eli5 Why can human embryo’s be frozen but not human adult?
In: Biology
Because as everybody know, once you defrost something is totally not good to frost it again!
Back in the 80s they were doing scientific experiments on freezing and heating hamsters.
They had problems with the reheating process which left burns on the hamsters.
To solve this, they developed the microwave.
Anything larger than a hamster (ie rabbit) could not be frozen quick enough to survive the freezing and warming process.
Ergo, it won’t work on humans. But hamsters can enjoy the trip.
Have you ever heard the story of Birdseye? It’s not just a frozen food company that has frozen corn in the grocery store, it is named after a man that revolutionized the food and agriculture industries by developing a way to freeze produce without turning it into mush.
When water freezes it expands, which can rip apart the cells that make up people, or corn, or anything. The result is they are damaged at the time of freezing, and when thawed they are mush. Not good for corn or for people.
Birdseye championed flash freezing after noticing that the speed with which something is frozen, directly affects whether the freezing process will damage it or not. By flash freezing produce, the ice crystals don’t have time to grow large and damage the cells.
That’s step 1, you have to be able to freeze something without the freezing process causing damage. That means it has to be frozen very fast. This is easier to do to something very small as there is not much latent heat to be removed from it. The larger the thing you want to freeze, the longer it will take to freeze. An embryo can be frozen in seconds. A human being might take hours even in extreme cold.
Step 2 is you have to later reverse this and thaw the frozen item without damaging it. In the case of cells, an embryo, some small animals, their small size again helps them thaw quickly so that all of it thaws more or less at the same time. It wouldn’t do well for one part to still be frozen, while the rest had thawed.
For something large like a person, imagine thawing. The limbs would thaw first, even the head, while the main part of the body containing the heart, the lungs, would stay frozen for far longer. So you have thawed limbs and a thawed brain, not getting blood, not getting oxygen, because the heart is still frozen solid. That’s no good. So you would need a way to warm the body at the same rate, so that everything thawed at once. Very tricky to do with something as large as a person.
Finally remember that an embryo is not the same thing as a fetus. It’s just a bundle of cells, not much different from freezing an amoeba or cell cultures. It doesn’t have a heart or a brain to become damaged. Just some cellular walls.
It’s much harder to flash freeze lots of cells at once. Adults are made up of 30 to 40 million cells. Frozen embryos are 100-120. Freezing a small number of cells lets you control more of the things that could go wrong, like the forming of ice crystals that damage cells.
EDIT: I’d intended to type 30 to 40 trillion, but either blanked on it or had an auto correct. Likely that I had a brain fart moment. That number is the number of cells which are genetically “you”. There are also trillions which are not “you” but are a part of the operation of your body and its biological functions.
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