53 research outputs found

    Flexible nanocomposites based on polydimethylsiloxane matrices with dna-modified graphene filler: Curing behavior by differential scanning calorimetry

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    Novel silicone-based nanocomposites with varied elastic properties were prepared by blending standard polydimethylsiloxane (PDMS) with a lower viscosity component (hydroxyl-terminated PDMS) and integrating a graphene nanoplatelets (GNP) filler modified by strands of deoxyribonucleic acid (DNA). The curing behavior of these nanocomposites was studied by dynamic and isothermal differential scanning calorimetry. The activation energies of the polymerization reactions were determined using the Kissinger method and two model-free isoconversional approaches, the Ozawa–Flynn–Wall and the Kissinger–Akahira–Sunose methods. Results show that the complex trend of the curing behavior can be described using the isoconversional methods, unveiling lower activation energies for the nanocomposites with standard PDMS matrices. The role of the DNA modification of graphene on the curing behavior is also demonstrated. The curing reactions of the nanocomposites with the PDMS matrix are favored by the presence of the GNP–DNA filler. PDMS/PDMS–OH blends generate softer nanocomposites with hardness and reduced elastic modulus that can be tuned by varying the amount of the filler

    Hybrid carbon nanocomposites made of aerospace-grade epoxy showing synergistic effects in electrical properties and high processability

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    In this work, we investigate the processability and the volumetric electrical properties of nanocomposites made of aerospace-grade RTM6, loaded with different carbon nanoparticles. Nanocomposites with graphene nanoplatelets (GNP), single-walled carbon nanotubes (SWCNT) and hybrid GNP/SWCNT in the ratio 2:8 (GNP2SWCNT8), 5:5 (GNP5SWCNT5) and 8:2 (GNP8SWCNT2) were manufactured and analyzed. The hybrid nanofillers are observed to have synergistic properties as epoxy/hybrid mixtures showed better processability than epoxy/SWCNT, while maintaining high values of electrical conductivity. On the other hand, epoxy/SWCNT nanocomposites present the highest electrical conductivities with the formation of a percolating conductive network at lower filler content, but very large viscosity values and filler dispersion issues, which significantly affect the final quality of the samples. Hybrid nanofiller allows us to overcome the manufacturing issues typically associated with the use of SWCNTs. The combination of low viscosity and high electrical conductivity makes the hybrid nanofiller a good candidate for the fabrication of aerospace-grade nanocomposites with multifunctional properties

    Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

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    BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

    Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

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    Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

    Functional nanocomposites based on graphene/DNA interface: Towards a bio-inspired sensing of UV radiation effects

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    Ultraviolet (UV) radiation naturally characterizes the Earth environment and the outer space, representing one of the most hazardous agents for human health and for the useful lifetime of organic materials. The possibility to develop a UV-detecting system able to ensure a good sensitivity and stability during measurements, and possessing at the same time low weight and real-time response, represents a fascinating challenge towards new technological advances in the field of radiation sensitive materials. This thesis is focused on the design, preparation and testing of bio-inspired UV sensitive nanocomposites based on graphene/DNA interface. The sensing principle of such nanocomposites relies on the highly conductive nature of graphene combined with the chemical sensitivity of DNA strands to UV radiation, particularly in the UV-C band (100 nm to 280 nm). The engineering of these bio-hybrid nanomaterials in the form of thin films or miniaturized materials would be desirable to overcome traditional problems that affect space mission equipment, such as onboard encumbrance, or that can limit their use on terrestrial environments involving a daily use of UV radiation, such as sterilization plants. To this aim, the UV sensitive graphene/DNA filler was integrated in different polymer matrices based on poly(3,4-ethylenedioxythio-phene):poly(styrenesulfonate) (PEDOT:PSS) or polydimethylsiloxane (PDMS), obtaining stiff and flexible UV sensitive materials, respectively. The UV response was investigated using several techniques, including electrical impedance spectroscopy, Raman microscopy, optical contact angle, electrical tomography resistance. In addition, differential scanning calorimetry was used to analyze the curing behavior of the PDMS-based prepolymers and the thermal stability of the related nanocomposites. Results revealed that the bio-hybrid nanocomposites with graphene/DNA filler show a specific UV response, in particular in terms of electrical conductivity variations, and therefore these materials have the potential to be applied in UV monitoring systems, with the additional advantages of real-time response, low weight/mass and reduced siz

    Home is Where You are Needed?: The Role of Government-Provided Incentives in Determining the Outcome of International Student Mobility in the Source Country

