Single spermatozoon freezing using cryotop

Conventional freezing procedures are not appropriate for surgically retrieved spermatozoa from the epididymis or testis because of their low numbers. Techniques for the cryopreservation of small numbers of spermatozoa have not been fully established. We tried to develop a cryopreservation method for a single spermatozoon using Cryotop, which has a simple structure and is easy to handle. Different parameters influencing the freezing procedure, types of container, sources of spermatozoa, and cryoprotectants were evaluated. The sperm recovery rate after thawing was similar between the sperm frozen using Cryotop or zona pellucida as containers (98.0% vs. 88.0%). Freezing of motile single spermatozoa obtained from ejaculates and testes were evaluated for recovery rate (90.0% vs. 95.0%) and motility rate (44.4% vs. 42.1%), which were not significantly different. The survival rate was significantly higher when sperm were treated with sucrose rather than with SpermFreeze (65.3% vs. 37.3%, P < 0.01). Cryotop was a highly effective tool for the cryopreservation of a single spermatozoon, and sucrose was determined to be an efficient cryoprotectant.