Advanced Microfluidic Concentration Gradient Generator Platform with Controlled Shear Stress.

Understanding concentration dynamics is critical to advancing biological research and drug screening applications. Microfluidic concentration gradient generator (µCGG) technologies allow for the precise spatial and temporal control of concentration gradients in microfluidic environments. The challenge of managing shear stress while maintaining consistent concentration profiles remains significant. This study presents a two-input µCGG architecture that combines hydraulic-resistance-guided distribution with sequential dosing of a concentrated stream. This approach differs from traditional µCGG systems by using a unique configuration where concentrated fluid is introduced through designated channels and then merged in mixing channels. This sequential addition enables the formation of concentration gradients ranging from nearly pure diluent to highly concentrated solutions. The range of the concentration gradient is determined by the differential flow rates in the distribution channels, which are influenced by variations in hydraulic resistance, resulting in a linear concentration gradient from 0% of the concentrated fluid to 90% that in 10% increments. To optimize performance, flow rates and channel dimensions were precisely measured, after which rigorous simulations were conducted. The µCGG design was validated through CFD simulations and dye-based experimental measurements. To this end, the experimental measurements confirmed its ability to generate stable concentration gradients with values of 0, 8, 22, 40, 45, 60, 65, 80, and 82% of the concentrated fluid at each section.