ORCID Profile
0000-0003-1954-8423
Current Organisations
Nanyang Technological University
,
Monash University
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Nanomaterials | Manufacturing Engineering | Manufacturing Processes and Technologies (excl. Textiles) | Metals and Alloy Materials |
Education and Training Systems not elsewhere classified | Expanding Knowledge in Engineering | Coated Metal and Metal-Coated Products
Publisher: Elsevier BV
Date: 04-2012
Publisher: Elsevier BV
Date: 02-2002
Publisher: Elsevier BV
Date: 03-2001
Publisher: Elsevier BV
Date: 08-2007
Publisher: Elsevier BV
Date: 04-2005
Publisher: Elsevier BV
Date: 05-2007
Publisher: Springer Science and Business Media LLC
Date: 06-2002
Publisher: Springer Science and Business Media LLC
Date: 07-11-2013
Publisher: Elsevier BV
Date: 09-2003
Publisher: Wiley
Date: 14-05-2007
DOI: 10.1002/JBM.B.30864
Abstract: This study investigated the osteoblast behaviors on various hydroxyapatite based biomaterials that were consolidated at 1100 degrees C for 3 min by a spark plasma sintering technique. The osteoblasts from human fetal osteoblast cell line were cultured in the medium on the various biomaterials surfaces (HA, RF21, 1SiHA, and 5SiHA) to assess the cell morphology and proliferation as well as cell differentiation (alkaline phosphatase activity). Moreover, the bone gamma-carboxyglutamic protein or osteocalcin in the medium were determined at different periods of culture. The present results indicated that the amount of osteocalcin in the medium decreased during the periods of culture. The highest osteocalcin production obtained from the biomaterial 5SiHA after cell culture for 2 days demonstrated that the presence of silica in the biomaterials enhanced the cell differentiation by the rapid release of silicate and calcium ions.
Publisher: Elsevier BV
Date: 09-2003
Publisher: Elsevier BV
Date: 05-2003
Publisher: Elsevier BV
Date: 06-2000
Publisher: Elsevier BV
Date: 06-2008
Publisher: Elsevier BV
Date: 2003
Publisher: American Chemical Society (ACS)
Date: 27-07-2012
DOI: 10.1021/NL302017W
Abstract: Control of competing parameters such as thermoelectric (TE) power and electrical and thermal conductivities is essential for the high performance of thermoelectric materials. Bulk-nanocomposite materials have shown a promising improvement in the TE performance due to poor thermal conductivity and charge carrier filtering by interfaces and grain boundaries. Consequently, it has become pressingly important to understand the formation mechanisms, stability of interfaces and grain boundaries along with subsequent effects on the physical properties. We report here the effects of the thermodynamic environment during spark plasma sintering (SPS) on the TE performance of bulk-nanocomposites of chemically synthesized Bi(2)Te(2.7)Se(0.3) nanoplatelets. Four pellets of nanoplatelets powder synthesized in the same batch have been made by SPS at different temperatures of 230, 250, 280, and 350 °C. The X-ray diffraction, transmission electron microscopy, thermoelectric, and thermal transport measurements illustrate that the pellet sintered at 250 °C shows a minimum grain growth and an optimal number of interfaces for efficient TE figure of merit, ZT∼0.55. For the high temperature (350 °C) pelletized nanoplatelet composites, the concurrent rise in electrical and thermal conductivities with a deleterious decrease in thermoelectric power have been observed, which results because of the grain growth and rearrangements of the interfaces and grain boundaries. Cross section electron microscopy investigations indeed show significant grain growth. Our study highlights an optimized temperature range for the pelletization of the nanoplatelet composites for TE applications. The results provide a subtle understanding of the grain growth mechanism and the filtering of low energy electrons and phonons with thermoelectric interfaces.
Publisher: Elsevier BV
Date: 10-2001
Publisher: Springer Science and Business Media LLC
Date: 2003
Publisher: Elsevier BV
Date: 02-2002
DOI: 10.1016/S0142-9612(01)00208-3
Abstract: The lack of exotherm during setting, absence of monomer and improved release of incorporated therapeutic agents has resulted in the development of glass ionomer cements (GICs) for biomedical applications. In order to improve biocompatibility and biomechanically match GICs to bone, hydroxyapatite-ionomer (HAIonomer) hybrid cements were developed. Ultra-fine hydroxyapatite (HA) powders were produced using a new induction spraying technique that utilizes a radio-frequency source to spheriodize an atomized suspension containing HA crystallites. The spheriodized particulates were then held at 800 degrees C for 4 h in a carbolite furnace using a heating and cooling rate of 25 degrees C/min to obtain almost fully crystalline HA powders. The heat-treated particles were characterized and introduced into a commercial glass ionomer cement. 4 (H4), 12 (H12) and 28 (H28) vol% of fluoroalumino silicate were substituted by crystalline HA particles that were dispersed using a high-speed dispersion technique. The HAIonomer cements were subjected to hardness, compressive and diametral tensile strength testing based upon BS6039:1981. The storage time were extended to one week to investigate the effects of cement maturation on mechanical properties. Commercially available capsulated GIC (GC) and GIC at maximum powder:liquid ratio (GM) served as comparisons. Results were analyzed using factorial ANOVA/Scheffe's post-hoc tests and independent s les t-test at significance level 0.05. The effect of time on hardness was material dependent. With the exception of H12, a significant increase in hardness was observed for all materials at one week. A significant increase in compressive strength was, however, observed for H12 over time. At 1 day and 1 week, the hardness of H28 was significantly lower than for GM, H4, and H12. No significant difference in compression and diametral tensile strengths were observed between materials at both time intervals. Results show that HAIonomers is a promising material, which possess good mechanical properties. Potential uses of this new material include bone cements and performed implants for hard tissue replacement in the field of otological, oral-maxillofacial and orthopedic surgery.
Publisher: Springer Science and Business Media LLC
Date: 1999
Abstract: Hydroxyapatite powders were made by reacting orthophosphoric acid with calcium hydroxide and dense bioactive coatings were subsequently produced by the plasma spray technique. Three types of hydroxyapatite (flame spheroidized) monolayer coatings and three types of functionally graded coatings were manufactured. It was found that average microhardness values of monolayer coatings decreased as the indentation load increased. The relationship between indentation load and indent diagonal length observed Meyer's law. Microhardness and fracture toughness of coatings were affected by characteristics of feedstock powders for plasma spraying. The indentation fracture toughness of coatings could be significantly increased by incorporating a toughening phase.
Publisher: Elsevier BV
Date: 11-2001
Publisher: Wiley
Date: 2002
DOI: 10.1002/JBM.10082
Abstract: This article reports the morphology and mechanical properties of sintered powder injection molded Ti-6Al-4V/HA parts in a simulated physiological environment. Sintered Ti-6Al-4V/HA parts were immersed in a simulated body fluid (SBF) with ion concentrations that were comparable to those of human blood plasma for a total period of 12 weeks. At intervals of 2 weeks, the immersed Ti-6Al-4V/HA parts were analyzed with the use of scanning electron microscopy (SEM), X-ray diffractometry (XRD), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Mechanical properties such as flexural strength, flexural modulus, compressive strength, and compressive modulus were also evaluated. Results showed that complete dissolution of the more soluble phases such as tricalcium phosphate (TCP), tetracalcium phosphate (TTCP), and calcium oxide (CaO) were found after 2 weeks of immersion in SBF. ICP analysis showed that high calcium concentration release of around 200 ppm was observed in the SBF solution after 2-4 weeks of immersion, indicating that dissolution has taken place. Next, a gradual decrease in calcium concentration release in the SBF solution was observed after immersion for 4-6 weeks, with increasing amounts of calcium phosphate precipitates being observed on the Ti-6Al-4V/HA surface. Mechanical properties such as strength and modulus were found to deteriorate during 2-4 weeks of immersion, followed by gradual increment as the immersion period increased. This study also showed that parts sintered at 1150 C exhibited faster dissolution and precipitation rates than parts sintered at 1050 C in a physiological environment.
