A research team at Japan's RIKEN Center for Developmental Biology took a pile of mouse stem cells and got them to turn into a working pituitary gland, which is a small organ that lives at the base of your brain and produces hormones that help you grow up big (but not too big) and strong (but not too strong).
Getting stem cells to cooperate to turn into complete organs as opposed to just some other type of cells is tricky, because on their own, the rely on lots of different signals from a developing brain that tell them what to do and when. To replicate this, the researchers grew the stem cells using a three-dimensional cell culture, and through trial and error, sent the cells "messages" of growth factors and developmental proteins in the right amounts and at the right times such that the cells self-assembled into a functioning organ. The cultured pituitary gland was then implanted into a mouse, where it performed flawlessly, completely replacing a non-functioning natural organ.
I guess technically, you would call an organ constructed in this manner synthetic. But what's the difference? If it comes from your stem cells and works exactly like the original, your body won't care in the least. There's an enormous amount of potential here, and at some point in the future, any failing organ you ever have may be able to be replaced with a new one, and your body won't even be able to tell. This future point is probably at least a decade away, though: the researchers say that it'll probably take two or three years to reproduce this experiment with human stem cells instead of stem cells from mice.
Via Tech Review