Multidrug-resistant (MDR) enterococci are important nosocomial pathogens and a growing clinical challenge. These organisms have developed resistance to virtually all antimicrobials currently used in ...clinical practice using a diverse number of genetic strategies. Due to this ability to recruit antibiotic resistance determinants, MDR enterococci display a wide repertoire of antibiotic resistance mechanisms including modification of drug targets, inactivation of therapeutic agents, overexpression of efflux pumps and a sophisticated cell envelope adaptive response that promotes survival in the human host and the nosocomial environment. MDR enterococci are well adapted to survive in the gastrointestinal tract and can become the dominant flora under antibiotic pressure, predisposing the severely ill and immunocompromised patient to invasive infections. A thorough understanding of the mechanisms underlying antibiotic resistance in enterococci is the first step for devising strategies to control the spread of these organisms and potentially establish novel therapeutic approaches.
Additive manufacturing technologies provide new opportunities for the manufacturing of components with customisable geometries and mechanical properties. In particular, fused deposition modelling ...(FDM) allows for customisable mechanical properties by controlling the void density and filament orientation. In this work, a methodology is provided for the prediction of the mechanical properties and mesostructure of FDM polymers. To this end, we propose a computational framework for the simulation of the printing process taking as input data specific manufacturing parameters and filament properties. A new two-stage thermal and sintering model is developed to predict the bond formation process between filaments. The model predictions are validated against original experimental data for acrylonitrile butadiene styrene (ABS) components manufactured by FDM. A parametric study is finally presented to interpret the effects of different manufacturing parameters on the mechanical performance of ABS specimens. Overall, the proposed framework offers new avenues for the design of 3D printed polymeric components with custom properties, directly in terms of manufacturing settings.
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•FDM ABS specimens are tested for different combinations of printing parameters.•A two-stage model is proposed to simulate the FDM manufacturing process.•The model predicts thermal conditions and sintering within filaments.•Analytical expressions are established for FDM ABS.•Layer height and environment temperature main drivers for mechanical properties.
This paper deals with the mechanical behavior of polyether–ether–ketone (PEEK) under impact loading. PEEK polymers are the great interested in the field of medical implants due to their ...biocompatibility, weight reduction, radiology advantage and 3D printing properties. Implant applications can involve impact loading during useful life and medical installation, such as hip systems, bone anchors and cranial prostheses. In this work, the mechanical impact behavior of PEEK is compared with Ti6Al4V titanium alloy commonly used for medical applications. In order to calculate the kinetic energy absorption in the impact process, perforation tests have been conducted on plates of both materials using steel spheres of 1.3g mass as rigid penetrators. The perforation test covered impact kinetic energies from 21J to 131J, the equivalent range observed in a fall, an accidental impact or a bike accident. At all impact energies, the ductile process of PEEK plates was noted and no evidence of brittle failure was observed. Numerical modeling that includes rate dependent material is presented and validated with experimental data.
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•Review of WGS and reforming of oxygenated hydrocarbons over Cu, Ni and Co catalysts.•Microstructure/interfacial chemistry of the supported metal catalysts upon interaction with ...respective reactant mixture.•Structural/morphological/redox properties and behavior toward deactivation under reaction conditions.
The work provides a review of water-gas shift and processes of reforming of oxygenated hydrocarbons, basically alcohols, employed for hydrogen production and focusing mainly on advances produced during last five years on catalysts of the base metals copper, nickel and cobalt. Particular attention is paid to analysis of the interplay between microstructure and interfacial chemistry of the supported metal catalysts and its interaction with the reaction mixture in each case. In this sense, the report basically covers how the interactions between the components of the catalysts in the various employed formulations and the presence of promoters affect to structural/morphological/chemical properties of the active metal in each case, their redox properties as well as processes involved in their deactivation under reaction conditions.
