Showing papers by "Iain R. Gibson published in 2002"
TL;DR: The findings indicate that the early in vivo bioactivity of hydroxyapatite was significantly improved with the incorporation of silicate ions into the HA structure, making SiHA an attractive alternative to conventional HA materials for use as bone substitute ceramics.
Abstract: Phase pure hydroxyapatite (HA) and a 0.8 wt % silicon substituted hydroxyapatite (SiHA) were prepared by aqueous precipitation methods. Both HA and SiHA were processed into granules 0.5-1.0 mm in diameter and sintered at 1200 degrees C for 2 h. The sintered granules underwent full structural characterization, prior to implantation into the femoral condyle of New Zealand White rabbits for a period of 23 days. The results show that both the HA and SiHA granules were well accepted by the host tissue, with no presence of any inflammatory cells. New bone formation was observed directly on the surfaces and in the spaces between both HA and SiHA granular implants. The quantitative histomorphometry results indicate that the percentage of bone ingrowth for SiHA (37.5%+/-5.9) was significantly greater than that for phase pure HA (22.0%+/-6.5), in addition the percentage of bone/implant coverage was significantly greater for SiHA (59.8%+/-7.3) compared to HA (47.1%+/-3.6). These findings indicate that the early in vivo bioactivity of hydroxyapatite was significantly improved with the incorporation of silicate ions into the HA structure, making SiHA an attractive alternative to conventional HA materials for use as bone substitute ceramics.
481 citations
TL;DR: A novel synthesis route has been developed to produce a high-purity mixed AB-type carbonate-substituted hydroxyapatite (CHA) with a carbonate content that is comparable to the type and level observed in bone mineral.
Abstract: A novel synthesis route has been developed to produce a high-purity mixed AB-type carbonate-substituted hydroxyapatite (CHA) with a carbonate content that is comparable to the type and level observed in bone mineral. This method involves the aqueous precipitation in the presence of carbonate ions in solution of a calcium phosphate apatite with a Ca/P molar ratio greater than the stoichiometric value of 1.67 for hydroxyapatite (HA). The resulting calcium-rich carbonate-apatite is sintered/heat-treated in a carbon dioxide atmosphere to produce a single-phase, crystalline carbonate-substituted hydroxyapatite. In contrast to previous methods for producing B- or AB-type carbonate-substituted hydroxyapatites, no sodium or ammonium ions, which would be present in the reaction mixture from the sodium or ammonium carbonates commonly used as a source of carbonate ions, were present in the final product. The chemical and phase compositions of the carbonate-substituted hydroxyapatite was characterized by X-ray fluorescence and X-ray diffraction, respectively, and the level and nature of the carbonate substitution were studied using C-H-N analysis and Fourier transform infrared spectroscopy, respectively. The carbonate substitution improves the densification of hydroxyapatite and reduces the sintering temperature required to achieve near-full density by approximately 200 degrees C compared to stoichiometric HA. Initial studies have shown that these carbonate-substituted hydroxyapatites have improved mechanical and biologic properties compared to stoichiometric hydroxyapatite.
424 citations
TL;DR: This study investigates whether compaction significantly alters the specific surface area and pore-size distribution of CPC prepared according to the method of Brown and Chow, which resulted in an increase in the wet compressive strength.
Abstract: Hydroxyapatite (HA) calcium phosphate cements (CPCs) are attractive materials for orthopedic applications because they can be molded into shape during implantation. However their low strength and brittle nature limits their potential applications to principally non-load-bearing applications. Little if any use has been made of the HA cement systems as manufacturing routes for preset HA bone grafts, which although not moldable pastes, are resorbable, unlike HA sintered ceramic. It is known that the strength of cements can be increased beyond that attainable from slurry systems by compaction, and this study investigates whether compaction significantly alters the specific surface area and pore-size distribution of CPC prepared according to the method of Brown and Chow. Compaction pressures of between 18 and 106 MPa were used to decrease the porosity from 50 to 31%, which resulted in an increase in the wet compressive strength from 4 to 37 MPa. The Weibull modulus was found to increase as porosity decreased; in addition the amount of porosity larger than the reactant particle size increased as porosity decreased. It is proposed that this was caused by a combination of voids created by the aqueous solvent used in fabrication and shrinkage that occurs on reaction. The specific surface area was unchanged by compaction.