Publisher: Elsevier BV
Date: 2009
Publisher: Elsevier BV
Date: 2000
Publisher: Elsevier BV
Date: 05-2005
Publisher: Elsevier BV
Date: 05-2005
Publisher: The Electrochemical Society
Date: 2007
DOI: 10.1149/1.2780866
Publisher: Elsevier BV
Date: 16-01-2006
Publisher: Elsevier BV
Date: 04-2004
Publisher: Elsevier BV
Date: 04-2004
Publisher: Elsevier BV
Date: 02-2001
Publisher: Elsevier BV
Date: 11-2002
Publisher: Mark Allen Group
Date: 06-2007
Publisher: Elsevier BV
Date: 03-1999
Publisher: Elsevier BV
Date: 08-2000
Publisher: Elsevier BV
Date: 02-2002
Publisher: Elsevier BV
Date: 04-2003
Publisher: Elsevier BV
Date: 11-2000
Publisher: Elsevier BV
Date: 06-2007
DOI: 10.1016/J.BIOS.2007.01.006
Abstract: In this paper, a novel erometric glucose biosensor was constructed by alternative self-assembly of positively charged poly(diallydimethylammonium chloride) (PDDA) and negatively charged glucose oxidase (GOx) onto a 3D Nafion network via electrostatic adsorption. The amount of Nafion in the electrode and the number of the (PDDA/GOx)(n) multilayers were optimized to develop a sensitive and selective glucose biosensor. Under optimal conditions, the glucose biosensor with (PDDA/GOx)(5) multilayers exhibited remarkable electrocatalytic activity, capable of detecting glucose with enhanced sensitivity of 9.55 microA/mM cm(2) and a commendably low detection limit of 20 microM (S/N=3). A linear response range of 0.05-7 mM (a linear correlation coefficient of 0.9984, n=20) was achieved. In addition, the glucose biosensor demonstrated superior selectivity towards glucose over some interferents, such as ascorbic acid (AA) and uric acid (UA), at an optimized detection potential of 0.6 V versus Ag/AgCl reference.
Publisher: Springer Science and Business Media LLC
Date: 12-2006
Publisher: Wiley
Date: 17-07-2007
DOI: 10.1002/JBM.A.31289
Abstract: Initial cell attachment and spreading of anchorage-dependent cells onto the material surface are crucial concerns for the development of more effective implants. In this study, MG63 cells were employed to investigate the initial cell response to sol-gel derived fluoridated hydroxyapatite (FHA) coatings. Along with that, surface roughness, wettability, and protein adsorption were also characterized for those FHA coatings, respectively. It was observed that both the surface roughness and contact angle have a slight increase in response to the incorporation of more fluorine ions. All FHA coatings showed similar amount of adsorbed proteins (approximately 1.6 microg/cm(2)) upon testing in culture medium. Cell counting showed that no significant difference was observed for the amount of initially attached cells between HA and fluoridated HA coatings during the first 4 h culture. On the other hand, the well-spread cell on all prepared coating surface indicates that the incorporated fluorine ions have no adverse effect on cell spreading process. Therefore, it was suggested from this study that the prepared fluoridated hydroxyapatite coatings have comparable bioactivity to that of pure hydroxyapatite coating, and these results are meaningful for further investigation for application of FHA coatings.
Publisher: Springer Science and Business Media LLC
Date: 07-10-2010
Publisher: Elsevier BV
Date: 03-2001
Publisher: Elsevier BV
Date: 04-2001
Publisher: Elsevier BV
Date: 06-2003
DOI: 10.1016/S0142-9612(03)00027-9
Abstract: Hydroxyapatite (HA) based bioceramic coatings were deposited onto titanium alloy substrates using the high velocity oxy-fuel (HVOF) spray technique. This study aimed to reveal the relations among processing parameters, microstructure, and properties of the bioceramic coatings. The processing conditions were altered through changing the starting HA powder size, content of bioinert ceramic additives or composite powder preparation techniques. Coating structure was characterized through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the mechanical properties, Young's modulus and fracture toughness, of the coatings were evaluated through indentation techniques. Results demonstrated dominant influence of the melt state of HA powders on the phase composition of resultant coatings, and it was found that the HVOF HA coatings possess competitive mechanical properties. Furthermore, addition of titania or zirconia, as secondary phase in HA, showed promising effect on improving the mechanical properties of the HVOF HA-based coatings. Chemical reactions between HA and titania and, HA and zirconia during coating deposition were revealed and characterized. Incorporation modes of the additives into HA and their reinforcing mechanisms were elucidated. The relationship among the processing, microstructure, and mechanical properties of the HVOF sprayed bioceramic coatings was summarily examined.
Publisher: Elsevier BV
Date: 2000
Publisher: Elsevier BV
Date: 05-2003
Publisher: Wiley
Date: 07-2006
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 02-2011
Publisher: Elsevier BV
Date: 05-2004
Publisher: American Chemical Society (ACS)
Date: 07-11-2006
DOI: 10.1021/JP065200X
Abstract: Conductometry was employed to study the phase evolution of calcium phosphate compounds during the wet-chemical synthesis of hydroxyapatite (HA). Calcium hydroxide and orthophosphoric acid were used to prepare HA at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity and pH of the reaction mixture were measured at regular intervals of time during acid addition, and the rate of change of conductivity was used to decipher the end point of the reaction. Our previous studies have shown that the end product of this reaction route yields mildly carbonated crystalline HA. The trend of the change in conductivity with time was similar at all temperatures. The conductivity curves were ided into three regions based on the variation in slope of the curves. The slope of the curves decreased with increasing temperatures in the first two regions, and the slope is greater in the second region than in the first. From the conductivity and pH measurement results, the possible precursor phase was identified and it had the composition Ca(3)(PO(4))(2). The kinetics of phase transformation was also analyzed and compared to previous work. The similarities between this work and the traditionally adapted experimental work for phase formation and transformation kinetics are highlighted, and the novelty in the current work is discussed.
Publisher: Springer Science and Business Media LLC
Date: 31-10-2009
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 2002
DOI: 10.1016/S0142-9612(01)00082-5
Abstract: Hydroxyapatite (HA) coatings with titania addition were produced by the high velocity oxy-fuel (HVOF) spray process. Mechanical properties of the as-sprayed coatings in terms of adhesive strength, shear strength and fracture toughness were investigated to reveal the effect of the titania reinforcement on HA. Qualitative phase analysis with X-ray diffraction (XRD) showed that mutual chemical reaction between TiO2 and HA, that formed CaTiO3 occurred during coating formation. Differential scanning calorimetry (DSC) analysis of the starting powders showed that the mutual chemical reaction temperature was approximately 1410 degrees C and the existence of TiO2 can effectively inhibit the decomposition of HA at elevated temperatures. The positive influence of TiO2 addition on the shear strength was revealed. The incorporation of 10 vol% TiO2 significantly improved the Young's modulus of HA coatings from 24.82 (+/- 2.44) GPa to 43.23 (+/- 3.20) GPa. It decreased to 38.51 (+/- 3.65) GPa as the amount of TiO2 increased to 20 vol%. However, the addition of TiO2 has a negative bias on the adhesive strength of HA coatings especially when the content of TiO2 reached 20 vol%. This is attributed to the weak chemical bonding and brittle phases existing at the splats' interface that resulted from mutual chemical reactions. The fracture toughness exhibited values of 0.48 (+/- 0.08) MPa m0.5, 0.60 (+/- 0.07) MPa m0.5 and 0.67 (+/- 0.06) MPa m0.5 for the HA coating, 10 vol% TiO2 blended HA coating and 20 vol% TiO2 blended HA coating respectively. The addition of TiO2 in HA coating with the amount of less than 20 vol% is suggested for satisfactory toughening effect in HVOF HA coating.
Publisher: Elsevier BV
Date: 2002
DOI: 10.1016/S0142-9612(01)00116-8
Abstract: The control of phase transformations in plasma sprayed hydroxyapatite (HA) coatings are critical to the clinical performance of the material. This paper reports the use of high temperature X-ray diffraction (HT-XRD) to study, in-situ, the phase transformations occurring in plasma sprayed HA coatings. The coatings were prepared using different spray power levels (net plasma power of 12 and 15 kW) and different starting powder size ranges (20-45 45-75 microm). The temperature range employed was room temperature (approximately 26 degrees C) to 900 degrees C in normal atmosphere and pressure. High temperature differential scanning calorimetry (DSC) was also employed to investigate and determine the precise onset temperature of phase transformations during the recrystallization process. Results showed that actual onset of thermal degradation in the coating into other metastable phases like TTCP, beta-TCP and CaO occurred at 638 degrees C. The aforementioned phase transitions were independent of the selected spraying parameters. The degree of melting and thermal dissociation of HA actually determines the amount of calcium phosphate phases that are formed. A high power level of 15 kW produced a greater degree of melting, resulting in more CaO, TTCP and beta-TCP being formed as a result.
Publisher: Elsevier BV
Date: 06-2002
Publisher: Elsevier BV
Date: 10-2003
Publisher: Elsevier BV
Date: 06-2001
DOI: 10.1016/S0142-9612(00)00272-6
Abstract: Hydroxyapatite-coated titanium alloy composite powders (Ti-6Al-4V/HA) was produced by a ceramic slurry approach. The aim was to evaluate the stability of the coating when subjected to a physiological medium simulated body fluid (SBF). Three consolidation conditions (700 degrees C for 5 h, 700 degrees C for 8 h and 700 degrees C for 11 h) were used in the production of the Ti-6Al-4V/HA composite powders. Results showed that biodissolution followed by apatite precipitation had taken place after soaking in SBF. In addition, it was found that consolidation at 700 degrees C for 5 h resulted in a weak mechanical locking of calcium phosphate on the Ti-6Al-4V surfaces and the formation of small crystallites, which would increase the dissolution rate.
