Vannereau H, Novakoviteh G, Carin M
Hôpital Lapeyronie, Montpellier.
Contracept Fertil Sex. 1998 Jul-Aug;26(7-8):573-7.
Cooling biomaterials to liquid-nitrogen temperature is probably the most effective procedure for the preservation of their biochemical and morphological parameters, in so far as adverse effects of cooling are controlled. Potential damage has not the same explanation under different conditions of cold exposure. Even a moderate decrease of temperature leads to irreversible damage when applied to untreated organisms. Deep freezing injuries are due to crystallization of ice, and cellular consequences are quite different according to the temperature kinetics. The fraction survival, as a function of hypothermic kinetics, has a bimodal distribution, reflecting two distinct mechanisms: a first process, concomitant of a slow cooling rate, with extracellular ice formation, and a second one, during fast cooling rates, with intracellular ice formation. Thereby, cryopreservation protocols have to focus on many variable factors, including choices of a cryoprotectant, which delays ice formation, and a cooling rate leading to an optimal cell survival. Under these conditions, osmotic effects are almost neutralized. Nevertheless, these methods can be applied only to isolated cells. For tissues or organs, ice formation should be avoided at low temperatures. Vitrification is the corresponding process by which tissue water is undercooled to the glass transition temperature and solidified into the amorphous or glassy state. Very high cooling and warming rates are needed. The use of an appropriate cryoprotective agent mixture, called a "vitrification solution" should be useful: however, high-concentration vitrification solutions have still undesired toxic effects. Finally, an optimal cryoprotectant, in terms of cooling/warming rates and toxicity, has to be found.
将生物材料冷却至液氮温度可能是保存其生化和形态学参数最有效的方法，只要能控制冷却的不利影响。在不同的冷暴露条件下，潜在损伤的原因并不相同。即使是适度的温度降低，应用于未经处理的生物体时也会导致不可逆的损伤。深度冷冻损伤是由于冰的结晶，根据温度动力学，细胞后果差异很大。作为低温动力学函数的存活分数具有双峰分布，反映了两种不同的机制：第一个过程伴随着缓慢的冷却速率，细胞外形成冰；第二个过程发生在快速冷却速率下，细胞内形成冰。因此，冷冻保存方案必须关注许多可变因素，包括选择一种能延迟冰形成的冷冻保护剂以及能实现最佳细胞存活的冷却速率。在这些条件下，渗透效应几乎被抵消。然而，这些方法仅适用于分离的细胞。对于组织或器官，应避免在低温下形成冰。玻璃化是相应的过程，通过该过程组织水被过冷至玻璃化转变温度并固化成无定形或玻璃态。这需要非常高的冷却和升温速率。使用一种合适的冷冻保护剂混合物，称为“玻璃化溶液”应该会有帮助：然而，高浓度的玻璃化溶液仍然有不良的毒性作用。最后，必须找到一种在冷却/升温速率和毒性方面都最佳的冷冻保护剂。
