  In Nature, liquids often circulate in channels textured with leaflets, cilia
or porous walls that deform with the flow. These soft structures are optimized
to passively control flows and inspire the design of novel microfluidic and
soft robotic devices. Yet so far the relationship between the geometry of the
soft structures and the properties of the flow remains poorly understood. Here,
taking inspiration from the lymphatic system, we devise millimetric scale
fluidic channels with asymmetric soft leaflets that passively increase (reduce)
the channel resistance for forward (backward) flows. Combining experiments,
numerics and analytical theory, we show that tuning the geometry of the
leaflets controls the flow properties of the channel through an interplay
between asymmetry and nonlinearity. In particular, we find the conditions for
which flow asymmetry is maximal. Our results open the way to a better
characterization of biological leaflet malformations and to more accurate
control of flow orientation and pumping mechanisms for microfluidics and soft
robotic systems.