Semi-crystalline polymers often present a complex non-linear behaviour that combines thermo-viscoelastic and thermo-viscoplastic contributions associated to different deformation mechanisms. During ...the initial deformation stages, the process is influenced by the rupture and reorientation of crystalline phases while, during the final deformation stages, the process is mainly governed by the mobility and orientation of the amorphous molecular chains. Moreover, the level of reorientation of crystalline and amorphous phases is strongly affected by variables such as temperature and strain rate. This work focusses on the role of such mechanisms in the mechanical behaviour of polyether-ether-ketone (PEEK) within its different thermal-behaviour regions: initial glassy region, glass transition and final rubbery region. To this end, samples of PEEK are subjected to large deformations under uniaxial tension at temperatures from 20 to 240 °C, and strain rates from 0.0001 to 0.1 s−1 (covering both isothermal and adiabatic conditions). In addition, a constitutive model is proposed to complementarily explain the experimental observations by means of entropic strain hardening due to reorientation of polymer chains influenced by thermo-viscoelastic effects, as well as thermo-viscoplastic behaviours defining the material yielding by means of crystallites deformation and breaking. These results provide new insights into the deformation mechanisms of semi-crystalline polymers below and above glass transition, which are significantly relevant for thermoforming processes of biomedical prosthesis.
Daptomycin (DAP) is a cyclic lipopeptide with in vitro activity against a variety of Gram‐positive pathogens, including multidrug‐resistant organisms. Since its introduction into clinical practice in ...2003, DAP has become an important key frontline antibiotic for severe or deep‐seated infections caused by Gram‐positive organisms. Unfortunately, DAP resistance (DAP‐R) has been extensively documented in clinically important organisms such as Staphylococcus aureus, Enterococcus spp., and Streptococcus spp. Studies on the mechanisms of DAP‐R in Bacillus subtilis and other Gram‐positive bacteria indicate that the genetic pathways of DAP‐R are diverse and complex. However, a common phenomenon emerging from these mechanistic studies is that DAP‐R is associated with important adaptive changes in cell wall and cell membrane homeostasis with critical changes in cell physiology. Findings related to these adaptive changes have provided novel insights into the genetics and molecular mechanisms of bacterial cell envelope stress response and the manner in which Gram‐positive bacteria cope with the antimicrobial peptide attack and protect vital structures of the cell envelope, such as the cell membrane. In this review, we will examine the most recent findings related to the molecular mechanisms of resistance to DAP in relevant Gram‐positive pathogens and discuss the clinical implications for therapy against these important bacteria.
Autism spectrum disorders (ASDs) and autistic traits in the general population may share genetic susceptibility factors. In this study, we investigated such potential overlap based on common genetic ...variants. We developed and validated a self-report questionnaire of autistic traits in adults. We then conducted genome-wide association studies (GWASs) of six trait scores derived from the questionnaire through exploratory factor analysis in 1981 adults from the general population. Using the results from the Psychiatric Genomics Consortium GWAS of ASDs, we observed genetic sharing between ASDs and the autistic traits 'childhood behavior', 'rigidity' and 'attention to detail'. Gene-set analysis subsequently identified 'rigidity' to be significantly associated with a network of ASD gene-encoded proteins that regulates neurite outgrowth. Gene-wide association with the well-established ASD gene MET reached significance. Taken together, our findings provide evidence for an overlapping genetic and biological etiology underlying ASDs and autistic population traits, which suggests that genetic studies in the general population may yield novel ASD genes.
Oxide nanoparticles can exhibit unique chemical products due to size limitations and a high density of corner or edge surface sites. Fernandez-Garcia, et al provide a review of recent studies that ...deal with the chemistry of nanostructured oxides.
A major goal of energy research is to use visible light to cleave water directly, without an applied voltage, into hydrogen and oxygen. Although SrTiO3 requires ultraviolet light, after four decades, ...it is still the “gold standard” for the photo-catalytic splitting of water. It is chemically robust and can carry out both hydrogen and oxygen evolution reactions without an applied bias. While ultrahigh vacuum surface science techniques have provided useful insights, we still know relatively little about the structure of these electrodes in contact with electrolytes under operating conditions. Here, we report the surface structure evolution of a n-SrTiO3 electrode during water splitting, before and after “training” with an applied positive bias. Operando high-energy X-ray reflectivity measurements demonstrate that training the electrode irreversibly reorders the surface. Scanning electrochemical microscopy at open circuit correlates this training with a 3-fold increase of the activity toward the photo-induced water splitting. A novel first-principles joint density functional theory simulation, constrained to the X-ray data via a generalized penalty function, identifies an anatase-like structure as the more active, trained surface.
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