title: Ultra-rapid freezing of very low numbers of sperm using cryoloops.
abstract: BACKGROUND
  With the availability of ICSI, men with severe oligozoospermia (<5x10(6)/ml) are able to reproduce. Current methods for cryopreservation of severe oligozoospermic samples are labour intensive and costly. The objective of this study was to evaluate whether freezing small numbers of motile sperm (approximately 100) was feasible using cryoloops.
  
  
  METHODS
  Initial tests assessed the effect of various dilutions of cryoprotectants on pre-freezing sperm motility. Several solutions were further evaluated for their ability to cryoprotect sperm during ultra-rapid freezing. Sperm were placed on cryoloops and held in liquid nitrogen vapour for 5 min prior to freezing (ultra-rapid freezing) or directly submerged into liquid nitrogen. Using the optimal cryoprotectant and technique from these experiments, ultra-rapid and standard slow-rate freezing protocols were compared.
  
  
  RESULTS
  Optimal sperm survival was seen when sperm in cryoloops were placed in liquid nitrogen vapour in test yolk buffer with 12% v/v glycerol versus other cryoprotectants. Using this cryoprotectant, post-thaw sperm motility is comparable between ultra-rapid and slow-rate freezing methods.
  
  
  CONCLUSIONS
  Ultra-rapid freezing of very low numbers of sperm is feasible using cryoloops suspended in liquid nitrogen vapour for 5 min.
authors.affiliation: Department of Urology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Schuster
authors.forename: Laura M
authors.initials: LM
authors.lastname: Keller
authors.forename: Rodney L
authors.initials: RL
authors.lastname: Dunn
authors.forename: Dana A
authors.initials: DA
authors.lastname: Ohl
authors.forename: Gary D
authors.initials: GD
authors.lastname: Smith
mesh_terms: D002470:Cell Survival; D015925:Cryopreservation / Q000295:instrumentation*; D003451:Cryoprotective Agents / Q000494:pharmacology*; D005240:Feasibility Studies; D005990:Glycerol / Q000494:pharmacology; D006801:Humans; D008297:Male; D013081:Sperm Motility / Q000187:drug effects; D013094:Spermatozoa / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
chemical_list: D003451:Cryoprotective Agents; D005990:Glycerol