A mouse with 3D-printed ovaries has successfully given birth to healthy pups, according to a new study. Researchers hope that one day we can use similar techniques to help women who struggle with fertility.

For the study, published today in the journal Nature Communications, the team replaced a mouse’s ovaries with 3D-printed ones. These 3D-printed ovaries held ovarian follicles, or fluid-filled sacs that hold immature eggs. The new ovaries supported the follicles and eggs long enough for the mouse to ovulate, conceive, and give birth. (The study was done by the same Northwestern University team that earlier built a tiny reproductive system in a dish.)

The key to success is the structure of the material used for 3D printing. It has to be made out of organic materials that the body won’t reject, but it also can’t be too soft because then it’ll fall apart during surgery and transplantation. Previous attempts to 3D print ovaries used a substance that is mostly water, which makes it unstable. The Northwestern team used a jelly-like substance called collagen instead. The gelatin was built in multiple layers that made it sturdy, and so it didn’t collapse.

Unfortunately, similar 3D-printed ovaries can’t be directly used in humans. Human follicles are much bigger than mice’s, and they grow so quickly that the shape of this existing ovary would need to be changed. There might be problems with implantation, too. Still, this is an advance in regenerative medicine that could bring us closer to solving infertility problems in women in the future.