User:Granto uw/peerreviewdraft

Journal Title: SHORT COMMUNICATION

Microfluidic sorting of droplets by size

Yung-Chieh Tan; Yao Li Ho; Abraham Phillip Lee

This article introduces a method by which droplets of a small size can be sorted automatically based on their size. The authors created microfluidic devices that created droplets with a distribution of sizes which were then introduced into a bifurcating junction that led to two outlets creating two different flows. The flow rate ratio of the two outlets (V and Z) was varied and depending on the ratio of the flows and their force exerted on the droplet of a radius r the droplets would be directed to one of the two outlets.This paper does a good job outlining the method by which the criteria for droplet separation at the junction are calculated, opening up the possibility for further design iterations to suit the needs of the analyst. The authors were able to achieve sorting of droplets with two configurations, achieving at best droplet size selection precision of 4 μm. I believe that this paper is worth citing in my Wikipedia page on microfluidic droplet sorting since it deals with one of the main aspects of droplets. It will need to be framed appropriately as not to oversell the capabilities of the method.

Revisions to the paper/ questions to the author:


 * 1) It is mentioned that in Σψ design the actual shear ratio is less than the calculated shear ratio. How were the shear ratios confirmed to be accurate throughout the different designs?
 * 2) The experiments presented only deal with 4 different flow rate ratios and 3 different schematic designs. I think it would be beneficial to explain what changes to these parameters, flow rate ratio, schematic fine adjustments, have on the sorting capabilities of the design.
 * 3) Is it possible to force droplet sorting into the V channel in Σβ by decreasing the flow rate ratio further? Will the shear rate ratio predict this accurately?
 * 4) Have you considered any method to increase the sorting precision of the devices? In device Σα the authors mention that the sorting precision was around 14 μm. Can this be confirmed? If so what change in parameters can help decrease this number?
 * 5) In future work this would be great to see applied as a sorting device incorporated into a microfluidic device, allowing for an opportunity to test the robustness of the design.

Minor Revisions:


 * 1) It doesn't seem well defined what the lines are representing in the figures 2d, 3d, 4d. It took some time to realize that they are the plotted shear rate ratios. This could be explained in the figure captions.
 * 2) It could be explained what the fate of droplets between the two cutoff sizes were for sorting. Were they sorted into both channels? Is there a distribution of the sizes between the two channels?

References