In a significant development for the field of biology, scientists have reported creating artificial human embryos, or "embryo mimics", that emulate real embryos up to 14 days old, using various types of human stem cells, including some that were genetically modified. These models can aid in the understanding of early human growth which has long remained elusive to study.

The details of the groundbreaking research were first unveiled by developmental biologist Magdalena Zernicka-Goetz during the International Society for Stem Cell Research (ISSCR) conference. Other experts in the field, such as developmental biologist Jesse Veenvliet, were quick to express their admiration for the closely resembling embryo models developed by stem cell biologist Jacob Hanna's lab.

These embryo analogs have the potential to shed light on congenital abnormalities, aid in the understanding of drug safety during pregnancy, and elucidate early human growth. However, they also spark ethical dilemmas, as they are exempt from the UK law that restricts research on donated in-vitro fertilization (IVF) embryos that are older than 14 days, due to being formed from human stem cells rather than eggs and sperm.

Previously, researchers had been successful in using human stem cells to develop structures that emulate the blastocyst stage of an embryo, which implants in the womb around five days post-fertilization. Yet these pseudo-blastocysts could not progress beyond this stage, limiting research into later developmental phases. Hanna's team, employing cultured cell lines from early human embryos and adult cells converted into stem cells, used their own and others' developed cell culture media to guide their stem cells into differentiating into cell lineages found in a genuine embryo. The resulting cell clusters exhibited characteristics of post-blastocyst embryos.

Zernicka-Goetz's team took a unique approach, using genetically modified human embryonic stem cells, exposed to the antibiotic doxycycline, to generate extraembryonic cell lineages. These were combined with unmodified human embryonic stem cells, yielding embryo-like clusters.

Meanwhile, two other research teams also reported creating models that mimic post-implantation embryos. One was from the University of Pittsburgh, using genetically modified induced pluripotent stem cells to form cell clusters they call "iDiscoids", and another from a Chinese team at Kunming University of Science and Technology, creating "E-assembloids" by combining human embryonic stem cells and extraembryonic cells.

As the field moves forward, researchers aim to enhance their methodologies to create even more realistic embryo stand-ins. This progress brings with it the necessity of revisiting and possibly redefining the ethical boundaries around such models.