Decellularization involves stripping out the original cells from a donor organ and then repopulating it with cells grown from the recipient's tissue - thereby removing the possibility of immune rejection. One implication of this approach is that the donor doesn't necessarily have to be human: "In proof-of-concept research [a] team successfully used pig kidneys to make 'scaffolds' or support structures that could potentially one day be used to build new kidneys for human patients. The idea is to remove all animal cells - leaving only the organ structure or 'skeleton.' A patient's own cells would then be placed on the scaffold, making an organ that the patient theoretically would not reject. ... this is one of the first studies to assess the possibility of using whole pig kidneys to engineer replacement organs ... For the research, pig kidneys were soaked in a detergent to remove all cells, leaving behind the organ's 'skeleton,' including its system of blood vessels. In addition, the structure of the nephron - the kidney's functional unit - was maintained. The scaffolds were implanted in animals, where they were re-filled with blood and were able to maintain normal blood pressure, proving that the process of removing cells doesn't affect the mechanical strength of the vessels. ... It is important to identify new sources of transplantable organs because of the critical shortage of donor organs. These kidneys maintain their innate three-dimensional architecture, as well as their vascular system, and may represent the ideal platform for kidney engineering."