bluuebunny/crossref_metadata_2025_split huggingface dataset:
Micromechanics-Based Modeling of Biological Tissues Using the High-Fidelity Generalized Method of Cells
Authors: Pindera Marek-Jerzy 
Published: April 2011

ABSTRACTThe fundamental problem of micromechanics is the prediction of overall response of a composite material given the properties or response of the individual constituents and their internal geometric arrangement. The recently developed High-Fidelity Generalized Method of Cells is a promising micromechanics model whose predictive capability has been demonstrated for infinitesimal deformations in the presence of inelastic constituent behavior. The extension of this micromechanics model to the finite-deformation regime and incorporation of the quasi-linear viscoelasticity theory for the constituent response extends the range of this model's applicability to the bio-engineering area. Herein, an application involving the response of mitral valve chordae tendineae is presented that demonstrates the model's capability to mimic experimentally-observed response of this class of biological tissues rooted in their characteristic microstructures.
Nanoscale Origins of Spider Dragline Mechanical Properties
Authors: Trancik Jessika E. , Czernuszka Jan T. , Bell Fraser I. , Viney Christopher 
Published: April 2011

ABSTRACTSeveral mechanical models, in which a material is treated as a composite of crystalline and amorphous and/or interphase material, were used to predict the tensile modulus of spider dragline along the fiber direction. The models included the Voigt average (which assumes that the fibers/crystals are continuous, and that the strain is the same in all components of the composite); a modified Halpin-Tsai model (which is suitable for predicting the longitudinal elastic modulus for short aligned fiber composites, and is thus more appropriate for silk); and the shear-lag or Cox model (which is a modification of the Voigt average that takes into account a discontinuous nature of stiff fibers/crystals and the resulting shear stress in the amorphous matrix). The latter two models yielded close approximations of an experimentally measured elastic modulus of Latrodectus hesperus (black widow spider) dragline under conditions of controlled temperature and humidity, given realistic inputs for the moduli of the individual components and the percent crystallinity. A literature model for the stress-strain behavior of silk [1] was also considered, in the context of our experimental results from transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies of L. hesperus dragline. TEM and XRD results indicated a bimodal size distribution of ordered regions; one population of crystals has a mean size of 2 nm, and another spans the size range 40–120 nm. The average elastic modulus measured from L. hesperus dragline is 23 GPa - close to the 25 GPa theoretical modulus for the case of large crystals in Termonia's model. The tensile strength of L. hesperus dragline is ca. 1.7 GPa, close to the case predicted for small crystals in Termonia's model. A combination of the small and large crystals could explain the forced elongation behavior of L. hesperus dragline.
Towards a Mechanical Model of Skin: Insights into Stratum Corneum Mechanical Properties from Hierarchical Models of Lipid Organisation
Authors: O'Malley Brendan , Moore David J. , Noro Massimo , Anwar Jamshed , Notman Becky , Dauskhardt Reinhold , Bedford Eilidh 
Published: April 2011

ABSTRACTThe stratum corneum (SC), the outermost layer of the skin, provides the body with a physiologically essential barrier to unregulated water loss and the influx of exogenous substances. Furthermore, the 10–20 micron thick SC, composed of overlapping protein-rich corneocytes surrounded by a heterogeneous multilamellar lipid matrix, displays tremendous mechanical cohesion and thermal integrity. To understand the contribution of these components to SC mechanical properties requires building a complete mechanical model of the skin. In this study we focus on modelling the hierarchical microstructure of the lipid phase and its relation to mechanical properties using a combination of atomistic and mesoscale simulations. The modelling approaches are parameterised with experimental data from FT-IR spectroscopy, X-ray scattering and, in the case of the mesoscale simulations, with detailed density profiles derived from atomic models. The atomistic models are used to probe the role of specific lipid species in maintaining the thermal and structural stability of the SC extracellular lipid matrix and to investigate the role of hydrogen bonding networks in SC lipid cohesion. Mesoscale models are used to investigate domain formation and lipid bilayer organisation on length and time scales inaccessible with atomistic models. These coarse grained models display transitions between ordered hexagonal gel phases and fluid phases, reproducing the experimentally observed ordering of the hydrophilic and hydrophobic regions.
Solving materials design problems in biology and technology – a case study
Authors: Vincent Julian F. V. 
Published: April 2011

