Advancing microfluidics using softness

Microfluidics devices are typically made from soft elastomer but the influence of softness is often overlooked. Increasingly, this softness is being exploited in applications ranging from passive microfluidics to fundamental studies of biological network flows. Behaviours of these systems is underpinned by fundamental fluid-structure interaction, which can be tuned by integrating appropriate deformable components into a microfluidic device. Here we consider two examples of devices formed of rigid channels with elastic boundaries. In the first, the soft boundary is a thick slab of elastomer embedded into a rigid enclosure which deforms non-uniformly in response to the fluid pressure, resulting in a bulge near the channel outlet. For high enough flow rates, the bulge constricts the channel and can interrupt the flow, a useful phenomenon for the design of passive flow limiters. In the second, shape-morphing channels are achieved by swelling a thin elastic membrane. Having such membranes as the deformable wall also permits the flow resistance of the channel network to be adjusted rapidly in response to an applied fluid pressure.