Improved wear performance of ultra high molecular weight polyethylene coated with hydrogenated diamond like carbon

Hydrogenated diamond like carbon (DLCH) thin films were deposited on medical grade ultra high molecular weight polyethylene (UHMWPE) by radio frequency plasma enhanced chemical vapor deposition. The DLCH coating thicknesses ranged from 250 to 700. nm. The substrates were disks made of UHMWPEs typically used for soft components in artificial joints, namely virgin GUR 1050 and highly crosslinked (gamma irradiated in air to 100. kGy) UHMWPEs. Mechanical and tribological properties under bovine serum lubrication at body temperature were assessed on coated and uncoated polyethylenes by means of nano-hardness and ball-on-disk tests, respectively. Morphological features of the worn surfaces were obtained by confocal microscopy and scanning electron microscopy. This study confirms an increase in surface hardness and good wear resistance for coated materials after 24. h of sliding test compared to uncoated polyethylene. These results point out that to coat UHMWPE with DLCH films could be a potential method to reduce backside wear in total hip and knee arthroplasties.Ministerio de Ciencia y Educación MAT2006-12603- C02-01, CSD2008-0002

Hacia una metodología para la caracterización experimental del comportamiento a compresión de la mampostería de adobe

In the Iberian Peninsula there are numerous houses and heritage sites built with earthen materials. Nowadays, there is also a significant revival of the use of raw earth in modern architecture due to its ecological value and architectural performance. However, there is still a lack of scientific knowledge about its mechanical behavior, as well as specifications for a rigorous characterization. In this paper, an experimental analysis is carried out in order to develop a methodology for the characterization of the adobe masonry as a building material. Methodological issues for obtaining the strain field of the specimens and the choice of the Young module estimators are considered. The mechanical properties of the adobe masonry and the failure mechanisms are analyzed. In the present study, the mechanical behavior of the adobe masonry coming from the Guadalquivir riverbank in Seville (Spain) is specifically studied under compressive loads.En la Península Ibérica existen numerosas viviendas y elementos patrimoniales construidos con tierra cruda. Por otro lado, actualmente hay una tendencia creciente a revitalizar el empleo de este material en la arquitectura moderna debido a su valor ecológico y arquitectónico. Sin embargo, existe aún una falta de conocimiento científico acerca de su comportamiento mecánico, así como una falta de especificaciones para realizar una caracterización rigurosa. En este artículo se realiza un análisis experimental en aras de desarrollar una metodología para la caracterización de la mampostería de ladrillos de adobe como material estructural. Se plantean cuestiones metodológicas relativas a la obtención de las deformaciones de los especímenes y se analizan las propiedades mecánicas de la mampostería de adobe y los mecanismos de fallo. La presente investigación estudia concretamente el comportamiento mecánico de mampostería de adobe fabricada con tierra proveniente de la rivera del Guadalquivir en Sevilla (España) a compresión simple

Mechanistic Framework for the Formation of Different Sulfur Species by Electron Irradiation of n-Dodecanethiol Self-Assembled Monolayers on Au(111) and Au(100)

The electron-induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy. The same irradiation dose produced different adsorbed groups. The damage at the headgroup–substrate interface leads to find dialkyl sulfide (RS–R′) on Au(111), while dialkyl disulfide (RS–SR) and/or thiol (RSH) were produced on Au(100). With regard to C species, significant amounts of C═C are generated on Au(111) but not on Au(100), showing that double bond formation is not triggered through the same pathways on these surfaces. Detailed analysis of a variety of mechanisms, which involved cationic (RS+), anionic (RS–), or thiyl radical (RS•) species, in combination with ab initio density functional theory (DFT) calculation, leads to the conclusion that the radical pathways successfully explain the experimental results. Molecular dynamics simulations show that the n-dodecanethiolate SAMs on both surfaces are equivalent with regard to the van der Waals interactions. The breakage of the S–Au bonds is studied by means of DFT calculations. The thiyl radical would form close to the Au(100) surface, making it likely to react with another thiyl radical or thiolate to form the RS–SR species. On the other hand, for Au(111), the thiyl radical would form farther from the surface, reacting with the alkyl chains of neighboring molecules to form RS–R′ species. The mechanistic framework proposed here is very useful to explain the behavior of related systems.This work was supported in part by CONICET (PIP 0333), ANPCyT (PICT 2017-4519), Universidad Nacional de La Plata (UNLP X786) of Argentina, and Universidad Nacional de Cuyo. J.O.-A. and M.M.M. acknowledge financial support from CONICET through Grant PIP 11220150100141CO, FONCyT PICT-2015-2191, and SeCyT UNC. This work has used computational resources from CCAD, Universidad Nacional de Córdoba (http://ccad.unc.edu.ar/) and resources provided by the CYTED co-funded Thematic Network RICAP (517RT0529)

