Biothermal Technology Laboratory, Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Cryo Letters. 2022 Jan-Feb;43(1):1-9.
Density is a key thermophysical property, affecting the response of materials to temperature changes in different ways, consistent with the phase of state. In fluids, temperature variation across the domain leads to colder areas being heavier than warmer areas, where buoyancy effects drive fluid flow and thereby increase heat transfer. This phenomenon is known as natural heat convection, which in general is a more efficient heat transfer mechanism than heat conduction in the absence of flow. In solids, where the material is locked in place, colder areas tend to contract while warmer areas tend to expand, leading the material to deform. When this deformation is constrained by the geometry of the domain and/or its container, mechanical stresses develop. This phenomenon is known as thermomechanical stress (or thermal stress), which can lead to structural damage such as fractures. The picture becomes even more complex during vitrification (or glass formation), where the material gradually changes from liquid to an amorphous solid over a significant temperature range. There, due to temperature variation across the domain, fluid mechanics and solid mechanics effects may coexist. It follows that characterization of the density as a function of temperature is crucial for the analyses of thermal, fluid, and mechanical effects during cryopreservation, with the goals of protocol planning, optimization, and preserving structural integrity. For this purpose, the current study focuses on the density of the material and its companion property of thermal expansion. Specifically, this paper reviews literature data on thermal expansion of cryoprotective agents (CPAs), discusses the mathematical relationship between thermal expansion and density, and presents new calculated density data. This study focuses on the CPA cocktails DP6, VS55, M22, and their key ingredients at various concentrations, including DMSO, propylene glycol, and formamide. Data for DP6 combined with a selection of synthetic ice modulators (SIMs) are further presented.
密度是一个关键的热物理性质，以不同的方式影响材料对温度变化的响应，与物态一致。在流体中，域内的温度变化导致较冷区域比较暖区域更重，浮力效应驱动流体流动，从而增加热传递。这种现象称为自然热对流，一般来说，在没有流动的情况下，它是一种比热传导更有效的传热机制。在固体中，材料被锁定在原地，较冷区域往往会收缩，而较暖区域往往会膨胀，导致材料变形。当这种变形受到域和/或其容器的几何形状的限制时，机械应力会发展。这种现象称为热机械应力（或热应力），可能导致结构损坏，如断裂。在玻璃化转变（或玻璃形成）过程中，情况变得更加复杂，在这个过程中，材料在相当大的温度范围内逐渐从液体转变为无定形固体。在那里，由于域内的温度变化，流体力学和固体力学效应可能同时存在。因此，作为温度函数的密度特性对于冷冻保存过程中的热、流体和机械效应的分析至关重要，其目的是规划、优化和保持结构完整性。为此，本研究侧重于材料的密度及其伴随的热膨胀特性。具体来说，本文综述了关于冷冻保护剂（CPAs）的热膨胀文献数据，讨论了热膨胀与密度之间的数学关系，并提出了新的计算密度数据。本研究侧重于 DP6、VS55、M22 等 CPA 鸡尾酒及其关键成分在不同浓度下的密度，包括 DMSO、丙二醇和甲酰胺。还进一步介绍了 DP6 与一些合成冰调节剂（SIMs）组合的数据。
