bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enzyme-Pretreatment RemovesIn VitroCytoxic Effects of Dermal Sheep Collagen
Authors: van Luyn M. J. A. , van Wachem P. B. , Damink L. H. H. Olde , Dijkstra P. J. , Feijen J. , Nieuwenhuis P. 
Published: March 2011

ABSTRACTWe investigated thein vitrocytotoxicity of commercially available hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC). HDSC was found to induce medium cytotoxic effects, as measured with methylcellulose cell culture. Apart from primary cytotoxicity, due to direct release of (extractable) cytotoxic products, HDSC was found to containsecondarycytotoxicity, possibly released by enzymatic interactions. In this study we found proof for this hypothesis, by exposing extracted HDSC to enzyme-containing medium. Furthermore we observed, that enzymatic pre-treatment can remove all secondary cytotoxic products, possibly due to detachment of pendants, which are still coupled to fragments of collagen molecules. The possibility of enzymatic pretreatment of HDSC, to obtain a non-cytotoxic/biocompatible material, may be important forin vivoapplications.
Effects of Process Parameters on Physical and Biological Properties of a Small Caliber Vascular Prosthesis
Authors: Carr R. M. , Ekstein B. A. , Kemp P. D. , O'Neil K. D. , Weinberg C. B. , Garcia J. P. 
Published: March 2011

ABSTRACTA method is described for the production of collagen constructs formed from densely packed, native-banded collagen fibrils. This “Dense Fibrillar Collagen” is formed by concentrating collagen in situ prior to self assembly of the collagen into fibrils. The effect of altering the pH, ionic strength, and osmolarity of the concentrating solution was measured. Increasing the ionic strength and osmolarity of the concentrating solution increased the burst strength of the constructs; increasing the pH from 3.8 to 7.1 reduced the surface fibrillarity, degree of platelet uptake and “short term in vivo thrombogenicity. This construct is being considered as the basis of a small-caliber vascular prosthesis to support guided tissue regeneration.
Induction of Hepatocyte Differentiation by the Extracellular Matrix and an RGD-Containing Synthetic Peptide
Authors: Mooney David J. , Langer Robert , Hansen Linda K. , Vacanti Joseph P. , Ingber Donald E. 
Published: March 2011

ABSTRACTTo design novel biomaterials for hepatocyte transplantation it will be necessary to determine whether specific extracellular matrix (ECM) molecule(s) or the adhesive interactions between the surface and hepatocytes are responsible for regulation of hepatocyte function. Purified ECM molecules (laminin, fibronectin, types I and IV collagen) and a synthetic peptide containing the arginine-glycine-aspartate (RGD) cell-binding sequence were precoated at defined densities to non-adhesive polystyrene dishes. Hepatocytes cultured on dishes coated with a low density of ECM molecules (1 ng/cm2) maintained a round morphology, and high liver-specific protein secretion rates. In contrast, culturing hepatocytes on increasing ECM densities (50–1000 ng/cm2) resulted in extensive cell spreading, a loss of liver-specific protein secretion, and cell growth. Hepatocytes cultured on dishes coated with the RGD-containing peptide did not spread even on a high density of the peptide (10,000 ng/cm2), and albumin secretion remained high for hepatocytes cultured on all peptide densities (1–10,000 ng/cm2). These results suggest that a variety of ECM molecules and synthetic peptides are capable of inducing hepatocyte differentiation in vitro, and these effects depend on their ability to promote cell spreading.
A New Enzyme Immunoassay for Activation of Platelets by Biomaterials: Reduced Activation by Phosphorylcholine-Coated Surfaces
Authors: Campbell Ewan J. , Wiles Martin C. , New Roger R. C. , Charles Stephen A. 
Published: March 2011

