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Cryopreservation technology

Cryopreservation (from the Greek for cold and the Latin for conservare = preserve or keep) is defined as the storage of cells by freezing them in liquid nitrogen.

Cells are placed in a state of suspended biological activity at temperatures as low as -196 °C, at which all metabolic processes in the cell come to a halt. Once they have been thawed, the cells resume their normal physiological processes. It is possible to store the cells over many years.

Freezing equipment for cells

Different freezing systems for different cells
Freezing equipment 2

However, different cells and tissues require different forms of preparation, such as the addition of solutions to provide protection during freezing and various rates of freezing. The storage containers also vary. Storage not only in liquid nitrogen but also in the gaseous phase just above this is possible.

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Sperm in a straw Sperm in what are called "straws", thin 12 cm long plastic tubes, the ends of which are welded closed after filling. Each "straw" of this type can be expected to contain approximately 5 -10 million sperm cells.
Straws used to hold eggs 'Straws' of approximately 6 cm in length, used to hold 1 - 3 (fertilised) eggs These are tightly sealed using a 1.5 mm steel ball. Alternatively, straws may be used which can be sealed by welding.
Fertilised eggs in the 'straw' Fertilised eggs in the 'straw' - here in liquid nitrogen. Each straw generally contains 1 - 3 fertilised eggs.

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The 'quality upon thawing' will vary depending on the type of cell and tissue and on the freezing technique selected. Sperm cells can generally be cryopreserved very effectively. This means only a minor loss of quality. The same applies for testicular tissue. Unfertilised eggs can only be frozen with a significant loss of quality, even using the latest available procedures.

The situation is quite different with what are known as "fertilised eggs" (more accurately: pre-fertilised), which are generated during the test tube fertilisation process. In this case, an 80 - 100 % chance of further development (i.e. completion of the fertilisation process) can be expected. Freezing of embryos has similar prospects for success. The cryopreservation of ovarian and testicular tissue has also now become an established process. These tissues can be obtained by surgery before the start of radiotherapy and/or chemotherapy.


There are thousands of sperm samples and hundreds of fertilised eggs in storage at the Berlin Sperm Bank (Berliner Samenbank).

The filling level of each individual storage tank is monitored and maintained at regular intervals, mostly automatically.

A computerised file with multiple backups is used to ensure that the containers can be traced with certainty to each individual person or to each respective donor. It is therefore impossible for samples to be mixed up or lost.

Each batch of sperm (several straws from one lot of sperm) is stored in special holders. Both the "straws" and these holders are clearly labelled and placed together in metal canisters.

Each nitrogen storage tank contains 6 - 8 of these canisters.

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Empty sperm 'straws' next to a 'straw holder' (Empty) sperm 'straws' next to a 'straw holder'
Storing straw holders in the canister Storing straw holders in the canister
Storage tanks Storage tanks, each with the capacity to hold 8 canisters of this type
Nitrogen top-up tank Head of the liquid nitrogen tank, which is topped up weekly. The consumption depends firstly on the size of the opening of the nitrogen tank and secondly on the number of times the respective tank is used for procedures. Therefore, an additional nitrogen top-up tank is required.

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Welding each individual "straw" prevents any direct contact between samples. Another option for sealing the "straw" is the use of a small steel ball. The possibility of leakages and any other conceivable form of contamination (microbial transmission) is therefore excluded with certainty.

The storage system is not dependent on mains electricity. Even in the event of a total loss of power and, with it, of the automated measurement and filling systems, samples are protected from damage by the filling in the containers for at least 2 - 3 weeks without the intervention of our employees. However, our laboratory is staffed every day.


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