bluuebunny/crossref_metadata_2025 huggingface dataset:
Field observations, rheological testing and numerical modelling of a debris‐flow event
Authors: Sosio R. , Crosta G. B. , Frattini P.
Published: August 2006

Debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy.

We investigate the dynamics and the rheological properties of a 90 000 m3 debris‐flow event triggered by a rapid regressive landslide with high water content. Field evidence revealed a maximum flow depth of 7–8 m, with an estimated peak discharge of 350–400 m3 s−1. Depositional evidence and grain‐size distribution of the debris pose the debris flow in an intermediate condition between the fluid‐mud and grain‐flow behaviour.

The debris‐flow material has silt–clay content up to 15 per cent. The rheological behaviour of the finer matrix was directly assessed with the ball measuring system. The measurements, performed on two samples at 45–63 per cent in sediment concentration by volume, gave values of 3·5–577 Pa for the yield strength, and 0·6–27·9 Pa s for the viscosity. Based on field evidence, we have empirically estimated the yield strength and viscosity ranging between 4000 ± 200 Pa, and 108–134 Pa s, respectively.

We used the Flo‐2D code to replicate the debris‐flow event. We applied the model with rheological properties estimated by means of direct measurements and back‐analyses. The results of these models show that the rheological behaviour of a debris‐flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts. For debris flows composed by a significant number of coarse clasts a back‐analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows. In these cases, the back‐estimated coefficients do not adequately describe the rheological properties of the debris flow. Copyright © 2006 John Wiley & Sons, Ltd.
The interaction between armouring and particle weathering for eroding landscapes
Authors: Sharmeen Saniya , Willgoose Garry R.
Published: August 2006

The interaction between particle weathering and surface armouring and its effect on erosion has been investigated. The effect of soil armouring is to decrease sediment transport with time by preferentially stripping away fine particles. On the other hand the effect of weathering, which breaks down the particles in the armour, is generally believed to increase erosion. By extending an existing armouring model, ARMOUR, and using a variety of published weathering mechanisms this interaction has been explored. The model predicts that while this is generally true, in some cases erosion can be decreased by weathering. When the particles generated by weathering were approximately of equal diameter, erosion increased while armouring decreased. When weathering produced very fine particles by spalling, erosion increased and armouring also increased. When weathering produced a range of particles from fine to coarse, the armour layer broke down and erosion decreased relative to the no‐weathering case. This latter decrease in erosion was due to the high entrainment of coarser transportable materials from the bed decreasing the sediment transport capacity of the flow. In these studies clear regimes could be identified where erosion was limited by either the energy of the flow alone (i.e. ‘transport‐limited’), or the rate of weathering (‘weathering‐limited’); however, for some mechanisms there was an interaction between the two, which we called ‘weathering/transport limited’. Copyright © 2006 John Wiley & Sons, Ltd.
The use of GIS‐based digital morphometric techniques in the study of cockpit karst
Authors: Lyew‐Ayee P. , Viles H. A. , Tucker G. E.
Published: August 2006

Cockpit karst landscapes are among the most distinctive landscapes in the world, and have been the focus of long‐standing scientific interest. Early researchers used largely descriptive techniques to categorize the terrain, and subsequent work has not attempted to critically re‐evaluate descriptions of landscapes using more sophisticated methods. The distinctive surface topography of cockpit karst areas can be characterized in order to compare them with other karst as well as non‐karst areas, and to determine geological and/or climatic conditions that are responsible for the observed terrain. Process models of the rate of karst denudation or evolution can only be accurate if the contemporary morphology of the landscape is quantitatively and unambiguously defined. A detailed analysis of cockpit karst terrain is carried out using the latest GIS‐based digital morphometric techniques in order to assess the nature of such terrain and provide further information for subsequent modelling, as well as other non‐geomorphological applications, such as environmental management and conservation issues. The paper presents the methodology used for the digital analysis of terrain and landforms in the distinctive Cockpit Country area of Jamaica and its environs. The results indicate that cockpit karst may be categorized based on its vertical, horizontal and shape characteristics, as well as by looking at the semivariogram, slope characteristics, and landscape relief scale, which combine measures of vertical and horizontal scales. Copyright © 2006 John Wiley & Sons, Ltd.
Effects of variable attribute weights on landform classiﬁcation
Authors: Deng Y. X. , Wilson J. P. , Sheng J.
Published: August 2006

This paper focuses on the attribute weight issue and advocates use of modiﬁable attribute weights in terrain‐based environmental analysis and classiﬁcation. A question was asked: ‘How much will the result of a terrain‐based environmental analysis be affected if the weights of used terrain attributes are changed?’ The literature on landform classiﬁcation and the fuzzy k‐means method was reviewed in particular to help clarify the background and importance of this weight assignment issue. As an example, the effects of modifying attribute weights were evaluated for fuzzy k‐means landform classiﬁcation in a case study area. A total of 102 classiﬁcations were compared with each other and with a soil map, and comparison methods were speciﬁcally designed to evaluate the differences between these classiﬁcations. The results show that fuzzy k‐means landform classiﬁcation is sensitive to weight adjustments of adopted terrain attributes. The sensitivity is particularly high when the attribute weights started to be tuned away from the standard (i.e. uniform) weight of one. Better matching between landform classiﬁcation and a soil map may be produced when attribute weights are tuned. In all, we advocate the widespread adoption of an exploratory attitude in assigning attribute weights for environmental analysis and classiﬁcation. Copyright © 2006 John Wiley & Sons, Ltd.
Textural and compositional controls on modern beach and dune sands, New Zealand
Authors: Kasper‐Zubillaga J. J. , Ortiz‐Zamora G. , Dickinson W. W. , Urrutia‐Fucugauchi J. , Soler‐Arechalde A. M.
Published: August 2006

