Why blood and ficoll cannot be mixed?

Question

In most of the protocols i am reading stated that blood should be overlayed carefully on top of ficol layer. Mixing should not be done. Why is it so?

Answer 1

Ficoll is normally placed at the bottom of a column, and blood is then slowly layered above the ficoll. After being centrifuged, the following layers will be visible in the column, from top to bottom: plasma and other constituents, mono-nuclear cells (PBMC/MNC), ficoll, and erythrocytes & granulocytes which should be present in pellet form. This separation allows easy harvest of PBMC's. Note that some red blood cell trapping (presence of erythrocytes & granulocytes) may occur in the PBMC or ficoll layer. Major blood clotting may sometimes occur in the PBMC layer. Ethylene diamine tetra-acetate (EDTA) is commonly used in conjunction with ficol separation to prevent clotting.