Generation of Linear and Parabolic Concentration Gradients by Using a Christmas Tree-Shaped Microfluidic Network

This paper describes a simple method of generating concentration gradients with linear and parabolic profiles by using a Christmas tree-shaped microfluidic network. The microfluidic gradient generator consists of two parts: a Christmas tree-shaped network for gradient generation and a broad microchannel for detection. A two-dimensional model was built to analyze the flow field and the mass transfer in the microfluidic network. The simulating results show that a series of linear and parabolic gradient profiles were generated via adjusting relative flow rate ratios of the two source solutions (R_L² ≥0.995 and R_P² ≥0.999), which could match well with the experimental results (R_L² ≥0.987 and R_P² ≥0.996). The proposed method is promising for the generation of linear and parabolic concentration gradient profiles, with the potential in chemical and biological applications such as combinatorial chemistry synthesis, stem cell differentiation or cytotoxicity assays.