3. 人の細胞と臓器を0℃以下でガラス化保存する方法の困難性-零下医学の立場から(セミナー「ビトリフィケーション」)
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There are four basic methods to cryopreserve human parts:hypothermia, freezing, lyophilization, and vitrification, each using various cryoprotectants. With the exception of hypothermia, the other three methods involve preservation in a hybrid or polycrystalline state of supercooling, solid freezing and vitrification. It is very difficult to indefinitely cryopreserve large human organs, blood cells and tissue grafts by vitrification as they are not in a fixed state but in a process of relaxation except at a temperature of absolute zero (-273℃). Any ice crystals present eventually change to a damaging hexagonal form. Vitrified water relaxes to devitrify to ice crystals. Devitrification accompanies an increase of specific volume frequently resulting in a formation of cracks in the grafts. It is difficult to observe this time of phase transition. This author had spent 35 years cryopreserving human blood cells and tissue grafts at a temperature of mechanical freezer (-80℃), liquid nitrogen (-196℃), liquid helium (-273℃) and presents several observations: 1. Using an optimal preservation regimen, the frozen solid state is the safest for preservation of large volumes of blood cells for transfusion and tissue grafts for transplantation. 2. Vitrified blood cells in large volume and tissue grafts are solidified in a polycrystalline hybrid state, but contain numerous glassy transformed areas with many grain boundaries at liquid nitrogen temperature. Glass inevitably has Griffith's flaw which is a cause of cracking. Recently, cardiovascular surgeons have encountered crack formations of tissue grafts during thawing process. The more glassy areas that exist, the greater the occurrence of crack formation during devitrification results. 3. The author recommends cryopreserving cells and tissues at a temperature which is far higher or lower temperature than that of the glass transformation. Unfortunately except at zero degrees Kelvin (-273℃), devitrification will spontaneously generate due to the relaxation phenomenon, resulting in crack formation. This cracking causes cryobanked heart valves and vessels to be fatally damaged. 4.The prospect of vitrification or of freeze preservation of large human parts is still far from certain. Greater efforts for interdisciplinary studies of medicine, biology, chemistry and physics must be made to achieve successful vitrification of human organs and tissues.
- 低温生物工学会の論文
- 1997-07-11
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- 3. 人の細胞と臓器を0℃以下でガラス化保存する方法の困難性-零下医学の立場から(セミナー「ビトリフィケーション」)
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