and 2500 µm in length), enabling precise application of mechanical load. A pump system allowed accurate control of flow conditions, ranging from complete immobilisation to defined shear stress by adjusting flow rates. Under immobilised conditions, the recovery time constant of RBCs increased with longer loading durations, consistent with previous studies. However, when shear stress was introduced, recovery dynamics changed significantly. Notably, a 30-fold difference in recovery time constant was observed between a 5 s immobilisation and a 5 s load applied at a flow speed of 0.5 mm/s. Furthermore, the rapid elastic recovery typically occurring within approximately 0.1 s after unloading was suppressed under flow conditions. These results demonstrate that viscous interactions between channel walls and surrounding fluid play a critical role in determining cellular responses during microfluidic manipulation.