But scientists believe that it might not be long before they can synthesize embryos in the lab that are almost indistinguishable from naturally created ones. Already, research on artificial mouse embryos has progressed to the point where scientists are transferring them to female surrogates and trying to make live animals, though they haven’t succeeded yet.

The concern is that if scientists could make human embryos in the lab, someone might use the systems to generate genetically modified people, a dystopian scenario similar to the central hatcheries described in the novel Brave New World.

Last December, Martinez Arias joined Fu and several others who wrote an editorial calling on regulators to permit scientific research with the models but enact a legal prohibition on using them to try to start a pregnancy. “We urge regulators to ban the use of stem-cell-based entities for reproductive purposes,” they said.

Fu says only someone “crazy” would try to make a person using a synthetic embryo. However, given the rapid advance of the science, he sees a legal ban as important. “Many scientists are trying to push boundaries, and people are crossing lines. If you let scientists self-regulate, that is how the gene-edited babies happened. I don’t trust self-regulation,” says Fu.

Here is how they did it

It’s known that stem cells left in a dish will spontaneously turn into heart muscle and start beating. As well, there are blob-like brain organoids that emit electrical waves, and mini-guts that can be used to test whether drugs work.

The new research goes further, efficiently mimicking an embryo’s opening days of development. According to the report, Fu’s team placed individual stem cells into tiny slots on a microfluidic chip, and then provided chemical cues that helped them start dividing and taking the shape of an embryo.

The Michigan team, whose preliminary results made the news in 2017, now say they can get the stem cells to turn into embryo-like structures more than 90% of the time, and that they’ve made hundreds of them.

“This is the new standard for controllability, which makes it into an experimental platform,” says Fu. “Each channel has many chambers, and each can trap a little ball of pluripotent stem cells. Chemicals only reach one side of the ball, so when and where the stem cells are stimulated is very controlled.”

To developmental biologists—those who study how bodies form—systems that model the human embryo are cause for keen excitement. Fu says teams in Japan and the UK are already using the Michigan microfluidic device to investigate how certain cells in the embryo get designated as future sperm or eggs cells. If they can determine that, it could lead to ways to make reproductive cells for people who lack them.

Funding confusion

The rapid development of embryo models is posing a challenge to the National Institutes of Health, which isn’t sure it can fund this type of research because of a law that forbids it from paying for experiments involving human embryos. That law, the Dickey-Wicker Amendment, is written to say any human “organism” made from cells would count as an embryo.

Because it’s not obvious what qualifies as an organism—that term means a life form, but isn’t defined in the law—the agency has started passing grant applications from researchers like Fu to a special “human embryo research steering committee” staffed by agency officials that will determine whether they would violate the statute.

“We don’t have a funding policy, but we need to judge each grant that raises concerns,” says Carrie Wolinetz, associate director for science policy at the NIH. “They can say [this] poses too great a legal risk.” She agrees the question is whether embryo-like entities such as the ones Fu is creating “could constitute an organism or not,” adding that “this is a very rapidly evolving area of research and science and we want to understand it.”

To do that, the NIH is participating in a one-day workshop, planned for early next year at the National Academies, in Washington. The workshop’s goals include trying to identify “differences between mammalian embryo model systems and bona fide mammalian embryos.” As well, the International Society for Stem Cell Research, a scientific organization representing stem-cell biologists, says it will be addressing the lab models as it revises its guidelines for scientists.

Politics can’t keep up

The funding confusion, say scientists, has been compounded by recent federal policy changes that limit money for research involving abortions. In June, the Department of Health and Human Services said it would end all government research employing fetal tissue from elective terminations. It may still fund academic scientists, but only after an involved ethics review.

As part of the clampdown, which most ascribed to abortion politics, HHS said it would be working to “ensure” that alternatives to fetal tissue “are funded and accelerated” and indicated it would prioritize models that mimic embryos. However, when a branch of the NIH issued invitations to apply for money to develop fetal-tissue alternatives this year, the solicitation specifically excluded “human embryo model systems” made from stem cells.

Scientists say such contradictions show that funding is being influenced by politics. “It’s bizarre—brain organoids are fine, but vaguely embryo stuff is not,” said one researcher, who wanted to speak off the record because he has pending grants.

This week, in a separate report, a team at Rockefeller University described how they’d mimicked groups of cells whose organization is similar to the early formation of the brain, nervous system, and skin of a month-old embryo. At that stage, a human embryo is a minute shrimp-like structure with tiny limb buds.

The Rockefeller researchers, led by Eric Siggia and Ali Brivanlou, call their structures neuruloids. They say because of the “difficulty” of obtaining or studying actual human embryos at this early stage, they judge their technology the “only practical solution.” They have formed a startup company, Rumi Scientific, that plans to screen drugs on the neuruloids for conditions like Huntington’s disease.

Siggia calls the government’s shifting positions a sign of its “current state of confusion” as it attempts to figure out “what is an embryo and what is not.” But he says his research is unaffected: “We are not slowed down by any of this. We just use private funds.”