Cryonics isn't currently classified under a specific branch of science. It's more accurately described as an emerging field that draws on principles from various existing branches:

* Biotechnology: Cryonics utilizes methods like vitrification to preserve biological tissues at extremely low temperatures.

* Cryogenics: This branch of physics deals with the production and application of very low temperatures.

* Medicine: Cryonics aims to preserve the body for future potential revival, which involves medical considerations.

* Nanotechnology: Future revival of cryopreserved individuals might rely on advanced nanotechnological interventions.

* Ethics: Cryonics raises numerous ethical and philosophical questions about the definition of life, death, and the implications of future revival.

While cryonics borrows principles from these fields, it's not fully established within any of them. It's considered experimental and controversial, with no guarantees of success in reviving cryopreserved individuals.