I believe that certain model organism worms can be frozen and thawed without consequences, and likely certain amphibians. The main features that allow freezing

I believe that certain model organism worms can be frozen and thawed without consequences, and likely certain amphibians. The main features that allow freezing traditionally in these creatures is that they're small (easy to quickly permeate completely with cryoprotectant, assuming they're using that method) and already live in an aqueous environment. It's important to remember that these animals are much smaller than typical human organs, which (correct me if I'm wrong) we are yet to successfully freeze, re-thaw, and implant functionally. Won't work so smoothly on most living creatures or organ structures for a few reasons. First, for cells in a liquid media solution or very small/simple animals, you can guarantee that the cryoprotectant is going to permeate into all the proper places, preventing destructive ice crystals from forming inside of the cells. For an entire living creature, there's a bunch of barriers-- rate of seeping of cryoprotectant through tissues, large internal solid and liquid volumes, and difficult-to-permeate epithelial tissue or fur. The cryoprotectants can seep through outer skin without additional help, but there are likely to be some spots where they can't or don't get to. It's important to remember that this process would have to occur in a race against two separate death clocks: race one is against irreversible damage as a result of stalled metabolic output (death of neurons or other irreplaceables from lack of oxygen or nutrients) and race two is against the toxicity of the cryoprotectant/freezing process causing irreversible damage in the first-permeated tissues before metabolic activity is completely stopped by freezing temperatures. I have no idea if these spots are understood or identified. Second, the far larger problem is removing the toxic cryoprotectant once metabolic activity has resumed during thawing. For cells in a liquid media solution, you can pellet cells to the bottom of a test tube in a centrifuge, then suction off the cryoprotectant. For an entire living creature, I don't even know where you'd begin, or how you'd guarantee all the cryoprotectant was flushed out. For cells in liquid media, you have about a 30 minute time window to remove the cryoprotectant before your cells are kaput.