A time-lapse film provides a rare glimpse of a pivotal moment in human development: the instant when a newly formed embryo attaches to and burrows into the uterine lining. Researchers have captured real-time footage of the embryo pulling on a high-fidelity replica of the lining to embed itself, effectively remodeling its new "home." The team’s findings are reported today in Science Advances.
The inspiration behind simulating the implantation process stems from the inaccessibility of studying it in real-time. “It’s very inaccessible because it’s all happening inside the mother,” explains co-author Samuel Ojosnegros, a bioengineer at the Institute for Bioengineering of Catalonia (IBEC) in Barcelona, Spain. “It’s such an important process for human reproduction, but at the same time, we don’t have the technology to study it.”
Previous studies explored how human embryos interact with glass, but the embryo cannot penetrate this material as it does real human tissue. To address this, the team created a more lifelike mock uterine lining: a gel rich in collagen and proteins essential for embryonic development.
To produce the stop-motion film, researchers placed human embryos (donated by a local hospital) near the gel. As the embryo attached to the simulated uterus, they used a microscope to capture images every 20 minutes over 16–24 hours, then stitched the stills together into a continuous video.
Amélie Godeau, a biomechanics researcher at IBEC and co-author, was surprised by the embryo’s speed and force in burrowing into the gel. “My first reflex was to think my experiment had gone wrong and there was some drift in the microscope,” she recalls. In contrast, the team observed that mouse embryos merely adhere to the uterine surface rather than embedding themselves—a key difference in implantation behavior between species.
A confocal microscopy image of a nine-day-old human embryo (shown with embryonic stem cell protein in green, developing tissue in magenta, and DNA in blue) and additional footage of the embryo compacting to minimize exposure to the external environment complement the findings, offering a detailed view of this crucial developmental step.
Credit for images: Institute for Bioengineering of Catalonia (IBEC)