Collective motility of sperm in confined cells

Abstract

Mammalian fertility analysis is an important industrial issue because of the selection for breeding. This is one reason, beside fundamental interest, for which many studies analyse the individual motion of the spermatozoon (Gaffney et al. 2011). On the other hand, more recent reviews suggest that neither individual motion indicators or molecular markers can be clearly correlated to fertility (Kastelic and Thundathil 2008; Nathali and Turek 2011). This is why the industry still uses the scoring of sperm motility from the observation of semen sessile drop with a phase-contrast microscope. This observation of pure semen displays wave motion associated with millions of sperm moving together in circular waves and whirlpools. The moving speed, deformation and size of whirlpools were ranked and scored. Similar collective movements have also been observed in different biological suspensions above a certain concentration (Sokolov et al. 2007). But until today, there has been no clear analysis of the origin of the observed whirlpools dynamics in semen. In this article, we provide new insights on the origin of whirlpools. As the sessile drops do not permit a careful control of the micro-hydrodynamic boundary conditions associated with surface tension variations, we investigate collective effects in controlled rectangular cells confined span wise with 20 and 100mm depth. We mainly analyse the influence of the confinement and the concentration on the appearance of whirlpools.