Abstract Snap-freezing of a tissue is usually realized by enclosing it in a polypropylene cryo-vial and subsequently immersing the vial in liquid nitrogen. The cooling rate of the vial is very critical to the frozen-tissue quality. However, quantitative information on the heat transfer process at the vial-liquid interface is still a mystery limiting the cool-down prediction of the vial and the tissue. In this paper, an analytical model is developed to predict the temperature variation inside the polypropylene vial-wall and the tissue. This model also include temperature-dependent thermal properties of the polypropylene material. The cooling time of an empty polypropylene tube of wall thickness 1.5 mm, replicating a typical commercial polypropylene vial is predicted with a maximum error of less than 10%. We also verified the model using temperature-time measurements performed with several other polypropylene tubes of different wall thickness. An interesting finding from this work is that the difference in the cool-down time of a tissue in a tube and an empty tube is proportional to the product of the tissue heat capacity and the tube-wall thermal resistance. This enables researchers to estimate the cooling trajectory of the tissue during the cooling process allowing the development of improved snap-freezing protocols.

中文翻译：

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在液氮中骤冷的聚丙烯小瓶的冷却时间

摘要 组织的速冻通常是通过将其封闭在聚丙烯冷冻瓶中，然后将其浸入液氮中来实现的。小瓶的冷却速度对冷冻组织的质量非常关键。然而，关于小瓶-液体界面传热过程的定量信息仍然是一个谜，限制了小瓶和组织的冷却预测。在本文中，开发了一种分析模型来预测聚丙烯小瓶壁和组织内部的温度变化。该模型还包括聚丙烯材料的温度相关热特性。一个壁厚为 1.5 毫米的空聚丙烯管的冷却时间，复制了一个典型的商业聚丙烯小瓶，预计最大误差小于 10%。我们还使用其他几种不同壁厚的聚丙烯管进行的温度-时间测量来验证模型。这项工作的一个有趣发现是，管中组织和空管中组织的冷却时间差异与组织热容和管壁热阻的乘积成正比。这使研究人员能够估计冷却过程中组织的冷却轨迹，从而开发改进的快速冷冻方案。