The fabrication and characterization of surface-anchored hydrogel microstructures are described. The hydrogel structures are constructed from poly(N-isopropylacrylamide), or poly(NIPAAm), which is a well-known thermoresponsive polymer that swells and contracts with changes in temperature. When patterned on a surface, these structures can experience a variety of shape changes induced by nonuniform swelling. Depending on the aspect ratio, patterns can, for instance buckle upon swelling and form wave-like patterns. Such structural changes replicate oscillatory motion of the smooth muscle cells and can be used to transport objects in microfluidics. The work, herein, investigates methods of pattern production and introduces a new technique for characterizing local swelling in the patterns. In order to achieve the latter, fluorescent microspheres were embedded in hydrogel patterns and their positions were mapped in three-dimensions using confocal microscopy. The measurements permit, for the first time, swelling maps of the structures based on relative movements of the microspheres. This information will ultimately aid in understanding how swollen macroscopic structures are related to gradients in localized swelling.

The overall thrust of this dissertation is to gain a comprehensive understanding over the factors that govern the performance and behavior of ultra-thin, cross-linked polymer films. Poly(NIPAAm) was used as a model polymer to study volume phase transition in surface tethered networks. Poly(NIPAAm) undergoes a reversible phase transition at approximately 32°C between a swollen hydrophilic random coil to a collapsed hydrophobic globule state, thought to be caused by increased hydrophobic attractions between the isopropyl groups at elevated temperatures. We present a simple photochemical technique for fabricating structured polymer networks, enabling the construction of responsive surfaces with unique properties. The approach is based on the photo-cross-linking of copolymers synthesized from N-isopropylacrylamide and methacroyloxybenzophenone (MaBP). In order correlate layer swelling to the MaBP content, we have studied the swelling behavior of such layers in contact with aqueous solutions with neutron reflection. The cross-linked networks provide a three-dimensional scaffold to host a variety of functionalities. These networks serve as a platform which can be used to amplify small local perturbations induced by various stimuli like temperature, pH, solvent, ionic strength and peptide modified hydrogels to bring about a macroscopic change. Neutron reflection experiments have shown that the volume-phase transition of a surface-tethered, cross-linked poly(NIPAAm) network coincided with the two-phase region of uncross-linked poly(NIPAAm) in solution. Parallel measurements with ATR-FTIR investigating the effect of temperature, pH and salts suggest that the discontinuous transition is the result of cooperative dehydration of the isopropyl groups, with water remaining confined between amide groups in the collapsed state as weakly hydrogen bonded bridges. Hybrid polymers with specific peptide sequences have shown specific response to external cues such as pH and metal ions exhibiting unique phase behavior.