Showing papers by "Iain R. Gibson published in 2001"
TL;DR: In this article, a coating of crystalline monetite oriented along the [112] axis was electrochemically deposited on titanium substrates and was subsequently converted to hydroxyapatite by immersion in alkaline solutions.
Abstract: Calcium phosphates have a wide range of pH stability, depending on their Ca/P ratio. Under physiological conditions (pH ≈7), the most stable calcium phosphate is hydroxyapatite, Ca 10 (PO 4 ) 6 (OH) 2 . Acidic calcium phosphates, like dicalcium phosphate, CaHPO 4 (monetite) and dicalcium phosphate dihydrate, CaHPO 4 ·2H 2 O (brushite), are thermodynamically unstable under pH values greater than 6–7 and undergo transformation into more stable calcium phosphates. It means that, when placed in vivo (pH ≈7), acidic calcium phosphates convert to hydroxyapatite. In the present study, a coating of crystalline monetite oriented along the [112] axis was electrochemically deposited on titanium substrates. This monetite coating was subsequently converted to hydroxyapatite by immersion in alkaline solutions. The result was a crystalline hydroxyapatite coating oriented along the [002] axis. Different alkaline solutions produced the same result. Studying the effect of immersion time on the transformation indicated that 4 h were required to complete the conversion from monetite to hydroxyapatite. The transformation occurred by a dissolution–reprecipitation mechanism, i.e. the monetite coating was continuously dissolved and reprecipitated as hydroxyapatite. This combined electrochemical deposition and chemical conversion process produced hydroxyapatite coatings with satisfactory adhesion to the substrate and a thickness between 10 and 30 μm.
170 citations
TL;DR: Kinetics studies have indicated the possibility of using hydroxyapatite and glass-reinforced hydroxyaptite composites as possible carriers for drug delivery.
100 citations
TL;DR: Treating the tetracycline HCI with calcium sulphate solution prior to reaction conserved the activity of the antibiotics, limited the influence of the antibiotic on the cement evolution and retained the physical properties of the cement.
83 citations
TL;DR: It is demonstrated that professionally applied in-office products containing oxalate are capable of covering the dentine surface and/or occluding the tubules to varying degrees, however, X-ray diffraction analysis was unable to confirm the oxalates profile for all products as described in the available commercial literature.
Abstract: In-office products containing oxalates have been claimed to be clinically effective in reducing dentine sensitivity, although there has been limited supporting clinical data. The rationale for their use appears to be based on their potential to act as occluding and/or nerve desensitizing agents. Four commercially available oxalate-containing products were applied to etched dentine discs and the extent of tubule occlusion was observed by scanning electron microscopy. Tenure Quick (aluminium oxalate), Sensodyne Sealant (ferric oxalate) and MS Coat (oxalic acid) covered the dentine surface and occluded the tubules. However, Butler Protect (potassium oxalate) did not cover the surface to any great extent but provided some occlusion. The presence of oxalates after application to glass slides and dentine discs was examined using thin film X-ray diffraction. From samples on glass, only potassium oxalate could be clearly identified (JCPDS 14-0845). No oxalate was detected on dentine discs in either thin film geometry or standard theta two theta mode. We have demonstrated that professionally applied in-office products containing oxalate are capable of covering the dentine surface and/or occluding the tubules to varying degrees. However, X-ray diffraction analysis was unable to confirm the oxalate profile for all products as described in the available commercial literature.
76 citations
TL;DR: The effect of different sintering conditions on the sintered density and microstructure of two different hydroxyapatite (HA) powders was examined, resulting in a lower green density and trends can be related to the sinterability of the two materials.
Abstract: The effect of different sintering conditions on the sintered density and microstructure of two different hydroxyapatite (HA) powders was examined. The powder characteristics of a laboratory synthesized HA powder (Lab HA) were low crystallinity, a bimodal particle size distribution, a median particle size of 22 μm and a high specific surface area (SSA) of 63 m2/g. By contrast, a commercial calcined HA (commercial HA) was crystalline and had a median particle size of 5 μm and a low SSA of 16 m2/g. The different powder characteristics affected the compactability and the sinterability of the two HA powders. Lab HA did not compact as efficiently as commercial HA, resulting in a lower green density, but the onset of sintering of powder compacts of the former was approximately 150 °C lower than the later. The effect of compaction pressure, sintering temperature, time and heating rate on the sintered densities of the two materials was studied. Varying all these sintering conditions significantly affected the sintered density of commercial HA, whereas the sintered density of Lab HA was only affected significantly by increasing the sintering temperature. The Vickers hardness, Hv, of Lab HA was greater than commercial HA for low sintering temperatures, below 1200 °C, whereas for higher sintering temperatures the commercial HA produced ceramics with greater values of hardness. These trends can be related to the sinterability of the two materials.
76 citations
TL;DR: The results of this study have illustrated that for applications where HA may be used in powder form, for example in plasma-spraying and for the production of HA-polymer composites, calcining the HA will significantly affect the powder properties, namely the surface area and morphology of the powders.
