We conclude that this plug-based microfluidic platform is capable of accommodating viscous fluids, although several questions remain to be addressed. We used the viscosity of the non-viscous phase to calculate threshold values of Ca for flows of fluids with contrasting viscosities. In this case,
threshold values of Ca are lower than those of a flow of fluids with matched viscosity. When we used the viscosity of the viscous phase, the threshold values were higher than those for a flow of fluids with matched viscosity. Therefore,it is important to establish how to average these viscosities
to obtain threshold values of Ca that are consistent for all combinations of fluids