Hi all- I work with artificial insemination and have recently wondered how sperm/ eggs/ embryos be frozen in liquid nitrogen (for years!) and then later thawed (in about 60 seconds) where it’s then back to functioning like normal, but you can’t freeze a living person and then unfreeze them again? At what developmental point can you stop freezing biological material before it won’t work again? (No political motive here, just questioning the science behind it, please please no arguing)
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When water freezes it forms ice crystals. Large ice crystals poke holes in cell walls, which kills them (permanently). If you freeze tissue fast enough, the ice crystals don’t have time to grow, so they don’t pose a problem. It’s easy to flash-freeze a small tissue sample like a small volume of sperm. It’s much harder (impossible, with current technology) to quickly freeze something as large as a human body, or even a whole organ. The problem being that you can only “apply cold” (take away heat) from the outside of the tissue, and it takes time for the heat to dissipate out of the center of the tissue. So this center cools down too slowly, (large) ice crystals form, and the tissue is destroyed.
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