ABSTRACTAn enzyme immunoassay has been developed to semi-quantitate the degree of activation of platelets adhering to biomaterials. The method employs a monoclonal mouse anti-GMP-140 antibody. The glycoprotein GMP-140 is contained in alpha granules of resting platelets and is translocated to the outer membrane of platelets during activation via the thrombin-dependent pathway. A polyclonal anti-mouse IgG peroxidase conjugate is then added and platelet activation can be semi-quantitated by use of a suitable substrate, such as OPD.The results obtained by this method compare well with scanning electron microscopy, and are shown to be less prone to the misinterpretation often associated with other conventional assay systems such as the determination of platelet adhesion by detection of ATP.The adhesion and activation of platelets by biomaterials has been compared before and after coating these materials with phosphorylcholine (PC) derivatives. PC, in its form as a headgroup in membrane phosphoglyceride (lecithin) and ceramide (sphingomyelin) is a ubiquitous component of cell membranes, and displays extremely low interaction and binding with plasma proteins such as Factor XII [1,2], complement [2], fibrinogen [3,2], immunoglobulins [2] and albumin [2,4].Using the immunoassay described here activation of platelets is seen to be dramatically reduced after coating surfaces, such as polyethylene, with PC compared with the untreated control. A PCcoated surface should therefore be an ideal starting point for developing tissue-inducing biomaterials. In addition endothelial cells contain GMP-140 in their secretory granules [5]. This would make this assay a potential tool in the investigation of endothelial cell - biomaterial interaction.
Quantitative Ruthenium Method for Analysis of Nitrogen Ion-Implanted Titanium Alloy (Ti-6AI-4V) and the Effect on Bacterial Adherence
Authors: Giammara Beverly L. , Williams James M. , Birch David J. , Dobbins Joanne J. 
Published: March 2011

ABSTRACTThe effects of nitrogen ion implantation of Ti-6AI-4V alloy on growth ofPseudomonas aeruginosabacteria on surfaces of the alloy have been investigated. Results for ion implanted samples were compared with controls with similarly smoothly polished surfaces and with controls that had intentionally roughened surfaces. The test consisted of exposing sterile alloy samples to a microbiological broth, to which 24 hour-old cultures ofPseudomonas aeruginosahad been added. After bioassociation at normal temperature 37°C, bacteria adhering to the surface were fixed and treated with a new ruthenium tetroxide staining method, and quantified by use of scanning electron microscopy (SEM), back-scattered electron imaging and EDAX energy dispersive microanalysis. For smooth samples of the alloy, after a 12 hour growth period, the retained bacteria (revealed by the biologically incorporated ruthenium), decreased monotonically with nitrogen dose out to a total fluence of approximately 7 × 1017/cm2in an affected depth of approximately 0.1500μm. The SEM confirmed that thePseudomonas aeruginosaadhered equally to control materials. The ruthenium studies revealed that the amount of bacterial adhesion is indirectly proportional to the nitrogen ion implantation of the titanium. The greater the percentage of nitrogen ion implantation in the titanium alloy, the less bacteria colonized the disk.
Technological Development of Lipid-Based Microcylinders: Biocompatibility and Controlled Release
Authors: Spargo Barry J. , Stilwell Geoffrey E. , Cliff Richard O. , Monroy Rod L. , Rollwagen Florence M. , Rudolph Alan S. 
Published: March 2011

ABSTRACTWe have developed a lipid-based microcylinder for the controlled release of biological response modifiers. Lipid microcylinders are composed of 1,2-ditricosa-10,12-diynoyl-sn-glycerol-3-phosphocholine which form hollow cylinders 50–250 μm in length with a diameter approximately 0.5–1.0 μm. Amphiphilic molecules such as ganglioside (5–6 mol%) can be incorporated into the bilayers of the microcylinder, modulating surface characteristics of the structure.In this study, we have examined the biocompatibility of lipid microcylinders and lipid microcylinders containing 6 mol% ganglioside. The interaction of microcylinders with peripheral blood monocytes and three cell lines: U937, a histocytic monocyte; K562, an erythroblast, and; a Jurkat derivative, a lymphoblast was assessed. Toxicity, as measured by proliferative status of the cell lines, was not evident at lipid concentrations up to 100 μg/ml lipid. Peripheral blood monocytes were observed to closely associate, but not engulf lipid microcylinders. However, when ganglioside was present in the lipid microcylinders this interaction was markedly decreased.We have begun to measure the release rates of growth factors such as transforming growth factor-beta (TGF-β) from lipid microcylinders. Release of TGF-β from the microcylinders follows first-order kinetics. The rate of release can be modulated by increasing the temperature which results in a thermotrophic phase transition of the lipid at 43 °C.
Physiological Cultured Skin Substitutes for Wound Healing
Authors: Halberstadt Craig , Anderson Phil , Bartel Ronnda , Cohen Ron , Naughton Gail 
Published: March 2011

