The effect of temperature gradients on stress development during cryopreservation via vitrification
The effect of temperature gradients on stress development during cryopreservation via vitrification
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DOI：
10.1089/cpt.2007.9994
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发表时间：
2007-06-01
影响因子：
--
通讯作者：
Rabin, Yoed
中科院分区：
文献类型：
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作者：
Steif, Paul S.;Palastro, Matthew C.;Rabin, Yoed
这项研究解决了通过玻璃化（玻璃体在拉丁语中的意思是玻璃状的）低温保存过程中大体积标本的热应力发展的问题。虽然这项研究是将不断发展的机械应力与冷冻保存介质的相关物理特性及其热历史联系起来的持续努力的一部分，但当前论文专门关注温度梯度的作用。由于促进玻璃化所需的高冷却速率而产生温度梯度;所产生的不均匀温度分布导致不同的热应变，可能导致开裂。在这项研究中，外表面的冷却速率假定为常数，材料特性假定为常数。它表明，在这些假设下，机械应力的发展，只有当试样中的温度分布接近在低温存储温度下的热平衡。它示出，对于一个给定的冷却速率的最大可能的应力可以计算与一个简单的热弹性分析，这些应力与冷却到足够低的温度，是独立的粘度随温度的变化。这些应力的分析估计得到几个理想化的形状，而有限元分析用于确定应力的几何形状中使用的冷冻保存实践。应力的发展在更广泛的存储温度范围内也进行了研究与有限元分析，结果进行了总结与适当的归一化。据发现，没有应力出现，如果冷却停止以上的设定温度，这定义了从粘性为主的弹性为主的行为的过渡;设定温度主要是由粘度对温度的依赖性。从结果中推断出快速达到低温和避免高应力的策略。
This study addresses the problem of thermal stress development in bulky specimens during cryopreservation via vitrification (vitreous means glassy in Latin). While this study is a part of an ongoing effort to associate the developing mechanical stress with the relevant physical properties of the cryopreserved media and to its the thermal history, the current paper focuses exclusively on the role of temperature gradients. Temperature gradients arise due to the high cooling rates necessary to facilitate vitrification; the resulting nonuniform temperature distribution leads to differential thermal strain, possibly resulting in cracking. The cooling rate is assumed constant on the outer surface in this study, and the material properties are assumed constant. It is demonstrated that under these assumptions, mechanical stress develops only when the temperature distribution in the specimen approaches thermal equilibrium at a cryogenic storage temperature. It is shown that the maximum possible stresses for a given cooling rate can be computed with a simple thermoelastic analysis; these stresses are associated with cooling to sufficiently low temperatures, and are independent of the variation of viscosity with temperature. Analytic estimates for these stresses are obtained for several idealized shapes, while finite element analysis is used to determine stresses for geometries used in cryopreservation practice. Stresses that develop under a wider range of storage temperatures are also studied with finite element analysis, and the results are summarized with suitable normalizations. It is found that no stresses arise if cooling ceases above the set temperature, which defines the transition from viscous-dominated to elastic-dominated behavior; the set temperature is determined principally by the dependency of viscosity upon temperature. Strategies for rapidly reaching low temperatures and avoiding high stresses are inferred from the results.