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    ABSTRACT: As yet, no standard equipment exists for the measurement of heat transfer through porous materials, such as metal foams (metals with a high volume fraction of porosity). Most research in this area has been carried out using bespoke test rigs. Here the creation of a test rig specifically developed for the measurement of the heat transfer of metal foams is reported. This method has been applied to laboratory made samples processed by replication and examples of commercially available aluminium foams (Duocel and Corevo), and should be suitable for the testing of all materials with comparable permeability. As this equipment is new and unique, the design will be discussed in detail, along with the various tests that were performed to ensure reliability and consistency with other methods and published data.
    Measurement 10/2014; 56:37–49.
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    ABSTRACT: The main reaction product in Ca-rich alkali-activated cements and hybrid Portland cement (PC)-based materials is a calcium (alkali) aluminosilicate hydrate (C-(N-)A-S-H) gel. Thermodynamic models without explicit definitions of structurally-incorporated Al species have been used in numerous past studies to describe this gel, but offer limited ability to simulate the chemistry of blended PC materials and alkali-activated cements. Here, a thermodynamic model for C-(N-)A-S-H gel is derived and parameterised to describe solubility data for the CaO–(Na2O,Al2O3)–SiO2–H2O systems and alkali-activated slag (AAS) cements, and chemical composition data for C-A-S-H gels. Simulated C-(N-)A-S-H gel densities and molar volumes are consistent with the corresponding values reported for AAS cements, meaning that the model can be used to describe chemical shrinkage in these materials. Therefore, this model can provide insight into the chemistry of AAS cements at advanced ages, which is important for understanding the long-term durability of these materials.
    Cement and Concrete Research 08/2014; 66:27-47.
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    ABSTRACT: Based on careful design of composition, a two-glassy-phase Cu47.2Zr46.5Al5.5Nb0.8 bulk metallic glass with a large plasticity (∼16%) was successfully prepared. Energy-dispersive spectroscopy and electron energy loss spectroscopy confirm that the bright matrix phase is rich in Zr/Nb while the dark particle phase is rich in Cu/Al. Theoretical calculations suggest that a small difference in shear modulus between phases may be necessary before pronounced plastic deformation can occur.
    Scripta Materialia 02/2014; s 72–73:47–50.
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    ABSTRACT: The reduction of graphene oxide at body temperature by using a biopolymer, chitosan, was proven to be successful. This biocompatible reduction approach will provide a versatile platform for applying graphene in biomedical fields including tissue engineering and therapeutic delivery. The use of this approach for therapeutic delivery is demonstrated.
    Materials science & engineering. C, Materials for biological applications. 01/2014; 34C:50-53.
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    ABSTRACT: Open cell aluminium foams produced by replication have their strength enhanced by ceramic surface layers generated using plasma electrolytic oxidation. The composite materials produced show, in some cases, greater relative increases in strength–weight ratio than those produced by applying other coatings to porous structures; however, the behaviour depends on the characteristics of the layer generated. The most significant increases appear to correlate with conditions that produce more uniform coating thicknesses with depth of penetration into the foam structure.
    Scripta Materialia. 01/2014; 75:38-41.
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    ABSTRACT: The structure and magnetic properties of thin Co90Fe10 films have been studied to determine how different soft magnetic underlayers (Fe81B13.5Si3.5C2 (Metglas) and Ni81Fe19) influence these properties with the aim to achieve soft fcc Co90Fe10 films with large magnetostriction constants. The thickness of the Co90Fe10 films was 25 nm with the thickness of the magnetic underlayer ranging from 15 nm to 35 nm. The effect of applying a magnetic field during the growth of both layers was also investigated. From X-ray diffraction, it was found that the Co90Fe10 films grown on NiFe had lower in-plane stresses compared to those grown on silicon and Metglas. While the coercive fields of all the Co90Fe10 films were smaller than the monolith Co90Fe10 film, the magnetostriction constants were strongly dependent on the underlayer they were grown on. Thus it is possible to tune the magnetostriction constant of the Co90Fe10 film to be positive or negative by selecting the correct soft magnetic underlayer.
    Journal of Magnetism and Magnetic Materials 01/2014; 357:87–92.