ABSTRACTPhysiological dermal and dermal-epidermal skin analogs have been developed in our laboratory using a novel technology for three-dimensional tissue culture. Human neonatal dermal fibroblasts are seeded on a biodegradable mesh made of polyglycolic or polyglactic acid (PGAIPGL). As the fibroblasts proliferate, they stretch across the mesh openings and secrete growth factors and human dermal matrix proteins, including collagen types I & HI and elastin. This process forms a metabolically active, three-dimensional dermal tissue around the mesh scaffolding. The mesh fibers are hydrolyzed over time and is completely resorbed in vivo within four to eight weeks. Multiple sheets of the PGA/PGL-dermal analog are grown simultaneously in a closed, continuous media-flow system, also developed in our laboratory. After attaining confluence, the dermal sheets may be seeded with keratinocytes, to create a living dermal-epidermal composite tissue.
Biological Response of Intramedullary Bone to Poly-L-Lactic Acid
Authors: Suganuma J. , Alexander H. , Traub J. , Ricci J. L. 
Published: March 2011

ABSTRACTBioabsorbable synthetic polymers have been studied for their possible application in absorbable internal fracture fixation devices. The current study examines the biological response of intramedullary bone to PLLA (poly-L-lactic acid). PLLA degrades at a rate sufficiently slow to be useful for fracture fixation and undergoes hydrolytic deesterification to form metabolites normally found in the body. Nevertheless, the lactic-acid-rich degradation products have the potential to significantly lower the local pH in a closed space surrounded by bone. It is hypothesized that this acidity may tend to cause abnormal bone resorption and/or demineralization.
Effective Dielectric function of a Composite with Aligned Spheroidal Inclusions
Authors: Barrera Ruben G. , Giraldo Jairo , Mochan W. Luis 
Published: March 2011

ABSTRACTThe effective dielectric response εM of a composite with aligned spheroidal inclusions is calculated. Using the dipolar and the mean-field approximation (MFA) an analytical expression for εM as a functional of the two-particle distribution function p(2) is obtained. It is shown that previous expressions reported in the literature correspond to different choices of p(2), thus, clarifying the origin of their discrepancies. The theory is further extended beyond the MFA by including the dipolar fluctuations through a renormalization of the polarizability tensor of the inclusions. The absorption peaks are diminished and broadened by the spatial disorder, which also yields an easily identified coupling among electromagnetic modes with perpendicular polarizations.
Multipolar Expansions for Multiple Scattering Theory
Authors: Brown R. G. , Ciftan M. 
Published: March 2011

ABSTRACTA simple derivation (based on a derived identity of integral equation theory) of fully separable, non–muffin–tin multiple scattering theory is presented. Three multipolar representations have been proposed for use in this theory: the original representation by Williams and Morgan, a more recent one by Brown and Ciftan, and a “Bloch periodic” representation by Badralexe and Freeman (which was addressed in earlier work). We study the properties of the Williams and Morgan representation in the context of the 2D empty square lattice, where the representation of Brown and Ciftan is manifestly exact and correct (so that MST derived in terms of it is a “natural” theory). We show that the representation of Williams and Morgan contains an explict divergence predicted by its implicit use of a wrong-order Green's function expansion but that MST expressed in terms of this representation is still a fairly good asymptotic approximation to the formally exact theory.
Solution of the Single-Site Aspherical Scattering Problem for the Dirac Equation
Authors: Lovatt Stephen C. , Gyorffy B.L. , Guo Guang-Yu 
Published: March 2011

ABSTRACTWe study the scattering solutions of the Dirac equation numerically for anisotropic, finite range (warped muffin-tin), potentials. In particular, we calculate the partial-wave scattering matrix, ƒAA'(ε) and S-matrix SAA′(ε), for a potential characteristic of crystalline Silicon. We illustrate the consequences of aspherical scattering with reference to Silicon.
Ab Initio-Calculations of Residual Resistivities For Dilute Ni-Alloys
Authors: Mertig I. , Zeller R. , Dederichs P.H. 
Published: March 2011

