Dynamics of Complex Fluids in Microfluidic Devices Microfluidic Viscometer We operate the viscometer using two co-flowing miscible laminar streams - one of which is the  test fluid and the other is the reference fluid. By measuring the width of one of the streams and  knowing the flow rates of both streams and viscosity of the reference fluid we are able to extract  the viscosity of the test fluid. We operate the device in two modes - interface displacement and  interface compensation. We also characterize the sensitivity and limits of operation of this  device.            By exploiting the interface displacement technique, we developed a multiplexed version of this  device that allows simultaneous viscosity measurements on four different fluids. We further use  the multiplexed device for investigating the role of channel confinement on the viscosity of red  blood cell suspensions.            Polymer-Induced Elastic Instabilities To be updated.