A fluidic micromixer comprises a plurality of fluid inlets in communication with a mixing chamber, the plurality of fluid inlets being adapted to introduce into the chamber a corresponding plurality of distinct fluid streams. The mixing chamber comprises at least one surface patterned to define hydrophobic and hydrophilic regions spaced apart along a principal direction of fluid flow within the chamber from the fluid inlets to a fluid outlet, the regions being adapted to induce fluid flow in a direction transverse to the principal direction of fluid flow to mix the fluid streams. At least one of the hydrophobic regions may comprise microstructures patterned on the at least one surface. Also disclosed are a method for fabricating the micromixer, a method of mixing a plurality of fluid streams by vortex mixing or instability mixing, and a system comprising the micromixer, fluid reservoirs and a pump for generating flow of fluids from the reservoirs to the micromixer.