ABSTRACTIn a series of studies we have reclassified the TRIZ categories of ‘contradiction’ and ‘inventive principle’ derived by Altshuller and his colleagues and show that the hierarchical relationships of the parts of a problem are important, such that at low levels of hierarchy, materials and structure predominate, but at high levels, it's information which is important.By identifying the functional conflicts in its design, the cuticle of arthropods can be shown to cope with IR and UV irradiation in the same manner as our technology – by controlling spectral properties. However the skeletal properties of cuticle are integrated with demands for sensing, movement, etc, by controlling the local properties of the material rather than by changing global parameters (which would be the technical solution). The biomimetic similarity of cuticle with technology is only about 20%, suggesting that we can learn from the design of arthropod cuticle.
Effects of Aging on the Toughness of Human Cortical Bone: A Study from Nano to Macro Size-Scales
Authors: Nalla Ravi K. , Kruzic Jamie J. , Kinney John H. , Balooch Mehdi , Ager Joel W. , Martin Michael C. , Tomsia Antoni P. , Ritchie R. O. 
Published: April 2011

ABSTRACTAge-related deterioration of both the fracture properties and the architecture of bone, coupled with increased life expectancy, are factors leading to the increasing incidence of bone fracture in the elderly. In order to facilitate the development of treatments which counter this increased fracture risk, a thorough understanding of how fracture properties degrade with age is required. The present study describes ex vivo fracture experiments to quantitatively assess the effects of aging on the fracture toughness of human cortical bone in the longitudinal direction. Because cortical bone exhibits rising crack-growth resistance with crack extension, we depart from most previous studies by evaluating the toughness in terms of resistance-curve (R-curve) behavior, measured for bone taken from donors 34 to 99 years old. Using this approach, both the crack-initiation and crack-growth toughness are determined and are found to deteriorate with age; the initiation toughness decreases ∼40% from 40 to 100 years, while the growth toughness is effectively eliminated over the same age range. Evidence from x-ray synchrotron tomography is provided to support the hypothesis that the reduction in crack-growth toughness is associated primarily with a degradation in the degree of extrinsic toughening, in particular involving crack bridging at the microstructural level in the wake of the crack. Atomic force microscope-based nanoidentation of individual collagen fibers revealed changes at the collagen fibrillar level and deep-ultraviolet Raman spectroscopy showed that the cross-linking at the nanostructural level also changes with age. These results should provide for a better mechanistic understanding of the increased propensity for bone fracture with age.
Poro-Micromechanics of Bone: Impact Loading and Wave Propagation
Authors: Hellmich Christian , Ulm Franz-Josef 
Published: April 2011

ABSTRACTBased on ‘universal’ mechanical building blocks inherent to all different bones, this paper shows the integration of two classically separated fields of bone biomechanics, namely bone micromechanics[1] on the one hand, and bone poromechanics[2] on the other. Indeed, despite the complex hierarchical organization of bone, it was recently possible to identify such elementary components at the micro and nanolevel of the material for the explanation of the diversity of macroscopic (poro-)elastic properties of different bones. The mechanical properties (i.e. elasticity) of these elementary components are (within limits of experimental scatter) the same for all bones; they are ‘universal’, i.e. independent of tissue type, species, and anatomical location. The mechanical interaction between these elementary components (mechanical morphology) and the dosages of these components in different tissues determine the macroscopic material properties.Continuum micromechanics has turned out as well-suited theoretical tool to derive tissue-dependent elastic properties at different length scales from upscaling the elasticity of ‘universal’ building blocks from the nanometer scale. Once respective micromechanics models are developed and validated, poro-micromechanics allows for the quantification of poroelastic properties such as the Biot and Skempton coefficients, as functions of the volume fractions of mineral, collagen, and the micropore space (Haversian and Volkmann canals, and the inter-trabecular space). Skempton coefficients, related to undrained conditions, allow for quantification of the marrow pressure rise due to impact loading, as can be shown by model predictions of non-destructive impact experiments. Moreover, the aforementioned poroelastic properties enter the governing equations for wave propagation in anisotropic porous media. They allow for the prediction of undrained, fast and slow waves, as is verified by comparison of model results with experimental findings.
Controlling Fracture Behavior of Polymeric Hydrogels
Authors: Kong Hyun Joon , Mooney David J. 
Published: April 2011

