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New study may finally settle one of neuroscience's greatest debates Scientists transform pee into material fit for medical implants Fertility, Pregnancy & Birth Scientists grow mini amniotic sacs in the lab using stem cells RJ Mackenzie 11 July 2025 A newly created cell model of the amniotic sac could reveal new insights into early pregnancy, as well as generate helpful products for medical use. When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works. This image shows one of the new lab models, called PGAs, at day 18 of growth. PGAs are composed of two different cell populations (magenta, the extra-embryonic mesoderm and yellow, the amniotic endoderm). (Image credit: Gharibi, B. (2025). Cell.) Researchers have developed a new laboratory model grown from stem cells that replicates the human amniotic sac in the first two to four weeks after fertilization. The structure, which the researchers say is the most advanced and mature amniotic model ever created, could offer new insight into human development and lead to cell products for medical procedures, from burn treatments to cornea reconstruction, the team reported in a study published July 10 in the journal Cell. The growing human embryo isn't alone on its developmental journey. "Supporting tissues like the placenta, like the amniotic sac, grow with the embryo and are really important for the embryo's growth and survival," said study co-author Silvia Santos, a group leader at the Francis Crick Institute in London. You may like Lab-grown teeth could offer alternative to fillings and implants, scientists say 'Useless' female organ may actually support the ovaries, study finds Scientists discover never-before-seen part of human cells The amniotic sac is a fluid-filled, biological balloon that cushions and protects the growing embryo. The liquid it contains is thought to be essential for healthy embryo development. But it hasn't been easy to investigate this interplay between the embryo and its entourage, largely because this stage of development is logistically difficult and ethically fraught to study inside human beings. Previous attempts at modeling the amniotic sac in the lab were unable to replicate its complex 3D structure, which has two distinct cell layers. In addition, previous models tended to last only a few days, making it harder to get insight into the extended process of development. By contrast, Santos' new cell models, called post-gastrulation amnioids (PGAs), can survive in their lab dishes for at least three months and develop to the same degree as a month-old amniotic sac. Remarkably, they grow to a similar size, too — up to about an inch (2.5 centimeters). Related: Scientists invent 1st 'vagina-on-a-chip' Sign up for the Live Science daily newsletter now Get the world’s most fascinating discoveries delivered straight to your inbox. Contact me with news and offers from other Future brandsReceive email from us on behalf of our trusted partners or sponsorsBy submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. This image shows a PGA at day 8 of growth, showing the early tissues supporting the embryo, including the amniotic sac and the yolk sac-like structures, surrounded by extraembryonic mesoderm tissue. (Image credit: Gharibi, B. (2025). Cell.) "They are little golf balls," Santos told Live Science. The PGAs also form the amniotic sac's distinct two-layer structure. To achieve this, Santos' team used a new cell-culture method. They began with embryonic stem cells, which can grow to become any other cell type in the body if nudged with specific signaling molecules. The team exposed these cells to two of these signals, called BMP4 and CHIR. They made sure to space out the signals, adding BMP4 over the first 24 hours of growth, followed by CHIR for another 24 hours. Then, the researchers left the cells alone in round-bottomed culture dishes. "The rest was complete self-organization," meaning the maturing stem cells orchestrated their own assembly into a structure, Santos said. Single cells aggregated in the dishes and formed the distinct two-layered, fluid-filled structure the team had searched for. "This just shows you that these embryonic stem cells have this amazing propensity to specialize and to become everything given the right instructions, which I'm still in awe about," Santos said. This microscopy image of a PGA shows that it's a two-membrane sac. The inner membrane represents amniotic endoderm cells and the outer extraembryonic mesoderm cells. The dark space in the middle represents the fluid within PGAs. (Image credit: Gharibi, B. (2025). Cell.) Armed with their new models, the team set out to answer key questions about how amniotic sacs influence their environment. They wanted to know what genes might be directing cells to turn into PGAs. By interfering with a long list of genes that they suspected might influence cell development, they found that a single gene, GATA3, could convert cells into amniotic sacs without any other signals. GATA3 codes for a transcription factor — a protein that turns other genes on or off. Santos and her team showed that two of the genes GATA3 regulates are BMP4 and CHIR, the same genes their culture protocol had involved. To explore how the amniotic sac may influence nearby cells, they mixed their PGAs with additional stem cells that hadn't been nudged to become any particular cell type. Left on their own, these cells would have continued to exist in their unspecialized state. But next to the PGAs, they changed into a host of other "extraembryonic" cell types, showing that the amniotic sac was capable of driving the transformation of cells around it. This diagram shows how the PGAs develop through time, largely through self-assembly. (Image credit: Gharibi, B. (2025). Cell.) Santos and her team are now exploring possible applications for their new system. Amniotic sacs have antimicrobial and anti-inflammatory properties, and people who have had elective C-sections can opt to donate their amniotic sacs for use as transplant tissue in burn treatments or cornea repairs. These donated materials can be difficult to standardize, Santos said, but PGAs could theoretically provide a reliable source of these desired cells. Yi Zheng, an assistant professor in biomedical and chemical engineering at Syracuse University who was not involved in the study, said further tests would be required to see whether PGAs could provide clinically useful materials for such procedures. RELATED STORIES —Could mini space-grown organs be our 'cancer moonshot'? —Body parts grown in the lab —Lab-grown mini-placentas reveal clue to why pregnancy complications happen He added that mature, non-stem cells can be transformed back into stem cells called induced pluripotent stem cells (iPSCs). Perhaps, Zheng said, iPSCs converted into PGAs could be particularly useful for medical applications, in part because you could use a patient's own cells to generate them. Better models of the amniotic sac could also help researchers understand why this critical structure sometimes malfunctions. Some congenital disorders — meaning those babies are born with — are tied to differences in the size or content of the sac prior to birth, and Santos said the PGAs could help explain that link. "I'm extremely excited about the potential of these little structures," she concluded. RJ Mackenzie Live Science Contributor RJ Mackenzie is an award-nominated science and health journalist. He has degrees in neuroscience from the University of Edinburgh and the University of Cambridge. He became a writer after deciding that the best way of contributing to science would be from behind a keyboard rather than a lab bench. He has reported on everything from brain-interface technology to shape-shifting materials science, and from the rise of predatory conferencing to the importance of newborn-screening programs. He is a former staff writer of Technology Networks. 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