Solanki Prem K, Bischof John C, Rabin Yoed
Biothermal Technology Laboratory, Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
Bioheat and Mass Transfer Laboratory, Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, United States.
Cryobiology. 2017 Jun;76:129-139. doi: 10.1016/j.cryobiol.2017.02.001. Epub 2017 Feb 10.
Cryopreservation by vitrification is the only promising solution for long-term organ preservation which can save tens of thousands of lives across the world every year. One of the challenges in cryopreservation of large-size tissues and organs is to prevent fracture formation due to the tendency of the material to contract with temperature. The current study focuses on a pillow-like shape of a cryobag, while exploring various strategies to reduce thermo-mechanical stress during the rewarming phase of the cryopreservation protocol, where maximum stresses are typically found. It is demonstrated in this study that while the level of stress may generally increase with the increasing amount of CPA filled in the cryobag, the ratio between width and length of the cryobag play a significant role. Counterintuitively, the overall maximum stress is not found when the bag is filled to its maximum capacity (when the filled cryobag resembles a sphere). Parametric investigation suggests that reducing the initial rewarming rate between the storage temperature and the glass transition temperature may dramatically decrease the thermo-mechanical stress. Adding a temperature hold during rewarming at the glass transition temperature may reduce the thermo-mechanical stress in some cases, but may have an adverse effect in other cases. Finally, it is demonstrated that careful incorporation of volumetric heating by means on nanoparticles in an alternating magnetic field, or nanowarming, can dramatically reduce the resulting thermo-mechanical stress. These observations display the potential benefit of a thermo-mechanical design of the cryopreservation protocols in order to prevent structural damage.
玻璃化冷冻保存是长期器官保存唯一有前景的解决方案，每年可为全球数万人挽救生命。大型组织和器官冷冻保存面临的挑战之一是防止材料因温度变化而收缩导致断裂。当前研究聚焦于冷冻袋的枕状形状，同时探索各种策略以降低冷冻保存方案复温阶段的热机械应力，该阶段通常会出现最大应力。本研究表明，虽然应力水平通常会随着冷冻袋中填充的 CPA 量增加而升高，但冷冻袋的宽长比起着重要作用。与直觉相反的是，当袋子填充至最大容量时（即填充后的冷冻袋类似球体），并未发现总体最大应力。参数研究表明，降低储存温度与玻璃化转变温度之间的初始复温速率可能会显著降低热机械应力。在复温过程中于玻璃化转变温度保持一段时间，在某些情况下可能会降低热机械应力，但在其他情况下可能会产生不利影响。最后，研究表明通过在交变磁场中利用纳米颗粒进行体积加热（即纳米升温），谨慎地引入该方法可显著降低由此产生的热机械应力。这些观察结果显示了冷冻保存方案热机械设计在防止结构损伤方面的潜在益处。
