43 research outputs found
Single Diamond Structured Titania Scaffold
Single diamond (SD) network, discovered in beetles and weevils skeletons, is
the holy grail in photonic materials with widest complete bandgap to date. Such
structure influences the propagation of electromagnetic waves in defined
frequency and is significant in photonic crystals, light-harvesting
applications, optical waveguides, laser resonators, etc. However, efforts until
now have not allowed a start-to-finish understanding on the production process
of the unbalanced single network scaffold in natural organisms and the
thermodynamical instability of SD makes it extremely difficult to be obtained
by self-assembly compared to the energetically favored bicontinuous double
diamond and other easily formed lattices, thus the artificial fabrication of
such photonic structure in practical synthesis has last-long as a formidable
challenge. Herein, we report the unprecedented bottom-up fabrication of SD
titania scaffold through a one-pot co-folding scenario employing a simple
diblock copolymer poly(ethylene oxide)-block-polystyrene (PEO45-b-PS241) as
template and titanium diisopropoxide bis(acetylacetonate) as inorganic
precursor in a mixed solvent, in which the inorganic species selectively
organized in one of the skeleton enclosed by diamond minimal surface of the
polymer matrix in a simultaneous assembling process. Electron crystallography
investigations exhibited the tetrahedral-connected SD frameworks with space
group Fd-3m in polycrystalline anatase form. Photonic bandgap calculation shows
that the structure reveals a complete bandgap of 11.54 % with the dielectric
contrast of titania (6.25). This work provides a straightforward solution to
the complex synthesis puzzle and offers a new reference for biological relevant
materials, next-generation optical devices, etc
Mechanoresponsive Alignment of Molecular Self-Assembled Negatively Charged Nanofibrils
Inspired by the mechanoresponsive orientation of actin filaments in cell, we introduce a design paradigm of synthetic molecular self-assembling fibrils that respond to external mechanical force by transforming from a macroscopically disorder state to a highly ordered uniaxial aligned state. The incorporation of aromatic-containing amino acids and negatively charged amino acids lead to self-assembly motifs that transform into uniform nanofibrils in acidic solution. Adjusting the pH level of aqueous solution introduces optimal negative charge to the surface of self-assembling nanofibrils inducing long-range electrostatic repulsion forming a nematic phase. Upon external mechanical force, nanofibrils align in the force direction. Via evaporation casting in capillary confinement, the solvated synthetic self-assembling nanofibrils transform into scalable lamellar domains. Adjusting capillary geometry and drying procedure offers further parameters for tuning the mesoscale alignment of nanofibrils generating a variety of interference colors. The design paradigm of mechanoresponsive alignment of self-assembled nanofibrils as an addition of nanofabrication techniques is potentially employable for realizing biomimetic optical structures
Direct observation and analysis of york-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer
Nanometal particles show characteristic features in chemical and physical properties depending on their sizes and shapes. For keeping and further enhancing their features, the particles should be protected from coalescence or degradation. One approach is to encapsulate the nanometal particles inside pores with chemically inert or functional materials, such as carbon, polymer, and metal oxides, which contain mesopores to allow permeation of only chemicals not the nanometal particles. Recently developed low-voltage high-resolution scanning electron microscopy was applied to the study of structural, chemical, and electron state of both nanometal particles and encapsulating materials in york-shell materials of Au@C, Ru/Pt@C, Au@TiO2, and Pt@Polymer. Progresses in the following categories were shown for the york-shell materials: (i) resolution of topographic image contrast by secondary electrons, of atomic-number contrast by back-scattered electrons, and of elemental mapping by X-ray energy dispersive spectroscopy; (ii) sample preparation for observing internal structures; and (iii) X-ray spectroscopy such as soft X-ray emission spectroscopy. Transmission electron microscopy was also used for characterization of Au@C. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.close0
Control cell migration by engineering integrin ligand assembly
Advances in mechanistic understanding of integrin-mediated adhesion highlight the importance of precise control of ligand presentation in directing cell migration. Top-down nanopatterning limited the spatial presentation to sub-micron placing restrictions on both fundamental study and biomedical applications. To break the constraint, here we propose a bottom-up nanofabrication strategy to enhance the spatial resolution to the molecular level using simple formulation that is applicable as treatment agent. Via self-assembly and co-assembly, precise control of ligand presentation is succeeded by varying the proportions of assembling ligand and nonfunctional peptide. Assembled nanofilaments fulfill multi-functions exerting enhancement to suppression effect on cell migration with tunable amplitudes. Self-assembled nanofilaments possessing by far the highest ligand density prevent integrin/actin disassembly at cell rear, which expands the perspective of ligand-density-dependent-modulation, revealing valuable inputs to therapeutic innovations in tumor metastasis
Advanced scanning electron microscopy techniques for structural characterization of zeolites
International audienceChemical etching after Ar ion beam cross sectioning enables the formation of zeolite internal nano structures to be observed directly using a newly developed highly sensitive scanning electron microscope