Publisher: Informa UK Limited
Date: 06-2005
Publisher: Elsevier BV
Date: 10-2002
Publisher: Elsevier BV
Date: 05-1999
Publisher: The Electrochemical Society
Date: 2005
DOI: 10.1149/1.1843791
Publisher: SPIE
Date: 11-2002
DOI: 10.1117/12.469745
Publisher: Elsevier BV
Date: 12-2006
Publisher: Elsevier BV
Date: 03-2005
Publisher: IOP Publishing
Date: 23-06-2011
Publisher: Elsevier BV
Date: 11-2000
Publisher: Elsevier BV
Date: 05-2000
Publisher: Springer Science and Business Media LLC
Date: 04-03-2019
Publisher: Elsevier BV
Date: 2012
Publisher: Elsevier BV
Date: 03-2003
Publisher: Elsevier BV
Date: 03-2005
Publisher: Wiley
Date: 08-2002
DOI: 10.1002/JBM.10315
Abstract: One of the most important concerns with the clinical use of plasma-sprayed hydroxyapatite (HA) coatings is the resorption of the coating, and dissolution at neutral pH is one of the two major resorption mechanisms. In this study, highly crystalline pure HA powders were atmospherically plasma sprayed using various parameters. Dissolution of both HA powders and coatings was measured using a calcium ion meter. Surface characteristics, including phase, morphology, and roughness, were compared for the coatings before and after dissolution. Pulverized HA coatings exhibited significantly higher dissolution compared with the same quantity of feedstock HA powders because of the decreased crystallinity and fine crystal size of the coating. Furthermore, the dissolution decreased with the crystallinity of the coating. Dissolution of HA coatings did not show much difference with respect to the coatings in the initial stage of immersion (4 h). However, dissolution of all coatings reached saturation in a fresh physiological solution. The saturation values were much lower compared with their counterparts in the form of powders, which may imply the stability of HA coatings in long-term use. In addition to crystallinity, the particle melting status in the coatings, i.e., the volume of nanocrystals, and porosity, was found to be another important factor for the dissolution of the HA coating. X-ray diffraction patterns of HA coatings indicated the complete dissolution of impurity phases and amorphous phase after the coatings were immersed in the solution for 4 days. Coatings sprayed at lower power (27.5 kW) exhibited a pattern of crystalline HA whereas coatings sprayed at higher power (42 kW) exhibited a pattern of bone apatite. Surface morphologies showed preferential dissolution of amorphous phase in all coatings accompanied with precipitation of bone apatite observable for coatings sprayed at higher power. Surface roughness measured after the dissolution studies increased for the two coatings sprayed at lower power level but decreased for coatings sprayed at higher power level. This decrease is attributed to the better match in solubility characteristics between the fine crystals and the amorphous calcium phosphate within the coating.
Publisher: Elsevier BV
Date: 04-2007
Publisher: Elsevier BV
Date: 09-2002
Publisher: Elsevier BV
Date: 09-2001
Publisher: Informa UK Limited
Date: 09-2004
Publisher: Elsevier BV
Date: 11-2009
Publisher: Elsevier BV
Date: 10-2006
Publisher: American Chemical Society (ACS)
Date: 20-05-2004
DOI: 10.1021/LA049304F
Abstract: Hydroxyapatite (HA) is synthesized by a wet chemical route using calcium hydroxide and ortho-phosphoric acid at various temperatures (40, 80, and 100 degrees C). X-ray diffraction of the precipitate particles revealed HA as the predominant phase (>99%) with a small amount of beta-tricalcium phosphate. Fourier transform infrared spectroscopy indicated the presence of carbonate substitution, which decreased with increasing temperature. Transmission electron microscopy observations revealed needle-shaped particles with a high aspect ratio at 40 degrees C, which changed to spheroidal when the precipitation temperature was increased to 100 degrees C. The changes in the morphology with temperature were analyzed taking into account the driving force for the HA precipitation and the supersaturation level of Ca2+ and PO4(3-) ions with respect to HA. The analysis indicated that the supersaturation level of the reactants, especially the concentration of Ca2+ ions, played a predominant role on the precipitate morphology for this classical acid-base reaction.
Publisher: Elsevier BV
Date: 07-2001
Publisher: Elsevier BV
Date: 11-2000
Publisher: Elsevier BV
Date: 12-2006
Publisher: Elsevier BV
Date: 02-2001
Publisher: Elsevier BV
Date: 09-2003
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 1996
DOI: 10.1016/0142-9612(96)82729-3
Abstract: Biomedical coatings generally have to satisfy specific requirements such as a high degree of crystallinity (for positive biological responses), good coating adhesion and optimal porosity. These are necessary to enhance biocompatibility, accelerate post-operative healing and improved fixation. Thermal spray processes have been frequently used to deposit functionally active biomedical coatings, such as hydroxyapatite (HA), onto prosthetic implants. The benefits of HA materials in coated implants have been widely acknowledged, but the occurrence of several poor performances has generated concerns over the consistency and reliability of thermally sprayed HA coatings. Recent investigations using HA coatings have shown that process related variability has significant influence on coating characteristics such as phase composition, structure and chemical composition and performance such as bioresorption, degradation and bone apposition. Variation in process parameters such as powder morphology can induce microstructural and mechanical inconsistencies that have an effect on the service performance of the coating. In order to reach some acceptable level of reliability, it may be necessary to control existing variability in commercially available HA feedstock. In addition, certain opposing factors severely constrain the means to achieve the necessary coating conditions via thermal spraying alone therefore, creating the need to introduce other innovative or secondary treatment stages to attain the desired results. This paper highlights some of the problems associated with plasma spray coating of HA and suggests that tailoring the powder feedstock morphology and properties through suitable conditioning processes can aid the deposition efficiency and produce an acceptable coating structure.
Publisher: Elsevier BV
Date: 05-1999
Publisher: The Royal Society
Date: 14-08-2007
Abstract: The synthesis and subsequent assembly of nearly spherical nano-hydroxyapatite (nHA) particles in the presence of trace amounts of the polysaccharide chitosan was carried out employing a wet chemical approach. Chitosan addition during synthesis not only modulated HA crystallization but also aided in the assembly of nHA particles onto itself. Solvent extraction from these suspensions formed iridescent films, of which the bottom few layers were rich in self-assembled nHA particle arrays. The cross-section of these hybrid films revealed compositional and hence structural grading of the two phases and exhibited a unique morphology in which assembled nHA particles gradually gave way to chitosan-rich top layers. Transmission electron microscope and selected area electron diffraction studies suggested that the basal plane of HA had interacted with chitosan, and scanning electron microscope studies of the hybrid films revealed multi-length scale hierarchical architecture composed of HA and chitosan. Phase identification was carried out by X-ray diffraction (XRD) and Rietveld analysis of digitized XRD data showed that the basic apatite structure was preserved, but chitosan inclusion induced subtle changes to the HA unit cell. The refinement of crystallite shape using the Popa method clearly indicated a distinct change in the growth direction of HA crystallites from [001] to [100] with increasing chitosan concentration. The paper also discusses the likelihood of chitosan phosphorylation during synthesis, which we believe to be a pathway, by which chitosan molecules chemically interact with calcium phosphate precursor compounds and orchestrate the crystallization of nHA particles. Additionally, the paper suggests several interesting biomedical applications for graded nHA–chitosan nanostructured films.
Publisher: Trans Tech Publications, Ltd.
Date: 05-2010
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.652.309
Abstract: Residual strains in plasma sprayed and heat-treated hydroxyapatite (HA) coatings deposited on a titanium alloy (Ti-6Al-4V) substrate were investigated by means of neutron diffraction. Strain measurements were performed in vertical scan (“z-scanning”) mode to provide a through thickness strain profile in the coating and substrate materials. Results are discussed in terms of the influence of heat-treatment on the residual strain profile of these biomedical coatings. This investigation concluded that the heat-treatment had a significant effect on the residual strain profile in HA coatings.
Publisher: Elsevier BV
Date: 03-2008
Publisher: Springer Science and Business Media LLC
Date: 17-03-2012
DOI: 10.1007/S10856-012-4578-6
Abstract: Keratoprosthetic devices are subject to chronic inflammatory, pathological processes and the external environment that affect their stability and biocompatibility with the ocular surface and adjacent ocular tissues. We compared the corrosion resistance property and tissue-implant reaction of titanium oxide (TiO(2)) with hydroxyapatite (HA) in artificial tear fluid and a rabbit skin implantation model. The dissolution properties of the implant surfaces were evaluated with scanning electronic microscope (SEM) and atomic force microscope (AFM). Tissue inflammatory reactions were evaluated by Hematoxylin & Eosin staining, avidin biotin peroxidase complex (ABC) immunoassay and immunofluorescence. SEM and AFM images showed that there was less pitting corrosion on the surface of TiO(2) implants compared with HA. TiO(2) and HA exhibited a similar pattern of foreign body capsule formation and inflammatory cellular responses. The Collagen I/Collagen III ratio of the TiO(2) capsule was higher than that of the HA capsule. TiO(2) implants possess a high corrosion resistance property both in vitro and in vivo and the inflammatory cellular response to TiO(2) is similar to HA. With regards to corrosion resistance and inflammatory tissue responses, TiO(2) appears to be a promising material for keratoprosthetic skirt devices.
