Self-organizing human heart organoids in a dish

Biologist Sasha Mendjan at the Austrian Academy of Sciences in Vienna and his team have used human pluripotent stem cells to grow sesame-seed-sized heart models, called cardioids, that spontaneously self-organize to develop a hollow chamber without the need of experimental scaffolds. This advance, which allows for the creation of some of the most realistic heart organoids to date, appears on May 20th in the journal Cell.

Previously, scientists have built 3D cardiac organoids via tissue engineering, an approach that generally involves assembling cells and scaffolds like building a house out of brick and mortar. But these engineered organoids do not have the same physiological responses to damages as human hearts and thus often fail to serve as good disease models.

"Tissue engineering is very useful for many things like, for example, if you want to do measurements on contraction," says Mendjan. But in nature, the organs aren't built this way. In the embryo, organs develop spontaneously through a process called self-organization. During development, the cellular building blocks interact with each other, moving around and changing shape as an organ's structure emerges and grows.

"Self-organization is how nature makes snowflake crystals or birds behave in a flock. This is difficult to engineer because there seems to be no plan, but still something very ordered and robust comes out," he says. "The self-organization of organs is much more dynamic, and a lot is going on that we do not understand. We think that this 'hidden magic' of development, the stuff we do not yet know about, is the reason why currently diseases are not modeled very well."