BIO-INSPIRED PHOTONIC MATERIALS
Architectures with periodic arrays of hollow spaces are responsible for the vivid structural colors of butterflies, beetles, and birds. Synthetic analogues of these structures, known as inverse opals, offer a low-cost and simple method to develop unique 3D photonic materials. Top-down lithographic methods can be used to generate 3D photonic structures or inverse opals; however, a simpler method is to use self-assembling colloidal crystals as a sacrificial template to produce the porous inverse opal structures. One drawback of this technique is uncontrolled crack and defect formation over the length scales required for applications. Our current research revolves around synthetic strategies to improve the fabrication of large-scale inverse opal structures, tuning the optical properties of the structures, and eliminating defects.
BIONANOINTERFACES
The stiffness, chemistry, topography, and the materials properties of a surface can dictate whether a mammalian cell will grow, migrate, divide, or differentiate. In mammalian cells, the stiffness or mechanical stimuli of a surface can induce biochemical signals that result in morphological changes in the cell. Morphology is often an important indicator of lineage commitment in stem cells. The interplay between biochemical signals and mechanical cues at the cell-substrate interface that result in changes in cell morphology are not well understood. In our research one aim is to develop methods and materials to systematically vary the stiffness, chemistry, topography, and materials properties of a surface to decouple the physical factors from the biochemical signals that result in morphogenesis.
CELLULAR UPTAKE
The PI and her group are systematically studying how the size and surface chemistry of nanoparticles influence endocytosis, a mechanism by which cells engulf material from their environment using their plasma membrane. Questions of how nanoscale particles interact with cellular membranes and enter the cytoplasm are of great interest in drug delivery. Factors such as the size, shape, surface chemistry, and roughness can influence the type of cellular mechanism used to recognize and internalize particles.
CRYSTAL GROWTH
Inorganic materials can crystallize into various shapes, sizes and even different crystal structures. Often, subtle changes in substrate chemistry, topography, or geometry can result in intricate morphologies. We have demonstrated that inorganic semiconductors can be grown as high aspect ratio nanorods on natural cotton fibers (ZnO), or nanowires on substrates with topography (CuS), and that we can tune the cubic to hexagonal crystalline transition of CdS by adjusting the pH of the growth solution.
NANOPARTICLE SYNTHESIS
Solid-state materials have traditionally been synthesized using high temperature (1,000°C) regimens to overcome the slow rate of diffusion between two bulk-scale reactants. Re-grinding and re-heating treatments improve the rate of diffusion; however, high temperatures limit the accessible products to the most thermodynamically stable phases. The high surface area and the coordinatively unsaturated bonds of nanoparticles make them more reactive than bulk solids at lower temperatures. One of our interests is to synthesize novel alloys and intermetallic compounds in compositions and morphologies not accessible in the bulk. By using nanoparticles as reactants in place of bulk solids, it is possible to access metastable phases of intermetallics and alloys at temperatures significantly below those used in traditional solid-state synthesis. We are particularly interested in nanoparticle systems with applications in catalysis, as image contrast agents, or as drug delivery vehicles.