Scientists continue to make steady progress towards the use of rapid prototyping technologies in tissue engineering. A little insight into progress from ScienceDaily: "For the past four years, [researchers have] been working to refine the process of 'printing' tissue structures of complex shape with the aim of eventually building human organs. In the latest study, a research team [determined] that the process of building such structures by printing does not harm the properties of the composing cells and the process mimics the naturally occurring biological assembly of living tissues. ... As the tissue structure begins to form, the cells go through a natural process called 'sorting,' which is nature's way of determining where specific cells need to be. For example, an artery has three specific types of cells - endothelial cells, smooth muscle cells and fibroblast cells, each type needing to be in a specific location in the artery. As thousands and thousands of cells are added to the bio-paper under controlled conditions, the cells migrate automatically to their specific locations to make the structure form correctly."