Nature has shown us that cryopreservation of animals such as reptiles, amphibians, worms, and insects is possible. Roundworms trained to recognize certain odors have been observed to retain their olfactory memories after being frozen. The wood frog (Rana sylvatica) can be found frozen in a block of ice during the winter and can regain its vitality and return to life in the spring. However, every freezing and thawing process in human tissue causes significant damage. One of the goals of cryobiology is to understand and minimize this damage.

These damages occurring at the cellular level during cryopreservation are still not fully understood, but they are controllable. Every discovery in this field relies on two aspects: improving preservation during freezing and advancing recovery after thawing. During freezing, damage can be avoided by carefully/controlledly changing the heat and using various cryoprotectants. One of the main goals is to prevent the formation of ice crystals that damage cells and tissues and cause them to disintegrate. Therefore, the aim is to achieve a smooth transition to the “glassy phase” (vitrification) by rapid cooling instead of “freezing”. For this, simple substances like sugar and starch are used to change viscosity and protect the cell membrane. Chemicals such as dimethyl sulfoxide (DMSO), ethylene glycol, glycerol, and propanediol are used to prevent intracellular ice formation, and antifreeze proteins prevent the growth and recrystallization of ice crystals during thawing.

But this is not the only thing we need to worry about for the cells we are trying to keep alive. In the frozen state, tissues are generally biologically stable. Biochemical reactions involving degradation are slowed down to the point where they are effectively stopped at extremely low temperatures. However, there is a risk that the frozen body may be exposed to physical deterioration such as hairline cracks. The temperature fluctuation that occurs during subsequent thawing causes a series of serious problems. This temperature fluctuation can damage tissues and cells. This situation leads to epigenetic (how environmental factors and lifestyle choices affect our genes) reprogramming, having an impact on our entire “epigenetic” structure.

However, antioxidants and other substances can help recovery after thawing and prevent damage. Reviving the whole body is a challenge in itself, as organs need to start functioning homogeneously. The difficulties of restoring blood flow to organs and tissues are already well known in emergency medicine. Nevertheless, the cooling process does not always have a negative effect; for example, it is actually used to alleviate trauma. As another example, in cases of cold water drowning, high rates of return to life have been observed due to the anti-trauma effect of cold water. One purpose of lowering body temperature during surgery is to reduce the effects of trauma. These examples lead to extensive research into the cryopreservation approach.

The scientific innovation pioneers of cryobiology are the medical sector and the economy. The infertility and regenerative (restorative) medicine sectors are leading the advances in this field. Cryopreservation and vitrified cells and simple tissues (eggs, sperm, bone marrow and cord blood stem cells, umbilical cord tissue, tooth enamel, cornea, skin) are already regularly frozen, thawed, and transplanted. Studies on the cryopreservation of “simple” body parts such as fingers and legs have also begun. Some complex organs (kidney, stomach, intestines) have been cryopreserved, thawed again, and successfully transplanted into animals. Although the transfer of human organs is currently limited to cooled but not frozen organs, research continues to accelerate to develop the cryopreservation of all organs for therapeutic purposes.

In our next blog post, we will discuss “Cryogenics”, the project of people already frozen as whole bodies around the world. You can subscribe to our newsletter below to be informed about our blog posts created based on this and similar scientific information.