Microfluidic model of micro-haemodynamics in complex porous media*

The human placenta relies on well-orchestrated haemodynamics to deliver its multiple functions. Its geometrical complexity and lack of appropriate animal models mean that laboratory models offer a powerful tool to investigate haemodynamics and haemorheology in the human placenta and other complex biological tissues. We develop a model of RBCs with polydimethylsiloxane (PDMS) capsules of adjustable diameter and membrane thickness, which are microfabricated using a 3D nested glass capillary device. The elastic modulus of the membrane can be varied by an order of magnitude by adjusting the chemistry and the capsules are further deflated by osmosis to match the surface-area-to-volume ratio of real RBCs. We test the aptitude of these capsules to mimic the motion and large deformations of single RBC and of suspensions of RBCs in straight capillaries and arrays of contractions and expansions. Planar porous media of controlled geometry, porosity and different levels of disorder are then constructed by positioning cylindrical pillars in different spatial arrangements within a Hele-Shaw cell. Capsule suspension flows in porous media are then characterised in terms of the dynamic distribution and flow resistance as functions of haematocrit, disorder of the medium and capillary number.