Publisher: Elsevier BV
Date: 04-2013
Publisher: Elsevier BV
Date: 05-2005
DOI: 10.1016/J.BIOMATERIALS.2004.07.028
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.
Publisher: Springer Science and Business Media LLC
Date: 09-2002
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 06-2007
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 23-09-2002
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 2004
Publisher: Springer Science and Business Media LLC
Date: 12-2006
Publisher: Wiley
Date: 10-2008
Abstract: Hydroxyapatite (HA) and its derived bioceramic materials have been widely used for skeletal implants and/or bone repair scaffolds. It has been reported that carbon nanotube (CNT) is able to enhance the brittle ceramic matrix without detrimental to the bioactivity. However, interaction between osteoblasts and these bioceramics, as well as the underlying mechanism of osteoblast proliferation on these bioceramic surfaces remain to be determined. Using iTRAQ-coupled 2-D LC-MS/MS analysis, we report the first comparative proteomics profiling of human osteoblast cells cultured on plane HA and CNT reinforced HA, respectively. Cytoskeletal proteins, metabolic enzymes, signaling, and cell growth proteins previous associated with cell adhesion and proliferation were found to be differentially expressed on these two surfaces. The level of these proteins was generally higher in cells adhered to HA surface, indicating a higher level of cellular proliferation in these cells. The significance of these findings was further assessed by Western blot analysis. The differential protein profile in HA and CNT strengthened HA established in our study should be valuable for future design of biocompatible ceramics.
Publisher: BMJ
Date: 16-07-2012
Publisher: Elsevier BV
Date: 14-05-2004
Publisher: Elsevier BV
Date: 05-1999
Publisher: Springer Science and Business Media LLC
Date: 10-12-2008
Publisher: The Electrochemical Society
Date: 2004
DOI: 10.1149/1.1630036
Publisher: Elsevier BV
Date: 02-2004
Publisher: Elsevier BV
Date: 12-1999
Publisher: Elsevier BV
Date: 04-1998
Publisher: Elsevier BV
Date: 07-2004
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 02-2003
Publisher: Elsevier BV
Date: 06-2012
Publisher: Elsevier BV
Date: 2005
Publisher: The Electrochemical Society
Date: 2004
DOI: 10.1149/1.1645751
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 10-2009
DOI: 10.1016/J.BIOMATERIALS.2009.07.002
Abstract: The use of synthetic hydroxyapatite as bone substitute calls for the knowledge of the influence on adjacent cells. The aim of this study was to investigate the proteins with differential protein expression levels in the proteome of human osteoblast cell line incubated separately with various nano sized hydroxyapatite powders with different shapes and chemical compositions using iTRAQ-coupled 2D LC-MS/MS approach. In the present study, we investigated several intracellular signaling molecules involved in calcium regulation to analyze how osteoblast cells respond to dissimilar HA nanoparticles. It was found there was a significant decrease in cell population after adding the HA nanoparticles to the osteoblasts. Our results combining proteomics analysis and RT-PCR validation on targeted genes involved in calcium regulation confirmed the differences in the cellular response to dissimilar HA nanoparticles.
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0142-9612(02)00381-2
Abstract: Hydroxyapatite (HA) ceramics have been conventionally strengthened and toughened in the form of composites and coatings. New microstructural designs and processing methodologies are still needed for the improvement of the mechanical properties of HA-based ceramics. This study was to prepare laminated and functionally graded HA/yttria stabilized tetragonal zirconia (Y-TZP) composites by the relatively new process of spark plasma sintering (SPS). The microstructure and the mechanical properties of the laminated and functionally graded composites were studied for possible orthopedic applications. It was found that the laminated and functionally graded HA/Y-TZP composites could be densified at 1200 degrees C within 5 min by the SPS process and the average HA grain size in the composite layers was reduced by half due to the well-dispersed Y-TZP second phase. The HA phase in the composite layers was stable up to 1200 degrees C and the Y-TZP second phase remained the tetragonal zirconia (t-ZrO(2)) phase after being processed at the highest temperature of 1250 degrees C. The laminated and functionally graded HA/Y-TZP composites exhibited much improved mechanical properties compared with the pure HA ceramics the bending strength of the composites reached about 200 MPa, double the strength of the pure HA ceramics.
Publisher: Elsevier BV
Date: 03-2008
Publisher: American Chemical Society (ACS)
Date: 08-12-2005
DOI: 10.1021/LA0522348
Abstract: Derived from reaction kinetics, a simple but useful method, based on "apatite forming capacity" or AFC of solutions mimicking blood plasma, is proposed to decipher the rate of calcium phosphate mineralization. Apatite growth rate constants were calculated using this method for a model composite surface varying the volume fraction of synthetic hydroxyapatite (HA) in a polymer matrix. Previously reported data for mineralized surfaces on Ta, Ti, and its alloys are also analyzed similarly and compared. Utilizing the growth rate constant, the bioactivity of the materials was indexed in vitro. Complementarily, semiempirical quantum mechanical calculation (ZINDO method) showed that the interaction of cations with TRIS-hydroxymethyl aminomethane molecules in the solution is stronger than that with the polymer substrate considered, but weaker than hydrated Ti and TiO(2) surfaces. This analysis then quantifies for ex le the extent of polymer inertness and the "bioactivity" of alkali treated Ti. The growth rate constants for the model materials prepared in this work are explained on the basis of localized dissolution of HA, the amount of which simply increases with increasing volume fraction of HA in the composite.
Publisher: American Chemical Society (ACS)
Date: 17-11-2006
DOI: 10.1021/LA0621665
Abstract: Two differing wet-chemical synthesis routes, Ca(OH)2 + H3PO4 and CaCl2 + Na3PO4/NaOH, were used to prepare hydroxyapatite (HA) at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity of the solution was measured at regular intervals of time during H3PO4 and Na3PO4 addition to the suspension/solution containing Ca2+ ions. The rate of change of conductivity is used to note the end point of the reaction. X-ray diffraction of the dried, precipitated particles revealed HA as the predominant phase, and the FTIR spectroscopy studies indicated the presence of CO3(2-) groups which substituted PO4(3-) groups in the HA lattice (B-type). FESEM observations revealed that the aspect ratio of the particles decreased with increasing precipitation reaction temperature in one system [Ca(OH)2 + H3PO4] and in the other system it increased with increasing temperature. The changes in the morphology with temperature were analyzed through conductivity measurements and the thermochemical properties of the reaction systems. Conductivity measurements showed that the concentration of dissolved ions at the end point of the reaction between Ca(OH)2 and H3PO4 increased, indicating an increased apparent solubility of HA with increasing temperature, whereas the end-point conductivity did not increase noticeably in the other reaction system.
Publisher: Elsevier BV
Date: 06-2004
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 05-01-2011
DOI: 10.1167/IOVS.10-6186
Abstract: Osteo-odonto keratoprosthesis is one of the most successful forms of keratoprosthesis surgery for end-stage corneal and ocular surface disease. There is a lack of detailed comparison studies on the biocompatibilities of different materials used in keratoprosthesis. The aim of this investigation was to compare synthetic bioinert materials used for keratoprosthesis surgery with hydroxyapatite (HA) as a reference. Test materials were sintered titanium oxide (TiO(2)), aluminum oxide (Al(2)O(3)), and yttria-stabilized zirconia (YSZ) with density >95%. Bacterial adhesion on the substrates was evaluated using scanning electron microscopy and the spread plate method. Surface properties of the implant discs were scanned using optical microscopy. Human keratocyte attachment and proliferation rates were assessed by cell counting and MTT assay at different time points. Morphologic analysis and immunoblotting were used to evaluate focal adhesion formation, whereas cell adhesion force was measured with a multimode atomic force microscope. The authors found that bacterial adhesion on the TiO(2), Al(2)O(3), and YSZ surfaces were lower than that on HA substrates. TiO(2) significantly promoted keratocyte proliferation and viability compared with HA, Al(2)O(3,) and YSZ. Immunofluorescent imaging analyses, immunoblotting, and atomic force microscope measurement revealed that TiO(2) surfaces enhanced cell spreading and cell adhesion compared with HA and Al(2)O(3). TiO(2) is the most suitable replacement candidate for use as skirt material because it enhanced cell functions and reduced bacterial adhesion. This would, in turn, enhance tissue integration and reduce device failure rates during keratoprosthesis surgery.
