Acoustic Concepts in Micro-Scale Flow Control and Advances in Modular Microfluidic Construction.

Abstract

Despite thirty years of research, the full scientific and social impact of microfluidics has not been realized. This dissertation focuses on addressing two key issues to accelerate this realization: micro-scale flow control and microfluidic device construction. We introduce the design of a new acoustic-based mechanism for multiplexed pressure- driven flow control. The device we have developed converts the frequency content of an acoustic signal into four individually addressable pressure outputs, tunable over a range 0-200 Pa with a control resolution of 10 Pa. The pressure generating components of the device consist of a bank of four resonance cavities (404, 484, 532, and 654 Hz), each with an attached rectification structure. We demonstrate how this scheme can be used for programmatic operation of both droplet-based and continuous-flow microfluidic systems using only a single control line. We then explore an alternative acoustic actuation scheme involving frequency dependent attenuation within finite phononic crystals. Specifically, finite element analysis of the band properties of peri- odic two-dimensional microstructures subject to a variety of geometric lattice perturbations is presented. Phononic structures with periodicity over the range of 100-1400 μm were found to exhibit rich band gap effects over 100-300 kHz. We also discuss the utility of one-dimensional transfer matrix method approximations and analysis in the infinite limit as methods for understanding and predicting crystal transmission. Lastly, we describe an advanced modular microfluidic construction scheme using prefabricated polymeric building blocks (MABs) that can be assembled into working devices on-site within minutes. We discuss: (1) development of flexible silicone casting trays for dramatically improved production and extraction of MABs, (2) reliable “off-the-shelf” preparation of 1-3 μm PDMS thin films for facile block assembly with simultaneous block/block and block/substrate bonding, and (3) modification of MAB block design to include self-alignment and sealing structures. Completed MAB assemblies possessed an average channel offset of ±12μm, an average channel angle of ±1 degree, and were found to exhibit the fewest inter-block gaps at a piece convexity of 0 μm. Exemplary MAB devices for performing on-chip gradient synthesis, droplet generation, and total internal reflectance microscopy are also presented.