"A microfluidic chip, like the one shown above, directly separates neutrophils from blood with ultrahigh purity and high efficiency without the need for cumbersome sample preparation. The chip works by mimicking the physiological process of 'cell rolling' where patterns of adhesive molecules are used to draw out neutrophils (blue) from a stream of blood (red) into a parallel buffer stream as shown in the bottom panel."


http://web.mit.edu/newsoffice/2013/research-update-new-microchip-sorts-white-blood-cells-from-whole-blood-0806.html