Every scientific model has its strengths and weaknesses. The structures seen here are mammary glands grown in the laboratory from healthy patient cells implanted in a three-dimensional matrix. Notice how the outer ductal structure (green) stems from inner progenitor cells (red) at the root of each branch.

This striking resemblance to mammary glands observed in the human body offers scientists a robust in vitro model for studying how living organs develop. A controlled system like this presents could replace traditional cell culture models currently used in biology labs.