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Date of Award
Doctor of Philosophy (PhD)
Acoustofluidics utilizes ultrasonic standing waves in microscale fluidic channels to manipulate cells, microorganisms, and other objects sized from tens of nanometers to tens of microns. When exposed to an ultrasonic standing wave field, particles suspended in a fluid become confined to potential minima (nodes) of the acoustic field. I will present a number of related studies that involve the interactions between acoustic fields and motile microorganisms. First, I will show how an acoustic trap-and-release method enables rapid quantification of cell motility. As a demonstration, the newly developed motility assay is applied to discriminate swimming of wild-type and mutant Chlamydomonas reinhardtii cells. Results closely approximate the average speed of a population estimated from the mean squared displacement of individual cells, without the need to trace discrete trajectories. Thus large-population acoustic trap-and-release allows for automated analysis of hundreds of cells in minutes.The calibrated swimming C. reinhardtii cells are then used as active probes to map the acoustic fields within fluid-filled channels and chambers driven at resonance. Accurate characterization of the field performance is critical for design and optimization of acoustofluidic devices, and also for translation of such devices into clinical and industrial settings. However, extant computational modeling and experimental methods that use passive microparticles do not adequately capture the pressure distributions in intricate chamber geometries. This work introduces a method that can precisely assess acoustofluidic device performance while circumventing the aforementioned problems. The proposed method enables real-time characterization and continuous monitoring of acoustofluidic device performance. The optimal device resonances within a specified frequency range can be automatically identified. Qualitative mapping of the acoustic field strength with varying voltage amplitude is also possible for any type of field shape. Accurate quantification of field characteristics (e.g., acoustic energy density) in a simple straight rectangular microchannel driven at the first half-wavelength resonance is accomplished. This demonstration highlights the advantages of living probes enabling field quantification over a range of actuation voltages in a single experiment. The presented work lays the foundation for a measurement tool that can accelerate translation of research prototypes to commercial products, improving the long-term viability of acoustofluidic devices.
John Mark Meacham
Philip V. Bayly, Susan K. Dutcher, Anders Carlsson, Patricia Weisensee,
Movie 2.1: Low-population release of wild-type (CC-125) C. reinhardtii cells from the acoustic trap overlaid with manually-traced trajectories for the ballistic swimming regime (t = 0.75 s).
Movie 2-2.mp4 (2364 kB)
Movie 2.2: Large-population comparison of swimming after release for the three C. reinhardtii strains studied in the manuscript.
Movies 3-1.mp4 (14631 kB)
Movie 3.1: Resonance identification for the straight microfluidic channel using C. reinhardtii cells as active probes.
Movies 3-2.mp4 (14711 kB)
Movie 3.2: Resonance identification for the circular chamber using C. reinhardtii cells as active probes.
Movies 3-3.mp4 (25128 kB)
Movie 3.3: Multi-resonance identification for the circular microfluidic chamber using C. reinhardtii cells as active probes.
Movies 3-4.mp4 (12655 kB)
Movie 3.4: Qualitative mapping of the acoustic field strength for the second half-wavelength resonance of the straight microfluidic channel (f(2) = 1.76 MHz).
Movies 3-5.mp4 (12305 kB)
Movie 3.5: Qualitative mapping of the acoustic field strength for the (0 5 0) r-axial mode of the circular microfluidic chamber (f(0,5) = 4.23 MHz)
Available for download on Sunday, May 15, 2022