February 21st 2017, ASRC
1:30 PM - 5:30 PM
Evolution, Optics and Biomimcry of Natural Optical Nanostructures
Matthew D. Shawkey Department of Biology, University of Ghent, Belgium
Colors are useful for functions ranging from crypsis to communication to thermoregulation. Those produced by materials organized at the nanometer scale (structural colors) have numerous advantages over those produced by pigments, including greater color diversity, iridescence, resistance to fading, tunability, and potentially low cost of manufacture due to their formation by self-assembly. Birds have an astonishing diversity of structural colors, with one class based on organized arrays of melanin particles (melanosomes) and the other on quasi-ordered matrices of keratin and air. Here I will first discuss how these colors are produced at the nanometer scale, using examples of color types spanning the visual spectrum and including both chromatic and achromatic colors. I will then discuss their evolutionary patterns (including some hints from the fossil record) and their potential effects on avian diversification. Finally I will describe our use of these materials as inspiration for new color-producing materials, including both non-iridescent and iridescent coatings.
How to Make a Bird Egg Shine? Structural and Pigmentary Bases of Egg Color and its Mimicry in Birds
Mark E. Hauber Office of Research, City University of New York
The role of pigments in generating the colour and maculation of birds' eggs is well characterized, whereas the effects of the eggshell's nanostructure on the visual appearance of eggs are little studied. I survey the pigmentary basis of egg coloration in birds, and examine the nanostructural basis of glossiness in select avian lineages. Using experimental manipulations in conjunction with angle-resolved spectrophotometry, scanning electron microscopy, atomic force microscopy and chemical analyses, we discovered that the glossy appearance of some bird eggshells is produced by an extremely smooth cuticle, composed of calcium carbonate, calcium phosphate and, potentially, organic compounds such as proteins and pigments. Optical calculations corroborate surface smoothness as the main factor producing gloss. Our work highlights the need for further exploration into the nanostructural mechanisms for the production of colour and other optical effects of avian eggshells.
Peptide Melanins with Sequence-Tunable Properties
Ayala Lampel CUNY Advanced Science Research Center
Melanin pigments are shared across the living world, providing UV protection, structural support, coloration and free radical scavenging. These materials are of considerable interest for technological applications, however, the formation of synthetic melanins is challenging, involving poorly controlled oxidation and polymerization of (poly-) phenols and catechols. Here we report methodology to produce tunable melanin-like materials based on supramolecular self-assembly of tyrosine-peptide precursors that are subjected to biocatalytic oxidation and polymerization. The use of variable sequence tripeptides enables tyrosine phenols to be presented in a chemical and steric context which enables subsequent biocatalytic oxidation to be controlled. This aqueous processing method allows for the formation of melanin-like materials with tunable morphological, electrical and optical properties over a considerable range that are dictated by peptide sequence.
Bioinspired Adaptive Material Systems: Sensing, Sorting, and Harvesting
Ximin He University of California, Los Angeles
From the cellular level up to the body system level, living organisms cooperatively sensing and adapting to local environment, to transport specific biological species in the complex bio-fluids and harvesting energy from the environment to keep alive and perform various functionalities. These graceful capabilities arise from the coordination of the chemo-mechanical actions of their muscles and/or tissues with their environmentally vigilant cells, such as the molecular configuration changes and micro/macroscopic mechanical motions in response to a variety of signals. Inspired by these unique abilities, we have developed a series of dynamic material systems, which are based on stimuli-responsive hydrogel and its adaptively reconfigurable microarchitecture. This presentation will introduce several novel functionalities that this broad-based platform has demonstrated, ranging from ultrafast optical sensing of chemical and biological species, programmable and autonomous sorting of target molecules in complex biofluids or wastewater, and adaptive light tracking and harvesting. Overall, the environment-adaptive, dynamic material systems would have transformative impacts in areas ranging from medical implants that help stabilize bodily functions, to a low-coat high-throughput point-of-care diagnostic tool of diseased indicators in solution, and to smart devices that regulate energy usage.
Powering Colloidal Machines with Contact Charge Electrophoresis
Kyle Bishop Columbia University
The sustained operation of colloidal machines - that is, dynamic assemblies of colloidal components that perform useful functions - requires a steady input of energy, which must be delivered remotely and converted efficiently into useful motions. In this context, we have developed an electric motor that operates efficiently at small scales using electrostatic forces powered by steady electric (or electrochemical) currents. The underlying mechanism - termed contact charge electrophoresis (CCEP) - relies on the electrostatic actuation of conductive particles or droplets, which are repeatedly charged by contact with biased electrodes. In contrast to traditional forms of electrophoresis or dielectrophoresis, CCEP allows for rapid and sustained particle motions driven by low power DC voltages, which make it an ideal mechanism for powering the active components of small machines (e.g., mobile microfluidic technologies). This talk will describe the basic physics underlying CCEP motions and present several strategies for rectifying these motions to achieve useful functions such as microfluidic droplet generation, transport, and mixing.
Using Bio-inspired Water-responsive Materials to Harvest Energy from Evaporation
Xi Chen CUNY Advanced Science Research Center Department of Chemical Engineering, City College of New York
Biological organisms have developed interesting nanoscale structures to facilitate their functions. Water-responsive nanostructures in many plants can effectively harness changes in relative humidity (RH) to power vital tasks, suggesting the potential of using these materials for mechanical actuators and energy harvesting devices. Bacillus spores are microscale water-responsive materials that expand and contract with changing RH. We found that spores demonstrate energy densities significantly higher than those of existing actuator materials and artificial muscles. The energy densities were measured by an environment-controlled atomic force microscope (AFM), which was used to apply periodically varying forces and RH on individual spores. The experiments also showed an extremely fast response of spores to changes in RH (<0.1 s). We then created hygroscopy-driven artificial muscles (HYDRAs) by depositing spores into patterns on thin plastic films. These HYDRAs can lift 50 times their own weight and quadruple their length while exchanging less than 5% moisture by weight. Using HYDRAs, we developed two kinds of evaporation-driven engines that can self-start and continuously convert evaporation into mechanical motions, and subsequently into electricity, when placed at air-water interfaces. The energy harvested from evaporation is enough to power a small light source as well as a miniature car. These studies illustrate that further investigation and development of nanostructured water-responsive materials will contribute to new types of renewable energy, energy storage, actuators, and medical technologies.