ABSTRACTRefined control over the mechanical properties of hydrogels formed from cross-linking of polymers is increasingly regarded as critical for their successful application. In general, increasing the cross-linking density (ρ) of polymer gels raises the mechanical rigidity, but makes the gels more brittle. We proposed that controlling properties of the cross-linking junction and the cross-linking type would mediate the fracture response of the gels, and allow one to decouple the dependency of the mechanical stiffness and toughness from ρ of the gel. This possibility was investigated with alginate hydrogels, because alginate can be gelled via ionic or covalent cross-linking. Increasing ρ of the gels formed using covalent cross-linking with adipic acid dihydrazide or poly (acrylamide-co-hydrazide) raised the elastic modulus (E), but led to a reduction in the toughness of the gels. In contrast, increasing the number of calcium cross-links slowed the crack opening of the gels, and subsequently raised both E and work to fracture (W). From the results of this study, we could demonstrate a novel approach to regulate different mechanical properties of gels in an independent manner. This study provides a valuable guideline to the design of a broad array of polymer hydrogels.
Synthesis of Hydrophilic Two-Photon Absorptive Fullerene-diphenylaminoflourene Dyads for Molecular Self-assembly in Water
Authors: Verma Sarika , Hauck Tanya , Padmawar Prashant A. , Canteenwala Taizoon , Chiang Long Y. , Pritzker Kenneth P.H. 
Published: April 2011

ABSTRACTSynthetic conditions for the preparation of amphiphilic two-photon absorptive poly(ethylene glycolated) diphenylaminofluorene[60]fullerene conjugates C60(>DPAF-PEG6) were investigated. UV-vis spectra of C60(>DPAF-PEG6) collected at the concentration of 1.0 × 10–5 M in water showed absorption bands with a slight red shift, broadened, and in a less intensity as compared with those of the bands obtained in CHCl3. These features are important characteristics of C60(>DPAF-PEG6) molecular aggregation in water. Transmission electron micrographs taken at the concentration of 1.0 × 10–5 M in H2O clearly displayed images of spherical aggregates in a diameter of 200–400 nm. That substantiated high hydrophobic intermolecular interactions between these amphiphilic molecules for assemblies in water.
Fabrication of Polydiacetylene Nanocrystals Deposited with Silver Nanoparticles for a Nonlinear Optical Material
Authors: Onodera Tsunenobu , Oikawa Hidetoshi , Kasai Hitoshi , Nakanishi Hachiro , Sekiguchi Takashi 
Published: April 2011

ABSTRACTNoble metal-coated polydiacetylene (PDA) nanocrystals are expected to enlarge effective third-order nonlinear optical susceptibility, owing to the enhancement of optical electric field induced by localized surface plasmon. The surface of PDA nanocrystals was decorated with silver nanoparticles, and the linear optical properties were investigated. The well-defined PDA nanocrystals were first prepared by the conventional reprecipitation method as an aqueous dispersion. The following two-steps of reduction methods, namely, seed deposition and seed growth, enabled higher silver coverage on the surface of PDA nanocrystals. Silver fine seeds were successfully deposited on the PDA surface by particularly employing an anionic surfactant as a binder. The extinction spectra of the PDA nanocrystals covered with silver exhibited the red-shift and broadening of surface plasmonic peak for silver nanoparticles, which would indicate the interaction among silver nanoparticles on the same PDA nanocrystal. In addition, the red-shift of excitonic peak for PDA nanocrystals was observed, resulting from the changes of dielectric properties around PDA nanocrystal. Both spectral changes would have an influence on nonlinear optical properties of PDA nanocrystal.
Size-effect on Fluorescence Spectrum of Perylene Nanocrystal Studied by Single-particle Microspectroscopy Coupled with Atomic Force Microscope Observation
Authors: Matsune Hideki , Asahi Tsuyoshi , Masuhara Hiroshi , Kasai Hitoshi , Nakanishi Hachiro 
Published: April 2011

