|WikiProject Biology||(Rated Start-class, Mid-importance)|
|WikiProject Transhumanism||(Rated Start-class, Mid-importance)|
A paragraph in the article Cryopreservation said:
- It is a commonly held misconception that the sharp edges of growing ice crystals cause physical damage to cells when they are freezing, and that this is a mechanism of freezing-related damage. This is incorrect, since crystals do not "move" during crystallisation, but rather add new molecules individually to the surface of the growing crystal. Thus, crystals grow around any solid object in their path.
This is a straw man that has the effect of ignoring the question of whether cell damage occurs due to volume increase of aqueous solutions on freezing. (Let's be precise: unconfined fluids expand as freezing progresses; confined ones exert increasing outward pressure on the confining vessel, and move their own outer surfaces outward when the pressure reaches the maximum that the vessel can resist; in many cases, that motion is explosive due to local rupture of the vessel lowering the strength of adjacent portions. Likewise, the cracks in the ice on frozen lakes permit and/or reflect expansion-driven upward motion, which contradicts the "no motion" assertion, even tho the lake-crack mechanisms do not obviously operate at cellular scales. Hmm, does the lake amount to failure of self-containment?) If there is a common misconception, it must be that cells are analogous to a sealed can of carbonated beverage left in a domestic freezer. (The soda can is a lot more fun bcz of the decompression of the supersaturated CO2 solution, but the principles are the same as what i outline above.) This 'graph needs a rewrite, and should not be included at all without explainng how cell membranes differ relevantly from other containing vessels.
Even if that is done, the 'graph is inadequate to prove its point: cells are heterogeneous, and some structures may freeze into "sharp" crystals while liquids remain. Expansion of those liquids upon their own freezing can press corners of crystals against membranes, bending them into higher curvatures than are normal for them, and that may dramatically increase fracture of the membranes. (This 'graph of mine has many "may"s in it, so it cannot prove anything about cryopreservation. But its purpose is to prove the moved 'graph is guilty at least of handwaving, and currently unsuitable for the article.) --Jerzy 18:39, 2003 Nov 21 (UTC)
The article does not mention the techique of slow freezing. The authors are heavily biased towards vitrification which is only one way of crypreservation. Slow freezing using Controlled Rate Freezers is more common and to date something like 350,000 live births have occurred from embryos frozen this way. PaulTheOnlyOne (talk) 16:29, 10 November 2008 (UTC)
5.2 Vitrification - ambiguity about glass transition temperature
"Rather than a phase change from liquid to solid by crystallization, the amorphous state is like a "solid liquid", and the transformation is over a small temperature range described as the "glass transition" temperature."
Does this mean the transformation happens at a temperature higher than the GTT, or that the transition happens as the sample crosses the GTT, and that the GTT is not a precise temperature but is a small range? I think the language could be tidied up a bit here. Although I'm not the person to do it as my grasp of the science is kinda lacking. — Preceding unsigned comment added by T0m0akl3y (talk • contribs) 22:10, 10 October 2013 (UTC)
- The sentence you quoted seems perfectly clear and straightforward; "the transformation is over a small temperature range described as the 'glass transition' temperature." In other words, the "glass transition temperature" is a "small range." 23:16, 10 October 2013 (UTC) — Preceding unsigned comment added by Blacksun1942 (talk • contribs)