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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Novel synthesis routes to conventional and modified bioceramics and composite bone cements

Author: HAQUE, Saba

Year: 2007

Supervisor(s): Jawwad Darr

Hydroxyapatites (HA) and carbonated apatites (CA) have a chemical composition and crystal structure similar to the mineral phase of bone.

The work in this thesis involved the development of several novel bioceramics. For example, high-pressure CA was prepared by reacting calcium and phosphate solutions in dense-phase carbon dioxide (CO2) (a highly compressible medium that acted as a carbonating source). The CA powder was heat-treated in an atmosphere of dry CO2 and subsequent spectral analyses showed an excellent match to human bone mineral with a calculated carbonate content of 8 wt% after heat-treatment. The mild acidity of the dense-phase CO2 medium was also used to synthesise a low pH phase calcium orthophosphate (brushite).

Sodium-substituted HA and monetite syntheses were carried out using a conventional water-in-oil emulsion method. Emulsion processing is advantageous since it allows products of increased homogeneity and surface area, whilst the minimised particle agglomeration allows better sinterability. The difficulties in obtaining phase-pure bioceramics in an emulsion are discussed.

In the final parts of the work, three different bifunctional coupling agents were successfully grafted onto the surface of HA, via phosphonate [-P(O)(O)22-] or carboxylate (-COO-) groups. Their solubility in water allowed them to be used directly in a modified, wet co-precipitation reaction. These surface-grafted HAs were incorporated as fillers into poly(ethyl methacrylate)/n-butyl methacrylate (PEMA/nBMA) bone cement, using 10 and 20 wt% HA filler content. In the case of 20 wt% filler content, the flexural strength, flexural modulus, tensile strength and fatigue life of the injectable HA/PEMA/nBMA bone cements were significantly improved for grafted-HA compared to ungrafted-HA.