Synthetic Human Embryo Models Created Without Sperm or Egg

23 June 2025

A recent but major breakthrough in developmental and reproductive biology along with regenerative medicine is the ex vivo generation of synthetic human embryos without the need for a sperm or egg from stem cells long enough for some organs to develop. It represents a revolutionary leap in science that opens up a whole new series of ethical, regulatory, and societal debates. A new world where life is reimagined in a laboratory using advanced stem cell techniques. This seems like something taken off a sci-fi movie but it is now a reality where scientists can study the earliest stages of human development and address some of the most perplexed questions of early life. 

Why Do We Need Synthetic Embryo Models? 

There have been huge limitations in embryological research. Studying natural human embryos comes with its own set of ethical challenges, as does the lack of embryo donation. This drove scientists to create synthetic models to avoid controversies about the need and use of natural embryos to study early human developmental processes. 

Robin Lovell-Badge, the head of stem cell biology and developmental genetics at the Francis Crick Institute in London, said: “The idea is that if you model normal human embryonic development using stem cells, you can gain an awful lot of information about how we begin development, what can go wrong, without having to use early embryos for research.” 

This can be helpful for investigating congenital disorders, miscarriages, and infertility. It can also be used as a platform model for testing the safety of various drugs and medicines during pregnancy, thus reducing the reliance on animal models. The branch of tissue engineering and organoid technologies used in disease modeling and transplantation could also greatly benefit from the acceleration in advances in regenerative medicine. By studying such models, scientists can study how cells organize and differentiate, potentially recreating processes important to human health. 

Background 

Stem cells are unspecialized cells that can develop into more specialized cells, such as skin, blood, or liver cells. There are two basic types of stem cells - those found in the developing embryo, and those found in much smaller numbers in adults. Those from the umbilical cord are hematopoietic (blood-forming) cells, similar to those found in adults, but less mature and more able to develop into other types - hence their value. 

The journey to creating synthetic human embryos began with mouse models. Early studies demonstrated the self-organization of mouse embryonic stem cells into structures that resembled embryos. The idea was taken from here for the advancement of human biology. 

In June 2023, scientists from the Weizmann Institute of Science announced that they had created synthetic human embryos that resembled structures observed at the blastocyst stage, approximately 5 - 7 days after fertilization. A subsequent milestone which was reported in September 2023, described the creation of synthetic embryo models that mimicked embryos at the 14-day post-implantation stage. 

How Have the Scientists Achieved the Result? 

As discussed earlier, the creation of such models was achieved by advanced stem cell engineering by the usage of pluripotent stem cells. The motivation for the work is for scientists to understand the “black box” period of development that is so called because scientists are only allowed to cultivate embryos in the lab up to a legal limit of 14 days. They then pick up the course of development much further along by looking at pregnancy scans and embryos donated for research. The structures do not have a beating heart or the beginnings of a brain but include cells that would typically go on to form the placenta, yolk sac, and the embryo itself. 

Previously, Żernicka-Goetz’s team at the University of Cambridge and the California Institute of Technology and a rival group at the Weizmann Institute in Israel showed that stem cells from mice could be encouraged to self-assemble into early embryo-like structures with an intestinal tract, the beginnings of a brain and a beating heart. Since then, a race has been underway to translate this work into human models, and several teams have been able to replicate the very earliest stages of development.

Ethical and Legal Quagmire 

This exquisite creation has sparked intense ethical debates. While these models are not advanced enough to develop into viable human beings, they do challenge long-standing definitions of life and the boundaries of research.

One of the major concerns is that there are no existing regulations for it whereas the widely accepted 14-day rule applies to natural embryos. There will be a need for a concrete regulatory framework that must adapt as scientists develop more advanced models mimicking the later stages of development. Another concern is the potential misuse of this technology. Questions such as the use of synthetic embryos for cloning or other ethically questionable purposes are vital and need to be addressed. This research has to ensure that it also aligns with societal, religious, and public values and prevents its exploitation. 

Public Perception 

Public reactions to the development of synthetic embryo models have been polarized. For many, it is an exciting prospect to unravel the mysteries of embryo development and cure genetic diseases, while others are concerned and skeptical and think that scientists are “playing God.” 

James Gallagher (2023) speaks about effective science communication to bridge the gap between scientists and the public. By conducting open sessions, seminars, and talks and encouraging open discussions by addressing ethical concerns as transparently as possible, scientists should be able to build trust and ensure that the societal benefits are well understood. 

Future Prospects 

There is also a significant unanswered question on whether these structures, in theory, have the potential to grow into living creatures. The synthetic embryos grown from mouse cells were reported to appear almost identical to natural embryos. But when they were implanted into the wombs of female mice, they did not develop into live animals. In April 2023, researchers in China created synthetic embryos from monkey cells and implanted them into the wombs of adult monkeys, a few of which showed the initial signs of pregnancy but none of which continued to develop beyond a few days. Scientists say it is not clear whether the barrier to more advanced development is merely technical or has a more fundamental biological cause. Thus, more advanced research and thoughtful experiments are needed for better prospects of understanding the early and later developments of our life which will benefit a lot of fields immensely. 

Veeranshi Makdani | Writer, The STEM Review