Show Abstract ▼

Abstract: Globally, more than 1000 tonnes of titanium (Ti) is implanted into patients in the form of biomedical devices on an annual basis. Ti is perceived to be ‘biocompatible’ owing to the presence of a robust passive oxide film (approx. 4 nm thick) at the metal surface. However, surface deterioration can lead to the release of Ti ions, and particles can arise as the result of wear and/or corrosion processes. This surface deterioration can result in peri-implant inflammation, leading to the premature loss of the implanted device or the requirement for surgical revision. Soft tissues surrounding commercially pure cranial anchorage devices (bone-anchored hearing aid) were investigated using synchrotron X-ray micro-fluorescence spectroscopy and X-ray absorption near edge structure. Here, we present the first experimental evidence that minimal load-bearing Ti implants, which are not subjected to macroscopic wear processes, can release Ti debris into the surrounding soft tissue. As such debris has been shown to be pro-inflammatory, we propose that such distributions of Ti are likely to effect to the service life of the device.

Show Abstract ▼

Abstract: Tris(8-quinolinolato)gallium(III) (1, KP46) is a very promising investigational anticancer drug. Its interaction with serum proteins, elemental distribution, and coordination in tissue were investigated with X-ray absorption (XAS) methods. Model compounds with mixed O, N, and/or S donor atoms are reported. The coordination and structure of 1 in cell culture medium (minimum essential medium, MEM) and fetal calf serum (FCS) were probed by XANES and EXAFS. The interaction of 1 with the serum proteins apotransferrin (apoTf) and human serum albumin (HSA) was addressed as well. By application of micro-XAS to tissue samples from mice treated with 1, the gallium distribution pattern was analyzed and compared to those of physiological trace elements. The complex 1 turned out to be very stable under physiological conditions, in cell culture media and in tissue samples. The coordination environment of the metal center remains intact in the presence of apoTf and HSA. The gallium distribution pattern in tumor and liver tissue revealed high similarities to the distribution patterns of Zn and Fe, minor similarities to Cu and Ni, and no similarity to Ca.

Show Abstract ▼

Abstract: Gas-phase Fe nanoparticles with a diameter ~ 2nm, have been used in all the nanostructured material in this thesis. In pure Fe nanoparticle systems with different thicknesses, two important parameters the exchange interaction (Hex) and random anisotropy (Hr) were investigated using the Random Anisotropy Model (RAM). This reveals that for the same particle size Hex remains almost constant for varying Fe thicknesses; whereas Hr increases with the increase of Fe film thickness. This is ascribed to increasing strain imposed at the nanoparticle level. The observed high values of Hr are related to an oxide on the cluster surface in these films, whose effect is also observed in low temperature magnetometry data. This shows the appearance of exchange bias in the films. The RAM approach when applied to Fe clusters in Co matrices, reveals much lower values of Hr than found in pure Fe nanoparticles and both Hr and Hex show an increase with the Volume Fraction (VF) of Fe in Co. The increase in Hex is ascribed to the increasing spin moment with Fe volume fraction. The nature of Fe clusters in very thick layers produce a high frequency Ferromagnetic Resonance response in the radio frequency range, which is an important finding for many applications. The EXAFS study of Fe nanoparticles in Cr matrices show no structural modification relative to the bulk bcc structure of both elements. The magnetometry results suggest that in dilute Fe concentration films, the observed decrease in the overall magnetization is due to the development of a nonmagnetic shell at the interface between Fe and Cr at each cluster boundary. This is reinforced by the lack of any evidence of EB. With increasing VF at about 10% of Fe there is strong evidence of the formation of a super-spin-glass (SSG) that shows the characteristic memory effect. Increasing the Fe nanoparticles VF to 20% Fe in Cr, the magnetization exceeds that expected for Fe indicating that the interaction induces some of the Cr to order ferromagnetically. Core-shell nanoparticle systems have been synthesised by a method that allows a complete control over the morphology of these assemblies. Atomic investigations in Fe@Cu CS nanoparticles reveal that Fe nanoparticles adopt the fcc structure with a 20 monolayer Cu shell thickness and stay in the bcc structure for 1-2 monolayer thick Cu shells. No alteration in the Fe atomic structure has been reported for different Au shell thicknesses in Fe@Au. The magnetic data show a reduced magnetization of the FM-AFM Fe@Cr CS nanoparticles as compared to the bulk value which is also ascribed to the formation of a non-magnetic Fe shell at the interface.

Show Abstract ▼

Abstract: X-ray Absorption Fine Structure techniques have been used on Comet Wild2/81P tracks from the Stardust mission. Fe-XANES and EXAFS have been performed on aerogel sections from Tracks 41 and 162 as well as the mid and terminal positions of Track 134. This is the first use of EXAFS in the study of early Solar System materials. With EXAFS, we have measured Fe–O and Fe–S bond lengths and thus, together with complementary XANES measurements, identified Fe-rich phases. In particular, we show that ferric-rich phases in 2 Tracks (41, 162) have Fe–O bond 1st shell bond lengths of 1.99–2.01 Å and Fe K absorption edge and pre edge centroid positions consistent with being hematite-dominated grains. These iron oxides can be clearly distinguished from a magnetite grain, present in Track 134. We also demonstrate the identification of the Mg-rich end member olivine using EXAFS with XANES in Track 162. The terminal grain of Track 134 is pyrrhotite, its first atomic shell has an Fe–S structure, with 4 nearest neighbouring S atoms at a distance of 2.29 ± 0.05 Å. Our XANES results show the presence of Fe3+-bearing grains along the Stardust tracks and suggest either flash-cooling of an Fe–S–SiO–O2 gas during capture or the presence of a Fe–Ni–S–O melt along the cometary tracks during impact capture in the aerogel, rather than the capture process being solely associated with reduction of cometary phases. Accurate determination of Comet Wild2 redox conditions requires the identification of phases, in particular terminal grains, which have not experienced this melting. For instance, the larger hematite-rich grains (>10 μm) are more likely to be cometary in origin. EXAFS provides a valuable new analytical technique to study fine-grained early Solar System materials.