Counterflow Centrifugation Elutriation (CCE) is a cell separating technique. This method enables scientists to separate different cells with different sizes. Since cell size is correlated with cell cycle stages this method also allows the separation of cells at different stages of the cell cycle.
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Principle
The key concept is that larger cells tend to stay within the flowing buffer solution while smaller cells will be washed away follow the buffer solution (different sedimentation property within the buffer solution), and cells will have different sedimentation properties in different cell cycle stages.
The basic principle of separating the cells inside CCE is the balance between centrifugal force and the counter flow drag force. When the cells enter the elutriation chamber, all the cells will stay at the outer edge of the chamber due to centrifugal force. Then when we increase the flow rate of the buffer solution, due to the special design of the CCE, the solution tends to push the cells towards the middle of the CCE: we call this counter flow drag force. As the flow rate of the buffer solution increase, when the counter flow drag force outweigh the centrifugal force the smaller cells will be driven by the net force and leave the chamber first. In contrast the larger cells will stay within the elutriation chamber. So the cells escape from the elutriation chamber can be collected in the exit of the system.
Advantages
During the separation, the cell only needs to be suspended in a buffer solution and enter a centrifuge, the whole processes does not involve any chemical (e.g. staining) and physical (e.g. attachment of antibody, lyses of cell membrane) effect on the cells, so the cell will remain unchanged before and after the separation. Because of this, the collected cells can be used for further experiment or further separation by other techniques. Finally the CCE rely on centrifugal force and the counter flow drag force to separate the cells, so the speed of separation is fast. In summary:
Disadvantages
As mentioned above, the CCE separates cells based on their sedimentation property but not specific features (e.g. surface protein, cell shape). It cannot separate different types of cells which have similar sedimentation properties. This means that previous purification needs to be done for mixed cell type sample. The CCE is also limited to cells which are able to be individually suspended in the buffer solution. Cells which always attach to something cannot be separated by the CCE.