Sebbowa, TM; (2013) Surface Modification of a Titanium Alloy via Electrospraying for Biomedical Engineering Applications. Doctoral thesis (PhD), UCL (University College London).

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Abstract

Hydroxyapatite (HA) coated titanium (Ti) based dental and orthopaedic implants are widely utilised owing to their bone-bonding capability. However, the longevity of such implants is restricted by poor HA-Ti interfacial adhesion. In contrast, alternative coating materials such as titania (TiO2) and zirconia (ZrO2) have superior mechanical properties but are generally bioinert. Therefore, the performance of coated implants has been optimised by combining highly bioactive HA with mechanically superior TiO2 or ZrO2. This thesis investigated the deposition of novel electrosprayed bioceramic films with enhanced bioactivity and mechanical properties. Sol-gel derived TiO2 and ZrO2 nano-particles were synthesized using a range of precursors and solvents whereas nano-sized HA was synthesized by precipitation. Composite suspensions with a range of HA:TiO2 and HA:ZrO2 compositions were prepared by mixing. The liquid physical properties such as electrical conductivity and surface tension were affected by suspension composition which in turn influenced the electrospray process. Film morphology was dependent on deposition parameters such as needle-to-substrate distance and suspension flow rate as well as post deposition annealing. The in vitro bioactivity was generally enhanced by post deposition annealing temperature and was further improved by the presence of HA. However, the TiO2/HA composite films were more bioactive than the ZrO2/HA composite films. The mechanical integrity of the electrospray films was assessed by scratch testing. The scratch hardness improved with an increase in the post deposition annealing temperature and declined with an increase in HA content. Furthermore, the scratch resistance was affected by materials composition and was in the order ZrO2>TiO2>HA. The scratch resistance was further enhanced by the deposition of HA-based bi-layer and functionally graded films with a comparable in vitro response to the electrosprayed HA films. Thus the electrospray process is a promising route for the deposition of bioceramic composite films for biomedical applications.

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