Biostabilization Laboratory - Lower Saxony Centre for Biomedical Engineering, Implant Research and Development, Hannover, Germany; Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine Hannover, Hannover, Germany.
Institute of Thermodynamics, Leibniz University Hannover, Garbsen, Germany.
Cryobiology. 2024 Jun;115:104879. doi: 10.1016/j.cryobiol.2024.104879. Epub 2024 Mar 4.
Solid surface freezing or vitrification (SSF/SSV) can be done by depositing droplets of a sample, e.g., cells in a preservation solution, onto a pre-cooled metal surface. It is used to achieve higher cooling rates and concomitant higher cryosurvival rates compared to immersion of samples into liquid nitrogen. In this study, numerical simulations of SSF/SSV were conducted by modeling the cooling dynamics of droplets of cryoprotective agent (CPA) solutions. It was assumed that deposited droplets attain a cylindrical bottom part and half-ellipsoidal shaped upper part. Material properties for heat transfer simulations including density, heat capacity and thermal conductivity were obtained from the literature and extrapolated using polynomial fitting. The impact of CPA type, i.e., glycerol (GLY) and dimethyl sulfoxide (DMSO), CPA concentration, and droplet size on the cooling dynamics was simulated at different CPA mass fractions at temperatures ranging from -196 to 25 °C. Simulations show that glycerol solutions cool faster compared to DMSO solutions, and cooling rates increase with decreasing CPA concentration. However, we note that material property data for GLY and DMSO solutions were obtained in different temperature and concentration ranges under different conditions, which complicated making an accurate comparison. Experimental studies show that samples that freeze have a delayed cooling response early on, whereas equilibration times are similar compared to samples that vitrify. Finally, as proof of concept, droplets of human red blood cells (RBCs) were cryopreserved using SSV/SSF comparing the effect of GLY and DMSO on cryopreservation outcome. At 20% (w/w), similar hemolysis rates were found for GLY and DMSO, whereas at 40%, GLY outperformed DMSO.
固态冷冻或玻璃化（SSF/SSV）可以通过将样品（例如保存溶液中的细胞）滴沉积到预冷的金属表面上来完成。与将样品浸入液氮中相比，它可以实现更高的冷却速率和相应更高的冷冻存活率。在这项研究中，通过模拟冷冻保护剂（CPA）溶液液滴的冷却动力学来进行 SSF/SSV 的数值模拟。假设沉积的液滴达到圆柱形的底部和半椭圆形的上部。用于传热模拟的材料特性，包括密度、比热容和热导率，从文献中获得并使用多项式拟合进行外推。模拟了不同 CPA 质量分数下，CPA 类型（甘油（GLY）和二甲基亚砜（DMSO））、CPA 浓度和液滴大小对冷却动力学的影响，温度范围从-196 到 25°C。模拟结果表明，与 DMSO 溶液相比，甘油溶液冷却速度更快，并且冷却速率随 CPA 浓度的降低而增加。然而，我们注意到 GLY 和 DMSO 溶液的材料特性数据是在不同的温度和浓度范围内以及不同的条件下获得的，这使得进行准确的比较变得复杂。实验研究表明，与玻璃化相比，冷冻的样品在早期会有延迟的冷却响应，而平衡时间与玻璃化的样品相似。最后，作为概念验证，使用 SSV/SSF 冷冻保存了人红细胞（RBC）的液滴，比较了 GLY 和 DMSO 对冷冻保存结果的影响。在 20%（w/w）时，GLY 和 DMSO 的溶血率相似，而在 40%时，GLY 优于 DMSO。