ABSTRACTWe report about residual resistivity calculations for dilute Ni alloys which are based on density-functional theory and the Korringa-Kohn-Rostoker Green's-function method. The transport is described quasiclassically by means of the Boltzmann equation using a two current model for the ferromagnetic host. In particular we consider 3d, 4d, 4sp and 5sp impurities in Ni and include in addition to the impurity atom one shell of perturbed host atoms in the calculation. For the residual resistivity satisfactory agreement with the experiments is obtained in practically all cases. We clarify the role of both subbands for the transport properties.
Compositional Disorder, Magnetism, and Their Interplay in Metallic Alloys
Authors: Johnson D. D. , Staunton J. B. , Pinski F. J. , Gyorffy B. L. , Stocks G. M. 
Published: March 2011

ABSTRACTChemical disorder leads to a variety of intriguing phenomena in alloys which have yet to be fully understood, particularly those phenomena occuring when chemical and magnetic effects interplay with one another. For example, magnetic order gives rise to chemical ordering in alloys, as in Ni-rich NiFe alloys. Two examples of the interplay of chemical disorder and magnetism will be discussed. Our recently developed ab-initio Landau (mean-field) theory for calculating the chemical-chemical, magneto-chemical, and magnetic-magnetic correlation functions in substitutional random alloys is used to describe electronic/magnetic mechanisms (e.g. in FeV) which give rise to the chemical short-range order as determined by neutron, X-ray, or electron diffuse scattering intensities. New developments within this approach that account for charge rearrangement effects will be mentioned. These calculations are performed within the multiplescatteringframework, developed by Korringa, Kohn, and Rostoker (KKR), combined with the coherent potential approximation (CPA) to describe the disorder. This approach allows a firstprinciples description of the electronic structure of the high-temperature, chemically disordered state and its instability to ordering at low temperatures. This method provides not only a direct comparison of diffuse scattering data with theory but a means to understand more fully the underlying mechanisms which drive chemical and/or magnetic ordering.
Spin-Polarized Relativistic Band Structure Calculations for Dilute and Concentrated Disordered Alloys
Authors: Ebert H. , Akai H. 
Published: March 2011

ABSTRACTApplications of the spin-polarized relativistic version of multiple scattering theory (SPRKKR) to study the electronic properties of dilute and concentrated disordered alloys are presented. This approach, developed recently, allows to investigate magnetic systems containing heavy elements and also gives access to a detailed discussion of phenomena, which are linked to the simultanous presence of spin-polarisation and spin-orbit coupling. This is demonstrated by discussing the hyperfine properties of 5d-transition metals dissolved substitutionally in Fe, where pronounced relativistic effects could be found. In addition the magnetic X-ray dichroism (MXD), denoting the difference in absorption of left and right circularly polarized radiation, is studied for these dilute alloys.To be able to deal also with concentrated alloys, we have combined the Coherent Potential Approximation (CPA) alloy theory with the SPRKKR-formalism. Results for the spin-orbit induced orbital contributions to the magnetic moments as well as the MXD in FexCol-x and CoxPtl-x clearly show that remarkable relativistic effects are present even for relatively light elements.
A Full-Potential KKR-GREEN's Function Method to Calculate the Electronic Structure of Surfaces
Authors: Zeller R. , Lang P. , Drittler B. , Dederichs P.H. 
Published: March 2011

ABSTRACTWe present a multiple-scattering Green's function method to calculate the electronic structure of ideal surfaces and surfaces with point defects. In our method we use the full potential in each atomic cell and describe the surface as a twodimensional defect of the bulk crystal by removing several (three to five) adjacent layers. We have implemented our method within density-functional theory in the local-spin-density approximation and present first results for the Cu (001)-surface, for magnetic monolayers on this surface and for such monolayers in bulk Cu.
A Simple Derivation of the Layer-Kkr Theory of Leed
Authors: Marcus P.M. 
Published: March 2011

ABSTRACTThe equations of the layer-KKR method for finding the intensities of electrons diffracted by a semi-infinite layered structure are derived in a simple way by use of three identities relating spherical and plane waves and by use of a compact notation. The third identity, which transforms a sum of outgoing spherical waves on a twodimensional array intoa sum of plane waves or beams, is a very useful simplification of the derivation, which does not appear in texts on LEED. Explicit linear equations are derived for amplitudes of outgoing spherical waves produced by diffraction of an incident beam first by a singleBravais net and then generalized to a composite layer made up of several Bravais nets; matrix elements of the beam reflection and transmission matrices for a single Bravais netand for a composite layer are given, and also the exact interlayer matrix equation for the reflection matrix of the semi-infinite structure.
Advanced Multiple Scattering Theories of Low-Energy Electron Diffraction (LEED)
Authors: Hove M.A. Van 
Published: March 2011

