Vitrification of Human Spermatozoa: Effect of Cryoprotectants and Cooling Methods on Sperm Cryopreservation

Cryopreservation is a procedure to freeze several types of cells and tissues, documented since the early nineteenth century. The conventional slow-freezing methods of human spermatozoa are widely used in ART, but the preferred expectations have not been achieved. These methodologies promote dehydration of their intracellular water through cryoprotectants (CPA) to avoid ice formation and physical cell damage. However, these procedures imply an increased concentration of freezing media, triggering the possibility of osmotic shock and intracellular and extracellular ice formation, leading to mechanical damage and cell death. Spermatozoa vitrification has been proposed as an alternative method, leading to the formation of a glass stage avoiding ice crystal formation instead of procedures that try to control a reduced ice formation as slow-freezing methods. In our group, we confirm that permeable cryoprotectant-free vitrification preserves sperm quality better than slow freezing. The vitrification technique is based on the ultrarapid cooling of human spermatozoa by directly into liquid nitrogen with or without the use of permeable CPA; lethal intracellular ice crystal formation and harmful effects of high salt concentration are prevented, reducing the damage on spermatozoa functions, making this procedure much less labor intensive, quicker, and simpler in application than conventional freezing. Therefore, human spermatozoa vitrification demonstrated superior potential on sperm cryopreservation, but the procedure requires further optimization. This chapter focuses on human spermatozoa vitrification, describing the current vitrification methodologies in use, advantages over other cryopreservation methods, and clinical application.