Suspended animation is frequently confused with cryonics, even by most scientists. In suspended animation, the patient wakes up after an induced "hibernation" or "suspension". While this is theoretically possible, it really has nothing at all to do with cryonics. There is broad scientific consensus that suspended animation technology would be so incredibly complex that it could not possibly be developed in any of our lifetimes.
Cryonics is quite different and is broken down into two distinct phases.
Phase I: Structural preservation that we are able to perform with current technology. We have shown with Electron Micrographs that Phase I already works well.
Phase II: Reconstruction of memories using very advanced Future Technology.
Viability refers to the ability of living cells to recover spontaneously. This could never happen in cryonics because viability is always lost long before the final cooling takes place. Viability might eventually be important in suspended animation, but viability is completely secondary in cryonics. Instead, structural preservation is the only goal. Structural quality must never be sacrificed simply in order to maintain viability of some cells further into the procedure. For example, irreversible chemical preservation techniques are desirable because they result in better final structural preservation, even though viability is lost sooner.
Toxicity is when chemicals injure or kill a living organism. We use formaldehyde chemical fixation, which immediately halts all biological activity. It is, by definition, toxic, but that label is meaningless in the context of attempting to preserve structure rather than viability.
The confusion between the concepts of suspended animation and cryonics tends to lie at the heart of much of the opposition to cryonics. We are most certainly not proposing that we can revive anyone by simply warming them up. The cells are not viable.