Textural, compositional, physical and geophysical determinations were carried out on 111 beach and dune sand samples from two areas in New Zealand: the Kapiti–Foxton coast sourced by terranes of andesite and greywackes and the Farewell Spit–Wharariki coast sourced by a wide variety of Paleozoic terranes. Our aim is to understand how long‐shore drift, beach width and source rock control the sedimentological and petrographic characteristics of beach and dune sands. Furthermore, this study shows the usefulness of specific minerals (quartz, plagioclase with magnetite inclusions, monomineralic opaque grains) to interpret the physical processes (fluvial discharges, long‐shore currents, winds) that distribute beach and dune sands in narrow and wide coastal plains. This was done by means of direct (grain size and modal analyses) and indirect (specific gravity, magnetic/non‐magnetic separations M/NM, magnetic susceptibility measurements, hysteresis loops) methods. Results are compared with beach sands from Hawaii, Oregon, the Spanish Mediterranean, Elba Island and Southern California.

Compositionally, the Kapiti–Foxton sands are similar to first‐order immature sands, which retain their fluvial signature. This results from the high discharge of rivers and the narrow beaches that control the composition of the Kapiti–Foxton sands. The abundance of feldspar with magnetite inclusions controls the specific gravity of the Kapiti–Foxton sands due to their low content of opaque minerals and coarse grain size. Magnetic susceptibility of the sands is related mainly to the abundance of feldspars with Fe oxides, volcanic lithics and free‐opaque minerals.

The Farewell Spit–Wharariki sands are slightly more mature than the Kapiti–Foxton sands. The composition of the Farewell Spit–Wharariki sands does not reflect accurately their provenance due to the prevalence of long‐shore drift, waves, little river input and a wide beach. Low abundance of feldspar with magnetite inclusions and free opaque grains produces poor correlations between specific gravity (Sg) and Fe oxide bearing minerals. The small correlation between opaque grains and M/NM may be related to grain size. The magnetic susceptibility of Farewell Spit–Wharariki sands is low due to the low content of grains with magnetite inclusions. Hysteresis and isothermal remnant magnetization (IRM) agree with the magnetic susceptibility values. Copyright © 2006 John Wiley & Sons, Ltd.
Soil properties controlling seepage erosion contributions to streambank failure
Authors: Wilson G. V. , Periketi R. K. , Fox G. A. , Dabney S. M. , Shields F. D. , Cullum R. F.
Published: August 2006

The majority of sediment leaving catchments may be from streambank failure. Seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks. The objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure. Seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern Mississippi. Using field observations as a guide, the soil profile conditions of a shallow (45 cm) streambank, consisting of 30 cm of topsoil, a 10 cm conductive layer, and a 5 cm restrictive layer, were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head. The time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer. Seepage erosion began within minutes of flow initiation and resulted in substantial (3 to 34 cm) undercutting of the bank. Sediment concentrations of seeps were as high as 660 g l−1 in situ and 4500 g l−1 in the lysimeters. Sediment concentrations were related to the layer slope, thereby indicating the importance of detailed site characterization. The USDA‐ARS Streambank Stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion, but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks. Published in 2006 by John Wiley & Sons, Ltd.
The Mechanism of Forming H2O from H2 and O2 over a Pt Catalyst via Direct Oxygen Reduction
Authors: Jacob T.
Published: August 2006

Density functional theory (DFT) was used with the B3LYP gradient‐corrected exchange–correlation functional to study the mechanism for the reaction of H2 + ${1 \over 2}$ O2 → H2O over a Pt catalyst via direct oxygen reduction.

Within these studies we first examined the binding characteristics and energetics for each likely intermediate chemisorbed on the Pt(111) surface, modeled by a 35 atom cluster: O, H, O2, H2, OH, OOH, H2O.

Then, the pathways for the dissociation processes of the various intermediates on the Pt35 cluster were calculated. For convenience in comparing different reaction steps, these energetics were used to calculate heats of formation (ΔHf), which were combined with the dissociation barriers. Two main reaction pathways were found for the formation of H2O from H2 and O2:

•(OO‐Dissociation: Here O2 adsorbs on the surface, dissociates, and finally reacts with H sequentially to firstly form OH and then water. The rate‐determining step (RDS) for this mechanism is the Oad + Had → OHad with a barrier of 31.66 kcal mol–1 and not the dissociation of O2ad (barrier of 15.02 kcal mol–1).

•OOH‐Formation: Here O2 reacts firstly with Had to form OOHad, which then dissociates to form OHad and Oad (the RDS, with a barrier of 17.13 kcal mol–1), which finally reacts with another Had to form water.

