Characterisation of hydroxyapatite-coated titanium for biomedical applications

Lee, Jiin Woei (2014) Characterisation of hydroxyapatite-coated titanium for biomedical applications. PhD thesis, University of Nottingham.

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Orthopaedic implants function to replace or support damaged or diseased bone. Due to a global rise in demand, there is a need to prolong the service life of these implants. The current work focuses on crystallised hydroxyapatite (HA)-coated titanium (Ti) implants. One specific problem during the annealing of as-deposited amorphous HA, to induce crystallisation, is the formation of unwanted titanium oxide (Ti-O) species at the HA/Ti interface that leads to HA layer disruption. This necessitates the introduction of a diffusion barrier layer at the HA/Ti interface. Another reason for implant failure is bone disintegration around the implant; therefore enhancing early bone cell growth on the implant may be beneficial.

The current work investigates the radio-frequency magnetron co-sputtering (RF-McoS) method to coat silicon-substituted hydroxyapatite (Si:HA) on commercially pure Ti (CpTi) substrates, with and without a titanium nitride (TiN) barrier coating. Processed coatings were designated according to the sputtering targets used, namely HA/TiN, Si:HA, Si:HA/TiN and Si+O2:HA/TiN (i.e. reactively sputtered Si:HA/TiN in a mixed Argon, Ar, and oxygen, O2, atmosphere). The as-deposited amorphous HA layers were crystallised by annealing at 700oC for 2 hours and 4 hours in Ar/trace O2 (sample set 1) or for 2 hours in pure Ar (sample set 2). Coatings were assessed using a combination of complementary analytical bulk and near-surface techniques, combined with in vitro biological tests using an MG63 cell line to appraise the early stages of osseointegration.

In both sample sets, coatings containing TiN were generally more effective at retarding the development of rutile (TiO2). Coatings annealed in trace levels of O2 (set 1) were more prone to delamination due to the development of Ti2N. Better process control was achieved following annealing in pure argon (sample set 2), with Si:HA/TiN showing significantly improved cell proliferation, whilst most closely resembling stoichiometric HA. Cell trials demonstrated both sample sets to be biocompatible, despite variations in coating morphologies, crystallinities and stoichiometries reflecting the issues of process control. Suggestions on improving the process control of these orthopaedic implant coatings are discussed.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Brown, Paul D.
Hoque, Md. Enamul
Grant, David M.
Scotchford, Colin A.
Spowage, Andrew C.
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Item ID: 14406
Depositing User: EP, Services
Date Deposited: 22 Jan 2015 06:20
Last Modified: 23 Jul 2021 10:15

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