Publisher: Elsevier BV
Date: 05-2001
Publisher: Elsevier BV
Date: 06-2001
Publisher: Elsevier BV
Date: 06-2000
DOI: 10.1016/S0142-9612(99)00275-6
Abstract: Flame-spheroidized feedstock, with excellent known heat transfer and consistent melting capabilities, were used to produce hydroxyapatite (HA) coatings via plasma spraying. The characteristics and inherent mechanical properties of the coatings have been investigated and were found to have direct and impacting relationship with the feedstock characteristics, processing parameters as well as microstructural deformities. Processing parameters such as particle sizes (SHA: 20-45, 45-75 and 75-125 microm) and spray distances (10, 12 and 14 cm) have been systematically varied in the present study. It was found that the increase of particle sizes and spray distances weakened the mechanical properties (microhardness, modulus, fracture toughness and bond strength) and structural stability of the coatings. The presence of inter- and intralamellar thermal microcracks, voids and porosities with limited true contact between lamellae were also found to degrade the mechanical characteristics of the coatings, especially in coatings produced from large-sized HA particles. An effort was made to correlate the effects of microstructural defects with the resultant mechanical properties and structural integrity of the plasma-sprayed hydroxyapatite (HA) coatings. The effects of different heat treatment temperatures (600, 800 and 900 degrees C) on the mechanical properties of the coatings were also studied. It was found that a heat treatment temperature of 800 degrees C does enhance the microhardness and elastic modulus of the coatings significantly (P 0.1). The elastic response behaviour and fracture toughness of both the as-sprayed and heat-treated HA coatings using Knoop and Vickers indentations at different loadings have been investigated. Results have shown that the mechanical properties of the coatings have improved significantly despite increasing crack density after heat treatment in air. Coatings produced from the spheroidized feedstock of 20-45 microm (SHA 20-45 microm) sprayed at a stand-off distance of 10 cm were found to possess the most favourable mechanical properties.
Publisher: Elsevier BV
Date: 02-2002
Publisher: Elsevier BV
Date: 05-2002
DOI: 10.1016/S0142-9612(01)00326-X
Abstract: The influence of crystallization, upon heat treatment, on the properties of high-velocity oxy-fuel (HVOF) sprayed hydroxyapatite (HA) coatings was investigated. The characterization of the HA coating was performed by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Differential Scanning Calorimeter (DSC) was employed to determine the crystallization temperature of the amorphous phase in an as-sprayed HA coating. The study demonstrated the effect of crystallization on the coating properties by considering the changes in materials chemistry, crystallinity level, and mechanical performance. Results showed that complete crystallization of the amorphous phase occurred at approximately 700 degrees C and the crystallization temperature was dependent on s le heating rate in the DSC test. The changes of ion groups were detected by FTIR, before and after the phase transformation. The crystallization of the coating after annealing at 750 degrees C resulted in a significant increase of the coatings' adhesive strength and shear strength, which attained maximum values 34 +/- 3 and 14.1 -/+ 0.8 MPa, respectively. Young's modulus increased from 21 +/- 1 to 25 +/- 2 GPa. Microhardness measurements confirmed the changes in coating properties. It is also found that the transformation from the amorphous phase has crystalline HA as the only resultant phase detected by XRD.
Publisher: Elsevier BV
Date: 02-2007
Publisher: Elsevier BV
Date: 02-2002
DOI: 10.1016/S0142-9612(01)00183-1
Abstract: The in vitro behaviour and characteristics of plasma sprayed hydroxyapatite (HA) coatings using flame-spheroidized HA feedstock powder on titanium alloy (Ti-6Al-4V) substrates were investigated in a simulated physiological environment as an attempt to reflect the actual incubational condition of an implant in a human body system. As-sprayed and heat-treated HA coatings were immersed in a simulated body fluid with ionic concentrations comparable to that of human blood plasma for time intervals 2, 4, 6, 8 and 10 weeks. Rapid dissolution of calcium phosphate was found to occur within the first 4 weeks, and after the 5th week a retarding rate of 4.1 mM week(-1) was observed where precipitation, nucleation, and, growth of a carbonate-containing, poorly crystallized or amorphous calcium phosphate layer on the as-sprayed coatings were noted. The heat-treated coatings showed minimal or no precipitation on the surface except for the presence of calcite minerals that is due to carbonation effect. Complete dissolution of other calcium phosphate phases such as tetracalcium phosphate, tricalcium phosphate and calcium oxide was also noted after 2 weeks of immersion due to higher ionic solubility relative to HA. A declining trend in respective microhardness and elastic modulus of the as-sprayed HA coatings from 207.06 +/- 3.2 H(k300) to 131.8 +/- 5.2 H(k300) and from 31.37 +/- 1.4 to 19.81 +/- 1.6 GPa was observed after 10 weeks of immersion. Tensile bond strength of both types of coatings showed similar declining trend, with an average dip from 24.5 +/- 2.4 to 7.9 +/- 2.6 MPa. Nevertheless. the heat-treated s les showed rather reasonable mechanical stability and structural integrity of 26.7 +/-1.4 GPa in elastic modulus after soaking.
Publisher: Elsevier BV
Date: 07-2001
Publisher: Elsevier BV
Date: 07-2007
Publisher: Springer Science and Business Media LLC
Date: 06-08-2005
Publisher: Elsevier BV
Date: 02-2007
DOI: 10.1016/J.JINORGBIO.2006.09.030
Abstract: Silica (SiO(2)) and the silicate-based biomaterials play an important role due to their in vitro and in vivo biological response. The present study synthesized a novel nano-structured amorphous silica doped hydroxyapatite (HA) via an aqueous precipitation route. HA was prepared with 0, 1, 3 and 5 wt% silica, which are comparable to the measured silicon content of natural bone. After spray drying into micron sized powders, the silica doped HA (SiHA) powders were consolidated at 1000 degrees C with a dwell time of 3 min using a spark plasma sintering (SPS) technique. X-ray diffraction analysis showed a main apatite phase with minor secondary beta-tricalcium phosphate (beta-TCP) was observed in the as-consolidated SiHA compacts. Substitution of PO(4)(3-) by SiO(4)(4-) in the apatite structure resulting in a small increase in the lattice parameters in both a-axis and c-axis of the unit cell were identified by X-ray photoelectron spectrometer (XPS) analysis and Raman spectrometer investigation. The cell culture in vitro investigation demonstrated that the presence of silicon in the SPS consolidated compacts contributed to the relatively high cell proliferation ability when compared with phase pure HA.
Publisher: Elsevier BV
Date: 03-2007
Publisher: Elsevier BV
Date: 07-2008
Publisher: Wiley
Date: 24-06-2009
Publisher: Elsevier BV
Date: 2003
Publisher: Elsevier BV
Date: 2009
Publisher: Elsevier BV
Date: 05-2005
DOI: 10.1016/J.BIOMATERIALS.2004.06.042
Abstract: The present study describes the synthesis of spheroidized hydroxyapatite (HA) powders using a radio frequency (rf) inductively coupled plasma (ICP) torch. The spheroidized powders were consolidated through a spark plasma sintering (SPS) system. The microstructure and crystallographic phases in the synthesized powders were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and Raman spectrometry. Results showed that the HA feedstock decomposed after rf plasma processing. Crystalline HA, alpha-tri-calcium phosphate (alpha-TCP), tetra-calcium phosphate (TTCP) and calcium oxide (CaO) were detected in the plasma-spheroidized powders. Raman spectra results indicated strong presence of amorphous calcium phosphate (ACP) in the spheroidized powders. The particle size distribution and specific surface area were influenced through the rf plasma working plate power levels. The sintering behavior of the rf plasma synthesized powders was analyzed through the SPS process and the results indicated that the spheroidized powders commence sintering at approximately 900 degrees C and through to 1150 degrees C. After sintering above 1100 degrees C for 3min, the relative densities of the SPS compacts reached 96% of the theoretical value. The SPS compacts were immersed in simulated body fluids (SBF) for different durations and the results confirmed their bioactivities.
Publisher: Elsevier BV
Date: 10-1996
DOI: 10.1016/0142-9612(95)00146-8
Abstract: Plasma-sprayed hydroxyapatite (HA) coatings have complex microstructures. There are often variations in phase, structure and chemical composition among the starting material and coating. Some of these changes may not be acceptable for biomedical applications. Attaining all the requirements for a functional coating in a single spraying process is not easily achieved. Additional post-treatment may be necessary. This study examines the use of a pulsed laser to enhance the coating characteristics of plasma-sprayed HA coatings. Preliminary results show the laser-treated coatings having a modified microstructure with crack networks and pores in the size range 5-30 microns. The pores and cracks were quantified by an image analyser. The crack network is less significant in coatings that are treated at lower energy intensity and this could be interesting in that the laser can be used to alter the surface phase composition as well as the morphology. However, repetitive passes with the pulsed laser did not help to seal the cracks that formed.