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    The scale of movement of students going overseas to seek higher education has increased dramatically in the past several decades. According to the United Nations Education, Scientific and Cultural Organization (UNESCO), there were 4.1 million students pursuing tertiary level studies abroad in 2013. Despite the numerical significance, international students remain to be an under-studied group in migration studies. Thus this study largely draws from the international South-North labor migration debate, which revolves around whether this phenomenon is good (brain gain) or bad (brain drain) for the home countries. Using a comparative case study approach, this study investigates how the governments of the home or source countries can utilize international student mobility as a tool for national development by providing professional incentives to lure students abroad to return home after completing their studies overseas. This study emphasizes the important role of government-provided professional incentives in increasing the likelihood of students to return after the completion of their studies which could lead to the economic growth of their home countries. The study concludes that the home country can experience economic growth despite the failure of government-provided incentives to entice students to return after completing their student overseas. At the same time, it also suggests that the absence of government-provided incentives is detrimental to the economic growth of the home country because it leads to a shortage in human capital as students fail to return to their home countries

    Polymer composites filled with DNA-functionalized graphene nanoplatelets. Effects of DNA modification on the curing behavior and properties of PDMS-based matrices

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    In this paper, we report our recent results on the preparation and characterization of biocompatible nanocomposites made of a silicone-based polymer matrix with tunable elasticity (polydimethylsiloxane, PDMS, and its mixtures with hydroxyl-terminated PDMS) and DNA-functionalized graphene nanoplatelets as fillers. The aim is to exploit the biocompatible character and the high flexibility of the PDMS matrix, together with the exceptional mechanical strength, and good thermal and electrical conductivity of the graphene nanofillers (GNP) for applications in biomedical and sensing devices. Thermal analysis by differential scanning calorimetry (DSC) was conducted to study the curing process of the PDMS-based composites containing the DNA-functionalized graphene nanoplatelets. The properties of the final composites after cure were characterized using several techniques, including optical microscopy, surface wettability, and nanoindentation. We show that the elasticity of the polymer matrix can be varied by adding a less viscous component (PDMS-OH), whereas the electrical conductivity of the nanocomposite can be tuned by acting on the concentration and type of graphene-DNA assembly

    Curing reactions and thermal stability of nanocomposites with DNA/graphene nanoplatelets by differential scanning calorimetry

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    Nanocomposite materials containing DNA-functionalized graphene are characterized by multifunctional properties that make them potentially useful for applications in biomedical devices, such as cell-instructive devices, or in radiation monitoring systems. In this work, DNA-graphene fillers were embedded in a silicone-based polymer matrix made of polydimethylsiloxane (PDMS) or its mixtures with hydroxyl-terminated polydimethylsiloxane (PDMS-OH). Double stranded DNA was selected because of its sensitivity to UV radiation and, at the same time, efficient exfoliation ability for the graphene nanoplatelets. Differential scanning calorimetry (DSC) was conducted at different heating rates to investigate the curing reactions of the PDMS and PDMS/PDMS-OH matrices filled with DNA/graphene nanoplatelets. The thermal stability of the nanocomposites in a wide temperature range (from -40°C to 250 °C) was also tested, providing information for the application of these materials in extreme environments, such as in space, where large temperature gradients are present. Results by DSC showed larger activation energies for the curing reactions (determined using the maximum reaction rate method) of the PDMS/PDMS-OH matrices filled with pure GNP as compared to the same matrices filled with the DNA-functionalized GNP. This result revealed a favorable contribution of the DNA element on the curing behaviour of the nanocomposites. In order to test the effects of UV exposure on the nanocomposite properties, the thermal analysis was also conducted after irradiation under UV light. Results revealed a change in the behaviour of the nanocomposites containing DNA upon UV exposure. In fact, these exhibited a shift of the DNA denaturation peak to higher temperatures, which could be ascribed to a DNA crosslinking promoted by UV radiation

    Recent trends in graphene/polymer nanocomposites for sensing devices: synthesis and applications in environmental and human health monitoring

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    Graphene-based nanocomposites are largely explored for the development of sensing devices due to the excellent electrical and mechanical properties of graphene. These properties, in addition to its large specific surface area, make graphene attractive for a wide range of chemical functionalization and immobilization of (bio)molecules. Several techniques based on both top-down and bottom-up approaches are available for the fabrication of graphene fillers in pristine and functionalized forms. These fillers can be further modified to enhance their integration with polymeric matrices and substrates and to tailor the sensing efficiency of the overall nanocomposite material. In this review article, we summarize recent trends in the design and fabrication of graphene/polymer nanocomposites (GPNs) with sensing properties that can be successfully applied in environmental and human health monitoring. Functional GPNs with sensing ability towards gas molecules, humidity, and ultraviolet radiation can be generated using graphene nanosheets decorated with metallic or metal oxide nanoparticles. These nanocomposites were shown to be effective in the detection of ammonia, benzene/toluene gases, and water vapor in the environment. In addition, biological analytes with broad implications for human health, such as nucleic bases or viral genes, can also be detected using sensitive, graphene-based polymer nanocomposites. Here, the role of the biomolecules that are immobilized on the graphene nanomaterial as target for sensing is reviewed
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