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Title: Mechanisms of the Improved Biological Response with Silicate Substitution in Hydroxy Apatite
Author: Guth, Katharina
ISNI:       0000 0004 2677 6229
Awarding Body: Queen Mary, University of London
Current Institution: Queen Mary, University of London
Date of Award: 2008
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Hydroxyapatite (HA) is a bioactive calcium phosphate based ceramic commonly used. as a bone graft substitute. The bioactivity of this material has been reported to be enhanced through site specific substitution of 0.8wt% silicate for phosphate into the HA lattice (SiHA). The aim of this thesis was to explore the possible mechanisms behind this bioactivity enhancement. Two hypothesises were proposed whereby bioactivity may be enhanced by either (1) an 'indirect effect', where alterations in the ion concentrations in the fluid surrounding the graft materials influenced osteoblast development or metabolism and/or (2) by a 'direct effect', where differences in the material physiochemistry influenced protein adsorption, which in subsequently promotes osteoblast attachment and consequently development or metabolism. In order to probe these two hypotheses a broad area of activity was undertaken, including production of morphologically matched HA and. SiHA, analysis of surface physiochemistry and chemical interactions under cell culture conditions in addition to analysis of material-protein interactions, cell attachment, metabolism and development. . Whilst the morphological parameters of the microporous HA and SiHA were matched, differences in the physiochemical properties were noted, such' as the increase in surface free energy from 29.43±6.39mJ/m2 (HA) to 56.67±1.07mJ/m2 (SiHA). Exposure of HA and SiHA to cell culture . medium led to a depletion of 10.8% and 27.1 % phosphate ions in medium respectively. Moreover, exposure to SiHA resulted in a significant increase in pH and release of up to 0.22mM silicon in the medium. Serum proteins were identified to influence the ionic interactions between the apatite and medium. However, these significant changes in ion composition were not seen to impact on the development of osteoblast-like cells. Impro\red bioactivity through the 'indirect effect' of ionic interactions between SiHA and the surrounding medium was therefore not established. Analysis of serum protein adsorption demonstrated that within 24 hours, 50±5.2J.lg and 35.9±4.0J.lg total protein was adsorbed to SiHA and HA specimens respectively. Further to the determination of ...
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available