For the first time, scientists have grown human eggs to full maturity in a lab, in a move that could open the doors to new fertility treatments.

This monumental feat was achieved by scientists at the University of Edinburgh in Scotland. Their research is published in the journal Molecular Human Reproduction. A similar venture has previously been achieved with mouse eggs, even using the lab-grown eggs to create live mice offspring. However, even after decades of work, researchers have always struggled with replicating the research with human cells.

The lab-grown human eggs start off life, so to speak, as immature egg cells that were removed from ovarian tissue at their earliest stage of development. Scientists then cultured the immature egg cells in a multi-stage process over a few weeks, sensitively controlling the fine balance of oxygen, hormones, and necessary proteins. This process matured the immature egg cells to the same stage “normal” eggs would be when released from the ovaries.

Because of how much it impairs the ability to breathe, a seemingly simple injury—a broken rib—is the second leading cause of trauma deaths. A team of Penn State surgeons and a biomedical engineer have invented a better way to help broken ribs heal.