Re: How does Cryopreservation work?

Cryopreservation is long term storage of cells or tissues by freezing them 
in such a way as to minimize ice crystal formation.  In general, when a 
tissue is subjected to low temperatures ice crystals will eventually form 
which will disrupt the cell membrane leading to the death of the cell.  The 
goal of cryopreservation is to replace some of the water with other 
compounds that will not form large crystals when frozen.  The most commonly 
used replacements are DMSO (dimethylsulfoxide) and glycerol.  These are 
mixed into a solution with media or serum and cells are suspended in it and 
placed in a liquid nitrogen freezer.  As the media begins to freeze the 
salt concentration outside the cells will become greater than that in the 
cells and water will leave the cells to be replaced by the DMSO or 
glycerol.  

These methods work fairly well for single cells but are less successful for 
tissues because of the diffuculties in dealing with a mass of cells and the 
resulting permeability problems.  In addition, while the water in the cells 
in often successfully replaced, it is more difficult to displace water from 
extracellular spaces and thus these are often damaged. 

A manual on cryopreservation has been prepared by Nalgene and is available 
at:
http://nalgenelab.nalgenunc.com/select/app/cryo/