Thus, under gas‐phase conditions, the OOH‐Formation mechanism is found to be the most favorable.
Covalent‐Ionically Cross‐linked Poly(Etheretherketone)‐Basic Polysulfone Blend Ionomer Membranes
Authors: Kerres J.
Published: August 2006

Sulfinated‐sulfonated PEEK was synthesized via partial reduction of sulfochlorinated PEEK with aqueous Na2SO3. From these polymers, covalent‐ionically cross‐linked ionomer blend membranes were prepared by mixing the sulfinated‐sulfonated PEEK with different base‐modified polysulfones (PSU‐base), followed by cross‐linking with 1,4‐diiodobutane. These membranes have been compared with covalently cross‐linked membranes which were obtained by the cross‐linking of sulfinated‐sulfonated PEEK and with ionically cross‐linked membranes obtained by mixing sulfonated PEEK with different PSU bases. The membranes have been characterized in terms of thermal stability by means of thermogravimetry (TGA) and coupled TGA‐FTIR, in terms of cross‐linking extent by extraction experiments, in terms of proton conductivity by impedance spectroscopy, and finally, in terms of water uptake by gravimetric analysis.
Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane
Authors: Scharfenberger G. , Meyer W. H. , Wegner G. , Schuster M. , Kreuer K.‐D. , Maier J.
Published: August 2006

Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self‐dissociation of the imidazole moieties and “structure diffusion” of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities.

To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized.

The materials are thermally stable up to 200 °C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around σ = 1.5.10–3 S cm–1 at T = 160 °C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers.

Proton self‐diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers.
Development of Hybrid Polymer Electrolyte Membranes Based on the Semi‐Interpenetrating Network Concept
Authors: Colicchio I. , Keul H. , Sanders D. , Simon U. , Weirich T. E. , Moeller M.
Published: August 2006

Hybrid inorganic/organic polymer electrolyte membranes for potential fuel cell applications are prepared by centrifugal casting from solutions of sulfonated polyetheretherketone (SPEEK) (DS 64%) and polyethoxysiloxane (PEOS) in dimethylacetamide, following the concept of a semi‐interpenetrating network. The in situ transformation of PEOS into SiO2 occurs in a “water free” process. The morphology of the films obtained is controlled by the phase segregation process, determined by the rate of evaporation of the solvent and by the transformation of PEOS into SiO2‐particles. The latter process is influenced by the presence of a catalyst. Moreover, N‐(3‐triethoxysilylpropyl)‐4,5‐dihydroimidazole is added to the mixture to enhance the interaction between SPEEK and PEOS and to influence the membrane morphology. The size and size‐distribution of the SiO2 particles formed in the organic matrix are examined by means of transmission electron microscopy. The TEM investigations show a strongly reduced particle size when N‐(3‐triethoxysilylpropyl)‐4,5‐dihydroimidazole is added to the mixture. Proton conductivity measurements are performed on the membranes by impedance spectroscopy in an open set‐up that allows measurements along the longitudinal direction of the sample. All the samples show a plateau in impedance at medium frequencies that represents the proton conducting process. Nafion® 115 is measured in the same set‐up for comparison.
On the Role of Reactant Transport and (Surface) Alloy Formation for the CO Tolerance of Carbon Supported PtRu Polymer Electrolyte Fuel Cell Catalysts
Authors: Kaiser J. , Colmenares L. , Jusys Z. , Mörtel R. , Bönnemann H. , Köhl G. , Modrow H. , Hormes J. , Behm R. J.
Published: August 2006

The role of atomic scale intermixing for the electrocatalytic activity of bimetallic PtRu anode catalysts in reformate operated polymer electrolyte fuel cells (PEFC) was investigated, exploiting the specific properties of colloid based catalyst synthesis for the selective preparation of alloyed and non‐alloyed bimetallic catalysts. Three different carbon supported PtRu catalysts with different degrees of Pt and Ru intermixing, consisting of (i) carbon supported PtRu alloy particles (PtRu/C), (ii) Pt and Ru particles co‐deposited on the same carbon support (Pt+Ru/C), and (iii) a mixture of carbon supported Pt and carbon supported Ru (Pt/C+Ru/C) as well as the respective monometallic Pt/C and Ru/C catalysts were prepared and characterized by electron microscopy (TEM), X‐ray absorption spectroscopy, and CO stripping. Their performance as PEFC anode catalysts was evaluated by oxidation of a H2/2%CO gas mixture (simulated reformate) under fuel cell relevant conditions (elevated temperature, continuous reaction and controlled reactant transport) in a rotating disk electrode (RDE) set‐up. The CO tolerance and H2 oxidation activity of the three catalysts is comparable and distinctly different from that of the monometallic catalysts. The results indicate significant transport of the reactants, COad and/or OHad, between Pt and Ru surface areas and particles for all three catalysts, with only subtle differences from the alloy catalyst to the physical mixture. The high activity and CO tolerance of the bimetallic catalysts, through the formation of bimetallic surfaces, is explained, e.g., by contact formation in nanoparticle agglomerates or by material transport and subsequent surface decoration/surface alloy formation during catalyst preparation, conditioning, and operation. The instability and mobility of the catalysts under these conditions closely resembles concepts in gas phase catalysis.
Alterations in the oligodendrocyte lineage, myelin, and white matter in adult mice lacking the chemokine receptor CXCR2
Authors: Padovani‐Claudio Dolly A. , Liu Liping , Ransohoff Richard M. , Miller Robert H.
Published: August 2006

