A millisecond passive micromixer with low flow rate, low sample consumption and easy fabrication

Area of Science:

• Microfluidics
• Chemical Engineering
• Biotechnology

Background:

• Efficient mixing of small volumes is crucial for microfluidic applications in biological and chemical studies.
• Low Reynolds numbers (Re < 100) in microfluidic devices typically hinder effective mixing.
• Existing methods for complex mixing structures often rely on additive manufacturing, which can be costly and time-consuming.

Purpose of the Study:

• To develop and validate a novel microfluidic mixer design for enhanced mixing efficiency at low flow rates.
• To optimize mixer geometry using "staggered herringbone" (SHB) patterns and "split-recombination" strategies.
• To demonstrate a cost-effective fabrication method for microfluidic mixers.

Main Methods:

• Computational fluid dynamics (CFD) simulations using COMSOL Multiphysics to optimize mixer geometry and predict performance.
• Experimental validation of the most promising mixer design through visualization.
• Fabrication of microfluidic devices using standard soft-lithography techniques.

Main Results:

• The optimized SHB mixer design achieved approximately 98% mixing efficiency within the millisecond timescale (4.5-78 ms).
• Effective mixing was demonstrated at very low flow rates (1-12 µL·min⁻¹) and low Reynolds numbers (3.3-40).
• The mixer operates with a small working volume of approximately 3 nL and moderate pressure drops.

Conclusions:

• The novel microfluidic mixer effectively enhances mixing through controlled vortex generation and lamellar structure formation.
• Soft-lithography fabrication offers a more accessible alternative to additive manufacturing for complex microfluidic mixers.
• This technology minimizes sample consumption, making it suitable for precious sample analysis in various scientific fields.