Advanced Components of Microfluidic Systems for Bioanalytical Applications.

Abstract

The need for detailed understanding of fundamental and advanced components towards the widespread use of microfluidic systems are addressed in this dissertation. First, to understand mixing in microfluidic lab-on-a-chip systems, discrete droplet mixing in microchannels was examined using mathematical modeling, simulations, and experiments. The microfluidic mixing occurs in three distinct regimes (diffusion-dominated, dispersion-dominated, and convection-dominated) depending on the Péclet number and the droplet dimensions. Using mathematically developed asymptotic curves, it was possible to predict the mixing time and required channel distance for any Péclet numbers. The mixing of typical drops (~3000um long) in microchannels (100~500um) resulted in mixing times of 0.001~10000 seconds depending on the drop velocity. Simulations and experiments of the mixing of two discrete drops agreed well with the theoretical limits. Second, novel microfluidic components for discrete drop mixing and routing in lab-on-a-chip systems have been developed. The membranous air bypass valve (MBV) in PDMS allows air to pass through but stops liquid. Using two-dimensional and three-dimensional MBVs, the trapped air between discrete drops was rapidly removed at the aspiration rate of ~65nL/s. MBVs with semicircular membranes could also act as fluidic diodes that allow only unidirectional flow at operating pressures of 12~24kPa. Complex drop routing was possible with multiple fluidic diodes embedded. Third, a user-friendly device construction methodology using prefabrication of microfluidic assembly blocks in PDMS was introduced to allow users to build custom microfluidic systems without any fabrication expertise. Complete sealing was done by applying adhesive materials such as the PDMS curing agent and UV-curable glues between blocks. Using the square blocks of the size of 16mm2, we demonstrated common microfluidic applications including laminar flow development, valve control, and cell culturing. Finally, digital pneumatic microprocessors have been developed as universal on-chip control platforms to multiplex a single pneumatic input. Logic components such as AND, NOR, flip-flops, and shift-registers were constructed and linked to compute, store, and parallelize serially-encoded input signals. The resulting parallel outputs were used to control multiple valves, pumps, channels, and chambers, independently. By significantly reducing the need for external controllers, digital pneumatic microprocessors could facilitate the widespread use of microfluidic systems.