ABSTRACTThis paper presents single particle fluorescence spectroscopy of perylene nanocrystals coupled with AFM observation of their topographic shapes. The fluorescence spectra of individual nanocrystals confirmed clearly and precisely a blue-shift in the excimer emission maximum on the reduction of their volume. The result can be explained in terms of “lattice softening”, which makes intermolecular interaction weaker and modified the energy level of the excimer state in nanocrystal.
A Novel Light-Emitting Mixed-Ligand Iridium(III) Complex With a Polymeric Terpyridine-PEG Macroligand: Synthesis And Characterization
Authors: Holder Elisabeth , Marin Veronica , Meier Michael A. R. , Kozodaev Dmitry , Schubert Ulrich S. 
Published: April 2011

ABSTRACTThe synthesis of mixed ligand orthometalated iridium(III) complexes as well as the characterization of their electro-optical properties is briefly illustrated. The cyclic voltammetry results exemplify an enhanced stability of the complex with a poly(ethylene glycol (PEG) side chain compared to the corresponding organometallic model material. Less degradation of the electrically active centers was found to occur on the electrode surface. Furthermore the morphology of thin films of the described polymeric material was investigated with respect to potential applications in thin film devices.
Optical Properties of Polystyrene Opals Infiltrated with Cyanine Dyes in the form of J-Aggregates
Authors: Marabelli F. , Comoretto D. , Bajoni D. , Galli M. , Fornasari L. 
Published: April 2011

ABSTRACTWe report preliminary data on the infiltration of polystyrene opals with cyanine dye water solutions, which are known to form J-aggregates. Different approaches are used to infiltrate cyanines inside opals. The degree of infiltration is evaluated by scanning and transmission electron microscopy as well as micro reflectance spectroscopy. Data show that in spite of the low wettability of polystyrene with water solutions, some infiltration can be achieved. Even though this degree of infiltration is still not enough to observe strong modification on the photonic band structures, further strategies to improve it are in progress.
Complex, 3D Photonic Crystals Fabricated by Atomic Layer Deposition
Authors: King J. S. , Gaillot D. , Yamashita T. , Neff C. , Graugnard E. , Summers C. J. 
Published: April 2011

ABSTRACTRecently we have demonstrated the potential of Atomic Layer Deposition (ALD) for the fabrication of advanced luminescent photonic crystal (PC) structures based on the inverse opal architecture.[1–3] PC's offer efficiency enhancement, decreased threshold, and other enhancements that improve phosphor performance. 3D PC structures are being extensively modeled, revealing that changes in the structures such as shifting the distribution of dielectric material can significantly improve photonic band gap (PBG) properties. For example, in the inverted “shell” structure, the width of the PBG can be increased from 4.25% to 8.6%.[4] Similarly, the PBG width can also be increased to 9.6% by formation of a non-close-packed structure.[5] Using the FDTD method, we have found that the PBG in a TiO2 non-closed packed structure can be as high as 5%. The performance of these structures depends critically on precisely and accurately placed high dielectric material. Using ALD, we have demonstrated infiltration of TiO2 films with extremely smooth surfaces (0.2–0.4 nm RMS roughness) while maintaining a high level of control over the infiltration coating thickness, enabling formation of composite infiltrated and inverse opals with nano-scale precision.Here we report progress in fabrication of multi-layered and non-close packed PCs using ALD. Two and three-layer inverse opals were formed by the deposition of thin layers of ZnS:Mn and TiO2 in stacked configuration, each exhibiting luminescence when excited by UV light. Evidence for modification of the emission characteristics by high order PBGs (gaps other than between the 2nd and 3rd bands) has been observed. In addition, non-close packed inverse opals have been formed by infiltrating heavily sintered silica opals with TiO2, etching the spheres with hydrofluoric acid, and backfilling the resulting inverse opal. Resulting structures were characterized using specular reflectance and transmission, photoluminescence, and SEM. This work demonstrates the enormous potential that ALD offers for the realization of high performance photonic crystal structures.
Two-dimensional Magneto-photonic Crystal Circulators
Authors: Wang Zheng , Fan Shanhui 
Published: April 2011

