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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: A new modified injectable brushite-based calcium phosphate bone cement

Author: SAADALLA, ME

Year: 2006

Supervisor(s): Julia Shelton

Two commercial cements, Norian SRS (α-TCP-based cement) and Biobon (DCPD-based cement), widely used in clinical practice, were selected to compare their performance and understand their chemistry.

The properties of the commercial cements were affected by both the setting temperature and the soaking medium. Norian cement was 5 times stronger in compression than Biobon cement, while Biobon was more resorbable and injectable. Different ratios of CaCO3 and H3PO4 were added to the original Biobon cement, which resulted in a set cement with an improved chemical and mechanical stability displaying 24-40% apatite precipitation in 10 days compared to 0.4% precipitation for non-modified Biobon cement. Chemical modification also resulted in an increase in the compressive strength (UCS) to approximately 9 MPa after soaking for one hour, compared to 2.5 MPa for the non-modified cement. One system was selected as an optimised formulation (5.8wt% CaCO3-0.35 M H3PO4) as it gave properties that were comparable to, or better than, the two commercial cements. The addition of an accelerator (Na2HPO4) reduced the setting time although it also altered the mechanical and chemical properties. Further, the presence of H3PO4 decreased the setting time while maintaining the UCS and obtaining comparable apatite precipitation to the initial optimised system. The optimum modification, that produced a cement with all of the required properties, was a Biobon cement (50% ACP + 50% DCPD) with 5.8 wt% CaCO3, 0.35 M H3PO4 and 1% Na2HPO4, and a liquid/powder ratio of 0.8.

The modified cement developed in this study may be a candidate as an orthopaedic calcium phosphate bone cement that is suitable for a range of applications. Further modifications in the chemistry may be introduced in order to optimise the cement for a specific application.