Two years ago, Shao, a mechanical engineer with a flair for biology, was working with embryonic stem cells, the kind derived from human embryos able to form any cell type. As he experimented with ways of getting cells to form more organized three-dimensional structures by growing them in scaffolds of soft gel, he was looking for signs of primitive neural tissue.

What drew his attention was that the cells seemed to change much faster than expected—they arranged themselves rapidly over a few days into a lopsided circle.

What was it? Shao startled Googling to see if he could identify the structure. That’s when he landed on a website called TheVirtual Human Embryo and found some microscope photos of ten-day old human embryos shortly after implantation, fused to the uterine wall. There was the beginning of the amniotic sac and, inside it, the embryonic disc, or future body. They matched what he was seeing.

In this microscope movie, filmed over four days, stem cells self-organize in ways that mimic a human embryo.


Shao informed his coworkers, a mixed team of biologists and engineers, at the University of Michigan. “When I showed the image to the team, everyone said, “Wow, we need to figure out what to do,” says Shao. Had they somehow made a real human embryo from stem cells? “At that point, we started to be more cautious.”

The embryo-like structures, the team soon determined, are not complete and couldn’t become a person. They lack the cell types needed to make a placenta, a heart, or a brain. Even so, the Michigan “embryoids” are realistic enough that the lab has been destroying them using a bath of detergent or formaldehyde to make sure they don’t develop any further.

The work in Michigan is part of a larger boom in organoid research—scientists are using stem cells to create clumps of cells that increasingly resemble bits of brain, lungs, or intestine (see “10 Breakthrough Technologies: Brain Organoids”). Now some like Shao are finding it’s possible to mimic the embryo itself. This year, for example, researchers in Cambridge, U.K., built a convincing replica of a six-day-old mouse embryo by combining two types of stem cells. That group is now trying to do the same with human cells, as are a few others, including one at Rockefeller University in New York. What’s emerging, say scientists, is a new technology, which they call “synthetic embryology,” and which they believe may let them probe the fascinating opening chapters of human development in detail for the first time.