ABSTRACTRecent advances in the theory of low-energy electron diffraction (LEED) are reviewed. They primarily concern methods to handle the multiple scattering of electrons in an atomiclattice. These advances have allowed the structure determination by LEED of complex surface structures, including large-unit-cell overlayers of molecules, disordered and incommensurate overlayers, complex reconstructions and adsorbate-induced relaxations.
Multiple Scattering of Electrons in Condensed Matter Physics: An Overview
Authors: Gyorffy B.L. 
Published: March 2011

ABSTRACTThe Multiple Scattering strategy for studying electrons in condensed matter is reviewed. It is emphasized that this approach is effective for the Dirac and Bogoliubov-de Gennes equations, describing relativistic and superconducting quasi-particles respectively, as well as the usual Schrödinger's equation which arises during the implementation of the Density Functional Theory.
Hierarchy in Extended Chain Polymers
Authors: Klunzinger P. E. , Eby R. K. , Adams W. W. 
Published: March 2011

AbstractRigid rod polymers are of potential use in fibers for composites because of their high specific tensile strength and modulus as well as their high thermal stability. Some other common properties of systems meeting these criteria are a nonlinear elasticity (increasing Young's modulus with increasing tensile stress) and a negative coefficient of thermal expansion along the fiber axis. In composites, these two properties can combine to cause an increase of Young's modulus with increasing temperature and can lead to yielding or interfacial failure. The source of the nonlinear elasticity resides at two length scales: 1) the scale of the crystallites, (the reversible realignment of the crystallites along the fiber axis with increasing stress), and 2) at the scale of the molecules, (an inherent nonlinear elasticity of the molecules themselves). The former effect is reviewed and computational results for the latter are presented along with computational results for the molecular origin of the negative coefficient of thermal expansion.
Polymer Microlayer Composites
Authors: Hiltner A. , Sung K. , Shin E. , Bazhenov S. , Im J. , Baer E. 
Published: March 2011

AbstractContinuous microlayer composites of polycarbonate (PC), a ductile glassy polymer, and styrene-acrylonitrile copolymer (SAN), a glassy relatively brittle polymer, were discussed. Microlayered systems composed of 49 to 776 continuous layers, in which the primary variable was the variation in thickness of the continuous layers between 30 and 2μm, were emphasized. The bulk properties of these microlayered composites showed a dramatic improvement in the toughness or ductility and in the fatigue properties as the layer thickness decreased. Investigation of the irreversible deformation processes revealed that when the layers were thicker (30μm, 49 layers) the SAN layers crazed and the PC shear banded in the usual manner. Subsequently the composite system fractured in a relatively brittle manner due to the development of large voids in the SAN layers. When the layer thickness was reduced to 2μm (776 layers) the entire system behaved in a ductile manner and both the PC and SAN shear banded due to a new cooperative process. This was analyzed by considering the micromechanics of these irreversible processes at the PC-SAN interface. As a result of this work, it is expected that ultra-thin layered structures of other alternating composite systems will reveal synergistic properties if the interfacial properties are designed so that the ductile component will dominate the yield and failure characteristics of the entire system.
Failure Problems In Composites
Authors: Mcgarry Frederick J. 
Published: March 2011

AbstractFiber reinforced polymer matrix composites have become very useful in chemical processing systems, in transportation applications such as automobiles, aircraft and boats, in electrical hardware and in sports equipment. Failures in these rarely involve gross cohesive fracture; usually leaks develop, the stiffness decreases, local delamination occurs, the dielectric properties degrade or the strength declines. Almost all of these failures can be traced to local cracking, either at the fiber matrix interface or within the matrix itself. The cracks are generated by mechanical loads, by thermal excursions or by fluid absorption, because the relevant properties of the fiber and the matrix often differ by orders of magnitude. Current technology attempts to avoid the cracks by maximizing the fiber-matrix adhesion and great progress has been made in this area. An alternative interposes a thin compliant layer, rubber, between the two constituents thereby reducing the stress concentrations which exist because of their greatly different properties. Cracking is inhibited, composite strength is increased and its energy absorption also rises; if the rubber layer is thin (a few thousand Angstroms) no loss of stiffness or heat resistance is evident.