This study proposes a new design of millior micro-mixers based on the split-intersect-recombine principle. The vascular flow topology mimics the respiratory or circulatory architectures existing in nature, including tree-like bifurcated networks and meshed flow circuit. Special focus is given to the enhancement of mixing performance by fluid collisions and flow deviations at the intersections of the meshed circuit. To do that, an optical tracer is added in one of the fluids to be mixed and its progression is monitored and recorded by a high-definition CCD camera. The mixing efficiency of the meshed circuit is then characterized by the evolution of the tracer's local concentration profiles based on the Beer-Lambert absorption. Experimental results obtained show that compared to straight channels, the mixing performance can be improved by about 20% owing to the numerous flow intersections in the meshed circuit. Moreover, the viscosity difference between two fluids to be mixed has a positive effect on the mixing performance by augmenting the chance of flow deviation from one stream into another at the crossroads. An optimum performance can be noticed in the form of a plateau of the estimated shear stress. (c) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.