Single sperm cryopreservation on cryoloops: an alternative to hamster zona for freezing individual spermatozoa

Methodology enabling cryopreservation of individual spermatozoa in extreme cases of oligozoospermia would tremendously benefit patients. This study explores the use of a nylon loop for cryopreservation of small quantities of spermatozoa, and also describes a novel technique for freezing individual spermatozoa with this cryoloop. Experiments were conducted to compare sperm recovery and viability after cryopreservation in conventional vials versus on the cryoloops. Discarded human sperm specimens with varying parameters were utilized. The study also examines two different glycerolbased cryoprotectants, with and without test yolk buffer. For single sperm cryopreservation, 5-10 spermatozoa were selected and loaded onto cryoloops with the aid of a microscope and micromanipulation equipment. Sperm function testing was performed on both human and bovine spermatozoa frozen on cryoloops. Microquantities of spermatozoa frozen on cryoloops exhibited overall motility and viability parameters similar to control samples frozen in cryovials. Individually selected spermatozoa cryopreserved on loops were easily recovered and post-thaw motility was generally good. Sperm function testing demonstrated that both human and bovine spermatozoa cryopreserved on loops were able to undergo sperm head decondensation when injected into oocytes. Cryoloops may be an excellent alternative to hamster zonae for cryopreserving small numbers of human spermatozoa.