Folch, AlbertSip, Christopher G.2013-11-142014-05-142013-11-142013Sip_washington_0250E_11827.pdfhttp://hdl.handle.net/1773/24182Thesis (Ph.D.)--University of Washington, 2013The sensing of chemical gradients plays an important role in the guidance of cells for tissue development, migration of cells in the immune system, and human disease. We have developed a microfluidic transwell insert for generating concentration gradients in a user-friendly and modular format that is compatible with conventional cell cultures. The device is simply inserted into a standard 6-well plate were it hangs self-supported at a distance of 250 µm above the cell culture surface. The core aspect of our design is the delivery of small microflows through a track-etched membrane into the cell culture well. The microfluidic transwell can deliver quantifiable, large-area gradients to a large number of cells or tissue explants with extremely low fluid shear stress. Finite-element modeling was used to describe porous membrane flow and molecular transport for predicting gradients generated by the device. Transwell microfluidic gradients were applied to a large population of neutrophil-like cells to demonstrate the direct observation of chemotaxis. Additionally, the modular design and low fluid shear stress made it possible to apply gradients to sensitive neuronal explant cultures. With a simplified interfacing scheme and well-defined, quantifiable gradients, the microfluidic transwell device has potential for broad applications to gradient sensing biology.application/pdfen-USCopyright is held by the individual authors.Biological gradients; BioMEMS; Cell migration; Chemotaxis; Microfluidics; Porous membranesBiomedical engineeringCellular biologyMechanical engineeringbioengineeringThesis