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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: Development of a Self-Assembly Technique for HA Coatings and Antibiotic Delivery for Titanium- Based Implants

Author: AJAMI, Elnaz

Year: 2010

Supervisor(s): Xiao Guo

This work investigates the novel route of Ti surface functionalization with self-assembled monolayers (SAMs) in order to facilitate hydroxyapatite deposition and strengthen its bonding with the Ti surface and further equip the surface with localized antibiotic delivery to combat post-implantation infections. The main findings demonstrate that the formation of SAMs on non-model Ti substrates is challenging, since it requires the simultaneous control of many factors to achieve a densely packed well-organized SAM on a large surface area. By pre-treating the substrate with techniques such as electropolishing, the initial surface contamination can be kept at minimum while the hydroxylated surface remains smooth for the formation of well-oriented SAMs. Hence, after electropolishing, the Ti surface could be functionalized with molecules carrying reactive or neutral groups to facilitate hydroxyapatite deposition and/or antibiotic immobilization. Such a surface functionalization is found to facilitate hydroxyapatite deposition. The hydroxyapatite formed on SAM-modified Ti surfaces is made of small crystals of 6 nm and a 12 μm thick hydroxyapatite film, which can grow in 1 month. The SAM modified surfaces are covered with hydroxyapatite spheres in less than 7 days, while no spheres are observed on the unmodified Ti surface under similar conditions. Enhanced hydroxyapatite deposition rates on SAM-modified surfaces are explained by a decrease of nucleation barrier for hydroxyapatite. Additionally, preliminary investigations demonstrate the possibility of further functionalizing the Ti surface to allow the immobilization of antibiotic (Ciprofloxacin here) simultaneously with hydroxyapatite growth. The release of Ciprofloxacin was found to occur after 1 day and continue up to 20 days. The combination of these two functionalities on the Ti surfaces could find applications in load-bearing implants.