The headline blared from newspapers all the way back in 2006: "First Lab-Grown Organs Implanted in Humans!" A team from Wake Forest University had biopsied cells from the bladders of patients with spina bifida and used them to create brand new full-size bladders, which they then implanted. Although the bladders had to be emptied via catheter, they were still functioning a few years after implantation, and the public grew confident that doctors had climbed an intermediary step on the way to the medicine of science fiction. Ten years later, though, more than 20 people a day are still dying while waiting for an organ transplant, which leads to a simple question: Where are our fake organs?

"We can make small organs and tissues but we can't make larger ones."

Not coming anytime soon, unfortunately. The company that was created to transition Wake Forest's bladders to the market failed. And while there are a few simple bioengineered skins and cartilages already on the market, they are hardly identical to the real thing. Something like a liver could take another 20 to 25 years, says Shay Soker, professor at Wake Forest's Institute for Regenerative Medicine. "The first barrier is the technology: We can make small organs and tissues but we can't make larger ones," he says. "Also there are several cell types or functions that you can reliably make from stem cells, but not all of them, so the technology of stem cells has to catch up with what the body can do." Finally, he says, you have support the new organ inside the body, providing it with a circulatory and nervous system and integrating it with the immune system.

While these are all challenging problems, circulation appears to be the most intractable. "Tissue's not able to survive if the cells don't have oxygen, and the bigger it gets, the more complex vasculature you need to keep that alive," says Chiara Ghezzi, research professor in the Tufts University Department of Biomedical Engineering. "Vasculature is highly organized in the body. It has a hierarchical structure, with different branches that have different roles depending on where they are." So far, she says, researchers have had trouble scaling up from capillaries to larger vessels that could be grafted onto blood vessels in a patient's body.

"The FDA is still getting its hands and minds around the field of tissue engineering."

Last, but hardly least, is the question of FDA approval. Lab-grown organs are neither drugs nor medical devices, and the agency is not set up to quickly or easily approve new technologies that don't fit into current categories. "The FDA is still getting its hands and minds around the field of tissue engineering," says Soker. "They were not used to that… so it requires the regulatory and financial federal agencies to really help and support these initiatives."

A pencil eraser-size model of the human brain is now being used for drug development and research.

If all of this sounds discouraging, it's worth mentioning some of the incredible progress the field has made since the first strides toward lab-grown organs began nearly 30 years ago: Though full-size replacement organs are still decades away, many labs have diverted their resources into what they consider an intermediate step, developing miniature organs and systems that can be used for drug development and research. This platform will yield more relevant results (Imagine! Testing cardiovascular drugs on an actual human heart!) and require the deaths of far fewer animals. And it's already here: Two years ago, scientists at Ohio State University developed a pencil eraser-size model of the human brain they intend to use for this exact purpose.

Perhaps the most exciting line of research these days is one that at first doesn't seem to have anything to do with bioengineered organs at all. Along with his colleagues, Chandan Sen, Director of the Center for Regenerative Medicine and Cell-based Therapies at Ohio State University, has developed a nanoscale chip that can turn any cell in the body into any other kind of cell—reverting fully differentiated adult cells into, essentially, stem cells, which can then grow into any tissue you want. Sen has used his chip to reprogram skin cells in the bodies of mice into neurons to help them recover from strokes, and blood vessels to save severe leg injuries. "There's this concept of a bioreactor, where you convince an organ to grow outside the body. They're getting more and more sophisticated over time. But to my mind it will never match the sophistication or complexity of the human body," Sen says. "I believe that in order to have an organ that behaves the way you want it to in the live body, you must use the body itself as a bioreactor, not a bunch of electronic gadgetry." There you have it, the next step in artificial organ manufacture is as crazy as it is intuitive: Grow it back where it was in the first place.