We study theoretically the capturing of paramagnetic beads by a magnetic
field gradient in a microfluidic channel treating the beads as a continuum.
Bead motion is affected by both fluidic and magnetic forces. The transfer of
momentum from beads to the fluid creates an effective bead-bead interaction
that greatly aids capturing. We demonstrate that for a given inlet flow speed a
critical density of beads exists above which complete capturing takes place.Comment: 4 pages including 5 figure