CONTROLL OF INTRACELLULAR ICE FORMATIOM BY MICROWAVE IRRADIATION AND ITS APPLICATION FOR CRYOPRESERVATION

以洋葱表皮为材料，研究了微波辐射对组织细胞内结冰的影响。利用恒冷阶段和定向凝固阶段对凝固过程进行了微观观察。为了定量测定细胞冷冻温度与微波辐射能量之间的关系，在实验系统中安装了光纤温度计和微波强度计。用点天线辐射频率为2.45GHz的微波，功率变化到50 mW/cm ^2。恒速冷却实验表明，在10 ~ 15 mW/cm ^2范围内，微波辐射功率的增加使冻结温度降低，当功率为25 mW/cm ^2时，冻结温度又升高。这表明，最佳的辐射功率存在抑制细胞内冰形成的微波辐射。在微波辐照条件下，定向凝固阶段的实验也显示了相同的平均游离温度的结果。此外，我们在测试中有特别有趣的发现。定向凝固阶段使我们能够模拟发生在组织细胞中的细胞冷冻的传播。结果表明，微波辐射降低了相邻细胞冻结引起的传播型冻结的概率。因此，我们可以抑制，在相对较小的过冷度，给细胞的机械损伤发生的细胞间的冰形成。我们还进行了分子动力学模拟，使用SPC/E势作为水势模型。模拟结果表明，微波辐射对低温保存的有效性，并发现可能存在一个有效的波长，而不是2.45GHz。

Effects of microwave irradiation on intracellular ice formation of tissue cells have been examined precisely by using onion epidermis. Microscopic observations of the freezing processes have been carried out with use of a constant cooling stage and a directional solidification stage. In order to quantify the relation between the freezing temperature of cells and the microwave irradiation energy, the optical fiber thermometers and the microwave intensity meter were installed in the experimental systems. The microwave at 2.45GHz was irradiated from a spot antenna and the power was changed up to 50 mW/cm^2.The constant cooling rate tests show that an increase of the irradiation power of microwave decreases the freezing temperature in a range between 10mW/cm^2 and 15 mW/cm^2 while at 25 mW/cm^2 the freezing temperature increase again. This indicates that the optimum irradiation power exists for a suppression of intracellular ice formation by microwave irradiation. The experiments using the directional solidification stage also show the same results on the average freeing temperature under the microwave irradiation conditions. In addition, special interesting findings we have in the test. The directional solidification stage enables us to simulate the propagation of cell freezing which occurs in the tissue cells. It is found that the microwave irradiation reduces the probability of the propagation-type freezing induced by neighboring-cell freezing. Therefore, we can restrain from, the intercellular ice formation occurring at relatively small supercooling which gives a mechanical damage to the cell.We have also done the molecular dynamics simulation by using a SPC/E potential as water potential model. The simulations indicate us the, effectiveness of microwave irradiation for the cryopreservation and it is found that there may exist an effective wave-length rather than 2.45GHz.