Publisher: Elsevier BV
Date: 08-2000
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0142-9612(02)00404-0
Abstract: Hydroxyapatite (HA) coatings and splats deposited by high velocity oxy-fuel (HVOF) spray technique was investigated in vitro. HA coatings prepared from two different HA powder size range (30+/-5 and 50 +/-5 microm) were immersed in a simulated body fluid with various incubation periods of maximum 6 weeks. The dissolution recipitation behavior was studied and the degradation of HA coatings caused by in vitro ageing was demonstrated by measuring the changes in flexural modulus through a 3-point bend test. It was found that the dissolution and precipitation behavior of the coatings was significantly dependent upon the incipient coating phase composition and the precipitation of bone-like hydroxyapatite on the coating's surface was found to be directly related to the dissolution process. Higher dissolution rates of tricalcium phosphate, tetracalcium phosphate and amorphous calcium phosphate relative to HA, resulted in accelerated precipitation. Furthermore, analysis of coatings' surface morphology demonstrated that advanced precipitation invariably occurred at regions where dissolution took place. Results showed that the changes in flexural modulus of investigated HA coatings accompanying different incubation duration was not systematic but was found to be dependent upon changes of coating structure and other factors brought about by in vitro ageing. In vitro investigation of in idual HA splats collected from different HA particle sizes revealed, after 3 days ageing, that the rate ratio of precipitation to dissolution was directly determined by the local phase composition, and this phenomenon could be effectively used to explain the behavior of thermally sprayed HA coatings in vitro. It implied that the precipitation was strongly dependent on the first molecule attachment. To achieve rapid precipitation in vitro, partial molten state of HA particles during HVOF coating deposition was recommended.
Publisher: Springer Science and Business Media LLC
Date: 22-10-2010
Publisher: Elsevier BV
Date: 05-1999
Publisher: Elsevier BV
Date: 07-2002
DOI: 10.1016/S0142-9612(01)00422-7
Abstract: Taguchi method with an L9 orthogonal array was employed to investigate the sintered properties of Ti-6Al-4V/HA tensile bars produced by powder injection molding. The effects of sintering factors at the 90% significance level: sintering temperature (1050 degrees C, 1100 degrees C and 1150 degrees C), heating rate (5 degrees C/min, 7.5 degrees C/min and 10 degrees C/min), holding time (30, 45 and 60 min) and cooling rate (5 degrees C/min, 20 degrees C/min and 40 degrees C/min) were investigated. Results showed that sintering temperature, heating rate and cooling rate have significant effects on sintered properties, whereas the influence of holding time was insignificant. It was found that a sintering temperature of 1100 degrees C, a heating rate of 7.5 degrees C/min and a cooling rate of 5 degrees C/min increased the relative density, Vicker's microhardness, flexural strength and flexural modulus. However, a further increment of sintering temperature to 1150 degrees C did not show any discernable improvement in the relative density and Vicker's microhardness, but there was a slight increase of 0.6% and 0.9% in the flexural strength and flexural modulus, respectively. Mechanically strong Ti-6Al-4V/HA parts with an open porosity of around 50% were developed.
Publisher: Elsevier BV
Date: 11-2000
Publisher: Elsevier BV
Date: 11-2008
Publisher: Springer Science and Business Media LLC
Date: 09-2003
Publisher: Elsevier BV
Date: 08-03-2004
Publisher: Elsevier BV
Date: 02-2013
Publisher: Elsevier BV
Date: 08-2007
DOI: 10.1016/J.BIOS.2007.03.014
Abstract: ZnO:Co nanoclusters were synthesized by nanocluster-beam deposition with averaged particle size of 5 nm and porous structure, which were for the first time adopted to construct a novel erometric glucose biosensor. Glucose oxidase was immobilized into the ZnO:Co nanocluster-assembled thin film through Nafion-assisted cross-linking technique. Due to the high specific active sites and high electrocatalytic activity of the ZnO:Co nanoclusters, the constructed glucose biosensor showed a high sensitivity of 13.3 microA/mA cm2. The low detection limit was estimated to be 20 microM (S/N=3) and the apparent Michaelis-Menten constant was found to be 21 mM, indicating the high affinity of the enzyme on ZnO:Co nanoclusters to glucose. The results show that the ZnO:Co nanocluster-assembled thin films with nanoporous structure and nanocrystallites have potential applications as platforms to immobilize enzyme in biosensors.
Publisher: Elsevier BV
Date: 06-2004
Publisher: Elsevier BV
Date: 03-2003
DOI: 10.1016/S0142-9612(02)00431-3
Abstract: Formation mechanism of hydroxyapatite (HA)/titania (TiO(2)) composite coating deposited by high velocity oxy-fuel (HVOF) thermal spray process was studied, and its structural characterization was conducted and elaborated in this paper. The impact theory was employed to analyze the formation procedure of the HA/titania composite coatings. Results revealed that the crater caused by the impact of entirely unmelted TiO(2) particles on the HA matrix during coating formation was of smaller dimensions than the original size of the reinforcements. It was found that chemical reaction between the mechanically blended HA and TiO(2) powder took place exclusively during the impingement stage, and calcium titanate, CaTiO(3), was one notable by-product. The bonding between the HA matrix and TiO(2) reinforcement might have been achieved predominantly through a chemical bond that resulted from the mutual chemical reactions among the components. Differential scanning calorimetry analyses showed that the chemical reaction between HA and TiO(2) was at approximately 1410 degrees C. The TiO(2) addition was found to exert particular effects on the thermal behavior of HA at elevated temperatures, during both heating and cooling cycles. Transmission electron microscopy observation identified the chemical reaction zone between HA and TiO(2), which revealed an improved splats' interface. The reaction zone demonstrated some influence on the grain size of HA nearby during resolidification of the melted portion. A structural model was proposed to illustrate the location of the different phases in the HA/titania composite coating.
Publisher: MIT Press - Journals
Date: 2022
DOI: 10.1162/QSS_A_00193
Abstract: Scientific research is an essential stage of the innovation process. However, it remains unclear how a scientific idea becomes applied knowledge and, after that, a commercial product. This paper describes a hypothesis of innovation based on the emergence of new research fields from more mature research fields after interactions between the latter. We focus on graphene, a rising field in materials science, as a case study. First, we used a coclustering method on titles and abstracts of graphene papers to organize them into four meaningful and robust topics (theory and experimental tests, synthesis and functionalization, sensors, and supercapacitors and electrocatalysts). We also demonstrated that they emerged in the order listed. We then tested all topics against the literature on nanotubes and batteries, and the possible parent fields of theory and experimental tests, as well as supercapacitors and electrocatalysts. We found incubation signatures for all topics in the nanotube papers collection and weaker incubation signatures for supercapacitors and electrocatalysts in the battery papers collection. Surprisingly, we found and confirmed that the 2004 breakthrough in graphene created a stir in both the nanotube and battery fields. Our findings open the door for a better understanding of how and why new research fields coalesce.
Publisher: Elsevier BV
Date: 09-2002
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 03-2003
Publisher: Springer Science and Business Media LLC
Date: 06-1994
DOI: 10.1007/BF02648273
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 09-2004
Publisher: The Electrochemical Society
Date: 2004
DOI: 10.1149/1.1701584
Publisher: Elsevier BV
Date: 04-2004
Publisher: Springer Science and Business Media LLC
Date: 04-2004
Publisher: Wiley
Date: 05-2007
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 03-2004
DOI: 10.1016/J.BIOMATERIALS.2003.08.008
Abstract: Microstructure characterization and property evaluation of high velocity oxy-fuel (HVOF) sprayed hydroxyapatite (HA) splats and coatings were conducted in the present study as a function of the proportion of melting that occurred in HA particles during HVOF spray. In vitro behavior of single and folded HA splats in simulated body fluid was also investigated. Results showed that phase composition of as-sprayed HA coatings was influenced significantly by the melt fraction in HVOF sprayed particles. Melt fraction of the HA powders were experimentally determined from particle morphology analysis. It was found that the spray parameters and starting powder size influenced the melt fraction of the particles. In vitro investigation of in idual HA splats made from different HA particles revealed decisive role of local phase composition in influencing their dissolution recipitation behavior during the test. Furthermore, Raman spectroscopy qualitative inspection on the sprayed HA particles (partial melted) revealed that thermal decomposition occurred within the melted part rather than the unmelted zone. Young's modulus and micro-hardness of the as-sprayed particles and coatings were determined using nano-indentation technique. The resolidified zone of the sprayed HA particles exhibited an average Young's modulus value of 41.25 GPa. The measured values ranged from 23.1 to 65.3 GPa. The unmelted part of the HA powders showed a markedly narrower range. Young's modulus value of 83.9 GPa (+/-9.4 GPa) was recorded for this region. This succinctly highlight the difference between the unmelted region and melted regions of a HA particle. Young's moduli values measured on HVOF coatings were found to mirror the trend found in the spheroidised particles and splats with apt fidelity.
