I think most cryobiologists are going about it the wrong way, trying to get incrementally better at cryopreserving tissue. The work I'm aware of that seems most promising (I say, having almost no familiarity with the field) is Ken Storey's work with wood frogs. They can freeze and thaw naturally.

I looked into it because I hoped I might be able to move some genes from a wood frog into a mouse, freeze it, thaw it later, and win the Methuselah Mouse prize. But it turns out that the frog has an anti-dessicant response to protect tissue from lack of water, an anti-ischemia response to protect tissue from lack of oxygen, a glucose response to produce glucose as a cryoprotectant, an anti-glucose response to protect cells from the huge amounts of glucose, and a bunch of other mysterious responses. It involves hundreds of genes. It's going to take a large program to import entire gene pathways from one organism to another.

Done, though not at LN2 temperatures:

http://www.ncbi.nlm.nih.gov/pubmed/15094092

http://www.cryostasis.com/perspectivesandadvances.pdf