Title: Theoretical design of hard and soft biomimetic materialsTheoretical design of hard and soft biomimetic materialsC. Nadir KaplanPaulson School of Engineering and Applied Sciences, Harvard UniversityRealizing next-generation materials with intricate shapes or complex signal processing abilities to perform adaptive functions greatly benefits inspiration from biological systems. In the first part of this talk, I will present a geometrical theory that explains the growth and form of carbonate-silica precipitates, which exemplify biomineralization-inspired formation of inorganic brittle microarchitectures. The theory predicts new assembly pathways of arbitrarily complex morphologies and thereby guides the synthesis of light-guiding optical structures. The second part will concern a soft matter analog of information storage and differentiation in living organisms, which constantly process dynamic environmental signals. Specifically, I will introduce a continuum framework of a hydrogel system that utilizes unique cascades of mechanical responses, transport and complexation of chemical stimuli to expand the sensing repertoire beyond standard hydrogels that rapidly equilibrate to their surroundings. Altogether, the confluence of theory and experiment enables the design of optimized hard or soft biomimetic materials for applications ranging from bottom-up manufacturing to soft robotics to data encoding. [more]

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Bio-inspired Material Assembly and Applications Abstract In nature, helical macromolecules such as collagen, chitin and cellulose are critical to the morphogenesis and functionality of various hierarchically structured materials. During morphogenesis, these chiral macromolecules are secreted and undergo self-templating assembly, a process whereby multiple kinetic factors influence the assembly of the incoming building blocks to produce non-equilibrium structures. A single macromolecule can form diverse functional structures when self-templated under different conditions. Collagen type I, for instance, forms transparent corneal tissues from orthogonally aligned nematic fibers, distinctively colored skin tissues from cholesteric phase fiber bundles, and mineralized tissues from hierarchically organized fibers. Nature’s self-templated materials surpass the functional and structural complexity achievable by current top-down and bottom-up fabrication methods. However, self-templating has not been thoroughly explored for engineering synthetic materials. In my seminar, I will demonstrate a facile biomimetic process to create functional nanomaterials utilizing chiral colloidal particles (M13 phage). A single-step process produces long-range-ordered, supramolecular films showing multiple levels of hierarchical organization and helical twist. Using the self-templating materials assembly processes, we have created various biomimetic supramolecular structures. The resulting materials show distinctive optical and photonic properties, functioning as chiral reflector/filters and structural color matrices. Through the directed evolution of the M13 phages, I will also show how resulting materials can be utilized as functional nanomaterials for biomedical, biosensor and bioenergy applications^1-3. References: Chung, W.-J., Oh, J.-W., Kwak, K.-W., Lee, B.-Y., Mayer, J., Wang, E., Hexemer, A., & Lee, S.-W. Biomimetic Self-Templating Supramolecular Structures. Nature 478, 364 (2011).Lee, B.-Y., Zheng, J., Zueger, C., Chung, W.-J., Yoo, S.-Y., Wang, E., Meyer, J., Ramesh, R., Lee, S.-W., Virus-based Piezoelectric Energy Generation. Nature Nanotechnology. 7, 351 (2012).Oh, J.-W., Chung, W.-J., Heo, K, Jin, H.-E., Lee, B.-Y., Wang E., Meyer, J., Kim C., Lee, S.-Y., Kim, W.-G., Zemla, M, Auer, M , Hexemer, A, and Lee, S.-W., Biomimetic Virus-Based Colourimetric Sensors, Nature Communication 5, Article number: 3043 (2014). [more]

Ion transport in block copolymer electrolytesIon conducting polymers play a central role in the development of safer and more efficient electrochemical devices such as batteries, fuel cells, and electrolyzers. Self-assembling polymeric materials with multiple components offer pathways to simultaneously optimize more than one material function, as well as control structure at the nanoscale. In the first part of my talk, I will highlight the advantages and new information that can be derived from the use of custom microfabricated interdigitated electrodes (IDEs) as a platform to probe extrinsic and intrinsic transport properties of polymer electrolytes films through electrochemical impedance spectroscopy (EIS). The second part of my talk will address the use block copolymer electrolytes (BCEs) as ion conducting membranes. BCEs provide the means to realize high ionic conductivity and mechanical robustness by judicious choice of block chemistry. To understand the potential of these materials, however, transport properties through BCEs, with domain structure at the nanoscale, must be understood at a fundamental level at the device scale, 10s to 100s of microns. Extrinsic properties of BCEs depend strongly on the presence of grain boundaries and defects. Conductivity is found to be directly proportional to the number and length of domains of the BCE that are connected from one electrode to the other. Any conducting domain within the film impeded with even a single non-conducting defect (e.g. a dislocation) does not contribute to the conductivity and increases the capacitance of the material. Finally, by completely aligning and connecting the conductive domains between electrodes, we can quantitatively investigate the intrinsic transport properties of BCEs and compare them to their homopolymer analogs. We conclude that the interfacial mixing between the blocks at domain interfaces is the dominant factor in reducing ionic mobility in BCEs, reducing the expected conductivity based on volume fraction by as much a factor of 2. [more]