Tissue engineers have long dreamed of starting with a small clutch of cells in a petri dish and growing new organs that can then be transplanted into patients. The strategy has worked for relatively simple, thin tissues such as skin and cartilage that don’t depend on a well-formed network of blood vessels to deliver food and oxygen. But it hasn’t panned out for more complex tissues shot through with vessels, such as bone and liver. Now a novel approach to tissue engineering that grows bone inside a patient’s own body could change all that.