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CHAPTER 5.2
such keeping the pellet soft (Fig. 6B). Using the cushioned technique, higher sperm yields are
obtained without impairing sperm quality, which results in a 30% increase of produced semen doses
per ejaculate (Delhomme et al., 2004). The major downside of the cushioned centrifugation is the
necessity to remove the majority of cushion fluid at the bottom, underneath the sperm pellet
following aspiration of the supernatant. The cushion is aspirated with a syringe by placing a blunt
tipped spinal needle gently through the pellet to the bottom of the tube, as indicated in Fig. 1 from
Chapter 4.2. This additional step requires some technical skills, and might explain the lack of
popularity of cushioned centrifugation in practice. This downside was remedied by Waite et al. (2008)
who adapted the protocol and used only 30 µL of cushion fluid (Fig. 5b). However, this technique
requires special designed glass nipple-bottom centrifugation tubes with matching adapters.
Unfortunately, the glass tubes are rather fragile and do not withstand high centrifugation forces,
implying the use of severely reduced centrifugation forces (400 × g), which inevitably results in minor
reductions in sperm yield. Whether the modified cushioned centrifugation will result in increased use
in practice remains questionable. The requirement of the custom made, fragile glass nipple tubes
might prove to be a larger obstacle compared to cushion aspiration when using the regular approach.
A.
Fig. 6. Schematic representation of (A) classical centrifugation where the rather compacted sperm
pellet is located at the tip of the conical centrifuge tube, and (B) cushioned centrifugation
where the spermatozoa are located on top of and in the upper layer of the cushion, which
results in less compaction of the sperm pellet.
B.
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