Oligodendrocyte precursor cell (OPC) proliferation and migration are critical for the development of myelin in the central nervous system (CNS). Previous studies showed that localized expression of the chemokine CXCL1 signals through the receptor CXCR2 to inhibit the migration and enhance the proliferation of spinal cord OPCs during development. Here, we report structural and functional alterations in the adult CNS of Cxcr2−/− mice. In Cxcr2−/− adult mice, we observed regional alterations in the density of oligodendrocyte lineage cells in Cxcr2−/− adult mice, with decreases in the cortex and anterior commissure but increases in the corpus callosum and spinal cord. An increase in the density and arborization of spinal cord NG2 positive cells was also observed in Cxcr2−/− adult mice. Compared with wild‐type (WT) littermates, Cxcr2−/− mice exhibited a significant decrease in spinal cord white matter area, reduced thickness of myelin sheaths, and a slowing in the rate of central conduction of spinally elicited evoked potentials without significant changes in axonal caliber or number. Biochemical analyses showed decreased levels of myelin basic protein (MBP), proteolipid protein (PLP), and glial fibrillary acidic protein (GFAP). In vitro studies showed reduced numbers of differentiated oligodendrocytes in Cxcr2−/− spinal cord cultures. Together, these findings indicate that the chemokine receptor CXCR2 is important for the development and maintenance of the oligodendrocyte lineage, myelination, and white matter in the vertebrate CNS. © 2006 Wiley‐Liss, Inc.
Role of N‐cadherin in Schwann cell precursors of growing nerves
Authors: Wanner Ina B. , Guerra Nicole K. , Mahoney James , Kumar Aman , Wood Patrick M. , Mirsky Rhona , Jessen Kristján R.
Published: August 2006

In the present paper, we determine the localization and developmental regulation of N‐cadherin in embryonic rat nerves and examine the role of N‐cadherin in this system. We also identify a major transition in the architecture of embryonic nerves and relating it to N‐cadherin expression. We find that in early embryonic nerves, N‐cadherin is primarily expressed in Schwann cell precursors. Pronounced expression is seen at distal nerve fronts where these cells associate with growth cones, and the proximal nerve ends, in boundary cap cells. Unexpectedly, N‐cadherin is downregulated as precursors generate Schwann cells, coinciding with the time at which most axons make target connections. Therefore, glial N‐cadherin expression is essentially restricted to the period of axon outgrowth. We also provide evidence that N‐cadherin supports the formation of contacts between Schwann cell precursors and show that these cells are a favorable substrate for axon growth, unlike N‐cadherin‐negative Schwann cells. Induction of N‐cadherin expression in Schwann cells by neuregulin‐1 restores their ability to form contacts and support axon growth. Finally, we show that the loss of glial N‐cadherin during embryonic nerve development is accompanied by a transformation of nerve architecture, involving the appearance of endoneurial connective tissue space, fibroblasts, Schwann cell basal lamina, and blood vessels. Because N‐cadherin is likely to promote the extensive glial contacts typical of the compact embryonic nerve, we suggest that N‐cadherin loss at the time of Schwann cell generation allows endoneurial space to appear between the glial cells, a development that eventually permits the extensive interactions between connective tissue and individual axon–Schwann cell units necessary for myelination. © 2006 Wiley‐Liss, Inc.
The developmental expression of K+ channels in retinal glial cells is associated with a decrease of osmotic cell swelling
Authors: Wurm Antje , Pannicke Thomas , Iandiev Ianors , Wiedemann Peter , Reichenbach Andreas , Bringmann Andreas
Published: August 2006

A major function of glial cells is the control of osmotic and ionic homeostasis, mediated by K+ and water movements predominantly through inwardly rectifying K+ (Kir) and aquaporin water channels. It has been suggested that K+ currents through Kir channels are implicated in the regulation of glial cell volume. Here, we investigated whether the developmental increase in Kir channel expression in Müller glial cells of the rat retina is associated with an alteration of cell volume regulation under anisoosmotic conditions. Around the time of eye opening at postnatal day (P) 15, developing retinal glial cells fully alter the profile of their membrane conductances, from a current pattern with prominent fast transient K+ and Na+ currents to a pattern of noninactivating currents through Kir and delayed rectifier K+ channels. Concomitantly, aquaporins‐1 and ‐4 are expressed in the developing retina. This is accompanied by a conspicuous alteration of the swelling characteristics of cells; somata of immature glial cells in early postnatal retinas (P5–P15) swell under hypotonic stress but no swelling is inducible in mature cells at P18 and thereafter. However, glial cells at all developmental stages swell when their Kir channels are blocked by Ba2+. The postnatal maturation of Kir channel currents and volume regulation in retinal glial cells is delayed by visual deprivation. The data suggest that Kir channels are crucially involved in osmotic volume homeostasis of mature glial cells, and that the absence of Kir channels in immature cells is a major cause of their insufficient volume regulation. © 2006 Wiley‐Liss, Inc.
Differential effects of agarose and poly(lactic‐co‐glycolic acid) on dendritic cell maturation
Authors: Yoshida Mutsumi , Babensee Julia E.
Published: August 2006

