What is the Science behind Cryogenic Sleep Pods we often see in Sci-Fi so characters don't age on long space journeys?

If you’re looking for an explanation of the materials needed to construct a chamber, I don’t think that we’re quite there yet. We can freeze things down to a certain level, but not so much as to stop the natural decaying of things without causing permanent damage. Perhaps there’s an illegal lab funded by an evil billionaire that’s working on it. Or maybe when the space station starts to expand they can somehow use the vacuum of space as a cooling agent to create the effect required. But you’ve also got to consider the moral implications. Would you really want to? You’re going to leave the world as you know it behind, and only bond with your peers. Anything could happen while you’re away, including the destruction of everything and there’s also a possibility that you might not recover afterwards. You’re putting a lot of trust in technology and your fellow man to get you to your destination.