Stem cells grown from mouse embryos helped power a liver replacement device, Japanese and US researchers reported. Their experiment suggests another use for the cells, controversial when taken from human embryos. They used the cells in a bioartificial liver, an implanted device that uses liver cells to replace some liver function. Writing in the journal Nature Biotechnology, Ira Fox of the University of Nebraska Medical Center, Naoya Kobayashi of Okayama University in Japan said their cells saved lives of mice that otherwise would have died of liver failure.