Just as the fetus is surrounded by the amniotic liquid inside the mom's uterus, the plastic bag-like womb is filled with a liquid which has the same physiological properties as its biological counterpart.
An important part of this incubator, or extra-uterine support device, is the ability to sustain infants without using a ventilator, which can strain their underdeveloped lungs or cause scarring that leads to chronic lung disease.
To test the artificial womb, the premature lambs were delivered by C-section and immediately put into a temperature-controlled bag that was filled with a substitute for the amniotic fluid that they need to swallow and take into their lungs for properly developing them.
Designer of the flow apparatus, Marcus Davey (also from CHOP) explains: "Fetal lungs are created to function in fluid, and we simulate that environment here, allowing the lungs and other organs to develop, while supplying nutrients and growth factors".
The lambs remained in the "womb" for up to a month. Based on the results, which have been called "heroic and monumental" by other physicians, Children's Hospital researchers say that a version of the Biobag may be available to try on human preemies within three years.
In the not-so-distant future, researchers believe that this technology when developed holds great promise for premature human babies born at or before 25 weeks.
The study was in Nature Communications.
Associate professor David Tingay, a neonatal researcher at Murdoch Childrens Research Institute, said people had been trying to create an artificial womb for more than 50 years and this model was the most promising yet. Baby lambs developed to the age equivalent of 23-week-old human babies.
Rather, it is meant to function as a bridge between the mother's womb and the outside world, supporting the infant from 23 weeks to 28 weeks of gestational age, after which time the effects of prematurity are minimal.
The system was comprised of a few main factors to support stable development: a circulatory system, a closed fluid environment and use of the fetus' own heart to pump blood around the system - not an external pump.
Before too long, the same technologies could be used on humans.
One of the biggest risks for premature babies is that their lungs aren't ready to breathe air.
The artificial womb or the biobag helped the lamb develop some of its organs.
"We know that even a few hours of that [current technology] damages the lungs of a 24-week infant", says Dr. George Mychaliska, a pediatric and fetal surgeon at C.S. Mott Children's Hospital.
The artificial womb study has been fast tracked by the US Food and Drug Administration and the researchers are now undertaking further animal trials, which they hope to complete within two years, "then move on to first in human use within three to four years", Dr Davey said. "This could establish a new standard of care for this subset of extremely premature infants".