Microfluidic Mixer Combines Fluids without Backflow to Make Advanced Portable Diagnostics Practical

Lab on a chip devices are designed to perform advanced diagnostics and drug testing using small samples of blood and other body fluids. We’ve written about many such devices, including for assessing the effectiveness of chemo and for picking out circulating tumor cells, but microfluidic technologies that rely on capillary or vacuum powered techniques have had the same consistent problem: backflows are created when different fluids, such as blood and a reagent, are combined within a microfluidic interfaces. The pressure differences between the fluids causes the mixture to travel in the wrong direction, making it difficult to create practically useful microfluidic diagnostic tools.

Researchers at the University of Buffalo have now developed a technology, described in the latest issue of journal Lab on a Chip, that prevents such backflows and liberates much of the field of microfluidics for clinical use. Their “micromixing” device uses both capillary and vacuum power to combine two liquids, whether they have similar or different viscosity, without producing any backflow. The device can now be used as a component within larger, more complicated microfluidic devices to combine liquids efficiently and consistently.

Here’s a bit of detail of how device works, according to the study’s abstract:

A capillary-driven pressure balancing bypass connected between two inlet ports diminished the initial pressure difference caused by capillarity and gravity present in each liquid at the two inlet ports. Then, using manual syringe-assisted vacuum-driven pumping that operated based on the high gas permeability of polydimethylsiloxane, the two pre-balanced liquid streams could synchronously enter a dead-end micromixing channel without any backflow.