I asked my teacher this morning why certain insects can survive freezing, and the answer was we know there are chemicals in their blood which are responsible. Normally, because freezing happens slowly, large and sharp ice crystals form inside the body. The compounds in certain bugs end up rounding off the edges of ice crystals, to stop them from slicing and dicing cells. Bugs have an exteremely low metabolism and very little actual living tissue, but it is unclear whether their metabolism completely stops (in tardigrades I’m pretty sure it does).
Arthropods all have an open circulatory system, which essentially means they have holes across their entire body surface, with vents leading inside. This leaves them open to infection, like pneumonia all over. It turns out they have a powerful and active immune system, which constantly excretes antibodies. As soon as a bug dies, it gets eaten by bacteria and fungus roughly four times quicker than a normal animal like a rat.
The open way of breathing works because they have so little demand for oxygen. It makes them hard to drown or starve. And it limits them in size significantly. Human cryogenics at this point seems impossible due to the high oxygen and nutrient demand of our cells. Even if we successfully flash freeze our bodies to avoid sharp ice forming inside them, we still might starve to death.