Superparamagnetic iron oxide nanoparticles (SPIONs) are promising materials for various biomedical applications including targeted drug delivery and imaging, hyperthermia, magneto-transfections, gene therapy, stem cell tracking, molecular/cellular tracking, magnetic separation technologies (e.g. rapid DNA sequencing), and detection of liver and lymph node metastases. The most recent applications for SPIONs for early detection of inflammatory, cancer, diabetes and atherosclerosis have also increased their popularity in academia. In order to increase the efficacy of SPIONs in the desired applications, especial surface coating/characteristics are required. The aim of this article is to review the surface properties of magnetic nanoparticles upon synthesis and the surface engineering by different coatings. The biological aspects, cytotoxicity, and health risks are addressed. Special emphasis is given to organic and inorganic-based coatings due to their determinant role in biocompatibility or toxicity of the final particles.

A. SIMCHI The effects of powder particle size on the densification and microstructure of iron powder in the direct laser sintering process were investigated. Iron powders with particle sizes ranging from 10 to 200 m were used. It was found that the sintered density increases as the laser energy input is increased. There is, however, a saturation level at which higher density cannot be obtained even at very intensive energy input. This saturation density increases as the size of the iron particles decreases. Meanwhile fine powders with narrow particle size distributions have a tendency toward agglomeration, and coarse powders with broad particle size distributions have a tendency toward segregation, both of them resulting in lower attainable density. In order to investigate the role of particle size, a "densification coefficient (K)" was defined and used. This coefficient depends on the particle size and the oxygen content of iron powder. The results of this investigation demonstrate that the presence of oxygen significantly influences the densification and pore morphology of laser-sintered iron. At higher oxygen concentrations, the iron melt pool is solidified to agglomerates, and formation of pores with orientation toward the building direction is more likely to occur. When the oxygen concentration is kept constant, the densification coefficient decreases with decreasing the particle size, meaning the densification kinetics enhances. This article presents the role of powder characteristics and the processing parameters in the laser sintering of iron powder as a model material. The mechanism of particle bonding and microstructural features of lasersintered parts are addressed.

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Haynes.1 The presence of pores is accompanied by a decrease in strength and ductility as well as a detrimental in uence The role of porosity on the wear behaviour of sintered on conductivity and magnetic properties.2 Meanwhile the iron was investigated. Sintered iron was used in initial attempts for mechanical characterisation of sintered preference to steel because the various alloy additions materials were focused on static tests. However, in order and matrix heterogeneity in the latter might aVect the to favour the use of these materials in new applications, microwear behaviour and the role of porosity. The their performance under diVerent loading conditions must wear tests were performed in a pin on disc test bed be taken into account. In particular for the production of under 10-40 N loads at 0•56 m sÕ 1 sliding speed in air.high performance PM parts, dynamic properties have to be For the given tribological conditions, it was found that carefully assessed. In recent years the fatigue behaviour of the wear mechanism is delamination or mechanical sintered steels has been studied in numerous investigations wear, which is basically similar to that of wrought (e.g. . In this context, the role of microstructure materials according to subsurface crack generation and particularly the eVect of porosity as indispensable and crack propagation processes. However, the open characteristics of PM parts on the fatigue properties were pores on the surface act as a site for generation and studied both phenomenologically and scienti cally. Some collection of wear debris. Furthermore, the pores aVect useful models have also been developed for predicting the the stress distribution and the metal deformation of endurance limit.4,5 The in uence of the pores on crack subsurface layers during dry sliding. Accumulation initiation and crack propagation under cyclic loading was of the plastic shearing on the subsurface results in determined as well.3,8,10 nucleation of cracks that further grow by shearing:It is obvious that numerous sintered parts are being used the fracture process. The propagation of subsurface not only under cyclic loading but also under sliding concracks at a critical depth parallel to and eventually up dition. In fact, many applications require a sliding contact to the sliding surface results in the formation of akebetween mechanical components. Therefore, a complete like debris. This paper presents the role of porosity, understanding of sliding wear of sintered parts has to be which is the peculiar property of PM materials, on achieved. Similar to the fatigue properties, several investithe dry sliding behaviour of sintered iron as a model gations into dry sliding behaviour of sintered ferrous material. The implication of Archard's law for describing materials can be found in the literature (e.g. . the results obtained is presented. The shortcomings inIn conclusion, the results of previous investigations highevaluation of the wear behaviour of sintered materials light the peculiar role of porosity (and, for alloy ...