Application of biomaterials in combination products in which the biomaterial is presented to the host with a biological component prompts the need for understanding the biomaterial‐associated adjuvant effect in the immune response against antigens associated with such a product. We have previously demonstrated that a polymer commonly used in tissue engineering and vaccine delivery, poly(lactic‐co‐glycolic acid) (PLGA), exerts an adjuvant effect in vivo, which was supported by PLGA‐induced dendritic cell (DC) maturation in vitro. In this study, the effects of agarose and PLGA on DC maturation were compared in vitro to establish differential biomaterial effects. Human monocyte‐derived DCs were treated with agarose or PLGA microparticles or films, and their maturation effect was measured as expression of costimulatory and MHC class II molecules, allostimulatory capacity, and proinflammatory cytokine secretion. Direct comparison of DC maturation phenotype indicated that PLGA was a stronger stimulus of DC maturation than agarose, and this maturation was not affected by microparticle phagocytosis. However, agarose‐treated DCs showed higher activation of nuclear factor κB (NFκB) 24 h after the initial stimulation of DCs. Taken together, these results demonstrate differential biomaterial effects on DC maturation, substantiating the maturation effect of PLGA, and provide screening methods for biomaterial adjuvant effect for applications in combination products. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Biomimetic artificial ECMs stimulate bone regeneration
Authors: Chung Eugene H. , Gilbert Michele , Virdi Amarjit S. , Sena Kotaro , Sumner Dale R. , Healy Kevin E.
Published: August 2006

We demonstrate that a biomimetic polymer network is capable of affecting bone regeneration in vivo. Starting with a foundation consisting of an environmentally responsive poly(N‐isopropylacrylamide‐co‐acrylic acid) hydrogel, we incorporated matrix metalloproteinase‐13 (MMP‐13) degradable crosslinkers and peptides containing integrin‐binding domains (i.e., Arg‐Gly‐Asp) to create a biomimetic matrix designed to encourage osteoblast migration and proliferation. We independently tuned matrix stiffness and peptide concentration to generate a response surface model of osteoblast proliferation on different types of matrices. Osteoblast proliferation was significantly influenced by matrix stiffness (i.e., its complex modulus) and peptide concentration. When implanted in a rat femoral ablation model, these matrices induced bone regeneration only when protease degradable crosslinks were used to create the network. For the matrices with MMP‐13 degradable crosslinkers, the bone formed had a trabecular‐like structure and was distributed throughout the marrow space. Based on the correlated effects of matrix stiffness and ligand concentration, the response surface model will facilitate improvements in the regenerative capacity of these artificial extracellular matrices. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Gelatin–tricalcium phosphate membranes immobilized with NGF, BDNF, or IGF‐1 for peripheral nerve repair: An in vitro and in vivo study
Authors: Chen Ming‐Hong , Chen Pei‐Ru , Chen Mei‐Hsiu , Hsieh Sung‐Tsang , Lin Feng‐Huei
Published: August 2006

In the present study, NGF, BNDF from the neurotrophin family and IGF‐1 were covalently immobilized on gelatin–tricalcium phosphate (GTG) membrane using carbodiimide. We investigated the effects of these growth factors released from the GTG composites on cultured PC12 cells and sciatic nerve regeneration across a 10‐mm‐long gap in rats. In PC12 cell culture, the total protein content and MTT assay indicated more cell attachment on the composites modified with growth factors. The IGF‐1 group showed a higher survival promotion effect on PC12 cells than did BDNF and NGF groups. On the other hand, NGF released from the composite showed the highest level of neuritogenesis for PC12 cells in neurite outgrowth assay. In the animal study, the GTG conduits modified with various growth factors were well tolerated by the host tissue. In the regenerated nerves, the number of the axons per unit area of the BDNF group was significantly higher than that of NGF and GTG groups but similar to that of IGF‐1 group. However, the average axon size was the largest in NGF group. This result was in concordance with the neurite outgrowth assay in which NGF showed the highest neuritogenic potential. In the assessment of motor and sensory recovery after nerve repair, conduits modified with various neurotrophic factors showed a more favorable outcome in compound muscle action potential. The BDNF group had a better gastrocnemic muscle weight ratio than blank GTG repair. Nevertheless, the different effects of GTG conduits modified with various neurotrophic factors on functional recovery cannot be simply illustrated in the sciatic function index. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Low‐intensity ultrasound stimulates the viability and matrix gene expression of human articular chondrocytes in alginate bead culture
Authors: Choi Byung Hyune , Woo Jeong‐Im , Min Byoung‐Hyun , Park So Ra
Published: August 2006

