Elastocapillary flow driven blood-plasma separation.

We report a lab-on-a-membrane device which can separate plasma from whole blood due to a combined effect of capillary flow and sedimentation of blood cells. The initial length of the polydimethylsiloxane (PDMS) membrane is made hydrophilic by exposing to oxygen plasma and it is stuck to the PDMS substrate forming a 90\textdegree wedge. As the dispensed whole blood comes in contact with the membrane, force due to surface tension deflects the membrane and the consequent evolution of blood meniscus results in a Laplace pressure drop that drives the flow. The high velocity gained in the hydrophilic region is sufficient to drive the flow in to the hydrophobic region. As the flow advances, sedimentation of blood cells occurs along the length resulting in cell free layer of plasma. The geometry of the membrane and the hydrophilic length are adjusted such that the time scale required for sedimentation of blood cells is smaller than the flow time scale. As a proof of concept, a detection strip is embedded with the device to detect the level of glucose present in blood plasma.