BackgroundQuantum dots (QDs) have numerous possible applications for in vivo imaging. However, toxicity data are scarce.ObjectivesTo determine the acute in vivo toxicity of QDs with carboxyl surface coating (carboxyl-QDs) and QDs with amine surface coating (amine-QDs), we investigated the inflammatory properties, tissue distribution, and prothrombotic effects after intravenous injection.MethodsWe performed particle characterization by transmission electron microscopy and dynamic light scattering. Carboxyl-QDs and amine-QDs were intravenously injected in mice (1.44–3,600 pmol/mouse). At different time intervals, analyses included fluorescence microscopy, blood cell analysis, bronchoalveolar lavage, wet and dry organ weights, and cadmium concentration in various organs. We examined the prothrombotic effects in vivo by assessing the effect of pretreatment with the anticoagulant heparin and by measuring platelet activation (P-selectin), and in vitro by platelet aggregation in murine and human platelet-rich plasma exposed to QDs (1.44–1,620 pmol/mL).ResultsAt doses of 3,600 and 720 pmol/mouse, QDs caused marked vascular thrombosis in the pulmonary circulation, especially with carboxyl-QDs. We saw an effect of surface charge for all the parameters tested. QDs were mainly found in lung, liver, and blood. Thrombotic complications were abolished, and P-selectin was not affected by pretreatment of the animals with heparin. In vitro, carboxyl-QDs and amine-QDs enhanced adenosine-5′-diphosphate–induced platelet aggregation.ConclusionAt high doses, QDs caused pulmonary vascular thrombosis, most likely by activating the coagulation cascade via contact activation. Our study highlights the need for careful safety evaluation of QDs before their use in human applications. Furthermore, it is clear that surface charge is an important parameter in nanotoxicity.

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Because of their excellent tribological properties and potential to replace problematic lubricant additives currently in use, WS 2 nanoparticles have spurred considerable interest over the last two decades from academia and industry to decipher their mechanism of action. To elucidate the mechanism, this study carried out tribological tests at low and high temperatures and investigated the wear track and friction properties. It was found that in highpressure, high-temperature sliding contacts, WS 2 nanoadditives react with the metal substrate to generate thick chemical tribofilms which account for their excellent tribological properties. Based on XPS and FIB/SIMS results, a layered structure was proposed for the chemically formed tribofilms. The large amount of W in the composition of the reacted tribofilm could explain the excellent mechanical and antiwear properties, while the exfoliated squashed WS 2 NPs which fill the gaps and cover the reacted tribofilm account for the striking reduction in the boundary friction.

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Organic friction modifiers (OFMs) are important additives in the lubrication of machines and especially of car engines where performance improvements are constantly sought-after. Together with zinc dialkyldithiophosphates (ZDDPs) antiwear additives, OFMs have a predominant impact on the tribological behaviour of the lubricant. In the current study, the influence of OFMs on the generation, tribological properties and chemistry of ZDDP tribofilms has been investigated by combining tribological experiments (MTM) with in-situ film thickness measurements through optical interference imaging (SLIM), Alicona profilometry and X-ray photoelectron spectroscopy.OFMs and antiwear additives have been found to competitively react/adsorb on the rubbing ferrous substrates in a tribological contact. The formation and removal (through wear) of tribofilms are dynamic processes which result from the simultaneous interaction of these two additives with the surface of the wear track.By carefully selecting the chemistry of OFMs, the formulator can achieve lubricants that generate ZDDP antiwear films of optimum thickness, morphology and friction according to the application-specific requirements.

Although the use of oil-in-water (O/W) emulsions as metalworking fluids is widespread, the mechanisms of emulsion lubrication are not yet well understood. Several theories have been proposed but there is not a clear agreement about the effect of different operating conditions and emulsion properties on the lubricating performance of O/W emulsions. In the present study, the film forming ability of O/W emulsions as a function of emulsifier concentration is studied. The emulsifier content exerts a strong influence on all the emulsion properties, such as stability, droplet size distribution, surface and interfacial tension, wetting ability, etc., as well as on the lubricating behaviour, so it has been used to ascertain the relationship between all the properties involved. Three different emulsifiers-anionic, nonionic and cationic-were used at different concentrations in the design of lubricant O/W emulsions. Experimental results show that the work of adhesion of oil droplets on the metal surface is a valuable parameter to predict the ability of emulsions to form thick films in elastohydrodynamic (EHD) contacts. The influence of pH value of O/W emulsions on their lubricating behaviour is also verified. The overall conclusion is that the interactions between metal and oil droplets rule the mechanism of lubrication and that this interaction is primarily controlled by emulsifier concentration.

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The effect of dispersed soot in engine oils is a n increasingly important issue i n terms of both engine drtrability and fuel efficiency. Using carbon black as a soot analogue, a study has been carried out to investigate the main factors that determine the impact of soot on friction and ZDDP film formation i n formulated oils, It has been found that dispersed carbon black can rapidly remove ZDDP reaction films by abrasion. However, this removal can be prevented or limited by the citoice of a n optimal dispersant additive.