209 citations
TL;DR: This study reports a novel method for the formation of macroporous CPC scaffolds, which has two main advantages over the previously reported manufacturing route: the cement matrix is considerably denser than CPC formed from slurry systems and the scaffold is formed at temperatures below room temperature.
206 citations
TL;DR: XPS results indicated that silicon seems to be preferentially leached out from Si–HA surface compared to other ionic species after dissolution studies in tris-buffer using a dynamic system.
Abstract: The aim of this study was to determine the effect of the incorporation of silicon on the surface charge of hydroxyapatite (HA) and to assess surface structural changes of HA and Si-HA induced by dissolution in both static and dynamic systems. X-ray photoelectron spectroscopy (XPS) analysis showed that SiO(4)(4-) groups were substituted for PO(4)(3-) groups in the silicon-hydroxyapatite (Si-HA) lattice according to a previously proposed substitution mechanism without the formation of other crystalline phases, such as tricalcium phosphate or calcium oxide. The substituted silicon induced a decrease in the net surface charge and the isoelectric point of HA as determined by zeta potential (ZP) measurements. At physiological pH=7.4 the surface charge of Si-HA was significantly lowered compared to unmodified HA, i.e. -50+/-5 to -71+/-5 eV, caused by the presence of silicate groups in the HA lattice, which may account for a faster in vitro apatite formation using SBF testing. XPS results indicated that silicon seems to be preferentially leached out from Si-HA surface compared to other ionic species after dissolution studies in tris-buffer using a dynamic system.
169 citations
TL;DR: Although the magnesium/carbonate co-substitution had a positive effect in preventing phase decomposition during sintering, it appeared to have a negative effect on the densification of the MgCO3–HA ceramics, compared to stoichiometric HA.
Abstract: A new synthesis/processing method has been devised to produce magnesium/carbonate co-substituted hydroxyapatite ceramics that do not decompose to tricalcium phosphate (TCP) on sintering. Using this method, a series of magnesium/carbonate co-substituted hydroxyapatite (Mg/CO3–HA) compositions, containing between 0 and 0.35 wt % Mg and approximately 0.9 wt % CO3 were prepared. Sintering the Mg/CO3–HA compositions in a CO2/H2O atmosphere yields a single crystalline phase that appears to be identical to stoichiometric HA. In contrast, when the compositions were prepared in the absence of carbonate and were sintered in air, the phase composition was a biphasic mixture of HA and TCP e.g. for 0.25 wt % Mg substitution the phase composition was approximately 60%HA/40% TCP. Clearly, both the synthesis route and the processing (i.e. sintering) route are of importance in the production of a single-phase Mg/CO3–HA ceramic. Fourier transform infrared (FTIR) spectroscopy has indicated that the Mg/CO3–HA ceramics still contained carbonate groups after sintering at 1200 °C. Chemical analysis by X-ray fluorescence spectroscopy (XRF) and C–H–N analysis has shown that the cation/anion molar ratio (i.e. [Ca+Mg]/[P+C/2]) of the different compositions were 1.68(±0.01), which is equivalent to the Ca/P molar ratio of stoichiometric HA. Although the magnesium/carbonate co-substitution had a positive effect in preventing phase decomposition during sintering, it appeared to have a negative effect on the densification of the MgCO3–HA ceramics, compared to stoichiometric HA.
146 citations
TL;DR: In this paper, three different organic additives were used to produce porous structures of a CaO-P2O5 glass reinforced hydroxyapatite potato starch, almond crust and wax spheres.
Abstract: In the present study three different organic additives were used to produce porous structures of a CaO–P2O5 glass reinforced hydroxyapatite potato starch, almond crust and wax spheres. The produced samples were analysed by scanning electron microscopy, X-ray diffraction with Rietveld refinement, differential thermal analysis and mercury porosimetry. The techniques used in this study enabled the production of glass reinforced hydroxyapatite samples with various pore diameters. Two different techniques were used to produce porous glass reinforced hydroxyapatite samples: a dry method using wax spheres as pore formers and a wet method in alcoholic suspension, where almond crust and potato starch were used as pore formers. The final microstructure consists of hydroxyapatite, α-tricalcium phosphate and β-tricalcium phosphate. X-ray diffraction and scanning electron microscopy analysis revealed different percentages of phases when comparing dense and porous glass reinforced hydroxyapatite specimens. These hard materials are intended to be used as bone defect fillers.
52 citations