Search

Delivery of cells into tubular tissue constructs with large diameters poses significant spatial and temporal challenges. This study describes preliminary findings for a novel process for rapid and uniform seeding of cells onto the luminal surface of large tubular constructs. Fibroblasts, tagged with superparamagnetic iron oxide nanoparticles (SPION), were directed onto the luminal surface of tubular constructs by a magnetic field generated by a k4-type Halbach cylinder device. The spatial distribution of attached cells, as measured by the mean number of cells, was compared with a conventional, dynamic, rotational cell-delivery technique. Cell loading onto the constructs was measured by microscopy and magnetic resonance imaging. The different seeding techniques employed had a significant effect on the spatial distribution of the cells (p< 0.0001). The number of attached cells at defined positions within the same construct was significantly different for the dynamic rotation technique (p< 0.05). In contrast, no significant differences in the number of cells attached to the luminal surface were found between the defined positions on the construct loaded with the Halbach cylinder. The technique described overcomes limitations associated with existing cell-delivery techniques and is amenable to a variety of tubular organs where rapid loading and uniform distribution of cells for therapeutic applications are required.

Abstract??The sensing, detection, imaging and measurement of magnetic nanoparticles in the human body is a vibrant area of advancing technology. Potential applications cover a variety of therapies and diagnoses, including in vitro magnetic separation assays, targeted delivery of therapeutic drugs, genes and radionuclides, radio frequency methods for the catabolism of tumours via hyperthermia, and contrast enhancement agents for magnetic resonance imaging. In this paper the physical principles underlying these technologies are reviewed, and the current application space is discussed.

A series of amorphous Fe-Zr-B-based nanocomposites have been prepared by borohydride chemical reduction. The structural, magnetic and crystallisation properties of these materials have been investigated by Mössbauer spectroscopy, differential scanning calorimetry, X-ray diffraction, EXAFS and SQUID magnetometry. Nanocrystals of iron and iron boride form at ca. 470 °C, while the zirconium remains in an amorphous matrix until the samples are heated above 600 °C, after which crystalline zirconia is formed. No intermetallic iron-zirconium phases are observed, implying that in the as made state the materials comprise nanocomposites of amorphous iron-boron and amorphous zirconium oxide. Unusually large magnetic coercivities are observed, due to interfacial exchange pinning between the magnetically soft Fe-B nanoparticles and a surface passivation layer. Further magnetic anomalies observed in the heat treated samples indicate the influence of exchange interactions between nanocrystalline grains in an amorphous and insulating matrix.

Cobalt and titanium substituted barium ferrites BaFe12-2xCoxTixO19with 0≤x≤1.5 have been made by self-propagating high-temperature synthesis (SHS). Comparison was made between the SHS samples and x=0 and 0.75 materials prepared commercially by conventional methods. X-ray and Mössbauer data for all the SHS samples showed that the majority product was M-type hexagonal ferrite, with up to 10 wt % hematite impurity. Systematic changes in the hexagonal unit cell lattice parameters were seen as a function of CoTi content. Scanning electron microscopy and X-ray line broadening showed that the SHS crystallites were comparable in size and morphology to those prepared by conventional routes. Mössbauer and magnetic hysteresis data showed no significant change in sublattice and net magnetizations in the SHS samples, in contrast to the reduction found in CoTi-doped conventional ferrites. The coercive forces in the CoTi-doped SHS ferrites are larger than those in conventional samples at the same doping level, implying that a greater concentration of pinning centers are introduced via the SHS reaction route. © 2001 Kluwer Academic Publishers

Mechanical alloying is a versatile technique for the solid state synthesis of many materials, including alloys such as iron-copper where the elements are immiscible under equilibrium conditions. The structural and magnetic state of these alloys, and their thermal stability, have been investigated by means of thermomagnetometry, DSC, X-ray diffraction and Mössbauer spectroscopy. Comparison of the thermomagnetometry curves for the various alloys together with analysis of intermediate reaction products enabled the individual thermal processes to be identified. The Curie temperature of the alloys was measured, and it was found that on heating the metastable alloys underwent phase segregation between 300-400°C.

NH4FeCl3 is a quasi one-dimensional magnet. Mössbauer spectra of powder samples of NH4FeCl3 have been recorded in the temperature range 1.3 to 250 K. The structural phase change between 10 and 30 K was not accompanied by changes in the Mössbauer spectra. Apparently, the changes in the local environment of the Fe2+ ions are not sufficient to affect the quadrupole splitting. The Mössbauer spectrum at 1.3 K, belowTN=1.7(2) K, is magnetically split, but cannot be fitted to just one iron site. It appears to be a superposition of at least two broadened spectra, one with an internal fieldB=4.7(1) T perpendicular to the principalz-axis of the electric field gradient, the other with zero field. The intensity for these sites was found to be 3.3∶1. The fit is improved if slow relaxation is allowed between the two sites. Broadening of the lines starts to occur at 6 K, well aboveTN. This has not been reported for the other members of the AFeX3 group.

