Investigation on the change of spermatozoa flagellar beating forces before and after capacitation

: The swimming forces exerted by mammalian spermatozoa during the pathway to the ovary and during the interaction with the oocyte are thought to play a fundamental role in the fertilization of the egg. In particular, a process named capacitation is of key relevance for its success. Capacitation enables spermatozoa to undergo the acrosome reaction and to exhibit different motility called hyperactivation with a change in the sperm cell tail motion from symmetric to a more asymmetric beating, characterized by wider flagellar bending at lower frequencies. Despite several studies about the mechanism that underlies capacitation, no quantitative information is available about the forces associated with sperm motility. Sperm cell motility has been widely studied with digital imaging tools and video microscopy, but these methodologies cannot provide information about the forces exerted by spermatozoa during the motion and the contribution of every single frequency of flagellar beating to the sperm cell movement. For this purpose, fluidic force microscopy was used to trap single swimming spermatozoa allowing to evaluate these parameters. We observe significant differences between capacitated and non-capacitated spermatozoa in terms of force exerted and beating frequencies. The description of the dynamics of this process is of great interest in the field of reproductive medicine. Such information could be useful to clarify unknown causes of male infertility or for the development of novel methods to assess the quality of semen samples.