Professor Magdalena Zernicka-Goetz, from the University of Cambridge and California Institute of Technology, described fostering the embryos to a stage just beyond the equivalent of 14 days of development for a natural embryo at the International Society for Stem Cell Research’s annual meeting in Boston on Wednesday.

The structures do not require eggs or sperm, do not have a beating heart or beginnings of a brain but contain cells that would typically develop to form the placenta, yolk sac and the embryo itself, according to the Guardian.

It remains unknown whether the synthetic models could develop into viable embryos if implanted.

The details are yet to be published in a journal paper, The Guardian said.