Publisher: Elsevier BV
Date: 10-2003
Publisher: Wiley
Date: 02-2007
DOI: 10.1002/JBM.A.31143
Abstract: This study aimed to fabricate bulk nanostructured hydroxyapatite (HA) pellets with improved properties using spark plasma sintering (SPS) for orthopedic applications. Spray-dried nanostructured HA (nSD-HA) powders were consolidated using the rapid SPS processing. The SPS processed nSD-HA was characterized using Raman spectroscopy and field emission scanning electron microscopy (FESEM). Mechanical properties of the consolidates were also evaluated through indentation approach. The nanostructures ( approximately 80 nm in grain size) of the starting powders were successfully retained after the SPS processing operated at 950 degrees C with <15 min holding time. The SPS consolidated nSD-HA showed promising mechanical properties, approximately 118 GPa for Young's modulus, and up to 2.22 MPa m(0.5) for fracture toughness. SPS holding time showed minor influence on the phases of the pellets. Furthermore, the spheroidized nanostructured HA retained the HA structure after the SPS consolidation. Preliminary cytotoxicity and cell attachment studies were also carried out using a human osteoblast cell line hFOB 1.19. Enhanced cell attachment and proliferation on the nanostructured pellets were revealed. The presence of the nanostructures accounts mainly for the enhanced mechanical properties and promoted proliferation of the osteoblast cells. This study suggests that the SPS technique is an appropriate process for fabrication of bulk nSD-HA from nanostructured powder.
Publisher: Elsevier BV
Date: 2002
DOI: 10.1016/S0142-9612(01)00076-X
Abstract: Dense hydroxyapatite (HA) compacts have been successfully fabricated by a spark plasma sintering (SPS). The sintering behavior of HA powders at different temperatures ranging from 850 degrees C to 1100 degrees C was studied. Results showed that spark plasma sintering resulted in rapid densification to near theoretical density. The HA compact was homogeneously sintered at 950 degrees C in a short sintering duration of 5 min, while maintaining high quality and high relative density (>99.5%). The density, microhardness and Young's modulus of HA sintered compact initially increased with the sintering temperature, reached a maximum value at around 950-1000 degrees C, then decreased with further increase in the temperature due to the decomposition of HA into beta-tricalcium phosphates. Fracture toughness results showed no significant difference with increasing temperature due to the combined influences of density and grain size. Microstructure analysis showed no noticeable grain growth under different sintering temperatures due to the short time exposure at high temperatures.
Publisher: The Electrochemical Society
Date: 2003
DOI: 10.1149/1.1558351
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 06-2003
DOI: 10.1016/S0142-9612(03)00028-0
Abstract: Polyetheretherketone-hydroxyapatite composites were developed as alternative materials for load-bearing orthopedic applications. The amount of hydroxyapatite (HA) incorporated into the polyetheretherketone (PEEK) polymer matrix ranges from 5 to 40 vol% and these materials were successfully fabricated by injection molding. This study presents the mechanical and biological behavior of the composite materials developed. It was found that the amount of HA in the composite influenced the tensile properties. Dynamic behavior under tension-tension fatigue revealed that the fatigue-life of PEEK-HA composites were dependent on the HA content as well as the applied load. The biological responses of PEEK-HA composites carried out in vivo verified the biocompatibility and bioactive nature of the composite materials.
Publisher: Elsevier BV
Date: 04-2005
Publisher: Elsevier BV
Date: 07-2003
DOI: 10.1016/S0142-9612(03)00066-8
Abstract: Ultra-fine hydroxyapatite (HA)/ZrO(2) composite powders was synthesised by radio frequency (RF) induction suspension plasma spray. A wet suspension of HA/ZrO(2) was employed as feedstock. The suspension was injected axially into the RF plasma to produce the nano-composite powders, which were subsequently accumulated in cyclone collectors. The particle size and morphology was resolved by using the Zeta potential nano-particle size analyser, scanning electron microscopy, transmission electron microscopy, field emission microscopy techniques. The phase composition, phase concentration, and, molecular structure of the powders were characterised using differential scanning calorimetry, Fourier transform infra-red and X-ray diffractometry with quantitative phase analysis empowered by the Rietveld method. Results indicated that nano-size, spherical HA/ZrO(2) composite powders were produced with varying morphological features that depend on the thermal treatment. Calcium zirconate (CaZrO(3)) was produced as a byproduct whose biocompatibility is not well documented. Results also showed that the HA decomposed into alpha and beta-TCP due to decreasing Ca/P ratio with the formation of CaZrO(3).
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0142-9612(02)00413-1
Abstract: Bone-like apatite was precipitated on the surface of thermal sprayed calcium phosphate coatings following in vitro incubation in a simulated body fluid. The coatings were initially deposited on titanium alloy substrates by the high velocity oxy-fuel (HVOF) spray technique. Structural characterization and mechanical evaluation of the precipitated apatite layer were conducted. Results showed that the precipitation rate was directly influenced by the local Ca(2+) concentration in the vicinity of the coating's surface and that preferential dissolution of certain phases was found to accelerate the precipitation of the bone-like apatite. The dense precipitates exhibited a competitive Young's modulus value of approximately 120GPa, which was obtained through nanoindentation. This compared favorably to the calcium phosphate matrix. Differences in microstructure at various locations within the layer resulted in altered Young's modulus and microhardness values. Precipitation mechanism investigation was carried out through a comparative experiment. Chemical analysis showed that the precipitation of bone-like apatite on the calcium phosphate coating was quite conceivably a partial diffusion-controlled process.
Publisher: Elsevier BV
Date: 2000
Publisher: IOP Publishing
Date: 22-02-2010
DOI: 10.1088/0957-4484/21/11/115707
Abstract: The low temperature sintering behaviour of nanocrystalline Ag powder (with an average size of 70 nm) was characterized. Using spark plasma sintering (SPS), the Ag nanopowders can be successfully sintered at low pressure for only 5 min without external heating, and the sintering density increases and porosity decreases significantly with increase in the sintering temperature. Nanoindentation has been used to characterize the SPS sintered Ag s les. The mechanisms of the low sintering temperature behaviour of the nano-Ag powder and the nanoscale mechanical performance have been discussed. Compression tests were also used to characterize the mechanical properties of the sintered Ag s le with a maximum strain up to 15%.
Publisher: Elsevier BV
Date: 06-2001
Publisher: Elsevier BV
Date: 12-2008
Publisher: Springer Science and Business Media LLC
Date: 16-09-2009
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.JMBBM.2011.07.003
Abstract: The failure of an orthopaedic implant can be initiated by residual strain inherent to the hydroxyapatite coating (HAC). Knowledge of the through-thickness residual strain profile in the thermally sprayed hydroxyapatite coating/substrate system is therefore important in the development of a new generation of orthopaedic implants. As the coating microstructure is complex, non-destructive characterization of residual strain, e.g. using neutron diffraction, provides a useful measure of through thickness strain profile without altering the stress field. This first detailed study using a neutron diffraction technique, non-destructively evaluates the through thickness strain measurement in nanostructured hydroxyapatite plasma sprayed coatings on a titanium alloy substrate (as-sprayed, heat treated, and heat treated then soaked in simulated body fluid (SBF)). The influence of crystallographic plane orientation on the residual strain measurement is shown to indicate texturing in the coating. This texturing is expected to influence both the biological and fracture response of HA coatings. Results are discussed in terms of the influence of heat-treatment and SBF on the residual stress profile for these biomedical coatings. The results show that the through thickness residual strain in all three coatings was different for different crystallographic planes but was on average tensile. It is also concluded that the heat-treatment and simulated body fluid exposure had a significant effect on the residual strain profile in the top layers of HAC.
