As scientists learn more, all organs will become open to engineered replacements. From EurekAlert!: "urothelial cells [are] the specialised lining cells of the bladder that enable it to retain urine. The cells have a very low turnover rate, but scientists have found that if the bladder is damaged, the urothelial cells are able to rapidly re-grow to repair the wound. The researchers hope to harness this property to engineer new bladders. ... researchers have developed a series of models that mean they can study human urothelial cells in the laboratory. Of these models, the most important is their development of a urothelial cell sheet that functions as it would in the bladder. When the researchers create a wound in this model, the cells regenerate to repair the damage - just as they would in the body. Pharmaceutical companies should soon be able to use the research models to test therapies for the bladder, but the longer term aim for this research is to help patients who have lost bladder function or have had all or part of their bladder removed because of cancer. ... Our most exciting work moving forward is to develop natural and synthetic biomaterials that could be combined with regenerating urothelial cells. This has the potential to produce viable bladder tissue for transplant."