We have widely demonstrated that simple organisms like nematodes can be easily cryopreserved and recovered viability after several years later. See Irdani et al., 2006 Cryobiology; Irdani et al., 2011 Cryobiology.

It all depends upon the complexity of the organism. Single cell organisms and simple organisms, such as mentioned by Tiziana, some insects are freeze tolerant. Drophosophila has been cryopreserved. Some amphibians can tolerate freezing. Most animals can not tolerate freezing whether you use DMSO or not.

It is a possibility. Depends on several factors. In the literature have several papers about this subject.

It also depends on the purpose of freezing. If you want to get viable animals after thawing, currently because of complexity, variability in tissue response to and permeability of cryoprotectants and water, as well as issues related to heat transfer, only relatively small animals can be frozen. Although large organs (sheep ovaries, pig and mice livers) were cryopreserved successfully, the complexity of such organs is far less than a whole animals. If, on the other hand, the purpose is to preserve the genetic material, large animals can also be frozen and viable offspring can then be generated using nuclear transfer. This was first reported in 2008 by Wakayama et al. (in PNAS 105(45): 17318-17322) when they cloned mice that were kept at -20 degrees C without any cryoprotectants for 16 years.

Until now it is impossible to successful cryopreserve large animals. The complexity of the organism is the key. Even for spermatozoa the survival rate normally is close to 50 % in species that have been selected for cryopreservation of their semen, like bulls. In other species semen cryopreservation can have worse results. Even those cells that survived cryopreservation have their lifespan reduced and function impaired. The cryopreservation process submit the cell to several damaging factor including the increase of exposition to Reactive Oxygen Species (ROS). During the process of cryopreservation, the cell suffer a process that in some manner promotes an aging of the cell, or even can kill the cell. Even for large organs until now is very difficult to cryopreserve efficiently Tissues and entirely organs. The cryopresevation of a entire organism (such as mammals) with the current technology is impossible. We should focus on the cryopreservation of Tissues and cells, and maybe in a far future more complex organs can be cryopreserved. The most difficult thing in cryopreserve entire organs is that every kind of cell have a complete different need for Cryoprotective media, and CPA (Cryoprotective permeant Agent) e.g.: Glycerol, DMSO, Ethylene glycol ... etc. We need a macromolecular source of lipids and proteins as LDL and other cryoprotectors. For a entire organism we should remove the blood an substitute for a cryoprotective media .... So the complexity of this procedure is completely out of reach for the modern Cryobiology. A lot of work and studies need to be done.

Human embryos, sperm and oocytes can be successfully cryopreserved in liquid nitrogen. This is a relatively routine clinical procedure. Survival after vitrification of pre-implantation embryos (1 to >100 cells) or oocytes is usually in excess of 90%, but does depend on starting quality and technical expertise. Small pieces of ovarian cortex and testicular tissue can also be cryopreserved, with gametes in situ, for later use.

Dear all, it is possible nature has 2 amazing animals , there is a Canadian frog (Rana sylvatica) and a Siberian salamander (Hynobius

keyserlingi) who are hibernating at -50 and -80. The secret of their success lies in their metabolism which changes glucose into glycerol so all their tissues are slowly but continuously impregnated with a very natural and non-toxic cryprotectant.

I have read about few proteins present in the cytoplasm of a cell, which are chaperones and they help in retaining protein function after severe stress. I guess some animals have them in high number so they can tolerate stress like very low temperature. It might just be possible to check same kind of proteins in human case as well. After all mankind survived the historical ice age.

There is an optimal cryoprotectant and cooling rate for nearly each cell type. Freezing complex organisms is there for a technical dilemma so far as I can see and the applied technology will therefore always be a compromise and not really a solution.

To sum up:

1. It is quite complicated but not impossible.

2. A common method to freeze all different tissues is not known or difficult to formulate.

3. Simple organisms have been cryopreserved- nematode, drosophila. etc..

4. Existing reagents as cryoprotectants might not work and are toxic.

5. There are natural examples available in amphibians, which needs to be studied.

Thanks everyone for your answers.

• It means due to the variability of cells reaction that the way could be in triggering the body to self adjust the cells individually for the condition of hibernation first. Is there a study about triggering the human body to do some localised changes itself? A trigger like a hormone?

I´d say it depends on if you can prevent the formation of ice crystals. Rapid cooling and vitrificationof water works only over distances of about 200µm, so your organism needs to be smaller. If the tissues survive being infiltrated with cryoprotectant, you could do larger organisms, sure. Some Insects and Lissamphibia prepare themselves for hiberantion by drastically altering their body liquid composition to prevent crystal formation, and survive subzero temperatures for several month.