Abstract: The effect of different calcination temperatures on the powder characteristics and the sintered density of synthetic hydroxyapatite (HA) powders, produced using two different processing routes, was examined. Powders were produced by either drying, milling and sieving an as-precipitated HA or by spray-drying a slurry of precipitated HA. Calcining the two powders at temperatures between 400 and 1000 °C did not significantly affect the powder particle size. The specific surface areas of the two powders, however, were reduced from 70–80 m2/g for a calcination temperature of 400 °C to approximately 5–7 m2/g for 1000 °C. Analysis of the surfaces of the HA powders using scanning electron microscopy (SEM) illustrated the coarsening and subsequent sintering of the sub-micron crystallites that constitute a powder particle as the calcination temperature increased, corresponding to the decrease in surface area of the powders. The sintered densities of the final ceramics were not significantly affected by calcining the powders. Microhardness measurements of ceramics prepared from powders calcined at different temperatures showed no significant variations with calcination temperature or powder processing method. The results of this study have illustrated that for applications where HA may be used in powder form, for example in plasma-spraying and for the production of HA-polymer composites, calcining the HA will significantly affect the powder properties, namely the surface area and morphology of the powders. For applications requiring HA in a dense ceramic form, for example as granules or blocks, calcining the powders does not significantly affect the properties of the final ceramic.
61 citations
TL;DR: In this article, the identification and discrimination of cubic (c) and metastable t′-zirconia phases by conventional X-ray diffraction has proved to be a difficult problem because of the crystallographic similarities of the two phases.
Abstract: The identification and discrimination of cubic (c) and metastable t′-zirconia phases by conventional X-ray diffraction has proved to be a difficult problem because of the crystallographic similarities of the two phases. In this study, the c-phase and t′-phase in biphasic metastable zirconia samples have been successfully distinguished by X-ray diffraction; data were collected using a high-resolution powder diffractometer with monochromatic radiation and the peak shapes were fitted using a peak-fitting program to distinguish the different phases. From this study, the minimum temperature, T0, at which the t′-phase can be obtained on cooling rapidly compositions in the range 3–7 mol% Y2O3–ZrO2 to room temperature was estimated as ∼1425°C. For a constant temperature above 1425°C, the lattice parameters of the t′-phase of 3–7 mol% Y2O3–ZrO2 compositions within the two-phase region of the phase diagram were unaffected by the yttria content; only the amount of t′-phase formed was affected by the yttria content.
56 citations
TL;DR: In this article, an approach on how to bind Hydroxyapatite (HA) to the Ti alloy was introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding.
Abstract: Among the various techniques that have been investigated to produce Hydroxyapatite (HA) coatings in order to promote fixation and osteointegration of cementless prosthesis, the plasma spray (PS) technique is the most popular method commercially in use. PS presents some disadvantages such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, an approach on how to bind HA to the Ti alloy will be introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding. Different techniques were applied to characterize the coated samples, including x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis.
48 citations
TL;DR: It is demonstrated that the surface properties of those coatings may be modified by the addition of CaO-P2O5 glass and that composite coatings presented a higher net negative charge than HA coatings and that ZP values were also influenced by the content of the glass.
43 citations
TL;DR: In this article, the authors investigated the effect of silicate ion substitution in hydroxyapatite on the rate of bone healing in vivo and found that significant amounts of bone formation was only consistently found at the center of the machined slots of the silicate substituted implants.
Abstract: This paper describes an investigation into the effect of silicate ion substitution in hydroxyapatite on the rate of bone healing in vivo. Slotted cylinders composed of stoichiometric hydroxyapatite and 1.2 wt% silicate substituted hydroxyapatite (S-HA) were implanted in the distal end of the femur of 6 month old New Zealand white rabbits for a period of 3 weeks. Tetracycline and alizarine red fluorochrome labels were administered 7 and 14 days post-operatively, respectively. After retrieval the implants were sectioned and examined using optical and fluorescence microscopy. Optical microscopy demonstrated that significant amounts of bone formation was only consistently found at the center of the machined slots of the silicate substituted implants. Moreover, fluorescence microscopy demonstrated that of the new bone laid down around and in contact with the implants, significant quantities of tetracycline labeled bone (i.e. bone laid down seven days after implantation) was only present in S-HA implants. These results indicate that the bioactivity of hydroxyapatite is significantly enhanced by the incorporation of silicate ions into its lattice
34 citations
Journal Article•
TL;DR: In this article, an approach on how to bind Hydroxyapatite (HA) to the Ti alloy was introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding.
Abstract: Among the various techniques that have been investigated to produce Hydroxyapatite (HA) coatings in order to promote fixation and osteointegration of cementless prosthesis, the plasma spray (PS) technique is the most popular method commercially in use. PS presents some disadvantages such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, an approach on how to bind HA to the Ti alloy will be introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding. Different techniques were applied to characterize the coated samples, including x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis.