IVF vitrification uses a combination of permeable and impermeable cryoprotectants, typically including DMSO (dimethyl sulphoxide) and ethylene glycol as the primary permeable agents, combined with sucrose as an impermeable agent. The role of the cryoprotectant is to replace the water inside and around the cell to prevent ice crystal formation during both cooling and warming.
The specific concentrations, equilibration times, and solution sequence are defined by the vitrification kit manufacturer and are validated for the particular carrier geometry and cooling rate of that system. The cryoprotectant solutions supplied with CBS High Security Vitrification Kits (cryolab.co.uk/product-category/vitrification-kits/) are not interchangeable with solutions from other manufacturers.
Cryoprotectants are cytotoxic at physiological temperature. This is not a theoretical concern – it is the reason why equilibration times in vitrification protocols are strictly limited and tightly controlled. Every extra minute a cell spends in high-concentration cryoprotectant before cooling is a minute of unnecessary toxicity exposure. The equilibration timing in the protocol is the validated limit for that specific solution concentration and carrier volume, not a conservative estimate with built-in margin.
Why are two different types of cryoprotectant used?
Permeable cryoprotectants (DMSO and ethylene glycol) enter the cell and replace intracellular water. Impermeable cryoprotectants (sucrose) remain outside the cell and draw residual water out through osmosis. Together they reduce the total water content available to form ice crystals to a level at which vitrification is achievable at the cooling rates produced by the carrier system. Neither type alone achieves the required dehydration.
Are vitrification cryoprotectants regulated as medical devices?
Cryoprotectant solutions used in licensed human IVF treatment are subject to regulatory oversight as part of the overall quality management requirements imposed by the HFEA. Clinics should ensure any vitrification kit used in licensed fertility treatment is supplied by a manufacturer that can provide the documentation required for the clinic’s quality management system and HFEA compliance file.
