| In this research a viscous microfluidic pump was designed and fabricated. The pump was formed in a MEMS based microfluidic channel and was actuated by the rotary motion of the flagellar motors found in Escherichia coli (E. coli). Typically, E. coli bacteria swim by the rotation of flagellar filaments that are driven by a nanoscale rotary motor. In this study we utilized a strain of E. coli that allowed the flagellar filament to adhere to various substrates, a process known as tethering. When tethering occurred the motor continued to rotate, but because the flagellar filament was adhered to a substrate the cell body rotated like a merry-go-round. The rotation of the cell body caused a flow field to be generated in the fluid. Typically, in a free swimming state, flagellar motors rotate at a speed of about 100 Hz. However, when tethered, the drag force of the cell body caused the cells to rotate at a much lower speed. In fact, for the KAF95 strain used in this study, it was found that the tethered cells rotated at an average of 6.5 Hz.;In the early stages of the project it was found that approximately 67% of the cells that tethered onto the substrate rotated, but this value decreased to 30% in the closing stages of the project. This reduction in rotational efficiency was unexpected and hindered the actual implementation of the designed pump. However, the ability of the tethered bacteria to act as actuators was demonstrated by its ability to move particles in the microchannel from one point to another, at a speed of about 10% of the tip velocity of the cells. When extrapolated into a microchannel of known dimensions it was determined that the flow rate could reach approximately 0.23 nL/min, a 43% difference from the value determined by ANSYS simulations.;One of the major parts of this research was to pattern single flagellar motors in a linear array inside the microchannel. This was accomplished by utilizing a microfabricated sieve in conjunction with a dip pen. The sieve was a thin PDMS membrane with patterned through holes formed by the casting of liquid PDMS onto a silicon mold.;Another important aspect of this research was to determine the tethering interaction between the flagellar filament of the bacteria and the substrate surface on which they tethered. Initially it was thought that the flagellar filament adhered only to glass substrates. However from this study it was determined that the tethering mechanism was non-specific and that the flagellar filaments adhered to many different surfaces, regardless of its charge or hydrophobicity. (Abstract shortened by UMI.)... |
