Microfluidic Mixer Based on Logarithmic Spirals
"Lab-on-chip" technologies promise miniaturized and rapid point-of-care diagnostics. However, technical challenges are myriad as working with fluids and samples on the micro-scale presents many engineering challenges, such as fluid mixing. During my senior year at LSU, I invented a novel micro-fluidic mixer that was easy to construct, compatible with biological samples, and had superior mixing performance relative to other designs of its type.
Here's the publication that was eventually written based on the design.
The Problem
Mixing fluids on a micro-scale is a challenge because there is no turbulence (think stirring milk into coffee). Instead, fluid moves in straight lines (known as laminar flow) and mixing occurs slowly via diffusion processes which is inadequate in any sort of high throughput testing application. To solve this, several micro-mixer designs were explored that attempt in various ways to increase mixing speed, but those introduced other problems such as incompatibility with biological samples and difficult fabrication... and most still left much to be desired in the way of mixing efficiency.
Solution
Taking inspiration from the nautilus, I designed and experimented with numerous logarithmic spiral micro-mixer designs in COMSOL Multiphysics, eventually fabricating several of the designs and testing them using fluorescence microcopy. The logarithmic curvature proved to create asymmetric advantages as an easy to fabricate micromixer that was ideal for biological samples and provided superior mixing efficiency vs. other designs of its kind.
Results
The chart on the left shows relative performance at different Reynolds numbers (Re) which is a ratio of inertial and viscous forces and can be thought of as a measure of the amount of turbulence in a fluid system-- generally in micro-fluidic environments, the higher the Re number, the higher the fluid speed through the micro-system. Relative to other single layer, passive micro-mixers, the SeLMA micromixer outperformed other designs at every range of Re tested, making it compatible for a wide range of micro-system applications.