Scientists today revealed they are 'extremely close' to creating artificial embryos after a huge breakthrough. Researchers used mouse stem cells to produce artificial embryo-like structures capable of 'gastrulation' - a key life event. Gastrulation occurs when embryonic cells self-organise themselves into the correct structure for an embryo to form. The breakthrough offers hope of shedding light on one of the biggest causes of infertility - embryos failing to implant in the womb. Biologists have for years tried to create embryos from stem cells in order to create an unlimited supply that could be used for medical research.