The fleshy blob looks essentially like a human liver, the vital internal organ that—among many functions—aids digestion and filters blood. But it didn’t come from a person. Instead, scientists crafted this mini-liver from human cells, creating the most complex organ of its kind yet grown in a lab.

What’s more, as they report today in the journal Cell Metabolism, the team had a very specific purpose in mind: They wanted to give this liver a disease.

As obesity cases rise, so does the occurrence of non-alcoholic fatty liver disease, in which fats collect in liver cells and can eventually lead to organ failure. In the United States alone, some 80 to 100 million people are currently affected, but how