Figure 2.

Microhexagon array for gradient generation. (A) Optimization of the microhexagon dimensions. To improve the microHIVE platform's lateral resolution for gradient generation, through numerical simulation, we varied the lengths of the microhexagons while keeping constant the inter-structure spacing and the final divergent length of the culture chamber. The performance of the microhexagon arrays were also compared against that of a conventional “Christmas-tree” serpentine mixer, designed to occupy the same device footprint as the microHIVE platform. Lateral resolution was defined as the lateral length of the culture chamber, normalized by the number of branched channel openings into the chamber. (B) Effects of repeated fluid branching and mixing at recurring junctions on the platform's mixing efficiency. Numerical simulations were performed to investigate the effects of microhexagon dimensions, as well as the number of recurrent junctions, on fluidic branching and mixing, so as to decrease striation length and improve fluid diffusion per microhexagon unit. (C) Versatile and accurate generation of complex gradients. By varying the respective positions, concentrations and flow rates at the three inlets, we designed and implemented representative gradient profiles on the microHIVE platform. Numerical simulations (top) were first performed to determine the shapes and slopes of the profiles. This was followed by experimental validation using colored dyes (middle). Quantitative correlation of the simulated and experimental profiles (bottom) illustrated the smoothness and accuracy of the generated gradients.