Acoustics-induced Fluid Motions
Acoustic waves, as a form of mechanical vibration, not only induces the force directly on the object, but also induces the motion of the medium that propagates throughout the system. The study of acoustofluidic mainly focuses on the exploration of the underlying mechanism of the acoustic waves and fluid motion and the methodology of applying this technique to practical applications. Featuring its contactless, versatile, and biocompatible capabilities, the acoustofluidic method makes itself an ideal tool for biosample handling. As the majority of the bio-related samples (e.g., cell, small organism, exosome) possess their native environment within liquids, there is an urgent need to study the acoustic induced fluid motion in order to cooperate with the development of the acoustic tweezing technique. While both the theoretical study and application exploration have been established for the combination of acoustics and microfluidics, the fluid motion on a larger scale is still under-developed. One reason is that, although the acoustofluidic methods hold great potential in various biomedical applications, there is a limited way to form an organized motion in a larger fluid domain, which may lead to the imprecise manipulation of the target. On the other hand, the theoretical study for the microfluidic domain is on the basis of a simplified model with certain assumptions, when applying to the larger fluid area, and significantly influences both the accuracy and computation cost. In this dissertation, we have first developed a series of theoretical and numerical methods in order to provide insights into the acoustofluidic phenomenon in different domain scales. Specifically, we explored the non-linear acoustic dynamics in fluids with the perturbation theory and Reynolds’ stress theory. Then we presented that the vortex streaming can be predicted and designed with our theoretical and numerical study, which can be utilized for various fluid systems and expanded to practical biomedical applications. The boundary-driven streaming and Reynolds’ stress-induced streaming are studied and applied to the digital acoustofluidic droplet handling platform and droplet spinning system, respectively. We demonstrated that within the digital acoustofluidic platform, the droplet can be manipulated on the oil layer in a dynamic and biocompatible manner. Meanwhile, in the droplet spinning system, we can predict and guide the periodic liquid-air interface deformation, as well as the particle motion inside the droplet. We demonstrated that with the theoretical and experimental study, this platform can be utilized for the nanoscale particle (e.g., DNA molecule and exosome) concentration, separation, and transport. Next, based on our study of the acoustically induced fluid motion, we developed an integrated acoustofluidic rotational tweezing platform that can be utilized for zebrafish larvae rapid rotation (~1s/rotation), multi-spectral imaging, and phenotyping. In this study, we have conducted a systematic study including theory development, acoustofluidic device design/fabrication, and flow system implementation. Moreover, we have explored the multidisciplinary expansion combining the acoustofluidic zebrafish phenotyping device with the computer-vision-based 3D model reconstruction and characterization. With this method, we can obtain substantial information from a single zebrafish sample, including the 3D model, volume, surface area, and deformation ratio. Moreover, with the design of the continuous flow system, a flow-cytometry-like system was developed for zebrafish larvae morphological phenotyping. In this study, a standard workflow is established which can directly transfer the groups of samples to a statistical digital readout and provide a new guideline for applying acoustofluidic techniques to biomedical applications. This work represents a complete fusion of acoustofluidic theory, experimental function, and practical application implementation.
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