Apparatuses and methods for generating a chemical gradient within a flow channel include providing at least one bubble support structure within the flow channel. A bubble support structure helps maintain a bubble at a predetermined location in flow channel when a fluid flow passes therethrough. Oscillations are induced in the bubble using acoustic waves, which may be provided by a piezoelectric transducer located proximate the flow channel. Two or more inlets provide fluids of different chemical compositions into the flow channel, and bubble oscillations are used to generate a dynamically controllable mixing process.