Beating heart-on-a-chip

Justin Williams pokes his brain with a sharp object, then watches what happens through a microscope. Needless to say, the brain Williams, at the University of Wisconsin, Madison, is needling is not his own. It is a small sample taken from a mouse and held in a "brain-on-a-chip" device: the tissue is suspended between two layers of plastic and surrounded by a nutrient-rich fluid.