Inertia effect on deformation of viscoelastic capsules in microscale flows

The deformation of capsules (i.e., cells, bacterial) in microscale flows plays an important role in biofluid flows such as blood flow in capillaries and cell manipulation in microfluidics. In previous studies on capsule deformation in microscale flows, the inertia effect was often assumed to be negligible and thus omitted. However, this assumption may not reflect real situations, as indicated by recent studies of inertial microfluidics. As such, we aimed to study the inertia effect on capsule deformation in microscale flows and to determine under which conditions this effect may be omitted. Using a collocated grid projection scheme, we developed a finite difference-front tracking method, and investigated the deformation of viscoelastic capsules in microscale flows for Reynolds number (Re) ranging from 0.01 to 10 as seen in vitro and in vivo. The results showed that the transient and steady-state deformation of capsules was significantly affected by inertia, and the flow structure varied considerably when Re was varied from 0.1 to 10. No significant changes were found for Re ranging from 0.01 to 0.1, and hence the inertia effect on capsule deformation in the microscale flows can be omitted when Re is less than 0.1. These findings improve the current understanding of the mechanism underlying cell movement in capillaries and can be applied to optimize the conditions for cell manipulation and separation in microfluidic devices.