The Future Is Now, Vol. LXXXVIII: Researchers Grow Rat Limb In A Jar

A team from Massachusetts General Hospital under Harald Ott regrew rat and primate forelimbs ex vivo, and then transplanted it back into a host animal. They did it by removing all of the cells from an amputated arm, reseeding it with appropriate cell types for the various tissues in a bioreactor atop the existing extracellular scaffolding, and then reattaching it.

This is not quite as impressive as growing it up from nothing, but it represents a substantial step forward from existing technology which is capable of doing single or dual cell type tissue growth. This is multiple tissue, structured repopulation and regrowth of tissue. That's huge.