Tiny functioning human livers have been grown from stem cells in the laboratory by scientists in Japan. They said they were "gobsmacked" when liver buds, the earliest stage of the organ's development, formed spontaneously.
The team, reporting their findings in Nature, hope that transplanting thousands of liver buds could reverse liver failure. Experts welcomed the findings, describing them as "exciting". Scientists around the world are trying to grow organs in the lab to overcome a shortage of organ donors.
Some patients already have bladders made from their own cells, but dense solid organs such as the liver and kidneys are much harder to produce. The team at the Yokohama City University were reproducing the earliest stages of liver development - similar to that in an embryo.
They had mixed three types of cells - two types of stem cells and material taken from the umbilical cord.