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Gradient heterogeneous surfaces
The strength of the interfacial interactions and the length scale over which these interactions occur are two important factors to understand the behavior of polymer blends, diblock copolymers, cell recognition, adhesion and wettability on a surface. This has important implications in pattern recognition applications, biosensors and random recognition processes. A simple means of examining patterns and the influence of patterns on many length scales simultaneously is with gradient surfaces, where the lateral distribution of the chemical nature and functionality of surface interactions can be varied in a systematic manner. Surfaces with gradient heterogeneous topographies were prepared, using blends of homopolymers and diblock copolymers, to vary the lateral size scale of the heterogeneities from the microscopic to nanoscopic correlation of heterogeneity. By tuning the lateral size scale of the heterogeneities, surface patterning can be engineered to have a specific function. Mixtures of homopolymers macroscopically phase separate, whereas diblock copolymers microphase separate on nanoscopic length scales. By gradually varying the relative concentrations of homopolymers and block copolymers, the length scale of the domains can be continuously varied from the nanoscopic to the macroscopic length scale. A method to generate gradient surfaces based in such mixtures is described in Chapter 1. Several examples demonstrating their utility are shown in Chapters 2 and 3. Polystyrene film dewetting and polystyrene/poly(methyl methacrylate) phase separation in thin films are discussed in Chapter 2. In Chapter 3, cell adhesion and migration are shown to be vastly different when the cells are grown on surfaces with nanometer to micrometer features. In Chapter 4, cell migration on patterned surfaces is investigated to tackle the sole effect of topography. Cell migration on polystyrene surfaces with micron sized topographic features is compared to cell migration on flat polystyrene substrate. Actin cytoskeleton, focal adhesion and cell migration speed were characterized to understand cell movement on topographic surfaces. Cell movements on hydrophilic polystyrene posts show strong similarities to cells cultured in 3D environment. This may provide a simple model system to study cell migration in physiological relevant conditions and contribute to our understanding in cell migration to better design surfaces for medical applications.
Tsai, Irene Y, "Gradient heterogeneous surfaces" (2004). Doctoral Dissertations Available from Proquest. AAI3188681.