A Method for Small Number of Human Sperm Cryopreservation

Recently, some sperm vitrification devices were developed to simplify the procedures to freeze small number of human sperm. In the present study, we used these devices to further examine some factors that affect sperm motility after fast freezing. Experiments were designed to examine the effects of 1) direct immersion of the devices to liquid nitrogen and indirect immersion of the devices to liquid nitrogen in which the devices were sealed in cryogenic storage vials; 2) different freezing volumes (1–5 μl); 3) different equilibration times (1–5 min); and 4) different ratio of freezing solution (0,1-5,1) on post thawing sperm motility. It was found that fast sperm freezing in the sealed vials had high post thawing sperm motility (91.3–93.7% of recovered sperm motility rates) while direct immersion of the devices to liquid nitrogen had 0% post thawing sperm motility. No differences in the recovered sperm motility rates were observed between different freezing solution volumes (87.4–90.5%), different equilibration times (89.5–94.0%), and different freezing solution ratios (90.8–94.6%). However, only 6.8% of recovered sperm motility rate was obtained if sperm were frozen in the medium without sperm freezing solution. These results indicate that human sperm can be rapidly frozen after the devices are sealed in the vials with different equilibration time in the medium containing sperm freezing solution. High post thawing sperm motility can be recovered with this method so that ~90% of sperm are usable after freezing.