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    ABSTRACT: Squamous cell carcinoma is usually cancer of the upper oesophagus and is very aggressive cancer. The cancer of the cervical oesophagus causes a serious complication called dysphagia, which is difficulty in eating or swallowing and which is indicative of incurability. Oesophageal stents have been used as a relatively better palliative method for patients who are suffering from advanced stage squamous cell carcinomas of oesophagus and also for the effective relief of dysphagia. There are still problems in currently available self-expanding metals and plastic stents, which are associated with high rates of early and late complications. This research work is aimed to use Auxetic (rotating-squares) geometry for the production of a novel Auxetic oesophageal stents and stent-grafts relevant to the palliative treatment of squamous cell carcinomas of the proximal and mid oesophagus and also for the prevention of dysphagia. This study also endeavoured to manufacture a significantly small diameter Auxetic oesophageal stent and stent-graft. In order to easily deploy the Auxetic stent orally using a commercial balloon dilatational catheter, and hence it also obviates the need of an expensive dedicated delivery system. A novel manufacturing route was employed in this research to develop both Auxetic films and Auxetic oesophageal stents, which ranged from conventional subtractive techniques to new generative manufacturing methods. Polyurethane was selected as a material for the fabrication of Auxetic films and Auxetic oesophageal stents because of its good biocompatibility and non-toxicological properties. The developed Auxetic films were later used for the fabrication of seamed Auxetic oesophageal stents. The flexible polyurethane tubular grafts were also attached to the inner luminal side of the seamless Auxetic oesophageal stents, in order to prevent tumour in-growth.
    Journal of Manufacturing Systems. 01/2014;
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    ABSTRACT: Polyurethane (PU) is a promising polymer to support bone-matrix producing cells due to its durability and mechanical resistance. In this study two types of medical grade poly-ether urethanes Z3A1 and Z9A1 and PU-Hydroxyapatite (PU-HA) composites were investigated for their ability to act as a scaffold for tissue engineered bone. PU dissolved in varying concentrations of dimethylformamide (DMF) and tetrahydrofuran (THF) solvents were electrospun to attain scaffolds with randomly orientated non-woven fibres. Bioactive polymeric composite scaffolds were created using 15%wt Z3A1 in a 70/30 DMF/THF PU solution and incorporating micro or nano-sized HA particles in a ratio of 3:1 respectively, whilst a 25%wt Z9A1 PU solution was doped in ratio of 5:1. Chemical properties of the resulting composites were evaluated by FTIR and physical properties by SEM. Tensile mechanical testing was carried out on all electrospun scaffolds. MLO-A5 osteoblastic mouse cells and human embryonic mesenchymal progenitor cells, hES-MPs were seeded on the scaffolds to test their biocompatibility and ability to support mineralised matrix production over a 28 day culture period. Cell viability was assayed by MTT and calcium and collagen deposition by Sirius red and alizarin red respectively. SEM images of both electrospun PU scaffolds and PU-HA composites scaffolds showed differences in fibre morphology with changes in solvent combinations and size of HA particles. Inclusion of THF eliminated the presence of beads in fibers that were present in scaffolds fabricated with 100% DMF solvent, and resulted in fibers with a more uniform morphology and thicker diameters. Mechanical testing demonstrated that the Young's Modulus and yield strength was lower at higher THF concentrations. Inclusion of both sizes of HA particles in PU-HA solutions reinforced the scaffolds leading to higher mechanical properties, whilst FTIR characterization confirmed the presence of HA in all composite scaffolds. Although all scaffolds supported proliferation of both cell types and deposition of calcified matrix, PU-HA composite fibres containing nano-HA enabled the highest cell viability and collagen deposition. These scaffolds have the potential to support bone matrix formation for bone tissue engineering.
    Journal of the Mechanical Behavior of Biomedical Materials 01/2014;
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    ABSTRACT: Biodegradable chitosan–graphene oxide (GO) nanocomposites possess improved mechanical properties and drug delivery performance over chitosan and could prove to be a viable, controlled and pH-sensitive transdermal drug delivery system. Chitosan nanocomposites containing varying GO contents and drug loading ratios were investigated. The nanocomposite with 2 wt % GO provided the optimal combination of mechanical properties and drug-loading capacity. It offered a faster and a more substantial release of drug than chitosan as well as a slower biodegradation rate, owing to the abundant oxygenated functional groups, hydrophilicity and large specific surface area of GO sheets. The drug delivery profiles of the nanocomposite were dependent on the drug loading ratio, with 0.84:1 being the best ratio of drug to GO for a quick and high release of the loaded drug. The nanocomposite also demonstrated pH sensitivity of drug release, releasing 48% less drug in an acidic condition than in a neutral environment.
    Carbohydrate Polymers 01/2014; 103:70–80.
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    ABSTRACT: Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm(-1) at 600 °C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.
    Nature Material 11/2013;
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