Cryoprotectant solutions are the chemical media used in IVF and reproductive biology to protect biological specimens from the damaging effects of freezing and thawing. Without cryoprotection, the formation of ice crystals during cooling and the osmotic stresses associated with the freezing process would cause irreversible damage to cell membranes, organelles, and DNA. Selecting the appropriate cryoprotectant solution for a specific application is as important as the physical freezing method used, and the two must be matched to achieve optimal outcomes.
Cryoprotectants are classified into penetrating and non-penetrating types. Penetrating cryoprotectants such as glycerol, dimethyl sulphoxide, ethylene glycol, and propanediol cross the cell membrane and replace intracellular water, reducing the concentration of ice-forming solutes inside the cell during cooling. Non-penetrating cryoprotectants such as sucrose and trehalose remain outside the cell and create an osmotic gradient that draws intracellular water out before freezing. Most clinical cryopreservation media combine both types.
For slow freezing of human sperm using a system such as the CBS Digitcool Controlled Rate Freezer, glycerol-based extenders remain the standard, used at a final glycerol concentration of typically 7 to 10 percent by volume. For oocyte and embryo vitrification using the CBS High Security Vitrification Kit, the cryoprotectant concentrations are substantially higher, combining ethylene glycol and dimethyl sulphoxide with sucrose as a non-penetrating agent to achieve the glass-forming viscosity required at ultra-rapid cooling rates.
Browse our range of certified IVF vitrification media and consumables and slow freezing equipment for sperm, oocyte, and embryo cryopreservation across UK programmes.
