(a) Effect of flow rate ratios (1:5, 1:10, and 1:20) of [PLGA stream] to [outer lipid streams] on nanoparticle size with respect to Reynolds number (30, 75, and 150) and PLGA-to-lipid ratios (10, 25, and 50). (b) Effect of PLGA-to-lipid ratios (10, 25, and 50) on nanoparticle size with respect to Reynolds number (30, 75, and 150) and flow rate ratios (1:5, 1:10, and 1:20). Error bars are standard deviations of different nanoparticle batches (n=5). (c) Controllable microvortices in the xy and yz planes. In a flow rate ratio of 1:5, microvortex patterns were not well developed due to relatively higher portion of the central stream in the channel while the vortices were well developed in flow rate ratios of 1:10 and 1:20. Increasing the Reynolds number resulted in clearer microvortex formation while vortex patterns were undeveloped at Re=3 (Figure S5).