Pontificia Universidad Católica Argentina, Cap. Gral. Ramón Freire, Buenos Aires, Argentina.
Cryobiology. 2011 Aug;63(1):32-7. doi: 10.1016/j.cryobiol.2011.04.006. Epub 2011 Apr 21.
Oocyte cryopreservation is of key importance in the preservation and propagation of germplasm. Interest in oocyte cryopreservation has increased in recent years due to the application of assisted reproductive technologies in farm animals such as in vitro fertilization, nuclear transfer and the need for the establishment of ova/gene banks worldwide. However, the cryopreservation of the female gamete has been met with limited success mainly due to its small surface-area:volume ratio. In the past decade, several vitrification devices such as open pulled straws (OPS), fine and ultra fine pipette tips, nylon loops and polyethylene films have been introduced in order to manipulate minimal volumes and achieve high cooling rates. However, experimental comparison of cooling rates presents difficulties mainly because of the reduced size of these systems. To circumvent this limitation, a numerical simulation of cooling rates of various vitrification systems immersed in liquid nitrogen was conducted solving the non-stationary heat transfer partial differential equation using finite element method. Results indicate the nylon loop (Cryoloop®) is the most efficient heat transfer system analyzed, with a predicted cooling rate of 180,000°C/min for an external heat transfer coefficient h= 1000 W/m(2)K when cooling from 20 to -130°C; in contrast, the open pulled straw method (OPS) showed the lowest performance with a cooling rate of 5521°C/min considering the same value of external heat transfer coefficient. Predicted cooling rates of Miniflex® and Cryotop® (polyethylene film system) were 6164 and 37,500°C/min, respectively, for the same heat transfer coefficient.
卵母细胞冷冻保存对于种质的保存和繁殖至关重要。近年来，由于辅助生殖技术在农场动物中的应用，如体外受精、核转移以及在全球范围内建立卵/基因库的需要，人们对卵母细胞冷冻保存的兴趣日益增加。然而，由于其表面积与体积比小，雌性配子的冷冻保存一直收效甚微。在过去的十年中，已经引入了几种玻璃化设备，例如开放式拉制吸管（OPS）、细和超细移液器吸头、尼龙环和聚乙烯薄膜，以便操作最小体积并实现高冷却速率。然而，由于这些系统的尺寸较小，实验比较冷却速率存在困难。为了规避这一限制，对浸入液氮中的各种玻璃化系统的冷却速率进行了数值模拟，使用有限元方法求解非稳态传热偏微分方程。结果表明，尼龙环（Cryoloop®）是分析的最有效的传热系统，当从 20°C 冷却到-130°C 时，外部传热系数 h=1000 W/m(2)K 下，预测冷却速率为 180,000°C/min；相比之下，开放式拉制吸管法（OPS）显示出最低的性能，相同的外部传热系数下冷却速率为 5521°C/min。对于相同的传热系数，Miniflex®和 Cryotop®（聚乙烯薄膜系统）的预测冷却速率分别为 6164°C/min 和 37,500°C/min。
