Martin Brandenbourger (Univ Amsterdam) - Transport induced by geometrical asymmetries and activity in bio-inspired systems

Ranging from locomotion to signal transfer and including fluid flow, transport is one of the key elements in living systems. While biology has evidenced these mechanisms, fundamental physical models are needed to characterize their origin and quantify their efficiency. Taking inspiration from lymph transport in the lymphatic system, we studied how the combination of geometrical asymmetries and active feedback loops leads to fine tuning of fluid transport. We first devise millimetric scale fluidic channels with asymmetric soft valve leaflets that passively increase (reduce) the channel resistance for forward (backward) flows. Combining experiments, numeric and analytical models, we show that, at low Reynolds, 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 the flow asymmetry is maximal. We then study how strain-based feedback loops control the deformation of active solids and lead to active waves transport. Beyond the lymphatic system, we show that active solids can be used to tilt and power impacts and demonstrate that the central mechanism is thermodynamic deformation cycles induced by non-reciprocal active hinges. Our results open the way to a better understanding of active transport and in particular a better characterization of lymphatic system malfunction and more accurate control of flow orientation and pumping mechanisms in microfluidics and soft robotic systems.