What is the shear forces on beads (or cells) passing through a FACS instrument

[Armenm]

Is there any way to determine this from first principles of field theory? I suspect a pretty rigorous understanding of FACS sorting is required, but although I understand the theory I don't even know where to start to determine the forces.
Are the forces enough to lyse cells? What is the minimum affinity of a ligand to its receptor on a bead that will stay attached through the process?

Any insight?

Thanks.

[Warthaug]

FACS machines suspend the cells in sheath fluid; the main purpose of this fluid is to reduce/eliminate shear forces on the cells. As such, the shear experienced by cells tends to be quite low, although the exact value will vary from model-to-model. Because of the sheath fluid there is no easy way to calculate the shear forces involved.

That said, the forces are small enough that most FACS machines will not disrupt weak interactions between particles and cells; we often measure cell-cell binding for phagocytosis assays using FACS, and extracellular cells, often held in place by a small number of modest affinity receptors, remain attached.

If you need to know the absolute shear values involved, you're best off contacting th technical support of your FACS machine's manufacturer. They should have this information.

Bryan