Sperm Selection by Colloid Centrifugation

Colloid centrifugation has several uses within spermatology. It has traditionally been used as a biomimetic method to select the most robust, fertile spermatozoa from a sperm sample. However, any sub-population can be selected, or the spermatozoa can be separated from seminal plasma, by changing the density of the colloid used. The colloids described here are silane-coated silica colloids in a buffered salt solution, optimized for different species. Although various other methods have been reported to select spermatozoa based on one or more physical properties, only colloid centrifugation is suitable for routine use on semen collection stations.Several variants of the method are available, depending on the volume of sample to be processed and the degree of separation required. All of them involve layering the sperm sample on top of the colloid in a suitably sized centrifuge tube, followed by gently centrifugation using a swingout rotor at 300 g for 20 min. After removal of the supernatant, the sperm pellet is resuspended in a suitable medium, depending on the intended use, e.g., semen extender for artificial insemination, cryomedium for sperm freezing, medium for in vitro fertilization. Thus, the method is practical for most semen collection facilities.