Merging orthogonal microfluidic flows to generate multi-profile concentration gradients

This work describes a novel microfluidic device capable of generating multi-profile gradients that include sigmoidal, parabolic, and exponential concentration variations across its main channel. The main distinguishing feature of this device is its simple geometry: it contains fewer fluidic channels that provide versatility and ease of operation. The narrow orthogonal side channels transport analyte into a wider buffer stream, and by merely altering flow rates of either one or both streams, gradient profiles are switched from one to another. Finite element simulations match well with the experimental results and demonstrate simple manipulation of the generated gradients. Results show that the gradient's slope, extent, and position can be modulated by subtle flow rate variations, making the platform adaptable for various biological applications. The simplicity of the device offers potential for stable chemotactic studies for long durations.