Surface tension-controlled three-dimensional water molds: Theory and applications

This paper presents a lab-on-a-chip development method that applies the Young-Laplace equation to design the geometries of a patterned water droplet, and then using the droplet as a mold to fabricate three-dimensional polydimethylsiloxane (PDMS) channels. We demonstrate the method by designing and fabricating an on-chip funnel. We then subsequently trap beads of graded diameter in the tapered section of the funnel to make on-chip filters of controllable pore size. After packing the funnel with beads, the cutoff pore size of the fabricated filter agrees closely with our estimate. This approach provides a straight-forward, low-cost, yet powerful way to design and fabricate microfluidic devices with 3D features.