[Show abstract][Hide abstract] ABSTRACT: The effect of auxeticity on the velocity of elastic wave propagation is investigated herein for isotropic solids. Three types of dimensionless wave velocities are proposed for investigating longitudinal waves in prismatic bars, plane waves of dilatation, plane waves of distortion, and surface waves. Results show that the velocity of surface waves is slightly less than that of plane waves of distortion for conventional solids, but the difference becomes large for auxetic solids. The velocity of longitudinal waves in prismatic bars is higher than that of plane waves of distortion for conventional solids but the gap narrows for solids of the low auxetic range of −0.5 < ν < 0. The velocity of longitudinal waves in prismatic bars become lower than that of plane waves of distortion for intermediate auxetic range of −0.733 < ν < −0.5, and lower than that of surface waves for high auxetic range of −1 < ν < −0.733.
Full-text · Article · Feb 2014 · physica status solidi (b)
[Show abstract][Hide abstract] ABSTRACT: This paper examines the engineering education programs provided by SIM University (UniSIM) especially in the teaching, assessment, and learning for working adults. In terms of engineering education, the paper emphasized the changes brought about especially in areas like blended learning, capstone project, continuous assessment, quality control and working with engineering accreditation bodies like ABET. All these helped to ensure that UniSIM is able to offer a quality engineering education that is comparable to other institutions in the region and can serve as a model for working adults to upgrade themselves.
[Show abstract][Hide abstract] ABSTRACT: Deposition of amorphous aluminium powder using cold spray technology as a corrosion prevention measure was studied. Amorphous aluminium (Al-Ni-Ce) powder was successfully deposited on 7000-series aluminium substrates using cold spray parameters of 13-15 bars under helium gas and temperature of between 300-400 deg C. The coatings were subjected to tensile bond strength and salt-water immersion test and comparative studies with cold sprayed pure Al6061 coatings were conducted. The results obtained showed that the amorphous aluminium coatings exhibited comparable adhensive strength while demonstrated relatively better corrosion properties. The amorphous aluminium coating was not only able to resist corrosion itself but also exhibited signs of ability to actively prevent corrosion on imperfections such as scratches in the coatings.
[Show abstract][Hide abstract] ABSTRACT: The WC particle size and its influence on the deposition of Co-based cermets are examined. Micron and nanostructured powders with similar Co content were employed. Varying the WC particle size influenced significantly the deposition efficiency of the coating process. Micrometer-structured WC–Co feedstocks did not permit coating build up when processed under comparable or elevated thermal spray parameters used for the nanostructured WC–Co feedstocks. In addition, micrometer-structured WC–Co coatings exhibited a conjoint erosion and deposition effect on the surface. Fine WC particles (
No preview · Article · Feb 2011 · Surface and Coatings Technology
[Show abstract][Hide abstract] ABSTRACT: The antibacterial behavior of CS-Cu (chitosan-copper complex) powder and their composite coatings were investigated against
Escherichia coli (DH5α). CS-Cu powder and Al (aluminum) based CS-Cu composite powders were synthesized using in-house powder processing techniques.
The results indicated that the antibacterial effect of all the powders increased with the proportion of CS-Cu powder. These
composite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios
of CS-Cu to Al in their composite powders were 25:75, 50:50, and 75:25 (wt.%). Microstructural characterization and phase
analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and FTIR. Antibacterial composite
CS-Cu/Al coatings were successfully deposited using cold spraying parameters of 6-8 bars at preheated helium gas, temperature
between 140 and 150°C. The coatings retained the antibacterial properties of the original feedstock powders.
