Different research groups use different approaches to grow an organ in the lab since every organ is different, but many of them have similar steps.
What's needed next are cells from the patient to populate that organ skeleton. Currently most lab-grown organs have been using stem cells taken from bone marrow – but there's hope that this could one day be replaced by adult stem cells or even something easier to harvest like skin cells, which could be turned into different kinds of cells using special chemicals.
There are also some new ideas about how to create organs on demand, like using a 3D printer to create an organ.
"In reality our biggest challenges are the solid organs," Anthony Atala, a researcher at Wake Forest, said in a TED talk in 2011. "Ninety percent of the patients on the transplant list are actually waiting for a kidney. Patients are dying every day because we don't have enough of those organs to go around."
Many organs are grown using biological scaffolds taken from humans, though some can be manufactured or taken from animals.
For something like a liver, you can use a liver or a piece of liver that isn't suited for live donation, and put it through a digestion process that gets rid of all the donor cells, but leaves all of the connective tissue and the outlines of their blood vessels untouched.
"We basically can lift this organ up, it feels like a liver, we can hold it like a liver, it looks like a liver, but it has no cells," Atala said. "All we are left with is the skeleton, if you will, of the liver. All made up of collagen, a material that's in our body."
Sources of a patient's stem cells, like their cord blood or amniotic fluid from when they were born, could be saved for a long time and may provide a source of any cell type they want, once the science is perfected.
Once a patient's cells are grown up in the lab and turned into the right kind of cell, they can be inserted into the organ to attach to the biological scaffold. Many of the organs with lots of blood vessels, like the liver and kidneys, require a two-step process (at least). First, the patients own blood vessel cells can be inserted and grown in the blood vessels, then the rest of the organ can be seeded with their other cells.
In his TED talk, Atala discussed the idea of using a three-dimensional printer to print organs on demand. His team modified a desktop printer and put cells in the cartridge. In his lecture, he said it takes about seven hours to print a kidney, putting down one layer of cells at a time. That's just a prototype though.
His team has created bone and implanted it in an animal, he said. They are currently working on more sophisticated printers, which could print right on the patient, including printed skin cells, an incredible technology that could change how we treat burns forever.
He imagines a similar approach could use an MRI to non-invasively analyze a person's organ, then send information through a computer and design the organ for the patient.