Two-photon lithography for reconfigurable microstructures

Two-photon lithography is a promising three-dimensional (3D) laser writing technique to construct miniature structures at the sub-micrometer to micrometer length scale. Moreover, two-photon lithography can achieve structures with spatial resolution down to 120 nm, and this lithographic technique is highly flexible in constructing arbitrary shapes and architectures. However, two-photon lithography is limited by the typical use of epoxy based and acrylate-based photoresists, and hence the developed structures are typically stationary microstructures. There is currently no stable aqueous-based stimuli-responsive hydrogel photoresists for the construction of shape-shifting microstructures. The objectives of my thesis aim to render acrylate microstructures a new function as plasmonic anti counterfeiting substrates with two-tier of security features (Chapter 2), and to formulate aqueous-based stimuli-responsive hydrogel photoresists for constructing shape-shifting biomimetic microstructures (Chapter 3 to Chapter 5). In Chapter 3, we create a formulation for a protein-based photoresist, which allows stable and consistent fabrication during two photon laser writing process. This is a major breakthrough in generating aqueous-based polymer photoresists for construction three-dimensional (3D) of suspending and high aspect-ratio (HAR ≥ 10) hydrogel microstructures. By using the established protein photoresist, we also accomplish the first Kagome arrays of pH-responsive dynamically shape-shifting microstructures (Chapter 4). The shape-shifting microstructures undergo reversible shape change from polygons to circles against external pH, hence grant reconfigurability to the Kagome arrays. In Chapter 5, two-photon polymerizable aqueous based N-isopropylacrylamide (NIPAAm) photoresist is formulated. Effects of processing parameters are systematically investigated for the construction of structurally stable temperature-responsive microstructures. Lastly, in Chapter 6, I outline my four-year PhD research project and present an outlook on significant progress on future design of multi-functional “smart” microstructures.Doctor of Philosoph