Why can sperm be frozen and used later?
Keep the dirty puns out of this thread please. This is GQ.
Well - because they don’t ‘die’ or get worn out if they’re frozen properly?
If that doesn’t answer your question, maybe you should clarify it further.
Why doesn’t it die and rot when just thawed?
OK. Why don’t they die? Why doesn’t the freezing and thawing process not rupture cellular walls enough to kill the lot off?
Wasn’t there a case some years back of a woman wanting to use her dead husband’s frozen sperm to get pregnant?
Because when they freeze they are not doing anything so they do not get worn down. Your body is always doing things, and doing things makes it wear down. This is called aging. It makes you get old. But the freezing makes it all stop so the sperms are healthy.
You cannot freeze a body because the ice will make it tear, but the sperm does not tear.
When we freeze bacteria, we use glycerol as an antifreeze additive. It helps prevent the formation of harmful spiky ice crystals. I’ve not frozen sperm myself or looked into it carefully, but as an educated WAG, I’d suspect they do something similar. They also freeze them very very quickly, which also helps prevent large crystals from forming. And I’d wager a guess that the large surface area to volume ratio plays an important role as well - the freeze penetrates the cell quickly enough that it’s “flash frozen”, so to speak.
I don’t know about freezing sperm specifically, but other types of human cells can be frozen down by using a cryoprotectant (e.g., dimethyl sulfoxide), which prevents the cells from rupturing. I believe that the DMSO solubilizes the cell membrane, making it more resistant to puncture by ice crystals.
The Integrity of Frozen Spermatozoa
(Conference Proceedings, 1976)
The introduction and first chapter “Fundamentals of the Preservation of Spermatozoa” should tell you more than you want to know.
Basically lots of people tried lots of different things, until they found something that worked well. Isn’t rampant empiricism grand? 
So if we could watch a frozen sperm unfreeze in some kind of sperm-friendly liquid, we’d see slow little movements on the end of the tail, then they’d start getting a little faster, then more and more of the tail would start to move, and before we knew it, the sperm would be swimming around blissfully?
Is there a specific reason sperm freezes without rupturing compared to a different cell type, or are all cells capable of freezing without rupturing and a large cell mass ruptures because you can’t freeze it fast enough with the sperm process, or does the speed of thawing also mater? Yes it’s one long sentence.
I won’t be back until the morning.
Other cell types, including embryos (e.g. after in vitro fertilization), survive freezing/thawing, if appropriate cryoprotectants and cooling down/ warming up protocols are used. Cryopreservation of whole organs is more difficult. See this link (PBS/NOVA or U.Calgary Cryo course) on the problems that currently still prevent the freezing and recovery of whole organs.
You can freeze pretty much any cell type. As someone mentioned above, DMSO. Whenever I freeze cells in the lab, they are frozen in 10% DMSO, which acts to protect them during the freezing process. There is then the optimal freezedown time of one degree per minute to make sure they don’t rupture. I’m sure that sperm freezing has a similar protocol.
Does it help that Sperm are hardy little things? They may not last long, but they are remarkably able to move and survive unusually unpleasant environments if neccessary.
Thanks for the responses. I have enough now. Anybody that wants to comment further is welcome to do so.