Papers by Author: David Farrar

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Authors: Liam M. Grover, Uwe Gbureck, David Farrar, J.E. Barralet
Abstract: In this study, we have shown that by incorporating pyrophosphoric acid into a brushite cement system, it is possible to produce a cement that exhibits adhesive tensile strengths with cortical bone, alumina, sintered hydroxyapatite and 316L stainless steel of 700 kPa. To our knowledge, this is the first report of a calcium phosphate cement formulation that exhibits such adhesive properties without the addition of an organic additive. The production of a bond between medical prostheses and bone may further widen the field of application of calcium phosphate cements, additionally the adhesive nature of the calcium phosphate cement may be a desirable ‘handling characteristic’ during reconstructive surgery.
Authors: K.J. Lilley, Adrian J. Wright, David Farrar, J.E. Barralet
Abstract: Brushite cement is more soluble than apatite cement in physiological conditions and therefore may be more resorbable in vivo. Brushite cement has been formed previously by mixing β-tricalcium phosphate, water and an acidic source of phosphate ions. However, brushite cement may be formed by the mixture of H3PO4 solution and poorly crystalline precipitated hydroxyapatite (HA). Several additives have been used to alter the physicochemical properties of brushite cement. In this study sulphate ions where added to the cement system by addition of ammonium sulphate to HA during HA preperation. Sulphate ions were found to alter the structure, composition and mechanical performance of cement.
Authors: K.J. Lilley, Uwe Gbureck, David Farrar, C. Ansell, J.E. Barralet
Authors: M.E. Clark, C. Engel, P.J.C. Felstead, D.M. Walter, David Farrar, Gavin S. Walker, Colin A. Scotchford, D.M. Grant
Authors: S. Akhtar, J.E. Barralet, David Farrar, Adrian J. Wright
Abstract: Amorphous calcium carbonate (ACC) occurs with varying stabilities in different organisms. It is thought that the stability is influenced by certain ions and proteins. We describe here a study investigating the particular influence of phosphate ions on the stability of ACC. Synthesised ACC was treated with different concentrations of Na2HPO4 and molar ratios of PO4:Ca ≥ 12:1 were shown to be effective in preventing crystallisation of ACC to calcite. The nature of the resulting sample is discussed.
Authors: K.J. Lilley, Uwe Gbureck, Adrian J. Wright, David Farrar, J.E. Barralet
Abstract: Bajpai et al. originally reported the formation of cements by the mixture of carboxylic acids and β-tricalcium phosphate (β-TCP). In the current study, we report and contrast four such cement systems formed from mixing citric, malic, 2-oxoglutaric or phosphoric acid with β-TCP. Cements formed from malic or 2-oxoglutaric appeared to contain crystalline phases and were determined to contain brushite, β-TCP and unreacted acid. In contrast, cement formed with citric acid was poorly crystalline, containing little evidence of brushite formation and was unstable in water and therefore does not appear to be a feasible cement system.
Authors: Liam M. Grover, Uwe Gbureck, A. Hutton, David Farrar, C. Ansell, J.E. Barralet
Authors: Lisa M. Ehrenfried, David Farrar, David Morsley, Ruth Cameron
Abstract: Co-continuous degradable polymer-ceramic composites were produced via in-situ polymerization of (D,L-lactic)acid monomer within a porous β-tricalcium phosphate matrix. The mechanical properties of both the composite and the unfilled porous ceramic were investigated with compressive testing. The average stress to failure increased from 1.3±0.1 MPa for the unfilled ceramic matrix to 82±2 MPa for the composite. The Young’s modulus increased from approximately 20 MPa to 700±42 MPa. A combination of X-ray micro-tomography and mechanical testing provided insight into the failure mechanisms of the composite. Stress may be deflected by crack bridging around the polymer phase leading to debonding of the polymer along the crack lines.
Authors: E.C. Pegg, David Farrar, Colin A. Scotchford, Gavin S. Walker, D.M. Grant
Authors: M.R. Cave, David Farrar, Adrian J. Wright
Abstract: Calcium alkyl phosphates and their strontium and magnesium analogues were synthesised by the reaction of aqueous metal salts with a range of alkyl phosphates of varying chain length and were characterised by X-ray diffraction, thermogravimetric and FTIR analyses. These hybrid structures are based on alternating organic/metal phosphate regions and were found to exhibit a linear increase in interlayer separation upon increasing the length of the alkyl chain. Our analysis suggests a general formula for these phases of M(ROPO3).nH2O (where M = Ca, Sr, Mg and R = alkyl group), containing alkyl bilayers reminiscent of phospholipid bilayers found in biological membranes.
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