Why freeze slowly and thaw quickly? - (Dec/25/2006 )
Hi, why do we have to freeze the cells slowly, and thaw them rapidly?
"For bacteria it's important to freeze quickly.
That's because when freezig slowly, ice cristals may form.
Strange that it's opposite for other cells.
When cells are frozen slowly in aqueous suspensions, the solutes in the suspending solution concentrate as the amount of ice increases; the cells undergo osmotic dehydration and are sequestered in ever-narrowing liquid-filled channels. Cryoprotective solutes, such as glycerol, reduce the amount of ice that forms at any specified subzero temperature, thereby controlling the buildup in concentration of those other solutes present, as well as increasing the volume of the channels that remain to accommodate the cells. It has generally been thought that freezing injury is mediated by the increase in electrolyte concentration in the milieu surrounding the cells, rather than reduction of temperature or any direct action of ice.
If you are freezing you must be slow, if you are thawing you cant let them in the medium + DMSO or something else, so you have to be quick!
slow freezing generally refers to freezing in steps. Like u dont dip ur cells in R.T straight into Liq N2.
U freeze to -15 and then to -196 or they will die.
Actually, I believe we thaw slowly.
Cryoprotective compounds -like DMSO- could be toxic for cells and they must be the less time possible in that suspension, so freezing must be quick to avoid the cell damage before they are cryopreserved and thaw quick to wash cells from the toxic compunds.
My understanding is that it is to do with the ice crystal formation when freezing, if you freeze rapidly - even in the presence of cryopreserivatives such as DMSO the crystals formed are jagged and are able to tear cellular membranes (a bit simplified but the general concept is true), freezing slowly the crytal structure is more compact and less haphazard. You freeze quickly to avoid prolonged exposure to toxic elements such as DMSO.
it also depends on the cell type you're going to freeze down. there's a girl here who deals with hundreds of cell lines, and many of them, she just sticks straight into liq N2.