Preserving frozen stallion sperm on dry ice using polymers that modulate ice crystalization kinetics.

The research evaluates the suitability of using dry ice as an alternative to liquid nitrogen for the storage and transportation of cryopreserved stallion sperm. The scientists also investigated the effects of adding synthetic polymers (PVP-40, Ficoll-70) which can regulate ice crystal formation, thereby enhancing the preservation of the sperm samples.

Study Goals

• The prime objectives of the study were to determine the critical temperatures for the storage of frozen stallion sperm, while also evaluating the impact of adding synthetic polymers to the mix.
• The researchers tested the effects of cooling sperm samples to different temperatures below freezing point (-10 °C to -80 °C) before storing them in Liquid Nitrogen (LN2).
• They also examined the stability of sperm samples kept under several temperature conditions such as in LN2, dry ice, at -80 °C and -20 °C, in a 4 °C refrigerator, and during storage on dry ice (particularly when kept below -70 °C and during warming).

Use of Synthetic Polymers

• The researchers analysed the effects of adding synthetic polymers: PVP-40 and Ficoll-70 on the ice crystallization process during cryopreservation hoping it improved the stability of the specimens.
• They discovered that using these synthetic polymers could reduce the size and growth of ice crystals during annealing, a process used to alter the physical properties of a substance, in this case, the sperm samples.

Measuring Cryosurvival

• Sperm motility and membrane intactness were used to measure cryosurvival, with an artificial insemination trial conducted to ascertain fertilizing capability.
• Results indicated that sperm samples needed to be cooled below -40 °C before they could be safely stored in LN2.

Results and Recommendations

• The researchers found no adverse effects of switching samples from dry ice to LN2 and vice versa. However, they recommended avoiding warming the sample above -50 °C during transport in dry ice to preserve viability and fertility.
• The addition of either PVP-40 or Ficoll-70 was determined to enhance sperm cryosurvival, particularly under non-ideal storage conditions where ice recrystallization may occur. The introduction of these polymers could potentially improve the preservation process.