Papers by Author: Iain R. Gibson

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Authors: Marcelo Henrique Prado da Silva, Gloria Dulce de Almeida Soares, Carlos Nelson Elias, Iain R. Gibson, Serena Best
Authors: S. Ke, Iain R. Gibson, Karen A. Hing
Authors: M.E. Saadalla, N. Ahad, Iain R. Gibson, J.C. Shelton
Authors: J.A. Stephen, C. Pace, J.M.S. Skakle, Iain R. Gibson
Abstract: Carbonate hydroxyapatite (CHA) bioceramics can be synthesised to contain sodium ions as a co-substituted ion, or as sodium-free compositions. It is unclear, however, which composition would produce the optimum biological response. The aim of this study was to find a reliable method to produce sodium co-substituted and sodium-free CHA compositions that would have the same level of carbonate substitution, and to characterise the effects of the two different substitutions on the structure of the CHA samples. After sintering at 900oC in a CO2 atmosphere, all samples contained approximately equal amounts of carbonate groups on the A- and B-sites, as observed by FTIR. The sample produced with NaHCO3 and the sodium-free sample (CHA1) have comparable carbonate contents, whereas the sample produced with Na2CO3 contains significantly more carbonate, probably due to the excess sodium ions allowing more carbonate co-substitution. The sodium-free CHA sample, however, has significantly smaller unit cell parameters compared to both sodium co-substituted CHA samples, and also to HA. This characterisation of the samples shows that the sodium-free CHA sample (CHA1) and the sample produced with NaHCO3 would provide CHA compositions for biological testing with similar carbonate contents and distributions, but with structural differences due to the sodium substitution.
Authors: Nelesh Patel, E.L. Follon, Iain R. Gibson, Serena Best, William Bonfield
Authors: Flora E. Imrie, Marta Corno, Piero Ugliengo, Iain R. Gibson
Abstract: The properties of hydroxyapatite can be improved by substitution of biologically relevant ions, such as magnesium (Mg) and strontium (Sr), into its structure. Previous work in the literature has not reached agreement as to site preferences in these substitutions, and there are suggestions that these may change with differing levels of substitution. The current work adopted a quantum mechanical approach based on density functional theory using the CRYSTAL09 code to investigate the structural changes relating to, and site preferences of, magnesium and strontium substitution (to 10 mol%) in hydroxyapatites and also to predict the corresponding vibrational spectra in the harmonic approximation. The structures underwent full geometrical optimisation within the P63 space group, indicating an energetic site preference for the Ca (2) site in the case of Mg substitution, and the Ca (1) site in the case of Sr. Shrinkage of the unit cell was observed in the case of Mg substitution, and expansion in the case of Sr substitution, in agreement with the corresponding ionic radii. Thermodynamic properties of the structures obtained from the harmonic vibrational frequency calculations confirmed that the structures were minima on the potential energy surface. Isotopic substitutions indicated that the main contribution of Sr and Mg to vibrational modes is at frequencies < 400 cm-1.
Authors: Iain R. Gibson, Karen A. Hing, Peter A. Revell, José D. Santos, Serena Best, William Bonfield
Authors: Karen A. Hing, Iain R. Gibson, Peter A. Revell, Serena Best, William Bonfield
Authors: D.J. Hadden, J.M.S. Skakle, Iain R. Gibson
Abstract: Silicon-substituted hydroxyapatite (SiHA) bioceramics are widely used as bone replacement materials. There are various synthesis methods used to produce SiHA samples using different sources of silicon. This study aims to investigate the role of tetraethyl orthosilicate (TEOS) as the silicon source in the precipitation reaction synthesis of silicate-substituted HA. Four different synthesis methods were studied by changing the order of addition of the TEOS solution during the precipitation reaction. XRD and QXRD were used to determine the phase purity of the prepared samples. FTIR and SSNMR were used to assess silicon/silicate substitution in the prepared materials. Of the initial four methods used, only one resulted in a sample that was phase pure. The other three syntheses, which produced biphasic compositions, were modified and a further single phase sample was prepared. Results showed that the final composition is strongly dependant on how and when the TEOS was added during the precipitation reaction.
Authors: Nelesh Patel, Serena Best, Iain R. Gibson, S. Ke, Karen A. Hing, William Bonfield
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