(Georgia Institute of Technology, 2020-07-06)
Morbioli, Giorgio
Microfluidics uses the manipulation of fluids in microchannels to accomplish innumerous goals, and is attractive to analytical chemistry because it can reduce the scale of larger analytical processes. The benefits of the use of microfluidic systems, in comparison with conventional processes, include efficient sample and reagent consumption, low power usage and portability. Most microfluidic applications require a development process based on iterative design and testing of multiple prototype microdevices. Typical microfabrication protocols, however, can require over a week of specialist time in high-maintenance cleanroom facilities, making the iterative process resource-intensive and prohibitive in many locations. Rapid prototyping techniques can alleviate these issues, enabling faster development of microfluidic structures at lower costs. Print-and-peel techniques (PAP), including wax printing and xurography, are low-cost fast-prototyping tools used to create master molds for polydimethylsiloxane (PDMS) miniaturized systems.
In this work, three different methods were created to improve the rapid-prototyping of PDMS-based microfluidic devices. Using the wax printing method, PDMS microdevices can now be fabricated from design to testing in less than 1 hour, at the cost of $0.01 per mold, being one of the fastest and cheapest methods to date. If extensive fluidic manipulation is required, xurography becomes the method of choice. The xurography technique presented here is the most rapid tool to fabricate PDMS-based microdevices to date, presenting turnaround times as fast as 5 minutes. The first hybrid technique that can be used either as a PAP or a scaffolding method is also presented here, using the same materials and fabrication process. The green, low-cost, user-friendly elastomeric (GLUE) rapid prototyping method to fabricate PDMS-based devices uses white glue as the patterning material, and is capable of fabricating multi-height molds in a single step, improving even further the development of PDMS microfluidic devices.
Device fabrication is only one of the steps in the iterative process of designing a fully-functional microfluidic tool. The design of the microdevice itself plays a crucial role in its performance, which directly impacts processes conducted in miniaturized devices. In this work, the influence of hydrodynamic resistance in sample dispersion on a microfluidic multiplexer was studied using paper-based analytical microfluidic devices (µPADs) as the testbed. When microfluidic devices are not rationally designed, and when the influence of fluidic resistance is not taken into account, sample dispersion can be biased. A bias can influence the output of colorimetric enzymatic assays supported on these microstructures, which are the most common applications of µPADs, demonstrating the need for rational design of microdevices.
The third essential component of developing microfluidic devices is their effective testing, especially when incorporating active pumping elements on-chip. To overcome issues in the manual operation or coding for operation of microvalves, a program that can automatically generate sequences for fluidic manipulation in microfluidic processors was written in Python, with the only inputs required from the user being reservoir positions, mixing ratio and the desired input and output reservoirs. To further improve testing and avoid the use of fixed mounts, a modular system was created to aid the testing of devices with different designs, another advance in the area. This research enables better design and testing of microfluidic devices in shorter times and at lower costs, enabling improvements in the interfacing between different unit operations on-chip, a challenge in the microfluidics area. More than that, it also makes this area, traditionally confined into expensive cleanroom facilities, available to more research groups worldwide.