  Guided by extensive numerical simulations, we propose a microfluidic device
that can sort elastic capsules by their deformability. The device consists of a
duct embedded with a semi-cylindrical obstacle, and a diffuser which further
enhances the sorting capability. We demonstrate that the device can operate
reasonably well under changes in the initial position of the the capsule. The
efficiency of the device remains essentially unaltered under small changes of
the obstacle shape (from semi-circular to semi-elliptic cross-section).
Confinement along the direction perpendicular to the plane of the device
increases its efficiency. This work is the first numerical study of cell
sorting by a realistic microfluidic device.
