Flow-based manipulation of particles is used for studying soft materials. Historically, flow-based manipulations have relied nearly exclusively on two-dimensional flows generated in planar microfluidic geometries. Hung Nguyen, a Materials Science and Engineering PhD student in the Schroeder Group at the University of Illinois at Urbana Champaign, was looking for a way to demonstrate three-dimensional flow fields using automated flow control.
Looking for a Solution
Flow-based trappings have previously relied on 2D flow fields due to limitations in the layer-by-layer assembly technique used in soft lithography. Manufacturing microfluidic devices capable of generating 3D flows was challenging. Nguyen initially manufactured his microfluidic device using a SLA 3D printer. The smallest achievable channel using SLA was 500µm x 500µm with significant surface roughness making it difficult to perform single molecule experiments.
Next, Nguyen used 2 Photon Polymerization (2PP). While the 2PP printer was able to manufacture the part he was looking for, the process was costly and time consuming due to the size needed for the microfluidic device to interface with the other hardware systems in the lab.
Using PµSL Technology to Create 3D Flow Fields
After SLA and 2PP didn’t work, Nguyen turned to using Projection Micro Stereolithography (PµSL) technology. Using the microArch S240 the team was able to achieve the resolution, precision, and accuracy necessary for single molecule study at a manageable time scale and cost, allowing Nguyen to prototype their parts multiple times in a short time scale without having to sacrifice resolution and accuracy. After a few rounds of prototyping, the team created a microfluidic device with six 300 x 300 µm channels that converge at a cross-slot.
In the experimental set-up, Nguyen can generate 3D flows inside of the cross-slot. An open channel in the device allows the team to observe the flow inside the cross-slot under a microscope.
“Overall, saying that we are happy with the results would be an understatement. We have checked the printed parts with CT scans and the precision and resolution of the part is exactly as we designed it within ±0.010mm tolerance. We also performed initial testing of the parts “in flow” and confirmed that the geometry of the device and the generated flow topography were nominal. The surface finish was better than any 3D printed parts we have seen using FDM, SLA, or SLS technologies.”– Hung Nguyen, Material Science and Engineering PhD student
Future Uses
The ability to demonstrated 3D flow fields will open up flow-based manipulation to many more applications including the study of how blood cells flow, how polymers stretch in pipes, and more.
