A superfluity of cancers and genetic diseases can destroy women's ovaries. Or treatments like radiation—used to save a woman's life—can render those egg-producing organs useless. Ovaries also mediate female hormones. Without them, young patients might never go through puberty; grown women could enter menopause early.

Today, a team of bioengineers reported a possible fix: 3-D printed ovaries. Their proof of concept—published in Nature Communications—only works on mice so far, but they could end up replacing the uterus-flanking, chestnut-sized organs in humans, too.

Ovaries are filled follicles—these are immature eggs surrounded by sacs of estrogen and other essential hormones. "The function of the ovary is to shepherd these follicles through maturity into full grown eggs every month," says Teresa Woodruff, a reproductive scientist at Northwestern University's Feinberg School of Medicine, and co-author of the study.