| Creating in vitro microenvironments for the study of important biological processes, examples of which include chemotaxis, haptotaxis, axonal guidance and angiogenesis, has been a relevant research focus for many years. Microfabrication techniques involving soft lithography, microfluidic devices and direct-write assembly can be used to create such microenvironments. Soft lithography techniques, which typically include microcontact printing and decal transfer, rely on elastomeric molds, stamps or flexible photomasks to create patterns on or transfer patterns to, an underlying surface; these molds or stamps themselves have also been used for study. In microfluidic devices, small fluid volumes are transported through microchannels via gravity or pressure-driven methods. Biological studies are either conducted within the gradients maintained by laminar flow through the microchannels, or on the residually patterned underlying rigid surface, created via physi-adsorption or through chemical interactions with the surface. Both soft lithography and residual substrate microfluidic patterning approaches yield planar patterned substrates. In contrast, fluidic gradients maintained in microchannels are three-dimensional in nature, but are only used for specific applications---e.g. the study of non adherent cell types such as white blood cells. Recent studies, however, have shown that different cell types present important biological differences, in their differentiation, proliferation rates, migration and cell signaling, in two- versus three-dimensional culture systems. Thus, there has been increased interest in the development of three-dimensional fabrication techniques to create microenvironments that can better mimic those found in vivo. Direct-write assembly is an example of a three-dimensional fabrication method that enables the creation of micro-periodic structures with well defined features and an interconnected porous network, 1-100mum in size. Other 3D fabrication techniques include electrospinning, solvent/particulate leaching and freeze drying, however they usually yield random three-dimensional structures with an unpredictable porous structure. This thesis describes three different in vitro systems generated using three distinct microfabrication techniques, including a modified decal transfer lithography, a combination of microfluidic assembly and microcontact printing, as well as direct-write assembly, for the study of primary mammalian hippocampal neuron development, one of the most well characterized in vitro models of neurite development currently available. |
