Artificial Wombs

Liu, 63, is a short woman with full cheeks, a rounded middle and smooth, unlined
skin who bustles along the corridors of her lab like a cartoon teapot. She is, by any measure, maternal, with two grown sons. Twenty-one years ago, Liu, then an assistant professor, joined the first team in the U.S. to have produced a test-tube baby. Now she and her partners can boast an enviable success rate. In the past several years, about 40 percent of the couples that came to her group conceived, and in 2004, the center’s 10,000th IVF baby was born.

Her artificial-womb work was a natural outgrowth of the IVF efforts and is motivated by the same ache. “I see so many women who want their own baby so badly,” she says. Among them are women whose embryos have failed to take hold and grow and who might benefit from her current research.

Liu’s artificial womb is a surprisingly simple construction. She created it after researching the making of artificial skin and adapting those methods. First she and her co-workers mold a base, a womb-shaped matrix of collagen and chondroitin, substances that are biodegradable. Over time, they dissolve, leaving only the endometrial tissue that is placed over the matrix. Each womb is shaped like a section of the mammalian version it mimics: The artificial human mold is bowl-shaped; the faux mouse womb is a doughnut-shaped section of a mouse’s tubular uterus.

In the beginning, Liu used endometrial cells donated by some of the clinic’s female patients to grow human tissue. Then she added human embryos left over from IVF treatments, donated by other patients. These zygotes implanted and started to grow. But after they had gestated for 10 days, Liu ended the experiments, well short of viability. Under current federal regulations, two weeks is the limit for human fetal growth in the lab. “So we switched to an animal model,” Liu says with a shrug. In 2002 she and her colleagues started making mouse wombs and growing mouse embryos inside them.

In outline, the gestation process seems straightforward. Sperm and egg meet. An embryo implants. Between them, mother and baby build a placenta and an amniotic sac. Fluid builds up around the growing embryo. Hormones move in and out. Nutrition, blood and oxygen pass through the placenta. Waste products are removed. There’s a gentle hum of maternal heartbeat and digestion. It’s like a well-modulated, high-end aquarium.

Except, of course, that it’s not. The actual sequence of events is exceedingly intricate. Miss one minor step, delete a gene expression, add a dribble too much or too little of a single hormone, and you’ll wind up with a baby who is dead or monstrous or, in what may be a blessing, both.