Some of the best engineers and inventors are copycats. They look at how the natural world solves complex problems and use those mechanisms as the basis for innovations. But Mother Nature doesn’t always give up her secrets easily.

One of those secrets is how heart valves and other biological valves work. They keep fluids moving in one direction while preventing backflow, all without needing any active motors or powered controls to drive them. To find out how, Mengfei He of Harvard University and colleagues studied pig mitral valves.

They wanted to set up a system to see how the valve leaflets, the thin flaps of tissue that act as doors, react when fluid pushes back against them.