We investigated the effects of low‐intensity ultrasound (LIUS) on the activity of human articular chondrocytes isolated from osteoarthritis patients and cultured in the three‐dimensional alginate beads. LIUS was treated at 0, 100, 200, and 300 mW/cm2 for 10 min everyday for 2, 7, or 15 days. LIUS induced the viability of cells only at day 15 but not until day 7 after treatment, when examined by trypan blue exclusion and LIVE/DEAD® assay kit. When examined at day 7, the proliferation of cells was not changed by LIUS in the 3H‐thymine incorporation. The expression of matrix producing proteins (type II collagen and proteoglycan) was clearly induced by 200–300 mW/cm2 LIUS in the incorporation of radioactivity and Northern blot analysis. Although the expression of MMP‐1, a matrix degrading protein, was decreased, that of TIMP‐1, an inhibitor of MMPs, was not affected by LIUS. Histological analysis revealed an increase in the number and size of glycosaminoglycan‐positive lacunae and cellular organelles, appearing as rough endoplasmic reticulum and mitochondria by LIUS. These results showed that the viability and metabolism of human articular chondrocytes in alginate culture was induced by LIUS treatment, suggesting that they could be a promising autologous source for cartilage tissue engineering. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Evaluation of chondrogenesis within PEGT: PBT scaffolds with high PEG content
Authors: Mahmood Tahir A. , Shastri V. Prasad , van Blitterswijk Clemens A. , Langer Robert , Riesle Jens
Published: August 2006

Porous poly(ethylene glycol) terephthalate:poly (butylene terephthalate) (PEGT:PBT) scaffolds with high PEG molecular weight (1000 g/mole) and PEGT content (60%) were fabricated using two different processes—paraffin templating and compression molding—for cartilage engineering applications. This polymer composition has previously been shown to enable chondrocyte adhesion and maintain differentiated phenotype in 2D monolayer culture. The influence of 3D polymer scaffold processing on the formation of cartilaginous tissue was studied by seeding primary immature bovine chondrocytes within cylindrical scaffolds in mixed flask reactors for 3 days, followed by cultivation in culture plates for a total of 10 or 24 days. Tissue–polymer constructs were evaluated morphologically by SEM and histology, and quantitatively for cellularity, total collagen, and glycosaminoglycan content, all of which remained statistically equivalent for each time point tested, irrespective of fabrication method. These data demonstrate that the polymers engineered for this study were able to support chondrogenesis independent of scaffold fabrication process, with the influence of pore architecture lessened by the highly hydrated scaffold microenvironments induced by high PEG content. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Application of the lithium and magnesium initiators for the synthesis of glycolide, lactide, and ϵ‐caprolactone copolymers biocompatible with brain tissue
Authors: Dobrzyński Piotr , Kasperczyk Janusz , Jelonek Katarzyna , Ryba Mirosław , Walski Michał , Bero Maciej
Published: August 2006

The subject of this work is new method of the synthesis of biodegradable copolymers compatible with brain tissue. Copolymerization of glycolide with lactide was conducted in solution or in bulk in the presence of LiBu, LiAcac, MgBu2, Mg(acac)2 as initiators. In all cases, copolymers with molecular weight of 20000–40000 were obtained, which enables to use them as drug carriers. During the reactions of copolymer chain growth, the intermolecular transesterification occurs, changing the distribution of comonomeric units in copolymer chain. Magnesium initiators showed a lower contribution to transesterification in comparison with lithium and calcium compounds. The copolymerization of glycolide with ε‐caprolactone using magnesium compounds as initiators was also described. The random glycolide/ε‐caprolactone copolymer (10/90) obtained with MgBu2 was used in in vivo study in the forms of microspheres and foils. Complete degradation of microspheres during 6 weeks was observed after the implantation to brain tissue. All implanted copolymers are compatible with brain tissue. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Bacteriostatic polymer film immobilization
Authors: El‐Hayek Rami F. , Dye Kevin , Warner John C.
Published: August 2006

Coatings of quaternary ammonium tertiary structures (QUATS) copolymerized with 4‐vinylbenzylthymine (VBT) exhibited high antimicrobial activity against Escherichia coli. Immobilization of QUATS improves environmental performance by preventing release of antibacterials to the environment, helping to preclude the emergence of resistant strains. The crosslinking immobilization scheme reported herein provides a more environmentally benign and more inexpensive synthesis than previously reported, thus reducing the use of solvents, energy, and production time. Development of water soluble, thymine‐based photopolymers was inspired by the UV‐induced 2π + 2π photocyclodimerization of thymine in DNA. Copolymers of 4‐vinylbenzylthymine and trimethylammonium chloride, triethylammonium chloride, or dimethyloctylammonium chloride were synthesized in different monomer ratios. The antibacterial properties were tested by coating VBT:QUATS in sterilized petri dishes, crosslinking under short UV light, spraying with aqueous suspensions of bacterial cells, air drying, and then applying agar media to promote bacterial growth. The plates were incubated for 24 h at 37°C. The number of viable cells ranged from 17 to 0% growth. Immobilized VBT:QUAT copolymers are antiseptic surfaces that can be produced in an environmentally benign fashion. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res, 2006
Damage and recovery of the bone growth mechanism in young rats following 5‐fluorouracil acute chemotherapy
Authors: Xian Cory J. , Cool Johanna C. , Pyragius Tim , Foster Bruce K.
Published: August 2006

