Can organ donations be gifts?

I read recently about a Long Island doctor who is demanding compensation for the kidney he donated to his wife prior to their divorce. Wow. From the article I read, it seems that the doctor donated the kidney to his wife, who then had an affair and divorced him. Now he is demanding the kidney back, or at least the value of it, priced at $1.5 million.

So the question, it seems, is whether the kidney was a gift, a loan or a sale (which somehow is only triggered upon divorce).  I suppose a kidney can be considered to be a tangible asset.  I have to say however, that what he gave his wife was intangible: life, or at least life without dialysis. I don’t think that that can be returned.