From the Guardian, another modest step towards bioengineered replacement hearts: "A British research team led by the world's leading heart surgeon has grown part of a human heart from stem cells for the first time. If animal trials scheduled for later this year prove successful, replacement tissue could be used in transplants for the hundreds of thousands of people suffering from heart disease within three years. ... By using chemical and physical nudges, the scientists first coaxed stem cells extracted from bone marrow to grow into heart valve cells. By placing these cells into scaffolds made of collagen, [scientists] then grew small 3cm-wide discs of heart valve tissue. Later this year, that tissue will be implanted into animals - probably sheep or pigs - and monitored to see how well it works as part of a circulatory system. ... Growing a suitably-sized piece of tissue from a patient's own stem cells would take around a month but he said that most people would not need such individualised treatment. A store of ready-grown tissue made from a wide variety of stem cells could provide good matches for the majority of the population."