Chemotherapy‐induced bone growth arrest and osteoporosis are significant problems in paediatric cancer patients, and yet how chemotherapy affects bone growth remains unclear. This study characterised development and resolution of damage caused by acute chemotherapy with antimetabolite 5‐fluorouracil (5‐FU) in young rats in the growth plate cartilage and metaphyseal bone, two important tissues responsible for bone lengthening. In metaphysis, 5‐FU induced apoptosis among osteoblasts and preosteoblasts on days 1–2. In growth plate, chondrocyte apoptosis appeared on days 5–10. Interestingly, Bax was induced prior to apoptosis and Bcl‐2 was upregulated during recovery. 5‐FU also suppressed cell proliferation on days 1–2. While proliferation returned to normal by day 3 in metaphysis, it recovered partially on day 3, overshot on days 5–7 and normalised by day 10 in growth plate. Histologically, growth plate heights decreased by days 4–5 and returned normal by day 10. In metaphysis, primary spongiosa height was also reduced, mirroring changes in growth plate thickness. In metaphyseal secondary spongiosa, a reduced bone volume was observed on days 7–10 as there were fewer but more separated trabeculae. Starting from day 4, expression of some cartilage/bone matrix proteins and growth factors (TGF‐β1 and IGF‐I) was increased. By day 14, cellular activity, histological structure and gene expression had returned normal in both tissues. Therefore, 5‐FU chemotherapy affects bone growth directly by inducing apoptosis and inhibiting proliferation at growth plate cartilage and metaphyseal bone; after the acute damage, bone growth mechanism can recover, which is associated with upregulated expression of matrix proteins and growth factors. J. Cell. Biochem. 99: 1688–1704, 2006. © 2006 Wiley‐Liss, Inc.
Molecular and immunohistochemical analyses of cardiac troponin T during cardiac development in the Mexican axolotl, Ambystoma mexicanum
Authors: Zhang C. , Pietras K.M. , Sferrazza G.F. , Jia P. , Athauda G. , Rueda‐de‐Leon E. , Maier J.A. , Dube D.K. , Lemanski S.L. , Lemanski L.F.
Published: August 2006

The Mexican axolotl, Ambystoma mexicanum, is an excellent animal model for studying heart development because it carries a naturally occurring recessive genetic mutation, designated gene c, for cardiac nonfunction. The double recessive mutants (c/c) fail to form organized myofibrils in the cardiac myoblasts resulting in hearts that fail to beat. Tropomyosin expression patterns have been studied in detail and show dramatically decreased expression in the hearts of homozygous mutant embryos. Because of the direct interaction between tropomyosin and troponin T (TnT), and the crucial functions of TnT in the regulation of striated muscle contraction, we have expanded our studies on this animal model to characterize the expression of the TnT gene in cardiac muscle throughout normal axolotl development as well as in mutant axolotls. In addition, we have succeeded in cloning the full‐length cardiac troponin T (cTnT) cDNA from axolotl hearts. Confocal microscopy has shown a substantial, but reduced, expression of TnT protein in the mutant hearts when compared to normal during embryonic development. J. Cell. Biochem. 100: 1–15, 2007. © 2006 Wiley‐Liss, Inc.
Mouse translation elongation factor eEF1A‐2 interacts with Prdx‐I to protect cells against apoptotic death induced by oxidative stress
Authors: Chang Ruying , Wang Eugenia
Published: August 2006

eEF1A‐1 and eEF1A‐2 are two isoforms of translation elongation factor eEF1A. In adult mammalian tissues, isoform eEF1A‐1 is present in all tissues except neurons, cardiomyocytes, and myotubes, where its isoform, eEF1A‐2, is the only form expressed. Both forms of eEF1A have been characterized to function in the protein elongation step of translation, and eEF1A‐1 is shown to possess additional non‐canonical roles in actin binding/bundling, microtubule bundling/severing, and cellular transformation processes. To study whether eEF1A‐2 has similar non‐canonical functions, we carried out a yeast two‐hybrid screening using a full sequence of mouse eEF1A‐2 as bait. A total of 78 hits, representing 23 proteins, were identified and validated to be true positives. We have focused on the protein with the highest frequency of hits, peroxiredoxin I (Prdx‐I), for in‐depth study of its functional implication for eEF1A‐2. Here we show that Prdx‐I coimmunoprecipitates with eEF1A‐2 from extracts of both cultured cells and mouse tissues expressing this protein, but it does not do so with its isoform, eEF1A‐1, even though the latter is abundantly present. We also report that an eEF1A‐2 and Prdx‐I double transfectant increases resistance to peroxide‐induced cell death as high as 1 mM peroxide treatment, significantly higher than do single transfectants with either gene alone; this protection is correlated with reduced activation of caspases 3 and 8, and with increased expression of pro‐survival factor Akt. Thus, our results suggest that eEF1A‐2 interacts with Prdx‐I to functionally provide cells with extraordinary resistance to oxidative stress‐induced cell death. J. Cell. Biochem. 100: 267–278, 2007. © 2006 Wiley‐Liss, Inc.
Phosphatidic acid regulates the affinity of the murine phosphatidylinositol 4‐phosphate 5‐kinase‐Iβ for phosphatidylinositol‐4‐phosphate
Authors: Jarquin‐Pardo Marta , Fitzpatrick Abbie , Galiano Floyd J. , First Eric A. , Davis J. Nathan
Published: August 2006

