Cryopreservation of Human Spermatozoa: A New Frontier in Reproductive Medicine

Cryopreservation is a worldwide technique that makes it possible to preserve different living cells and tissues, including male and female gametes and embryos, in a structurally intact state using low temperature over time. Since the starting point of the cryopreservation era in 1776, until today, this was one of the most important steps in assisted reproductive techniques. Conventional slow freezing of spermatozoa is commonly used for cryopreservation of both ejaculated and surgically retrieved spermatozoa. The technique of the slow freezing is principally based on dehydration of cells which is performed through slow cooling combined with low concentrations of a cryoprotectant agent for achieving a balance. Besides of slow freezing, for more than a decade, many reports suggest the sperm vitrification technique as an alternative to slow freezing. Contrary to the slow freezing method, with vitrification, the effects of the cryoprotectants in spermatozoa are eliminated since this method is cryoprotectant-free. All of these interesting and promising protocols of vitrification, however, have not been implemented in the lab routine yet, and slow freezing remains the standard cryopreservation method in most laboratories worldwide.