Full-text · Article · Dec 2009 · Journal of Thermal Spray Technology
[Show abstract][Hide abstract] ABSTRACT: Human mesenchymal stem cells (MSCs) have increasingly been used as cellular vectors for the delivery of therapeutic genes to tumors. However, the precise mechanism of mobilization remains poorly defined. In this study, MSCs that expressed similar cell surface markers and exhibited multilineage differentiation potentials were isolated from various donors. Interestingly, different MSC isolates displayed differential migration ability toward human glioma cells. We hypothesized that distinct molecular signals may be involved in the varied tumor tropisms exhibited by different MSC isolates. To test this hypothesis, gene expression profiles of tumor-trophic MSCs were compared with those of non-tumor-trophic MSCs. Among the various differentially regulated genes, matrix metalloproteinase one (MMP1) gene expression and its protein activities were enhanced by 27-fold and 21-fold, respectively, in highly migrating MSCs compared with poorly migrating MSCs. By contrast, there was no change in the transcriptional levels of other MMPs. Functional inactivation of MMP1 abrogated the migratory potential of MSCs toward glioma-conditioned medium. Conversely, the nonmigratory phenotype of poorly migrating MSC could be rescued in the presence of either recombinant MMP1 or conditioned medium from the highly migrating MSCs. Ectopic expression of MMP1 in these poorly migrating cells also rendered the cells responsive to the signaling cues from the glioma cells in vivo. However, blocking the interaction of MMP1 and its cognate receptor PAR1 effectively diminished the migratory ability of MSCs. Taken together, this study provides, for the first time, supporting evidence that MMP1 is critically involved in the migration capacity of MSCs, acting through the MMP1/PAR1 axis.
[Show abstract][Hide abstract] ABSTRACT: The antibacterial behavior of HA-Ag (silver-doped hydroxyapatite) nanopowder and their composite coatings were investigated against Escherichia coli (DH5alpha). HA-Ag nanopowder and PEEK (poly-ether-ether-ketone)-based HA-Ag composite powders were synthesized using in-house powder processing techniques. Bacteria culture assay of HA-Ag nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of HA-Ag nanoparticle in these composite powders. These nanocomposite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of HA-Ag to PEEK in their composite powders were 80:20, 60:40, 40:60, and 20:80 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite HA-Ag/PEEK coatings were successfully deposited using cold spraying parameters of 11-12 bars at preheated air temperature between 150 and 160 °C. These as-sprayed coatings of HA-Ag/PEEK composite powders comprising varying HA-Ag and PEEK ratios retained their inherent antibacterial property as verified from bacterial assay. The results indicated that the antibacterial activity increased with increasing HA-Ag nanopowder concentration in the composite powder feedstock and cold-sprayed coating.
Full-text · Article · Mar 2009 · Journal of Thermal Spray Technology
[Show abstract][Hide abstract] ABSTRACT: Bioactive particulate reinforced polymer composite comprising synthetic Hydroxyapatite (HA) and Polyetheretherketone (PEEK) has been fabricated by injection molding for loadbearing applications in these past few years. The limited degree of customization of injection molding process and the high cost of the mold fabrication and processing cost lead to the fabrication of HA-PEEK composites by pressureless sintering method. The aim of the project is prepared a HA-PEEK composite block from HA-PEEK powder blends using simple detachable cubic stainless steel mold in the furnace with specific temperature and duration. The resultant HA-PEEK composite block will be machine with CAD machining system to produce desired final shape and size of the implant device.
The microstructural observations by scanning electron microscopy (SEM), mechanical testing and biological testing of the composites were performed. The averaged tensile and compressive strengths were around 15 MPa and 55 MPa respectively. On the other hand, biological tests showed very positive results which verified bioactivity, biocompatibility and nontoxicity of the composite with the formation of biological apatite layer deposited on the surface of the materials which is critical to establishing bonding between living tissue and biomaterials, without forming the fibrous tissue among them. These results suggested that pressureless sintered HA-PEEK biocomposites have the potential to replace injection molded composites in the loadbearing applications.
[Show abstract][Hide abstract] ABSTRACT: The antibacterial behaviour of ZnO nanopowder and their composite coatings were investigated against E. Coli. ZnO nanopowder and Aluminum based ZnO composite powders were synthesized using in-house powder processing techniques. Bacteria culture results showed that ZnO nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of ZnO nanoparticle in their composite powders as well as increasing surface area of compacted pellets. These nanocomposite powders were subsequently used to generate antibacterial coatings using cold spray technology. The ratio of Al to ZnO in their composite powders were 80:20, 50:50 and 20:80 (wt.%). Micro structural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite Al-ZnO coatings were successfully deposited using cold spraying parameters of 15 Bars at air temperature of between 200-300degC. These as- sprayed coatings of Al-ZnO composite powders with varying Al and ZnO ratios retained their inherent antibacterial property as verified from bacterial counting test. The results indicated that the antibacterial activity increased with increasing ZnO nanopowder concentration in the composite powder feedstock and cold sprayed coating.
