Effect of morphology and hydrophobization of MoS2 microparticles on the stability of poly-α-olefins lubricants

International audienceThe use of MoS ⁠ 2 nanoparticles as additive to lubricating oils is restricted by their low stability in oily media, which limits their use despite the enormous benefits associated with their intrinsic properties in terms of reduction of friction and wear coefficients. In this context, we investigated the effect of morphologies (platelets vs spheres) and surface functionalization of nanoparticles on the stability of their suspensions in poly-α-olefins (PAO) with various viscosities, which are base oils used in wind turbines. The particles were characterized by XRD, FTIR, scanning electron microscopy, atomic force microscopy and dynamic light scattering, and the stability of the resultant formulations was followed by optical (non-contact) measurements. It was found that the dispersions had similar stability despite the larger size of platelet-like particles compared to spherical ones (1-5 μm vs 600-800 nm). The dispersibility could be increased through grafting of alkylsilane on the surface defects (the longer the alkyl chain, the more stable the formulation) and with the increase of the oil kinematic viscosity (from 34 to 1705 cps at 25 °C)

Assessment of silicone rods for passive sampling of pesticides in freshwaters

International audiencePassive sampling has recently been developed as an alternative to grab or average automated sampling, in order to obtain, at lower cost, more realistic estimates of the average concentrations of contaminants in aquatic environments. This technique allows the accumulation of chemicals from large amounts of water, resulting in ultratrace level detection and smoothed integrative sampling over periods ranging from days to months. In small agricultural watersheds, pesticide concentrations quickly fluctuate due to episodic events such as heavy rain. Monitoring of such compounds by a reactive passive sampler appears as an alternative to grab sampling. Silicone rod, investigated in this work, is a reactive, single-use and low cost passive sampler. This new passive sampler was inspired by research works on the analytical technique SBSE (Stir Bar Sorptive Extraction) and first trials of in situ exposition as "Passive SBSE" (Assoumani et al., 2013) and MESCO (Vrana et al., 2001). The nature and mass of pesticides sorbed on in situ exposed silicone rods can be used as qualitative and semi-quantitative measures, to assess trends and gradients of contamination in aquatic environments. For quantitative purposes, the estimation of the average concentration of contaminants in water requires the determination of kinetic parameters (Rs, equilibration time). Even if sampling rates (Rs) are obtained in laboratory thanks to the calibration of the passive sampler for each compound, performance reference compounds (PRCs) (Huckins et al., 2002) have to be loaded on samplers prior to their deployment in order to correct the measured concentration in relation to exposure conditions by using their dissipation data. The first aim of this study was to calibrate silicone rods as a passive sampling technique for the water monitoring of 27 pesticides (herbicides, fungicides and insecticides) and metabolites with a large range of polarity (1.5 3, whereas polar pesticides have been less sorbed. Sampling rates of the pesticides were in most cases positively related to their hydrophobicity. In a second part of this study, desorption kinetics of deuterium labelled pesticides were monitored and the corresponding elimination rate constants were calculated. These results allowed us to define a new set of deuterium labelled compounds as potential PRCs for correction of environmental influences (temperature and flow velocity) on time-weighted average pesticide concentrations determined by silicone rods. Calibration constants and PRC correction were applied to field data and allowed to highlight a clear gradient of contamination in a river located in a vineyard watershed

External validation of the PAGE-B score for HCC risk prediction in people living with HIV/HBV coinfection

Background & Aims: HBV coinfection is common among people living with HIV (PLWH) and is the most important cause of hepatocellular carcinoma (HCC). While risk prediction tools for HCC have been validated in patients with HBV monoinfection, they have not been evaluated in PLWH. Thus, we performed an external validation of PAGE-B in people with HIV/HBV coinfection. Methods: We included data on PLWH from four European cohorts who were positive for HBsAg and did not have HCC before starting tenofovir. We estimated the predictive performance of PAGE-B for HCC occurrence over 15 years in patients receiving tenofovir-containing antiretroviral therapy. Model discrimination was assessed after multiple imputation using Cox regression with the prognostic index as a covariate, and by calculating Harrell's c-index. Calibration was assessed by comparing our cumulative incidence with the PAGE-B derivation study using Kaplan-Meier curves. Results: In total, 2,963 individuals with HIV/HBV coinfection on tenofovir-containing antiretroviral therapy were included. PAGE-B was <10 in 26.5%, 10–17 in 57.7%, and ≥18 in 15.7% of patients. Within a median follow-up of 9.6 years, HCC occurred in 68 individuals (2.58/1,000 patient-years, 95% CI 2.03–3.27). The regression slope of the prognostic index for developing HCC within 15 years was 0.93 (95% CI 0.61–1.25), and the pooled c-index was 0.77 (range 0.73–0.80), both indicating good model discrimination. The cumulative incidence of HCC was lower in our study compared to the derivation study. A PAGE-B cut-off of <10 had a negative predictive value of 99.4% for the development of HCC within 5 years. Restricting efforts to individuals with a PAGE-B of ≥10 would spare unnecessary HCC screening in 27% of individuals. Conclusions: For individuals with HIV/HBV coinfection, PAGE-B is a valid tool to determine the need for HCC screening. Impact and implications: Chronic HBV infection is the most important cause of hepatocellular carcinoma (HCC) among people living with HIV. Valid risk prediction may enable better targeting of HCC screening efforts to high-risk individuals. We aimed to validate PAGE-B, a risk prediction tool that is based on age, sex, and platelets, in 2,963 individuals with HIV/HBV coinfection who received tenofovir-containing antiretroviral therapy. In the present study, PAGE-B showed good discrimination, adequate calibration, and a cut-off of <10 had a negative predictive value of 99.4% for the development of HCC within 5 years. These results indicate that PAGE-B is a simple and valid risk prediction tool to determine the need for HCC screening among people living with HIV and HBV