How does the centrifuge rotor affect the yield from a PureSperm gradient?
The centrifuge rotor can have a big influence on the outcome of your density gradient.
Centrifugation using a swing-out rotor is more likely to give a better yield of motile sperm than a fixed rotor centrifuge.
With a swing-out rotor, the tubes are vertical when they are placed in the centrifuge, but when the rotor starts to spin, the tubes swing out to be horizontal, so the sperm pass directly through the gradient layers, in the direction of the centrifugal force, and collect in a pellet at the bottom of the tube (as illustrated in the figure).
In contrast, the sperm that pass through the gradient in a fixed-rotor centrifuge are not in a tight pellet, rather the pellet is more of a smear across the side/ bottom of the conical centrifuge tube.
This is because the direction of movement through the gradient is not the same as the direction of the centrifugal force, so it is less efficient.
As it is harder to retrieve sperm from a more diffuse pellet than a tight pellet, centrifugation using a swing-out rotor is more likely to give a better yield of motile sperm.