In-vitro-Studien zur Deposition von Siliziumdioxid-Partikeln auf Zellen

In-vitro (lat. „im Glas“) Experimente stellen die gängigste Form der toxikologischen Risikoabschätzung von Nanopartikeln (NP) dar. In der vorliegenden Arbeit wurde das Depositionsverhalten von SiO2-NP auf A549-Zellen in-vitro untersucht. Mittels Rasterelektronenmikroskopie (REM) wurden sedimentierte Partikel-Flächendichten quantifiziert und mit berechneten Flächendichten verglichen. Dabei zeigte sich eine ausgeprägte Abhängigkeit des Depositions- und Adhäsionsverhaltens der NP von Oberflächeneigenschaften, verursacht durch die Zellen. Die Abbildung von SiO2-NP auf zellulären Oberflächen mit REM stellt eine besondere Herausforderung dar. Aus diesem Grund wurde mit Hilfe von Monte-Carlo-Simulationen eine Optimierung des NP-Kontrastes vorgenommen

Contrast of Backscattered Electron SEM Images of Nanoparticles on Substrates with Complex Structure

This study is concerned with backscattered electron scanning electron microscopy (BSE SEM) contrast of complex nanoscaled samples which consist of SiO2 nanoparticles (NPs) deposited on indium-tin-oxide covered bulk SiO2 and glassy carbon substrates. BSE SEM contrast of NPs is studied as function of the primary electron energy and working distance. Contrast inversions are observed which prevent intuitive interpretation of NP contrast in terms of material contrast. Experimental data is quantitatively compared with Monte-Carlo- (MC-) simulations. Quantitative agreement between experimental data and MC-simulations is obtained if the transmission characteristics of the annular semiconductor detector are taken into account. MC-simulations facilitate the understanding of NP contrast inversions and are helpful to derive conditions for optimum material and topography contrast

Intravenous Thrombolysis Facilitates Successful Recanalization with Stent-Retriever Mechanical Thrombectomy in Middle Cerebral Artery Occlusions

Aim: Several factors influence the outcome after acute ischemic stroke secondary to proximal occlusions of cerebral vessels. Among others, noneligibility for intravenous thrombolysis (IVT) and incomplete revascularization have been identified as predictors of unfavorable outcome. The aim of this study was to investigate whether concomitant IVT influences the revascularization efficacy in mechanical thrombectomy (MT). Methods: This study conducted a retrospective analysis of all consecutive patients presenting with an anterior circulation stroke due to large-artery occlusion with imaging evidence who were treated with MT between July 2012 and December 2013 at 2 high-volume stroke centers. Imaging data were regraded and re-evaluated according to the modified Treatment in Cerebral Ischemia scale and its respective vessel occlusion site definitions. Clinical end points included National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale; imaging and procedural measures were technical end points. Results: We identified 93 patients who presented with an occlusion of the middle cerebral artery (MCA): of these patients, 66 (71%) received IVT. We did not find statistically significant differences in the baseline NIHSS score, time from symptom onset to groin puncture, and age when comparing the IVT group with the non-IVT group. The rate of successful recanalizations (modified Treatment in Cerebral Ischemia score >= 2b) was significantly higher in patients with MCA occlusion and concomitant IVT (P = .01). Stepwise logistic regression identified IVT and thrombus length as predictive factors for successful mechanical recanalization (P = .004, P = .002). Conclusion: IVT and thrombus length are predictive factors for a successful recanalization in MT for acute ischemic stroke with underlying MCA occlusion

Assessment of in vitro particle dosimetry models at the single cell and particle level by scanning electron microscopy

Abstract Background Particokinetic models are important to predict the effective cellular dose, which is key to understanding the interactions of particles with biological systems. For the reliable establishment of dose–response curves in, e.g., the field of pharmacology and toxicology, mostly the In vitro Sedimentation, Diffusion and Dosimetry (ISDD) and Distorted Grid (DG) models have been employed. Here, we used high resolution scanning electron microscopy to quantify deposited numbers of particles on cellular and intercellular surfaces and compare experimental findings with results predicted by the ISDD and DG models. Results Exposure of human lung epithelial A549 cells to various concentrations of differently sized silica particles (100, 200 and 500 nm) revealed a remarkably higher dose deposited on intercellular regions compared to cellular surfaces. The ISDD and DG models correctly predicted the areal densities of particles in the intercellular space when a high adsorption (“stickiness”) to the surface was emulated. In contrast, the lower dose on cells was accurately inferred by the DG model in the case of “non-sticky” boundary conditions. Finally, the presence of cells seemed to enhance particle deposition, as aerial densities on cell-free substrates were clearly reduced. Conclusions Our results further validate the use of particokinetic models but also demonstrate their limitations, specifically, with respect to the spatial distribution of particles on heterogeneous surfaces. Consideration of surface properties with respect to adhesion and desorption should advance modelling approaches to ultimately predict the cellular dose with higher precision

Fruehe Hilfen als Aufgabe gemeindenaher psychosozialer Versorgung eine Untersuchung im Landkreis Reutlingen

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