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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: Chemical coupling in biocomposites: surface modification of bioceramics creating chemically bound polymer composites with potential osteological applications

Author: PHILLIPS, Monisha

Year: 2005

Supervisor(s): Ihtesham Rehman

The surface properties and activity of the inorganic phase, hydroxyapatite, were investigated. Synthesis and processing techniques including emulsion synthesis and freeze-drying, respectively were used to produce hydroxyapatite powders of increased surface area. It is proposed that this increased surface area may result in an increased availability of surface reactive (hydroxyl) groups that enhance interphase coupling (via covalent bonding).

Coupling of methacrylic acid, bisphosphonic acid and poly(vinyl phosphonic acid) [PVPA] with HA have been investigated and characterised using Fourier Transform Infrared Spectroscopy (FTIR). Although successful, the single functionality of bisophosphonic acid and PVPA lead to the development of a specifically tailored bifunctional allyl phosphonic acid [CH=CH2CHP(O)(OH)2], characterised using Nuclear Magnetic Resonance Spectroscopy (NMR). This bifunctionality allows for bonding to hydroxyapatite [via P(O)(OH)2] and polymers [via C=C].

The allyl phosphonic acid was applied in a “co-precipitation” reaction to form a calcium phosphate/allyl phosphonic acid “co-precipitate”. The P=O and P-OH functional groups of the allyl phosphonic acid appear to replace a proportion of the phosphate groups in the calcium phosphate, as characterised by FTIR, FT Raman and solid state NMR. X-ray photoelectron spectroscopy (XPS) confirmed the presence of reactive groups (C=C), from the allyl phosphonic acid, on the surface of the co-precipitate.

Grafting of hydroxyethyl methacrylate (HEMA) to the surface of the reactive co-precipitate was confirmed, by FTIR, indicating that bonding had occurred between monomer and co-precipitate. Upon polymerisation of the grafted HEMA, a chemically bound poly(HEMA)-ceramic composite was formed.