Embryo models are typically made from genetically tweaked or chemically treated stem cells, which are either embryonic or derived from adult human cells. Under carefully controlled conditions, scientists can "persuade" these stem cells to self-organize into blobs of tissue that resemble different stages of early embryonic development, said Roger Sturmey, a professor in reproductive medicine at Hull York Medical School in the U.K. who was not involved in the Cell paper.
Models called blastoids can recreate one of the earliest stages of embryo development — a hollow ball of cells called a blastocyst — at around five days after fertilization. More-complex models, called gastruloids, model gastrulation, when the embryo goes from being made of just one cell layer to becoming a 3D structure around two weeks after fertilization.
Theoretically, gastruloids could be grown in a lab for more than 14 days. But they generally aren't, due to a "14-day rule" upheld by law or by research regulations in various countries. Some researchers, including an influential scientific panel, have called for the rule to be loosened to allow for embryos and embryo models to be grown for longer.
These models could provide a detailed look at the first 30 days of embryonic development, enabling scientists to improve the efficiency of fertility treatments such as in vitro fertilization (IVF) and uncover causes of early miscarriage, Nicolas Rivron, lead author of the Cell paper and a principal investigator at the Institute of Molecular Biotechnology in Vienna, told Live Science. They could also reveal how development in the womb influences health in adulthood — for example, how it might affect the risk of developing cardiovascular diseases or diabetes, he added.
Such research would be technically challenging and unethical to do in a pregnant person, making embryo models especially appealing to researchers studying early development.