Type I phosphatidylinositol 4‐phosphate 5‐kinase (PI4P5K) catalyzes the phosphorylation of phosphatidylinositol 4 phosphate [PI(4)P] at carbon 5, producing phosphatidylinositol 4,5 bisphosphate [PI(4,5)P2]. Phosphatidic acid (PA) activates PI4P5K in vitro and plays a central role in the activation of PIP5K pathways in vivo. This report demonstrates that actin fiber formation in murine fibroblasts involves PA activation of PIP5Ks and defines biochemical interactions between PA and the PIP5Ks. Inhibition of phospholipase D production of PA results in the loss of actin fibers. Overexpression of the beta isoform of the type I murine phosphatidylinositol 4‐phosphate 5‐kinase (mPIP5K‐Iβ) maintains actin fiber structure in the face of phospholipase D inhibition. PA activates mPIP5K‐Iβ by direct binding to mPIP5K‐Iβ through both electrostatic and hydrophobic interactions, with the fatty acid acyl chain length and degree of saturation acting as critical determinants of binding and activation. Furthermore, kinetic analysis suggests that phosphorylation of the PI(4)P substrate does not follow classical Michaelis–Menten kinetics. Instead, the kinetic data are consistent with a model in which mPIP5K‐Iβ initially binds to the lipid micelle and subsequently binds the PI(4)P substrate. In addition, the kinetics indicate substrate inhibition, suggesting that mPIP5K‐Iβ contains an inhibitory PI(4)P‐binding site. These results suggest a model in which mPIP5K‐Iβ is surrounded by PI(4)P, but is unable to catalyze its conversion to PI(4,5)P2 unless PA is bound. J. Cell. Biochem. 100: 112–128, 2007. © 2006 Wiley‐Liss, Inc.
Focal adhesion signaling is required for myometrial ERK activation and contractile phenotype switch before labor
Authors: Li Yunping , Gallant Cynthia , Malek Sabah , Morgan Kathleen G.
Published: August 2006

In late pregnancy rapidly increasing fetal growth dramatically increases uterine wall tension. This process has been implicated in the activation of the myometrium for labor, but the mechanisms involved are unclear. Here, we tested, using a rat model, the hypothesis that gestation‐dependent stretch, via activation of focal adhesion signaling, contributes to the published activation of myometrial ERK at the end of pregnancy. Consistent with this hypothesis, we show here that ERK is targeted to adhesion plaques during late pregnancy. Furthermore, myometrial stretch triggers a dramatic increase in myometrial contractility and ERK and caldesmon phosphorylation, confirming the presence of stretch sensitive myometrial signaling element. Screening by anti‐phosphotyrosine immunoblotting for focal adhesion signaling in response to stretch reveals a significant increase in the tyrosine phosphorylated bands identified as focal adhesion kinase (FAK), A‐Raf, paxillin, and Src. Pretreatment with PP2, a Src inhibitor, significantly suppresses the stretch‐induced increases in FAK, paxillin, Src, ERK and caldesmon phosphorylation and myometrial contractility. Thus, focal adhesion‐Src signaling contributes to ERK activation and promotes contraction in late pregnancy. These results point to focal adhesion signaling molecules as potential targets in the modulation of the myometrial contractility and the onset of labor. J. Cell. Biochem. 100: 129–140, 2007. © 2006 Wiley‐Liss, Inc.
Twist negatively regulates osteoblastic differentiation in human periodontal ligament cells
Authors: Komaki Motohiro , Karakida Takeo , Abe Mayumi , Oida Shinichiro , Mimori Kaori , Iwasaki Kengo , Noguchi Kazuyuki , Oda Shigeru , Ishikawa Isao
Published: August 2006

Periodontal ligament (PDL) is a thin fibrous connective tissue located between two mineralized tissues, alveolar bone and cementum, which maintains a constant width physiologically. The mechanisms by which PDL resists mineralization are not well understood. Twist is a basic helix loop helix protein that plays a central role in regulation of early osteogenesis. We investigated the localization of Twist in PDL and compared the expression of Twist and osteoblast‐related genes in PDL cells with those in osteoblast‐like cells in the presence or absence of recombinant human bone morphogenetic protein (BMP)‐2. Histochemical analysis showed that Twist was expressed along alveolar bone surface in PDL. PDL cells constitutively expressed Twist gene and the expression level was higher than that in osteoblast‐like cells. In osteoblast‐like cell culture, BMP‐2 enhanced osteoblast‐related gene expression, while Twist expression was slightly decreased. In contrast, BMP‐2 increased runt‐related transcription factor (Runx)‐2, but failed to enhance alkaline phosphatase (ALP) and osteocalcin (OCN) gene expression in PDL cells. Interestingly, unlike in osteoblast‐like cells, Twist expression was upregulated by BMP‐2 in PDL cells. We transiently knocked down Twist gene in PDL cells using a short interference RNA expression vector (siTwist) and found that ALP, osteopontin (OPN), bone sialoprotein (BSP) genes expression and basal level of ALP activity were slightly increased, whereas Runx2 and OCN genes were not affected. Collectively, these results suggest that Twist may act as a negative regulator of osteoblastic differentiation in PDL cells. J. Cell. Biochem. 100: 303–314, 2007. © 2006 Wiley‐Liss, Inc.