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Artificial Mouse Embryos

Author: Isabel Zhang

From: Chicago, IL, US

By A. Aguilera-Castrejon Et Al., Nature 2021


The mouse embryos looked absolutely ordinary. Their organs, limbs, and circulatory and nervous were developing as expected. They had a normal heartbeat of 170 beats per minute.

But wait... these embryos were not growing inside their mother’s womb! Instead, they were growing inside an artificial uterus at the Weizmann Institute of Science in Israel.

Sounds like some kind of supernatural science fiction movie, right? How is it possible?

How The Researchers Did It

Previously, researchers fertilized eggs from mammals in the laboratory and were only able to grow them for a short time. Embryos from placental mammals needed a living womb. This prevented scientists from answering fundamental questions about the earliest stages of development.

As Dr. Paul Tesar from the Case Western Reserve University School of Medicine puts it, “The holy grail of developmental biology is to understand how a single cell, a fertilized egg, can make all of the specific cell types in the human body and grow into 40 trillion cells. Since the beginning of time, researchers have been trying to develop ways to answer this question.”

Researchers needed a way to see inside the uterus— to watch and tweak the development of tissues and organs in mammals as it happened.

To get there, Dr. Jacob Hanna, a developmental biologist at the Weizmann Institute of Science, spent seven years developing an artificial uterus that includes incubators, nutrients and a ventilation system. Mouse embryos are placed in glass vials inside incubators, where they float in a special nutrient fluid. The vials are attached to a slowly-spinning wheel so the embryos don’t attach to the walls, where they would deform and die. The incubators are connected to a ventilation machine that provides oxygen and carbon dioxide to the embryos, controlling the gas concentrations, gas pressure, and flow rate.

Dr. Hanna and his research team removed embryos from the uteruses of mice at five days of gestation (development) and grew them for six more days within this artificial uterus. It was a record for the development of a mammal outside a womb!

Days later on Day 11 of gestation (more than halfway through a mouse pregnancy), Dr. Hanna and his team examined the embryos, comparing them to those developing in the uteruses of living mice. The results: the lab embryos were identical!

New Possibilities/Next Steps

The success of these experiments is promising. According to Magdalena Zernicka-Goetz, professor of biology and biological engineering at Caltech, the ability to keep embryos alive and developing halfway through pregnancy “opens the door to a new age of studying development in the experimental mouse model”.

Hanna said his research will advance understanding of organ formation in mammals. It could facilitate medical advances, since it allows unprecedented views of the process unfolding which was previously constrained by the need to image the uterus inside. With this new development, researchers may be able to watch individual cells migrate to their ultimate destinations.

In addition, the artificial womb may allow researchers to learn more about pregnancy failures, like why some pregnancies end in miscarriages or why fertilized eggs fail to implant. Scientists will be able to study how gene mutations or deletions affect fetal development.

Furthermore, if scientists could make embryos without fertilizing eggs and study their development without a uterus, they could avoid embryo destruction. They wouldn’t need to fertilize mouse eggs, only to end up destroying them in the course of study.

Conclusion: The Ethical Questions

Despite how revolutionary this work is, it may one day raise questions about whether other animals, even humans, should or could be cultured outside a living womb. Indeed— there have been reports on attempts that edge near creating human embryos through the artificial womb.

According to researchers though, creation of human embryos is years away. For now, scientists refrain from studying human embryos beyond 14 days of fertilization.

Still, it may not be unreasonable to say we may one day have the capacity to develop a human embryo from fertilization to birth, all completely outside the uterus. This science fiction scenario can certainly be terrifying. Again, it is early, and we have no assurance that human fetuses could ever develop entirely outside the womb. If we assume they could, whether or not it is appropriate becomes a question for ethicists, regulators, and society.

Thus, the artificial womb breakthrough remains a complex case for now.


About the Author: Isabel Zhang

Isabel is a senior in high school, and is interested in biology and engineering. In her free time, she loves to bake, sketch, and hang out with her family.



  1. Kolata, G. (2021, March 17). Scientists Grow Mouse Embryos in a Mechanical Womb. Retrieved from®i_id&segment_id=53661&te=1&user_id=aedc27282f3db6e26bd2752510a9b548

  2. Regalado, A. (2021, March 18). A mouse embryo has been grown in an artificial womb-humans could be next. Retrieved from

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