Two-dimensional (2D) and three-dimensional (3D) periodic-lattice-based microstructures have found multifaceted applications in photonics, microfluidics, tissue engineering, biomedical engineering, and mechanical metamaterials. To fabricate functional periodic microstructures, in particular in 3D, current available technologies have proven to be slow and thus, unsuitable for rapid prototyping or large-volume manufacturing. To address this shortcoming, the new innovative field of pattern-integrated interference lithography (PIIL) was introduced. PIIL enables the rapid, single-exposure fabrication of 2D and 3D custom-modified periodic microstructures through the non-intuitive combination of multi-beam interference lithography and photomask imaging. The research in this thesis aims at quantifying PIIL’s fundamental capabilities and limitations through modeling, simulations, prototype implementation, and experimental demonstrations. PIIL is first conceptualized as a progression from optical interference and holography. Then, a comprehensive PIIL vector model is derived to simulate the optical intensity distribution produced within a photoresist film during a PIIL exposure. Using this model, the fabrication of representative photonic-crystal devices by PIIL is simulated and the performance of the PIIL-produced devices is studied. Photomask optimization strategies for PIIL are also studied to mitigate distortions within the periodic lattice. The innovative field of 3D-PIIL is also introduced. Exposures of photomask-integrated, photomask-shaped, and microcavity-integrated 3D interference patterns are simulated to illustrate the richness and potential of 3D-PIIL. To demonstrate PIIL experimentally, a prototype pattern-integrated interference exposure system is designed, analyzed with the optical design program ZEMAX, and used to fabricate pattern-integrated 2D square- and hexagonal-lattice periodic microstructures. To validate the PIIL vector model, the proof-of-concept results are characterized by scanning-electron microscopy and atomic force microscopy and compared to simulated PIIL exposures. As numerous PIIL underpinnings remain unexplored, research avenues are finally proposed. Future research paths include the design of new PIIL systems, the development of photomask optimization strategies, the fabrication of functional devices, and the experimental demonstration of 3D-PIIL.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

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Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 122-130). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Poly (ethylene glycol) (PEG) hydrogels have been used extensively in biological and tissue engineering, because of their outstanding biocompatibility and processability. However, it is not yet possible to process soft materials like PEG hydrogels with the requisite precision and throughput needed to recapitulate macroscopic biological tissue with control over every hierarchical scale. In this study, porous PEG hydrogels are processed by a phase separation method and patterned in a single photolithographic step. The thermodynamics of the temperature triggered spinodal decomposition of a ternary mixture of water, salt, and polymer are studied resulting in a ternary phase diagram and a spinodal temperature plot. Importantly, the state of porosity can be frozen by exposing the hydrogel to UV light to form a crosslinked hydrogel network. The average pore size can be tuned by changing delay between the application of heat and UV exposure. By utilizing grey-scale photomasks, a single process can be used to define regions of pure hydrogel, porous hydrogel with a programmed average pore size, and blank substrate with no hydrogel. In addition to representing a combination of a top-down and a bottom-up processes that enables the realization of complex samples, the simplicity of this process and the versatility of the resultant patterns could provide a useful capability for the definition of hydrogel samples for the development of advanced biomaterials.

Fabrication of Tissue Engineering Scaffolds Using Stereolithography Benita M. Comeau 226 Pages Directed by Dr. Clifford L. Henderson New methods and materials for the fabrication of hierarchically structured, 3D tissue scaffolds using stereolithography (SL) are presented. The ability to chemically modify selected areas on a scaffold is one way to direct cell growth in deliberate patterns; which is necessary for the engineering of complex, functioning tissues. SL will allow for the building of complex 3D structures with well defined geometries, and a second level of order is created by subsequent modification of chemical groups via catalyzing a de-protection event through exposure to another wavelength of light. The investigated system utilizes an acid-catalyzed de-protection event to change the surface chemistry of an SL-made polymer, analogous to conventional chemically amplified photoresists. The chemical modification alters the surface energy, affecting how proteins interact with the material. This allows selective areas to be more favorable towards cell adhesion. The results of this work include the identification of cytocompatible photo-acid generators that are necessary for the acid-catalyzed de-protection, the demonstration that traditional photolithographic materials may be used for cell patterning, quartz crystal microbalance studies which illuminate why these patterning methods work, the design and performance of a mirror array based stereolithographic apparatus capable of multi-wavelength exposures, and the synthesis and formulation of a novel stereolithographic resin for use in this system. The findings suggest that this system has great potential for use in cell and tissue studies, and possibilities for future use and research are discussed.