Cryopreservation

What is Cryopreservation?

The process of storing or preserving the biological samples in extremely cold or subzero temperatures in a deep freeze, commonly at −196°C is termed as cryopreservation. The word “Cryopreservation” is derived from the Greek word “krúos”, meaning icy cold or frost.

At such low temperatures, all the biological activities of the cells stop and the cell dies. Cryopreservation helps the cells to survive cooling to extreme temperatures and again thawing them to physiological conditions.

The ice formation inside the cells breaks the cell membrane and causes cell death. The freezing rate and the composition of the freezing medium are the two factors that can prevent this intercellular freezing.

Cryopreservation

What happens in Cryopreservation?

In this process, biological materials including cells, tissues, organs, oocytes, spermatozoa, ovarian tissues, pre-implantation embryos, and other prepared culture media are preserved in extremely cold temperatures for extended periods without affecting the cell’s viability.

Dry Ice and liquid nitrogen are generally used in this method of preservation.

At these subzero temperatures, all the biological activities of cells, tissues and other biological materials cease or effectively stopped and are presumed to provide indefinite longevity to cells.

Applications of Cryopreservation

Cryopreservation is a long-term storage technique, which is mainly used for preserving the biological material without decline or decaying the biological samples for an extended period of time at least for several thousands of years.

This method of preservation is widely used in different sectors including cryosurgery, molecular biology, ecology, food science, plant physiology, and in different medical applications. Other applications of cryopreservation process are:

  1. Seed Bank.

  2. Gene Bank.

  3. Blood transfusion.

  4. In vitro fertilization.

  5. Organ transplantation.

  6. Artificial insemination.

  7. Freezing of cell cultures.

  8. Storage of rare germplasm.

  9. Conservation of biodiversity.

  10. Conservation of endangered and disease free plant species.

Process of Cryopreservation

The complete procedure steps involved in preserving the obtained biological samples are as follows:

  1. Harvesting or Selection of material– Few important criteria should be followed while selecting the biological materials such as – volume, density, pH, morphology, and damaged free.

  2. Addition of cry-protectant – Cryoprotective agents such as glycerol, FBS, salts, sugars, glycols are added to the samples as it reduces the freezing point of the medium and also allow slower cooling rate, which reduces the risk of crystallization.

  3. Freezing – Different methods of freezing are applied in this method of cryopreservation to protect cells from damage and cell death by their exposure to the warm solutions of cryoprotective agents.

  4. Storage in liquid nitrogen– The cryopreserved samples are stored in extreme cold or -80°C in a freezer for at least 5 to 24 hours before transferring it to the storage vessels.

  5. Thawing- The process of warming the biological samples in order to control the rate of cooling and prevent the cell damage caused by the crystallization.

Further Reading: Cell Theory

Cryopreservation of Embryos

During the infertility treatment, hormones are used to stimulate the development of eggs. The eggs are then retrieved and fertilized in the lab. More embryos can be created to be transferred to the woman’s uterus. These embryos can be cryopreserved and can be transferred at some later date. By this, the female can get an additional embryo transfer in future without spending on another IVF cycle.

Oocyte Cryopreservation

In the vitrification method, the eggs freeze rapidly so that there is little time for the ice crystals to form. New cryoprotectants are used that very high concentration of anti-freeze-like products.

The oocyte is first placed in a bath containing low concentration anti-freeze like cryoprotectant. Some sucrose is added to help draw some water out of the egg.  The egg is then shifted to high concentration anti-freeze cryoprotectant for very few seconds and then immediately transferred to liquid nitrogen. When the egg has to be transplanted into the woman, the egg is thawed and used.

Cryopreservation of Sperm

The semen sample is mixed with a special solution to provide protection during freezing and thawing. The samples are then transferred to plastic vials and frozen in liquid nitrogen.

This process ensures the chances of conception in future. The sperm can also be deposited, froze and stored in cryobanks for less than a year. These sperms can later be used for certain infertility treatment procedures.

Benefits of Cryopreservation

There are numerous benefits of cryopreservation technique. These include:

  • Fertility preservation.

  • Minimal space and labour required.

  • Safety from genetic contamination.

  • Safeguards genetic integrity of valuable stains.

  • Safeguards the germplasm of endangered species.

  • Biological samples can be preserved for a longer period of time.

  • Protects the samples from disease and microbial contamination.

  • Prevents genetic drift by cryopreservation of gametes, embryos, etc.

This was an introduction to Cryopreservation, its Applications, process, and advantages. For more information, stay tuned with BYJU’S.

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