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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To add to the other answers, sperm cells are one of the smallest cells in a human organism and don’t have much water in them. Also normally a sperm sample has millions of live sperm cells, of which you really need only a few for in vitro fertilization, so there is plenty of room for error. This makes it easy to freeze sperm more or less however you can and still have some usable sperm cells after thawing.
Egg cells are one of the largest cells in the human body, but they are still single cells. Early stage embryos are of the same size as egg cells (they initially divide “inside”, without actually growing). Freezing them uses a process called vitrification. It prevents ice crystals from forming by basically lowering the temperature extremely fast. It can’t really be done with larger objects, like whole human bodies, because there is no way to lower the temperature so fast everywhere at the same time.
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