A great many interesting demonstrations of tissue engineering have taken place in recent years, and here is another: "Every organ in the human body has a scaffold or a structure, which provides it with its shape, and within this scaffold are many different types of cells with different functions. Tissue engineering aims to create the organ scaffold - either through the use of synthetic materials such as polymers, or through decellularization, which uses the whole organ as a scaffold after removing its cells. Decellularization is ideal for tissue regeneration because it preserves the three-dimensional structure of the organ and the extracellular matrix (ECM) - the framework between the cells - that are complex and difficult to mimic. While current methods use specific ECM proteins to transform stem cells into a particular cell type, scientists have found it difficult to imitate the natural ECM. Using the decellularization approach, a team of [researchers] removed the cells from the heart of a mouse and implanted the empty heart scaffold with [human embryonic stem cells] to observe if these cells could attach to the scaffold and develop into heart cells. After 14 days, the cells developed into two different types of cells found in the heart: cardiac marker expressing cells and endothelial or blood vessel cells. The cell-laden scaffold was then implanted back into the mouse where it was observed to develop visible blood vessels. The formation of blood vessels in the scaffold is critical for the transport of nutrients and oxygen to the heart, and has posed a major challenge in tissue engineering."