Generation of complex concentration profiles by partial diffusive mixing in multi-stream laminar flow

This paper proposes novel microfluidic concentration gradient generator (CGG) devices that are capable of constructing complex profiles of chemical concentrations by laterally combining the constituent profiles (e.g., linear and bell-shaped) generated in simple Y- or ψ-shaped mixers. While the majority of currently existing CGG devices are based on complete mixing of chemical species, our design harnesses partial diffusive mixing in multi-stream laminar flow, and hence, features simple network structures and enhanced device reliability. An iterative simulation approach that incorporates our previous system-level models of CGG networks is developed to locate best-matched combinations of geometrical and operating parameters (e.g., inlet flow rates and inlet sample concentrations) for the device design. Microfluidic CGG chips are fabricated and experimentally characterized using optimal layout and operating conditions selected by the design process. The experimental results not only serve as a benchmark for model verification but also establish the feasibility of concentration gradient generation based on partial mixing for a variety of microfluidic applications.