ABSTRACTPrevious research has demonstrated enhanced Faraday rotation in one-dimensional magnetic photonic crystals, where nonreciprocity in magneto-optical cavities is resonantly enhanced to provide optical isolation in optical paths on the scale of a few microns. In this paper, we study the nonreciprocity of two-dimensional magnetic photonic crystal resonators to allow further miniaturization and monolithic in-plane integration with current integrated optical devices. The nonreciprocal magnetic resonators are constructed by alternating the magnetization directions of the ferromagnetic domains in cavities side-coupled to photonic crystal waveguides. We show analytically that the gyrotropic splitting and the strength of the magnetic hybridization of the cavity modes are determined by the overlap integral between the domain magnetization vector and the modal cross product. With a large overlap obtained from optimizing the domain structures, we circularly hybridize two nearly degenerate modes to form a pair of counter-rotating whispering-gallery like modes, oscillating at different frequencies. As a physical realization, we synthesize two singly-degenerate circularly-hybridized modes in a two-dimensional crystal formed of a triangular air hole lattice in bismuth iron garnet with a TE bandgap. We tune the magnetic splitting and the decay constants of the rotating modes to demonstrate numerically a three-port optical circulator with a 30dB extinction bandwidth of 35GHz at 1550nm. An alternative implementation of a four-port circulator is achieved by side-coupling a point defect to two parallel waveguides. Our numerical experiments are performed with finite-difference time-domain simulations and agree well with the analytical coupled-mode theory predictions.
Highly Ordered Pseudo-Discotic Chromophore Systems for Electro-Optic Materials and Devices
Authors: Bhatambrekar Nishant , Hammond Scott , Sinness Jessica , Clot Olivier , Rommel Harry , Chen Antao , Robinson Bruce , Jen Alex K-Y. , Dalton Larry 
Published: April 2011

ABSTRACTIn order to achieve the near-ferroelectric order desired in organic electro-optic (EO) chromophore systems, a pseudo-discotic chromophore is under investigation. Calculations suggest head-to-tail inter-chromophore dipole-dipole interactions should drive chromophores with an appropriate aspect ratio into ferroelectric columns similar to those seen in discotic liquid crystals (DLCs). Therefore, the liquid crystalline properties of these chromophores are being examined by differential scanning calorimetery (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD). Furthermore, the effect of this discotic behavior on the order and EO properties of the system are being examined both dynamically by second harmonic generation (SHG) and statically by attenuated total reflection (ATR). Additionally, these chromophores are being incorporated into waveguide-based photonic devices.
Large Area Microcontact Printing Presses for Plastic Electronics
Authors: Lee Hee Hyun , Menard Etienne , Tassi Nancy G. , Rogers John A. , Blanchet Graciela B. 
Published: April 2011

ABSTRACTLow cost fabrication is key to the successful introduction of organic electronics and roll to roll manufacturing processes. We propose here that extending flexography into the micron size resolution regime may provide an economical commercialization path for plastic devices. Flexography is a high-speed technique commonly used for printing onto very large area flexible substrates.[1] Although low resolution and poor registration are characteristics of today's flexographic process, it has many similarities with soft lithographic techniques. This work shows that large, (12”×12”) high-resolution printing plates appropriate for use on small tag and label flexographic presses can be prepared using simple and inexpensive flexographic compatible processes. We illustrate the use of these plates for three representative soft lithographic processes: microcontact printing, replica molding, and phase shift lithography.