For years, researchers have been trying to figure out how to grow duplicates of human organs in laboratories so that they can transplant them into people who need them. But while they've had success growing tissue, the cell structures and vascular systems of full-scale organs such as kidneys and livers are really, really difficult to reproduce. Or at least, they have been up to now.
Medical researchers are making strides with bioprinting, in which they harvest human cells from biopsies or stem cells, multiply them in a petri dish, and use that to create a sort of biological ink that printers can spray. (The 3-D printer is programmed to sort the different cells types and other materials into a 3-D shape.)
Scientists are hoping that bioprinting someday will enable them to arrange cells so precisely that they can mimic the function of human organs, making them useful for testing new drugs or even as organ transplants. If the organs could be fashioned from a patient's own tissue or stem cells, they'd be less likely to be rejected by his or her immune system [source: Griggs].