Freezing and storage of biological material is performed
at low temperatures.

These temperatures can be achieved by using liquid nitrogen (-196°). Under these conditions, oocytes can be stored over a long period without impairment of their viability and function. In order to prevent damage to the eggs / tissue it is crucial to consider the various damaging impacts that cooling may have on them and thus being able to apply the appropriate cell and tissue specific freezing technique.

Details:
Controlling the cooling rates and using an appropriate concentration
of specific cryoprotectants has dramatically improved the procedure of egg freezing.

This method allows to prevent metabolic changes in the cells, irreversible damage to the lipoproteins that are embedded in the cell membranes, increased solubility of gases as well as increased osmotic pressure as a result of dehydration and ice crystal formation.

Cryoprotectants are designed to protect the cells (e.g. oocytes) during the egg freezing process as they interact directly with the cell membrane. They lower the freezing point of the solution. The “effect of dehydration” of non-permeable cryoprotectants is based on the principle of osmosis and reduces the quantity of water that crystallizes within the egg cell. Intracellular ice-formation can thus largely be avoided.

During the thawing process, cryoprotectants reduce the amount of water that tends to flow into the cell.

Thus the biological material remains protected from damage due to excessive and uncontrolled (too fast) rehydration. The negative impact of ice-crystal formation on the cell membranes plays a crucial role in the survival of oocytes after thawing.

Learn more about the special technique of vitrification ....