The main difference between cryopreservation and lyophilization is that cryopreservation is the preservation of biological tissue at cryogenic temperatures, typically at -80°C or at -196 °C, whereas lyophilization is the removal of moisture from a frozen material using a vacuum.
Freezing is a transition of phase in which the liquid turns into a solid when the temperature is lowered below its freezing point. Freezing is usually due to cooling. The average energy of the molecules decreases when a liquid becomes cool. At a certain point, the amount of heat removed is great enough that the attractive forces between molecules attract the molecules close together, making the liquid freeze. So, even after removing more heat, the temperature of a freezing liquid remains constant. The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases are in equilibrium. Both cryopreservation and lyophilization are associated with proteins.
Key Areas Covered
1. What is Cryopreservation
– Definition, Storage, Benefits
2. What is Lyophilization
– Definition, Storage, Phases
3. Difference Between Cryopreservation and Lyophilization
– Comparison of Key Differences
Key Terms
Cryodesiccation, Cryopreservation, Freeze-drying, Lyophilization
What is Cryopreservation
Cryopreservation is the preservation of biological tissue at cryogenic temperatures, typically at -80°C(dry ice) or at -196 °C (liquid nitrogen). This technique preserves live cells, tissues, and biological samples. Some biological materials we preserve using this method include spermatozoa, oocytes, ovarian tissues, pre-implantation embryos, and organs. The preservation happens without affecting their viability. Generally, the samples need a temperature of -196°C. Certain small molecules enter cells and prevent dehydration and the formation of intracellular ice crystals. This is the basic principle in cryopreservation. During the freezing process, this can cause the destruction of cell organelles and even cell death.
In this process, ice can break the cell membrane. However, the correct and careful choice of the freezing medium and regulating the freezing rate can prevent this. The cryopreservation steps include harvesting and selection of material, the addition of cryoprotectant, freezing, storage in liquid nitrogen, and thawing. Furthermore, there are many benefits of cryopreservation, as below.
- This technique is useful in fertility treatments.
- This technique requires minimal labor and space.
- It keeps the genetic information and integrity of valuable strains safe.
- It also ensures the samples are safe from genetic contamination.
- This technique safeguards the germplasm of endangered species.
- Moreover, it preserves biological samples for a longer period of time.
- Different fields use this method, including ecology, molecular biology, plant physiology, and food science.
- Additionally, this technique is useful in blood transfusion, seed banks, gene banks, freezing of cell cultures, organ transplantations, etc.
What is Lyophilization
Lyophilization is the removal of moisture from a frozen material using a vacuum. Another name for this process is freeze-drying or cryodesiccation. The dehydration process occurs at low temperatures where the product is frozen and the pressure is reduced. Sublimation is used to remove the ice. This process is a contradiction to dehydration by conventional methods, where the water evaporates using heat.
Lyophilization happens in three phases. These three phases are the freezing phase, sublimation phase, and secondary drying phase. The first phase is the freezing phase. In this phase, the product undergoes freezing via various methods. To ensure sublimation, technicians cool the material below the triple point in this stage. This also helps to preserve the physical form of the sample. Moreover, in the sublimation phase, which is the second stage, technicians lower the pressure and add heat to the material. This makes the water sublimate. Additionally, the process of sublimation speeds up by the vacuum. In this stage, most of the water (about 95%) is removed. However, technicians should take measures to ensure that they do not supply too much heat. This is because too much heat alters the structure of the material or the sample.
The final stage is the adsorption stage or the secondary drying stage. This involves the removal of ionically bound water molecules by raising the temperature higher than that of the primary drying stage. This allows the bonds between the materials and the water molecules to break. Generally, materials are dried up to the point where only 1-5% of moisture retains.
Difference Between Cryopreservation and Lyophilization
Definition
Cryopreservation is the preservation of biological tissue at cryogenic temperatures, typically at -80°C or at -196 °C, whereas lyophilization is the removal of moisture from a frozen material using a vacuum.
Storage Conditions
Moreover, cryopreservation requires very low temperatures, usually below 130°C, and typically involves the use of liquid nitrogen or other cryogenic liquids. Lyophilization allows long-term storage of materials at room temperature, although they should still be stored in a dry, protected environment.
Preservation of Biological Materials
Cryopreservation is typically used for preserving living cells, tissues, and organs as well as biological fluids and samples such as sperms and embryos, while lyophilization is commonly used for preserving proteins, enzymes, vaccines, and other biological molecules that are sensitive to pressure, heat, or other harsh conditions.
Conclusion
Freezing is a transition of phase in which the liquid turns into a solid when the temperature lowers below its freezing point. The main difference between cryopreservation and lyophilization is that cryopreservation is the preservation of biological tissue at cryogenic temperatures, typically at -80°C or at -196 °C, whereas lyophilization is the removal of moisture from a frozen material using a vacuum.
Reference:
1. “Principles of cryopreservation.” Pubmed. National Library of Medicine.
2. “Lyophilization of Parenteral (7/93).” U.S. Food & Drug Administration.
Image Courtesy:
1. “Cryopreservation USDA Gene Bank” By USDA Gene Bank – USDA Gene Bank (CC0) via Commons Wikimedia
2. “Lyophilized Vials” By clappstar (CC BY-NC 2.0) via Flickr
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