Life truly is a miracle at every step of the process, all the way from conception to birth. One of the coolest aspects is how, out of a clump of indistinguishable stem cells, a living thing complete with hair and skin and organs is formed. The stem cells begin to “specialize” to form their respective components, but for years science has searched for the catalyst in humans (the process has been understood in other animals). Now, it appears that researchers from Rockefeller University have cracked the code: In a laboratory setting ,the missing component wasn’t chemical, but geometric. Confine the stem cells properly, and they organize on their own.

“Understanding what happens in this moment, when individual members of this mass of embryonic stem cells begin to specialize for the very first time and organize themselves into layers, will be a key to harnessing the promise of regenerative medicine,” says lead researcher Ali Brivanlou. “It brings us closer to the possibility of replacement organs grown in petri dishes and wounds that can be swiftly healed.”

Inside the womb, embryonic stem cells receive chemical prompts from surrounding tissue to begin layers based on their respective functions, a process called gastrulation. Cells in the center begin to form ectoderm, the brain and skin of the embryo, while those migrating to the outside become mesoderm and endoderm, destined to become muscle and blood and many of the major organs, respectively. Scientists knew how to replicate the chemical signals, but were still unable to produce gastrulation.

The trick was some creative geometry. Using special treated glass plates with tiny, circular “micropatterns,” the scientists were able to confine colonies of embryonic stem cells and prevent them from spreading freely. Once this happened, confined colonies receiving chemical treatment began to form layers and organize just as they would naturally – those that were unconfined did not.

“At the fundamental level, what we have developed is a new model to explore how human embryonic stem cells first differentiate into separate populations with a very reproducible spatial order just as in an embryo,” says postdoc Aryeh Warmflash. “We can now follow individual cells in real time in order to find out what makes them specialize, and we can begin to ask questions about the underlying genetics of this process.”

The team hopes that in the future, tweaking the geometry will allow for faster, more specialized stem cell development, with immense medical potential.