Publisher: Elsevier BV
Date: 05-2012
Publisher: Elsevier BV
Date: 07-2005
Publisher: Wiley
Date: 24-04-2006
DOI: 10.1002/JBM.A.30743
Abstract: Porous NiTi with an average porosity of 55 vol % and a general pore size of 100-600 microm was synthesized by self-propagating high temperature synthesis (SHS) with the addition of mechanically alloyed nanocrystalline Ni-Ti as the reaction agent. The SHS of porous NiTi using elemental powders was also performed for comparison. To enhance the bioactivity of the metal surface, porous NiTi synthesized by nanocrystalline Ni-Ti was subjected to chemical treatment to form a layer of TiO(2) coating. The porous NiTi with TiO(2) coating was subsequently immersed in a simulated body fluid (SBF) to investigate its apatite forming ability. The effects of the addition of nanocrystalline Ni-Ti as reaction agent and the application of apatite coating on osteoblastic behavior were studied in primary cultures of human osteoblast cells. Results showed that the main phases in porous NiTi synthesized by elemental powders were NiTi, Ti(2)Ni, and unreacted free Ni. By using nanocrystalline Ni-Ti as reaction agent, the secondary intermetallic phase of Ti(2)Ni was significantly reduced and the free Ni was eliminated. TiO(2) coating with anatase phase was formed on the surface of porous NiTi after the chemical treatment. A layer consisting of nanocrystalline carbonate-containing apatite was formed on the surface of TiO(2) coating after soaking in SBF. The preliminary cell culture studies showed that the porous NiTi synthesized with the addition of nanocrystalline Ni-Ti attracted marked attachment and proliferation of the osteoblast cells. This gives the evidence of the potential biomedical applications of the porous NiTi.
Publisher: Elsevier BV
Date: 05-2003
Publisher: Elsevier BV
Date: 02-2003
Publisher: Springer Science and Business Media LLC
Date: 2001
Publisher: Elsevier BV
Date: 05-2005
Publisher: SPIE
Date: 21-12-2007
DOI: 10.1117/12.759383
Publisher: Elsevier BV
Date: 06-2008
Publisher: Elsevier BV
Date: 09-2000
Publisher: Elsevier BV
Date: 06-2008
Publisher: Elsevier BV
Date: 2001
Publisher: Elsevier BV
Date: 2004
Publisher: Elsevier BV
Date: 08-2002
Publisher: Elsevier BV
Date: 07-2003
DOI: 10.1016/S0142-9612(03)00082-6
Abstract: The crystalline phases and degree of crystallinity in plasma sprayed calcium phosphate coatings on Ti substrates are crucial factors that influence the biological interactions of the materials in vivo. In this study, plasma sprayed hydroxyapatite (HA) coatings underwent post-spray treatment by the spark plasma sintering (SPS) technique at 500 degrees C, 600 degrees C, and 700 degrees C for duration of 5 and 30 min. The activity of the HA coatings before and after SPS are evaluated in vitro in a simulated body fluid. The surface microstructure, crystallinity, and phase composition of each coating is characterized by scanning electron microscopy and X-ray diffractometry before, and after in vitro incubation. Results show that the plasma sprayed coatings treated for 5 min in SPS demonstrated increased proportion of beta-TCP phase with a preferred-orientation in the (214) plane, and the content of beta-TCP phase corresponded to SPS temperature, up to 700 degrees C. SPS treatment at 700 degrees C for 30 min enhanced the HA content in the plasma spray coating as well. The HA coatings treated in SPS for 5 min revealed rapid surface morphological changes during in vitro incubation (up to 12 days), indicating that the surface activity is enhanced by the SPS treatment. The thickest apatite layer was found in the coating treated by SPS at 700 degrees C for 5 min.
Publisher: IEEE
Date: 2006
Publisher: Wiley
Date: 29-09-2010
Publisher: Springer Science and Business Media LLC
Date: 2001
Publisher: Elsevier BV
Date: 11-2006
Publisher: Wiley
Date: 10-2008
Publisher: Elsevier BV
Date: 02-2002
Publisher: American Chemical Society (ACS)
Date: 08-02-2012
DOI: 10.1021/NL2034859
Abstract: We report on the enhanced thermoelectric properties of selenium (Se) doped bismuth telluride (Bi(2)Te(3-x)Se(x)) nanoplatelet (NP) composites synthesized by the polyol method. Variation of the Se composition within NPs is demonstrated by X-ray diffraction and Raman spectroscopy. While the calculated lattice parameters closely follow the Vegard's law, a discontinuity in the shifting of the high frequency (E(g)(2) and A(1g)(2)) phonon modes illustrates a two mode behavior for Bi(2)Te(3-x)Se(x) NPs. The electrical resistivity (ρ) of spark plasma sintered pellet composites shows metallic conduction for pure Bi(2)Te(3) NP composites and semiconducting behavior for intermediate Se compositions. The thermal conductivity (κ) for all NP composites is much smaller than the bulk values and is dominated by microstructural grain boundary scattering. With temperature dependent electrical and thermal transport measurements, we show that both the thermoelectric power S (-259 μV/K) and the figure of merit ZT (0.54) are enhanced by nearly a factor of 4 for SPS pellets of Bi(2)Te(2.7)Se(0.3) in comparison to Bi(2)Te(3) NP composites. Tentatively, such an enhancement of the thermoelectric performance in nanoplatelet composites is attributed to the energy filtering of low energy electrons by abundant grain boundaries in aligned nanocomposites.
Publisher: Elsevier BV
Date: 05-2005
Publisher: Elsevier BV
Date: 04-2005
Publisher: Elsevier BV
Date: 2003
DOI: 10.1016/S0142-9612(02)00267-3
Abstract: A cogent understanding of the microstructure, and indeed nano-structure, of hydroxyapatite (HA) and the interface between Ti-6Al-4V and HA is crucial to its appropriateness as a biomaterials. This paper reports the analysis of plasma-sprayed HA/Ti-6Al-4V composites by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to elucidate the intricate nature of the materials following plasma spray processing and in vitro evaluation. The novel Ti-6Al-4V/HA composite coating, with approximately 48 wt% HA, had demonstrated attractive tensile adhesion strength (approximately 28 MPa) and improved Young's modulus (approximately 55 GPa). Experimental results demonstrated that amorphous calcium phosphate and fine HA grains were formed during rapid splat solidification in the as-sprayed composite coatings. Small Ti-6Al-4V grains were observed adjacent to the amorphous calcium phosphate. The coatings were further heat treated at 600 degrees C for 6 h, and significant crystallisation of the amorphous calcium phosphate phase took place. However, complete crystallisation was not achieved at this temperature, as the coatings invariably contained a small amount of amorphous calcium phosphate phase in some local regions. After immersion in simulated body fluid for 2 weeks and 10 weeks, TEM and STEM confirmed that the interfaces inside the coating maintained good microstructural integrity.
Publisher: Springer Science and Business Media LLC
Date: 14-09-2013
Publisher: Elsevier BV
Date: 27-02-2004
Publisher: Elsevier BV
Date: 2001
Publisher: Elsevier BV
Date: 04-2003
DOI: 10.1016/S0142-9612(02)00573-2
Abstract: The bioactivity of plasma-sprayed hydroxyapatite (HA)/Ti-6Al-4V composite coatings was studied by soaking the coatings in simulated body fluid (SBF) for up to 8 weeks. This investigation was aimed at elucidating the biological behaviour of plasma-sprayed HA/Ti-6Al-4V composite coatings by analyzing the changes in chemistry, and crystallinity of the composite coating in a body-analogous solution. Phase composition, microstructure and calcium ion concentration were analyzed before, and after immersion. The mechanical properties, such as tensile bond strength, microhardness and Young's modulus were appropriately measured. Results demonstrated that the tensile bond strength of the composite coating was significantly higher than that of pure HA coatings even after soaking in the SBF solution over an 8-weeks period. Dissolution of Ca-P phases in SBF was evident after 24h of soaking, and, a layer of carbonate-apatite covered the coating surface after 2 weeks of immersion. The mechanical properties were found to diminish with soaking duration. However, slight variation in mechanical properties was found after supersaturation of the calcium ions was attained with the precipitation of the calcium phosphate layers.
Publisher: Wiley
Date: 28-09-2010
DOI: 10.1002/JBM.A.32907
Abstract: An adhesion test procedure applied to plasma-sprayed hydroxyapatite (HA) coatings to measure the "LASAT threshold" (LAser Shock Adhesion test) is described. The good repeatability and minimal discrepancy of the laser-driven adhesion test data were ascertained for conventional plasma sprayed HA coatings. As a further demonstration, the procedure was applied to HA coatings with erse characteristics on the ceramic/metal interface. Different preheating and grit blasting conditions and the presence of a thick plasma-sprayed Ti sublayer or a thin TiO(2) layer prepared by oxidation were investigated through LASAT. It was assessed that a rough surface can significantly improve the coating's bond strength. However, it was also demonstrated that a thin TiO(2) layer on a smooth Ti-6Al-4V substrate can have a major influence on adhesion as well. Preheating up to 270°C just prior to the first HA spraying pass had no effect on the adhesion strength. Further development of the procedure was done to achieve an in situ LASAT with in vitro conditions applied on HA coatings. To that end, different crystalline HA contents were soaked in simulated body fluid (SBF). Beyond the demonstration of the capability of this laser-driven adhesion test devoted to HA coatings in dry or liquid environment, the present study provided empirical information on pertinent processing characteristics that could strengthen or weaken the HA/Ti-6Al-4V bond.
Start Date: 03-2019
End Date: 03-2025
Amount: $4,889,410.00
Funder: Australian Research Council
View Funded Activity