Effect of surface roughness and sterilization on bacterial adherence to ultra-high molecular weight polyethylene

AbstractSterilization with ethylene oxide (EO) and gas plasma (GP) are well-known methods applied to ultra-high molecular weight polyethylene (UHMWPE) surfaces in the belief that they prevent major material changes caused by gamma irradiation. However, the influence of these surface sterilization methods on bacterial adherence to UHMWPE is unknown. UHMWPE samples with various degrees of roughness (0.3, 0.8 and 2.0 µm) were sterilized with either GP or EO. The variations in hydrophobicity, surface free energy and surface functional groups were investigated before and after sterilization. Sterilized samples were incubated with either Staphylococcus aureus or Staphylococcus epidermidis in order to study bacterial adherence to these materials. Fewer bacteria adhered to UHMWPE after sterilization with EO than after sterilization with GP, especially to the smoothest surfaces. No changes in chemical composition of the UHMWPE surface due to sterilization were observed using X-ray photoemission spectroscopy analysis. The decreased bacterial adherence to UHMWPE found at the smoothest surfaces after sterilization with EO was not directly related to changes in chemical composition. Increased bacterial adherence to rougher surfaces was associated with increased polar surface energy of EO-sterilized surfaces

A Modified View on Octocorals: Heteroxenia fuscescens Nematocysts Are Diverse, Featuring Both an Ancestral and a Novel Type

Cnidarians are characterized by the presence of stinging cells containing nematocysts, a sophisticated injection system targeted mainly at prey-capture and defense. In the anthozoan subclass Octocorallia nematocytes have been considered to exist only in low numbers, to be small, and all of the ancestral atrichous-isorhiza type. This study, in contrast, revealed numerous nematocytes in the octocoral Heteroxenia fuscescens. The study demonstrates the applicability of cresyl-violet dye for differential staining and stimulating discharge of the nematocysts. In addition to the atrichous isorhiza-type of nematocysts, a novel type of macrobasic-mastigophore nematocysts was found, featuring a shaft, uniquely comprised of three loops and densely packed arrow-like spines. In contrast to the view that octocorals possess a single type of nematocyst, Heteroxenia fuscescens features two distinct types, indicating for the first time the diversification and complexity of nematocysts for Octocorallia

Crossed-beam energy transfer : Polarization effects and evidence of saturation

Recent results on crossed-beam energy transfer are presented. Wavelength tuning was used to vary the amount of energy transfer between two beams in a quasi-stationary plasma with carefully controlled conditions. The amount of transfer agreed well with calculations assuming linear ion acoustic waves (IAWs) with amplitudes up to . Increasing the initial probe intensity to access larger IAW amplitudes for otherwise fixed conditions yields evidence of saturation. The ability to manipulate a beam's polarization, which results from the anisotropic nature of the interaction, is revisited; an example is provided to demonstrate how polarization effects in a multibeam situation can dramatically enhance the expected amount of energy transfer

“Estudio de las resistencias a Aminoglicósidos en enterobacterias de origen hospitalario”

The aminoglycoside antibiotics modifying enzymes and their genetic properties from 97 entero bacteria strains resistant to several aminoglycoside antibiotics isolated at the Universitary Hospital of Granada were studied. These enzymes were detected in 82 strains (84,5 %) and their genetics determinants were localized in 74 strains (90,2 %) on conjugative plasmids. 8 strains (9,8 %) had their genetics determinant on plasmid transferred only by transformation. Four types of enzymes were found, APH(3'), AAC(3), AAC(6') and ANT(2") in this strains. Our results show a situation of endemic resistance towards those antibiotics without control in this hospital.Se estudia la presencia de enzimas modificantes de antibióticos aminoglicósidos y su origen genético en 97 cepas de enterobacterias resistentes a diversos aminoglicósidos y aisladas en el Hospital Universitario de Granada. La presencia de tales enzimas se detectó en 82 cepas (84,50/0) cuyos determinantes génicos se localizaron en 74 casos (90,2 %) sobre plásmidos conjugativos, y en 8 (9,8 %) en plásmidos que únicamente se pudieron transferir mediante transformación. Se identificaron 4 tipos de enzimas, APH(3'), AAC(3), AAC(6') Y ANT(2") respectivamente según su frecuencia de aparición. Los resultados obtenidos indican la existencia de un estado de resistencia endémica, acentuado en el caso de aquellos antibióticos cuyo uso prácticamente no se controla, y aportan la base de conocimientos necesaria para la determinación de la evolución de las mismas en nuestro hospital con fines epidemiológicos