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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: Surface Modification of Bioceramics: Chemically Enhanced laser Surface Microstructuring of Hydroxyapatite

Author: NORTON, Jude

Year: 2008

Supervisor(s): Ihtesham Rehman

The present study combines the developments in the fields of bioceramic materials and laser surface microstructuring of materials. The use of lasers in this context is largely to tailor the topography, surface properties and composition with a view to enhancing the implant biocompatibility.

Conventionally manufactured bioceramic hydroxyapatite (HA, Formula: Ca10(PO4)6(OH)2) has poor mechanical properties as a bulk material such that wide usage is restricted to non-load bearing situations, including coating on metallic implant substrates, maxillo-facial and middle ear reconstruction. Nanocrystalline HA has been produced by synthesis and processing techniques involving emulsion technology and freeze-drying. It is proposed that the ultrafine powder with high surface area, small particle size distribution and little agglomeration has greater potential in the manufacture of thermally stable, dense implants with superior mechanical properties.

Methods of chemically enhanced laser-assisted etching have been developed to produce microstructural features on the surface of bioceramic HA. The type of surface microtopography was unique to the reactive gas (SF6 or NH3) employed, characterised by Scanning Electron Microscopy (SEM). Chemically enhanced microstructural development resulted from the use of SF6 with the production of a fluorine-substituted HA surface distinguished by X-ray microdiffraction, Energy Dispersive X-ray Analysis (SEM-EDS) and Fourier Transform Raman Spectroscopy (FTIR-Raman). It is envisaged that the structurally and chemically modified surface is of improved bioactivity whilst the mechanical and chemical stability of the bulk composition are maintained. In both cases, the proposed result based on previous studies is a bioceramic interface of enhanced osteoconductivity through increased surface area in addition to the presence of concavities and pores.