  We present a method for the direct and continuous separation of red and white
blood cells from plasma at the microscale. The method is implemented in a
microfluidic system with magnetic functionality. The fluidic structure within
the microsystem consists of an inlet and a single microfluidic channel with
multiple outlets. The magnetic functionality is provided by an array of
integrated soft-magnetic elements that are embedded transverse and adjacent to
the microchannel. The elements are magnetized using an external field, and once
magnetized they produce a magnetic force on blood cells as they flow through
the microchannel. In whole blood, white blood cells (WBCs) behave as
diamagnetic microparticles, while red blood cells (RBCs) exhibit diamagnetic or
paramagnetic behavior depending on the oxygenation of their hemoglobin. We
study the motion of blood cells through the microchannel using a mathematical
model that takes into account the magnetic, fluidic and gravitational forces on
the cells. We use the model to study blood cell separation, and our analysis
indicates that the microsystem is capable of separating WBC-rich plasma,
deoxygenated RBC-rich plasma and cell-depleted plasma into respective outlets.
