Philip Cheang

Nanyang Technological University, Tumasik, Singapore

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Publications (7)16.53 Total impact

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    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.
    Journal of Thermal Spray Technology 01/2009; 18:10-15. · 1.48 Impact Factor
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    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.
    12/2008: pages 261-264;
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    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.
    Biomaterials 06/2005; 26(15):2343-52. · 8.31 Impact Factor
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    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.
    Journal of Power Sources 01/2003; · 5.26 Impact Factor
  • Khiam A. Khor, Philip Cheang, Hua Li, R. Kumar
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    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.
    Proc SPIE 01/2002;
  • Khiam Aik. Khor, Philip Hong Ning. Cheang
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    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.
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    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.
    Journal of Thermal Spray Technology 18(4):600-608. · 1.48 Impact Factor