| This research evaluates a novel microfluidic actuation mechanism using tethered, rotating bacteria. Naturally occurring, flagellated bacteria swim with flagellar filaments driven by rotary motors embedded in the cell membrane. These flagella are randomly distributed over the cell surface and each flagellar motor rotates (∼100Hz) independently of the others. When a single flagellum tethers down to a surface, the entire cell body counter-rotates (∼10Hz) around that flagellum. This distinctive rotary motion imparts motion on the surrounding fluid, and thus can be utilized to perform various mechanical functions in microfluidic systems such as pumping, mixing, and/or valving. Using computational fluid dynamics (CFD), this research shows that these tethered, rotating cells can be arranged inside a microchannel to form a viscous micropump. The micropump consists of several non-pathogenic Escherichia coli (E. coli) strain KAF95 with unidirectional motors arranged in a linear array inside a microchannel. The design of the micropump was optimized using CFD. During the design optimization, the effect of the stochastic rotational behavior of tethered bacteria as well as geometry of the microchannel was investigated. The pump's flowrate was maximized to 12 pL/hr for a rectangular microchannel with dimensions above 8 mum. The low volumetric flowrate that this pump delivers makes it well-suited as a localized micropump for cleaning and/or supplementary pumping purposes in micro- and nanofluidic systems.;The hybrid actuation mechanism offers substantial advantages compared to conventional MEMS-based actuators. The rotating, microscopic bacteria can live on minuscule amounts of nutrients, therefore they do not require any external power source. Also, they self-replicate, so no multi-step lithographic fabrication is required. However, bacterial flagellar motors respond to changes in the acidity level of their surroundings in a stochastic fashion. This study shows that the sensitivity to pH can be predicted through a mathematical model and can be used to control their rotational behavior as microfluidic actuators. The model incorporates nanoscale motor interactions into continuum level simulations using the Fokker-Planck Equation (FPE). The predictions of the model show a good agreement with experiments. (Abstract shortened by UMI.)... |