[Show abstract][Hide abstract] ABSTRACT: The formation of biologically equivalent carbonate-containing apatite on the surface of synthetic hydroxyapatite (HA) is an important step leading to good bone healing. In this study, HA-reinforced polyetheretherketone (PEEK) composites were prepared by homogeneous mixing of HA and PEEK powders, compaction, and pressureless sintering. The bioactivity of HA/PEEK composite with 10, 20, 30 and 40 vol% HA was evaluated by immersing the composite disks in the simulated body fluid (SBF) for up to 4 weeks. The surface of composite with 40 vol% HA was covered by a layer of bone-like apatite just after 3 days of immersion, while 10 vol% HA was covered only after 28 days. This apatite layer was characterized by SEM, thin film X-ray diffractometer, attenuated total reflectance-Fourier transform infrared spectrometer (FTIR)/FTIR. Introducing a concept called apatite-forming capacity of SBF, growth kinetics of the apatite layer on the surface of the composite disks was carried out. The growth rate constant increased with HA volume fraction of the composite, suggesting that the bioactivity of the HA/PEEK composite increases with increasing HA volume fraction in the composite.
[Show abstract][Hide abstract] ABSTRACT: A comparative study is carried out on the effect of nano-sized and micron-sized Y2O3/ZrO2 (YSZ) powders on the fabrication and performance of anode-supported solid oxide fuel cells. It is found that pellets made of nano-sized YSZ powder can achieve a relative density of 96% at a sintering temperature of 1400 °C and 92% at sintering temperature as low as 1200 °C. For pellets made of micron-sized YSZ powder, densification only occurred at a sintering temperature of 1400 °C. On co-sintering the nano-sized YSZ electrolyte film with the anode support/substrate, the electrolyte is unable to sinter fully at 1400 °C, but forms a porous structure which leads to a reduced open-circuit potential and poor cell performance. This is most likely due to the nano-sized YSZ electrolyte thin film having a very low green density and there being a significant difference in the sintering behaviour of the YSZ thin layer and the Ni/YSZ cermet substrates. The sintering behaviour and the nature of YSZ powders exert a significant effect on the fabrication and performance of Ni/YSZ anode-supported thin YSZ electrolyte cells.
Full-text · Article · May 2003 · Journal of Power Sources
[Show abstract][Hide abstract] ABSTRACT: Nanobioceramics based on Hydroxyapatite (HA) and its composites were synthesized using radio frequency (RF) induction suspension plasma spraying with a wet suspension as feedstock. The liquid suspension precursors were axially injected into the RF plasma at various plate powers (plasma energies), chamber pressures, probe distances and plasma gas flow rates. The processed powders varied in size according to the cyclones designed to collect the powders from medium to ultra-fine. The chamber collecting ultra-fine powder contained particles ranging from 10nm to 4mum. This study suggests that the processing parameters associated with the production of the ultra-fine powders interact in a complex manner but can be rationalised by considering the overall thermal treatment experienced by the particulates during plasma treatment.
No preview · Article · Nov 2002 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: Coated implants have, in recent years, been actively researched and put to use in many biomedical engineering applications. The coating is hydroxyapatite(HA), a calcium phosphate compound with attractive bioactive and biocompatible properties that can enhance the fixation process of biomedical implants. Thermal spraying provides a potent means for depositing the HA coatings on implants. Amongst the popular thermal spray techniques are combustion flame spray, plasma spray and high velocity oxy-fuel spray (HVOF). Past research has shown that plasma spraying normally induce undesirable phase changes to the HA feedstock. Hence, the coatings usually contain many bioinert or bioresorbable phases. These deleterious effects can be effectively curtailed through proper process settings, powder modification, and powder sizing. This report investigates the versatility of thermal spray techniques to perform: (i) spheroidisation of HA powders (ii) preparation of HA-based biocomposite powders and coatings and, (iii) depostion of HA coatings. The combustion flame was utilized to produce fine spheroidised HA powders and HA-based composite powders while plasma spray and HVOF spray deposit the spheroidised HA powders to form dense coatings.