The magnetic properties of a series of fine particle iron oxides, oxyhydroxides and hydrated oxyhydroxides are discussed with reference to the data obtained from low-temperature, high-field Mössbauer spectroscopy experiments, using a two-sublattice atomic spin Hamiltonian model to help in the interpretation of the results.

Applied field Mössbauer spectra obtained from ferritin and haemosiderin have been fitted using a spin-Hamiltonian model, to determine the effect of the applied field on the direction of the iron magnetic moments. The results of these fits indicate that the ordering of magnetic moments within the ferrihydrite core of these proteins is antiferromagnetic. The values of the anisotropy field obtained from these fits correspond to much higher values of the superparamagnetic blocking temperatures than those actually observed. This anomaly has implications for our understanding of the superparamagnetic relaxation processes in these materials.

Mössbauer spectroscopic and magnetic measurements have been made on a novel magnetic protein produced by the controlled reconstitution of ferritin. The data indicate that the predominant mineral form in the iron-containing cores is maghemite (γ-Fe2O3) rather than magnetite (Fe3O4).

Magnetism in fine particles of goethite which contain 5, 11, 18 and 30 mole % aluminium has been investigated. Mössbauer spectroscopy was used, with the samples at 4.2 K and in applied magnetic fields of 0–8 T. Analysis was via a mean field model, in which the spectra from each sample were simultaneously least-squares fitted. The presence of aluminium increases the effective anisotropy, introduces a range of anisotropy fields, and induces ferrimagnetism. Quantitative measurements of these effects are presented. It is surmised that the anisotropy is principally determined by the local environment of ferric ions, and that the distribution of anisotropy fields is the result of a variety of atomic neighbour configurations. Ferrimagnetism is understood to arise from a strong preference, with 100% success at intermediate concentrations, for aluminium ions to crystallise on the same sublattice. Simulations of the net magnetic moment in small particle systems are presented, and it is shown that statistical fluctuations and the effects of surfaces are unimportant in the particles studied.

Mössbauer spectra are obtained for a single crystal of α-FeOOH, with a magnetic field of up to 10T applied along the c axis. No spin reorientation is observed, indicating a lower limit of 6 × 104 J/m3 for the anisotropy constant K. A theoretical estimate gives K > 1.1 × 106 J/m3.

Abstract: The characteristics of the spin-flop transition in K2FeF5 and Rb2FeF5 are found by Mssbauer spectroscopy to be very different, and are discussed in relation to the ordered magnetic structures of the two systems.

Abstract: Samples of the series of compounds YBa2(Cu1−x Fe x )3 O6.5+p with 03+/Cu2+ and Fe4+/Fe3+.

Abstract: In Mssbauer studies of the series FeAl1−xCux (0

It is shown that a double-Gaussian-shaped probability distribution of moment directions is an adequate model of the spin structures in as-cast, stress-relieved and field-annealed samples of Fe78B13Si9 at room temperature and in zero applied field. The distribution comprises the convolution of two independent Gaussian distributions, one in the ribbon plane, and the other normal to the ribbon plane. The double-Gaussian distribution is more physically realistic than some alternative models of the moment distribution in amorphous metals.

Abstract: Spin-flop transitions in K2FeF5 subject to an applied field (i) parallel to the easy axis, and (ii) directed at 33 to the easy axis are found to be (i) abrupt and (ii) smooth, in accordance with theoretical predictions.

Abstract: The high-temperature superconductor with the nominal composition YBa2Cu3O7−σ has been doped with iron 93% enriched in57Fe. When 1.5 at % Fe substitutes for Cu, the transition temperature is reduced by about 30 K with full ac shielding (X′=−1/4π) achieved by ≈40 K. At room temperature the Mssbauer spectrum consists of three overlapping doublets. Below 10 K, hyperfine-field splitting is observed; relaxation still takes place at T=1.8 K.

57Fe Mössbauer spectra of two synthetic samples of ferrihydrite, recorded at 4.2 K in applied fields of up to 9 T, have been analysed by a mean-field model. The samples exhibit two and six X-ray diffraction peaks. It is shown that only one ferric ion site is present in the mineral, and that in this site the ions are octahedrally coordinated. The spectra show the presence of different magnetic states: ferrimagnetism in two-line ferrihydrite, and antiferromagnetism in six-line ferrihydrite. The ferrimagnetism in two-line ferrihydrite is analysed in terms of random fluctuations arising from the small numbers of ferric ions per particle, and it is shown that the different magnetic states may arise purely as a result of these fluctuations.

Abstract: 57Fe Mssbauer spectra for a natural single crystal of ludlamite have been recorded at temperatures between room temperature and 4.2 K. Computer analysis reveals that at 4.2 K the Fe2+ moments lie on two distinct magnetic sublattices separated by at least 35.

Abstracts are not published in this journal

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.