Capillary Flow Dynamics in 3D Printed, Open Microchannels

Three-dimensional (3D) printing is a potentially valuable tool for micro-scale manufacturing processes due to its relative speed and low cost as well as the high degree of part customization that it affords its users. Microchannels are an important component of many micro-manufactured parts, including microfluidic devices and micromolds. In this work, we investigate open microchannels printed with two different 3D printing technologies: fused deposition modeling (FDM) with a Stratasys Dimension printer and stereolithography (SLA) with a FormLabs Form 1+ printer. First, the ability of these two technologies to print open microchannels is assessed, both with respect to minimum printable feature size and dimensional accuracy. Microchannels as small as 250 µm x 250 µm (width x height) were printed using both FDM and SLA. Second, the flow dynamics of liquid traveling through these microchannels is investigated over timescales spanning five orders of magnitude, from milliseconds to hundreds of seconds, using high speed optical microscopy. The surface roughness characteristic of many 3D printing processes (including FDM and SLA) is found to cause local pinning of the contact line during capillary flow, leading to inhomogeneous wetting and a reduction in the capillary pressure driving the flow. Flow dynamics are evaluated with respect to print technology, print orientation, channel dimensions, and the properties of the liquid. Based on these results, specific recommendations are made for designing 3D printed microchannels for flow. 3D printing is shown to be appropriate and convenient in many scenarios for rapidly manufacturing viable microchannels.