system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How come people can't be cryogenically frozen safely as the ice crystals destroy the cell membranes, but sex cells such as sperm are kept frozen for long periods of time yet remain functional?
gpt
Sperm is frozen in liquid nitrogen, and the water in the cells is replaced by glycerol (basically antifreeze) as a "cryoprotectant", which displaces the water and does not form the crystalline structure that damages cells.

However, the freezing and thawing process is still pretty harsh and many sperm don't survive.  Luckily, there are billions and you only need 1.